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+The Project Gutenberg eBook, A Textbook of Assaying: For the Use of Those
+Connected with Mines., by Cornelius Beringer and John Jacob Beringer
+
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+
+
+
+Title: A Textbook of Assaying: For the Use of Those Connected with Mines.
+
+
+Author: Cornelius Beringer and John Jacob Beringer
+
+
+
+Release Date: July 3, 2006  [eBook #18751]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+
+***START OF THE PROJECT GUTENBERG EBOOK A TEXTBOOK OF ASSAYING: FOR THE
+USE OF THOSE CONNECTED WITH MINES.***
+
+
+E-text prepared by Peter Yearsley, Josephine Paolucci, and the Project
+Gutenberg Online Distributed Proofreading Team (https://www.pgdp.net/)
+
+
+
+Note: Project Gutenberg also has an HTML version of this file which
+      includes the original illustrations and in which the chemical
+      equations are easier to read.
+      See 18751-h.htm or 18751-h.zip:
+      (https://www.gutenberg.org/dirs/1/8/7/5/18751/18751-h/18751-h.htm)
+      or
+      (https://www.gutenberg.org/dirs/1/8/7/5/18751/18751-h.zip)
+
+
+Transcriber's Note:
+
+   Text:
+
+      Words surrounded by a tilde such as ~this~ means the word is
+      in bold face.
+
+      Words surrounded by underscores like _this_ means the word is
+      in italics in the text.
+
+      Letters in brackets with an = sign before it means that the
+      letters have a macron over them, e.g. H[=A=c] signifies that
+      the Ac has a macron over it.
+
+   Numbers and equations:
+
+      Parentheses have been added to clarify fractions.
+
+      Underscores before bracketed numbers in equations denote a
+      subscript.
+
+      Superscripts are designated with a caret and brackets, e.g.
+      11.1^{3} is 11.1 to the third power.
+
+      The symbol .'. designates the symbol usually used for therefore
+      (three periods in a triangle shape).
+
+      A down arrow is represented by a vertical line over a capital
+      V. Like this:  |
+                     V
+
+   Minor typographical errors have been corrected. Footnotes have
+   been moved to the end of the chapter, and all advertisements
+   have been moved to the end of the book.
+
+
+
+
+
+A TEXT-BOOK OF ASSAYING:
+FOR THE USE OF THOSE CONNECTED WITH MINES.
+
+by
+
+C. AND J. J. BERINGER.
+
+Revised by
+
+J. J. BERINGER,
+
+Assoc. of the Royal School of Mines; Fellow of the Chemical Society and
+of the Inst. of Chemistry; Principal of the Camborne Mining School; and
+Late Public Analyst for the County of Cornwall.
+
+With numerous Diagrams and Tables.
+
+Ninth Edition.
+
+
+
+
+
+
+
+London:
+Charles Griffin and Company, Limited,
+Exeter Street, Strand.
+1904.
+[All rights reserved.]
+
+
+
+
+PUBLISHER'S NOTE TO THE NINTH EDITION
+
+
+The continued popularity of the present work, the last edition of which
+was published only a little over a year ago, continues to be a source of
+gratification to the publishers, who have much pleasure in issuing the
+present edition.
+
+_January 1904._
+
+
+PREFACE TO THE SIXTH EDITION
+
+The principal changes in this edition are additions to the articles on
+Gold, Cyanides, and Nickel, and a much enlarged Index. The additional
+matter covers more than forty pages.
+
+J. J. BERINGER.
+
+CAMBORNE,
+_January 1900._
+
+
+
+
+PREFACE.
+
+
+The Text-book now offered to the public has been prepared to meet the
+existing want of a practical "handy book" for the Assayer.
+
+To mining men the word "assaying" conveys a sufficiently clear meaning,
+but it is difficult to define. Some writers limit it to the
+determination of silver and gold, and others imagine that it has only to
+do with "furnace-work." These limitations are not recognised in
+practice. In fact, assaying is becoming wider in its scope, and the
+distinction between "assayers" and "analysts" will in time be difficult
+to detect. We have endeavoured rather to give what will be of use to the
+assayer than to cover the ground within the limits of a faulty
+definition.
+
+At first our intention was to supply a description of those substances
+only which have a commercial value, but on consideration we have added
+short accounts of the rarer elements, since they are frequently met
+with, and occasionally affect the accuracy of an assay.
+
+Under the more important methods we have given the results of a series
+of experiments showing the effect of varying conditions on the accuracy
+of the process. Such experiments are often made by assayers, but seldom
+recorded. Statements like those generally made--that "this or that
+substance interferes"--are insufficient. It is necessary to know under
+what conditions and to what extent.
+
+Students learning any particular process cannot do better than repeat
+such a series of experiments. By this means they will, at the same time,
+acquire the skill necessary for performing an assay and a confidence in
+their results based upon work under different conditions.
+
+The electrolytic method of copper assaying given under _Copper_ is a
+modification of Luckow's; it was introduced by us into the offices of
+the Rio Tinto Copper Company, and has been in use for many years with
+success. This modification is now employed in copper-works in Spain,
+Germany, and England, and is used in place of the dry assay for the
+commercial valuation of copper ores.
+
+We have adhered to the gram and the "c.c." as the units of weight and
+volume. Those who prefer working with grains and grain-measures can use
+the figures given, multiplied by ten. For example:--When 1 gram is
+mentioned, 10 grains should be used, and 10 grain-measures take the
+place of 1 "c.c." It is not advisable to mix the two systems, as by
+using gram weights and grain-measures.
+
+We have intentionally to a large extent omitted to mention the names of
+those who have originated or modified the various processes. The
+practice of naming a process after its discoverer has developed of late
+years, and is becoming objectionable. It is a graceful thing to name a
+gas-burner after Bunsen, or a condenser after Liebig; but when the
+practice has developed so far that one is directed to "Finkenerise" a
+residue, or to use the "Reichert-Meissl-Wollny" process, it is time to
+stop.
+
+We are indebted to the standard works of Allen, Crookes, Fresenius,
+Lunge, Michell, Percy, and Sutton, and wish to express our sense of
+special indebtedness to Mr. Richard Smith, of the Royal School of Mines.
+One or two of the illustrations are taken from Mr. Sexton's excellent
+little book on _Qualitative Analysis_. Our obligation to some others is
+mentioned in the text.
+
+Finally, we have to thank for assistance in the experimental work
+Messrs. Bailey, Beswick, Clarke, Grant, Higgins, and Smith.
+
+THE AUTHORS.
+
+CAMBORNE, _Nov. 1889_.
+
+
+
+
+CONTENTS.
+
+
+PART I.
+
+
+CHAPTER I.
+
+INTRODUCTORY.
+                                                       Page
+Object of assaying                                        1
+Sampling                                                  1
+Drying: determination of moisture                         5
+Calculation and statement of results                      7
+Laboratory books and report forms                         9
+Quantity to be taken for an assay                        11
+Exercises                                                14
+
+
+CHAPTER II.
+
+METHODS OF ASSAYING.--DRY GRAVIMETRIC METHODS.
+
+Methods of assaying                                      15
+Gravimetric methods                                      15
+Mechanical separations                                   16
+Dry assays                                               16
+  (a) Fluxes                                             16
+  (b) Reducing agents                                    21
+  (c) Oxidising agents                                   22
+  (c) Apparatus                                          24
+
+
+CHAPTER III.
+
+WET GRAVIMETRIC METHODS.
+
+Wet gravimetric methods                                  27
+  (a) Solution                                           29
+  (b) Precipitation                                      30
+  (c) Filtration                                         31
+  (c) Drying and igniting                                32
+
+
+CHAPTER IV.
+
+VOLUMETRIC ASSAYS.
+
+Titrometric assays                                       35
+  (a) Standard solutions                                 36
+  (b) Standardising                                      37
+  (c) Methods of working                                 42
+  (c) Indirect titration                                 43
+Colorimetric assays                                      44
+Gasometric assays                                        44
+
+
+CHAPTER V.
+
+WEIGHING AND MEASURING.
+
+Weighing                                                 47
+Measuring liquids                                        49
+  (a) Graduated flasks                                   49
+  (b) Pipettes                                           50
+  (c) Burettes                                           51
+Measuring gases                                          52
+
+
+CHAPTER VI.
+
+REAGENTS.
+
+Acids, &c.                                               54
+Bases, salts, &c.                                        59
+
+
+CHAPTER VII.
+
+Formulę, equations, &c.                                  68
+
+
+CHAPTER VIII.
+
+SPECIFIC GRAVITY.
+
+Introductory                                             75
+
+Determination of specific gravity--
+  (a) Hydrometers                                        76
+  (b) Specific gravity bottles                           78
+Calculations depending on specific gravity               84
+
+
+PART II.
+
+
+CHAPTER IX.
+
+SILVER, GOLD, PLATINUM, CYANIDES, MERCURY.
+
+SILVER--Detection                                        87
+  Dry assay                                              87
+    (1) Scorification                                    88
+    (2) Pot assays, average ores                         90
+           "        ores with metallic oxides            91
+           "        ores with metallic sulphides         91
+  Explanatory notes on the fusion                        93
+  The effect of charcoal, flour, &c.                     94
+  The effect of nitre                                    95
+  The effect of mineral sulphides                        95
+    (3) Cupellation                                      98
+      The loss of silver                                101
+      Condition affecting the loss                      102
+      Methods of correction                             103
+      Lead required for cupellation                     105
+    (4) Calculation of the results in ounces to the
+      ton of 2240 lbs. Table                            107
+      Ores with metallic particles                      108
+    (5) Explanatory notes                               110
+    (6) Examples of dry silver assays                   113
+  Wet assays                                            116
+    Gravimetric method                                  117
+    Gay-Lussac's method                                 119
+    Volhard's method                                    121
+    A modified Gay-Lussac                               123
+    Volhard's method applied to arsenic                 124
+GOLD--Detection                                         126
+  Amalgamation assay                                    126
+  Dry assay                                             127
+    (1) Size of charges                                 127
+    (2) Sampling                                        127
+    (3) Assay tons                                      131
+    (4) Small buttons, weighing                         131
+          "      "     measuring                        133
+    (5) Concentration in lead                           136
+      Quartz ores                                       136
+      Ores with oxide of iron                           138
+      Ores with metallic sulphides                      139
+    (6) Cyanide charges, residues, &c.                  140
+    (7) Cupellation                                     142
+      Cupels                                            142
+      Cupellation temperature                           143
+      Cupellation loss                                  145
+    (8) Inquartation                                    146
+    (9) Flatting                                        149
+   (10) Parting, in flasks                              151
+          "      in test tubes                          152
+          "      in glazed crucibles                    153
+          "      Loss, &c.                              154
+   (11) Check assays, surcharge                         154
+   (12) Bullion assays in special apparatus             156
+      Silver, &c., in gold bullion                      157
+   (13) Sampling of base bullion, &c.                   157
+CYANIDES--Commercial cyanides                           160
+  Double cyanides                                       161
+  Prussic acid                                          162
+  Gold-dissolving power of cyanide liquor               162
+  Assay for cyanide strength                       163, 165
+  Assay of commercial cyanide                           167
+  Alkalinity of cyanides                                167
+  Acidity of ores                                       168
+  Metals in cyanide liquors                             169
+  Cyanicides                                            169
+PLATINUM                                                170
+IRIDIUM                                                 171
+MERCURY                                                 171
+    Dry assay                                           172
+    Wet method                                          173
+
+
+CHAPTER X.
+
+COPPER, LEAD, THALLIUM, BISMUTH, ANTIMONY.
+
+COPPER--Introductory                                    175
+    Dry assay                                           176
+    Valuation of copper ores                            181
+  Wet methods                                           183
+    (1) Electrolytic assay                              184
+  Volumetric methods                                    194
+    (1) Cyanide method                                  194
+    (2) Iodide method                                   199
+    (3) Colorimetric method                             203
+  Examination of commercial copper                      205
+LEAD                                                    211
+  Dry assay                                             211
+  Wet assay                                             213
+    (1) Gravimetric method                              213
+    (2) Volumetric method                               214
+    (3) Colorimetric method                             218
+THALLIUM                                                219
+BISMUTH                                                 220
+    Dry assay                                           221
+    Wet method                                          221
+      (1) Gravimetric determination                     222
+      (2) Colorimetric assay                            223
+ANTIMONY                                                225
+  Dry assay                                             225
+  Wet method                                            227
+    (1) Gravimetric assay                               228
+    (2) Volumetric method                               229
+
+
+CHAPTER XI.
+
+IRON, NICKEL, COBALT, ZINC, CADMIUM.
+
+IRON                                                    231
+  Gravimetric determination                             233
+  Permanganate and bichromate methods                   234
+  Stannous chloride method                              244
+  Colorimetric determination                            247
+NICKEL                                                  251
+  Dry assay                                             251
+  Electrolytic assay                                    254
+  Titration by cyanide                                  255
+COBALT                                                  259
+ZINC                                                    261
+  Gravimetric method                                    262
+  Volumetric method                                     263
+  Gasometric method                                     266
+CADMIUM                                                 269
+
+
+CHAPTER XII.
+
+TIN, TUNGSTEN, TITANIUM.
+
+TIN                                                     271
+  Vanning                                               273
+  Dry assay                                             276
+  Detection, &c.                                        279
+  Gravimetric determination                             281
+  Volumetric determination                              282
+  Examples                                              284
+TITANIUM                                                292
+TUNGSTEN                                                295
+NIOBIC AND TANTALIC OXIDES                              297
+
+
+CHAPTER XIII.
+
+MANGANESE, CHROMIUM, ETC.
+
+MANGANESE                                               298
+  Gravimetric determination                             300
+  Volumetric determination                              300
+    Ferrous sulphate assay                              301
+    Iodine assay                                        302
+  Colorimetric determination                            306
+CHROMIUM                                                307
+VANADIUM                                                310
+MOLYBDENUM                                              311
+URANIUM                                                 312
+
+
+CHAPTER XIV.
+
+EARTHS, ALKALINE EARTHS, ALKALIES.
+
+ALUMINA                                                 314
+THORIA                                                  317
+ZIRCONIA                                                317
+CERIUM                                                  318
+LANTHANUM AND DIDYMIUM                                  319
+YTTRIA                                                  319
+BERYLLIA                                                319
+LIME                                                    320
+STRONTIA                                                324
+BARYTA                                                  326
+MAGNESIA                                                328
+THE ALKALIES                                            330
+  SODIUM                                                334
+  POTASSIUM                                             336
+  LITHIUM                                               338
+  CĘSIUM                                                339
+  RUBIDIUM                                              340
+  AMMONIUM                                              340
+
+
+PART III.
+
+
+CHAPTER XV.
+
+OXYGEN AND OXIDES--THE HALOGENS.
+
+OXYGEN                                                  344
+OXIDES                                                  345
+WATER                                                   350
+THE HALOGENS                                            358
+  CHLORINE                                              359
+  BROMINE                                               361
+  IODINE                                                362
+  FLUORINE                                              363
+
+
+CHAPTER XVI.
+
+SULPHUR AND SULPHATES.
+
+SULPHUR                                                 367
+  Gravimetric determination                             369
+  Volumetric determination                              370
+SULPHATES                                               377
+SELENIUM                                                379
+TELLURIUM                                               379
+
+
+CHAPTER XVII.
+
+ARSENIC, PHOSPHORUS, NITROGEN.
+
+ARSENIC                                                 381
+  Gravimetric determination                             383
+  Volumetric method, "iodine"                           384
+      "        "     "uranic acetate"                   389
+PHOSPHORUS                                              394
+  Gravimetric determination                             396
+  Volumetric determination                              397
+NITROGEN AND NITRATES                                   400
+
+
+CHAPTER XVIII.
+
+SILICON, CARBON, BORON.
+
+SILICON AND SILICATES                                   405
+CARBON AND CARBONATES                                   414
+  COALS                                                 418
+  SHALES                                                420
+  CARBONATES                                            424
+BORON AND BORATES                                       429
+
+
+APPENDIX A.
+
+Table of atomic weights and other constants             433
+Table for converting degrees of the centigrade
+  thermometer into degrees of Fahrenheit's scale        435
+Tables showing strengths of aqueous solutions of nitric
+  and hydrochloric acids, of ammonia and of sulphuric
+  acid                                                  436
+
+
+APPENDIX B.
+
+Estimation of small quantities of gold                  440
+Practical notes on the iodide process of
+   copper assaying                                      441
+Method of separating cobalt and nickel                  442
+
+
+APPENDIX C.
+
+A lecture on the theory of sampling                     444
+
+INDEX                                                   450
+
+
+
+
+A TEXT-BOOK OF ASSAYING.
+
+
+
+
+CHAPTER I.
+
+INTRODUCTORY.
+
+
+Assaying has for its object the determination of the quantities of those
+constituents of a material which add to or detract from its value in the
+arts and manufactures. The methods of assaying are mainly those of
+analytical chemistry, and are limited by various practical
+considerations to the determination of the constituents of a small
+parcel, which is frequently only a few grains, and rarely more than a
+few ounces, in weight. From these determinations calculations are made,
+which have reference to a mass of material of, perhaps, hundreds of
+tons. But in all cases, whether the mass under consideration be large or
+small, whether the material be obtained by mining, grown, or
+manufactured, the assayer is supposed to receive a small quantity,
+called "the sample," which is, or ought to be, the exact counterpart of
+the mass of material that is being dealt with. The taking and making of
+this sample is termed "sampling"; and the men whose special work it is
+to select such samples are "the samplers."
+
+But although "sampling" is thus distinct from "assaying," the assayer
+should be familiar with the principles of sampling, and rigorous in the
+application of these principles in the selecting, from the sample sent
+him, that smaller portion upon which he performs his operations.
+
+~Sampling.~--_In the case of gases_, there is absolutely no trouble in
+mixing. The only difficulty is in drawing off a fair sample where, as in
+flues, the body of the gas is in motion, and varies a little in
+composition from time to time. In this case, care must be taken to draw
+off uniformly a sufficient volume of the gas during a prolonged period;
+any portion of this larger volume may then be taken for the analytical
+operation.
+
+_In the case of liquids_, which mix more or less easily--and this class
+includes metals, &c., in the state of fusion--more or less severe
+agitation, followed by the immediate withdrawal of a portion, will yield
+a fairly representative sample.
+
+_In the case of solids_, the whole mass must be crushed, and, if not
+already of fairly uniform quality, mixed, before sampling can take
+place. Most of the material which a sampler is called upon to deal with,
+is, however, in a more or less divided state and fairly uniform. In
+practice it is assumed that 5 per cent. of the whole (= 1/20th), if
+taken in portions of equal weight and at frequent and regular intervals,
+will represent the mass from which it was taken. Taking a heap of ore,
+A, and selecting one out of every twenty spade-, bag-, barrow-, or
+wagon-fuls, according to the quantity of stuff in the heap, there is
+obtained a second heap, B, containing one-twentieth of the stuff of the
+heap A. If we crush the stuff in B until this heap contains
+approximately the same number of stones as A did--which means, crushing
+every stone in B into about twenty pieces--B will become the counterpart
+of A. Selecting in the same manner 5 per cent. of B, there is got a
+third heap, C. This alternate reduction and pulverising must be carried
+on until a sample of suitable size is obtained. This may be expressed
+very clearly thus:--
+
+     A  =  1000     tons of rocks and lumpy ore.
+     B  =    50      "   "  rough stones,  1/20th of A.
+     C  =     2.5    "   "  small stones,  1/20th of B.
+     D  =     0.125  "   "  coarse powder, 1/20th of C.
+
+[Illustration: FIG. 1.
+
+CONE
+
+PARTLY REDUCED CONE
+
+PLAN OF FRUSTRUM DIVIDED.
+
+ELEVATION OF FRUSTRUM DIVIDED.]
+
+If the material to be sampled is already a dry powder, 5 per cent. of it
+should be heaped in a cone; each lot being added on the apex of the
+cone already formed, so that it may distribute itself by falling evenly
+in all directions. When the cone is completed, convert it into a low
+frustrum of a cone by drawing stuff uniformly and in a direct line from
+the centre to the circumference. Draw two diameters at right angles to
+each other, and reserving any two alternate quarters, reject the others.
+Mix; and form another cone, and proceed until a sample is got of the
+bulk required.
+
+This is the usual plan, and all samples should be treated in this way
+when the stuff is fine enough to fall evenly down the sides of a cone.
+
+Samples as they reach the assay office are seldom in a fit state for the
+work of the assayer; they are generally too coarse, and ought always to
+be more than he wants for any particular determination. The portion he
+requires should never be taken at hap-hazard; the sample must be reduced
+systematically to the quantity required.
+
+1. _If the sample is a liquid:_ it is sufficient to shake the bottle,
+and take out a measured or weighed quantity for the assay.
+
+2. _If a liquid with a solid in suspension:_ measure the whole of it.
+Filter. Make up the filtrate with the wash-water or water to the
+original bulk. Assay it. Dry and weigh the residue, and make a separate
+assay of it.
+
+3. _If of a creamy consistency, free from heavy particles:_ mix well;
+spread out evenly on a glazed tile. Take up equal portions at equal
+distances. Mix and assay.
+
+4. _If a mud of coarse and fine particles, or of particles of unequal
+density:_ weigh and transfer to a porcelain dish, or weigh in the dish.
+Dry at 100° C., weigh. Treat the residue as a solid capable of being
+powdered.
+
+5. _If a solid capable of being powdered, or already powdered:_ heap up
+into a cone; flatten with a spatula; divide along two diameters at right
+angles, and carefully reject the whole of two alternate quarters,
+brushing away any fine powder. Mix the other quarters, and repeat (if
+necessary). For small quantities a fine state of division is essential.
+
+6. _If a solid with metallic particles:_ powder and pass through a
+sieve; the metallic particles will not pass through. Weigh both portions
+and assay separately. _Sifting should be followed by a very thorough
+mixing._
+
+7. _If a metal or alloy in bar or ingot:_ clean the upper surface of the
+bar, and bore through the bar. Use the borings. If the ingot or bar is
+small, cut it through and file the section. Filings must be freed from
+fragments of the file by means of a magnet; and from oil, if any be
+present, by washing with a suitable solvent.[1] Where practicable,
+metals and alloys are best sampled by melting and granulating. The
+student must carefully avoid any chance of mixing dirt or particles of
+other samples with the particular sample which he is preparing. One ore
+should be done at a time, and when finished, it should be labelled and
+wrapped up, or bottled, before starting on a fresh sample.
+
+When an ore requires to be very finely ground in an agate mortar, it is
+often advisable to mix with a little pure alcohol and rub until free
+from grit; dry at 100° C. and mix well before weighing.
+
+When an assay is required of a quantity of ore made up of parcels of
+different weight and quality, each parcel should be separately sampled
+and parts of each sample, bearing to each other the same proportion by
+weight as the original parcels, should be taken and mixed. For example,
+a lot of ore is made up of one parcel of A, 570 tons, one of B, 180
+tons, and another of C, 50 tons; a sample representing the whole may be
+got by mixing 57 parts of a sample of A with 18 parts of a sample of B,
+and 5 parts of a sample of C.
+
+[Illustration: FIG. 2.]
+
+A bruising plate, like that in fig. 2, is convenient for general office
+work. The slab is of cast iron, about an inch thick. It is firmly
+supported on a solid block of wood, and pivoted for convenience in
+emptying. The bruising-hammer is steel-faced, about 4 inches square, and
+1-1/2 inch thick. The block is firmly fixed to a small table or tressel,
+so that the slab is about 2 feet 6 inches from the ground. The slab is
+cleaned, and the sample collected with the help of a stiff-haired brush.
+
+~Drying: Determination of Moisture.~--In practice, the moisture is
+generally determined by the samplers, and the proportion is specified in
+grains per pound on the label attached to the sample when it reaches the
+assay office. The method adopted is usually to dry 1 lb. = 7000 grs. of
+the ore in a frying-pan heated over a gas flame, or in an ordinary oven,
+until a cold bright piece of metal or glass is no longer damped when
+held over it. The loss of weight in grains = moisture.
+
+Properly, however, this work should be done by the assayer, if only for
+the following reason. It is assumed that the dry ore of the sampler and
+of the assayer are the same thing; according to the nature of the ore,
+this may or may not be the case. The assayer, however, uses the sample
+which he has dried for his moisture-determination, as the dry ore on
+which he makes his other assays, and no variation in moisture would
+influence the other and more important determinations. Some ores are
+sent to the smelter with from 5 to 15 per cent. of adherent water. In
+these cases it is best to spread out the sample, and taking equal
+portions fairly at regular intervals, weigh into a Berlin dish 20 grams.
+This should then be dried over a sand-bath, or if the ore is likely to
+be injured by excess of heat, over a water-bath until the weight is
+constant. The loss of weight multiplied by 5 gives the percentage of
+water present.
+
+Example:--
+
+  Weight of dish + wolfram      32.67 grms.
+    "    "  dish                12.67   "
+                                -----
+    "    "  wolfram             20.00   "
+
+    "    "  dish + wolfram      32.67   "
+    "    "    "    dried        30.15   "
+                                -----
+    "    "  water                2.52   "
+
+  2.52 × 5 = 12.6                        ~12.6%.~
+
+There are other ores which are not apparently wet, but in the state
+called "air-dried." It is easier to take fair samples of these, and,
+consequently, it is not necessary to use so large a quantity as 20
+grams. But with a smaller quantity, extra precautions must be taken. All
+dry solids at ordinary temperatures absorb moisture from the air. The
+amount varies with the nature of the material and with the quantity of
+surface exposed. Light bulky powders absorb more than heavy ones,
+because of the greater condensing surface. It is on this account that it
+is well to weigh substances, which have been dried, between
+close-fitting watch-glasses. The method of determining moisture is to
+weigh out into the glasses 5 grams of ore, and dry in the water-oven
+until there is no further loss of weight. On taking the glasses out of
+the oven, they should be at once closed, the clip put on, and after
+cooling in a desiccator weighed. If after a second trial the loss is the
+same, or only increased by a milligram, the determination is finished.
+
+Example:--
+
+  Weight of glasses + pyrites                    31.0470 grms.
+    "    "  glasses                              26.0470   "
+                                                 -------
+    "    "  pyrites                               5.0000   "
+    "    "  glasses + pyrites, dried 1 hour      30.8965   "
+    "    "    "         "      dried 1-1/2  "    30.8957   "
+    "    "    "         "                        31.0470   "
+    "    "    "         "      dried             30.8957   "
+                                                 -------
+    "    "  moisture                              0.1513   "
+
+    0.1513 × 20 = 3.026                                   ~3.02%.~
+
+[Illustration: FIG. 3.]
+
+Sometimes it may be advisable to dry 10 grams, in which case multiplying
+the loss by 10 will give the percentage. The dried ore should be
+transferred to a weighing-tube (fig. 3), and reserved for the subsequent
+determinations. The weighing-tube with the ore must be marked, and kept
+in a desiccator.
+
+Most ores and inorganic substances can be dried, and their moisture
+determined by the loss in this way. When, however, the substance
+contains another somewhat volatile ingredient, it is exposed over
+sulphuric acid in a desiccator for two days (if _in vacuo_, all the
+better), and the loss determined. Moisture in dynamite should be
+determined in this way.
+
+When water is simply mechanically mixed with a substance it presents but
+little difficulty. The combined water is a different matter. Slaked
+lime, even when perfectly dry, contains much water; and if the water of
+soda crystals were separated and frozen, it would occupy a volume equal
+to that of the original crystals. Perfectly dry substances may contain
+much water, and this combined water is retained by different materials
+with very unequal vigour. Sodium sulphate and sodium phosphate crystals
+lose water even when exposed under ordinary conditions to dry air. Soda
+crystals when heated melt, and at a moderate temperature give off their
+water with ebullition. The temperature at which all the water is given
+up varies with each particular salt; the actual determination of the
+water in each case will require somewhat different treatment. Such
+determinations, however, are seldom required; and from a practical
+point of view this combined water causes no trouble.
+
+_In assaying ores_, we term "moisture" all water which is lost by
+exposure in a water-oven at 100° C., and the "dry ore" is the ore which
+has been dried at this temperature. No advantage, but rather endless
+confusion, would be caused by varying the temperature with the object of
+estimating the whole of the water which a hydrated salt may contain. The
+results of the assay of the other components should be calculated on the
+"dry ore." One advantage of this is obvious:--The dry ore has a constant
+composition, and the results of all assays of it will be the same, no
+matter when made; the moisture, however, may vary from day to day, and
+would be influenced by a passing shower of rain. It is well to limit
+this variability to the moisture by considering it apart, and thus avoid
+having the percentage, say, of copper rising and falling under the
+influence of the weather.
+
+In the case of certain salts, however, such as soda crystals and
+hydrated sulphate of copper (when these constitute the bulk of the
+substance to be assayed), it is as well to perform the assay on the
+moist, or at any rate air-dried, substance.[2] It would be equally
+convenient to calculate on the substance dried at 100° C.; but in this
+case it would be well, in order to avoid a somewhat shallow criticism,
+to replace the term "moisture" by the longer but equivalent phrase
+"water lost at 100° C."
+
+~Calculation and Statement of Results.~--By far the most generally
+convenient method of stating the results of an assay is that of the
+percentage or parts in a hundred, and to avoid a needlessly troublesome
+calculation it is well to take such a quantity of ore for each assay as
+by a simple multiplication will yield the percentage. In these
+calculations decimals are freely employed, and students should make
+themselves familiar with the methods of using them.
+
+Other methods of statement are in use, and have advantages in certain
+special cases. With bullion the parts in a thousand are given, and in
+those cases in which the percentage is very small, as in water analysis,
+it is convenient to report on parts in 100,000, or even on parts per
+1,000,000. These are easily got from the corresponding percentages by
+shifting the decimal point one, three, or four places to the right. Thus
+92.5 per cent. is 925 per thousand; and 0.0036 per cent. is 3.6 per
+100,000, or 36 per million.
+
+With ores of tin, silver, and gold, the result is stated as so many
+cwts., lbs., or ozs., in the ton. With dressed tin ores as they are
+sent to the smelter, the produce is given in cwts. and quarters to the
+ton. The corresponding percentage may be obtained by multiplying by
+five; or, inversely, if the percentage is given, the produce may be got
+by dividing by five. A produce of 13-1/2 equals a percentage of 13.5×5
+= 67.5; and a percentage of 70.0 equals a produce of 70/5 = 14. With
+tin ores as raised (in which the percentage is small) the reduction must
+be carried to pounds per ton. One per cent. equals 22.4 lbs. to the ton;
+consequently, if we multiply the percentage by 22.4, the produce will be
+given. Thus, if an ore contains 6.7 per cent. of oxide of tin, the
+produce is 6.7×22.4 = 150 lbs. (or 1 cwt., 1 quarter, and 10 lbs.) to
+the ton. With gold and silver ores, the proportion of precious metal is
+small, and it is necessary to carry the reduction to ozs. and dwts. to
+the ton; and since gold and silver are sold by troy weight, whilst the
+ton is avoirdupois, it is of importance to remember that the ounces in
+the two systems are not the same. A ton contains 15,680,000 grains,
+which equal 653,333.3 dwts. or 32,666.6 ozs. (troy). The following rules
+are useful:--
+
+  To get ozs. (troy) per ton, multiply parts per 100,000 by 0.327;
+  To get dwts. per ton, multiply parts per 100,000 by 6.53;
+  To get grains per ton, multiply parts per 100,000 by 156.8.
+
+Where liquids are being assayed, cubic centimetres are held to be
+equivalent to grams, and the usual method of statement is, "so many
+parts by weight in so many by measure." Where the statement is made as
+grams per litre or grains per gallon, there can be no doubt as to what
+is meant; and even if it be expressed in parts per 100,000, parts by
+weight in a measured volume must be understood unless the contrary is
+expressly stated.
+
+In some cases, where the density of the solution differs greatly from
+that of water, the percentage by weight may be given; and in others,
+mixtures of two or more liquids, the percentages may be given by volume
+or by weight; as so many c.c. in 100 c.c., or as so many grams in 100
+grams, or even as so many grams in 100 c.c. In such cases it must be
+distinctly shown which method of statement is adopted.
+
+One grain per gallon means 1 grain in 70,000 grain-measures, or one part
+in 70,000. Dividing by 7 and multiplying by 10 will convert grains per
+gallon into parts per 100,000. Inversely, dividing by 10 and multiplying
+by 7, will convert parts per 100,000 into grains per gallon.
+
+Grams per litre are parts per 1000; multiplying by 100 will give parts
+per 100,000, and multiplying by 70 will give grains per gallon.
+
+Among foreign systems of weights, the French is by far the best.
+Kilograms (2.205 lbs.) per quintal (220.5 lbs.) are parts per cent.; and
+grams (15.43 grs.) per quintal are parts per 100,000. From the rule
+already given, grams per quintal may be converted into ounces to the ton
+by multiplying by 0.327.
+
+The German loths per centner (1/2 oz. (avoirdupois) to 100 lbs.) equal
+parts per 3200; they are converted into parts per cent. by dividing by
+32, or into ounces (troy) per ton by multiplying by 10.208.
+
+In the United States, as a sort of compromise between the avoirdupois
+and metric systems, a ton is taken as 2000 lbs. There, too, the custom
+is adopted of reporting the gold and silver contents of an ore as so
+many dollars and cents to the ton. In the case of gold, an ounce is
+considered to be worth 20.6718 dollars. With silver, the _nominal_ value
+is 1.2929 dollars per ounce, but frequently in assay reports it is taken
+as one dollar. The practice is objectionable. The prices of metals vary
+with the fluctuations of the market, and if the assayer fixed the price,
+the _date_ of his report would be all important; if, on the other hand,
+he takes a fixed price which does not at all times agree with the market
+one, it leaves a path open for the deception of those unacquainted with
+the custom. American "dollars on the ton of 2000 lbs." may be converted
+into "ounces in the ton of 2240 lbs." by dividing by 1.1544 in the case
+of silver, and by 18.457 in the case of gold.
+
+~Laboratory Books and Report Forms.~--The record which the assayer makes
+of his work must be clear and neat, so that reference, even after an
+interval of years, should be certain and easy. One method should be
+adopted and adhered to. Where there are a large number of samples, three
+books are required.
+
+_Sample Book._--This contains particulars of the samples (marks, &c.),
+which are entered by the office-clerk as they arrive. He at the same
+time puts on each sample the distinguishing number.
+
+            EXAMPLE OF PAGE OF SAMPLE BOOK.
+
+ +----------+----------+--------------------------+----------------+
+ |  Date.   |  Number. |        Sample.           |      Remarks.  |
+ +----------+----------+--------------------------+----------------+
+ |  Feb. 1  |   482    | Tough Copper             | For Arsenic.   |
+ |   "   2  |    X     | Piece of Metal           | For Ni and Cu. |
+ |   "      |   483    | Tough Copper.            |                |
+ |   "      |    73    | Silver Precipitate,      | With Letter.   |
+ |          |          |   4 casks, 24 cwt. 1 qr. |                |
+ |   "      |   494    | Purple Ore, 200 tons.    |                |
+ |   "      |  1 J.T.  | Lead Ore, 1 J.T.         | From Corsica.  |
+ |   "      |  2 J.T.  |    "      2 J.T.         |                |
+ +----------+----------+--------------------------+----------------+
+
+_Laboratory Book._ This is the Assayer's note-book, in which he enters
+clearly the particulars of his work--the results obtained, as well as
+how these results were arrived at. The calculations should be done on
+scrap-paper, and should not be entered, although, of course, detail
+enough must be shown to enable the results to be recalculated.
+
+            EXAMPLE OF PAGE OF LABORATORY BOOK.
+______________________________________________________________
+
+  Purple Ore                                     5 grams
+    19/10/89          0.0042 grm.
+                      0.0021  "
+                      ------
+       Colorimetric   0.0063 × 20         =  0.13% Copper
+______________________________________________________________
+
+      482
+  Tough Copper                              10 grams
+    Feb. 1/89        10.5 c.c. Uranium.
+                                          =  0.52% Arsenic
+______________________________________________________________
+
+     2082
+  Tough Copper                              10 grams
+                     12.7 c.c. Uranium.
+                                          =  0.63% Arsenic
+______________________________________________________________
+
+      491                                   10 grams
+  Tough Copper       13.7 c.c. Uranium
+    Feb. 1/89
+                                          =  0.68% Arsenic
+______________________________________________________________
+
+  Standard of Uranium acetate.
+            0.150 gram As_{2}O_{3} = 23.3 c.c. Uranium.
+              .'. 100 cc. Uranium  =  0.5 gram As.
+______________________________________________________________
+
+     10071                                    5 grams
+   Tin Ore          Cruc. and SnO_{2} 9.6065 grms.
+  Feb. 3/89         Cruc. and Ash     9.4235   "
+                                   ------
+                         SnO_{2} = 0.1830  = 2.88% Tin
+______________________________________________________________
+
+_The Assay Book._--This is the Official book, and is a combination of
+the Sample and Laboratory books. It corresponds with the report-forms.
+Without being loaded with detail, it should contain sufficient to
+characterise each sample.
+
+Key to following example page of Assay book:
+DR = DATE REPORTED.
+Not Det. = Not detected
+
+            EXAMPLE OF PAGE OF ASSAY BOOK.
+
+-------------------------------------------+----+-------+---------------+----
+     DESCRIPTION OF SAMPLE.                |    | Water | Assay on      |
+------+--------------------+---------------|    |Lost at|   the Dry     |
+Date. |    Material.       |    Weight.    |No. |100° C.|Material.      | DR
+------+--------------------+---+---+---+---+----+-------+---------------+----
+1889  |                    |ton|cwt|qrs|lbs|    |       |               |
+Feb. 1|Tough cake copper   |   |   |   |   | 482|       |Arsenic, 0.52% |  7
+  "   |Tough cake copper   |   |   |   |   |2082|       |Arsenic, 0.63% |  7
+  "   |Tough cake copper   |   |   |   |   | 491|       |Arsenic, 0.68% |  7
+      |                    |   |   |   |   |    |       |               |
+Feb. 2|Nickel disc for C.R.|   |   |   |   | X  |       |Copper, 73.75  |  7
+      |                    |   |   |   |   |    |       |Nickel, 24.34  |
+      |                    |   |   |   |   |    |       |Iron,    2.18  |
+      |                    |   |   |   |   |    |       |        -----  |
+      |                    |   |   |   |   |    |       |       100.27  |
+      |                    |   |   |   |   |    |       |       ------  |
+  "   |Silver precipitate, |   | 24|  1|  0|  73| Not   |               |
+      | 4 casks            |   |   |   |   |    | det.  |Silver,  4.851 | 10
+      |                    |   |   |   |   |    |       |Gold,    0.0215|
+      |                    |   |   |   |   |    |       |Lead,   19.37  |
+      |                    |   |   |   |   |    |       |Zinc,    2.00  |
+      |                    |   |   |   |   |    |       |Silver, 1584.7 |
+      |                    |   |   |   |   |    |       |  ozs. per ton |
+      |                    |   |   |   |   |    |       |Gold, 7.0      |
+      |                    |   |   |   |   |    |       |  ozs. per ton |
+  "   |Purple ore          |200|   |   |   | 494| Not   |Copper,  0.13% | 11
+      |                    |   |   |   |   |    | det.  |Sulphur  0.15% |
+------+--------------------+---+---+---+---+----+-------+---------------+----
+
+When the number of samples is small, the Sample Book may be omitted, and
+the entries made in the Assay Book as the samples arrive.
+
+_Report-forms._ These should entail as little writing as possible in
+making out the report. For general purposes the form given on p. 12 is
+useful.
+
+~The quantity of substance~ to be taken for any particular assay depends
+largely upon the method of assay adopted. There are, however, some
+general considerations which should be remembered, and some devices for
+simplifying the calculations which should be discussed.
+
+The smaller the percentage of the substance to be determined, the larger
+should be the amount of the ore taken. The following table will give a
+general idea as to this:--
+
+Percentage of the substance    Amount of ore, &c. to
+     to be determined.             be weighed.
+        100-10                      1 gram.
+         10-5                       2 grams.
+          5-1                       5   "
+          1-0.1                    10   "
+        0.1-0.01                   20   "
+
+[Illustration: ASSAY NOTE]
+
+The rougher the method of assay adopted, the larger should be the
+quantity of ore taken. If the degree of accuracy attainable with the
+methods and instruments at the assayer's service is known, it is easy to
+calculate what quantity should be taken for any particular case. If the
+results are good within 0.001 gram, then, taking 1 gram of ore we can
+report within 0.1 per cent., or if they are good within 0.0002 gram,
+taking 20 grams of ore, we can report within 1 part per 100,000, or very
+closely within 6-1/2 dwt. to the ton. If it is wished to be yet more
+particular in reporting, larger quantities must be taken. The difficulty
+of manipulating very small or very large precipitates, &c., must be
+borne in mind. So, too, must the fact that the greater the weight of the
+final product of an assay, the less, as a rule, is the percentage error.
+The distinction between absolute and percentage error, often overlooked,
+is important. If 0.5 gram of silver be cupelled with 20 grams of lead,
+there may be obtained a button of 0.495 gram; the absolute loss is 0.005
+gram, and this equals 1 per cent. of the silver present. Similarly,
+cupelling 0.1 gram, the resulting button may be 0.098; the absolute loss
+is only 0.002 gram, but this equals 2 per cent. of the silver present.
+In the same way the student should see that the two results, 91.5 per
+cent. and 92.0 per cent., are really more concordant than the results
+9.1 per cent. and 9.2 per cent.
+
+A device often adopted in practice where a large number of assays of one
+kind are made, and the report is given as so many ounces or pounds to
+the ton, is that known as the _assay ton_. The assay ton may be any
+arbitrary and convenient weight, but its subdivisions must bear to it
+the same relations as pounds and ounces bear to the actual ton. On the
+other hand, in a laboratory where many kinds of work are performed,
+different sets of weights of this kind would only tend to confusion,
+even if they were not unnecessary. With a set of gram weights and its
+subdivisions anything may be done. If it is desired to report as pounds
+to the ton, then, since there are 2240 lbs. to the ton, a weight of
+2.240 grams may be taken as the assay ton, and each 0.001 gram yielded
+will equal 1 lb., or 22.4 grams may represent the ton, and each 0.01
+gram a pound. Similarly, since there are 32,666.6 ozs. troy to the ton;
+if we take 32.6667 grams as the assay ton, each 0.001 gram will equal 1
+oz. to the ton. In some cases it may be convenient to have, in addition
+to the usual gram weights, one or other of the "assay tons" mentioned
+above, but generally it is better to work on a purely decimal system,
+and convert when required into ounces per ton, &c., either by actual
+calculation or by reference to a set of tables.
+
+
+PRACTICAL EXERCISES.
+
+The student should practise such calculations as the following:--
+
+1. Calculate the percentages in the following cases:--
+  (a) Ore taken, 2 grams; copper found, 0.2155.
+  (b)    "       1.5 gram; iron found, 0.8340.
+  (c)    "       30 grams; lead found, 23.2.
+
+2. Calculate the parts per thousand in the following:--
+  (a) Bullion taken, 1.1 gram; silver found, 1.017.
+  (b)        "       1.14 gram; silver found, 1.026.
+  (c)        "       0.6 gram; gold found, 0.5500.
+
+3. Calculate parts per 100,000 in the following:--
+  (a) Ore taken, 20 grams; silver found, 0.0075.
+  (b)    "       50 grams; gold found, 0.0026.
+  (c) Water taken, 500 c.c.; solids found, 0.1205.
+
+4. Calculate cwts. to the ton in the following:--
+  (a) Ore taken, 5 grams; tin found, 2.816.
+  (b)    "       5 grams; tin found, 3.128.
+  (c) An ore with 68.2 per cent. of tin.
+
+5. Calculate lbs. to the ton in the following:--
+  (a) An ore with 3.28 per cent. oxide of tin.
+  (b) Ore taken, 20 grams; oxide of tin found, 1.67.
+
+6. Calculate ozs. (troy) to the ton in the following:--
+  (a) Ore taken, 50 grams; gold found, 0.0035.
+  (b)    "       20 grams; silver found, 0.0287.
+  (c)    "       25 grains; silver found, 0.0164.
+
+7.  Calculate in grains per gallon:--
+  (a) 0.51 gram per litre.
+  (b) 24.6 parts per 100,000.
+  (c) Solution taken, 100 c.c.; copper found, 0.0045 gram.
+  (c)         "        50 c.c.; iron found, 0.165 gram.
+
+8. Convert into ozs. (troy) per ton:--
+  (a) 7 loths per centner.
+  (b) 30 grams per quintal.
+  (c) 15 parts per 100,000.
+
+FOOTNOTES:
+
+[1] Ether or carbon bisulphide.
+
+[2] Such substances are best dried by pressing between folds of dry
+filter-paper.
+
+
+
+
+CHAPTER II.
+
+METHODS OF ASSAYING.--DRY GRAVIMETRIC METHODS.
+
+
+The methods of assaying are best classed under two heads, Gravimetric
+and Volumetric, in the former of which the final results are weighed,
+whilst in the latter they are measured. A commoner and older division is
+expressed in the terms much used in practice--wet assays and dry assays.
+Wet assays include all those in which solvents, &c. (liquid at the
+ordinary temperature), are mainly used; and dry assays, those in which
+solid re-agents are almost exclusively employed. Dry assays form a
+branch of gravimetric work, and we shall include under this head all
+those assays requiring the help of a wind furnace. Wet assays, as
+generally understood, would include not only those which we class as wet
+gravimetric assays, but also all the volumetric processes.
+
+~Gravimetric Methods~ aim at the separation of the substance from the
+other matters present in the ore, so that it may be weighed; and,
+therefore, they must yield the _whole_ of the substance in a pure state.
+It is not necessary that a metal should be weighed as metal; it may be
+weighed in the form of a compound of definite and well known
+composition. For example, one part by weight of silver chloride contains
+(and, if pure, always contains) 0.7527 part of silver; and a quantity of
+this metal can be as exactly determined by weighing it as chloride as by
+weighing it in the metallic state. But in either case the metal or its
+chloride must be pure.
+
+Exact purity and complete separation are not easily obtained; and
+methods are used which are defective in one or both of these respects.
+It is well to note that an impure product increases the result, whilst a
+loss of the substance decreases it; so that if both defects exist in a
+process they tend to neutralise each other. Of dry methods generally, it
+may be said that they neither give the whole of the substance nor give
+it pure; so that they are only calculated to show the amount of metal
+that can be extracted on a manufacturing scale, and not the actual
+quantity of it present. Their determinations are generally rough and
+always low. The gold and silver determinations, however, will compare
+very favourably with any of the other processes for the estimation of
+these metals in their ores.
+
+The calculation of the results of a gravimetric assay has already been
+referred to. If the result is to be stated as percentage, it may always
+be done by the following rule:--_Multiply the weight of the substance
+got by the percentage of metal it contains, and divide by the weight of
+ore taken._
+
+Gravimetric methods are divided into three groups: (1) mechanical
+separations; (2) dry methods; and (3) wet methods.
+
+~Mechanical Separations.~--Under this head are classed the method of
+assaying tin ores, known as vanning, and the amalgamation assay for
+gold. A set of sieves to determine the relative proportion of powders of
+different degrees of fineness is sometimes useful. A set with 10, 20, 40
+and 80 meshes to the inch is convenient.
+
+~Dry Assays.~--An important distinction between wet and dry methods of
+assaying is, that in the former the substance is got into the liquid
+state by solution, whilst in the latter fusion is taken advantage of.
+
+The difference between solution and fusion is easily illustrated: a lump
+of sugar heated over a candle-flame melts or fuses; suspended in water
+it dissolves. Many substances which are insoluble or infusible of
+themselves, become soluble or fusible when mixed with certain others;
+thus, in this way, solution is got with the aid of reagents, and fusion
+with the help of fluxes. For example, lead is insoluble in water, but if
+nitric acid be added, the metal rapidly disappears. It is convenient,
+but somewhat inaccurate, to say that the acid dissolves the lead. If the
+lead be acted on by nitric acid alone, without water, it is converted
+into a white powder, which does not dissolve until water is added; in
+this case it is obvious that the water is the solvent. The function of
+the acid is to convert the lead into a soluble compound.
+
+~Fluxes~ may act as true solvents. Fused carbonate of soda dissolves
+baric carbonate, and perhaps in many slags true solution occurs; but in
+the great majority of cases a flux is a solid reagent added for the
+purpose of forming a fusible _compound_ with the earthy or stony
+minerals of the ore. Few of the minerals which occur in the gangue of an
+ore are fusible; and still fewer are sufficiently fusible for the
+purposes of the assayer, consequently the subject is one of importance,
+and it ought to be treated on chemical principles. An idea of the
+composition of some of the more frequently occurring rocks may be
+gathered from the following table, which represents rough averages:--
+
+  -----------------------------------------------------------------
+                       |       |        |Oxide|Lime and |
+                       |Silica.|Alumina.| of  |Magnesia.|Alkalies.
+                       |       |        |iron |         |
+  -----------------------------------------------------------------
+                       |   %   |    %   |  %  |      %  |   %
+  Sandstone, grit,     |       |        |     |         |
+    quartzite, &c.     |80-100 |   --   | --  |     --  |  --
+  Granite, gneiss,     |       |        |     |         |
+    quartz-porphyry,   |       |        |     |         |
+    fire-clay, &c.     | 70-75 | 13-20  |  2  |      2  | 5-8
+                       |       |        |     |         |Less in
+                       |       |        |     |         |fire-clay.
+  Mica-schist          |    65 |    18  |  5  |      3  |   3
+  Trachyte, syenite    |    60 |    17  |  7  |    4-7  | 6-9
+  Clay-slate           |    60 |    18  | 10  |      8  |   3
+  Diorite              |    54 |    17  | 12  |      9  | 3-4
+  Horneblende-rock     |    50 |    18  | 15  |     12  | 3-4
+  Brick-clay           |    50 |    34  |  8  |      6  |  --
+  China-clay           |    47 |    39  | --  |     --  |  --
+  Basalt, dolerite, &c.|    50 |    15  | 15  |     16  |   3
+  Serpentine           |    44 |    --  | --  |     44  |  --
+  Chalk, limestone,    |       |        |     |         |
+    dolomite, &c.      |    -- |    --  | --  |  45-55  |  --
+  -----------------------------------------------------------------
+
+Silica itself, and the silicates of alumina, of lime, and of magnesia,
+are practically infusible; the silicates of soda, of potash, and of iron
+are easily fusible if the base (soda, potash, or oxide of iron) be
+present in sufficient quantity, and if, in the case of the iron, it is
+present mainly as lower oxide (ferrous silicate). The addition of lime,
+oxide of iron, or alkali to silicate of alumina results in the formation
+of a double silicate of alumina and lime, or of alumina and iron, &c.,
+all of which are easily fusible. Similarly, if to a silicate of lime we
+add oxide of iron, or soda, or even alumina, a fusible double silicate
+will be formed. Thus lime, soda, oxide of iron, and clay, are _fluxes_
+when properly used; but since lime, clay (and oxide of iron if there be
+any tendency to form peroxide), are of themselves infusible, any excess
+of these fluxes would tend to stiffen and render pasty the resulting
+slag. So, too, soda, which is a very strong base, may act prejudicially
+if it be in sufficient excess to set free notable quantities of lime and
+magnesia, which but for that excess would exist in combination as
+complex fusible silicates. There are many minerals which with but little
+soda form a glass, but with more yield a lumpy scoriacious mass. There
+are many minerals, too, which are already basic (for example, calcite),
+and which, when present, demand either a less basic or an acid flux
+according to the proportions in which they exist. For purposes of this
+kind borax, or glass, or clay with more or less soda may be used, and of
+these borax is by far the most generally useful. An objection to too
+basic a slag (and a very important one) is the speed with which it
+corrodes ordinary crucibles. These crucibles, consisting of quartz and
+clay, are rapidly attacked by lime, soda and bases generally.
+
+[Illustration: FIG. 4.]
+
+In considering what is and what is not a good slag, certain chemical
+properties are of importance. If a mixture of many substances be fused
+and allowed to solidify in a crucible, there will be found some or all
+of the following. At the bottom of the crucible (fig. 4) a button of
+metal, resting on this a speise; then a regulus, next a slag made up of
+silicates and borates and metallic oxides, and lastly, on the top
+another layer of slag, mainly made up of fusible chlorides and
+sulphates. In assaying operations the object is generally to concentrate
+the metal sought for in a button of metal, speise or regulus, and to
+leave the earthy and other impurities as far as possible in the slag;
+whether there be one or two layers of slag is a matter of
+indifference;[3] but the chemical action of the lower layer upon the
+speise, or regulus, or metal, is of great importance.
+
+A _regulus_ is a compound of one or more of the metals with sulphur; it
+is usually brittle, often crystalline, and of a dull somewhat greasy
+lustre. It is essential that the slag, when solid, shall be so much more
+brittle than the regulus, that it shall be easy to crumble, and remove
+it without breaking the latter; and it must not be basic. The effect of
+fusing a regulus with a basic slag is well seen when _sulphide of lead_
+is fused with _carbonate of soda_; the result is a button of metal (more
+or less pure), and a slag containing sulphides of lead and sodium; and
+again, if sulphide of lead be fused with an excess of oxide of lead, a
+button of lead will be got, and a slag which is simply oxide of lead
+(with whatever it may have taken up from the crucible), or if a
+sufficient excess has not been used, oxide of lead mixed with some
+sulphide. When (as is most frequently the case) the desire is to prevent
+the formation of regulus, these reactions may be taken advantage of, but
+otherwise the use of a flux having any such tendency must be avoided. A
+good slag (from which a regulus may be easily separated) may be obtained
+by fusing, say, 20 grams of ore with borax 15 grams, powdered glass 15
+grams, fluor spar, 20 grams, and lime 20 grams; by quenching the slag in
+water as soon as it has solidified, it is rendered very brittle.
+
+Sulphide of iron formed during an assay will remain diffused through
+the slag, instead of fusing into a button of regulus, if the slag
+contain sulphide of sodium. The same is true of other sulphides if not
+present in too great a quantity, and if the temperature is not too high.
+
+_Speises_ are compounds of a metal or metals with arsenic. They are
+chiefly of interest in the metallurgy of nickel, cobalt, and tin. They
+are formed by heating the metal or ore in covered crucibles with arsenic
+and, if necessary, a reducing agent. The product is fused with more
+arsenic under a slag, consisting mainly of borax. They are very fusible,
+brittle compounds. On exposure to the air at a red heat the arsenic and
+the metal simultaneously oxidize. When iron, cobalt, nickel, and copper
+are present in the same speise, they are eliminated in the order
+mentioned.
+
+_Slags_ from which metals are to be separated should not be too acid; at
+least, in those cases in which the metal is to be reduced from a
+compound, as well as separated from earthy impurities. Where the object
+is simply to get a button of metal from a substance in which it is
+already in the metallic state, but mixed with dross (made up of metallic
+oxides, such as those of zinc or iron), from which it is desired to
+separate it, an acid flux like borax is best; or, if the metal is easily
+fusible, and there would be danger of loss of metal by oxidation or
+volatilising, it may be melted under a layer of resin or fat. Common
+salt is sometimes used with a similar object, and is often useful. Under
+certain conditions, however, it has a tendency to cause the formation of
+volatile chlorides with a consequent loss of metal.
+
+In the great majority of cases, the fusion of the metal is accompanied
+by reduction from the state of oxide; in these the slag should be basic.
+It is not easy to reduce the whole of a reducible oxide (say oxide of
+copper or of iron) from a slag in which it exists as a borate or
+silicate; there should be at least enough soda present to liberate it.
+When the object is to separate one metal, say copper, without reducing
+an unnecessary amount of another (iron) at the same time, a slag with a
+good deal of borax is a distinct advantage. The slag then will probably
+not be free from copper, so that it will be necessary to powder and mix
+the slag with some soda and a reducing agent, and to again fuse the slag
+in order to separate this residual metal. In all those cases in which
+the slag retains an oxide of a heavy metal, this cleaning of the slag is
+advisable, and in the case of rich ores necessary. Slags containing
+sulphides are especially apt to retain the more easily reducible metals.
+
+The following are the ordinary and most useful fluxes:--
+
+~Soda.~--The powdered bicarbonate, sold by druggists as "carbonate of
+soda," is generally used. It gives off its water and excess of carbonic
+acid readily and without fusion. Where the melting down is performed
+rapidly, the escaping gas is apt to cause trouble by frothing, and so
+causing waste of the material. Ordinary carbonate of soda, when hydrated
+(soda crystals), melts easily, and gives off its water with ebullition.
+It is unfit for use in assaying, but when dried it can be used instead
+of the bicarbonate. One part of the dried carbonate is equivalent to
+rather more than one and a half parts of the bicarbonate. From two to
+four parts of the flux are amply sufficient to yield a fluid slag with
+one part of earthy matter. This statement is also true of the fluxes
+which follow.
+
+~Borax~ is a hydrated biborate of soda, containing nearly half its
+weight of water. When heated it swells up, loses its water, and fuses
+into a glass. The swelling up may become a source of loss in the assay
+by pushing some of the contents out of the crucible. To avoid this,
+_fused_ or _dried borax_ may be used, in which case a little more than
+half the amount of borax indicated will suffice. Borax will flux almost
+anything, but it is especially valuable in fluxing lime, &c., and
+metallic oxides; as also in those cases in which it is desired to keep
+certain of the latter in the slag and out of the button of metal.
+
+~Oxide of Lead~, in the form of red lead or litharge, is a valuable
+flux; it easily dissolves those metallic oxides which are either
+infusible or difficultly fusible of themselves, such as oxides of iron
+or copper. The resulting slag is strongly basic and very corrosive; no
+crucible will long withstand the attack of a fused mixture of oxides of
+lead and copper. With silicates, also, it forms very fusible double
+silicates; but in the absence of silicates and borates it has no action
+upon lime or magnesia. Whether the lead be added as litharge or as red
+lead, it will exist in the slag as monoxide (litharge); the excess of
+oxygen of the red lead is thus available for oxidising purposes. If this
+oxidising power is prejudicial, it may be neutralised by mixing the red
+lead with 1 per cent. of charcoal.
+
+~Glass~: broken beakers and flasks, cleaned, dried, and powdered will
+do. It should be free from lead.
+
+~Fluor~: fluor-spar as free as possible from other minerals, powdered.
+It helps to flux phosphate of lime, &c., and infusible silicates.
+
+~Lime~: should be fresh and powdered. It must not be slaked. Powdered
+white marble (carbonate of lime) will do; but nearly double the quantity
+must be taken. One part of lime produces the same effect as 1.8 parts of
+the carbonate of lime.
+
+~Tartar~ and "black flux," are reducing agents as well as fluxes. The
+"black flux," which may be obtained by heating tartar, is a mixture of
+carbonate of potash and charcoal.
+
+REDUCING AGENTS.--The distinction between reducing agents and fluxes
+(too often ignored) is an important one. Fluxes yield slags; reducing
+agents give buttons of regulus or of metal. The action of a reducing
+agent is the separation of the oxygen or sulphur from the metal with
+which it is combined. For example, the mineral anglesite (lead sulphate)
+is a compound of lead, sulphur, and oxygen; by carefully heating it with
+charcoal the oxygen is taken away by the charcoal, and a regulus of lead
+sulphide remains. If the regulus be then fused with metallic iron the
+sulphur is removed by the iron, and metallic lead is left. The charcoal
+and the iron are reducing agents. But in defining a reducing agent as
+one which removes oxygen, or sulphur, from a metallic compound so as to
+set the metal free, it must be remembered that sulphur itself will
+reduce metallic lead from fused litharge, and that oxygen will similarly
+set free the metal in fused lead sulphide. There is no impropriety in
+describing sulphur as a reducing agent; but it is absurd to call oxygen
+one. Some confusion will be avoided if these substances and those which
+are opposite to them in property be classed as oxidising and
+de-oxidising, sulphurising, and de-sulphurising agents. Most oxidising
+agents also act as de-sulphurisers.
+
+_The de-oxidising agents_ most in use are the following:--
+
+~Charcoal.~--Powdered wood charcoal; it contains more or less
+hygroscopic moisture and about 3 or 4 per cent. of ash. The rest may be
+considered carbon. Carbon heated with metallic oxides takes the oxygen;
+at low temperatures it forms carbon dioxide, and at higher ones, carbon
+monoxide. Other conditions besides that of temperature have an influence
+in producing these results; and as the quantity of charcoal required to
+complete a definite reaction varies with these, it should be calculated
+from the results of immediate experience rather than from theoretical
+considerations.
+
+~Flour.~--Ordinary wheat flour is convenient in use. On being heated it
+gives off inflammable gases which have a certain reducing effect, and a
+residue of finely divided carbon is left. It is likely to vary in the
+quantity of moisture it contains. Two parts of flour should be used
+where one part of charcoal would be otherwise required.
+
+~Tartar.~--This is crude hydric potassic tartrate; the purified salt,
+cream of tartar, may be used. On being heated it gives off inflammable
+gases, and leaves a residue formed of potassic carbonate mixed with
+finely divided carbon. Five parts of tartar should be used in the place
+of one of charcoal.
+
+~Anthracite~ or ~Culm~ is a kind of coal containing 90 per cent. or more
+of carbon. It gives off no inflammable gas. It is denser, and takes
+longer in burning, than charcoal. Its reducing effect is little inferior
+to that of charcoal. Almost any organic substance can be used as a
+reducing agent, but it is well not to select one which melts, swells up,
+or gives off much water and gas when heated in the furnace.
+
+~Potassic Cyanide~ is an easily fusible and somewhat volatile salt,
+which, when fused, readily removes oxygen and sulphur from metallic
+compounds, and forms potassic cyanate or sulphocyanate as the case may
+be. Commercial samples vary much in purity; some contain less than 50
+per cent. of the salt. For assaying, only the better qualities should be
+used.
+
+~Iron~ is a de-sulphurising rather than a de-oxidising agent. Iron is
+used in the form of rods, 1/2-inch in diameter, or of nails, or of hoop
+iron. In the last case it should be thin enough to be bent without
+difficulty. Wrought iron crucibles are very useful in the processes
+required for making galena assays.
+
+_The chief oxidising agents (which are also de-sulphurisers)_ are the
+following:--
+
+~Nitre~, or Potassic Nitrate.--This salt fuses very easily to a watery
+liquid. It oxidises most combustible substances with deflagration, and
+thereby converts sulphides into sulphates, arsenides into arsenates, and
+most metals into oxides. In the presence of strong bases, such as soda,
+the whole of the sulphur is fully oxidised; but in many cases some
+arsenic is apt to escape, and to give rise to a peculiar garlic-like
+odour. The sulphates of soda and potash are thus formed, and float as a
+watery liquid on the surface of the slag.
+
+~Red lead~ is an oxide of lead. About one-quarter of its oxygen is very
+loosely held, and, hence, is available for oxidising purposes, without
+any separation of metallic lead. The rest of the oxygen is also
+available; but for each part of oxygen given off, about 13 parts of
+metallic lead are deposited. In silver assays this power of readily
+giving up oxygen is made use of. The residual oxide (litharge) acts as a
+flux.
+
+~Hot air~ is the oxidising agent in roasting operations. The sulphur and
+arsenic of such minerals as mispickel and pyrites are oxidised by the
+hot air and pass off as sulphur dioxide and "white arsenic." The metals
+generally remain in the form of oxide, mixed with more or less sulphate
+and arsenate. The residue may remain as a powdery substance (a calx), in
+which case the process of roasting is termed calcination; or it may be a
+pasty mass or liquid. In the calcination of somewhat fusible minerals,
+the roasting should be done at a low temperature to avoid clotting;
+arsenic and sulphur being with difficulty burnt off from the clotted
+mineral. A low temperature, however, favours the formation of sulphates;
+and these (if not removed) would reappear in a subsequent reduction as
+sulphides. These sulphates may be decomposed by a higher temperature
+towards the end of the operation; their removal is rendered more certain
+by rubbing up the calx with some culm and re-roasting, or by strongly
+heating the calx after the addition of solid ammonic carbonate. In
+roasting operations, as large a surface of the substance as possible
+should be exposed to the air. If done in a crucible, the crucible should
+be of the Cornish type, short and open, not long and narrow. For
+calcinations, _roasting dishes_ are useful: these are broad and shallow,
+not unlike saucers, but unglazed. In those cases in which the products
+of the roasting are liquid at the temperature used, a _scorifier_ (fig.
+38) is suitable if it is desired to keep the liquid; but if the liquid
+is best drained off as quickly as it is formed, a _cupel_ (fig. 5)
+should be used.
+
+[Illustration: FIG. 5.]
+
+A scorifier is essentially a roasting dish sufficiently thick to resist,
+for a time, the corrosive action of the fused metallic oxides it is to
+contain. The essential property of a cupel is, that it is sufficiently
+porous to allow the fused oxide to drain into it as fast as it is
+formed. It should be large enough to absorb the whole of the liquid; and
+of course must be made of a material upon which the liquid has no
+corrosive action. Cupels do not bear transport well; hence the assayer
+generally has to make them, or to supervise their making. A quantity of
+bone ash is carefully mixed with water so that no lumps are formed, and
+the mixture is then worked up by rubbing between the hands. The bone ash
+is sufficiently wet when its cohesion is such that it can be pressed
+into a lump, and yet be easily crumbled into powder. Cupel moulds should
+be purchased. They are generally made of turned iron or brass. They
+consist of three parts (1) a hollow cylinder; (2) a disc of metal; and
+(3) a piston for compressing the bone ash and shaping the top of the
+cupel. The disc forms a false bottom for the cylinder. This is put in
+its place, and the cylinder filled (or nearly so) with the moistened
+bone ash. The bone ash is then pressed into shape with the piston, and
+the cupel finished with the help of three or four smart blows from a
+mallet. Before removing the piston, turn it half-way round upon its axis
+so as to loosen and smooth the face of the cupel. The cupel is got out
+by pressing up the disc of metal forming the false bottom; the removal
+is more easily effected if the mould is somewhat conical, instead of
+cylindrical, in form. The cupels are put in a warm place to dry for two
+or three days. A conveniently sized cupel is 1-1/4 inches in diameter
+and about 3/4 inch high. The cavity of the cupel is about 1/4 inch deep,
+and something of the shape shown in fig. 5.
+
+[Illustration: FIG. 6.]
+
+[Illustration: FIG. 7.]
+
+[Illustration: FIG. 8.]
+
+There are two kinds of furnaces required, the "wind" and "muffle"
+furnaces. These are built of brick, fire-brick, of course, being used
+for the lining. They are connected with a chimney that will provide a
+good draught. Figure 6 shows a section of the wind furnace, fig. 7 a
+section of the muffle furnace, and fig. 8 a general view of a group
+comprising a muffle and two wind furnaces suitable for general work.
+When in operation, the furnaces are covered with iron-bound tiles. The
+opening under the door of the muffle is closed with a loosely fitting
+brick. The floor of the muffle is protected with a layer of bone-ash,
+which absorbs any oxide of lead that may be accidentally spilt. The fire
+bars should be easily removable.
+
+Few tools are wanted; the most important are some cast-iron moulds,
+tongs (fig. 9), stirrers for calcining (fig. 10), and light tongs of a
+special form for handling scorifiers and cupels (_see_ SILVER).
+
+[Illustration: FIG. 9.]
+
+[Illustration: FIG. 10.]
+
+The coke used should be of good quality; the formation of a fused ash
+(clinker), in any quantity, causes ceaseless trouble, and requires
+frequent removal. The coke should be broken into lumps of a uniform size
+(about 2 in. across) before being brought into the office. The furnace
+should be well packed by stirring, raising the coke and not ramming it,
+and it should be uniformly heated, not hot below and cold above. In
+lighting a furnace, a start is made with wood and charcoal, this readily
+ignites and sets fire to the coke, which of itself does not kindle
+easily.
+
+In commencing work, add (if necessary) fresh coke, and mix well; make
+hollows, and into these put old crucibles; pack around with coke, so
+that the surface shall be concave, sloping upwards from the mouths of
+the crucibles to the sides of the furnace; close the furnace, and, when
+uniformly heated, substitute for the empty crucibles those which contain
+the assays. It is rarely advisable to have a very hot fire at first,
+because with a gradual heat the gases and steam quietly escape through
+the unfused mass, while with too strong a heat these might make some of
+the matter in the crucible overflow. Moreover, if the heat should be too
+strong at first, the flux might melt and run to the bottom of the
+crucible, leaving the quartz, &c., as a pasty mass above; with a gentler
+heat combination is completed, and the subsequent fiercer heat simply
+melts the fusible compound into homogeneous slag.
+
+The fused material may be left in the crucible and separated from it by
+breaking when cold. It is generally more convenient to pour it into
+cast-iron moulds. These moulds should be dry and smooth. They act best
+when warmed and oiled or black-leaded.
+
+Air entering through the fire-bars of a furnace and coming in contact
+with hot coke combines with it, forming a very hot mixture of carbonic
+acid and nitrogen; this ascending, comes in contact with more coke, and
+the carbonic acid is reduced to carbonic oxide; at the top of the
+furnace, or in the flue, the carbonic oxide meeting fresh air, combines
+with the oxygen therein and re-forms carbonic acid. In the first and
+third of these reactions, much heat is evolved; in the second, the
+furnace is cooled a little. It must always be remembered, that the
+carbonic oxide of the furnace gases is a reducing agent. When these
+gases are likely to exert a prejudicial effect, and a strongly oxidising
+atmosphere is required, the work is best done in a _muffle_.
+
+FOOTNOTES:
+
+[3] There is an exception to this, as when the slag is liable to be
+acted on when exposed to the air and to the gases of the furnace. In
+this case a layer of fused common salt floating on the slag, so as to
+protect it from the air and furnace gases, is a distinct advantage.
+
+
+
+
+CHAPTER III.
+
+WET GRAVIMETRIC METHODS.
+
+
+In _dry assays_ the metal is almost always separated and weighed as
+metal; in _wet_ gravimetric assays the metal is more usually weighed in
+the form of a definite compound of known composition. The general
+methods of working resemble those of ordinary chemical analysis, and
+their successful working is greatly helped by a knowledge of, at any
+rate, those compounds of the metal which enable it to be separated, and
+of those which are the most convenient forms in which it can be weighed.
+But the work of the assayer differs from that of the analyst, inasmuch
+as the bulk of his estimations are made upon material of practically the
+same kind, varying only in richness; consequently in assaying, it is
+possible (and necessary) to work on such a definite plan as will involve
+the least amount of labour in weighing and calculating.
+
+The assayer connected with mining has generally two classes of material
+to deal with: those comparatively rich and those comparatively poor. For
+example, silver in bullion and in ores; copper precipitates or regulus,
+and copper ores and slags; and "black tin" and tin ores. He is only
+occasionally called on to assay the intermediate products. It is
+indispensable that he should have an approximate knowledge of the
+substance to be determined. With new ores this information is best got
+by a qualitative testing. Knowing that only certain bodies are present,
+it is evident that the number of separations can be reduced, and that
+simple methods can be devised for arriving at the results sought for.
+The best method is that which involves the least number of separations.
+The reactions must be sharp and complete, and yet not be liable to error
+under varying conditions.
+
+To bring the richer and poorer materials under the same conditions for
+the assay, a small weight, say 1 gram of the richer, and a larger weight
+(5 or 10 grams) of the poorer, substance is weighed up. A method is then
+adopted which will concentrate the whole of the metal (either during or
+after solution) in a product which need not necessarily be pure. The
+work on this product is comparatively easy. In separating small
+quantities of a substance from a large bulk of impurities, the group
+separations must not as a rule be too much relied on. Very large
+precipitates carry down small quantities of bodies not belonging to the
+group, more especially when there is a tendency to form weak double
+compounds. The re-dissolving and re-precipitating of bulky precipitates
+should be avoided.
+
+When a large number of assays of the same kind have to be carried out, a
+plan something like the following is adopted:--The samples, after having
+been dried, are placed in order on a table at the left hand of the
+assayer. He takes the first, marks it with a number, samples and weighs
+up the quantity required, and transfers it to a flask, which is
+similarly marked. As the weighings are finished, the samples are placed
+in the same order on his right hand. The assistant takes the flasks in
+batches of four or five at a time to the fume cupboard, where he adds a
+measured quantity of acid. When solution has been effected, dilution
+with a measured volume is generally necessary. The assayer sees to this
+and (whilst the funnels and filters are being prepared) makes any
+separation that is necessary. The filters are arranged in order on a
+rack (fig. 11), and need not be marked unless the precipitates or
+residues have subsequently to be dried. The filters are washed with hot
+water, and if the filtrates are wanted flasks are placed beneath, if
+not, the solution is drained off down the sink. Precipitation or
+reduction (or whatever it may be) is now made; the assistant filters the
+prepared samples, one at a time, whilst the assayer is engaged with the
+others. The same style of work is continued until the assays are
+completed. If one should be spoiled, it is better to allow it to stand
+over for assaying along with the next batch. If one filters slowly or is
+in any way less forward than the rest, it may lessen the accuracy of the
+other assays, owing to oxidation, &c., it should, therefore, be put on
+one side. The assays are dealt with in batches of ten or twenty, so that
+a large quantity of work can be quickly finished.
+
+[Illustration: FIG. 11.]
+
+When the assays are finished, it is the duty of the assistant to clean
+the apparatus (with reagents, if necessary), and to put the vessels in
+the place set apart for them. Flasks are best kept inverted on a rack,
+so that they may be dry and clean by the next morning. Berlin crucibles
+must be cleaned and ignited.
+
+The amount of apparatus employed should be as little as is feasible. The
+assay should be carried out as much as possible in the same flask. The
+bench must be clean, and altogether free from apparatus not in actual
+use. Crucibles and dishes in which weighings are made should be marked
+with numbers or letters; and their weights recorded, together with the
+date of weighing, in a small ledger, which is kept in the drawer of the
+balance. By this means a record of the "wear" of each piece of apparatus
+is obtained, and, what is more important, much weighing is saved, and
+increased confidence is gained. The weight of each piece of apparatus
+need not be taken daily. It will be seen from the record in the book and
+a knowledge of the use it has been put to how often a checking of the
+weight is necessary. The entries are made in black lead as follows:--
+
+  Dish, A.  Feb. 3    9.4210 grams.
+                 5    9.4225
+                 6    9.4230
+                 7    9.4200
+
+Platinum vessels and apparatus lose, and porcelain ones slightly gain,
+weight with continued use.
+
+The special details of the work is given under each assay; certain
+general instructions will be given here.
+
+~Solution.~--It is not always necessary to get the whole of the mineral
+in solution, provided the body sought for is either completely dissolved
+or altogether left in the residue. It is often only by a qualitative
+examination of the solution (or residue, as the case may be) that the
+assayer can satisfy himself that it is free from the substance sought.
+But previous experience with the same kind of ore will show to what
+extent this testing is necessary.
+
+Solution is generally best effected in flasks; but where the resulting
+liquid has afterwards to be evaporated to dryness and ignited,
+evaporating dishes (fig. 12) are used. With them clock glasses are used
+as covers during solution to avoid loss through effervescence.
+Evaporating dishes are also best when an insoluble residue has to be
+collected, since it is difficult to wash out most residues from a flask.
+Bumping occurs less frequently in dishes than in flasks.
+
+[Illustration: FIG. 12.]
+
+After the addition of the acid, and mixing by agitation, the vessel
+containing the substance is heated. This is best done on the "hot
+plate" (fig. 13). This consists of a slab of cast iron about half or
+three-quarters of an inch thick, supported on loose fire bricks, and
+heated by two or three ring burners (figs. 14 and 15). The burners are
+connected to the gas supply by means of _lead_ tubing, to which they are
+soldered. Flasks and dishes after being put on the plate are not further
+handled until solution is complete or the evaporation is carried to
+dryness. The hot plate is contained in a cupboard so as to be out of the
+reach of cold draughts.
+
+[Illustration: FIG. 13.]
+
+[Illustration: FIG. 14.]
+
+[Illustration: FIG. 15.]
+
+The action of the acids and other solvents is described in the chapter
+on Reagents.
+
+~Precipitation.~--In precipitating add sufficient of the reagent to
+complete the reaction. The student must be on his guard against adding a
+very large excess, which is the commoner error. In some reactions the
+finishing point is obvious enough; either no more precipitate is formed,
+or a precipitate is completely dissolved, or some well-marked colour or
+odour is developed or removed.
+
+In those cases in which there is no such indication, theoretical
+considerations should keep the use of reagents within reasonable limits.
+The solutions of the reagents (_see_ REAGENTS) are generally of five or
+ten per cent. strength. A small excess over that demanded by theory
+should be sufficient.
+
+[Illustration: FIG. 16.]
+
+[Illustration: FIG. 17.]
+
+[Illustration: FIG. 18.]
+
+[Illustration: FIG. 19.]
+
+~Filtration.~--Solutions are best filtered hot whenever the assay allows
+of this being so done. The precipitate should be allowed to settle, and
+the clear liquid decanted on the filter with the aid of a glass rod if
+necessary. The filter-paper must not be too large, but at the same time
+it must not be overloaded with the precipitate. There should be ample
+room for washing. For general use three sizes of filter-paper are
+sufficient. Common quick filtering-paper (English) is best for most work
+in assaying. The specially prepared paper (Swedish or Rhenish) is used
+for collecting those precipitates which have to be weighed. The papers
+are folded as shown in fig. 16, and should not project above the funnel.
+The filter-paper works better if damped with hot water. In special cases
+filtering is hastened by means of an air-pump. The apparatus used
+consists of a water-jet (fig. 17), which is connected with the tap, as
+also with a bottle fitted as shown in fig. 18. The pump draws the air
+out from the bottle, and atmospheric pressure forces the liquid through
+the filter-paper. The bottom of the funnel is provided with a platinum
+cone, which supports the filter-paper, and prevents its breaking. The
+pump is only used in exceptional cases; nearly all the filtrations
+required by the assayer can be made without it. The usual methods of
+supporting the funnel during filtration are shown in fig. 19. Where the
+filtrate is not wanted, pickle bottles make convenient supports. After
+the precipitate has been thrown on the filter, it is washed. In washing,
+several washings with a small quantity of water are more effective than
+a few with a larger quantity of that fluid. The upper edge of the
+filter-paper is specially liable to escape complete washing. Excessive
+washing must be avoided; the point at which the washing is complete is
+found by collecting a little of the filtrate and testing it. The
+precipitate is removed from the filter-paper for further treatment by
+opening out the paper and by washing the precipitate with a jet of water
+from a wash-bottle into a beaker, or back through the funnel into the
+flask. In some cases, when the precipitate has to be dissolved in
+anything in which it is readily soluble, solution is effected in the
+filter itself allowing the liquid to run through as it is formed.
+
+~Drying and Igniting.~--Precipitates, as a rule, require drying before
+being ignited. With small precipitates the filter-paper may be opened
+out, and placed on a warm asbestos slab till dry; or the funnel and the
+filter with the precipitate is placed in a warm place, and supported by
+any convenient means. The heat must never be sufficient to char the
+paper. Some precipitates must be dried at a temperature not higher than
+100° C. These are placed in the water-oven (fig. 20), and, when
+apparently dry, they are taken from the funnel, placed between glasses,
+and then left in the oven till they cease to lose weight. Such
+precipitates are collected on tared filters. Those precipitates which
+will stand a higher temperature are dried in the hot-air oven at a
+temperature of from 120° to 150°. The drying is continued until they
+appear to be free from moisture, and until the precipitate ceases to
+adhere to the filter. In drying sulphides the heat must not be raised to
+the melting point of sulphur, since, if there is any free sulphur
+present, it fuses and filters through.
+
+[Illustration: FIG. 20.]
+
+The precipitate, having been dried, is transferred to a watch-glass. The
+filter-paper is opened out over a sheet of note-paper, and, with a
+camel-hair brush, the precipitate is gently brought into the glass. Most
+precipitates come away easily, and the transfer can be made without
+apparent loss. The watch-glass is covered by the funnel, and the
+filter-paper (folded into a quadrant) held by the tweezers and set fire
+to with the flame of a Bunsen burner. It is allowed to burn over the
+crucible, into which the black bulky ash is allowed to drop, and two or
+three drops of nitric acid are then added. The crucible is placed on a
+pipe-stem triangle (fig. 21), supported on a tripod. It is at first
+heated gently with a Bunsen burner, and afterwards more strongly, until
+the residue is free from carbon. It is cooled, and treated with any acid
+necessary to convert the small amount of precipitate into the state in
+which it is to be weighed; heated again, and cooled. The main
+precipitate is transferred to the crucible, and the heating repeated
+very gently at first, but more strongly towards the end of the
+operation. It is next placed in the muffle, and, after two or three
+minutes at a red heat, it is removed and allowed to cool in the
+desiccator before weighing. This is for bodies that will bear a red
+heat; for those compounds that require a lower temperature the heating
+in the muffle is omitted. The muffle used for this purpose must not be
+used at the same time for cupelling; a gas muffle (fig. 22), such as one
+of Fletcher's, is best. A desiccator (fig. 23) is an air-tight vessel
+which prevents access of moisture, &c., to the substance. Usually the
+air in it is kept dry by means of a basin containing sulphuric acid.
+
+[Illustration: FIG. 21.]
+
+[Illustration: FIG. 22.]
+
+[Illustration: FIG. 23.]
+
+The crucible is removed from the muffle with the tongs and carried to
+the desiccator. It is best, in an office, to have a large desiccator
+permanently fixed alongside the balance, into which all substances may
+be put before being weighed. The substance is removed from the bench or
+muffle in the small hand apparatus generally sold, and carried to the
+balance room to be transferred to the large desiccator, where it is
+allowed to become thoroughly cold before being weighed. Twenty minutes
+is generally the time allowed after ignition before it is advisable to
+weigh. Bodies allowed to cool in the air after they have been ignited will
+absorb moisture, and hot bodies placed in the balance-pan will disturb
+the equilibrium and show false results. Compounds that absorb moisture
+must be weighed quickly; they should, therefore, be weighed in covered
+vessels. Such compounds are detected by their continually-increasing
+weight. They should be ignited and weighed again
+in a well-covered dish.
+
+Substances that have been washed with alcohol, ether, or any readily
+volatile liquid are dried in the water oven. They quickly dry if there
+is no water present, and are generally fit for weighing in less than one
+hour. Sometimes drying for a few minutes only will be sufficient.
+
+The weight of the crucible and precipitate having been obtained, the
+weight of the crucible and ash is deducted; for example--
+
+  Crucible and precipitate    10.183 grams.
+  Crucible and ash             9.527   "
+                              ------
+                               0.656   "
+
+The weight of the ash is best added to that of the crucible. The amount
+of ash in filter-papers must not be neglected, although papers are now
+made almost free from ash, and the amount to be deducted is found by
+taking eight or ten papers and burning them until they become white, and
+then weighing the ash. The amount varies from 0.004 to 0.0005 gram for
+different papers. Having determined the ash, place in the balance-drawer
+three of the filter-papers pinned together, with the weights marked on
+them in the way shown in fig. 24, so as to be readily seen when there is
+occasion to refer to them.
+
+[Illustration: FIG. 24.]
+
+It must be remembered that the determination of small quantities of
+substances generally involves the use of reagents which are often
+contaminated, as an impurity, with the body sought for. Thus, in
+assaying silver, the oxide of lead or metallic lead used is rarely free
+from silver; and in the case of arsenic, the acids, zinc or ferric
+chloride are sure to contain arsenic. The same observation applies to
+the precipitation of lead by zinc, &c. The errors caused by these
+impurities are more marked in the determination of material having small
+quantities of metal than in that of ores which contain larger
+quantities. Errors of this kind are counteracted or neutralised by
+"blank" or "blind" determinations. These consist in carrying out by the
+side of and during the assay a duplicate experiment with the reagents
+only, which are thereby subjected to the same processes of solution,
+evaporation, filtration, &c. The final result thus obtained is deducted
+from that given by the assay, the difference gives the corrected result.
+In some cases, where it is desired or necessary to have a tangible
+residue or precipitate, some _pure_ inert material is added.
+
+
+
+
+CHAPTER IV.
+
+VOLUMETRIC ASSAYS.
+
+
+These have been already described as those in which the results are got
+by measuring, either--(1) the volume of a reagent required to complete
+some reaction, or (2) the volume of the resulting product. For example,
+if a permanganate of potash solution be added to a solution containing a
+weighed amount of iron, dissolved in sulphuric acid, the strong colour
+of the permanganate of potash will be removed until a certain quantity
+of it has been added. Repeating the experiment, it will be found that
+the same amount of iron decolorises the same volume of the permanganate
+solution within certain narrow limits of variation, known as "error of
+experiment." This error is due to variation in the method of working and
+to slight differences in the weighings and measurings; it is present in
+all experimental methods, although the limits of variation are wider in
+some than in others. Apart from this error of experiment, however, it is
+certain that a given volume of the permanganate of potash solution
+corresponds to a definite weight of iron, so that if either is known the
+other may be calculated. Similarly, if a known weight of zinc (or of
+carbonate of lime) be dissolved in hydrochloric acid, a gas will be
+given off which can be measured, and so long as the conditions of the
+experiment do not vary, the same weight of zinc (or of carbonate of
+lime) gives off the same volume of gas. The weight of the one can be
+determined from the volume of the other.
+
+Or, again, the quantity of some substances may be measured by the colour
+of their solutions, on the principle that, other things being equal, the
+colour of a solution depends upon the quantity of colouring matter
+present. So that if two solutions of the same substance are equally
+coloured they are of equal strength. In this way an unknown may be
+compared with a known strength, and a fairly accurate determination may
+be made. These three illustrations serve as types of the three chief
+classes of volumetric assays--titrometric, gasometric, and colorimetric.
+
+~Titrometric Assays.~--Within the limits of the error of experiment, a
+definite volume of a solution or gas represents a certain weight of
+metal or other substance, hence the exact weight may be determined by
+experiment. The error of experiment may be reduced to insignificant
+dimensions by repeating the experiment, and taking the mean of three or
+four determinations. This will at the same time show the amount of
+variation. Thus, if 0.5 gram of iron were dissolved and found to require
+50.3 cubic centimetres of the solution of permanganate of potash, and if
+on repeating, 50.4, 50.2, and 50.3 c.c. were required, the experimenter
+would be justified in saying that 50.3 c.c. of the permanganate solution
+represent 0.5 gram of iron, and that his results were good within 0.2
+c.c. of the permanganate solution. So that if in an unknown solution of
+iron, 50.5 c.c. of the permanganate solution were used up, he could
+state with confidence that it contained a little more than 0.5 gram of
+iron. With a larger experience the confidence would increase, and with
+practice the experimental error will diminish.
+
+But supposing that the unknown solution required, say, 100.5 instead of
+50.5 c.c., he would not be justified in saying that, since 50.3 c.c. are
+equivalent to 0.5 gram, 100.6 c.c. are equivalent to twice that amount;
+and that, consequently, the unknown solution contained a little less
+than 1 gram of iron; or, at least, he could not say it except he (or
+some one else) had determined it by experiment. But if on dissolving 1
+gram of iron, he found it to require 100.6 c.c. of the solution, and in
+another experiment with 0.8 gram of iron that 80.5 c.c. of the solution
+were required, he would be justified in stating that _the volume of
+solution required is proportional to the quantity of metal present_.
+There are a large number of volumetric assays of which this is true, but
+that it is true in any particular case can only be proved by experiment.
+Even where true it is well not to rest too much weight upon it, and in
+all cases the quantity of metal taken, to determine the strength of the
+solution used, should not differ widely from that present in the assay.
+There are certain terms which should be explained here. When the
+solution of a reagent is applied under such conditions that the volume
+added can be correctly determined, the operation is called "titrating,"
+the solution of the reagent used the "standard solution," and the
+process of determining the strength of the standard solution is
+"standardising." The "standard" is the quantity of metal equivalent to
+100 c.c. of the standard solution.
+
+~Standard Solutions.~--In making these the salt is accurately weighed
+and transferred to a litre flask, or to the graduated cylinder, and
+dissolved. The method of dissolving it varies in special cases, and
+instructions for these will be found under the respective assays.
+Generally it is dissolved in a small quantity of liquid, and then
+diluted to the mark. For those substances that require the aid of heat,
+the solution is made in a pint flask, cooled, and transferred; after
+which the flask is well washed out. After dilution, the liquids in the
+measuring vessel must be thoroughly mixed by shaking. This is more
+easily and better done in the cylinder than in the litre flask. The
+solution is next transferred to a dry "Winchester" bottle and labelled.
+The label may be rendered permanent by waxing it.
+
+Standard solutions should not be kept in a place exposed to direct
+sunlight. Oxidising and reducing solutions, such as those of
+permanganate of potash, ferrous sulphate, iodine, hyposulphite of soda,
+&c., gradually weaken in strength; the solutions of other salts are more
+stable; while those of potassium bichromate and baric chloride are
+almost permanent. Solutions of potassium permanganate may be kept for a
+month or so without much change. The solutions of hyposulphite of soda
+and of iodine should be examined weekly. Ferrous sulphate solutions, if
+acidulated with sulphuric acid, may be depended on for two or three
+weeks without fresh standardising. Before filling the burette, the
+"Winchester" bottle should be well shaken and a portion of about 50 or
+100 c.c. poured into a dry beaker or test-glass. Besides the standard
+solutions, which are required for titrating an assay, permanent
+solutions of the metal or acid of equivalent strength are very useful.
+When the finishing point of a titration has been overstepped (_i.e._,
+the assay has been "overdone"), a measured volume, say 5 or 10 c.c., of
+a solution containing the same metal may be added. The titration can
+then be continued, but more cautiously, and the value in "c.c." for the
+quantity added be deducted from the final reading.
+
+~Standardising.~--Suppose the object is to standardise a solution of
+permanganate similar to that referred to above. A convenient quantity of
+iron (say 0.5 gram) would be weighed out, dissolved in dilute sulphuric
+acid, and the solution titrated. Suppose 49.6 c.c. of the permanganate
+solution are required, then
+
+        49.6 : 0.5 :: 100 : _x_
+                            _x_ = 1.008 gram.
+
+This result, 1.008 gram, is the "_standard_." When a gas is measured,
+the standard may be calculated in the same way. For example: with 0.224
+gram of zinc, 75.8 c.c. of gas were obtained. Then the quantity of zinc
+equivalent to 100 c.c. of the gas is got by the proportion.
+
+        75.8 : 0.224 :: 100 : _x_
+                              _x_ = 0.2955 gram.
+
+Using the term "standard" in this sense, the following rules hold
+good:--
+
+To find the weight of metal in a given substance:--_Multiply the
+standard by the number of c.c. used and divide by 100._ For example: a
+piece of zinc was dissolved and the gas evolved measured 73.9 c.c. Then
+by the rule, 0.2955×73.9/100 should give the weight of the piece of
+zinc. This gives 0.2184 gram.
+
+To find the percentage of metal in a given substance:--_Multiply the
+standard by the number of c.c. used and divide by the weight of
+substance taken._ For example: if 2 grams of a mineral were taken, and
+if on titrating with the permanganate solution (standard 1.008) 60.4
+c.c. were required, then (1.008×60.4)/2 = 30.44. This is the
+percentage.
+
+If the standard is exactly 1 gram, and 1 gram of ore is always taken,
+these calculations become very simple. The "c.c." used give at once the
+percentage, or divided by 100 give the weight of metal.
+
+If it is desired to have a solution with a standard exactly 1.0 gram, it
+is best first to make one rather stronger than this, and then to
+standardise carefully. Divide 1000 by the standard thus obtained and the
+result will be the number of c.c. which must be taken and be diluted
+with water to 1 litre. For example: suppose the standard is 1.008, then
+1000/1.008 gives 992, and if 992 c.c. be taken and diluted with water to
+1000 c.c. a solution of the desired strength will be obtained. The
+standard of this should be confirmed. A simpler calculation for the same
+purpose is to multiply the standard by 1000; this will give the number
+of c.c. to which 1 litre of the solution should be diluted. In the above
+example a litre should be diluted to 1008 c.c.
+
+It has been assumed in these rules that the titration has yielded
+proportional results; but these are not always obtained. There can be no
+doubt that in any actual re-action the proportion between any two
+re-agents is a fixed one, and that if we double one of these then
+exactly twice as much of the other will enter into the re-action; but in
+the working it may very well be that no re-action at all will take place
+until after a certain excess of one or of both of the re-agents is
+present. In titrating lead with a chromate of potash solution, for
+example, it is possible that at the end of the titration a small
+quantity of the lead may remain unacted on; and it is certain that a
+small excess of the chromate is present in the solution. So, too, in
+precipitating a solution of silver with a standard solution of common
+salt, a point is reached at which a small quantity of each remains in
+solution; a further addition either of silver or of salt will cause a
+precipitate, and a similar phenomenon has been observed in precipitating
+a hydrochloric acid solution of a sulphate with baric chloride. The
+excess of one or other of the re-agents may be large or small; or, in
+some cases, they may neutralise each other. Considerations like these
+emphasise the necessity for uniformity in the mode of working. Whether a
+process yields proportional results, or not, will be seen from a series
+of standardisings. Having obtained these, the results should be arranged
+as in the table, placing the quantities of metal used in the order of
+weight in the first column, the volumes measured in the second, and the
+standards calculated in the third. If the results are proportional,
+these standards will vary more or less, according to the delicacy of the
+process, but there will be no apparent order in the variation. The
+average of the standards should then be taken.
+
+  +-------------+---------------+----------+
+  |   Weight.   | Volume found. | Standard |
+  +-------------+---------------+----------+
+  | 0.2160 gram |   72.9 c.c.   |  0.2963  |
+  | 0.2185  "   |   73.9  "     |  0.2957  |
+  | 0.2365  "   |   79.9  "     |  0.2959  |
+  | 0.2440  "   |   82.3  "     |  0.2964  |
+  | 0.2555  "   |   85.9  "     |  0.2974  |
+  +-------------+---------------+----------+
+
+Any inclination that may be felt for obtaining an appearance of greater
+accuracy by ignoring the last result must be resisted. For, although it
+would make no practical difference whether the mean standard is taken as
+0.2961 or 0.2963, it is well not to ignore the possibility that an error
+of 0.4 c.c. may arise. A result should only be ignored when the cause of
+its variation is known.
+
+In this series the results are proportional, but the range of weights
+(0.216-0.2555 gram) is small. All processes yield fairly proportional
+results if the quantities vary within narrow limits.
+
+As to results which are not proportional, it is best to take some
+imaginary examples, and then to apply the lesson to an actual one. A
+series of titrations of a copper solution by means of a solution of
+potassic cyanide gave the following results:--
+
+  +---------------+---------------+-----------+
+  | Copper taken. | Cyanide used. | Standard. |
+  +---------------+---------------+-----------+
+  |   0.1 gram    |   11.9 c.c.   |   0.8403  |
+  |   0.2  "      |   23.7  "     |   0.8438  |
+  |   0.3  "      |   35.6  "     |   0.8426  |
+  |   0.4  "      |   47.6  "     |   0.8403  |
+  +---------------+---------------+-----------+
+
+These are proportional, but by using a larger quantity of acid and
+ammonia in the work preliminary to titration, we might have had to use
+1 c.c. of cyanide solution more in each case before the finishing point
+was reached. The results would then have been:
+
+  +---------------+---------------+-----------+
+  | Copper taken. | Cyanide used. | Standard. |
+  +---------------+---------------+-----------|
+  |    0.1 gram   |   12.9 c.c.   |   0.7752  |
+  |    0.2   "    |   24.7  "     |   0.8097  |
+  |    0.3   "    |   36.6  "     |   0.8191  |
+  |    0.4   "    |   48.6  "     |   0.8230  |
+  +---------------+---------------+-----------+
+
+It will be noted that the value of the standard increases with the
+weight of metal used; and calculations from the mean standard will be
+incorrect.
+
+By subtracting the lowest standardising from the highest, a third result
+is got free from any error common to the other two; thus:--
+
+    0.4 gram = 48.6 c.c. "cyanide."
+    0.1  "   = 12.9   "     "
+    ---        ----
+    0.3  "   = 35.7   "     "
+
+And the standard calculated from this corrected result is 0.8404.
+Further, if 0.3 gram requires 35.7 c.c., then 0.1 gram should require
+11.9 c.c., or 1.0 c.c. less than that actually found.
+
+We may therefore use the following rules for working processes which do
+not yield proportional results. Make a series of two or three
+titrations, using very different quantities of metal in each. Subtract
+the lowest of these from the highest, and calculate the standard with
+the remainder. Calculate the volume required by this standard in any
+case, and find the excess or deficit, as the case may be. If an excess,
+subtract it from the result of each titration; if a deficit, add it; and
+use the standard in the usual way. The following table shows an actual
+example:--
+
+  +--------------+---------------+-----------+
+  | Chalk taken. | Gas obtained. | Standard. |
+  +--------------+---------------+-----------+
+  |  0.0873 gram |   17.8 c.c.   |  0.4904   |
+  |  0.1305  "   |   27.3  "     |  0.4780   |
+  |  0.1690  "   |   35.8  "     |  0.4721   |
+  |  0.1905  "   |   40.4  "     |  0.4715   |
+  |  0.2460  "   |   52.5  "     |  0.4686   |
+  |  0.3000  "   |   64.0  "     |  0.4687   |
+  +--------------+---------------+-----------+
+
+It will be seen that the standard decreases as the quantity of chalk
+increases; this points to a deficiency in the quantity of gas evolved.
+
+Then
+
+    0.3000 = 64.0 c.c.
+    0.0873 = 17.8  "
+    ------ = ----
+    0.2127 = 46.2  "
+
+and 0.2127×100/46.2 = 0.4604. Then, multiplying the weight of chalk
+taken by 100, and dividing by 0.4604, we get the calculated results of
+the following table:--
+
+  +--------------+------------+-----------------+-------------+
+  | Chalk taken. | Gas found. | Gas calculated. | Difference. |
+  +--------------+------------+-----------------+-------------+
+  | 0.0873 gram  | 17.8 c.c.  |    18.9 c.c.    | -1.1 c.c.   |
+  | 0.1305  "    | 27.3  "    |    28.3  "      | -1.0  "     |
+  | 0.1690  "    | 35.8  "    |    36.7  "      | -0.9  "     |
+  | 0.1905  "    | 40.4  "    |    41.4  "      | -1.0  "     |
+  | 0.2460  "    | 52.5  "    |    53.4  "      | -0.9  "     |
+  | 0.3000  "    | 64.0  "    |    65.1  "      | -1.1  "     |
+  +--------------+------------+-----------------+-------------+
+
+By adding 1 c.c. to the quantity of gas obtained, and taking 0.4604 as
+the standard, the calculated results will agree with those found with a
+variation of 0.1 c.c. When a large number of assays of the same kind are
+being made, this method of calculation is convenient; when, however,
+only one or two determinations are in question, it is easier to make a
+couple of standardisings, taking quantities as nearly as possible the
+same as those present in the assays.
+
+Sometimes it is necessary to draw up a table which will show, without
+calculation, the weight of substance equivalent to a given volume of gas
+or of solution. The substance used for standardising should be, whenever
+possible, a pure sample of the substance to be determined--that is, for
+copper assays pure copper should be used, for iron assays pure iron, and
+so on; but when this cannot be got an impure substance may be used,
+provided it contains a known percentage of the metal, and that the
+impurities present are not such as will interfere with the accuracy of
+the assay. Including compounds with these, the standard may be
+calculated by multiplying the standard got in the usual way, by the
+percentage of metal in the compound or impure substance, and dividing by
+100. If, for example, the standard 1.008 gram was obtained by using a
+sample of iron containing 99.7 per cent. of metal, the corrected
+standard would be 1.008×99.7/100 = 1.005.
+
+In volumetric analysis the change brought about must be one in which the
+end of the reaction is rendered prominent either by a change of colour
+or by the presence or absence of a precipitate. If the end of the
+reaction or finishing-point is not of itself visible, then it must be
+rendered visible by the use of a third reagent called an indicator.
+
+For example, the action of sulphuric acid upon soda results in nothing
+which makes the action conspicuous; if, however, litmus or
+phenolphthalein be added the change from blue to red in the first case,
+or from red to colourless in the second, renders the finishing-point
+evident. Some indicators cannot be added to the assay solution without
+spoiling the result; in which case portions of the assay solution must
+be withdrawn from time to time and tested. This withdrawal of portions
+of the assay solution, if rashly done, must result in loss; if, however,
+the solution is not concentrated, and if the portions are only withdrawn
+towards the end of the titration, the loss is very trifling, and will
+not show-up on the result. The usual plan adopted is to have a solution
+of the indicator placed in drops at fairly equal intervals distributed
+over a clean and dry white porcelain-plate: a drop or two of the
+solution to be tested is then brought in contact with one of these and
+the effect noted. Another plan is to have thin blotting-paper, moistened
+with a solution of the indicator and dried; a drop of the solution to be
+tested placed on this shows the characteristic change. When the assay
+solution contains a suspended solid which interferes with the test, a
+prepared paper covered with an ordinary filter-paper answers very well;
+a drop of the solution to be tested is placed on the filter-paper, and,
+sinking through, shows its effect on the paper below.
+
+Except when otherwise stated, all titrations should be made at the
+ordinary temperature; cooling, if necessary, by holding the flask under
+the tap. When a titration is directed to be made in a boiling solution,
+it must be remembered that the standard solution is cold, and that every
+addition lowers the temperature of the assay.
+
+On running the solution from the burette into the assay, do not let it
+run down the side of the flask. If a portion of the assay has to be
+withdrawn for testing, shake the flask to ensure mixing, and then take
+out a drop with the test-rod; the neglect of these precautions may give
+a finishing-point too early. This is generally indicated by a sudden
+finish, in which case on shaking the flask and again testing no reaction
+is got. Do not remove the drop on the point of the burette with the
+test-rod; let it remain where it is or drop it into the solution by
+carefully opening the clip.
+
+Generally the methods of working are as follows:--
+
+(1) _When the finishing-point depends on a change of colour in the
+solution._--Increase the bulk of the assay up to from 100 to 150 c.c.
+with water. Boil or cool, as the case may be. Run in the standard
+solution from a burette speedily, until the re-agent appears to have a
+slower action, and shake or stir all the time. Then run 1 c.c. or so at
+a time, still stirring, and finally add drops until the colour change is
+got.
+
+(2) _When an outside-indicator is used._--Pour the standard solution
+from a burette into the assay until 5 or 6 c.c. from the
+finishing-point; then run in 1 c.c. at a time (stirring and testing on
+the plate between each) until the indicator shows the change wanted, and
+deduct 0.5 c.c. for excess. When greater accuracy is sought for a
+duplicate assay is made. In this case the standard solution is run in
+close up to the end, and the operation is finished off with a few drops
+at a time.
+
+(3) _Where the finishing-point depends upon the absence of a precipitate
+and no outside-indicator is used._--As in the last case, run in the
+standard solution up to within a few c.c. of the end, then run in 1 c.c.
+at a time until a precipitate is no longer formed, but here 1.5 c.c.
+must be deducted for excess, since it is evident that the whole of the
+last "c.c." must have been, and a portion of the previous one may have
+been, in excess.
+
+~Indirect Titration.~--The action of permanganate of potash upon a
+ferrous solution is one of oxidation, hence it is evident that if any
+other oxidising agent is present it will count as permanganate. In such
+a case the titration can be used (indirectly) to estimate the quantity
+of such oxidising agent, by determining how much less of the
+permanganate is used. For example, suppose that 1 gram of iron dissolved
+in sulphuric acid requires 100 c.c. of standard permanganate to fully
+oxidise it, but that the same amount of iron only requires 35.6 c.c. of
+the same standard permanganate if it has been previously heated with 0.5
+gram of black oxide of manganese. Here it is evident that 0.5 gram of
+black oxide does the work of 64.4 c.c.[4] of the permanganate solution,
+and that these quantities are equivalent; moreover, if 64.4 c.c.
+correspond with 0.5 gram, then 100 c.c. correspond with 0.7764 which is
+the standard. On theoretical grounds, and by a method of calculation
+which will be explained further on (under the heading "Calculations from
+Formulę"), it can be found that if the standard for iron is 1 gram, that
+for the black oxide will be 0.7764 gram.
+
+The principles of these indirect titrations become clearer when
+expressed in a condensed form. Thus, in the example selected, and using
+the formulę Fe = Iron, KMnO_{4} = permanganate of potash, and MnO_{2} =
+oxide of manganese, we have:--
+
+(1)                1 gram Fe = 100 c.c. KMnO_{4}
+
+(2)                1 gram Fe = 35.6 c.c. KMnO_{4} + 0.5 gram MnO_{2}
+       .'. 100 c.c. KMnO_{4} = 35.6 c.c. KMnO_{4} + 0.5 gram MnO_{2}
+    (100-35.6) c.c. KMnO_{4} = 0.5 gram MnO_{2}
+          64.4 c.c. KMnO_{4} = 0.5 gram MnO_{2}
+
+The iron does not enter into the calculation if the same quantity is
+present in the two experiments.
+
+An indirect titration thus requires three determinations, but if more
+than one assay is to be carried on, two of these need not be repeated.
+The standard is calculated in the usual way.
+
+~Colorimetric Assays.~--These are assays in which the colour imparted to
+a solution by some compound of the metal to be determined is taken
+advantage of; the depth of colour depending on the quantity of metal
+present. They are generally used for the determination of such small
+quantities as are too minute to be weighed. The method of working is as
+follows:--A measured portion of the assay solution (generally 2/3, 1/2,
+1/3, or 1/4 of the whole), coloured by the substance to be estimated, is
+placed in a white glass cylinder standing on a sheet of white paper or
+glazed porcelain. Into an exactly similar cylinder is placed the same
+amount of re-agents, &c., as the portion of the assay solution contains,
+and then water is added until the solutions are of nearly equal bulk.
+Next, a standard solution of the metal being estimated is run in from a
+burette, the mixture being stirred after each addition until the colour
+approaches that of the assay. The bulk of the two solutions is equalised
+by adding water. Then more standard solution is added until the tints
+are very nearly alike. Next, the amount added is read off from the
+burette, still more is poured in until the colour is slightly darker
+than that of the assay, and the burette read off again. The mean of the
+readings is taken, and gives the quantity of metal added. It equals the
+quantity of metal in the portion of the assay. If this portion was
+one-half of the whole, multiply by two; if one-third, multiply by three,
+and so on. When the quantity of metal in very dilute solutions is to be
+determined, it is sometimes necessary to concentrate the solutions by
+boiling them down before applying the re-agent which produces the
+coloured compound. Such concentration does not affect the calculations.
+
+~Gasometric Assays.~--Gasometric methods are not much used by assayers,
+and, therefore, those students who wish to study them more fully than
+the limits of this work will permit, are recommended to consult Winkler
+and Lunge's text-book on the subject. The methods are without doubt
+capable of a more extended application. In measuring liquids, ordinary
+variations of temperature have but little effect, and variations of
+atmospheric pressure have none at all, whereas with gases it is
+different. Thus, 100 c.c. of an ordinary aqueous solution would, if
+heated from 10° C. to 20° C., expand to about 100.15 c.c. 100 c.c. of a
+gas similarly warmed would expand to about 103.5 c.c., and a fall of one
+inch in the barometer would have a very similar effect. And in
+measuring gases we have not only to take into account variations in
+volume due to changes in temperature and atmospheric pressure, but also
+that which is observed when a gas is measured wet and dry. Water gives
+off vapour at all temperatures, but the amount of vapour is larger as
+the temperature increases.
+
+By ignoring these considerations, errors of 3 or 4 per cent. are easily
+made; but, fortunately, the corrections are simple, and it is easy to
+construct a piece of apparatus by means of which they may be reduced to
+a simple calculation by the rule of three.
+
+The volume of a gas is, in practice, usually reduced to that which it
+would be at a temperature of 0° C., when the column of mercury in the
+barometer is 760 mm. high. But, although convenient, this practice is
+not always necessary. The only thing required is some way of checking
+the variations in volume, and of calculating what the corrected volume
+would be under certain fixed conditions.
+
+Suppose that at the time a series of standardisings is being made, 100
+c.c. of air were confined in a graduated tube over moist mercury. These
+100 c.c. would vary in volume from day to day, but it would always be
+true of them that they would measure 100 c.c. under the same conditions
+as those under which the standardisings were made. If, then, in making
+an actual assay, 35.4 c.c. of gas were obtained, and the air in the tube
+measured 105 c.c., we should be justified in saying, that if the
+conditions had been those of the standardising, the 105 c.c. would have
+measured 100 c.c., and the 35.4 c.c. would have been 33.7; for 105:
+100:: 35.4: 33.7. The rule for using such a piece of apparatus for
+correcting volumes is:--_Multiply the c.c. of gas obtained by 100, and
+divide by the number of c.c. of air in the apparatus._
+
+If it is desired to calculate the volumes under standard conditions
+(that is, the gas dry, at 0° C. and 760 mm. barometric pressure) the
+calculations are easily performed, but the temperature and pressure must
+be known.
+
+_Correction for Moisture._--The "vapour tension" of water has been
+accurately determined for various temperatures, and it may be looked
+upon as counteracting the barometric pressure. For example, at 15° C.
+the vapour tension equals 12.7 millimetres of mercury; if the barometer
+stood at 750 mm., the correction for moisture would be made by
+subtracting 12.7 from 750, and taking 737.3 mm. to be the true
+barometric pressure.
+
+The vapour tensions for temperatures from 0° C. to 20° C. are as
+follows:--
+
+  -------+----------++-------+----------++-------+----------
+   Temp. | Tension. || Temp. | Tension. || Temp. | Tension.
+  -------+----------++-------+----------++-------+----------
+     0°  | 4.6 mm.  ||   7°  |  7.5 mm. ||  14°  | 11.9 mm.
+     1°  | 4.9 mm.  ||   8°  |  8.0 mm. ||  15°  | 12.7 mm.
+     2°  | 5.3 mm.  ||   9°  |  8.6 mm. ||  16°  | 13.5 mm.
+     3°  | 5.7 mm.  ||  10°  |  9.2 mm. ||  17°  | 14.4 mm.
+     4°  | 6.1 mm.  ||  11°  |  9.8 mm. ||  18°  | 15.3 mm.
+     5°  | 6.5 mm.  ||  12°  | 10.5 mm. ||  19°  | 16.3 mm.
+     6°  | 7.0 mm.  ||  13°  | 11.2 mm. ||  20°  | 17.4 mm.
+  -------+----------++-------+----------++-------+-----------
+
+The _correction for pressure_ is:--Multiply the volume by the actual
+pressure and divide by 760.
+
+The _correction for temperature_:--Multiply the volume by 273 and divide
+by the temperature (in degrees Centigrade) added to 273.
+
+For all three corrections the following rules hold good. _To reduce to
+0° C. and 760 mm. dry._
+
+                        Volume × 0.3592 × (Pressure-tension)
+  Corrected volume = --------------------------------------
+                              Temperature + 273
+
+To find the volume, which a given volume under standard conditions would
+assume, if those conditions are altered.
+
+                      Volume × 2.784 × (Temperature + 273)
+  Resulting volume =  ------------------------------------
+                               Pressure - tension
+
+As an example, we will suppose that it is desired to enclose in the
+apparatus referred to on p. 45, a volume of air, which, when dry (at 0°
+C. and 760 mm.), shall measure 100 c.c., whilst the actual temperature
+is 15° C., and the pressure 750 mm.
+
+The second formula is the one to be used, and we get 108.7 c.c.
+
+                       100 c.c.×2.784×288
+  Required volume =  ----------------------
+                           750-12.7
+
+                    80179.2
+                  = -------
+                     737.3
+
+                  = 108.7 c.c.
+
+FOOTNOTES:
+
+[4] 100-35.6 = 64.4.
+
+
+
+
+CHAPTER V.
+
+WEIGHING AND MEASURING.
+
+
+~Weighing.~--The system of weights and measures which we have adopted is
+the French or metric system; in this the gram (15.43 grains) is the unit
+of weight; the only other weight frequently referred to is the
+milligram, which is 0.001, or 1/1000 gram. The unit of volume is the
+cubic centimetre, which is approximately the volume of 1 gram of water,
+and which thus bears to the gram the same relation as grain-measures
+bear to grains. It is usual to write and even pronounce cubic centimetre
+shortly as c.c., and the only other denomination of volume we shall have
+occasion to use is the "litre," which measures 1000 c.c., and is roughly
+1-3/4 pints.
+
+The weights used are kept in boxes in a definite order, so that the
+weights on the balance can be counted as well by noting those which are
+absent from the box as by counting those present on the scale-pan. The
+weights run 50, 20, 10, 10, 5, 2, 1, 1 and 1 grams, and are formed of
+brass. The fractions of the gram are generally made of platinum or of
+aluminium, and are arranged in the following order:--0.5, 0.2, 0.1, 0.1,
+and 0.05, 0.02, 0.01, 0.01. These may be marked in this way, or they may
+be marked 500, 200, 100, 100, 50, 20, 10, 10; the 500 meaning 500
+milligrams.
+
+Some makers send out weights in the series 50, 20, 20, 10, &c.
+
+Weights of less than 0.01 gram are generally present in a box, but it is
+much more convenient to work with a rider. This is a piece of wire which
+in the pan weighs 0.01 gram; it is made in such a form that it will ride
+on the beam, and its effective weight decreases as it approaches the
+centre. If the arm of the beam is divided into tenths, then each tenth
+counting from the centre outward equals 0.001 gram or 1 milligram, and
+if these tenths be further subdivided the fractions of a milligram are
+obtained; and these give figures in the fourth place of decimals. A
+fairly good balance should be sensitive to 0.0001 gram. The weights must
+never be touched with the fingers, and the forceps for moving them is
+used for no other purpose. When not in actual use the box is kept
+closed. The weights must not be allowed to remain on the pan of the
+balance. The balance-case must not be open without some reason. It must
+be fixed level, and, once fixed, must not be needlessly moved. The bench
+on which it stands should be used for no other purpose, and no one
+should be allowed to lean upon it.
+
+[Illustration: FIG. 25.]
+
+When using a balance sit directly in front of it. Ordinarily the
+substance to be weighed is best put on the pan to the user's left; the
+weights and the rider are then easily manipulated. Powders, &c., should
+not be weighed directly on the balance; a counterpoised watch-glass or
+metal scoop (fig. 25) should be used. In some cases it is advisable to
+use a weighing-bottle. This is a light, well-stoppered bottle (fig. 3)
+containing the powdered ore. It is first filled and weighed; then some
+of the substance is carefully poured from it into a beaker or other
+vessel, and it is weighed again; the difference in the two weighings
+gives the weight of substance taken. A substance must always be cold
+when weighed, and large glass vessels should be allowed to stand in the
+balance-box a little while before being weighed. Always have the balance
+at rest when putting on or taking off anything from the pans. Put the
+weights on systematically. In using the rider (except you have a reason
+to the contrary), put it on at the 5; if this is too much, then try it
+at the 3; if then the weights are too little, try at the 4, if still not
+enough, the correct weight must be between the 4 and 5; try half-way
+between.
+
+It is best to work with the balance vibrating; equilibrium is
+established when the vibration to the left is the mean of the preceding
+and succeeding vibrations to the right. For example, if it vibrates 6
+divisions to the right on one swing, and 5 divisions on the next, the
+intermediate vibration to the left should have been 5-1/2.
+
+Note whether the substance increases in weight whilst on the balance. If
+it does it may be because it was put on warm, and is cooling, or it may
+be because it is taking up moisture from the air. Substances which take
+up moisture rapidly should be weighed in clipped watch-glasses or in
+light-weighing bottles or tubes.
+
+Students, in recording the weights, should first read off those missing
+from the box, writing down each order of figures as determined; first
+tens, then units, and so on. Remember that the first four platinum
+weights give the figures of the first place of decimals, the second four
+give the second place, and that the third and fourth places are given by
+the rider. Having taken down the figures, confirm them by reading off
+the weights as you put them back into the box. Do not rest a weight on
+the palm of your hand for convenience in reading the mark upon it.
+Remember one weight lost from a box spoils the set. Do not take it for
+granted that the balance is in equilibrium before you start weighing:
+try it.
+
+[Illustration: FIG. 26.]
+
+~Measuring Liquids.~--For coarse work, such as measuring acids for
+dissolving ores, graduated glasses similar to those used by druggists
+may be used. It is well to have two sizes--a smaller graduated into
+divisions of 5 c.c. (fig. 26), and a larger with divisions equal to 10
+c.c. No measurement of importance should be made in a vessel of this
+kind, as a slight variation in level causes a serious error.
+
+~Graduated flasks~ must be used when anything has to be made up to a
+definite bulk, or when a fixed volume has to be collected. If, for
+example, a certain weight of substance has to be dissolved and diluted
+to a litre, or if the first 50 c.c. of a distillate has to be collected,
+a flask should be used. Each flask is graduated for one particular
+quantity; the most useful sizes are 1000 c.c., 500 c.c., 200 c.c., 100
+c.c., and 50 c.c. The mark should be in the narrowest part of the neck,
+and should be tangential to the curved surface of the liquid when the
+flask _contains_ the exact volume specified. The level of a curved
+surface of liquid is at first somewhat difficult to read: the beginner
+is in doubt whether the surface should be taken at A, B, or C (fig. 27).
+It is best to take the lowest reading C. In some lights it is difficult
+to find this; in such cases a piece of white paper or card held behind
+and a little below, so as to throw light up and against the curved
+surface, will render it clear. In reading, one should look neither up at
+nor down upon the surface, but the eye should be on the same level with
+it. It must be kept in mind that flasks _contain_ the quantity
+specified, but deliver less than this by the amount remaining in them
+and damping the sides. If it is desired to transfer the contents say of
+a 100 c.c. flask to a beaker, it will be necessary to complete the
+transfer by rinsing out the flask and adding the washings; otherwise
+there will be a sensible loss. Graduated cylinders (fig. 28) are
+convenient for preparing standard solutions.
+
+[Illustration: FIG. 27.]
+
+[Illustration: FIG. 28.]
+
+[Illustration: FIG. 29.]
+
+~Pipettes~ and burettes are graduated to _deliver_ the quantities
+specified. The principle of the pipette, and the advantages and
+disadvantages of its various forms, may be understood by considering the
+first form shown in fig. 29. It is essentially a bulbed tube drawn out
+to a jet at its lower end, and having on each side of the bulb a mark so
+placed that when the surface of the liquid falls from the upper to the
+lower mark the instrument shall deliver exactly 100 c.c. The bore of the
+jet should be of such a size as will allow the level of the liquid to
+fall at the rate of about one foot in two minutes. If it runs more
+quickly than this, an appreciable error arises from the varying amount
+of liquid remaining, and damping the sides of the bulb. The flow of
+liquid from a pipette must not be hastened by blowing into it. The lower
+tube or nose of the pipette should be long enough to reach into the
+bottle or flask containing the liquid about to be measured. The pipette
+is filled by sucking at the open end with the mouth; this method of
+filling renders the use of the instrument dangerous for such liquids as
+strong acids, ammonia, and such poisonous solutions as that of potassic
+cyanide. One attempt with a fairly strong solution of ammonia will teach
+the beginner a very useful lesson. As soon as the liquid rises above the
+upper mark in the pipette, the mouth is withdrawn, and the pipette
+quickly closed by pressing the upper aperture with the index finger of
+the right hand; it is well to have the finger slightly moist, but not
+damp. The neck of the pipette should be long enough to allow its being
+firmly grasped by the fingers and thumb of the right hand without
+inconvenience. The pipette is first held in a vertical position long
+enough to allow any moisture outside the tube to run down, and then the
+liquid is allowed to run out to the level of the upper mark; this is
+easily effected by lessening the pressure. If the finger is wet, the
+flow will be jerky, and good work impossible. The pipette is next held
+over the vessel into which the 100 c.c. are to be put, and the liquid
+allowed to run out. When the bulb is nearly empty, the flow should be
+checked by replacing the finger, and the liquid allowed to escape slowly
+until the lower mark is reached. The pipette is then withdrawn; it is in
+the withdrawing that the disadvantage of this particular form[5] makes
+itself felt. It must be withdrawn very steadily, as the slightest shock
+causes the remaining column of liquid to vibrate, whereby air is drawn
+in and the liquid is forced out.
+
+This disadvantage is got rid of by making the mouth of the jet the lower
+limit, or, in other words, allowing the instrument to empty itself.
+There are two forms of such pipettes; in the one generally recommended
+in Gay-Lussac's silver assay (the last shown in fig. 29) the nose is
+replaced by a jet. This is most conveniently filled by stopping the jet
+with the finger, and allowing the liquid to flow in a fine stream into
+the neck until the pipette is filled, and then working as just
+described. The other form is the one in general use; in fact, a long
+nose to a pipette is so convenient that it may almost be said to be
+necessary. But the accuracy is slightly diminished; a long narrow tube
+makes a poor measuring instrument because of the amount of liquid it
+finally retains. A defect possessed by both forms is the retention of a
+drop of varying size in the nozzle. Whatever method is adopted for
+removing this drop must be always adhered to. The most convenient form
+is the one last described, and the most useful sizes are 100 c.c., 50
+c.c., 20 c.c., 10 c.c., and 5 c.c. Ten c.c. pipettes graduated into
+tenths of a cubic centimetre are very useful: those are best in which
+the graduation stops short of the bottom.
+
+All measurements should be made at the ordinary temperature; and, before
+being used, the pipette should be rinsed out with a cubic centimetre or
+so of the solution to be measured. After using, it should be washed out
+with water.
+
+~Burettes~ differ mainly from pipettes in having the flow of liquid
+controlled from below instead of from above. The best form is that known
+as Mohr's, one kind of which is provided with a glass stopcock, while
+the other has a piece of india-rubber tube compressed by a clip. The
+latter cannot be used for solutions of permanganate of potash or of
+iodine, or of any substance which acts on india-rubber; but in other
+respects there is little to choose between the two kinds. A burette
+delivering 100 c.c., and graduated into fifths (_i.e._, each division =
+0.2 c.c.), is a very convenient size. For some kinds of work, 50 c.c.
+divided into tenths (_i.e._, each division = 0.1 c.c.) may be selected.
+
+Burettes may be fixed in any convenient stand; they must be vertical and
+should be so placed that the assayer can read any part of the graduated
+scale without straining. When not in use, they should be kept full of
+water. When using a burette, the water must be run out; the burette is
+next rinsed with some of the solution to be used, and drained; and then
+it is filled with the solution. Next squeeze the india-rubber tube so as
+to disentangle air-bubbles and, by smartly opening the clip, allow the
+tube and jet to be filled; see that no bubbles of air are left. Then
+run out cautiously until the level of the liquid in the burette stands
+at zero. In reading the level with very dark-coloured liquids it is
+convenient to read from the level A (fig. 27), and, provided it is done
+in each reading, there is no objection to this. The accuracy of the
+reading of a burette is sensibly increased by the use of an Erdmann
+float. This is an elongated bulb, weighted with mercury, and fitting
+(somewhat loosely) the tube of the burette. It floats in the solution,
+and is marked with a horizontal line; this line is taken as the level of
+the liquid. If the burette is filled from the top, the float rises with
+aggravating slowness, and this is its chief disadvantage. The float must
+come to rest before any reading is made.
+
+[Illustration: FIG. 30.]
+
+A convenient plan for filling a burette from below is shown in fig. 30.
+The diagram explains itself. The bottle containing the standard solution
+is connected with the burette by a syphon arrangement through the glass
+tube and T-piece. The flow of liquid into the burette is controlled by
+the clip. When this clip is opened, the burette fills; and when it is
+closed, the burette is ready for use in the ordinary way.
+
+~Measuring Gases.~--Lange's nitrometer (fig. 69) is a very convenient
+instrument for many gasometric methods. It requires the use of a fair
+quantity of mercury. In fig. 31, there is a representation of a piece of
+apparatus easily fitted up from the ordinary material of a laboratory.
+It is one which will serve some useful purposes. It consists of a
+wide-mouthed bottle fitted (by preference) with a rubber cork. The cork
+is perforated, and in the perforation is placed a glass tube which
+communicates with the burette. The burette is connected by a rubber tube
+and a Y-piece, either with another burette or with a piece of ordinary
+combustion-tube of about the same size. The wide-mouthed bottle contains
+either a short test-tube or an ordinary phial with its neck cut off. In
+working the apparatus the weighed substance is put in the bottle and the
+re-agent which is to act on it, in the test-tube; the cork is then
+inserted. The liquid in the two burettes is next brought to the same
+level, either by pouring it in at A or running it out at B. The level of
+the liquid in the apparatus for correcting variation in volume is then
+read and noted. Next, after seeing that the level of the liquid in the
+burette has not changed, turn the bottle over on its side so that the
+re-agent in the test-tube shall be upset into the bottle. Then, as the
+volume of the gas increases, lower the liquid in the burette by running
+it out at B, and at the same time keep the level in A half an inch or so
+lower than that in the burette. When the action has finished bring the
+liquid in the two vessels to the same level and read off the burette.
+This part of the work must always be done in the same manner.
+
+[Illustration: FIG. 31.]
+
+_The volume corrector for gas analysis_ is a graduated glass tube of 120
+c.c. capacity inverted over a narrow glass cylinder of mercury. It
+contains 0.2 or 0.3 c.c. of water and a volume of air, which, if dry and
+under standard conditions, would measure 100 c.c. The actual volume
+varies from day to day, and is read off at any time by bringing the
+mercury inside and outside to the same level. This is done by raising or
+lowering the tube, as may be required. Any volume of gas obtained in an
+assay can be corrected to standard temperature and pressure by
+multiplying by 100 and dividing by the number of c.c. in the corrector
+at the time the assay is made.
+
+FOOTNOTES:
+
+[5] It is best to use this form with a glass stopcock, or with an
+india-rubber tube and clip, after the manner of a Mohr's burette.
+
+
+
+
+CHAPTER VI.
+
+RE-AGENTS.--ACIDS, ETC.
+
+
+~Acetic Acid~, H[=A=c] or C_{2}H_{4}O_{2}. (sp. gr. 1.044, containing 33
+per cent. real acid).--An organic acid, forming a class of salts,
+acetates, which are for the most part soluble in water, and which, on
+ignition, leave the oxide or carbonate of the metal. It is almost always
+used in those cases where mineral acids are objectionable. To convert,
+for example, a solution of a substance in hydrochloric acid into a
+solution of the same in acetic acid, alkali should be added in excess
+and then acetic acid. Many compounds are insoluble in acetic acid, which
+are soluble in mineral acids, such as ferric phosphate, ferric arsenate,
+zinc sulphide, calcium oxalate, &c., so that the use of acetic acid is
+valuable in some separations. The commercial acid is strong enough for
+most purposes, and is used without dilution.
+
+~"Aqua Regia"~ is a mixture of 1 part by measure of nitric acid and 3
+parts of hydrochloric acid. The acids react forming what is practically
+a solution of chlorine.[6] The mixture is best made when wanted, and is
+chiefly used for the solution of gold and platinum and for "opening up"
+sulphides. When solutions in aqua regia are evaporated, chlorides are
+left.
+
+~Bromine~, Br. (sp. gr. 3.0). Practically pure bromine.--It is a heavy
+reddish-brown liquid and very volatile. It boils at 60° C., and,
+consequently, must be kept in a cool place. It gives off brown
+irritating vapours, which render its use very objectionable. Generally
+it answers the same purpose as aqua regia, and is employed where the
+addition of nitric acid to a solution has to be specially avoided. It is
+also used for dissolving metals only from ores which contain metallic
+oxides not desired in the solution.
+
+~"Bromine Water"~ is simply bromine shaken up with water till no more is
+dissolved.
+
+~Carbonic Acid~, CO_{2}.--A heavy gas, somewhat soluble in water; it is
+mainly used for providing an atmosphere in which substances may be
+dissolved, titrated, &c., without fear of oxidation. It is also used in
+titrating arsenic assays with "iodine" when a feeble acid is required
+to prevent the absorption of iodine by the alkaline carbonate. It is
+prepared when wanted in solution, by adding a gram or so of bicarbonate
+of soda and then as much acid as will decompose the bicarbonate
+mentioned. When a quantity of the gas is wanted, it is prepared, in an
+apparatus like that used for sulphuretted hydrogen, by acting on
+fragments of marble or limestone with dilute hydrochloric acid.
+
+~Citric Acid~ (H_{3}[=C=i] or C_{6}H_{8}O_{7}.H_{2}O) is an organic acid
+which occurs in colourless crystals, soluble in less than their weight
+of water. The solution must be freshly prepared, as it gets mouldy when
+kept. It forms a comparatively unimportant class of salts (citrates). It
+is used in the determination of phosphoric acid, chiefly for the purpose
+of preventing the precipitation of phosphates of iron and alumina by
+ammonia, and in a few similar cases. The commercial crystals are used;
+they should be free from sulphuric acid and leave no ash on ignition.
+
+~Hydrochloric Acid~, HCl in water, (sp. gr. 1.16. It contains 32 per
+cent. of hydrogen chloride).--It is sometimes called "muriatic acid,"
+and when impure, "spirit of salt." The acid solution should be
+colourless and free from arsenic, iron, and sulphuric acid. It forms an
+important family of salts, the chlorides. It is the best acid for
+dissolving metallic oxides and carbonates, and is always used by the
+assayer when oxidising agents are to be avoided. The acid is used
+without dilution when no directions are expressly given to dilute it. It
+has no action on the following metals: gold, platinum, arsenic, and
+mercury; it very slightly attacks antimony, bismuth, lead, silver, and
+copper. Tin is more soluble in it, but with difficulty; whilst iron,
+zinc, nickel, cobalt, cadmium, and aluminium easily dissolve with
+evolution of hydrogen and the formation of the lower chloride if the
+metal forms more than one class of salts. All the metallic oxides,
+except a few of the native and rarer oxides, are dissolved by it with
+the formation of chlorides of the metal and water.
+
+~Dilute Hydrochloric Acid~ is made by diluting the strong acid with an
+equal volume of water. This is used for dissolving precipitates obtained
+in the general course of analysis and the more easily soluble metals.
+
+~Hydrofluoric Acid, HF.~--A solution in water may be purchased in
+gutta-percha or lead bottles. It is of variable strength and doubtful
+purity. It must always be examined quantitatively for the residue left
+on evaporation. It is used occasionally for the examination of
+silicates. It attacks silica, forming fluoride of silicon, which is a
+gas. When the introduction of another base will not interfere with the
+assay, the substance may be mixed in the platinum dish with fluoride of
+ammonium, or of potassium, or of calcium, and hydrochloric acid,
+instead of treating it with the commercial acid. It is only required in
+special work. The fumes and acid are dangerous, and, of course, glass or
+porcelain vessels cannot be used with it.
+
+~Iodine, I.~--This can be obtained in commerce quite pure, and is often
+used for standardising. It is very slightly soluble in water, but
+readily dissolves in potassium iodide solution. It closely resembles
+chlorine and bromine in its properties, and can be used for dissolving
+metals without, at the same time, attacking any oxide which may be
+present. It is chiefly used as an oxidizing agent in volumetric work,
+being sharp in its reactions and easily detected in minute quantities.
+It cannot be used in alkaline solutions, since it reacts with the
+hydrates, and even with the carbonates, to form iodides and iodates.
+Iodine is soluble in alcohol.
+
+~Nitric Acid, HNO_{3}.~ (Sp. gr. 1.42; boiling point 121° C.; contains
+70 per cent. by weight of hydrogen nitrate).--It is convenient to
+remember that one c.c. of this contains 1 gram of real acid. It combines
+the properties of an acid and of an oxidising agent. One c.c. contains
+0.76 gram of oxygen, most of which is very loosely held, and easily
+given up to metals and other oxidisable substances. Consequently it will
+dissolve many metals, &c., upon which hydrochloric acid has no action.
+All sulphides (that of mercury excepted) are attacked by it, and for the
+most part rendered soluble. It has no action on gold or platinum, and
+very little on aluminium. The strong acid at the ordinary temperature
+does not act on iron or tin; and in most cases it acts better when
+diluted. Some nitrates being insoluble in nitric acid, form a protecting
+coat to the metal which hinders further action. Where the strong acid
+does act the action is very violent, so that generally it is better to
+use the dilute acid. When iron has been immersed in strong nitric acid
+it not only remains unacted on, but assumes a _passive_ state; so that
+if, after being wiped, it is then placed in the dilute acid, it will not
+dissolve. Tin and antimony are converted into insoluble oxides, while
+the other metals (with the exception of those already mentioned)
+dissolve as nitrates. During the solution of the metal red fumes are
+given off, which mainly consist of nitrogen peroxide. The solution is
+often coloured brown or green because of dissolved oxides of nitrogen,
+which must be got rid of by boiling. Generally some ammonium nitrate is
+formed, especially in the cases of zinc, iron, and tin, when these are
+acted on by cold dilute acid. Sulphur, phosphorus, and arsenic are
+converted into sulphuric, phosphoric, and arsenic acids respectively,
+when boiled with the strong acid.
+
+~Dilute Nitric Acid.~--Dilute 1 volume of the strong acid with 2 of
+water.
+
+~Oxalic Acid~, H_{2}[=O] or (H_{2}C_{2}O_{4}.2H_{2}O.)--This is an organic
+acid in colourless crystals. It forms a family of salts--the oxalates.
+It is used in standardising; being a crystallised and permanent acid, it
+can be readily weighed. It is also used in separations, many of the
+oxalates being insoluble. For general use make a 10 per cent. solution.
+Use the commercially pure acid. On ignition the acid should leave no
+residue.
+
+[Illustration: FIG. 32.]
+
+~Sulphuretted Hydrogen.~ Hydrosulphuric acid, SH_{2}.--A gas largely
+used in assaying, since by its action it allows of the metals being
+conveniently classed into groups. It is soluble in water, this liquid
+dissolving at the ordinary temperature about three times its volume of
+the gas. The solution is only useful for testing. In separations, a
+current of the gas must always be used. It is best prepared in an
+apparatus like that shown in fig. 32, by acting on ferrous sulphide with
+dilute hydrochloric acid. When iron has to be subsequently determined in
+the assay solution, the gas should be washed by bubbling it through
+water in the smaller bottle; but for most purposes washing can be
+dispensed with. The gas is very objectionable, and operations with it
+must be carried out in a cupboard with a good draught. When the
+precipitation has been completed, the apparatus should always be washed
+out. The effect of this acid on solutions of the metals is to form
+sulphides. All the metallic sulphides are insoluble in water; but some
+are soluble in alkaline, and some in acid, solutions. If sulphuretted
+hydrogen is passed through an acid solution containing the metals till
+no further precipitation takes place, a precipitate will be formed
+containing sulphides insoluble in the acid. On filtering, adding ammonia
+(to render the filtrate alkaline), and again passing the gas, a further
+precipitate will be obtained, consisting of sulphides insoluble in an
+alkaline solution, but not precipitable in an acid one; the filtrate may
+also contain sulphides not precipitable in an acid solution, which are
+soluble in an alkaline one; these will be thrown down on neutralising.
+Again, the metals precipitated in the acid solution form sulphides which
+may be divided into groups, the one consisting of those which are
+soluble, and the other of those which are not soluble, in alkalies. This
+classification is shown in the following summary:--
+
+1. _Precipitable in an acid solution._
+
+(a) Soluble in Alkalies.--Sulphides of As, Sb, Sn, Au, Pt, Ir, Mo, Te,
+and Se.
+
+(b) Insoluble in Alkalies.--Sulphides of Ag, Pb, Hg, Bi, Cu, Cd, Pd, Rh,
+Os, and Ru.
+
+2. _Not precipitated in an acid solution, but thrown down in an alkaline
+one._
+
+Sulphides of Mn, Zn, Fe, Ni, Co, In, Tl, and Ga.
+
+These can again be divided into those which are dissolved by dilute
+acids and those which are not.
+
+3. _Not precipitated in an acid or alkaline solution, but thrown
+down on neutralising the latter._
+
+Sulphides of V and W.
+
+Sulphuretted hydrogen is a strong reducing agent. Ferric salts are
+thereby quickly reduced to ferrous; in hot solutions nitric acid is
+decomposed. These changes are marked by a precipitation of sulphur, and
+the student must be careful to pass the gas sufficiently long, and not
+be too hasty in concluding that no sulphide will form because it does
+not at once make its appearance. The best indication that it has been
+passed long enough is the smell of the gas in the solution after
+shaking.
+
+~Sulphurous Acid~, H_{2}SO_{3}.--The reagent used may be regarded as a
+saturated solution of sulphur dioxide in water. It may be purchased, and
+keeps for a long time. It may be made by heating copper with sulphuric
+acid and passing the gas formed into water. The heat should be withdrawn
+when the gas is coming off freely. It is used as a reducing agent, and
+should not be diluted.
+
+~Sulphuric Acid~, H_{2}SO_{4}. (Sp. gr. 1.84, containing 96 per cent. of
+real acid, H_{2}SO_{4}.)--This acid forms insoluble sulphates with salts
+of lead, strontium, and barium. It has a high boiling point, 290° C.,
+and, when evaporated with salts of the more volatile acids, converts
+them into sulphates. When nitrates or chlorides are objectionable in a
+solution, evaporation with sulphuric acid removes them. In working with
+this acid caution is necessary, since, on mixing with water, great heat
+is evolved; and, if either the acid or water has been previously heated,
+a serious accident may result. In diluting the acid it should be poured
+into cold water. Glass vessels containing boiling sulphuric acid should
+be handled as little as possible, and should not be cooled under the
+tap. The action of diluted sulphuric acid on metals closely resembles
+that of dilute hydrochloric acid. Magnesium, aluminium, iron, zinc,
+nickel, cobalt, manganese, and cadmium dissolve, with evolution of
+hydrogen, in the cold acid, or when warmed. The action of hot and strong
+sulphuric acid is altogether different; it acts as an oxidising agent,
+and is itself reduced to sulphur dioxide or even to sulphur. The
+following metals are attacked in this way:--copper, bismuth, mercury,
+silver, antimony, tin, and lead. Gold, platinum, and arsenic are not
+affected. This property is made use of in parting silver from gold and
+platinum. Metallic sulphides are similarly attacked; but this method of
+opening up minerals has the disadvantage of giving rise to the formation
+of anhydrous sulphates of iron, &c., which are not readily dissolved
+when afterwards diluted. The use of sulphuric acid in assaying is (for
+these reasons) to be avoided. Its chief use is as a drying agent, since
+it has a strong affinity for water. Air under a bell jar may be kept dry
+by means of a basin of sulphuric acid, and gases bubbled through it are
+freed from water-vapour.
+
+~Dilute Sulphuric Acid.~--This is made by diluting 1 volume of the
+strong acid with 4 of water.
+
+~Tartaric Acid~, H_{2}[=T] or C_{4}H_{6}O_{6}.--A crystallised organic
+acid, soluble in less than its own weight of water, or in less than
+three parts of alcohol. It is used for the same purposes as citric acid
+is. The solution is made when required.
+
+
+BASES, SALTS, &c.
+
+~Alcohol~, C_{2}H_{6}O. (Commercial alcohol of sp. gr. 0.838; it
+contains 84 per cent. by weight of alcohol.)--It should burn with a
+non-luminous flame and leave no residue. It is used for washing
+precipitates where water is inapplicable, and for facilitating drying.
+
+~Ammonia~, NH_{3}. (Commercial ammonia, a solution having a sp. gr. of
+0.88 to 0.89, and containing about 33 per cent. of ammonia.)--It is used
+as an alkali (more commonly than soda or potash), since an excess of it
+is easily removed by boiling. The salts of ammonium formed by it may be
+removed by igniting, or by evaporating in a porcelain dish with an
+excess of nitric acid. It differs in a marked way from soda or potash in
+its solvent action on the oxides or hydrates of the metals. Salts of the
+following metals are soluble in an ammoniacal solution in the presence
+of ammonic chloride:--copper, cadmium, silver, nickel, cobalt,
+manganese, zinc, magnesium, sodium, potassium, and the alkaline earths.
+
+~Dilute Ammonia~ is made by diluting 1 vol. of commercial ammonia with 2
+of water. The dilute ammonia is always used; but in assays for copper a
+stronger solution (1 of strong ammonia to 1 of water) is required.
+
+~Ammonic Carbonate~ (Am_{2}CO_{3}) is prepared by dissolving one part of
+the commercial sesquicarbonate of ammonia in four parts of water, and
+adding one part of strong ammonia.
+
+~Ammonic Bicarbonate~ (HAmCO_{3}) is prepared by saturating a solution
+of the sesquicarbonate of ammonia with carbon dioxide.
+
+~Ammonic Chloride~, AmCl.--Use the commercial salt in a 20 per cent.
+solution in water. The salt should leave no residue on ignition.
+
+~Ammonic Molybdate.~--The solution is prepared as follows:--Dissolve 100
+grams of the powdered commercial salt in 200 c.c. of dilute ammonia, and
+pour the solution in a slow stream into 750 c.c. of dilute nitric acid;
+make up to 1 litre, and allow the mixture to settle before using. It is
+used for the purpose of separating phosphoric oxide from bases and from
+other acids, and also as a test for phosphates and arsenates. In using
+this solution the substance must be dissolved in nitric acid, and a
+considerable excess of the reagent added (50 c.c. is sufficient to
+precipitate 0.1 gram P_{2}O_{5}); when the phosphate is in excess no
+precipitate will be got. The precipitate is phospho-molybdate of
+ammonia.
+
+~Ammonic Nitrate~ (AmNO_{3}) is used in the separation of phosphoric
+oxide by the molybdate method, and occasionally for destroying organic
+matter. It is soluble in less than its own weight of water. The solution
+is made when wanted.
+
+~Ammonic Oxalate~ (Am_{2}C_{2}O_{4}.2H_{2}O) is used chiefly for the
+separation of lime. The solution is made by dissolving 15 grams of the
+salt in 100 c.c. of water.
+
+~Ammonic Sulphide~ may be purchased in the state of a strong solution.
+It is yellow, and contains the disulphide, S_{2}Am_{2}. It serves the
+same purpose as is obtained by passing a current of sulphuretted
+hydrogen through an ammoniacal solution; but has the disadvantage of
+loading the solution with sulphur, which is precipitated when the
+solution is subsequently acidified. It is useful for dissolving the
+lower sulphide of tin (SnS).
+
+~Baric Carbonate~ (BaCO_{3}) is sometimes used for precipitating the
+weaker bases. It should be prepared when wanted by precipitating a
+solution of baric chloride with ammonic carbonate and washing. The moist
+precipitate is used without drying.
+
+~Baric Chloride~, BaCl_{2}.2H_{2}O.--A crystallised salt, soluble in
+2-1/2 parts of water. It is used for the detection and separation of
+sulphates. Make a 10 per cent. solution.
+
+"~Black Flux.~"--A mixture of finely divided carbon with carbonate of
+potash or with carbonates of potash and soda. It is prepared by heating
+tartar or "rochelle salt" until no more combustible gas is given off.
+One gram will reduce about 2 grams of lead from litharge.
+
+~Borax~, Na_{2}B_{4}O_{7}.10H_{2}O.--It is chiefly used as a flux in dry
+assaying, as already described. It is also used in testing before the
+blowpipe; many metallic oxides impart a characteristic colour to a bead
+of borax in which they have been fused.
+
+~Calcium Chloride.~--The crystallised salt is CaCl_{2}.6H_{2}O; dried at
+200° C. it becomes CaCl_{2}.2H_{2}O, and when fused it becomes
+dehydrated. The fused salt, broken into small lumps, is used for drying
+gases. It combines with water, giving off much heat; and dissolves in a
+little more than its own weight of water. Strong solutions may be used
+in baths in which temperatures above the boiling-point of water are
+required. One part of the salt and 2 of water give a solution boiling at
+112°, and a solution of 2 parts of the salt in 1 of water boils at 158°.
+The salt is very little used as a reagent.
+
+~Calcium Fluoride~ or "~Fluor Spar~," CaF_{2}.--The mineral is used as a
+flux in dry assaying; it renders slags which are thick from the presence
+of phosphates, &c., very fluid. Mixed with hydrochloric acid it may
+sometimes be used instead of hydrofluoric acid.
+
+~Calcium Carbonate~, CaCO_{3}.--It is precipitated in a pure state by
+ammonic carbonate from a solution of calcium chloride. It is used for
+standardising. In the impure state, as marble or limestone, it is used
+in the preparation of carbonic acid.
+
+~Calcium Hydrate~ or ~"Lime Water."~--This is used in testing for carbon
+dioxide and in estimating the amount of that gas present in air. It may
+be made by slaking quicklime and digesting the slaked lime with water.
+One hundred c.c. of water at 15° C. dissolves 0.1368 grams of the
+hydrate (CaH_{2}O_{2}), and hot water dissolves still less. "_Milk of
+lime_" is slaked lime suspended in water.
+
+~Cobalt Nitrate~ (Co(NO_{3})_{2}.6H_{2}O) is used in a 10 per cent.
+solution for the detection of oxides of zinc, aluminium, &c.; on
+ignition with which it forms characteristically coloured compounds.
+
+~Copper~, Cu.--Pure copper, as obtained by electrolysis, can be
+purchased. This only should be used.
+
+~Copper Oxide~, CuO.--It occurs as a black, heavy, and gritty power, and
+is used for the oxidation of carbon and hydrogen in organic substances.
+It should be ignited and cooled out of contact with air just before
+using, since it is hygroscopic. Oxide of copper which has been used may
+be again utilised after calcination.
+
+~Copper Sulphate~ (CuSO_{4}.5H_{2}O) contains 25.4 per cent. of copper.
+It is used in the outer cell of a Daniell-battery. The commercial salt
+is used for this purpose. The re-crystallised and pure salt is used for
+preparing the anhydrous sulphate, which is used for detecting moisture
+in gases. For this purpose it is dried at 200° C. till no trace of
+green or blue colour remains. It must be prepared when wanted. It may be
+conveniently used in the form of pumice-stone, saturated with a solution
+of the salt and dried. Traces of moisture develop a green colour.
+
+~Ferric Chloride~, Fe_{2}Cl_{6}. (When crystallised,
+Fe_{2}Cl_{6}.6H_{2}O.)--The solution is prepared as described under
+iron. The commercial salt contains arsenic, and, since the chief use of
+ferric chloride is for the determination of this substance, it must be
+purified (_see_ under ARSENIC).
+
+~Ferric Sulphate~ (Fe_{2}(SO_{4})_{3}) is a yellowish white deliquescent
+salt. It is used as an indicator in volumetric silver assaying, and for
+the separation of iodine from bromine. It may be purchased as iron alum,
+Am_{2}Fe_{2}(SO_{4})_{4}.24H_{2}O. But it is best prepared by adding
+strong sulphuric acid to ferric hydrate in equivalent proportions. Use
+it as a solution containing 2 or 3 per cent. of iron.
+
+~Ferrous Sulphate~, FeSO_{4}.7H_{2}O.--The granulated form is best, and
+can be purchased pure. It is used for standardising. It keeps better in
+crystals than in solution. It is readily soluble in water, but the
+solution is best made with the help of a little free acid. As a re-agent
+use a 10 per cent. solution. The crystals should be clear bluish-green;
+if their colour is dark green, brown, or blue, they should be rejected.
+
+~Ferrous Sulphide~ (FeS) is used for the preparation of sulphuretted
+hydrogen. It may be purchased and broken in small lumps, nut-size, for
+use.
+
+"~Fusion Mixture~" (K_{2}CO_{3}.Na_{2}CO_{3}) is a mixture of potassic
+and sodic carbonates in the proportions of 13 of the former to 10 of the
+latter, by weight. It is hygroscopic. A mixture of the bicarbonates is
+better, being purer and less apt to get damp.
+
+~Gallic Acid~ (C_{7}H_{6}O_{5}.H_{2}O) is an organic acid, occurring as
+a pale fawn-coloured crystalline powder, soluble in 100 parts of cold
+water, or in 3 parts of boiling water. It is used for the determination
+of antimony. A 10 per cent. solution in warm water is made when
+required.
+
+~Hydrogen~ (H) is a gas. It is obtained by acting on zinc with dilute
+hydrochloric or sulphuric acid. It is used as a reducing agent, and for
+providing an atmosphere free from oxygen. It reduces metallic oxides at
+a high temperature. It must be freed from water; and special precautions
+should be taken to prevent an admixture with air. It is generally
+required in a current which can be continued for an hour or more without
+interruption. The preparation can be conveniently carried out in the
+apparatus shown (fig. 33). A quart bottle is half filled with sheet
+zinc, and connected with bulbs filled with sulphuric acid, and with a
+calcium chloride tube. The last is connected with the apparatus through
+which the gas has to be passed. Dilute hydrochloric acid mixed with a
+few cubic centimetres (20 c.c. to 1 pint) of stannous chloride sol. to
+fix any dissolved oxygen, is placed in the funnel, and let into the
+bottle by opening the stopcock when required. Care must be taken to let
+the hydrogen escape for some time before starting the reduction.
+
+[Illustration: FIG. 33.]
+
+~Gold~, Au.--Gold, obtained by cupelling and "parting," is for most
+purposes sufficiently pure. It is best kept in the shape of foil. When
+the purer metal is required, gold should be dissolved in aqua regia, the
+solution evaporated to a paste, diluted, allowed to stand, and filtered.
+The filtered solution is acidified with hydrochloric acid, warmed, and
+precipitated with sodium sulphite. The precipitate is collected, washed,
+and fused on charcoal.
+
+~Iron~, Fe.--The soft wire (thin) is used for standardising. Rods are
+used in dry assays as a desulphurising agent. Steel must not be used,
+since it is not pure, and contains a variable amount of iron.
+
+~Lead~, Pb.--Granulated lead or lead-foil is used in the dry assay for
+silver and gold, and in the preparation of lead salts. It can be
+obtained very pure, but always contains more or less silver, 1 or 2
+milligrams in 100 grams. The amount of silver it contains must be
+determined and recorded.
+
+~Lead Acetate~ (Pb[=A=c]_{2}.3H_{2}O, or
+Pb(C_{2}H_{3}O_{2})_{2}.3H_{2}O) is used as a test, specially for the
+detection and estimation of sulphuretted hydrogen. Prepare a 10 per
+cent. solution for use.
+
+~Lead Nitrate~ (Pb(NO_{3})_{2}) can be purchased pure. It is used for
+standardising.
+
+~Lead Dioxide~ (PbO_{2}) occurs as a dark-brown powder. It is used as an
+oxidizing agent and for absorbing sulphurous oxide. It can be prepared
+by digesting red lead with warm dilute nitric acid; washing and drying
+the residue.
+
+"~Litharge~," PbO.--It can be purchased as a yellow heavy powder. It is
+used in dry assaying as a flux, as a desulphurising agent, and also as a
+source of lead. It always contains some silver, the amount of which must
+be determined.
+
+~Litmus.~--This is an organic colouring matter which is turned red by
+acids and blue by alkalies. For ordinary purposes it is best used as
+litmus paper, which may be purchased in small books. A solution is
+prepared by digesting 15 or 20 grams of the commercial litmus in 100
+c.c. of water on the water bath. After being allowed to settle, it is
+filtered and made just faintly red with acetic acid. Then there is
+added a drop or two of a solution of soda and 10 c.c. of alcohol. It
+should be kept in a loosely-covered bottle.
+
+~Magnesia~, MgO.--It may be purchased as "calcined magnesia." It is used
+for making "magnesia mixture," and should be kept in a corked
+wide-mouthed bottle.
+
+"~Magnesia Mixture.~"--Dissolve 22 grams of magnesia in about a quarter
+of a litre of dilute hydrochloric acid, avoiding excess. Add 5 grams of
+magnesia, boil, and filter. Add 300 grams of ammonic chloride, and 250
+c.c. of strong ammonia; and dilute with water to 2 litres. It should be
+kept in a stoppered winchester.
+
+~Magnesium Sulphate~, MgSO_{4}.7H_{2}O.--It can be purchased very pure,
+and is occasionally used as a standard salt.
+
+~Manganese Dioxide~, MnO_{2}.--It is used in the preparation of
+chlorine. The commercial article is not pure, but is sufficiently so for
+this purpose.
+
+~Marble~, CaCO_{3}.--Fragments of the white crystalline variety only
+should be used. It is used as a source of lime and of carbon dioxide.
+
+~Mercury~, Hg.--This can be purchased pure. It should have a bright
+surface, flow without a tail, and leave no residue on ignition. It is
+used as a standard; for amalgamation; and as a confining liquid in gas
+analysis.
+
+~Mercuric Chloride~ (HgCl_{2}) may be purchased pure. Make a 5 per cent.
+solution in water. It is used for destroying an excess of stannous
+chloride; for removing sulphuretted hydrogen from solution; and as a
+test for stannous salts.
+
+~Microcosmic Salt~, HAmNaPO_{4}.8H_{2}O.--When fused NaPO_{3} is formed.
+It is used in testing for metallic oxides and silica before the
+blowpipe. The crystals are sometimes used as a standard for phosphoric
+acid.
+
+"~Nessler's Solution.~"--Mode of preparation: Dissolve 35 grams of
+potassium iodide in 100 c.c. of water; dissolve 17 grams of mercuric
+chloride in 300 c.c. of water, and pour this solution into that of the
+iodide till a permanent precipitate is produced; make up to 1 litre with
+a 20 per cent. solution of potash; add mercuric chloride till a
+precipitate is again formed; allow to settle and decant. It is used for
+detecting ammonia.
+
+~Nitre.~--This is potassium nitrate.
+
+~Platinum Chloride~, 2HCl.PtCl_{4}. (In the crystallised form it has
+6H_{2}O).--It may be made as follows:--Take 5 grams of clean platinum
+scrap and dissolve in a flask at a gentle heat in 50 c.c. of
+hydrochloric acid with the occasional addition of some nitric acid;
+evaporate to a paste; and then dissolve in 100 c.c. of water. It is used
+for separating and determining potassium.
+
+~Phenolphthalein~ is an organic compound used as an indicator; more
+especially in determining the weaker acids, it cannot be used in the
+presence of ammonia. Dissolve half a gram in 100 c.c. of dilute alcohol.
+
+~Potassium Bicarbonate~, KHCO_{3}.--It may be purchased pure; on
+ignition it leaves the carbonate, K_{2}CO_{3}, which may be used as a
+standard.
+
+~Potassium Cyanide~, KCN.--It is used in the dry assay as a reducing
+agent. The commercial salt is very impure. Purchase that sold as
+potassic cyanide (gold) which contains about 95 per cent. of KCN. It is
+used for copper assaying and occasionally in separation. Make a 10 per
+cent. solution when wanted.
+
+~Potassium Bichromate~, K_{2}Cr_{2}O_{7}. It may be purchased nearly
+pure. It is used as an oxidising agent, for determining iron; and as a
+test solution. For this last purpose a 10 per cent. solution is
+prepared.
+
+~Potassium Chlorate~ (KClO_{3}) can be purchased pure. It is used with
+hydrochloric acid as a substitute for aqua regia.
+
+~Potassium Ferrocyanide~ (K_{4}Fe(CN)_{6}.3H_{2}O), or "yellow prussiate
+of potash," is used as a test; as an indicator; and for the
+determination of zinc. Make a 5 per cent. solution.
+
+~Potassium Ferricyanide~ (K_{6}Fe_{2}(CN)_{12}), or "red prussiate of
+potash," is used for testing; and as an indicator. Make a 5 per cent.
+solution when wanted, as it decomposes on keeping.
+
+~Potassium Hydrate~, KHO. Purchase that purified with alcohol. It is an
+alkali, and is used for absorbing carbonic acid, &c.
+
+~Potassium Iodide~, KI. It may be purchased nearly pure. It is used as a
+test and for dissolving iodine. It should be used in a 10 per cent.
+solution freshly made. The solution decomposes on exposure to light,
+with separation of iodine.
+
+~Potassium Nitrate~ (KNO_{3}) can be purchased pure. It is used in the
+dry way as an oxidizing agent. It is very fusible. It decomposes at a
+low temperature into potassium nitrite (KNO_{2}) and free oxygen; and at
+a higher temperature leaves potash (K_{2}O). It oxidizes sulphur and
+carbon with explosive violence. This action may be moderated by mixing
+the nitre with carbonate of soda, common salt, or some other inert body.
+
+~Potassium Nitrite~, KNO_{2}.--The commercial article is not pure, but
+is sufficiently so for the purpose required. A saturated solution is
+used in the separation of cobalt; the solution is made when wanted.
+
+~Potassium Permanganate~, KMnO_{4}.--This salt can be purchased
+sufficiently pure. It is much used as an oxidizing agent.
+
+~Potassium Bisulphate~ (KHSO_{4}) is used as a dry reagent for opening
+up minerals. It fuses; and at a much higher temperature is converted
+into potassium sulphate with loss of sulphuric acid.
+
+~Potassium Sulphocyanate~ (KCNS) is used for the detection and
+determination of traces of ferric iron; as also in the separation of
+silver and copper from some of the other metals. Make a 10 per cent.
+solution. It should show no colour on the addition of hydrochloric acid.
+
+"~Red Lead~" (Pb_{3}O_{4}) is used in the dry assay as a flux instead of
+litharge, from which it differs in containing a little more oxygen. When
+acted on by nitric acid a brown residue of lead dioxide is left, nitrate
+of lead going into solution. Like litharge it always carries silver;
+about 2 milligrams in 100 grams.
+
+~Silver~, Ag.--Pure silver in foil is required as a standard. It may be
+prepared as follows:--Dissolve scrap silver in dilute nitric acid and
+decant off from any residue; dilute the solution with hot water and add
+hydrochloric acid until there is no further precipitate, stir; allow the
+precipitate to settle; decant and wash; dry the precipitate, mix it with
+twice its bulk of carbonate of soda and fuse the mixture in a crucible
+until tranquil; clean the button and roll or hammer it into foil.
+
+~Sodium Acetate~, NaC_{2}H_{3}O_{2}.3H_{2}O.--The crystals may be
+purchased sufficiently pure. Make a 20 per cent. solution in water. It
+is used for replacing mineral acids by acetic acid.[7]
+
+~Sodium Acetate and Acetic Acid.~--A solution is used in the
+determination of phosphates and arsenates; 100 grams of the salt is
+dissolved in 500 c.c. of acetic acid, and diluted with water to one
+litre.
+
+~Sodium Bicarbonate~ (NaHCO_{3})is used as a flux in dry methods. On
+ignition it leaves the carbonate (Na_{2}CO_{3}), which is used as a
+standard reagent. Make a 20 per cent. solution of the carbonate for use.
+It should be free from chlorides or sulphates, or if impure the amount
+of impurities must be determined.
+
+~Sodium Hydrate~, NaHO. It may be purchased in sticks, which should be
+kept in a well-corked bottle. It is sometimes called "caustic soda." It
+is a strong alkali. It is used for neutralizing acid solutions and for
+separations where ammonia is unsuitable. Make a 5 per cent. solution for
+use.
+
+~Sodium Hyposulphite~, Na_{2}S_{2}O_{8}.5H_{2}O.--It may be purchased
+pure. It is generally known as "hypo." It is used as a standard.
+
+~Sodium Sulphite~ (Na_{2}SO_{3}.7H_{2}O) is used as a reducing agent.
+
+~Sodium Phosphate~, Na_{2}HPO_{4}.12H_{2}O. The crystals may be
+purchased pure, but they effloresce in dry air with loss of water. It
+is used as a standard and for precipitating magnesia, &c. Make a 10 per
+cent. solution.
+
+~Stannous Chloride~, SnCl_{2}.2H_{2}O.--The crystals are best purchased.
+If kept dry and free from air they are fairly permanent. A solution is
+made by dissolving 20 grams in 10 c.c. of hydrochloric acid and diluting
+to 1 litre. The solution is not permanent. It is a strong reducing
+agent, and is chiefly used in solution for this purpose.
+
+~Tin~, Sn.--Grain tin should be purchased. It is not pure, but contains
+99.5 per cent. of the metal. The chief impurity is copper. It can be
+used as a standard. When acted on with hot hydrochloric acid it slowly
+dissolves (more rapidly in contact with platinum) and forms stannous
+chloride.
+
+~Uranium Acetate~, UO_{2}(C_{2}H_{3}O_{2})_{2}.H_{2}O.--It is best
+purchased in crystals. The solution is used for the determination of
+phosphates and arsenates. A solution of 3 per cent. strength is
+occasionally used as an indicator.
+
+~Uranium Nitrate~, UO_{2}(NO_{3})_{2}.6H_{2}O.--This salt is very
+soluble in water and is sometimes used instead of the acetate, which is
+somewhat difficult to dissolve.
+
+"~Water~," H_{2}O.--Spring or well water is sufficiently pure for most
+purposes, 100 c.c. will leave a residue of from 10 to 30 milligrams, so
+that where a salt has to be dissolved out, evaporated, and weighed it
+should be replaced by distilled water. Rain water, melted snow, &c.,
+always leave less residue than spring water; but in other respects they
+are often dirtier. Distilled water is best prepared in the office, a
+glass or tin condenser being used.
+
+~Zinc~, Zn.--It is sold in a granulated form or in sticks. It generally
+contains over 1 per cent. of lead, with a little iron and arsenic. It is
+used for separating metals from their solutions, and generally as a
+reducing agent. For the preparation of hydrogen, and in most other
+cases, scrap sheet zinc may be used.
+
+~Zinc Oxide~, ZnO.--The commercial oxide sometimes contains carbonate.
+
+~Zinc Sulphate~, ZnSO_{4}.7H_{2}O.--It is occasionally used as a
+standard, and can be purchased nearly pure.
+
+FOOTNOTES:
+
+[6] 3HCl + HNO_{3} = Cl_{2} + NOCl + 2H_{2}O.
+
+[7] NaC_{2}H_{3}O_{2} + HCl = H_{4}C_{2}O_{2} + NaCl.
+
+
+
+
+CHAPTER VII.
+
+FORMULĘ, EQUATIONS, ETC.
+
+
+Formulę and equations are a kind of short hand for expressing briefly
+and in the language of the atomic theory the facts of chemical
+composition and reaction. The convenience of this method of expressing
+the facts justifies a short description of it here.
+
+On comparing the percentage composition of a series of compounds the
+proportions in which the elements combine appears to be regulated by no
+simple law. For example:
+
+             Realgar.     Orpiment.     Mispickel.     Pyrites.
+  Arsenic     71.4          60.9          46.0            --
+  Sulphur     28.6          39.1          19.6           53.3
+  Iron         --            --           34.4           46.7
+             ------        ------        ------         ------
+             100.0         100.0         100.0          100.0
+
+But if in these examples the composition is calculated, not on 100
+parts, but on 107, 246, 163, and 120 parts respectively, evidence of a
+simple law becomes apparent.
+
+             Realgar.     Orpiment.     Mispickel.     Pyrites.
+  Arsenic     75.0          150.0         75.0           --
+  Sulphur     32.0           96.0         32.0          64.0
+  Iron         --             --          56.0          56.0
+             ------         ------       ------        ------
+             107.0          246.0        163.0         120.0
+
+It will be seen that the proportion of arsenic is 75 or twice 75, that
+of iron is 56, and that of sulphur 32 or some simple multiple of 32. The
+series of examples might be extended indefinitely, and it would still be
+found that the "combining proportions" held good. The number 75 is
+spoken of as the "combining weight," or, more frequently, as the "atomic
+weight" of arsenic. Similarly 56 is the atomic weight of iron, and 32
+the atomic weight of sulphur. The importance of this law of chemical
+combination is altogether independent of the atomic theory; but this
+theory furnishes the simplest explanation of the facts. According to it
+a chemical compound is made up of exactly similar groups of particles.
+The particles of each elementary substance are all alike, but differ
+from those of other elements in weight. Ultimate particles are called
+_atoms_, and the groups of atoms are called _molecules_. The atomic
+weight of any particular element is the weight of its atom compared with
+the weight of an atom of hydrogen. The atom of sulphur, for instance, is
+32 times as heavy as the atom of hydrogen, and the atomic weight of
+sulphur is 32. The _molecular weight_ is the sum of the atomic weights
+of the group. The molecule of pyrites contains two atoms of sulphur and
+one of iron: on referring to the table of atomic weights it will be seen
+that the atomic weights are--sulphur 32, and iron 56. The molecular
+weight, therefore, is 32+32+56--that is, 120. The meaning of this
+is, 120 parts by weight of iron pyrites contain 64 parts of sulphur and
+56 parts of iron; and this is true whether the "parts by weight" be
+grains or tons.
+
+_The symbol or formula of an atom_ is generally the initial letter or
+letters of the Latin or English name of the substance. The atom of
+hydrogen is written H, that of oxygen O, of sulphur S, of iron (ferrum)
+Fe, and so on. A list of these symbols is given in the table of atomic
+weights.
+
+_The formula of a molecule_ is obtained by placing together the symbols
+of the contained atoms. Thus, Fe represents an atom of iron, S an atom
+of sulphur, while FeS represents the molecule of sulphide of iron as
+containing one atom of each element.
+
+When more than one atom of an element is present this is shown by
+writing a figure under and after the symbol; thus, FeS_{2} represents a
+molecule with one atom of iron and two atoms of sulphur, Fe_{2}S_{3}
+similarly shows one with two atoms of iron and three of sulphur. When a
+group of atoms is enclosed in brackets, a figure after and under the
+bracket multiplies all within it; for example, Pb(NO_{3})_{2} is another
+way of writing PbN_{2}O_{6}. Sometimes it is convenient to represent the
+atoms of a molecule as divided into two or more groups; this may be done
+by writing the formulę of the groups, and separating each simple formula
+by a full stop. Slaked lime, for instance, has the formula CaH_{2}O_{2};
+or, as already explained, we may write it Ca(HO)_{2}; or, if for
+purposes of explanation we wished to look on it as lime (CaO) and water
+(H_{2}O), we could write it CaO.H_{2}O. A plus sign (+) has a different
+meaning; CaO + H_{2}O indicates quantities of two substances, water and
+lime, which are separate from each other. The sign of equality (=) is
+generally used to separate a statement of the reagents used from another
+statement of the products of the reaction; it may be translated into the
+word "yields" or "becomes." The two statements form an equation.
+
+Ignoring the quantitative relation, the meaning of the equation CaO +
+H_{2}O = CaO.H_{2}O is: "lime and water yield slaked lime." By referring
+to a table of atomic weights we can elicit the quantitative relations
+thus:--
+
+    CaO    +    H_{2}O       =     CaH_{2}O_{2}
+     |             |                   |
+     V             V                   V
+  Ca = 40    H_{2} =  2 = 1×2      Ca  = 40
+  O  = 16       O  = 16          H_{2} =  2 = 1×2
+       --            --          O_{2} = 32 = 16×2
+       56            18                  --
+                                         74
+
+Or, putting it in words, 56 parts of lime combine with 18 parts of water
+to form 74 parts of slaked lime. This equation enables one to answer
+such a question as this:--How much lime must be used to produce 1 cwt.
+of slaked lime? for, if 74 lbs. of slaked lime require 56 lbs. of lime,
+112 lbs. will require (56×112)/74, or about 84-3/4 lbs.
+
+As another example having a closer bearing on assaying take the
+following question:--"In order to assay 5 grams of 'black tin' (SnO_{2})
+by the cyanide process, how much potassic cyanide (KCN) will be
+required?" The reaction is
+
+      SnO_{2}   +   2KCN    =    Sn + 2KCNO
+        |             |
+        V             V
+     Sn = 118        K = 39
+  O_{2} =  32        C = 12
+          ---        N = 14
+          150            --
+                         65×2 = 130
+
+What is sought for here is the relation between the quantities of
+SnO_{2} and KCN. Note that a figure before a formula multiplies all that
+follows up to the next stop or plus or equality sign. The question is
+now resolved to this: if 150 grams of oxide of tin require 130 grams of
+cyanide, how much will 5 grams require?
+
+        150 : 130 :: 5 : _x_
+                         _x_ = 4.33 grams.
+
+A problem of frequent occurrence is to find the percentage composition
+of a substance when its formula has been given. For example: "What
+percentage of iron is contained in a mineral having the formula
+2Fe_{2}O_{3}.3H_{2}O?" Bringing this formula together we have
+Fe_{4}H_{6}O_{9}. Find the molecular weight.
+
+  Fe_{4}  =   224 = 56×4
+  H_{6}   =     6 = 1×6
+  O_{9}   =   144 = 16×9
+              ---
+              374
+
+Then we get: 374 parts of the mineral contain 224 of iron. How much will
+100 contain?
+
+        374 : 224 :: 100 : _x_
+                           _x_ = 59.89.
+
+And the answer to the question is 59.89 per cent.
+
+Again, suppose the question is of this kind:--"How much crystallised
+copper sulphate (CuSO_{4}.5H_{2}O) will be required to make 2 litres of
+a solution, 1 c.c. of which shall contain 0.0010 gram of copper?"
+
+A litre is 1000 c.c., so, therefore, 2 litres of the solution must
+contain 0.001 gram × 2000, or 2 grams. How much crystallised copper
+sulphate will contain this amount of metal?
+
+  Cu      = 63.3
+  S       = 32.0
+  O_{4}   = 64.0 = 16×4
+  5H_{2}O = 90.0 = 18×5
+           -----
+           249.3
+
+If 63.3 grams of copper are contained in 249.3 grams of sulphate, in how
+much is 2 grams contained.
+
+        63.3 : 249.3 :: 2 grams : _x_
+                                  _x_ = 7.8769 grams.
+
+The answer is, 7.8769 grams must be taken.
+
+As a sample of another class of problem similar in nature to the last
+(but a little more complicated) take the following:--"What weight of
+permanganate of potash must be taken to make 2 litres of a solution, 100
+c.c. of which shall be equivalent to 1 gram of iron?" In the first place
+the 2 litres must be equivalent to 20 grams of iron, for there are 20 ×
+100 c.c. in two litres. In the titration of iron by permanganate
+solution there are two reactions. First in dissolving the iron
+
+Fe + H_{2}SO_{4} = FeSO_{4} + H_{2}
+ |
+ V
+ 56
+
+and second, in the actual titration,
+
+10FeSO_{4} + 2KMnO_{4} + 9H_{2}SO_{4}= 2MnSO_{4}
+               |       + 5Fe_{2}(SO_{4})_{3} + 2KHSO_{4} + 8H_{2}O
+               V
+             K = 39
+            Mn = 55
+          O_{4}= 64
+                ---
+                158 × 2 = 316
+
+As before, attention is confined to the two substances under
+consideration--viz., Fe and KMnO_{4}. In the second equation, we find
+316 parts of the permanganate are required for 10 molecules of FeSO_{4};
+and in the first equation 56 parts of iron are equivalent to one
+molecule of FeSO_{4}, therefore 560 of iron are equivalent to 316 of
+permanganate; and the question is, How much of the permanganate will be
+equivalent to 20 grams of iron?
+
+        560 : 316 :: 20 grams : _x_.
+                                _x_= 11.286 grams.
+
+The answer is 11.286 grams.
+
+Very similar to this last problem is the question suggested under the
+head "Indirect Titration" (p. 43). "If 100 c.c. of the standard
+permanganate solution are equivalent to 1 gram of iron, how much
+peroxide of manganese will they be equivalent to?" The equation for
+dissolving the iron is already given; the second equation is
+
+2FeSO_{4} + MnO_{2} + 2H_{2}SO_{4}
+              |      = Fe_{2}(SO_{4})_{2} + MnSO_{4} + 2H_{2}O
+              |
+              V
+           Mn = 55
+        O_{2} = 32
+                --
+                87
+
+It will be seen that 87 grams of peroxide of manganese are equivalent to
+112 grams of iron. How much then is equivalent to 1 gram of iron?
+
+        112 : 87 :: 1 gram : _x_
+                             _x_ = 0.7767 gram.
+
+It is sometimes convenient to calculate the formula of a substance from
+its analysis. The method of calculating is shown by the following
+example. Required the formula of a mineral which gave the following
+figures on analysis:--
+
+  Cupric oxide (CuO)          10.58
+  Ferrous oxide (FeO)         15.69
+  Zinc oxide (ZnO)             0.35
+  Sulphuric oxide (SO_{2})    28.82
+  Water (H_{2}O)              44.71
+                             ------
+                             100.15
+
+First find the molecular weights of CuO, FeO, &c., and divide the
+corresponding percentages by these figures. Thus, CuO = 63.3+16 = 79.3
+and 10.58 divided by 79.3 gives 0.1334. Similarly FeO = 56+16 = 72 and
+15.69 divided by 72 gives 0.2179. Treated in the same way the oxide of
+zinc, sulphuric oxide and water give as results 0.0043, 0.3602 and
+2.484.
+
+Classify the results as follows:--
+
+    Bases.         Acids.         Water.
+
+  CuO 0.1334    SO_{3} 0.3602    H_{2}O 2.484
+  FeO 0.2179
+  ZnO 0.0043
+  ----------    -------------    ------------
+   RO 0.3556    RO_{3} 0.3602    R_{2}O 2.484
+
+The figures 0.3556, 0.3602 and 2.484 should be then divided by the
+lowest of them--_i.e._, 0.3556; or where, as in this case, two of the
+figures are very near each other the mean of these may be taken--_i.e._,
+0.3579. Whichever is taken the figures got will be approximately 1, 1
+and 7. The formula is then RO.SO_{3}.7H_{2}O in which R is nearly 2/5ths
+copper, 3/5ths iron and a little zinc.
+
+This formula requires the following percentage composition, which for
+the sake of comparison is placed side by side with the actual results.
+
+                 Calculated.   Found.
+  Cupric oxide     11.29       10.58
+  Ferrous oxide    15.37       15.69
+  Zinc oxide        nil         0.35
+  Sulphuric oxide  28.47       28.82
+  Water            44.84       44.71
+                   -----      ------
+                   99.97      100.15
+
+Trimming the results of an analysis to make them fit in more closely
+with the calculations from the formula would be foolish as well as
+dishonest. There can be no doubt that the actual analytical results
+represent the composition of the specimen much more closely than the
+formula does; although perhaps other specimens of the same mineral would
+yield results which would group themselves better around the calculated
+results than around those of the first specimen analysed. It must be
+remembered that substances are rarely found pure either in nature or in
+the arts; so that in most cases the formula only gives an approximation
+to the truth. In the case of hydrated salts there is generally a
+difficulty in getting the salt with exactly the right proportion of
+water.
+
+
+PRACTICAL EXERCISES.
+
+The following calculations may be made:--
+
+1. Calculate standards in the following cases--
+  (a) Silver taken, 1.003 gram. Standard salt used, 100.15 c.c.
+  (b) Iron taken, 0.7 gram. Bichromate used, 69.6 c.c.
+
+2. Calculate percentages:--
+  (a) Ore taken, 1 gram. Solution used, 65.2 c.c. Standard, 0.987
+    gram.
+
+  (b) Ore taken, 1 gram. Barium sulphate got, 1.432 gram. Barium
+    sulphate contains 13.73 per cent. of sulphur, and the percentage
+    of sulphur in the ore is wanted.
+
+  (c) Barium sulphate is BaSO_{4}. Calculate the percentage of sulphur
+    it contains, for use in the preceding question.
+
+3.  A method of estimating the quantity of peroxide in a manganese ore
+is based on the following reactions:--
+
+    (1) MnO_{2} + 4HCl = MnCl_{2} + Cl_{2} + 2H_{2}O.
+
+    (2) Cl + KI = KCl + I.
+
+To how much MnO_{2} is 1 gram of Iodine (I) equivalent?
+
+4. A mineral has the following composition:--
+
+  Carbonic acid (CO_{2})     19.09
+  Copper oxide (CuO)         71.46
+  Water (H_{2}O)              9.02
+
+What is its formula?
+
+5. How much copper is contained in 1.5 gram of crystallized copper
+sulphate (CuSO_{4}.5H_{2}O)? How much of these crystals must be taken to
+give 0.4 gram of copper?
+
+6. How much ferrous sulphate crystals (FeSO_{4}.7H_{2}O) must be taken
+to yield 2 litres of a solution, 100 c.c. of which shall contain 0.56
+gram of iron?
+
+7. Galena is PbS, and hęmatite Fe_{2}O_{3}. What percentages of metal do
+these minerals contain?
+
+
+
+
+CHAPTER VIII.
+
+SPECIFIC GRAVITY.
+
+
+The relation of the weight of a substance to its volume should be kept
+in mind in all cases where both weight and volume are dealt with.
+Students are apt to imagine that on mixing equal volumes of, say,
+sulphuric acid and water, an acid of half the strength must be obtained.
+If the statement of strength is in parts by weight this will lead to
+considerable error. For example, 100 c.c. of sulphuric acid containing
+98 per cent. by weight of real acid, will, if diluted with 100 c.c. of
+water, yield a solution containing not 49 per cent. by weight, but about
+63.5 per cent. of the acid. The reason is this: the 100 c.c. of
+sulphuric acid weighs 184 grams, and contains 180.32 grams of real acid,
+while the 100 c.c. of water weighs only 100 grams; the mixed water and
+acid weighs 284 grams, and contains 180.32 of real acid, which is
+equivalent to nearly 63.5 per cent. by weight. If, however, the method
+of statement be volumetric, it would be correct to say that doubling the
+volume halves the strength: if 100 c.c. of brine contains 10 grams of
+salt, and is diluted with water to 200 c.c., it would be of one-half the
+former strength, that is, 100 c.c. of the solution would contain 5 grams
+of salt.
+
+This confusion is avoided by always stating the strengths as so many
+grams or "c.c." in 100 c.c. of the liquid. But obviously it would be
+advantageous to be able to determine quickly the weight of any
+particular substance corresponding to 1 c.c. or some other given volume.
+Moreover, in descriptions of processes the strengths of acids and
+solutions are frequently defined neither by their gravimetric nor
+volumetric composition, but by a statement either of specific gravity or
+of the degrees registered by Twaddell's or Beaumé's hydrometer. Thus, in
+the description of the process of gold parting, one writer gives: "The
+acid should be of 1.2 specific gravity"; and another says: "The acid
+must not be stronger than 32° Beaumé."
+
+These considerations justify an account of the subject in such a work as
+this. And on other grounds the determination of a specific gravity is
+one of the operations with which an assayer should be familiar.
+
+The meaning of "specific gravity" is present in the mind of every one
+who uses the sentence "lead is heavier than water." This is meaningless
+except some such phrase as "bulk for bulk" be added. Make the sentence
+quantitative by saying: "bulk for bulk lead is 11.36 times heavier than
+water," and one has the exact meaning of: "the specific gravity of lead
+is 11.36." A table of the specific gravities of liquids and solids shows
+how many times heavier the substances are than water.
+
+It is better, however, to look upon the specific gravity (written
+shortly, sp. g.) as the weight of a substance divided by its volume. In
+the metric system, 1 c.c. of water at 4° C. weighs with sufficient
+exactness 1 gram; consequently, the sp. g., which states how many times
+heavier than water the substance is, also expresses the weight in grams
+of one c.c. of it. So that if a 100 c.c. flask of nitric acid weighs,
+after the weight of the flask has been deducted, 120 grams, 1 c.c. of
+the acid weighs 1.2 gram, and the sp. g. is 1.2. The specific gravity,
+then, may be determined by dividing the weight of a substance in grams
+by its volume in c.c.; but it is more convenient in practice to
+determine it by dividing _the weight of the substance by the weight of
+an equal volume of water_. And since the volumes of all substances,
+water included, vary with the temperature, the temperature at which the
+sp. g. is determined should be recorded. Even then there is room for
+ambiguity to the extent that such a statement as the following, "the
+specific gravity of the substance at 50° C. is 0.9010," may mean when
+compared with water at 50° C. or 4° C., or even 15.5° C. For practical
+purposes it should mean the first of these, for in the actual
+experiments the water and the substance are compared at the same
+temperature, and it is well to give the statement of results without any
+superfluous calculation. In the metric system the standard temperature
+is 4° C., for it is at this point that 1 c.c. of water weighs exactly 1
+gram. In England, the standard temperature is 60° F. (15.5° C.), which
+is supposed to be an average temperature of the balance-room. The
+convenience of the English standard, however, is merely apparent; it
+demands warming sometimes and sometimes cooling. For most purposes it is
+more convenient to select a temperature sufficiently high to avoid the
+necessity of cooling at any time. Warming to the required temperature
+gives very little trouble.
+
+~Determination of Specific Gravity.~--There is a quick and easy method
+of determining the density or sp. g. of a liquid, based upon the fact
+that a floating body is buoyed up more by a heavy liquid than by a light
+one. The method is more remarkable for speed than accuracy, but still
+is sufficiently exact. The piece of apparatus used for the purpose is
+endowed with a variety of names--sp. g. spindle, hydrometer, areometer,
+salimeter, alcoholimeter, lactometer, and so on, according to the
+special liquid upon which it is intended to be used. It consists of a
+float with a sinker at one end and a graduated tube or rod at the other.
+It is made of metal or glass. Generally two are required, one for
+liquids ranging in sp. g. from 1.000 to 2.000, and another, which will
+indicate a sp. g. between 0.700 and 1.000. The range depends on the size
+of the instrument. For special work, in which variations within narrow
+limits are to be determined, more delicate instruments with a narrower
+range are made.
+
+[Illustration: FIG. 34.]
+
+In using a hydrometer, the liquid to be tested is placed in a cylinder
+(fig. 34) tall enough to allow the instrument to float, and not too
+narrow. The temperature is taken, and the hydrometer is immersed in the
+fluid. The mark on the hydrometer stem, level with the surface of the
+liquid, is read off. With transparent liquids it is best to read the
+mark under and over the water surface and take the mean.
+
+The graduation of hydrometers is not made to any uniform system. Those
+marked in degrees Baumé or Twaddell, or according to specific gravity,
+are most commonly used. The degrees on Baumé's hydrometer agree among
+themselves in being at equal distances along the stem; but they are
+proportional neither to the specific gravity, nor to the percentage of
+salt in the solution. They may be converted into an ordinary statement
+of specific gravity by the following formulę:--
+
+  Sp. g. = 144.3/(144.3-degrees Baumé.)
+
+or putting the rule in words, subtract the degrees Baumé from 144.3, and
+divide 144.3 with the number thus obtained. For example: 32° Baumé
+equals a sp. g. of 1.285.
+
+  144.3/(144.3-32) = 144.3/(112.3) = 1.285
+
+This rule is for liquids heavier than water; for the lighter liquids the
+rule is as follows:--
+
+  Sp. g. = 146/(136 + degrees Baumé.)
+
+or in words divide 146 by the number of degrees Baumé added to 136. For
+example: ammonia of 30° Beaumé has a sp. g. of 0.880 (nearly).
+
+  146/(136+30) = 146/166 = 0.8795
+
+A simple series of calculations enables one to convert a Beaumé
+hydrometer into one showing the actual sp. g. Graduation, according to
+sp. g. is the most convenient for general purposes. In these instruments
+the distances between the divisions become less as the densities
+increase.
+
+Twaddell's hydrometer is graduated in this way: Each degree Twaddell is
+0.005 in excess of unity. To convert into sp. g. multiply the degrees
+Twaddell by 0.005, and add 1. For example: 25° Twaddell equals a sp. g.
+of 1.125.
+
+  25×.005 = 0.125; + 1.000 = 1.125.
+
+There is a practice which ignores the decimal point and speaks of a sp.
+g. of 1125 instead of 1.125. In some cases it is convenient, and
+inasmuch as no substance has a real sp. g. of much over 20, it can lead
+to no confusion. The figures expressed in this way represent the weight
+of a litre in grams.
+
+Some hydrometers are graduated so as to show at a glance the percentage
+composition of the liquid they are intended to be used with. Gay-Lussac
+designed one to show the alcoholic strength of mixtures of alcohol and
+water; the construction of others upon the same principle is easy and
+perhaps useful. But when the principle is applied to complex liquids and
+mixed solutions, it is misleading.
+
+The various methods of graduation ought all to give place to one showing
+a simple statement of the sp. g.
+
+The method of determining sp. g. with the hydrometer is obviously
+inapplicable to the case of solids, and in the case of liquids it should
+not be used where exact figures are required. There are several other
+methods which may be used, but on the whole those with the specific
+gravity bottle are most convenient.
+
+[Illustration: FIG. 35.]
+
+~The specific gravity bottle~ (fig. 35) is a light flask of about 25
+c.c. capacity, provided with a well-fitting perforated stopper. It is
+essentially a graduated flask, which measures a constant volume, but it
+does not much matter what the volume is.
+
+_In taking the sp. g. of a liquid_ (_or, what is the same thing, a fused
+solid_) there is wanted the weights (1) of the flaskful of water and (2)
+of the flaskful of the liquid. Dividing the second by the first gives
+the required sp. g. The actual weighings required are--
+
+  (1) of the dry and empty flask,
+
+  (2) of the flask filled with water, and
+
+  (3) of the flask filled with the liquid.
+
+The weighing of the flask once made need not be often repeated. It is
+well to do so now and then for safety's sake; but one weighing will
+serve for a large number of determinations. The same remarks apply to
+the weighing of the bottle filled with water. The bottle is dried by
+rinsing out first with alcohol and afterwards with ether; ether is very
+volatile, and a short exposure in a warm place will soon drive off the
+little remaining about the sides. The ether vapour should be sucked out
+through a glass tube. See that the bore of the stopper is dry as well as
+the bottle. Let the dry bottle stand in the box of the balance for a
+minute or two before weighing. The weight is, strictly speaking, not
+that of the empty bottle, but of the bottle filled with air. The empty
+bottle would weigh from 20 to 30 milligrams less. Correcting for this
+would, in most cases, only make a difference in the fourth place of
+decimals,[8] so that it is better to ignore the error.
+
+The weight of the flask filled with water is got by filling it with
+distilled water, and inserting the stopper. The excess of water will
+overflow at the margin and through the bore. The bottle is wiped with a
+soft, dry cloth, taking care not to squeeze or warm the bottle. The
+bottle will remain filled to the top of the stopper. It is allowed to
+stand in the balance box for a minute or two, and then weighed.
+
+Distilled water, as stated, should be used; the use of ordinary water
+may increase the weight by 5 or 6 milligrams. Many waters, if they have
+not previously been boiled, give off bubbles of air which render the
+weighing worthless.
+
+The temperature of the water is of greater importance; lowering the
+temperature 2° will increase the weight by 10 or 12 milligrams. A beaker
+of water may be warmed or cooled to the required temperature; then the
+bottle is filled from it, and quickly weighed. If the balance-room is
+cooler than the water, the latter will draw back into the bottle, and a
+few small bubbles of air will enter; but even in extreme cases this will
+only increase the weight by a very small fraction of a milligram. There
+is more trouble caused when the room is warmer, for the liquid then
+expands and protrudes as a drop resting on the top of the stopper.
+There will in this case be loss by evaporation, which in the case of the
+more volatile liquids, such as alcohol, is serious. To prevent this
+loss, as well as any that may arise by overflow, the stopper should be
+dilated above into a small cup, A (fig. 36), which may itself be
+stoppered. In a bottle of this kind the neck of the stopper is
+graduated, and the bottle is considered full when the liquid stands at
+the level of the mark in the neck. On inserting the stopper, the liquid
+rises into the cup, and is reduced to the level of the mark by
+absorption with pieces of filter-paper.
+
+[Illustration: FIG. 36.]
+
+For most purposes, however, there is no need for cooling and allowing
+room for subsequent expansion. The assayer, as a rule, can select his
+own standard temperature, and may choose one which will always
+necessitate warming. It will be handier in this case to have a bottle
+with a thermometer stopper. Of the two types shown in fig. 37, that with
+the external thermometer tube (A) is more generally useful.
+
+[Illustration: FIG. 37.]
+
+The bottle is filled at a lower temperature, and is then gently warmed
+so as to slowly raise the temperature to the required degree. The
+superfluous liquid is then at once wiped off, and the bottle cooled and
+weighed.
+
+The weight of the flask filled with the liquid whose sp. g. has to be
+determined is ascertained in a similar way. Of course the temperature
+must be the same. If the liquid does not mix with water, the bottle
+should be dried before filling, but otherwise the flask need only be
+rinsed out two or three times with the liquid.
+
+Having obtained the three weighings, deduct the weight of the bottle
+from each of the others to get the weights of the water and liquid
+respectively. Divide the latter by the former, the result shows the sp.
+g. As an example, take the following, in which a rather large sp. g.
+bottle was used:--
+
+  1. Weight of bottle               39.299 gram
+
+  2. Weight of bottle and water     81.884  "
+
+  3. Weight of bottle and paraffin  73.146  "
+
+By subtracting 1 from 2 and 3 the result is as follows:--
+
+  81.884 grams         73.146 grams
+  39.299   "           39.299   "
+  ------               ------
+  42.585 of water.     33.847 of paraffin.
+
+Divide the weight of the paraffin by that of the water--
+
+  42.585)33.8470(0.7948
+         29.8095
+         -------
+       .......
+
+The sp. g. of the paraffin is 0.7948.
+
+_The sp. g. of a fusible solid_ may be obtained in the same way at a
+temperature some degrees above its fusing point.
+
+_The sp. g. of a solid in powder or gravel sufficiently fine to pass
+through the neck of the bottle_ is easily determined. If the bottle
+filled with water weighs 50 grams, and there is placed on the pan
+alongside of it 20 grams of a sand, the weight of the two together will
+of course be 70 grams. But if the sand is put in the bottle, it
+evidently displaces its own bulk of water; and if, on again weighing,
+the weight is found to be 62 instead of 70 grams, it is because the 20
+grams of sand has displaced 8 grams of water. Bulk for bulk, the sand is
+2-1/2 times as heavy.
+
+In practice, the weight of the bottle filled with water will probably be
+already known; if not, it must be determined. A certain quantity, say 20
+grams, of the powdered substance is then transferred carefully to the
+bottle. The bottle need not be dry inside, but its neck and outside must
+be. In making this transference a careful worker will make no loss, and
+the mode of working saves a little time. But it is better to weigh the
+dry flask; put into it 10 to 20 grams of the powder, and weigh again.
+The increase in weight gives accurately the weight of powder in the
+bottle. About two-thirds fill the bottle with distilled water, and mix
+with the powder by gentle shaking. Air bubbles will disentangle
+themselves, and rise to the surface of the water. Wash back anything
+adhering to the stopper with a jet of water, and fill the bottle almost
+to overflowing. Allow it to stand for a minute or so; replace the
+stopper; warm to the required temperature; take off the superfluous
+moisture; wipe and weigh. As an example, take the following:--
+
+  1. Weight of bottle                         12.681 grams
+  2.   "    "  bottle filled with water       37.708   "
+  3.   "    "  bottle with wolfram            40.821   "
+  4.   "    "  bottle with wolfram and water  61.199   "
+
+Subtract (1) from (3) to get the weight of wolfram taken:
+
+  40.821 grams
+  12.681   "
+  ------
+  28.140   "
+
+add the weight of the wolfram to the weight of the bottle filled with
+water:
+
+  28.140 grams
+  37.708   "
+  ------
+  65.848   "
+
+subtract (4) from this to get the weight of water displaced:
+
+  65.848 grams
+  61.199   "
+  ------
+   4.649   "
+
+Divide the weight of the wolfram by the weight of the water displaced to
+get sp. g.:
+
+  4.649)28.140(6.053
+        27.894
+        ------
+        ......
+
+_If the solid is soluble in water, or has a tendency to float_, some
+liquid other than water is used. Paraffin oil or oil of turpentine will
+do. The process is as follows:--The weight of the dry and empty bottle
+having been determined, add a sufficiency of the substance and weigh
+again to find how much has been added. Fill up with paraffin oil and
+weigh again. Clean out the substance by rinsing with paraffin; fill up
+and weigh. Calculate the sp. g. as if water had been used, and multiply
+by the sp. g. of the paraffin.
+
+For example:
+
+  1. Weight of bottle                         39.299 grams
+  2.    "    " bottle and nitre               57.830   "
+  3.    "    " bottle and paraffin            73.146   "
+  4.    "    " bottle and paraffin and nitre  84.665   "
+  5.    "    " bottle and water               81.884   "
+
+First from (1),(3), and (5), calculate the sp. g. of the paraffin as
+already shown. It will be 0.7948. Deduct (1) from (2) to get the weight
+of the nitre:
+
+  57.830 grams
+  39.299   "
+  ------
+  18.531   "
+
+add this to (3):
+
+  18.531 grams
+  73.146   "
+  ------
+  91.677   "
+
+and deduct (4) to find the weight of the equal bulk of paraffin.
+
+  91.677 grams
+  84.665   "
+  ------
+   7.012   "
+
+divide the weight of the nitre by the weight of the paraffin:
+
+  7.012)18.531(2.6427
+        ------
+        ......
+
+The sp. g., taking paraffin as the standard instead of water, is 2.6427.
+Multiply this by the sp. g. of paraffin, 0.7948, and the result is
+2.1004 as the sp. g. of nitre compared with water.
+
+Similarly, a sp. g. compared with water at say 50° C. can be converted
+into one compared with water at standard temperature, by multiplying by
+the sp. g. of water at 50° C. The following table gives the sp. g. of
+water at various temperatures:--
+
+  -----------+------++-----------+------++-----------+-------
+   Degrees   |      || Degrees   |      || Degrees   |
+  Centigrade.|Sp. G.||Centigrade.|Sp. G.||Centigrade.|Sp. G.
+  -----------+------++-----------+------++-----------+-------
+       4°    |1.0000||    20°    |0.9982||    40°    |0.9923
+      10°    |0.9997||    25°    |0.9971||    50°    |0.9881
+      15°    |0.9991||    30°    |0.9957||   100°    |0.9586
+  -----------+------++-----------+------++-----------+-------
+
+If, for example, a substance at 50° C. has a sp. g. of 0.9010 as
+compared with water at 50° C., it will have (compared with water at 4°
+C.) a sp. g. of 0.9010×0.9881; or 0.8903. The figures 0.8903 represent
+the sp. g. of the substance at 50° C. compared with water at 4° C.
+Except in comparing the sp. gravities of the same substance at different
+temperatures, a calculation of this kind serves no useful purpose.
+
+_In taking the specific gravity of a solid not in powder_, a lump of it
+is freed from loose particles and its exact weight determined. By means
+of a horse hair with a slip knot it is suspended to the balance, and
+beneath it is placed, out of contact with the balance pan, a beaker of
+distilled water. The horse hair must be long enough to keep the mineral
+well beneath the surface of the water so as to allow the balance to
+vibrate. Air bubbles are removed by touching with a camel-hair pencil.
+Whilst the mineral is suspended in water the weight is again taken. It
+will weigh less than before, and the difference between the two
+weighings gives the weight of water (and consequently the volume)
+displaced by the mineral. The weight in air divided by the difference is
+the specific gravity. Thus
+
+  Weight in air     3.2170 grams
+  Weight in water   2.7050   "
+                    ------
+      Difference    0.5120 gram
+
+  3.2170/0.5120 equals 6.28, the sp. g.
+
+The sp. g. of a substance depends mainly on its composition, but is
+affected by certain conditions. The effect of temperature has been
+already considered. Air holes and empty spaces lessen the specific
+gravity of otherwise solid bodies; and metals, which after fusion become
+imperfect solids, have their density increased by hammering or rolling.
+But metals when free from pores have their density diminished when
+rolled, without annealing. The effects of these conditions are slight
+when compared with those due to the presence of impurities.
+
+For simple substances, or mixtures of only two substances, a
+determination of sp. g. is a sufficient check on the composition for
+many practical purposes; and with more complex mixtures, such as slags
+and some of the products of dressing operations in which the material
+does not differ much in its nature from time to time, such a
+determination will yield information of considerable value, and afford a
+check upon the proper working of a process.
+
+When the mixing of two substances is accompanied by a change in volume,
+the sp. g. of the mixture can only be learnt by experiment. But when the
+substances have no such action on each other the resulting sp. g. can be
+calculated. Some of these calculations have a practical interest as well
+as an educational value. Students should practise them so as to become
+familiar with the relations between weight and volume.
+
+_When substances are mixed by volume_, the sp. g. of the mixture is the
+mean of those of its constituents, and may be calculated in the usual
+way for obtaining averages. 1 c.c. of a substance having a sp. g. of 1.4
+mixed with 1 c.c. of another having a sp. g. of 1.0 will yield 2 c.c. of
+a substance having a sp. g. of 1.2. If, however, we write gram instead
+of c.c. in the above statement, the resulting sp. g. will be 1.16. The
+simplest plan is to remember that the sp. g. is the weight divided by
+the volume (sp. g. = w/v) and the sp. g. of a mixture is the sum of the
+weights divided by the sum of the volumes (sp. g. = (w + w' + w",
+&c.)/(v + v' + v", &c.)). In the above example the sum of the volumes is
+2 c.c.; the weights (got by multiplying each volume by its
+corresponding sp. g.) are 1.4 gram and 1 gram. The sum of the weights
+divided by the sum of the volumes is 2.4/2 or 1.2.
+
+The sp. g. of a mixture of 10 c.c. of a substance having a sp. g. of
+1.2, with 15 c.c. of another having a sp. g. of 1.5 may be thus found:--
+
+  sp. g. = (12+22.5)/(10+15) = 1.38
+
+multiply each volume by its sp. g. to get its weight:
+
+  10×1.2 = 12   15×1.5 = 22.5
+
+add these together (12+22.5 = 34.5) and divide by the sum of the volumes
+(10+15 = 25):
+
+   25)34.5(1.38
+      25
+      --
+      95, &c.
+
+The sp. g. will be 1.38, provided the mixture is not accompanied by any
+change of volume.
+
+The same formula will serve when the proportion of the ingredients is
+given by weight. A mixture of 4 parts by weight of galena (sp. g. 7.5)
+with 5 parts of blende (sp. g. 4) will have a sp. g. of 5.06:
+
+  sp. g. = (4+5)/(0.53+1.25) = 9/1.78 = 5.06
+
+It is necessary in this case to calculate the volumes of the galena and
+of the blende, which is done by dividing the weights by the sp.
+gravities: thus, 4 divided by 7.5 gives 0.53 and 5 divided by 4 gives
+1.25.
+
+The converse problem is a little more difficult. Given the sp. g. of a
+mixture and of each of the two ingredients, the percentage by weight of
+the heavier ingredient may be ascertained by the following rule, which
+is best expressed as a formula. There are three sp. gravities given; if
+the highest be written H, the lowest L and that of the mixture M, then:
+
+  Percentage of heavier mineral = (100×H×(M-L))/(M×(H-L))
+
+Suppose a sample of tailings has a sp. g. of 3.0, and is made up of
+quartz (sp. g. 2.6) and pyrites (sp. g. 5.1): then the percentage of
+pyrites is 27:
+
+  (100×5.1×(3-2.6))/(3×(5.1-2.6)) = (510×0.4)/(3×2.5) = 204/7.5 = 27.2
+
+The same problem could be solved with the help of a little algebra by
+the rule already given, as thus: the sp. g. of a mixture equals the sum
+of the _weights_ of the constituents divided by the sum of the
+_volumes_. Then 100 grams of the tailings with _x_ per cent. of pyrites
+contain 100-_x_ per cent. of quartz. The sum of the weights is 100. The
+volume of the pyrites is _x_/5.1 and of the quartz (100-_x_)/2.6.
+
+Then we have by the rule
+
+  3 = 100/((_x_/5.1)+(100-_x_)/2.6)
+  3 = 1326/(510-2.5_x_)
+  204 = 7.5_x_
+    and _x_ = 27.2
+
+If the percentage (P) and sp. g. (H) of one constituent and the sp. g.
+(M) of the mixture are known, the sp. g. of the other constituent may be
+calculated by the following formula, in which _x_ is the required sp.
+g.:
+
+  _x_ = ((100-P)×M×H)/((100×H)-(P×M))
+
+For example, "tailings" (sp. g. 3.0) containing 27.2 per cent. of
+pyrites (sp. g. 5.1) will contain (100-27.2), 72.8 per cent. of earthy
+matter having a mean sp. g. of _x_:
+
+  _x_ = ((100-27.2)×3×5.1)/((100×5.1)-(27.2×3))
+      = 1113.84/428.4 = 2.6
+
+The differences in sp. g. corresponding to differences in strength have
+been carefully determined and tabulated in the case of the stronger
+acids and of many other liquids. Such tables are given at the end of
+this book.
+
+_To Calculate the Weight of a Measured Volume of Mineral or
+Rock._--Multiply the cubic feet by 62.4 and then multiply by the sp. g.
+of the stuff, the answer gives the weight in pounds. For example, 100
+cubic feet of quartz weighs 100×62.4×2.6 = 16,224 lbs. The weight of any
+mass of mineral of known extent and sp. g. is ascertained in this way.
+
+The following table gives the specific gravities of some of the commoner
+minerals.
+
+  Barytes              4.5
+  Blende               4.0
+  Calcite              2.6
+  Cassiterite          6.9
+  Chalybite            3.8
+  Copper pyrites       4.2
+  Fluor                3.1
+  Galena               7.5
+  Hęmatite             5.0
+  Mispickel            6.2
+  Pyrites              5.0
+  Quartz               2.6
+
+FOOTNOTES:
+
+[8] The difference of 20 or 30 milligrams is disregarded here because it
+detracts equally from the actual weight of the water and liquid to be
+determined. If the liquid is a heavy one the difference shows itself in
+the third or second place of decimals. The correction may be made by
+deducting from the weight of the flask 0.0012 grams for each gram of
+water it holds.
+
+
+
+
+PART II.--THE METALS.
+
+
+
+
+CHAPTER IX.
+
+SILVER, GOLD, CYANIDES, PLATINUM, MERCURY.
+
+
+SILVER.
+
+Silver is widely diffused, and has been found in most mining districts.
+It occurs native in sufficient quantity to constitute one of the chief
+ores of the metal. It also occurs combined with sulphur (as in
+argentite), with sulphur and antimony (as in stephanite or brittle
+silver ore, and in pyrargyrite or ruby silver), and with copper,
+sulphur, antimony, and arsenic, as in polybasite. Chloride of silver
+occurs native as horn silver or kerargyrite. Silver is found in the ores
+of other metals, such as fahlerz, which sometimes contains from two to
+ten per cent. of the metal, and galena, which is an important source of
+it; in fact, galena is never found entirely free from silver. It is
+present also in greater or less quantity in the ores of copper and zinc.
+
+Silver dissolves readily in nitric acid, forming silver nitrate. It only
+forms one family of salts, and of these the chloride and nitrate are of
+chief importance to the assayer. The formation of the chloride of silver
+on the addition of hydrochloric acid or a soluble chloride to the nitric
+acid solution, serves for the recognition and separation of silver. The
+precipitated chloride is white (becoming violet on exposure to light),
+insoluble in nitric acid, soluble in ammonia, hyposulphite of soda, or
+concentrated solutions of chlorides. The best confirmatory test is made
+by wrapping the precipitate in a little sheet lead, and cupelling, when
+the silver will be left in the metallic state, and is easily recognized.
+
+~Dry Assay.~--This assay is made up of two parts: (1) the concentration
+of the silver in a button of lead; and (2) the cupellation of the
+resulting alloy. The concentration of the button of lead may be
+effected either by scorification or by fusion in a crucible.
+
+The scorification assay is performed in a scorifier, which is a shallow
+open-mouthed dish about 2-1/2 inches across, with a very thick bottom to
+enable it to withstand the corrosive action of the slag. A charge of
+more than 3 or 5 grams of the ore cannot be worked in one, and with such
+small charges the unavoidable variations have a serious effect on the
+figures reported. A difference of one milligram on the weight of the
+button of silver got represents a difference of 6 or 10 ounces per ton.
+With rich ores such variation is unavoidable under any conditions, and
+the only safe plan is to take the mean of several assays. But with
+poorer ores the accuracy of the assay, as well as convenience in
+working, is much increased by working in a crucible with larger charges.
+
+In scorification the proportion of lead required for scorifying 1 gram
+of ore is in average cases from 10 to 15 grams, sinking in the case of
+galena to 2 grams, and rising with earthy and refractory substances to
+from 30 to 40 grams. But by fusing in a crucible with well-selected
+fluxes, a proportion of 4 of flux to 1 of ore is generally sufficient;
+and not only is the proportion of added matter less, but it is also
+easier to manipulate large quantities in crucibles, so that, although in
+some cases the crucible assay is more troublesome and less satisfactory,
+yet with poor and earthy ores it is the best method of dealing with
+them; while when properly worked it yields results as accurate as
+scorification does. As a general rule, if more than 5 grams of ore must
+be taken, the crucible assay should be adopted.
+
+[Illustration: FIG. 38.]
+
+~Scorification Assay.~--The charge of ore is usually 3 grams, sometimes
+5; the lead varies from 30 to 70 grams, and the quantity of soda, borax,
+or powdered glass added varies from 0.3 to 3 or 4 grams. It is generally
+recommended to have the lead granulated,[9] and to mix the ore with
+about half of it in the scorifier; then to put on the rest of the lead;
+and finally to sprinkle the borax or glass on the top. It answers just
+as well, however, to use the lead in the shape of foil, and wrap the ore
+up in it; and if the ore contains much sulphur, the borax may with
+advantage be added (wrapped in a little tissue paper) some five or ten
+minutes after the operation has started.
+
+[Illustration: FIG. 39.]
+
+The process of scorification is as follows:--A scorifier (fig. 38) of
+convenient size having been selected (one 2-1/2 inches across is most
+generally useful), it is dried at a gentle heat for about ten minutes.
+The charge is then put into it, and it is introduced, with the help of a
+scorifier tongs (fig. 39), into a muffle heated considerably above
+redness. The muffle is then closed, and when the metal has melted down,
+it is opened, but the temperature is kept up. A ring of slag will, after
+a time, form around the metal, and when this appearance (known as the
+eye) presents itself, the temperature may be lowered. When the eye has
+disappeared--that is, when the layer of slag has quite closed in--a
+pinch of powdered culm wrapped in tissue paper is added. As soon as the
+slag has again become tranquil, the scorifier is taken out, and its
+contents are poured into a mould (fig. 40), the slag is detached, and
+saved. If the button of metal weighs more than 30 grams, its size is
+reduced by another scorification in the same scorifier, which should
+have been replaced in the muffle immediately after the contents had been
+poured out. If the ore is not a very rich one, the button of lead will
+carry practically all the silver; but with rich ores it is more
+satisfactory to save the slag, and subsequently to melt it down with the
+cupel on which the lead has been treated, so as to recover the silver
+lost in the slag, together with that absorbed in the cupel, at one
+operation. Or, if the cupellation loss is neglected or calculated in
+some other manner, the slag or slags from the scorifier may be powdered
+and mixed with 20 grams of oxide of lead, 5 grams of borax, and 1 gram
+of charcoal. This should be melted down in a small crucible, and the
+resulting button of lead cupelled.
+
+[Illustration: FIG. 40.]
+
+If the scorification has been unsatisfactory, the quantity of silver
+obtained from the slag will be by no means inconsiderable. The usual
+explanation is that with sulphury ores compounds of metallic oxides and
+sulphides (oxysulphides) are formed, which remain in the slag, retaining
+considerable quantities of the precious metal. It is said that under
+certain conditions such a slag may contain as much as 10 per cent. of
+silver. An excess of lead and a high temperature prevents the formation
+of these oxysulphides. But if much silver is present in the ore, the
+slag cannot be safely thrown away, even if sulphur is absent, and the
+process has been satisfactorily performed.
+
+If the crust which appears on the surface of the lead does not clear,
+add a small lump of borax and 20 grams more lead; then close the muffle,
+and keep the temperature as high as possible. If the slag forms
+properly, but shows unfused or only half-fused lumps, even when the
+scorification has proceeded for some time, add more borax, and stir with
+an iron rod. The slag adhering to the rod must be detached by hammering,
+and replaced in the scorifier.
+
+If the ore consists largely of quartz, soda should be added instead of
+borax; or, if it contains much copper, powdered quartz may be used. If
+the scorifier at the end of an operation is more than usually corroded,
+the borax should be replaced in subsequent assays on similar ores by
+powdered glass or quartz.
+
+If a fairly fluid slag is formed which does not clear from the metal and
+show the eye, more lead and a higher temperature is wanted.
+
+As a general rule, it may be stated that when a scorification is
+unsatisfactory, what is wanted is more heat, more lead, or more borax.
+
+It is a safe plan when work has to be done on a strange ore, to make
+three or four assays with varying quantities of lead. The proportion of
+lead is right when a further addition does not yield a higher result.
+The proper proportion having been found, a note of it should be made for
+future use.
+
+
+POT ASSAYS.
+
+The object of the fusion in a crucible, like that of scorification, is
+to concentrate the silver in a button of lead which is to be
+subsequently cupelled; and to retain the earthy and waste matters in the
+slag. It is necessary to consider the quality of the slag and the weight
+and quality of the lead. The slag when fused should be liquid and
+homogeneous, and not too corrosive on the crucible. The button of lead
+should be soft, malleable, and free from a coating of regulus.[10] In
+weight it should not differ much from the ore taken. With 20 grams of
+ore, for example, a button of lead weighing from 18 to 25 grams will be
+satisfactory: less than this would leave an undue proportion of silver
+in the slag; and more would be unnecessarily large for cupelling, and
+would increase the loss in that operation.
+
+With average ores, take 20 grams of the powdered ore and mix with 30
+grams of "soda," 40 grams of red-lead or litharge, 5 grams of borax, and
+from 2 to 2.5 grams of flour, and place in an E crucible (Battersea
+round). Put these in the furnace at a red heat, cover the crucible, and
+gradually raise the temperature until the whole charge has melted down
+and is in a state of tranquil fusion. Pour into a mould, and replace the
+crucible in the furnace. As soon as the lead is solid, detach the slag
+and put it back into the crucible; and when it is again fluid, charge on
+to it with a copper scoop a mixture of 20 grams of oxide of lead, and 1
+gram of charcoal: when fusion has again become tranquil, pour and detach
+the button of lead. The lead buttons should be hammered into discs with
+rounded edges, and be freed from slag; if too big for a cupel they may
+be scorified together in a small scorifier, but it is better to cupel
+them separately.
+
+~Ores containing Metallic Oxides.~--Peroxides of iron, manganese, and
+copper interfere by counteracting the effect of the charcoal or flour,
+and thus reducing the size of the lead button. Peroxide of iron will
+reduce the weight of lead by a little more than its own weight; and
+peroxide of manganese has about twice this effect. When these oxides are
+present an additional quantity of flour must be used, and precautions
+must be taken to prevent reoxidation of the slag by the furnace gases.
+This may best be prevented by using a layer of common salt as a cover to
+the charge. When the ores contain a good deal of quartz or stony matter,
+the fluxes just given (for average ores) will do; but the proportion of
+soda should be diminished, and that of the borax, oxide of lead, and
+flour increased as the quantity of metallic oxides become greater. If
+the ore contains practically no quartz, the soda may be altogether
+omitted, and some glass or powdered quartz added. The following charge
+may be taken as an example: weigh up 20 grams of the powdered ore, 15
+grams each of "soda" and borax, 60 grams of oxide of lead, and 5 grams
+of flour. Mix and place them in an E crucible, and cover with a layer of
+from a quarter to half an inch of common salt. Place in the furnace as
+before. The salt will give off a considerable amount of fume, which
+will, to a certain extent, conceal the state of the charge: when the
+crucible has been in the furnace for about 25 minutes remove it and pour
+out the contents immediately. With ores that produce a thick slag the
+addition of 5 grams of fluor spar will be an advantage. It may happen
+that with an unknown ore the first assay will be more or less
+unsatisfactory: but from it the necessity for adding more or less flour
+will be learnt, and a second assay, with the necessary modification of
+the charge, should give a good result.
+
+~Ores containing much Sulphides.~--Ores of this class may be easily
+recognized, either by the appearance of the minerals they contain or by
+the odour of sulphurous oxide (SO_{2}) which they evolve when roasted on
+a spatula. The sulphides most commonly present, in addition to the
+sulphurized minerals of silver, are pyrites, galena, blende, and
+mispickel. When they are present in only a moderate amount, their effect
+is simply to increase the weight of the button of lead; and this is
+easily counteracted by reducing the amount of flour, or by omitting it.
+When in larger amounts, they not only yield large buttons, but also
+render the metal sulphury, sometimes even giving a button of regulus
+instead of lead. This last evil may be remedied (1) by putting in a rod
+of iron as soon as the charge has fused, or (2) it may be counteracted
+by a proper addition of nitre, or (3) when the sulphides present are
+only those of iron or copper the sulphur may be removed by calcining,
+and the ore converted into one of the class containing metallic oxides.
+The calcination is effected as follows:--Weigh up 20 grams of the
+powdered ore and place it in a wide-mouthed crucible sufficiently large
+to perform the subsequent melting down in. The roasting must be done at
+a gentle heat at first, so as to avoid clotting: the mouth of the
+crucible should project considerably above the coke, and should slope
+forward towards the worker. The charge must be occasionally stirred with
+the stirrer (fig. 10) so as to expose fresh surfaces to the action of
+the air, and to prevent adhesion to the sides of the crucible. The
+stirrer should not be removed till the calcination is finished. The
+temperature should be raised at the end to a good red heat; and (to
+ensure the decomposition of any sulphate that may be formed) the roasted
+ore should be rubbed up in a mortar with a pinch of anthracite, and
+again calcined. It is then mixed with fluxes as described, and fused in
+the same crucible.
+
+The calcination of an ore is a work occupying a good deal of time, and,
+in most cases, it is better to take advantage of the desulphurizing
+power of red lead or nitre. Red lead by itself will do, but a large
+quantity of it will be required; 1 part of a metallic sulphide needs
+from 20 to 50 parts of red lead to yield a button free from sulphur;
+whereas at most from 2 to 2-1/2 parts of nitre are sufficient. There is
+sometimes an advantage in having a considerable excess of oxide of lead
+in the slag, but where there is no such reason, 2 parts of red lead to 1
+of ore is enough. A charge which will do for most sulphides is the
+following: 20 grams of ore, 40 to 100 grams of red lead, 20 grams of
+"soda," 5 of borax, and sufficient nitre (or perhaps flour) to give a
+button of about 25 grams of lead. How much this must be (if not already
+known) may be approximately determined by fusing 3 grams of the ore and
+3 grams of "soda" in a small crucible (C) with 50 grams of litharge (not
+red lead) under a cover of salt, and weighing the resulting button of
+lead. Subtract 3 from the weight of lead obtained, and the difference
+multiplied by 1.3 will give the quantity in grams of nitre required. If
+the button of lead weighs less than 3 grams flour must be added. If this
+is not satisfactory repeat the assay, adding an extra gram of nitre for
+each 4 grams of lead in excess of that required, or 1 gram of flour for
+a 12-gram deficiency.
+
+In the method in which iron is used as a de-sulphurising agent, only as
+much oxide of lead should be added as will give a button of lead of the
+required size. Rather a large button of lead should be got, and the slag
+should be strongly alkaline; if the ore does not already carry a large
+amount of sulphur some should be added. The fusion should be performed
+at a low temperature (similar to that for a galena assay), and should be
+continued for some time after it has become tranquil. Take 20 grams of
+the ore, 40 grams of "soda," 40 grams of oxide of lead, and 5 or 10
+grams of borax; place this mixture in a crucible (with a rod of iron, as
+in the galena assay), cover, and fuse for about half an hour. Take out
+the rod, washing it in the slag, and, in a minute or two, pour. Clean
+and cupel the button of lead.
+
+~General Remarks on the Fusion.~--Other things being equal, the smaller
+the quantity of the slag the better, provided there is sufficient to
+cover the metal. The presence of peroxides of the heavy metals is
+prejudicial, since they tend to increase the quantity of silver retained
+in the slag. It may be given as a general rule that when iron, copper,
+manganese, &c., are present, there is a more than ordinary need for
+cleaning the slags, and care must be taken to keep these metals in the
+state of lower oxide.
+
+In selecting the fluxes, it should be remembered that soda is the best
+for quartz, and borax for lime and metallic oxides. And that with ores
+almost free from gangue some quartz or glass should be added to protect
+the crucible. Two parts of soda are enough to flux 1 part of quartz;
+whilst of borax, or oxide of lead, 4 parts are barely sufficient. Oxide
+of lead has the advantage of being heavy and so does not occupy much
+space in the crucible; on the other hand, if the melting down be
+performed too quickly, or if oxide of lead only is used, this high
+specific gravity is a disadvantage, for the lighter earthy matter floats
+as a pasty mass on the more fluid oxide of lead, and thus escapes its
+action.
+
+When metallic sulphides are present in the ore, an excess of oxide of
+lead helps to keep the sulphur out of the button of metal. In addition
+to the oxide of lead required as a flux, some will be required to
+provide the lead in which the silver is to be collected. Oxide of lead,
+mixed with charcoal or flour, yields, when heated, a multitude of minute
+buttons of metal uniformly distributed through the mass of the charge;
+as the charge melts down these run together and fall to the bottom; this
+shower of lead collects the silver more easily than a single button at
+the bottom of the crucible could do. Only that portion of the oxide of
+lead which remains in the slag can be considered as a flux; very often
+the first indication of an excessive reduction of lead is the pastiness
+of the slag rendered thick by the withdrawal of the oxide of lead which
+would have kept it fluid. If, in an assay, it is found that 5 parts of
+flux are not sufficient for 1 part of ore, the remedy lies in using a
+different flux rather than in taking a larger quantity.
+
+_On the Reducing Effect of Charcoal, Flour, and Tartar._--The weight to
+be got from a given charge will depend (provided sufficient oxide of
+lead is present) upon the proportion of the reducing agents in it. We
+have thought it well to illustrate this part of the subject by a series
+of experiments which the learner will do well to practise for himself
+before proceeding to the assay of actual ores. Take 80 grams of litharge
+and 20 grams of a mixture of borax and soda. Fuse three lots (1) with
+1.5 gram of charcoal, (2) with 3 grams of flour, and (3) with 7.5 grams
+of tartar. Weigh the buttons of lead obtained, and divide each by the
+weight of reducing agent used. The results will differ somewhat with the
+dryness and quality of the flour, etc., used; in one series of
+experiments they were as follows:--
+
+  Gram.             Grams.        Gram.        Grams.
+  1.5 charcoal gave 34.0 lead .'. 1 charcoal = 22.6 lead.
+  3.0 flour      "  33.5   "  .'. 1 flour    = 11.2   "
+  7.5 tartar     "  38.0   "  .'. 1 tartar   =  5.0   "
+
+The use of flour as a reducing agent has many advantages, and it is well
+to remember that _1 gram of flour reduces about 11 grams of lead_; and
+that charcoal has twice, and tartar one-half, this reducing effect.
+
+_On the Reducing Effect of Charcoal, &c., on Red Lead._--It is often
+easier to obtain red lead of good quality than it is litharge, and by a
+large number of assayers red lead is the form of oxide of lead always
+used. Red lead, however, contains an excess of oxygen which will use up
+some of the reducing agent before lead separates out. On making a series
+of experiments (similar to the last, but using 80 grams of red lead
+instead of the litharge) the results were, with the same quantities of
+the reducing agents:--
+
+  With charcoal, 18 grams of lead.
+   "   flour,    18   "      "
+   "   tartar,   22   "      "
+
+Comparing these with the results with litharge, in the previous table it
+will be seen that the same quantity of reducing agent has in each case
+brought down 16 grams less of lead, so that a larger amount of the
+reducing agent must be added to get a button of the same weight as that
+obtained with litharge. To get a button of a desired weight, say 22
+grams, we must add reducing agent sufficient to throw down 22 + 16 or 38
+grams of lead, which would require 3.4 grams of flour. If this amount of
+flour is fused with 80 grams of red lead, a button of lead weighing 22
+grams will be formed, the other 16 grams being kept up by the oxygen of
+the red lead.
+
+If the quantity of red lead differs from 80 grams, this rule must be
+modified. With 40 grams of red lead, for example, we should add an
+excess of reducing agent sufficient to throw down 8 grams of lead
+instead of 16. Similarly, with 160 grams of red lead, we should add
+enough to throw down 32 grams.
+
+The following rule will enable one to calculate the weight of flour
+required to produce a button of lead of any desired weight from any
+given quantity of red lead. Each 5 grams of red lead present diminishes
+the weight of the lead by 1 gram. If then we _divide the weight of red
+lead in a charge by 5, and add this to the weight of lead required, the
+sum divided by 11 will give the weight of flour which must be added_.
+Using 80 grams of red lead and wanting a button of 20 grams, we should
+add 3.3 grams of flour.
+
+  80/5 = 16; 16+20 = 36; 36/11 = 3.3 nearly.
+
+The following are some results obtained which will illustrate the
+rule:--
+
+  Red Lead used.    Flour used.    Lead got.
+   40 grams         3 grams        25.0 grams
+  100   "           3   "          13.5   "
+   80   "           4   "          30.0   "
+   80   "           5   "          40.0   "
+
+_On the Reducing Effect of Metallic Sulphides, and the Counteracting
+Effect of Nitre._--The sulphides found in ores will reduce a button of
+lead from oxide of lead just as flour does; and, as charcoal, flour and
+tartar differ in their reducing power, so equal weights of the different
+mineral sulphides throw down different weights of lead.
+
+One gram of iron pyrites yields about 11 grams of lead. One gram of
+copper pyrites, blende, fahlerz, or mispickel, yields 7 or 8 grams of
+lead, whilst 1 gram of antimonite will give 6, and 1 gram of galena only
+a little over 3 grams. It is evident that if an ore carries much of
+these sulphides, the quantity of lead reduced will be very much larger
+than that required for an assay. To counteract this effect nitre is
+added; _1 gram is added for each 4 grams of lead in excess of that
+required_. For example: with a 20-gram charge of an ore containing 50
+per cent. of pyrites, if no nitre were added, 110 grams of lead would be
+got; or, if there was not sufficient oxide of lead to yield this
+quantity of metal, the button would be sulphury. To reduce the weight of
+the button by 80 grammes, we should add 20 grams of nitre, if litharge
+were used; or if red lead were used, we should add 16 grams of nitre,
+_since the oxidizing effect of 20 grams of red lead is equivalent to
+that of 1 of nitre_, and since 80 grams of red lead are generally used
+in a charge. Two assays of an ore of this kind with these quantities of
+nitre gave 26.0 grams of lead with litharge, and 22.5 grams with red
+lead.
+
+It is best to use in these assays 80 grams of red lead, 20 of soda, and
+5 of borax, with 20 grams of the ore. If the lead got by the preliminary
+fusion in a small crucible with litharge (described under "_ores
+containing much sulphides_") is known, the following table will indicate
+the quantity of nitre, or flour, to be added with this charge:--
+
+  -------------------------------+-------------------+------------------
+  Lead got in Preliminary Fusion | Flour to be added | Nitre to be added
+        with 3 grams of Ore.     |   to the Assay.   |   to the Assay.
+  -------------------------------+-------------------+------------------
+             0.0 gram            |     3.3 grams     |      none
+             3.0 grams           |     1.3 gram      |       --
+             6.0   "             |       none        |     4.0 grams
+             9.0   "             |        --         |     9.0   "
+            12.0   "             |        --         |    14.0   "
+            15.0   "             |        --         |    19.0   "
+            18.0   "             |        --         |    24.0   "
+            21.0   "             |        --         |    29.0   "
+  -------------------------------+-------------------+------------------
+
+If litharge is used in the assay instead of red lead 4 grams more nitre,
+or 1.5 gram less flour must be used. When more than a few grams of nitre
+are added to a charge the proportion of "soda" and borax should be
+increased, because one of the products of the reaction of nitre upon
+sulphides in the presence of soda is sulphate of soda, and because the
+"soda" thus used up no longer serves as a flux; more borax should be
+added, as it is the best flux for the metallic oxides which are formed
+in the process. If in an assay too large a button of lead is got, even
+after this calculation has been made, and the assay is repeated, add 1
+gram more nitre for each 4 grams of lead in excess. Sometimes the assay
+appears tranquil before the nitre has produced its full effect; in such
+cases it is well to seize the crucible with the tongs and mix its fused
+contents by rotating them; if this causes an effervescence, the crucible
+should be replaced in the fire and the fusion continued. The following
+experiments will illustrate the extent to which the above rules may be
+relied on. In all of them the standard flux was used, viz.:--80 grams of
+red lead, 20 of soda, and 5 of borax.
+
+  _Pyrites_          5     5     5     5     2.5   5    10    15    20
+  Quartz            --    20    --    20    17.5  15    10     5
+  Nitre             --    --     5     5    --     4    16    28.5  41
+  Lead got          42.5  36.0  16.0  19.0  11.5  22.5  22.5  26.5  27.5
+
+  _Copper Pyrites_   8     8     8     8
+  Quartz            --    12    --    12
+  Nitre             --    --     4     4
+  Lead got          47.5  34.0  33.0  26.0
+
+  _Antimonite_       8     8     8     8
+  Quartz            --    12    --    12
+  Nitre             --    --     4     4
+  Lead got          29.0  26.0  13.0  13.0
+
+  _Galena_          10     10    10    10    15    20
+  Quartz.           --     15    --    15     5    --
+  Nitre             --     --     3     3     3.5   7
+  Lead got          17.0   19.0   8.0   8.0  18.5  18.5
+
+A similar set of experiments, with 80 grams of litharge instead of 80
+grams of red lead, gave:--
+
+  _Pyrites_          4     4     4     4     7    10
+  Quartz            --    15    --    15    13    10
+  Nitre             --    --     5     5    12.5  20
+  Lead got          46.5  40.5  25.5  24.5  27.0  26.5
+
+  _Copper Pyrites_   5     5     5     5
+  Quartz            --    15    --    15
+  Nitre             --    --     5     5
+  Lead got          44.5  32.5  23.0  25.0
+
+  _Blende_           5     5     5     5    10
+  Quartz            --    15    --    15    10
+  Nitre             --    --     5     5    15
+  Lead got          41.5  38.5  21.5  22.5  21.6
+
+  _Antimonite_       5     5     5     5    10
+  Quartz            --    15    --    15    10
+  Nitre             --    --     5     5    10
+  Lead got          31.0  32.5  11.5  12.5  18.7
+
+  _Galena_          10    10    10    10    15    20
+  Quartz            --    15    --    15     5    --
+  Nitre             --    --     5     5     7.5  11
+  Lead got          33.5  33.5  13.0  14.0  19.5  22.7
+
+The variation in some of these experiments, in which we might have
+expected similar results, is due to the fact that the sulphur, and in
+some cases the metals, are capable of two degrees of oxidation. For
+example: theoretically 1 gram of iron pyrites (FeS_{2}) would yield 8.6
+grams of lead if the sulphur were oxidised to sulphurous oxide (SO_{2}),
+and the iron to ferrous oxide (FeO); whilst if the sulphur were oxidised
+to sulphate (SO_{3}), and the iron to ferric oxide, 12.9 grams of lead
+will be thrown down. Similarly the yield with copper pyrites would be
+7.5 or 11.6; with blende, 6.4 or 8.5; with antimonite, 5.5 or 8; and
+with galena, 2.6 or 3.4. As regards the metals, the lower oxide will
+always be formed if the assay is carried out properly (fused under a
+cover, and with a sufficiency of reducing agent). But the proportion of
+sulphur oxidised completely will vary with the conditions of the assay.
+With a slag containing much soda the tendency will be to form sulphate,
+and, in consequence, a big reduction of lead; whilst with an acid slag
+containing much quartz the tendency will be for the sulphur to go off as
+sulphurous oxide (SO_{2}). In a fusion with litharge alone all the
+sulphur will be liberated as the lower oxide, whilst with much soda it
+will be wholly converted into sulphate. For example: 3 grams of an ore
+containing a good deal of pyrites and a little galena, gave, when fused
+with litharge, 16.5 grams of lead. A similar charge, containing in
+addition 20.0 grams of soda, gave 22.5 grams of lead.
+
+It will be noted from the experiments that 1 gram of nitre kept up on
+the average 4 grams of lead; the range being from 3.2 with acid slags to
+5.3 with very basic ones. These facts serve to explain some apparently
+irregular results got in practice.
+
+
+CUPELLATION.
+
+The process is as follows:--The cupels, which should have been made some
+time before and stored in a dry place, are first cleaned by gentle
+rubbing with the finger and blowing off the loose dust; and then placed
+in a hot muffle and heated to redness for from 5 to 10 minutes before
+the alloy to be cupelled is placed on them. The reasons for this are
+sufficiently obvious: the sudden evolution of much steam will blow a
+cupel to pieces; and, if the whole of the water has not been removed
+before the cupel is filled with molten lead, the escaping steam will
+bubble through, and scatter about particles of the metal. If some
+particles of unburnt carbon remain in the bone ash, a similar result
+will be produced by the escape of bubbles of carbonic acid as soon as
+the fused litharge comes in contact with them. The cupels having been
+prepared are arranged in a definite order in the muffle, and the assay
+buttons are arranged in a corresponding order on some suitable tray
+(cupel tray, fig. 41); the heat of the muffle being at bright redness.
+Then with the help of the tongs (fig. 42) the assay buttons should be
+placed each in its proper cupel; a note having been previously made of
+the position it is to occupy, and the door of the muffle closed.
+
+[Illustration: FIG. 41.]
+
+This part of the work should be done promptly, so as not to unduly cool
+the muffle: the start requires a fairly high temperature, and is a
+critical part of the process. A black crust forms at once on the surface
+of the lead; but this ought soon to fuse and flow in greasy drops from
+off the face of the metal, so as to leave the latter fluid with a
+well-defined outline, and much brighter than the cupel. If this clearing
+does not take place, the buttons are said to be frozen; in which case
+the temperature must be raised, some pieces of charcoal put in the
+muffle, and the door closed. If they still do not clear, the heat must
+have been much too low, and it is best to reject them and repeat the
+assays.
+
+[Illustration: FIG. 42.]
+
+When the buttons have cleared it is well to check the draught of the
+furnace, and to partly open the door of the muffle, so as to work at as
+low a temperature as is compatible with the continuation of the
+process.[11] Too low a temperature is indicated by the freezing of the
+buttons and the consequent spoiling of the assays. Experience soon
+enables one to judge when the heat is getting too low. A commoner error
+is to have the heat too high: it should be remembered that that which
+was high enough to clear the buttons at starting is more than sufficient
+to keep the process going. At the finish a higher temperature is again
+required: therefore the door of the muffle should be closed and the
+furnace urged. The finish is easily recognised. The drops of litharge
+which in the earlier stages flow steadily from the surface of the alloy,
+thin off later to a luminous film. At the end this film appears in
+commotion, then presents a brilliant play of colours, and, with a sudden
+extinction, the operation is finished. The metal again glows for an
+instant whilst becoming solid.
+
+If the button is a small one the cupel is withdrawn at once and placed
+on that square of the cupel tray which corresponds to the position it
+occupied in the muffle. If, however, it is fairly large precautions must
+be taken to prevent spirting.
+
+Molten silver dissolves oxygen from the air and gives it off on
+solidifying; the escape of the gas on sudden cooling is violent and, by
+throwing off particles of the metal, may cause loss. This is called
+"vegetation" or "spirting." The silver is apparently solid when spirting
+takes place; the crust breaks suddenly and some of the metal is forced
+out. The evil is best guarded against by slow cooling and avoiding
+draughts. With large buttons of silver precautions should never be
+omitted. One plan is to allow the cupels to cool in the muffle itself,
+the mouth being closed with hot charcoal. Another is to cover the cupel
+with another cupel previously heated to redness; in this case the silver
+cools between two hot cupels, and, of course, cools slowly. A third plan
+is to withdraw the cupel to the door of the muffle, holding it until it
+begins to get solid and then immediately to put it back into the hotter
+part of the muffle.
+
+Silver remains after cupellation in flattened elliptical buttons,
+adhering but only slightly to the cupel. Its upper surface should show
+faint markings as if it were crystalline. The presence of platinum
+renders it still more crystalline, but removes the characteristic lustre
+and renders the metal dull and grey. Copper, if not completely removed,
+has a very marked effect on the appearance of the button: the metal is
+spread out, damping, as it were, and firmly adhering to the cupel, which
+latter in the neighbourhood of the metal is almost black with oxide of
+copper. Sometimes the silver button is globular, or even more sharply
+rounded on its under than on its upper surface; it is said that this is
+due to the presence of lead. Gold may be present even to the extent of
+50 per cent. without showing any yellow colour.
+
+The appearance of the cupel affords some useful information. The
+presence of cracks evidently due to shrinkage indicates a badly made
+cupel. If, however, they are accompanied by a peculiar unfolding of the
+cupel, the margin losing its distinctness, it is because of the presence
+of antimony. When lead is the only easily oxidisable metal present, the
+stained portion of cupel is yellow when cold. A greenish tint may be due
+to small quantities of copper or, perhaps, nickel, cobalt, or platinum.
+Larger quantities of copper give a greenish grey or almost black colour.
+A dark green and corroded cupel may be due to iron. Rings of
+pale-coloured scoria may be due to tin, zinc, antimony, or arsenic. When
+the cupel shows signs of the presence of these metals in objectionable
+quantity, it is well to repeat the assay and scorify so as to remove
+them before cupellation.
+
+The button should be detached from the cold cupel by seizing with a
+pair of pliers: the under surface should be distorted by squeezing or
+hammering the button so as to loosen the adhering bone ash. The cleaning
+is easily completed by rubbing with a clean hard brush. After cleaning
+the buttons are best put on a tray of marked watch-glasses, and then
+taken to the balance and weighed. The weight of silver got needs a small
+correction; (1) by deducting for the amount of silver introduced by the
+lead or oxide of lead used in the assay;[12] and (2) by adding for the
+cupellation loss.
+
+~Loss in Cupellation.~--During the whole process of cupelling a silver
+lead alloy a more or less abundant fume may be observed rising from the
+cupel. This furnishes an evident loss of lead and a possible loss of
+silver; for although silver at the temperature of cupellation gives off
+no appreciable vapour, it is known that such fume formed on a large
+scale contains silver. It is, however, difficult to believe that the
+small amount of lead vapourised carries with it a weighable amount of
+silver. That it does not do so in the ordinary way of working is shown
+by the fact that a button of silver equal in weight to the silver lost
+in cupelling may be got by smelting the cupel and cupelling the
+resulting button of lead. The loss of silver by volatilisation is
+altogether inconsiderable, unless the temperature at which the operation
+is performed is much too high.
+
+Another possible source of loss is the infiltration of small particles
+of alloy into the cupel. The cupel is necessarily porous, and particles
+of metal may perhaps drain into it, more especially if the bone ash is
+not in fine powder; but if this is the main source of loss it is hard to
+see why, in cupelling equal weights of silver and gold, the loss is not
+equal in each case. It is not easy to believe that the mere filtration
+of the fused alloy will effect such a change in the proportion of the
+metals as that which actually occurs. For example: a cupel on which an
+alloy consisting of 0.80 gram of silver, 0.47 gram of gold, and 25 grams
+of lead had been cupelled, was found to contain 7-1/2 milligrams of
+silver, and rather less than half a milligram of gold. Assuming, for the
+sake of argument, that the gold present had filtered into the cupel in
+the form of small drops of alloy, it would have been accompanied by less
+than a milligram of silver, and the presence of the extra 6 or 7
+milligrams of silver must have been due to a different cause. There can,
+thus, be little doubt that the cause of the greater part of the
+"cupellation loss" is a chemical one and cannot be counteracted by a
+mechanical contrivance.[13] In cupellation, then, there is a loss,
+apart from imperfect working, inherent in the process itself; and as the
+amount of this loss varies under different conditions, it is necessary
+to study it somewhat in detail.
+
+The following experiments are taken without selection from the work of
+one student. Three experiments were made for each determination, and the
+mean result is given. By "range" is meant the difference between the
+highest and lowest result and the percentage loss is calculated on the
+silver present. The silver added in the lead used has been deducted.
+
+~Effect of Varying Lead.~--In each experiment 0.4 gram of silver was
+taken and cupelled with the lead. The silver loss and "range" are
+expressed in milligrams.
+
+  ------------+--------------+--------+------------------
+   Lead Used. | Silver Lost. | Range. | Percentage Loss.
+  ------------+--------------+--------+------------------
+     Grams.   |              |        |
+       10     |      6.5     |   1.0  |       1.62
+       20     |      7.0     |   1.0  |       1.75
+       40     |     12.0     |   1.5  |       3.00
+       60     |     12.7     |   0.5  |       3.17
+  ------------+--------------+--------+------------------
+
+The loss increases with the lead used.
+
+~Effect of Varying Temperature.~--0.4 gram of silver was cupelled with
+20 grams of lead.
+
+  Temperature.    Silver Lost.    Range.    Percentage Loss.
+
+  Bright red          7.0          1.0            1.75
+  Clear yellow       17.3          1.7            4.32
+
+The difference in temperature in these experiments was much greater than
+would occur even with careless work.
+
+~Effect of Varying Silver.~--20 grams of lead were used in each
+cupellation.
+
+  ---------------+--------------+--------+------------------
+   Silver Taken. | Silver Lost. | Range. | Percentage Loss.
+  ----------------------------------------------------------
+    Milligrams.  |              |        |
+       12.5      |      0.7     |   0.2  |       5.6
+       25.0      |      1.4     |   0.1  |       5.6
+       50.0      |      1.6     |   0.4  |       3.2
+      100.0      |      2.9     |   0.3  |       2.9
+      200.0      |      5.6     |   0.5  |       2.8
+      400.0      |      7.0     |   1.0  |       1.7
+      800.0      |      9.7     |   1.0  |       1.2
+  ---------------+--------------+--------+------------------
+
+It will be seen that, although the quantity of silver lost increases
+with the silver present, the percentage loss is greater on the smaller
+buttons.
+
+The following results are often quoted:--Cupelling 1 grain of silver
+with 10 grains of lead, the loss was 1.22 per cent.; 10 grains of silver
+with 100 grains of lead, loss 1.13 per cent.; 25 grains of silver
+cupelled with 250 grains of lead, lost 1.07 per cent. The proportion of
+silver to lead was the same in the three experiments, and the largest
+button gave the best result. Evidently, if the quantities of lead had
+been the same in the three experiments (say, 250 grains in each case),
+the loss on the smaller quantities of silver would appear worse in the
+comparison.
+
+In judging these results, it must be borne in mind that it is difficult
+to regulate the temperature, &c., in consecutive experiments so as to
+get exactly similar results, so that the range in consecutive
+cupellations is greater than that in a batch cupelled side by side.
+
+~Effect of Copper and Antimony.~--0.1 gram of silver was cupelled with
+20 grams of lead, and to one batch 0.5 gram of antimony, and to another
+0.5 gram of copper was added.
+
+                                                Loss in
+                     Silver Lost.    Range.   Percentage.
+
+  Without addition        2.9         0.3         2.9
+  With antimony           3.2         0.2         3.2
+  With copper             4.9         1.7         4.9
+
+Perhaps the antimony has so small an effect because it is eliminated in
+the earlier part of the process, while the silver is still alloyed with,
+and protected by, a large proportion of lead; whilst the copper on the
+other hand makes its fiercest attack towards the close, when the silver
+is least capable of resisting it. The ill effects of copper are most
+strongly felt when the quantity of lead present is not sufficient to
+remove it: the coppery button of silver got under these conditions is
+very considerably less than the weight of silver originally taken.
+
+Although the above is a fair statement of the loss attending average
+work, it will not do in very important and exact work to place too much
+reliance on the figures given, or, indeed, on any other set of figures,
+with the object of correcting the result of an assay. Each man must rely
+on his own work.
+
+It is easy to determine what allowance must be made for the loss in
+cupellation by cupelling side by side with the assay piece an alloy of
+similar and _known_ composition. For, if the two pieces are very nearly
+alike, we may justly conclude that the loss on each will be the same;
+and if, further, we take the average of three or four such
+determinations we shall get results accurate within 0.1 per cent. The
+method of getting such results may be best explained by one or two
+illustrations. This method of working is termed "assaying by checks."
+
+Suppose we have an alloy of silver and lead in unknown proportions and
+that by cupelling two lots of 10 grams each there is got from I. 0.1226
+gram of silver, and from II. 0.1229 gram. We should know from general
+experience that the actual quantity of silver present was from 2 to 4
+milligrams more than this. To determine more exactly what the loss is,
+the following plan is recommended:--The two silver buttons are wrapped
+up each in 10 grams of lead, and cupelled side by side with two other
+lots of 10 grams of the original alloy. If now the two buttons I. and
+II. weigh 0.1202 and 0.1203, they will have suffered in this second
+cupellation an average loss of 2.5 milligrams. Suppose the two fresh
+lots of alloy gave 0.1233 and 0.1235 of silver, the average loss on
+these would also be 2.5 milligrams. Add this loss to each result, and
+take the mean; which is in this case 0.1259.
+
+If copper is present in the alloy as well as silver, it is necessary to
+add about the same quantity of copper to the checks as is supposed, or
+known, to be present in the assays. If the substance to be assayed is an
+alloy of silver and copper, first cupel 0.5 gram of it, with, say, 10
+grams of lead, and weigh the resulting button of silver, in order to get
+an approximate knowledge of its composition. Suppose the button weighs
+0.3935 gram. We know that this is below the truth: for the sake of round
+numbers take it as 0.4, and assume that the rest of the alloy (0.1 gram)
+was copper. Two check pieces are then weighed out, each containing 0.4
+gram silver and 0.1 gram of copper wrapped in 5 grams of lead. Of course
+the silver must be pure. And there is also weighed out two (or better,
+four) assay pieces each containing half a gram of the alloy wrapped in 5
+grams of lead. The whole lot are then cupelled as nearly as possible
+under the same conditions. With four assay pieces, the cupels should be
+placed close together in two rows of three across the muffle; the two
+check pieces are put in the middle cupels. Suppose the buttons of silver
+got weighed as follows:--
+
+  Check pieces      I.  0.3940    II.  0.3945
+  Assay pieces      I.  0.3905    II.  0.3912
+                  III.  0.3910    IV.  0.3909
+
+The average loss on the two check pieces is 5.7 milligrams, and the
+average result of the four assay pieces is 0.3909. Add the average loss
+to the average result, and there is got the corrected result, 0.3966.
+And if 0.5 gram of alloy contain 0.3966 of silver, 1000 will contain
+793.2 of silver, and this is the degree of fineness.
+
+A correction for the loss in cupellation is always made in this way
+when rich alloys are being assayed; and in the case of rich ores it may
+be done after the manner of the first of the above illustrations. There
+is another method of working which relies more on experiment. This is to
+smelt the cupel as described further on (p. 114), and to again cupel the
+resulting button of lead. The button of silver got in this second
+cupellation is added to that first obtained. It will sometimes, but not
+often, happen that the two buttons together will slightly exceed in
+weight the silver which was actually present. This is because of the
+retention in the buttons of a small quantity of lead. It has been stated
+that the proportion of lead thus retained may be as much as 1% of the
+silver present; this, however, can only be under exceptional conditions.
+A determination of the actual silver in the buttons got in the series of
+cupellations quoted on pages 102, 103, gave an average percentage of
+99.85, so that even with the larger buttons the effect of the retained
+lead would be only to increase the weight by about 1 milligram. In the
+method of working with checks, the retained lead has no disturbing
+influence.
+
+~The proportion of lead required~ for the cupellation of any particular
+alloy requires consideration. With too much lead the time occupied in
+the process is increased, and so is the loss of silver; on the other
+hand, too little lead is of greater disadvantage than too much. From 8
+to 16 parts of lead are required for each part of silver alloy, or, if
+gold is present, about twice as much as this must be used. For the
+cupellation of 1 gram of a silver copper alloy containing different
+percentages of copper, the following quantities of lead should be
+used:--
+
+  Percentage of Copper
+      in Alloy.          Lead Required.
+
+           5                 6 grams
+          10                 8   "
+          20                10   "
+          30                12   "
+          40                14   "
+      50-100             16-18   "
+
+The alloy, in not too large pieces, is wrapped in the required weight of
+lead foil and charged into the cupel at once; or the lead may be put in
+first, and, when the cupellation has fairly started, the alloy may be
+added wrapped in tissue paper; or a portion of the lead may be first
+started and the alloy wrapped in the remaining lead and subsequently
+added. The cupellation of large quantities of alloy or of alloys which
+contain tin, antimony, iron, or any substance which produces a scoria,
+or corrodes the cupel, must be preceded by a scorification. The
+advantages of this are that the slag is poorer in precious metal than
+that found on a cupel and is more easily collected and cleaned; that
+larger quantities of metal can be treated, and that, even if the
+substance is in part infusible, or produces at the start a clinkery mass
+or scoria, the oxide of lead gradually accumulates, fluxes the solid
+matters, and produces a good final result; but if the oxide of lead by
+itself is not sufficient for the purpose, borax or some other flux can
+be easily added.
+
+If the button of silver got is very small its weight may be estimated
+from its size; but it must be remembered that the weight varies as the
+cube of the diameter. If one button has twice the diameter of another it
+is eight times as heavy and so on. Scales specially constructed for
+measuring silver and gold buttons may be purchased; but it is much
+better to make the measurement with the help of a microscope provided
+with an eyepiece micrometer.
+
+If the length of the long diameter of a silver button be taken the
+following table will give the corresponding weight in milligrams:--
+
+  ------------+-----------++------------+---------
+   Diameter.  | Weight.   || Diameter.  | Weight.
+  ------------------------------------------------
+   0.04  inch |   3.6     || 0.015 inch |  0.19
+   0.035   "  |   2.4     || 0.014  "   |  0.15
+   0.03    "  |   1.5     || 0.013  "   |  0.12
+   0.025   "  |   0.9     || 0.012  "   |  0.097
+   0.02    "  |   0.45    || 0.011  "   |  0.075
+   0.019   "  |   0.4     || 0.010  "   |  0.056
+   0.018   "  |   0.33    || 0.008  "   |  0.028
+   0.017   "  |   0.27    || 0.006  "   |  0.012
+   0.016   "  |   0.23    || 0.004  "   |  0.004
+  ------------+-----------++------------+---------
+
+The weight of a corresponding button of gold is got by multiplying by
+2.25. These figures are based on those given by Plattner, and apply only
+to buttons of such shape as those left after cupellation. A sphere of
+silver 0.01 inch in diameter would weigh 0.09 milligram, and a similar
+sphere of gold weighs 0.167 milligram.
+
+It is safer, however, to compare with a micrometer the diameter of the
+button whose weight has to be determined with that of a standard button
+of nearly equal size whose weight is known. The weights of the two
+buttons are proportional to the cubes of their diameters. This plan of
+working is described more fully in Appendix B., page 440.
+
+~Calculation of the Results.~--After deducting for the silver added, and
+correcting for the cupellation loss, the calculation is made in the
+usual way; reporting as so many parts per thousand in the case of rich
+alloys and as so many ounces and pennyweights, or better as ounces and
+decimals of an ounce, in the case of poor alloys and ores.
+
+In this last case, however, it is less fatiguing to refer to a set of
+tables which give, either directly or by means of simple addition, the
+produce corresponding to any weight obtained from certain given weights
+of the substance. The following table gives the produce in ounces and
+decimals of an ounce per ton of 2240 pounds:--
+
+  ------------+----------------------------------------------------------
+              |                    Weight of Ore taken.
+   Weight of  |----------+----------+-----------+-----------+------------
+   Metal got. | 3 grams. | 5 grams. | 20 grams. | 50 grams. | 100 grams.
+  ------------+----------+----------+-----------+-----------+------------
+     0.0001   |     1.09 |     0.65 |     0.16  |    0.06   |     0.03
+     0.0002   |     2.18 |     1.31 |     0.33  |    0.13   |     0.06
+     0.0003   |     3.27 |     1.96 |     0.49  |    0.20   |     0.10
+     0.0004   |     4.36 |     2.61 |     0.65  |    0.26   |     0.13
+     0.0005   |     5.44 |     3.27 |     0.82  |    0.33   |     0.16
+     0.0006   |     6.53 |     3.92 |     0.98  |    0.39   |     0.19
+     0.0007   |     7.62 |     4.57 |     1.14  |    0.46   |     0.23
+     0.0008   |     8.71 |     5.23 |     1.31  |    0.52   |     0.26
+     0.0009   |     9.80 |     5.88 |     1.47  |    0.59   |     0.29
+     0.001    |    10.89 |     6.53 |     1.63  |    0.65   |     0.33
+     0.002    |    21.78 |    13.07 |     3.27  |    1.31   |     0.65
+     0.003    |    32.67 |    19.60 |     4.90  |    1.96   |     0.98
+     0.004    |    43.56 |    26.13 |     6.53  |    2.61   |     1.31
+     0.005    |    54.44 |    32.67 |     8.17  |    3.27   |     1.63
+     0.006    |    65.33 |    39.20 |     9.80  |    3.92   |     1.96
+     0.007    |    76.22 |    45.73 |    11.43  |    4.57   |     2.29
+     0.008    |    87.11 |    52.27 |    13.07  |    5.23   |     2.61
+     0.009    |    98.00 |    58.80 |    14.70  |    5.88   |     2.94
+     0.01     |   108.89 |    65.33 |    16.33  |    6.53   |     3.27
+     0.02     |   217.78 |   130.67 |    32.67  |   13.07   |     6.53
+     0.03     |   326.67 |   196.00 |    49.00  |   19.60   |     9.80
+     0.04     |   435.56 |   261.33 |    65.33  |   26.13   |    13.07
+     0.05     |   544.44 |   326.67 |    81.67  |   32.67   |    16.33
+     0.06     |   653.33 |   392.00 |    98.00  |   39.20   |    19.60
+     0.07     |   762.22 |   457.33 |   114.33  |   45.73   |    22.87
+     0.08     |   871.11 |   522.67 |   130.67  |   52.27   |    26.13
+     0.09     |   980.00 |   588.00 |   147.00  |   58.80   |    29.40
+     0.1      |  1088.89 |   653.33 |   163.33  |   65.33   |    32.67
+     0.2      |  2177.78 |  1306.67 |   326.67  |  130.67   |    65.33
+     0.3      |  3266.67 |  1960.00 |   490.00  |  196.00   |    98.00
+     0.4      |  4355.56 |  2613.33 |   653.33  |  261.33   |   130.67
+     0.5      |  5444.44 |  3266.67 |   816.67  |  326.67   |   163.33
+     0.6      |  6533.33 |  3920.00 |   980.00  |  392.00   |   196.00
+     0.7      |  7622.22 |  4573.33 |  1143.33  |  457.33   |   228.67
+     0.8      |  8711.11 |  5226.67 |  1306.67  |  522.67   |   261.33
+     0.9      |  9800.00 |  5880.00 |  1470.00  |  588.00   |   294.00
+     1.0      | 10888.89 |  6533.33 |  1633.33  |  653.33   |   326.67
+  ------------+----------+----------+-----------+-----------+------------
+
+When, as in this table, the fraction of an ounce is expressed by two
+places of decimals, it may be reduced to pennyweights (dwts.) by
+dividing by 5. For example, 0.40 of an ounce is 8 dwts. The fraction of
+a dwt. similarly expressed may be converted into grains with sufficient
+exactness by dividing by 4. Thus, 1.63 ozs. equal 1 oz. 12.60 dwts., or
+1 oz. 12 dwts. 15 grains. In England it is usual to report in ounces and
+decimals of an ounce.
+
+The way to use the table is best shown by an example. Suppose a button
+of silver weighing 0.0435 gram was obtained from 20 grams of ore. Look
+down the 20-gram column of the table, and select the values
+corresponding to each figure of the weight, thus:--
+
+  0.04   = 65.33 ozs. to the ton
+  0.003  =  4.90         "
+  0.0005 =  0.82         "
+  ------   -----
+  0.0435 = 71.05         "
+
+Add these together. The produce is 71.05 ozs., or 71 ozs. 1 dwt. to the
+ton.
+
+Or, suppose an ore is known to contain 1.24 per cent. of silver. Look
+down the 100-gram column, select the values, and add them together as
+before.
+
+  1.0  = 326.67 ozs. per ton
+  0.2  =  65.33      "
+  0.04 =  13.07      "
+  ----   ------
+  1.24 = 405.07      "
+
+This gives 405 ozs. 1 dwt. 10 grains to the ton.
+
+The calculation becomes more complicated when, as is frequently the
+case, the ore contains metallic particles. These show themselves by
+refusing to pass through the sieve when the ore is powdered. When they
+are present, a large portion, or if feasible the whole, of the sample is
+powdered and sifted. The weights of the sifted portion and of the
+"metallics," or prills, are taken; the sum of these weights gives that
+of the whole of the sample taken. It is very important that nothing be
+lost during the operation of powdering.
+
+Each portion has to be assayed separately. It is usual to assay a
+portion of the sifted sample, say, 20 or 50 grams, and to add to the
+produce of this its share of the "metallics." This way of calculating,
+which is more convenient than correct, is illustrated by the following
+example:--
+
+  Weight of whole sample       400 grams
+  Made up of sifted portions   399   "
+       "     "Metallics"         1   "
+                               ---
+                               400   "
+
+Twenty grams of the sifted portion, when assayed, gave 0.1050 gram of
+silver. The whole of the "metallics" scorified and cupelled gave 0.842
+gram of silver. Since the 20 grams assayed was 1-20th of the whole,
+1-20th part of the 0.842 gram of silver (from the metallics) must be
+added to its produce. We thus get 0.1471 gram (0.1050 + 0.0421).
+
+Referring to the 20 gram column, we get--
+
+  0.1    = 163.33
+  0.04   =  65.33
+  0.007  =  11.43
+  0.0001 =   0.16
+  ------   ------
+  0.1471 = 240.25 ounces per ton.
+
+A more legitimate method of calculation is as follows:--Calculate
+separately the produce of each fraction as if they were from different
+ores. Multiply each produce (best stated in per cents.) by the weight of
+the corresponding fraction. Add together the products, and divide by the
+weight of the whole sample. Taking the same example for illustration, we
+have:--
+
+  _Metallics._--Weight 1 gram.
+         1 gram of it yielded 0.842 grams of silver.
+     .'. Produce = 84.2 per cent.
+         Produce multiplied by the weight is still ~84.2~.
+  _Sifted Portion._--Weight 399 grams.
+         20 grams of it yielded 0.105 gram of silver.
+     .'. Produce = 0.525 per cent.
+         Produce multiplied by weight (0.525 × 399) is ~209.475~.
+
+Add together; and divide by 400, the weight of the whole sample--
+
+             84.2
+            209.475
+            -------
+       400) 293.675 (0.7342
+
+
+0.7342 is the total produce of the ore in per cents.
+
+Referring to the 100-gram column in the table we find 239.84 ounces to
+the ton as the produce.
+
+  0.7    = 228.67
+  0.03   =   9.80
+  0.004  =   1.31
+  0.0002 =   0.06
+           ------
+           239.84
+
+Comparing this with the result calculated by the first method--viz.,
+240.26, we see that that was 0.38 oz., or between 7 and 8 dwts. too
+high.
+
+With ores containing "metallics" it is of great importance to powder the
+whole of the selected sample without loss during the process; and of
+even greater importance to well mix the sifted portion, of which the
+last portions to come through the sieve are apt to be more than
+ordinarily rich through the grinding down of some portions of the
+metallic prills.
+
+~Remarks on Cupellation.~--Cupellation is at once the neatest and the
+most important of the dry methods of assaying. Its purpose is to remove
+easily oxidisable metals, such as lead and copper, from silver and gold,
+which are oxidisable with difficulty. Metals of the first class are
+often spoken of as _base_, and gold and silver as _noble_ metals.
+
+When lead is exposed to the action of air at a temperature a little
+above redness, it combines with the oxygen of the air to form litharge,
+an oxide of lead, which at the temperature of its formation is a
+_liquid_. Consequently, if the lead rests on a porous support, which
+allows the fused litharge to drain away as fast as it is formed, a fresh
+surface of the lead will be continually exposed to the action of the
+air, and the operation goes on until the whole of the lead has been
+removed. Silver or gold exposed to similar treatment does not oxidise,
+but retains its metallic condition; so that an alloy of lead and silver
+similarly treated would yield its lead as oxide, which would sink into
+the support, while the silver would remain as a button of metal.
+
+The porous support, which is called _a cupel_(fig. 5), should absorb the
+slag (oxide of lead, etc.) just as a sponge absorbs water, but must be
+sufficiently fine-grained to be impervious to the molten metal. At first
+sight it appears difficult to filter, as it were, a fluid slag from a
+fluid metal; but an ordinary filter-paper damped with oil will allow
+oils to run through and yet retain the water; but damped with water it
+will allow water to run through and retain oils. Similarly, fused slags
+damp and filter through a cupel, but the molten metal not damping it
+withdraws itself into a button, which is retained. Although, of course,
+if the cupel is very coarse-grained the metal may sink into the hollows.
+
+Copper, antimony, tin, and most other metals, form powdery oxides, which
+are not of themselves easily fusible, and it is necessary when these are
+present to add some solvent or flux to render the oxide sufficiently
+fluid. Fortunately, oxide of lead is sufficient for the purpose; hence,
+mixed oxides of copper and lead, provided the lead is present in proper
+proportion, form a fluid slag. In separating copper from silver or gold,
+advantage is taken of this fact; for, although we cannot cupel an alloy
+of copper and silver, it is easy to cupel an alloy of copper, silver and
+lead. If, however, the lead is not present in sufficient quantity, the
+whole of the copper will not be removed, and the button of silver, still
+retaining copper, will be found embedded in a coating of black oxide of
+copper. Copper oxidises less easily than lead does; and, consequently,
+the alloy which is being cupelled becomes relatively richer in copper
+as the operation proceeds. It is on this account that the ill-effects of
+the copper make themselves felt at the close of the operation, and that
+the oxide of copper is found accumulated around the button of silver.
+Tin and antimony, on the other hand, are more easily oxidised; and the
+tendency of their oxides to thicken the slag makes itself felt at the
+commencement: if the button of alloy once frees itself from the ring or
+crust of unfused oxide first formed, the cupellation proceeds quietly,
+and leaves a clean button of silver in the centre. But in either case
+the cupellation is imperfect, and should be repeated with a larger
+proportion of lead. An unfused and, consequently, unabsorbed slag tends
+to retain small buttons of alloy or metal, and thus cause serious loss.
+
+There is a principle underlying many of the phenomena of dry silver
+assaying which the student should endeavour to understand; and which
+serves to emphasise and explain some facts which without an explanation
+may present difficulties. If a button of melted lead be covered with a
+layer of slag rich in oxide of lead, and a second metal be added, this
+other metal distributes itself between the metal and slag in proportions
+which depend mainly upon the ease with which it is oxidised, and to a
+large extent upon the relative quantities of material present. Easily
+oxidisable metals such as zinc, iron, antimony and tin, will go mainly
+into the slag, and, if the proportion of the slag is large, very little
+will go into the metal. On the other hand, with metals oxidisable with
+difficulty, such as silver, gold, and platinum, the reverse holds true;
+nearly the whole of the metals will go into the lead, and very little
+into the slag. If, however, the slag be very rich, say in antimony, the
+lead will contain antimony; and, on the other hand, if the lead be very
+rich in silver, the slag will contain silver in appreciable quantity.
+Copper, which is near lead in the facility with which it is oxidised,
+will serve for the purpose of a detailed example. The results of actual
+analyses of metal and slag formed in contact with each other are shown
+in the following table:--
+
+  ---------------------------+--------------------------
+     Percentage Composition  | Percentage Composition
+      of the Metal.          |   of the Slag.
+  ----------+----------------+-----------+--------------
+     Lead.  |   Copper.      |   Lead.   |   Copper.
+      6.8   |    93.2        |    71.4   |    21.4
+     20.0   |    80.0        |    78.0   |    17.0
+     28.0   |    72.0        |    80.0   |    12.5
+     32.0   |    68.0        |    86.0   |     6.7
+     85.0   |    15.0        |    90.0   |     3.6
+  ----------+----------------+-----------+--------------
+
+It will be seen from this table that the slag is always much richer in
+lead and poorer in copper than the metal with which it is in contact.
+The ratio of lead to copper in these five samples is:--
+
+               In the Metal.       In the Slag.
+                1 : 14              1 : 0.3
+                1 : 4               1 : 0.2
+                1 : 2.5             1 : 0.16
+                1 : 2               1 : 0.08
+                1 : 0.16            1 : 0.04
+
+Assuming these figures to be correct, the following statement is
+approximately true. On oxidising an alloy of 10 grams of copper and 10
+grams of lead, and pouring off the slag when 3 grams of lead have gone
+into it, there will be a loss of (owing to the slag carrying it off)
+about 0.2 gram of copper. On repeating the operation, the next 3 grams
+of lead will carry with them about 0.5 gram of copper; and on again
+repeating, 3 grams of lead will remove 0.8 gram of copper. Finally, the
+last gram of lead will carry with it 0.3 gram of copper, and there will
+be left a button of copper weighing 8.3 grams. The slag will have
+carried off altogether 1.7 gram of copper, which is 17 per cent. of the
+metal originally present.
+
+With the more perfect exposure to the air, and quicker removal of the
+slag, which results from heating on a cupel, the loss would be heavier.
+Karsten got by actual experiment on cupelling copper and lead in equal
+proportions, a loss of 21.25 per cent.
+
+Going back to the example: if the slag were collected and fused with a
+suitable reducing agent so as to convert, say, half of it into metal,
+that half would contain nearly the whole of the copper (such a reduction
+is called "cleaning the slag"). On reoxidising this metal, another
+button of copper is formed which, added to the first, would reduce the
+loss from 17 per cent. to, say, 7 or 8 per cent. And it is conceivable
+that by a series of similar operations, almost the whole of the 10 grams
+of copper originally taken might be recovered. In practice the problem
+is (as far as the copper is concerned) not how to save, but how most
+easily to remove it; and since the removal of this metal is quicker from
+an alloy containing not too much lead, it is evident that two or three
+operations with small quantities of lead will be more effectual than a
+single treatment with a larger quantity. With those metals (tin,
+antimony, &c.) which pass quickly into the slag, the contrary is true;
+hence with these it is necessary to have enough lead present, so that
+the slag formed at the outset shall contain enough oxide of lead to make
+it fluid. As silver is so much less easily oxidised than copper, we
+should reasonably expect that the proportion of silver carried off in
+the oxide of lead would be considerably less than that of the copper
+indicated in the above example. Indeed, there are one or two facts
+which tend to encourage the hope that the operation may be conducted
+without any loss. If a piece of pure silver foil is exposed on a cupel
+to air at the usual temperature of cupellation, it undergoes very little
+change; it does not even fuse; it loses nothing in weight, and does not
+oxidise. In fact, even if oxide of silver were formed under these
+conditions, it could not continue to exist, for it is decomposed into
+silver and oxygen at a temperature considerably below redness. On the
+other hand, oxide of silver is not reduced to metal by heat alone, when
+mixed with an excess of oxide of lead; while metallic silver is
+converted into oxide when heated with the higher oxides of lead, copper,
+and some other metals. That silver, and even gold (which is more
+difficult to oxidise than silver), may be carried off in the slag in
+this way, is in agreement with general experience. If 10 grams of silver
+are cupelled with 10 grams of lead, there will be a loss of about 50
+milligrams of silver, which is in round numbers 1-30th of the
+corresponding copper loss; with 10 grams of gold and 10 grams of lead,
+the loss will be 4 or 5 milligrams, which is about 1-12th of the
+corresponding silver loss.
+
+~Determination of Silver in Assay Lead.~--Scorify 50 grams of the lead
+with 0.5 gram of powdered quartz or glass at not too high a temperature.
+When the eye has "closed in," pour; reject the slag, and cupel the
+button of lead. Remove the cupel from the muffle immediately the
+operation is finished. Weigh, and make a prominent note of the result in
+the assay book, as so many milligrams of silver contained in 100 grams
+of lead.
+
+~Determination of Silver in Red Lead or Litharge.~--Fuse 100 grams of
+the oxide with from 10 to 20 grams of borax; and in the case of litharge
+with 2 grams or with red lead 4 grams of flour. Cupel the lead, and
+weigh the button of silver. Note the result as in the last case.
+
+~Determination of Silver in Argentiferous Lead.~--Be careful in taking
+the sample, since with rich silver lead alloys the error from bad
+sampling may amount to several parts per cent. Cupel two lots of 20
+grams each, and weigh the buttons of silver. Add to these the estimated
+cupel loss, and calculate the result. Or wrap each button of silver in
+20 grams of assay lead, and re-cupel side by side with two fresh lots of
+20 grams each of the alloy. Calculate the loss incurred, and add on to
+the weight of the two fresh buttons got.
+
+~Determination of Silver in Bullion.~--The remarks made under the last
+heading as to the importance of correct sampling apply with equal force
+here. Make a preliminary assay by cupelling 0.1 gram of the alloy with 1
+gram of assay lead; calculate the percentage composition. Refer to the
+table on page 105 to find what weight of lead is required for cupelling
+1 gram of alloy.
+
+Weigh out four lots of 1 gram each, and wrap them in the required
+quantity of lead. Make two check pieces by weighing up two lots of fine
+silver equal to that which you believe to be present in the assay
+pieces; add copper to make up the weight to 1 gram, and wrap in the same
+quantity of lead as was used for the assays.
+
+[Illustration: FIG. 43.]
+
+Prepare six cupels and charge them in the annexed order (fig. 43), and
+cupel. Guard against spirting. Clean and weigh the buttons of silver.
+Add the mean loss on the two check pieces to the mean weight of the four
+assay pieces; this multiplied by 1000 will give the degree of fineness.
+
+~Determination of Silver in Copper.~--The silver is best separated in
+the wet way before cupelling, but if the proportion is not too small, it
+can be found by cupellation. Weigh up 3 grams of the metal, wrap in 30
+grams of sheet lead, and cupel; when the cupellation has proceeded for
+fifteen minutes, add 20 grams more lead, and continue till finished.
+Weigh the button of silver.
+
+The cupellation loss will be five or six per cent. of the silver
+present. Determine it by powdering the saturated portion of the cupel
+and fusing in a large Cornish crucible with 30 grams each of soda and
+borax, 10 grams of fluor spar, and 1-1/2 gram of charcoal. Cupel the
+resulting button of lead, and add 10 grams more of lead towards the
+close of the operation. Deduct the weight of silver contained in the
+lead used from the weight of the two buttons, and calculate to ounces to
+the ton.
+
+In an experiment in which 0.1975 gram of silver was present, the weight
+of the button from the first cupellation was 0.1867, and that of the
+button from the second, after correcting for the lead added, was 0.0110
+gram.
+
+~Determination of Silver in Galena.~ _By Pot Assay._--Mix 20 grams of
+the powdered ore with 30 grams of red lead, 20 grams of soda, and 5
+grams of borax, as also with from 7 to 10 grams of nitre. Fuse and pour.
+Clean the slag if the ore is rich. Cupel the buttons of lead. Make the
+usual corrections and calculate in ounces to the ton.
+
+_By Scorification._--Take 10 grams of the ore, 30 grams of lead, and
+0.5 gram of borax. Scorify, clean the slag by adding anthracite after
+the "eye" has closed in: cupel the button of lead. Weigh the button of
+silver, make the necessary corrections, and calculate to ounces to the
+ton.
+
+The determination may also be made by cupelling the button of lead got
+in the dry lead assay.
+
+A sample of galena determined by the three methods gave the following
+results:--
+
+  By pot assay       7.18 ozs. per ton.
+   " scorification   7.02      "
+   " lead assay      6.72      "
+
+~Determination of Silver in an Ore.~ _By Pot Assay._--Take 20 grams of
+the powdered ore and mix with 30 grams of soda, 40 grams of red lead,
+and 5 grams of borax, as also with from 2 to 3 grams of flour. Fuse:
+pour. Clean the slag by fusing with 20 grams of red lead and two grams
+of flour. Cupel the buttons of lead; weigh; make the necessary
+corrections, and calculate to ounces to the ton.
+
+_By Scorification._--Take 5 grams of the powdered ore, 50 grams of lead,
+and 0.5 gram of "soda" or borax. Scorify. Clean the slag by fusing in a
+crucible as in the pot assay. Cupel, &c.
+
+  _Examples._--_By Pot Assay._--Ore taken 20 grams.
+  Silver got                 0.2893 gram
+  Silver from slag           0.0060   "
+  Silver lost in cupellation 0.0100   "
+                             ------
+                             0.3053   "
+  Deduct silver in red lead  0.0017   "
+                             ------
+  Silver in ore              0.3036   "  =  495.9 ozs. per ton.
+
+       _By Scorification._--Ore taken, 3 grams.
+  Silver got.                0.0425 gram
+  Silver from slag           0.0022   "
+  Silver lost in cupellation 0.0020   "
+                             ------
+                             0.0467   "
+  Deduct silver in lead      0.0015   "
+                             ------
+  Silver in ore              0.0452   "  =  492.2 ozs. per ton.
+
+~Determination of Silver in Silver Precipitate.~--This substance
+contains, in addition to metallic silver and gold, sulphates of lead and
+lime; oxides of zinc, copper, and iron; and more or less organic matter.
+The sample as received is generally free from "water at 100° C."; and,
+since it rapidly absorbs water, care should be taken in weighing it.
+
+Since it contains combined water it is not suited for scorifying;
+therefore the determination of silver and gold (fine metal) is made by
+pot assay. Weigh up 5 grams of the precipitate, mix with 100 grams of
+litharge and 1 gram of charcoal. Melt in a crucible at a moderate heat
+and pour. Detach the slag, replace in the crucible, and, when fused, add
+a mixture of 20 grams of litharge and 1 gram of charcoal. When the
+fusion is again tranquil, pour; and cupel the two buttons of lead.
+
+In a sample worked in this manner the mean of four determinations gave
+0.6819 gram of "fine metal"; deducting 1 milligram for the silver
+contained in the oxide of lead, and adding 8 milligrams for the
+cupellation loss, there is got 0.6889 gram or 13.778 per cent. of silver
+(and gold) in the sample.
+
+~Determination of Silver in Burnt Ores.~ _By Pot Assay._--Roasted
+cupriferous pyrites containing small quantities of gold and silver comes
+under this heading. The following mixture will give a fluid slag which
+is heavy and tough when cold:--
+
+  Ore.   Borax.   Sand.   Litharge.   Charcoal.
+  100      50      50       100           7
+
+Mix; place in a large crucible; cover with salt; and melt down under
+cover. When fused drop in an iron rod for a few minutes, and about a
+couple of minutes after its withdrawal, pour the charge quickly into a
+large conical mould. The button of lead should weigh about 50 grams.
+Cupel and weigh the silver. The litharge may be replaced by red lead, in
+which case another gram of charcoal powder must be added.
+
+In our experience the results obtained by this method are about 20 per
+cent. less than the actual content of the ore. The results of two
+assays, after deducting for the silver in the litharge used, were 3.9
+and 4.1 milligrams; and a third assay, in which 5.4 milligrams of silver
+had been added, gave 9.2, which, after deducting the added silver,
+leaves 3.8 milligrams. The average of the three results is 3.9
+milligrams from the 100 grams of ore.
+
+Two lots of 100 grams of the same ore treated in the wet way gave 5.2
+and 5.0 milligrams of silver. Burnt ores from Spanish pyrites carry
+about 0.005 per cent. of silver.
+
+
+WET METHODS.
+
+Silver is got into solution from its ores by attacking with nitric acid,
+but it is best, after dissolving, to cautiously add dilute hydrochloric
+acid, and to carefully avoid excess. If the quantity of silver is very
+small the solution is allowed to stand twenty-four hours, but,
+otherwise, it is warmed and filtered as soon as it clears. Dry the
+residue and concentrate the silver in a button of lead by pot method or
+scorification, according to the amount of stony matter present. Cupel
+the lead, and the resulting button will be free from all metals, except
+perhaps gold. It may be weighed; or dissolved in nitric acid, and the
+silver determined gravimetrically in the diluted and filtered solution.
+It is better to weigh the metal and afterwards to determine the gold in
+it, estimating the silver by difference. Silver alloys are dissolved in
+dilute nitric acid (free from chlorides), diluted, and filtered. The
+solution is then ready for gravimetric determination.
+
+Sulphuretted hydrogen precipitates silver (like copper), completely,
+even from fairly acid solutions.
+
+
+GRAVIMETRIC DETERMINATION.
+
+Add dilute hydrochloric acid in small excess to the hot dilute solution,
+which must contain free nitric acid. Heat and stir until the solution
+clears. Decant through a small filter, and wash with hot water,
+acidulated at first with a little nitric acid if bismuth is suspected to
+be present. Dry quickly, transfer as much as possible of the precipitate
+to a watch-glass; burn and ignite the filter paper, treating the ash
+first with two drops of nitric acid and then with one of hydrochloric,
+and again dry. Add the rest of the silver chloride and heat slowly over
+a Bunsen burner until it begins to fuse. Cool and weigh.
+
+The precipitate is silver chloride (AgCl) and contains 75.27 per cent.
+of silver. The moist precipitate is heavy and curdy; it is decomposed by
+direct sunlight, becoming violet under its influence. When heated it is
+yellowish; and, since it is volatile at a high temperature, it must not,
+in drying, be heated above its fusing point. The fused chloride can be
+removed from the crucible (to which it adheres strongly) by digesting
+with dilute acid and zinc.
+
+For the determination of silver in nearly pure bullion the following
+process is used:--Weigh up 1.5054 gram of the alloy. With this amount of
+alloy each 2 milligrams of silver chloride formed is equivalent to 1
+degree of fineness, so that the weight of the silver chloride obtained
+(stated in milligrams and divided by 2) will give the degree of
+fineness. Transfer to a bottle (known as "bottles for the Indian mint
+assay") and dissolve in 10 c.c. of dilute nitric acid, then make up with
+water to 200 c.c. and add 3 c.c. of dilute hydrochloric acid. Allow to
+stand a few minutes and then shake. Fill the bottle completely with
+water, allow to settle, and syphon off the clear liquid; pour on more
+water, shake gently to break up the lumps, and again fill the bottle
+with water. Invert over the mouth of the bottle a porous Wedgwood
+crucible, somewhat similar to those used in gold parting. Take firm hold
+of the crucible and bottle, and invert promptly so that the silver
+chloride may be collected in the crucible. Allow to stand a little while
+for the precipitate to settle, and then carefully remove the crucible
+under water.[14] Drain off most of the water and break up the silver
+chloride with the help of a well-rounded glass rod. This greatly
+facilitates the subsequent drying. Dry first on the water bath and then
+on the iron plate. Remove the dried silver chloride, by inverting the
+crucible, and weigh it.
+
+As an example, 3 determinations of silver in a coin carried out in this
+way gave:--
+
+  (1) 1.8500 gram AgCl = 925.0 fineness.
+  (2) 1.8498     "     = 924.9     "
+  (3) 1.8502     "     = 925.1     "
+
+~Determination of Silver in Burnt Ores.~--Take 100 grams of the ore and
+place in a large beaker of 2-1/2 litres capacity, and cover with 375
+c.c. of hydrochloric acid. Boil for half an hour until the oxides are
+dissolved and the residue looks like sand and pyrites; then add 20 c.c.
+of nitric acid, and boil till free from nitrous fumes. Dilute to 2
+litres with water, and pass a current of sulphuretted hydrogen till the
+iron is reduced, the copper and silver precipitated, and the liquor
+smells of the gas. This takes about one hour and a half.
+
+Filter off the precipitate (rejecting the solution) and wash with warm
+water. Dry and transfer to an evaporating dish, adding the ashes of the
+filter paper. Heat gently with a Bunsen burner until the sulphur burns,
+and then calcine until no more sulphurous oxide comes off. When cold add
+30 c.c. of nitric acid, boil and dilute to 100 c.c. Add 1 c.c. of very
+dilute hydrochloric acid (1 to 100),[15] stir well, and allow to stand
+overnight. Decant on to a Swedish filter paper, dry and calcine.
+
+Mix the ashes with 100 grams of litharge and 1 gram of charcoal, and
+fuse in a small crucible. Detach the button of lead and cupel. Weigh and
+make the usual corrections. As an example, 100 grams of ore treated in
+this way gave 5.8 milligrams of silver; deducting 0.8 for the silver
+added in the oxide of lead leaves 5 milligrams obtained from the ore.
+Another experiment on 100 grams of the same ore to which 5 milligrams of
+silver had been added gave 11.0 milligrams. Deduct 5.8 for the silver
+added; this leaves 5.2 milligrams as the silver obtained from the ore.
+These give, as a mean result, 0.0051 per cent., or 1.66 ounce per ton.
+
+~Determination of Silver in Commercial Copper.~--For the method of doing
+this, with an example and experiment, see under the heading of
+_Examination of Commercial Copper_.
+
+
+VOLUMETRIC METHODS.
+
+There are two of these, one adapted for the determination of silver in
+alloys of approximately known composition, and the other of more general
+application. The first of these, generally known as "Gay-Lussac's"
+method is, as regards its working, perfect in principle; but it requires
+a practically constant quantity of silver, that is, one which varies by
+a few milligrams only in each determination. It is a confirmatory method
+rather than a determinative one. The other is known as "Volhard's," and
+resembles in principle and method an ordinary volumetric process.
+
+~Gay-Lussac's method~ is based on the precipitation of silver from a
+nitric acid solution by a solution of sodium chloride. The point at
+which the whole of the silver is precipitated being recognised by the
+standard solution ceasing to give a precipitate. The process depends for
+its success upon, (1) the ease which silver chloride separates out from
+the solution leaving it clear after shaking, and, (2), the cloudiness
+produced by the reaction of very small quantities of silver nitrate and
+sodium chloride. In working, a quantity of the sodium chloride solution
+equal to 1 gram of silver is added at once to the assay; and, when the
+solution has been rendered clear by shaking, the residual silver (which
+should not exceed a few milligrams) is estimated with the help of a
+weaker solution of sodium chloride. The success in working evidently
+depends upon the accuracy with which the first addition of the salt
+solution is made. On this account the standard solution is run in from a
+special pipette capable of delivering a practically invariable volume of
+solution. It is not so important that this shall deliver exactly 100
+c.c. as that in two consecutive deliveries the volume shall not differ
+by more than 0.05 c.c. The dilute salt solution is one-tenth of the
+strength of that first run in, and 1 c.c. of it is equivalent to 1
+milligram of silver. Ordinarily it is run in 1 c.c. at a time (and an
+ordinary burette may be used for this purpose), shaking between each
+addition until it ceases to give a precipitate. If many such additions
+have to be made the operation not only becomes tedious, but the
+solution also ceases to clear after shaking, so that it becomes
+impossible to determine the finishing point.
+
+If the assay contains less than one gram of silver the first addition of
+the dilute salt solution of course produces no precipitate. Five
+milligrams of silver in solution (5 c.c.) is then added, and the assay
+proceeded with in the usual way; 5 milligrams of silver being deducted
+from the amount found.
+
+There is required for the assay a _standard solution of sodium
+chloride_, which is prepared by dissolving 5.4162 grams of the salt
+(made by neutralizing carbonate of soda with hydrochloric acid) in water
+and diluting to one litre. 100 c.c. of this is equivalent to 1 gram of
+silver.
+
+The weaker solution of salt is made by diluting 100 c.c. of the stronger
+one to one litre. One c.c. of this will equal 1 milligram of silver, or
+0.1 c.c. of the stronger solution.
+
+A _standard solution of silver_ equivalent to the dilute salt solution
+is made by dissolving 1 gram of fine silver in 10 c.c. of dilute nitric
+acid, and diluting with water to one litre.
+
+[Illustration: FIG. 44.]
+
+The solution of salt is standardised as follows:--Weigh up 1.003 gram of
+fine silver and dissolve in 25 c.c. of dilute nitric acid in a bottle
+provided with a well-fitting flat-headed stopper. Heat on the water bath
+to assist solution, resting the bottle in an inclined position. When
+dissolved blow out the nitrous fumes with the help of a glass tube bent
+at right angles. Run in from a stoppered pipette (as shown in fig. 44)
+100 c.c. of the standard salt solution, and shake vigorously until the
+solution clears. Fill an ordinary burette with the weaker standard salt
+solution, and run 1 c.c. into the assay bottle, letting it run down the
+side so that it forms a layer resting on the assay solution. If any
+silver remains in solution a cloudy layer will be formed at the junction
+where the two liquids meet. This is best observed against a black
+background If a cloudiness is seen, shake, to clear the liquid, and run
+in another c.c. of salt, and continue this until a cloudiness is no
+longer visible. Deduct 1.5 c.c. from the amount of the weaker sodium
+chloride solution run in. Divide the corrected reading by 10, and add to
+the 100 c.c. This will give the volume of strong salt solution
+equivalent to the silver taken.
+
+If the first addition of the weaker salt solution causes no cloudiness
+add 5 c.c. of the silver solution from an ordinary pipette, shake, and
+then run in the weaker salt solution, working as before. These 5
+milligrams of silver added must be allowed for before calculating. As
+an example:--1.0100 gram of fine silver was taken for standardising a
+solution and 4 c.c. of the weaker salt solution were run in. Deducting
+1.5 and dividing by 10 gives 0.25 c.c. to be added to the 100 c.c.
+
+        100.25 : 1.0100 :: 100 : _x_
+                                 _x_ = 1.0075
+
+which is the standard of the salt solution.
+
+The method of working an assay may be gathered from the following
+example:--In the determination of silver in some buttons left after
+cupellation, it was assumed that these would contain 99.5 per cent. of
+silver. For the assay it was necessary to take a quantity that should
+contain a little more than 1.0075 grams of silver; then
+
+        99.5 : 100 :: 1.0075 : _x_
+                               _x_ = 1.0125
+
+To ensure a slight excess, there was taken 1.0150 gram of the buttons,
+which was treated in exactly the same way as for the standardising. The
+quantity of the weaker salt solution required was 7 c.c.; deducting 1.5
+c.c., and dividing by 10, gives 100.55 c.c. of strong salt solution,
+which is equivalent to 1.0130 gram of silver. This being obtained from
+1.015 gram of alloy, is equal to 99.8 per cent., or 998.0 fine.
+
+~The Effect of Temperature.~--The standardising and the assay must be
+done at the same time, since a difference of 5° C. makes a difference of
+0.1 c.c. in measuring the 100 c.c. of strong solution of salt. It is
+always best to prepare a standard with each batch of assays.
+
+~SULPHOCYANATE METHOD.~--Volhard's process is based upon the
+precipitation of silver in nitric acid solutions with potassium
+sulphocyanate, the finishing point being the development of a
+reddish-brown colour, produced by the action of the excess of
+sulphocyanate upon ferric sulphate. The white sulphocyanate settles
+readily, leaving the liquor clear; and a persistent brown coloration in
+the liquid indicates the finish. The assay must be carried out in the
+cold; and water free from chlorides[16] must be used.
+
+_The standard sulphocyanate of potassium_ solution is made by dissolving
+4-1/2 or 5 grams of the salt (KCyS) in water, and diluting to 1 litre.
+100 c.c. are about equivalent to 0.5 gram of silver.
+
+_The standard silver nitrate solution_ is made by dissolving 5 grams of
+fine silver in 50 c.c. of dilute nitric acid, boiling off nitrous fumes,
+and diluting to 1 litre.
+
+The _indicator_ is a saturated solution of iron alum, or a solution of
+ferric sulphate of equivalent strength made by titrating acid ferrous
+sulphate with potassium permanganate. Use 2 c.c. for each assay.
+
+The sulphocyanate solution is standardised by placing 50 c.c. of the
+silver nitrate solution in a flask with 20 c.c. of dilute nitric acid,
+diluting to 100 c.c. with water, and running in the sulphocyanate until
+the greater part of the silver is precipitated; then adding 2 c.c. of
+the ferric indicator, and continuing the titration until a reddish-brown
+colour is developed, and remains permanent after shaking continuously.
+The assay is similarly performed, the silver being used in the state of
+a nitric acid solution.
+
+The effect of variations in the conditions of the assay may be seen from
+the following experiments, in which 20 c.c. of standard silver nitrate
+were used:--
+
+~Effect of Varying Temperature~:--
+
+  Temperature            10° C.      30° C.      70° C.      100° C.
+  Sulphocyanate reqd.   19.6 c.c.   19.3 c.c.   19.0 c.c.   18.6 c.c.
+
+~Effect of Varying Nitric Acid~:--Varying nitric acid has no effect,
+except that with a fairly acid solution the finishing point is somewhat
+sharper.
+
+  Nitric acid added      5 c.c.      10 c.c.     20 c.c.     50 c.c.
+  Sulphocyanate reqd.   19.6 c.c.   19.5 c.c.   19.6 c.c.   19.6 c.c.
+
+~Effect of Varying Bulk~:--
+
+  Bulk                   50 c.c.    100 c.c.    200 c.c.    300 c.c.
+  Sulphocyanate reqd.   19.5 c.c.   19.6 c.c.   19.6 c.c.   19.7 c.c.
+
+~Effect of Varying Ammonic Nitrate~:--
+
+  Ammonic nitrate        0 gram      1 gram      5 grams    10 grams
+  Sulphocyanate reqd.   19.6 c.c.   19.6 c.c.   19.7 c.c.   19.9 c.c.
+
+~Effect of Varying Silver~:--
+
+  Silver added         1 c.c.   10 c.c.    20 c.c.    50 c.c.   100 c.c.
+  Sulphocyanate reqd.  1.0 c.c.  9.70 c.c. 19.6 c.c.  49.4 c.c.  99.0 c.c.
+
+This method is valuable for determining silver in salts, alloys, and
+solutions, where no more than an ordinary degree of accuracy is
+demanded. It is easy, and applicable under most of the usual conditions.
+Its greatest disadvantage is the brown coloration produced by the
+sulphocyanate when the assay is nearly, but not quite, finished; and the
+slowness with which this is removed on shaking up with the precipitate.
+This is worse with large quantities of precipitate, and if about 1 gram
+of silver is present, it gives an indefiniteness to the finish which
+lowers the precision of the process to about 1 in 500; this is useless
+for the assays of bullion. One writer states that this inconvenience is
+due to portions of liquid being entangled in the precipitate, but it
+appears much more likely to be due to the action of the precipitate
+itself. In attempting to apply the process to the assay of bullion by
+working it on the principle of a Gay-Lussac assay, it was found that a
+very considerable excess of silver was required to complete the
+reaction. In these experiments 100 c.c. of "sulphocyanate" (very
+accurately measured) was run into the solution containing the weighed
+portion of bullion (fine silver) and, after shaking the solution, was
+filtered. In the filtrate the remaining silver, if there should be any,
+was determined by the ordinary titration, but with "sulphocyanate" of
+one-tenth the strength. This final titration was quite satisfactory. The
+amount of silver precipitated by the first 100 c.c., however, varied
+with the quantity of silver present as in the following series.[17]
+
+  Silver present.    Silver precipitated.
+  1.1342 gram.         1.1322 gram.
+  1.1375   "           1.1335   "
+  1.1405   "           1.1351   "
+  1.1484   "           1.1379   "
+
+These, of course, preclude a method of the kind aimed at, and at the
+same time emphasise the importance of uniformity of work in the ordinary
+process. In the determination of chlorides in sea-water, Dittmar used a
+combined method: precipitating the bulk of the silver as chloride, and
+after filtering, determining the small excess of silver by
+sulphocyanate. This modification answers admirably when applied to the
+assay of bullion. In the ordinary Gay-Lussac method, the precipitation
+of the bulk of the silver by the 100 c.c. of salt solution leaves
+nothing to be desired, either as to ease in working or accuracy of
+result; the silver precipitate settles quickly, and leaves a clear
+liquor admirably fitted for the determination of the few milligrams of
+silver remaining in solution. But the method of determining this
+residual silver by adding successive small quantities of salt so long as
+they continue to give a precipitate is unsatisfactory, and, judged on
+its own merits apart from the rest of the process, could hardly escape
+condemnation. It is clumsy in practice, for the continued adding of
+small portions of salt solution is laborious and becomes impossible with
+more than a few milligrams of silver in solution. The proposed
+modification is simple; having precipitated the silver with the 100 c.c.
+of salt solution, as described under Gay-Lussac's method (page 120),
+shake till the liquor clears, and filter into a flask, washing with a
+little distilled water. Add 2 c.c. of "ferric indicator" to the filtrate
+and titrate with a standard "sulphocyanate solution" made by diluting
+the ordinary standard solution to such an extent that 100 c.c. after
+diluting shall be equivalent to 0.1 gram of silver.[18] Calculate the
+weight of silver found by "sulphocyanate" and add it to the weight which
+100 c.c. of the salt solution will precipitate.
+
+An advantage of this modification is that an excess of 15 milligrams may
+be determined as easily and exactly as 5. In standardising the salt
+solution, then, weigh up, say 1.0150 gram of pure silver, dissolve and
+titrate. Suppose 13.5 c.c. of "sulphocyanate" required; then these are
+equivalent to .0135 gram of silver, (100 c.c. = .1); the silver
+precipitated by the salt is 1.0150-.0135--_i.e._, 1.0015 gram, which is
+the standard.
+
+~Application of the Method to Assays for Arsenic.~--If silver nitrate be
+added to a neutral solution of an arsenate of one of the alkali metals,
+silver arsenate (Ag_{3}AsO_{4}), is thrown down as a dark-red
+precipitate. If, after adding excess of silver nitrate to insure a
+complete precipitation, the arsenate of silver be filtered off, the
+weight of the arsenic could be estimated from the weight of silver
+arsenate formed. But this may be done much more conveniently by
+dissolving the precipitate in nitric acid, and titrating with
+sulphocyanate; the silver found will be to the arsenic present as 324
+(108×3) is to 75.
+
+The mineral is best treated by the method given in the third paragraph
+on page 382; but the solution, after being acidified with nitric acid,
+should be made exactly neutral with ammonia. A small excess of silver
+nitrate should then be added, and since acid is liberated in the
+reaction, the liquor must again be neutralised.[19] The precipitate must
+then be filtered off, and washed with distilled water. Then dissolve it
+in the paper by slowly running over it 20 c.c. of dilute nitric acid.
+Wash the filter with distilled water, collecting with the filtrate in a
+small flask. Add 2 c.c. of "ferric indicator" and titrate.
+
+If the sulphocyanate solution be made up with 11 or 12 grams of the
+potassium salt to the litre, and be then standardised and diluted, so
+that for 100 c.c. it shall equal 1.08 gram of silver, (see p. 38), then
+it will also equal .25 gram of arsenic (As). Except for ores rich in
+arsenic, it will be better to work with a solution one half this
+strength. The standard as calculated from an experiment with pure silver
+should be checked by another using pure resublimed white arsenic,
+As_{2}O_{3}, which contains 75.75 % of the metal. The quantity of white
+arsenic taken, .1 or .2 gram, should contain about as much arsenic as
+will be present in the assays. It is converted into sodium arsenate by
+evaporating to a small bulk with nitric acid and neutralising with soda.
+The precipitation and titration of the silver arsenate should be exactly
+as in the assays.
+
+The difficulty of the method is in the neutralising; which has to be
+very carefully done since silver arsenate is soluble in even faintly
+acid solutions; one drop of nitric acid in 100 c.c. of water is enough
+to produce an absolutely worthless result; and an excess of acid much
+less than this is still very prejudicial. The addition of a little
+sodium acetate to the solution after the final neutralising has a good
+effect.
+
+~Arsenic in Mispickel.~--Weigh up .250 gram of the finely-powdered ore,
+and place in a Berlin crucible about 1-1/4 or 1-1/2 inch in diameter.
+Treat with 10 or 12 drops, one drop at a time, of strong nitric acid,
+warm very gently, but avoid much heating. Put on a thin layer of nitre,
+and rather more than half fill the crucible with a mixture of equal
+parts of soda and nitre. Heat quickly in the blow-pipe flame, and when
+the mass is fused and effervescing, withdraw and allow to cool. Boil out
+with water, filter and wash. Insert a piece of litmus paper and
+cautiously neutralise with nitric acid, using ammonia to neutralise any
+accidental excess of the acid. Add a gram or so of ammonium nitrate and
+silver nitrate in excess, neutralise again with ammonia and add two or
+three grams of sodium acetate. Filter off the precipitate, wash and
+titrate. In the fusion care should be taken to avoid much effervescence
+(an excess of the soda mitigates this) and the operation should be
+stopped as soon as the whole has entered into fusion.
+
+
+COLORIMETRIC DETERMINATION.
+
+There is, properly speaking, no colorimetric method, but the following,
+which is sometimes used, is based on similar principles. It is useful
+for the determination of small quantities of silver in substances which
+yield clear solutions with nitric acid.
+
+Dissolve a weighed quantity of the substance in nitric acid, and dilute
+to a definite bulk. Divide into two equal parts. To one, add a drop or
+two of dilute hydrochloric acid, stir and filter. To the other, add a
+similar amount of dilute acid, and then to the filtered portion run in
+from a burette standard silver nitrate (1 c.c. = 0.5 milligram silver)
+until the solutions are equally turbid. Calculate in the usual way.
+
+
+GOLD.
+
+Gold occurs in nature chiefly as metal. It always contains more or less
+silver, and, in alluvial sands, &c., may be associated with platinum and
+iridium.
+
+Gold is insoluble in hydrochloric or nitric acid, but is dissolved by
+aqua regia or by solutions of iodine, bromine, or chlorine. It is taken
+up by mercury, forming an amalgam, from which the mercury may be driven
+off by heat.
+
+When gold occurs in particles of any size, it is readily detected by its
+appearance, but when finely disseminated through a large quantity of
+rock, it is separated and detected by the amalgamation assay--described
+below--or by a process of washing somewhat similar to vanning, or by the
+following test:--Powder and, if necessary, roast 50 to 100 grams of the
+ore, put on it three or four crystals of iodine and enough alcohol to
+cover it; allow to stand for half an hour; a piece of filter paper
+moistened with the liquid and burnt leaves an ash with a distinctly
+purple tint if any gold is present. It is better, however, to filter off
+the solution, evaporate, and ignite. Then, either take up with mercury,
+and ignite the amalgam so as to get a speck of the metallic gold; or
+treat with a few drops of aqua regia, and test the solution with
+stannous chloride: a purple coloration indicates gold.
+
+~AMALGAMATION ASSAY.~--This does not attempt to give the total produce
+of gold, but rather the quantity which can be extracted on a large
+scale; therefore it should imitate as closely as possible the process
+adopted in the mine or district for extracting the metal.
+
+Take 2 lbs of the ore in powder and roast; make into a stiff paste with
+hot water and rub up for an hour or so with a little mercury. Wash off
+the sand carefully, and collect the amalgam. Drive off the mercury by
+heat, and weigh the residual gold. It is best to cupel it with lead
+before weighing.
+
+In an experiment on a lot of ore which contained 0.189 gram of gold,
+0.179 gram was obtained by the above process, equal to about 94-1/2 per
+cent. recovered. With ores generally, the yield may be from 80 to 90 per
+cent. of the actual gold present.
+
+
+DRY ASSAY.
+
+The dry assay of gold ores resembles in its main particulars the dry
+assay for silver by the crucible method; and for much that is of
+importance in its discussion the student is referred to what is written
+under Silver on pp. 90-113.
+
+~Size of Assay Charges.~--Gold ores rarely contain more than a few
+ounces, often only a few pennyweights of gold to the ton; consequently,
+the button of gold obtainable from such quantities of ore as may be
+conveniently worked by assaying methods is often so small as to require
+more than ordinary care in its manipulation. One milligram of gold forms
+a button of about the size of one of the full-stops on this page, and
+compared with a million similar particles of quartz (about four ounces),
+represents a produce of a quarter of an ounce to the ton: a proportion
+such as the assayer is frequently called on to determine. It is evident,
+therefore, that a charge of half an ounce or less of the ore, such as is
+usual with silver ores, would demand of the worker both skill and care
+in the handling of the minute quantity of gold to be obtained from it.
+Fortunately the work is simple and precise, so that in practised hands
+and with only a 5-gram charge the assay of a 5-dwt. ore is practicable;
+with so small a charge, however, the result is barely perceptible on a
+sensitive balance: the button of gold should be measured under a
+microscope. It follows, therefore, that larger charges of say 50, 100,
+or even 200 grams, have an advantage in that they lessen the strain on
+the worker's attention, and, except in the case of the poorest mineral,
+bring the button of gold within the scope of the balance. On the other
+hand, the inconvenience of the larger charges lies in the amount of
+fluxes and consequent size of the crucibles required to flux them.
+
+~Sampling.~--A further consideration in favour of the larger charges is
+the matter of sampling. In preparing his ore, the student should ask
+himself what reasonable expectation he has that the portion he puts in
+the furnace will be of average richness. The larger charges are likely
+to be nearer than the smaller ones to the average of the parcel of ore
+from which they are taken. In explanation of this, let us suppose a
+large heap of 5-dwt. ore, in sand of the coarseness of full-stops, and
+containing all its gold in particles of 1 milligram, as uniformly
+distributed as care and labour in the mixing can accomplish. Such a heap
+could not possibly occur in practice, but it will serve for purposes of
+illustration. Now, one ton of the sand, however taken, would contain
+appreciably the same quantity of gold as any other ton. For a ton would
+contain about 8000 particles of gold; and even if two separate tons
+differed by as much as 100 particles (which they are just likely to do),
+this would mean only a difference of 1 or 2 grains to the ton. On the
+other hand, two portions of 14 lbs., which should contain on the average
+50 particles of gold, are likely enough to differ by 10 particles, and
+this, calculated on a ton, means a difference of 1 dwt. It is easy to
+see that something like this should be true; for on calculating the
+14-lb. lot up to a ton, the deviation from the average, whatever it may
+be, is multiplied by 160; whereas, if the ton were made up by adding
+14-lb. lot to 14-lb. lot, up to the full tale, then a large proportion
+of the errors (some being in excess and some in defect) would neutralise
+each other. An average which is practically true when dealing with
+thousands, and perhaps sufficiently exact with hundreds, would be merely
+misleading when applied to tens and units. Reasonable safety in
+sampling, then, is dependent largely on the number of particles of gold
+in the charge taken, and the risk of an abnormal result is less, the
+larger the charge taken.
+
+By doubling the charge, however, we merely double the number of
+particles. Powdering finely is much more effective; for, since the
+weight of a particle varies as the cube of the diameter, halving the
+diameter of the particles increases their number eight-fold. If, now, we
+modify our illustration by assuming the particles to have only one-sixth
+the diameter of a full-stop (which would represent a powder of a
+fineness not unusual in ores prepared for assaying), we should multiply
+the number of particles by 200 (6 × 6 × 6 = 216). We should then
+reasonably expect a 14-lb. parcel of the powder to give as safe a sample
+as a ton of the sand would give; and portions of a size fit for crucible
+work, say 50 or 100 grams, would be as safe as 10 or 20-lb. samples of
+the coarser stuff. For example, 60 grams of such powder would contain,
+for a 5-dwt. ore, about 100 particles; and in the majority of cases the
+error due to sampling would be less than 10 or 12 grains to the ton, and
+would only occasionally exceed a pennyweight. With richer ores the
+actual deviation stated as so much to the ton of ore might be greater,
+but it would represent a smaller proportion, stated in percentage of
+the gold actually present, and would ultimately fall within the limits
+of unavoidable error.
+
+It will be seen that the size of the quartz particles has no direct
+bearing on the argument; and, in fact, the coarseness of the quartz only
+interferes by preventing the uniform mixing of the sand and by binding
+together several particles of gold; in this last case, particles so
+united must, of course, count as one larger particle. Now, there are
+some natural ores in which the gold particles are all very small; with
+these fine powdering and mixing yields a product from which a sample may
+be safely taken. Then, again, in "tailings," before or after treatment
+with cyanide, we have a similar material, inasmuch as the coarser gold
+has been removed by previous amalgamation. With these, it is not unusual
+to take the portion for assay without any further powdering, since they
+are poor in gold, and have already been stamped and passed through a
+sieve of say thirty holes to the inch (linear).
+
+But there are other ores, in lump showing no visible gold, which contain
+the gold in all possible degrees of fineness, from say prills of a
+milligram or so down to a most impalpable powder. The treatment of these
+cannot be so simple and straightforward. Suppose a parcel of 1000 grams
+(say 2 lbs.) of such ore in fine powder, containing on an average 1
+particle of 1 milligram (the presence or absence of which makes a
+difference of .6 dwt. on the ton), 10 others of about .5 milligram (each
+representing .3 dwt.), and 100 others, which are too coarse to pass
+through an 80 sieve, and having an average weight of .1 milligram (each
+.06 dwt.), and that the rest of the gold, equivalent altogether to 2
+ounces to the ton, is so finely divided that a charge of 50 grams may be
+taken without any considerable risk of its interfering with the
+sampling. Then in a 50-gram charge there would be one chance in twenty
+of getting the milligram particle, in which case the result would be
+12.35 dwts. too high; on the other hand, if it were not present the
+result would on this account be .65 dwt. too low. Of the ten
+.5-milligram particles, it is as likely as not that one will be present,
+and its presence or absence would cause an error of 3.3 dwts., more or
+less. Of the 100 particles of .1 milligram, there would probably be from
+3 to 7, instead of 5, the proper number; this would mean a variation of
+2.6 dwts. from the true proportion. So that the probable result would
+range about 5 dwts. more or less than the 2-1/2 ozs., which is the true
+produce, and there are possibilities of astounding results. It is true
+that the majority of the results would be well within these limits, and
+now and again the heart of the student would be gladdened by a beautiful
+concordance in duplicate assays; nevertheless, there can be no
+reasonable expectation of a good assay, and to work in this way, on a
+50-gram charge, would be to court failure. The coarse gold must ruin the
+assay.
+
+The difficulty may be met by concentrating the whole of the coarse gold
+in a small fraction of the ore, by sifting and making a separate assay
+of this fraction. A portion of the ore, of about 1000 grams, is ground
+to a very fine powder and passed through an 80 sieve, re-grinding when
+necessary, until only 20 or 30 grams is left of the coarser powder. This
+is mixed with fluxes and carried through as a separate assay. The sifted
+portion is _thoroughly mixed_, and a portion of it, say 30 or 50 grams,
+taken for assay. The weights of the two portions must be known, and care
+must be taken that nothing is lost in the powdering. The method of
+calculating the mean result from the two assays is shown on page 109. In
+this way of working there is no advantage in continuing the grinding
+until the coarser fraction is reduced to a gram or so--rather the
+contrary; and rubbing on until all the gold is sent through the sieve is
+to be distinctly avoided. The student must bear in mind that what he is
+aiming at is the exclusion of all coarse gold from the portion of ore of
+which he is going to take only a fraction.
+
+The question of the smaller sampling of gold ores has been dwelt on at
+considerable length, as befits its importance, in order that the student
+may be impressed with a sense of its true meaning. Sampling is not a
+mystery, nor does the art lie in any subtle manner of division. It is,
+of course, absolutely necessary that the stuff to be sampled shall be
+well mixed, and the fractions taken, so that each part of the little
+heap shall contribute its share to the sample. Moreover, it must be
+remembered that tossing about is a poor sort of mixing, and that
+everything tending to separate the large from the small, the light from
+the heavy, or the soft from the hard (as happens in sifting), must be
+avoided, or, if unavoidable, must be remedied by subsequent mixing.
+
+With a well-taken sample, we may rely on a great majority of our results
+falling within normal limits of error; but nothing can be more certain
+than that, in a moderately large experience we shall get, now and again,
+deviations much more considerable. These erratic assays can only be met
+by the method of working duplicates, which call attention to the fault
+by discordant results. Such faulty assays should be repeated in
+duplicate, so that we may rest the decision on three out of four
+determinations.
+
+The likelihood of two very faulty assays being concordant is remote;
+but with very important work, as in selling parcels of ore, even this
+risk should be avoided, as concordance in these cases is demanded in the
+reports of two or more assayers. The following actual reports on a
+disputed assay will illustrate this: (a) 5 ozs. 1 dwt.; (b) 5 ozs.
+10 dwts. 12 grains; (c) 5 ozs. 11 dwts.; (c) 5 ozs. 11 dwts. 12 grs.
+The mean result of several assays, unless there be some fault in the
+method, will be very fairly exact; and individual assays, with an
+uncertainty of 1 in 20, may, by repetition, have this reduced to 1 in
+100 or less.
+
+~Assay Tons, etc.~--Having decided on taking a larger or smaller
+portion, the exact quantity to be used will be either some round number
+of grams, such as 50 or 100, easily calculable into percentage; or it
+will be that known as the "Assay Ton" (see page 13) or some simple
+multiple or fraction of it, which is easily calculable into ounces. The
+reports, too, are at least as often made as ounces in the short ton of
+2000 lbs., as on the more orthodox ton of 2240 lbs. Now the short ton is
+equal to 29,166.6 troy ounces; and the corresponding "assay ton" is got
+from it by replacing ounces by milligrams. The advantage of its use is
+that if one assay ton of ore has been taken, the number of milligrams of
+gold obtained is also the number of ounces of gold in a ton of the ore,
+and there is absolutely no calculation. Even if half an assay ton has
+been taken the only calculation needed is multiplying the milligrams by
+two. On the other hand with a charge of two assay tons the milligrams
+need halving. Where weights of this kind (_i.e._, assay tons) are not at
+hand they may be easily extemporised out of buttons of tin or some
+suitable metal, and it is better to do this than to array out the grams
+and its fractions at each weighing. The sets of "assay tons," however,
+are easily purchased. As stated on page 13, the assay ton for 2240 lbs.
+is 32.6667 grams; and for the short ton, 29.1667 grams. If, however, the
+round number of grams be used and the result brought by calculation to
+the produce on 100 grams, the conversion to ounces to the ton may be
+quickly effected by the help of the table on page 107. As this table
+only deals with the ton of 2240 lbs., it is supplemented here by a
+shortened one dealing only with _the produce of 100 grams_ and stating
+the result in _ounces troy to the short ton of 2000 lbs_.
+
+~Estimation of Small Quantities of Gold.~--_By the Balance._ In
+estimating minute quantities of gold there are one or two points, of
+importance to an assayer only in this assay, where they will often allow
+one to avoid the working of inconveniently large charges. One of these
+is known as "weighing by the method of vibrations."
+
+            TABLE FOR CALCULATING OUNCES TO THE SHORT TON FROM THE
+                    YIELD OF GOLD FROM 100 GRAMS OF ORE.
+  ----------+---------+-----------+---------+-----------+---------
+  Milligram.|Ounces to|Milligrams.|Ounces to|Milligrams.|Ounces to
+            | the Ton.|           | the Ton.|           | the Ton.
+  ----------+---------+-----------+---------+-----------+---------
+     0.01   |  0.003  |    0.4    |  0.117  |    7.0    |  2.042
+     0.02   |  0.006  |    0.5    |  0.145  |    8.0    |  2.333
+     0.03   |  0.009  |    0.6    |  0.175  |    9.0    |  2.625
+     0.04   |  0.012  |    0.7    |  0.204  |   10.0    |  2.916
+     0.05   |  0.014  |    0.8    |  0.233  |   20.0    |  5.833
+     0.06   |  0.017  |    0.9    |  0.262  |   30.0    |  8.750
+     0.07   |  0.020  |    1.0    |  0.292  |   40.0    | 11.666
+     0.08   |  0.023  |    2.0    |  0.583  |   50.0    | 14.583
+     0.09   |  0.026  |    3.0    |  0.875  |   60.0    | 17.500
+     0.10   |  0.029  |    4.0    |  1.167  |   70.0    | 20.416
+     0.20   |  0.058  |    5.0    |  1.458  |   80.0    | 23.333
+     0.30   |  0.087  |    6.0    |  1.750  |   90.0    | 26.250
+  ----------+---------+-----------+---------+-----------+---------
+
+Suppose a balance at rest in perfect equilibrium, with the
+pointer exactly over the middle point of the scale. Let the scale be a
+series of points at equal distances along a horizontal line; then, if a
+small weight be placed on one pan, the pointer will deviate from its
+vertical position and come to rest opposite some definite part of the
+scale, which will depend upon the magnitude of the weight added. The law
+determining this position is a very simple one; the deviation as
+measured along the points of the scale varies directly as the weight
+added. For example, with an ordinarily sensitive balance, such as is
+used for general purposes, one milligram will move the pointer along,
+say, three divisions of the scale; then two milligrams will move it six
+divisions; half a milligram, one and a half divisions; and so on. Of
+course, with a more sensitive balance the deviations will be greater.
+Now the point at which the needle comes to rest is also the middle point
+about which it vibrates when swinging. For example, if the needle swings
+from the third to the seventh division on the right then [(7+3)/2] it
+will come to rest on the fifth. In working by this method the following
+conventions are useful: Always place the button to be weighed on the
+left pan of the balance, the weights on the right; count the divisions
+of the scale from the centre to right and left, marking the former + and
+the latter -; thus -5 is the fifth division to the left. Then the
+position of rest is half the algebraic sum of two readings. For example,
+let the readings be 7 to the right and 3 to the left, then (+7-3)/2 =
++2. The mean division is the second division to the right. If the
+student will place himself in front of a balance and repeat the
+following observations and replace the figures here given by his own, he
+will have no difficulty in grasping the method. First determine the
+_bias_ of the balance; suppose the unloaded balance swings +1.25 and -1;
+the bias then is (1.25-1)/2 = +.125 or one-eighth of a division to the
+right. Now having put on the button to be weighed let the readings be
++7.5 and +9.25, and (7.5+9.25)/2 = +8.375. Then the effect of the button
+has been to move the pointer from +.125 to +8.375, or 8.25 divisions to
+the right; we should, therefore, add the weight equivalent of 8.25
+divisions to the weights, whatever they may be on the right hand pan of
+the balance; if the divisions were to the left (- divisions) we should
+subtract. The value of 1 division is easily determined. Suppose the
+button in the example were a 1 milligram weight, then we should have
+found that 1 milligram = 8.25 divisions .'. 1 division = .121 milligram.
+This method of working adds very considerably to the power of a balance
+in distinguishing small quantities.
+
+[Illustration: FIG. 44_a._]
+
+_By the Microscope_.--The use of the microscope also is a real advantage
+in estimating the weights of minute buttons of gold where there is no
+undue risk in sampling, and where an error of say 1 in 20 on the
+quantity of gold is tolerable. For ores with copper, lead, zinc, &c., as
+well as for tailings rather poor in gold, this leaves a wide field of
+usefulness. The method is described on page 440, but the description
+needs supplementing for those who are not accustomed to the use of a
+microscope. The eye-piece of a microscope (fig. 44_a_, A) unscrews at
+_a_, showing a diaphragm at _b_, which will serve as a support for an
+eye-piece micrometer. This last, B, is a scale engraved on glass, and
+may be purchased of any optical instrument maker, though it may be
+necessary to send the eye-piece to have it properly fitted. When resting
+on the diaphragm it is in focus for the upper lens, so that on looking
+through the microscope, the scale is clearly seen in whatever position
+the instrument may be as regards the object being looked at. Suppose
+this to be a small button of gold on a shallow, flat watch-glass, on the
+stage of the microscope. Bring the button under the "objective" (_i.e._,
+the nose of the microscope), which should be about a quarter of an inch
+above the watch-glass; then looking through the instrument, raise the
+tube until the button of gold, or at least some dust on the glass, comes
+into focus. If the button is not in the field, rest the thumbs and index
+fingers, using both hands, on the edge of the watch-glass, pressing
+lightly but steadily, and give the glass a slow, short, sweeping motion;
+the button will perhaps appear as an ill-defined blackness, because not
+quite in focus. Bring this into the centre of the field. Raise or lower
+the microscope until the button appears with sharp outlines. If the
+scale does not cover the button, rotate the eye-piece; this will bring
+the scale into a new position. Since the divisions over the button are
+less distinct than the others, it is best to read the latter. Thus, in
+fig. 44_b_, there are 36 divisions on one side of the button, and 35 on
+the other, making altogether 71. The whole scale is 80, therefore the
+diameter of the button is 9 divisions. The value of each division
+obviously varies with the magnifying power employed. With most
+microscopes there is a telescopic arrangement whereby the tube may be
+lengthened; if this be done and the button again brought in focus, it
+will be seen that, as measured on the scale, the button is much larger
+than before. It is evident, therefore, the micrometer must always be
+used in the same way. The method given in the appendix (page 440), for
+finding the value of the scale when gold buttons are to be measured is
+easy and satisfactory. When the button of gold is so small that there is
+considerable risk of losing it in transferring to a watch-glass, it may
+be measured on the cupel, but for this purpose it must be well
+illuminated; this is best done by concentrating light on it with a lens,
+or with what comes to the same thing, a clean flask filled with water.
+
+[Illustration: FIG. 44_b._]
+
+Most assayers, however, using a micrometer in this way, would like to
+know its absolute value. To do this, a stage micrometer must be
+purchased. This is like an ordinary microscope slide (fig. 44_a_, C),
+and when looked at through a microscope it shows (fig. 44_c_) lines
+ruled on the glass at distances of tenths and hundredths of a
+millimetre, ten of each, so that the full scale is 1.1 mm. In the case
+illustrated, 60 divisions of the scale in the eye-piece are just equal
+to the 1.1 mm., therefore 1 division equals .0183 mm. A cube of this
+diameter would contain (.0183×.0183×.0183) .0000061285 cubic mm. The
+corresponding sphere is got by multiplying by .5236; this gives
+.000003209 cb. mm. The weight of 1 cb. mm. of water is 1 milligram; and,
+since gold is 19.2 times as heavy as water (sp. g. = 19.2), the contents
+in cb. mm. must be multiplied by 19.2. This gives .0000616 milligram as
+the weight of a sphere of gold measuring 1 division.
+
+[Illustration: FIG. 44_c._]
+
+If every result had to be calculated in this way the method would be
+very laborious; but, having the figures for the first division, those of
+the others may be calculated by multiplying by the cube of the
+corresponding number. Thus, for the third division (3×3×3 = 27), the
+content of the cube (.0000061285×27) is .0001655 cb. mm.; the content of
+the sphere (.000003209×27) is .0000866 cb. mm.; and the corresponding
+sphere of gold (.0000616×27) is .00166 milligram. With the help of a
+table of cubes the whole calculation for 25 or 30 divisions may be made
+in half an hour, and the results preserved in the form of a table will
+simplify all future work.
+
+~Assay Operations.~--The actual work of the assay resolves itself into
+three operations:--(1) The fusion of the ore and concentration of the
+"fine metal" (_i.e._, gold and silver) in a button of lead; (2) The
+cupellation of the lead, whereby a button of fine metal is obtained; and
+(3) the "parting" of the gold which separates it from the accompanying
+silver. The following description takes the order as here given, but the
+student, in learning the method, should first practise cupellation if he
+has not already done so; next he should practise the separation of gold
+from silver, taking known weights of fine gold (p. 63), varying from .5
+or .3 gram down to quite minute quantities, and not resting satisfied
+until a sensitive balance can barely distinguish between the weights of
+gold taken and found. It may be noted here that if he has not a flatting
+mill at his disposal, then for large buttons it is better to make an
+alloy with eight or nine parts of silver to one of gold, and attack it
+with acid without previous flattening, rather than accept the risk and
+labour of beating out a less easily attacked alloy to the necessary
+thinness with a hammer. It is only after a sense of security in gold
+parting has been acquired, that the attack of an ore can be profitably
+accomplished, and even then simple and easy ores should be first taken,
+passing on to others more difficult, either because of a more complex
+mineral composition or a difficulty in sampling.
+
+~Concentration of the fine Metal in Lead.~--The best flux for quartz,
+which makes up the earthy matter of most gold ores, is soda, and this is
+best added as carbonate or bicarbonate. By theory,[20] 50 grams of
+quartz will require 88.5 grams of the carbonate, or 140 grams of the
+bicarbonate, to form sodium silicate, which is a glassy, easily-fusible
+substance, making a good slag. If the bicarbonate is used, and heat is
+applied gradually, steam and carbonic acid are given off at a
+comparatively low temperature, and the carbonate is left; at a higher
+temperature (about 800° C., or a cherry-red heat) the carbonate fuses
+attacking the quartz, and giving off more carbonic acid; as the heat
+increases, and the attack on the quartz (which of itself is infusible)
+becomes complete, the whole mass settles down to a liquid sodium
+silicate, which is sufficiently fluid to allow the gold and lead to
+settle to the bottom. The fluid slag does to a certain extent dissolve
+some of the crucible, but not seriously. In a perfect working of this
+experiment, the first evolution of gases (steam and carbonic acid)
+should be gentle, so as to run no risk of its blowing the fine powder
+out of the crucible; and the heat at which the second evolution of
+carbonic acid is produced should be maintained until the reaction is
+completed, so that there may be little or no formation of gas in the
+fused mass to cause an effervescence which may force some of the charge
+over the edges of the crucible. Of course, in practice the ideal fusion
+is not attained, but there is no difficulty in approaching it closely
+enough to prevent the charge at any time rising above the level it
+reached at first in the crucible, and this should be accomplished. It is
+usual with quartzose ores to rely mainly on the action of carbonate of
+soda, but not entirely. Litharge is also used; it forms, on fusion with
+quartz, a silicate of lead, which is a yellow glass, easily fusible, and
+more fluid in the furnace than silicate of soda is. By theory, 50 grams
+of quartz would require 186 grams of litharge.[21] The reaction takes
+place without evolution of gas, and in its working the only point is to
+so regulate the heat that the litharge shall not fuse and drain under
+the unattacked quartz, leaving it as a pasty mass on the surface. Now,
+if in making up a charge for 50 grams of ore, we took 100 grams of
+bicarbonate of soda (equivalent to about 63 grams of the carbonate),
+this being five-sevenths of 140 grams (which by itself would be
+sufficient), leaves two-sevenths of the quartz to be fluxed by other
+reagents: two-sevenths of 186 grams (say 52 grams) of litharge would
+serve for this purpose. But if we used 10 grams of borax, which has a
+fluxing action about equal to that of the litharge, then 40 grams of the
+latter, or (making an allowance for the quartz being not quite pure) say
+35 grams, will suffice. The fluxes, then, for the 50 grams of ore would
+be: bicarbonate of soda 100 grams, litharge 35 grams, and borax 10
+grams; we could decrease any of these, and proportionately increase
+either or both of the others, and still rely on getting a fusible slag,
+which is the whole of the function of a flux, considered simply as a
+flux. It should be remembered, however, that the slag is a bi-silicate
+or acid slag, and that its acid character is increased by increasing the
+proportion of borax.
+
+But in addition to the fluxes there is required about 30 or 40 grams of
+lead to collect the silver and gold. This is best added as litharge (say
+40 grams) and flour (4 grams), or charcoal powder (2 grams). See pages
+93 and 94. The full charge, then, would be:
+
+  Ore                    50 grams.
+  Bicarbonate of soda   100  "
+  Litharge               75  "
+  Borax                  10  "
+  Flour                   4  "
+
+These should be mixed, placed in a suitable crucible (a G Battersea,
+round, will do), and heated, at first at a red heat, but finally much
+hotter, so as to get a fluid and clean slag. When the charge has been in
+tranquil fusion for some little time, take it out and pour it into an
+iron mould. When cold, detach the button of lead. The slag should be
+glassy, all through alike, and easily separable from the metal. With
+ordinary ores, this slag may be considered as free from gold. In an
+experiment in which 90 milligrams of gold were added, the full amount
+was obtained from the lead produced by the first fusion. But in certain
+cases, more especially where large amounts of metallic oxides are
+present, the slag is not so clean, and with these the slag should be
+powdered, mixed with 40 grams of litharge and 4 of flour, and melted
+again; it is an advantage to add a small prill of say 2 or 3 milligrams
+of silver to the charge, as it insures a visible product in the
+cupellation. Indeed, this last precaution is a good one to be taken
+wherever there is reason to expect very small buttons. It has the
+further advantage, that, if the quantity of silver necessary for
+inquartation is known, the right quantity may be added here, so as to
+save a subsequent operation.
+
+~Ores containing Oxides of Iron.~--Of the metallic oxides likely to be
+present in a slag, oxide of iron is the most important. Gold is
+occasionally found in a matrix of this substance, and in the assay of
+"concentrates" largely made up of pyrites, this oxide will be formed in
+the preliminary calcination. Now, the lower oxide of iron (ferrous
+oxide, FeO) is easy to deal with; fused borax will dissolve about its
+own weight of it, and a silicate of soda (such as makes up the bulk of a
+slag in a gold assay) will take up at least half as much. But the higher
+oxide (ferric oxide, Fe_{2}O_{3}) is more refractory; even 6 parts of
+borax yields a poor product, and slags with any considerable percentage
+of it are not satisfactory. A student attempting to recover gold from
+some hęmatite (in which there was about half an ounce of the metal),
+found in the slag nearly a gram of gold, although in the first fusion
+the slag appeared perfectly fluid. There is, however, no difficulty in
+getting good slags, even with large quantities of iron. For example,
+with 50 grams of ferric oxide, 10 of quartz, 30 of borax, 30 of
+soda,[22] 50 of litharge, and 7 of flour, the result was quite
+satisfactory. So, too, was 25 of quartz, 50 of soda, 50 of litharge, and
+7 of flour. It is well, however, in such cases to have an ample
+proportion of flux and to aim at a larger button of lead than usual by
+increasing the proportion of flour or charcoal (see also page 91). A
+charge used on the Randt for roasted "concentrates" (which we may
+roughly speak of as quartz and ferric oxide), is one assay ton (about 30
+grams) each of ore, soda, and borax, and one and a half assay ton of
+litharge and 2 grams of charcoal. Whilst, for the same material, from
+which most of the gold has been extracted by "chloridising," 2.5 tons
+each of ore, borax, and soda, 4 of litharge, and 4 grams of charcoal are
+needed. This quantity requires a large crucible (I Battersea, round). In
+this the proportion of silicate of soda and borax counted together is to
+the oxide of iron as 4 to 1, on the supposition that the quartz and
+oxide of iron of the ore are in about equal quantities; but, in the
+larger charge especially, much oxide of lead would also remain as a
+flux.
+
+~Ores containing Sulphides.~--In assaying ores containing a large
+proportion of pyrites or mispickel, or both, the best plan is to take a
+portion and calcine so as to convert it into a product of the kind just
+considered. The weighed portion of ore should be placed in a clean
+crucible and be heated to incipient redness: with pyrites the first
+effect is to drive off about half the sulphur as vapour which burns as
+flame over the ore. At this stage care should be taken that there is no
+great increase of temperature, otherwise there may be more or less
+fusion, which would spoil the operation. When the sulphur flame ceases
+the solid sulphide of iron burns with visible incandescence and the
+charge should now be stirred with a flattened iron rod so as to expose
+fresh portions to the air. The top of the furnace must be open, so that
+air may have free access to the crucible. When stirring is no longer
+followed by visible burning the heat may be raised to full redness. The
+crucible is then lifted out (the stirrer still resting in it) and if the
+charge gives off no odour of burning sulphur it is shaken out into an
+iron mortar and mixed with the fluxes, taking care to clean the stirrer
+in the mixture. The charge is then replaced in the crucible in which the
+roasting was done and fused in the furnace. The resulting button of lead
+is cupelled for fine metal. Ores rich in sulphides requiring this
+treatment are frequently "concentrates." For their assay take 1 assay
+ton (30 grams), calcine and mix with an equal weight of soda and of
+borax (30 grams each), and half as much again of litharge (1.5 tons or
+45 grams), and with 2 grams of charcoal or 5 grams of flour.
+
+Where the sulphides are present in smaller proportion (10 per cent. or
+less), they may be taken as serving the purpose of flour or charcoal
+(see page 95); the sulphur and iron are oxidised at the expense of the
+litharge with a consequent separation of lead as metal. If the
+proportion of sulphides is not sufficient to give a large enough button
+of lead, some charcoal or flour should be added. On the other hand, if
+they are in small excess and give a button of lead somewhat sulphury,
+_i.e._, hard and brittle, it may be remedied by the judicious addition
+of nitre; this last reagent, however, should not be used in large
+quantity. A plan much used to prevent sulphury buttons is to insert an
+iron rod or a nail in the charge in the crucible; the iron takes the
+sulphur forming sulphide of iron which in moderate quantity does not
+form a separate layer of matte but dissolves in the slag. A slag formed
+of 50 grams of quartz, 100 soda, and some borax, may take up in this way
+some 10 or 12 grams of sulphide of iron. If, however, an ore gives a
+layer of matte or speise, it is best to repeat the assay by the method
+of calcining before fusion.
+
+~Cyanide Charges, etc.~--In assaying the "tailings" which are to be
+treated in a cyaniding plant the following charge is used:
+
+  Tailings   3   assay tons or 100 grams.
+  Litharge   4.5      "        150   "
+  Soda       4.5      "        150   "
+  Borax       .75     "         25   "
+
+The sand is assayed without any further crushing and the assay is made
+in duplicate.
+
+The residues after treatment with cyanide, differing from the tailings
+merely in being poorer in gold because of the extraction by the solution
+of cyanide, are run down with the same fluxes in the same relative
+proportions. But four charges of 2.5 assay tons (say 75 grams) are
+worked, and two of the resulting buttons are scorified together and then
+cupelled, etc., so as to give duplicate assays on charges of 5 assay
+tons. This is one of the cases in which it is desirable to add a small
+portion of silver before cupelling.
+
+In assaying the "cyanide liquors" for gold, 2 assay tons of the liquor
+are measured out (58.3 c.c. for the ton of 2000 lbs., 65.3 c.c. for the
+other) and are evaporated to dryness in a lead dish weighing about 35
+grams. Such a dish is easily extemporised out of a piece of lead foil,
+if the ordinary vessel is not at hand; but care must be taken that the
+lead is free from gold. The dish with the dried residue is then
+scorified and the resulting button of lead is cupelled.
+
+[Illustration: FIG. 44c.]
+
+In some cases the fusion of the ore may be replaced by a treatment with
+solution of cyanide of potassium and the gold recovered from the
+solution in the way just described. For this purpose the ore should be
+in not too fine powder, otherwise there will be great difficulty in
+filtering; a sand which will pass a 30 sieve and having no large
+proportion of very fine stuff will do. Not less than 200 grams should be
+taken; and as an extraction apparatus a bell jar capable of holding half
+as much again may be used. Such a jar may be extemporised by cutting off
+the bottom of a bottle by leading a crack around it with a red hot
+poker; or a lamp chimney will serve the purpose. The smaller mouth of
+the jar is closed by a perforated cork provided with a clipped tube
+after the manner of a burette (see fig. 44c). In the jar, just over
+the cork, put a plug of loose asbestos or glass wool, or a piece of
+sponge to act as a filter; a layer of broken glass, coarse at the bottom
+and fine at the top, will serve the same purpose. On this, place the
+charge of ore to be extracted. Prepare a solution of cyanide of
+potassium in water, with 5 or 10 grams of the salt to the litre. It may
+be that the whole point of the assay depends on the solution being of a
+definite strength; as, for example, where the relative efficiency of
+solutions of different strengths is being determined, when it will be
+best to estimate the quantity of cyanide of potassium in the dilute
+solution by the method given at the end of this article (page 160). Pour
+the cyanide solution on to the ore, letting the first portions to come
+through run into the beaker, but as soon as the ore is thoroughly wetted
+close the clip and allow to stand for several hours. Then, opening the
+clip, run through more cyanide solution and then water, so as to wash
+the gold-carrying liquor thoroughly into the beaker. It is no matter if
+the liquor is a little bit turbid; transfer it to a lead dish,
+evaporate, scorify, and cupel in the usual fashion.
+
+The assay of gold-zinc slimes, which is the precipitate formed by zinc
+acting on cyanide solutions of gold, may be made by wrapping 2 or 3
+grams in 40 grams of sheet lead and scorifying, cupelling, &c. The
+amount of impurity in the stuff varies greatly; it is usually calcined
+and mixed thoroughly with soda 40 per cent., borax 30 per cent., and
+sand 10 per cent., and melted in graphite pots. The buttons of bullion
+obtained are afterwards remelted with borax and run into bars, the
+fineness of which varies from 600 to 830 thousandths. The bars are
+sampled by chipping off diagonally opposite corners: or better, by
+drilling, the drillings being freed from pieces of steel with the help
+of a magnet.
+
+~Cupellation.~[23]--The cupellation of lead for gold differs very little
+from that of lead carrying silver. When the gold is accompanied by a
+larger proportion of silver, and both have to be determined, the
+cupellation must be conducted exactly as in a silver assay, the usual
+precautions being taken to moderate the temperature so as to lessen the
+cupellation loss and to promote a slow and undisturbed solidification in
+order to avoid spirting. If, however, the gold predominates the finish
+should be effected at a higher heat, as the melting-point of gold is
+100° higher than that of silver. The bad effect of a higher temperature
+in increasing the cupellation loss need hardly be considered in the case
+of such small buttons of gold as are obtained in assaying gold ores, as
+any loss there may be is hardly appreciable by the balance. With larger
+quantities of gold, however (as in assaying gold bullion), this loss
+becomes important; and it is therefore necessary to very carefully
+regulate the temperature of the muffle so as to minimise the loss.
+
+~The cupels~ are made of well-burnt bone-ash, of the fineness of coarse
+wheat flour, moistened with one-twelfth its weight of water and
+compressed into shape in suitable moulds. The moulds sold for this
+purpose are often of unsuitable shape. Since lead has a specific gravity
+of over 11, a cup to hold from 15 to 25 grams of molten lead need not
+have a capacity of more than about 2 c.c. A hollow about 1 inch across
+and 1/4 inch deep is sufficient; and the body of the cupel to absorb
+this weight of lead should itself weigh from 20 to 25 grams. The button
+of lead in a gold assay may be twice as heavy as this. For these larger
+buttons a hollow 1-1/3 inch across and 1/3 inch deep will be sufficient.
+If these larger cupels are not at hand the larger buttons will have to
+be reduced in size by a scorification before cupelling. In some cases
+this preliminary scorification is advantageous or even necessary: this
+may be because the lead is hard and impure, or it may be that a very
+small button of gold is expected. In the latter case it is best to
+scorify the lead down to something less than 1 gram, and to perform the
+cupellation on a specially prepared small fine cupel. These small cupels
+are best made by grinding the unsaturated portion of a used cupel to a
+fine powder, and compressing the dry powder into a small Berlin crucible
+or scorifier; the face should be made quite smooth by pressure from a
+pestle. On such cupels a small speck of gold (less than .01 milligram)
+will be left in a good shape and easily visible; but the cupel must be
+withdrawn from the muffle as soon as the cupellation is finished to make
+sure of always getting the button in good condition. In places, such as
+Mints, where large numbers of bullion assays are regularly made a
+special form of cupel is used so that not less than six dozen assays may
+all be cupelled at the same time in a muffle of ordinary size. These
+cupels are square blocks, a little less than 2 inches across, and a
+little more than three quarters of an inch deep. Each block carries four
+hollows of about .7 inch across and .3 inch deep. A muffle, on a floor
+space of 6 inches by 12, would take 3 of these blocks abreast and 6
+deep, and thus provide the means for 72 assays.[24]
+
+Cupels made with wet bone-ash should be slowly dried; and if in the
+muffle they can be slowly brought to an orange-red heat it is all the
+better. Under no circumstances must the lead be placed on the cupel
+before the latter has been so thoroughly heated that it can no longer
+give off steam or gas of any kind. For this gas bubbling through the
+molten metal spatters it, thus spoiling one assay and throwing doubt on
+all the rest. Again, the risk of freezing at the start is much greater
+with a cupel which has not been properly heated.
+
+The best plan is to do all the cupellations in batches. After the muffle
+has cooled down for the withdrawal of the last batch, and the old cupels
+have been taken out, the new cupels for the next batch should be put in
+their place. The furnace should then be stoked and made ready for the
+next cupellations; by the time the furnace is ready the cupels will be
+ready also. There should be no unnecessary handling of the cupels once
+they have been placed in the muffle.
+
+~The cupellation temperature for gold~ is an orange-red heat or perhaps
+a little hotter. Beginners, who are apt to overheat their furnace,
+should avoid a heat which can properly be called yellow. Dr. T.K.
+Rose[25] has determined the temperature of a muffle during the
+cupellation of gold-silver alloys at the Royal Mint. In one muffle the
+temperature ranged from 1065° to 1095° C.; the lower temperature was of
+course in the front of the muffle. In another it ranged from 1022° to
+1062°, and here the muffle appeared to the eye "decidedly cooler than
+usual." The alloy left after cupelling was made up of 1 part of gold to
+2-1/2 parts of silver, and was fused at 952°; hence the usual
+temperature of cupellation was, say, 120° or 130° above the
+melting-point of the residual metal. To obtain some real knowledge as to
+the meaning of these figures, the student should prepare pointed pieces
+of the following metals: silver, which melts at 945°; gold, which melts
+at 1035°; and an alloy, half silver, half gold, which melts at 990°.
+These should be placed on clean cupels in a muffle almost entirely
+closed; the temperature should be very slowly raised, and the appearance
+of the muffle when each metal begins to melt should be carefully noted.
+The cupelling temperature in Dr. Rose's experiment was as much above the
+melting-point of gold as this is above that of the silver-gold alloy.
+The _finish of the cupellation_ of gold or gold-silver alloys is
+practically the same as with pure silver; there is the same thinning out
+of the litharge into a luminous film which becomes iridescent before the
+brightening. But the danger of spirting decreases as the proportion of
+gold becomes greater, and disappears when the gold is much over 30 per
+cent. Nevertheless it is well to let such buttons become solid
+undisturbed and protected from draughts in the body of the muffle. This
+means closing the muffle and allowing the furnace to cool down somewhat
+before withdrawing the cupels. Buttons solidified in this way are more
+malleable than when they are withdrawn promptly on the finish of the
+cupellation. This is important with large buttons, as in a bullion
+assay. On the other hand, very small buttons, especially such as have to
+be measured rather than weighed, should be withdrawn as soon as the
+luminous film has disappeared. For when this is done the button can be
+loosened from the cupel by merely touching it with the point of a pin,
+and is then safely and easily transferred to a watch glass by touching
+it with the head of a pin which has been moistened. It adheres to this,
+and if the pin is not too wet comes off at once on touching the glass,
+or in any case will do so on gentle warming.
+
+Molten gold, with little or no silver, has a peculiar colour which is
+easy to recognise; it is more globular than a button of silver of the
+same size would be, and it shows less adhesion to the cupel. Just after
+becoming solid it glows beautifully, and this is so marked that it is a
+valuable help in finding the position of a button when it is more than
+ordinarily minute.
+
+If the button left from cupellation is yellow it is at least half gold,
+and a rough guess as to the proportion of gold may be made from its
+yellowness; the rest of the metal is generally silver. The presence of
+platinum or one of the platinum group of metals makes the surface of the
+button dull and crystalline. The native alloy of osmium and iridium does
+not alloy with gold, however, but falls to the bottom of the molten
+metal. It shows itself in the subsequent parting as a black spot or
+streak on the under surface.
+
+The buttons are removed from the cupel with a pair of pliers and then
+brushed to remove adherent litharge and bone-ash. Some assayers advise
+cleaning by dipping in warm dilute hydrochloric acid followed by washing
+in water and drying. The button is next weighed. When the quantity of
+silver obtained is not required to be known the weighing may sometimes
+be omitted. The next operation in either case is parting either with or
+without a previous inquartation.
+
+_The loss of gold in cupellation_ is by no means always inconsiderable.
+In three cupellations of 1 gram of gold with 20 grams of lead made
+purposely at a very high temperature the cupel absorbed 6.04, 6.20, and
+6.45 milligrams of gold. Hence at a high temperature there may easily be
+a loss of more than half a per cent. of the gold. In ten cupellations
+with the same quantities of gold and lead, but at an ordinary
+temperature, the gold recovered from the cupels varied from 1.37 to 1.92
+milligrams, and gave an average of 1.59 milligrams. In round numbers the
+cupellation loss of pure gold is .15 per cent.
+
+But if the gold be alloyed with _silver_ the loss is diminished, as is
+shown by the following experiments. Gold, .3 gram, was cupelled with 10
+grams of lead and varying amounts of silver, and the cupels were assayed
+for gold with the following results:
+
+  Silver in the alloy  .3 gram         .6 gram           .9 gram
+  Gold in the cupel    .47 milligram   .32 milligram   .17 milligram
+
+These, calculated on the .3 gram of gold, give the loss as .157, .107
+and .057 per cent. respectively. The effect of _copper_, on the other
+hand, is to increase the cupellation loss, which, silver being absent,
+may from this cause rise to .3 per cent., even when the temperature is
+not excessive.
+
+In the ordinary assay of gold-copper alloys a constant weight of the
+alloy is always taken; hence as the weight of copper in a cupel charge
+increases, the weight of gold decreases. The silver, on the other hand,
+is always very nearly two and a half times as much as the gold, whatever
+its quantity may be. But the cupellation loss is smaller with less gold
+and greater with more copper, and it so happens in these assays that
+these two opposites nearly neutralise one another. Mr. W.F. Lowe[26]
+found the gold recoverable from the cupels on which 20 grains of gold
+bullion had been treated varied only between .014 and .015 grain (_i.e._
+from .07 to .075 per cent. of the bullion treated), although the quality
+of the bullion varied from 9 to 22 carat.[27] But in the poorest bullion
+there was only 7.5 grains of pure gold, while in the richest there were
+18.3 grains; yet each lost on the cupel the same weight of gold, viz.,
+.014 grain. When reckoned in percentages of the actual gold present the
+losses are .187 per cent. and .076 per cent. respectively. The heavier
+percentage loss is mainly due to the increased quantity of copper.
+
+As with silver so with gold the predominant cause of the cupellation
+loss is the solution of the metal in the molten litharge which passes
+into the cupel. Three lots of 1 gram of gold cupelled each with 20 grams
+of lead repeatedly, so as to make 13 cupellations in all, lost in actual
+weight 35.72 milligrams. The gold recovered from the cupels amounted
+altogether to 34.56 milligrams. This shows that, compared with the
+absorption by the cupel, the other causes of loss are inconsiderable.
+
+The loss of gold by _volatilisation_ is, however, a real one. The dust
+from the flues of assay furnaces has been tested on several occasions
+and found to contain gold, though in small quantity. Thus Mr. Lowe found
+.073 per cent. of silver and .00033 per cent. of gold in such a
+material. The lead volatilised from a gold bullion assay would need to
+be ten times as rich as this to account for a loss of gold equal to the
+hundredth part of a milligram. Dr. Rose, in the paper already quoted,
+believes that on a .5 gram charge of standard bullion the loss from
+volatilisation is not less than .025 nor more than .05 milligram of
+gold.
+
+By way of conclusion it may be said that the cupellation loss of gold is
+about .07 per cent., and that it is largely met or even over corrected
+by a compensating error due to silver retained in the gold after
+parting.
+
+~Inquartation.~--The method of separating the gold from the silver in
+gold-silver alloys by boiling with nitric acid does not act equally well
+in all cases. An alloy half silver half gold, rolled to thin sheet and
+boiled for half an hour with nitric acid, may still retain more than
+two-thirds of its silver. An alloy of 1 part gold and 1.7 parts of
+silver gives up practically the whole of its silver under similar
+treatment. The gold is left in a coherent, though easily broken, sheet
+retaining the shape of the original alloy. The gold thus left is quite
+spongy and porous, so that the acid can penetrate into its innermost
+portions. But if the silver is in large excess in the alloy, the
+removal of the silver is less complete, and the residual gold, instead
+of holding together in a form easy to manipulate, falls to a powder
+which requires care and time in its treatment. The older assayers,
+therefore, added silver to their gold in such proportion that the alloy
+for parting should be one quarter gold to three quarters silver. This
+operation they called _inquartation_.
+
+The modern practice is to aim at getting an alloy with 2-1/2 parts of
+silver and 1 part of gold. In gold bullion assays this proportion should
+be obtained with fair exactness. And in the parting of such gold buttons
+as are obtained in assaying ores it is well to aim at this proportion,
+though absolute precision is not a matter of importance.
+
+If the button left on cupelling the lead from an assay of an ore appears
+white, it is best to assume that it already contains at least a
+sufficiency of silver, in the absence of any knowledge to the contrary.
+This will be true in almost all cases. But if, on parting, it does not
+lose at least two-thirds of its weight, this indicates that the
+assumption was not justified; and also what quantity of silver must be
+added to the button before again attempting to part. Generally the fault
+will be in the other direction; the silver will be in excess and the
+gold will break up and demand very careful treatment.
+
+If, however, such a button is yellow, then, from its weight and depth of
+colour, a rough estimate can be made of how much gold is contained in
+it. Silver must be added to make the total weight 3-1/2 times as much as
+that of the gold supposed to be present. Thus, if the button weighs 10
+milligrams and is supposed to contain 8 milligrams of gold, then 8
+multiplied by 3-1/2 is 28; the button must, in such case, be made up to
+28 milligrams by adding 18 milligrams of silver. In judging of the
+quality of the gold button, no ordinary error will very seriously affect
+the result. If, in the example just given, the quantity of gold present
+was really 7 or even 9 milligrams of gold, the resulting alloy would
+still have been suitable for such partings. In fact, in routine assays,
+where the quantity as well as the quality of the gold is known within
+fair limits, it is often the custom to add the silver for inquartation
+to the lead during the first cupellation.
+
+But in the assay of rich gold alloys such approximate work will not do.
+If the composition is not already known with a fair degree of accuracy
+_preliminary assays_ must be made. Weigh up two lots of 100 milligrams
+of the alloy and wrap each in 3 grams of lead. To one add 300 milligrams
+of silver. Cupel both. The button containing the added silver must be
+flattened and boiled with 15 c.c. of nitric acid; and the resulting
+gold must be washed, dried, ignited and weighed. This, in milligrams,
+gives directly the percentage of gold. The weight of the other button
+gives the percentage of gold and silver; the difference between the two
+gives the percentage of silver. The rest will, perhaps, be copper.
+
+The composition of the alloy being known, or having been determined as
+just described, the calculation of how much silver must be added is
+fairly simple. The following is an example. Suppose the bullion contains
+92 per cent. of gold, 1 per cent. of silver and 7 per cent. of copper,
+and that .5 gram of it is to be taken for an assay. The .5 gram, then,
+will contain
+
+  Gold        .460 gram
+  Silver      .005  "
+  Copper      .035  "
+
+But the total silver required is .46 gram × 2.5. This equals 1.15.
+Allowing for the .005 gram of silver already present, 1.145 gram of
+silver must be added.
+
+The silver is incorporated with the gold, and at the same time the
+copper is eliminated, by cupelling with sheet lead. How much sheet lead
+must be used will depend partly on how much bullion is taken, partly on
+how much copper it contains. Four grams of lead will do for a .5 gram
+charge; and for a .3 gram charge, 3 grams may be used. But with 20 per
+cent. of copper these amounts should be doubled; with 40 per cent. of
+copper they should be trebled; and with over 60 per cent. of copper four
+times as much lead should be used. For small buttons of gold as little
+lead as may be relied on to start cupelling may be taken; the lead may
+conveniently be in the form of little cups made by folding lead foil on
+a piece of glass rod. With a large number of bullion assays
+systematically worked and checked a simple plan would be to always use
+the quantity of lead required by the alloy containing most copper which
+turns up for assay. This weight, cut out of lead foil, would be kept in
+stock folded into little bags ready to receive the bullion and silver.
+
+The silver used for inquartation must, of course, be free from gold and
+is best prepared by the assayer who is to use it (see p. 66). It should
+not be in long strips or angular pieces likely to perforate the lead in
+which it is folded. When wrapped in the lead it should be in the middle
+and should make as compact a parcel as possible.
+
+Each little parcel, as completed, should be placed on a tray in its
+properly numbered compartment. Its position here should correspond to
+that it will occupy in the muffle and eventually in the cupel tray. The
+cupellation must be made with all the requisite precautions. A good
+smooth malleable button is needed for the next operation, which is known
+as flatting.
+
+[Illustration: FIG. 45.]
+
+~Flatting.~--Small buttons, such as are got in assaying most gold ores,
+are placed on a polished steel anvil and flattened by one or two blows
+with a hammer. The flattened discs are heated to dull redness on a clean
+cupel and are then ready for parting. Somewhat larger buttons may be
+similarly treated, but they should be annealed (_i.e._ heated to redness
+and allowed to cool) during the flattening. The silver-gold alloy left
+from the cupellation is soft and bends like lead; but after hammering or
+rolling it becomes harder, gets a spring in it like a piece of
+mainspring and cracks or splits somewhat easily. There should be no
+cracks or stripping or even roughness on the flattened metal, since such
+defects may cause the loss of small particles either during the
+flattening or in the subsequent treatment with acid. The softness of the
+metal is restored by heating. In bullion assays the flatting of the
+buttons requires care and practice for its skilful working. The strips
+of alloy for parting should be of uniform thickness and condition so
+that the action of the acid shall be equal in all cases. The button is
+taken from the cupel, cleaned and placed on the anvil: it is then struck
+a heavy blow which widens it to about 3/4 inch in diameter; this blow is
+followed by two others, one a little in front, the other behind, which
+lengthen the disc and give a very blunt roof-like slope to its upper
+face. It should then be annealed. This may be done by putting it in a
+just red-hot scorifier heated in a muffle: it very soon attains the
+right heat and may then be transferred to a cold scorifier; the hot
+scorifier should be put back into the muffle. The softened disc is then
+taken to the rolls (Fig. 45). The rolls are loosened until the disc can
+be pressed between them. Looking through the interval between them the
+rolls should appear exactly parallel; if they are not, one adjusting
+screw should be loosened and the other tightened until parallelism is
+obtained. The rolls are now turned and the disc should be drawn through
+without any great effort. Beginners are apt to err by trying to do too
+much with one turn of the handle. It is easy to stop whilst the rolls
+are only just gripping the metal and then to bring the disc back by
+reversing the action. If the disc was originally level and the rolls
+are parallel, the metal will appear as a strip which has been merely
+lengthened. If the rolls are tighter on one side the strip will be
+bowed; the tighter side will correspond with the outer curve of the
+crescent. A mistake of this kind may be amended by passing the strip
+through the rolls the other way, so as to reverse the irregularity and
+so straighten the strip. The screw on the looser side should then be
+tightened until parallelism is obtained; after which more care should be
+taken to tighten the two screws equally. The rolling should be stopped
+when the strip is 3 or 4 inches long and of the thickness of an ordinary
+visiting card. The strip should be annealed during the rolling and again
+at the finish.
+
+~Parting.~--The thin sheet of metal is dropped into hot dilute nitric
+acid and boiled for five or six minutes after the brisk action of the
+acid on the metal has ceased. At this stage nearly all the silver has
+gone into solution as nitrate of silver and the acid is charged with
+this salt. This acid is poured off and the residual metal is again
+boiled for from 20 to 30 minutes with a second lot of stronger acid.
+This leaves the gold almost pure, though it may still retain from .05 to
+.1 per cent. of silver. Treatment with the first acid only would
+probably leave three or four times as much.
+
+The _nitric acid_ used should be free from hydrochloric, sulphuric,
+iodic and telluric acids. In testing it for the first of these add
+nitrate of silver and dilute with distilled water; there should be no
+turbidity. In testing for the others evaporate three lots in dishes over
+a water-bath. Test one for sulphates by adding water and barium
+chloride. Test another for iodates by taking up with a little water,
+adding a few drops of starch paste and then dilute sulphurous acid
+solution a little at a time; there should be no blue colour. Test the
+third for tellurium by heating with 1 c.c. of strong sulphuric acid
+until dense fumes come off; allow to cool considerably; a piece of tin
+foil added to the warm acid develops a fine purple colour if only a
+trace of tellurium is present.
+
+The presence of lower oxides of nitrogen, which impart a brown colour to
+the acid, is objectionable; they, however, are removed by boiling the
+diluted acid before using it for parting. It is usual to keep a stock of
+the acid suitably diluted to the two strengths required for the parting.
+These are known as the parting acids. The _first parting acid_ is the
+weaker and is used in the first attack on the metal. The specific
+gravity generally recommended for it is about 1.2. It may be prepared
+either by diluting the strong acid with about its own volume of
+distilled water, or by suitably diluting the second parting acid which
+has been already used in an assay; the small proportion of silver this
+contains is not harmful for this purpose. The _second parting acid_ has
+a specific gravity of about 1.3, and may be made by diluting the strong
+acid with half its volume of distilled water.
+
+_Parting in Flasks._--Flasks are most convenient for the larger
+partings, as in bullion assays; and should always be used for this
+purpose unless some of the special parting apparatus, like that used in
+Mints, is available. Many assayers use flasks, though of a smaller size,
+for the ordinary partings in assaying gold ores. The flasks are either
+bulbs with long necks (Fig. 46) which ought to be heated on rose burners
+of special construction; or they are small flat-bottomed conical flasks
+which may be conveniently heated on a hot-plate and are, in this
+respect, much easier to deal with in general work. The following
+instructions apply to the parting of an alloy containing a few decigrams
+of gold together with the proper proportion of silver.
+
+[Illustration: FIG. 46.]
+
+The strip from the rolls, after being softened by annealing, is folded
+on itself on a glass rod into a roll or cornet. It should be so plastic
+that it will retain the shape thus given it and not spring open on
+removing the pressure of the fingers. About 50 c.c. of the first parting
+acid are placed in a 6-ounce conical flask and heated to boiling; the
+flask is then withdrawn, and tilted a little to one side, whilst the
+cornet is cautiously dropped into it; there will be a sudden issue of
+hot vapours and a prompt withdrawal of the hand is advisable. The flask
+is replaced on the hot plate and the acid is kept boiling for 10 or 15
+minutes. The flask is then withdrawn and the acid diluted with about an
+equal volume of distilled water. If the flask has a thick glass band
+around its neck, a little way down,[28] care must be taken to use hot
+water, for any sudden chill will certainly crack the flask where it is
+thus thickened. The liquor is carefully decanted into a clean beaker and
+is then thrown into a jar marked "waste silver." About 40 c.c. of the
+second parting acid, heated to boiling, is then poured into the flask,
+which is then replaced on the hot plate. The boiling is continued for 15
+or 20 minutes or even longer. At this stage bumping has to be specially
+guarded against; after a little experience it is easy to see when this
+is imminent and the flask should be withdrawn to a cooler part of the
+plate; it is better to prolong the heating at a temperature below
+boiling than to run the risk of disaster. Some of the older writers,
+however, are rather insistent on vigorous boiling with large bubbles.
+The addition of a small ball of well-burnt clay of about the size of a
+pea has been recommended, as it lessens the tendency to irregular and
+dangerous boiling. At the end of the treatment with the second acid the
+flask is withdrawn from the plate and the acid is diluted with an equal
+volume of distilled water. The liquor is carefully decanted into a
+beaker, and then poured into a jar or Winchester marked "acid waste"; it
+serves for making the first parting acid. The flask is then washed twice
+with hot distilled water; the washings must be carefully decanted from
+the gold. The flask is then filled with water. A parting cup (size B) is
+then placed over its mouth, like a thimble on the tip of a finger. This
+cup is of unglazed porous earthenware of such texture that it absorbs
+the last few drops of water left on drying; and with a surface to which
+the gold does not adhere even on ignition. The gold should fall out
+cleanly and completely on merely inverting the cup over the pan of the
+balance. The flask and cup are then inverted so that the flask stands
+mouth down in the cup; a little of the water from the flask flows into
+the cup, but only a little. The gold falls steadily through the water
+into the cup. When time has been allowed for even the finest of the gold
+to have settled into the cup, the flask is removed. This is easiest done
+under water. The cup, with the flask still resting in it, is dipped
+under water in a basin; as soon as the neck of the flask is immersed the
+crucible can safely be drawn away from under it and then lifted out of
+the water. The flask should not be taken away first, for the rush of
+water from it may easily sweep the gold out of the cup. The water in the
+cup is then drained off and the cup is dried at not too high a
+temperature; for if the last drop or two of water should boil there is
+danger of spattering the gold out of the crucible. When it is dry, the
+cup is heated on a pipe-clay triangle over a Bunsen burner, or on a slab
+of asbestos in a muffle, to a dull-red heat. This brings the gold to
+"colour"; that is, the loose tender dark coloured gold becomes bright
+yellow and coherent; and is in a state fit to be transferred to the
+balance and weighed. All unnecessary transferences must be avoided. As
+soon as the cup is cool it may be inverted over the pan of the balance,
+when the gold will fall out cleanly or, at the worst, a gentle tap with
+the finger will be sufficient to detach it.
+
+_Parting in test-tubes_, or in the smaller conical flasks, is used in
+the assay of gold ores of ordinary richness. The work is exactly like
+that just described in all its main features. Generally speaking much
+less acid will be used; for example, in test-tubes and for small
+buttons, 3 or 4 c.c. of each acid is quite enough. Again, the action
+need not be so prolonged; 10 or 15 minutes in each acid is sufficient.
+So, too, the heating may be less; it is very convenient to support the
+test-tubes in a water-bath, or merely to rest them in a beaker of
+boiling water; and there is no serious objection to doing this. A
+smaller parting cup should be used; the A size is suitable. The button,
+on the other hand, should be beaten thinner than is needed for the
+larger partings. If the silver should be in excess and the gold becomes
+much broken up, ample time should be given for subsidence from the
+test-tube or flask into the parting cup.
+
+_Parting in glazed crucibles or dishes._--This method of working has the
+advantage that there is no transference of the gold until it is placed
+on the pan of the balance. On the other hand, in the boiling more care
+is required in adjusting the temperature. The following instructions
+apply to the treatment of very small buttons, to which the method is
+more particularly applicable; but very little modification is needed for
+the treatment of larger buttons. The smallest sized Berlin crucibles
+answer admirably. They should be cleaned by treatment with hot and
+strong sulphuric acid, followed by washing in distilled water; the
+comfort and ease of working mainly depends on the thoroughness of this
+cleaning. The crucible, one-third full with the first parting acid, is
+heated on the hot plate until the acid is almost boiling. The flattened
+and annealed button is dropped into it and the heating continued with,
+at most, gentle boiling for a few minutes. The crucible is then filled
+with distilled water, which cools it enough for easy handling; and when
+the gold has settled the liquor is poured off along a glass rod into a
+clean beaker. Any greasiness of the crucible makes itself felt here and
+is very objectionable. The crucible is then one-third filled with the
+second parting acid and the heating resumed, care being taken not to
+raise the temperature too high; this should be continued much longer
+than before, say for five or ten minutes or even longer according to the
+size of the button. Distilled water is again added and, when it is
+drained off, the washing with distilled water is twice repeated. It will
+not be possible to drain off the last drop of water; but if the gold is
+coherent, the crucible can be so inclined that this drop drains away
+from the gold, in which case the drying can be done rapidly; the boiling
+of the water will do no harm. But when the gold is much broken up, it
+will collect in the middle of this drop and the drying must be done
+gently; best by putting the crucible in a warm place. When dry, the
+crucible is heated till the gold changes colour, but the heat must be
+kept well below redness. When cold, the gold is transferred directly to
+the pan of the balance. With minute specks of gold which will require
+measuring, it is best to put a small piece of lead foil (say .1 gram) in
+the crucible over the gold, and then heat the crucible to above redness
+over a blowpipe. Whilst the lead is oxidising it is easily swept round
+in a bath of molten litharge by merely tilting the crucible. In this way
+any separated specks of gold can be taken up with certainty. When the
+worker is satisfied that the lead has had ample opportunity for taking
+up the gold, the lead must be kept in one place and the heat slowly
+lowered. By this means the button becomes supported in comparatively
+pure litharge and when solid can be picked out quite easily with a pair
+of pliers and in a very clean condition. The lead button is then
+cupelled on a very fine cupel, as already described. The method of
+working last described destroys the crucible. If the gold is not quite
+so small this may be avoided. A small piece of lead foil should be
+hammered out until it is perfectly flexible. It is then shaped into a
+tray and the gold is transferred to it. The lead is then folded over,
+with the help of two pins; and cupelled.
+
+If the crucible shows a black stain on heating it is because some silver
+remains through bad washing. It shows poor work and the assay should be
+repeated.
+
+_The silver retained in the gold after parting_ is, in bullion assays,
+an important matter; it is roughly equal to the loss of gold due to
+absorption by the cupel. Mr. Lowe working on .5 oz. of gold, obtained by
+parting in assaying bullion, found it to contain .123 per cent. of
+silver. Dr. Rose in some special assay pieces found by a less direct
+method of assaying, from .06 to .09 per cent. of silver. The proportion
+of silver retained varies in a marked way with the proportion of gold to
+silver in the alloy before parting. It is generally stated that the
+retained silver is least when this proportion is 1 to 2-1/2, and more or
+less silver than this leads to a less pure gold after parting.
+
+_Platinum_ in an alloy being parted is dissolved along with the silver
+either altogether or in part. It imparts a straw yellow colour to the
+parting acid. _Palladium_ gives an orange colour to the acid.
+
+_The loss of gold by solution in the acid during parting_ is small, but
+easily demonstrable. On a 500-milligram charge of bullion it may amount
+to from .05 to .15 milligram; _i.e._ from .01 to .03 per cent. It is due
+to gold actually dissolved and not merely held in suspension.
+
+~Assaying with checks. Surcharge.~--It will be seen from what has been
+stated that the errors in gold parting are of two kinds: viz. (1) a loss
+of gold on the cupel and to a less extent by solution in the acid, and
+(2) an apparent gain of gold due to the retention of silver in the
+parted material. Both errors are small, and as they are of an opposite
+character they tend to neutralise each other. Hence they are altogether
+without effect on the accuracy of the assays of ores when the total gold
+is reckoned in milligrams. And even with the larger amounts present in
+bullion assays their influence is so small that an uncorrected result is
+still fairly accurate; the resultant error would not be more than one
+part in two or three thousand.
+
+It is customary to report the purity of bullion, or its fineness as it
+is called, in parts per thousand of bullion. The sum of the errors of an
+assay, which is called the _surcharge_, is reported in the same way.
+Thus a surcharge of + .3 means that the gold as weighed was .3 part per
+1000 more than the gold actually present. But a surcharge - .3 means
+that on the whole there was a loss of .3 part per 1000 in the assay.
+
+Speaking roughly the retained silver will vary with the weight of gold
+present; if one alloy contains twice as much gold as another the
+retained silver will be about twice as much also. On the other hand, as
+already explained, the cupellation loss on the poorer alloy is as much
+as, or even more than, with the richer one, because of the copper, &c.
+present. With rich gold alloys the silver more than compensates for the
+loss and the surcharge is positive; but with poorer alloys the loss is
+greater and the surcharge is negative.
+
+In Mints and places where bullion assays must be made with the highest
+attainable accuracy, the surcharge is determined by experiment, and the
+proper correction is made in the reports on the bullion. This is done by
+making assays of gold of the highest degree of purity alongside of those
+of the bullion whose quality has to be determined. These "checks" are so
+made that they do not differ from the actual assays in any material
+point. Thus, being of the same quality and weight and undergoing exactly
+the same treatment, they may reasonably be expected to have the same
+surcharge as the assays they imitate. Suppose the bullion being assayed
+varies only a little, up or down, from 900 gold and 100 copper in the
+thousand, and that .5 gram of it is used in each assay. A quantity of
+gold differing only a little from .450 gram would be very exactly
+weighed and placed with .050 gram of copper in the same weight of lead
+as is being used in the other assays. It would be cupelled, parted, &c.,
+as nearly as possible under the same conditions as the actual assays.
+Suppose the pure gold weighed .45016 gram and the parted gold weighed
+.45025 gram, the gain in weight, .00009 gram, would be deducted from the
+actual assays. A surcharge correction is never applied except to bullion
+of the same quality as that represented by the "check assay" it was
+calculated from.
+
+It is evident that unless the gold is of the highest degree of purity
+these check assays will introduce an error almost equal to that which it
+is designed to remedy. Moreover, to work the checks to the greatest
+advantage, a very systematic and uniform method of working must be
+adopted.
+
+~Parting in special apparatus.~--One plan for obtaining greater
+uniformity is to stamp each cornet with a number for purposes of
+identification, and to treat several, including one or more check assays
+in the same acid contained in a beaker; all the assays under these
+conditions evidently receive precisely the same acid treatment. Such a
+plan can of course only be adopted where there is no risk of the gold
+breaking up during the parting. An improvement on this is to have a
+porcelain basin[29] about 8-1/2 inches in diameter and with a capacity
+of about 1-1/2 litres. It is provided with a porcelain cover with 30
+numbered holes through which tubes dip into the acid. The cover is
+removable. The tubes are like test-tubes and are supported by the cover;
+their bottoms are perforated with holes or slits. The acid is placed in
+the basin and boiled over a flat burner; it enters the tubes through the
+slits. The cornets are placed each in its proper tube. When the boiling
+is finished, the cover with the tubes is lifted and at the same time the
+acid drains back into the basin. A dip into a basin of distilled water
+washes at one operation all 30 assays. The cover is then put on a basin
+containing the stronger parting acid which is already boiling. This
+boiling is continued for half an hour. The cover with the 30 cornets is
+then lifted out from the acid and dipped two or three times in distilled
+water to wash off the last traces of acid. To transfer the cornets from
+the tubes to the porous cups the whole of the tube must be dipped under
+the water; otherwise the operation is exactly as when working with
+test-tubes.
+
+A still simpler method of working is to use small platinum cups[30]
+provided with fine slits which admit the acid but retain the gold. A
+number of these, say 60, are supported on a platinum tray. The parting
+acids are boiled in platinum dishes under a hood; and the 60 cornets
+(each in its proper cup) are placed in the acid all at once: the tray
+carrying the cups is provided with a handle suitable for this purpose.
+After a proper boiling the tray is lifted out of the weaker acid into
+the stronger one, where it undergoes the second boiling. It is next
+dipped several times in distilled water and lastly, after a gentle
+drying, it is raised to an annealing temperature which must not be too
+high for fear of the gold sticking to the platinum. After cooling, the
+cornets are transferred from the platinum cups directly to the pan of
+the balance. Here all 60 cornets have exactly the same treatment and the
+"checks" may be compared with great exactness with the other assays
+accompanying them. There is, too, a great saving of labour.[31]
+
+~Silver, &c., in gold bullion.~--The base metals are generally
+determined by cupelling .5 gram of the alloy with 5 grams of lead. The
+loss in cupellation having been allowed for by any of the usual methods
+(see p. 104) the gold and silver contents are given. By deducting the
+gold the proportion of silver is obtained. The silver is generally
+determined by difference in this way. If it is desired to dissolve out
+the copper, silver, &c., and to determine them in the wet way, the gold
+must first be alloyed with a sufficiency of some other metal to render
+it amenable to the attack by acid. Cadmium is the metal generally
+recommended, and the alloy is made by melting together a weighed portion
+of the gold with five or six times its weight of cadmium in a Berlin
+crucible and under a thin layer of potassium cyanide.
+
+~Lead with gold or silver.~--Large quantities of lead carrying gold and
+silver are sold to refiners in bars weighing about 100 lbs. each. The
+assay of these alloys presents no special difficulties, but the sampling
+of them is a question which may be profitably discussed.[32]
+
+A molten metal may be conceived to have all the physical states observed
+in ordinary liquids, although these cannot be actually seen owing to its
+opaqueness. There is no doubt that _pure_ lead at a temperature only a
+little above its melting-point can contain a large proportion of gold in
+such a manner that it may in a figurative way be spoken of as a clear
+solution. Any small portion withdrawn from the molten metal would afford
+a perfect sample. The same would be true of any pure alloy of lead and
+silver in which the silver does not exceed the proportion of 2-1/2 per
+cent.[33] On the other hand, if the molten metal contains much more than
+.5 per cent. of zinc, more than .1 per cent. of copper, or a larger
+quantity of silver, it may be likened to a turbid liquor. The
+resemblance holds good so far that if the molten lead be further heated,
+whereby its solvent power on the added metal is increased, the turbidity
+will disappear, or at least be considerably diminished. A portion taken
+at random from such a molten metal may, or may not, give a good sample.
+The suspended insoluble matter will tend to concentrate itself in the
+upper or lower parts of the liquid according to whether it is heavier or
+lighter than it; and this separation may occur with extreme slowness or
+with fair rapidity. However, it is generally agreed that in the case of
+such alloys as occur in practice, samples taken in this way are quite
+satisfactory and are the best obtainable. The precautions insisted on
+are that the lead shall be made as hot as practicable; that it shall be
+stirred up at the time of taking the sample; and that the portion
+withdrawn shall be taken out with a ladle at least as hot as the molten
+metal. The further precaution that if any dross be on the surface of the
+metal it shall be skimmed off and separately sampled and assayed is
+almost too obvious to require mention. An alternative and, perhaps,
+better way of taking the sample is to withdraw portions at equal
+intervals from the stream of metal whilst the pot is being emptied;
+equal weights taken from these portions and mixed (by melting or in some
+other way) give a fair sample of the whole. In addition, separate assays
+of each portion will show to what extent the metal lacks uniformity in
+composition For example, samples taken at the beginning, middle, and end
+of a run gave the following results in ozs. of silver per ton: 475, 472,
+466, showing an average result of 471 ozs. Fifteen fractions taken at
+regular intervals during the same pouring ranged from 475 ozs. to 464
+ozs.: the average result was 469.8 ozs. The same lead cast into bars and
+sampled by sawing gave an average of 470 ozs.[34] In another case[35]
+samples drawn at the beginning, middle, and end of a run gave 1345 ozs.,
+1335 ozs. and 1331 ozs. The mean result in such cases is always a
+reasonably safe one, but evidently where the metal varies a good deal it
+is safer to take more than three dips.
+
+Imagine such lead run into moulds and allowed to become solid as bars;
+the difference between bar and bar would not be greater than that
+between corresponding dip samples. But in each bar the distribution of
+the silver and gold is very seriously affected during solidification.
+Chips taken from the same bar of auriferous lead may show in one place
+23 ozs. of gold to the ton, in another 39 ozs.; similarly with silver
+they may vary as much as from 900 ozs. to 1500 ozs. to the ton.
+
+This rearrangement of the constituents of a bar takes place whilst the
+lead is partly solid, partly liquid. The most useful conception of such
+half-solidified metal is that of a felted spongy mass of skeleton
+crystals of comparatively pure lead saturated with a still fluid
+enriched alloy. If the solidification of an ingot of impure tin be
+watched it will be evident that the frosted appearance of the surface is
+due to the withdrawal of the fluid portion from a mat of crystals of
+purer tin which have been for some time solid and a contraction of the
+mass. The shrinking of the last part to become solid is further shown by
+the collapse of the surface of the ingot where weakest; that is, a
+furrow is formed on the flat surface. In other cases of fused metal
+there is expansion instead of contraction in this final stage of the
+solidification, and the enriched alloy then causes the upper face of the
+ingot to bulge outwards. There are other causes effecting the
+redistribution of the metals through the ingot. There can be no general
+rule of wide application showing which part of a bar is richest and
+which poorest in the precious metals. This will depend on the quantities
+of gold or silver, on the quantities and kinds of other metals present
+and on the manner of casting. The student is advised to consult Mr.
+Claudet's paper which has been already referred to.
+
+The best method of sampling such bars is to melt them all down and to
+take a dip sample of the molten metal in one or other of the methods
+already described. According to Mr. Claudet this should be done in all
+cases where the gold exceeds one or two ounces or where the silver
+exceeds 200 ozs. to the ton. If during the melting down some dross has
+formed this must be skimmed off, weighed and separately sampled and
+assayed. The clean lead also must be weighed, sampled and assayed. The
+mean result must be calculated. Thus 14 tons 5 cwts. of clean lead
+assaying 32 ozs. to the ton will contain 456 ozs. of silver; 15 cwt.
+dross assaying 20 ozs. to the ton will contain 15 ozs. of silver. The 15
+tons of lead and dross will contain 471 ozs. of silver or 31.4 ozs. per
+ton.
+
+Of the methods of sampling which avoid melting the bars, that known as
+sawing is the only one which is thoroughly satisfactory. In it the bars
+are brought to a circular saw having fine teeth and are sawn across
+either completely or halfway through; in this way a quantity of lead
+sawdust is obtained (say 1 lb. or so from a bar) which represents
+exactly the average of the bar along the particular cross section taken
+and approximately that of the whole bar. A bar of lead, which by dip
+assay gave 334 ozs. to the ton, gave on three transverse sections 333
+ozs., 335 ozs. and 331 ozs. The variation may be greater than this, but
+with a large number of bars, where each bar is cut across in as far as
+possible a different place, these variations tend to neutralise each
+other and a good sample is obtained. Two or three cwt. of sawdust may be
+obtained in this way; this is thoroughly mixed and reduced by
+quartering in the usual way or by a mechanical sampler. A sample of 2 or
+3 lbs. is sent to the assayer. This being contaminated with the oil used
+in lubricating the saw is freed from it by washing with carbon
+bisulphide, ether or benzene and dried. Then, after mixing, 100 to 200
+grams of it are carefully weighed and placed in a hot crucible, the heat
+of which should be sufficient to melt all the lead. The molten lead
+should not be overheated and should show no loss due to the melting. The
+removal of the oil may have decreased the weight by perhaps one half per
+cent. If the lead gives dross on heating it may be melted under 10 or 20
+grams of potassium cyanide, which prevents the formation of dross.
+Samples are sometimes taken with a drill, gouge or chisel, though no
+method of this kind is quite satisfactory. One plan adopted is to use a
+punch which, when driven into the bar, gives a core or rod of metal
+about half as long as the bar is thick and about one-eighth of an inch
+across. With five bars side by side it is customary to drive in the
+punch at one end on the first bar, and at the opposite end on the last
+one, and on the others in intermediate positions in such a manner that
+all the holes will be along a diagonal of the rectangle enclosing the
+bars. The bars are then turned over and similar portions punched out
+through the bottoms of the bars and along the other diagonal. Or one set
+of five may be sampled along the top and the next set along the bottom
+of the bars.
+
+Silver and gold present in bars of copper are subject to the same
+irregularity of distribution as in lead. The sampling of such bars is
+guided by the same principles.[36]
+
+
+CYANIDES.
+
+The cyanides ought perhaps to be considered along with chlorides,
+bromides and iodides in Chapter XV. But they are treated here because
+they owe their importance to their use in the extraction of gold and
+because their determination has become a part of the ordinary work of an
+assayer of gold ores.
+
+Formerly, the cyanide most easily obtained in commerce was potassium
+cyanide; and it was generally sold in cakes which might contain as
+little as 40 per cent. or as much as 95 per cent. of the pure salt. It
+became customary to express the quality of a sample of commercial
+cyanide by saying it contained so much per cent. of potassium cyanide.
+The commercial product now made by improved methods of manufacture is
+actually sodium cyanide, but is called "potassium cyanide" (probably
+with the words "double salt" on the label); it contains cyanide
+equivalent to something over 100 per cent. of potassium cyanide in
+addition to a large proportion of sodium carbonate and other impurities.
+What is wanted in most cases is merely a soluble cyanide, and it is a
+matter of indifference whether the base be sodium or potassium. But
+since 49 parts of sodium cyanide (NaCN = 49) are equivalent to 65 parts
+of potassium cyanide (KCN = 65) it is evident that a pure sample of
+sodium cyanide would contain cyanide equivalent to little less than 133
+per cent. of potassium cyanide. Therefore a sample of cyanide reported
+on in this way may be rich in cyanide, and yet have much impurity.
+
+The commonest impurity in commercial cyanide is carbonate of sodium or
+potassium. This may be tested for by dissolving, say, 2 grams in a
+little water and adding barium chloride. There may be formed a white
+precipitate of barium carbonate, which if filtered off, washed and
+treated with acid, will dissolve with effervescence. Cyanate may be
+tested for in the solution from which the barium carbonate has been
+filtered by adding a little soda and boiling; if cyanates are present
+they decompose, giving off ammonia (which may be tested for in the
+steam) and yielding a further precipitate of barium carbonate.[37] If
+the soda alone gave a further precipitate of barium carbonate, this may,
+perhaps, be due to the presence of bicarbonates. Alkaline sulphides may
+be present in small quantity in commercial cyanide. Their presence is
+shown at once when the sample is being tested for its strength in
+cyanide, inasmuch as the first few drops of silver nitrate solution
+produce at once a darkening of the liquor. A special test for sulphide
+may be made by adding a drop or two of solution of acetate of lead to
+four or five c.c. of soda solution and adding this to a clear solution
+of the suspected cyanide. This will cause a black precipitate or colour,
+if any sulphide is present.
+
+The cyanides of the heavier metals combine with the alkaline cyanides to
+form double cyanides. Some of these, ferrocyanide and ferricyanide of
+potassium for example, have such characteristic properties that the fact
+that they are cyanides may be overlooked. Others, such as potassium zinc
+cyanide (K_{2}ZnCy_{4}), have much less distinctiveness: they behave
+more or less as a mixture of two cyanides and are, moreover, so easily
+decomposed that it may be doubted if they can exist in dilute alkaline
+solutions. In reporting the cyanide strength of a cyanide liquor as
+equivalent to so much per cent. of potassium cyanide, there is a
+question as to whether the cyanide present in the form of any of these
+double cyanides should be taken into account. It must be remembered that
+the object of the assay is not to learn how much of the cyanide exists
+in the solution as actual potassium cyanide; reporting the strength in
+terms of this salt is a mere matter of convenience; what is really
+desired is to know how much of the cyanide present in the liquor is
+"free" or "available" for the purposes of dissolving gold. Every one is
+agreed as to the exclusion of such cyanides as the following: potassium
+ferrocyanide (K_{4}FeCy_{6}), potassium ferricyanide (K_{3}FeCy_{6}),
+potassium silver cyanide (KAgCy_{2}), and potassium aurocyanide
+(KAuCy_{2}); and the double cyanides with copper or nickel. But with
+cyanide liquors containing zinc the position is less satisfactory. One
+method of assay gives a lower proportion of cyanide when this metal is
+present; and the loss of available cyanide thus reported depends, though
+in a fitful and uncertain way, upon the quantity of zinc present. The
+other method of assay reports as full a strength in cyanide as if no
+zinc were present. Unfortunately, using both methods and accepting the
+difference in the results as a measure of the quantity of zinc present,
+or at any rate of the zinc present as cyanide, is not satisfactory. It
+appears best to use the method which ignores the zinc; and to determine
+the amount of zinc by a special assay of the liquor for this metal.
+
+The cyanide present as hydrogen cyanide or prussic acid (HCy) is
+practically useless as a gold solvent. Hence any report on the strength
+of a cyanide liquor which assigned to this the same value as its
+equivalent of alkaline cyanide would be misleading. On the other hand,
+it is "available cyanide" inasmuch as a proper addition of sodium
+hydrate[38] would restore its value. The question of the presence or
+absence of free prussic acid is involved in the larger one as to whether
+the cyanide solution has the right degree of alkalinity. The assay for
+"cyanide" should include the hydrogen cyanide with the rest.
+
+A rough test of the power of a cyanide liquor for dissolving gold may be
+made by floating a gold leaf on its surface and noting the time required
+for its solution. This test might, perhaps, be improved by taking, say,
+20 c.c. of the liquor and adding three or four gold leaves so that the
+gold shall always be in considerable excess. The liquor should not be
+diluted as this will affect the result. It should be allowed to stand
+for a definite time, say at least two or three hours, or better, that
+corresponding to the time the liquor is left in contact with the ore in
+actual practice. The liquor should then be filtered off and, with the
+washings, be evaporated in a lead dish as in the assay of cyanide
+liquors for gold (p. 141). The gold obtained on cupelling, less any gold
+and silver originally present in the liquor, would be the measure of the
+gold dissolving power.
+
+
+THE ASSAY FOR CYANIDE BY TITRATION WITH SILVER NITRATE.
+
+The determination of the quantity of a cyanide is made by finding how
+much silver nitrate is required to convert the whole of the cyanide into
+potassium silver cyanide[39] or one of the allied compounds. It will be
+seen from the equation that 170 parts by weight of silver nitrate are
+required for 130 parts by weight of potassium cyanide. As already
+explained it is customary to report the cyanide-strength in terms of
+potassium cyanide, even when only the sodium salt is present. One gram
+of potassium cyanide will require 1.3076 gram of silver nitrate. _The
+standard solution of silver nitrate_ is made by dissolving 13.076 grams
+of silver nitrate in distilled water and diluting to 1 litre; 100 c.c.
+of such a solution are equivalent to 1 gram of potassium cyanide.[40]
+
+The titration is performed in the usual way, running the standard
+solution of silver nitrate into a solution containing a known weight or
+volume of the material containing the cyanide. The _finishing point_ is
+determined in one of two ways, both of which are largely used. In the
+first place, as long as there remains any free cyanide in the solution
+the silver nitrate will combine with it forming the double cyanide and
+yielding a clear solution; but as soon as all the free cyanide is used
+up the silver nitrate will react with the double cyanide[41] forming
+silver cyanide, which separates as a white precipitate and renders the
+solution turbid. But, in the second place, if potassium iodide is
+present in the solution the excess of silver nitrate will react with
+it,[42] rather than with the double cyanide; and silver iodide will
+separate as a yellowish turbidity which is easily recognised.
+
+In working with pure solutions, the two finishing points give the same
+results; and this is true even when there is much difference in the
+degree of dilution. The finishing point with the iodide, however, has
+an advantage in precision. Moreover, it is but little affected by
+variations in alkalinity, which render the other finishing point quite
+useless. The great difference between the two is shown when zinc is
+present in the solution. In this case, when working without the iodide,
+the first appearance of a turbidity is less distinct; the turbidity
+increases on standing and as a finishing point is unsatisfactory. It can
+be determined with precision only by very systematic working and after
+some experience. The turbidity is due to the separation of an insoluble
+zinc compound. A most important point (to which reference has already
+been made) is that less silver nitrate is required to give this
+turbidity and, consequently, a lower strength in cyanide is reported. On
+the other hand, as much silver nitrate is required to give the yellow
+turbidity due to silver iodide as would be required if no zinc were
+present.
+
+Unfortunately the difference in the two titrations does not depend
+merely on the quantity of zinc present; as it is also influenced by the
+extent of dilution, the degree of alkalinity of the solution, and the
+quantity of cyanide present. In an experiment with .055 gram of zinc
+sulphate and .1 gram of potassium cyanide the difference in the two
+finishing points was only .1 c.c.; whereas with .4 gram of potassium
+cyanide, the other conditions being the same, the difference was 1.5
+c.c. of standard silver nitrate. On the assumption that all the zinc was
+present as potassium zinc cyanide (K_{2}ZnCy_{4}) the difference should
+have been 5 c.c. in each case. Again, repeating the experiment with .4
+gram of potassium cyanide, but with .11 gram of crystallised zinc
+sulphate, the difference was 6.5 c.c.: that is, merely doubling the
+quantity of zinc increased the difference by more than four times. Hence
+it would appear better to use the method with the iodide and make a
+separate assay for the zinc. But since the student may be called on to
+use the other method, he is advised to practice it also.
+
+~The assay without iodide.~--The standard solution of silver nitrate is
+placed in a small burette divided into tenths of a c.c. Ten c.c. of the
+cyanide solution to be assayed is transferred to a small flask and
+diluted with water to about 70 c.c. The silver solution is then run in
+from the burette (with constant shaking of the flask), a little at a
+time but somewhat rapidly, until a permanent turbidity appears. Since 1
+c.c. of the silver nitrate solution corresponds to .01 gram of potassium
+cyanide, it also corresponds to .1 per cent. of this salt counted on the
+10 c.c. of cyanide solution taken. The titration should be performed in
+a fairly good uniform light. The learner should practice on a fairly
+pure solution of potassium cyanide at first, and this may conveniently
+have a strength of about 1 per cent. For practice with solutions
+containing zinc make a solution containing 1.1 gram of crystallised zinc
+sulphate in 100 c.c. and slowly add measured quantities of from 1 to 5
+c.c. of this to the 10 c.c. of cyanide liquor before diluting for the
+titration.
+
+If a cyanide solution blackens on the addition of the silver nitrate it
+contains sulphide. In this case, shake up a considerable bulk of the
+liquor with a few grams of lead carbonate, allow to settle and make the
+assay on 10 c.c. of the clear liquor.
+
+If the cyanide liquor be suspected to contain free prussic acid, take 10
+c.c. for the assay as usual; but, before titrating, add .1 or .2 gram of
+sodium carbonate. On no condition must caustic soda or ammonia be added.
+The difference between the results, with and without the addition of
+carbonate of soda, is supposed to measure the quantity of free prussic
+acid. If this has to be reported it is best done as "prussic acid
+equivalent to ... per cent. of potassium cyanide." Suppose, for example,
+the difference in the two titrations equals 1 c.c. of standard silver
+nitrate; the prussic acid found would be equivalent to .1 per cent. of
+potassium cyanide.
+
+~The assay with iodide.~--The standard solution of silver nitrate is
+placed in a burette divided into tenths of a c.c. Take 10 c.c. of the
+cyanide liquor, which should previously have been treated with white
+lead for the removal of sulphides if these happened to be present.
+Transfer to a small flask, add 3 or 4 drops of a solution of potassium
+iodide and 2 or 3 c.c. of a solution of sodium hydrate; dilute to 60 or
+70 c.c. with water. If much zinc is present the soda may be increased to
+20 or 30 c.c. with advantage. The standard solution should be run in
+somewhat rapidly, but a little at a time, so that the precipitate at
+first formed shall be small and have only a momentary existence. The
+titration is continued until there is a permanent yellowish turbidity.
+The most satisfactory and exact finish is got by ignoring any faint
+suspicion of a turbidity and accepting the unmistakable turbidity which
+the next drop of silver nitrate is sure to produce. This finishing point
+gives results which are exactly proportional to the quantity of cyanide
+present; and it can be recognised with more than ordinary precision even
+in solutions which are not otherwise perfectly clear.
+
+Each c.c. of the standard silver nitrate solution corresponds to .01
+gram of potassium cyanide; and if 10 c.c. of the liquor are taken for
+assay this corresponds to .1 per cent. or 2 lbs. to the short ton or
+2.24 lbs. to the long ton. As already explained the result should be
+reported as "cyanide equivalent to so much per cent. of potassium
+cyanide."
+
+The following experimental results were obtained with a solution of
+potassium cyanide made up to contain about 1.2 per cent. of the salt.
+
+~Effect of varying cyanide.~--The bulk before titration was in each case
+60 c.c.; 2 c.c. of soda and 3 drops of potassium iodide were used in
+each case.
+
+  Cyanide added   40 c.c.   30 c.c.    20 c.c.   10 c.c.   5 c.c.   1 c.c.
+  Silver required 47.0 c.c. 35.25 c.c. 23.5 c.c. 11.7 c.c. 5.8 c.c. 1.15 c.c.
+
+Accepting the result for 40 c.c. as correct, the others are in very
+satisfactory agreement.
+
+~Effect of varying dilution.~--The conditions were those of the 40 c.c.
+experiment in the last series; but varying amounts of water were used in
+diluting.
+
+  Water added        none       100 c.c.   200 c.c.   400 c.c.
+  Silver required    47.0 c.c.  47.0 c.c.  47.0 c.c.  47.05 c.c.
+
+Very considerable dilution therefore has no effect.
+
+~Effect of varying soda.~--The conditions were those of the 40 c.c.
+experiment in the first series, except that varying amounts of soda
+solution were used.
+
+  Soda added        none        10 c.c.   30 c.c.
+  Silver required   46.95 c.c.  47.0 c.c. 47.0 c.c.
+
+This alkali therefore has no prejudicial effect.
+
+~Effect of ammonia.~--Soda causes turbidity in some cyanide liquors;
+with these it should be replaced by 2 or 3 c.c. of dilute ammonia with a
+gram or so of ammonium chloride. The following experiments with dilute
+ammonia show that larger quantities of this reagent must be avoided.
+
+  Ammonia added      none      10 c.c.     30 c.c.    60 c.c.
+  Silver required  46.95 c.c.  47.15 c.c.  47.7 c.c.  49.5 c.c.
+
+~Effect of sodium bicarbonate.~--In this experiment 1 gram of
+bicarbonate of soda was used instead of the soda or ammonia of the other
+experiments. The silver nitrate required was only 46.45 c.c. instead of
+the 47.0 c.c. which is the normal result. This is probably due to the
+liberation of prussic acid and shows the importance of having the
+solution alkaline.
+
+~Effect of zinc.~--In each experiment 40 c.c. of the cyanide solution
+and .5 gram of zinc sulphate crystals were used and the bulk was made up
+to 100 c.c. before titrating.
+
+  Soda added        1 c.c.     5 c.c.    10 c.c.    25 c.c.
+  Silver required  47.1 c.c.  47.0 c.c.  46.9 c.c.  46.9 c.c.
+
+The work was easier with the more alkaline solutions. The titration in
+the presence of zinc is comparatively easy, but, in learning it, it is
+well to have a burette with cyanide so that if a titration be overdone
+it can be brought back by the addition of 1 or 2 c.c. more cyanide and
+the finish repeated; a quarter of an hour's work in this way will ensure
+confidence in the method.
+
+~Effect of other substances.~--It was found that an alkaline cyanate,
+sulphocyanate, ferrocyanide, nitrite, borate, silicate or carbonate has
+no effect. The ferricyanide had a small influence and, as might be
+expected, hyposulphite is fatal to the assay. The addition of salts of
+lead and cadmium was without effect. On the other hand, nickel produces
+its full effect; and the quantity of nickel added can be calculated with
+accuracy from the extent of its interference with the titration.
+
+~Assay of commercial cyanide of potassium.~--Break off 20 or 30 grams of
+the cyanide in clean fresh pieces, weigh accurately to the nearest
+centigram. Dissolve in water containing a little sodium hydroxide;
+transfer to a 2-litre flask: dilute to 2 litres; add a few grams of
+white lead; shake up and allow to settle. Run 50 c.c. of the clear
+liquor from a burette into an 8 oz. flask; add 2 or 3 c.c. of soda
+solution and 3 drops of potassium iodide. Titrate with the standard
+solution of silver nitrate. The percentage may be calculated by
+multiplying the number of c.c. used by 40 (50 c.c. is one fortieth of
+the 2 litres) and dividing by the weight of commercial cyanide
+originally taken.
+
+~Alkalinity of commercial potassium cyanide and of cyanide
+solutions.~--Hydrocyanic acid like carbonic acid has no action on
+methyl-orange;[43] hence the alkaline cyanides may be titrated with
+"normal acid" as easily as the carbonates or hydrates. 100 c.c. of
+normal acid will neutralise 6.5 grams of pure potassium cyanide.[44] A
+solution of commercial cyanide prepared as for the assay last described,
+but best without the addition of white lead, may be used for the test.
+Take 50 c.c. of it; tint faintly yellow with methyl-orange and titrate
+with normal acid till the liquor acquires a permanent reddish tint. In
+the case of the purer samples of cyanide the quantity of acid used will
+correspond exactly with that required to neutralise the actual quantity
+of cyanide present as determined by the assay with nitrate of silver.
+The less pure samples will show an excess of alkalinity because of the
+presence of sodium carbonate or of potassium carbonate.
+
+In comparing the alkalinity and cyanide strength of a solution the
+simplest plan is to take 65 c.c. of the solution and titrate with
+normal acid; for in this case each c.c. of normal acid corresponds to .1
+per cent. of potassium cyanide. In systematic assays of this kind, the
+alkalinity would no doubt be generally in excess of that required by the
+cyanide present: there would be no inconvenience in recording such
+excess in terms of potassium cyanide.
+
+~Determination of the acidity of an ore.~--Most ores have the power of
+destroying more or less of the alkalinity of a cyanide solution and in a
+proportionate degree of damaging its efficiency. An assay is needed to
+determine how much lime or soda must be added for each ton of ore in
+order to counteract this. Whether this acidity should be reported in
+terms of the lime or of the soda required to neutralise it will depend
+on which of these reagents is to be used in the actual practice. Again,
+if the ore is washed with water before treating with cyanide on the
+large scale, then the assay should be made of the acidity of the ore
+after a similar washing.
+
+The _standard solutions of acid and alkali_ used for this determination
+may be one-fifth normal. 200 c.c. of the normal solution should be
+diluted to 1 litre in each case, 1 c.c. of the resulting solutions would
+be equivalent to 8 milligrams of soda (NaHO) or 5.6 milligrams of lime,
+CaO. It must be remembered this refers to the pure bases in each case.
+Suppose it is desired to report as so many lbs. of lime to the short ton
+(2000 lbs.) of ore. Since 1 c.c. of the standard solution is equivalent
+to 5.6 milligrams of lime, if we take 2000 times this weight of ore
+(_i.e._ 11,200 milligrams or 11.2 grams) for the assay, each c.c. of
+standard solution will be equivalent to 1 lb. of lime to the short
+ton.[45]
+
+~Total acidity.~--Weigh out 11.2 grams of the ore, place them in a
+four-inch evaporating dish and measure on to it from a burette 10 or 20
+c.c. of the standard solution of soda. Stir the soda solution into the
+ore and allow to stand for 15 or 20 minutes with occasional stirring.
+Stir up with 30 or 40 c.c. of water, float a piece of litmus paper on
+the liquid and titrate with the standard solution of acid. If the ore is
+strictly neutral the quantity of "acid" required to redden the litmus
+will be the same as the quantity of "soda" originally used. If the ore
+is acid, less acid will be used. For example, if 10 c.c. of soda were
+used and only 7 c.c. of acid were required, the ore will have done the
+work of the remaining 3 c.c. of acid. And the ton of ore will require 3
+lbs. of lime to neutralise its acidity.
+
+~Acidity after washing.~--Take 11.2 grams of the ore; wash thoroughly
+with water and immediately treat the residue, without drying, exactly as
+just described.
+
+~Examination of cyanide solutions for metals, &c.~--Take a measured
+quantity of the solution, say 20 c.c.[46] and evaporate in a small dish
+with, say, half a c.c. of strong sulphuric acid. Evaporate at first, on
+a water-bath in a well ventilated place, but finish off with a naked
+Bunsen flame, using a high temperature at the end in order to completely
+decompose the more refractory double cyanides. Allow to cool; moisten
+with strong hydrochloric acid; warm with a little water and test for the
+metals in the solution by the ordinary methods. Since the quantities of
+the metals likely to be present may be given in milligrams the work must
+be carefully performed. It may be worth while to determine the
+proportions of lime and magnesia as well as those of the metals proper.
+
+Or the 20 c.c. of cyanide liquor may be evaporated with 5 c.c. of strong
+nitric acid to dryness and gently ignited and the residue taken up with
+2 or 3 c.c. of strong hydrochloric acid.
+
+Copper, iron, and zinc can be rapidly determined in such a solution, as
+follows. Dilute with water to 10 or 15 c.c., add an excess of ammonia,
+and filter. The precipitate will contain the iron as ferric hydrate;
+dissolve it in a little hot dilute sulphuric acid: reduce with
+sulphuretted hydrogen; boil off the excess of gas, cool and titrate with
+standard potassium permanganate (p. 236). Determine the copper in the
+filtrate colorimetrically (p. 203); but avoid further dilution. Then add
+dilute hydrochloric acid, so as to have an excess of 4 or 5 c.c. after
+neutralising the ammonia; add some clean strips of lead foil, and boil
+until the solution has for some time become colourless. Titrate with
+standard potassium ferrocyanide (p. 263) without further dilution, and
+bearing in mind that at most only one or two c.c. will be required.
+
+~Examination of an ore for "cyanicides."~--Place 100 grams of the ore
+with 200 c.c. of a cyanide solution of known strength (say .1 or .2 per
+cent.) in a bottle and agitate for a definite time, such as one or two
+days. Filter off some of the liquor and assay for cyanide, using say 20
+c.c. Calculate how much cyanide has been destroyed in the operation.
+Evaporate 20 c.c. with sulphuric or nitric acid and examine for metal.
+Test another portion for sulphides, &c.
+
+The student who has mastered the methods of assaying can greatly improve
+himself by working out such problems as the above.
+
+
+PLATINUM.
+
+Platinum occurs in nature in alluvial deposits associated with gold and
+some rare metals, generally in fine metallic grains, and, occasionally,
+in nuggets. It is a grey metal with a high specific gravity, 21.5 when
+pure and about 18.0 in native specimens. It is fusible only at the
+highest temperature, and is not acted on by acids.
+
+It is dissolved by warm aqua regia, forming a solution of "platinic
+chloride," H_{2}PtCl_{6}. This substance on evaporation remains as a
+brownish red deliquescent mass; on drying at 300° C. it is converted
+into platinous chloride, PtCl_{2}, and becomes insoluble, and at a
+higher temperature it is converted into platinum. All platinum compounds
+yield the metal in this way. Platinic chloride combines with other
+chlorides to form double salts, of which the ammonic and potassic
+platino-chlorides are the most important.
+
+Platinum alone is not soluble in nitric acid; but when alloyed with
+other metals which dissolve in this acid it too is dissolved; so that in
+gold parting, for example, if platinum was present, some, or perhaps the
+whole of it would go into solution with the silver. Such alloys,
+however, when treated with hot sulphuric acid leave the platinum in the
+residue with the gold.
+
+Platinum is detected when in the metallic state by its physical
+characters and insolubility in acids. In alloys it may be found by
+dissolving them in nitric acid or in aqua regia, evaporating with
+hydrochloric acid, and treating the filtrate with ammonic chloride and
+alcohol. A heavy yellow precipitate marks its presence.
+
+The assay of bullion, or of an alloy containing platinum, may be made as
+follows: Take 0.2 gram of the alloy and an equal weight of fine silver,
+cupel with sheet lead, and weigh. The loss in weight, after deducting
+that of the silver added, gives the weight of the base metals, copper,
+lead, &c. Flatten the button and part by boiling with strong sulphuric
+acid for several minutes. _When cold_, wash, anneal, and weigh. The
+weight is that of the platinum and gold. The silver may be got by
+difference. Re-cupel the metal thus got with 12 or 15 times its weight
+of silver, flatten and part the gold with nitric acid in the usual way
+(see under _Gold_), and the platinum will dissolve. The gold may contain
+an alloy of osmium and iridium; if so, it should be weighed and treated
+with aqua regia. The osmiridium will remain as an insoluble residue,
+which can be separated and weighed. Its weight deducted from that
+previously ascertained will give the weight of the gold.
+
+When the platinum only is required, the alloy must be dissolved by
+prolonged treatment with aqua regia, the solution evaporated to dryness,
+and the residue extracted with water. The solution thus obtained is
+treated with ammonic chloride in large excess and with some alcohol. A
+sparingly soluble[47] yellow ammonic platinum chloride is thrown down,
+mixed, perhaps, with the corresponding salts of other metals of the
+platinum group. Gold will be in solution. The solution is allowed to
+stand for some time, and then the precipitate is filtered off, washed
+with alcohol, dried, and transferred (wrapped in the filter paper) to a
+weighed crucible. It is ignited, gently at first, as there is danger of
+volatilising some of the platinum chloride, and afterwards intensely.
+With large quantities of platinum the ignition should be performed in an
+atmosphere of hydrogen. Cool and weigh as metallic platinum.
+
+
+IRIDIUM
+
+Occurs in nature alloyed with osmium as osmiridium or iridosmine, which
+is "rather abundant in the auriferous beach sands of Northern
+California" (Dana). It occurs in bright metallic scales, which do not
+alloy with lead, and are insoluble in aqua regia. Iridium also occurs in
+most platinum ores, and forms as much as two per cent. of some
+commercial platinum. In chemical properties it resembles platinum, but
+the ammonic irido-chloride has a dark red colour, and on ignition leaves
+metallic iridium, which does not dissolve in aqua regia diluted with
+four or five times its volume of water and heated to a temperature of
+40° or 50° C.
+
+The other metals of the platinum group are Palladium, Rhodium, Osmium,
+and Ruthenium. They differ from gold, platinum, and iridium by the
+insolubility of their sulphides in a solution of sodium sulphide.
+Palladium is distinguished by the insolubility of its iodide; and Osmium
+by the volatility of its oxide on boiling with nitric acid.
+
+
+MERCURY.
+
+Mercury occurs native and, occasionally, alloyed with gold or silver in
+natural amalgams; but its chief ore is the sulphide, cinnabar. It is
+comparatively rare, being mined for only in a few districts. It is
+chiefly used in the extraction of gold and silver from their ores
+(amalgamation); for silvering mirrors, &c.
+
+Mercury forms two series of salts, mercurous and mercuric, but for the
+purposes of the assayer the most important property is the ease with
+which it can be reduced to the metallic state from either of these.
+Mercury itself is soluble in nitric acid, forming, when the acid is hot
+and strong, mercuric nitrate. Cinnabar is soluble only in aqua regia.
+Mercurous salts are generally insoluble, and may be converted into
+mercuric salts by prolonged boiling with oxidising agents (nitric acid
+or aqua regia). The salts of mercury are volatile, and, if heated with a
+reducing agent or some body capable of fixing the acid, metallic mercury
+is given off, which may be condensed and collected.
+
+Mercury is separated from its solutions by zinc or copper, or it may be
+thrown down by stannous chloride, which, when in excess, gives a grey
+powder of metallic mercury, or, if dilute, a white crystalline
+precipitate of mercurous chloride. Nitric acid solutions of mercury
+yield the metal on electrolysis; and, if the pole on which the metal
+comes down be made of gold or copper, or is coated with these, the
+separated mercury will adhere thereto. It may then be washed and
+weighed.
+
+The best tests for mercury next to obtaining globules of the metal are:
+(1) a black precipitate with sulphuretted hydrogen from acid solutions,
+which is insoluble in nitric acid; and (2) a white precipitate with
+stannous chloride.
+
+
+DRY METHOD.
+
+[Illustration: FIG. 47.]
+
+Weigh up 5 grams, if the ore is rich, or 10 grams, if a poorer mineral.
+Take a piece of combustion tube from 18 inches to 2 feet long, closed at
+one end, and place in it some powdered magnesite, so as to fill it to a
+depth of 2 or 3 inches, and on that a layer of an equal quantity of
+powdered lime (not slaked). Mix the weighed sample of ore in a mortar
+with 10 grams of finely powdered lime and transfer to the tube; rinse
+out the mortar with a little more lime, and add the rinsings. Cover with
+a layer of six or seven inches more lime and a loosely fitting plug of
+asbestos. Draw out the tube before the blowpipe to the shape shown in
+fig. 47, avoiding the formation of a ridge or hollow at the bend which
+might collect the mercury. Tap gently, holding the tube nearly
+horizontal, so as to allow sufficient space above the mixture for the
+passage of the gases and vapours which are formed. Place the tube in a
+"tube furnace," and, when in position, place a small beaker of water so
+that it shall just close the opening of the tube. The point of the tube
+should not more than touch the surface of the water. Bring the tube
+gradually to a red heat, commencing by heating the lime just behind the
+asbestos plug, and travelling slowly backwards. When the portion of the
+tube containing the ore has been heated to redness for some time the
+heat is carried back to the end of the tube. The magnesite readily gives
+up carbonic acid, which fills the tube and sweeps the mercury vapour
+before it. Some of the mercury will have dropped into the beaker, and
+some will remain as drops adhering to the upper part of the neck. Whilst
+the tube is still hot cut off the neck of the tube just in front of the
+asbestos plug (a drop of water from the wash bottle will do this), and
+wash the mercury from the neck into the beaker. The mercury easily
+collects into a globule, which must be transferred, after decanting off
+the bulk of the water, to a weighed Berlin crucible. The water is
+removed from the crucible, first by the help of filter paper, and then
+by exposing in a desiccator over sulphuric acid, where it should be left
+until its weight remains constant. It should not be warmed.
+
+_Example_:--5 grams of an ore treated in this way gave 4.265 grams of
+mercury, equivalent to 85.3 per cent. Pure cinnabar contains 86.2 per
+cent.
+
+
+WET METHODS.
+
+_Solution._--Since solutions of chloride of mercury cannot be boiled
+without risk of loss,[48] nitric acid solutions should be used wherever
+possible. No mercury-containing minerals are insoluble in acids; but
+cinnabar requires aqua regia for solution. In dissolving this mineral
+nitric acid should be used, with just as much hydrochloric acid as will
+suffice to take it up.
+
+To separate the mercury, pass sulphuretted hydrogen in considerable
+excess through the somewhat dilute solution. The precipitate should be
+black, although it comes down at first very light coloured. It is
+filtered, washed, and transferred back to the beaker, and then digested
+with warm ammonic sulphide. The residue, filtered, washed, and boiled
+with dilute nitric acid, will, in the absence of much lead, be pure
+mercuric sulphide. If much lead is present, a portion may be
+precipitated as sulphate, but can be removed by washing with ammonic
+acetate. To get the mercury into solution, cover with nitric acid and a
+few drops of hydrochloric, and warm till solution is effected. Dilute
+with water to 50 or 100 c.c.
+
+
+GRAVIMETRIC DETERMINATION.
+
+This may be made by _electrolysis_. The same apparatus as is used for
+the electrolytic copper assay may be employed, but instead of a cylinder
+of platinum one cut out of sheet copper should be taken, or the platinum
+one may be coated with an evenly deposited layer of copper. Fix the
+spiral and weighed copper cylinder in position, couple up the battery,
+_and when this has been done_ put the nitric acid solution of the
+mercury in its place.[49] The student had better refer to the
+description of the _Electrolytic Copper Assay_.
+
+The mercury comes down readily, and the precipitation is complete in a
+few hours: it is better to leave it overnight to make sure of complete
+reduction. Disconnect the apparatus, and wash the cylinder, first with
+cold water, then with alcohol. Dry by placing in the water oven for two
+or three minutes. Cool and weigh: the increase in weight gives the
+amount of metallic mercury.
+
+It must be remembered that copper will precipitate mercury without the
+aid of the battery; but in this case copper will go into solution with a
+consequent loss in the weight of the cylinder: this must be avoided by
+connecting the battery before immersing the electrodes in the assay
+solution. The electrolysed solution should be treated with an excess of
+ammonia, when a blue coloration will indicate copper, in which case the
+electrolysis is unsatisfactory. With a little care this need not happen.
+Gold cylinders may preferably be used instead of copper; but on platinum
+the deposit of mercury is grey and non-adherent, so that it cannot be
+washed and weighed.
+
+
+VOLUMETRIC METHODS.
+
+Several methods have been devised: for the details of these the student
+is referred to Sutton's "Handbook of Volumetric Analysis."
+
+
+QUESTIONS.
+
+1. The specific gravity of mercury is 13.596. What volume would 8 grams
+occupy?
+
+2. If 3.169 grams of cinnabar gave 2.718 grams of mercury, what would be
+the percentage of the metal in the ore?
+
+3. Pour solution of mercuric chloride on mercury and explain what
+happens.
+
+4. On dissolving 0.3 gram of mercury in hot nitric acid, and passing
+sulphuretted hydrogen in excess through the diluted solution, what
+weight of precipitate will be got?
+
+FOOTNOTES:
+
+[9] Lead may be granulated by heating it to a little above the melting
+point, pouring it into a closed wooden box, and rapidly agitating it as
+it solidifies.
+
+[10] A rod of iron placed in the crucible with the assays will decompose
+any regulus that may be formed.
+
+[11] With buttons poor in silver the lowering of the temperature at this
+stage is not a matter of importance.
+
+[12] 100 grams of the lead, or of its oxide, will contain from 1.5 to
+2.5 milligrams.
+
+[13] Still the precautions of having cupels well made from bone ash in
+fine powder, and of working the cupellation at as low a temperature as
+possible are very proper ones, provided they are not carried to an
+absurd excess.
+
+[14] Be careful to remove the crucible before taking the bottle out of
+the basin of water; if this is not done the chloride may be washed out
+of it.
+
+[15] 1 c.c. of this dilute acid will precipitate 8 or 9 milligrams of
+silver.
+
+[16] Chlorides interfere not merely by removing silver as insoluble
+silver chloride, but also by making it difficult to get a good finishing
+point, owing to the silver chloride removing the colour from the
+reddened solution.
+
+[17] These results were obtained when using ammonium sulphocyanate, and
+cannot be explained by the presence of such impurities as chlorides, &c.
+
+[18] Multiply the _standard_ by 1000, and dilute 100 c.c. of the
+standard solution to the resulting number of c.c. Thus, with a solution
+of a standard .495, dilute 100 c.c. to 495 c.c., using, of course,
+distilled water.
+
+[19] HNa_{2}AsO_{4} + 3AgNO_{3} = Ag_{3}AsO_{4} + HNO_{3} + 2NaNO_{3}.
+
+[20] SiO_{2} + Na_{2}CO_{3} = CO_{2} + Na_{2}SiO_{3}
+     SiO_{2} + 2NaHCO_{3} = 2CO_{2} + Na_{2}SiO_{3} + H_{2}O.
+
+[21] PbO + SiO_{2} = PbSiO_{3}
+
+[22] Here and elsewhere in this article when a flux is spoken of as soda
+the bicarbonate is meant.
+
+[23] See the description of the process commencing on p. 98 and the
+explanatory remarks on p. 110.
+
+[24] Percy, _Metallurgy of Silver and Gold_, p. 258.
+
+[25] "Limits of Accuracy attained in Gold-bullion Assay," _Trans. Chem.
+Soc._, 1893.
+
+[26] "Assaying and Hall-marking at the Chester Assay Office." W.F. Lowe.
+_Journ. Soc. Chem. Industry_, Sept. 1889.
+
+[27] Fine or pure gold is 24 carat. Nine carat gold therefore contains 9
+parts of gold in 24 of the alloy; eighteen carat gold contains 18 parts
+of gold in 24; and so on.
+
+[28] The mouth of the flask must not have a rim around it.
+
+[29] See "Assaying and Hall-marking at the Chester Assay Office," by
+W.F. Lowe. _Journ. Soc. Chem. Industry_, Sept. 1889.
+
+[30] Percy, _Metallurgy of Silver and Gold_, p. 263.
+
+[31] See also "The Assaying of Gold Bullion," by C. Whitehead and T.
+Ulke. _Eng. and Mining Journal_, New York, Feb. 12, 1898.
+
+[32] Consult Percy's _Metallurgy of Silver and Gold_, p. 172; A.C.
+Claudet, _Trans. Inst. Mining and Metallurgy_, vol. vi. p. 29; G.M.
+Roberts _Trans. Amer. Inst. Mining Engineers_, Buffalo Meeting, 1898; J.
+and H.S. Pattinson, _Journ. Soc. Chem. Industry_, vol. xi. p. 321.
+
+[33] Heycock and Neville, _Journ. Chem. Soc._, 1892, p. 907.
+
+[34] G.M. Roberts.
+
+[35] A.C. Claudet.
+
+[36] "The Sampling of Argentiferous and Auriferous Copper," by A.R.
+Ledoux. _Journ. Canadian Mining Institute_, 1899.
+
+[37] NaCNO + BaCl_{2} + NaHO + H_{2}O = NH_{3} + BaCO_{3} + 2 NaCl.
+
+[38] HCy + NaHO = NaCy + H_{2}O.
+
+[39] 2KCN + AgNO_{3} = KAg(CN)_{2} + KNO_{3}.
+
+[40] If it be desired to make a solution so that 100 c.c. shall be
+equivalent to 1 gram of sodium cyanide, then 18.085 grams of silver
+nitrate should be taken for each litre.
+
+[41] AgNO_{3} + KAgCy_{2} = 2 AgCy + KNO_{3}.
+
+[42] AgNO_{3} + KI = AgI + KNO_{3}.
+
+[43] See pp. 322, 323, and 324 for a description of the methods for
+measuring the quantity of acid or alkali.
+
+[44] KCN + HCl = KCl + HCN
+
+[45] Taking 16.0 grams of ore, each c.c. = 1 lb. of soda to the short
+ton. The corresponding figures for the long ton are 12.544 grams for
+lime and 17.92 grams for soda.
+
+[46] In which case each .01 gram of metal found equals 1 lb to the short
+ton of solution.
+
+[47] 100 c.c. of water dissolves 0.66 gram of the salt; it is almost
+insoluble in alcohol or in solutions of ammonic chloride.
+
+[48] According to Personne mercuric chloride is not volatilised from
+boiling solutions when alkaline chlorides are present.
+
+[49] The solution should contain about 0.25 gram of mercury, and a large
+excess of nitric acid must be avoided.
+
+
+
+
+CHAPTER X.
+
+COPPER--LEAD--THALLIUM--BISMUTH--ANTIMONY.
+
+
+COPPER.
+
+
+Copper occurs native in large quantities, especially in the Lake
+Superior district; in this state it is generally pure. More frequently
+it is found in combination. The ores of copper may be classed as oxides
+and sulphides. The most abundant oxidised ores are the carbonates,
+malachite and chessylite; the silicates, as also the red and black
+oxides, occur less abundantly. All these yield their copper in solution
+on boiling with hydrochloric acid.
+
+The sulphides are more abundant. Copper pyrites (or yellow ore),
+erubescite (or purple ore), and chalcocite (or grey ore) are the most
+important. Iron pyrites generally carries copper and is frequently
+associated with the above-mentioned minerals. These are all attacked by
+nitric acid. They nearly all contain a small quantity of organic matter,
+and frequently considerable quantities of lead, zinc, silver, gold,
+arsenic, bismuth, &c.
+
+The copper ores are often concentrated on the mine before being sent
+into the market, either by smelting, when the product is a regulus or
+matte, or by a wet method of extraction, yielding cement copper or
+precipitate. A regulus is a sulphide of copper and iron, carrying from
+30 to 40 per cent. of copper. A precipitate, which is generally in the
+form of powder, consists mainly of metallic copper. Either regulus or
+precipitate may be readily dissolved in nitric acid.
+
+Copper forms two classes of salts, cuprous and cupric. The former are
+pale coloured and of little importance to the assayer. They are easily
+and completely converted into cupric by oxidising agents. Cupric
+compounds are generally green or blue, and are soluble in ammonia,
+forming deep blue solutions.
+
+
+DRY ASSAY.
+
+That, for copper, next after those for gold and silver, holds a more
+important position than any other dry assay. The sale of copper ores has
+been regulated almost solely in the past by assays made on the Cornish
+method. It is not pretended that this method gives the actual content of
+copper, but it gives the purchaser an idea of the quantity and quality
+of the metal that can be got by smelting. The process is itself one of
+smelting on a small scale. As might be expected, however, the assay
+produce and the smelting produce are not the same, there being a smaller
+loss of copper in the smelting. The method has worked very well, but
+when applied to the purchase of low class ores (from which the whole of
+the copper is extracted by wet methods) it is unsatisfactory. The
+following table, which embodies the results of several years' experience
+with copper assays, shows the loss of copper on ores of varying produce.
+The figures in the fourth column show how rapidly the proportion of
+copper lost increases as the percentage of copper in the ore falls below
+30 per cent. For material with more than 30 per cent. the proportion
+lost is in inverse proportion to the copper present.
+
+
+LOSS OF COPPER.
+
+  -----------------+------------+-----------+------------------
+   Copper present. | Dry Assay. |  Margin.  |   Loss on 100
+                   |            |           | Parts of Copper.
+  -----------------+------------+-----------+------------------
+      Per cent.    |  Per cent. | Per cent. |
+        100        |    98      |    2.0    |        2.0
+         95        |    92-1/2  |    2.5    |        2.6
+         90        |    87-3/8  |    2.6    |        2.9
+         85        |    82-3/8  |    2.6    |        3.0
+         80        |    77-3/8  |    2.6    |        3.2
+         75        |    72-3/8  |    2.6    |        3.5
+         70        |    67-1/2  |    2.5    |        3.6
+         65        |    62-1/2  |    2.5    |        3.8
+         60        |    57-5/8  |    2.4    |        4.0
+         55        |    52-3/4  |    2.3    |        4.2
+         50        |    47-3/4  |    2.2    |        4.4
+         45        |    43      |    2.0    |        4.5
+         40        |    38-1/8  |    1.8    |        4.6
+         35        |    33-1/4  |    1.7    |        4.8
+         30        |    28-1/2  |    1.50   |        5.0
+         25        |    23-1/2  |    1.50   |        6.0
+         20        |    18-1/2  |    1.56   |        7.8
+         18        |    16-1/2  |    1.53   |        8.5
+         16        |    14-1/2  |    1.48   |        9.3
+         14        |    12-5/8  |    1.40   |       10.0
+         12        |    10-5/8  |    1.37   |       11.4
+         10        |     8-3/4  |    1.28   |       12.8
+          8        |     6-7/8  |    1.14   |       14.3
+          6        |    5       |    1.05   |       17.5
+          5        |    4       |    1.00   |       20.0
+          4        |    3       |    1.00   |       25.0
+          3.75     |    2-3/4   |    0.97   |       26.0
+          3.50     |    2-9/16  |    0.94   |       27.0
+          3.25     |    2-5/16  |    0.91   |       28.0
+          3.00     |    2-1/8   |    0.87   |       29.0
+          2.75     |    1-15/16 |    0.82   |       30.0
+          2.50     |    1-3/4   |    0.77   |       31.0
+          2.25     |    1-1/2   |    0.72   |       32.0
+          2.00     |    1-5/16  |    0.66   |       33.0
+  -----------------+------------+-----------+------------------
+
+The wet assay being known, the dry assay can be calculated with the help
+of the above table by deducting the amount in the column headed "margin"
+opposite the corresponding percentage. For example, if the wet assay
+gives a produce of 17.12 per cent., there should be deducted 1.5; the
+dry assay would then be 15.62, or, since the fractions are always
+expressed in eighths, 15-5/8. With impure ores, containing from 25 to 50
+per cent. of copper, the differences may be perhaps 1/4 greater.
+
+Wet methods are gradually replacing the dry assay, and it is probable
+that in the future they will supersede it; for stock-taking, and the
+various determinations required in smelting works and on mines, they are
+generally adopted, because they give the actual copper contents, and
+since it is obvious that a knowledge of this is more valuable to the
+miner and smelter. Moreover, the working of the dry method has been
+monopolised by a small ring of assayers, with the double result of
+exciting outside jealousy and, worse still, of retarding the development
+and improvement of the process.
+
+The principal stages of the dry assay are: (1) the concentration of the
+copper in a regulus; (2) the separation of the sulphur by calcining; (3)
+the reduction of the copper by fusion; and (4) the refining of the metal
+obtained.
+
+The whole of these operations are not necessary with all copper
+material. Ores are worked through all the stages; with mattes, the
+preliminary fusion for regulus is omitted; precipitates are simply fused
+for coarse copper, and refined; and blister or bar coppers are refined,
+or, if very pure, subjected merely to washing.
+
+The quantity of ore generally taken is 400 grains, and is known as "a
+full trial"; but for rich material, containing more than 50 per cent. of
+copper, "a half trial," or 200 grains, is used.
+
+~Fusion for Regulus.~--The ore (either with or without a previous
+imperfect roasting to get rid of any excess of sulphur) is mixed with
+borax, glass, lime, and fluor spar; and, in some cases, with nitre, or
+iron pyrites, according to the quality of the ore. The mixture is placed
+in a large Cornish crucible, and heated as uniformly as possible in the
+wind furnace, gradually raising the temperature so as to melt down the
+charge in from 15 to 20 minutes. The crucible is removed and its
+contents poured into an iron mould. When the slag is solid, it is taken
+up with tweezers and quenched in water. The regulus is easily detached
+from the slag. It should be convex above and easily broken, have a
+reddish brown colour, and contain from 40 to 60 per cent. of copper. A
+regulus with more than this is "too fine," and with less "too coarse." A
+regulus which is too fine is round, compact, hard, and of a dark bluish
+grey on the freshly broken surface. A coarse regulus is flat and coarse
+grained, and more nearly resembles sulphide of iron in fracture and
+colour.
+
+If an assay yields a regulus "too coarse," a fresh determination is made
+with more nitre added, or the roasting is carried further. With low
+class ores a somewhat coarse regulus is an advantage. If, on the other
+hand, the regulus is too fine, less nitre or less roasting is the
+remedy. With grey copper ores and the oxidised ores, iron pyrites is
+added.
+
+~Calcining the Regulus.~--It is powdered in an iron mortar and
+transferred to a small Cornish crucible, or (if the roasting is to be
+done in the muffle) to a roasting dish or scorifier. The calcining is
+carried out at a dull red heat, which is gradually increased. The charge
+requires constant stirring at first to prevent clotting, but towards the
+end it becomes sandy and requires less attention. If the temperature
+during calcination has been too low sulphates are formed, which are
+again reduced to sulphides in the subsequent fusion. To prevent this the
+roasted regulus is recalcined at a higher temperature, after being
+rubbed up with a little anthracite. The roasted substance must not smell
+of burning sulphur when hot. It is practically a mixture of the oxides
+of copper and iron.
+
+~Fusion for Coarse Copper.~--The calcined regulus is mixed with a flux
+consisting of borax and carbonate of soda, with more or less tartar
+according to its weight. Some "assayers" use both tartar and nitre, the
+former of course being in excess. The charge is returned to the crucible
+in which it was calcined, and is melted down at a high temperature, and,
+as soon as tranquil, poured. When solid it is quenched and the button of
+metal separated.
+
+The slag is black and glassy. The small quantity of copper which it
+retains is recovered by a subsequent "cleaning," together with the slags
+from the next operation.
+
+The button of "coarse copper" obtained must be free from a coating of
+regulus. It will vary somewhat in appearance according to the nature and
+quantity of the impurities.
+
+~Refining the Coarse Copper.~--The same crucible is put back in the
+furnace, deep down and under the crevice between the two bricks. When it
+has attained the temperature of the furnace the coarse copper is dropped
+into it and the furnace closed. The copper will melt almost at once with
+a dull surface, which after a time clears, showing an "eye." Some
+refining flux is then shot in from the scoop (fig. 48), and, when the
+assay is again fluid, it is poured. When cold the button of metal is
+separated.
+
+[Illustration: FIG. 48.]
+
+The button of "fine" copper is flat or pitted on its upper surface, and
+is coated with a thin orange film; it must have the appearance of good
+copper. If it is covered with a red or purple film, it is overdone or
+"burnt." If, on the other hand, it has a rough, dull appearance, it is
+not sufficiently refined. Assays that have been "burnt" are rejected.
+Those not sufficiently fine are treated as "coarse copper," and again
+put through the refining operation.
+
+~Cleaning the Slags.~--These are roughly powdered and re-fused with
+tartar, etc., as in the fusion for coarse copper. The button of metal
+got is separated (if big enough refined) and weighed.
+
+The details of the process are slightly varied by different assayers:
+the following will be good practice for the student.
+
+~Determination of Copper in Copper Pyrites.~--Powder, dry, and weigh up
+20 grams of the ore. Mix with 20 grams each of powdered lime and fluor,
+15 grams each of powdered glass and borax, and 5 or 10 grams of nitre.
+Transfer to a large Cornish crucible and fuse under a loose cover at a
+high temperature for from 15 to 20 minutes. When fluid and tranquil pour
+into a mould. When the slag has solidified, but whilst still hot, quench
+by dipping two or three times in cold water. Avoid leaving it in the
+water so long that it does not dry after removal. When cold separate the
+button, or perhaps buttons, of regulus by crumbling the slag between the
+fingers. See that the slag is free from regulus. It should be light
+coloured when cold and very fluid when hot. Reject the slag.
+
+Powder the regulus in a mortar and transfer to a small crucible.
+Calcine, with occasional stirring, until no odour of sulphurous oxide
+can be detected. Shake back into the mortar, rub up with about 1 gram of
+powdered anthracite, and re-calcine for 10 minutes longer.
+
+Mix the calcined regulus with 10 grams of tartar, 20 grams of soda, and
+3 grams of borax; and replace in the crucible used for calcining. Fuse
+at a bright red heat for 10 or 15 minutes. Pour, when tranquil.
+
+As soon as solid, quench in water, separate the button of copper, and
+save the slag.
+
+To refine the copper a very hot fire is wanted, and the fuel should not
+be too low down in the furnace. Place the crucible well down in the fire
+and in the middle of the furnace. The same crucible is used, or, if a
+new one is taken, it must be glazed with a little borax. When the
+crucible is at a good red heat, above the fusing point of copper, drop
+the button of copper into it, and close the furnace. Watch through the
+crevice, and, as soon as the button has melted and appears clear showing
+an eye, shoot in 10 grams of refining flux, close the furnace, and, in a
+few minutes, pour; then separate the button of copper. Add the slag to
+that from the coarse copper fusion, and powder. Mix with 5 grams of
+tartar, 0.5 gram of powdered charcoal, and 2 grams of soda. Fuse in the
+same crucible, and, when tranquil, pour; quench, and pick out the prills
+of metal.
+
+If the copper thus got from the slags is coarse looking and large in
+amount, it must be refined; but, if small in quantity, it may be taken
+as four-fifths copper. The combined results multiplied by five give the
+percentage of copper.
+
+The refining flux is made by mixing 3 parts (by measure) of powdered
+nitre, 2-1\2 of tartar, and 1 of salt. Put in a large crucible, and stir
+with a red-hot iron until action has ceased. This operation should be
+carried out in a well-ventilated spot.
+
+For pure ores in which the copper is present, either as metal or oxide,
+and free from sulphur, arsenic, &c., the concentration of the copper in
+a regulus may be omitted, and the metal obtained in a pure state by a
+single fusion.[50] It is necessary to get a fluid neutral slag with the
+addition of as small an amount of flux as possible. The fusion should be
+made at a high temperature, so as not to occupy more than from 20 to 25
+minutes. Thirty grams of ore is taken for a charge, mixed with 20 grams
+of cream of tartar, and 10 grams each of dried borax and soda. If the
+gangue of the ore is basic, carrying much oxide of iron or lime, silica
+is added, in quantity not exceeding 10 grams. If, on the other hand, the
+gangue is mainly quartz, oxide of iron up to 7 grams must be added.
+
+_Example._--Twenty grams of copper pyrites, known to contain 27.6 per
+cent. of copper, gave by the method first described 5.22 grams of
+copper, equalling 26-1/8 per cent. Another sample of 20 grams of the
+same ore, calcined, fused with 40 grams of nitre, and washed to ensure
+the removal of arsenic and sulphur, and treated according to the second
+method, gave a button weighing 5.27 grams, equalling 26-3/8 per cent.
+The ore contained a considerable quantity of lead. Lead renders the
+assay more difficult, since after calcination it remains as lead
+sulphate, and in the fusion for coarse copper reappears as a regulus on
+the button.
+
+~The Estimation of Moisture.~--The Cornish dry assayer very seldom makes
+a moisture determination. He dries the samples by placing the papers
+containing them on the iron plate of the furnace.
+
+It is well known that by buying the copper contents of pyrites by
+Cornish assay, burning off the sulphur, and converting the copper into
+precipitate, a large excess is obtained.
+
+
+NOTES ON THE VALUATION OF COPPER ORES.
+
+Closely bound up with the practice of dry copper assaying is that of
+valuing a parcel of copper ore. The methods by which the valuation is
+made have been described by Mr. Westmoreland,[51] and are briefly as
+follows:--The produce of the parcel is settled by two assayers, one
+acting for the buyer, the other for the seller; with the help, in case
+of non-agreement, of a third, or referee, whose decision is final. The
+dry assayers who do this are in most cases helped, and sometimes,
+perhaps, controlled, by wet assays made for one or both of the parties
+in the transaction.
+
+In the case of "ticketing," the parcels are purchased by the smelters by
+tender, and the value of any particular parcel is calculated from the
+average price paid, as follows:--The "standard," or absolute value of
+each ton of fine copper in the ore, is the price the smelters have paid
+for it, plus the returning charges or cost of smelting the quantity of
+ore in which it is contained. The value of any particular parcel of ore
+is that of the quantity of fine copper it contains, calculated on this
+standard, minus the returning charges. The ton consists of 21 cwts.,
+and it is assumed that the "settled" produce is the actual yield of the
+ore.
+
+If at a ticketing in Cornwall 985 tons of ore containing 63.3 tons of
+fine copper (by dry assay) brought £2591 12s., the standard would be
+£83 15s. This is calculated as follows:--The returning charge is fixed
+at 55s. per ton of ore. This on 985 tons will amount to £2708 15s.
+Add this to the actual price paid, and there is got £5300 as the value
+of the fine copper present. The weight of copper in these 985 tons being
+63.3 tons, the standard is £5300/63.3, or £83 15s. (nearly).
+
+The value of a parcel of 150 tons of a 6 per cent. ore on the same
+standard would be arrived at as follows:--The 150 tons at 6 per cent.
+would contain 9 tons (150×6/100) of fine copper. This, at £83 15s.
+per ton, would give £753 15s. From this must be deducted the returning
+charges on 150 tons of ore at 55s. per ton, or £412 10s. This leaves
+£341 5s. as the value of the parcel.
+
+At Swansea the returning charge is less than in Cornwall, and varies
+with the quality of the ore. This appears equitable, since in smelting
+there are some costs which are dependent simply on the number of tons
+treated, and others which increase with the richness. The returning
+charge then is made up of two parts, one fixed at so much (12s. 2d.)
+per ton of ore treated, and the other so much (3s. 9d.) per unit of
+metal in the ore. In this way the returning charge on a ton of ore of
+8-3/4 produce would be (12s. 2d.)+(8-3/4×(3s. 9d.)), or £2 5s.
+
+If, for example, Chili bars, containing 96 per cent. of copper, bring
+£50 per ton, the standard is £71 9s. 4d. It is got at in this way.
+The returning charge on a 96 per cent. ore is (12s. 2d.)+(96×(3s.
+9d.)), or £18 12s. 2d. This added to £50 gives £68 12s. 2d.,
+and this multiplied by 100 and divided by 96 (100 tons of the bars will
+contain 96 tons of fine copper) will give £71 9s. 4d.
+
+The price of 100 tons of pyrites, containing 2-1/4 per cent. of copper
+by dry assay, would be got on this standard as follows:--The parcel of
+ore would contain 2-1/4 tons of copper. This multiplied by the standard
+gives £160 16s. 0d. From this must be deducted the returning charge,
+which for 1 ton of ore of this produce would be (12s. 2d.) + (2-1/4×(3s.
+9d.)) or £1 0s. 7d., and on the 100 tons is £102 18s. 4d. This would
+leave £57 17s. 10d. as the price of the parcel, or 11s. 7d. per ton.
+This would be on the standard returning charge of 45s. (for 8-3/4 per
+cent. ore); if a smaller returning charge was agreed on, say 38s., the
+difference in this case, 7s., would be added to the price per ton.
+
+
+WET METHODS.
+
+The solubility of the ores of copper in acid has already been described,
+but certain furnace products, such as slags, are best opened up by
+fusion with fusion mixture and a little nitre.
+
+The method of dissolving varies with the nature of the ore. With 5 grams
+of pyrites, a single evaporation with 20 c.c. of nitric acid will give a
+residue completely soluble in 30 c.c. of hydrochloric acid. If the ore
+carries oxide of iron or similar bodies, these are first dissolved up by
+boiling with 20 c.c. of hydrochloric acid, and the residue attacked by
+an addition of 5 c.c. of nitric. When silicates decomposable by acid are
+present, the solution is evaporated to dryness to render the silica
+insoluble; the residue extracted with 30 c.c. of hydrochloric acid, and
+diluted with water to 150 c.c. It is advisable to have the copper in
+solution as chloride. To separate the copper, heat the solution nearly
+to boiling (best in a pint flask), and pass a rapid current of
+sulphuretted hydrogen for four or five minutes until the precipitate
+settles readily and the liquid smells of the gas. When iron is present
+it will be reduced to the ferrous state before the copper sulphide
+begins to separate. The copper appears as a brown coloration or black
+precipitate according to the quantity present. Filter through a coarse
+filter, wash with hot water containing sulphuretted hydrogen, if
+necessary. Wash the precipitate back into the flask, boil with 10 c.c.
+of nitric acid, add soda till alkaline, and pass sulphuretted hydrogen
+again. Warm and filter, wash and redissolve in nitric acid, neutralise
+with ammonia, add ammonic carbonate, boil and filter. The copper freed
+from impurities will be in the solution. Acidulate and reprecipitate
+with sulphuretted hydrogen. When the nature of the impurities will allow
+it, this process may be shortened to first filtering off the gangue,
+then precipitating with sulphuretted hydrogen and washing the
+precipitate on the filter first with water and then with ammonium
+sulphide.
+
+Having separated the copper as sulphide, its weight is determined as
+follows. Dry and transfer to a weighed porcelain crucible, mix with a
+little pure sulphur, and ignite at a red heat for 5 or 10 minutes in a
+current of hydrogen. Allow to cool while the hydrogen is still passing.
+Weigh. The subsulphide of copper thus obtained contains 79.85 per cent.
+of copper; it is a greyish-black crystalline mass, which loses no weight
+on ignition if air is excluded.
+
+Copper may be separated from its solutions by means of sodium
+hyposulphite. The solution is freed from hydrochloric and nitric acids
+by evaporation with sulphuric acid; diluted to about a quarter of a
+litre; heated nearly to boiling; and treated with a hot solution of
+sodium hyposulphite (added a little at a time) until the precipitate
+settles and leaves the solution free from colour. The solution contains
+suspended sulphur. The precipitate is easily washed, and under the
+proper conditions the separation is complete, but the separation with
+sulphuretted hydrogen is more satisfactory, since the conditions as to
+acidity, &c., need not be so exact.
+
+Zinc or iron is sometimes used for separating copper from its solutions,
+but they are not to be recommended.
+
+
+ELECTROLYTIC ASSAY.
+
+The separation of copper by means of a current of electricity is largely
+made use of, and forms the basis of the most satisfactory method for the
+determination of this metal. If the wire closing an electric circuit be
+broken, and the two ends immersed in a beaker of acidulated water or
+solution of any salt, the electricity will pass through the liquid,
+bringing about some remarkable changes. Hydrogen and the metals will be
+liberated around that part of the wire connected with the zinc end of
+the battery, and oxygen, chlorine, and the acid radicals will be set
+free around the other. Different metals are deposited in this way with
+varying degrees of ease, and whether or not any particular metal will be
+deposited depends--(1) on the conditions of the solution as regards acid
+and other substances present, and (2) on the _intensity_ of the current
+of electricity used. For analytical purposes the metal should be
+deposited not only free from the other metals present, but also as a
+firm coherent film, which may afterwards be manipulated without fear of
+loss. This is, in the case of copper and many other metals, effected by
+a simple control of the conditions. It is necessary that the electrodes,
+or wires which bring the electricity into the solution, should be made
+of a material to which the deposited metal will adhere, and which will
+not be attacked by substances originally present or set free in the
+solution. They are generally made of platinum. There are various
+arrangements of apparatus used for this purpose, but the following plan
+and method of working is simple and effective, and has been in daily use
+with very satisfactory results for the last five or six years.
+
+The battery used is made up of two Daniell cells, coupled up for
+intensity as shown in fig. 49--that is, with the copper of one connected
+with the zinc of the other. For eight or ten assays daily the quart size
+should be used, but for four or five two pint cells will be sufficient.
+
+[Illustration: FIG. 49.]
+
+The outer pot of each cell is made of sheet copper, and must be clean
+and free from solder on the inside. It is provided near the top with a
+perforated copper shelf in the shape of a ring, into which the inner or
+porous cell loosely fits. It is charged with a saturated solution of
+copper sulphate, and crystals of this salt must be added, and always
+kept in excess. When the battery is at work copper is being deposited on
+the inner surface of this pot.
+
+The inner or porous pot contains the zinc rod, and is charged with a
+dilute acid, made by diluting one volume of sulphuric acid up to ten
+with water. The object of the porous pot is to prevent the mixing of the
+acid and copper sulphate solutions, without interrupting the flow of
+electricity. The copper sulphate solution will last for months, but the
+acid must be emptied out and recharged daily.
+
+The zinc rods must be well amalgamated by rubbing with mercury under
+dilute acid until they show a uniformly bright surface. They should not
+produce a brisk effervescence when placed in the acid in the porous pot
+before coupling up.
+
+The battery when working is apt to become dirty from the "creeping" of
+the copper and zinc sulphate solution. It must be kept away from the
+working bench, and is best kept in a box on the floor.
+
+[Illustration: FIG. 50.]
+
+The connection of the battery with, and the fixing of, the electrodes
+may be made by any suitable arrangement, but the following is a very
+convenient plan. The wire from the zinc is connected by means of a
+binding screw with a piece of stout copper wire, which, at a distance
+sufficiently great to allow of easy coupling with the battery, is led
+along the back of a piece of hard wood. This is fixed horizontally
+about one foot above the working bench. The general arrangement is shown
+in fig. 50, in which, however, for the sake of economy of space, the
+battery is placed on the working bench instead of on the floor. The
+piece of wood is one inch square and three or four feet long. It is
+perforated from front to back at distances of six inches by a number of
+small holes, in which are inserted screws like that shown in fig. 51.
+These are known as "terminals," and may be obtained of any electrician.
+The head of each screw is soldered to the wire mentioned above as
+running along the back and as being connected with the zinc end of the
+battery. These terminals serve to fix the electrodes on which the copper
+is to be deposited. The wire from the copper end of the battery is
+similarly connected by a connecting screw (fig. 52) with another wire (H
+in fig. 53), which runs along the top of the rod and has soldered to it,
+at distances of six inches, cylindrical spirals of copper wire. These
+should project from the rod at points about half-way between the
+terminals already described. They may be made by wrapping copper wire
+around a black-lead pencil for a length of about three inches.
+
+[Illustration: FIG. 51.]
+
+[Illustration: FIG. 52.]
+
+[Illustration: FIG. 53.]
+
+The rod is perforated from top to bottom with a series of small holes,
+one in advance of each terminal but as near it as possible. Into these
+short pieces of glass tube are inserted to ensure insulation. These
+receive the other electrodes, which are connected with the wire leading
+to the copper end of the battery, through the spirals, with the help of
+a binding screw. The figure will make this clear. (Fig. 53.)
+
+[Illustration: FIG. 54]
+
+~The electrodes~ consist of a platinum spiral and cylinder. The spiral
+should have the shape shown in A, fig. 54. When in work it is passed
+through one of the holes fitted with glass tubes and connected with the
+copper end of the battery. The thickness of the wire of which it is made
+is unimportant, provided it is stout enough to keep its form and does
+not easily bend. The spiral will weigh about 8 grams. The cylinder (C,
+fig. 54) will weigh about 12 grams. It should have the shape shown in
+the figure. In working it is clamped to one of the terminals, and on it
+the copper is deposited. A cylinder will serve for the deposition of
+from 1 to 1.5 gram of copper. It is made by rivetting a square piece of
+foil on to a stiff piece of wire, and then bending into shape over a
+glass tube or piece of rounded wood. Each cylinder carries a distinctive
+number, and is marked by impressing Roman numerals on the foil with the
+blade of a knife. The weight of each is carefully taken and recorded.
+They lose slightly in weight when in use, but the loss is uniform, and
+averages half a milligram per month when in daily use. The cylinders are
+cleaned from deposited copper by dissolving off with nitric acid and
+washing with water; and from grease by igniting.
+
+The ~beakers~, to contain the solution of copper to be electrolysed, are
+ordinary tall beakers of about 200 c.c. capacity, and are marked off at
+100 c.c. and 150 c.c. They are supported on movable stands, consisting
+of wooden blocks about six inches high and three inches across. The bar
+of wood which carries the connecting wires and electrodes is permanently
+fixed over the working bench, at such a height that, with the beakers
+resting on these blocks, the electrodes shall be in position for
+working.
+
+To fix the electrodes to the rod, remove the stand and beaker and pass
+the long limb of the spiral up through one of the glass tubes. Connect
+it with the free end of the copper spiral by means of a connecting screw
+(fig. 52), and then draw out and bend the copper spiral so that the
+platinum one may hang freely. Screw the wire of the cylinder to the
+terminal, and, if necessary, bend it so that the cylinder itself may be
+brought to encircle the rod of the spiral in the manner shown in fig.
+53.
+
+The ~general method of working~ is as follows:--The quantity of ore to
+be taken for an assay varies with the richness of the ore, as is shown
+in the following table:--
+
+  Percentage of Copper     Quantity of Ore
+      in the Ore.           to be taken.
+
+       1 to   5               5 grams
+       5 to  10               3   "
+      10 to  30               2   "
+      30 to  50               1.5 "
+      50 to 100               1   "
+
+The weighed quantity of ore is dissolved by evaporating with nitric acid
+and taking up with hydrochloric, as already described. Any coloured
+residue which may be left is generally organic matter: it is filtered
+off, calcined, and any copper it contains is estimated colorimetrically.
+Nearly always, however, the residue is white and sandy. The copper is
+separated from the solution as sulphide by means of a rapid current of
+sulphuretted hydrogen. The liquid is decanted off through a filter, the
+precipitate washed once with hot water and then rinsed back into the
+flask (the filter paper being opened out) with a jet of water from a
+wash bottle. Fifteen c.c. of nitric acid are added to the contents of
+the flask, which are then briskly boiled until the bulk is reduced to
+less than 10 c.c. The boiling down is carried out in a cupboard free
+from cold draughts, so as to prevent the condensation of acid and steam
+in the neck of the flask. Twenty c.c. of water are next added, and the
+solution is warmed, and filtered into one of the beakers for
+electrolysis. The filtrate and washings are diluted with water to the
+100 c.c. mark, and the solution is then ready for the battery. It must
+not contain more than 10 per cent. by volume of nitric acid.
+
+The number and weight of the platinum cylinder having been recorded,
+both electrodes are fixed in position and the wooden block removed from
+under them. The beaker containing the copper solution is then brought up
+into its place with one hand, and the block replaced with the other so
+as to support it. All the assays having been got into position, the
+connecting wires are joined to the battery. If everything is right
+bubbles of oxygen at once stream off from the spiral, and the cylinder
+becomes tarnished by a deposit of copper. If the oxygen comes off but no
+copper is deposited, it is because the assay solution contains too much
+nitric acid. If no action whatever takes place, it is because the
+current is not passing. In this case examine the connections to see that
+they are clean and secure, and the connecting wires to see that they are
+not touching each other.
+
+The action is allowed to go on for sixteen or seventeen hours, so that
+it is best to let the current act overnight. In the morning the
+solutions will appear colourless, and a slow stream of oxygen will still
+be coming off from the spiral.
+
+A wash-bottle with cold distilled water and two beakers, one with
+distilled water and the other with alcohol, are got ready. The block is
+then removed, the spiral loosened and lowered with the beaker. The
+cylinder is next detached and washed with a stream of water from the
+wash-bottle, the washings being added to the original solution. The
+current from the battery is not stopped until all the cylinders are
+washed. After being dipped in the beaker of water and once or twice in
+that with the alcohol, it is dried in the water-oven for about three
+minutes, and then weighed. The increase in weight is due to deposited
+copper. This should be salmon-red in colour, satin-like or crystalline
+in appearance, and in an even coherent deposit, not removed by rubbing.
+It is permanent in air when dry, but sulphuretted hydrogen quickly
+tarnishes it, producing coloured films. With ores containing even very
+small proportions of bismuth, the deposited copper has a dark grey
+colour, and when much of this metal is present the copper is coated with
+a grey shaggy deposit.
+
+It still remains to determine any copper left undeposited in the
+solution. This does not generally exceed four or five milligrams, and
+is estimated colorimetrically. Thirty c.c. of dilute ammonia (one of
+strong ammonia mixed with one of water) are added to the electrolysed
+solution, which is then diluted up to the 150 c.c. mark with water. It
+is mixed, using the spiral as stirrer, and, after standing a few minutes
+to allow the precipitate to settle, 100 c.c. of it are filtered off
+through a dry filter for the colorimetric determination. Since only
+two-thirds of the solution are taken for this, the quantity of copper
+found must be increased by one-half to get the quantity actually
+present.
+
+[Illustration: FIG. 55.]
+
+The ~colorimetric determination~ may be made in the manner described
+under that head, but where a number of assays are being carried out it
+is more convenient to have a series of standard phials containing known
+amounts of copper in ammoniacal solution. By comparing the measured
+volume of the assay solution with these, the amount of copper present is
+determined at a glance. These standard bottles, however, can only be
+economically used where a large number of assays are being made daily.
+
+A convenient plan is to get a quantity of white glass four-ounce phials,
+like that in fig. 55, and to label them so that they shall contain 100
+c.c. when filled up to the bottom of the labels. The labels should be
+rendered permanent by coating with wax, and be marked with numbers
+indicating the milligrams of copper present. The bottles are stopped
+with new clean corks, and contain, in addition to the specified quantity
+of copper, 6 c.c. of nitric acid and 10 c.c. of strong ammonia, with
+sufficient water to make up the bulk to 100 c.c. The copper is best
+added by running in the requisite amount of a standard solution of
+copper, each c.c. of which contains 0.001 gram of the metal.
+
+The standard bottles should be refilled once every three or four months,
+since their colorimetric value becomes slowly less on keeping. The
+following determinations of a set which had been in use for three months
+will illustrate this. The figures indicate milligrams of copper in 100
+c.c.: the first row gives the nominal and the second row the actual
+colorimetric value of the standards. The difference between the two
+shows the deterioration.
+
+  1  2  3  4    6    8   10  12  14
+  1  2  3  3.7  5.5  7.5  9  11  13
+
+The amount of copper in the assay is got by increasing that found
+colorimetrically by one-half and adding to that found on the platinum
+cylinder. The percentage is calculated in the usual way. The following
+examples will illustrate this, as well as the method of recording the
+work in the laboratory book:--
+
+  ---------------------------------------------
+  Cylinder I. + Cu                       9.5410
+  Cylinder I.                            9.5170
+                                         ------
+                                         0.0240
+  By colour 100 c.c. = 0.0015}
+                       0.0007}           0.0022
+                       ------            ------
+                       0.0022            0.0262
+  IX. Sample.    Took 5 grams.
+                                Copper = 0.52%
+  ---------------------------------------------
+  Cylinder VI. + Cu                     10.5705
+  Cylinder VI.                          10.0437
+                                        -------
+                                         0.5268
+  By colour, 100 c.c. = 0.0070}
+                        0.0035}          0.0105
+                        ------           ------
+                        0.0105           0.5373
+  Matte, No. 1070. Took 1.5 gram.
+                               Copper = 35.82%
+  ---------------------------------------------
+  Cylinder XIII. + Cu                   12.0352
+  Cylinder XIII.                        11.0405
+                                        -------
+                                         0.9947
+  By colour 100 c.c. = 0.0005}
+                       0.0002}           0.0007
+                       ------            ------
+                       0.0007            0.9954
+  X. Sample, Cake copper. Took 1.0053 gram.
+                               Copper = 99.00%
+  ---------------------------------------------
+
+In the electrolytic assay of metals, alloys, precipitates, and other
+bodies rich in copper, the preliminary separation of the copper by
+sulphuretted hydrogen is unnecessary. It is sufficient to dissolve the
+weighed sample in 10 c.c. of nitric acid, boil off nitrous fumes, dilute
+to 100 c.c. with water, and then electrolyse.
+
+~General Considerations.~--In the preliminary work with the copper
+sulphide there is a small loss owing to its imperfect removal in washing
+the filter paper, and another small loss in dissolving in nitric acid
+owing to the retention of particles in the fused globules of sulphur. To
+determine its amount the filter-papers and sulphur were collected from
+forty assays, and the copper in them determined. The average amount of
+copper in each assay was 0.175 gram; that left on the filter paper was
+0.00067 gram; and that retained by the sulphur 0.00003 gram; thus
+showing an average loss from both sources of 0.00070 gram. The
+determinations from another lot of forty-two similar assays gave on an
+average
+
+  Copper left on filter paper      0.00070 gram
+  Copper retained by sulphur.      0.00004  "
+
+The loss from these sources is trifling, and need only be considered
+when great accuracy is required.
+
+The deposition of the copper under the conditions given is satisfactory,
+but, as already stated, if the solution contain more than 10 per cent.
+of nitric acid it is not thrown down at all; or if a stronger current is
+used, say that from three Bunsen cells, it will be precipitated in an
+arborescent brittle form, ill adapted for weighing. It may be noted here
+that increasing the size of the cells does not necessarily increase the
+intensity of the current.
+
+In two determinations on pure electrotype copper the following results
+were obtained:--
+
+  Copper Taken.       Copper Found.
+   0.8988 gram         0.8985 gram
+   0.8305  "           0.8303  "
+
+The presence of salts of ammonia, &c., somewhat retards the deposition,
+but has no other ill effect.
+
+The organic matter generally present in copper ores interferes more
+especially in the colorimetric determination of the residual copper. It
+can be detected on dissolving the ore as a light black residue insoluble
+in nitric acid. It is filtered off at once, or, if only present in small
+amount, it is carried on in the ordinary process of the assay and
+separated in the last filtration before electrolysis.
+
+The following experiments were made to test the effect of the presence
+of salts of foreign metals in the solution during the precipitation of
+copper by electrolysis:--
+
+  --------------+----------------------------------------+---------------
+  Copper Taken. |           Other Metal Added.           | Copper Found.
+  --------------+----------------------------------------+---------------
+   0.1000 gram  | 0.1000 gram of silver                  |    0.1800
+   0.1050   "   | 0.1000   "       "                     |    0.2000
+   0.1030   "   | 0.1000   "     mercury                 |    0.2010
+   0.1037   "   | 0.1000   "       "                     |    0.2015
+   0.1020   "   | 0.1000   "     lead                    |    0.1020
+   0.1030   "   | 0.1000   "       "                     |    0.1028
+   0.1010   "   | 0.1000   "     arsenic                 |    0.1010
+   0.1007   "   | 0.1000   "       "                     |    0.1022
+   0.1030   "   | 0.1000   "     antimony                |    0.1050
+   0.1034   "   | 0.1000   "       "                     |    0.1057
+   0.0990   "   | 0.1200   "     tin                     |    0.0990
+   0.1014   "   | 0.1000   "       "                     |    0.1015
+   0.1000   "   | 0.1000   "     bismuth                 |    0.1662
+   0.1040   "   | 0.1000   "     cadmium                 |    0.1052
+   0.1009   "   | 0.1300   "    zinc                     |    0.1017
+   0.1014   "   | 0.1000   "    nickel                   |    0.1007
+   0.1079   "   | 0.1200   "    iron                     |    0.1089
+   0.1054   "   | 0.1000   "    chromium (Cr_{2}O_{3})   |    0.1035
+   0.1034   "   | 0.1000   "        "    (K_{2}CrO_{4})  |    0.1010
+   0.1075   "   | 0.1000   "    aluminium                |    0.1078
+   0.1010   "   | 0.1000   "    manganese                |    0.0980
+  --------------+----------------------------------------+---------------
+
+It will be seen from these that mercury, silver, and bismuth are the
+only metals which are precipitable[52] along with the copper under the
+conditions of the assay. Mercury, which if present would interfere, is
+separated because of the insolubility of its sulphide in nitric acid.
+
+Bismuth is precipitated only after the main portion of the copper is
+thrown down. It renders the copper obviously unsuitable for weighing. It
+darkens, or forms a greyish coating on, the copper; and this darkening
+is a delicate test for bismuth. In assaying ores containing about three
+and a half per cent. of copper, and known to contain bismuth in
+quantities scarcely detectable in ordinary analysis, the metal deposited
+was distinctly greyish in colour, and would not be mistaken for pure
+copper. Ten grams of this impure copper were collected and analysed,
+with the following results:--
+
+  Copper       99.46 per cent.
+  Bismuth      00.30    "
+  Iron         00.14    "
+  Arsenic      00.10    "
+              ------
+              100.00
+
+The quantity of copper got in each assay was 0.175 gram, and
+consequently the bismuth averaged 0.00053 gram.
+
+To separate the bismuth in such a case the deposit is dissolved off by
+warming it in the original solution. The bismuth is precipitated by the
+addition of ammonic carbonate, and the solution, after filtering and
+acidifying with nitric acid, is re-electrolysed.
+
+~Determination of Copper in Commercial Copper.~--Take from 1 to 1.5
+gram, weigh carefully, and transfer to a beaker; add 20 c.c. of water
+and 10 c.c. of nitric acid; cover with a clock glass, and allow to
+dissolve with moderate action; boil off nitrous fumes, dilute to 100
+c.c., and electrolyse. The cylinder must be carefully weighed, and the
+electrolysis allowed to proceed for 24 hours. The weight found will be
+that of the copper and silver. The silver in it must be determined[53]
+and deducted.
+
+~Determination of Copper in Brass, German Silver, or Bronze.~--Treat in
+the same manner as commercial copper. If nickel is present, the few
+milligrams of copper remaining in the electrolysed solution should be
+separated with sulphuretted hydrogen, the precipitated sulphide
+dissolved in nitric acid, and determined colorimetrically.
+
+
+VOLUMETRIC PROCESSES.
+
+There are two of these in use, one based on the decolorising effect of
+potassic cyanide upon an ammoniacal copper solution, and the other upon
+the measurement of the quantity of iodine liberated from potassic iodide
+by the copper salt. The cyanide process is the more generally used, and
+when carefully worked, "on certain understood and orthodox conditions,"
+yields good results; but probably there is no method of assaying where a
+slight deviation from these conditions so surely leads to error. An
+operator has no difficulty in getting concordant results with duplicate
+assays; yet different assayers, working, without bias, on the same
+material, get results uniformly higher or lower; a difference evidently
+due to variations in the mode of working. Where a large number of
+results are wanted quickly it is a very convenient method. The iodide
+process is very satisfactory when worked under the proper conditions.
+
+
+CYANIDE METHOD.
+
+The process is based upon the facts--(1) that when ammonia is added in
+excess to a solution containing cupric salts, ammoniacal copper
+compounds are formed which give to the solution a deep blue colour; and
+(2) that when potassic cyanide is added in sufficient quantity to such a
+solution the colour is removed, double cyanides of copper and potassium
+or ammonium being formed.[54] In the explanation generally given the
+formation of cuprous cyanide is supposed[55]; but in practice it is
+found that one part of copper requires rather more than four parts of
+cyanide, which agrees with the former, rather than the latter,
+explanation.
+
+Reliance on the accuracy of the process cannot rest upon the
+supposition that the cyanide required for decoloration is proportional
+to the copper present, for varying quantities of ammonia salts, ammonia
+and water, and differences of temperature have an important effect. The
+results are concordant and exact only when the cyanide is standardised
+under the same conditions as it is used. It is best to have the assay
+solution and that used for standardising as nearly as possible alike,
+and to titrate the two solutions side by side. This demands an
+approximate knowledge of the quantity of copper contained in the ore and
+a separation of the bulk of the impurities.
+
+For the titration there is required a standard solution of potassium
+cyanide made by dissolving 42 grams of the salt, known to dealers as
+Potassium Cyanide (Gold), in water and diluting to one litre: 100 c.c.
+of this will be about equivalent to one gram of copper. For poor ores
+the solution may conveniently be made half this strength.
+
+The solution of the ore and the separation of the copper as sulphide are
+effected in the same ways as have been already described for
+electrolysis. Similarly, too, the sulphide is attacked with 15 c.c. of
+nitric acid and the assay boiled down to 10 c.c. Add 20 c.c. of water
+and warm, filter into a pint flask, wash well with water, and dilute to
+about 150 c.c.; add 30 c.c. of dilute ammonia, and cool.
+
+Prepare a standard by dissolving a quantity of electrotype copper
+(judged to be about the same as that contained in the assay) in 20 c.c.
+of water and 10 c.c. of nitric acid, boil off the nitrous fumes, and
+dilute to 150 c.c.: add 30 c.c. of dilute ammonia and cool.
+
+Fill a burette with the standard cyanide solution. The burette with
+syphon arrangement, figured on page 52, is used. A number of titrations
+can be carried on at the same time provided the quantity of copper
+present in each is about the same. This is regulated in weighing up the
+ore. The flasks must of course be marked, and should be arranged in
+series on a bench in front of a good light and at such a height that the
+liquid can be looked through without stooping. Supposing about 50 c.c.
+of cyanide will be required, 30 c.c. should be run into each, and each
+addition be recorded as soon as made; then run 15 c.c. into each. The
+solutions will now probably show marked differences of tint: add 1 c.c.
+of cyanide to the lighter ones and more to the darker, so as to bring
+the colours to about the same depth of tint. They should all be of
+nearly equal tint just before finishing. At the end add half a c.c. at a
+time until the colours are completely discharged. A piece of damp filter
+paper held between the light and the flask assists in judging the
+colour when nearly finished. Overdone assays show a straw yellow colour
+which deepens on standing.
+
+The following will illustrate the notes recorded of five such assays and
+one standard:--
+
+  (1) 30 c.c. 15 c.c. 5 c.c. 2 c.c. 1 c.c. 1/2 c.c. -- c.c. = 53-1/2 c.c.
+  (2) 30  "   15  "   1  "   1  "   1  "   1/2  "   --  "   = 48-1/2  "
+  (3) 30  "   15  "   3  "   1  "   1  "   1/2  "   --  "   = 50-1/2  "
+  (4) 30  "   15  "   5  "   2  "   1  "   1/2  "  1/2  "   = 54      "
+  (5) 30  "   15  "   2  "   1  "   1  "   1/2  "   --  "   = 49-1/2  "
+  (6) 30  "   15  "   2  "   1  "   1  "   1/2  "  1/2  "   = 50  standard
+
+Three grams of ore were taken, and the standard contained 0.480 gram of
+copper.
+
+In this series the difference of half a c.c. means about 0.15 per cent.
+on the ore; with a little practice it is easy to estimate whether the
+whole or half of the last addition should be counted.
+
+To get satisfactory results, the manner of finishing once adopted must
+be adhered to.
+
+The following experiments show the effect of variation in the conditions
+of the assay:--Use _a solution of copper nitrate_, made by dissolving 10
+grams of copper in 50 c.c. of water and 35 c.c. of nitric acid, and
+diluting to a litre. 100 c.c. = 1 gram of copper.
+
+~Effect of Varying Temperature.~--In these experiments 20 c.c. of copper
+nitrate were used, with 10 c.c. of nitric acid, 30 c.c. of dilute
+ammonia, and water to 200 c.c. The results were--
+
+  Temperature         15°        30°        70°       100°
+  Cyanide required  21.5 c.c.  20.8 c.c.  19.7 c.c.  18.8 c.c.
+
+The temperature is that of the solution _before_ titrating. These show
+the importance of always cooling before titrating, and of titrating the
+assay and standard at the same temperature.
+
+~Effect of Varying Bulk.~--The quantities of copper, acid, and ammonia
+were the same as in the last-mentioned experiments. The results were:--
+
+  Bulk             100.0 c.c.  200.0 c.c.  300.0 c.c.  400.0 c.c.
+  Cyanide required  23.3  "     21.7  "     21.4  "     21.4  "
+
+These show that large variations in bulk must be avoided.
+
+~Effect of Varying Ammonia.~--The quantities of copper and acid were the
+same as in the series of experiments last noticed. The bulk was 200 c.c.
+The results were:--
+
+  Dilute ammonia    20.0 c.c.  30.0 c.c.  50.0 c.c.  100.0 c.c.
+  Cyanide required  20.9  "    21.7  "    22.3  "     24.6  "
+
+~Effect of Varying Acid.~--The quantities of copper and water were the
+same as in the last-noticed set of experiments: 30 c.c. of dilute
+ammonia were used.
+
+  Nitric acid        5.0 c.c.  10.0 c.c.  15.0 c.c.
+  Cyanide required  21.6  "    21.7  "    21.5 "
+
+On adding nitric acid to the solution it combines with a portion of the
+ammonia to form ammonic nitrate; it will be seen from the last series of
+experiments that the lessening of the amount of free ammonia will
+decrease the quantity of cyanide required; but, on the other hand, the
+ammonic nitrate which is at the same time formed will increase the
+amount required; under the conditions of the assay these two effects
+neutralise each other, and such differences in the quantity of acid as
+are likely to occur are unimportant.
+
+~Effect of Varying Ammonic Salts.~--The quantities of copper, water, and
+ammonia were the same as in the last mentioned set of experiments, but
+no nitric acid was used.
+
+  Ammonic nitrate added  1 gram     5 grams   10 grams   20 grams
+  Cyanide required      21.2 c.c.  22.1 c.c.  23.1 c.c.  24.1 c.c.
+
+These show that combined ammonia seriously affects the titration, and
+that the principle sometimes recommended of neutralising the acid with
+ammonia, and then adding a constant quantity of ammonia, is not a good
+one, because there is then an interference both by the ammonia and by
+the variable quantity of ammonic salts.
+
+The same quantity of combined ammonia has the same effect, whether it is
+present as sulphate, nitrate, chloride, or acetate, as the following
+experiments show. Four lots of 20 c.c. of "copper nitrate" were taken,
+and 20 c.c. of dilute ammonia added to each. These were carefully
+neutralised with the respective acids, rendered alkaline with 30 c.c.
+more of ammonia, cooled, diluted to bulk, and titrated. The results
+were:--
+
+  With sulphuric acid     22.5 c.c. of cyanide
+    "  nitric acid        22.6  "        "
+    "  hydrochloric acid  22.6  "        "
+    "  acetic acid        22.5  "        "
+
+~Effect of Foreign Salts.~--Sulphates, nitrates and chlorides of sodium
+or potassium have no action, whilst the hydrates, carbonates,
+bicarbonates, sulphites, and nitrites have an important effect. The
+interference of ammonic salts has already been shown.
+
+Salts of silver, zinc, and nickel react with cyanide just as copper
+does, and consequently interfere. Ferrous salts are sure to be absent,
+and ferric salts yield ferric hydrate with the ammonia, which is not
+acted on by the cyanide, but, owing to its bulkiness, it settles slowly;
+this lengthens the time required for titration, and so modifies the
+manner of working. _An assay should not be worked with ferric hydrate
+present, unless the standard contains about the same amount of it._ On
+mines it is often inconvenient to separate the copper by means of
+sulphuretted hydrogen; hence it is customary to titrate without
+previous separation. In this case, instead of standardising the cyanide
+with electrotype copper, a standard ore should be used. This should be
+an ore (of the same kind as those being assayed) in which the copper has
+been carefully determined.
+
+~Effect of Varying Copper.~--In these experiments 10 c.c. of nitric
+acid, 30 c.c. of ammonia, and water to 200 c.c. were used.
+
+  Copper nitrate present 1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
+  Cyanide required       0.7  "   11.2  "   21.7  "   54.5 "    108.1  "
+
+These results show that under the conditions laid down the various
+causes of disturbance nearly neutralise one another, and the results
+within a fair range are practically proportional.
+
+~Determination of Copper in Copper Pyrites.~--Weigh up 2 grams of the
+dried and powdered ore, and place in an evaporating dish about four
+inches in diameter. Cover with 20 c.c. of nitric acid and put on a hot
+plate. Evaporate to dryness without further handling. Allow to cool and
+take up with 30 c.c. of hydrochloric acid, boil, dilute, and transfer to
+a pint flask, filtering if necessary. Make up the bulk with the washings
+to about 150 c.c. Precipitate with sulphuretted hydrogen, filter, and
+wash back the precipitate into the flask. Add 15 c.c. of nitric acid,
+and boil down rapidly to 10 c.c. Dilute, add 30 c.c. of dilute ammonia,
+make up to 150 c.c., and cool. For the standard, weigh up 0.5 gram of
+copper, more or less, according to the quantity judged to be present in
+the assay. Dissolve in 20 c.c. of dilute nitric acid, boil off nitrous
+fumes, add 30 c.c. of dilute ammonia, make up to the same bulk as that
+of the assay, and cool. Titrate the two solutions side by side and as
+nearly as possible in the same manner.
+
+Since the assay solution is often turbid from the presence of small
+quantities of lead and of iron from incomplete washing, and since this
+slight precipitate is very slow in settling, the standard can hardly be
+compared strictly with the assay. This can be counteracted by
+precipitating in both solutions a mixture of ferric and aluminic
+hydrates, which settles readily and leaves the supernatant liquor clear.
+To effect this, boil the nitric acid solutions with 30 c.c. of a
+solution containing 15 grams each of alum and ferrous sulphate to the
+litre. In an actual determination 2 grams of the ore were taken and
+compared with 0.5 gram of copper. The assay required 57.7 c.c. of
+cyanide and the standard 52.5 c.c.
+
+        52.5 : 0.5 :: 57.7 : 0.5495
+
+This on 2 grams of ore = 27.47 per cent.; the same sample by
+electrolysis gave 27.60 per cent. of copper.
+
+~Determination without Previous Separation.~--Dissolve up 2 grams as
+before, but, instead of passing sulphuretted hydrogen, add 30 c.c. of
+dilute ammonia, shake well, and cool. Prepare a standard by dissolving
+0.5 gram of copper in 1 c.c. of nitric acid, add 0.6 gram of iron in the
+form of ferric chloride and 20 c.c. of hydrochloric acid, dilute to
+about 150 c.c., add 30 c.c. of dilute ammonia, and cool. Titrate the two
+solutions side by side. In a determination on the sample last used, 58
+c.c. were required for the assay and 53 c.c. for the standard, which
+indicates 27.3 per cent. of copper.
+
+This method of working is somewhat rough.
+
+
+IODIDE METHOD.
+
+This is based upon the fact that when potassic iodide in excess is added
+to a strong solution of a cupric salt in a faintly acid solution,
+cuprous iodide is formed and an equivalent of iodine liberated.[56] The
+iodine is measured by titrating with a solution of sodium
+hyposulphite,[57] using starch paste as indicator. The iodine is soluble
+in the excess of potassium iodide, forming a deep brown solution; the
+hyposulphite is added until this brown colour is almost removed. Starch
+paste is then added, and strikes with the remaining iodine a dirty blue
+colour. The addition of the "hypo" is continued until the blue colour is
+discharged. The end reaction is sharp; a drop is sufficient to complete
+it.
+
+As regards the titration, the process leaves little to be desired; the
+quantity of "hypo" required is strictly proportional to the copper
+present, and ordinary variations in the conditions of working are
+without effect. The presence of salts of bismuth masks the end reaction
+because of the strong colour imparted to the solution by the iodide of
+bismuth. Under certain conditions there is a return of the blue colour
+in the assay solution after the finishing point has apparently been
+reached, which is a heavy tax on the patience and confidence of the
+operator. This is specially apt to occur when sodium acetate is present,
+although it may also be due to excessive dilution.
+
+~The standard "hypo" solution~ is made by dissolving 39.18 grams of the
+crystallised salt (Na_{2}S_{2}O_{3}.5H_{2}O) in water and diluting to
+one litre. One hundred c.c. will equal one gram of copper.
+
+The starch solution is made by mixing 1 gram of starch into a thin paste
+with cold water, pouring it into 200 c.c. of boiling water, and
+continuing the boiling for a minute or so. The solution must be cold
+before use, and about 2 c.c. is used for each assay. It should not be
+added until the bulk of the iodine has been reduced.
+
+To standardise the "hypo," weigh up 0.3 or 0.4 gram of pure copper,
+dissolve in 5 c.c. of dilute nitric acid, boil off nitrous fumes, and
+dilute with an equal bulk of cold water. Add "soda" solution until a
+permanent precipitate is obtained, and then 1 c.c. of acetic acid. This
+should yield a clear solution. Fill an ordinary burette with the "hypo."
+Add 3 grams of potassium iodide crystals to the copper solution, and,
+when these are dissolved, dilute to 100 c.c. with water. Run in the
+"hypo" solution rather quickly until the brown colour is nearly
+discharged--_i.e._, to within 3 or 4 c.c. of the finish. Add 2 c.c. of
+the starch solution, and continue the addition of the "hypo" a few drops
+at a time until the tint suddenly changes to a cream colour. The blue
+colour must not return on standing three or four minutes. Calculate the
+standard in the usual way.
+
+In assaying ores, the copper is dissolved and separated with
+sulphuretted hydrogen as in the other processes, but the sulphide should
+be washed more completely to ensure the absence of iron salts.
+
+The following experiments show the effect of variation in the conditions
+of the assay. Use a solution of copper sulphate containing 39.38 grams
+of copper sulphate crystals (CuSO_{4}.5H_{2}O) in the litre. 100 c.c.
+equal 1.00 gram of copper.
+
+~Effect of Varying Temperature.~--The assay after the addition of the
+potassic iodide must be kept cold, else iodine may be volatilised.
+
+~Effect of Varying Potassium Iodide.~--In various descriptions of the
+process the amount of iodide required is variously stated at from "a few
+crystals" to as much as 10 grams. The proportion required by theory for
+1 gram of copper is a little over 5 grams: an excess, however, is
+required to keep the liberated iodine in solution. On economic grounds
+this excess should not be extravagant; if the student uses 10 parts of
+the iodide for each part of copper in the assay he will have sufficient.
+In the experiments there were used 20 c.c. of the copper sulphate, with
+varying amounts of potassic iodide, and the following results were
+got:--
+
+  Potassic iodide added    1.5 gram      3 grams       5 grams
+  "Hypo" required          20.0 c.c.     20.0 c.c.     20.0 c.c.
+
+In these the iodide was added direct to the solution containing the
+copper, which was afterwards diluted to 100 c.c. and titrated. In
+another series the iodide was added after the dilution to 100 c.c., and
+the results were:--
+
+  Potassic iodide added   1.5 gram   3 grams    5 grams    10 grams
+  "Hypo" required         20.0 c.c.  20.1 c.c.  20.0 c.c.  20.0 c.c.
+
+~Effect of Varying Bulk.~--In these experiments, 20 c.c. of copper
+sulphate were taken, 3 grams of potassic iodide added, and also water to
+the required bulk.
+
+  Bulk               20.0 c.c.    100.0 c.c.   200.0 c.c.    500.0 c.c.
+  "Hypo" required    20.0  "       20.0  "      20.0  "       19.9  "
+
+In the last of these experiments the colour was discharged at 18 c.c.,
+but gradually returned until 19.9 c.c. had been run in. It will be seen
+that considerable variation in bulk does not interfere.
+
+~Effect of Acetic Acid.~--These experiments were like the last series
+mentioned, but the bulk was 100 c.c., and varying amounts of acetic acid
+were added.
+
+  Acetic acid added       0 c.c.  1.0 c.c.  5.0 c.c. 10.0 c.c. 20.0 c.c.
+  "Hypo" required      20.0  "   20.1  "   20.1  "   20.0  "   20.2  "
+
+Acetic acid, then, does not interfere to any serious extent.
+
+~Effect of Varying Sodium Acetate.~--These experiments were like those
+last mentioned, but without acetic acid, and with varying amounts of
+sodium acetate.
+
+  Sodium acetate added   0 gram     1 gram     2 grams    5 grams   10 grams
+  "Hypo" required       20.0 c.c.  20.0 c.c.  20.2 c.c.  19.3 c.c.  18.2 c.c.
+
+In the 5 grams experiment, when the finishing point had been apparently
+reached the colour slowly returned; but as the results generally on
+titrating were not satisfactory a repetition of the experiment was made
+with the addition of 5 c.c. of acetic acid, which gave an equally bad
+result.
+
+~Effect of Foreign Salts.~--The conditions of these experiments were the
+same as before. The salts were added and dissolved before the addition
+of the potassium iodide. Using 5 grams (or in the case of the acids, 5
+c.c.), the results were as follows:--
+
+                               dilute       Acetic
+  Salt added          --      H_{2}SO_{4}   acid       NaAc         NaCl
+  "Hypo" required  20.0 c.c.  20.0 c.c.     20.1 c.c.  19.3 c.c.    20.1 c.c.
+
+  Salt added       KNO_{3}    Na_{2}SO_{4}  AmCl       Am_{2}SO_{4}
+  "Hypo" required  20.2 c.c.  18.7 c.c.     20.0 c.c.  19.9 c.c.
+
+The low result with the sulphate of soda was evidently due to the
+formation of a sparingly soluble double salt, which removed copper from
+the solution; on adding a little acetic acid the full amount of "hypo"
+was required. The effect of the presence of certain metals is important.
+The method of determining it was to add the substance to the solution
+containing the copper, and partly precipitate with soda solution; then
+treating with 1 c.c. of acetic acid, adding the iodide, and proceeding
+as before.
+
+      Substance Added.                   "Hypo" Required,
+            -                                20. c.c
+  0.050 gram arsenic as As_{2}O_{5}          20.0 "
+  0.050   "  antimony as SbCl_{5}            19.8 "
+  0.050   "  lead as Pb(NO_{3})_{2}          20.1 "
+
+A similar experiment with 0.050 gram of bismuth nitrate could not be
+determined, the end-reaction being masked. Bismuth iodide is soluble in
+potassic iodide, forming a brown solution, the colour of which is very
+similar to that produced by iodine; and although it does not strike a
+blue colour with starch, "hypo" has an action on it.
+
+A similar experiment with 0.050 gram of iron as ferric chloride required
+22.3 c.c. of "hypo," and the colour returned on standing. This shows
+that ferric acetate liberates iodine under the conditions of the assay.
+Trying to counteract this, by adding to a similar solution 0.5 gram of
+phosphate of soda dissolved in a little water, 19.7 c.c. of "hypo" were
+required instead of 20.0, but the assay showed signs of returning
+colour.
+
+In standardising, the same result was obtained, whether the copper was
+present as nitrate or sulphate before neutralising.
+
+~Effect of Varying Copper.~--With the same conditions as before, but
+with varying amounts of copper and a proportionally increasing quantity
+of iodide, the results were:--
+
+  Copper present   1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
+  "Hypo" required  1.0  "   10.0  "   20.0  "   50.0  "   100.0  "
+
+showing the results to be exactly proportional.[58]
+
+~Determination of Copper in Copper Pyrites.~--Take 2 grams of the dried
+and powdered ore and treat in a porcelain dish with 20 c.c. of nitric
+acid, and evaporate to dryness. Take up with 30 c.c. of hydrochloric
+acid, dilute, and transfer to a pint flask; make up with water to 200
+c.c., warm, and pass sulphuretted hydrogen to excess. Filter, and wash
+the precipitate with water acidified with sulphuric acid. Wash the
+precipitate back into the flask, and dissolve with 15 c.c. of nitric
+acid. Evaporate almost to dryness; add 20 c.c. of water, and boil till
+free from nitrous fumes; filter off the sulphur and gangue; neutralise
+with soda, avoiding excess; add 1 or 2 c.c. of acetic acid, and shake
+till clear. Add 5 grams of potassium iodide, dilute to 100 c.c., and
+titrate. The following is an example:--
+
+  0.5 gram of copper required    50.5 c.c. "hypo."
+  The assay required             55.6  "     "
+
+which is equal to 27.5 per cent. of copper.
+
+
+COLORIMETRIC PROCESS.
+
+This is based on the blue coloration of ammoniacal copper solutions. The
+quantity of copper in 100 c.c. of the assay solution should not be more
+than 15 milligrams, or less than half a milligram. It is not so delicate
+as most other colorimetric methods, but nevertheless is a very useful
+one.
+
+The manner of working is the same as that described under iron.
+
+~Standard Copper Solution.~--Weigh up 0.5 gram of electrotype copper,
+dissolve in 10 c.c. of nitric acid, boil off nitrous fumes, and dilute
+to 1 litre. 1 c.c. = 0.5 milligram.
+
+In nearly all cases it will be necessary to separate the copper with
+sulphuretted hydrogen from a solution of about 5 grams of the material
+to be assayed. The filter paper containing the sulphide (and, probably,
+much sulphur) is dried and burnt. The ashes are dissolved in 5 c.c. of
+dilute nitric acid, 10 c.c. of dilute ammonia added, and the solution
+filtered through a coarse filter into a Nessler tube, washing the paper
+with a little dilute ammonia.
+
+The estimation of the colour and calculation of the result are made in
+the way described on page 44.
+
+The effect of varying conditions on the assay may be seen from the
+following experiments.
+
+~Effect of Varying Temperature.~--The effect of increased temperature is
+to slightly decrease the colour, but this can only be observed when a
+fair quantity of copper is present.
+
+   1.0 c.c. at 15° showed the colour of 1.0 c.c. at 70°
+   2.5          "     "    "          " 2.7      "
+   5.0          "     "    "          " 5.0      "
+  10.0          "     "    "          " 9.0      "
+
+~Effect of Varying Ammonia.~--The solution must, of course, contain free
+ammonia; about 5 c.c. of dilute ammonia in 50 c.c. bulk is the quantity
+to be used in the experiments. A larger quantity affects the results,
+giving lower readings and altering the tint. With small quantities of
+ammonia the colour approaches a violet; with larger, a sky-blue.
+
+   2.5 c.c. with 25 c.c. of strong ammonia read 2.2 c.c.
+   5.0       "       "        "      "      "   4.0  "
+  10.0       "       "        "      "      "   8.0  "
+
+~Effect of Ammonic Salts.~--The following table shows the results after
+addition of ammonic salts:--
+
+  --------------+-----------------+------------------+------------------
+   C.c. Present.|  With 10 grams  |   With 10 grams  |   With 10 grams
+                | Ammonic Nitrate.| Ammonic Chloride.| Ammonic Sulphate.
+  --------------+-----------------+------------------+------------------
+        2.5     |      2.5        |        2.5       |        2.0
+        5.0     |      5.0        |        5.3       |        4.3
+       10.0     |     10.0        |       10.0       |        8.5
+  --------------+-----------------+------------------+------------------
+
+These show that sulphates should be avoided, and either nitrate or
+chloride solutions be used in the standard as well as in the assay.
+
+~Determination of Copper in a Manganese Ore.~--Treat 3 grams of the ore
+with 20 c.c. of hydrochloric acid, and evaporate to dryness. Take up
+with 10 c.c. of hydrochloric acid; dilute to about 200 c.c., and pass
+sulphuretted hydrogen until the solution smells of the gas; filter,
+burn, take up with 5 c.c. of dilute nitric acid, add 10 c.c. of dilute
+ammonia, and filter into the Nessler tube, and make up with the washings
+to 50 c.c. Into the "standard" tube put 5 c.c. of dilute nitric acid and
+10 c.c. of dilute ammonia. Make up to nearly 50 c.c. with water, and run
+in the standard copper until the colours are equal. In a determination 4
+c.c. (= 2.0 milligrams of copper) were required; this in 3 grams of ore
+= 0.07 per cent.
+
+~Determination of Copper in "Black Tin."~--Weigh up 3 grams of the dried
+ore, boil with 10 c.c. of hydrochloric acid, and afterwards add 1 c.c.
+of nitric; boil off nitrous fumes, evaporate to about 5 c.c., dilute to
+50 c.c., add 20 c.c. of dilute ammonia; stir, and filter. If much iron
+is present, dissolve the precipitate of ferric hydrate in acid, and
+reprecipitate with ammonia. Mix the two filtrates, and dilute to 100
+c.c. Take 50 c.c. for the test. A sample of 3 grams of an ore treated in
+this way required 5.2 c.c. of standard copper to produce equality of
+tint. This gives 0.35 per cent.
+
+~Determination of Copper in Tin.~--Weigh up 1 gram of the sample,
+transfer to an evaporating dish, and cover with 30 c.c. of aqua regia.
+Warm until the metal has dissolved, then evaporate almost to dryness.
+Take up with a few c.c. of hydrochloric acid and again evaporate.
+
+Dissolve the residue in 10 c.c. of dilute hydrochloric acid and transfer
+to a 100 c.c. flask. Add 10 c.c. of dilute ammonia and make up with
+water to the containing mark.
+
+Filter off 50 c.c. of the solution into a Nessler glass and determine
+the copper in it colorimetrically.
+
+
+EXAMINATION OF COMMERCIAL COPPER.
+
+Very pure copper can be obtained in commerce, owing to the demand for
+metal of "high conductivity" for electrical purposes, which practically
+means for metal free from impurities.
+
+Much of the metal sold contains as much as one per cent. of foreign
+substances, of which arsenic is the most important. The other elements
+to be looked for are bismuth, lead, antimony, silver, gold, iron,
+nickel, cobalt, sulphur, and oxygen. In "blister copper" (which is the
+unrefined metal), aluminium, silicon, and phosphorus may be met with.
+
+~Oxygen.~--All commercial copper carries oxygen; most of it is present
+as cuprous oxide, which is dissolved by molten copper. The estimation of
+oxygen is often made "by difference." The copper and the other
+impurities being determined, the rest is assumed to be oxygen. Probably
+this is nearly correct, but the whole of the oxygen should not be
+ascribed to cuprous oxide; for any arsenic the metal contained would be
+present as cuprous arsenite, since arsenide of copper and cuprous oxide
+could not exist together at the temperature of fusion without
+interacting. In the report of the analysis, it is best to state the
+proportion of oxygen thus:--
+
+  Oxygen  ---- per cent. by difference.
+
+There is a method of determination by fusing 5 or 10 grams in a brasqued
+crucible, and counting the loss as oxygen; and another method for the
+determination of cuprous oxide based on the reaction of this substance
+with nitrate of silver.[59] About 2 grams of silver nitrate, dissolved
+in 100 c.c. of water, is allowed to act upon 1 gram of the copper in the
+cold. The precipitate is filtered off, washed thoroughly with water, and
+the basic salt dissolved and determined colorimetrically.
+
+One part of copper found represents 1.68 part of cuprous oxide, or 0.19
+part of oxygen. Copper generally carries from 0.1 to 0.2 per cent. of
+oxygen.
+
+~Silver~ is found in most samples, but occurs in variable proportions;
+when it amounts to 30 ounces per ton it has a commercial value. To
+determine its amount, dissolve 10 grams of the copper in 35 c.c. of
+nitric acid and 50 c.c. of water, boil off nitrous fumes, and dilute to
+about 100 c.c. One or two c.c. of dilute hydrochloric acid (one to 100
+of water) are added, stirred in, and the precipitate allowed to settle
+for twenty-four hours. Filter through a double Swedish paper, dry, burn,
+and cupel the ashes with one gram of sheet lead.
+
+Ten grams of a sample of copper gave in this way 4.7 milligrams of
+silver. Ten grams of the same copper, to which 24 milligrams of silver
+had been added gave 28.2 milligrams.
+
+~Gold.~--To determine it, dissolve 10, 20, or 50 grams of the sample in
+35, 70, or 175 c.c. of nitric acid and an equal volume of water, boil
+till free from nitrous fumes, and dilute to double its volume. Allow to
+stand for some time, decant on to a filter, dry, burn, and cupel the
+ashes with 1 gram of sheet lead. If silver is present, owing to traces
+of chlorides in the re-agents used, "parting" will be necessary. (See
+_Gold_.)
+
+Working in this way on 20 grams of copper, to which 1.8 milligram of
+gold had been added, a button weighing 2.0 milligrams was obtained.
+
+~Antimony~ is not a frequent impurity of copper: it can be detected in
+quantities over 0.1 per cent. by a white residue of Sb_{2}O_{4},
+insoluble in nitric acid. With material containing only small quantities
+of antimony the white oxide does not show itself for some time, but on
+long-continued boiling it separates as a fine powder. It is best (when
+looking for it) to evaporate the nitric acid solution to the
+crystallising point, to add a little fresh nitric acid and water, and
+then to filter off the precipitate. After weighing it should be examined
+for arsenic and bismuth.
+
+~Lead.~--Refined coppers are often free from lead, anything more than
+traces being seldom found; in coarse coppers it is sometimes present in
+considerable quantities.
+
+Its presence may be detected in the estimation of the copper
+electrolytically, the platinum spiral becoming coated with a brown or
+black deposit of lead dioxide. The depth of colour varies with the lead
+present, and obviously could be made the basis of an approximate
+estimation. The colour shows itself within an hour or so, but is best
+observed when all the copper has been deposited.
+
+Electrolysing a solution of one gram of pure copper, to which 0.5
+milligram of lead had been added, the deposit was dark brown; in a
+similar solution with 1 milligram of lead it was much darker, and with 2
+milligrams it was black. Under the conditions of the assay the dioxide
+cannot be weighed, as it partly dissolves on breaking the current. When
+lead has been found, its quantity may be estimated by evaporating to
+dryness the nitric acid solution to which an excess of sulphuric acid
+has been added, taking up with water, and filtering off and weighing the
+lead sulphate.
+
+The separation of traces of lead as chromate is a fairly good one.
+Dissolve 5 grams of the copper in 17 c.c. of nitric acid and an equal
+volume of water; boil off nitrous fumes, neutralise with soda, and
+afterwards acidulate with acetic acid; and dilute to a litre. Add 20
+grams of sodium acetate, warm, and precipitate the lead with a dilute
+solution of potassium chromate. Copper chromate (yellow) may be at the
+same time thrown down, but it is readily soluble on diluting. Filter off
+the precipitate; wash it into a beaker and pass sulphuretted hydrogen;
+oxidise the sulphide and weigh as lead sulphate. Treated in this way 5
+grams of copper yielded sulphate of lead equal to 2.0 milligrams of
+lead. Five grams of the same sample to which 10 milligrams of lead were
+added gave 11.4 milligrams.
+
+~Nickel and Cobalt.~--Nickel is always present in larger or smaller
+quantities in commercial copper, and, perhaps, has an influence on the
+properties of the metal. It is determined as follows:--Dissolve 10 grams
+of the copper in 35 c.c. of nitric acid and an equal bulk of water, boil
+off nitrous fumes and neutralise with soda, add 2 grams of carbonate of
+soda dissolved in water, boil, and filter. Acidify the filtrate with 2
+or 3 c.c. of dilute nitric acid and dilute to 1 or 1-1/2 litres. Pass
+sulphuretted hydrogen through the cold solution till the copper is all
+down and the liquid smells of the gas. Filter and evaporate the filtrate
+to a small bulk, and determine the nickel by electrolysing the solution
+rendered ammoniacal, or by precipitating as sulphide and weighing as
+sulphate. (See under _Nickel_.) The precipitate, after weighing, should
+be tested for cobalt. If present it is separated with potassium nitrite
+as described under _Cobalt_. Ten grams of copper gave 6.0 milligrams of
+nickel; and another lot of 10 grams of the same copper, to which 10.0
+milligrams of nickel had been added, gave 17.2 milligrams.
+
+~Sulphur.~--The amount of sulphur in refined copper is very small,
+seldom exceeding 0.005 per cent. In coarse copper, as might be expected,
+it is found in larger quantities.
+
+In determining it, it is first converted into sulphuric acid, and then
+precipitated and weighed as barium sulphate. The precipitation cannot be
+effected from a nitric acid solution. Ten grams of copper are dissolved
+in nitric acid, as for the other determinations, and then boiled with
+excess of hydrochloric acid till the nitric acid is completely removed.
+There is then added a few drops of a dilute solution of baric chloride,
+and the solution is allowed to stand for some hours. The baric sulphate
+is filtered off and weighed.
+
+The necessity for precipitating from a hydrochloric acid solution is
+seen from the following determinations. In each experiment 10 grams of
+copper was used, and a known weight of sulphur, in the form of copper
+sulphate, added.
+
+  --------------+---------------------------+---------------------
+  Sulphur added.|     Sulphur found in      |  Sulphur found in
+                |Hydrochloric Acid Solution.|Nitric Acid Solution.
+  --------------+---------------------------+---------------------
+   5 milligrams |        8 milligrams       |    0.03 milligrams
+  10     "      |       11      "           |    0.03      "
+  15     "      |       17      "           |   12.00      "
+  --------------+---------------------------+---------------------
+
+~Bismuth.~--Nearly all samples of copper contain bismuth, but only in
+small quantities. It is best determined colorimetrically as described
+under _Bismuth_. The method of concentrating and preparing the solution
+for colorimetric assay is as follows. Dissolve 10 grams of copper in
+nitric acid, as in the other determinations; neutralise with soda; add 1
+or 1.5 grams of bicarbonate of soda and boil for ten minutes; filter,
+dissolve the precipitate in hot dilute sulphuric acid; add sulphurous
+acid and potassium iodide in excess, and boil till free from iodine.
+Filter and dilute to 500 c.c. Take 50 c.c. of the yellow solution for
+the determination. A few c.c. of a dilute solution of sulphurous acid (1
+in 100) will prevent the liberation of iodine. The following experiments
+test the method of separation. Ten grams of copper were treated as above
+and precipitated with 1.5 gram of "soda;" the precipitate contained 0.6
+milligram of bismuth (= 0.006 per cent.). The filtrate treated with
+another 1.5 gram of "soda" gave a precipitate which was free from
+bismuth. To the filtrate from this was added 1.0 milligram of bismuth,
+and another fraction was precipitated with 1.5 gram of "soda." In this
+precipitate was found 1.0 milligram of bismuth. To the filtrate another
+milligram of bismuth was added and the separation with "soda" repeated.
+The bismuth was separated from this precipitate with ammonic carbonate
+before determination, and 0.9 milligram was found.
+
+~Arsenic.~--The proportion of arsenic in copper varies from 0.01 to 0.75
+per cent. whilst in coarse copper it may amount to 2 or even 3 per cent.
+To determine it, dissolve 5, 10, or 20 grams of the copper (according to
+the amount of arsenic present) in 18 c.c., 35 c.c., or 70 c.c. of nitric
+acid, and an equal volume of water. Boil off the nitrous fumes, dilute
+to 100 c.c. and neutralise with soda; add 1.5 or 2 grams of carbonate of
+soda dissolved in a little water, and boil. Filter (washing is
+unnecessary) and dissolve back into the flask with a little dilute
+hydrochloric acid; add 30 c.c. of dilute ammonia and 25 c.c. of
+"magnesia mixture," and allow to stand overnight. The whole of the
+arsenic is precipitated as ammonic-magnesic arsenate in one hour, but it
+is advisable to leave it longer. The precipitate may be dried and
+weighed, or, better, titrated with uranium acetate. (See _Arsenic_.) To
+test this method of separation 10 grams of pure copper were taken and
+0.200 gram of arsenic dissolved with it. The arsenic was determined by
+titration with uranium acetate, and 0.200 gram was found. Two other
+similar experiments with 0.080 and 0.010 gram of arsenic added, gave
+0.079 and 0.012 gram respectively.
+
+Antimony or bismuth may be present without interfering with the
+titration. With 0.100 gram of antimony and 0.100 gram of arsenic, 0.100
+gram of arsenic was found; and in another case, with 0.100 gram of
+bismuth and 0.060 gram of arsenic, 0.060 gram was found. In these
+experiments the antimony and bismuth were present in the assay solution
+when titrated. For a gravimetric determination they would require to be
+removed before precipitating with "magnesia mixture."
+
+Phosphorus, if present, counts as arsenic in the proportion of 1 to 2.4;
+but, except in the case of coarse coppers, it is always absent.
+
+Iron, if present, interferes by forming a white flocculent precipitate
+of ferric arsenate after the addition of the sodium acetate and
+preliminary to the titration. Each milligram of iron abstracts, in this
+way, 1.3 milligrams of arsenic.
+
+~Iron.~--Refined coppers carry traces of iron, varying from 0.001 to
+0.01 per cent. It is best determined during the arsenic estimation. The
+precipitate of the ammonic-magnesic arsenate will contain the whole of
+the iron as ferric hydrate. On dissolving in hydrochloric acid,
+neutralising with ammonia, adding 5 c.c. of sodic acetate, diluting, and
+boiling, it reappears as a white precipitate of ferric arsenate. It is
+filtered off (the arsenic being estimated in the filtrate), dissolved in
+warm hydrochloric acid, and determined colorimetrically as described
+under _Iron_. A series of experiments testing the separation is there
+given.
+
+~Phosphorus.~--Refined coppers do not carry phosphorus, although it may
+be present in "coarse copper" up to 1 per cent. or more. In such samples
+the following method is adopted for the estimation of both phosphorus
+and arsenic. Dissolve 10 grams of copper and 0.1, 0.2, or 0.3 gram of
+iron wire (according to the amount of arsenic and phosphorus present) in
+35 c.c. of nitric acid and an equal volume of water. Add soda till the
+free acid is nearly neutralised. Next add a strong solution of sodium
+acetate, until the solution ceases to darken on further addition, then
+dilute with water to half a litre. The solution is best contained in a
+large beaker; it is next heated to the boiling point, and at once
+removed and allowed to settle. If the precipitate is light coloured it
+is evidence that sufficient iron has not been added, or, if it is green,
+from basic copper salts, it shows that the solution was not sufficiently
+acid. In either case start afresh. Filter off the precipitate and wash
+with hot water containing a little sodium acetate, dissolve it off the
+filter with hot dilute hydrochloric acid, add ammonia in excess, and
+pass sulphuretted hydrogen for five minutes. Warm at about 70° C. for a
+quarter of an hour. Filter. The clear yellow filtrate contains the
+arsenic and phosphorus. Add dilute sulphuric acid in excess; filter off
+the yellow precipitate of sulphide of arsenic, dissolve it in nitric
+acid, and titrate with uranium acetate, as described under _Arsenic_.
+
+The filtrate from the sulphide of arsenic is rendered alkaline with
+ammonia and "magnesia mixture" added. The solution is stirred, and
+allowed to stand overnight. The precipitate of ammonic-magnesic
+phosphate is filtered off, dissolved, and titrated with uranium acetate,
+using the same standard solution as is used in the arsenic assay: 0.5
+gram of arsenic equals 0.207 gram of phosphorus.
+
+~Copper.~--The method of determining this has been described under
+_Electrolytic Assay_.
+
+In the method of concentration by fractional precipitation with sodic
+carbonate (which is adopted in most of these determinations) the
+precipitate will contain all the bismuth, iron, and alumina; the arsenic
+and phosphorus as cupric arsenate and phosphate; and the greater part of
+the lead, antimony, and silver. The nickel and cobalt, and the sulphur
+as sulphuric acid, will remain in solution with the greater part of the
+copper.
+
+
+PRACTICAL EXERCISES.
+
+1. According to a wet assay 2 grams of a certain ore contained 0.3650
+gram of copper. What would you expect the dry assay produce to be?
+
+2. A standard solution is made by dissolving 25 grams of potassic
+cyanide and diluting to a litre. Assuming the salt to be 98 per cent.
+real cyanide, what would 100 c.c. of the solution be equivalent to in
+grams of copper?
+
+3. How would you make a solution of "hypo" of such strength that 100
+c.c. shall equal 0.633 gram of copper?
+
+4. What weight of ore, containing 17.0 per cent. of copper, would you
+take in order to get about 0.5 gram of copper in solution for
+electrolysis?
+
+5. The solution of copper in nitric acid is effected by the following
+reaction:--
+
+3Cu + 8HNO_{3} = 3Cu(NO_{3})_{2} + 4H_{2}O + 2NO.
+
+What volume of nitric acid will be required to dissolve 1 gram of
+copper?
+
+
+LEAD.
+
+The chief ore of lead is galena, a sulphide of lead, common in most
+mining districts, and frequently associated with blende and
+copper-pyrites. It always carries more or less silver; so that in the
+assay of the ore a silver determination is always necessary. Carbonate
+(cerussite), sulphate (anglesite), and phosphate (pyromorphite) of lead
+also occur as ores, but in much smaller quantities.
+
+Lead ores are easily concentrated (owing to their high specific gravity,
+&c.) by mechanical operations, so that the mineral matter sent to the
+smelter is comparatively pure.
+
+Lead is readily soluble in dilute nitric acid. The addition of sulphuric
+acid to this solution throws down heavy, white, and insoluble lead
+sulphate.
+
+Galena is soluble in hot hydrochloric acid, sulphuretted hydrogen being
+evolved; but the action is retarded by the separation of the sparingly
+soluble lead chloride. If a rod of zinc is placed in this solution,
+metallic lead is precipitated on it as a spongy mass, the lead chloride
+being decomposed as fast as it is formed. The opening up of the ore is
+thus easily effected, the sulphur going off as sulphuretted hydrogen,
+and the lead remaining in a form easily soluble in dilute nitric acid.
+Galena itself is readily attacked by nitric acid, part of the lead going
+into solution, and the rest remaining as insoluble lead sulphate. The
+sulphate is due to the oxidation of the sulphur by nitric acid; its
+amount will vary with the quantity and concentration of the acid used.
+Sulphate of lead is soluble in solutions of ammonium or sodium acetate;
+or it may be converted into carbonate by boiling with carbonate of soda.
+The carbonate, after washing off the sulphate of soda, dissolves easily
+in nitric acid. The precipitation of lead from acid solutions with
+sulphuric acid, and the solubility of the precipitate in ammonium
+acetate, distinguishes it from all other metals. The addition of
+potassium chromate to the acetate solution reprecipitates the lead as a
+yellow chromate.
+
+
+DRY ASSAY.
+
+The dry assay of lead is largely used, but it is only applicable to rich
+or concentrated ores, and even with these only gives approximate
+results. Both lead and lead sulphide are sensibly volatile at a
+moderately-high temperature; hence it is necessary to obtain a slag
+which is easily fusible. As a reducing agent iron is almost always used,
+and this is added either in the form of an iron rod, or the crucible
+itself is made of this metal. The flux used is carbonate of soda.
+
+When a clay crucible is used, the method of working is as
+follows:--Weigh up 25 grams of the dry and powdered ore, mix with an
+equal weight of "soda" and 2 grams of tartar; place in a crucible (E.
+Battersea round), and then insert a piece of iron rod about half an inch
+in diameter, and of such a length that it will just allow the crucible
+to be covered. The rod should be pushed down so as to touch the bottom
+of the crucible, and the mixture should be covered with a sprinkling of
+borax. Place in a furnace heated to, but not above, redness, and cover
+the crucible. In about twenty minutes the charge will be fused: the
+fusion is complete when bubbles of gas are no longer being evolved; and
+then, but not till then, the iron is withdrawn, any adhering buttons of
+lead being washed off by dipping the rod a few times in the slag. Cover
+the crucible, leave it for a minute or two, and then pour. Detach the
+slag, when cold, by hammering. The weight of the button multiplied by 4
+gives the percentage. The commoner errors of students in working the
+process are too high a temperature and too quick a withdrawal.
+
+A sample of ore treated in this manner gave on duplicate assay 17.5 and
+17.6 grams of lead, equalling 70.0 and 70.4 per cent. respectively. By
+wet assay the sample gave 73.3 per cent. Using an iron crucible, the
+results will be 1 per cent. or so higher. The crucible must be made of
+wrought iron; and, if it has been previously used, should be cleaned by
+heating to dull redness and scraping the scale off with a stirrer. Take
+30 grams of the ore, mix with 30 grams of "soda" and 3 grams of tartar;
+put the mixture in the crucible, and cover with a sprinkling of borax;
+heat for about twenty minutes at not too high a temperature, and then
+scrape down the slag adhering to the side with a stirrer. Leave in the
+furnace till action has ceased. Before pouring, tap the pot gently, and
+then tilt it so as to make the slag wash over the part of the crucible
+along which the charge is to be poured. Pour; and, when cold, clean and
+weigh the button of metal. A crucible may be used from ten to twenty
+times.
+
+These assays are for ores containing the lead chiefly as sulphide. For
+oxidised ores, charcoal or tartar is employed as the reducing agent. The
+student may practise on red lead as follows:--Take 30 grams of red lead;
+mix with 10 grams each of borax and "soda" and about 1.5 gram of
+powdered charcoal; place in a small clay crucible with a cover (C.
+Battersea round), fuse at a gentle heat, and pour when action ceases.
+This assay will only take a few minutes.
+
+Where lead is present as phosphate (as in the case of pyromorphite), or
+mixed with phosphates (as sometimes happens), carbonate of soda is a
+suitable flux; but the phosphate of soda which is formed makes a thick
+tenacious slag, which is very apt to be carried out of the pot by the
+escaping gas. A wide-mouthed clay pot is taken and a little fluor spar
+added. For the assay of pyromorphite the following charge may be
+used:--Ore, 20 grams; "soda," 25 grams; tartar, 7 grams; and fluor spar,
+5 grams; and 2 grams of borax as a cover. This will melt down in about
+ten minutes, and should be poured as soon as tranquil.
+
+
+WET ASSAY.
+
+In the case of galena the best method of getting the lead into solution
+is to treat with hydrochloric acid and zinc. Put 1 gram of the ore in an
+evaporating dish 4 inches across, and cover with 10 c.c. of dilute
+hydrochloric acid. Heat till the evolution of sulphuretted hydrogen
+becomes sluggish, and then drop in a piece of zinc rod. If the solution
+effervesces too strongly, dilute it. Continue the heating until the
+sulphide is seen to be all dissolved; when the lead is all precipitated,
+pour off the liquid and wash twice with cold water. Peel off the
+precipitated lead with the help of a glass rod, and then clean the zinc.
+Cover the lead with 20 c.c. of water and 5 c.c. of dilute nitric acid,
+and heat gently till dissolved; all the lead will be in solution, and,
+when filtered off from the gangue, will be ready for a gravimetric
+determination. For volumetric work this filtering is unnecessary.
+
+The chief objection to this method is that commercial zinc carries
+considerable quantities of lead. Although this can be determined and
+allowed for, the correction required is in most cases too large to be
+satisfactory. The following method is applicable in all cases, but is
+more troublesome:--Treat 1 gram of the ore with 10 c.c. of dilute nitric
+acid in an evaporating dish covered with a clock-glass, and evaporate
+till nearly dry. Take up with 50 c.c. of water, and add 10 c.c. of
+dilute sulphuric acid. Filter. The residue contains the lead as
+sulphate, together with the insoluble matter of the ore and globules of
+sulphur. Warm with a solution of ammonium acetate, and filter. The lead
+will be in the filtrate, and is recovered in a state fit for direct
+gravimetric estimation by the addition of dilute sulphuric acid. If the
+volumetric method is to be used, the lead sulphate should be dissolved
+out with a solution of sodium acetate instead of with the ammonium salt
+solution.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The lead is separated and precipitated as sulphate, as already
+described. The solution must be allowed to stand, and the clear liquid
+be decanted through a filter. Transfer the precipitate, and wash with
+very dilute sulphuric acid (1 or 2 c.c. in 100 c.c. of water). The acid
+must be completely removed with one or two washes with cold water, and
+then with alcohol. The volume of liquid required for washing is small,
+as the precipitate is dense and easily cleaned; but the washing must be
+carefully done, since if any acid remains it will, on drying, char the
+paper, and render the subsequent work troublesome. Dry, transfer to a
+watch-glass, and burn the filter paper, collecting its ash in a weighed
+porcelain crucible. The filter paper must be freed as much as possible
+from the lead sulphate before burning, and the ash treated with a drop
+or two of nitric and sulphuric acids. Transfer the lead sulphate to the
+crucible; ignite gently, keeping the temperature below redness; cool,
+and weigh. The precipitate will contain 73.6 per cent. of lead oxide or
+68.3 per cent. of lead.
+
+~Determination of Lead in Commercial Zinc.~--Take 10 grams of zinc, and
+treat (without heating) with 60 c.c. of dilute hydrochloric acid. When
+the zinc is nearly all dissolved, decant off the clear liquid, and
+dissolve the residue in 2 c.c. of dilute nitric acid. Evaporate till
+most of the acid is removed; dilute to 20 or 30 c.c. with water, and add
+10 c.c. of dilute sulphuric acid. Filter off, and weigh the lead
+sulphate. Ten grams treated in this way gave--0.1610 gram of lead
+sulphate, equivalent to 1.10 per cent. of lead.
+
+
+VOLUMETRIC METHOD.
+
+This is based upon the reaction between chromate of potash and soluble
+lead salts in neutral solutions, whereby an insoluble yellow chromate of
+lead is produced.[60] An excess of the chromate is required to complete
+the reaction, so that the point at which an indicator shows the presence
+of undecomposed chromate cannot be satisfactorily taken as the finish.
+Therefore an excess of the standard chromate must be run in, and such
+excess determined.
+
+
+Chromate of lead is not precipitated from strong nitric acid solutions,
+and only incompletely from dilute ones. Acids generally are detrimental
+to the precipitation, and must be neutralised before titrating. If the
+lead is present as sulphate in sodic acetate solution, it is well to
+render it distinctly alkaline with ammonia.
+
+Lead chromate precipitated in the cold is a lemon-yellow, light
+precipitate, very difficult to filter: on heating to 40° C. the colour
+becomes orange; at 60° C. it assumes a deeper hue, and becomes
+flocculent; and at a boiling temperature it still further darkens and
+settles readily. These changes in colour are not due to any chemical
+change, as will be seen by testing the filtrate for chromium or lead:
+this is an advantage to the assay, since it is only at the higher
+temperature that the precipitate can be easily filtered. The lead is not
+completely precipitated, but the amount remaining in solution is only 2
+or 3 milligrams, which is just sufficient to give a dark coloration with
+sulphuretted hydrogen.
+
+_The standard chromate of potash solution_ is made by dissolving 7.13
+grams of bichromate of potash and 2.0 grams of caustic soda in water,
+and diluting to 1 litre; or 9.40 grams of the neutral chromate
+(K_{2}CrO_{4}) may be dissolved and diluted to 1 litre: 100 c.c. will be
+equivalent to 1.000 gram of lead.
+
+_Standard Lead Solution._--16 grams of nitrate of lead (Pb(NO_{3})_{2})
+are dissolved in water and diluted to 1 litre; 100 c.c. will contain
+1.000 gram of lead.
+
+_Acetate of Soda Solution._--250 grams of the crystallised salt
+(NaAc.3H_{2}O) are dissolved, and diluted to 1 litre. Use 40 c.c. for
+each assay.
+
+In the titration the assay solution should measure 150 to 200 c.c., and
+should be boiling or nearly so. It is best contained in a pint flask,
+and the standard chromate solution used with an ordinary burette. Run in
+the chromate solution in a steady stream until the whole of the lead has
+been precipitated. The amount required for this may be calculated: for
+example, 1 gram of an 80 per cent. ore would require 80 c.c. A little of
+the assay may be filtered off, and if it does not show a yellow colour
+in the filtrate run in 2 c.c. more of the standard solution and continue
+this addition till a colour is shown. After this run in another c.c. to
+ensure an excess, dilute to 250 c.c., and heat to boiling; allow to
+settle for three or four minutes, filter off 50 c.c. into a Nessler
+glass, and determine the excess of chromate colorimetrically. The excess
+found in the 50 c.c. must, of course, be multiplied by five, and then be
+deducted from the quantity of chromate originally run into the assay
+solution. The quantity to be deducted should not exceed 3 c.c. Where a
+number of determinations are made the colorimetric estimation is
+facilitated by using a series of standard phials similar to those
+described under the _Electrolytic Copper Assay_. The determination is
+rendered sharper and less liable to error by the addition of a few drops
+of acetic acid to convert the chromate into bichromate. The same
+chromate solution must be used in this determination as was used in the
+precipitation.
+
+In standardising the chromate solution, the standard lead nitrate
+solution is used. A quantity containing about as much lead as the assay
+is supposed to contain is measured off, rendered alkaline with dilute
+ammonia, and then neutralised with acetic acid, using a small piece of
+litmus paper dropped into the solution as indicator. Then dilute, boil,
+and titrate. When the lead in the assay has been separated as sulphate
+and dissolved in sodic acetate, less chromate is apparently required,
+and in this case it will be necessary to precipitate the lead in the
+standard with an equivalent of sodic sulphate and redissolve in sodic
+acetate just as in the assay. In these solutions (although there is
+considerable chromate in excess) a further addition of 5 or 6 c.c. of
+the chromate solution will cause a further precipitate. The following
+experiments show the effect of variation in the conditions of the
+assay:--
+
+~Effect of Varying Temperature.~--Twenty c.c. of lead nitrate solution
+and 10 grams of sodium acetate were used; diluted to 200 c.c., heated to
+the desired temperature, and titrated. The results were:--
+
+  Temperature             15°        30°        50°        100°
+  "Chromate" required  19.8 c.c.  19.5 c.c.  19.3 c.c.   19.2 c.c.
+
+The first two of these filtered badly, the precipitate coming through
+the filter; the last was very satisfactory in the working.
+
+~Effect of Varying Bulk.~--Using 20 c.c. of lead nitrate, and 10 grams
+of sodium acetate as before, diluting to the required bulk, heating to
+boiling, and titrating, the results were:--
+
+  Bulk                 100.0 c.c. 200.0 c.c.  500.0 c.c. 1000.0 c.c.
+  "Chromate" required   19.6  "    19.3  "     19.4  "     19.4  "
+
+~Effect of Varying Acetic Acid.~--Since the experiments are carried out
+in the presence of sodic acetate, acetic acid is the only acid whose
+effect need be considered. Working as before, but with 200 c.c. bulk and
+varying amounts of the acid, the results were:--
+
+  Acid present           --        10.0 c.c.   20.0 c.c.   40.0 c.c.
+  "Chromate" required  19.7 c.c.   19.1  "     18.5  "     17.3  "
+
+These experiments show that only slight quantities of acid are
+admissible.
+
+~Effect of Varying Sodium Acetate.~--With the same conditions as before,
+but with varying weights of sodium acetate, the results were:--
+
+  Sodium acetate present   --      5 grams  10 grams  25 grams  50 grams
+  "Chromate" required   19.7 c.c. 19.6 c.c. 19.6 c.c. 18.8 c.c. 17.8 c.c.
+
+These experiments show that excessive quantities of sodium acetate must
+be avoided. Ammonium acetate interferes to a greater extent, and if
+both acetic acid and this salt are present, each exerts its disturbing
+influence. With 10 grams of ammonium acetate, 19.4 c.c. of the chromate
+solution were required instead of 19.7 c.c. in the absence of this salt;
+with 10 grams of the acetate and 10 c.c. of acetic acid, only 18.6 c.c.
+were required.
+
+~Effect of Foreign Salts.~--As already stated, sulphates interfere.
+Twenty c.c. of the lead nitrate solution were taken, precipitated with
+sulphate of soda, and the precipitate dissolved in 10 grams of sodium
+acetate and titrated as before. Duplicate experiments required 18.6 c.c.
+and 18.7 c.c. of the chromate solution. A similar experiment with 40
+c.c. of lead nitrate required 37.4 c.c. of chromate. If the sulphate had
+not been present, the results would have been 19.7 c.c. and 39.4 c.c.
+respectively.
+
+~Effect of Varying Lead.~--In these experiments the conditions were as
+before, but with varying amounts of lead.
+
+  Lead nitrate solution present  10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
+  Chromate solution required.     9.4  "   19.7  "   48.8  "    98.2  "
+
+~Determination of Lead in Galena.~--Weigh up 1 gram of the powdered and
+dried ore, and boil in an evaporating dish with 10 c.c. of dilute
+hydrochloric acid. When the action becomes sluggish, dilute with an
+equal bulk of water, and add a weighed piece of zinc rod about 1 inch
+long and quarter-inch across. Keep up a moderate action by warming till
+the ore is seen to be completely attacked and the lead precipitated.
+Decant off the solution, wash once, strip off the lead, wash and weigh
+the remaining zinc. Dissolve the lead in 5 c.c. of dilute nitric acid,
+and 5 c.c. of water with the aid of heat. Dilute and transfer to a pint
+flask; add a slight excess of dilute ammonia, and render faintly acid
+with acetic acid. Dilute to 150 c.c., heat to boiling, and run in the
+standard chromate in slight excess, noting the amount required, and make
+up to 250 c.c. with water. Boil the solution, allow to settle for a
+minute or so, filter off 50 c.c., and determine the excess of chromate
+colorimetrically. As an example, 1 gram of an impure galena was
+precipitated with 75 c.c. of standard chromate (100 c.c. = 1.020 gram
+lead). The excess found in 50 c.c. was 0.3 c.c., which, multiplied by 5,
+gives 1.5 c.c. as the excess in the whole solution. The remaining 73.5
+c.c. of "chromate" required by the assay, are equivalent to 0.7497 gram
+of lead. The zinc used up weighed 1.5 grams, and contained 0.0165 gram
+of lead. Thus we get--
+
+      Lead in the assay    0.7497 gram
+      Lead from the zinc   0.0165  "
+                           ------
+  .'. Lead in the galena   0.7332  "
+
+  Equivalent to 73.3 per cent.
+
+Another sample, in which the galena was accompanied with a large
+quantity of pyrites, gave the following results:--Three grams were
+treated with 30 c.c. of dilute hydrochloric acid and a rod of zinc. The
+zinc and lead were carefully transferred to another vessel, the zinc
+cleaned, and the lead (dissolved in 5 c.c. of dilute nitric acid and 20
+c.c. of water) treated as before.
+
+  14.5 c.c. of the chromate were required = 0.1479 gram lead
+  Lead in 2 grams of zinc                 = 0.0220     "
+                                            ------
+  .'. Lead in 3 grams of the ore          = 0.1259     "
+
+  Equivalent to 4.20 per cent.
+
+The same ore gave by separation of the lead with sulphuretted hydrogen,
+and conversion into sulphate, 4.16 per cent.
+
+With fairly pure ores, free from sulphate, the assay may be made more
+quickly as follows: Dissolve 1 gram of the finely powdered ore by
+boiling gently with 40 c.c. of dilute hydrochloric acid for 15 minutes;
+cool; add a few drops of permanganate; neutralise with ammonia, add
+acetic acid and a little sodium acetate. Titrate with standard chromate.
+
+
+COLORIMETRIC PROCESS.
+
+This is based upon the brown coloration produced in very dilute
+solutions of lead by the action of a solution of sulphuretted hydrogen.
+The quantity of lead in the 50 c.c. of the assay solution must not much
+exceed 0.5 milligram, nor be less than 0.01. The sulphuretted hydrogen
+is used in the form of a solution, and is not bubbled through the assay.
+The principle of working is the same as previously described.
+
+_Standard Lead Solution._--Each c.c. of this should contain 0.1
+milligram of lead. It is made by diluting 10 c.c. of the solution of
+lead nitrate, described under the volumetric process, to 1 litre.
+
+_Sulphuretted hydrogen water_ is made by passing a current of the washed
+gas into water till the latter is saturated.
+
+Five c.c. of the sulphuretted hydrogen water are put into a Nessler
+tube, the measured portion of the assay solution added, and the whole
+diluted with water to the 50 c.c. mark. Into the standard Nessler tube
+the same amount of the sulphuretted hydrogen water is put, and diluted
+to nearly 50 c.c. The standard lead solution is then run in till the
+tints are equal. The assay solution must not contain much free acid, and
+if the conditions will allow it, may with advantage be rendered alkaline
+with ammonia. The chief cause of disturbance is the precipitation of
+lead sulphide forming a black turbid solution instead of a brown clear
+one. This may be caused by using hot solutions or an excess of acid.
+Other metals precipitable by sulphuretted hydrogen must be absent as
+well as strong oxidising agents.
+
+~Effect of Varying Temperature.~--The effect of increased temperature is
+to change the colour from brown to black, and to render the estimation
+difficult.
+
+  1 c.c. at 15° C. showed the colour of 0.5 c.c. at 60° C.
+  2  "      "        "          "      1.5   "   at 60° C.
+  3  "      "        "          "      5.0   "   at 50° C.
+
+~Effect of Varying Time.~--The colour becomes lighter on standing: 2
+c.c. on standing 10, 20, and 40 minutes became equal in colour to 1.7
+c.c.
+
+~Effect of Acids and Ammonia.~--Two c.c. of the solution with 2 c.c. of
+dilute hydrochloric acid became cloudy and equivalent to about 2.5 c.c.;
+and a similar result was got with 2 c.c. of dilute sulphuric acid. With
+2 c.c. of dilute ammonia the solution became somewhat darker, or equal
+to 2.3 c.c.; but gave a very clear solution easy to compare.
+
+~Determination of Lead in Commercial Zinc.~--Dissolve 0.1 gram of the
+metal in 1 c.c. of dilute nitric acid evaporates till a solid separates
+out, dilute to 100 c.c. with water, and take 20 c.c. for assay. A sample
+treated in this way required 2.4 c.c.; this multiplied by 5 gives 12.0
+c.c., equivalent to 1.2 milligram of lead, or 1.2 per cent. By
+gravimetric assay the sample gave 1.10 per cent.
+
+
+PRACTICAL EXERCISES.
+
+1. Thirty grams of galena gave on dry assay 21 grams of lead; and this,
+on cupellation, gave 15 milligrams of silver. Calculate the results in
+per cents. of lead and in ounces of silver to the ton of ore.
+
+2. How many ounces of silver to the ton would be contained in the lead
+got from this ore if the loss in smelting is equal to that of the assay?
+
+3. Having given you a sample of white lead freed from oil by washing
+with ether, how would you proceed to determine the percentage of lead in
+it?
+
+
+THALLIUM.
+
+Thallium is a rare metal, found in small quantities in some varieties of
+iron and copper pyrites, and in some lithia micas. It resembles lead in
+appearance. Its compounds resemble the salts of the alkalies in some
+respects; and, in others, those of the heavy metals.
+
+It is detected by the green colour which its salts impart to the flame.
+This, when examined with the spectroscope, shows only one bright green
+line.
+
+It is separated and estimated by dissolving in aqua regia; converting
+into sulphate by evaporation with sulphuric acid; separating the second
+group of metals with sulphuretted hydrogen in the acid solution, boiling
+off the excess of the gas; nearly neutralising with carbonate of soda;
+and precipitating the thallium with an excess of potassic iodide. On
+allowing the liquid to stand for some time a bright yellow precipitate
+of thallous iodide separates out. This is collected on a weighed filter;
+washed with cold water, finishing off with alcohol; dried at 100° C.,
+and weighed. The precipitate is thallous iodide TlI, and contains 61.6
+per cent. of thallium.
+
+
+BISMUTH.
+
+Bismuth is nearly always found in nature in the metallic state; but
+occasionally it is met with as sulphide in bismuthine and as carbonate
+in bismutite. It is also found in some comparatively rare minerals, such
+as tetradymite, combined with tellurium, and associated with gold. In
+minute quantities it is widely distributed: it is a common constituent
+of most copper ores; hence it finds its way into refined copper, which
+is seldom free from it. It is occasionally met with in silver in
+sufficient quantity to interfere with the working qualities of that
+metal.
+
+Bismuth compounds are used in medicine and in the manufacture of alloys.
+Bismuth possesses many useful properties. It has considerable commercial
+value, and sells at a high price.
+
+The metal is brittle, breaks with a highly crystalline fracture, and has
+a characteristic reddish-yellow colour. It is almost insoluble in
+hydrochloric, but readily dissolves in nitric, acid; and gives, if the
+acid is in excess, a clear solution. Bismuth salts have a strong
+tendency to separate out as insoluble basic compounds; this is more
+especially true of the chloride which, on diluting with a large volume
+of water, becomes milky; the whole of the bismuth separating out. The
+nitrate, carbonate, and hydrate yield the oxide (Bi_{2}O_{3}) on
+ignition. This oxide closely resembles litharge. It combines with
+silica, forming fluid slags; and at a red heat is liquid enough to be
+absorbed by a cupel; in fact, bismuth may take the place of lead in
+cupellation. The metal itself is easily fusible, and may be separated
+from its ores by liquation.
+
+The assay of bismuth by wet methods presents little difficulty, and is
+fairly accurate. The price of the metal is such that only methods which
+yield good results should be adopted; and, since bismuth is volatile at
+the temperature of the furnace, and is found mixed with ores not easy to
+flux, as also with metals which are not easily separated by the dry
+method, the dry assay can only be considered as having a qualitative
+value.
+
+
+DRY ASSAY.
+
+~By Liquation.~--This is adapted to ores containing the bismuth as
+metal. Take 20 grams of the powdered ore and place in a crucible with a
+perforated bottom, put this crucible into another of about the same size
+and lute the joint. Lute on a cover, place in the furnace and heat to
+redness. The bismuth melts readily and drains into the lower crucible
+from which, when cold, it is taken and weighed.
+
+~By Fusion.~--For fairly pure ores the process is as follows:--Take 20
+grams of the ore and mix with 20 grams of fusion mixture, 10 grams of
+salt and 5 or 10 grams of potassium cyanide; place in a crucible, cover,
+and fuse at a moderate temperature for about fifteen minutes; pour; when
+cold detach the metal and weigh.
+
+For coppery ores in which the metals are present as sulphides use the
+fluxes just given with 2 grams of charcoal (instead of the cyanide) and
+a little sulphur.
+
+For coppery ores in which the metals are present as oxides, mix 20 grams
+of the ore with 10 grams of fusion mixture, 4 grams of salt, 4 grams of
+sulphur and 2 grams of charcoal; and fuse.
+
+A considerable percentage of bismuth is lost in these assays; it is
+stated as being nearly 8 per cent. of the metal present.
+
+
+WET METHODS.
+
+~Detection.~--Bismuth is detected by dissolving the substance in nitric
+or hydrochloric acid and precipitating the diluted solution with
+sulphuretted hydrogen. The precipitated sulphides, after digesting with
+soda and washing, are dissolved in nitric acid and the solution boiled
+with ammonium carbonate. The precipitate is washed and then warmed with
+dilute sulphuric acid. The solution will contain the bismuth. Add a
+solution of potassium iodide in excess, and boil; a yellow or dark brown
+solution proves that bismuth is present. Another good test for small
+quantities of bismuth is to add tartaric acid to the solution to be
+tested, and then to make it alkaline with potash. Add a few c.c. of
+Schneider's liquid,[61] and heat. A brownish-black colour is produced by
+as little as one part of bismuth in 200,000 of solution. The test is not
+applicable in the presence of mercury, copper, or manganese.
+
+Compounds of bismuth fused with cyanide of potassium in a Berlin
+crucible readily give a globule of bismuth which is recognised by its
+appearance and fracture.
+
+~Solution and Separation.~--The solution of bismuth compounds presents
+no difficulty. They are soluble in nitric acid or aqua regia, and,
+provided the solution is sufficiently acid, they remain dissolved. In
+separating it from other metals the solution is made up to about 100
+c.c. and treated with a current of sulphuretted hydrogen. The bismuth
+comes down in a tolerably strong acid solution. The sulphide is decanted
+on to a filter and washed. It is next digested with ammonic sulphide;
+or, better (especially when other metals are present), dissolved in
+nitric acid, and treated with an excess of ammonia and a current of
+sulphuretted hydrogen. The precipitate is filtered off and evaporated to
+dryness with nitric acid. It is taken up with a few drops of sulphuric
+acid and a little water; and warmed and filtered, if necessary. The
+filtrate is nearly neutralised with ammonia; ammonium carbonate added in
+slight excess; and the liquid heated to boiling and filtered. The
+bismuth will be contained in the precipitate with perhaps traces of
+lead, antimony, tin, or sometimes iron from incomplete separation or
+washing. When only traces of a precipitate are got it must be tested.
+The bismuth precipitate is readily soluble in dilute nitric acid.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The bismuth having been separated and dissolved in nitric acid[62] is
+precipitated (after dilution) by the addition of carbonate of ammonium
+in slight excess, and boiling. The precipitate is filtered off, washed
+with hot water, dried, ignited, and weighed. The ignition should be
+performed carefully at not above a low red heat. The oxide which is
+formed has, at this temperature, a dark yellow or brown colour, and
+becomes yellow on cooling. It is bismuthic oxide (Bi_{2}O_{3}) and
+contains 89.65 per cent. of bismuth. Fusion with potassium cyanide at a
+temperature just sufficient to melt the salt reduces it to the metal
+which falls to the bottom and runs into a globule. The button of metal
+may be weighed, but it often sticks tenaciously to the bottom of the
+crucible. The precipitation with ammonic carbonate must not be made in a
+sulphate or chloride solution; since basic compounds would then be
+thrown down, and the result on weighing would either be too low (because
+of the volatilisation of the chloride), or too high (because of the
+retention of sulphuric acid).
+
+Bismuth compounds in a nitric acid solution are readily decomposed by
+the electric current, but the deposited bismuth is not coherent. It
+comes down in shaggy tufts which are difficult to wash and easy to
+oxidise.
+
+
+VOLUMETRIC ASSAY.
+
+There are two methods which have been proposed; one based on the
+precipitation as chromate and the estimation of the chromic acid; and
+the other on the precipitation as oxalate and subsequent titration with
+permanganate of potash. These offer little advantage over the easy
+gravimetric determination.
+
+
+COLORIMETRIC METHOD.
+
+Bismuth iodide dissolves in excess of potassium iodide, forming a
+yellow-coloured solution, indistinguishable in colour from that given by
+iodine. The colour, however, is not removed by boiling or by sulphurous
+acid. Since none of the commoner metals give such a colour, and free
+iodine is easily separated by boiling, this method is specially suited
+for small determinations of bismuth.
+
+It requires a _solution of bismuth_, made by dissolving 0.1 gram of
+bismuth in a drop or so of nitric acid, evaporating with a little
+sulphuric acid and diluting with water to 1 litre. 1 c.c. will contain
+0.1 milligram of bismuth. And a _solution of sulphurous acid_, made by
+diluting 10 c.c. of the commercial acid to 1 litre with water.
+
+The determination is made in the usual way: 50 c.c. of the prepared
+solution, which should not carry more than 0.75 milligram nor less than
+0.01 milligram of bismuth, are placed in a Nessler tube and the colour
+compared with that observed in a similar tube containing water and
+potassium iodide on adding the standard solution of bismuth.
+
+The assay solution is prepared by separating the bismuth with
+sulphuretted hydrogen, boiling the precipitate with nitric acid, and
+evaporating with sulphuric acid. Take up with water, add 10 or 20 c.c.
+of solution of potassium iodide, boil off any iodine liberated, dilute,
+filter, and make up to 100 c.c. According to the depth of colour take
+10, 20, or 50 c.c. and transfer to the Nessler tube. Add a few c.c. of
+the solution of sulphurous acid. Into the other Nessler tube put as much
+potassium iodide solution as is contained in the assay tube, with
+sulphurous acid and water to within a few c.c. of the bulk. Then add the
+standard bismuth solution till the tints are equal.
+
+The student must be careful not to confuse the colour of the bismuth
+iodide with that of free iodine. If the yellow colour is removed by
+boiling and returns on standing it is due altogether to iodine; if it is
+lessened by the addition of a few drops of the dilute sulphurous acid,
+it is in part due to it. Hence the necessity of having a little free
+sulphurous acid in each tube. A strong solution must not be used, since
+it liberates iodine from potassium iodide.
+
+The following experiments illustrate the effect of variation in the
+conditions of the assay:--
+
+~Effect of Varying Temperature.~--At a higher temperature the colour is
+somewhat lessened.
+
+  1.0 c.c. at 15° C. showed the colour of 0.8 c.c. at 70° C.
+  2.5  "       "        "          "      2.0          "
+  5.0  "       "        "          "      5.0          "
+
+~Effect of Free Acid.~--
+
+  2.5 c.c. with 5 c.c. of nitric acid equalled 2.5 c.c.
+  5.0  "        "       sulphuric acid    "    5.0  "
+
+Hydrochloric acid almost completely removes the colour, which, however,
+is restored by the addition of a few crystals of potassium iodide.
+
+~Effect of Alkalies.~--Ammonia, soda, or potash destroys the colour, but
+it is restored on acidifying with nitric or sulphuric acid.
+
+~Effect of Ammonic Salts.~--The following table shows the results after
+addition of ammonic salts:--
+
+  -------------+----------------+-----------------+-----------------
+  C.c. present.|With 10 grams   |With 10 grams    |With 10 grams
+               |Ammonic Nitrate.|Ammonic Sulphate.|Ammonic Chloride.
+  -------------+----------------+-----------------+-----------------
+    1.0 c.c.   |    0.9 c.c.    |    1.1 c.c.     |       --
+    2.5  "     |    2.5  "      |    2.7  "       |       --
+    5.0  "     |    5.0  "      |    5.5  "       |       --
+  -------------+----------------+-----------------+-----------------
+
+Ammonic chloride, like hydrochloric acid, removes the colour, which may
+be restored on the addition of more potassium iodide. Nitrates and
+sulphates do not thus interfere.
+
+~Effect of Foreign Salts.~--Sodic hyposulphite almost completely removes
+the colour. Copper salts liberate iodine; but when this has been removed
+by boiling and the cuprous iodide has been filtered off there is no
+further interference. Dilute solutions of lead salts give no colour.
+
+
+PRACTICAL EXERCISES.
+
+1. A fusible alloy is made up of 8 parts of bismuth, 5 of lead, and 3 of
+tin. What weight of oxide of bismuth, Bi_{2}O_{3}, would you get on the
+analysis of 1 gram of it?
+
+2. What weight of bismuth can be got from 2 grams of the subnitrate
+BiONO_{3}.H_{2}O?
+
+3. How would you detect and separate arsenic, lead, and copper in a
+sample of bismuth?
+
+
+ANTIMONY.
+
+Antimony occurs in the native state, but is rare; its common ore is
+antimonite, the sulphide (Sb_{2}S_{3}). Jamesonite and other sulphides
+of lead and antimony are frequently met with. Sulphide of antimony is
+also a constituent of fahlerz and of many silver ores.
+
+Antimonite occurs generally in fibrous masses, has a lead-like metallic
+lustre, is easily cut with a knife, and melts in the flame of a candle.
+
+Antimony itself has a very crystalline fracture, is brittle, and has a
+bluish-white colour. It is used in the preparation of alloys with lead
+and tin for the manufacture of type-metal. It is readily fusible, and
+imparts hardness and the property of taking a sharp cast to its alloys.
+It is practically insoluble in hydrochloric acid. On boiling with strong
+nitric acid it is converted into antimonic oxide (Sb_{2}O_{5}), which is
+a powder almost insoluble in this acid or in water, but which may be got
+into solution with difficulty by the prolonged action of hydrochloric
+and tartaric acids. Antimonic oxide is converted on ignition into the
+tetroxide (Sb_{2}O_{4}) with loss of oxygen. Antimony forms two series
+of salts, antimonious and antimonic; and advantage is taken of this in
+its determination volumetrically. Either sulphide of antimony yields
+antimonious chloride on boiling with hydrochloric acid, sulphuretted
+hydrogen being given off; and, in the case of antimonic sulphide,
+sulphur is deposited. Antimonious is converted into antimonic chloride
+by treatment with permanganate of potash in an acid solution. Antimonic
+chloride and potassium iodide react, forming antimonious chloride and
+free iodine. This latter may be got rid of by boiling. Sulphide of
+antimony is separated from the ore by liquation; this regulus is met
+with in commerce as "crude antimony."
+
+
+DRY ASSAY.
+
+An approximate determination of the amount of sulphide of antimony in an
+ore may be made by fusing and liquating in a luted double crucible in
+the manner described under bismuth. This is unsatisfactory. The
+determination of metallic antimony in an ore is made either by fusion
+with potassium cyanide or by fusion with iron, as in the galena assay.
+Both methods yield poor results; and, where iron is used, it must be
+added in quantity only sufficient for desulphurising; this amounts to
+about 40 per cent. in pure ores. If the iron is in excess it alloys with
+the reduced antimony. If, on the other hand, it is insufficient, the
+metal will contain sulphur; or sulphide of antimony will be lost in the
+slag.
+
+The following note, for which we are indebted to Mr. Bedford McNeill,
+A.R.S.M., gives a description of the method adopted in the commercial
+valuation of a parcel of antimony ore:--
+
+The antimony smelter, when he wishes to determine the value of any
+parcel of ore--usually the sulphide--that may be offered for sale,
+practically has recourse to the smelting operation. That is, a quantity
+of 2 or 3 cwts. taken by his sampler having been obtained, he treats it
+under the immediate supervision of the foreman smelter as if it formed
+part of the ore in process of daily reduction at his works. He thus
+determines by actual trial the output which it may fairly be anticipated
+will be yielded by the bulk, and upon the result of this trial or assay,
+and the knowledge gained of the actual behaviour of the ore under
+treatment, he bases his tender, knowing that, should he secure the
+parcel, he may confidently expect a similar return.
+
+Briefly, the process consists of the three ordinary operations of--
+
+  (a) Singling or removing most of the antimony from the ore;
+  (b) Doubling;
+  (c) Refining or "starring."
+
+But in the assay sufficient information is generally given by the first
+two of these.
+
+A new pot having been taken and made hot in the furnace, 40 or 45 lbs.
+of the ore is weighed in (the mineral from the necessities of sampling
+not exceeding walnut size); 1 to 3 lbs. of salt cake is now added to
+render the separation of the resulting sulphide of iron more easy, as
+also to assist in the fusion of the gangue; 20 to 25 lbs. of tin-plate
+scrap, beaten more or less into ball shape, is weighed, placed on the
+top of the ore and salt cake, and the whole brought to a state of
+fusion. The foreman from time to time takes notice of the behaviour of
+the ore under the working conditions. Ores that manifest a tendency to
+"boil" or "froth " require the admixture of other more sluggish mineral
+in order to render their reduction economically practicable.
+
+After 1-1/4 to 1-1/2 hours (the time depending mainly on the
+temperature), the contents of the crucible are usually in a state of
+tranquil fusion. The pot is now lifted from the fire, and its contents
+transferred to a conical iron mould, the empty pot being immediately put
+back into the fire, and the latter "mended" with sufficient coke for
+another run. The conical mould (when dealing with a "strange" ore, and
+the possibility of insufficient iron being present to satisfy the
+sulphur contents) is wiped inside with clay previous to pouring in the
+molten charge. Otherwise the mould itself will be attacked, and the
+contents after solidifying will require to be chiselled out piecemeal.
+
+A further 40 lbs. of the ore is now charged into the crucible with iron
+as above; but before this second charge is ready to be drawn an
+inspection of the first may suggest the addition of either 3 or 5 lbs.
+more iron, or 5 or 10 lbs. more ore.
+
+It is a good fault rather to aim at an excess of iron as tending to
+clean the ore from antimony, any of the latter that (from an
+insufficiency of iron) may be left in the slag from the first process
+being irretrievably lost; whereas, if the iron be in excess, that which
+is combined with the crude antimony resulting from the first process is
+easily got rid of by adding 3 to 5 lbs. or so of ore in the second
+process.
+
+This latter, as practised for the determination of the value of a parcel
+of ore, consists in selecting two of the best quality singles, resulting
+from perhaps four or five trials as above, and running them down with a
+few pounds of salt cake, or a mixture of salt cake with American potash,
+and (as is generally necessary) a small addition of ore.
+
+Upon the final result (confirmed perhaps on another pair of singles,
+and, judging from the total weight or output of the metal as calculated
+from the ore used in "singling," plus any added in the "doubling," the
+crystalline fracture and face of the metal, its colour, etc.) the price
+to be offered for the parcel of ore is fixed.
+
+
+WET METHODS.
+
+~Detection.~--The antimony, if any, being got into solution by treating
+the ore with hydrochloric acid or aqua regia may be detected by
+evaporating with hydrochloric acid, diluting, and filtering into the
+cover of a platinum crucible or (better) a platinum dish. A small lump
+of zinc is then added, and, if antimony is present, _the dish_ will in a
+minute or so be stained black with a deposit of metallic antimony. This
+stain is removed by nitric, but not by hydrochloric, acid. The reaction
+is delicate and characteristic; arsenic under like conditions is evolved
+as arseniuretted hydrogen, and tin is deposited as metal _on the zinc_.
+
+~Solution.~--Ores, &c., containing antimony are best opened up by
+boiling with hydrochloric acid or aqua regia; treatment with nitric
+acid should be avoided wherever possible, since it forms antimonic acid,
+which is subsequently dissolved only with difficulty. Salts of antimony
+in solution have a tendency to form insoluble basic salts; so that care
+must be exercised in diluting. Compounds such as antimonite which are
+soluble in hydrochloric should be dissolved at once in that acid.
+
+~Separation.~--To the solution add potash in excess and a little free
+sulphur, and pass a current of sulphuretted hydrogen for some minutes;
+allow to digest for an hour or so on a hot plate; filter; and wash the
+residue. Acidulate the filtrate with hydrochloric acid: the precipitate
+will contain the antimony (as Sb_{2}S_{5}), and possibly arsenic or tin.
+The precipitate is transferred to a beaker and boiled with hydrochloric
+acid; the solution is filtered off and diluted. Add a few crystals of
+tartaric acid, and pass a current of sulphuretted hydrogen for some
+time. The first flocculent precipitate will become denser, and render
+the filtering more easy. Transfer the precipitate (after washing free
+from chlorides) to a Berlin dish, and treat cautiously with fuming
+nitric acid. The action of this acid on the sulphide is very violent.
+Evaporate and ignite, transfer to a silver dish, and fuse with four or
+five times its weight of caustic soda, cool and extract with a little
+water, then add an equal volume of alcohol, and allow to stand
+overnight. Filter, wash with dilute alcohol. (The filtrate will contain
+the tin.) The residue contains the antimony as antimonate of soda, and
+is dissolved off the filter with hot dilute hydrochloric, with the help
+of a little tartaric, acid. The filtrate is now ready for the
+gravimetric determination.
+
+
+GRAVIMETRIC ASSAY.
+
+Pass a current of sulphuretted hydrogen through the solution containing
+the antimony to which a little tartaric acid has been previously added.
+Pass the gas till the precipitate becomes dense, and the antimony is all
+down. The solution must not be too strongly acid. Filter off the
+precipitate, wash with hot water, dry in the water oven, transfer to a
+weighed porcelain dish, and cautiously treat with fuming nitric acid.
+Continue the action on the water bath till the sulphur and antimony are
+completely oxidised. Evaporate; ignite, gently at first, then strongly
+over the blast; cool, and weigh. The residue is a white infusible
+powder, and consists of antimony tetroxide, Sb_{2}O_{4}, containing
+78.94 per cent. of the metal.
+
+~Determination of Antimony as Bigallate.~--What appears to be a very
+good method has been worked out by M.A. Guyard, and is described in
+Crookes' _Select Methods_, p. 398.
+
+The antimony must be in solution as antimonious chloride, and must not
+be accompanied by an excess of hydrochloric acid. To ensure these
+conditions, the solution is treated with potassium iodide until no more
+iodine is evolved, and is then evaporated to remove the excess of
+hydrochloric acid. To the concentrated, and nearly neutral, solution a
+freshly-prepared solution of gallic acid is added in slight excess. A
+bulky white precipitate is formed that settles rapidly. The solution is
+diluted with hot water and washed by decantation. Then the precipitate
+is collected on a weighed double filter, washed once or twice with hot
+water, and dried at 100° C. The dried substance is antimony bigallate,
+and contains 40.85 per cent. of antimony. It should be completely
+soluble in ammonium sulphide. The solution in which the antimony is
+precipitated need not be quite free from other metals.
+
+
+VOLUMETRIC METHOD.
+
+This is based on the reduction of antimonic chloride (SbCl_{5}) to
+antimonious (SbCl_{3}) by the action of potassium iodide in strong
+hydrochloric acid solution.[63] Iodine is at the same time liberated,
+and the amount of antimony reduced is got at by titrating with sodium
+hyposulphite, which measures the iodine set free.
+
+The standard solution of sodium hyposulphite is made by dissolving 41.32
+grams of the salt (Na_{2}S_{2}O_{3}.5H_{2}O) in water, and diluting to 1
+litre. One hundred c.c. will be equivalent to about 1 gram of antimony.
+
+It is standardised with the help of a solution of antimony made as
+follows:--Weigh up 5 grams of powdered antimony, transfer to a flask,
+and cover with 50 c.c. of hydrochloric acid; boil, and add nitric acid
+(5 or 10 drops at a time) until the metal is dissolved. Allow the action
+of the nitric acid to cease before adding more. Boil down to a small
+bulk, add 250 c.c. of hydrochloric acid, and dilute to nearly 1 litre.
+Warm until any precipitate which has formed is redissolved; allow to
+cool slowly, and run in from a pipette a weak solution of permanganate
+until a faint brown colour is produced. Dilute to exactly 1 litre; 100
+c.c. contain 0.5 gram of antimony as antimonic chloride.
+
+In standardising, take 50 c.c. of the antimony solution, and transfer to
+a flask; add 2 grams of potassium iodide crystals, and when dissolved,
+after standing a few minutes, run in the solution of "hypo" from an
+ordinary burette until the greater part of the iodine has been reduced.
+Add a few drops of starch solution, and continue the addition of the
+"hypo" until the muddy-green colour changes to a clear brownish-yellow.
+The solution must be shaken after each addition of the "hypo."
+
+In determining antimony in ore, weigh up 0.5 to 1 gram, and dissolve in
+hydrochloric acid with, if necessary, the help of chlorate of potash.
+The antimony is separated as sulphide, redissolved in hydrochloric acid,
+and oxidised with a crystal of chlorate of potash. Chlorine is boiled
+off, and the solution diluted with an equal bulk of water. To the clear
+cold solution potassium iodide is added, and after a few minutes the
+liberated iodine is titrated with "hypo," as already described. The
+method only yields satisfactory results when the standard and assay are
+carried out alike.
+
+FOOTNOTES:
+
+[50] "Modern American Methods of Copper Smelting" (Dr. Peters).
+
+[51] "Journal of the Society of Chemical Industry," vol. v. No. 2.
+
+[52] Lead when present is precipitated on the _spiral_ in the form of a
+dark powder of dioxide (PbO_{2}). Manganese is also thrown down on the
+spiral as dioxide (MnO_{2}), the solution at the same time becomes
+violet from the formation of permanganic acid.
+
+[53] See the method given under _Examination of Commercial Copper_.
+
+[54] CuSO_{4} + 4KCy = 2KCy.CuCy_{2} + K_{2}SO_{4}.
+
+[55] 2CuSO_{4} + 3KCy + Am_{2}O = Cu_{2}Cy_{2} + Am_{2}SO_(4) +
+K_{2}SO_{4} + KCyO.
+
+[56] 2CuSO_{4} + 4KI = Cn_{2}I_{2} + 2I + 2K_{2}SO_{4}.
+
+[57] 2Na_{2}S_{2}O_{3} + 2I = 2NaI + Na_{2}S_{4}O_{6}.
+
+[58] For further information, see Appendix B., and a paper by J.W.
+Westmoreland, _Journal of the Society of Chemical Industry_, vol. v.
+p. 48.
+
+[59] 3Cu_{2}O + 6AgNO_{3} + 3H_{2}O = 2Cu_{2}H_{3}O_{3}NO_{3} +
+2Cu(NO_{3})_{2} + 6Ag. (Insoluble basic salt.)
+
+[60] K_{2}CrO_{4} + Pb(NO_{3})_{2} = PbCrO_{4} + 2KNO_{3}
+
+[61] Made by dissolving 12 grams of tartaric acid and 4 grams of
+stannous chloride in water, and adding potash solution till it is
+alkaline. The solution should remain clear on heating to 60° or 70° C.
+
+[62] It must be remembered that arsenate of bismuth is completely
+insoluble in this acid.
+
+[63] SbCl_{5} + 2KI = I_{2} + SbCl_{3} + 2KCl.
+
+
+
+
+CHAPTER XI.
+
+IRON--NICKEL--COBALT--ZINC--CADMIUM.
+
+
+IRON.
+
+Iron rusts or oxidises very readily, and, consequently, is rarely found
+in the metallic state in nature; such native iron as is found being
+generally of meteoric origin or imbedded in basalt and other igneous
+rocks. It chiefly occurs as oxide, as in magnetite, hęmatite, and in the
+brown iron ores and ochres. Chalybite, which is carbonate of iron, is an
+ore of great importance. Iron is found combined with sulphur in
+pyrrhotine and pyrites, and together with arsenic in mispickel. It is a
+common constituent of most rocks, imparting to them a green, black, or
+brown colour; and is present, either as an essential part or as an
+impurity, in most substances.
+
+The chemistry of iron is somewhat complicated by the existence of two
+oxides, each of which gives rise to a well-marked series of compounds.
+Those derived from the lower oxide, known as ferrous salts, are
+generally pale and greenish. Ferric salts are derived from the higher
+oxide, and are generally red, brown, or yellow. The existence of these
+two well-marked families of salts renders the assay of iron
+comparatively easy, for the quantity of iron present in a solution can
+be readily measured by the amount of oxidising or reducing agent
+required to convert it from the one state into the other--that is, from
+ferrous to ferric, or from ferric to ferrous, as the case may be.
+
+In the red and brown iron ores and ochres ferric iron is present; in
+chalybite the iron is in the ferrous state; and in magnetite it is
+present in both forms. Traces of iron in the ferrous state may be found
+(even in the presence of much ferric iron) by either of the following
+tests:--
+
+     1. Ferricyanide of potassium gives a blue precipitate or green
+     coloration; with ferric salts a brown colour only is produced.
+
+     2. A solution of permanganate of potassium is decolorised by a
+     ferrous salt, but not by a ferric one.
+
+Traces of ferric iron can be detected (even in the presence of much
+ferrous iron) by the following tests:--
+
+     (1) By the brown or yellow colour of the solution, especially
+     when hot.
+
+     (2) By giving a pink or red coloration with sulphocyanide of
+     potassium.
+
+Substances containing oxide of iron yield the whole of the iron as metal
+when fused at a high temperature with charcoal and suitable fluxes. The
+metal, however, will contain varying proportions of carbon and other
+impurities, and its weight can only afford a rough knowledge of the
+proportion of the metal in the ore. There are two or three methods of
+dry assay for iron, but they are not only inexact, but more troublesome
+than the wet methods, and need not be further considered. Chalybite and
+the hydrated oxides dissolve very readily in hydrochloric acid; hęmatite
+and magnetite dissolve with rather more difficulty. Iron itself, when
+soft, is easily soluble in dilute hydrochloric, or sulphuric, acid.
+Pyrites, mispickel, &c., are insoluble in hydrochloric acid, but they
+are readily attacked by nitric acid. Certain minerals, such as chrome
+iron ore, titaniferous iron ore, and some silicates containing iron,
+remain in the residue insoluble in acids. Some of these yield their iron
+when attacked with strong sulphuric acid, or when fused with the acid
+sulphate of potash. Generally, however, it is better in such stubborn
+cases to fuse with carbonate of soda, and then attack the "melt" with
+hydrochloric acid.
+
+When nitric acid, or the fusion method, has been used, the metal will be
+in solution in the ferric state, no matter in what condition it existed
+in the ore. But with dilute hydrochloric or sulphuric acid it will
+retain its former degree of oxidation. Hydrochloric acid, for example,
+with chalybite (ferrous carbonate) will give a solution of _ferrous_
+chloride; with hęmatite (ferric oxide) it will yield _ferric_ chloride;
+and with magnetite (ferrous and ferric oxides) a mixture of ferrous and
+ferric chlorides. Metallic iron yields solutions of _ferrous_ salts. It
+is convenient to speak of the iron in a ferrous salt as ferrous iron,
+and when in the ferric state as ferric iron. Frequently it is required
+to determine how much of the iron exists in an ore in each condition. In
+such cases it is necessary to keep off the air whilst dissolving; the
+operation should, therefore, be performed in an atmosphere of carbonic
+acid.
+
+~Separation.~--The separation of the iron from the other substances is
+as follows:--Silica is removed by evaporating the acid solution, and
+taking up with acid, as described under _Silica_; the whole of the iron
+will be in solution. The metals of Groups I. and II. are removed by
+passing sulphuretted hydrogen, and at the same time the iron will be
+reduced to the ferrous state. The solution should be filtered into a 16
+oz. flask, boiled to get rid of the gas, and treated (whilst boiling)
+with a few drops of nitric acid, in order to convert the whole of the
+iron into the ferric state. When this condition is arrived at, an
+additional drop of nitric acid causes no dark coloration. The boiling
+must be continued to remove nitrous fumes. Next add caustic soda
+solution until the colour of the solution changes from yellow to red.
+The solution must be free from a precipitate; if the soda be
+incautiously added a permanent precipitate will be formed, in which case
+it must be redissolved with hydrochloric acid, and soda again, but more
+cautiously, added. After cooling, a solution of sodium acetate is added
+until the colour of the solution is no longer darkened. The solution,
+diluted to two-thirds of the flaskful with water, is heated to boiling.
+Long-continued boiling must be avoided. The precipitate is filtered
+quickly through a large filter, and washed with hot water containing a
+little acetate of soda.
+
+The precipitate will contain all the iron and may also contain alumina,
+chromium, titanium, as well as phosphoric, and, perhaps, arsenic
+acids.[64]
+
+Dissolve the precipitate off the filter with dilute sulphuric acid,
+avoiding excess, add tartaric acid and then ammonia in excess. Pass
+sulphuretted hydrogen, warm, and allow the precipitate to settle. Filter
+and wash with water containing a little ammonic sulphide.
+
+
+GRAVIMETRIC METHOD.
+
+Dissolve the precipitate in dilute hydrochloric acid; peroxidise with a
+few drops of nitric acid and boil, dilute to about 200 c.c., add ammonia
+(with constant stirring) till the liquid smells of it, and heat to
+boiling. Wash as much as possible by decantation with hot water.
+Transfer to the filter, and wash till the filtrate gives no indication
+of soluble salts coming through. The filtrate must be colourless and
+clear. The wet precipitate is very bulky, of a dark-brown colour and
+readily soluble in dilute acids, but insoluble in ammonia and dilute
+alkalies. When thrown down from a solution containing other metals it is
+very apt to carry portions of these with it, even when they are by
+themselves very soluble in ammoniacal solutions. It must be dried and
+ignited, the filter paper being burnt separately and its ash added. When
+further ignition ceases to cause a loss of weight, the residue is ferric
+oxide (Fe_{2}O_{3}), which contains 70 per cent. of iron. The weight of
+iron therefore can be calculated by multiplying the weight of oxide
+obtained by 0.7.
+
+The presence of ammonic chloride causes loss of iron during the
+ignition, and organic matter causes an apparent loss by reducing the
+iron to a lower state of oxidation. When the iron in the solution much
+exceeds 0.2 gram the volumetric determination is generally adopted, as
+the bulkiness of the precipitate of ferric hydrate makes the gravimetric
+method very inconvenient.
+
+
+VOLUMETRIC METHODS.
+
+As already explained these are based on the measurement of the volume of
+a reagent required to bring the whole of the iron from the ferrous to
+the ferric state (oxidation), or from the ferric to the ferrous
+(reduction). Ferrous compounds are converted into ferric by the action
+of an oxidising agent in the presence of an acid. Either permanganate or
+bichromate of potash is generally used for this purpose.[65]
+
+Ferric compounds are reduced to ferrous by the action of:--
+
+  (1)  Stannous chloride;
+  (2)  Sulphuretted hydrogen;
+  (3)  Sodium sulphite; or
+  (4)  Zinc.[66]
+
+The processes, then, may be divided into two kinds, one based on
+oxidation and the other on reduction. In each case the titration must be
+preceded by an exact preparation of the solution to be assayed in order
+that the iron may be in the right state of oxidation.
+
+
+~PERMANGANATE AND BICHROMATE METHODS.~
+
+These consist of three operations:--
+
+  (1) Solution of the ore;
+  (2) Reduction of the iron to the ferrous state; and
+  (3) Titration.
+
+~Solution.~--The only point to be noticed concerning the first operation
+(in addition to those already mentioned) is that nitric acid must be
+absent. If nitric acid has been used, evaporate to dryness, of course
+without previous dilution; add hydrochloric or sulphuric acid, and boil
+for five or ten minutes. Dilute with water to about 100 c.c., and warm
+until solution is complete.
+
+The reduction is performed by either of the following methods:--
+
+1. _With Stannous Chloride._--Fill a burette with a solution of stannous
+chloride,[67] and cautiously run the liquid into the hot assay solution
+(in which the iron is present as _chloride_) until the colour is
+discharged. A large excess of the stannous chloride must be avoided.
+Then add 5 c.c. of a 2-1/2 per cent. solution of mercuric chloride, this
+will cause a white precipitate (or a grey one if too large an excess of
+the stannous chloride has been added). Boil till the solution clears,
+cool, dilute, and titrate.
+
+2. _With Sulphuretted Hydrogen._--Cool the solution and pass through it
+a current of washed sulphuretted hydrogen till the liquid smells
+strongly of the gas after withdrawal and shaking. A white precipitate of
+sulphur will be formed, this will not interfere with the subsequent
+titration provided it is precipitated in the cold. If, however, the
+precipitate is coloured (showing the presence of the second group
+metals), or if the precipitation has been carried out in a hot solution,
+it should be filtered off. Boil the solution until the sulphuretted
+hydrogen is driven off; this may be tested by holding a strip of filter
+paper dipped in lead acetate solution in the steam issuing from the
+flask. The presence of sulphuretted hydrogen should be looked for rather
+than its absence. It is well to continue the boiling for a few minutes
+after the gas has been driven off. Cool and titrate.
+
+3. _With Sodium Sulphite._--Add ammonia (a few drops at a time) until
+the precipitate first formed redissolves with difficulty. If a permanent
+precipitate is formed, redissolve with a few drops of acid. To the warm
+solution add from 2 to 3 grams of sodium sulphite crystals. The solution
+will become strongly coloured, but the colour will fade away on standing
+for a few minutes in a warm place. When the colour is quite removed, add
+20 c.c. of dilute sulphuric acid, and boil until the steam is quite free
+from the odour of sulphurous acid. Cool and titrate.
+
+4. _With Zinc._--Add about 10 grams of granulated zinc; if the hydrogen
+comes off violently add water; if, on the other hand, the action is very
+slow, add sufficient dilute sulphuric acid to keep up a brisk
+effervescence. The reduction is hastened by warming, and is complete
+when the solution is quite colourless and a drop of the liquid tested
+with sulphocyanate of potassium gives no reaction for ferric iron.
+Filter through "glass wool" or quick filtering paper. The zinc should be
+still giving off gas rapidly, indicating a freely acid solution; if not,
+acid must be added. Wash with water rendered acid. Cool and titrate.
+
+With regard to the relative advantages of the different methods they may
+be roughly summed up as follows:--The stannous chloride method has the
+advantage of immediately reducing the ferric iron whether in hot or cold
+solution and under varied conditions in regard to acidity, but has the
+disadvantage of similarly reducing salts of copper and antimony, which,
+in a subsequent titration, count as iron. Moreover, there is no
+convenient method of eliminating any large excess of the reagent that
+may have been used; and, consequently, it either leaves too much to the
+judgment of the operator, or entails as much care as a titration.
+Students generally get good results by this method.
+
+The sulphuretted hydrogen method also has the advantage of quick
+reduction under varying conditions, and the further one of adding
+nothing objectionable to the solution; in fact it removes certain
+impurities. The disadvantages are the necessity for boiling off the
+excess of the gas, and of filtering off the precipitated sulphur,
+although this last is not necessary if precipitated cold. The tendency
+with students is to get high results. The sodium sulphite method has the
+advantages of being clean and neat, and of requiring no nitration. On
+the other hand it requires practice in obtaining the best conditions for
+complete reduction; and, as with sulphuretted hydrogen, there is the
+necessity for boiling off the gas, while there is no simple and delicate
+test for the residual sulphurous acid. In addition, if an excess of
+sodium sulphite has been used and enough acid not subsequently added,
+the excess will count as iron. Students generally get low results by
+this method.
+
+The advantages of the zinc method are, that it is easily worked and that
+the excess of zinc is readily removed by simply filtering. The
+disadvantages are the slowness[68] with which the last portions of
+ferric iron are reduced, the danger of loss by effervescence, the
+precipitation of basic salts, and, perhaps, of iron, and the loading of
+the solution with salts of zinc, which in the titration with bichromate
+have a prejudicial effect. The tendency in the hands of students is to
+get variable results, sometimes low and sometimes high.
+
+Generally speaking, the sulphuretted hydrogen and sodium sulphite
+methods are to be preferred. Carefully worked each method will yield
+good results.
+
+The titration may be done with a standard solution of (1) permanganate
+of potash, or (2) bichromate of potash.
+
+1. _With Permanganate of Potash._--Prepare a standard solution by
+dissolving 2.82 grams of the salt and diluting to one litre. The
+strength of this should be 100 c.c. = 0.5 gram of iron, but it varies
+slightly, and should be determined (and afterwards checked every two or
+three weeks) by weighing up 0.2 gram of iron wire, dissolving in 10 c.c.
+of dilute sulphuric acid, diluting to about 100 c.c., and titrating.
+
+The standard solution must be put in a burette with a glass stopcock, as
+it attacks india-rubber. The assay should be contained in a pint flask,
+and be cooled before titrating. The standard solution must be run in
+until a pinkish tinge permeates the whole solution; this must be taken
+as the finishing point. When certain interfering bodies are present this
+colour quickly fades, but the fading must be ignored. With pure
+solutions the colour is fairly permanent, and a single drop of the
+potassium permanganate solution is sufficient to determine the finishing
+point.
+
+2. _With Bichromate of Potash._--Prepare a standard solution by
+dissolving 4.39 grams of the powdered and dried salt in water, and
+diluting to 1 litre. This solution is permanent, its strength is
+determined by dissolving 0.2 gram of iron wire in 10 c.c. of dilute
+sulphuric acid, diluting to about a quarter of a litre, and titrating.
+
+Also prepare a test solution by dissolving 0.1 gram of ferricyanide of
+potassium in 100 c.c. of water. This solution does not keep well and
+must be freshly prepared.
+
+An ordinary burette is used. The assay is best contained in a glazed
+earthenware dish, and may be titrated hot or cold. To determine the
+finishing point, place a series of drops of the ferricyanide solution on
+a dry white glazed plate. The drops should be of about the same size and
+be placed in lines at fairly equal distances. The bichromate is run in,
+in a steady stream, the assay solution being continuously stirred until
+the reaction is sensibly slackened. Then bring a drop of the assay with
+the stirrer in contact with one of the test drops on the plate. The
+standard can be safely run in 1 c.c. at a time, so long as the test drop
+shows signs of a precipitate. When only a coloration is produced run in
+cautiously a few drops at a time so long as two drops of the assay gives
+with the test a colour which is even faintly greener than two drops of
+the assay solution placed alongside. The finishing point is decided and
+practically permanent, although it demands a little practice to
+recognise it. The titration with permanganate of potassium has the
+advantage of a more distinct finishing point and easier mode of working;
+its application, however, is somewhat limited by the disturbing effects
+of hydrochloric acid. The bichromate method has the advantage of a
+standard solution which does not alter in strength, and the further one
+of being but little affected by altering conditions of assay.
+Hydrochloric acid has practically no effect on it. Both methods give
+accurate results and are good examples of volumetric methods.
+
+The following results illustrate the extent to which the methods may be
+relied on; and the influence which the various conditions of experiment
+have on the assay.
+
+Solutions of ferrous sulphate and of ferrous chloride were made
+containing 0.5 gram of iron in each 100 c.c., thus corresponding to the
+standard solutions of permanganate and bichromate of potassium. These
+last were prepared in the way already described. The solution of ferrous
+sulphate was made by dissolving 5.01 grams of iron wire in 100 c.c. of
+dilute sulphuric acid and diluting to 1 litre. A similar solution may be
+made by dissolving 24.82 grams of pure ferrous sulphate crystals in
+water, adding 100 c.c. of dilute sulphuric acid, and diluting to 1
+litre.
+
+~Rate of Oxidation by Exposure to Air.~--This is an important
+consideration, and if the rate were at all rapid would have a serious
+influence on the manner of working, since exclusion of air in the
+various operations would be troublesome. 20 c.c. of the solution of
+ferrous sulphate were taken in each experiment, acidified with 10 c.c.
+of dilute sulphuric acid, and diluted to 100 c.c. The solution was
+exposed, cold, in an open beaker for varying lengths of time, and
+titrated with permanganate of potassium.
+
+  Time exposed    1 hour  1 day   2 days  3 days
+  c.c. required    19.2    19.1    19.0    19.0
+
+These results show that the atmospheric oxidation in cold solutions is
+unimportant. With boiling solutions the results are somewhat different;
+a solution which at the outset required 20 c.c. of permanganate of
+potassium, after boiling for an hour in an open beaker (without any
+precautions to prevent oxidation), water being added from time to time
+to replace that lost by evaporation, required 19.2 c.c. If the solution
+be evaporated to dryness the oxidising power of concentrated sulphuric
+acid comes into play, so that very little ferrous iron will be left. A
+solution evaporated in this way required only 2.2 c.c. of permanganate
+of potassium.
+
+~Effect of Varying Temperature.~--In these experiments the bulk was in
+each case 100 c.c., and 10 c.c. of dilute sulphuric acid were present.
+The permanganate required by
+
+    1 c.c. of ferrous sulphate was, at 15° 1.0 c.c., and at 70° 1.1 c.c.
+   10  "            "            "         9.7           "      9.8   "
+  100  "            "            "        97.7           "     96.8   "
+
+The lower result with the 100 c.c. may be due to oxidation from
+exposure.
+
+~Effect of Varying Bulk.~--The following experiments show that
+considerable variations in bulk have no practical effect. In each case
+20 c.c. of ferrous sulphate solution and 10 c.c. of dilute acid were
+used.
+
+  Bulk of assay           30 c.c.   100 c.c.   500 c.c.   1000 c.c.
+  Permanganate required   20.0 "     20.0 "     20.2 "      20.5 "
+
+~Effect of Free Sulphuric Acid.~--Free acid is necessary for these
+assays; if there is an insufficiency, the assay solution, instead of
+immediately decolorising the permanganate, assumes a brown colour. The
+addition of 10 c.c. of dilute sulphuric acid suffices to meet
+requirements and keep the assay clear throughout. The following
+experiments show that a considerable excess of acid may be used without
+in the least affecting the results. In each case 20 c.c. of ferrous
+sulphate were used.
+
+Dilute sulphuric
+  acid       1.0 c.c.   5.0 c.c.  10.0 c.c.  20.0 c.c.  50.0 c.c.  100.0 c.c.
+Permanganate
+  required   19.3  "    19.3  "    19.3  "    19.3  "    19.3   "    19.3  "
+
+~Effect of Foreign Salts.~--When the assay has been reduced with zinc
+varying quantities of salts of this metal pass into solution, the amount
+depending on the quantity of acid and iron present. Salts of sodium or
+ammonium may similarly be introduced. It is essential to know by
+experiment that these salts do not exert any effect on the titration.
+The following series of experiments show that as much as 50 grams of
+zinc sulphate may be present without interfering.
+
+  Zinc sulphate present    0 gram       1 gram      10 grams    50 grams
+  Permanganate required   19.3 c.c.    19.3 c.c.    19.3 c.c.   19.3 c.c.
+
+Magnesium, sodium, and ammonium salts, are equally without effect.
+
+  Ammonic sulphate present     0 gram      1 gram    10 grams
+  Permanganate required       19.3 c.c.   19.2 c.c.  19.3 c.c.
+
+Sodic sulphate present       0 gram      1 gram    10 grams
+Permanganate required       19.3 c.c.   19.3 c.c.  19.3 c.c.
+
+Magnesic sulphate present    0 gram      1 gram    10 grams
+Permanganate required       19.3 c.c.   19.3 c.c.  19.3 c.c.
+
+~Effect of Varying Amounts of Iron.~--It is important to know within
+what limits the quantity of iron in an assay may safely vary from that
+used in standardising. In the following experiments the conditions as to
+bulk, acidity, and mode of working were the same as before:--
+
+  Ferrous sulphate solution taken  1 c.c. 10 c.c. 20 c.c. 50 c.c. 100 c.c.
+  Permanganate required            1.0 "   9.7 "  19.6 "  48.9 "   97.7 "
+
+The ferrous sulphate solution is here a little weaker than that of the
+permanganate of potassium, but the results show that the permanganate
+required is proportional to the iron present.
+
+~Titrations in Hydrochloric Solutions.~--These are less satisfactory
+than those in sulphuric solutions, since an excess of hydrochloric acid
+decomposes permanganate of potassium, evolving chlorine, and since the
+finishing point is indicated, not by the persistence of the pink colour
+of the permanganate, but by a brown coloration probably due to
+perchloride of manganese. Nevertheless, if the solution contains only
+from 5 to 10 per cent. of free hydrochloric acid (sp. g. 1.16) the
+results are the same as those obtained in a sulphuric acid solution.
+Equal weights (0.1 gram) of the same iron wire required exactly the same
+quantity of the permanganate of potassium solution (20 c.c.) whether the
+iron was dissolved in dilute sulphuric or dilute hydrochloric acid. The
+following series of experiments are on the same plan as those given
+above with sulphuric acid solutions. A solution of ferrous chloride was
+made by dissolving 5.01 grams of iron wire in 50 c.c. of dilute
+hydrochloric acid and diluting to 1 litre. The dilute hydrochloric acid
+was made by mixing equal volumes of the acid (sp. g. 1.16) and water.
+
+~Rate of Atmospheric Oxidation.~--20 c.c. of the ferrous chloride
+solution were acidified with 10 c.c. of the dilute hydrochloric acid and
+diluted to 100 c.c. This solution was exposed cold in open beakers.
+
+  Time exposed              --      1 hour    1 day     2 days    3 days
+  Permanganate required  19.6 c.c. 19.6 c.c. 19.5 c.c. 19.4 c.c. 19.5 c.c.
+
+Similar solutions boiled required, before boiling, 20 c.c.; after
+boiling for one hour, replacing the water as it evaporated, 19.3 c.c.;
+and after evaporation to a paste and redissolving, 17.0 c.c.
+
+~Effect of Varying Temperature.~--Solutions similar to the last were
+titrated and gave the following results:--
+
+  Temperature            15°        30°        50°          70°
+  Permanganate required  19.8 c.c.  19.6 c.c.  19.5 c.c.    19.4 c.c.
+
+~Effect of Varying Bulk.~--As before, 20 c.c. of the iron solution, and
+10 c.c. of the dilute acid were diluted to the required volumes and
+titrated.
+
+  Bulk                     30 c.c.    100 c.c.    500 c.c.    1000 c.c.
+  Permanganate required    20.4 "      20.3 "      20.8 "       21.5 "
+
+The variation due to difference in bulk here, although only equal to an
+excess of 0.7 milligram of iron for each 100 c.c. of dilution, are about
+three times as great as those observed in a sulphuric acid solution.
+
+~Effect of Free Hydrochloric Acid.~--In these experiments 20 c.c. of the
+ferrous chloride solution were used with varying quantities of acid, the
+bulk of the assay in each case being 100 c.c.
+
+  Dilute acid present      5 c.c.  10 c.c.  50 c.c.  100 c.c.
+  Permanganate required   20.2 "   20.2 "   20.5 "    21.0 "
+
+The last had a very indistinct finishing point, the brown coloration
+being very evanescent. The effect of the acid is modified by the
+presence of alkaline and other sulphates, but not by sulphuric acid.
+Repeating the last experiment we got--
+
+  Without further addition                 21.0 c.c.
+  With 100 c.c. of dilute sulphuric acid   22.0  "
+   "   10 grams ammonic sulphate           20.5  "
+   "   10   "   sodic sulphate             20.0  "
+   "   10   "   magnesium sulphate         20.4  "
+   "   10   "   manganese sulphate         20.2  "
+
+The results with these salts, in counteracting the interference of the
+acid, however, were not a complete success, since the end-reactions were
+all indistinct, with the exception, perhaps, of that with the manganese
+sulphate.
+
+~Effect of Varying Amounts of Iron.~--In these experiments the bulk of
+the assay was 100 c.c., and 10 c.c. of acid were present.
+
+  Ferrous chloride used   1 c.c.  10 c.c.  20 c.c.  50 c.c.  100 c.c.
+  Permanganate required   1.1 "   10.3 "   20.3 "   50.4 "   100.1 "
+
+In making himself familiar with the permanganate of potassium titration,
+the student should practise by working out a series of experiments
+similar to the above, varying his conditions one at a time so as to be
+certain of the cause of any variation in his results. He may then
+proceed to experiment on the various methods of reduction.
+
+_A solution of ferric chloride_ is made by dissolving 5.01 grams of iron
+wire in 50 c.c. of hydrochloric acid (sp. g. 1.16), and running from a
+burette nitric acid diluted with an equal volume of water into the
+boiling iron solution, until the liquid changes from a black to a
+reddish-yellow. About 4.5 c.c. of the nitric acid will be required, and
+the finishing point is marked by a brisk effervescence. The solution of
+iron should be contained in an evaporating dish, and boiled briskly,
+with constant stirring. There should be no excess of nitric acid. Boil
+down to about half its bulk; then cool, and dilute to one litre with
+water. Twenty c.c. of this solution diluted to 100 c.c. with water, and
+acidified with 10 c.c. of dilute hydrochloric acid, should not
+decolorise any of the permanganate of potassium solution; this shows the
+absence of ferrous salts. And 20 c.c. of the same solution, boiled with
+20 c.c. of the ferrous sulphate solution, should not decrease the
+quantity of "permanganate" required for the titration of the ferrous
+sulphate added. In a series of experiments on the various methods of
+reduction, the following results were got. The modes of working were
+those already described.
+
+(1) _With Stannous Chloride._--Twenty c.c. of the ferric chloride
+solution required, after reduction with stannous chloride, 20 c.c. of
+"permanganate." Fifty c.c. of a solution of ferrous chloride, which
+required on titration 49.8 c.c. of "permanganate," required for
+re-titration (after subsequent reduction with stannous chloride) 50 c.c.
+of the permanganate solution.
+
+(2) _With Sulphuretted Hydrogen._--Two experiments with this gas, using
+in each 20 c.c. of the ferric chloride solution, and 10 c.c. of
+hydrochloric acid, required (after reduction) 20.2 c.c. and 20.1 c.c. of
+"permanganate." Repeating the experiments by passing the gas through a
+nearly boiling solution, but in other respects working in the same way,
+21.3 c.c. and 21.6 c.c. of the permanganate solution were required. The
+sulphur was not filtered off in any of these. In another experiment, in
+which 50 c.c. of the ferrous sulphate solution were titrated with
+"permanganate," 48 c.c. of the latter were required. The titrated
+solution was next reduced with sulphuretted hydrogen, brought to the
+same bulk as before, and again titrated; 47.9 c.c. of the permanganate
+of potassium solution were required.
+
+(3) _With Sodium Sulphite._--Twenty c.c. of the ferric chloride
+solution, reduced with sodium sulphite, required 19.9 c.c. of
+"permanganate." In one experiment 50 c.c. of the ferrous sulphate
+solution were titrated with "permanganate"; 49.3 c.c. of the
+last-mentioned solution were required. The titrated solution was reduced
+with sodium sulphite, and again titrated; it required 49.2 c.c. of the
+permanganate of potassium solution.
+
+(4) _With Zinc._--Twenty c.c. of the ferric chloride solution, reduced
+with zinc and titrated, required 20.8 c.c. of "permanganate." Fifty c.c.
+of a solution of ferrous sulphate which required 49.7 c.c. of
+"permanganate," required for re-titration, after reduction with zinc,
+49.7 c.c.
+
+The student should next practise the titration with bichromate, which is
+more especially valuable in the estimation of hydrochloric acid
+solutions. The following experiments are on the same plan as those
+already given. In each experiment (except when otherwise stated) there
+were present 20 c.c. of the ferrous chloride solution, and 10 c.c. of
+dilute hydrochloric acid, and the bulk was 300 c.c.
+
+~Effect of Varying Temperature.~--The quantities of the bichromate of
+potassium solution required were as follows:--
+
+  Temperature           15°        30°        70°        100°
+  Bichromate required   20.2 c.c.  20.3 c.c.  20.3 c.c.  20.4 c.c.
+
+~Effect of Varying Bulk.~--
+
+  Bulk                  50 c.c.  100 c.c.  200 c.c.  500 c.c.  1000 c.c.
+  Bichromate required   20.4 "    20.4 "    20.4 "    20.5 "     20.8 "
+
+~Effect of Varying Acid.~--In these, variable quantities of dilute
+hydrochloric acid were used.
+
+  Acid present          10 c.c.  50 c.c.  100 c.c.
+  Bichromate required   20.3 "   20.3 "    20.2 "
+
+~Effect of Foreign Salts.~--The effect of the addition of 10 grams of
+crystallized zinc sulphate was to decrease the quantity of "bichromate"
+required from 20.3 c.c. to 20.1 c.c., but the colour produced with the
+test-drop was very slight at 18.5 c.c., and with incautious work the
+finishing point might have been taken anywhere between these extremes.
+Zinc should not be used as a reducing agent preliminary to a
+"bichromate" titration. Ten grams of ammonic sulphate had the effect of
+rendering the finishing point faint for about 0.5 c.c. before the
+titration was finished, but there was no doubt about the finishing point
+when allowed to stand for a minute. The student should note that a
+titration is not completed if a colour is developed on standing for five
+or ten minutes. Ten grams of sodic sulphate had no effect; 20.3 c.c.
+were required.
+
+~Effect of Varying Iron.~--The results are proportional, as will be seen
+from the following details:--
+
+  Ferrous chloride
+    present             1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
+  Bichromate required   1.0  "   10.2  "   20.3  "   51.0  "   102.3  "
+
+The student may now apply these titrations to actual assays of minerals.
+The following examples will illustrate the mode of working and of
+calculating the results:--
+
+~Determination of Iron in Chalybite.~--Weigh up 1 gram of the dry
+powdered ore, and dissolve in 10 c.c. of dilute sulphuric acid and an
+equal volume of water with the aid of heat. Avoid evaporating to
+dryness. Dilute and titrate. The result will give the percentage of iron
+existing in the ore in the ferrous state. Some ferric iron may be
+present. If it is wished to determine this also, add (in dissolving
+another portion) 10 c.c. of dilute hydrochloric acid to the sulphuric
+acid already ordered, and reduce the resulting solution before
+titrating. By dissolving and titrating (without previous reduction) one
+has a measure of the ferrous iron present; by dissolving, reducing, and
+then titrating, one can measure the total iron; and as the iron exists
+in only two conditions, the total iron, less the ferrous iron, is the
+measure of the ferric iron.
+
+~Determination of Iron in Brown or Red Ores or Magnetite.~--Weigh up 0.5
+gram of the ore (powdered and dried at 100° C.), and dissolve in from 10
+to 20 c.c. of strong hydrochloric acid, boiling until all is dissolved,
+or until no coloured particles are left. Dilute, reduce, and titrate.
+
+~Determination of Iron in Pyrites.~--Weigh up 1 gram of the dry powdered
+ore, and place in a beaker. Cover with 10 c.c. of strong sulphuric acid,
+mix well by shaking, and place on the hot plate without further handling
+for an hour or so until the action has ceased. _Allow to cool_, and
+dilute to 100 c.c. Warm until solution is complete. Reduce and titrate.
+
+~Determination of Iron in Substances Insoluble in Acids.~--Weigh up 1
+gram of the ore, mix with 5 or 6 grams of carbonate of soda and 0.5 gram
+of nitre by rubbing in a small mortar, and transfer to a platinum
+crucible. Clean out the mortar by rubbing up another gram or so of soda,
+and add this to the contents of the crucible as a cover. Fuse till
+tranquil. Cool. Extract with water. If the ore carries much silica,
+evaporate to dryness with hydrochloric acid to separate it. Re-dissolve
+in hydrochloric acid, and separate the iron by precipitating with
+ammonia and filtering. If only a small quantity of silica is present,
+the aqueous extract of the "melt" must be filtered, and the insoluble
+residue washed and dissolved in dilute hydrochloric acid. Reduce and
+titrate.
+
+A convenient method of at once separating iron from a solution and
+reducing it, is to add ammonia, pass sulphuretted hydrogen through it,
+filter, and dissolve the precipitate in dilute sulphuric acid. The
+solution, when boiled free from sulphuretted hydrogen, is ready for
+titrating.
+
+
+STANNOUS CHLORIDE PROCESS.
+
+The colour imparted to hot hydrochloric acid solutions by a trace of a
+ferric compound is so strong, and the reducing action of stannous
+chloride is so rapid, that a method of titration is based upon the
+quantity of a standard solution of stannous chloride required to
+completely decolorise a solution containing ferric iron. This method is
+more especially adapted for the assay of liquors containing much ferric
+iron and of those oxidised ores which are completely soluble in
+hydrochloric acid. It must be remembered, however, that it only measures
+the ferric iron present, and when (as is generally the case) the total
+iron is wanted, it is well to calcine the weighed portion of ore
+previous to solution in order to get the whole of the iron into the
+higher state of oxidation, since many ores which are generally supposed
+to contain only ferric iron carry a considerable percentage of ferrous.
+
+_The stannous chloride solution_ is made by dissolving 20 grams of the
+commercial salt (SnCl_{2}.2H_{2}O) in 100 c.c. of water with the help of
+20 c.c. of dilute hydrochloric acid, and diluting to a litre. The
+solution may be slightly opalescent, but should show no signs of a
+precipitate. The strength of this is about equivalent to 1 gram of iron
+for each 100 c.c. of the solution, but it is apt to lessen on standing,
+taking up oxygen from the air, forming stannic chloride. A larger
+proportion of hydrochloric acid than is ordered above would remove the
+opalescence, but at the same time increase this tendency to atmospheric
+oxidation, as the following experiments show. The stannous chloride
+solution (20 c.c.) was mixed with varying amounts of strong hydrochloric
+acid (sp. g. 1.16), diluted to 100 c.c., and exposed in open beakers for
+varying lengths of time; and the residual stannous chloride measured by
+titration with permanganate. The quantities required were as follows:--
+
+  Time Exposed.  50 per cent. Acid.  10 per cent. Acid.  1 per cent. Acid.
+     1 hour          33.2 c.c.            34.4 c.c.          34.5 c.c.
+     1 day            5.0  "              24.0  "            27.6  "
+     2 days           3.0  "              14.5  "            21.3  "
+
+These indicate very clearly the increased susceptibility to oxidation in
+strongly acid solutions.
+
+_A standard solution of ferric chloride_ is prepared in the same manner
+as that described under the experiments on the methods of reduction; but
+it should be of twice the strength, so that 100 c.c. may contain 1 gram
+of iron. This solution is used for standardising the stannous chloride
+when required; and must be carefully prepared; and tested for the
+presence of nitric acid.
+
+The titration is more limited in its application than either of the
+oxidising processes because of the restrictions as to bulk, quality and
+quantity of free acid present, and other conditions of the solution to
+be assayed. The following experiments show the conditions necessary for
+a successful titration.
+
+~Effect of Varying Temperature.~--Twenty c.c. of ferric chloride
+solution with 20 c.c. of strong hydrochloric acid, diluted to 50 c.c.,
+gave the following results when titrated:--
+
+  Temperature                 15°        30°        70°        100°
+  Stannous chloride required  22.8 c.c.  22.0 c.c.  22.1 c.c.   22.0 c.c.
+
+The finishing point, however, is more distinct the hotter the solution;
+so that it is best in all cases to run the standard into the boiling
+solution.
+
+~Effect of Varying Bulk.~--Solutions containing the same quantity of
+iron and acid as the last, but diluted to various bulks, and titrated
+while boiling, gave the following results:--
+
+  Bulk                          30 c.c.   100 c.c.   500 c.c.
+  Stannous chloride required    21.5 "     21.7 "     24.3 "
+
+~Effect of Varying Quantities of Hydrochloric Acid.~--In these
+experiments the bulk before titration was 50 c.c. except in the last, in
+which it was 70 c.c. With less than 5 c.c. of strong hydrochloric acid
+the finishing point is indistinct and prolonged.
+
+  Strong hydrochloric
+    acid present         5 c.c.  10 c.c.  20 c.c.  30 c.c.  50 c.c.
+  Stannous chloride
+    required            21.1 "   21.1 "   21.2 "   21.8 "   22.2 "
+
+~Effect of Free Sulphuric Acid.~--In these experiments 20 c.c. of
+hydrochloric acid were present, and the bulk was 50 c.c.
+
+  Strong sulphuric acid
+    present                -- c.c.   3 c.c.   5 c.c.  10 c.c.
+  Stannous chloride
+    required              21.6 "    22.3 "   22.9 "   23.1 "
+
+This interference of strong sulphuric acid may be completely
+counteracted by somewhat modifying the mode of working. Another
+experiment, like the last of this series, required 21.6 c.c.
+
+~Effect of Foreign Salts.~--Experiments in which 10 grams of various
+salts were added showed them to be without effect. The results were as
+follows:--
+
+  Salt present                    --        AmCl     Am_{2}SO_{4}  MgCl_{2}
+  Stannous chloride required  21.6 c.c.  21.6 c.c.    21.6 c.c.   21.6 c.c.
+
+  Salt present                 CaCl_{2}    FeCl_{2}    Al_{2}Cl_{6}
+  Stannous chloride required   21.8 c.c.   21.6 c.c.     21.6 c.c.
+
+~Effect of Varying Iron.~--Titrating a solution (with 20 c.c. of
+hydrochloric acid) measuring 50 c.c., and kept boiling, the quantity of
+stannous chloride solution required is practically proportional to the
+iron present.
+
+  Ferric chloride
+    added             1 c.c.  10 c.c.  20 c.c.  50 c.c.  100 c.c.
+  Stannous chloride
+    required          1.1 "   10.5 "   20.6 "   51.4 "   102.6 "
+
+The student, having practised some of the above experiments, may proceed
+to the assay of an iron ore.
+
+~Determination of Iron in Brown Iron Ore.~--Weigh up 1 gram of the dried
+and powdered ore, calcine in the cover of a platinum crucible, and
+dissolve up in an evaporating dish[69] with 20 c.c. of strong
+hydrochloric acid. When solution is complete, dilute to 50 c.c. after
+replacing any acid that may have been evaporated. Boil, and run in the
+stannous chloride solution until the colour is faintly yellow; boil
+again, and continue the addition of the stannous chloride solution,
+stirring continuously until the solution appears colourless. Note the
+quantity of the stannous chloride solution required. Suppose this to be
+59 c.c. Take 60 c.c. of the standard ferric chloride solution, add 20
+c.c. of hydrochloric acid, boil and titrate in the same way as before.
+Suppose this to require 61 c.c. Then as 61 is equivalent to 60 of the
+iron solution, 59 is equivalent to 58.13.[70] This gives the percentage.
+It is not necessary to standardise the stannous chloride solution in
+this way with each sample assayed, the ratio 61: 60 would serve for a
+whole batch of samples; but the standardising should be repeated at
+least once each day.
+
+
+COLORIMETRIC METHOD.
+
+This method is valuable for the determination of small quantities of
+iron present as impurities in other metals or ores. It is based on the
+red coloration developed by the action of potassic sulphocyanate on acid
+solutions of ferric salts.
+
+_Standard Ferric Chloride Solution._--Take 1 c.c. of the ferric chloride
+solution used for standardising the stannous chloride solution, add 2
+c.c. of dilute hydrochloric acid, and dilute to 1 litre with water. 1
+c.c. = 0.01 milligram.
+
+_Solution of Potassic Sulphocyanate._--Dissolve 60 grams of the salt in
+water, and dilute to a litre. It should be colourless. Use 10 c.c. for
+each test.
+
+The quantity of the substance to be weighed for the assay should not
+contain more than a milligram of iron; consequently, if the ore contain
+more than 0.1 per cent. of that metal, less than a gram of it must be
+taken.
+
+The method is as follows:--Weigh up 1 gram of the substance and dissolve
+in a suitable acid; dilute; and add permanganate of potash solution
+until tinted. Boil for some time and dilute to 100 c.c. Take a couple of
+Nessler tubes, holding over 100 c.c., but marked at 50 c.c.; label them
+"1" and "2"; and into each put 10 c.c. of the potassic sulphocyanate
+solution and 2 c.c. of dilute hydrochloric acid. The solutions should be
+colourless. To "1" add 10 c.c. of the assay solution, and dilute to the
+50 c.c. mark. To the other add water, but only to within 5 or 10 c.c. of
+this mark. Now run in the standard ferric chloride solution from a small
+burette, 1 c.c. at a time, stirring after each addition till the colour
+is nearly equal to that of the assay (No. 1). At this stage bring the
+solution to the same level by diluting, and make a further addition of
+the standard ferric chloride solution till the colours correspond. The
+amount of iron will be the same in each tube; that in the standard may
+be known by reading off the volume from the burette and multiplying by
+0.01 milligram.
+
+If the 10 c.c. of the assay solution gave a colour requiring more than 5
+or 6 c.c. of the standard ferric chloride solution, repeat the
+determination, taking a smaller proportion.
+
+The effect of varying conditions on the assay will be seen from the
+following experiments:--
+
+~Effect of Varying Temperature.~--The effect of increase of temperature
+is to lessen the colour; in fact, by boiling, the colour can be entirely
+removed. All assays are best carried out in the cold.
+
+  1 c.c. at 15° would only show the colour of 0.75 c.c. at 45°
+  2     "         "         "         "       1.75       "
+  5     "         "         "         "       4.0        "
+
+~Effect of Time.~--The effect of increase of time is to increase the
+colour, as will be seen from the following experiments:--
+
+  2 c.c. on standing 10 minutes became equal to 2.25 c.c.
+  2       "          20    "      "      "      2.75  "
+  2       "          40    "      "      "      3.00  "
+
+~Effect of Free Acid.~--If no acid at all be present, the sulphocyanate
+of potassium solution removes the colour it first produces, so that a
+certain amount of acid is necessary to develop the colour. The use of a
+large excess has a tendency to increase the colour produced.
+
+5 c.c. nitric acid (sp. g. 1.4) read 3.7 c.c. instead of 2 c.c. with the
+dilute acid.
+
+5 c.c. sulphuric acid (sp. g. 1.32) read 2.2 c.c. instead of 2 c.c. with
+the dilute acid.
+
+5 c.c. hydrochloric acid (sp. g. 1.16) read 2.5 c.c. instead of 2 c.c.
+with the dilute acid.
+
+
+~Effect of Foreign Metals.~--Lead, mercury, cadmium, bismuth, arsenic,
+tin, antimony, nickel, cobalt, manganese, aluminium, zinc, strontium,
+barium, calcium, magnesium, sodium, or potassium, when separately
+present in quantities of from 100 to 200 times the weight of iron
+present, do not interfere if they have previously been brought to their
+highest oxidised condition by boiling with nitric acid or by treating
+with permanganate. Arsenic and phosphoric acids interfere unless an
+excess of free hydrochloric or other acid is present. Oxalic acid (but
+not tartaric acid) in minute quantities destroys the colour. Nitrous
+acid strikes a red colour with the sulphocyanate of potassium;
+consequently, when nitric acid has been used in excess, high results may
+be obtained. Copper and some other metals interfere, so that in most
+cases it is advisable to concentrate the iron before estimating it. A
+blank experiment should always be made with the reagents used in order
+to determine the iron, if any, introduced during the solution, &c., of
+the substance assayed.
+
+~Determination of Iron in Metallic Copper.~--This may be most
+conveniently done during the estimation of the arsenic. The small
+quantity of white flocculent precipitate which may be observed in the
+acetic acid solution before titrating, contains the whole of the iron as
+ferric arsenate. It should be filtered off, dissolved in 10 c.c. of
+dilute hydrochloric acid, and diluted to 100 c.c.; 10 c.c. of this may
+be taken for the estimation. For example: 10 grams of copper were taken,
+and the iron estimated; 3.0 c.c. of standard ferric chloride solution
+were used, equivalent to 0.03 milligram of iron; this multiplied by 10
+(because only 1/10th of the sample was taken) gives 0.3 milligram as the
+iron in 10 grams of copper. This equals 0.003 per cent.
+
+In a series of experiments with this method working on 10-gram lots of
+copper, to which known quantities of iron had been added, the following
+were the results:--
+
+  Iron present   0.015%   0.070%   0.100%   0.495%
+  Iron found     0.015"   0.061"   0.087"   0.522"
+
+When no arsenic is present in the copper, the iron can be separated by
+fractionally precipitating with sodic carbonate, dissolving in ammonia,
+and filtering off the ferric hydrate. Coppers generally carry more iron
+the less arsenic they contain.
+
+~Determination of Iron in Metallic Zinc.~--Dissolve 1 gram of zinc in 10
+c.c. of dilute hydrochloric acid, adding a drop or two of nitric acid
+towards the end to effect complete solution. Boil, dilute, and tint with
+the permanganate of potassium solution; boil till colourless, and dilute
+to 100 c.c. Take 10 c.c. for the determination. Make a blank experiment
+by boiling 10 c.c. of dilute hydrochloric acid with a drop or two of
+nitric acid; add a similar quantity of the permanganate of potassium
+solution, boiling, &c., as before. The quantity of iron in zinc varies
+from less than 0.005 to more than 2.0 per cent. When 1 gram is taken
+and worked as above, each c.c. of ferric chloride solution required
+indicates 0.01 per cent. of iron.
+
+~Determination of Iron in Metallic Tin.~--Cover 1 gram of tin with 5
+c.c. of hydrochloric acid, add 1 c.c. of nitric acid, and evaporate to
+dryness. Take up with 2 c.c. of dilute hydrochloric acid, add 10 c.c. of
+the potassic sulphocyanate solution, and make up to 50 c.c. Probably the
+colour developed will be brown instead of red owing to the presence of
+copper; in this case, add to the standard as much copper as the assay is
+known to contain (which must have previously been determined; see
+_Copper_); the titration is then carried out in the usual way.
+
+Or the iron may be separated from the copper in the tin by the following
+process:--Dissolve 5 grams of metal in 30 c.c. of hydrochloric acid and
+5 c.c. of nitric acid, and evaporate to dryness. Take up with 5 c.c. of
+dilute hydrochloric acid, add 10 grams of potash dissolved in 30 c.c. of
+water, and warm till the tin is dissolved. Pass sulphuretted hydrogen,
+boil, cool, and filter. The iron and copper will be in the precipitate.
+They are separated in the ordinary manner.
+
+
+PRACTICAL EXERCISES.
+
+1. Calculate from the following determinations the percentages of
+ferrous, ferric, and total iron in the sample of ore used.
+
+1 gram of ore dissolved and titrated required 26.7 c.c. of bichromate of
+potassium solution.
+
+1 gram of ore dissolved, reduced, and titrated required 43.5 c.c. of
+bichromate of potassium solution.
+
+Standard = 1.014.
+
+2. One gram of an ore contained 0.307 gram of ferrous iron and 0.655
+gram of total iron. The iron existing as oxide, what are the percentages
+of ferrous oxide (FeO) and ferric oxide (Fe_{2}O_{3}) in the ore?
+
+3. One gram of brown iron ore dissolved in hydrochloric acid required
+59.2 c.c. of stannous chloride (standard = 0.930). Another gram
+dissolved in acid and titrated with "permanganate" required 8.2 c.c.
+(standard = 0.4951). Calculate the percentages of ferrous, ferric, and
+total iron.
+
+4. Another gram of the same ore, roasted, dissolved and titrated with
+stannous chloride, required 63.5 c.c. To what extent does this result
+confirm the others?
+
+5. Two grams of a metal were dissolved and diluted to 100 c.c. Five c.c.
+were taken for a colorimetric determination, and required 4.5 c.c. of
+the standard ferric chloride solution. What is the percentage of iron in
+the metal?
+
+
+NICKEL.
+
+Nickel and cobalt are closely related in their chemical properties, and
+may best be considered together. Nickel is the commoner of the two, and
+is met with in commerce alloyed with copper and zinc as German silver;
+as also in the coinage of the United States and on the Continent. It is
+used for plating polished iron and steel goods, forming a coating little
+liable to rust and taking a good polish. The ores of nickel are not very
+common. Kupfernickel and chloanthite are arsenides of nickel with,
+generally, more or less iron and cobalt. Noumeite and garnierite are
+hydrated silicates of nickel and magnesia. The chief sources of nickel
+are these silicates, which are found in large quantity in New Caledonia;
+and a pyrites found in Norway, containing three or four per cent. of the
+metal. In smaller quantities it is more widely distributed, being
+frequently met with in copper ores; consequently, commercial copper is
+rarely free from it.
+
+Nickel is readily soluble in moderately concentrated nitric acid. Its
+salts are mostly green, and soluble in excess of ammonia, forming blue
+solutions; in these respects it resembles copper. The acid solutions,
+however, are not precipitated by sulphuretted hydrogen, although in
+alkaline solutions a black sulphide is formed which is insoluble in
+dilute hydrochloric acid. If the sulphide is formed in a solution
+containing much free ammonia, the precipitation is incomplete, some
+sulphide remaining in the solution and colouring it dark brown. These
+reactions serve to distinguish and separate nickel from other metals,
+except cobalt. If the separated sulphide be heated in a borax bead, the
+colour obtained will be a sherry brown in the outer flame, and grey or
+colourless in the inner flame if nickel only is present. In the presence
+of cobalt these colours are masked by the intense and characteristic
+blue yielded in both flames by that metal.
+
+
+DRY ASSAY.
+
+The dry assay of nickel (cobalt being at the same time determined) is
+based on the formation of a speise which will carry the cobalt, nickel,
+copper, and some of the iron of the ore in combination with arsenic. A
+speise of this kind, fused and exposed at a red heat to air, first loses
+arsenide of iron by oxidation. It is only when the iron has been
+oxidised that the arsenide of cobalt begins to be attacked; and when the
+removal of the cobalt is complete, the nickel commences to pass into the
+slag, the copper being left till last. The changes are rendered evident
+by fusion in contact with borax. The process is as follows:--Weigh up 5
+grams of the ore, and calcine thoroughly on a roasting dish in the
+muffle. Rub up with some anthracite, and re-roast. Mix intimately with
+from 3 to 5 grams of metallic arsenic, and heat in a small covered clay
+crucible at dull redness in a muffle until no more fumes of arsenic come
+off (about 15 minutes). Take out the crucible, and inject a mixture of
+20 grams of carbonate of soda, 5 grams of flour, and 2 grams of fused
+borax. Place in the wind furnace, and raise the temperature gradually
+until the charge is in a state of tranquil fusion. Pour; when cold,
+detach the button of speise, and weigh.
+
+Weigh out carefully a portion of about 1 gram of it. Place a shallow
+clay dish in the muffle, and heat it to bright redness; then add about
+1.5 gram of borax glass wrapped in a piece of tissue paper; when this
+has fused, drop the piece of speise into it. Close the muffle until the
+speise has melted, which should be almost at once. The arsenide of iron
+will oxidise first, and when this has ceased the surface of the button
+brightens. Remove it from the muffle, and quench in water as soon as the
+button has solidified. The borax should be coloured slightly blue.
+Weigh: the loss is the arsenide of iron. Repeat the operation with the
+weighed button on another dish, using rather less borax. Continue the
+scorification until a film, green when cold, floating on the surface of
+the button shows that the nickel is beginning to oxidise. Cool,
+separate, and weigh the button as before. The loss is the arsenide of
+cobalt.
+
+If copper is absent, the speise is now arsenide of nickel.
+
+The weight of nickel corresponding to the arsenide got is calculated by
+multiplying by 0.607; and, similarly, the weight of the cobalt is
+ascertained by multiplying the loss in the last scorification by
+0.615.[71] It must be remembered that the nickel and cobalt so obtained
+are derived from a fraction only of the speise yielded by the ore taken,
+so that the results must be multiplied by the weight of the whole of the
+speise, and divided by the weight of the fragment used in the
+determination. As an example, suppose 5 grams of ore gave 3.3 grams of
+speise, and 1.1 gram of this gave 0.8 gram of nickel arsenide. Then--
+
+       0.8×0.607 = 0.4856 gram of nickel
+  0.4856×3.3/1.1 = 1.456 gram of nickel
+
+And this being obtained from 5 grams of ore is equivalent to 29.12 per
+cent.
+
+When copper is also present, weigh up accurately about 0.5 gram of gold,
+and place it on the scorifier with the button of nickel and copper
+arsenide, using borax as before. Scorify until the button shows the
+bluish-green colour of a fused gold-copper alloy. Then cool, and weigh
+the button of copper and gold. The increase in weight of the gold button
+gives the copper as metal. The weight of the copper multiplied by 1.395
+is the weight of the copper arsenide (Cu_{3}As) present. The difference
+will be the nickel arsenide.
+
+The student should enter the weighings in his book as follows:
+
+  Ore taken  -- grams
+  Speise got --   "
+
+  Speise taken                            -- grams
+  Arsenides of cobalt, nickel, and copper --  "
+      "        nickel and copper          --  "
+               Gold added                 --  "
+               Gold and copper got        --  "
+               Showing Cobalt             -- per cent.
+               Nickel                     --    "
+               Copper                     --    "
+
+
+WET METHODS.
+
+~Solution and Separation.~--Two or three grams of a rich ore, or 5 to 10
+grams if poor, are taken for the assay. If much arsenic is present (as
+is usually the case), the ore must be calcined before attacking with
+acids. Transfer to a flask; and boil, first with hydrochloric acid until
+the oxides are dissolved, and then with the help of nitric acid, until
+nothing metalliferous is left. Dilute, nearly neutralise with soda, and
+separate the iron as basic acetate,[72] as described in page 233.
+Through the filtrate pass sulphuretted hydrogen till saturated. Allow to
+settle (best overnight), filter, and wash. Transfer the precipitate to a
+beaker, and dissolve in nitric acid. Dilute with water, pass
+sulphuretted hydrogen, and filter off the precipitate, if any. Boil off
+the gas, add ammonia until a precipitate is formed, and then acidify
+somewhat strongly with acetic acid. Pass sulphuretted hydrogen in a slow
+stream until any white precipitate of zinc sulphide, there may be,
+begins to darken. Filter; to the filtrate add ammonia, and pass
+sulphuretted hydrogen. The precipitate will contain the nickel and
+cobalt as sulphides.
+
+Where small quantities of nickel and cobalt are present, and an
+approximate determination is sufficient, they can be concentrated as
+follows:--Remove the copper, &c., by passing sulphuretted hydrogen
+through the acid solution and filtering; add ammonia to the filtrate,
+and again pass sulphuretted hydrogen; then heat nearly to boiling, and
+filter. Dissolve the precipitate off the filter with dilute hydrochloric
+acid; the residue will contain nearly all the nickel and cobalt as
+sulphides.
+
+~Separation of Nickel and Cobalt.~--Dissolve the sulphides separated as
+above in nitric acid; render alkaline with a solution of potash, then
+acidify with acetic acid; add a concentrated solution of _nitrite_ of
+potash. The liquid after this addition must have an acid reaction. Allow
+to stand for 24 hours in a warm place. Filter off the yellow precipitate
+of nitrite of potash and cobalt, and wash with a 10 per cent. solution
+of acetate of potash. The cobalt is determined in the precipitate in the
+way described under _Cobalt_. The nickel is separated from the solution
+by boiling with sodic hydrate, filtering, and dissolving the precipitate
+in nitric acid. The solution will contain the nickel.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution, which contains the nickel free from other metals, is
+heated, and a solution of sodic hydrate added in slight excess. The
+precipitate is filtered off, washed with boiling water, dried, ignited
+at a red heat, and weighed when cold. The ignited substance is nickel
+oxide (NiO), and contains 78.67 per cent. of nickel. The oxide is a
+green powder, readily and completely soluble in hydrochloric acid, and
+without action on litmus paper. It is very easily reduced by ignition in
+hydrogen to metallic nickel.
+
+[Illustration: FIG. 56.]
+
+Nickel is also determined by electrolysis, as follows:--The nitric acid
+solution is rendered strongly ammoniacal, and placed under the
+electrolytic apparatus used for the copper assay. Three cells (fig. 56),
+however, must be used, coupled up for intensity, that is, with the zinc
+of one connected with the copper of the next. The electrolysis is
+allowed to go on overnight, and in the morning the nickel will be
+deposited as a bright and coherent film. A portion of the solution is
+drawn off with a pipette; if it smells of ammonia, has no blue colour,
+and gives no precipitate with ammonic sulphide, the separation is
+complete. Wash the cylinder containing the deposited metal, first with
+water and then with alcohol, as in the copper assay. Dry in the water
+oven, and weigh. The increase in weight is metallic nickel.
+
+As an example:--There was taken 1 gram of a nickel alloy used for
+coinage. It was dissolved in 10 c.c. of nitric acid, and diluted to 100
+c.c. with water. The copper was then precipitated by electrolysis. It
+weighed 0.734 gram. The solution, after electrolysis, was treated with
+sulphuretted hydrogen, and the remaining copper was thrown down as
+sulphide, and estimated colorimetrically. This amounted to 3-1/2
+milligrams. The filtrate was evaporated, treated with ammonia, warmed,
+and filtered. The ferric hydrate was dissolved in dilute acid, and
+reprecipitated, dried, ignited, and weighed. Its weight was 0.0310 gram.
+The two filtrates were mixed, and reduced in bulk to about 50 c.c.; a
+considerable excess of ammonia was added, and the nickel precipitated by
+electrolysis. It weighed 0.2434 gram. These quantities are equivalent
+to:
+
+  Copper   73.75 per cent.
+  Nickel   24.34    "
+  Iron      2.17    "
+          ------
+          100.26
+
+
+VOLUMETRIC DETERMINATION.
+
+An alkaline solution of potassium cyanide, to which a little potassium
+iodide has been added, can be assayed for its strength in cyanide by
+titrating with a standard solution of silver nitrate. Nickel interferes
+with this assay, doing the work of its equivalent of silver; and the
+quantity of nickel present can be calculated from the amount of its
+interference in the titration. A volumetric assay for nickel is based on
+this. It has the disadvantage of all indirect titrations in that it
+requires two standard solutions. On the other hand it gives good results
+even under unfavourable conditions, and is applicable in the presence of
+much zinc. Small quantities of cobalt will count as so much nickel, but
+larger quantities make the assay unworkable. Some of the other
+metals--lead for example--have no appreciable effect; but practically
+the solution demands a preliminary treatment which would result in their
+removal. Nevertheless it is a very satisfactory method and makes the
+determination of nickel quick and comparatively easy in most cases.
+
+_The standard solution of silver nitrate_ is made by dissolving 14.48
+grams of recrystallised silver nitrate in distilled water and diluting
+to 1 litre: 100 c.c. of this solution are equivalent to 0.25 gram of
+nickel.[73]
+
+_The standard solution of potassium cyanide_ should be made so as to be
+exactly equal to the silver nitrate solution. This can be done as
+follows: Weigh up 12 grams of good potassium cyanide (95 per cent.),
+dissolve in water, add 50 c.c. of a 10 per cent. solution of sodium
+hydrate and dilute to 1 litre. Fill one burette with this and another
+with the solution of silver nitrate. Run 50 c.c. of the cyanide into a
+flask; add a few drops of potassium iodide solution and titrate with the
+standard silver nitrate until there is a distinct permanent yellowish
+turbidity. The titration is more fully described under _Cyanide_, p.
+165. The cyanide solution will be found rather stronger than the silver
+nitrate; dilute it so as to get the two solutions of equal value. For
+example, 51.3 c.c. of silver nitrate may have been required: then add
+1.3 c.c. of water to each 50 c.c. of the cyanide solution remaining. If
+the full 950 c.c. are available, then add to them 24.7 c.c. of water.
+After mixing, take another 50 c.c. and titrate with the silver nitrate;
+the two solutions should now be exactly equal. The cyanide solution,
+being strongly alkaline with soda, keeps very well; but its strength
+should be checked from time to time by titrating with silver nitrate;
+should there be any slight inequality in the strengths of the two
+solutions it is easily allowed for in the calculations.
+
+~The titration.~--The solution, containing not much more than 0.1 gram
+of nickel, and free from the interfering metals, must be cooled. It is
+next neutralised and then made strongly alkaline with a solution of soda
+(NaHO); an excess of 20 or 30 c.c. suffices. This will produce a
+precipitate. The cyanide solution is now run in from a burette until the
+solution clears, after which an excess of about 20 c.c. is added. It is
+well to use some round number of c.c. to simplify the calculation. Add a
+few drops of potassium iodide solution, and run in the standard solution
+of silver nitrate from a burette. This should be done a little at a
+time, though somewhat rapidly, and with constant shaking, till a
+permanent yellow precipitate appears. If the addition of the cyanide did
+not result in a perfectly clear solution, this is because something
+besides nickel is present. The residue may be filtered off, though with
+a little practice the finishing-point may be detected with certainty in
+the presence of a small precipitate. If the student has the slightest
+doubt about a finish he should run in another 5 c.c. of the cyanide and
+again finish with silver nitrate. The second result will be the same as
+the first. For example, if 40 c.c. of cyanide and 30 c.c. of silver
+nitrate were required at the first titration, then the 45 c.c. of
+cyanide in the second titration will require 35 c.c. of silver nitrate.
+The difference between the quantities of the two solutions used in each
+case will be 10 c.c. It is this difference in the readings of the two
+burettes which measures the quantity of nickel present. Each c.c. of the
+difference is equal to .0025 gram of nickel. But if the cyanide solution
+is not exactly equal in strength to the silver nitrate, the quantity of
+cyanide used should be calculated to its equivalent in silver nitrate
+before making the subtraction.
+
+The following experimental results illustrate the accuracy of the assay
+and the effect upon it of varying conditions. A solution containing 1
+gram of nickel sulphate (NiSO_{4}.6H_{2}O) in 100 c.c. was used. By a
+separate assay the sulphate was found to contain 22.25 per cent. of
+nickel. For the sake of simplicity the results of the experiments are
+stated in weights of nickel in grams.
+
+~Effect of varying excess of Cyanide Solution.~--In each experiment
+there was 20 c.c. of the nickel solution, equal to .0445 gram of nickel.
+There were also 10 c.c. of soda solution, 3 or 4 drops of potassium
+iodide and sufficient water to bring the bulk to 100 c.c. before
+titrating.
+
+  Cyanide in excess  6 c.c.  4 c.c.  8 c.c.  12 c.c.  25 c.c.
+  Nickel found       .0434   .0436   .0440   .0442    .0444
+
+Although the difference between the highest and lowest of these results
+is only 1 milligram, their meaning is quite obvious. The excess of
+cyanide should not be less than 20 c.c.
+
+~Effect of varying the quantity of Soda.~--There were two series of
+experiments, one with 2 c.c. of nickel solution (= .0044 gram of
+nickel), the other with 20 c.c. The conditions were as before, except
+that the quantity of soda was varied.
+
+  Soda added                5 c.c.  15 c.c.  30 c.c.
+  Nickel found, 1st series  .0037   .0042    .0045
+    "      "    2nd series  .0444   .0444    .0442
+
+These show that the presence of much soda, though it has only a small
+effect, is beneficial rather than otherwise. Ammonia has a bad effect,
+if present in anything like the same quantities.
+
+~Effect of varying the Nickel.~--In experiments with 10, 20, and 40 c.c.
+of the nickel solution, the results were:--
+
+  Nickel present  .0222  .0445  .0890
+  Nickel found    .0220  .0442  .0884
+
+~Effect of Zinc.~--In these experiments 20 c.c. of nickel solution (=
+.0445 gram of nickel), 10 c.c. of soda, 6 drops of potassium iodide and
+water to 100 c.c. were used. The excess of cyanide was purposely kept at
+from 10 to 15 c.c., which is hardly sufficient.
+
+  Zinc added     0     .25 gram.  .5 gram.
+  Nickel found  .0442  .0440      .0407
+
+On increasing the excess of cyanide to over 20 c.c. and doubling the
+quantity of soda, the experiment with 0.5 gram of zinc gave 0.441 gram
+of nickel. Hence the titration is satisfactory in the presence of zinc
+provided that not fewer than 20 or 30 c.c. of soda are used, and that
+the excess of cyanide is such that not fewer than 20 or 30 c.c. of
+silver nitrate are required in the titration. Moreover, these
+precautions should be taken whether zinc is present or not.
+
+~Effect of other Metals.~--If metals of the first and second groups are
+present they should be removed by passing sulphuretted hydrogen and
+filtering. If _iron_ is present it must be removed, since ferrous salts
+use up much cyanide, forming ferrocyanides, and ferric salts yield
+ferric hydrate, which obscures the end reaction. Hence the sulphuretted
+hydrogen must be boiled off and the iron removed as basic ferric acetate
+by the method described on p. 233. If the precipitate is bulky it should
+be dissolved in a little dilute acid, neutralised and again precipitated
+as basic acetate. The nickel will be in the two filtrates. In the
+absence of manganese and cobalt the titration may be made without
+further separation.
+
+_Manganese_ does not directly interfere, but the precipitated hydrate,
+which rapidly darkens through atmospheric oxidation, obscures the end
+reaction. It may be removed by passing sulphuretted hydrogen through the
+filtrate from the acetate separation: sulphides of nickel, cobalt and
+zinc will be precipitated, whilst manganese remains in solution: the
+addition of more sodium acetate may assist the precipitation. The
+precipitate must be filtered off and dissolved in nitric acid: the
+solution should be evaporated to dryness. The filtrate may retain a
+little nickel; if so, add ammonia till alkaline, then acidify with
+acetic acid and again filter; any small precipitate obtained here should
+be added to that first obtained.
+
+It is only when _cobalt_ is present that any further separation is
+required. Cobalt hydrate takes up oxygen from the air, and on adding
+potassium cyanide some may refuse to dissolve; and the solution itself
+acquires a brown colour, which becomes deeper on standing. At this stage
+the cobalt is easily separated. The solution containing the nickel and
+cobalt with no great excess of acid, is made alkaline by adding 20 c.c.
+of soda exactly as in preparing for a titration. So, too, the solution
+of cyanide is added so as to have an excess of 20 or 30 c.c.; the
+solution may have a brown colour, but if it is not quite clear it _must_
+be filtered. Then warm (boiling is not needed) and add from 50 to 100
+c.c. of bromine water. This throws down all the nickel as black
+peroxide in a condition easy to filter. Filter it off and wash with
+water. The precipitate can be dissolved off the filter with the greatest
+ease by a little warm sulphurous acid. The filtrate and washings, boiled
+till free from sulphurous acid, yield the nickel as sulphate in a clean
+condition.
+
+~Determination of Nickel in Nickel Sulphate Crystals.~--Take 0.5 gram of
+the salt, dissolve in 50 c.c. of water and add 25 c.c. of solution of
+soda. Run in from a burette, say, 60 c.c. "cyanide." Add a few drops of
+potassium iodide and titrate back with "silver nitrate." Suppose 15.5
+c.c. of the latter is required. Then 15.5 c.c. subtracted from 60 c.c.
+leaves 44.5 c.c., and since 100 c.c. = 0.25 gram of nickel, 44.5 c.c.
+will equal 0.11125 gram of nickel. This in 0.5 gram of the salt equals
+22.25 per cent.
+
+~Determination of Nickel in German Silver.~--Weigh up 0.5 gram of the
+alloy, and dissolve in a dish with 5 or 10 c.c. of dilute nitric acid.
+Add 5 c.c. of dilute sulphuric acid and evaporate till all the nitric
+acid is removed. Cool, take up with 50 c.c. of water, and when dissolved
+pass sulphuretted hydrogen through the solution. Filter off the
+precipitate and wash with water containing sulphuretted hydrogen and
+dilute sulphuric acid. Boil down the filtrate and washings to get rid of
+the excess of the gas; add some nitric acid and continue the boiling.
+Cool, neutralise the excess of acid with soda, add 1 gram of sodium
+acetate and boil. Filter off the precipitate which contains the iron.
+The filtrate, cooled and rendered alkaline with soda, is ready for the
+titration.
+
+
+COBALT
+
+Occurs less abundantly than nickel. Its chief ores are smaltite and
+cobaltite, which are arsenides of cobalt, with more or less iron,
+nickel, and copper. It also occurs as arseniate in erythrine, and as
+oxide in asbolan or earthy cobalt, which is essentially a wad carrying
+cobalt.
+
+It is mainly used in the manufacture of smalts for imparting a blue
+colour to glass and enamels. The oxide of cobalt forms coloured
+compounds with many other metallic oxides. With oxide of zinc it forms
+"Rinman's green"; with aluminia, a blue; with magnesia, a pink. This
+property is taken advantage of in the detection of substances before the
+blow-pipe.
+
+The compounds of cobalt in most of their properties closely resemble
+those of nickel, and the remarks as to solution and separation given for
+the latter metal apply here. Solutions of cobalt are pink, whilst those
+of nickel are green.
+
+The detection of cobalt, even in very small quantity, is rendered easy
+by the strong blue colour which it gives to the borax bead, both in the
+oxidising and in the reducing flame. It is concentrated from the ore in
+the same way as nickel, and should be separated from that metal by means
+of potassic nitrite in the way described. The dry assay of cobalt has
+been given under _Nickel_.
+
+
+GRAVIMETRIC METHOD.
+
+The yellow precipitate from the potassium nitrite, after being washed
+with the acetate of potash, is washed with alcohol, dried, transferred
+to a weighed porcelain crucible, and cautiously ignited with an excess
+of strong sulphuric acid. The heat must not be sufficient to decompose
+the sulphate of cobalt, which decomposition is indicated by a blackening
+of the substance at the edges. The salt bears a low red heat without
+breaking up. If blackening has occurred, moisten with sulphuric acid,
+and ignite again. Cool and weigh. The substance is a mixture of the
+sulphates of cobalt and potash (2CoSO_{4} + 3K_{2}SO_{4}), and contains
+14.17 per cent. of cobalt.
+
+Cobalt is also gravimetrically determined, like nickel, by electrolysis,
+or by precipitation with sodic hydrate. In the latter case, the ignited
+oxide will be somewhat uncertain in composition, owing to its containing
+an excess of oxygen. Consequently, it is better to reduce it by igniting
+at a red heat in a current of hydrogen and to weigh it as metallic
+cobalt.
+
+
+PRACTICAL EXERCISES.
+
+1. In the dry assay of an ore containing cobalt, nickel, and copper, the
+following results were obtained. Calculate the percentages. Ore taken, 5
+grams. Speise formed, 0.99 gram. Speise taken. 0.99 gram. Arsenides of
+cobalt, nickel, and copper got, 0.75 gram. Arsenide of nickel and copper
+got, 0.54 gram. Gold added, 0.5 gram. Gold and copper got, 0.61 gram.
+
+2. Calculate the percentage composition of the following compounds:
+Co_{2}As, Ni_{2}As, and Cu_{2}As.
+
+3. A sample of mispickel contains 7 per cent. cobalt. What weight of the
+mixed sulphates of potash and cobalt will be obtained in a gravimetric
+determination on 1 gram of the ore?
+
+4. 0.3157 gram of metal was deposited by the electrolysis of a nickel
+and cobalt solution. On dissolving in nitric acid and determining the
+cobalt 0.2563 gram of potassium and cobalt sulphates were got. Find the
+weights of cobalt and nickel present in the deposit.
+
+5. What should be the percentage composition of pure cobaltite, its
+formula being CoAsS?
+
+
+ZINC.
+
+Zinc occurs in nature most commonly as sulphide (blende); it also occurs
+as carbonate (calamine) and silicate (smithsonite). Each of these is
+sufficiently abundant to be a source of the metal.
+
+The metal is known in commerce as "spelter" when in ingots, and as sheet
+zinc when rolled. It is chiefly used in the form of alloys with copper,
+which are known as brasses. It is also used in the form of a thin film,
+to protect iron goods from rusting--galvanised iron.
+
+Ores of zinc, more especially blende, are met with in most lead, copper,
+gold, and silver mines, in larger or small quantities scattered through
+the lodes. Those ores which generally come under the notice of the
+assayer are fairly rich in zinc; but alloys and metallurgical products
+contain it in very varying proportions.
+
+Zinc itself is readily soluble in dilute acids; any residue which is
+left after boiling with dilute hydrochloric or sulphuric acid consists
+simply of the impurities of the metal; this is generally lead.
+
+All zinc compounds are either soluble in, or are decomposed by, boiling
+with acids, the zinc going into solution. Zinc forms only one series of
+salts, and these are colourless. Their chief characteristic is
+solubility in an alkaline solution, from which sulphuretted hydrogen
+produces a white precipitate of zinc sulphide. Zinc is detected by
+dissolving the substance in hydrochloric or nitric acid, boiling, and
+adding sodic hydrate in excess, filtering, and adding ammonic sulphide
+to the filtrate. The precipitate contains the zinc, which can be
+dissolved out by boiling with dilute sulphuric acid, and detected by the
+formation of a white precipitate on the addition of potassic
+ferrocyanide.
+
+The dry assay of zinc can only be made indirectly, and is
+unsatisfactory. Zinc is volatile, and at the temperature of its
+reduction is a gas. It is impracticable to condense the vapour so as to
+weigh the metal, consequently its amount is determined by loss. The
+following method gives approximate results: Take 10 grams of the dried
+and powdered ore and roast, first at a low temperature and afterwards at
+a higher one, with the help of carbonate of ammonia to decompose the
+sulphates formed; cool and weigh. The metals will be present as oxides.
+Mix with 2 grams of powdered charcoal and charge into a black-lead
+crucible heated to whiteness, cover loosely, and leave in the furnace
+for about a quarter of an hour. Uncover and calcine the residue, cool
+and weigh. The loss in weight multiplied by 8.03 gives the percentage of
+zinc in the ore.
+
+
+WET METHODS.
+
+Solution and separation may be effected as follows: Treat 1 or 3 grams
+of the substance with 10 or 30 c.c. of hydrochloric acid or aqua regia;
+evaporate to dryness; take up with 10 c.c. of hydrochloric acid and
+dilute to 100 c.c.; heat nearly to boiling; saturate with sulphuretted
+hydrogen; filter, and wash with water acidulated with hydrochloric acid.
+Boil off the sulphuretted hydrogen and peroxidise with a few drops of
+nitric acid. Cool; add caustic soda till nearly, but not quite,
+neutralised, and separate the iron as basic acetate by the method
+described under _Iron_. To the filtrate add ammonia till alkaline, and
+pass sulphuretted hydrogen. Allow to settle and decant on to a filter.
+Dissolve off the precipitate from the filter with hot dilute
+hydrochloric acid. The solution will contain the zinc, together with any
+manganese the ore contained, and, perhaps, traces of nickel and cobalt.
+If the zinc is to be determined volumetrically, and manganese is
+present, this latter is separated with carbonate of ammonia, as
+described further on; but if a gravimetric method is used, and only
+small quantities of manganese are present, it is better to proceed as if
+it were absent, and to subsequently determine its amount, which should
+be deducted.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution containing the zinc is contained in an evaporating dish,
+and freed from sulphuretted hydrogen by boiling, and, if necessary, from
+an excess of acid by evaporation. The evaporating dish must be a large
+one. Cautiously add sodium carbonate to the hot, moderately dilute
+solution, until the liquid is distinctly alkaline, and boil. Allow the
+precipitate to settle, decant on to a filter, and wash with hot water.
+Dry, transfer to a porcelain crucible (cleaning the paper as much as
+possible), add the ash, ignite, and weigh. The substance weighed is
+oxide of zinc, which contains 80.26 per cent. of the metal. It is a
+white powder, becoming yellow when heated. It must not show an alkaline
+reaction when moistened. If it contains manganese this metal will be
+present as sesquioxide (Mn_{2}O_{3}). Its amount can be determined by
+dissolving in dilute acid and boiling with an excess of sodic hydrate.
+The oxide of manganese will be precipitated, and can be ignited and
+weighed. Its weight multiplied by 1.035 must be deducted from the weight
+of oxide of zinc previously obtained. The results yielded by the
+gravimetric determination are likely to be high, since the basic
+carbonate of zinc frequently carries down with it more or less soda
+which is difficult to wash off.
+
+
+VOLUMETRIC DETERMINATION
+
+This method is based on the facts that zinc salts in an acid solution
+decompose potassium ferrocyanide, forming a white insoluble zinc
+compound; and that an excess of the ferrocyanide can be detected by the
+brown coloration it strikes with uranium acetate. The method resembles
+in its working the bichromate iron assay. The standard solution of
+potassium ferrocyanide is run into a hot hydrochloric acid solution of
+the zinc until a drop of the latter brought in contact with a drop of
+the indicator (uranium acetate) on a white plate strikes a brown colour.
+The quantity of zinc in the solution must be approximately known; run in
+a little less of the ferrocyanide than is expected will be necessary;
+test a drop or two of the assay, and then run in, one or two c.c. at a
+time, until the brown colour is obtained. Add 5 c.c. of a standard zinc
+solution, equivalent in strength to the standard "ferrocyanide,"
+re-titrate, and finish off cautiously. Of course 5 c.c. must be deducted
+from the reading on the burette. The precipitate of zinc ferrocyanide
+formed in the assay solution is white; but if traces of iron are
+present, it becomes bluish. If the quantity of ferrocyanide required is
+known within a few c.c., the finishing point is exactly determined in
+the first titration without any addition of the standard zinc solution.
+Unfortunately this titration serves simply to replace the gravimetric
+determination, and does not, as many volumetric processes do, lessen the
+necessity for a complete separation of any other metals which are
+present. Most metals give precipitates with ferrocyanide of potassium in
+acid solutions. If the conditions are held to, the titration is a fairly
+good one, and differences in the results of an assay will be due to
+error in the separation. Ferric hydrate precipitated in a fairly strong
+solution of zinc will carry with it perceptible quantities of that
+metal. Similarly, large quantities of copper precipitated as sulphide by
+means of sulphuretted hydrogen will carry zinc with it, except under
+certain nicely drawn conditions. When much copper is present it is best
+separated in a nitric acid solution by electrolysis. The titration of
+the zinc takes less time, and, with ordinary working, is more
+trustworthy than the gravimetric method.
+
+_The standard ferrocyanide solution_ is made by dissolving 43.2 grams of
+potassium ferrocyanide (K_{4}FeCy_{6}.3H_{2}O) in water, and diluting to
+a litre. One hundred c.c. are equal to 1 gram of zinc.
+
+_The standard zinc solution_ is made by dissolving 10 grams of pure zinc
+in 50 c.c. of hydrochloric acid and 100 or 200 c.c. of water, and
+diluting to 1 litre, or by dissolving 44.15 grams of zinc sulphate
+(ZnSO_{4}.7H_{2}O) in water with 30 c.c. of hydrochloric acid, and
+diluting to 1 litre. One hundred c.c. will contain 1 gram of zinc.
+
+_The uranium acetate solution_ is made by dissolving 0.2 gram of the
+salt in 100 c.c. of water.
+
+To standardise the "ferrocyanide" measure off 50 c.c. of the standard
+zinc solution into a 10 oz. beaker, dilute to 100 c.c., and heat to
+about 50° C. (not to boiling). Run in 47 or 48 c.c. of the
+"ferrocyanide" solution from an ordinary burette, and finish off
+cautiously. Fifty divided by the quantity of "ferrocyanide" solution
+required gives the standard.
+
+In assaying ores, &c., take such quantity as shall contain from 0.1 to 1
+gram of zinc, separate the zinc as sulphide, as already directed.
+Dissolve the sulphide off the filter with hot dilute hydrochloric acid,
+which is best done by a stream from a wash bottle. Evaporate the
+filtrate to a paste, add 5 c.c. of dilute hydrochloric acid, dilute to
+100 c.c. or 150 c.c., heat to about 50° C., and titrate. Manganese, if
+present, counts as so much zinc, and must be specially separated, since
+it is not removed by the method already given. The following method will
+effect its removal. To the hydrochloric acid solution of the zinc and
+manganese add sodium acetate in large excess and pass sulphuretted
+hydrogen freely. Allow to settle, filter off the zinc sulphide and wash
+with sulphuretted hydrogen water. The precipitate, freed from manganese,
+is then dissolved in hydrochloric acid and titrated.
+
+The following experiments show the effect of variation in the conditions
+of the assay:--
+
+~Effect of Varying Temperature.~--Using 20 c.c. of the standard zinc
+solution, 5 c.c. of dilute hydrochloric acid, and diluting to 100 c.c.
+
+  Temperature               15° C.     30° C.     70° C.    100° C.
+  "Ferrocyanide" required  20.6 c.c.  20.3 c.c.  20.3 c.c.  20.3 c.c.
+
+The solution can be heated to boiling before titrating without
+interfering with the result; but it is more convenient to work with the
+solution at about 50° C. Cold solutions must not be used.
+
+~Effect of Varying Bulk.~--These were all titrated at about 50° C., and
+were like the last, but with varying bulk.
+
+  Bulk                     25.0 c.c.  50.0 c.c.  100.0 c.c.  200.0 c.c.
+  "Ferrocyanide" required  20.2  "    20.4  "     20.3  "     20.4  "
+
+Any ordinary variation in bulk has no effect.
+
+~Effect of Varying Hydrochloric Acid.~-- With 100 c.c. bulk and varying
+dilute hydrochloric acid the results were:--
+
+  Acid added        0.0 c.c.   1.0 c.c.   5.0 c.c.   10.0 c.c.   20.0 c.c.
+  "Ferrocyanide"
+    required       24.4  "    20.2  "    20.3  "     20.3  "     20.7  "
+
+~Effect of Foreign Salts.~--The experiments were carried out under the
+same conditions as the others. Five grams each of the following salts
+were added:--
+
+  Salt added         { Ammonic    Ammonic    Sodium      Sodium
+                     { chloride.  sulphate.  chloride.   sulphate.
+  "Ferrocyanide"
+    required           20.3 c.c.  20.5 c.c.  20.6 c.c.   20.4 c.c.
+
+  Salt added         { Potassium  Magnesium   Nil.
+                     { Nitrate.   sulphate.
+  "Ferrocyanide"
+    required           20.2 c.c.  20.4 c.c.   20.4 c.c.
+
+In a series of experiments in which foreign metals were present to the
+extent of 0.050 gram in each, with 20 c.c. of zinc solution and 5 c.c.
+of dilute hydrochloric acid, those in which copper sulphate, ferrous
+sulphate, and ferric chloride were used, gave (as might be expected) so
+strongly coloured precipitates that the end reaction could not be
+recognised. The other results were:--
+
+                                          "Ferrocyanide"
+                                            required.
+  With nothing added.                        20.3 c.c.
+   "   0.050 gram lead (as chloride)         20.9  "
+   "   0.050   "  manganese (as sulphate)    25.5  "
+   "   0.050   "  cadmium (as sulphate)      23.5  "
+   "   0.050   "  nickel (as sulphate)       26.2  "
+
+~Effect of Varying Zinc.~--These were titrated under the usual
+conditions, and gave the following results:--
+
+    Zinc added     1.0 c.c.  10.0 c.c.  20.0 c.c.  50.0 c.c.  100.0 c.c.
+  "Ferrocyanide"
+    required       1.1  "    10.2  "    20.3  "    50.6  "    101.0  "
+
+~Determination of Zinc in a Sample of Brass.~--Take the solution from
+which the copper has been separated by electrolysis and pass
+sulphuretted hydrogen until the remaining traces of copper and the lead
+are precipitated, filter, boil the solution free from sulphuretted
+hydrogen, put in a piece of litmus paper, and add sodic hydrate solution
+in slight excess; add 10 c.c. of dilute hydrochloric acid (which should
+render the solution acid and clear); warm, and titrate.
+
+A sample of 0.5 gram of brass treated in this manner required 16.4 c.c.
+of "ferrocyanide" (standard 100 c.c. = 0.9909 zinc), which equals 0.1625
+gram of zinc or 32.5 per cent.
+
+~Determination of Zinc in Blende.~--Dissolve 1 gram of the dried and
+powdered sample in 25 c.c. of nitric acid with the help of two or three
+grams of potassium chlorate dissolved in the acid. Evaporate to complete
+dryness, taking care to avoid spirting. Add 7 grams of powdered ammonium
+chloride, 15 c.c. of strong ammonia and 25 c.c. of boiling water; boil
+for one minute and see that the residue is all softened. Filter through
+a small filter, and wash thoroughly with small quantities of a hot one
+per cent. solution of ammonium chloride. Add 25 c.c. of hydrochloric
+acid to the filtrate. Place in the solution some clean lead foil, say 10
+or 20 square inches. Boil gently until the solution has been colourless
+for three or four minutes. Filter, wash with a little hot water; and
+titrate with standard ferrocyanide.
+
+~Determination of Zinc in Silver Precipitate.~--This precipitate
+contains lead sulphate, silver, copper, iron, zinc, lime, &c. Weigh up 5
+grams of the sample, and extract with 30 c.c. of dilute sulphuric acid
+with the aid of heat. Separate the copper with sulphuretted hydrogen,
+peroxidise the iron with a drop or two of nitric acid, and separate as
+acetate. Render the filtrate ammoniacal, pass sulphuretted hydrogen;
+warm, and filter. Dissolve the precipitated zinc sulphide in dilute
+hydrochloric acid, evaporate, dilute, and titrate. Silver precipitates
+carry about 2.5 per cent. of zinc.
+
+
+GASOMETRIC METHOD.
+
+Metallic zinc is readily soluble in dilute hydrochloric or sulphuric
+acid, hydrogen being at the same time evolved.[74] The volume of the
+hydrogen evolved is obviously a measure of the amount of zinc present in
+the metallic state. The speed with which the reaction goes on (even in
+the cold) and the insolubility of hydrogen renders this method of assay
+a convenient one. It is especially applicable to the determination of
+the proportion of zinc in zinc dust. The apparatus described in the
+chapter on gasometric method is used. The method of working is as
+follows: Fill the two burettes with cold water to a little above the
+zero mark, place in the bottle about 0.25 gram of the substance to be
+determined, and in the inner phial or test tube 5 c.c. of dilute
+sulphuric acid; cork the apparatus tightly and allow to stand for a few
+minutes; then bring the water to the same level in the two burettes by
+running out through the clip at the bottom. Read off the level of the
+liquid in the graduated burette. Turn the bottle over sufficiently to
+spill the acid over the zinc, and then run water out of the apparatus so
+as to keep the liquid in the two burettes at the same level, taking care
+not to run it out more quickly than the hydrogen is being generated.
+When the volume of gas ceases to increase, read off the level of the
+liquid, deduct the reading which was started with; the difference gives
+the volume of hydrogen evolved. At the same time read off the volume of
+air in the "volume corrector," which must be fixed alongside the gas
+burettes. Make the correction. For example: A piece of zinc weighing
+0.2835 gram was found to give 99.9 c.c. of gas at a time when the
+corrector read 104 c.c.[75] Then the corrected volume is
+
+        104 : 100 :: 99.9 : _x_.
+                            _x_ = 96.0 c.c.
+
+100 c.c. of hydrogen at 0° C. and 760 mm. is equivalent to 0.2912 gram
+of zinc; therefore the quantity of zinc found is
+
+        100 : 96 :: 0.2912 : _x_.
+                             _x_ = 0.2795 gram of zinc.
+
+This being contained in 0.2835 gram of metal is equivalent to 98.5 per
+cent.
+
+As an example of a determination in which reducing the volume of
+liberated hydrogen to 0° C. and 760 mm. is avoided, the following may be
+taken:--
+
+        0.2315 gram of pure zinc gave 82.1 c.c. of gas;
+and the volume of air in the corrector was 103.6 c.c.
+
+        0.2835 gram of the assay gave 99.9 c.c. of gas;
+and the volume of air in the corrector was 104.0 c.c.;
+
+        104 : 103.6 :: 99.9 : _x_.
+                              _x_ = 99.5 c.c.
+
+This is the volume of gas got in the assay if measured under the same
+conditions as the standard,
+
+        82.1 : 99.5 :: 0.2315 : _x_.
+                                _x_ = 0.2806.
+
+        Then 0.2835 : 0.2806 :: 100: _x_.
+                                     _x_ = 98.9 per cent.
+
+As these assays can be made quickly, it is well for the sake of greater
+accuracy to make them in duplicate, and to take the mean of the
+readings. One set of standardisings will do for any number of assays.
+The student must carefully avoid unnecessary handling of the bottle in
+which the zinc is dissolved.
+
+~Colorimetric Method.~--Zinc salts being colourless, there is no
+colorimetric determination.
+
+
+EXAMINATION OF COMMERCIAL ZINC.
+
+Take 20 grams of zinc, and dissolve them in dilute nitric acid; boil,
+allow to settle; filter; wash, dry; ignite the precipitate, if any, and
+weigh as oxide of tin. Examine this for arsenic.
+
+~Lead.~--Add ammonia and carbonate of ammonia to the liquid, and boil,
+filter off the precipitate, wash with hot water. Digest the precipitate
+with dilute sulphuric acid; filter, wash, and weigh the sulphate of
+lead.
+
+~Iron.~--To the filtrate from the sulphate of lead add ammonia, and pass
+sulphuretted hydrogen; digest, and filter. (Save the filtrate.) Dissolve
+the precipitate in hydrochloric acid, oxidise with nitric acid, and
+precipitate with ammonia. Wash, ignite, and weigh as ferric oxide.
+Calculate to iron.
+
+~Arsenic.~--To the filtrate from the sulphide of iron add hydrochloric
+acid in slight excess; filter off, and wash the precipitate. Rinse it
+back into the beaker, dissolve in nitric acid, filter from the sulphur,
+and add ammonia, in excess, and magnesia mixture. Filter off the
+ammonic-magnesic arsenate, and wash with dilute ammonia. Dry, ignite
+with nitric acid, and weigh as magnesic pyrarsenate. Calculate to
+arsenic, and add to that found with the tin.
+
+~Copper.~--To the filtrate from the ammonia and ammonic carbonate add
+sulphuric acid in small excess, and pass sulphuretted hydrogen. Allow to
+settle, filter, and wash. Rinse the precipitate into a beaker, boil with
+dilute sulphuric acid, and filter. (Save the filtrate.) Dry, burn the
+paper with the precipitate, treat with a drop or two of nitric acid,
+ignite, and weigh as copper oxide. Calculate to copper.
+
+~Cadmium.~--To the filtrate from the sulphide of copper add ammonia, so
+as to nearly neutralise the excess of acid, and pass sulphuretted
+hydrogen. Collect and weigh the precipitate as cadmium sulphide, as
+described under _Cadmium_.
+
+
+PRACTICAL EXERCISES.
+
+1. What weight of hydrogen will be evolved in dissolving 1 gram of zinc
+in dilute sulphuric acid?
+
+2. How many c.c. would this quantity of hydrogen measure at 0° C. and
+760 m.m.? (1 litre weighs 0.0896 gram).
+
+3. 0.23 gram of zinc are found to give 77.9 c.c. of hydrogen. In another
+experiment under the same conditions 80.2 c.c. are got. What weight of
+zinc was used for the second experiment?
+
+4. A sample of blende is found to contain 55 per cent. of zinc. What
+percentage of zinc sulphide did the sample contain?
+
+5. How much metallic lead would be precipitated from a solution of lead
+acetate by 1 gram of zinc?
+
+
+CADMIUM.
+
+Cadmium occurs in nature as cadmium sulphide in greenockite, CdS, which
+is very rare. It is widely diffused in calamine, blende, and other zinc
+ores, forming, in some cases, as much as 2 or 3 per cent. of the ore.
+Oxide of cadmium forms the "brown blaze" of the zinc smelters.
+
+Sulphide of cadmium is used as a pigment (cadmium yellow); and the metal
+and some of its salts are useful reagents.
+
+The salts of cadmium closely resemble those of zinc. The hydrate,
+however, is insoluble in excess of potash, and the sulphide is insoluble
+in dilute acids. It forms only one series of salts.
+
+Cadmium is detected by giving with sulphuretted hydrogen in solutions,
+not too strongly acid, a yellow precipitate, which is insoluble in
+solutions of the alkalies, alkaline sulphides, or cyanide of potassium.
+
+~Solution and Separation.~--Substances containing cadmium are soluble in
+acids. The solution is evaporated to dryness (to render any silica that
+may be present insoluble) and taken up with 10 c.c. of dilute
+hydrochloric acid. Dilute to 100 c.c., and pass sulphuretted hydrogen.
+Filter, digest the precipitate with soda, wash, and boil with dilute
+sulphuric acid. Filter; the filtrate contains the cadmium and, possibly,
+a small quantity of zinc, from which it is best separated by
+reprecipitating with sulphuretted hydrogen.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution containing the cadmium freed from the other metals is
+precipitated with sulphuretted hydrogen in a moderately-acid solution.
+The precipitate is collected on a weighed filter, and washed, first with
+an acid solution of sulphuretted hydrogen, and afterwards with water. It
+is dried at 100° C. and weighed. If free sulphur is suspected to be
+present, extract with bisulphide of carbon, and again weigh. The residue
+is cadmium sulphide, which contains 77.78 per cent. of cadmium. It is a
+yellow powder insoluble in solutions of the alkalies, alkaline
+sulphides, or cyanide of potassium. It dissolves readily in acid. It
+cannot be ignited in a current of hydrogen without loss.
+
+
+VOLUMETRIC METHOD.
+
+The solution containing the cadmium is concentrated by evaporation, and
+mixed with an excess of oxalic acid and alcohol. The precipitate is
+filtered, washed with alcohol, dissolved in hot hydrochloric acid, and
+titrated with permanganate of potassium.
+
+FOOTNOTES:
+
+[64] When chromium is present some of the iron may escape precipitation
+but it can be recovered from the solution by means of ammonic sulphide.
+
+[65]
+
+(1) 10FeSO_{4} + 2KMnO_{4} + 8H_{2}SO_{4} = 5Fe_{2}(SO_{4})_{3} +
+2MnSO_{4} + K_{2}SO_{4} + 8H_{2}O.
+
+(2) 6FeCl_{2} + K_{2}Cr_{2}O_{7} + 14HCl = 3Fe_{2}Cl_{6} + Cr_{2}Cl_{6}
++ 2KCl + 7H_{2}O.
+
+[66] (1) Fe_{2}Cl_{6} + SnCl_{2} = 2FeCl_{2} + SnCl_{4}.
+     (2) Fe_{2}Cl_{6} + SH_{2} = 2FeCl_{2} + 2HCl + S.
+     (3) Fe_{2}Cl_{6} + Na_{2}SO_{3} + H_{2}O = 2FeCl_{2}
+         + Na_{2}SO_{4} + 2HCl.
+     (4) Fe_{2}Cl_{6} + Zn = 2FeCl_{2} + ZnCl_{2}.
+
+[67] 20 grams of stannous chloride and 20 c.c. of dilute hydrochloric
+acid are diluted to one litre.
+
+[68] The maximum reducing effect of zinc is obtained by exposing as
+large a surface as possible of the metal in a hot concentrated solution
+containing but little free acid (Thorpe).
+
+[69] About 5 inches in diameter.
+
+[70] 61: 60:: 59: 58.13.
+
+The iron in the ore is, then, the same in amount as that in 58.13 c.c.
+of the ferric chloride solution; and since 100 c.c. of the latter
+contain 1 gram of iron, 58.13 c.c. of the same contains 0.5813 gram of
+iron; and, further, if 1 gram of ore carries this amount of iron, 100
+grams of ore will obviously give 58.13 grams of iron.
+
+[71] These compounds are Ni_{2}As and Co_{2}As.
+
+[72] With large quantities of iron the ferric precipitate should be
+re-dissolved and re-precipitated. The filtrate must be added to the
+original filtrate.
+
+[73] 4KCy + NiSO_{4} = K_{2}NiCy_{4} + K_{2}SO_{4} 2KCy + AgNO_{3}
+     = KAgCy_{2} + KNO_{3}
+     .'. 2AgNO_{3} = Ni
+
+[74] Zn + H_{2}SO_{4} = H_{2} + ZnSO_{4}.
+
+[75] These 104 c.c. are equivalent to 100 c.c. of dry air at 0° C. and
+760 mm.
+
+
+
+
+CHAPTER XII.
+
+TIN--TUNGSTEN--TITANIUM.
+
+
+TIN.
+
+Tin occurs in nature as cassiterite (containing from 90 to 95 per cent.
+of oxide of tin), which mineral is the source from which the whole of
+the tin of commerce is derived. Tin also occurs as sulphide combined
+with sulphides of copper and iron in the mineral stannine or bell-metal
+ore. It is a constituent of certain rare minerals, such as tantalite.
+
+The methods of assaying tin in actual use are remarkable when compared
+with those of other metals. The more strictly chemical methods are
+rendered troublesome by the oxide being insoluble in acids, resembling
+in this respect the gangue with which it is associated. Moreover, it is
+not readily decomposed by fusion with alkalies. The oxide has first to
+be reduced to metal before the tin can be dissolved. The reduction may
+be performed by fusing with potassic cyanide, by heating to moderate
+redness in a current of hydrogen or coal gas, or by heating to a higher
+temperature with carbon. The reduced metal is only slowly dissolved by
+hydrochloric acid, and although it is readily soluble in aqua regia, the
+solution cannot be evaporated or freed from the excess of acids, by
+boiling, without loss of tin, because of the volatility of stannic
+chloride. There has long been a difficulty in getting a quick wet
+method.
+
+The process of assaying tin ores adopted in the mines of Cornwall is a
+mechanical one known as "vanning," the object of which is to find the
+percentage of "black tin," which, it is well to remember, is not pure
+cassiterite, much less pure oxide of tin. Tin ore, as taken from the
+lode, contains from 2 to 5 per cent. of cassiterite, and is mainly made
+up of quartz, felspar, chlorite, schorl, and other stony minerals,
+together with more or less mispickel, iron and copper pyrites, oxide of
+iron, and wolfram. The cassiterite has a specific gravity (6.4 to 7.1)
+considerably higher than that of the vein-stuff (2.5 to 3.0), and is
+concentrated by a series of washings till it is free from the lighter
+material. Those minerals which have a specific gravity approaching that
+of the cassiterite are not completely removed. The mispickel and copper
+and iron pyrites are converted into oxides by roasting, and are in great
+part removed by a subsequent washing. The concentrated product is known
+as "black tin," and in this condition is sold to the smelter. The chief
+foreign matters in the black tin are silica, oxides of iron and copper,
+and wolfram, with traces of manganese and niobic acid; and in certain
+stream ores there may be as much as 6 or 7 per cent. of titaniferous
+iron. The black tin from the mines contains from 5 to 12 per cent. of
+water, and is sold and assayed wet. A series of typical samples of black
+tin ranged as follows:--
+
+  --------------------------+---------------------+-----------------
+      Source of Material.   | Percentage of Metal |Specific Gravity.
+                            |     in Dry Ore.     |
+  --------------------------+---------------------+-----------------
+   Good mine ore            |        72.0         |      6.39
+   Inferior do.             |        71.5         |      6.64
+   Titaniferous stream ore  |        67.0         |      6.39
+   Mine ore with wolfram    |        64.5         |      6.67
+   Ore from stream works    |        58.5         |      5.99
+  --------------------------+---------------------+-----------------
+
+It will be seen from these figures that black tin is a very variable
+substance; and that the specific gravity is largely influenced by the
+impurities; hence, it is only an indication of the percentage of metal
+when the same kind of ore is dealt with.
+
+As already pointed out, the object of vanning is to determine the
+proportion of black tin in the lode stuff. The relation between the
+actual content in oxide of tin and the produce got by vanning has been
+tested on several occasions with results which show a fair degree of
+approximation.
+
+The following are some published results of assays of the same batch of
+ore. The vanning results were obtained by a Cornish vanner of recognised
+ability, and the wet assays by two London firms of the highest
+standing:--
+
+  Vanning results:
+    (Average)        91 lbs. of "black tin."
+  Wet Assay results:
+    A                83.7 lbs. of stannic oxide.
+    B                79.7 lbs.       "
+
+The vanner reported his black tin as containing 70 per cent. of tin.
+This will bring his result, if calculated as stannic oxide, to 80.9 lbs.
+to the ton; which agrees with the others.
+
+According to our experience the "van" assay agrees fairly well with the
+"wet" one, if the black tin is assumed to contain 92.5 per cent. of
+stannic oxide (SnO_{2}).
+
+Vanners are, as a rule, skilful men, and show remarkable dexterity in
+separating the black tin, with the help of their apparatus, which
+consists simply of a shovel and a kieve of water. An account of the
+process is given below. But different vanners, all good men, will get
+different results working on material new to them. The black tin weighed
+by the vanner is supposed to correspond in quality with the black tin
+returned from the floors of the mine for which he is assaying, but this
+differs materially in different mines with the nature of the gangue. The
+process leaves too much to the judgment of the vanner. It is more than
+probable that in practice the returns from the dressing-floors check the
+assayer, instead of, as should properly be the case, the assayer
+checking the returns. It is only when this last is done that any control
+is had over the system of dressing. A correct assay of this ore is a
+matter of some importance, because of the high price of the metal.
+
+The method of assaying the black tin is a dry one, and consists of
+mixing it with "culm," and submitting it in a black-lead crucible to the
+highest temperature of a wind furnace. The sample is taken wet as it
+arrives at the smelting house, and is assayed direct. The product of the
+assay is examined, and a deduction of a considerable percentage is very
+properly made for impurities, since the assay really determines the
+percentage, not merely of tin, but of the bodies present which are
+reducible at a white heat. The judgment as to how much is to be deducted
+is assisted partly by an examination of the metal got from the assay,
+and partly by the experience acquired in smelting similar ores. The
+produce, which is that of the impure tin, is stated in parts in twenty;
+thus a produce of 14 is equivalent to 70 per cent., or to 14 cwt. per
+ton.
+
+[Illustration: FIG. 57.]
+
+MECHANICAL SEPARATION.--VANNING.
+
+This process, which has already been referred to, is carried out as
+follows:--After sampling the ore in the ordinary way, a quantity
+(varying with its richness) is weighed out. Special weights are
+generally used. The standard weight, marked 200, weighs about an ounce;
+with poor ores this quantity is taken for an assay, but with richer ores
+100 or even 50 is sufficient. The unit of weight has no special name,
+but the parts in 200 are spoken of as the produce; thus, if 200 of ore
+were taken and 9.5 of black tin were separated, the produce would be
+9-1/2: obviously half the "produce" will give the percentage. The
+weighed portion of the ore is placed on the vanning shovel. The vanner
+stands in front of a tub of water (kieve) and allows 30 or 40 c.c. of
+water to flow on to the ore. He then raises the shovel a little above
+the surface of the water, and, holding it nearly horizontal, briskly
+rotates the water by imparting to the shovel a slight circular motion,
+passing into an elliptical one (front to back). This causes the finer
+mud to be suspended in the liquid, which is then run off, leaving the
+body of the ore in the centre of the shovel. This is repeated until the
+water after standing a moment is fairly clear. About half as much water
+as before is brought on; then, with a motion which is similar to the
+previous one, but with a jerk added in one direction, the heavier
+minerals are thrown up, and the stony matter brought back. The jerk is
+produced just as the wave of water is returning. The descending wave of
+water draws with it the bulkier and lighter particles of the ore, whilst
+the heavier matter lying on the bottom is scarcely affected by it. The
+jerky motion, however, carries it to the front of the shovel. The
+lighter stuff is washed off, and the residue dried by holding the shovel
+over the furnace. It now corresponds, more or less, to the stuff which
+on the mine is sent to the calciner. It is swept from the shovel into a
+scoop, and transferred to a hot crucible; in which it is calcined until
+free from sulphur. Some vanners calcine their samples before commencing
+to van. The calcined ore is shaken out of the crucible on to the shovel;
+rubbed up with a hammer; and washed (as at first) to get rid of the
+finer and lighter "waste." The separating motions are again gone
+through; and the "head" of the best of the black tin is thrown well up
+on one side of the shovel in the form of a crescent, so as to leave room
+on the shovel to work with the "tailings." The quantity of water used is
+kept low, to prevent this "crop" tin from being washed back again. The
+tailings are then crushed to free the tin from adherent oxide of iron;
+and again washed to throw up the remaining tin ore. As this tin is
+finely divided, it is more difficult to bring it up, so that a vigorous
+and rapid motion is required. The tailings are now washed off, and the
+whole of the black tin is brought into the centre of the shovel. It
+requires two or three washings more to free it from the waste it
+contains. Very small quantities of water are used. The purity of the
+black tin can be seen by its appearance on the shovel. The cleaned ore
+is dried as before, freed from particles of iron with the aid of a
+magnet, and weighed. The weighings are carried to 1/8th of the unit
+used. The following example illustrates the method of calculation
+adopted on the mine. A parcel of 1 ton 2 cwt. 3 qrs. of tin ore with a
+produce of 45 (equal to 22-1/2 per cent.) contains 5 cwt. 0 qrs. 12 lbs.
+of black tin. This result is obtained as follows:--
+
+  ton   cwt.   qrs.
+    1     2     3
+                9   }
+  ----------------- }
+   10     4     3   } equivalent to multiplying by 45.
+                5   }
+  ----------------  }
+    5.1   3     3     strike off the first figure to the right.
+                4      multiply by 4 to reduce to quarters.
+  ---------
+    4    12
+          3
+  ---------
+    4    15
+   28                  multiply by 28 to reduce to pounds.
+  -----
+  112
+   15
+  -----
+   12.7                strike off the first figure to the right.
+
+Similarly, a parcel of 20 tons 10 cwt. with a produce of 9-1/2 contains
+19 cwt. 1 qr. 25 lbs. of black tin. For the following information, as
+well as for much of that already given about vanning, we are indebted to
+Captain Reynolds, of Cook's Kitchen Mine. "To have a complete set of
+tools for all vanning purposes, it will be necessary to get the
+following:--A vanning shovel 14 inches long and 13 inches wide, weighing
+not over 2-3/4 pounds. It is made of hammered sheet iron of the shape
+shown in fig. 57. It must have a light wooden handle (preferably of
+deal) 3 feet long. A bruising hammer, weighing 2-1/2 pounds, with a
+handle 1 foot long. A pair of tongs (furnace) 2-1/2 feet long, made of
+1/2-inch round iron. And a set of ordinary clay crucibles for calcining.
+There ought to be two sets of scales and weights: the first should be
+confined to weighing the powdered tin stuff, and the second ought to be
+a much higher class one, for weighing the black tin obtained. The
+furnace for roasting the sample should be 10 inches square and 12 inches
+deep, with the fire-bars at the bottom three-quarters of an inch apart.
+The water-box for vanning in should be at least 4 feet long, 2 feet 6
+inches wide, and 8 inches deep."
+
+
+DRY METHODS.
+
+For the following description of the process adopted in Cornwall we are
+indebted to Mr. A.K. Barnett, F.G.S., of Chyandour.
+
+~Cornish Method.~--_Tin Ore Assay._--The ore to be smelted or assayed
+should be concentrated to say not less than 50 per cent. of metallic
+tin; though to obtain satisfactory results it should be brought nearer
+70 per cent., as with ore containing less than 40 to 50 per cent. of
+metal there will be a considerable loss both in the assaying and in the
+smelting. If the ore to be operated on does not contain this quantity of
+metal, then the sample (if coarse) must be reduced to a fine state, the
+gangue being removed by vanning, and the ore saved for the fire assay.
+
+The method adopted for the determination of tin in the ore is as
+follows:--About 2-1/2 ounces troy (1200 grains, or about 80 grams) of
+the ore to be assayed is weighed out and mixed on a flat copper pan
+(shaped with a long lip) with one-fifth of its weight (240 grains, or
+15.5 grams) of powdered culm (anthracite). The mixture of ore and culm
+is either transferred to a black-lead crucible before the latter is put
+into the furnace, or, as some prefer, it is carefully swept into a
+crucible which has been imbedded in the fire. Some assayers cover their
+pots with a flat cover placed loosely on, while others leave the mixture
+in the open pot. The furnace, which has been previously fired to a
+strong heat, is then covered, and the sample is subjected to a sharp
+fire for a period of from twelve to twenty minutes. No definite time can
+be stated, as, besides the strength of the fire, the quality and
+condition of the ore, and the impurities associated with it, greatly
+affects the time required for the complete reduction of the ore. As soon
+as the mixture in the crucible has settled down to a uniform white heat,
+and any very slight ebullition which may have taken place has subsided,
+the crucible is gently shaken, removed from the fire (the culm-ash or
+slag which covers the metal being carefully drawn aside with an iron
+scraper), and the metal is poured quickly into an iron ingot-mould,
+which is usually placed on a copper pan to save the culm-slag and the
+adherent metal which comes out with it. The crucible is then carefully
+scraped, and the scrapings, together with the contents of the mould and
+pan, are transferred to a mortar. There the ingot of tin is freed from
+slag and then taken to the scales. The rest, after being finely
+powdered, is passed through a sieve. The flattened particles of tin
+which remain on the sieve are weighed with the ingot (the _lump_, as it
+is called); whilst the siftings are vanned on a shovel, and (the slag
+being washed off) the fine tin is collected, dried, and weighed with the
+rest: the whole gives the produce or percentage of metal in the ore.
+The results of the assays are expressed in cwts. of metal in the ton of
+ore. The percentage is rarely given and never used in Cornwall.
+Thus--"13-1/2 Produce" would mean that the assay yielded results at the
+rate of 13-1/2 cwts. of metal for one ton of the ore. Some assayers use
+a little powdered fluor-spar to assist the fusion of refractory slags. A
+small quantity of borax will also occasionally be of service for ores
+containing silica in excess of any iron that may be present. The borax
+renders the slag more fusible, and assists the formation of a larger
+lump (with less fine tin in the slag) than would be obtained by the use
+of culm alone.
+
+The quality and the percentage of _pure tin_ in the metal will vary
+considerably, according to the impurities that are associated with the
+ore to be assayed.
+
+The crude lump is then remelted in a small iron ladle at as low a
+temperature as possible, and the fused metal is poured into a shallow
+trench about 4 inches long by 3/4 of an inch wide cut in a block of
+white marble. The metal will be silvery-white if the temperature
+employed be correct; if too hot, the surface will show a yellow, red, or
+blue colour (according to the heat employed); in such case the metal
+should be remelted at a lower temperature. If the metal on cooling
+remains perfectly clear and bright, then it may be assumed that the tin
+is of good quality and commercially pure. A crystallised or frosted
+appearance of the metal indicates the presence of some alloy, say of
+iron, copper, zinc, lead, antimony, &c. The assayer who has had much
+practice can readily distinguish the metal or metals that are associated
+with the ore by noting the appearance of the tin on cooling; and can
+fairly judge the quantity of impurity present by the amount of the
+crystallisation or stain.
+
+Whilst the foregoing method of assaying cannot lay claim to scientific
+accuracy, it is by no means so imperfect as some writers would have us
+believe, who state that a loss of 5 to 10 per cent. arises in the
+operation. It is certainly the most ready and expeditious mode of
+determining the commercial value of a parcel of tin ore, which, after
+all, is the main object of all assaying operations.
+
+The difficulty which beginners find in obtaining satisfactory results,
+and any loss of metal which those not accustomed to the process may
+incur, will invariably occur in the vanning of the powdered slag for the
+fine tin, the rest of the operations being easy of execution, and
+requiring only the ordinary care necessary for all metallurgical work.
+
+There is no doubt that if low percentage ores containing silica are
+assayed in this manner, low results are obtained, as it is impossible
+to reduce the whole of the tin in the presence of free silica; with this
+class of ores, care should be taken to remove some of the silica by
+preliminary vanning, or some flux should be added which will combine
+with the silica, and so prevent its entering into combination with the
+tin. Low quality tin ores containing iron, copper, lead, zinc, antimony,
+etc., combined with arsenic, sulphur, or oxygen, will give very much
+higher results than the actual percentage of tin in the sample. The
+other metals (being readily reduced in the presence of tin) alloy with
+it, and give a hard lump difficult to fuse in the iron ladle; where the
+quantity of foreign metals is large, the metal can only be melted to a
+stiff pasty mass; so that (in determining the value of a ton of tin ore,
+or even reporting on the percentage of tin it contains) not only must
+the weight of the assay be the basis for calculation, but the quality
+and character of the metal obtained must also be considered. Thus two
+ores of tin might be assayed both yielding a similar _produce_, say
+13-1/2 (67-1/2 per cent.), and yet one might contain 5 per cent. less
+tin than the other.
+
+If it be required to obtain the pure metal from tin ores containing the
+ores of other metals associated with them, the latter must be removed by
+digesting in strong hydrochloric acid, and washing. The assay may then
+be conducted in the usual way, and a fairly pure lump will be obtained.
+
+If wolfram be present in any appreciable quantity in the ore, it
+considerably reduces the proportion of lump, and at the same time it
+increases the fine tin (or _prillion_, as it is termed) in the assay.
+This may be got rid of by boiling in aqua regia, and dissolving out the
+tungstic acid which has been liberated by means of ammonia.
+
+It will be seen that this method of assaying tin has its advantages and
+its drawbacks. It is quickly performed; with ores of good quality it
+gives results not to be excelled by any other process; and it gives the
+smelter the actual alloy and quality of metal he may expect to get in
+the smelting of the ore, which no other mode of assaying will do:
+against which may be set the skill required to obtain accurate results
+with the vanning shovel; the loss of metal in poor ores containing an
+excess of silica; and the high results from ores containing a large
+quantity of metallic impurities.
+
+~Cyanide Method.~--Weigh up 20 grams of the ore and dry it on a scoop
+over the Bunsen flame. When dry, weigh, and calculate the percentage of
+water from the loss in weight. Transfer the dried ore to an evaporating
+dish, and cover with 30 c.c. of hydrochloric acid; boil for 10 or 12
+minutes, and then add 5 c.c. of nitric acid and boil again. Dilute with
+water, and filter. Transfer the filter and its contents to an E
+Battersea crucible, and calcine it for a few minutes. Cool, and weigh
+the residue. The loss equals the oxides soluble in acid. Transfer the
+residue to the crucible and mix it with its own weight of cyanide of
+potassium; add a similar amount of "cyanide" as a cover. Place in the
+furnace, and when the charge has attained the temperature of the furnace
+(in from 3 to 6 minutes), remove it at once; tap the pot _vigorously_
+several times, and then pour its contents quietly into a mould. Dissolve
+the slag in water, clean, dry, and weigh the button of tin.
+
+
+WET METHODS.
+
+~Detection.~--Tin ore is detected by its insolubility in acids, high
+specific gravity, and characteristic appearance in water. The powder is
+separated from the lighter gangue by washing. It is fused in a Berlin
+crucible with five times its weight of potassic cyanide at a moderately
+high temperature in a muffle, or over the blowpipe. The slag is washed
+off with water, and the metallic buttons or residue treated with
+hydrochloric acid (not aqua regia), for some time. One portion of the
+solution strikes a purple colour with chloride of gold, another portion
+gives a white or grey precipitate or cloudiness with mercuric chloride.
+These reactions are characteristic of tin as stannous chloride.
+
+Metallic tin treated with nitric acid becomes converted into a white
+insoluble powder (metastannic acid). Aqua regia dissolves tin readily,
+forming stannic chloride, and in this solution the metal is detected by
+precipitation with sulphuretted hydrogen, which gives a yellow
+precipitate. Tin in solution as stannic or stannous chloride is
+precipitated as metal by means of zinc.
+
+The fact that tin forms two well-defined series of compounds is taken
+advantage of in assaying (just as in the case of iron), by determining
+how much of an oxidising agent is required to convert it from the
+stannous into the stannic state. For example, on the addition of a
+solution of permanganate of potash to a solution of stannous chloride
+the oxidation goes on rapidly, and the finishing point is sharp and
+distinct; but acid solutions of stannous chloride quickly take up oxygen
+from that dissolved in the water used and from the air. Unfortunately,
+there is no obvious sign that such oxidation has taken place, except
+that (fatal to the assay) a smaller volume of the permanganate is
+required. Great care is required with such solutions, both before and
+during titration. The addition of an excess of ferric chloride to the
+stannous solution, as soon as the whole of the tin has been dissolved,
+will lessen this liability to oxidation.
+
+~Separation.~--If the tin is present in an alloy, the substance is
+boiled in an evaporating dish with dilute nitric acid until the whole of
+the material is attacked. Evaporate nearly to dryness, dilute, boil for
+a few minutes, and filter off the white insoluble residue. Under certain
+circumstances this residue will be nearly free from other metals, in
+which case it is ignited and weighed. If not known to be pure it must be
+ignited, reduced in a current of hydrogen, and treated as subsequently
+described.
+
+When the tin is present as insoluble oxide in an ore, the substance is
+finely powdered, and from 1 to 5 grams of it (according to its richness)
+boiled with 30 c.c. of hydrochloric acid in an evaporating dish till the
+oxide of iron is seen to be dissolved. Then add 1 c.c. of nitric acid
+(or more if much pyrites, &c., is present) and continue the boiling till
+these are decomposed; dilute and filter off, washing first with dilute
+acid and afterwards with a little dilute ammonia, dry, ignite, and place
+in a combustion tube (together with the filter-ash) and heat to redness
+for about thirty minutes in a current of dried hydrogen.
+
+[Illustration: FIG. 58.]
+
+The oxide of tin is placed in a porcelain boat (fig. 58), which is then
+introduced into a piece of combustion tube. The latter, wrapped in a
+piece of wire gauze, is supported on a couple of iron rings, and heated
+by one or two Bunsen burners in a furnace fitted up with loose
+fire-brick tiles, as shown in fig. 59.
+
+[Illustration: FIG. 59.]
+
+When the reduction is complete the tube is allowed to cool; the boat is
+removed and the tin dissolved. Add a rod of zinc to the freely-acid hot
+solution, and in a few minutes decant through a filter and wash with
+water, after having removed the zinc. Wash the precipitated metal back
+into the beaker, and dissolve in 10 c.c. of dilute nitric acid,
+evaporate off the excess of acid; dilute, boil, and filter. Wash, dry,
+ignite strongly in a porcelain crucible, and weigh.
+
+In the absence of antimony the above separation works very well, but if
+this metal is present in quantity the metals precipitated on the zinc
+must be covered with hydrochloric acid and treated with a few drops of
+nitric. It is then warmed with iron wire until no more of the latter
+dissolves. The antimony is precipitated as metal, and the tin remains in
+solution as stannous chloride. The antimony is filtered off, and may be
+washed with alcohol, and weighed, whilst the tin in the filtrate is
+precipitated with zinc, and treated as already described.
+
+
+GRAVIMETRIC METHOD.
+
+If the tin is not already in the metallic state it is reduced to this
+condition by the method given (precipitation by zinc). Treat the
+finely-divided metal (washed free from chlorides) in a four-inch
+evaporating dish with 10 c.c. of dilute nitric acid, cover with a
+clock-glass, and apply a gentle heat until the precipitate appears of a
+white colour and the metal is completely attacked. Evaporate nearly to
+dryness on a water-bath; then add 50 c.c. of water, heat to boiling, and
+filter. Wash with hot water, dry, transfer to a weighed porcelain
+crucible, add the filter-ash, ignite strongly, and weigh. The
+precipitate after ignition is stannic oxide (SnO_{2}). It is a
+yellowish-white powder (darker whilst hot), insoluble in acids, and
+contains 78.67 per cent. of tin. Cold dilute nitric acid dissolves tin
+to a clear solution, which becomes a white enamel-like jelly on heating;
+this (filtered off, washed, and dried) forms an opal-like substance,
+which is converted on ignition into stannic oxide with evolution of
+nitrous fumes. Stannic oxide when ignited with chlorides is more or less
+completely converted into stannic chloride, which volatilises. The
+presence of chlorides during the evaporation with nitric acid causes a
+similar loss.
+
+~Determination of Tin in an Alloy.~--(_Bronze._)--Take 2 grams, and
+attack with 20 c.c. of dilute nitric acid in a covered beaker with the
+aid of heat. Boil till the bulk is reduced by one-half, dilute with 50
+c.c. of water, allow to settle for a few minutes, and filter; wash well
+first with water acidulated with a little nitric acid, and afterwards
+with water; dry, ignite, and weigh as stannic oxide.
+
+~Determination of Tin in Tin Ore.~--Treat 5 grams of the dried and
+finely-powdered ore with 30 c.c. of hydrochloric acid in a four-inch
+evaporating dish. After the soluble oxides have been dissolved add 1 or
+2 c.c. of nitric acid, boil off nitrous fumes, dilute, and filter. Dry
+the filter, transfer the cleaned ore to a piece of combustion tube ten
+or twelve inches long and narrowed at one end. Pass a current of
+hydrogen through the tube and heat to redness for 30 minutes; cool
+whilst the gas is still passing. Dissolve in 20 c.c. of dilute
+hydrochloric acid and keep the solution tinted with permanganate of
+potassium. When the colour of the permanganate becomes permanent dilute
+to a bulk of 50 c.c. with water, filter, and wash. Heat; add a rod of
+zinc weighing about 3 grams; allow to stand for a few minutes; decant
+through a filter; and wash, removing the remaining zinc and returning
+the tin to the beaker. Treat with 5 c.c. of dilute nitric acid, boil for
+some time, take up with water, filter, wash, dry, ignite, and weigh as
+stannic oxide.
+
+
+VOLUMETRIC METHOD.
+
+~Titration with Solution of Permanganate of Potassium.~--This titration
+may be made either directly on the solution of stannous chloride
+(prepared by dissolving the precipitated metal in hydrochloric acid), or
+indirectly, on a solution of ferrous chloride (produced by the reducing
+action of the precipitated metal on ferric chloride). The standard
+solution of permanganate of potassium is made by dissolving 5.356 grams
+of the salt in water and diluting to one litre. 100 c.c. are equivalent
+to 1.00 gram of tin.
+
+The precipitated tin is transferred to a flask; and dissolved in 10 c.c.
+hydrochloric acid, with the aid of heat and in an atmosphere of carbonic
+acid. The acid and metal are placed in the flask; which is then filled
+with the gas, and stopped with a cork provided with a rubber valve. When
+solution is complete the flask is again filled with carbonic acid. Fifty
+c.c. of water freed from air and saturated with carbonic acid are then
+added. This water is made by adding a gram of bicarbonate of soda and 2
+c.c. of hydrochloric acid to 100 c.c. of water: the effervescence sweeps
+out the dissolved oxygen. The permanganate of potassium solution is then
+run in from a stop-cock burette in the usual way until a faint pink
+tinge is obtained.
+
+The following experiments show the effect of variations in the
+conditions of the assay. A solution of stannous chloride equivalent in
+strength to the "permanganate" was made by dissolving 19.06 grams of the
+crystallised salt (SnCl_{2}.2H_{2}O.) in 50 c.c. of water and 10 c.c. of
+hydrochloric acid and diluting to 1 litre with water freed from
+dissolved oxygen. 100 c.c. contain 1 gram of tin. In the first
+experiments tap water was used and no precautions were taken for
+excluding air. Except when otherwise stated, 20 c.c. of the stannous
+chloride were used in each experiment with 10 c.c. of hydrochloric acid,
+and were diluted to 100 c.c. with water before titration.
+
+~Effect of Varying Hydrochloric Acid.~
+
+  Acid added                  1.0 c.c.  10.0 c.c.  20.0 c.c.  50.0 c.c.
+  "Permanganate" required    18.8  "    18.9  "    18.8  "    18.8  "
+
+The only effect of the increase in quantity of acid was to give the
+brown of perchloride of manganese instead of the pink of permanganic
+acid to mark the finishing point.
+
+~Effect of Varying Temperature.~
+
+  Temperature                15° C.     50° C.     70° C.     100° C.
+  "Permanganate" required    18.8 c.c.  18.7 c.c.  18.6 c.c.  18.4 c.c.
+
+~Rate of Atmospheric Oxidation.~--Solutions ready for titration were
+exposed to air at the ordinary temperature for varying lengths of time
+and then titrated.
+
+  Time exposed      0 min.     5 min.    10 min.    20 min.    60 min.
+  "Permanganate"
+    required       18.8 c.c.  18.8 c.c.  18.8 c.c.  18.8 c.c.  18.6 c.c.
+
+It is best to titrate at once, although the loss by oxidation is only
+small after one hour's exposure.
+
+~Effect of Varying Tin.~
+
+  Stannous chloride
+    added           1.0 c.c.  10.0 c.c.  20.0 c.c.  50.0 c.c.  100.0 c.c.
+  "Permanganate"
+    required        0.7  "     8.8  "    18.0  "    47.4  "     95.4  "
+
+~Effect of Varying Bulk.~
+
+  Bulk                       50.0 c.c.  100.0 c.c.  200.0 c.c.  500.0 c.c.
+  "Permanganate" required.    9.0  "     18.3  "     17.4  "     15.1  "
+
+The two last series show an interference, which is due to the oxygen
+dissolved in the water, as may be seen from the following similar
+experiments, which were, however, performed with water freed from oxygen
+and in which the titrations were effected in an atmosphere of carbonic
+acid.
+
+~Effect of Varying Tin.~--A new solution of stannous chloride was used.
+
+  Stannous chloride
+    added           1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
+  "Permanganate"
+    required        1.0  "   10.0  "   19.8  "   49.6  "    99.3  "
+
+~Effect of Varying Bulk.~
+
+  Bulk             30.0 c.c. 50.0 c.c. 100.0 c.c. 200.0 c.c. 500.0 c.c.
+  "Permanganate"
+    required       19.8  "   19.8  "    19.8  "    19.8  "    19.8  "
+
+It will be seen that in working under these conditions the results are
+proportional and the method satisfactory.
+
+~Examination of Tin Phosphide.~--(_Phosphor Tin_.)--This substance is
+used in the manufacture of "phosphor bronze" and similar alloys. It is a
+crystalline, imperfectly-malleable, metallic substance. It is soluble in
+hydrochloric acid with effervescence; phosphoretted hydrogen, which
+inflames on the addition of a drop or two of nitric acid, being evolved.
+It is attacked by nitric acid, yielding a white powder of stannic
+phosphate; this is not easily decomposed by ammonium sulphide or readily
+soluble in hydrochloric acid.
+
+"Phosphor-tin" is made up only of tin and phosphorus. For the estimation
+weigh up 1 gram. Place in a weighed Berlin dish; and cover with 10 c.c.
+of nitric acid and 3 or 4 c.c. of water. Let the reaction proceed (under
+a clock-glass) on the water-bath till complete. Remove the glass;
+evaporate to dryness, and ignite, at first gently over a Bunsen burner,
+and afterwards in the muffle at a red heat. Cool in the desiccator, and
+weigh as quickly as possible when cold. The substance contains the tin
+as stannic oxide, SnO_{2}, and the phosphorus as phosphoric oxide,
+P_{2}O_{5}. The increase in weight on the gram of substance taken gives
+the weight of the oxygen taken up by the phosphorus and tin, and since 1
+gram of tin takes up only 0.271 gram of oxygen, and 1 gram of phosphorus
+takes up 1.29 gram, the proportion of tin to phosphorus can be
+calculated from the increase in weight. For example, 1 gram of a sample
+gave 1.3410 gram of mixed oxides, which is 0.070 gram in excess of that
+which would be got with pure tin. If the substance was all phosphorus
+the excess would be 1.0190 gram; consequently the proportion of
+phosphorus in the substance is 0.070 / 1.019, or 6.87 per cent. The tin
+is calculated by difference, 93.13 per cent.
+
+Another method of separating and determining the phosphorus is as
+follows:--Take 1 gram of the substance and add to it 15 c.c. of hot aqua
+regia. Boil till dissolved, dilute, and precipitate the tin with
+sulphuretted hydrogen. To the filtrate add ammonia and "magnesia
+mixture." Filter; wash the precipitate with dilute ammonia; dry, ignite,
+and weigh as magnesic pyrophosphate. Calculate the phosphorus, and take
+the tin by difference.
+
+A sample of phosphor tin gave--
+
+  Tin            93.1 per cent. (by difference)
+  Phosphorus      6.9    "
+                -----
+                100.0
+
+~Tin Arsenide.~--This is met with in tin-smelting; it closely resembles
+the phosphide, but the crystals have a duller grey appearance. It
+contains simply tin and arsenic. The determination is made by treating 1
+gram of the substance with nitric acid and weighing the mixed oxides of
+tin and arsenic in the same manner as in the case of the phosphide. One
+gram of arsenic will give 1.533 gram of arsenic oxide, As_{2}O_{5};
+consequently the excess of weight of the mixed oxides over 1.271 gram
+must be divided by 0.262; the result multiplied by 100 gives the
+percentage of arsenic. In consequence of the higher atomic weight of
+arsenic the results by this method are not so close as with the
+phosphide. Each milligram of excess weight (over 1.271) represents 0.38
+per cent. of arsenic, As. Both in this and in the corresponding
+phosphide determination care must be taken to avoid absorption of
+moisture, by allowing the oxides to cool in a desiccator and weighing
+quickly.
+
+The percentage of arsenic is better determined as follows:--Weigh up 1
+gram of the substance, dissolve in aqua regia, dilute, and pass
+sulphuretted hydrogen. Render alkaline with ammonia, and add ammonium
+sulphide till the precipitate is dissolved. Add "magnesia mixture."
+Filter off the precipitate, wash with dilute ammonia, ignite with a few
+drops of nitric acid, and weigh as magnesic pyrarsenate. Calculate the
+arsenic and take the tin by difference. A sample treated in this way
+gave--
+
+  Tin       96.8 per cent. by difference
+  Arsenic    3.2           "
+           -----
+           100.0
+
+~Examination of Black Tin.~--Dry the ore, and reduce it to a fine
+powder. Weigh up 2 grams, and boil with 20 c.c. of hydrochloric acid and
+2 c.c. of nitric for ten or fifteen minutes. Filter, and reserve the
+filtrate.
+
+~Tungstic Acid.~--Digest the residue with about 50 c.c. of water and a
+few c.c. of dilute ammonia for a few minutes, and filter; collect the
+filtrate in a weighed porcelain dish, evaporate to dryness, ignite, and
+weigh as tungstic acid, WO_{3}.
+
+~Stannic Oxide.~--Dry, ignite, and weigh the insoluble residue. Transfer
+to a porcelain boat, and reduce in a current of hydrogen at a red heat
+for half an hour. Allow to cool whilst the hydrogen is still passing.
+Transfer the boat to a beaker, and dissolve up the tin in 10 c.c. of
+hydrochloric acid and a c.c. or so of nitric. Wash out the combustion
+tube with some acid and add the washing to the contents of the beaker.
+Warm gently, dilute with water, and filter. Collect, dry, ignite, and
+weigh the insoluble residue. Through the filtrate pass a rapid current
+of sulphuretted hydrogen, allow to settle, and filter. Wash the
+precipitate with hot water, dry, calcine gently; ignite with ammonium
+carbonate, and weigh as stannic oxide, SnO_{2}. The insoluble residue
+will in most cases retain some tin. Fuse it with fusion mixture, take up
+with hydrochloric acid, filter, pass sulphuretted hydrogen through the
+filtrate, collect and wash the sulphide of tin. Ignite and weigh as
+stannic oxide, and add it to that previously obtained.
+
+~Copper.~--Pass sulphuretted hydrogen through the acid filtrate obtained
+in the first cleaning of the ore, collect the precipitate, and wash
+first with soda solution and then with hot water. Dry, ignite, and weigh
+as cupric oxide, CuO. Mix the filtrate with that from the main portion
+of the sulphide of tin.
+
+~Ferric Oxide.~--Boil off the sulphuretted hydrogen from the mixed
+filtrates and peroxidise with nitric acid. Add ammonia in slight excess,
+boil, filter, dry, ignite, and weigh the precipitate as ferric oxide.
+This will be practically pure, but the iron in it must be determined by
+dissolving and titrating. The filtrate from the iron may contain zinc,
+lime, and magnesia, but rarely in quantities sufficient to be
+determined.
+
+~Silica, &c.~---The silica may be calculated from the weight of the
+residue insoluble in acid, after the reduction of the tin in hydrogen,
+by deducting from it the weight of the oxide of tin subsequently found.
+Or it may be determined as follows:--The insoluble portion is fused with
+fusion mixture, and taken up with hydrochloric acid, as already
+described. On filtering, the filter will retain a portion of the silica.
+The rest is recovered, after the removal of the stannous sulphide, by
+evaporating to dryness, taking up with hydrochloric acid, and filtering
+through the same filter. It is washed, dried, ignited, and weighed as
+silica. The filtrate from the silica is boiled with a little nitric acid
+and precipitated with ammonia. The precipitate is collected, washed,
+ignited, and weighed as ferric oxide and alumina (but it frequently
+contains oxide of titanium). When the last is present it is determined
+by fusing with bisulphate of potash and extracting with cold water. The
+solution is nearly neutralised with ammonia, charged with sulphurous
+acid, and boiled. The precipitate is collected, washed, dried, ignited,
+and weighed as oxide of titanium, TiO_{2}. The difference between this
+weight and that of the combined oxides gives the ferric oxide and
+alumina. The filtrate from the mixed oxides is examined for lime and
+magnesia.
+
+~Sulphur.~--Rub up 5 grams of the ore with 5 grams of nitre, transfer to
+a porcelain dish, and fuse over a Bunsen burner for fifteen minutes.
+When cold, extract with water, and determine the sulphur volumetrically
+with standard barium chloride. The sulphur may be present as sulphide or
+sulphate.
+
+~Arsenic.~--Take 5 grams, and evaporate with nitric acid; dilute, add
+ammonia, pass sulphuretted hydrogen, and filter.
+
+To the filtrate add "magnesia mixture." Collect the precipitate, ignite
+with nitric acid, and weigh as magnesic pyrarsenate.
+
+The following may be taken as an example of the composition of an impure
+black tin:--
+
+  Tungstic acid    1.8 %
+  Stannic oxide   79.0
+  Silica           2.6
+  Titanic oxide    0.8
+  Copper oxide     0.9
+  Ferric oxide    13.4
+  Sulphur          0.4
+  Arsenic          0.3
+                  ----
+                  99.2
+
+~Examination of Hardhead.~--In the smelting of tin ores a quantity of
+speise, known as "hardhead," is produced. It is essentially an arsenide
+of iron, carrying a considerable quantity of tin. Much of this last is
+present in the form of small buttons of metal distributed through the
+mass. The buttons can be seen on careful inspection, and become evident
+on powdering.
+
+In assaying the substance, a variation in the usual method of sampling
+is required, because of the quantity of metal present which cannot be
+powdered. After powdering as finely as possible, the coarse particles
+are sifted off and weighed. The weight of the powder is also taken. The
+method of working is best illustrated by an example. A sample of
+hardhead weighed 155.1 grams, and gave 21.0 grams of coarse particles,
+equivalent to 13.5 per cent. of the whole. The fine portion weighed 134
+grams, which is equivalent to 86.5 per cent.
+
+Thirteen and a half grams of the coarse material were dissolved in aqua
+regia, and diluted with water to 1 litre. Ten c.c. of this contain 0.135
+gram of the metallic portion, which is the amount contained in 1 gram of
+the original hardhead. If, in a determination, 1 gram of the substance
+is wanted, weigh up 0.865 gram of the powdered portion, and add to it 10
+c.c. of the solution. It will be seen that these together make up 1 gram
+of the original sample. The solution of the metallic portion must be
+saved until the analysis is finished.
+
+~Tin and Copper.~--Weigh up the portion of the powdered stuff equivalent
+to 1 gram of the sample. Transfer to a flask, and cover with 10 c.c. of
+the solution of the metallic portion and 10 c.c. of aqua regia. Boil
+gently till oxidation is complete and the nitric acid for the greater
+part driven off. Dilute to 100 c.c. with water, and pass sulphuretted
+hydrogen for some time. Filter, wash with hot water, and rinse through
+the funnel back into the flask. Digest with yellow sodium sulphide until
+only a light, flocculent, black precipitate is left. Filter this off,
+wash with hot water, dry, calcine, treat with a little nitric acid,
+ignite, and weigh as copper oxide, CuO. The weight multiplied by 0.7983
+gives the weight of copper.
+
+The filtrate containing the tin is rendered acid with hydrochloric acid,
+and filtered. The precipitate is rinsed into a half-pint beaker, covered
+with 20 c.c. of hydrochloric acid, and boiled down to about 20 c.c. The
+solution is filtered off from the sulphur and sulphide of arsenic,
+which, after washing with hot water, is transferred to a flask labelled
+"arsenic." A strip of sheet zinc (2 in. by 1 in.) is placed in the
+solution. The evolution of hydrogen should be brisk. In five or ten
+minutes decant off a few c.c. of the liquid, and test with sulphuretted
+hydrogen for tin. If no yellowish precipitate is formed, decant off the
+rest of the liquid, and wash the precipitated metal with hot water two
+or three times by decantation. The metal should be in a lump; if there
+are any floating particles they must be made to sink by compression with
+a glass rod. Transfer the washed metal to an evaporating dish 3 or 4 in.
+across, and cover with a few c.c. of hot water. Add nitric acid drop by
+drop till the tin is completely attacked. Evaporate nearly to dryness,
+and add a drop or two more of nitric acid and 20 c.c. of water. Boil and
+filter. Wash with hot water, dry, ignite, and weigh as stannic oxide,
+SnO_{2}. Calculate to metallic tin by multiplying by 0.7867.[76]
+
+The filtrate from the first treatment with sulphuretted hydrogen will
+probably no longer smell of the gas. Warm and pass the gas for a few
+minutes longer. Filter off any precipitate of sulphide of arsenic, and
+transfer it to the flask for "arsenic." Boil the filtrate (ignoring any
+signs of a further precipitation of arsenic) with a few c.c. of nitric
+acid, and separate the iron as basic acetate. Wash; reserve the filtrate
+for cobalt.
+
+~Iron.~--Rinse back the "basic acetate," precipitate into the flask, add
+ammonia, dilute with water to about 100 c.c., and pass sulphuretted
+hydrogen for a few minutes. Filter, and wash with hot water. Collect the
+filtrate in the flask labelled "arsenic." Boil the precipitate with
+dilute sulphuric acid, filter, and titrate the filtrate with the
+permanganate of potassium solution after boiling off the sulphuretted
+hydrogen. Report the result as iron. The sulphuric acid will not effect
+complete solution, a light black residue will remain, chiefly sulphur;
+this must be rinsed into the filtrate from the acetate separation. It
+contains cobalt.
+
+~Cobalt.~--The filtrate from the acetate separation will have a pink
+colour. Render it ammoniacal and pass sulphuretted hydrogen. Collect
+the precipitate on a filter, dry, and ignite. Dissolve in hydrochloric
+acid, and evaporate nearly to dryness with an excess of nitric acid.
+Dilute with 10 or 20 c.c. of water and add potash solution in slight
+excess. Add acetic acid until the solution is acid and the precipitate
+is quite dissolved. Add 20 or 30 c.c. of a strong solution of potassium
+nitrite, and determine the cobalt, as described on pp. 254, 256. Boil
+the filtrate from the cobalt, precipitate with hydrochloric acid, render
+ammoniacal, and test for zinc, nickel, and manganese.
+
+_The remainder of the tin_ will be contained in the flask labelled
+"arsenic." Acidify with hydrochloric acid and filter. Rinse into a
+beaker, and evaporate to a small bulk with 10 c.c. of nitric acid.
+Dilute and filter. Dry the precipitate, consisting of stannic arsenate
+(2SnO_{2}.As_{2}O_{5}), ignite, and weigh. Calculate the tin it contains
+by multiplying by 0.4453, and add to that already found.
+
+~Arsenic.~--This is determined in a separate portion. Weigh up a portion
+of the powder equivalent to 1 gram of the hardhead, place in a pint
+flask, and boil with 10 c.c. of nitric acid. When action has ceased add
+10 c.c. of the solution of the metallic portion and then hydrochloric
+acid (a few drops at a time) till solution is complete. Warm gently in
+dissolving, but do not boil. Dilute to about 100 c.c., render alkaline
+with ammonia, and add 20 c.c. of yellow ammonium sulphide. Digest at a
+gentle heat for about thirty minutes, filter, and wash. Add 50 c.c. of
+magnesia mixture, shake well, allow to stand for an hour, filter, and
+wash with dilute ammonia. The precipitate is dissolved and then titrated
+with uranium acetate, or it is evaporated with nitric acid, ignited, and
+weighed as pyrarsenate of magnesia. Calculate the result to arsenic, As.
+
+~Sulphur.~--Weigh up a portion of the powder equivalent to 2 or 3 grams
+of the hardhead. Rub up in a mortar with 5 grams of nitre and fuse in a
+porcelain dish for ten minutes. Extract with water, add 20 or 30 c.c.
+(as the case may be) of the solution of the "metallics." Add 10 grams of
+sodic acetate, and ferric chloride until the precipitate turns brown;
+dilute with water to half a litre, boil, and titrate with standard baric
+chloride, as described under _Sulphur_. Report as sulphur.
+
+A sample of hardhead examined in this way gave--
+
+  Sulphur              3.00%
+  Arsenic             27.10
+  Tin                 22.2
+  Copper               1.64
+  Iron                43.2
+  Cobalt               2.6
+                     ------
+                      99.74
+
+~Examination of Tin Slags.~--In tin smelting works the term "slag" is
+applied to the unfused portion of the charge. It is made up of unburnt
+anthracite and small lumps of slag proper together with some buttons of
+metallic tin. This is rarely, if ever, assayed. The slag proper (or, as
+it is generally called, "glass") is a silicate of iron, alumina, and
+lime, containing from 3 to 7 per cent. of tin. It is thus examined:--The
+sample after bruising on an iron plate, is reduced to a very fine powder
+by grinding in an agate mortar. In this state it is in most cases
+readily decomposed by hydrochloric acid.
+
+~Determination of Tin.~--Where the percentage of tin only is required,
+take 2 grams of the powdered slag and well mix with it 20 c.c. of
+hydrochloric acid, and heat to boiling. Add 1 c.c. of nitric acid, allow
+to stand for fifteen minutes, dilute with water, and filter. Pass a
+rapid current of sulphuretted hydrogen for some time. Allow to settle,
+and filter. The precipitate, after washing with hot water, is dried, and
+gently calcined until the greater part of the sulphur is burnt off. It
+is then strongly ignited in the muffle (or over the blowpipe) with the
+addition of a small lump of ammonic carbonate. The residue is weighed as
+stannic oxide (SnO_{2}); and is calculated to metallic tin by
+multiplying by 0.787. The percentage on the slag is calculated in the
+usual way.
+
+The tin is always best determined in the examination of slags by a
+separate assay carried out in this way. The determination of the other
+constituents is thus made:--
+
+~Silica.~--Take 2 grams of the powdered slag and cover them, in a small
+evaporating dish, with 20 c.c. of hydrochloric acid; mix well by
+stirring with a glass rod; and evaporate to dryness. If (as is generally
+the case) tungsten is present the solution will be blue. Take up with 20
+c.c. of hydrochloric acid. Add 1 c.c. of nitric acid; and reduce by
+boiling to about half the bulk. Add about 20 c.c. of water, boil, and
+filter. Wash the residue with hot dilute hydrochloric acid. It consists
+of silica with the tungstic acid. Wash it back into the dish; and digest
+with 5 or 10 c.c. of a cold solution of ammonic carbonate. Filter; and
+collect the filtrate and washings in a weighed porcelain dish. Dry the
+residue, ignite strongly, and weigh as silica, SiO_{2}. In certain
+exceptional cases this may contain some unaltered cassiterite, which is
+easily recognised by its appearance.
+
+~Tungsten.~--The ammonic carbonate filtrate from the silica is
+evaporated to dryness, ignited strongly over the blowpipe, and weighed.
+The residue is tungstic acid, WO_{3}. The tungsten may be conveniently
+reported in this form, although it is probably present as a lower
+oxide.
+
+~Tin.~--The acid filtrate from the silica and tungstic acid is treated
+with sulphuretted hydrogen. The sulphide of tin is filtered off. Since
+the percentage of tin has been already determined, this precipitate may
+be neglected; or may be treated in the same way as the previous one, so
+as to check the result. Since some stannic chloride will have been lost
+in the evaporation, a low result may be expected. The tin should be
+reported as stannous oxide; and is calculated by multiplying the
+percentage of tin by 1.136.
+
+The filtrate from the tin is boiled rapidly down to remove sulphuretted
+hydrogen; and then peroxidised with 1 or 2 c.c. of nitric acid. It is
+cooled, transferred to a graduated flask, and diluted with water to 200
+c.c.
+
+~Ferrous Oxide and Alumina.~--Half the filtrate from the tin (that is,
+100 c.c.) is taken, nearly neutralised with soda, and treated with
+sodium acetate. The basic acetate precipitate obtained on boiling is
+filtered off and washed. Reserve the filtrate. The precipitate is
+dissolved off the filter with hot dilute hydrochloric acid; and the
+solution thus formed is treated with a slight excess of ammonia, and
+boiled. The precipitate is filtered off, washed with hot water, dried,
+ignited, and weighed as mixed ferric oxide and alumina. The ignited
+precipitate is then dissolved with sulphuric and hydrochloric acids; and
+the iron determined in the solution by titration with the solution of
+stannous chloride. The iron found is calculated to and reported as
+ferrous oxide, FeO (factor = 1.286). To find the alumina, which is best
+estimated by difference, multiply the iron by 1.428 to get the weight of
+ferric oxide, and deduct this from the weight of alumina and ferric
+oxide found. This, of course, gives the alumina. A direct determination
+may be made by removing the tin from the titrated solution with
+sulphuretted hydrogen, filtering, nearly neutralising with ammonia, and
+boiling with a few grams of hyposulphite of soda. The precipitate,
+filtered, washed, and ignited, is the alumina, which is weighed. The
+direct determination gives a slightly low result.
+
+~Oxides of Zinc and Manganese.~--These are determined in the filtrate
+from the basic acetate precipitate by rendering alkaline with ammonia,
+and passing a current of sulphuretted hydrogen. Generally a small, but
+decided, precipitate of alumina comes down, together with sulphides of
+any zinc or manganese which is present. The precipitate is allowed to
+settle, dried, ignited, and weighed. The metals are separately
+determined in it; and the residue is counted as alumina, and added to
+that already found. The mixed precipitate amounts to from 1 to 2 per
+cent. of the sample.
+
+~Lime.~--The filtrate from the last is treated with ammonic oxalate,
+boiled for a few minutes, allowed to settle, and filtered. The
+precipitate is washed with hot water; dried; ignited; and weighed as
+carbonate, after gentle ignition; or as lime, after strong ignition in
+the muffle.
+
+~Magnesia.~--The filtrate from the lime is treated with sodic phosphate
+and ammonia. It is well mixed by stirring, and allowed to stand
+overnight. The precipitate is washed with dilute ammonia, dried,
+ignited, and weighed as pyrophosphate.
+
+~Soda and Potash.~--These are determined in the remaining half of the
+filtrate from the tin. The solution is rendered ammoniacal with ammonia;
+and treated, first with sulphuretted hydrogen, and then with ammonium
+oxalate. The precipitate is filtered off and rejected. The filtrate is
+evaporated in a small porcelain dish over a Bunsen burner, or on the
+sand bath; and towards the close (or earlier if the evaporation is not
+proceeding well) nitric acid is added. The evaporation is carried to
+dryness; and the residue heated nearly to redness. The residue, which
+consists of magnesia with carbonates and chlorides of the alkalies, is
+extracted with water; and filtered. The filtrate is evaporated with
+hydrochloric acid in a weighed platinum dish, ignited gently, and
+weighed. This gives the weight of the mixed chlorides of sodium and
+potassium; which are then separated and determined as described under
+_Potash_.
+
+It must be remembered when calculating the percentage that (with the
+exception of the silica, tungstic acid, and tin) the determinations have
+been made on 1 gram of the sample.
+
+The following analysis will illustrate the composition of such a slag:--
+
+  Tungstic acid                  1.3%
+  Silica                        39.4
+  Stannous oxide                 8.1
+  Ferrous oxide                 26.2
+  Alumina                       14.8
+  Oxide of manganese           traces
+  Lime                           7.9
+  Magnesia                       0.5
+  Alkalies calculated as soda    1.7
+                               -----
+                                99.9
+
+
+TITANIUM.
+
+Titanium only occurs as a mineral in its oxidised state, or as titanic
+oxide (TiO_{2}). It is a substance which has little commercial value,
+and is generally recognised as one of the rare bodies; although, in
+small quantities, it is widely disseminated. It occurs in granite,
+basalt, and other igneous rocks in quantities up to as much as 1 per
+cent. It is also met with in clays and iron ores, and in river sands, in
+which it is often associated with stream tin. The proper minerals of
+titanium are rutile (TiO_{2}), titaniferous iron (titanate of iron), and
+sphene (titanate and silicate of lime).
+
+The oxide of titanium (like cassiterite and quartz) is undecomposed by
+hydrochloric or nitric acid; so that it is generally found in the
+residue insoluble in acids. The titanates, however, are attacked, and a
+portion of the titanium dissolves; so that it must be looked for in both
+the filtrate and residue. Oxide of titanium in its native form, or after
+ignition, may be made soluble by fusing the finely-divided substance
+with fusion mixture in a platinum dish. The resulting titanate is
+dissolved out of the "melt" by cold hydrochloric acid.
+
+The method most commonly used is fusion with bisulphate of potash. This
+renders the oxide of titanium soluble in cold water. The process is as
+follows:--The substance is extracted with hydrochloric and nitric acids,
+and the solution reserved for further treatment; the residue is dried,
+moistened with sulphuric acid, and evaporated once or twice to dryness
+with hydrofluoric acid. It is then fused with bisulphate of potash, and
+the "melt" extracted with cold water until all soluble matter is
+removed. The solution is filtered. The residue may consist of unremoved
+silica, and oxides of tantalum, niobium, and, perhaps, chromium. On the
+prolonged boiling of the filtrate, the oxide of titanium (and oxide of
+zirconium, if any) is precipitated.
+
+Any titanium dissolved by the first extraction with acids is recovered
+in the following way:--Sulphuretted hydrogen is passed into the acid
+solution, and any precipitate that may be formed is filtered off. The
+filtrate is oxidised, and the iron, aluminium, and titanium are
+separated as basic acetates (see under _Iron_). The precipitate is dried
+and fused with bisulphate of potash. The "melt" is extracted with cold
+water, filtered if necessary, and the solution rendered first faintly
+alkaline with ammonia, then very slightly acid with sulphuric acid. 30
+or 40 c.c. of a saturated solution of sulphurous acid is added, and the
+oxide of titanium precipitated by prolonged boiling. It is filtered off,
+added to the precipitate previously got, ignited with ammonic carbonate
+towards the end, and then weighed.
+
+~Detection.~--Titanium is detected in an insoluble residue by fusing the
+residue for some time in a bead of microcosmic salt. In the reducing
+flame it gives a violet colour, which becomes reddish-brown if much iron
+is present. In the oxidising flame it gives a colourless or whitish
+bead. It is best detected in acid solutions by the deep brown or iodine
+colour developed on adding hydroxyl. A solution of this can be prepared
+by pouring peroxide of barium (BaO_{2}) diffused in water into dilute
+hydrochloric acid (a little at a time), and keeping the acid in excess.
+
+~Separation.~--In the usual course of an analytical separation the
+hydrate of titanium will be thrown down with ferric hydrate, &c., on the
+addition of ammonic chloride and ammonia. It is best separated from this
+precipitate by fusion with bisulphate of potash, as already described,
+but it must be remembered that the presence of much mineral acid
+prevents complete precipitation when the solution is boiled. Further, if
+phosphates are present, the precipitate will contain phosphoric oxide;
+it may be freed from this by fusion with sodium carbonate. A very good
+method of separating titanium from iron is to add tartaric acid and
+ammonia to the solution, and then precipitate the iron (as sulphide)
+with sulphuretted hydrogen. The filtrate contains the titanium, which is
+recovered by evaporating and igniting. It may be separated from zirconia
+by the action of sodium carbonate, which precipitates both; but when
+concentrated, redissolves the zirconia. The separation from large
+quantities of silica is best effected by evaporating with hydrofluoric
+acid, which volatilises the silicon; but sulphuric acid must be present,
+otherwise some titanium also will be lost, as may be seen from the
+following experiments,[77] in which oxide of titanium (pure, ignited)
+was evaporated to dryness with a quantity of hydrofluoric acid known by
+experiment to be sufficient to volatilise 1 gram of silica.
+
+_Without sulphuric acid_, 0.0466 gram of titanic oxide left 0.0340 gram,
+showing a loss of about 25 per cent.
+
+_With sulphuric acid_ the following results were obtained:--
+
+  Oxide taken.    Left after Evaporation
+                      and Ignition.
+  0.0340 gram          0.0340 gram
+  0.0414  "            0.0413  "
+  0.0520  "            0.0520  "
+  0.0352  "            0.0352  "
+
+
+GRAVIMETRIC DETERMINATION.
+
+The titanic hydrate thrown down by ammonia (or on boiling the solution
+from the bisulphate) is collected, washed, dried, ignited strongly with
+the addition of a little ammonic carbonate, and weighed. The substance
+is titanic oxide (TiO_{2}), and is generally reported as such. It
+contains 60.98 per cent. of titanium. It should be white, if pure
+(Holland), white, yellow, or brown (Fresenius), or black (Tidy).
+
+
+VOLUMETRIC METHOD.
+
+A method has been proposed based on the reduction of titanic oxide by
+zinc in hydrochloric acid solutions to the sesquioxide. The reduction is
+marked by the development of a violet or green colour, the former with
+chlorides and the latter when fluorides are present. The quantity of
+titanium reduced is measured by titrating with permanganate of potassium
+solution. The water used must be free from dissolved oxygen.
+
+
+TUNGSTEN AND TUNGSTATES.
+
+Tungsten occurs in nature only in the oxidised state, or as tungstic
+acid (WO_{3}), either free, as in wolframine, or combined with oxides of
+manganese and iron, as in wolfram, or with lime, as in scheelite.
+Wolfram occurs associated with tin ores, the value of which is
+consequently lowered. Both wolfram and scheelite are of considerable
+importance as a source of tungstic acid for the manufacture of sodium
+tungstate, which is used as a mordant and for some other purposes, and
+as a source of metallic tungsten, which is used in steel-making.
+
+The tungsten minerals have a high specific gravity (6 to 7.5). On
+treatment with hydrochloric acid or aqua regia they are decomposed; the
+yellow tungstic acid separates and remains insoluble.
+
+Tungsten itself is insoluble in nitric acid or aqua regia; but is
+converted into tungstic acid (WO_{3}) by prolonged and strong ignition
+in air. Alloys containing tungsten leave tungstic acid after treatment
+with nitric acid or aqua regia. Tungstic acid may be got into solution
+after fusion with alkalies or alkaline carbonates. This solution gives
+with hydrochloric acid a white precipitate of tungstic acid, which
+becomes yellow on boiling, but the separation is not complete. Fusion
+with bisulphate of potash gives a residue, which does not dissolve in
+water, but is soluble in ammonic carbonate. For the assay of minerals
+containing tungsten these reactions are only occasionally taken
+advantage of for testing or purifying the separated tungstic acid.
+
+~Detection.~--The minerals are easily recognised by their physical
+characters, and the yellow tungstic acid separated by boiling with acids
+is the best test for its presence; this, after decanting and washing,
+immediately dissolves in a few drops of dilute ammonia. A solution of
+tungstate acidulated with hydrochloric acid becomes intensely blue on
+the addition of stannous chloride and warming. Fused in a bead of
+microcosmic salt it gives a clear blue colour (reddish-brown if iron is
+also present) in the reducing flame, but is colourless in the oxidising
+flame.
+
+~Solution and Separation.~--The decomposition and solution of natural
+tungstates is difficult to effect owing to the separation of tungstic
+acid; the method of treatment is as follows:--Boil the finely-powdered
+substance with hydrochloric acid or aqua regia till it apparently ceases
+to be attacked; dilute, filter, and wash with dilute hydrochloric acid.
+Cover with dilute ammonia, and filter the solution, which contains
+ammonic tungstate, into an evaporating dish. Treat the residue again
+with acid, and again dissolve out the separated tungstic acid with
+ammonia, and repeat this operation until decomposition is complete. By
+this means there will be obtained--(1) a solution containing tungstate
+of ammonia; (2) an insoluble residue with silicates, and oxides of tin,
+niobium, tantalum, &c.; and (3) an acid solution containing the soluble
+bases. The tungstate of ammonia requires simple evaporation on the
+water-bath and gentle ignition in order to cause the tungstic acid to be
+left in an almost pure state; possibly, it may carry a little silica.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The tungstic acid is dissolved, and separated as ammonic tungstate, and,
+after evaporation, is gently ignited, the heat being increased towards
+the end. The residual tungstic acid is fixed, so that when the ammonia
+has been driven off it may be strongly heated without loss. It is a dark
+yellow or brown powder whilst hot, which becomes a light yellow on
+cooling. If any reduction has taken place it will be more or less
+greenish. It is weighed when cold, and is the trioxide or "tungstic
+acid" (WO_{3}), which contains 79.31 per cent. of tungsten. After its
+weight has been taken its purity is checked by fusing with hydric
+potassic sulphate, extracting with water, and treating the residue with
+ammonic carbonate. Any silica present will be left undissolved; it
+should be separated and weighed, and its weight deducted from that of
+the tungstic acid found.
+
+~Determination of Tungstic Acid in Wolfram.~--Take 2 grams of the
+finely-powdered sample and boil with 50 c.c. of hydrochloric acid for
+half an hour, adding 5 c.c. of nitric acid towards the end. Allow to
+stand overnight and boil again for 15 or 20 minutes; dilute with an
+equal volume of water, and filter. Wash with dilute hydrochloric acid,
+dissolve in a few c.c. of warm dilute ammonia, and dilute to 200 c.c.
+with distilled water; allow to settle, and filter. Evaporate in a
+weighed dish, ignite, and weigh.
+
+The following analysis will illustrate the composition of a sample of
+Cornish wolfram as brought into the market:--
+
+  Tungstic acid                  50.1%
+  Cassiterite                    10.9
+  Ferrous oxide                  24.6
+  Manganous oxide                 5.4
+  Niobic oxide, alumina,  &c.     3.5
+  Silica                          1.2
+  Copper oxide                    2.7
+  Zinc oxide                      0.22
+  Arsenic                         0.51
+  Sulphur                         0.20
+                                 -----
+                                 99.33
+
+
+NIOBIC AND TANTALIC OXIDES.
+
+These oxides are commonly met with in samples of wolfram and tinstone,
+especially niobic. They are probably present in the form of columbite, a
+niobate of iron and manganese; and tantalite, a tantalate of the same
+metals.
+
+On boiling with hydrochloric acid they are both liberated, and remain
+for the greater part (all the niobic) in the insoluble residue with the
+tungstic acid. On removing the latter with dilute ammonia they remain as
+a white insoluble precipitate, very prone to run through the filter on
+washing. They may be dissolved in hydrofluoric acid either at once or
+after fusion with bisulphate of potash, and extraction with cold water.
+To the solution in hydrofluoric acid gradually add a boiling solution of
+acid potassium fluoride (HF, KF.). Potassic fluotantalate (soluble in
+200 parts of water) separates out first, and afterwards potassic
+fluoniobate (soluble in 12 parts of water). The separated salts (after
+heating with sulphuric acid and washing out the potassium sulphate
+formed) are ignited with ammonic carbonate, and weighed as tantalic
+oxide (Ta_{2}O_{5}) and niobic oxide (Nb_{2}O_{5}) respectively.
+
+They are both white powders. The oxide of niobium dissolved in a bead of
+microcosmic salt gives a bluish colour in the reducing flame. The oxide
+of tantalum dissolves in the bead, but gives no colour.
+
+FOOTNOTES:
+
+[76] This will give almost the whole of the tin; a further portion will
+be got in subsequent work, and must be added to this result.
+
+[77] Published by P. Holland, in the _Chemical News_, vol. lix. p. 27.
+
+
+
+
+CHAPTER XIII.
+
+MANGANESE, CHROMIUM, &c.
+
+
+MANGANESE.
+
+Manganese occurs mainly as black oxide (MnO_{2}) in the mineral
+pyrolusite; and, in a less pure form, in psilomelane and wad. The value
+of the ore depends rather on the percentage of available oxygen than on
+the proportion of metal present. The results of assays are generally
+reported as so much per cent. of the dioxide (MnO_{2}). In smaller
+quantities it is very widely distributed. Manganese itself has a value
+for steel-making; or, rather, for the making of spiegeleisen and
+ferro-manganese, which are used in the Bessemer and Siemens processes.
+For this purpose the percentage of the metal (Mn) is required.
+Consequently the minerals of manganese may be considered in two
+aspects--(1) as a source of oxygen; and (2) as a source of manganese.
+These will require separate consideration.
+
+The black oxide is mainly used in the preparation of chlorine,
+liberation of which it brings about when treated with hot hydrochloric
+acid, or with a mixture of common salt and sulphuric acid. The quantity
+of chlorine which is obtained depends upon the proportion of dioxide
+present;[78] and in assaying may either be measured by its equivalent of
+iodine liberated, or by the oxidising effect on an acid solution of
+ferrous sulphate. When the ore also carries substances which have a
+reducing effect (such as ferrous compounds), such assays will give, not
+the total dioxide (MnO_{2}), but less, by the amount required to oxidise
+these impurities; and this is exactly what is required in valuing such
+an ore for commercial purposes. Manganese compounds are characterised by
+the readiness with which they may be converted into highly-oxidised
+bodies. Solution of manganese in hydrochloric acid, rendered alkaline
+with ammonia, yields a clear solution,[79] which rapidly takes up oxygen
+from the air, forming a brown precipitate of the oxide (Mn_{2}O_{3}).
+The addition of bromine or chlorine to such a solution determines the
+precipitation of a still higher oxide (approximately MnO_{2}). On
+treating a compound containing manganese with nitric acid and dioxide of
+lead (PbO_{2}), the oxidation is carried still further, a
+purple-coloured solution of permanganic acid (HMnO_{4} or
+H_{2}O.Mn_{2}O_{7}) being formed. On fusing minerals containing (even
+traces of) manganese with sodium carbonate in an open crucible, a green
+"melt" is obtained which owes its colour to sodium manganate
+(Na_{2}MnO_{4} or Na_{2}O.MnO_{3}). This salt is soluble in water,
+forming a green solution; which, when rendered acid, rapidly changes
+into the permanganate with the characteristic purple colour.
+Permanganate of potash is a salt much used in assaying, with some
+properties of which the student will have already become familiar.
+
+Compounds of manganese, on boiling with strong hydrochloric acid, yield
+manganous chloride[80] (MnCl_{2}).
+
+The properties given above serve for the detection of manganese; the
+higher oxides are distinguished by causing the evolution of chlorine
+(with its peculiarly suffocating smell) when acted on with hydrochloric
+acid; while the green "melt," with sodium carbonate, can be relied on
+for the recognition of manganese itself. There is no dry assay of
+manganese ores.
+
+
+WET METHODS.
+
+Strong hydrochloric acid is the best solvent for ores of manganese; but
+where the proportion of dioxide (MnO_{2}) is required, the solution is
+effected during the assay. The ore should be in a very fine state of
+division before treatment with acids.
+
+The separation of manganese from other metals is thus effected: Ignite,
+in order to destroy any organic matter which may be present; dissolve in
+hydrochloric acid, and evaporate to dryness, to separate silica. Take up
+with hydrochloric acid, dilute, pass sulphuretted hydrogen, and filter.
+Boil off the excess of gas, peroxidise the iron with a drop or two of
+nitric acid, and separate the iron as basic acetate (as described under
+_Iron_).[81] If the iron precipitate is bulky, it is dissolved in a
+little hydrochloric acid, reprecipitated, and the filtrate added to the
+original one. Neutralise with soda, and add bromine in excess; heat
+gradually to boiling, allow to settle, and filter. The precipitate is
+impure dioxide of manganese (containing alkalies and, possibly, cobalt
+or nickel).
+
+
+GRAVIMETRIC DETERMINATION.
+
+Dissolve the precipitate in hydrochloric acid, and boil; add a slight
+excess of carbonate of soda, warm, and filter. Wash with hot water, dry,
+carefully ignite in an open Berlin crucible, and weigh. The substance is
+the brown oxide (Mn_{3}O_{4}), and contains 72.05 per cent. of
+manganese. If the percentage of dioxide is required it may be calculated
+by multiplying the percentage of manganese by 1.582. It must be borne in
+mind that the manganese should never be calculated to dioxide except
+when it is known to exist in the ore only in that form.
+
+
+VOLUMETRIC METHODS.
+
+The two methods are based on the oxidising effect of manganese dioxide;
+and if the metal does not already exist in this form it will require a
+preliminary treatment to convert it. The following method due to Mr. J.
+Pattinson[82] effects this: A quantity of the ore containing not more
+than .25 grams of the metal (Mn), is dissolved in hydrochloric acid in a
+pint beaker, and, if necessary, 3 or 4 c.c. of nitric acid are added to
+peroxidise the iron, and ferric chloride is added if required, so that
+there may be at least as much iron as manganese. Calcium carbonate is
+added till the solution is slightly red; and next the redness is removed
+by the cautious addition of acid; 30 c.c. of zinc chloride solution
+(containing 15 grams of zinc per litre) are added, the liquid is brought
+to boil and diluted to about 300 c.c. with boiling water; 60 c.c. of a
+solution of bleaching powder (33 grams to the litre and filtered),
+rendered slightly greenish by acid, are then run in and are followed by
+3 grams of calcium carbonate suspended in 15 c.c. of boiling water.
+During effervescence the beaker is covered, the precipitate is stirred,
+and 2 c.c. of methylated spirit are mixed in. The precipitate is
+collected on a large filter, washed with cold water, and then with hot,
+till free from chlorine, which is tested for with starch and potassium
+iodide. The acid ferrous sulphate solution (presently described) is then
+measured into the beaker, and the precipitate, still in the paper,
+added; more acid is added (if necessary), and the solution is diluted
+and titrated. In place of bleaching powder solution, 90 c.c. of bromine
+water (containing 22 grams per litre) may be used.
+
+
+FERROUS SULPHATE ASSAY.
+
+This method, which is the one commonly used, is based on the
+determination of the amount of ferrous iron oxidised by a known weight
+of the ore. It is known that 87 parts of the dioxide will oxidise 112
+parts of ferrous iron;[83] therefore 1 gram will oxidise 1.287 gram of
+ferrous iron, or 1 gram of ferrous iron oxidised will be equivalent to
+0.7768 gram of the dioxide. The finely-divided substance containing the
+dioxide is digested in a solution of a known quantity of iron in
+sulphuric acid. The iron, of course, must be in excess, which excess is
+determined when the ore is dissolved by titrating with standard
+permanganate or bichromate of potash solution. The assay resolves itself
+into one for the determination of ferrous iron, for which the standard
+solutions and method of working described under _Iron_ are used.
+
+The assay is as follows:--For rich ores, 2 grams of clean soft iron wire
+are treated, in a pint flask, with 100 c.c. of dilute sulphuric acid and
+warmed till dissolved. Carefully sample the ore, and in one portion
+determine the "moisture at 100° C.;" grind the rest in a Wedgwood mortar
+with a little pure alcohol until free from grit. This reduces the
+substance to a finely-divided state and assists solution. Evaporate off
+the alcohol and dry at 100° C., mix well, and keep in a weighing-bottle.
+Weigh up 2 grams and add them to the solution of iron in the flask;
+carefully wash it all down into the acid liquid. On rotating the flask
+the ore will rapidly dissolve, but gentle heat may be used towards the
+end to complete the solution. When the residue is clean and
+sandy-looking, and free from black particles, the flask is cooled, and
+the residual ferrous iron is determined by titration with
+"permanganate." The iron thus found, deducted from the 2 grams taken,
+will give the amount of iron peroxidised by the dioxide contained in the
+2 grams of ore. This divided by 2 and multiplied by 77.68 will give the
+percentage of dioxide in the sample, or multiplied by 49.41 will give
+that of metallic manganese.
+
+When the quantity of manganese or of the dioxide to be determined is
+small, it is not necessary to use 2 grams of iron; 1 gram, or even less,
+may be taken. The iron may be used in the form of a standard solution of
+ferrous sulphate and portions measured off, thus saving the labour of
+weighing.
+
+~Determination of Dioxide in a Manganese Ore.~--Weigh up 1 or 2 grams of
+the finely-powdered ore[84] and an equal weight of pure iron wire,
+dissolve the wire in 50 or 100 c.c. of dilute sulphuric acid, and, when
+solution is complete, add the ore and warm till it too is dissolved.
+Cool and titrate the remaining ferrous iron with the permanganate or
+bichromate of potassium solution.
+
+For example, 0.7560 gram of pyrolusite and 1.000 gram of iron were taken
+and treated as above; 13.9 c.c. of "permanganate" (standard 100 c.c. =
+0.4920 gram iron) were required; this indicates that 0.0684 gram of iron
+was left unoxidised by the ore. The iron oxidised, then, was 0.9316 gram
+(1.000 - 0.0684); multiplying this by 0.7768, we find that 0.7237 gram
+is the quantity of manganese dioxide which was present. This is
+equivalent to 95.77 per cent.;
+
+        0.7560 : 0.7237 :: 100 : 95.77.
+
+
+IODINE METHOD.
+
+It has been already stated that when dioxide of manganese is boiled with
+strong hydrochloric acid chlorine is given off, and that the amount of
+chlorine so liberated is a measure of the dioxide present. If the
+chlorine is passed into a solution of potassium iodide, an equivalent of
+iodine will be set free.[85] This is apparently a very indirect way of
+determining how much of the dioxide is present; but the reactions are
+very sharp, and the final determination of the iodine is an easy one.
+
+[Illustration: FIG. 60.]
+
+The finely-powdered sample of dioxide is placed in a small flask
+provided with an exit tube leading into a solution of potassic iodide
+(fig. 60). On adding hydrochloric acid and boiling, the chlorine evolved
+is driven into the iodide solution and there absorbed; the boiling is
+continued till the steam and hydrochloric acid fumes have driven the
+last portions of the chlorine out of the flask and into the solution. In
+this experiment there is a strong tendency for the iodide solution to
+rush back into the flask. This tendency is overcome by avoiding draughts
+and regulating the heat; or by placing a lump of magnesite in the flask,
+which acts by evolving carbonic acid and so producing a steady outward
+pressure. When the distillation is finished the tube containing the
+iodine is detached and washed out into a beaker. If the solution is
+strongly acid it should be almost neutralised by the cautious addition
+of dilute ammonia. If crystals of iodine have separated, potassium
+iodide must be added in quantity sufficient to dissolve them. The
+condenser must be kept cool whilst the chlorine is passing into it.
+
+The solution, transferred to a beaker, is titrated with a standard
+solution of sodic hyposulphite (100 c.c. = 1.27 gram iodine or 0.435
+gram of dioxide of manganese). In titrating, the solution should be
+cold, or not warmer than 30° C. The bulk may vary from 100 to 200 c.c.;
+but it is best always to work with the same volume. The "hypo" is run in
+with constant agitation until the brown colour has been reduced to a
+light yellow; 5 c.c. of starch solution are then added and the titration
+cautiously continued until the end is reached; the finish is indicated
+by a change from blue to colourless.
+
+The assay solution may be acidified with acetic, sulphuric, or
+hydrochloric acid before titrating with "hypo;" but it must be only
+faintly so. An excess of acid may be nearly neutralised with ammonia
+without interference, but excess of alkali is fatal. Bicarbonate of soda
+must not be used in excess; it is best to avoid it altogether. The assay
+solution should be titrated at once, as it weakens on standing; and the
+"hypo" solution should be standardised every two or three days, as its
+strength is not constant.
+
+_The standard solution of hyposulphite of soda_ is made by dissolving 25
+grams of the salt (Na_{2}S_{2}O_{3}.5H_{2}O) in water and diluting to 1
+litre. 100 c.c. are equivalent to 1.27 gram of iodine.
+
+This solution is standardised by weighing, in a small beaker, about half
+a gram of iodine, to which is added a crystal or two of potassium iodide
+and a few drops of water. When dissolved, the solution is diluted to 100
+c.c., and titrated in the manner described. The starch solution is made
+in the manner described under the iodide copper assay. 5 c.c. are used
+for each titration.
+
+In determining the effects of variations in the condition of the assay a
+solution of iodine was used, which was equivalent in strength to the
+"hypo" solution. It was made by dissolving 12.7 grams of iodine with 25
+grams of potassium iodide in a little water and diluting to 1 litre. 100
+c.c. of this solution were found (at the time of the experiments) to be
+equivalent to 102.0 c.c. of the "hypo."
+
+~Effect of Varying Temperature.~--The bulk of the solution was 100 c.c.;
+20 c.c. of iodine were taken, and 5 c.c. of starch solution were added
+towards the end as indicator. These conditions are also those of the
+other experiments, except where otherwise stated. Iodine being volatile,
+it is to be expected that with hot solutions low results will be
+obtained.
+
+  Temperature        15°        20°        40°        60°        80°
+  "Hypo" required  20.4 c.c.  20.4 c.c.  20.1 c.c.  19.2 c.c.  15.5 c.c.
+
+These show that the temperature should not much exceed 20°.
+
+~Effect of Exposure of the Iodine Solution.~--Twenty c.c. of the iodine
+were diluted to 100 c.c., and exposed for varying lengths of time in
+open beakers at the ordinary temperature, and then titrated.
+
+  Time exposed       --         1 day      2 days    3 days
+  "Hypo" required  20.4 c.c.  16.1 c.c.  13.6 c.c.  9.4 c.c.
+
+~Effect of Varying Bulk.~--These experiments were carried out in the
+usual way, bulk only varying.
+
+  Bulk             100.0 c.c.  200.0 c.c.  300.0 c.c.  500.0 c.c.
+  "Hypo" required   20.4  "     20.4  "     20.4  "     20.4  "
+
+~Effect of Varying Acid.~--These experiments were under the usual
+conditions, the bulk being 100 c.c. The results were--
+
+  Acetic acid          --        1.5 c.c.  30.0 c.c.
+  "Hypo" required    20.4 c.c.  20.7  "    20.7  "
+
+  Hydrochloric acid    --        1.5 c.c.  15.0 c.c.
+  "Hypo" required    20.4 c.c.  20.6  "    20.9  "
+
+  Sulphuric acid       --        0.5 c.c.  20.0 c.c.
+  "Hypo" required    20.4 c.c.  20.7  "    15.2  "[86]
+
+  Nitric acid          --        0.5 c.c.  10.0 c.c.
+  "Hypo" required    20.4 c.c.  21.5  "    could not be titrated.
+
+In the application of this titration to the assay of manganese ores,
+hydrochloric and hydriodic acids are the only ones likely to be present.
+
+~Effect of Alkalies.~--On theoretical grounds the presence of these is
+known to be inadmissible. A solution rendered faintly alkaline with
+ammonia required only 11.2 c.c. of "hypo;" and another, with 0.5 gram of
+caustic soda, required 4.0 c.c. instead of 20.4 c.c. as in neutral
+solutions.
+
+~Effect of nearly Neutralising Hydrochloric Acid Solutions with
+Ammonia.~--Provided care is taken not to add excess of ammonia, this
+has a good effect, counteracting the interference of excess of acid.
+Thus 20 c.c. of iodine (as before) required 20.4 c.c. of "hypo;" with 15
+c.c. of hydrochloric acid 20.7 c.c. were required, but with 15 c.c. of
+acid, nearly neutralised with dilute ammonia 20.4 c.c. were used.
+
+~Effect of the Addition of Starch.~--The addition of varying quantities
+of starch has no effect, provided it is added when the titration is
+nearly finished, as the following experiments show:--
+
+  Starch added       1.0 c.c.   5.0 c.c.  10.0 c.c.  50.0 c.c.
+  "Hypo" required   20.4  "    20.4  "    20.4  "    20.5  "
+
+But if the starch is added before the titration, the results are liable
+to error.
+
+  Starch added       1.0 c.c.  50.0 c.c.
+  "Hypo" required   20.4  "    24.0  "
+
+The starch should be used fresh, and is best made on the day it is used;
+after four days the finishing point is not so good.
+
+~Effect of Varying Potassium Iodide.~--An excess of iodide is always
+required to keep the iodine in solution; a larger excess has little
+effect.
+
+  Iodide added       --        1 gram    20 grams
+  "Hypo" required  20.4 c.c.  20.5 c.c.  20.6 c.c.
+
+The 20 c.c. of iodine used, itself contained 0.5 gram of potassium
+iodide.
+
+~Effect of Foreign Salts.~--
+
+  Bicarbonate of soda
+    added                --        0.5 gram    1.5 gram    5.0 grams
+  "Hypo" required      20.4 c.c.  18.2 c.c.   17.1 c.c.   16.0 c.c.
+
+The solution obviously must be free from bicarbonate of soda. This
+should be remembered, since when titrating arsenic assays with iodine it
+must be present; and students must avoid confounding the two titrations.
+
+In some other experiments, in which 10 grams each of the salts were
+taken, the following results were obtained:--
+
+  Salt added          --         AmCl      AmNO_{3}    Am_{2}SO_{4}
+  "Hypo" required   20.4 c.c.  20.5 c.c.   20.3 c.c.     20.2 c.c.
+
+  Salt added         NaCl       NaNO_{3}   Na_{2}SO_{4}
+  "Hypo" required   20.3 c.c.  20.4 c.c.   20.4 c.c.
+
+~Effect of Varying Iodine.~--
+
+  Iodine added     1.0 c.c.  10.0 c.c.  20.0 c.c.  50.0 c.c.   100.0 c.c.
+  "Hypo" required  1.3  "    10.2  "    20.4  "    51.0  "     102.0  "
+
+~Determination of Dioxide in a Manganese Ore.~--Weigh up 0.25 to 0.3
+gram of the powdered ore; place in a flask, cover with 10 c.c. of
+hydrochloric acid, and close the flask with a paraffined cork, and bulbs
+(as shown in fig. 60), having previously charged the bulb with 5 grams
+of potassium iodide in strong solution. Heat the flask, and boil
+cautiously for about fifteen minutes. Wash the contents of the bulbs
+into a large beaker, nearly (but not quite) neutralise with dilute
+ammonia, and titrate with the standard "hypo."
+
+As an example, 0.2675 gram of pyrolusite was taken, and required 60.3
+c.c. of standard "hypo" (100 c.c. equal 1.185 gram iodine, or 0.4042
+gram MnO_{2}), which equals 0.2437 gram of the dioxide or 91.1 per cent.
+
+
+COLORIMETRIC METHOD.
+
+When compounds of manganese free from chlorides are boiled with nitric
+acid and dioxide of lead,[87] the manganese is converted into
+permanganic acid, which is soluble and tints the solution violet. The
+depth of colour depends on the amount of manganese present, and this
+should not much exceed 10 milligrams. A quantity of substance containing
+not more than this amount of manganese should be boiled for a few
+minutes with 25 c.c. of a solution containing 5 c.c. of nitric acid, and
+10 or 20 c.c. of dilute sulphuric acid, with 2 or 3 grams of lead
+dioxide. Filter through asbestos, wash by decantation with dilute
+sulphuric acid, make up with distilled water[88] to a definite bulk, and
+take a measured portion for the colorimetric determination.
+
+The standard solution of manganese is made by dissolving 0.1435 gram of
+permanganate of potash (KMnO_{4}) in a little water acidulated with
+nitric acid, and diluting to 1 litre. One c.c. will contain 0.05
+milligram of manganese.
+
+
+PRACTICAL EXERCISES.
+
+1. What percentage of manganese (Mn) is contained in permanganate of
+potash (KMnO_{4})?
+
+2. Ten c.c. of a solution of permanganate of potash is found to oxidise
+10 c.c. of an acid solution of ferrous sulphate. The manganese is
+determined in the titrated solution by precipitation as dioxide and
+titrating. How much of the ferrous solution will be oxidised in the
+second titration?
+
+3. What weight of potassium iodide would be just sufficient to absorb
+the chlorine evolved by 0.5 gram of pure dioxide of manganese?
+
+4. What weight of iron must be dissolved up so as to have an excess of
+0.25 gram after oxidation by 1 gram of pure dioxide?
+
+5. What weight of the brown oxide, Mn_{2}O_{4} will be left on igniting
+1 gram of the pure dioxide?
+
+
+CHROMIUM.
+
+Chromium occurs in nature chiefly as chromite or chrome iron ore
+(FeO_{2}Cr_{2}O_{3}, with more or less MgO and Al_{2}O_{3}), which is
+the chief ore. It is a constituent of some silicates, and is frequently
+met with in very small quantities in iron ores. It occurs as chromate in
+crocoisite (PbCrO_{4}), and some other rare minerals.
+
+The metal is used in steel-making. Steel containing about 0.5 per cent.
+of it is rendered very hard; but its chief value is in its salts, the
+chromates. These are highly-coloured compounds, generally red or yellow.
+Some of the insoluble chromates are used as pigments; chromate of lead
+or chrome-yellow is the most important. The soluble chromates, those of
+soda and potash, are valuable chemicals, and are largely used in the
+preparation of pigments, dyeing and tanning, and as oxidising agents.
+
+Chromium forms two important classes of compounds--chromic salts,
+corresponding to the oxide Cr_{2}O_{3}, and chromates, which contain the
+trioxide CrO_{3}. Solutions of chromic salts are green, whilst those of
+the chromates are yellow. Chromates are reduced to chromic salts by the
+action of most reducing agents in the presence of an acid; and this
+property is used in assaying for the volumetric determination of ferrous
+iron, &c. The chromates in solution are more stable than other similar
+oxidising agents, and consequently are generally used in the laboratory
+as one of the standard oxidising agents for volumetric analysis. They
+have the disadvantage of requiring an outside indicator. Bichromate of
+potash (K_{2}Cr_{2}O_{7}) is the salt generally used for this purpose.
+
+Chromic salts are oxidised to chromate by fusion with "fusion mixture"
+and nitre, or by treating with chlorine in an alkaline solution.
+
+Chromic salts closely resemble those of ferric iron, and in the ordinary
+course of analysis chromic hydrate (green) is precipitated together with
+ferric hydrate, alumina, &c., on the addition of ammonic chloride and
+ammonia. The ignited oxide, Cr_{2}O_{3}, however, is not reduced on
+heating to redness in a current of hydrogen.
+
+~Detection.~--Chromium is detected by fusing the powdered substance with
+"fusion mixture" and nitre. The melt is extracted with water and
+filtered. The filtrate is acidified with acetic acid, and treated with a
+few drops of a solution of lead acetate. A yellow precipitate indicates
+chromium. Substances containing chromium impart a green colour to the
+borax bead in both flames. Small quantities of chromate in neutral
+solution can be found by the dark or violet-red colouration imparted
+thereto on boiling with a dilute decoction of logwood.
+
+~Solution and Separation.~--Chromates and chromic salts are generally
+soluble in water or dilute acids. Chrome iron ore, however, and ignited
+chromic oxide are insoluble; and the former presents considerable
+difficulty on attempting to open up by the usual methods. A large number
+of mixtures have been tried in order to get all the chromium in a
+soluble form. Among these are the following. One part of the very
+finely-powdered ore is fused with any of these mixtures.
+
+  (1) 10 parts of bisulphate of potash.
+  (2)  5 parts of bisulphate of potash and 5 parts of potassium fluoride.
+  (3)  5 parts of hydric potassic fluoride.
+  (4) 12 parts of bisulphate of potash; and, afterwards, with 6 parts of
+       carbonate of soda and 6 parts of nitre.
+  (5)  8 parts of borax; afterwards, with carbonate of soda till it ceases
+       to effervesce; then, with 3 parts of carbonate of soda and 3 of
+       nitre.
+  (6)  4 parts of borax and 6 parts of fusion mixture.
+  (7) 12 parts of caustic potash.
+  (8) 10 parts of caustic soda and 30 of magnesia.
+  (9)  5 parts of caustic soda and 3 of magnesia.
+  (10) 2 parts of carbonate of soda and 1 of lime.
+  (11) 6 parts of soda-lime and 2 of chlorate of potash.
+  (12)   Sodium peroxide.
+
+Of these, numbers 1, 2, and 3 yield the chromium in a form soluble in
+dilute acids, as chromic salt. The rest in a form soluble in water, as
+potassium or sodium chromate.
+
+On boiling an insoluble chromium compound with chlorate of potash and
+nitric acid, the chromium passes into solution as chromate. This method,
+however, does not answer for chrome iron ore. In the fusion methods the
+ore must be very finely powdered, well mixed with the fluxes, and
+subjected to a prolonged fusion in a platinum vessel at a high
+temperature. Undecomposed particles require re-fusion.
+
+The aqueous extract containing the chromate is ready for volumetric
+work, except in those cases where nitre has been used. For gravimetric
+work the solution is acidified with hydrochloric acid, then mixed with
+ammonia in slight excess, boiled, and filtered. The filtrate is
+acidified with hydrochloric acid, and treated with sulphuretted
+hydrogen, warmed, rendered slightly alkaline with ammonia, and the gas
+again passed. The chromium is precipitated as chromic hydrate mixed with
+sulphur from the reduction with sulphuretted hydrogen. It is filtered
+off, washed with hot water, and ignited. It is weighed as chromic oxide.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution containing the chromium, freed from other metals and earths
+and in the form of (green) chromic salt, is heated to boiling. If any
+chromate is present reduce it with sodium sulphite or sulphuretted
+hydrogen. Add ammonia in slight excess, boil till the liquid is free
+from a red tint, and allow to settle for a few minutes. Filter, wash
+with hot water, dry, and ignite strongly in a loosely-covered crucible.
+Cool, and weigh. The substance is chromic oxide, Cr_{2}O_{3}, and
+contains 68.62 per cent. of chromium. It is a dark-green powder
+insoluble in acids.
+
+When, as is generally the case, the chromium exists altogether as
+chromate (phosphates and arsenates being absent) it is best to proceed
+as follows:--Render the solution acid with acetic acid, then add sodium
+acetate to the solution and heat nearly to boiling; next treat with a
+slight excess of acetate of lead, and boil. Allow to settle, and filter.
+Wash the precipitate with hot water, dry in the water-oven or at a low
+temperature. Transfer the precipitate to a weighed Berlin crucible, burn
+the filter separately, ignite below redness, cool in the desiccator, and
+weigh. The substance is lead chromate, PbCrO_{4}, and contains 16.1 per
+cent. of chromium, or 23.53 per cent. of chromic oxide (Cr_{2}O_{3}).
+
+
+VOLUMETRIC METHOD.
+
+This is based on the oxidation of ferrous iron by the solution
+containing the chromium as chromate. A known weight of iron (0.5, 1, or
+1.5 gram, according to the quantity of chromate) is dissolved in 50 c.c.
+of dilute sulphuric acid. The solution containing the chromate is added,
+and the remaining ferrous iron titrated with the permanganate or
+bichromate of potassium solution, as described under _Iron_. The iron
+thus found is deducted from that taken, and the difference gives the
+iron oxidised by the chromate. This multiplied by 0.3101 gives the
+chromium, Cr, and when multiplied by 0.4529 gives the chromic oxide,
+Cr_{2}O_{3}.
+
+
+COLORIMETRIC METHOD.
+
+Small quantities of chromium may be determined, after conversion into
+chromate, colorimetrically. The solution, which should not contain more
+than a few milligrams in 100 c.c., is acidified with acetic acid and
+compared against an equal volume of water rendered acid with acetic
+acid and tinted with a standard bichromate of potassium solution. This
+standard bichromate is made by dissolving 2.827 grams of the salt in
+water and diluting to 1 litre. One c.c. will contain 1 milligram of
+chromium, Cr. The manner of working this assay is the same as that
+adopted in the other colorimetric processes.
+
+~Determination of Chromium in Steel.~[89]--Weigh up 2.4 grams, dissolve
+in hydrochloric acid, and evaporate to dryness. Fuse with sodium
+carbonate and nitre, extract with water, and make up to 301 c.c. Take
+250 c.c. of the clear liquor, boil with hydrochloric acid, add sodium
+phosphate, and then ammonia in slight excess. Heat till clear. Filter
+off the precipitate, dissolve it in hydrochloric acid, and evaporate to
+dryness. Take up with a little acid, filter, and precipitate with a
+slight excess of ammonia. Wash, ignite, and weigh as chromium phosphate
+(3Cr_{2}O_{3},2P_{2}O_{5}), which contains 42.2 per cent. of chromium.
+
+
+VANADIUM.
+
+Vanadium occurs in certain rare minerals, such as vanadinite
+(3Pb_{3}(VO_{4})_{2}.PbCl_{2}), a vanadate of lead; mottramite, a
+vanadate of copper and lead; and dechenite, a vanadate of lead and zinc.
+It is occasionally found in iron and copper ores and in the slags from
+them. In Spanish copper-precipitates it is found along with chromium,
+and is probably derived from the iron used for precipitating. The
+vanadates, like the chromates, are coloured compounds, generally yellow
+or red. On reduction, blue solutions are got. In their general reactions
+vanadates resemble phosphates.
+
+Vanadium is detected by the red colouration produced by passing
+sulphuretted hydrogen into ammoniacal solutions for some time. On adding
+an acid to the filtered solution a brown precipitate of the sulphide is
+produced. This gives with borax a colourless bead in the oxidising, and
+a green one in the reducing, flame.
+
+It is separated by fusing the ore with potassic nitrate, extracting with
+water and precipitating with baric chloride. The precipitate is boiled
+with dilute sulphuric acid, filtered, neutralised with ammonia, and
+saturated with ammonic chloride. Ammonium vanadate separates out. It is
+filtered off, ignited, and weighed as vanadic oxide, V_{2}O_{5},
+containing 56.18 per cent. of vanadium.
+
+
+MOLYBDENUM.
+
+Molybdenum occurs in nature chiefly as molybdenite (MoS_{2}); it also
+occurs in wulfenite, a molybdate of lead (PbMoO_{4}), and in molybdic
+ochre (MoO_{3}).
+
+Molybdate of ammonia is an important reagent in the determination of
+phosphates, the manufacture of which compound is the chief purpose to
+which molybdenum is applied.
+
+Iron and copper ores frequently contain molybdenum, sometimes in
+quantity; consequently it is met with in slags and pig-iron.
+
+Molybdenum forms several series of salts. In those corresponding to the
+lower oxides it is basic; but the trioxide (MoO_{3}) is the acid oxide
+which forms a series of salts called the molybdates. All molybdenum
+compounds are converted into the trioxide by boiling with nitric acid.
+The trioxide is a white powder readily dissolved by ammonia. It fuses at
+a red heat, and volatilises freely in contact with air. It is slightly
+soluble in water.
+
+Molybdates are easily reduced, with the production of coloured
+solutions, by most reducing agents. Sulphuretted hydrogen first produces
+a blue tint, and then precipitates a brown sulphide. The precipitation
+as sulphide is only complete on prolonged treatment; a green colour
+indicates that some molybdenum still remains in solution. The
+precipitated sulphide is soluble in ammonium sulphide.
+
+~Detection.~--Molybdenum is detected by its behaviour with sulphuretted
+hydrogen. Molybdenite can only be mistaken for graphite, from which it
+is easily distinguished by yielding sulphur dioxide on roasting, and by
+giving, on charcoal, a yellowish white incrustation, which becomes blue
+on touching it for a moment with the reducing flame. The borax-bead is
+colourless in the oxidising, and dark-brown in the reducing, flame.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution containing the molybdate is neutralised and treated with an
+excess of mercurous nitrate. The precipitate is allowed to settle for
+some time, filtered, and washed with a dilute solution of mercurous
+nitrate. Then it is dried, transferred to a weighed Berlin crucible
+containing ignited oxide of lead, mixed, ignited, and weighed. The
+increase in weight gives the amount of trioxide, MoO_{3}. This contains
+66.7 per cent. of molybdenum.
+
+
+URANIUM.
+
+Uranium occurs chiefly as pitchblende, which is an impure oxide
+(U_{3}O_{8}). It is also found as sulphate in uranochre, johannite, &c.;
+and as phosphate in the uranites, torbernite (hydrated phosphate of
+uranium and copper), and autunite (hydrated phosphate of uranium and
+lime). It also occurs in some rarer minerals.
+
+The oxide is used for colouring glass; and the nitrate and acetate are
+used as reagents. "Uranium yellow," used for enamel painting, is sodium
+uranate. The uranates, in which the oxide of uranium acts as an acid,
+are mostly insoluble and of secondary importance.
+
+Uranium forms two families of salts, uranous and uranic; corresponding
+to the oxides UO_{2} and UO_{3} respectively. The former are generally
+green and the latter yellow. Uranous salts are converted into uranic by
+boiling with nitric acid or other oxidising agents. Uranic salts, on the
+other hand, are easily reduced by sulphuretted hydrogen, stannous
+chloride or zinc. This property is made use of in determining the
+quantity of uranium in pure solutions by titrating with permanganate of
+potassium solution as in the case with iron.
+
+~Detection.~--The most characteristic reaction of the uranium compounds
+is their behaviour in the presence of alkaline carbonates in which they
+are freely soluble; even ammonium sulphide will not precipitate uranium
+from these solutions. On neutralising the carbonate with an acid a
+uranate of the alkali is precipitated. Ammonia or sodic hydrate (free
+from carbonates) give yellow precipitates, which are insoluble in excess
+of the reagent, but are soluble in acids. Ferrocyanide of potassium
+gives a reddish-brown precipitate. Uranium colours the borax-bead
+yellowish-green in the oxidising, and green in the reducing, flame.
+
+~Solution and Separation.~--The compounds of uranium are soluble in
+acids. Powder the substance and evaporate with an excess of nitric acid.
+Take up with hydrochloric acid, dilute, pass sulphuretted hydrogen, and
+filter. Peroxidise the filtrate with a little nitric acid, add an excess
+of ammonic carbonate and some ammonium sulphide, and filter. Render the
+solution acid, boil; and precipitate the uranium by means of ammonia.
+Filter off, and wash it with dilute ammonic chloride. Ignite, and weigh
+as protosesqui-oxide, U_{3}O_{8}.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution containing the uranium free from other metals is, if
+required, first peroxidised by boiling with nitric acid. Ammonia in
+slight excess is added to the nearly-boiling solution. A yellow
+precipitate is formed, which is filtered off hot and washed with a
+dilute solution of ammonium chloride. The precipitate is dried and
+ignited; and weighed as U_{3}O_{8}, which contains 84.8 per cent. of
+uranium.
+
+
+VOLUMETRIC METHOD.
+
+This is based on the precipitation of uranium as phosphate from acetic
+acid solutions and the recognition of complete precipitation by testing
+with potassic ferrocyanide; it is the converse of the process for the
+volumetric determination of phosphate.
+
+_The standard solution of phosphate_ is prepared by dissolving 29.835
+grams of hydric sodic phosphate (Na_{2}HPO_{4}.12H_{2}O) in water and
+diluting to 1 litre. 100 c.c. will be equivalent to 2 grams of uranium.
+
+Take 1 gram of the sample (or, if poor in uranium, 2 grams) and separate
+the uranium as described. Dissolve the precipitate in nitric acid and
+evaporate to a small bulk, add 2 grams of sodium acetate, dilute with
+water to 100 c.c., and boil. Titrate the boiling solution with the
+sodium phosphate till it ceases to give a brown colouration with
+potassium ferrocyanide. Calculate the percentage in the usual way.
+
+FOOTNOTES:
+
+[78] MnO_{2} + 4HCl = MnCl_{2} + Cl_{2} + 2H_{2}O.
+
+[79] Provided a sufficiency of ammonic chloride is present.
+
+[80] With some silicates, &c., a preliminary fusion with sodium
+carbonate will be necessary.
+
+[81] Instead of sodium acetate, ammonium succinate can be used.
+
+[82] _Journ. Soc. Chem. Industry_, vol. x. p. 333.
+
+[83] MnO_{2} + 2FeSO_{4} + 2H_{2}SO_{4} = Fe_{2}(SO_{4})_{3} + MnSO_{4}
++ 2H_{2}O.
+
+[84] If the ore is very rich, a smaller quantity (0.75 or 1.5 gram) must
+be taken; otherwise the iron will be insufficient.
+
+[85] MnO_{2} + 4HCl = MnCl_{2} + 2H_{2}O + Cl_{2}.
+      Cl_{2} + 2KI  = 2KCl + I_{2}.
+
+[86] Iodine probably lost by volatilisation.
+
+[87] Obtained as a brown powder by digesting red lead with nitric acid
+and filtering.
+
+[88] The water for dilution and the dilute sulphuric acid used for
+washing should be previously tested, to see they have no reducing
+action, with dilute permanganate of potassium solution.
+
+[89] Arnold and Hardy, _Chemical News_, vol. lvii. p. 153.
+
+
+
+
+CHAPTER XIV.
+
+EARTHS, ALKALINE EARTHS, ALKALIES.
+
+
+ALUMINA.
+
+Alumina, the oxide of aluminium (Al_{2}O_{3}), is found in nature fairly
+pure in the mineral corundum; transparent and coloured varieties of
+which form the gems sapphire and ruby. A coarser compact variety
+contaminated with oxide of iron constitutes emery. Compounded with
+silica, alumina forms the base of clays and many rock-forming minerals.
+China clay (or kaolin) is used as a source of alumina. Bauxite, hydrated
+alumina, is also used for the same purpose--that is, for the preparation
+of sulphate of alumina. The mineral cryolite is a fluoride of aluminium
+and sodium.
+
+Corundum is characterised by a high specific gravity (4.0) and extreme
+hardness. By these it is distinguished from felspar and similar
+minerals, which it somewhat resembles in general appearance.
+
+Aluminium is used for a variety of small purposes: it is white, light,
+and very tenacious; but owing to the difficulty of its reduction it is
+expensive.
+
+Aluminium forms one series of salts which closely resemble those of
+ferric iron. It forms an interesting series of double sulphates, known
+as the alums. Common potash alum is
+Al_{2}(SO_{4})_{3},K_{2}SO_{4},24H_{2}O.
+
+~Detection.~--Alumina is not precipitated from its acid solution by
+sulphuretted hydrogen, but it is thrown down by ammonia (with the other
+earths) as a white hydrate, soluble in soda and insoluble in ammonic
+carbonate. Filtered off and ignited, it assumes, after treatment with
+nitrate of cobalt before the blowpipe, a blue colour which is
+characteristic. With natural compounds containing metallic oxides this
+colour is masked. It is more satisfactory to make a separation in the
+wet way and to test the ignited oxide.
+
+~Separation and Solution.~--If the substance is insoluble in
+hydrochloric acid it is finely powdered and fused with "fusion mixture"
+with the help, in the case of corundum (which is very refractory) of a
+little caustic soda or potash. The method of working is the same as
+that described for opening up silicates. See under _Silica_. Corundum
+cannot be powdered in Wedgwood, or even agate, mortars; since it rapidly
+wears these away and becomes contaminated with their powder. It is best
+to use a hard steel mortar and to extract the metallic particles from
+the bruised sample with a magnet or dilute acid.
+
+When the substance has been completely attacked and dissolved, it is
+evaporated to dryness with an excess of hydrochloric acid on the
+water-bath to render any silica present insoluble. The residue is
+extracted with hydrochloric acid and freed from the second group of
+metals by means of sulphuretted hydrogen. The filtrate from this (after
+removing the sulphuretted hydrogen by boiling) is nearly neutralised,
+and treated with 8 or 10 grams of hyposulphite of soda[90] in solution.
+It is then boiled till the sulphurous oxide is driven off. The
+precipitate is filtered off, ignited, and weighed as alumina.
+
+It is sometimes more convenient to proceed as follows:--After boiling
+off the sulphuretted hydrogen peroxidise the iron with a little nitric
+acid, add a solution of ammonic chloride, and then ammonia in very
+slight excess; boil, filter, wash, ignite, and weigh the oxides. These
+generally consist of ferric oxide and alumina. It is a common practice
+to determine the iron, calculate it to ferric oxide, and so to estimate
+the alumina indirectly. This may be done either by igniting in a current
+of hydrogen and estimating the iron by the weight of oxygen lost; or, by
+dissolving with sulphuric and hydrochloric acids, and determining the
+iron volumetrically. It should be borne in mind that these oxides will
+also contain any phosphoric oxide that happened to be in the mineral.
+
+In general analyses of samples containing alumina, it may be contained
+in both the soluble and insoluble portions. In these cases it is better
+to fuse the sample with "fusion mixture" before treatment with acids.
+The alumina in the fused mass will exist in a state soluble in acids.
+
+
+GRAVIMETRIC DETERMINATION.
+
+Solutions containing alumina free from the other metals are diluted to a
+convenient bulk and heated nearly to boiling. Add chloride of ammonium,
+and then ammonia in slight excess; boil, allow to settle, filter, and
+wash with hot water. Dry the precipitate, and ignite in a platinum or
+porcelain crucible at the strongest heat. Cool, and weigh. The substance
+is alumina, Al_{2}O_{3}, which contains 52.94 per cent. of aluminium.
+It is only in special cases, such as the analysis of metals and alloys,
+that it is reported as aluminium. The percentage of alumina is generally
+given.
+
+Ignited alumina is difficultly soluble in acids; it is not reduced by
+hydrogen at a red heat. Ignited with ammonium chloride portions are
+volatilised.
+
+~Direct Determination of Alumina in the Presence of Iron.~--The iron and
+alumina are precipitated as hydrates by ammonia. The precipitate is
+dissolved in hydrochloric acid and the iron reduced to the ferrous
+state. It is then added to a hot solution of potash or soda. The
+solution is boiled till the precipitate settles readily, filtered, and
+washed with hot water. The alumina is contained in the filtrate, which
+is acidified with hydrochloric acid and the alumina precipitated
+therefrom as hydrate with ammonia, as just described.
+
+~Determination of Alumina in the Presence of Phosphates and Iron.~--For
+details, see a paper by R.T. Thomson in the "Journal of the Society of
+Chemical Industry," v. p. 152. The principles of the method are as
+follows:--If the substance does not already contain sufficient
+phosphoric oxide to saturate the alumina, some phosphate is added. The
+iron is reduced to the ferrous state and phosphate of alumina
+precipitated in an acetic acid solution. It is purified by
+reprecipitation, ignited, and weighed as phosphate
+(Al_{2}O_{3},P_{2}O_{5}), which contains 41.8 per cent. of alumina,
+Al_{2}O_{3}.
+
+
+EXAMINATION OF CLAYS.
+
+~Moisture.~--Take 5 grams of the carefully-prepared sample and dry in
+the water-oven till the weight is constant.
+
+~Loss on Ignition.~--Weigh up 2 grams of the sample used for the
+moisture determination, and ignite in a platinum-crucible to redness,
+cool, and weigh.
+
+~Silica and Insoluble Silicates.~--Weigh up another 2 grams of the dried
+sample, and place them in a platinum dish; moisten with water, and cover
+with 20 c.c. of sulphuric acid. Evaporate and heat gently to drive off
+the greater portion of the free acid. Allow to cool; and repeat the
+operation. Extract by boiling with dilute hydrochloric acid, filter,
+wash, dry, ignite, and weigh. The quantity of insoluble silicates is
+determined by dissolving out the separated silica with a strong boiling
+solution of sodium carbonate. The residue (washed, dried, and ignited)
+is weighed, and reported as "sand."
+
+~Alumina and Ferrous Oxide.~--To the filtrate from the silica add "soda"
+solution till nearly neutral, and then sodium acetate. Boil and filter
+off the precipitate. Reserve the filtrate. Dissolve the precipitate in
+hydrochloric acid, and dilute to exactly 200 c.c. Divide into two parts
+of 100 c.c. each. In one determine the iron by reducing and titrating in
+the way described under volumetric iron. Calculate the percentage as
+ferrous oxide, unless there are reasons to the contrary, also calculate
+its weight as ferric oxide. To the other portion add ammonia in slight
+excess, and boil. Filter, wash with hot water, dry, ignite, and weigh as
+mixed alumina and ferric oxide. The weight of the ferric oxide has
+already been determined in the first portion: deduct it, and the
+difference is the weight of alumina.
+
+~Lime.~--To the reserved filtrate, concentrated by evaporation, add
+ammonium oxalate and ammonia; boil, filter, ignite strongly, and weigh
+as lime.
+
+~Magnesia~ is separated from the filtrate by adding sodium phosphate. It
+is weighed as magnesium pyrophosphate.
+
+~Potash and Soda.~--These are determined in a fresh portion of the
+sample by Lawrence Smith's method, as described on page 333.
+
+
+THORIA.
+
+This is an oxide of thorium, ThO_{2}. It is only found in a few rare
+minerals. It is a heavy oxide, having, when strongly ignited, a specific
+gravity of 9.2. In the ordinary course of analysis it will be separated
+and weighed as alumina. It is separated from this and other earths by
+the following method. The solution in hydrochloric acid is nearly
+neutralised and then boiled with sodium hyposulphite. The thoria will be
+in the precipitate. It is dissolved, and the solution heated with
+ammonium oxalate in excess. The precipitate is thorium oxalate, which is
+washed with hot water, dried, and ignited. It is then weighed as thoria,
+ThO_{2}. Thoria which has been ignited is not readily soluble in acids.
+
+
+ZIRCONIA.
+
+The oxide of zirconium, ZrO_{2}, is found in the mineral zircon, a
+silicate of zirconia, ZrSiO_{4}. When heated intensely it becomes very
+luminous, and is used on this account for incandescent lights.
+
+In the ordinary course it is thrown down by ammonia with the other
+earths, from which it is thus separated:--The hydrates precipitated in
+the cold, and washed with cold water, are dissolved in hydrochloric
+acid, nearly neutralised with soda, and precipitated by boiling with
+hyposulphite of soda. Dissolve; and from the hydrochloric acid solution
+precipitate the thoria (if any) with ammonium oxalate. To the filtrate
+add carbonate of ammonia, which will precipitate any titanium present.
+The zirconia will be in solution, and is recovered by precipitating with
+potassium sulphate, or by evaporating the solution and igniting. It is
+separated from alumina by taking advantage of its insolubility in
+potassic hydrate.
+
+It is estimated in zircons in the following way:--The powdered substance
+is fused with bisulphate of potash, and extracted with dilute sulphuric
+acid. The residue is fused with caustic soda and extracted with water.
+The portion not dissolved, consisting of zirconate of soda, is dissolved
+in hydrochloric acid. The solution is diluted, filtered if necessary,
+and treated with ammonia in excess. The precipitate is filtered off,
+washed with hot water, dried, ignited, and weighed as zirconia, ZrO_{2}.
+This is a white powder, which is insoluble in acids; even in
+hydrofluoric acid it is only slightly attacked.
+
+
+CERIUM.
+
+Cerium occurs as silicate (together with the oxides of lanthanum,
+didymium, iron and calcium) in the mineral cerite, which is its chief
+source. It also occurs as phosphate in monazite, and as fluoride in
+fluocerite. The oxalate is used in medicine. Cerium forms two classes of
+salts corresponding to the oxides, cerous oxide (Ce_{2}O_{3}) and ceric
+oxide (CeO_{2}). Compounds of cerium with volatile acids yield dioxide
+on ignition; and this, on solution in hydrochloric acid, yields cerous
+chloride and chlorine.
+
+In the ordinary course cerium is thrown down along with alumina and the
+other earths by ammonia. It is separated by dissolving the hydrates in
+hydrochloric acid, and oxidizing with chlorine water. On treating with
+oxalic acid, cerium, lanthanum, and didymium are precipitated as
+oxalates, which on ignition are converted into oxides. These are soluble
+in acids. Their solution in hydrochloric acid is nearly neutralised;
+acetate of soda is then added, and an excess of sodium hypochlorite. On
+boiling, the cerium is precipitated as dioxide, which is filtered off,
+ignited, and weighed.
+
+Cerium is detected by giving with borax a bead which is yellow in the
+oxidising, and colourless in the reducing flame. Traces of cerium
+compounds boiled with dioxide of lead and nitric acid will give a yellow
+solution.
+
+
+LANTHANUM AND DIDYMIUM
+
+occur together with cerium in cerite, and are separated with that metal
+as oxalates, as described under _Cerium_.
+
+Didymium salts have a rose or violet colour, and impart (when in
+sufficient quantity) the same colour to the borax bead. Solutions have a
+characteristic absorption-spectrum.
+
+The separation of lanthanum and didymium in the solution from which the
+cerium has been precipitated is effected by precipitating them together
+as oxalates, igniting, and dissolving in dilute nitric acid. This
+solution is then evaporated to dryness and ignited, for a few minutes,
+just below redness. A subnitrate of didymium is formed, and remains as
+an insoluble residue on extracting with hot water. The separated salts
+are treated with ammonia and ignited, and weighed as oxides (La_{2}O_{3}
+and Di_{2}O_{3}).
+
+
+YTTRIA.
+
+Yttria is found in gadolinite and some other rare minerals. It is
+precipitated along with the other earths by ammonia. It is distinguished
+by the insolubility of its hydrate in potash, by the insolubility of its
+oxalate in oxalic acid, and by not being precipitated by hyposulphite of
+soda or potassium sulphate. Further, it is precipitated by potash in the
+presence of tartaric acid as an insoluble tartrate. This reaction
+distinguishes the members of the yttria group from most of the other
+earths. The other members of the group closely resemble it, and amongst
+them are erbia, terbia, ytterbia, scandia, &c.
+
+
+BERYLLIA.
+
+The oxide of beryllium, BeO (also known as glucina), occurs in nature
+mainly as silicate. Beryl, the green transparent variety of which is the
+emerald, is the best known of these. It is a silicate of alumina and
+beryllia.[91] Some other minerals in which it occurs are phenakite,
+euclase, and chrysoberyl.
+
+In the ordinary course of analysis, beryllia will be precipitated with
+alumina, &c., by ammonic hydrate. It is distinguished by the solubility
+of its hydrate in ammonic carbonate, by not being precipitated by
+boiling with sodium hyposulphite, and by not being precipitated by
+ammonic sulphide from an ammonic carbonate solution.
+
+The analysis of silicates containing beryllia is thus effected. The
+finely powdered substance is fused with twice its weight of potassium
+carbonate; and the "melt" is extracted with water, and evaporated with a
+slight excess of sulphuric acid to render the silica insoluble. Treat
+with water, filter, and evaporate the filtrate until a crust is formed.
+Potash alum crystallises out. The liquor is poured off into a warm
+strong solution of ammonium carbonate. Ferric hydrate and alumina will
+be precipitated. They are filtered off, re-dissolved, and again
+precipitated in ammonic carbonate solution; the combined filtrates are
+boiled for some time, and acidified slightly with hydrochloric acid. The
+carbon dioxide is boiled off, and the beryllia is then precipitated as
+hydrate with ammonia. The hydrate is washed with hot water, dried,
+ignited, and weighed as beryllia, BeO.
+
+Beryllia has a specific gravity of 3.08. It is white, infusible, and
+insoluble in water. After ignition, it is insoluble in acids, except
+sulphuric, but is rendered soluble by fusion with alkalies.
+
+Beryllia, in a solution of carbonate of ammonia, is precipitated as
+carbonate on boiling in proportion as the carbonate of ammonia is
+volatilised. The hydrate is dissolved by a boiling solution of ammonic
+chloride, ammonia being evolved.
+
+
+THE ALKALINE EARTHS.
+
+
+LIME.
+
+Lime is an oxide of calcium, CaO. It occurs abundantly in nature, but
+only in a state of combination. The carbonate (CaCO_{3}), found as
+limestone, chalk, and other rocks, and as the minerals calcite and
+arragonite, is the most commonly occurring compound. The hydrated
+sulphate, gypsum (CaSO_{4}.2H_{2}O), is common, and is used in making
+"plaster of Paris." Anhydrite (CaSO_{4}) also occurs in rock masses, and
+is often associated with rock salt. Phosphate of lime, in the forms of
+apatite, phosphorite, coprolite, &c., is largely mined. Lime is a
+component of most natural silicates. Calcium also occurs, combined with
+fluorine, in the mineral fluor (CaF_{2}). In most of these the acid is
+the important part of the mineral; it is only the carbonate which is
+used as a source of lime.
+
+Lime, in addition to its use in mortars and cements, is valuable as a
+flux in metallurgical operations, and as a base in chemical work on a
+large scale. A mixture of lime and magnesia is used in the manufacture
+of basic fire-bricks.
+
+Carbonate of lime on ignition, especially when in contact with reducing
+substances, loses carbonic acid, and becomes lime. This is known as
+"quicklime"; on treatment with water it becomes hot, expands, and falls
+to a powder of "slaked lime" or calcium hydrate (CaH_{2}O_{2}). The
+hydrate is slightly soluble in water (0.1368 gram in 100 c.c.), forming
+an alkaline solution known as lime-water. Calcium hydrate is more
+generally used suspended in water as "milk of lime."
+
+As a flux it is used either as limestone or as quicklime. Silica forms
+with lime a compound, calcium silicate, which is not very fusible; but
+when alumina and other oxides are present, as in clays and in most rocky
+substances, the addition of lime gives a very fusible slag.
+
+~Detection.~--Calcium is detected by the reddish colour which its salts
+impart to the flame. It is best to moisten with hydrochloric acid (or,
+in the case of some silicates, to treat with ammonium fluoride) before
+bringing the substance into the flame. When seen through a spectroscope,
+it shows a large number of lines, of which a green and an orange are
+most intense and characteristic. Calcium is detected in solution (after
+removal of the metals by treatment with sulphuretted hydrogen and
+ammonium sulphide) by boiling with ammonium oxalate and ammonia. The
+lime is completely thrown down as a white precipitate. Lime is
+distinguished from the other alkaline earths by forming a sulphate
+insoluble in dilute alcohol, but completely soluble in a boiling
+solution of ammonium sulphate.
+
+Lime compounds are for the most part soluble in water or in dilute
+hydrochloric acid. Calcium fluoride must be first converted into
+sulphate by evaporation in a platinum dish with sulphuric acid.
+Insoluble silicates are opened up by fusion with "fusion mixture," as
+described under _Silica_.
+
+~Separation.~--The separation of lime is effected by evaporating with
+hydrochloric acid, to separate silica; and by treating with sulphuretted
+hydrogen, to remove the second group of metals. If the substance
+contains much iron, the solution is next oxidised by boiling with a
+little nitric acid; and the iron, alumina, &c., are removed as basic
+acetates. The filtrate is treated with ammonia and sulphuretted
+hydrogen, and allowed to settle. The filtrate from this is heated to
+boiling, treated with a solution of ammonium oxalate in excess, boiled
+for five or ten minutes, allowed to settle for half an hour, and
+filtered. The precipitate contains all the lime as calcium oxalate.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The precipitate of calcium oxalate is washed with hot water, dried,
+transferred to a weighed platinum crucible, and ignited at a
+temperature not above incipient redness. This ignition converts the
+oxalate into carbonate, with evolution of carbonic oxide, which burns at
+the mouth of the crucible with a blue flame.[92] Generally a small
+quantity of the carbonate is at the same time converted into lime. To
+reconvert it into carbonate, moisten with a few drops of ammonic
+carbonate solution, and dry in a water-oven. Heat gently over a Bunsen
+burner, cool, and weigh. The substance is calcium carbonate (CaCO_{3}),
+and contains 56 per cent. of lime (CaO). It is a white powder, and
+should show no alkaline reaction with moistened litmus-paper.
+
+Where the precipitate is small, it is better to ignite strongly over the
+blowpipe, and weigh directly as lime. With larger quantities, and when
+many determinations have to be made, it is easier to make the
+determination volumetrically.
+
+
+VOLUMETRIC METHODS.
+
+These are carried out either by dissolving the oxalate at once in dilute
+sulphuric acid, and titrating with permanganate of potassium solution;
+or by calcining it to a mixture of lime and carbonate, and determining
+its neutralising power with the standard solutions of acid and alkali.
+
+~Titration with Permanganate of Potassium Solution.~--This solution is
+made by dissolving 5.643 grams of the salt in water, and by diluting to
+1 litre; 100 c.c. are equivalent to 0.5 gram of lime. The solution is
+standardised by titrating a quantity of oxalic acid about equivalent to
+the lime present in the assay; 0.5 gram of lime is equivalent to 1.125
+gram of crystallised oxalic acid. The standardising may be done with
+iron. The standard found for iron multiplied by 0.5 gives that for lime.
+
+The process is as follows:--The calcium oxalate (having been
+precipitated and washed, as in the gravimetric process) is washed
+through the funnel into a flask with hot dilute sulphuric acid, boiled
+till dissolved, diluted to 200 c.c. with water, and heated to about 80° C.
+The standard solution of "permanganate" is then run in, (not too
+quickly, and with constant shaking) until a permanent pink tinge is
+produced. The c.c. used multiplied by the standard, and divided by the
+weight of the substance taken, will give the percentage of lime.
+
+~Estimation of Lime by Alkalimetry.~--The methods of determining the
+amount of an alkali or base by means of a standard acid solution, or,
+conversely, of determining an acid by means of a standard alkaline
+solution, are so closely related that they are best considered under
+one head. The same standard solution is applicable for many purposes,
+and, consequently, it is convenient to make it of such strength that one
+litre of it shall equal an equivalent in grams of any of the substances
+to be determined. Such solutions are termed _normal_. For example, a
+solution of hydrochloric acid (HCl = 36.5) containing 36.5 grams of real
+acid per litre, would be normal and of equivalent strength to a solution
+containing either 17 grams of ammonia (NH_{3} = 17) or 40 grams of sodic
+hydrate (NaHO = 40) per litre. It will be seen in these cases that the
+normal solution contains the molecular weight in grams per litre; and,
+if solutions of these strengths be made, it will be found that they
+possess equal neutralising value.
+
+If, now, a solution containing 98 grams of sulphuric acid (H_{2}SO_{4} =
+98) per litre be made, it will be found to have twice the strength of
+the above solution, that is, 100 c.c. of the soda would only require 50
+c.c. of the acid to neutralise it. The reason for this will be seen on
+inspecting the equations:--
+
+  NaHO + HCl = NaCl + H_{2}O.
+  2NaHO + H_{2}SO_{4} = Na_{2}SO_{4} + 2H_{2}O.
+
+Acids like sulphuric acid are termed bibasic, and their equivalent is
+only half the molecular weight. Thus, a normal solution of sulphuric
+acid would contain 49 grams (98/2) of real acid per litre. Similarly,
+lime and most of the bases are bibasic, as may be seen from the
+following equations; hence their equivalent will be half the molecular
+weight.
+
+  2HCl + CaO = CaCl_{2} + H_{2}O.
+  2HCl + MgO = MgCl_{2} + H_{2}O.
+
+_The standard normal solution of hydrochloric acid_ is made by diluting
+100 c.c. of the strong acid to one litre with water. This will be
+approximately normal. In order to determine its exact strength, weigh up
+3 grams of recently ignited pure sodium carbonate or of the ignited
+bicarbonate. Transfer to a flask and dissolve in 200 c.c. of water; when
+dissolved, cool, tint faintly yellow with a few drops of a solution of
+methyl orange, and run in the standard "acid " from a burette till the
+yellow changes to a pink. Read off the number of c.c. used, and
+calculate to how much sodium carbonate 100 c.c. of the "acid" are
+equivalent. If the "acid" is strictly normal, this will be 5.3 grams. It
+will probably be equivalent to more than this. Now calculate how much
+strictly normal "acid" would be equivalent to the standard found. For
+example: suppose the standard found is 5.5 gram of sodium carbonate,
+then--
+
+        5.3 : 5.5 :: 100 : _x_
+         (where _x_ is the quantity of normal "acid" required).
+                           _x_ = 103.8 c.c.
+
+To get the "acid" of normal strength, we should then add 3.8 c.c. of
+water to each 100 c.c. of the standard solution remaining. Suppose there
+were left 930 c.c. of the approximate "acid," 35.3 c.c. of water must be
+added and mixed. It should then be checked by another titration with
+pure sodium carbonate.
+
+_The standard solution of semi-normal "alkali."_ The best alkali for
+general purposes is ammonia, but, since it is volatile (especially in
+strong solutions), it is best to make it of half the usual strength, or
+_semi-normal_. One litre of this will contain 8.5 grams of ammonia
+(NH_{3}), and 100 c.c. of it will just neutralise 50 c.c. of the normal
+"acid." Take 100 c.c. of dilute ammonia and dilute with water to one
+litre. Run into a flask 50 c.c. of the standard "acid," tint with methyl
+orange, and run in from a burette the solution of ammonia till
+neutralised. Less than 100 c.c. will probably be used. Suppose 95 c.c.
+were required, there should have been 100, hence there is a deficiency
+of five. Then, for each 95 c.c. of standard "ammonia" left, add 5 c.c.
+of water, and mix well. 100 c.c. will now be equivalent to 50 c.c. of
+the "acid."
+
+As an example of the application of this method, we may take the
+determination of lime in limestone, marble, and similar substances.
+
+~Determination of Lime in Limestone.~--Weigh up 1 gram of the dried
+sample, and dissolve in 25 c.c. of normal acid, cool, dilute to 100
+c.c., and titrate with the semi-normal solution of alkali (using
+methyl-orange as an indicator). Divide the c.c. of alkali used by 2,
+subtract from 25, and multiply by 0.028 to find the weight of lime. This
+method is not applicable in the presence of other carbonates or oxides,
+unless the weight of these substances be afterwards determined and due
+correction be made.
+
+
+STRONTIA.
+
+Strontia, the oxide of strontium (SrO), occurs in nature as sulphate, in
+the mineral celestine (SrSO_{4}), and as carbonate in strontianite
+(SrCO_{3}). It is found in small quantities in limestones, chalk, &c.
+
+Strontia is used in sugar-refining, and for the preparation of coloured
+lights.
+
+~Detection.~--It is detected by the crimson colour which its compounds
+(when moistened with hydrochloric acid) impart to the flame. The
+spectrum shows a large number of lines, of which a red, an orange, and a
+blue are most characteristic.
+
+It resembles lime in many of its compounds, but is distinguished by the
+insolubility of its sulphate in a boiling solution of ammonium sulphate,
+and by the insolubility of its nitrate in alcohol. From baryta, which it
+also resembles, it is distinguished by not yielding an insoluble
+chromate in an acetic acid solution, by the solubility of its chloride
+in alcohol, and by the fact that its sulphate is converted into
+carbonate on boiling with a solution formed of 3 parts of potassium
+carbonate and 1 of potassium sulphate.
+
+It is got into solution in the same manner as lime. The sulphate should
+be fused with "fusion mixture," extracted with water, and thoroughly
+washed. The residue will contain the strontia as carbonate, which is
+readily soluble in dilute hydrochloric or nitric acid.
+
+~Separation.~--It is separated (after removal of the silica and metals,
+as described under _Lime_) by adding ammonia and ammonia carbonate, and
+allowing to stand for some hours in a warm place. In the absence of
+baryta or lime it is filtered off, and weighed as strontium carbonate,
+which contains 70.17 per cent. of strontia. It is separated from baryta
+by dissolving in a little hydrochloric acid, adding ammonia in excess,
+and then acidifying with acetic acid, and precipitating the baryta with
+potassium bichromate, as described under _Baryta_. The strontia is
+precipitated from the filtrate by boiling for some time with a strong
+solution of ammonic sulphate and a little ammonia. Fifty parts of
+ammonic sulphate are required for each part of strontia or lime present.
+The precipitate is filtered off, and washed first with a solution of
+ammonic sulphate, and then with alcohol. It is dried, ignited and
+weighed as strontium sulphate.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The determination of strontia in pure solutions is best made by adding
+sulphuric acid in excess and alcohol in volume equal to that of the
+solution. Allow to stand overnight, filter, wash with dilute alcohol,
+dry, ignite at a red heat, and weigh as sulphate (SrSO_{4}). This
+contains 56.4 per cent. of strontia (SrO); or 47.7 per cent. of
+strontium.
+
+
+BARYTA.
+
+Baryta, oxide of barium (BaO), commonly occurs in combination with
+sulphuric oxide in the mineral barytes or heavy spar (BaSO_{4}), and in
+combination with carbon dioxide in witherite (BaCO_{3}). These minerals
+are not unfrequently found in large quantity (associated with galena and
+other metallic sulphides) in lodes. Small isolated crystals of these are
+frequently found in mining districts. Barium is a constituent of certain
+mineral waters. The minerals are recognised by their high specific
+gravity and their crystalline form.
+
+Compounds of barium are often used by the assayer, more especially the
+chloride and hydrate. The salts are, with the exception of the sulphate,
+generally soluble in water or hydrochloric acid. In such solutions
+sulphuric acid produces a white precipitate of baric sulphate, which is
+practically insoluble in all acids.
+
+The dioxide (BaO_{2}) is used for the preparation of oxygen. On strong
+ignition it gives up oxygen, and is converted into baryta (BaO), which,
+at a lower temperature, takes up oxygen from the air, re-forming the
+dioxide.
+
+~Detection.~--Barium is detected by the green colour its salts,
+especially the chloride, give to the flame. This, viewed through the
+spectroscope, shows a complicated spectrum, of which two lines in the
+green are most easily recognised and characteristic. The salts of barium
+give no precipitate with sulphuretted hydrogen in either acid or
+alkaline solution, but with sulphuric acid they at once give a
+precipitate, which is insoluble in acetate of soda. In solutions
+rendered faintly acid with acetic acid, they give a yellow precipitate
+with bichromate of potash. These reactions are characteristic of barium.
+
+Baryta is got into solution in the manner described under _Lime_; but in
+the case of the sulphate the substance is fused with three or four times
+its weight of "fusion mixture." The "melt" is extracted with water,
+washed, and the residue dissolved in dilute hydrochloric acid.
+
+~Separation.~--The separation is thus effected:--The solution in
+hydrochloric acid is evaporated to dryness, re-dissolved in hot dilute
+hydrochloric acid, and sulphuric acid is added to the solution till no
+further precipitate is formed. The precipitate is filtered off, and
+digested with a solution of ammonium acetate or of sodium hyposulphite
+at 50° or 60° C. to dissolve out any lead sulphate. The residue is
+filtered off, washed, dried, and ignited. The ignited substance is mixed
+with four or five times its weight of "fusion mixture," and fused in a
+platinum-dish over the blowpipe for a few minutes. When cold, it is
+extracted with cold water, filtered, and washed. The residue is
+dissolved in dilute hydrochloric acid, and (if necessary) filtered. The
+solution contains the barium as baric chloride mixed, perhaps, with
+salts of strontium or lime. To separate these, ammonia is added till the
+solution is alkaline, and then acetic acid in slight excess. Chromate of
+baryta is then thrown down, by the addition of bichromate of potash, as
+a yellow precipitate. It is allowed to settle, filtered and washed with
+a solution of acetate or of nitrate of ammonia. It is dried, ignited
+gently, and weighed. It is BaCrO_{4}, and contains 60.47 per cent. of
+baryta.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The gravimetric determination of baryta, when lime and strontia are
+absent, is as follows:--The solution, if it contains much free acid, is
+nearly neutralised with ammonia, and then diluted to 100 or 200 c.c. It
+is heated to boiling, and dilute sulphuric acid is added till no further
+precipitation takes place. The precipitate is allowed to settle for a
+few minutes, decanted through a filter, and washed with hot water; and,
+afterwards, dried, transferred to a porcelain crucible, and strongly
+ignited in the muffle or over the blowpipe for a few minutes. It is then
+cooled, and weighed as sulphate of baryta (BaSO_{4}). It contains 65.67
+per cent. of baryta (BaO).
+
+In determining the baryta in minerals which are soluble in acid, it is
+precipitated direct from the hydrochloric acid solution (nearly
+neutralised with ammonia) by means of sulphuric acid. The precipitated
+baric sulphate is digested with a solution of ammonic acetate; and
+filtered, washed, ignited, and weighed.
+
+
+VOLUMETRIC DETERMINATION.
+
+The principle and mode of working of this is the same as that given
+under the Sulphur Assay; but using a standard solution of sulphuric acid
+instead of one of barium chloride. The standard solution of sulphuric
+acid is made to contain 32.02 grams of sulphuric acid (H_{2}SO_{4}), or
+an equivalent of a soluble alkaline sulphate, per litre. 100 c.c. will
+be equal to 5 grams of baryta.
+
+Five grams of the substance are taken, and the baryta they contain
+converted into carbonate (if necessary). The carbonate is dissolved in
+dilute hydrochloric acid. Ten grams of sodium acetate are added, and the
+solution, diluted to 500 c.c., is boiled, and titrated in the manner
+described.
+
+Lead salts must be absent in the titration, and so must strontia and
+lime. Ferrous salts should be peroxidised by means of permanganate or
+chlorate of potash. Other salts do not interfere.
+
+
+MAGNESIA.
+
+Magnesia, the oxide of magnesium (MgO) occurs in nature in the rare
+mineral periclase (MgO); and hydrated, as brucite (MgH_{2}O_{2}). As
+carbonate it occurs in large quantity as magnesite (MgCO_{3}), which is
+the chief source of magnesia. Mixed with carbonate of lime, it forms
+magnesian limestone and dolomite. It is present in larger or smaller
+quantity in most silicates; and the minerals, serpentine, talc, steatite
+and meerschaum are essentially hydrated silicates of magnesia. Soluble
+magnesian salts occur in many natural waters; more especially the
+sulphate and the chloride. Kieserite (MgSO_{4}.H_{2}O) occurs in
+quantity at Stassfurt, and is used in the manufacture of Epsom salts.
+
+~Detection.~--Magnesia is best detected in the wet way. Its compounds
+give no colour to the flame, and the only characteristic dry reaction is
+its yielding a pink mass when ignited before the blowpipe (after
+treatment with a solution of cobalt nitrate). In solution, it is
+recognised by giving no precipitate with ammonia or ammonic carbonate in
+the presence of ammonic chloride, and by giving a white crystalline
+precipitate on adding sodium phosphate or arsenate to the ammoniacal
+solution.
+
+Magnesia differs from the other alkaline earths by the solubility of its
+sulphate in water.
+
+Magnesia is dissolved by boiling with moderately strong acids; the
+insoluble compounds are fused with "fusion mixture," and treated as
+described under _Silicates_.
+
+~Separation.~--It is separated by evaporating the acid solution to
+dryness to render silica insoluble, and by taking up with dilute
+hydrochloric acid. The solution is freed from the second group of metals
+by means of sulphuretted hydrogen, and the iron, alumina, &c., are
+removed with ammonic chloride, ammonia, and ammonic sulphide. The
+somewhat diluted filtrate is treated, first, with ammonia, and then with
+carbonate of ammonia in slight excess. It is allowed to stand for an
+hour in a warm place, and then filtered. The magnesia is precipitated
+from the filtrate by the addition of an excess of sodium phosphate and
+ammonia. It is allowed to stand overnight, filtered, and washed with
+dilute ammonia. The precipitate contains the magnesia as
+ammonic-magnesic phosphate.
+
+In cases where it is not desirable to introduce sodium salts or
+phosphoric acid into the assay solution, the following method is
+adopted. The solution (freed from the other alkaline earths by ammonium
+carbonate) is evaporated in a small porcelain dish with nitric acid. The
+residue (after removing the ammonic salts by ignition) is taken up with
+a little water and a few crystals of oxalic acid, transferred to a
+platinum dish, evaporated to dryness, and ignited. The residue is
+extracted with small quantities of boiling water and filtered off; while
+the insoluble magnesia is washed. The filtrate contains the alkalies.
+The residue is ignited, and weighed as magnesia. It is MgO.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution containing the magnesia is mixed with chloride of ammonium
+and ammonia in excess. If a precipitate should form, more ammonic
+chloride is required. Add sodium phosphate solution in excess, stir and
+allow to stand overnight. Filter and wash the precipitate with dilute
+ammonia. Dry, transfer to a platinum or porcelain crucible, and ignite
+(finally at intense redness); cool, and weigh. The substance is magnesic
+pyrophosphate (Mg_{2}P_{2}O_{7}), and contains 36.04 per cent. of
+magnesia.
+
+
+VOLUMETRIC METHOD.
+
+The magnesia having been precipitated as ammonic-magnesic phosphate,
+which is the usual separation, its weight can be determined
+volumetrically by the method of titration described under _Phosphates_.
+
+The same standard solution of uranium acetate is used. Its standard for
+magnesia is got by multiplying the standard for phosphoric oxide by
+0.5493. For example, if one hundred c.c. are equivalent to 0.5 gram of
+phosphoric oxide, they will be equivalent to (0.5 × .5493) 0.2746 gram
+of magnesia. The method of working and the conditions of the titration
+are the same as for the phosphate titration. The quantity of substance
+taken for assay must not contain more than 0.1 or 0.2 gram of magnesia.
+After precipitating as ammonic-magnesic phosphate with sodium phosphate,
+and well washing with ammonia, it is dissolved in dilute hydrochloric
+acid, neutralised with ammonia, and sodic acetate and acetic acid are
+added in the usual quantity. The solution is boiled and titrated.
+
+
+EXAMINATION OF A LIMESTONE.
+
+~Silica and Insoluble Silicates.~--Take one gram of the dried sample and
+dissolve it in 10 c.c. of dilute hydrochloric acid; filter; wash, dry,
+and ignite the residue.
+
+~Organic Matter.~--If the residue insoluble in hydrochloric acid shows
+the presence of organic matter, it must be collected on a weighed filter
+and dried at 100°. On weighing, it gives the combined weights of organic
+and insoluble matter. The latter is determined by igniting and weighing
+again. The organic matter is calculated by difference.
+
+~Lime.~--Where but little magnesia is present, this is determined by
+titration with standard acid. Take one gram, and dissolve it in 25 c.c.
+of normal hydrochloric acid. Tint with methyl-orange and titrate with
+semi-normal ammonia. Divide the quantity of ammonia used by 2, deduct
+this from 25, and multiply the remainder by 2.8. This gives the
+percentage of lime. Where magnesia is present, the same method is
+adopted, and the magnesia (which is separately determined) is afterwards
+deducted. The percentage of magnesia found is multiplied by 1.4, and the
+result is deducted from the apparent percentage of lime got by
+titrating.
+
+~Magnesia.~--Dissolve 2 grams of the limestone in hydrochloric acid, and
+separate the lime with ammonia and ammonium oxalate. The filtrate is
+treated with sodium phosphate, and the magnesia is weighed as
+pyrophosphate, or titrated with uranium acetate.
+
+~Iron.~--Dissolve 2 grams in hydrochloric acid, reduce, and titrate with
+standard permanganate of potassium solution. This gives the total iron.
+The ferrous iron is determined by dissolving another 2 grams in
+hydrochloric acid and at once titrating with the permanganate of
+potassium solution.
+
+~Manganese.~--Dissolve 20 grams in hydrochloric acid, nearly neutralise
+with soda, add sodium acetate, boil, and filter. To the filtrate add
+bromine; boil, and determine the manganese in the precipitate. See page
+300.
+
+~Phosphoric Oxide.~--This is determined by dissolving the ferric acetate
+precipitate from the manganese separation in hydrochloric acid, adding
+ammonia in excess, and passing sulphuretted hydrogen. Filter and add to
+the filtrate "magnesia mixture." The precipitate is collected, washed
+with ammonia, ignited, and weighed as pyrophosphate.
+
+
+THE ALKALIES.
+
+The oxides of sodium, potassium, lithium, cęsium, and rubidium and
+ammonia are grouped under this head. Of these cęsia and rubidia are
+rare, and lithia comparatively so. They are easily distinguished by
+their spectra. They are characterised by the solubility of almost all
+their salts in water, and, consequently, are found in the solutions from
+which the earths and oxides of the metals have been separated by the
+usual group re-agents.
+
+The solution from which the other substances have been separated is
+evaporated to dryness, and the product ignited to remove the ammonic
+salts added for the purpose of separation. The residue contains the
+alkali metals generally, as chlorides or sulphates. Before determining
+the quantities of the particular alkali metals present, it is best to
+convert them altogether, either into chloride or sulphate, and to take
+the weight of the mixed salts. It is generally more convenient to weigh
+them as chlorides. They are converted into this form, if none of the
+stronger acids are present, by simply evaporating with an excess of
+hydrochloric acid. Nitrates are converted into chlorides by this
+treatment. When sulphates or phosphates are present, the substance is
+dissolved in a little water, and the sulphuric or phosphoric acid
+precipitated with a slight excess of acetate of lead in the presence of
+alcohol. The solution is filtered, and the excess of lead precipitated
+with sulphuretted hydrogen. The filtrate from this is evaporated to
+dryness with an excess of hydrochloric acid, and the residue, consisting
+of the mixed chlorides, is gently ignited and weighed. In many cases
+(such as the analysis of slags and of some natural silicates where the
+percentage of alkalies is small) the percentage of soda and potash
+(which most commonly occur) need not be separately determined. It is
+sufficient to report the proportion of mixed alkalies; which is thus
+ascertained:--Dissolve the ignited and weighed chlorides in 100 c.c. of
+distilled water, and titrate with the standard solution of silver
+nitrate (using potassic chromate as indicator) in the manner described
+under _Chlorine_. The c.c. of silver nitrate used gives the weight in
+milligrams of the chlorine present. Multiply this by 0.775, and deduct
+the product from the weight of the mixed chlorides. This will give the
+combined weight of the alkalies (Na_{2}O and K_{2}O) present. For
+example, 0.0266 gram of mixed chlorides required on titrating 14.2 c.c.
+of silver nitrate, which is equivalent to 0.0142 gram of chlorine. This
+multiplied by 0.775 gives 0.0110 to be deducted from the weight of the
+mixed chlorides.
+
+  Mixed chlorides  0.0266 gram
+  Deduction        0.0110   "
+                   ------
+  Mixed alkalies   0.0156   "
+
+Assuming this to have been got from 1 gram of a rock, it would amount to
+1.56 per cent. of "potash and soda."
+
+The relative proportions of the potash and soda can be ascertained from
+the same determination. Sodium and potassium chlorides have the
+following composition:--
+
+  Sodium    39.38        Potassium  52.46
+  Chlorine  60.62        Chlorine   47.54
+            -----                   -----
+           100.00                  100.00
+
+The percentage of chlorine in the mixed chlorides is calculated. It
+necessarily falls somewhere between 47.5 and 60.6 per cent., and
+approaches the one or the other of these numbers as the proportion of
+the sodium or potassium preponderates. Each per cent. of chlorine in
+excess of 47.5 represents 7.63 per cent. of sodium chloride in the mixed
+chlorides. The percentage of potash and soda in the substance can be
+calculated in the usual way. Sodium chloride multiplied by 0.5302 gives
+its equivalent of soda (Na_{2}O), and potassium chloride multiplied by
+0.6317 gives its equivalent of potash (K_{2}O).
+
+The weight of sodium chloride in the mixed chlorides is also calculated
+thus:--Take the same example for illustration. Multiply the chlorine
+found by 2.103. This gives--
+
+  (0.0142×2.103) = 0.02987.
+
+From the product deduct the weight of the mixed chlorides found--
+
+  Product               0.02987
+  Mixed chlorides       0.02660
+                        -------
+  Difference            0.00327
+
+The difference multiplied by 3.6288 gives the weight of sodium chloride
+in the mixture. In this case it equals 0.0118 gram. The potassium
+chloride is indicated by the difference between this and the weight of
+the mixed chlorides. It equals 0.0148 gram. We have now got--
+
+  Sodium chloride          0.0118 gram
+  Potassium chloride       0.0148   "
+
+from 1 gram of the rock taken. Multiplying these by their factors we
+have (Soda = 0.0118×0.5302; Potash 0.0148×0.6317)--
+
+  Soda    = 0.625 per cent.
+  Potash  = 0.935     "
+
+~Concentration of the Alkalies.~--With the exception of magnesia, all
+the other bases are separated from the alkalies in the ordinary course
+of work without the addition of any re-agent which cannot be removed by
+simple evaporation and ignition. Consequently, with substances soluble
+in acids, successive treatment of the solution with sulphuretted
+hydrogen, ammonia, ammonic sulphide, and ammonic carbonate, filtering,
+where necessary, will yield a filtrate containing the whole of the
+alkalies with ammonic salts and, perhaps, magnesia.
+
+The filtrate is evaporated in a small porcelain dish, with the addition
+of nitric acid towards the finish. It is carried to dryness and ignited.
+The residue is taken up with a little water, treated with a few crystals
+of oxalic acid, and again evaporated and ignited. The alkaline salts are
+extracted with water, and filtered from the magnesia into a weighed
+platinum dish. The solution is then evaporated with an excess of
+hydrochloric acid, ignited at a low red heat, and weighed. The residue
+consists of the mixed alkaline chlorides.
+
+For substances (such as most silicates and similar bodies) not
+completely decomposed by acids, Lawrence Smith's method is generally
+used. This is as follows:--Take from 0.5 to 1 gram of the finely
+powdered mineral, and mix, by rubbing in the mortar, with an equal
+weight of ammonium chloride. Then mix with eight times as much pure
+calcium carbonate, using a part of it to rinse out the mortar. Transfer
+to a platinum crucible, and heat gently over a Bunsen burner until the
+ammonic chloride is decomposed (five or ten minutes). Raise the heat to
+redness, and continue at this temperature for about three quarters of an
+hour. The crucible must be kept covered. Cool, and turn out the mass
+into a 4-inch evaporating dish; wash the crucible and cover with
+distilled water, and add the washings to the dish; dilute to 60 or 80
+c.c., and heat to boiling. Filter and wash. Add to the filtrate about
+1.5 gram of ammonium carbonate; evaporate to about 40 c.c., and add a
+little more ammonic carbonate and some ammonia. Filter into a weighed
+platinum dish, and evaporate to dryness. Heat gently, to drive off the
+ammonic chloride, and ignite to a little below redness. Cool and weigh.
+The residue consists of the mixed alkaline chlorides.
+
+~Separation of the Alkali-Metals from each other.~--Sodium and lithium
+are separated from the other alkali-metals by taking advantage of the
+solubility of their chlorides in the presence of platinic chloride; and
+from one another by the formation of an almost insoluble lithic
+phosphate on boiling with a solution of sodium phosphate in a slightly
+alkaline solution. Cęsium, rubidium, and potassium yield precipitates
+with platinic chloride, which are somewhat soluble, and must be
+precipitated from concentrated solutions. Cęsium and rubidium are
+separated from potassium by fractional precipitation with platinum
+chloride. Their platino-chlorides, being less soluble than that of
+potassium, are precipitated first. One hundred parts of boiling water
+dissolve 5.18 of the potassium platino-chloride, 0.634 of the rubidium
+salt, and 0.377 of the corresponding cęsium compound. The separation of
+lithium, cęsium, and rubidium is seldom called for, owing to their
+rarity. The details of the separation of potassium from sodium are
+described under _Potassium_. Ammonia compounds are sharply marked off
+from the rest by their volatility, and it is always assumed that they
+have been removed by ignition; if left in the solution, they would count
+as potassium compounds. They will be considered under _Ammonia_.
+
+
+SODIUM.
+
+Sodium is the commonest of the alkali metals. It is found in nature
+chiefly combined with chlorine as "common salt" (NaCl). This mineral is
+the source from which the various compounds of sodium in use are
+prepared. Sodium occurs abundantly as nitrate (NaNO_{3}) in Chili
+saltpetre, and as silicate in various minerals, such as albite (or
+soda-felspar).
+
+It occurs as fluoride in cryolite (Na_{3}AlF_{6}), and as carbonate in
+natron, &c. Sulphates are also found. Sodium is very widely diffused,
+few substances being free from it.
+
+The detection of sodium is easy and certain, owing to the strong yellow
+colour its salts impart to the flame; this, when viewed by the
+spectroscope, shows a single yellow line.[93] The extreme delicacy of
+this test limits its value, because of the wide diffusion of sodium
+salts. It is more satisfactory to separate the chloride, which may be
+recognised by its taste, flame coloration, fusibility, and negative
+action with reagents. The chloride dissolved in a few drops of water
+gives with potassium metantimoniate, a white precipitate of the
+corresponding sodium salt.
+
+Sodium salts are dissolved out from most compounds on treatment with
+water or dilute acids. Insoluble silicates are decomposed and the alkali
+rendered soluble by Lawrence Smith's method, which has just been
+described. The separation of the sodium from the mixed chlorides is
+effected in the following way:--The chlorides are dissolved in a little
+water and the potassium separated as platino-chloride. The soluble
+sodium platino-chloride, with the excess of platinum, is boiled, mixed
+with sulphuric acid, evaporated to dryness, and ignited. On extracting
+with water, filtering, evaporating, and igniting, sodium sulphate is
+left, and is weighed as such.
+
+It is more usual, and quite as satisfactory, to calculate the weight of
+the sodium chloride by difference from that of the mixed chlorides, by
+subtracting that of the potassium chloride, which is separately
+determined. For example, 1 gram of a rock gave--Mixed chlorides, 0.0266
+gram, and 0.0486 gram of potassic platino-chloride. This last is
+equivalent to 0.0149 gram of potassium chloride.
+
+  Mixed chlorides found          0.0266
+  Deduct potassium chloride      0.0149
+                                 ------
+  Leaves sodium chloride         0.0117
+
+The weight of sodium chloride found, multiplied by 0.5302, gives the
+weight of the soda (Na_{2}O).
+
+
+GRAVIMETRIC DETERMINATION.
+
+The solution, which must contain no other metal than sodium, is
+evaporated in a weighed platinum crucible or dish. Towards the finish an
+excess, not too great, of sulphuric acid is added, and the evaporation
+is continued under a loosely fitting cover. The residue is ignited over
+the blowpipe, a fragment of ammonic carbonate being added towards the
+end, when fumes of sulphuric acid cease to be evolved. This ensures the
+removal of the excess of acid. The crucible is cooled in the desiccator,
+and weighed. The substance is sulphate of soda (Na_{2}SO_{4}), and
+contains 43.66 per cent. of soda (Na_{2}O), or 32.38 per cent. of sodium
+(Na).
+
+
+VOLUMETRIC METHODS.
+
+There are various methods used for the different compounds of sodium.
+There is no one method of general application. Thus with "common salt"
+the chlorine is determined volumetrically; and the sodium, after
+deducting for the other impurities, is estimated by difference.
+
+With sodic carbonate and caustic soda, a given weight of the sample is
+titrated with standard acid, and the equivalent of soda estimated from
+the alkalinity of the solution.
+
+With sodium sulphate, a modification of the same method is used. To a
+solution of 3.55 grams of the salt contained in a half-litre flask, 250
+c.c. of a solution of baryta water is added. The volume is made up to
+500 c.c. with water. The solution is mixed and filtered. Half of the
+filtrate is measured off, treated with a current of carbonic acid, and
+then boiled. It is transferred to a half-litre flask, diluted to the
+mark, shaken up, and filtered. 250 c.c. of the filtrate, representing a
+quarter of the sample taken, is then titrated with standard acid. The
+standard acid is made by diluting 250 c.c. of the normal acid to 1
+litre. The c.c. of acid used multiplied by 2 gives the percentage. A
+correction must be made to counteract the effect of impurities in the
+baryta as well as errors inherent in the process. This is small, and its
+amount is determined by an experiment with 3.55 grams of pure sodium
+sulphate.
+
+
+EXAMINATION OF COMMON SALT.
+
+~Moisture.~--Powder and weigh up 10 grams of the sample into a platinum
+dish. Dry in a water oven for an hour, and afterwards heat to bare
+redness over a Bunsen burner. Cool, and weigh. The loss gives the water.
+
+~Chlorine.~--Weigh up two separate lots of 1 gram each; dissolve in 100
+c.c. of water, and determine the chlorine by titrating with the standard
+silver nitrate solution, using chromate of potash as indicator. See
+_Chlorine_.
+
+~Insoluble Matter.~--Dissolve 10 grams of the salt in water with the
+help of a little hydrochloric acid. Filter off the sediment, wash,
+ignite, and weigh. This residue is chiefly sand. Dilute the nitrate to
+500 c.c.
+
+~Lime.~--Take 250 c.c. of the filtrate, render ammoniacal and add
+ammonium oxalate; wash, dry, and ignite the precipitate. Weigh as lime
+(CaO).
+
+~Magnesia.~--To the filtrate from the lime add phosphate of soda. Allow
+to stand overnight, filter, wash with dilute ammonia, dry, ignite, and
+weigh as pyrophosphate.
+
+~Sulphuric Oxide.~--To the remaining 250 c.c. of the filtrate from the
+"insoluble," add an excess of barium chloride. Collect, wash, dry,
+ignite, and weigh the barium sulphate.
+
+~Sodium.~--It is estimated by difference.
+
+The following may be taken as an example:--
+
+  Moisture             0.35
+  Insoluble matter     0.40
+  Lime                 0.40
+  Magnesia             0.05
+  Sulphuric oxide      0.60
+  Chlorine            59.60
+  Sodium              38.60
+                     ------
+                     100.00
+
+
+POTASSIUM.
+
+Potassium occurs in nature as chloride, in the mineral sylvine (KCl),
+and more abundantly combined with magnesium chloride, in earnallite
+(KCl.MgCl_{2}.6H_{2}O). It occurs as nitrate in nitre (KNO_{3}), and as
+silicate in many minerals, such as orthoclase (or potash-felspar) and
+muscovite (or potash-mica).
+
+Potassium compounds are detected by the characteristic violet colour
+they impart to the flame. The presence of sodium salts masks this tint,
+but the interference can be neutralised by viewing the flame through a
+piece of blue glass. Viewed through the spectroscope, it shows a
+characteristic line in the red and another in the violet. These,
+however, are not so easy to recognise or obtain as the sodium one.
+Concentrated solutions of potassium salts give a yellow crystalline
+precipitate with platinum chloride, and a white crystalline one with the
+acid tartrate of soda. For these tests the solution is best neutral.
+These tests are only applicable in the absence of compounds other than
+those of potassium and sodium.
+
+
+GRAVIMETRIC DETERMINATION.
+
+This process serves for its separation from sodium. Take 1 gram of the
+sample and dissolve it in an evaporating dish with 50 c.c. of water.
+Acidify with hydrochloric acid in quantity sufficient (if the metals are
+present as chlorides) to make it acid, or, if other acids are present,
+in at least such quantity as will provide the equivalent of chlorine.
+Add 3 grams of platinum, in solution as platinum chloride, and evaporate
+on a water-bath to a stiff paste, but not to dryness. Moisten with a few
+drops of platinic chloride solution without breaking up the paste by
+stirring. Cover with 20 c.c. of strong alcohol, and wash the crystals as
+much as possible by rotating the dish. Allow to settle for a few
+moments, and decant through a filter. Wash in the same way two or three
+times until the colour of the filtrate shows that the excess of the
+platinum chloride used is removed. Wash the precipitate on to the filter
+with a jet of alcohol from the wash-bottle; clean the filter-paper,
+using as little alcohol as possible. Dry in the water-oven for an hour.
+Brush the precipitate into a weighed dish, and weigh it. It is potassium
+platino-chloride (K_{2}PtCl_{6}), and contains 16.03 per cent. of
+potassium, or 30.56 per cent. of potassium chloride (KCl), which is
+equivalent to 19.3 per cent. of potash (K_{2}O).
+
+If the filter-paper is not free from precipitate, burn it and weigh
+separately. The excess of weight over that of the ash will be due to
+platinum and potassic chloride (Pt and 2KCl). This multiplied by 1.413
+will give the weight of the potassic platino-chloride from which it was
+formed. It must be added to the weight of the main precipitate.
+
+The mixed alkaline chlorides obtained in the usual course of analysis
+are treated in this manner; the quantity of platinum added must be about
+three times as much as the mixed chlorides weigh.
+
+
+VOLUMETRIC METHODS.
+
+These are the same as with soda.
+
+~Examination of Commercial Carbonate of Potash.~--The impurities to be
+determined are moisture, silica, and insoluble matter, chlorine,
+sulphuric oxide, and oxide of iron. These determinations are made in the
+ways described under the examination of common salt.
+
+The ~potassium~ is determined by converting it into chloride and
+precipitating with platinum chloride, &c., as just described.
+
+~Available Alkali.~--Weigh up 23.5 grams of the sample, dissolve in
+water, and make up to 500 c.c. Take 50 c.c., tint with methyl orange,
+and titrate with the normal solution of acid. The c.c. of acid used
+multiplied by 2 gives the percentage of available alkali calculated as
+potash (K_{2}O).
+
+~Soda.~--This is calculated indirectly in the following way:--Deduct
+from the potassium found the quantity required for combination with the
+chlorine and sulphuric oxide present, and calculate the remainder to
+potash (K_{2}O). The apparent surplus excess of available alkali is the
+measure of the soda present.
+
+~Carbon Dioxide.~--The c.c. of acid used in the available alkali
+determination, multiplied by 2.2 and divided by 2.35, gives the
+percentage of carbon dioxide.
+
+
+LITHIUM.
+
+Lithia, the oxide of lithium (Li_{2}O), occurs in quantities of 3 or 4
+per cent. in various silicates, such as lepidolite (or lithia-mica),
+spodumene, and petalite. It also occurs as phosphate in triphyline. It
+is a constituent of the water of certain mineral springs. A spring at
+Wheal Clifford contained as much as 0.372 gram of lithium chloride per
+litre. In small quantities, lithia is very widely diffused.
+
+The ~Detection~ of lithia is rendered easy by the spectroscope; its
+spectrum shows a red line lying about midway between the yellow sodium
+line and the red one of potassium. It also shows a faint yellow line.
+The colour of the flame (a crimson) is characteristic.
+
+The reactions of the lithium compounds lie between those of the alkalies
+and of the alkaline earths. Solutions are not precipitated by tartaric
+acid nor by platinic chloride. The oxide is slowly soluble in water.
+The carbonate is not freely soluble. Lithia is completely precipitated
+by sodic phosphate, especially in hot alkaline solutions.
+
+In its determination the mixed alkaline chlorides obtained in the
+separation of the alkalies are dissolved in water, a solution of soda is
+added in slight excess, and the lithia precipitated with _sodic_
+phosphate. Before filtering, it is evaporated to dryness and extracted
+with hot water rendered slightly ammoniacal. The residue is transferred
+to a filter, dried, ignited, and weighed. The precipitate is lithium
+phosphate (3Li_{2}O, P_{2}O_{5}), and contains 38.8 per cent. of lithia.
+The separation of lithia from magnesia is not given by the usual
+authorities. Wohler recommends evaporating the solution to dryness with
+carbonate of soda. On extracting the residue with water, the lithia
+dissolves out and is determined in the filtrate. One hundred parts of
+water dissolve, at the ordinary temperature, 0.769 parts of lithium
+carbonate (Li_{2}CO_{3}); the basic magnesia compound is almost
+insoluble in the absence of carbon dioxide and ammonium salts.
+
+
+CAESIUM.
+
+The oxide of caesium, caesia (Cs_{2}O), is found associated with lithia
+in lepidolite, &c., and, together with rubidium, in many mineral waters.
+The mineral pollux is essentially a silicate of alumina and caesia; it
+contains 34.0 per cent. of the latter oxide.
+
+Caesium is best detected by the spectroscope, its spectrum being
+characterised by two lines in the blue and one in the red; the latter is
+about midway between the lithium and sodium lines.
+
+If not detected by the spectroscope, or specially looked for, caesia
+would, in the ordinary course of work, be separated with the potash and
+weighed as potassium platino-chloride.
+
+Caesia is separated from all the other alkalies by adding to the acid
+solution of the mixed chlorides a strongly acid cold solution of
+antimonious chloride. The acid used must be hydrochloric. The caesium is
+precipitated as a white crystalline precipitate (CsCl.SbCl_{3}), which
+is filtered off, and washed, when cold, with strong hydrochloric acid;
+since it is decomposed by water or on warming. The precipitate is washed
+into a beaker, and treated with sulphuretted hydrogen; after filtering
+off the sulphide of antimony, the solution leaves, on evaporation, the
+caesium as chloride.
+
+
+RUBIDIUM.
+
+Rubidium occurs widely diffused in nature, but in very small quantities.
+It is generally associated with caesium.
+
+It is detected by the spectroscope, which shows two violet lines and two
+dark red ones. Like caesium, it is precipitated with platinic chloride,
+and in the ordinary course of work would be weighed as potassium. It is
+separated from potassium by fractional precipitation with platinic
+chloride. Rubidium platino-chloride is much less soluble than the
+potassium salt.
+
+
+AMMONIUM.
+
+It is usual to look upon the salts of ammonia as containing a compound
+radical (NH_{4} = Am), which resembles in many respects the metals of
+the alkalies. Ammonium occurs in nature as chloride in sal ammoniac
+(AmCl), as sulphate in mascagnine (Am_{2}SO_{4}), as phosphate in
+struvite (AmMgPO_{4}.12H_{2}O). Minerals containing ammonium are rare,
+and are chiefly found either in volcanic districts or associated with
+guano. Ammonia and ammonium sulphide occur in the waters of certain
+Tuscan lagoons, which are largely worked for the boracic acid they
+contain. The crude boracic acid from this source contains from 5 to 10
+per cent. of ammonium salts. It is from these that the purer forms of
+ammonium compounds of commerce known as "from volcanic ammonia" are
+derived. But the bulk of the ammonia of commerce is prepared from the
+ammoniacal liquors obtained as bye-products in the working of certain
+forms of blast furnaces and coke ovens, and more especially in
+gas-making.
+
+Ammonia hardly comes within the objects of assaying; but it is largely
+used in the laboratory, and the assayer is not unfrequently called on to
+determine it. Ammonium salts are mostly soluble in water. In strong
+solutions they give a yellow precipitate of ammonium platino-chloride on
+the addition of chloride of platinum; and with the acid tartrate of soda
+yield a white precipitate of hydric ammonic tartrate. These reactions
+are similar to those produced with potassium compounds.
+
+Heated with a base, such as lime or sodic hydrate, ammonium salts are
+decomposed, yielding ammonia gas (NH_{3}), which is readily soluble in
+water. The solution of this substance is known as ammonic hydrate or
+"ammonia."
+
+They are volatilised on ignition; either with, or without, decomposition
+according to the acid present. This fact is of importance in analytical
+work; since it allows of the use of alkaline solutions and reagents
+which leave nothing behind on heating. It must be remembered, however,
+that, although ammonic chloride is volatile, it cannot be volatilised in
+the presence of substances which form volatile chlorides without loss of
+the latter. For example: ferric oxide and alumina are thus lost,
+volatilising as chlorides; and there are some other compounds (notably
+ammonic magnesic arsenate) which on heating to redness suffer reduction.
+The presence of ammonic chloride in such cases must be avoided.
+
+~Detection.~--Compounds of ammonium are detected by their evolving
+ammonia when mixed or heated with any of the stronger bases. The ammonia
+is recognised by its odour, by its alkaline reaction with litmus paper,
+and by yielding white fumes, when brought in contact with fuming acid.
+In consequence of the use of ammonium salts and ammonia as reagents, it
+is necessary to make a special test for and determination of
+ammonium.[94] In the ordinary course of work it will be "lost on
+ignition." The determination presents little difficulty, and is based on
+the method used for its detection.
+
+[Illustration: FIG. 61.]
+
+~Solution and Separation.~--Although ammonium salts are soluble in
+water, there is no necessity for dissolving them. The compound
+containing the ammonia is boiled with an alkaline solution; and the
+liberated ammonia condensed and collected. The substance is weighed out
+into a flask of about 200 c.c. capacity. The flask is closed with a
+rubber cork perforated to carry a 20 c.c. pipette and a bulb exit tube.
+The latter is connected with a receiver, which is a small flask
+containing dilute hydrochloric acid (fig. 61). The flask containing the
+substance is corked, and the greater part of the soda solution is run in
+from the pipette. The solution is then boiled. The ammonia volatilises,
+and is carried over into the hydrochloric acid, with which it combines
+to form ammonic chloride. The distillation is carried on gently until
+the bulk of the liquid is driven over. The ammonia in the receiver will
+be mixed only with the excess of hydrochloric acid. This separation is
+used in all determinations.
+
+
+GRAVIMETRIC DETERMINATION.
+
+The contents of the flask are transferred to a weighed platinum dish,
+and evaporated on the water-bath. It is dried until the weight is
+constant. The chloride of ammonium remains as a white mass which, after
+cooling in a desiccator, is weighed. It contains 33.72 per cent. of
+ammonium (NH_{4}), or 31.85 per cent. of ammonia (NH_{3}). On heating
+over the Bunsen burner it is completely volatilised, leaving no residue.
+
+
+VOLUMETRIC DETERMINATION.
+
+Weigh up 1.7 gram of the substance and place it in the flask. Measure
+off 50 c.c. of the normal solution of acid, place them in the receiver,
+and dilute with an equal volume of water. Run in through the pipette (by
+opening the clip) 20 c.c. of a strong solution of soda, boil until the
+ammonia has passed over, and then aspirate a current of air through the
+apparatus. Disconnect the receiver, and tint its contents with methyl
+orange. Titrate the residual acid with a semi-normal solution of alkali.
+Divide the c.c. of the "alkali" solution used by 2, and deduct from the
+50 c.c. The difference will give the number of c.c. of the normal acid
+solution neutralised by the ammonia distilled over. Each c.c. of "acid"
+so neutralised, represents 1 per cent. of ammonia in the sample. If the
+results are to be reported as ammonium, 1.8 gram of the sample is taken
+instead of 1.7 gram.
+
+
+COLORIMETRIC DETERMINATION.
+
+This is effected by means of "Nessler's" reagent, which strikes a brown
+colour with traces of ammonia, even with a few hundredths of a milligram
+in 100 c.c. of liquid. With larger quantities of ammonia the reagent
+gives a precipitate. This reagent is a strongly alkaline solution of
+potassic mercuric iodide; and is thus made:--
+
+
+_Nessler's solution_: Dissolve 17 grams of mercuric chloride in 300 c.c.
+of water; and add the solution to one of 35 grams of potassium iodide in
+100 c.c. of water until a permanent precipitate is produced. Both
+solutions must be cold. Then make up to a litre by adding a 20 per cent.
+solution of potash. Add more of the mercuric chloride (a little at a
+time) until a permanent precipitate is again formed. Allow to settle,
+decant, and use the clear liquor. Four or five c.c. are used for each
+100 c.c. of liquid to be tested.
+
+_A Standard Solution of Ammonia_ is made by dissolving 0.315 gram of
+ammonic chloride in water, and diluting to 100 c.c. Ten c.c. of this are
+taken and diluted to 1 litre. One c.c. contains 0.01 milligram of
+ammonia (NH_{3}).
+
+In working, the solution containing the ammonia is diluted to a definite
+volume, and to such an extent that 50 c.c. of it shall not contain more
+than 0.02 or 0.03 milligram of ammonia. Fifty c.c. of it are transferred
+to a Nessler glass and mixed with 2 c.c. of Nessler's reagent. The
+colour is noted, and an estimate made as to the amount of ammonia it
+indicates. A measured quantity of the standard ammonia, judged to
+contain about as much ammonia as that in the assay, is then put into
+another Nessler glass. It is diluted to 50 c.c. with water, and mixed
+with 2 c.c. of "Nessler." After standing a minute or two, the colours in
+the two glasses are compared. If the tints are equal, the assay is
+finished; but if the standard is weaker or stronger than the assay,
+another standard, containing more or less ammonia, as the case may be,
+must be prepared and compared with the assay. Two such experiments will
+generally be sufficient; but, if not, a third must be made. The addition
+of more standard ammonia to the solution to which the "Nessler" has
+already been added does not give a satisfactory result.
+
+When the ammonia in 50 c.c. has been determined, that in the whole
+solution is ascertained by a suitable multiplication. By 10, for
+example, if the bulk was 500 c.c., or by 20 if it was a litre.
+
+Distilled water is used throughout. It must be free from ammonia; and is
+best prepared by distilling an ammonia-free spring water.
+
+FOOTNOTES:
+
+[90] Al_{2}Cl_{6} + 3Na_{2}S_{2}O_{3} + 3H_{2}O = Al_{2}(HO)_{6} + 6NaCl
++ 3S + 3SO_{2}
+
+[91] 3BeO,Al_{2}O_{3},6SiO_{2}
+
+[92] CaC_{2}O_{4} = CaCO_{3}+CO.
+
+[93] Resolved into two with a powerful spectroscope.
+
+[94] Ammonium compounds are frequently produced when dissolving metals
+in nitric acid; or when nitrates are heated in the presence of the
+metals.
+
+
+
+
+PART III--NON-METALS.
+
+
+
+
+CHAPTER XV.
+
+OXYGEN AND OXIDES.--THE HALOGENS.
+
+
+OXYGEN.
+
+Oxygen occurs in nature in the free state, forming 23 per cent. by
+weight, or 21 per cent. by volume of the atmosphere; but, since it is a
+gas, its presence is easily overlooked and its importance
+underestimated. Except in the examination of furnace-gases, &c., the
+assayer is not often called upon to determine its quantity, but it forms
+one of his most useful reagents, and there are many cases where he
+cannot afford to disregard its presence. It occurs not only in the air,
+but also dissolved in water; ordinary waters containing on an average
+0.00085 per cent. by weight, or 0.85 parts per 100,000.
+
+Chemically, it is characterised by its power of combining, especially at
+high temperatures, with the other elements, forming an important class
+of compounds called oxides. This combination, when rapid, is accompanied
+by the evolution of light and heat; hence oxygen is generally called the
+supporter of combustion. This property is taken advantage of in the
+operation of calcining, scorifying, cupelling, &c. The importance of a
+free access of air in all such work is seen when it is remembered that 1
+litre of air contains 0.2975 gram of oxygen, and this quantity will only
+oxidise 0.1115 gram of carbon, 0.2975 gram of sulphur, or 3.849 grams of
+lead.
+
+Oxidation takes place at the ordinary temperature with many substances.
+Examples of such action are seen in the weathering of pyrites, rusting
+of iron, and (in the assay office) the weakening of solutions of many
+reducing agents.
+
+For methods of determining the percentage of oxygen in gases, for
+technical purposes, the student is referred to Winkler & Lunge's
+"Technical Gas Analysis."
+
+
+OXIDES.
+
+Oxides are abundant in nature, almost all the commonly occurring bodies
+being oxidised. Water (H_{2}O) contains 88.8 per cent. of oxygen;
+silica, lime, alumina, magnesia, and the other earths are oxides, and
+the oxides of the heavier metals are in many cases important ores; as,
+for example, cassiterite (SnO_{2}), hęmatite (Fe_{2}O_{3}), magnetite
+(Fe_{3}O_{4}), and pyrolusite (MnO_{2}). In fact, the last-named mineral
+owes its value to the excess of oxygen it contains, and may be regarded
+as an ore of oxygen rather than of manganese.
+
+Most of the metals, when heated to redness in contact with air, lose
+their metallic lustre and become coated with, or (if the heating be
+prolonged) altogether converted into, oxide. This oxide was formerly
+termed a "calx," and has long been known to weigh more than the metal
+from which it was obtained. For example, one part by weight of tin
+becomes, on calcining, 1.271 parts of oxide (putty powder). The student
+will do well to try the following experiments:--Take 20 grams of tin and
+heat them in a muffle on a scorifier, scraping back the dross as it
+forms, and continuing the operation until the whole of the metal is
+burnt to a white powder and ceases to increase in weight.[95] Take care
+to avoid loss, and, when cold, weigh the oxide formed. The oxide should
+weigh 25.42 grams, which increase in weight is due to the oxygen
+absorbed from the air and combined with the metal. It can be calculated
+from this experiment (if there has been no loss) that oxide of tin
+contains 21.33 per cent. of oxygen and 78.67 per cent. of tin. Oxidation
+is performed with greater convenience by wet methods, using reagents,
+such as nitric acid, which contain a large proportion of oxygen loosely
+held. Such reagents are termed oxidising agents. Besides nitric acid,
+permanganate of potash, bichromate of potash, and peroxide of hydrogen
+are largely used for this purpose. One c.c. of nitric acid contains as
+much oxygen as 2.56 litres of air, and the greater part of this is
+available for oxidising purposes. Try the following experiment:--Take 2
+grams of tin and cover in a weighed Berlin dish with 20 c.c. of dilute
+nitric acid, heat till decomposed, evaporate to dryness, ignite, and
+weigh. The 2 grams of tin should yield 2.542 grams of oxide. The
+increase in weight will be proportionally the same as in the previous
+experiment by calcination, and is due to oxygen, which in this case has
+been derived from the nitric acid.
+
+The percentage of oxygen in this oxide of tin (or in any of the oxides
+of the heavier metals) may be directly determined by heating such oxides
+in a current of hydrogen, and collecting and weighing the water formed.
+
+It is found by experiment that 88.86 parts by weight of oxygen,
+combining with 11.14 parts of hydrogen, form 100 parts of water; so that
+from the weight of water formed it is easy to calculate the amount of
+oxygen the oxide contained.
+
+[Illustration: FIG. 62.]
+
+Take 1 gram of the dried and powdered oxide and place it in a warm dry
+combustion tube. Place the tube in a furnace, and connect at one end
+with a hydrogen apparatus provided with a sulphuric acid bulb for drying
+the gas, and at the other with a weighed sulphuric acid tube for
+collecting the water formed. The apparatus required is shown in fig. 62.
+Pass hydrogen through the apparatus, and, when the air has been cleared
+out, light the furnace. Continue the heat and current of hydrogen for
+half an hour (or longer, if necessary). Allow to cool. Draw a current of
+dry air through the weighed tube. Weigh. The increase in weight gives
+the amount of water formed, and this, multiplied by 0.8886, gives the
+weight of the oxygen. The percentage of oxygen thus determined should be
+compared with that got by the oxidation of the metal. It will be
+practically the same. The following results can be taken as examples:--
+
+Twenty grams of tin, calcined as described, gave 25.37 grams of oxide.
+
+Two grams of tin, oxidised with nitric acid and ignited, gave 2.551
+grams of oxide.
+
+One gram of the oxide of tin, on reduction in a current of hydrogen,
+gave 0.2360 gram of water (equivalent to 0.2098 gram of oxygen), and
+left 0.7900 gram of metal.
+
+Ten grams of ferrous sulphate gave, on strong ignition, 2.898 grams of
+ferric oxide (Fe_{2}O_{3})[96] instead of 2.877.
+
+The student should similarly determine the percentage of oxygen in
+oxides of copper and iron. The former oxide may be prepared by
+dissolving 5 grams of copper in 50 c.c. of dilute nitric acid,
+evaporating to dryness, and strongly igniting the residue. The oxide of
+iron may be made by weighing up 10 grams of powdered ferrous sulphate
+(= to 2.014 grams of iron) and heating, at first gently, to drive off the
+water, and then at a red heat, until completely decomposed. The weight
+of oxide, in each case, should be determined; and the percentage of
+oxygen calculated. Compare the figures arrived at with those calculated
+from the formula of the oxides, CuO and Fe_{2}O_{3}.
+
+It would be found in a more extended series of experiments that the same
+metal will, under certain conditions, form two or more oxides differing
+among themselves in the amount of oxygen they contain. These oxides are
+distinguished from one another by such names as "higher" and "lower
+oxides," "peroxides," "protoxides," "dioxides," &c.
+
+The oxides may be conveniently classified under three heads:--
+
+(1) _Those that are reduced to metal by heat alone_, such as the oxides
+of mercury, silver, platinum, gold, &c.;
+
+(2) _Those which are reduced by hydrogen at a red heat_, which includes
+the oxides of the heavy metals;
+
+(3) _Those which are not reduced by these means_, good examples of which
+are silica, alumina, the alkalies, and the alkaline earths.
+
+Another important classification is into acid, basic and neutral oxides.
+The oxides of the non-metallic elements, such as sulphur, carbon,
+phosphorus, &c., are, as a rule, acid; and the more oxygen they contain,
+the more distinctly acid they are. The oxides of the metals are nearly
+all basic; and, as a rule, the less oxygen they contain, the more
+distinctly basic they are.
+
+The basic oxides, which are soluble in acids, give rise to the formation
+of salts when dissolved therein. During the solution, water is formed,
+but no gas is evolved. The oxide dissolved in each case neutralizes an
+equivalent of the acid used for solution.[97] The basic properties of
+many of these can be taken advantage of for their determination. This is
+done in the case of soda, potash, lime, &c., by finding the quantity of
+acid required to neutralize a given weight of the substance.
+
+There are some oxides which, under certain conditions, are acid to one
+substance (a stronger base) and basic to another (a stronger acid). For
+example, the oxides of lead and of tin, as also alumina, dissolve in
+caustic soda, acting as acids; whilst, on the other hand, they combine
+with sulphuric or hydrochloric acid, playing the part of bases.
+
+The oxides known as "earths," when ignited, are many of them insoluble
+in acids, although easily dissolved before ignition.
+
+It is common in complete analyses of minerals to meet with cases in
+which the sum total of the elements found falls short of the amount of
+ore taken; and here oxygen must be looked for. For example, this occurs
+in the case of a mixture of pyrites with oxide of iron, or in a mixture
+of sulphides and sulphates. The state in which the elements are present,
+and the percentage (say of sulphides and sulphates) can in many cases be
+determined; but this is not always required. When the difference between
+the sum total and the elements found is small, it is reported as "oxygen
+and loss." When, however, it is considerable, the oxygen may be reported
+as such; and its amount be either determined directly in the way already
+described, or calculated from the best determination that can be made of
+the relative amounts of oxides, sulphides, sulphates, &c., present. Such
+cases require a careful qualitative analysis to find out that the
+substance is present; and then the separation of each constituent is
+made as strictly as possible. These remarks apply especially to ores of
+the heavy metals. The separation of the constituents is effected with
+suitable solvents applied in proper order. The soluble sulphates, for
+example, are extracted with water; the oxides by the dilute acids or
+alkalies in which they are known to be soluble. The oxygen in the
+sulphates and oxides thus obtained is estimated by determining the
+sulphur and metals in the solutions, and calculating the amount of
+oxygen with which they combine. The metals of the earths and alkalies
+are almost invariably present as oxides, and are reported as such;
+except it is known that they are present in some other form, such as
+fluoride or chloride. Thus, silica, alumina, lime, water, &c., appear in
+an analysis; even in those cases where "oxygen and loss" is also
+mentioned. As an example of such a report, take the following analysis
+of Spanish pyrites:--
+
+  Sulphur           49.00
+  Iron              43.55
+  Copper             3.20
+  Arsenic            0.47
+  Lead               0.93
+  Zinc               0.35
+  Lime               0.10
+  Silica, &c.        0.63
+  Water              0.70
+  Oxygen and loss    1.07
+                    -----
+                   100.00
+
+The following example will illustrate the mode of calculating and
+reporting. A mineral, occurring as blue crystals soluble in water, and
+found on testing to be a mixed sulphate of iron and copper, gave on
+analysis the following results:--
+
+  Water                44.51 per cent.
+  Sulphuric oxide      28.82    "
+  Copper                8.44    "
+  Ferrous iron         11.81    "
+  Ferric iron           0.38    "
+  Zinc                  0.28    "
+                       -----
+                       94.24
+
+There is here a deficiency of 5.76 per cent. due to oxygen. Nothing else
+could be found, and it is known that in the sulphates the metals exist
+as oxides. By multiplying the weight of the copper by 1.252, the weight
+of copper oxide (CuO) will be ascertained; in this case it equals 10.57
+per cent. The ferrous iron multiplied by 1.286 will give the ferrous
+oxide (FeO); in this case 15.19 per cent. The ferric iron multiplied by
+1.428 will give the ferric oxide (Fe_{2}O_{3}); in this case 0.54 per
+cent. The zinc multiplied by 1.246 will give the zinc oxide (ZnO); in
+this case it equals 0.35 per cent. The analysis will be reported as--
+
+  Water                 44.51
+  Sulphuric oxide       28.82
+  Copper oxide          10.57 equal to copper 8.44%
+  Ferrous oxide         15.19
+  Ferric oxide           0.54
+  Zinc oxide             0.35
+                        -----
+                        99.98
+
+The following (A) is an analysis of a sample of South American copper
+ore, which will serve as a further illustration. The analysis showed the
+presence of 6.89 per cent. of ferrous oxide, and some oxide of copper.
+
+The analysis (B) is that of an ore from the same mine after an imperfect
+roasting. It will be seen that the carbonates have been converted into
+sulphates. If the total sulphur simply had been determined, and the
+sulphate overlooked, the "oxygen and loss" would have been 5.65 per
+cent., an amount which would obviously require an explanation.
+
+                         A.             B.
+  Water                  0.25           0.59
+  Organic matter         0.54            --
+  Sulphur               29.50          21.33
+  Copper                10.92           9.80 {Copper        9.57
+                                             {Copper oxide  0.28
+  Iron                  32.09          39.73   {Iron         34.32
+                                               {Ferric oxide  7.73
+  Lead                   0.35           0.12
+  Zinc                   0.86           0.69
+  Cobalt                 0.06           0.11
+  Lime                   5.25           7.69
+  Magnesia               2.33           2.55
+  Sulphuric oxide        1.00           5.30
+  Carbon dioxide         8.87            --
+  "Insoluble silicates"  5.12           8.38
+  Oxygen and loss        2.86           2.47
+                        -----  Potash   0.15
+                       100.00  Soda     1.09
+                                       -----
+                                      100.00
+
+
+WATER.
+
+Water occurs in minerals in two forms, free and combined. The term
+"moisture" ought, strictly, to be limited to the first, although, as has
+already been explained, it is more convenient in assaying to apply the
+term to all water which is driven off on drying at 100° C. The combined
+water is really a part of the mineral itself, although it may be driven
+off at a high temperature, which varies with the base. In some cases a
+prolonged red heat is required; whilst with crystallised salts it is
+sometimes given off at the ordinary temperatures. This latter
+phenomenon, known as efflorescence, is mostly confined to artificial
+salts.
+
+The determination of the combined water may often be made by simply
+igniting the substance from which the moisture has been removed. The
+quantity of water may be determined, either indirectly by the loss, or
+directly by collecting it in a calcium chloride tube, and weighing. In
+some cases, in which the loss on ignition does not give simply the
+proportion of combined water, it can be seen from the analysis to what
+else the loss is due; and, after a proper deduction, the amount of water
+can be estimated. For example, 1 gram of crystallised iron sulphate was
+found to contain on analysis 0.2877 gram of sulphuric oxide; and on
+igniting another gram, 0.2877 gram of ferric oxide was left. As the salt
+is known to be made up of ferrous oxide, sulphuric oxide, and combined
+water, the combined water can be thus calculated: 0.2877 gram of ferric
+oxide is equal to 0.2589 gram of ferrous oxide,[98] and consequently,
+the loss on ignition has been diminished by 0.0288 gram, which is the
+weight of oxygen absorbed by the ferrous oxide during calcining. The
+loss on ignition was 0.7123 gram, to which must be added 0.0288 gram;
+hence 0.7411 gram is the weight of the combined sulphuric oxide and
+water present. Deducting the weight of sulphuric oxide found, 0.2877
+gram, there is left for combined water 0.4534 gram. The composition of 1
+gram of the dry salt is then:--
+
+  Water             0.4534
+  Sulphuric oxide   0.2877
+  Ferrous oxide     0.2589
+                    ------
+                    1.0000
+
+The following is another example:--A sample of malachite lost on
+ignition 28.47 per cent., leaving a residue which was found on analysis
+to be made up of oxide of copper (equal to 70.16 per cent. on the
+mineral), and silica and oxide of iron (equal to 1.37 per cent.). Carbon
+dioxide and water (but nothing else) was found to be present, and the
+carbon dioxide amounted to 19.64 per cent.; deducting this from the loss
+on ignition, we have 8.82 as the percentage of water present. The
+analysis was then reported as follows:--
+
+  Cupric oxide              70.16 equal to 56.0% copper.
+  Silica and ferric oxide    1.37
+  Carbon dioxide            19.64
+  Water                      8.82
+                            -----
+                            99.99
+
+[Illustration: FIG. 63.]
+
+~Direct Determination of Combined Water.~--Transfer about 3 grams of the
+substance to a piece of combustion tube (8 or 10 inches long), attached
+(as in fig. 63) at one end to a ~U~-tube containing sulphuric acid, and
+at the other end to a calcium chloride tube. The last is weighed
+previous to the determination. The tube should be warmed to ensure
+complete dryness, and must be free from a misty appearance. Aspirate a
+current of air through the apparatus, heat the mineral by means of a
+Bunsen burner, cautiously at first, and afterwards to redness (if
+necessary). The water is driven off and condenses in the calcium
+chloride tube, which is afterwards cooled and weighed. The increase in
+weight is due to the water. If the substance gives off acid products on
+heating, it is previously mixed with some dry oxide of lead or pure
+calcined magnesia.
+
+
+EXAMINATION OF WATERS.
+
+The assayer is occasionally called on to test water for the purpose of
+ascertaining the nature and quantity of the salts contained in it, and
+whether it is or is not fit for technical and drinking purposes.
+
+In mineral districts the water is generally of exceptional character,
+being more or less charged, not only with earthy salts, but also
+frequently with those of the metals. Distilled water is only used by
+assayers in certain exceptional cases, so that by many it would be
+classed among the rarer oxides. Water of ordinary purity will do for
+most purposes, but the nature and quantity of the impurities must be
+known.
+
+The following determinations are of chief importance:--
+
+~Total Solids at 100° C.~--Where simply the amount is required, take 100
+c.c. and evaporate on the water-bath in a weighed dish; then dry in the
+water-oven, and weigh.
+
+~Total Solids Ignited.~--The above residue is very gently ignited
+(keeping the heat well below redness), and again weighed. A larger loss
+than 4 or 5 parts per 100,000 on the water requires an explanation.
+
+~Chlorine.~--Take 100 c.c. of the water in a porcelain dish, add 2 c.c.
+of a 5 per cent. solution of neutral potassic chromate, and titrate with
+a neutral standard solution of nitrate of silver, made by dissolving
+4.789 grams of crystallised silver nitrate in distilled water, and
+diluting to 1 litre. The addition of the nitrate of silver is continued
+until the yellow of the solution assumes a reddish tint. The reaction is
+very sharp. Each c.c. of nitrate of silver used is equal to 1 part by
+weight of chlorine in 100,000 of water. At inland places this rarely
+amounts to more than 1 in 100,000; but near the sea it may amount to 3
+or 5. More than this requires explanation, and generally indicates
+sewage pollution.
+
+~Nitric Pentoxide (N_{2}O_{5}).~--It is more generally reported under
+the heading, "nitrogen as nitrates." Take 250 c.c. of the water and
+evaporate to 2 or 3 c.c.; acidulate with a few drops of dilute sulphuric
+acid, and transfer to a nitrometer (using strong sulphuric acid to wash
+in the last traces). The sulphuric acid must be added to at least twice
+the bulk of the liquid. Shake up with mercury. The mercury rapidly
+flours, and nitric oxide is given off (if any nitrate is present). The
+volume of the nitric oxide (corrected to normal temperature and
+pressure), multiplied by 0.25, gives the parts of nitrogen per 100,000;
+or, multiplied by 0.965, will give the nitric pentoxide in parts per
+100,000. In well and spring waters the nitrogen may amount to 0.3 or 0.4
+parts per 100,000; or in richly cultivated districts 0.7 or 0.8 parts
+per 100,000. An excess of nitrates is a suspicious feature, and is
+generally due to previous contamination.
+
+~Ammonia.~--Take 500 c.c. of the water and place them in a retort
+connected with a Liebig's condenser. Add a drop or two of a solution of
+carbonate of soda and distil over 100 c.c.; collect another 50 c.c.
+separately. Determine the ammonia in the distillate colorimetrically
+(with Nessler's solution, as described under _Ammonia_) and compare with
+a standard solution of ammonic chloride containing 0.0315 gram of
+ammonic chloride in 1 litre of water. One c.c. contains 0.01 milligram
+of ammonia. The second distillate will show little, if any, ammonia in
+ordinary cases. The amounts found in both distillates are added
+together, and expressed in parts per 100,000.
+
+Waters (other than rain and tank waters) which contain more than 0.003
+per 100,000 are suspicious.
+
+~Organic Matter.~--The organic matter cannot be determined directly; but
+for ordinary purposes it may be measured by the amount of permanganate
+of potassium which it reduces, or by the amount of ammonia which it
+evolves on boiling with an alkaline permanganate of potassium solution.
+
+A. _Albuminoid Ammonia._--To the residue left after distilling the
+ammonia add 50 c.c. of a solution made by dissolving 200 grams of potash
+and 8 grams of potassium permanganate in 1100 c.c. of water, and rapidly
+boiling till the volume is reduced to 1 litre (this should be kept in a
+well stoppered bottle, and be occasionally tested to see that it is free
+from ammonia). Continue the distillation, collecting 50 c.c. at a time,
+until the distillate is free from ammonia. Three or four fractions are
+generally sufficient. Determine the ammonia colorimetrically as before.
+If the total albuminoid ammonia does not exceed 0.005 in 100,000, the
+water may be regarded as clean as regards organic matter; if it amounts
+to more than 0.015, it is dirty.
+
+B. _Oxygen Consumed._--A standard solution of permanganate of potash is
+made by dissolving 0.395 gram of the salt in water and diluting to 1
+litre. Each c.c. equals 0.1 milligram of available oxygen. The following
+are also required:--1. A solution of sodium hyposulphite containing 1
+gram of the salt (Na_{2}S_{2}O_{3}.5H_{2}O) in 1 litre of water. 2.
+Dilute sulphuric acid, made by adding one part of the acid to three of
+water, and titrating with the permanganate solution till a faint pink
+persists after warming for several hours. 3. Starch paste. 4. Potassium
+iodide solution.
+
+Take 250 c.c. of the water in a stoppered bottle, add 10 c.c. of
+sulphuric acid and 10 c.c. of the permanganate, and allow to stand in a
+warm place for four hours. Then add a few drops of the solution of
+potassium iodide, and titrate the liberated iodine with "hypo," using
+starch paste towards the end as an indicator. To standardise the
+hyposulphite, take 250 c.c. of water and 10 c.c. of sulphuric acid, and
+a few drops of potassium iodide; then run in 10 c.c. of the
+"permanganate" solution, and again titrate; about 30 c.c. of the "hypo"
+will be used. The difference in the two titrations, divided by the last
+and multiplied by 10, will give the c.c. of permanganate solution used
+in oxidising the organic matter in the 250 c.c. of water. Each c.c.
+represents 0.04 parts of oxygen in 100,000.
+
+~Metals.~--These may for the most part be estimated colorimetrically.
+
+~Lead.~--Take 100 c.c. of the water in a Nessler tube, and add 10 c.c.
+of sulphuretted hydrogen water, and compare the tint, if any, against a
+standard lead solution, as described under _Colorimetric Lead_. Report
+in parts per 100,000.
+
+~Copper.~--Proceed as with the last-mentioned metal; but, if lead is
+also present, boil down 500 c.c. to about 50 c.c., then add ammonia,
+filter, and estimate the copper in the blue solution, as described under
+_Colorimetric Copper_.
+
+~Iron.~--Take 50 c.c., or a smaller quantity (if necessary), dilute up
+to the mark with distilled water, and determine with potassium
+sulphocyanate, as described under _Colorimetric Iron_.
+
+~Zinc.~--Zinc is the only other metal likely to be present; and, since
+it cannot be determined colorimetrically, it must be separately
+estimated during the examination of the "total solids."
+
+~Examination of "Total Solids."~--Evaporate 500 c.c. to dryness with a
+drop or two of hydrochloric acid. Take up with hydrochloric acid,
+filter, ignite, and weigh the residue as "silica." To the filtrate add a
+little ammonic chloride and ammonia, boil and filter, ignite, and weigh
+the precipitate as "oxide of iron and alumina." Collect the filtrate in
+a small flask, add a few drops of ammonium sulphide or pass sulphuretted
+hydrogen, cork the flask, and allow to stand overnight; filter, wash,
+and determine the zinc gravimetrically as oxide of zinc. If copper or
+lead were present, they should have been previously removed with
+sulphuretted hydrogen in the acid solution. To the filtrate add ammonic
+oxalate and ammonia, boil for some time, allow to stand, filter, wash,
+ignite, and weigh as "lime." Evaporate the filtrate with nitric acid,
+and ignite. Take up with a few drops of dilute hydrochloric acid, add
+baric hydrate in excess, evaporate, and extract with water. The residue
+contains the magnesia; boil with dilute sulphuric acid, filter,
+precipitate it with phosphate of soda and ammonia, and weigh as
+pyrophosphate. The aqueous extract contains the alkalies with the excess
+of barium. Add sulphuric acid in slight excess, filter, evaporate, and
+ignite strongly. The residue consists of the sulphates of the alkalies
+(which are separately determined, as described under _Potash_).
+
+~Sulphuric Oxide (SO_{3}).~--Take 200 c.c. and boil to a small bulk with
+a little hydrochloric acid, filter (if necessary), add baric chloride
+solution in slight excess to the hot solution, filter, ignite, and weigh
+as baric sulphate.
+
+~Carbon Dioxide (free).~--Carbon dioxide exists in waters in two forms,
+free and combined. The latter generally occurs as bicarbonate, although
+on analysis it is more convenient to consider it as carbonate, and to
+count the excess of carbon dioxide with the free. The method is as
+follows:--To determine the free carbon dioxide, take 100 c.c. of the
+water, place them in a flask with 3 c.c. of a strong solution of calcium
+chloride and 2 c.c. of a solution of ammonic chloride, next add 50 c.c.
+of lime-water. The strength of the lime-water must be known. Make up to
+200 c.c. with distilled water, stop the flask, and allow the precipitate
+to settle. Take out 100 c.c. of the clear solution with a pipette, and
+titrate with the standard solution of acid.[99] The number of c.c.
+required, multiplied by two, and deducted from that required for the 50
+c.c. of lime-water, and then multiplied by 0.0045, will give the carbon
+dioxide present other than as normal carbonates.
+
+~Carbon Dioxide combined~ as normal carbonate.--100 c.c. of the water
+are tinted with phenacetolin or lacmoid; then heated to near boiling,
+and titrated with standard acid. The number of c.c. used, multiplied by
+0.0045, will give the weight in grams of the combined carbon dioxide.
+
+~Free Acid.~--In some waters (especially those from mining districts)
+there will be no carbonates. On the contrary, there may be free mineral
+acid or acid salts. In these cases it is necessary to determine the
+amount of acid (other than carbon dioxide) present in excess of that
+required to form normal salts. This is done in the following way:--Make
+an ammoniacal copper solution by taking 13 grams of copper sulphate
+(CuSO_{4}.5H_{2}O), dissolving in water, adding solution of ammonia
+until the precipitate first formed has nearly dissolved, and diluting to
+1 litre. Allow to settle, and decant off the clear liquid. The strength
+of this solution is determined by titrating against 10 or 20 c.c. of the
+standard solution of sulphuric acid (100 c.c. = 1 gram H_{2}SO_{4}). The
+finishing point is reached as soon as the solution becomes turbid from
+precipitated cupric hydrate. At first, as each drop falls into the acid
+solution, the ammonia and cupric hydrate combine with the free acid to
+form ammonic and cupric sulphates; but as soon as the free acid is used
+up, the ammonia in the next drop not only precipitates an equivalent of
+cupric hydrate from the solution, but also throws down that carried by
+itself. This method is applicable in the presence of metallic sulphates
+_other than ferric_. The standardising and titration should be made
+under the same conditions. Since sulphuric acid and sulphates are
+predominant in waters of this kind, it is most convenient to report the
+acidity of the water as equivalent to so much sulphuric acid.
+
+~Dissolved Oxygen.~--For the gasometric method of analysing for
+dissolved oxygen, and for the Schützenberger's volumetric method, the
+student is referred to Sutton's "Volumetric Analysis." The following is
+an easy method of estimating the free oxygen in a water:--Take 20 c.c.
+of a stannous chloride solution (about 20 grams of the salt with 10 c.c.
+of hydrochloric acid to the litre); add 10 c.c. of hydrochloric acid,
+and titrate in an atmosphere of carbon dioxide with standard
+permanganate of potassium solution (made by dissolving 1.975 gram of the
+salt in 1 litre of water: 1 c.c. equals 0.5 milligram of oxygen). A
+similar titration is made with the addition of 100 c.c. of the water to
+be tested. Less permanganate will be required in the second titration,
+according to the amount of oxygen in the water; and the difference,
+multiplied by 0.5, will give the weight of the oxygen in milligrams.
+Small quantities of nitrates do not interfere.
+
+In REPORTING the results of the analysis, it is customary to combine the
+acids and bases found on some such principle as the following:--The
+sulphuric oxide is calculated as combined with the potash, and reported
+as potassic sulphate (K_{2}SO_{4}); the balance of the sulphuric oxide
+is then apportioned to the soda, and reported as sulphate of soda
+(Na_{2}SO_{4}); if any is still left, it is reported as calcium sulphate
+(CaSO_{4}), and after that as magnesic sulphate (MgSO_{4}). When the
+sulphuric oxide has been satisfied, the chlorine is distributed, taking
+the bases in the same order, then the nitric pentoxide, and lastly the
+carbon dioxide. But any method for thus combining the bases and acids
+must be arbitrary and inaccurate. It is extremely improbable that any
+simple statement can represent the manner in which the bases and acids
+are distributed whilst in solution; and, since different chemists are
+not agreed as to any one system, it is better to give up the attempt,
+and simply state the results of the analysis. This has only one
+inconvenience. The bases are represented as oxides; and, since some of
+them are present as chlorides, the sum total of the analysis will be in
+excess of the actual amount present by the weight of the oxygen
+equivalent to the chlorine present as chloride. The following is an
+example of such a statement:--
+
+                                                Parts per 100,000.
+  Total solids, dried at 100° C.                      28.73
+  Chlorine                                             1.70
+  Nitrogen as nitrate                                  0.03
+  Ammonia                                              0.001
+  Albuminoid ammonia                                   0.004
+  "Oxygen consumed" in 4 hours                         0.01
+
+The solids were made up as under:--
+
+                                            Per 100,000 of the Water.
+  Potash                                               0.38
+  Soda                                                 2.01
+  Magnesia                                             1.44
+  Lime                                                10.55
+  Ferric oxide                                         0.01
+  Silica                                               0.30
+  Sulphuric oxide                                      3.69
+  Nitrogen pentoxide                                   0.11
+  Carbon dioxide                                       8.38
+  Chlorine                                             1.70
+  Volatile and organic matter                          0.66
+                                                      -----
+                                                      29.23
+  Less oxygen equivalent to chlorine found             0.39
+                                                      -----
+                                                      28.84
+
+For the preparation of distilled water, the apparatus shown in fig. 64
+is convenient for laboratory use. It consists of a copper retort heated
+by a ring gas-burner, and connected with a worm-condenser.
+
+[Illustration: FIG. 64]
+
+
+PRACTICAL EXERCISE.
+
+A mineral, on analysis, gave the following results:--Water, 44.94 per
+cent.; sulphuric oxide, 28.72 per cent.; ferrous iron, 13.92 per cent.;
+ferric iron, 0.35 per cent.; copper, 6.1 per cent. The mineral was
+soluble in water, and showed nothing else on testing. How would you
+report the analysis? Calculate the formula for the salt.
+
+
+THE HALOGENS.
+
+There is a group of closely allied elements to which the name halogen
+(salt-producer) has been given. It comprises chlorine, bromine, iodine,
+and fluorine. These elements combine directly with metals, forming as
+many series of salts (chlorides, bromides, iodides, and fluorides),
+corresponding to the respective oxides, but differing in their formulę
+by having two atoms of the halogen in the place of one atom of oxygen.
+For example, ferrous oxide is FeO and ferrous chloride is FeCl_{2}, and,
+again, ferric oxide is Fe_{2}O_{3}, whilst ferric chloride is
+Fe_{2}Cl_{6}. These salts differ from the carbonates, nitrates, &c., in
+containing no oxygen. Consequently, it is incorrect to speak of such
+compounds as chloride of potash, fluoride of lime, &c., since potash and
+lime are oxides. It is important to bear this in mind in reporting
+analyses in which determinations have been made, say, of chlorine,
+magnesia, and potash, or of fluorine, silica, and alumina. It is
+necessary in all such cases to deduct from the total an amount of oxygen
+equivalent to the halogen found, except, of course, where the base has
+been determined and recorded as metal. Compounds containing oxides and
+fluorides, &c., do not lend themselves to the method of determining the
+halogen by difference. For example, topaz, which, according to Dana, has
+the formula Al_{2}SiO_{4}F_{2}, would yield in the ordinary course of
+analysis--
+
+  Alumina          55.4%
+  Silica           32.6
+  Fluorine         20.6
+                  -----
+                  108.6
+
+The oxygen equivalent to 20.6 per cent. fluorine may be found by
+multiplying the percentage of fluorine by 0.421; it is 8.7 per cent.,
+and must be deducted. The analysis would then be reported thus:--
+
+  Alumina                                 55.4%
+  Silica                                  32.6
+  Fluorine                                20.6
+                                         -----
+                                         108.6
+  Less oxygen equivalent to fluorine       8.7
+                                         -----
+                                          99.9
+
+Take as an illustration the following actual analysis by F.W. Clarke and
+J.S. Diller:--
+
+  Alumina                     57.38%
+  Silica                      31.92
+  Fluorine                    16.99
+  Potash                       0.15
+  Soda                         1.33
+  Water                        0.20
+                             ------
+                             107.97
+  Deduct oxygen equivalent     7.16
+                             ------
+                             100.81
+
+In calculating the factor for the "oxygen equivalent," divide the weight
+of one atom of oxygen (16) by the weight of two atoms of the halogen;
+for example, with chlorine it would be 16/71 or 0.2253; with bromine,
+16/160 or 0.1000; with iodine, 16/254 or 0.063; and with fluorine, 16/38
+or 0.421.
+
+
+CHLORINE AND CHLORIDES.
+
+Chlorine occurs in nature chiefly combined with sodium, as halite or
+rock salt (NaCl). With potassium it forms sylvine (KCl), and, together
+with magnesium, carnallite (KCl.MgCl_{2}.6H_{2}O). Of the metalliferous
+minerals containing chlorine, kerargyrite, or horn silver (AgCl), and
+atacamite, an oxychloride of copper (CuCl_{2}.3Cu(HO)_{2}.) are the most
+important. Apatite (phosphate of lime) and pyromorphite (phosphate of
+lead) contain a considerable amount of it. Chlorine is a gas of a
+greenish colour, possessing a characteristic odour, and moderately
+soluble in water. It does not occur native, and is generally prepared by
+the action of an oxidising agent on hydrochloric acid. It combines
+directly with metals at the ordinary temperature (even with platinum and
+gold), forming chlorides, which (except in the case of silver) are
+soluble.
+
+It is important in metallurgy, because of the extensive use of it in
+extracting gold by "chloridising" processes. It is also used in refining
+gold.
+
+~Detection.~--Compounds containing the oxides of chlorine are not found
+in nature, because of the readiness with which they lose oxygen. By
+reduction they yield a chloride; the form in which chlorine is met with
+in minerals. In testing, the compound supposed to contain a chloride is
+boiled with water, or, in some cases, dilute nitric acid. To the clear
+solution containing nitric acid a few drops of nitrate of silver
+solution are added. If, on shaking, a white curdy precipitate, soluble
+in ammonia, separates out, it is sufficiently satisfactory evidence of
+the presence of chlorides.
+
+~Solution and Separation.~--The chlorides are generally soluble in
+water, and are got into solution by extracting with warm dilute nitric
+acid. Or, if insoluble, the substance is fused with carbonate of soda,
+extracted with water, and the filtrate acidified with nitric acid. For
+the determination, it is not necessary to obtain the solution of the
+chloride free from other acids or metals. If tin, antimony, mercury, or
+platinum is present, it is best to separate by means of sulphuretted
+hydrogen. The chloride is determined in the solution after removal of
+the excess of the gas. Where traces of chlorides are being looked for, a
+blank experiment is made to determine the quantity introduced with the
+reagents. One hundred c.c. of ordinary water contains from 1 to 3
+milligrams of chlorine. On the addition of nitrate of silver to the
+nitric acid solution, chloride of silver separates out. This is free
+from other substances, except, perhaps, bromide and iodide.
+
+
+GRAVIMETRIC DETERMINATION.
+
+Freely mix the solution containing the chloride with dilute nitric acid,
+filter (if necessary), and treat with nitrate of silver. Heat nearly to
+boiling, and, when the precipitate has settled, filter, and wash with
+hot distilled water. Dry, and transfer to a weighed Berlin crucible.
+Burn the filter-paper separately, and convert any reduced silver into
+chloride by alternate treatment with drops of nitric and of hydrochloric
+acid. Add the main portion to this, and heat cautiously till the edges
+of the mass show signs of fusing (about 260°). Cool in the desiccator
+and weigh. The substance is chloride of silver (AgCl), and contains
+24.73 per cent. of chlorine.
+
+The precipitated chloride is filtered and washed as soon as possible
+after settling, since on exposure to light it becomes purple, and loses
+a small amount of chlorine.
+
+
+VOLUMETRIC METHOD.
+
+There are several volumetric methods; but that based on the
+precipitation of silver chloride in neutral solution, by means of a
+standard solution of silver nitrate (using potassium chromate as
+indicator), is preferred. Silver chromate is a red-coloured salt; and,
+when silver nitrate is added to a solution containing both chloride and
+chromate, the development of the red colour marks off sharply the point
+at which the chloride is used up. Silver chromate is decomposed and
+consequently decolorised by solution of any chloride. The solution for
+this method must be neutral, since free acid prevents the formation of
+the red silver chromate. If not already neutral, it is neutralised by
+titrating cautiously with a solution of soda. In a neutral solution,
+other substances (such as phosphates and arsenates) also yield a
+precipitate with a solution of nitrate of silver; and will count as
+chloride if they are not removed.
+
+_The Standard Solution of Nitrate of Silver_ is made by dissolving 23.94
+grams of the salt (AgNO_{3}) in distilled water, and diluting to 1
+litre; 100 c.c. are equal to 0.5 gram of chlorine.
+
+The _indicator_ is made by adding silver nitrate to a strong neutral
+solution of yellow chromate of potash (K_{2}CrO_{4}), till a permanent
+red precipitate is formed. The solution is allowed to settle, and the
+clear liquid decanted into a stoppered bottle labelled "chromate
+indicator for chlorine."
+
+Standardise the silver nitrate by weighing up 0.5 gram of pure sodium
+chloride (or potassium chloride). Transfer to a flask and dissolve in
+distilled water; dilute to 100 c.c. Fill an ordinary burette with the
+standard silver solution, and (after adjusting) run into the flask a
+quantity sufficient to throw down the greater part of the chlorine. Add
+a few drops of the chromate indicator and continue the addition of the
+silver nitrate until the yellow colour of the solution becomes
+permanently tinted red, after shaking. This shows that the chlorine is
+all precipitated, and that the chromate is beginning to come down. The
+further addition of a couple of drops of the silver solution will cause
+a marked difference in the tint. Read off the quantity run in, and
+calculate the standard. One gram of sodium chloride contains 0.6062 gram
+of chlorine; and 1 gram of potassium chloride contains 0.4754 gram.
+
+For the determination of small quantities of chloride (a few
+milligrams), the same method is used; but the standard solution is
+diluted so that each c.c. is equal to 1 milligram of chlorine; and the
+chromate indicator is added before titrating. The standard solution is
+made by measuring off 200 c.c. of the solution described above, and
+diluting with distilled water to 1 litre.
+
+
+BROMINE AND BROMIDES.
+
+Bromine closely resembles chlorine in the nature of its compounds. It
+does not occur free in nature, but is occasionally found in combination
+with silver as bromargyrite (AgBr) and, together with chloride, in
+embolite. It mainly occurs as alkaline bromides in certain natural
+waters. Nearly all the bromine of commerce is derived from the mother
+liquors of salt-works--_i.e._, the liquors from which the common salt
+has been crystallised out. Bromine combines directly with the metals,
+forming a series of salts--the bromides. In ordinary work they are
+separated with, and (except when specially tested for) counted as,
+chlorides. They are detected by adding chlorine water to the suspected
+solution and shaking up with carbon bisulphide. Bromine colours the
+latter brown.
+
+
+IODINE AND IODIDES.
+
+Iodine does not occur in nature in the free state; and iodides are rare,
+iodargyrite or iodide of silver (AgI) being the only one which ranks as
+a mineral species. Iodates are found associated with Chili saltpetre,
+which is an important source of the element.
+
+Iodine and Iodides are largely used in the laboratory, and have already
+been frequently referred to. It is used as an oxidising agent in a
+similar manner as permanganate and bichromate of potash, especially in
+the determinations of copper, arsenic, antimony, and manganese.
+
+Iodine is not readily soluble in water; but dissolves easily in a
+concentrated solution of potassium iodide. Its solutions are strongly
+coloured; a drop of a dilute solution colours a large volume of water
+decidedly yellow; on the addition of starch paste, this becomes blue.
+The delicacy of this reaction is taken advantage of in titrations to
+determine when free iodine is present. The blue colour may be
+alternately developed and removed by the addition of iodine (or an
+oxidising agent) and hyposulphite of soda (or some other reducing
+agent). In decolorising, the solution changes from blue or black to
+colourless or pale yellow according to circumstances. Sometimes the
+solution, instead of remaining colourless, gradually develops a blue
+which recurs in spite of the further addition of the reducing agent. In
+these cases the conditions of the assay have been departed from, or (and
+this is more often the case) there is some substance present capable of
+liberating iodine.
+
+Iodine forms a series of salts--the iodides--resembling in many respects
+the chlorides. These can be obtained by direct combination of the metals
+with iodine.
+
+~Detection.~--Free iodine is best recognised by the violet vapours
+evolved from the solution on heating, and by the blue or black colour
+which it strikes on the addition of starch paste. Iodides are detected
+by boiling with strong solutions of ferric sulphate or chloride. Iodine
+is liberated, distilled over, and collected. Chlorine also liberates
+iodine from iodides; and this reaction is frequently made use of in
+assaying. A process based on this is described under _Manganese_. All
+substances which liberate chlorine on boiling with hydrochloric acid
+(dioxides, bichromates, permanganates, &c.) are determined in a similar
+way.
+
+~Solution and Separation.~--Most iodides are soluble in water or dilute
+acids. The separation is effected by distilling the substance with
+solution of ferric sulphate, and collecting the vapour in a dilute
+solution of sulphurous acid or arsenite of soda. On the completion of
+the distillation, the iodine will be in the distillate as iodide; and
+the gravimetric determination is made on this.
+
+
+GRAVIMETRIC DETERMINATION.
+
+To the solution containing the iodine, as iodide, and which is free from
+chlorides (and bromides), add a little dilute nitric acid and nitrate of
+silver till no further precipitate is produced. Filter off, wash with
+hot water, and dry. Clean the filter-paper as much as possible, and burn
+it. Collect the ash in a weighed porcelain crucible, add the main
+portion, and heat to incipient fusion; cool, and weigh. The substance is
+silver iodide, and contains 54.03 per cent. of iodine.
+
+
+VOLUMETRIC METHOD.
+
+This is for the titration of free iodine, and is practically that which
+is described under _Manganese_. The substance to be determined is
+distilled with ferric sulphate, and the iodine is collected in a
+solution of potassium iodide, in which it readily dissolves. If flaky
+crystals separate out in the receiver, more potassium iodide crystals
+are added. When the distillation is finished, the receiver is
+disconnected, and its contents washed out into a beaker and titrated
+with "hypo." The standard solution of "hypo" is made by dissolving 19.58
+grams of hyposulphite of soda (Na_{2}S_{2}O_{3}.5H_{2}O) in water and
+diluting to 1 litre; 100 c.c. are equal to 1 gram of iodine. To
+standardise the solution, weigh up 0.25 gram of pure iodine in a small
+beaker. Add 2 or 3 crystals of potassium iodide; cover with water; and,
+when dissolved, dilute to 50 or 100 c.c. Titrate, and calculate the
+standard.
+
+
+FLUORINE AND FLUORIDES.
+
+Fluorine is frequently met with as calcium fluoride or fluor-spar
+(CaF_{2}). It occurs less abundantly as cryolite (Na_{3}AlF_{6}), a
+fluoride of aluminium and sodium, which is used in glass-making. Certain
+other rarer fluorides are occasionally met with. Fluorine is also found
+in apatite, and in some silicates, such as topaz, tourmaline, micas, &c.
+
+Hydrofluoric acid is used for etching glass and opening up silicates. It
+attacks silica, forming fluoride of silicon (SiF_{4}), which is
+volatile. Silica is by this means eliminated from other oxides, which,
+in the presence of sulphuric acid, are fixed. The commercial acid is
+seldom pure, and generally weak; and the acid itself is dangerously
+obnoxious. The use of ammonium fluoride (or sodium fluoride) and a
+mineral acid is more convenient. Determinations of this kind are made in
+platinum dishes enclosed in lead or copper vessels in a well-ventilated
+place. Fluor-spar is useful as a flux in dry assaying; it renders slags,
+which would otherwise be pasty, quite fluid. Fluorides generally are
+fusible, and impart fusibility to substances with which they form weak
+compounds. Their fluxing action does not depend on the removal of
+silicon as fluoride.
+
+~Detection.~--Fluorides in small quantity are easily overlooked unless
+specially sought for. In larger amounts they are recognised by the
+property hydrofluoric acid has of etching glass. A watch-glass is
+warmed, and a layer of wax is melted over the convex side. When cold,
+some lines are engraved on the waxed surface with any sharp-pointed
+instrument. The substance to be tested is powdered; and moistened, in a
+platinum dish, with sulphuric acid. The watch-glass is filled with cold
+water and supported over the dish. The dish is then carefully warmed,
+but not sufficiently to melt the wax. After a minute or two, the glass
+is taken off, and the wax removed. If the substance contained fluorine,
+the characters will be found permanently etched on the glass. An equally
+good, but more rapid, test is to mix the powdered substance with some
+silica, and to heat the mixture in a test tube with sulphuric acid.
+Silicon fluoride is evolved, and, if a moistened glass rod is held in
+the tube, it becomes coated with a white deposit of silica, formed by
+the decomposition of the silicon fluoride by the water. This is also
+used as a test for silica; but in this case the substance is mixed with
+a fluoride, and the experiment must obviously be carried out in a
+platinum vessel.
+
+~Separation and Determination.~--The determination of fluorine is
+difficult. In the case of fluorides free from silicates (such as
+fluor-spar), it is determined indirectly by decomposing a weighed
+portion with sulphuric acid, evaporating, igniting, and weighing the
+residual sulphate. The increase in weight multiplied by 0.655 gives the
+weight of fluorine.
+
+In the presence of silica this method does not answer, because of the
+volatilisation of silicon fluoride. In these cases Wöhler adopted the
+following plan, which resembles that for the indirect determination of
+carbon dioxide. Mix the weighed substance in a small flask with powdered
+silica and sulphuric acid. The mouth of the flask is closed with a cork
+carrying a tube which is filled, the first half with calcium chloride
+and the second half with pumice coated with dried copper sulphate. The
+apparatus is weighed quickly, and then warmed till decomposition is
+complete. A current of dry air is aspirated for a minute or two; and the
+apparatus again weighed. The loss in weight gives that of the silicon
+fluoride (SiF_{4}), which, multiplied by 0.7307, gives the weight of
+fluorine.
+
+Fresenius uses the same reaction; but collects and weighs the silicon
+fluoride. The finely powdered and dried substance is mixed with ten or
+fifteen times its weight of ignited and powdered silica. The mixture is
+introduced into a small dry flask connected on one side with a series of
+drying-tubes, and on the other with an empty tube (to condense any
+sulphuric acid). To this last is joined a drying-tube containing
+chloride of calcium and anhydrous copper sulphate. This is directly
+connected with a series of three weighed tubes in which the fluoride of
+silicon is collected. The last of these is joined to another
+drying-tube. The first weighed tube contains pumice and cotton wool,
+moistened with water; the second tube contains soda-lime as well as (in
+the upper half of the second limb) fused calcium chloride between plugs
+of wool; the third tube is filled half with soda-lime and half with
+fused calcium chloride. The distilling-flask containing the substance
+mixed with silica is charged with 40 or 50 c.c. of sulphuric acid, and
+placed on the hot plate. Alongside it is placed a similar dry flask
+containing a thermometer, and the temperature in this is kept at 150° or
+160° C. A current of air is sent through the tubes during the operation,
+which takes from one to three hours for from 0.1 to 1 gram of the
+substance. A correction is made by deducting 0.001 gram for every hour
+the dried air has been passed through. The increase in weight of the
+three tubes gives the weight of the silicon fluoride.
+
+Penfield uses a similar arrangement, but passes his silicon fluoride
+into an alcoholic solution of potassium chloride. Silica and potassium
+silico-fluoride are precipitated, and hydrochloric acid is set
+free.[100] The acid thus liberated is titrated, with a standard solution
+of alkali, in the alcoholic solution, and from the amount of free acid
+found the fluorine is calculated. The weight of hydrochloric acid (HCl)
+found, multiplied by 1.562, gives the weight of the fluorine. With this
+method of working, fewer ~U~-tubes are required. The exit tube from the
+flask is bent so as to form a small ~V~, which is kept cool in water;
+this is directly connected with the ~U~-tube containing the alcoholic
+solution of potassium chloride. The flask with the assay is heated for
+about two hours, and a current of dry air is aspirated throughout the
+determination. Fluoride of silicon is a gas not easily condensed to a
+liquid: but is immediately decomposed by water or moist air.
+
+FOOTNOTES:
+
+[95] This will require two or three hours to thoroughly complete. It is
+best to powder the oxide first produced, and recalcine.
+
+[96] No magnetic oxide was formed.
+
+[97] For example:--
+
+CaO + 2HCl = CaCl_{2} + H_{2}O.
+
+PbO + H_{2}SO_{4} = PbSO_{4} + H_{2}O.
+
+MgO + 2HNO_{3} = Mg(NO_{3})_{2} + H_{2}O.
+
+Al_{2}O_{3} + 6HCl = Al_{2}Cl_{6} + 3H_{2}O.
+
+Fe_{2}O_{3} + 3H_{2}SO_{4} = Fe_{2}(SO_{4})_{3} + 3H_{2}O.
+
+[98] Fe_{2}O_{3}: 2FeO:: 0.2877: 0.2589.
+
+[99] 100 c.c. contain 1 gram of sulphuric acid.
+
+[100] 3SiF_{4} + 4KCl + 2H_{2}O = 2K_{2}SiF_{6} + SiO_{2} + 4HCl.
+
+
+
+
+CHAPTER XVI.
+
+SULPHUR AND SULPHATES.
+
+
+Sulphur occurs native in volcanic districts, and is mined in Sicily,
+Italy, and California in considerable quantities. Combined with metals
+(sulphides), it is common in all mineral districts. Iron pyrites
+(FeS_{2}) is the most abundant source of this element. Sulphates, such
+as gypsum, are fairly common, but have no value so far as the sulphur in
+them is concerned. In coal it exists as an impurity, occurring partly as
+a constituent of organic compounds.
+
+Sulphur, whether free or combined with metals, forms, on burning,
+sulphurous oxide (SO_{2}), which by the action of oxidising agents and
+water is converted into sulphuric acid. It forms two oxides, sulphurous
+(SO_{2}) and sulphuric (SO_{3}), which combine with bases to form
+sulphites and sulphates. Sulphites are of little importance to the
+assayer, and are converted into sulphates by the action of nitric acid
+and other oxidising agents.
+
+The native sulphides, when acted on with hydrochloric acid, give off
+sulphuretted hydrogen; with nitric acid or aqua regia, sulphates are
+formed, and more or less sulphur separated.
+
+Sulphur is detected in sulphides by the irritating odour of sulphurous
+oxide given off on roasting, by the evolution of sulphuretted hydrogen
+when treated with hydrochloric acid, or by a white precipitate of barium
+sulphate formed when barium chloride is added to the aqua regia
+solution.
+
+~Dry Assay.~--There is no method of general application. Free or native
+sulphur may be volatilised, condensed, and weighed, but pyrites only
+gives up a portion of its sulphur when heated in a closed vessel, while
+most sulphides, and all sulphates, give up none at all.
+
+In the determination of sulphur in brimstone, 10 grams of the substance
+are taken, placed in a small porcelain dish, heated over a Bunsen burner
+in a well-ventilated place, and ignited. When the sulphur has been
+completely burnt off, the residue (which consists chiefly of sand) is
+collected and weighed. In a separate portion the moisture and arsenic
+are determined; the amounts of these are deducted from the loss in the
+first experiment. The difference, multiplied by 10, gives the percentage
+of sulphur.
+
+
+WET METHODS.
+
+~Solution.~--All sulphates, excepting those of lead, barium, strontium,
+and lime, are soluble in water or dilute acid. All sulphides, except
+cinnabar, are converted into sulphates by the action of nitric acid at a
+gentle heat; or, better, by the action of a mixture of three volumes of
+nitric acid and one volume of hydrochloric acid. This last attacks
+cinnabar as well. With most substances it is difficult to convert the
+whole of the sulphur into sulphuric acid. The sulphur separates out at
+first as a dark spongy mass, which (on continued treatment) changes to
+light-coloured flakes. When the solution becomes concentrated and the
+temperature rises sufficiently, the sulphur fuses into one or more
+honey-coloured globules which, owing to the small surface they oppose to
+the acid, are very slowly oxidised. It is not desirable to assist the
+formation of these globules; therefore, the temperature is kept as low
+as possible, and strong nitric acid is used. When such globules form, it
+is best to allow the solution to cool, when the globules will solidify.
+They can then be filtered off and picked out from the insoluble residue,
+dried, weighed, ignited, and again weighed, the loss being counted as
+sulphur. With iron pyrites this difficulty seldom occurs.
+
+Metallic sulphides when fused with an excess of nitre are completely
+oxidised. If the ore is rich in sulphur, some inert body (such as sodium
+chloride, or, better, sodium carbonate) is added to dilute the action.
+With pure sulphur, the action is so energetic as to cause an explosion,
+so that care should be taken. With burnt ores (incompletely calcined
+pyrites), there is sufficient oxide of iron present to prevent too rapid
+action.
+
+These fusions with nitre are best conducted in a platinum dish covered
+with a piece of platinum foil. The ore is ground with the nitre to
+ensure complete mixing. The heat need not be excessive, so that a single
+Bunsen burner placed beneath the dish will suffice; if the bottom of the
+dish is seen to be red-hot, it is sufficient. On cooling and extracting
+with water, the sulphur will pass into solution as potassium sulphate,
+which is then filtered off from the insoluble oxides of iron, copper,
+&c. The filtrate, after having been treated with a large excess of
+hydrochloric acid, evaporated to dryness, and re-dissolved in water, is
+ready for the determination.
+
+Lead sulphate may be dissolved by boiling with ammonium acetate. The
+insoluble sulphates of barium, strontium, and lime, are decomposed by
+fusing with 4 or 5 times their weight of "fusion mixture." The alkaline
+sulphates are then dissolved out with water, and filtered off from the
+insoluble residue. The filtrate is rendered acid with hydrochloric acid.
+
+~Separation.~--The determination of the sulphuric acid in these
+solutions by precipitation with barium chloride also serves as a
+separation; but in hot acid solutions containing copper, and more
+especially iron salts, the baric sulphate has a strong tendency to carry
+down amounts of those bodies, varying, no doubt, with the conditions of
+the precipitation. Boiling hydrochloric acid fails to completely extract
+them. Moreover, the use of hot concentrated hydrochloric acid causes a
+loss by dissolving barium sulphate. Nitric acid and nitrates must be
+decomposed by prolonged boiling and evaporation with hydrochloric acid.
+The iron may be removed by adding a slight excess of ammonia to the
+faintly acid solution, filtering off, and washing the precipitated
+ferric hydrate with hot water. By slightly acidulating the filtrate with
+hydrochloric acid, it will be rendered ready for the determination.
+
+
+GRAVIMETRIC METHOD.
+
+This assay is one of those which strikingly shows the necessity of
+getting the assay solution under proper conditions, in order to obtain
+satisfactory results. The method has been repeatedly investigated, and
+the conclusion arrived at, "that it can be correct only by accident."
+Yet there are many chemists who get good results, and place considerable
+faith in its accuracy. This can only be due to differences in the manner
+of working. It is generally understood that nitric acid or nitrates must
+be absent; and our experience fully confirms this. Precipitations in
+nitrate solutions are worthless, as the following experiments show. In
+each experiment the bulk of the solution was 150 c.c. The solutions
+contained 10 grams of nitre, were freely acid with hydrochloric acid,
+and were precipitated (while boiling) with slight excess of baric
+chloride.
+
+  Sulphuric acid taken  0.020 gram  0.050 gram  0.100 gram
+     "           found  0.019   "   0.047   "   0.098   "
+     "           taken  0.500   "   1.004   "   1.000   "
+     "           found  0.526   "   1.126   "   1.126   "
+
+All the precipitates were boiled with hydrochloric acid, and thoroughly
+washed before weighing. The results of some other experiments on this
+subject are given under "sulphur" in the "examination of commercial
+copper," page 207.
+
+The solution having been obtained free from nitrates and chlorates (and
+containing but little free hydrochloric acid), is largely diluted,
+heated to boiling, and precipitated with a moderate excess of a solution
+of chloride of barium (8 parts of the crystallized barium chloride are
+sufficient for 1 of sulphur). It is allowed to settle for half-an-hour,
+and then decanted through a filter. The precipitate is shaken up with
+boiling water, rendered slightly acid, filtered, washed, dried, ignited,
+and weighed. The ignited precipitate, when pure, is white, and is not
+decomposed at a red heat; it is barium sulphate (BaSO_{4}), and contains
+13.73 per cent. of sulphur, or 34.33 per cent. of sulphuric oxide
+(SO_{3}).
+
+~Determination of Sulphur in Pyrites.~--Weigh up half a gram of the
+dried and powdered sample, and treat with 10 c.c. of a mixture of 3
+volumes of nitric acid and 1 volume of hydrochloric acid, occasionally
+heating. Evaporate to dryness, treat with 5 c.c. of hydrochloric acid,
+and again evaporate; take up with 1 c.c. of hydrochloric acid and 100
+c.c. of hot water, filter through a small filter, and wash. The residue
+may contain sulphates of lead, barium, or lime; it must be separately
+examined, if the total sulphur is wanted. The filtrate is heated, and
+rendered slightly alkaline with ammonia. Filter off the precipitated
+ferric hydrate through a quick filter, and wash with hot water. If
+necessary, evaporate the bulk to about 200 c.c., render faintly acid
+with hydrochloric acid, and add 20 c.c. of solution of barium chloride;
+allow to stand for half-an-hour, and decant through a filter. Wash with
+hot water, dry, ignite, and weigh. Pure pyrites contains 53.33 per cent.
+of sulphur.
+
+
+VOLUMETRIC METHOD.
+
+This is based upon the easy conversion of all sulphur compounds into
+sulphates by fusion with nitre or by oxidation with nitric acid; and on
+the determination of the sulphate formed by titration in an acetic acid
+solution with baric chloride.[101] The finishing point is determined by
+filtering off portions of the assay solution, and testing with sulphuric
+acid. A slight excess of baric chloride will cause a precipitate.
+
+The process may be divided into--(1) the preparation of the solution,
+and (2) the titration.
+
+~Preparation of the Solution.~--Weigh up from 1 to 5 grams of the dried
+and powdered substance, and mix intimately with 4 grams of powdered
+nitre; clean out the mortar with another gram of nitre, and add this as
+a cover. Heat in a platinum crucible for fifteen minutes at a low
+temperature; cool, and extract with water in an evaporating-dish about
+9 inches across, and holding 700 or 800 c.c. Add 10 grams of sodium
+acetate and 10 c.c. of acetic acid, and dilute to half a litre. Boil.
+The solution is ready for titrating. Substances which lose sulphur on
+heating (such as pyrites) are thus treated:--Weigh up 1 gram, and
+evaporate nearly to dryness with 10 c.c. each of nitric and hydrochloric
+acids. Take up with 10 c.c. of hydrochloric acid, and again boil down to
+a small bulk; dilute and transfer to a 9-inch evaporating-dish; add 10
+grams of sodium acetate and 5 c.c. of acetic acid, dilute to half a
+litre, and boil. The solution is ready for titrating. Sulphates may be
+dissolved up in the dish itself with the help of a c.c. or so of
+hydrochloric acid; sodium acetate and acetic acid are then added; and,
+after dilution and boiling, the solutions are at once titrated.
+
+The solution before titration must contain no free mineral acid, but 5
+or 10 c.c. of acetic acid should be present. It must contain 10 grams of
+sodium acetate, or sufficient to convert any free mineral acid into its
+corresponding sodic salt; or, if chlorides, nitrates or sulphates of the
+metals are present, sufficient to decompose them. If a precipitation
+occurs, as is the case with ferric salts, &c., the solution is titrated
+with the precipitate in it.
+
+~The Titration.~--_The standard solution of barium chloride_ is made by
+dissolving 76.25 grams of the crystallized salt (BaCl_{2}.2H_{2}O) in
+distilled water, and diluting to 1 litre. 100 c.c. will equal 1 gram of
+sulphur. As indicator, use dilute sulphuric acid. The strength of the
+solution may be checked by the titration of 5 grams of ferrous sulphate
+(oxidized with permanganate of potassium or a few drops of nitric acid),
+which should require 57.5 c.c. of the barium chloride solution; or any
+pure sulphate of known composition can be used; anhydrous salts should
+be preferred.
+
+[Illustration: FIG. 65.]
+
+Fill an ordinary 100 c.c. burette with the solution of barium chloride.
+The evaporating dish containing the assay solution is placed on a round
+burner (as shown in fig. 65), and the solution is kept steadily boiling.
+An ordinary Bunsen-burner flame will cause bumping, and should not be
+used. Run in the standard solution in quantity known to be
+insufficient; then withdraw a portion of about 2 c.c., with a pipette,
+and filter through a fine filter-paper into a test tube. Run in another
+0.5 c.c. of the standard solution, and withdraw and filter into a test
+tube another portion of 2 c.c.; and continue this operation until
+half-a-dozen or more portions have been drawn off. The test tubes should
+be arranged in order in a stand resting on a piece of paper, so that
+each test tube representing 0.5 c.c. of the standard baric chloride may
+have its value recorded beneath it (fig. 66). Add to each test tube 3
+drops of dilute sulphuric acid; that which shows the first appearance of
+a precipitate marks the point at which the titration is complete.
+Suppose, for example, that the test tube marked 48.5 c.c. shows no
+precipitate, while that at 49.0 c.c. shows one, it is evident that the
+finishing point lies between these readings. With a little practice, one
+can judge from the appearance of the precipitate in the 49 c.c. tube,
+whether 1/4 c.c. should be deducted or not.
+
+[Illustration: FIG. 66.]
+
+It is better to add dilute sulphuric acid, and to watch for the
+appearance of a precipitate in the test tube, than to add baric chloride
+and to look for its non-appearance; besides, baric chloride is much less
+likely to be present in a test tube as impurity than sulphates are. In
+this way the chance of error from what are termed "accidental causes" is
+diminished.
+
+The following experiments show the effect of variation in the conditions
+of titration:--
+
+Make _a standard solution of sulphuric acid_ by diluting 43.65 grams of
+sulphuric acid (sp. g. 1.6165) to 1 litre: 100 c.c. will contain 1 gram
+of sulphur. An equivalent solution may be made by dissolving 100.62
+grams of sodium sulphate crystals (Na_{2}SO_{4}.10H_{2}O), or 86.88
+grams of ferrous sulphate (FeSO_{4}.7H_{2}O), in water (oxidising the
+latter), and diluting to 1 litre.
+
+The order in which these experiments are given is that in which they
+were made in an investigation into the conditions under which the
+titration could most accurately be effected.
+
+~Effect of Hydrochloric and Nitric Acids.~--The titrations were
+performed in the manner already described, but sodic acetate and acetic
+acid were absent. Twenty c.c. of the standard solution of sulphuric acid
+were used.
+
+  Hydrochloric acid present     0.0 c.c.  1.0 c.c.  2.0 c.c.  5.0 c.c.
+  "Baric chloride" required    20.0  "   20.0  "   19.7  "   12.5  "
+
+  Nitric acid present           0.0 c.c.  1.0 c.c.  2.0 c.c.  5.0 c.c.
+  "Baric chloride" required    20.0  "   19.5  "   18.0  "   10.0  "
+
+These show clearly the interference of free mineral acids, although very
+dilute hydrochloric acid (1 c.c. in 500 of water) has no effect.
+
+~Effect of Acetic and Citric Acids.~--A similar series of experiments
+with these acids gave the following results:--
+
+  Acetic acid present          0.0 c.c.  5.0 c.c. 50.0 c.c. 100.0 c.c.
+  "Baric chloride" required   20.0  "   20.0  "   20.0  "    20.0  "
+
+  Citric acid present          0   gram  1 gram    5 grams
+  "Baric chloride" required   20.0 c.c. 20.0 c.c. 20.0 c.c.
+
+These acids do not interfere.
+
+~Effect of Sodic Acetate and Acetic Acid.~--In each of these experiments
+5 c.c. of acetic acid was present.
+
+  Sodium acetate added         0 gram    1 gram    10 grams   50 grams
+  "Baric chloride" required   20.0 c.c. 20.0 c.c.  20.0 c.c.  20.0 c.c.
+
+As sodic acetate and acetic acid did not interfere, it became desirable
+to make some experiments on the _finishing point_. The first object
+sought for was the smallest amount of the standard baric chloride in 500
+c.c. of water, required to give an indication when tested in the manner
+already described.
+
+                                                    Baric Chloride
+         Conditions of Assay Solution.                required.
+
+  Water only                                           0.05 c.c.
+  With 10 grams of sodium acetate and 5 c.c. of
+    acetic acid                                        0.05  "
+  The same with 5 grams of nitre                       0.10  "
+  Like the last, but with 5 grams of salt instead of
+    nitre                                              0.10 "
+
+These show that as small an amount of baric chloride solution as is
+equal to only 0.000002 gram of sulphur in the 2 c.c. of solution tested
+yields a decided precipitate on the addition of 3 drops of sulphuric
+acid.
+
+To determine whether the same finishing point is obtained on testing the
+filtered portions in the test tubes with baric chloride as is obtained
+on testing with sulphuric acid, a titration was made with 20 c.c. of
+standard solution of sulphuric acid, together with the usual quantities
+of sodic acetate and acetic acid; and two lots of 2 c.c. each were
+filtered into two sets of test tubes after each addition of the standard
+baric chloride. To one series 3 drops of baric chloride solution were
+added, and to the other 3 drops of sulphuric acid. The results were--
+
+                                 With Dilute          With Baric
+  "Baric Chloride" added.      Sulphuric Acid.    Chloride Solution.
+
+        19.5   c.c.                Clear                Cloudy
+        19.75   "                  Clear                Cloudy
+        20.0    "                  Finished             Finished
+        20.25   "                  Cloudy               Clear
+        20.5    "                  Cloudy               Clear
+
+The two methods of testing give the same result. But this balance is
+disturbed in the presence of much nitre, the indications with baric
+chloride being disturbed by an opalescence for some c.c. beyond the
+finishing point. In solutions containing free hydrochloric or nitric
+acid, a precipitate is obtained with either baric chloride or sulphuric
+acid.
+
+~Effect of Varying Sulphur.~--In these and the subsequent experiments
+the titrations were performed in the presence of 10 grams of sodic
+acetate and 10 c.c. of acetic acid in the manner already described.
+
+  Standard sulphuric
+     acid used        5.0 c.c.  10.0 c.c.  20.0 c.c.  50.0 c.c. 100.0 c.c.
+
+  "Baric chloride"
+    required          5.0  "    10.0  "    20.0  "    50.0  "   100.0  "
+
+~Effect of Varying Temperature.~--With 5 c.c. of standard sulphuric acid
+titrated at 15° C., 5 c.c. of baric chloride were required; but with
+larger quantities the results were altogether unsatisfactory when
+titrated cold.
+
+~Effect of Varying Bulk.~--
+
+  Bulk               100.0 c.c.   200.0 c.c.   500.0 c.c.   1000.0 c.c.
+  "Baric chloride"
+    required          20.0  "      20.0  "      20.0  "       20.5  "
+
+Considerable variation in bulk has no effect, but 500 c.c. is the most
+convenient volume to work with. It is well to occasionally replace the
+water boiled off during titration.
+
+~Effect of Foreign Salts.~--In all these experiments 20 c.c. of
+"sulphuric acid" were used, and the titration was performed in the
+ordinary way.
+
+  _Sodic chloride_ added      0 gram      5 grams    10 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.   19.7 c.c.
+
+  _Ammonic chloride_ added    0 gram      5 grams    10 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.   19.5 c.c.
+
+  _Calcic chloride_ added     0 gram      1 gram     2 grams    5 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.  19.2 c.c.  19.0 c.c.
+
+  _Zinc chloride_ added       0  gram     1 gram     3 grams    5 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.  20.0 c.c.  20.0 c.c.
+
+  _Ferrous chloride_ added    0 gram      1 gram     3 grams    5 grams
+  "Baric chloride" required   20.0 c.c.   19.7 c.c.  19.5 c.c.  19.0 c.c.
+
+  _Ferric chloride_ added     0 gram      1 gram     3 grams    5 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.  20.0 c.c.  20.0 c.c.
+
+  _Copper chloride_ added     0 gram      1 gram     3 grams    5 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.  20.0 c.c.  20.0 c.c.
+
+  _Potassic Nitrate_ added    0 gram      1 gram     5 grams   10 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.  20.0 c.c.  19.0 c.c.
+
+  _Potassic Nitrite_ added    0 gram      1 gram     5 grams
+  "Baric chloride" required   20.0 c.c.   20.0 c.c.  20.0 c.c.
+
+  _Sodic phosphate_ added     0 gram      1 gram
+  "Baric chloride" required   20.0 c.c.   22.5 c.c.
+
+  _Sodic arsenate_ added      0 gram     1 gram
+  "Baric chloride" required   20.0 c.c.  20.5 c.c.
+
+In the absence of ferric salts, phosphates and arsenates count as
+sulphur.
+
+In two series of experiments for determining the effect of varying
+amounts of sulphur in the form of ferrous sulphate, we obtained the
+following results:--In the first series the assay solution was prepared
+in the manner we have described for _Pyrites_; and in the second series,
+by fusion with nitre.
+
+  Sulphur added                    0.050 gram     0.100 gram     0.200 gram
+  "Baric chloride" required (1)    5.0 c.c.      10.0 c.c.      20.0 c.c.
+         "          "       (2)    4.7  "        10.0  "        20.0  "
+
+  Sulphur added                    0.500 gram     1.000 gram
+  "Baric chloride" required (1)   50.0 c.c.     100.0 c.c.
+         "          "       (2)   50.0  "       100.0  "
+
+More than 5 grams of nitre must not be used in an assay; and, since the
+requisite amount of nitre considerably exceeds that sufficient to
+oxidise the sulphur, not more than 0.5 gram of unoxidised sulphur should
+be present in the portion of the sample weighed up for determination.
+When the amount of sulphur present is not known within reasonable
+limits, the test portions may be tried with a drop of baric chloride
+solution instead of sulphuric acid, so that the diminishing quantity of
+precipitate may give warning of an approach to the finishing point.
+
+~Determination of Sulphur in Blende.~--Weigh up 1 gram of dried and
+powdered blende, and mix and fuse with 5 grams of nitre in the manner
+described. Place the dish and its contents in the titrating-dish,
+extract with water, add 10 grams of sodium acetate and 10 c.c. of acetic
+acid, remove and wash the platinum-dish, and dilute to 500 c.c.; boil
+and titrate. In the example, duplicate determinations required (a)
+32.0 c.c., (b) 32.25 c.c., giving an average of 32.1 per cent. of
+sulphur.
+
+~Determination of Sulphur in Chalcopyrite~ (Yellow Copper Ore).--Take 1
+gram of the finely-powdered sample, and 5 grams of nitre. Sprinkle a
+little of the nitre in a small Wedgwood mortar, place the ore on it, and
+cover with 2 or 3 grams more of the nitre. Rub up together, and transfer
+to a small porcelain dish; clean out the mortar with the rest of the
+nitre, and add to the contents of the dish. Cover with a piece of
+platinum foil, and heat gently with a Bunsen burner till the nitre melts
+and the stuff shows signs of deflagrating; remove the heat, and allow
+the action to go on by itself for a minute or so, then heat over the
+Bunsen burner for 10 minutes. Cool; transfer the whole to the
+titrating-dish; boil with 500 c.c. of water; remove the small dish and
+foil; add sodic acetate and acetic acid, and titrate.
+
+For example, 1 gram required 34.5 c.c. of "barium chloride" (standard =
+1.005 gram S), which is equivalent to 34.7 per cent. sulphur. The
+theoretical percentage is 34.8.
+
+~Determination of Sulphur in Chalcocite~ (Grey Copper Ore).--Proceed as
+in the last experiment but, since the action with nitre is more
+moderate, no special precautions need be taken on heating. A platinum
+dish may be used.
+
+An example which was heated for 30 minutes required 20.5 c.c. of the
+barium chloride solution. This is equivalent to 20.6 per cent. of
+sulphur. The theoretical yield is 20.2 per cent.
+
+~Determination of Sulphur in Pyrites.~--Take 1 gram of the
+finely-powdered sample, cover with 10 c.c. of nitric acid, and, when
+action has ceased, evaporate to a small bulk. Add 3 or 4 c.c. of
+hydrochloric acid, and again evaporate to a paste. Take up with 1 or 2
+c.c. of dilute hydrochloric acid, dilute with water, transfer to a
+titrating-dish, add 10 grams of sodic acetate and 5 c.c. of acetic acid,
+and dilute with water to 500 c.c. Boil and titrate.
+
+An example with 1 gram of a pure crystallized pyrites required 52.7 c.c.
+of the barium chloride solution, which is equivalent to 53.0 per cent.
+of sulphur. Theory requires 53.3 per cent. of sulphur.
+
+~Determination of Sulphur in Mispickel.~--Take 1 gram of the powdered
+ore and evaporate with 10 c.c. of nitric acid, and take up with 3 or 4
+c.c. of hydrochloric acid. If any globules of sulphur remain, again
+evaporate with nitric acid. Dilute, and transfer to the titrating-dish.
+Add 10 grams of sodic acetate, dilute with water, boil, and titrate. The
+mispickel carries (according to theory) exactly sufficient iron to
+precipitate the arsenic as ferric arsenate in an acetic acid solution,
+so no more iron need be added. The ferric arsenate will separate out as
+a yellowish-white flocculent precipitate.
+
+An example required, in duplicate experiment, 18.5 c.c. and 18.7 c.c. of
+barium chloride, equivalent to 18.7 per cent. of sulphur. The formula,
+FeS_{2}.FeAs_{2}, requires 19.6 percent., but the sulphur generally
+varies considerably from this amount.
+
+~Determination of Sulphur in Burnt Ores.~--Take 5 grams of the dried and
+powdered ore, and rub up with 4 grams of nitre; transfer to the
+platinum-dish; clean out the mortar with another gram of nitre, and add
+this as a cover. Heat, and extract with water as before; add the sodium
+acetate and acetic acid; and titrate. Burnt ores carry from 2.5 to 5 per
+cent. of sulphur. A series of four determinations gave:--
+
+  "Baric Chloride" Required.  Percentage of Sulphur.  Gravimetric Results.
+           12.6 c.c.                2.52 %                 2.45 %
+           29.9  "                  5.98 "                 5.84 "
+           18.1  "                  3.62 "                 3.53 "
+           22.0  "                  4.40 "                 4.43 "
+
+For ores carrying less than 1 per cent. of sulphur, take 10 grams for
+the assay.
+
+~Determination of Sulphuric Oxide (SO_{3}) in Sulphates.~--When the
+sulphur exists in the sample received by the assayer in an oxidised
+state as sulphate, it is usual to report it in terms of sulphuric oxide
+(SO_{3}). In this case, the metal must also be reported as oxide. For
+example, an analysis of copper sulphate would be thus reported:--
+
+  Oxide of copper (CuO)         31.8 %
+  Sulphuric oxide (SO_{3})      32.1 "
+  Water                         36.1 "
+                               -----
+                               100.0
+
+The percentage of sulphur multiplied by 2.5 gives the percentage of
+sulphuric oxide. Thus a sample of copper sulphate containing 12.85 per
+cent. of sulphur will contain 12.85 × 2.5 or 32.12 per cent. of
+sulphuric oxide.
+
+In minerals and metallurgical products, it is common to find the sulphur
+in both conditions--_i.e._, as sulphate and sulphide. Generally in these
+the percentage of sulphur only is wanted; but this will depend entirely
+on commercial requirements, and not on the fancy of the assayer.
+Soluble sulphates are determined separately by extracting with small
+quantities of cold water, so as to avoid the separation of basic
+sulphates, or, if the sulphides present are not at the same time
+attacked, by dilute hydrochloric acid. Lead sulphate may be extracted by
+boiling with ammonic acetate; whilst barium, strontium, and, perhaps,
+calcium sulphate, will be mainly found in the residue insoluble in
+acids.
+
+Weigh up from 2 to 5 grams of the material according to the amount of
+sulphur judged to be present, and dissolve them in the titrating-dish
+with 1 c.c. of hydrochloric acid and 50 c.c. of water. Add 10 grams of
+sodic acetate, and 10 c.c. of acetic acid; dilute, boil, and titrate. In
+the case of ferric salts, half the quantity of acetic acid will be
+better, as then the ferric iron will be precipitated, and a colourless
+solution will be left, in which the end reaction is more readily
+distinguished.
+
+Determined in this way, 5 gram samples of the following salts gave the
+results indicated below:--
+
+                      "Barium Chloride"
+       Salt.              Required.       Sulphuric Oxide.
+  Copper sulphate         64.25 c.c.         32.12 %
+  Magnesium sulphate      65.25  "           32.62 "
+  Zinc sulphate           56.25  "           28.12 "
+  Ferrous sulphate        58.25  "           29.12 "
+  Sodium sulphate         51.25  "           25.60 "
+
+~Determination of Sulphuric Oxide in Barytes~ (Heavy spar).--Fuse 2
+grams of the powdered mineral with 5 grams of "fusion mixture" for five
+minutes; and, when cold, extract with water. Filter, acidulate the
+filtrate with an excess of 10 c.c. of acetic acid, dilute, boil, and
+titrate. For example, a transparent crystallised sample required 27.0
+c.c. of barium chloride, which is equivalent to 13.6 per cent. of
+sulphur, or 34.0 per cent. of sulphuric oxide. Theory requires 34.3 per
+cent. of the latter. Since both carbonate of soda and potash are liable
+to contain sulphates, a blank determination should be made on 5 grams of
+the "fusion mixture," and the amount found be deducted from that got in
+the assay.
+
+
+PRACTICAL EXERCISES.
+
+1. The price of sulphur in an ore being 4-1/2d. per unit in the
+northern markets, what would be the price of a ton of ore containing 49
+per cent. of sulphur? What would be the effect on the price of an error
+of 0.25 per cent. in the assay?
+
+2. Pyrites carries 50 per cent. of sulphur, and on calcining yields 70
+per cent. of its weight of burnt ore. Supposing the burnt ore carries
+3.5 per cent. of sulphur, what proportion of the sulphur will have been
+removed in the calcining?
+
+3. How would blende compare with pyrites as a source of sulphur for
+sulphuric acid making?
+
+4. How would you determine the percentage of sulphuric oxide in a sample
+of gypsum? What is sulphuric oxide, and what relation does it bear to
+sulphur?
+
+5. A mineral contains 20.7 per cent. of water, 32.4 per cent. of lime,
+and 18.6 per cent. of sulphur. What is its probable composition? What
+experiment would you try to determine the accuracy of your conclusion?
+
+
+SELENIUM
+
+occurs in nature combined with copper, mercury, and lead, in certain
+rare minerals. In small quantities it is found in many ores. It is
+detected in solution by the red precipitate produced on boiling the acid
+solution with sodium sulphite. This reaction is used for its
+determination.
+
+~Solution.~--The solution is effected by boiling with nitric acid or
+aqua regia, or by fusing with nitre. To separate the selenium, the
+solution is evaporated with an excess of hydrochloric acid and a little
+sodium or potassium chloride. This destroys any nitric acid that may be
+present, and reduces selenic acid (H_{2}SeO_{4}) to selenious
+(H_{2}SeO_{3}). The solution is diluted with water, and treated with a
+solution of sulphite of soda. It is warmed, and at last boiled. The
+selenium separates as a red precipitate, which (on boiling) becomes
+denser and black. It is collected on a weighed filter, washed with hot
+water, dried at 100° C., and weighed as pure selenium.
+
+Selenium can be precipitated with sulphuretted hydrogen as a sulphide,
+which is readily soluble in ammonium sulphide. This sulphide may be
+oxidised with hydrochloric acid and chlorate of potash; and the selenium
+separated in the manner described.
+
+
+TELLURIUM.
+
+Tellurium occurs in nature, native, and in combination with gold,
+silver, bismuth and lead. It is sometimes met with in assaying gold
+ores. It may be detected by the purple colour it imparts to strong
+sulphuric acid when dissolved in the cold, and by the black precipitate
+of metallic tellurium which its solutions yield on treatment with a
+reducing agent. Telluric acid is reduced to tellurous (with evolution of
+chlorine) on boiling with hydrochloric acid.
+
+~Solution~ is effected by boiling with aqua regia, or by fusing with
+nitre and sodium carbonate.
+
+~Separation.~--Tellurium closely resembles selenium in its reactions. It
+is separated and determined in the same way. Like it, it forms a
+sulphide soluble in ammonium sulphide. It is distinguished from selenium
+by the insolubility, in a solution of cyanide of potassium, of the metal
+precipitated by sodium sulphite; whereas selenium dissolves, forming a
+soluble potassic seleno-cyanide.[102]
+
+For the determination, solution is effected by fusing with nitre and
+sodium carbonate, dissolving out the tellurate of potash with water, and
+boiling with hydrochloric acid. Tellurous compounds are formed, with
+evolution of chlorine; and the solution, on treating with a reducing
+agent (such as sulphurous acid or stannous chloride), yields metallic
+tellurium; which is washed, dried at 100° C., and weighed.
+
+FOOTNOTES:
+
+[101] BaCl_{2} + Na_{2}SO_{4} = BaSO_{4} + 2NaCl.
+
+[102] Se + KCy = KCySe.
+
+
+
+
+CHAPTER XVII.
+
+ARSENIC, PHOSPHORUS, NITROGEN.
+
+
+ARSENIC.
+
+The chief source of the arsenic of commerce is arsenical pyrites, or
+mispickel, which contains about 45 per cent. of arsenic (As). Arsenic
+also occurs as a constituent of several comparatively rare minerals;
+and, as an impurity, it is very widely distributed. White arsenic is an
+oxide of arsenic, and is obtained by roasting arsenical ores, and
+refining the material (crude arsenic), which condenses in the flues.
+Arsenic itself is volatile, and many of its compounds have the same
+property. It forms two well-defined series of salts, corresponding to
+the oxides: arsenious oxide (As_{2}O_{3}), and arsenic oxide
+(As_{2}O_{5}). These combine with bases to form arsenites and arsenates
+respectively. Boiling with nitric acid converts the lower into the
+higher oxide; and powerful reducing-agents, such as cuprous chloride,
+have the opposite effect.
+
+Arsenic may be detected by dissolving the substance in hydrochloric
+acid, or in aqua regia (avoiding an excess of nitric acid), and adding a
+little of this solution to the contents of a small flask in which
+hydrogen is being made by the action of zinc and hydrochloric acid. The
+ignited jet of hydrogen assumes a blue colour if arsenic is present, and
+a cold porcelain dish held in the flame (fig. 67) becomes coated with a
+dark deposit of metallic arsenic. Antimony produces a similar effect,
+but is distinguished by the insolubility of its deposit in a cold
+solution of bleaching-powder.
+
+[Illustration FIG. 67.]
+
+Arsenites are distinguished by the volatility of the chloride; by
+decolorising a solution of permanganate of potassium, and by immediately
+giving a yellow precipitate with sulphuretted hydrogen. Arsenates are
+distinguished (after converting into soda salts by boiling with
+carbonate of soda and neutralising) by giving with nitrate of silver a
+red precipitate, and with "magnesia mixture" a white crystalline one.
+
+~Dry Assay.~--There is no dry assay which is trustworthy. The following
+method is sometimes used to find the proportion of arsenious oxide in
+"crude arsenic":--Weigh up 5 grams of the dried sample, and place them
+in a clean dry test-tube about 6 inches long. Tie a small filter-paper
+over the mouth of the tube, so as to prevent air-currents. Heat the tube
+cautiously so as to sublime off the white arsenic into the upper part of
+the tube. Cut off the bottom of the test-tube by wetting whilst hot.
+Scrape out the arsenic and weigh it. The weight gives an approximate
+idea of the quantity, and the colour of the quality, of the white
+arsenic obtainable from the sample. Some workers (sellers) weigh the
+residue, and determine the white arsenic by difference. In determining
+the percentage of moisture in these samples, the substance is dried on a
+water-bath or in a water-oven.
+
+
+WET METHODS.
+
+~Solution.~--Where, as in crude arsenic, the substance is arsenious
+oxide (As_{2}O_{3}) mixed with impurities, the arsenic is best got into
+solution by warming with caustic soda, and neutralising the excess with
+hydrochloric acid; it will be present as sodium arsenite. Metals and
+alloys are acted on by means of nitric acid; or the arsenic may be at
+the same time dissolved and separated by distilling with a strongly-acid
+solution of ferric chloride, in the way described under _Volumetric
+Methods_.
+
+With minerals, mattes, &c., solution is thus effected:--The
+finely-powdered substance is mixed (in a large platinum or porcelain
+crucible) with from six to ten times its weight of a mixture of equal
+parts of carbonate of soda and nitre. The mass is then heated gradually
+to fusion, and kept for a few minutes in that state. When cold, it is
+extracted with warm water, and filtered from the insoluble residue. The
+solution, acidified with nitric acid and boiled, contains the arsenic as
+sodium arsenate. With mispickel, and those substances which easily give
+off arsenic on heating, the substance is first treated with nitric acid,
+evaporated to dryness, and then the residue is treated in the way just
+described.
+
+When the arsenic is present as arsenite or arsenide, distillation with
+an acid solution of ferric chloride will give the whole of the arsenic
+in the distillate free from any metal except, perhaps, tin as stannic
+chloride. With arsenates, dissolve the substance in acid and then add an
+excess of soda. Pass sulphuretted hydrogen into the solution; warm, and
+filter. Acidulate the filtrate, and pass sulphuretted hydrogen. Decant
+off the liquid through a filter, and digest the precipitate with ammonic
+carbonate; filter, and re-precipitate with hydrochloric acid and
+sulphuretted hydrogen. Allow to stand in a warm place, and filter off
+the yellow sulphide of arsenic. Wash it into a beaker, clean the
+filter-paper (if necessary) with a drop or two of dilute ammonia;
+evaporate with 10 c.c. of dilute nitric acid to a small bulk; dilute;
+and filter off the globules of sulphur. The filtrate contains the
+arsenic as arsenic acid.
+
+
+GRAVIMETRIC METHOD.
+
+Having got the arsenic into solution as arsenic acid, and in a volume
+not much exceeding 50 c.c., add about 20 c.c. of dilute ammonia and 20
+c.c. of "magnesia mixture." Stir with a glass rod, and allow to settle
+overnight. Filter, and wash with dilute ammonia, avoiding the use of
+large quantities of wash water. Dry, transfer the precipitate to a
+Berlin crucible, and clean the filter-paper thoroughly. Burn this paper
+carefully and completely; and add the ash to the contents of the
+crucible, together with 4 or 5 drops of nitric acid. Evaporate with a
+Bunsen burner, and slowly ignite, finishing off with the blow-pipe or
+muffle. Cool, and weigh. The ignited precipitate is pyrarsenate of
+magnesia (Mg_{2}As_{2}O_{7}), and contains 48.4 per cent. of arsenic
+(As).
+
+Instead of igniting the precipitate with nitric acid, it may be
+collected on a weighed filter-paper, dried at 100° C., and weighed as
+ammonic-magnesic arsenate (2AmMgAsO_{4}.H_{2}O), which contains 39.5 per
+cent. of arsenic. The results in this case are likely to be a little
+higher. The drying is very tedious, and is likely to leave behind more
+water than is allowed for in the formula. In a series of determinations
+in which the arsenic was weighed in both forms, the results were:--
+
+  Ammonic-magnesic     Arsenic     Magnesium Pyrarsenate   Arsenic
+  Arsenate in grams.   in grams.         in grams.         in grams.
+        0.0080          0.0032            0.0065            0.0031
+        0.0400          0.0158            0.0330            0.0160
+        0.0799          0.0316            0.0633            0.0306
+        0.1600          0.0632            0.1287            0.0623
+        0.4000          0.1580            0.3205            0.1551
+        0.7990          0.3156            0.6435            0.3114
+
+
+VOLUMETRIC METHODS.
+
+There are two methods: one for determining the arsenic in the lower, and
+the other in the higher state of oxidation. In the first-mentioned
+method this is done by titrating with a standard solution of iodine; and
+in the latter with a solution of uranium acetate. Where the arsenic
+already exists as arsenious oxide, or where it is most conveniently
+separated by distillation as arsenious chloride, the iodine method
+should be used; but when the arsenic is separated as ammonic-magnesic
+arsenate or as sulphide, the uranium acetate titration should be
+adopted.
+
+
+IODINE PROCESS.
+
+This is based on the fact that sodium arsenite in a solution containing
+an excess of bicarbonate of soda is indirectly oxidised by iodine to
+sodium arsenate,[103] and that an excess of iodine may be recognised by
+the blue colour it strikes with starch. The process is divided into two
+parts--(1) the preparation of the solution, and (2) the titration.
+
+~Preparation of the Solution.~--For substances like crude arsenic, in
+which the arsenic is present as arsenious oxide, the method is as
+follows:--Take a portion which shall contain from 0.25 to 0.5 gram of
+the oxide, place in a beaker, and cover with 10 c.c. of sodic hydrate
+solution; warm till dissolved, put a small piece of litmus paper in the
+solution, and render acid with dilute hydrochloric acid. Add 2 grams of
+bicarbonate of soda in solution, filter (if necessary), and dilute to
+100 c.c. The solution is now ready for titrating.
+
+[Illustration: FIG. 68.]
+
+Where the arsenic has to be separated as arsenious chloride, the process
+is as follows:[104]--Weigh up 1 gram of the finely-powdered ore (metals
+should be hammered out into a thin foil or be used as filings), and
+place in a 16-ounce flask provided with a well-fitting cork, and
+connected with a ~U~-tube, as shown in the drawing (fig. 68). The
+~U~-tube should contain 2 or 3 c.c. of water, and is cooled by being
+placed in a jar or large beaker of cold water. The water used for
+cooling should be renewed for each assay.
+
+Pour on the assay in the flask 50 c.c. of a "ferric chloride mixture,"
+made by dissolving 600 grams of calcium chloride and 300 grams of ferric
+chloride in 600 c.c. of hydrochloric acid, and making up to 1 litre with
+water.
+
+Firmly cork up the apparatus, and boil over a small Bunsen-burner flame
+for fifteen or twenty minutes, but avoid evaporating to dryness.
+Disconnect the flask, and pour away its contents at once to prevent
+breakage of the flask by their solidification. The arsenic will be
+condensed in the ~U~-tube, together with the greater part of the
+hydrochloric acid; transfer the distillate to a beaker washing out the
+tube two or three times with water; add a small piece of litmus paper;
+neutralise with ammonia; render faintly _acid_ with dilute hydrochloric
+acid; add 2 grams of bicarbonate of soda in solution; and dilute to 250
+c.c. The solution is now ready for titrating.
+
+The arsenic comes over in the early part of the distillation, as will be
+seen from the following experiment, made on 1 gram of copper
+precipitate; in which experiment the distillate was collected in
+separate portions at equal intervals, and the arsenic in each portion
+determined:--
+
+      Time              Iodine        Equivalent to Arsenic
+   Distilling.         Required.       in the Distillate.
+
+  5 minutes           12.0 c.c.         0.0450 gram
+  5    "               0.17   "         0.0005  "
+  5    "               0.0    "
+  5    "               0.0    "
+  To dryness           0.0    "
+
+The volume of each distillate was about 5 c.c.
+
+In this operation the metals are converted into chlorides by the action
+of ferric chloride, which gives up a part of its chlorine, and becomes
+reduced to the ferrous salt. The calcium chloride does not enter into
+the chemical reaction, but raises the temperature at which the solution
+boils, and is essential for the completion of the distillation.[105] Two
+experiments with material containing 3.48 per cent. of arsenic gave--(1)
+with ferric chloride alone, 2.74 per cent.; and (2) with the addition of
+calcium chloride, 3.48 per cent.
+
+It is always necessary to make a blank determination with 1 gram of
+electrotype copper, to find out the amount of arsenic in the ferric
+chloride mixture.[106] Unfortunately, a correction is always required.
+This amounts to about 0.15 per cent. of arsenic on each assay, even when
+the mixture has been purified; and this constitutes the weakness of the
+method, since, in some cases, the correction is as much as, or even
+greater than, the percentage to be determined.
+
+The acid distillate containing the arsenious chloride may be left for an
+hour or so without much fear of oxidation; but it is safer to neutralise
+and then to add the bicarbonate of soda, as the following experiments
+show. Several portions of a solution, each having a bulk of 100 c.c.,
+were exposed for varying lengths of time, and the arsenic in each
+determined.
+
+   _____________________________________________________________________
+  |               |                           |                         |
+  |               |     Acid Solutions.       | Neutralised Solutions.  |
+  | Time Exposed. | "Iodine"   Arsenic Found. |"Iodine"  Arsenic Found. |
+  |               | Required.                 | Required                |
+  |_______________|___________________________|_________________________|
+  |               |                           |                         |
+  |     --        | 18.2 c.c. = 0.0136 gram   | 18.1 c.c. = 0.0136 gram |
+  | 1 hour        | 18.2  "   = 0.0136   "    | 18.2  "   = 0.0136   "  |
+  | 2 hours       | 17.7  "   = 0.0133   "    | 18.0  "   = 0.0135   "  |
+  | 4   "         | 17.5  "   = 0.0131   "    | 18.4  "   = 0.0138   "  |
+  | 5   "         | 17.0  "   = 0.0127   "    | 18.3  "   = 0.0137   "  |
+  |_______________|___________________________|_________________________|
+
+~The Titration.~--Make a _standard solution of iodine_ by weighing up in
+a beaker 16.933 grams of iodine and 30 grams of potassium iodide in
+crystals; add a few c.c. of water, and, when dissolved, dilute to 1
+litre: 100 c.c. will equal 0.500 gram of arsenic.
+
+A solution of starch similar to that used in the iodide-copper assay
+will be required. Use 2 c.c. for each assay. Variations in the quantity
+of starch used do not interfere; but the solution must be freshly
+prepared, as after seven or eight days it becomes useless.
+
+To standardise the iodine solution, weigh up 0.3 gram of white arsenic;
+dissolve in caustic soda; neutralise; after acidulating, add 2 grams of
+bicarbonate of soda and 2 c.c. of the starch solution, and dilute to 200
+c.c. with cold water. Fill a burette having a glass stop-cock with the
+iodine solution, and run it into the solution of arsenic, rapidly at
+first, and then more cautiously, till a final drop produces a blue
+colour throughout the solution. Calculate the standard in the usual way.
+White arsenic contains 75.76 per cent. of arsenic.
+
+The following experiments show the effect of variation in the conditions
+of the titration:--
+
+Make a solution of arsenic by dissolving 6.60 grams of white arsenic in
+100 c.c. of sodic hydrate solution; render slightly acid with
+hydrochloric acid; add 10 grains of bicarbonate of soda, and dilute to 1
+litre: 100 c.c. will contain 0.50 gram of arsenic.
+
+~Effect of Varying Temperature.~--The reaction goes on very quickly in
+the cold, and, since there is no occasion for heating, all titrations
+should therefore be carried out cold.
+
+~Effect of Varying Bulk.~--In these experiments, 20 c.c. of arsenic
+solution were taken, 2 grams of bicarbonate of soda and 2 c.c. of starch
+solution added, and water supplied to the required bulk. The results
+were:--
+
+  Bulk               50.0 c.c.  100.0 c.c.  250.0 c.c.  500.0 c.c.
+  "Iodine" required  20.0  "     20.0  "     20.0  "     20.0  "
+
+Considerable variation in bulk does not interfere.
+
+~Effect of Varying Bicarbonate of Soda.~--This salt must be present in
+each titration in considerable excess, to prevent the interference of
+free acid. The bicarbonate must be dissolved without heating, as neutral
+carbonates should be avoided.
+
+  Bicarbonate added   1 gram     2 grams    5 grams   10 grams
+  "Iodine" required  20.1 c.c.  20.0 c.c.  20.1 c.c.  20.0 c.c.
+
+These results show that large variation in the quantity of bicarbonate
+has no effect.
+
+~Effect of Free Acid.~--In these experiments, the arsenic taken, the
+starch, and the bulk were as before, but no bicarbonate was added. In
+one case the solution was rendered acid with 5 c.c. of acetic acid, and
+in the other with 5 c.c. of hydrochloric acid; in both cases the
+interference was strongly marked, and no satisfactory finishing point
+could be obtained. This was much more marked with the hydrochloric acid.
+
+~Effect of Foreign Salts.~--The process for getting the arsenic into
+solution will exclude all metals except tin, but the solution will be
+charged with sodium or ammonium salts in the process of neutralising, so
+that it is only necessary to see if these cause any interference. The
+alkaline hydrates, including ammonia, are plainly inadmissible, since no
+free iodine can exist in their presence. Monocarbonates similarly
+interfere, but to a much less extent; hence the necessity for rendering
+the assay distinctly acid before adding the bicarbonate of soda.
+
+With 20 c.c. of arsenic solution; and with bulk, soda, and starch as
+before, the results obtained were:--
+
+                                               "Iodine" required.
+  With 20 grams of ammonic chloride                 20.0 c.c.
+   "   20 grams of sodium chloride                  20.0  "
+   "   20 grams of sodium acetate                   20.0  "
+   "    0.050 gram of tin, as stannic chloride      19.6  "
+  Without any addition                              20.0  "
+
+The interference of the stannic salt is probably mechanical, the
+precipitate carrying down some arsenious acid.
+
+~Effect of Varying Arsenic.~--With bulk, starch, and soda as before, but
+with varying arsenic, the results were:--
+
+  Arsenic added      1.0 c.c. 10.0 c.c. 20.0 c.c. 50.0 c.c. 100.0 c.c.
+  "Iodine" required  1.1  "    9.9  "   20.0  "   50.0  "   100.0  "
+
+~Determination of Arsenic in Metallic Copper.~--Put 1 gram of the copper
+filings, freed from particles of the file with a magnet, into a
+16-oz.-flask; and distil with the ferric chloride mixture, as above
+described. Neutralise the distillate; acidify; add bicarbonate of soda
+and starch; dilute; and titrate with the standard solution of
+iodine.[107] Make a blank determination with 1 gram of electrotype
+copper, proceeding exactly as with the assay; and deduct the amount of
+arsenic found in this experiment from that previously obtained.
+
+Working in this way on a copper containing 0.38 per cent. of arsenic and
+0.80 per cent. of antimony, 0.38 per cent. of arsenic was found.
+
+~Determination of White Arsenic in Crude Arsenic.~--Weigh out 1 gram of
+the dried and powdered substance (or 0.5 gram if rich), and digest with
+10 c.c. of a 10 per cent. solution of soda; dilute to about 50 c.c., and
+filter. Render faintly acid with hydrochloric acid, and filter (if
+necessary); add 2 or 3 grams of bicarbonate of soda in solution, then 5
+c.c. of starch, and titrate the cold solution with the standard solution
+of iodine.
+
+The following is an example:--
+
+  1 gram of crude arsenic required 53.7 c.c. "Iodine;"
+    100 c.c. "Iodine" = 0.6000 gram white arsenic;
+      100 : 53.7 :: 0.6 : 0.3222, or 32.2 per cent.
+
+With the test-tube method of dry assaying, this same sample gave results
+varying from 33 to 35 per cent. of white arsenic, which (judging from
+its appearance) was impure.
+
+
+URANIC ACETATE PROCESS.
+
+This may be looked upon as an alternative to the gravimetric method. It
+is applicable in all cases where the arsenic exists in solution as
+arsenic acid or as arsenate of soda. The process may be considered in
+two parts: (1) the preparation of the solution, and (2) the titration.
+
+~Preparation of the Solution.~--If the arsenic has been separated as
+sulphide, it is sufficient to attack it with 10 or 15 c.c. of nitric
+acid, and to heat gently till dissolved, avoiding too high a temperature
+at first. Afterwards continue the heat till the separated sulphur runs
+into globules, and the bulk of the acid has been reduced to 3 or 4 c.c.
+Dilute with 20 or 30 c.c. of water; put in a piece of litmus paper; and
+add dilute ammonia until just alkaline. Then add 5 c.c. of the sodium
+acetate and acetic acid solution (which should make the solution
+distinctly acid); dilute to 150 c.c., and heat to boiling. The solution
+is ready for titrating.
+
+When the arsenic exists in a nitric acid solution mixed with much
+copper, it is separated in the way described under _Examination of
+Commercial Copper_ (Arsenic and Phosphorus), pages 208, 209.
+
+If the arsenic has been separated as ammonium-magnesium arsenate, and
+phosphates are known to be absent; dissolve the precipitate (after
+filtering, but without washing) in dilute hydrochloric acid. Add dilute
+ammonia till a slight precipitate is formed, and then 5 c.c. of the
+sodium acetate and acetic acid solution; dilute to 150 c.c., and heat to
+boiling. Titrate.
+
+If phosphates are present (which will always be the case if they were
+present in the original substance, and no separation with sulphuretted
+hydrogen has been made), the phosphorus will count in the subsequent
+titration as arsenic (one part of phosphorus counting as 2.4 parts of
+arsenic). It will be necessary to dissolve the mixed arsenate and
+phosphate of magnesia in hydrochloric acid. Add about four or five times
+as much iron (as ferric chloride) as the combined phosphorus and arsenic
+present will unite with, and separate by the "basic acetate" process as
+described under PHOSPHORUS in the _Examination of Commercial Copper_,
+page 209. Obviously, when phosphates are present, it is easier to
+separate the arsenic as sulphide than to precipitate it with the
+"magnesia mixture."
+
+~The Titration.~--The _standard solution of uranium acetate_ is made by
+dissolving 34.1 grams of the salt (with the help of 25 c.c. of acetic
+acid) in water; and diluting to 1 litre. The water and acid are added a
+little at a time, and warmed till solution is effected; then cooled, and
+diluted to the required volume: 100 c.c. will equal 0.50 gram of
+arsenic.
+
+The _sodic acetate and acetic acid solution_ is made by dissolving 100
+grams of sodic acetate in 500 c.c. of acetic acid, and diluting with
+water to 1 litre. Five c.c. are used for each assay.
+
+The solution of potassic ferrocyanide used as _indicator_ is made by
+dissolving 10 grams of the salt in 100 c.c. of water.
+
+To standardise the solution of uranium acetate, weigh up a quantity of
+white arsenic (As_{2}O_{3}) which shall be about equivalent to the
+arsenic contained in the assay (0.1 or 0.2 gram); transfer to a flask,
+and dissolve in 10 c.c. of nitric acid with the aid of heat. Evaporate
+to a small bulk (taking care to avoid the presence of hydrochloric
+acid); dilute with water; add a small piece of litmus paper; render
+faintly alkaline with ammonia; then add 5 c.c. of the sodic acetate
+mixture; dilute to 150 c.c.; and heat to boiling.
+
+Fill an ordinary burette with the uranium acetate solution, and run into
+the assay a quantity known to be insufficient. Again heat for a minute
+or two. Arrange a series of drops of the solution of ferrocyanide of
+potassium on a porcelain slab, and, with the help of a glass rod, bring
+a drop of the assay solution in contact with one of these. If no colour
+is produced, run in the uranium acetate, 1 c.c. at a time, testing after
+each addition, till a brown colour is developed. It is best to overdo
+the assay, and to count back. It is not necessary to filter off a
+portion of the assay before testing with the "ferrocyanide," since the
+precipitate (uranic arsenate) has no effect.
+
+The following experiments show the effect of variation in the conditions
+of titration. Make a solution of arsenic acid by dissolving 4.95 grams
+of arsenious acid (As_{2}O_{3}) in a covered beaker with 35 c.c. of
+nitric acid; evaporate down to 7 or 8 c.c.; and dilute with water to 1
+litre: 100 c.c. will contain 0.375 gram of arsenic. Use 20 c.c. for each
+experiment.
+
+~Effect of Varying Temperature.~--It is generally recommended to titrate
+the boiling solution, since it is possible that the precipitation is
+only complete on boiling. Low results are obtained in a cold solution,
+the apparent excess of uranium acetate striking a colour at once; on
+boiling, however, it ceases to do so; consequently, the solution should
+always be boiled directly before testing.
+
+In four experiments made in the way described, but with 20 c.c. of a
+solution of arsenic acid stronger than that given (100 c.c. = 0.5 gram
+As), the results at varying temperatures were:--
+
+  Temperature            15° C.       30° C.       70° C.       100° C.
+  "Uranium" required    18.0 c.c.    18.5 c.c.    18.5 c.c.    18.7 c.c.
+
+~Effect of Varying Bulk.~--These experiments were like those last
+mentioned, but were titrated boiling, and the volume was varied:--
+
+  Bulk                  50.0 c.c.  100.0 c.c.   200.0 c.c.   300.0 c.c.
+  "Uranium" required    14.0  "     14.0  "      14.5  "      15.0  "
+
+Considerable variations in bulk are to be avoided.
+
+~Effect of Varying Sodium Acetate.~--These experiments were carried out
+like those last noticed, but the bulk was 150 c.c., and varying amounts
+of sodic acetate were added in excess of the quantity used in the
+experiments previously described:--
+
+  Sodic acetate added    0 gram       1 gram     10 grams     20 grams
+  "Uranium" required    14.5 c.c.    14.5 c.c.   16.0 c.c.    18.0 c.c.
+
+It is evidently important that the quantity of this salt present in each
+titration be measured out, so as to avoid variation.
+
+~Effect of Varying the Sodium Acetate and Acetic Acid Solution.~--Acetic
+Acid also affects the results, but in the opposite direction, by
+preventing the precipitation of uranium arsenate. With varying volumes
+of the solution now under notice, the results were:--
+
+  Solution added         0.0 c.c.     5.0 c.c.   10.0 c.c.    15.0 c.c.
+  "Uranium" required    14.5   "     14.5   "    14.5   "     14.0  "
+  Solution added        20.0  "      30.0   "    40.0   "     50.0  "
+  "Uranium" required    13.2  "      10.0   "     6.0   "      2.0  "
+
+These show that the quantity ordered (5 c.c.) must be adhered to.
+
+~Effect of Foreign Salts.~--In these experiments, 10 grams of the salt
+(the effect of which it was desired to determine) were added to a
+solution in other respects resembling those previously used:--
+
+  Salt added           {Ammonic    Ammonic     Ammonic     Magnesium
+                       {sulphate   nitrate     chloride    sulphate
+  "Uranium" required    15.5 c.c.  15.5 c.c.   15.3 c.c.   15.3 c.c.
+
+Without any addition, 15.0 c.c. were required; and in another
+experiment, in which 30 grams of ammonic salts were present, 15.6 c.c.
+of uranium solution were required. Such variations in the amount of
+ammonic salts as occur in ordinary working are unimportant.
+
+Phosphates, of course, interfere. In fact, the uranium acetate solution
+can be standardised by titrating with a known weight of phosphate, and
+calculating its equivalent of arsenic. Thus, in an experiment with 0.6
+gram of hydric sodic phosphate (Na_{2}HPO_{4}.12H_{2}O), equivalent to
+0.05195 gram of phosphorus, or 0.1256 gram of arsenic, 23.25 c.c. of a
+solution of uranium acetate were required. The same solution
+standardised with white arsenic gave a standard of which 100 c.c. =
+0.5333 gram arsenic. On this standard the 0.6 gram of sodic phosphate
+should have required 23.5 c.c.
+
+Experiments in which 0.1 gram of bismuth and 0.1 gram of antimony were
+present with 0.1 gram of arsenic, showed no interference on the
+titration. Ferric or aluminic salts would remove their equivalent of
+arsenic, and, consequently, must be removed before titrating.
+
+~Effect of Varying Arsenic.~--Varying amounts of metallic arsenic were
+weighed up and dissolved in nitric acid, &c., and titrated:--
+
+  Arsenic taken   0.010 gram   0.050 gram   0.100 gram   0.200 gram
+  Arsenic found   0.010  "     0.050  "     0.100  "     0.197  "
+
+These experiments show that the method yields good results within these
+limits.
+
+~Determination of Arsenic in Mispickel.~--Weigh up 1 gram of the dried
+and powdered ore, and evaporate to near dryness with 20 c.c. of dilute
+nitric acid. Make up to 100 c.c. with water, and pass sulphuretted
+hydrogen to reduce the ferric iron to the ferrous state, then add 20
+c.c. of dilute ammonia, and again pass sulphuretted hydrogen. Warm,
+filter, and evaporate the filtrate to drive off the excess of ammonia;
+then add 10 c.c. of nitric acid, and boil down till the sulphide of
+arsenic at first precipitated is dissolved; neutralise; add 5 c.c. of
+sodium acetate and acetic acid solution; transfer to a pint flask, boil,
+and titrate.
+
+For example, an impure sample of ore required, in duplicate assay of
+half a gram each, when treated in the above-mentioned way, 39.6 and 39.5
+c.c. of the uranium acetate solution (100 c.c. = 0.537 gram of arsenic),
+equivalent to 0.2114 gram of arsenic, or 42.3 per cent.
+
+An alternative method is as follows. Powder the ore very finely and
+weigh up .5 gram. Place in a 2-3/4 inch berlin dish and add strong
+nitric acid, one drop at a time until the action ceases; with care there
+need be no very violent reaction. Dry over a water bath. Cover with 2
+grams of nitre and over this spread 5 grams of a mixture of equal parts
+of nitre and carbonate of soda. Fuse in a muffle or over a large gentle
+blow-pipe flame for 4 or 5 minutes. This will spoil the dish. Allow to
+cool and boil out in a larger dish with 100 c.c. of water. Filter and
+wash into an 8 oz. flask. Acidify the liquor with nitric and boil down
+to about 100 c.c. The acid should not be in too large excess, but an
+excess is needed to destroy nitrites. Neutralise with soda or ammonia.
+Add 5 c.c. of the mixture of sodium acetate and acetic acid. Titrate
+with uranium acetate.
+
+~Determination of Arsenic (As) in Crude Arsenic.~--The method given
+under the iodine titration simply determines that portion of the arsenic
+which is present in the substance as arsenious oxide or white arsenic.
+The following method will give the total arsenic in the sample. It would
+be incorrect to report this as so much per cent. of arsenious oxide,
+although it may be reported as so much per cent. of arsenic equivalent
+to so much per cent. of white arsenic, thus:--
+
+  Arsenic                          30.0 per cent.
+  Equivalent to white arsenic      39.6    "
+
+The equivalent of white arsenic is calculated by multiplying the
+percentage of arsenic by 1.32. The method of determining the percentage
+of arsenic is as follows:---Boil 1 gram of the sample with 10 c.c. of
+nitric acid. When the bulk of the solution has been reduced to one-half,
+and red fumes are no longer evolved, dilute with a little water, and
+filter into a flask. Neutralise the filtrate, add 5 c.c. of sodic
+acetate solution, boil and filter. The precipitate (ferric arsenate) is
+transferred to a small beaker, treated with 5 c.c. of dilute ammonia,
+and sulphuretted hydrogen passed through it. The iron sulphide is
+filtered off, and the filtrate evaporated with an excess of nitric acid.
+When the solution is clear, it is neutralised, and 1 or 2 c.c. of sodic
+acetate solution having been added, is then mixed with the first
+filtrate. The solution is boiled and titrated.
+
+A sample treated in this way required 49.2 c.c. of the uranium acetate
+solution (100 c.c. = 0.537 gram of arsenic), equivalent to 26.4 per
+cent.
+
+~Determination of Arsenic in Brimstone.~--Take 10 grams of the
+substance, and powder in a mortar; rub up with 10 c.c. of dilute ammonia
+and a little water; rinse into a pint flask; pass a current of
+sulphuretted hydrogen; and warm on a hot plate for a few minutes.
+Filter, acidulate the filtrate with sulphuric acid; filter off the
+precipitate; attack it with 10 c.c. of nitric acid; and proceed as in
+the other determinations.
+
+
+PRACTICAL EXERCISES.
+
+1. Mispickel contains 45.0 per cent. of arsenic, to how much white
+arsenic will this be equivalent?
+
+2. How would you make a standard solution of iodine so that 100 c.c.
+shall be equivalent to 1 gram of white arsenic?
+
+3. What weight of arsenic is contained in 1 gram of pyrarsenate of
+magnesia, and what weight of ammonic-magnesic arsenate would it be
+equivalent to?
+
+4. The residue, after heating 10 grams of crude arsenic, weighed 0.62
+gram. What information does this give as to the composition of the
+substance? If another 10 grams of the substance, heated on a water-bath,
+lost 0.43 gram, what conclusions would you draw, and how would you
+report your results?
+
+5. If a sample of copper contained 0.5 per cent. of arsenic, and 1 gram
+of it were taken for an assay, how much standard uranium acetate
+solution would be required in the titration?
+
+
+PHOSPHORUS AND PHOSPHATES.
+
+Phosphorus rarely occurs among minerals except in its highest oxidized
+state, phosphoric oxide (P_{2}O_{5}), in which it occurs abundantly as
+"rock phosphate," a variety of apatite which is mainly phosphate of
+lime. Phosphates of most of the metallic oxides are found. Phosphoric
+oxide in small quantities is widely diffused, and is a constituent of
+most rocks. Its presence in varying amounts in iron ores is a matter of
+importance, since it affects the quality of the iron obtainable from
+them.
+
+Phosphorus occurs in alloys in the unoxidized state. It is directly
+combined with the metal, forming a phosphide. In this manner it occurs
+in meteoric iron. The alloy phosphor-bronze is made up of copper, tin,
+zinc, and phosphorus.
+
+Phosphates are mined in large quantities for the use of manure
+manufacturers, and for making phosphorus.
+
+Phosphorus and arsenic closely resemble each other in their chemical
+properties, more especially those which the assayer makes use of for
+their determination. Phosphorus forms several series of salts; but the
+phosphates are the only ones which need be considered. Pyrophosphate of
+magnesia, which is the form in which phosphoric oxide is generally
+weighed, differs from the ordinary phosphate in the proportion of base
+to acid. Metaphosphates differ in the same way. If these are present, it
+must be remembered they act differently with some reagents from the
+ordinary phosphates, which are called orthophosphates. They are,
+however, all convertible into orthophosphates by some means which will
+remove their base, such as fusion with alkaline carbonates, boiling with
+strong acids, &c.[108]
+
+Phosphides are converted into phosphates by the action of nitric acid or
+other oxidizing agents. Dilute acids, when they act on the substance,
+evolve phosphuretted hydrogen (PH_{3}). The student should be on his
+guard against losing phosphorus in this manner.
+
+There is no dry assay for phosphorus. All assays for it are made either
+gravimetrically or volumetrically.
+
+The separation of phosphoric oxide is made as follows:--The ore or metal
+is dissolved in acid and evaporated, to render the silica insoluble. It
+is taken up with hydrochloric acid, diluted with water, and treated with
+sulphuretted hydrogen. The filtrate is boiled, to get rid of the excess
+of gas, and treated with nitric acid, to peroxidize the iron present. If
+the iron is not present in more than sufficient quantity to form ferric
+phosphate with all the phosphorus present, some ferric chloride is
+added. The iron is then separated as basic acetate. The precipitate will
+contain the phosphorus, together with any arsenic acid not reduced by
+the sulphuretted hydrogen. The precipitate should have a decided brown
+colour. The precipitate is washed, transferred to a flask, and treated
+first with ammonia, and then with a current of sulphuretted hydrogen.
+The filtrate from this (acidulated with hydrochloric acid, and, if
+necessary, filtered) contains the phosphorus as phosphoric acid. This
+method is not applicable in the presence of alumina, chromium, titanium,
+or tin, if the solution is effected with nitric acid. The precipitate
+obtained by the action of nitric acid on tin retains any phosphoric or
+arsenic oxide that may be present.
+
+A method of separation more generally applicable and more convenient to
+work is based on the precipitation of a yellow phospho-molybdate of
+ammonia,[109] by the action of an excess of ammonic molybdate upon a
+solution of a phosphate in nitric acid. Dissolve the substance by
+treatment with acid, and evaporate to dryness. Take up with 10 c.c. of
+nitric acid, and add 20 grams of ammonic nitrate, together with a little
+water. Next put in the solution of ammonium molybdate solution in the
+proportion of about 50 c.c. for each 0.1 gram of phosphoric oxide judged
+to be present. Warm to about 80° C., and allow to stand for an hour.
+Filter, and wash with a 10 per cent. solution of ammonic nitrate. It is
+not necessary that the whole of the precipitate be placed on the filter;
+but the beaker must be completely cleaned. Dissolve the precipitate off
+the filter with dilute ammonia, and run the solution into the original
+beaker. Run in from a burette, slowly and with stirring, "magnesia
+mixture," using about 15 c.c. for each 0.1 gram of phosphoric oxide.
+Allow to stand for one hour. The white crystalline precipitate contains
+the phosphorus as ammonium-magnesium phosphate.
+
+Phosphate of lead is decomposed by sulphuric acid; the lead is converted
+into the insoluble lead sulphate, and the phosphoric acid is dissolved.
+Phosphate of copper and phosphate of iron may be treated with
+sulphuretted hydrogen; the former in an acid, and the latter in an
+alkaline, solution. Phosphate of alumina is generally weighed without
+separation of the alumina, since this requires a fusion. In all cases
+the aim is to get the phosphoric oxide either free, or combined with
+some metal whose phosphate is soluble in ammonia.
+
+Joulie's method of separation is as follows:--One to ten grams of the
+sample are treated with hydrochloric acid, and evaporated to dryness
+with the addition (if any pyrites is present) of a little nitric acid.
+The residue is taken up with hydrochloric acid, cooled, transferred to a
+graduated flask, and diluted to the mark. It is then shaken up, filtered
+through a dry filter, and a measured portion (containing about 0.05 gram
+of phosphoric acid) transferred to a small beaker. Ten c.c. of a
+citric-acid solution of magnesia[110] is added, and then an excess of
+ammonia. If an immediate precipitate is formed, a fresh portion must be
+measured out and treated with 20 c.c. of the citrate of magnesia
+solution and with ammonia as before. The beaker is put aside for from
+two to twelve hours. The precipitate is then filtered off and washed
+with weak ammonia; it contains the phosphorus as ammonium-magnesium
+phosphate.
+
+
+GRAVIMETRIC DETERMINATION.
+
+If the phosphate is not already in the form of ammonic-magnesic
+phosphate, it is converted into this by the addition to its solution of
+an excess of ammonia and "magnesia mixture." In order to get the
+precipitate pure, the "magnesia mixture" is run in gradually (by drops)
+from a burette, with constant stirring. A white crystalline precipitate
+at once falls, if much phosphorus is present; but, if there is only a
+small quantity, it may be an hour or two before it shows itself. The
+solution is best allowed to rest for twelve or fifteen hours (overnight)
+before filtering. The presence of tartaric acid should be avoided; and
+the appearance of the precipitate should be crystalline. The solution is
+decanted through a filter, and the precipitate washed with dilute
+ammonia, using as little as may be necessary. The precipitate is dried,
+transferred to a weighed Berlin or platinum crucible; the filter-paper
+is carefully burnt, and its ash added to the precipitate, which is then
+ignited, at first gently over a Bunsen burner, and then more strongly
+over the blowpipe or in the muffle. The residue is a white mass of
+magnesium pyrophosphate containing 27.92 per cent. of phosphorus, or
+63.96 per cent. of phosphoric oxide.
+
+
+VOLUMETRIC METHOD.
+
+Instead of separating and weighing this compound, the phosphoric oxide
+in it can be determined by titration. In many cases the ore may be
+dissolved and immediately titrated without previous separation. It is
+better, however, to carry the separation so far as to get phosphoric
+acid, an alkaline phosphate, or the magnesia precipitate. It may then be
+prepared for titration in the following way:--The precipitate in the
+last case (without much washing) is dissolved in a little hydrochloric
+acid, and the solution in any case rendered fairly acid. Dilute ammonia
+is added till it is just alkaline, and then 5 c.c. of the sodic acetate
+and acetic acid mixture (as described under the Arsenic Assay). This
+should yield a clear distinctly-acid solution. It is diluted to 100 or
+150 c.c., heated to boiling, and titrated with the uranium acetate
+solution, using that of potassic ferrocyanide as indicator.
+
+The _standard solution_ required is made by dissolving 35 grams of
+uranium acetate in water with the aid of 25 c.c. of acetic acid, and
+diluting to 1 litre.
+
+An _equivalent solution of phosphoric oxide_ is made by dissolving 25.21
+grams of crystallised hydric disodic phosphate (HNa_{2}PO_{4}.12H_{2}O)
+in water, and making up to 1 litre. 100 c.c. will contain 0.5 gram of
+phosphoric oxide (P_{2}O_{5}), or 0.2183 gram of phosphorus. In making
+this solution, transparent crystals only must be used. The uranium
+acetate solution is only approximately equivalent to this, so that its
+exact standard must be determined.
+
+_Sodic Acetate and Acetic Acid Solution._--It is the same as that
+described under _Arsenic_.[111] Use 5 c.c. for each assay.
+
+The following experiments show the effect of variation in the conditions
+of the titration:--
+
+~Effect of Varying Temperature.~--The solution should be titrated while
+boiling. This is especially necessary for the last few c.c. in order to
+get a decided and fixed finishing point.
+
+  Temperature            15° C.       30° C.       70° C.       100° C.
+  "Uranium" required    18.0 c.c.   19.2 c.c.   19.0 c.c.   18.9 c.c.
+
+~Effect of Varying Bulk.~--
+
+  Bulk                 50.0 c.c.  100.0 c.c.  200.0 c.c.  300.0 c.c.
+  "Uranium" required   18.8  "     18.9  "     19.0  "     19.3  "
+
+Variation in bulk affects the results; therefore, a constant bulk should
+be adhered to.
+
+~Effect of Varying Sodium Acetate and Acetic Acid Solution.~--
+
+  Sodium acetate
+    and acetic
+    acid solution      0.0 c.c.  1.0 c.c.  5.0 c.c.  10.0 c.c. 20.0 c.c.
+  "Uranium" required  18.9  "   18.9  "   19.0  "    18.8  "   17.5  "
+
+As in the titration with arsenates, an excess is dangerous to the assay;
+a definite quantity (5 c.c.) should, therefore, be used.
+
+~Effect of Foreign Salts.~--Besides the sodium acetate, &c., added, the
+only salts likely to be present are those of ammonia and magnesia. In
+three experiments, in one of which no foreign salts were introduced,
+while in the other two 5 grams of ammonic chloride and of magnesium
+sulphate respectively were added, there were required:--
+
+  With ammonic chloride       18.8 c.c. "Uranium" solution
+  With magnesium sulphate     19.0  "          "
+  Without foreign salts       18.9  "          "
+
+~Effect of Varying Phosphate.~--
+
+  "Phosphate" solution added  10.0 c.c.  20.0 c.c.  50.0 c.c.  100.0 c.c.
+  "Uranium" required           9.8  "    18.9  "    47.6  "     94.5  "
+
+The quantity of phosphoric oxide in the assay solution for the
+conditions of titration should not be much less than 0.05 gram. For
+smaller quantities the uranium solution should be diluted to half its
+strength, and the assay solution concentrated by reducing its bulk to 50
+c.c. and using 2.5 c.c. of the sodium acetate and acetic acid solution.
+
+~Determination of Phosphoric Oxide in Apatite.~--Weigh up 0.5 gram of
+the dried and powdered sample, and dissolve it in 5 c.c. of hydrochloric
+acid. Evaporate to a paste, add 5 c.c. of the sodic acetate and acetic
+acid solution, dilute to 100 c.c. with water, boil, and titrate with
+uranium acetate solution.
+
+In an example, 0.5 gram of apatite required 37.4 c.c. of uranium acetate
+solution (standard equal to 0.5291 gram of phosphoric oxide). The sample
+therefore contained 0.1979 gram of P_{2}O_{5}, equal to 39.58 per cent.
+
+~Determination of Phosphoric Oxide in an Iron Ore.~--Take 10 grams, boil
+with 50 c.c. of hydrochloric acid, and evaporate to a paste; take up
+with 10 c.c. of dilute hydrochloric acid, and dilute with water to 400
+c.c. Pass sulphuretted hydrogen for nearly a quarter of an hour; warm,
+and filter. Boil off the excess of gas; cool, add ammonia till nearly
+neutral, and then a few drops of ferric chloride solution, and 4 or 5
+grams of sodium acetate, with a drop or two of acetic acid. Boil and
+filter. Dissolve the precipitate in hot dilute hydrochloric acid, and
+add citro-magnesia mixture and ammonia; allow to stand overnight;
+filter, ignite, and weigh.
+
+In an example, 10 grams of ore gave 28.5 milligrams of magnesic
+pyrophosphate, which is equivalent to 0.18 per cent. of phosphoric
+oxide.
+
+~Determination of Phosphorus in Iron.~--Take from 2 to 10 grams
+(according to the amount of phosphorus present), and dissolve in aqua
+regia, keeping the nitric acid in excess; evaporate to dryness and take
+up with hydrochloric acid, boil, dilute, and filter. Add 10 c.c. of
+nitric acid, nearly neutralise with ammonia, render acid with 3 or 4
+c.c. of nitric acid, and add 10 or 20 c.c. of ammonic molybdate
+solution. Heat for some time, allow to settle, filter, and wash the
+precipitate with a solution of ammonic nitrate. Dissolve the precipitate
+in dilute ammonia, nearly neutralise with dilute hydrochloric acid, and
+add first "magnesia mixture," and then ammonia; allow to stand
+overnight; filter, wash with dilute ammonia, dry, ignite, and weigh as
+magnesic pyrophosphate. Calculate to phosphorus.
+
+
+PRACTICAL EXERCISES.
+
+1. Ten grams of an iron yielded 12 milligrams of pyrophosphate of
+magnesia. What percentage of phosphorus did the metal contain?
+
+2. Ten grams of an iron ore gave 12 milligrams of pyrophosphate. What
+percentage of phosphoric oxide did it contain?
+
+3. What weight of apatite 3Ca_{3}(PO_{4})_{2}.CaClF would require 50
+c.c. of standard uranium solution (100 c.c. equal to 0.5 gram of
+P_{2}O_{5})?
+
+4. You have reason to believe that a precipitate which has been weighed
+as magnetic pyrophosphate contains some arsenate. How would you
+determine the amount of phosphate really present?
+
+5. Twenty c.c. of a solution of sodic phosphate containing 0.100 gram of
+P_{2}O_{5} was found to require a solution containing 0.700 gram of
+hydrated uranium acetate in a titration. The precipitate contains 80.09
+per cent. uranium oxide and 19.91 per cent. of phosphoric oxide. What
+percentage of uranium oxide was contained in the uranic acetate?
+
+
+NITROGEN AND NITRATES.
+
+Nitrogen occurs in nature in the free state, and forms about four-fifths
+of the atmosphere. In combination, as nitrate, it is found in nitre
+(KNO_{3}), and Chili saltpetre (NaNO_{3}), minerals which have a
+commercial importance. The latter occurs in beds, and is extensively
+worked for use as a manure and in the preparation of nitric acid.
+
+Nitrogen is mainly characterised by negative properties, although many
+of its compounds are very energetic bodies. It is a gas, present
+everywhere, but so inactive that the assayer can always afford to ignore
+its presence, and, except in testing furnace gases, &c., he is never
+called on to determine its quantity.
+
+The nitrates are an important class of salts, and may be looked on as
+compounds of the bases with nitric pentoxide (N_{2}O_{5}). They are,
+with the exception of a few basic compounds, soluble in water, and are
+remarkable for the ease with which they give up their oxygen. The
+alkaline nitrates fuse readily, and lose oxygen with effervescence
+forming nitrites; while at a higher temperature they yield more oxygen
+and lose their nitrogen, either as a lower oxide or as nitrogen. The
+nitrates of the metals, on heating, leave the oxide of the metal. It is
+as yielders of oxygen that nitrates are so largely used in the
+manufacture of explosives. Gunpowder contains from 65 to 75 per cent. of
+potassium nitrate (nitre).
+
+Nitrates are best detected and determined by their yielding nitric oxide
+when treated with sulphuric acid and a suitable reducing agent, such as
+ferrous sulphate, mercury, or copper. Nitric oxide is a colourless gas
+very slightly soluble in water. It combines at once with oxygen, on
+mixing with the air, to form brown "nitrous fumes," and dissolves in a
+solution of ferrous sulphate, producing a characteristic blackish-brown
+colour. It is this colour which affords the best and most easily-applied
+test for nitrates. The substance suspected to contain nitrates is
+dissolved in about 1 c.c. of water, and treated with an equal volume of
+strong sulphuric acid. After cooling, a solution of ferrous sulphate is
+poured on its surface, so as to form a layer resting on it. On standing,
+a brown or black ring is developed where the liquids join, if any
+nitrate or nitrite is present. Nitrites are distinguished from nitrates
+by effervescing and yielding brown fumes when treated with a little
+dilute sulphuric acid.
+
+The separation of nitrates is in many cases difficult. Generally, on
+treating the substance with water, the nitrate will be in the solution,
+and is filtered off from any insoluble matter. In the exceptional cases
+it is got into solution by treating with a boiling solution of sodium
+carbonate; the nitrate will contain it as an alkaline nitrate.
+
+Since, however, in their determination, nitrates are never separated and
+weighed as such, the difficulty of separating them has little
+importance. Usually, the determination can be made on the original
+aqueous solution, and it is never necessary to do more than remove any
+special substance which has a bad effect; and this is easily done by the
+usual reagents.
+
+
+GRAVIMETRIC DETERMINATION.
+
+It follows from what has been said that there is no direct gravimetric
+determination. The percentage of nitrogen pentoxide (N_{2}O_{5}) in a
+comparatively pure nitrate is sometimes determined indirectly in the
+following way:--Place in a platinum-crucible 4 or 5 grams of powdered
+and cleaned quartz. Ignite, cool in a desiccator, and weigh with the
+cover. Mix 1 gram of the dried and powdered salt with the quartz in the
+crucible by stirring with a stout platinum-wire. Cover the crucible, and
+heat in a Bunsen-burner flame at scarcely visible redness for
+half-an-hour. Cool and weigh. The loss in weight gives the amount of
+nitrogen pentoxide. Sulphates and chlorides in moderate quantity do not
+interfere. The following is an example of the process:--
+
+  Crucible and sand        26.6485 grams
+  Nitre taken               1.0000   "
+                           -------
+                           27.6485   "
+  Weight after ignition    27.1160   "
+                           -------
+  Loss on ignition          0.5325   "
+
+This is equal to 53.25 per cent. of nitrogen pentoxide.
+
+
+VOLUMETRIC DETERMINATION.
+
+This is based on the oxidising action of nitric acid, or of nitrates in
+acid solutions on ferrous salts. The pentoxide (N_{2}O_{5}) of the
+nitrate is reduced to nitric oxide (NO), so that 336 parts of iron
+peroxidised represent 108 parts of nitric pentoxide as oxidising
+agent.[112] The quantity of iron peroxidised is determined by taking a
+known quantity of ferrous salt, oxidizing with a weighed sample of
+nitrate, and then determining the residual ferrous iron by titration
+with bichromate or permanganate of potassium solution. The difference
+between the ferrous iron taken and that found, gives the amount oxidized
+by the nitrate. The speed with which nitric oxide takes up oxygen from
+the air, and thus becomes capable of oxidising more iron, renders some
+precautions necessary; ferrous chloride should, therefore, be used,
+since it is easier to expel nitric oxide (by boiling) from solutions of
+a chloride than it is from those of a sulphate. The process is as
+follows:--Dissolve 2 grams of thin soft iron wire in 50 c.c. of
+hydrochloric acid in a flask provided with an arrangement for
+maintaining an atmosphere of carbon dioxide. When the iron has
+dissolved, allow the solution to cool, and add 0.5 gram of the nitrate.
+Heat gently for a few minutes, and then boil until the nitric oxide is
+expelled. An atmosphere of carbon dioxide must be kept up. Dilute with
+water, and titrate the residual iron with standard solution of
+bichromate of potassium. The standard "bichromate" is made by dissolving
+17.5 grams of the salt (K_{2}Cr_{2}O_{7}) in water, and diluting to 1
+litre: 100 c.c. equal 2 grams of iron. Deduct the weight of iron found
+from the 2 grams originally taken, and multiply by 0.3214. This gives
+the weight of the pentoxide in the sample. In an example, 0.5 gram of
+nitre was taken, and 59.4 c.c. of the "bichromate" solution were
+required. The 59.4 c.c. thus used are equivalent to 1.198 gram of iron.
+This leaves 0.822 gram as the quantity oxidised by the nitre, which,
+multiplied by 0.3214, gives 0.2642 gram for the nitrogen pentoxide, or
+52.8 per cent.
+
+
+GASOMETRIC METHOD.
+
+This is based upon the measurement of the nitric oxide evolved on
+shaking up a weighed quantity of the nitrate with sulphuric acid over
+mercury in a nitrometer. Each c.c. of nitric oxide obtained, when
+reduced to normal temperature and pressure, is equivalent to:--
+
+  0.627 milligram  of nitrogen.
+  1.343     "      of nitric oxide.
+  2.418     "      of nitric pentoxide.
+  2.820     "      of nitric acid.
+  3.805     "      of sodium nitrate.
+  4.523     "      of potassium nitrate.
+
+In working on substances not rich in nitrates, an ordinary nitrometer
+(fig. 69) is used; but in the assay of sodium nitrate, nitroglycerine,
+&c., an instrument provided with a bulb having a capacity of 100 c.c. is
+employed.
+
+[Illustration: FIG. 69.]
+
+The plan of working is as follows:--The "measuring tube" is filled with
+mercury until it reaches up into the tap, and the levelling-tube is
+placed so that it contains an inch or two of mercury. If the nitrate is
+in solution, 2 or 3 c.c. of the liquid (dilute liquids are brought to
+this bulk by evaporation) are measured into the cup. The levelling-tube
+is lowered a little, and the tap cautiously opened until all but the
+last drop of the liquid has run in. The cup is then rinsed with 2 or 3
+c.c. of sulphuric acid, which is run in in the same way, and the
+operation is repeated with another lot of acid. The measuring-tube is
+now taken from the clamp, and shaken for two or three minutes, until no
+more gas is given off. It is replaced, and the mercury-level in the two
+tubes adjusted. Then it is allowed to stand until the froth has
+subsided, and the gas has cooled to the temperature of the room. The
+volume of the gas is then read off. In adjusting the level, account must
+be taken of the sulphuric acid in the measuring-tube; this is allowed
+for by having the mercury higher in the other tube by, say, 1 mm. for
+each 6.5 mm. of sulphuric acid, or it is counterpoised by an equal
+height of sulphuric acid in the levelling-tube, in which case the two
+mercury-levels are made to correspond. On opening the tap after reading
+off the volume, there should be no change in the level of the mercury.
+If it should rise or fall a little, a slight increase or decrease (say
+0.1 c.c.) is made to the volume previously read off.
+
+In working with nitrate of soda, &c., in the bulb nitrometer, it is
+necessary to take a quantity of the substance which will yield more than
+100 and less than 150 c.c. of the gas.
+
+FOOTNOTES:
+
+[103] Na_{3}AsO_{3} + H_{2}O + 2I = Na_{3}AsO_{4} + 2HI. The acid is at
+once neutralised.
+
+[104] Mr. Thomas Gibb is the originator of this ingenious process.
+
+[105] By taking hold of the water present, it may prevent the
+dissociation of arsenious chloride.
+
+[106] It is difficult to get ferric chloride free from arsenic; but the
+following treatment will remove 80 or 90 per cent. of the arsenic
+contained in the commercial material:--Dissolve 2 or 3 lbs. of ferric
+chloride with the smallest amount of water that will effect solution
+with the addition of 100 c.c. of hydrochloric acid; add a solution of
+sulphurous acid in quantity sufficient to reduce 2 or 3 per cent. of the
+iron to the ferrous state; allow to stand a week; and then boil, to
+remove the hydrochloric acid added. Nitric acid, which is prejudicial,
+is also removed by this treatment.
+
+[107] When the amount of arsenic to be estimated is small (as in refined
+coppers), it is better to use a weaker solution of iodine. This is made
+by diluting 200 c.c. of the standard solution with water to 1 litre.
+Each c.c. will equal 0.1 per cent., if 1 gram of the metal has been
+taken for the assay.
+
+[108] The constitution of these phosphates may be thus illustrated--
+
+      Magnesic meta-phosphate MgO.P_{2}O_{5}.
+      Magnesic pyro-phosphate 2MgO.P_{2}O_{5}.
+      Magnesic ortho-phosphate 3MgO.P_{2}O_{5}.
+
+[109] The composition of which is--
+
+      MoO_{2}        90.74,
+      P_{2}O_{5}      3.14,
+      (NH_{4})_{2}O   3.57,
+      H_{2}O          2.55 = 100.00.
+
+[110] This is made by adding 27 grams of magnesium carbonate (a little
+at a time) to a solution of 270 grams of citric acid in 350 c.c. of warm
+water; and, when dissolved, adding 400 c.c. of dilute ammonia, and
+making up the bulk to 1 litre; 20 c.c. of the solution is sufficient for
+0.1 gram of P_{2}O_{5}, although more will be required if much iron or
+alumina is present.
+
+[111] For the details of the titration, the student is referred to the
+same place.
+
+[112] N_{2}O_{5} + 6FeO = 3Fe_{2}O_{3} + 2NO.
+
+
+
+
+CHAPTER XVIII.
+
+SILICON, CARBON, BORON.
+
+
+SILICON AND SILICATES.
+
+In assaying, more especially products direct from the mine, there is
+always found, when the rock is siliceous, a quantity of white
+sandy-looking substance, insoluble in acids, which is sometimes
+accompanied by a light gelatinous material very difficult to filter.
+This is variously described as "insoluble," "sand," "insoluble
+silicates," "gangue," or "rocky matter." It may be pure quartz; but
+oftener it is mixed with silicates from the rock containing the mineral.
+Some silicates, but not many, are completely decomposed by boiling with
+hydrochloric acid or aqua regia; and others are partly so, they yield a
+gelatinous precipitate of silica which greatly interferes with the
+filtering. It is a common practice with assayers to carry the first
+attack of the sample with acids to dryness, and to take up with a fresh
+portion of acid. By this means the separated silica becomes granular and
+insoluble, and capable of being filtered off and washed with comparative
+ease.
+
+This residue may be ignited and weighed; and be reported as so much per
+cent. of "silica and silicates insoluble in acids." Unless specially
+wanted, a determination of its constituents need not be made. When
+required, the analysis is best made on the ignited residue, and
+separately reported as "analysis of the insoluble portion."
+
+Silicon only occurs in nature in the oxidised state; but the oxide
+generally known as silica (SiO_{2}) is common, being represented by the
+abundant minerals--quartz, flint, &c. Silica, combined with alumina,
+lime, oxide of iron, magnesia and the alkalies, forms a large number of
+rock-forming minerals. Most rock masses, other than limestones, contain
+over 50 per cent. of silica. The following are analyses of some of the
+commoner silicates; but it must be noted that these minerals often show
+great variation in composition. This is more especially true of
+chlorite, schorl, hornblende and augite.
+
+[Table has been split into two because of its width--Transcriber]
+
+------------------+--------+------------+------------+-------+----------------
+                  |        |            |   Ferric   |Ferrous|
+                  | Silica |  Alumina   |   Oxide,   | Oxide,|    Fluorine,
+                  |SiO_{2}.|Al_{2}O_{3}.|Fe_{2}O_{3}.|  FeO. |    Water &c.
+------------------+--------+------------+------------+-------+----------------
+Potash-felspar    |  65.2  |    18.2    |     0.2    |  --   |
+Soda-felspar      |  67.0  |    19.2    |     --     |  0.3  |
+Lime-felspar      |  43.3  |    35.4    |     --     |  1.3  |
+Potash-mica       |  45.7  |    33.7    |     3.1    |  --   |F (0.8)
+                  |        |            |            |       |  H_{2}O (4.9)
+Magnesia-mica     |  39.1  |    15.4    |     7.1    |  --   |F (0.7)
+Hornblende        |  40.6  |    14.3    |     5.8    |  7.2  |
+Augite            |  50.0  |     3.7    |     2.4    |  6.6  |MnO (0.1)
+Almandine (Garnet)|  39.7  |    19.7    |     --     | 39.7  |MnO (1.8)
+Chlorite (Peach)  |  32.1  |    18.5    |     --     |  --   |H_{2}O (12.1)
+Schorl            |  37.0  |    33.1    |     9.3    |  6.2  |B_{2}O_{3} (7.7)
+                  |        |            |            |       |  F (1.5)
+China-clay        |  46.7  |    39.6    |     --     |  --   |H_{2}O (13.4)
+Talc              |  61.7  |     --     |     --     |  1.7  |H_{2}O (3.8)
+Serpentine        |  42.9  |     --     |     --     |  3.8  |H_{2}O (12.6)
+Olivine           |  39.3  |     --     |     --     | 14.8  |
+------------------+--------+------------+------------+-------+----------------
+
+------------------+-----+--------+-------+--------+------------------------
+                  |     |        |       |        |
+                  |Lime,|Magnesia|Potash | Soda,  |    Fluorine,
+                  |CaO. |  MgO.  |K_{2}O.|Na_{2}O.|    Water, &c.
+------------------+-----+--------+-------+--------+------------------------
+Potash-felspar    | --  |  --    | 14.7  |  1.5   |
+Soda-felspar      | 1.2 |  1.8   |  2.2  |  7.2   |
+Lime-felspar      |17.4 |  0.35  |  0.5  |  0.9   |
+Potash-mica       | --  |  1.1   |  7.5  |  2.8   |F (0.8) H_{2}O (4.9)
+                  |     |        |       |        |
+Magnesia-mica     | --  | 23.6   |  7.5  |  2.6   |F (0.7)
+Hornblende        |12.5 | 14.0   |  1.5  |  1.6   |
+Augite            |22.8 | 13.5   |  --   |  --    |MnO (0.1)
+Almandine (Garnet)| --  |  --    |  --   |  --    |MnO (1.8)
+Chlorite (Peach)  | --  | 36.7   |  --   |  --    |H_{2}O (12.1)
+Schorl            | 0.5 |  2.6   |  0.7  |  1.4   |B_{2}O_{3} (7.7) F (1.5)
+                  |     |        |       |        |
+China-clay        | --  |  --    |  --   |  --    |H_{2}O (13.4)
+Talc              | --  | 31.7   |  --   |  --    |H_{2}O (3.8)
+Serpentine        | --  | 40.5   |  --   |  --    |H_{2}O (12.6)
+Olivine           | --  | 45.8   |  --   |  --    |
+------------------+-----+--------+-------+--------+------------------------
+
+Silicon, from a chemical point of view, is an interesting body. It
+combines with iron to form a silicide; and is present in this condition
+in cast iron. Only in the case of the analysis of this and similar
+substances is the assayer called on to report the percentage of
+_silicon_. Silicon is readily converted into silica by the action of
+oxidizing agents. Silica forms only one series of salts--the
+silicates--which have in many cases a complex constitution; thus there
+are a large number of double silicates, which vary among themselves, not
+only in the relation of base to acid (which is the essential
+difference), but also in the ratio of the bases between themselves
+(which varies with almost every specimen).
+
+Silica is detected by heating the substance with a fluoride and
+sulphuric acid in a platinum-crucible. On holding a rod, moistened with
+a drop of water, over the escaping fumes, the white crust of silica
+formed on the drop of water shows its presence. The insolubility of a
+fragment of the mineral in a bead of microcosmic salt, is also a very
+good test; the fragment, on prolonged heating, does not lose its angular
+form.
+
+There is no dry assay for this substance, nor volumetric method; when
+the determination is required, it is carried out gravimetrically and,
+generally, by the following plan.
+
+If the sample contains oxides, sulphides, &c., in any quantity, these
+are first dissolved out by treatment with acid, evaporated to dryness,
+taken up with hydrochloric acid, and filtered. The dried residue is
+treated in the same way as the silicates. Some silicates are completely
+decomposed by such treatment; but it saves time (unless one is sure that
+no undecomposable silicate is present) to treat these in the same way as
+the others. On the other hand, there are some silicates which are only
+attacked with difficulty even by fusion with alkaline carbonates;
+consequently, it is always well to have the substance reduced to the
+finest state of division by careful powdering, as this greatly assists
+the subsequent action. With very hard silicates, the grinding away of
+the mortar in this operation will be perceptible; the foreign matter
+thus introduced must not be ignored. Previously igniting the substance
+sometimes assists the powdering; but it is best to use a steel mortar.
+The particles of steel can be removed by a magnet, or, where the nature
+of the substance will allow it, by boiling with a little dilute
+hydrochloric acid.
+
+The dried and powdered material is intimately mixed with four times its
+weight of "fusion mixture" in a platinum-crucible or dish. It is then
+moderately heated over a Bunsen burner, and afterwards more strongly
+fused over a blast, or enclosed in a clay crucible in the wind-furnace.
+The action is continued until the fused mass is perfectly tranquil. With
+very refractory substances, the action must be long continued at a high
+temperature. When sufficiently cold, the crucible is examined to see
+that no particles of foreign matter are adhering to its outer surface.
+It is then transferred to a five- or six-inch evaporating-dish, where
+its contents are acted upon with warm water for some time. The "melt"
+will slowly dissolve, but the solution should be hastened by keeping the
+liquid moderately acid with hydrochloric acid. When the "melt" has
+dissolved, clean and remove the platinum-dish, and evaporate the
+solution to a paste. Continue the evaporation to dryness on a water-bath
+(not on the hot plate), and whilst drying stir with a glass rod, feeling
+at the bottom of the dish for any unfused particles, which, if present,
+can be detected by their grittiness. If there is much grit, it will be
+necessary to repeat the assay; but with a small quantity it will only be
+necessary to refuse the grit and silica after ignition.
+
+During solution of the "melt" and evaporation (which may be carried on
+together), a clear solution will not be obtained, a flocculent silica
+will separate out, and towards the end of the evaporation the mass will
+get gelatinous. The drying of the jelly must be finished on the
+water-bath; first, because at this temperature the silica is rendered
+insoluble in hydrochloric acid, whilst the solubility of the alumina,
+iron, &c., is unaffected, which would not be the case at a much higher
+temperature; and second, because the gelatinous residue requires very
+cautious drying to prevent loss from spirting.
+
+When dry, the substance is moistened, and heated with strong
+hydrochloric acid, and the sides of the dish are washed down with water.
+The silica is washed by decantation two or three times with hydrochloric
+acid and hot water, before being thrown on to the filter. The filtrate
+is again evaporated to dryness, taken up with a little hydrochloric acid
+and water and again filtered. The residue on the filter is silica. The
+two lots of silica are washed free from chlorides with hot water, dried
+on an air-bath, transferred to a platinum-crucible, ignited gently at
+first, at last strongly over the blast or in a muffle, cooled in a
+desiccator, and weighed.
+
+The white powdery precipitate is silica (SiO_{2}), and its weight,
+multiplied by 100, and divided by the weight of ore taken, gives the
+percentage of silica in the sample. Where the percentage of silicon is
+wanted, which is very rarely the case, it is got by multiplying this
+result by 0.4667. It is always necessary to examine the purity of the
+body weighed as silica. This is done by re-fusing the material weighed,
+and re-determining the silica in it; or, better, by mixing a weighed
+portion in a platinum-dish with a little strong sulphuric acid, covering
+with hydrofluoric acid, and evaporating. In the latter case, the silica
+will be converted into fluoride, which will be driven off, and the
+impurities will be left behind as sulphates of barium, phosphate and
+oxide of tin, titanium, &c. This must be weighed and deducted from the
+weight of the silica. In a complete examination of a silicate it should
+be treated with the precipitate containing alumina, ferric oxide, &c.
+
+
+EXAMINATION OF SILICATES.
+
+The student interested in the analysis of rocks and rock-forming
+minerals is advised to consult a valuable paper by Dr. W.F. Hillebrand
+in the _Bulletin of the United States Geological Survey_, _No._ 148, to
+which I am very largely indebted in the revision of the following pages.
+
+~Moisture.~--Five grams of the powdered sample is dried between
+watch-glasses in the water-oven for two hours, or till its weight is
+constant; and the loss is reported as water lost at 100° C. The rest of
+the determinations are made on this dried mineral.
+
+~Combined Water, &c.~--Weigh up 1 gram of the substance, and ignite
+over the blowpipe for some time in a platinum-crucible, cool in a
+desiccator, and weigh. Record the loss as "loss on ignition," not as
+"combined water."
+
+~Silica.~--The ignition should have been performed in an oxidising
+atmosphere in a muffle or over a slanting blowpipe flame; this will
+ensure the oxidation of any pyrites or other sulphide present, which if
+unoxidised would injure the crucible in the next operation. The ignited
+residue is mixed with 6 or 7 grams of anhydrous sodium carbonate. This
+reagent should be the purest obtainable, but its purity should be
+checked, or rather its impurities should be determined by running a
+"check" or "blank" assay with 10 grams of it through the stages of the
+analysis; the impurities will be chiefly silica, alumina and lime, and
+altogether they ought not to exceed 1 milligram. The crucible with the
+mixture is heated at first gently over a Bunsen and afterwards more
+strongly in an oxidising atmosphere in a muffle or over the blowpipe.
+The fused mass is allowed to cool in the crucible, and is then dissolved
+out in a basin with water and a small excess of hydrochloric acid. After
+the removal and cleaning of the crucible, the liquor is evaporated
+almost to dryness. Dr. Hillebrand advises stopping short of complete
+dryness. The residue is taken up with a little hydrochloric acid and
+water and filtered and washed. The liquor, including the washings, is
+again evaporated and taken up with water and a little acid. Usually
+about 1 per cent. of silica will be thus recovered. It is to be filtered
+off and washed and added to the main silica. The filtrate is reserved.
+The silica, thoroughly washed, is dried and ignited at a high
+temperature for twenty or thirty minutes. It is then weighed in a
+platinum crucible. After weighing it is treated with hydrofluoric acid
+and a little sulphuric, carefully evaporated and ignited strongly. The
+residue, which in extreme cases may amount to 2 or 3 per cent. of the
+rock, is weighed and deducted from the weight of the impure silica. It
+is retained in the crucible.
+
+~Alumina, &c.~--The filtrate from silica is treated by the basic acetate
+method. That is, it is first treated by a cautious addition of a
+solution of soda, almost to the point of producing a precipitate, in
+order to neutralise the excess of acid; 2 or 3 grams of sodium acetate
+are added, and the whole boiled for a minute or so. The precipitate is
+filtered off and washed only slightly. Save the filtrate. The
+precipitate is dissolved in hydrochloric, or, perhaps better, in nitric
+acid; and is reprecipitated by adding an excess of ammonia and boiling.
+The precipitate is filtered and washed with water containing 2 per cent.
+of ammonium nitrate. Both filtrates are evaporated separately to a small
+bulk, a drop or two of ammonia being added to the second towards the
+finish. They are next filtered into a 6 or 8-ounce flask through a small
+filter, the second filtrate coming after, and serving in a manner as
+wash water for the first[113]. The two washed alumina precipitates are
+dried and placed in the platinum crucible containing the residue from
+silica after treatment with hydrofluoric acid. They are then ignited in
+an oxidising atmosphere at a high temperature for about 10 minutes. The
+weight, including that of the residue from the silica, is noted as that
+of "alumina, &c."
+
+The weighed oxides are next fused with bisulphate of potash for some
+hours. The bisulphate should have been first fused, apart, until the
+effervescence from the escape of steam has stopped. The melt is
+dissolved out with cold water and dilute sulphuric acid, and any
+insoluble residue is filtered off, washed, ignited and weighed. The
+filtrate is reserved for determinations of iron and titanium. The
+residue, after weighing, may be treated with hydrofluoric and sulphuric
+acids for any silica,[114] which would be determined by loss. It may be
+tested for barium sulphate by treatment with hot strong sulphuric acid;
+in which this salt dissolves, but is again insoluble (and so comes out
+as a white precipitate) on diluting with cold water; the acid also must
+be cold before adding the water. The filtrate containing the iron is
+reduced with sulphuretted hydrogen, boiled till free from that gas,
+filtered and titrated with a standard solution of permanganate of
+potassium. The iron found is calculated to ferric oxide by dividing by
+.7. The iron solution after titration serves for the determination of
+titanium oxide (TiO_{2}). This is done colorimetrically, by adding
+peroxide of hydrogen free from hydrofluoric acid, and comparing the
+brown colour produced with that produced by the addition of a standard
+solution of titanium to an equal volume of water containing sulphuric
+acid.[115] The alumina is determined by difference. From the weight of
+the combined precipitate which has been recorded as "Alumina, &c.,"
+deduct (1) the residue, insoluble, after fusion with bisulphate; (2) the
+ferric oxide; (3) the titanium oxide; and (4) the phosphoric oxide
+(P_{2}O_{5}), the amount of which is subsequently determined in a
+separate portion. This gives the alumina.
+
+~Manganous oxide, &c.~--The filtrate from the "alumina, &c." contained
+in a 6 or 8-ounce flask, which it nearly fills, is made slightly
+alkaline with ammonia and treated with a small excess of ammonium
+sulphide; the flask is then corked and placed on one side for some time
+(a day or so) so that the manganese sulphide may separate. The
+precipitate is filtered off and washed with water containing ammonium
+chloride and a few drops of ammonium sulphide. The filtrate is reserved
+for lime, &c. The precipitate is digested with sulphuretted hydrogen
+water, to which one-fifth of its volume of strong hydrochloric acid has
+been added; this dissolves the sulphides of zinc and manganese; any
+black residue should be tested for copper and perhaps nickel. The
+solution is evaporated to dryness, taken up with a little water and
+treated with a small excess of solution of carbonate of soda. It is
+boiled and again evaporated, washed out with hot water and filtered on
+to a small filter, dried, ignited, and weighed as Mn_{3}O_{4}. It is
+calculated to MnO. It may contain, and should be tested for oxide of
+zinc, which, if present, must be deducted. If the dish becomes stained
+during evaporation, take up with a few drops of hydrochloric and
+sulphurous acids, evaporate, and then treat with carbonate of soda.
+
+~Lime, &c.~--The filtrate from the manganese sulphide is boiled, and
+without cooling, treated with ammonium oxalate in solution, which also
+should be heated to boiling. The liquid is filtered off and reserved for
+magnesia. The precipitate is dissolved in very little hydrochloric acid
+and reprecipitated by adding ammonium oxalate and ammonia to the boiling
+solution. The filtrate and washings from this are reserved for magnesia.
+The precipitate is either dissolved in dilute sulphuric and titrated
+with permanganate of potash as described under Lime (p. 322); or it is
+ignited and weighed as oxide. In this last case it may be examined for
+barium and strontium, the former of which will rarely be present.
+
+~Magnesia.~--The filtrate from the first lime precipitate is treated
+with sodium phosphate and ammonia, and allowed to stand overnight. It is
+then filtered. The precipitate is dissolved in hydrochloric acid; the
+solution is filtered into the beaker containing the solution from the
+second lime precipitate. Ammonia and sodium phosphate are again added,
+and the precipitate, after standing, is filtered off, washed with water
+containing ammonia; it is then dried, ignited and weighed as magnesium
+pyrophosphate. This is calculated into magnesia.
+
+~Potash and Soda.~--Weigh out .5 gram of the dried ore, and mix with an
+equal quantity of ammonic chloride; and to the mixture add gradually 4
+grams of calcium carbonate ("precipitated"). Introduce into a
+platinum-crucible and cover loosely. Heat, at first, gently; and then at
+a red heat for from forty to sixty minutes. Transfer to a porcelain
+dish, and digest with 60 or 80 c.c. of water; warm and filter: to the
+filtrate add ammonic carbonate and ammonia, and filter; evaporate the
+filtrate to dryness, adding a few drops more of ammonic carbonate
+towards the end; when dry, heat gently, and then raise the temperature
+to a little below redness. Dissolve in a small quantity of water, add a
+drop of ammonic carbonate, and filter through a small filter into a
+weighed platinum dish. Evaporate, ignite gently, and weigh. The residue
+contains the soda and potash of the mineral as chlorides.
+
+To determine the proportion of potassium, dissolve this residue in a
+little water, add platinum chloride in excess, evaporate to a paste,
+extract with alcohol, decant through a small weighed filter, wash with
+alcohol, and dry at 100° C. Weigh. The substance is potassium platinic
+chloride (2KCl.PtCl_{4}). Its weight, multiplied by 0.1941, will give
+the weight of potash (K_{2}O).
+
+To find the proportion of soda, multiply the weight of the potassium
+platinic chloride by 0.306; this gives the weight of potassium chloride.
+Deduct this from the weight of the mixed chlorides first got; the
+difference will be the sodium chloride, which weight, multiplied by
+0.53, will give the weight of soda (Na_{2}O).
+
+~Ferrous Oxide.~--When a qualitative test shows both ferric and ferrous
+oxide to be present, the proportion of the ferrous oxide must be
+separately determined. The finely ground mineral mixed with dilute
+sulphuric acid is treated on a water bath with hydrofluoric acid.
+Solution is best effected in an atmosphere of carbonic acid. In about an
+hour the decomposition is complete, and the solution is diluted with
+cold water, and titrated with the solution of bichromate or of
+permanganate of potassium. The iron found is multiplied by 1.286, and
+reported as ferrous oxide. To find the proportion of ferric oxide, the
+ferrous iron found is multiplied by 1.428, and this is deducted from the
+weight of ferric oxide obtained by precipitation with ammonia. The
+ammonia precipitate contains the whole of the iron as ferric oxide;
+hence the necessity for calculating the ferrous oxide as ferric, and
+deducting it.
+
+~Phosphoric Oxide (P_{2}O_{5}).~--Weigh up 5 grams of the finely-divided
+and dry sample, and digest with 10 or 20 c.c. of nitric acid; evaporate
+to dryness on the water-bath; take up with a little dilute nitric acid;
+dilute with water; and filter. Add a few grams of ammonic nitrate and 10
+c.c. of ammonium molybdate solution, heat nearly to boiling, and allow
+to settle; filter off, and wash the yellow precipitate. Dissolve with
+dilute ammonia, add "magnesia mixture," and allow to stand overnight.
+Filter, wash with dilute ammonia, dry, ignite, and weigh as
+pyrophosphate of magnesia. The weight, multiplied by 0.6396, gives the
+weight of phosphoric oxide.
+
+~Soluble Silica.~--Some silicates are acted on by hydrochloric acid, and
+leave on evaporation a residue; which, when the soluble salts have been
+washed out, consists generally of the separated silica with perhaps
+quartz and unattacked silicates. It should be ignited, weighed and
+boiled with a solution containing less than 10 per cent. of caustic
+soda: this dissolves the separated silica. The liquor is diluted,
+rendered faintly acid, and filtered. The residue is washed, ignited and
+weighed. The loss gives the soluble silica.
+
+~Estimation of Silica in Slags~ (Ferrous silicates).--Take 1 gram of the
+powdered slag, treat with aqua regia, evaporate to dryness, extract with
+hydrochloric acid, filter, dry, ignite, and fuse the ignited residue
+with "fusion mixture," then separate and weigh the silica in the usual
+way. Slags are for the most part decomposed by boiling with aqua regia,
+but it will be found more convenient and accurate to first extract with
+acids and then to treat the residue as an insoluble silicate.
+
+~Estimation of "Silica and Insoluble Silicates" in an Ore.~--Take 2
+grams of the powdered mineral, evaporate with nitric acid (if sulphides
+are present), treat the dried residue (or the original substance if
+sulphides are absent) with 10 or 20 c.c. of hydrochloric acid; again
+evaporate to dryness, take up with dilute hydrochloric acid, filter,
+wash, ignite, and weigh.
+
+~Estimation of Silicon in Iron.~--Place 2 grams of the metal (borings or
+filings) in a four-inch evaporating dish, and dissolve (with aid of
+heat) in 25 c.c. of dilute nitric acid. Evaporate to complete dryness,
+take up with 20 c.c. of hydrochloric acid, and allow to digest for one
+hour. Boil down to a small bulk, dilute with a 5 per cent. solution of
+hydrochloric acid, boil, and filter. Wash with acid and water, dry,
+ignite in a platinum crucible, and weigh the SiO_{2}. This, multiplied
+by 0.4673, gives the weight of the silicon. The percentage is calculated
+in the usual way.
+
+
+PRACTICAL EXERCISES.
+
+1. A certain rock is a mixture of 70 per cent. of quartz, 25 per cent.
+of potash-felspar, and 5 per cent. of potash-mica. What per cent. of
+silica will it contain?
+
+2. Two grams of a mixture of silica and cassiterite left, after
+reduction in hydrogen, 1.78 grams. Assuming all the oxide of tin to have
+been reduced, what will be the percentage of silica?
+
+3. The formula of a compound is 2FeO.SiO_{2}. What percentage of silica
+will it contain?
+
+4. Two grams of a sample of cast-iron gave 0.025 gram of silica. Find
+the percentage of silicon in the metal.
+
+5. What weights of quartz and marble (CaCO_{3}) would you take to make
+30 grams of a slag having the formula CaO.SiO_{2}?
+
+
+CARBON AND CARBONATES.
+
+Carbon compounds enter so largely into the structure of organised bodies
+that their chemistry is generally considered apart from that of the
+other elements under the head of _Organic Chemistry_. Carbon occurs,
+however, among minerals not only in the oxidised state (as carbonates),
+but also in the elementary form (as in diamond and graphite), and
+combined with hydrogen, oxygen, &c. (as in petroleums, bitumens,
+lignites, shales, and coals). In small quantities "organic matter" is
+widely diffused in minerals and rocks. In shales and clays it may amount
+to as much as 10 or 20 per cent. (mainly as bituminous and coaly
+matters).
+
+The assayer has only to take account of the organic matter when it is of
+commercial importance, so that in assays it is generally included under
+"loss on ignition."
+
+In coals, shales, lignites, &c., the carbon compounds are, on heating,
+split up into oils and similar compounds. The products of distillation
+may be classified as water, gas, tars, coke, and ash. The assay of these
+bodies generally resolves itself into a distillation, and, in the case
+of the shales, an examination of the distillates for the useful oils,
+paraffin, creosote, &c., contained in them.
+
+Elementary carbon is found in nature in three different forms, but these
+all re-act chemically in the same way. They combine with oxygen to form
+the dioxide.[116] The weight of oxygen required to burn a given weight
+of any form of carbon is the same, and the resulting product from all
+three has the same characteristic properties. Carbon dioxide is the
+common oxide of carbon. A lower oxide exists, but on burning it is
+converted into the dioxide. Wherever the oxidation of carbon takes
+place, if there is sufficient oxygen, carbon dioxide (carbonic acid) is
+formed; this re-action is the one used for the determination of carbon
+in bodies generally. The dioxide has acid properties, and combines with
+lime and other bases forming a series of salts called carbonates.
+
+The carbon-compounds (other than carbonates, which will be subsequently
+considered) occurring in minerals are generally characterised by their
+sparing solubility in acids. The diamond is distinguished from other
+crystals by its hardness, lustre, and specific gravity. It may be
+subjected to a red heat without being apparently affected, but at a
+higher temperature it slowly burns away. Graphite, also, burns slowly,
+but at a lower temperature. The other bodies (coals, shales, &c.) differ
+considerably among themselves in the temperature at which they commence
+to burn. Some, such as anthracite, burn with little or no flame, but
+most give off gases, which burn with a luminous flame. They deflagrate
+when sprinkled on fused nitre, forming carbonate of potash. In making
+this test the student must remember that sulphur and, in fact, all
+oxidisable bodies similarly deflagrate, but it is only in the case of
+carbon compounds that carbonate of potash is formed. Carbon unites with
+iron and some of the metals to form carbides; combined carbon of this
+kind is detected by the odour of the carburetted hydrogen evolved when
+the metal is treated with hydrochloric acid; for example, on dissolving
+steel in acid.
+
+The natural carbon compounds, although, speaking generally, insoluble in
+hydrochloric or nitric acids, are more or less attacked by aqua regia.
+The assayer seldom requires these compounds to be in solution. The
+presence of "organic matter"[117] interferes with most of the reactions
+which are used for the determination of the metals. Consequently, in
+such cases, it should be removed by calcination unless it is known that
+its presence will not interfere. When calcination is not admissible it
+may be destroyed by heating with strong sulphuric acid and bichromate or
+permanganate of potash or by fusion with nitre.
+
+Carbon may be separated from other substances by conversion into carbon
+dioxide by burning. In most cases substances soluble in acids are first
+removed, and the insoluble residue dried, weighed, and then calcined or
+burned in a current of air. The quantity of "organic matter" may be
+determined indirectly by the loss the substance undergoes, but it is
+better to determine the "organic carbon" by confining the calcination in
+a tube, and collecting and weighing the carbon dioxide formed. Each gram
+of carbon dioxide is equivalent to 0.2727 gram of carbon.
+
+[Illustration: FIG. 70.]
+
+[Illustration: FIG. 71.]
+
+Instead of a current of oxygen or air, oxide of copper may be more
+conveniently used. The operation is as follows:--Take a clean and dry
+piece of combustion tube drawn out and closed at one end, as shown in
+the figure (fig. 70), and about eighteen inches long. Fit it with a
+perforated cork connected with a ~U~-tube (containing freshly-fused
+calcium chloride in coarse grains) and a set of potash bulbs (fig. 71)
+(containing a strong solution of potash), the exit of which last is
+provided with a small tube containing calcium chloride or a stick of
+potash. Both the ~U~-tube and bulbs should have a loop of fine wire, by
+which they may be suspended on the hook of the balance for convenience
+in weighing. They must both be weighed before the combustion is
+commenced; to prevent absorption of moisture during weighing, &c., the
+ends are plugged with pieces of tube and glass rod.
+
+Fill the combustion tube to a depth of about eight inches with some
+copper oxide, which has been recently ignited and cooled in a close
+vessel. Put in the weighed portion for assay and a little fresh copper
+oxide, and mix in the tube by means of an iron wire shaped at the end
+after the manner of a corkscrew. Put in some more oxide of copper, and
+clean the stirrer in it. Close loosely with a plug of recently ignited
+asbestos, place in the furnace, and connect the ~U~-tube and bulbs in
+the way shown in the sketch (fig. 72).
+
+[Illustration: FIG. 72.]
+
+See that the joints are tight, and then commence the combustion by
+lighting the burners nearest the ~U~-tube; make the first three or four
+inches red hot, and gradually extend the heat backwards the length of
+the tube, but avoid too rapid a disengagement of gas. When gas ceases to
+come off, open the pointed end of the tube and draw a current of dried
+air through the apparatus.
+
+The carbon dioxide is absorbed in the potash bulbs, and their increase
+in weight multiplied 0.2727 gives the amount of carbon in the substance
+taken.
+
+The increase in weight in the calcium chloride tube will be due to the
+water formed by the oxidation of the combined hydrogen. If this last is
+required the increase in weight multiplied by 0.111 gives its amount.
+
+
+COALS.
+
+The determination of the actual carbon in coals and shales is seldom
+called for; if required, it would be performed in the way just
+described.[118] The ordinary assay of a sample of coal involves the
+following determinations--moisture, volatile matter, fixed carbon, ash,
+and sulphur. These are thus carried out:--
+
+~Determination of Moisture.~--Take 3 grams of the powdered sample and
+dry in a water-bath for an hour or so. The loss is reported as moisture.
+Coals carry from 1 to 2 per cent. If the drying is carried too far,
+coals gain a little in weight owing to oxidation, so that it is not
+advisable to extend it over more than one or two hours.
+
+~Determination of Volatile Matter.~--This determination is an
+approximate one, and it is only when working under the same conditions
+with regard to time, amount of coal taken, and degree of heat used, that
+concordant results can be arrived at. It is a matter of importance
+whether the coal has been previously dried before heating or not, since
+a difference of 2 per cent. may be got by working on the dried or
+undried sample. Take 2 grams of the powdered, but undried, sample of
+coal, place in a weighed platinum crucible, and support this over a good
+Bunsen burner by means of a thin platinum-wire triangle. The heat is
+continued until no further quantity of gas comes off and burns at the
+mouth. This takes only a few minutes. The cover is tightly fitted on,
+and when cold the crucible is weighed. The loss in weight, after
+deducting the moisture, gives the "volatile matter," and the residue
+consists of "fixed carbon" and "ash."
+
+~Determination of Ash.~--The coke produced in the last operation is
+turned out into a porcelain dish and ignited over a Bunsen burner till
+the residue is free from particles of carbon. Calcination is hastened by
+stirring with a platinum wire. The operation may be done in a muffle,
+but this gives results a few tenths of a per cent. too low. The dish is
+cooled in a dessicator, and weighed. The increase in weight gives the
+amount of "ash," and the difference between this and the weight of the
+coke gives the "fixed carbon."
+
+The assay is reported as follows:--
+
+  Moisture at 100° C.         ----  per cent.
+  Volatile matter             ----     "
+  Fixed carbon                ----     "
+  Ash                         ----     "
+  contains sulphur ---- per cent.
+
+~Determination of Sulphur.~--The sulphur exists in the coal partly in
+organic combination, partly as metallic sulphide (iron pyrites,
+marcasite, &c.), and, perhaps, as sulphate. So that the sulphur
+determination must be separately reported, since a portion will go off
+with the volatile matter, and the remainder would be retained and
+weighed with the coke.
+
+The sulphur is thus determined:--Take 1 gram of the coal and mix with
+1.5 gram of a mixture of 2 parts of calcined magnesia and 1 part of
+carbonate of soda, and heat in a platinum crucible for one hour or until
+oxidation is complete. Turn out the mass and extract it with water and
+bromine, filter, acidulate with hydrochloric acid, boil off the bromine,
+and precipitate with baric chloride (estimating gravimetrically as given
+under _Sulphur_). Another method is as follows:--Take 1 gram of the coal
+and drop it gradually from a sheet of note paper on to 5 grams of fused
+nitre contained in a platinum dish. Extract with water, acidify with
+acetic acid, and estimate volumetrically as described under _Sulphur_.
+
+[Illustration: FIG. 73.]
+
+~Calorific Effect of Coals.~--The heat-giving value of a coal is best
+expressed in the number of pounds of water, previously heated to the
+boiling point, which it will convert into steam. This is generally
+termed its evaporative-power. It may be determined by means of the
+calorimeter (fig. 73). This consists of a glass cylinder marked to hold
+29.010 grains of water. The instrument consists of a perforated copper
+stand, provided with a socket and three springs. The socket holds a
+copper cylinder which is charged with 30 grains of the dried coal mixed
+with 300 grains of a mixture of 3 parts of potassium chlorate and 1 part
+of nitre. The charge is well packed in the cylinder and provided with a
+small fuse of cotton saturated with nitre. Fill the glass cylinder to
+its mark with water and take the temperature with a thermometer marked
+in degrees Fahrenheit. Ignite the fuse and immediately cover with the
+outer copper cylinder (extinguisher-fashion), which will be held in its
+place by the springs. The stop-cock should be closed before this is
+done. Place the apparatus quickly in the cylinder of water. When the
+action is over open the stop-cock and agitate the water by raising and
+lowering the instrument a few times. Again take the temperature. The
+rise in temperature, plus 10 per cent. for the heat used in warming the
+apparatus and lost by radiation, gives the evaporative-power.
+
+The following is an example:--
+
+  Temperature before experiment  67.0° F.
+  Temperature after      "       79.0° "
+                                 --------
+  Rise                           12.0° "
+      + 1/10th                    1.2° "
+                                 --------
+  Gives                          13.2° "
+
+One pound of the coal will evaporate 13.2 pounds of water.
+
+
+SHALES, ETC.
+
+The assay of these is carried out in the same way as that of coals, but
+the volatile matters are separately examined, and, in consequence, a
+larger quantity of material must be used. For the moisture, volatile
+matter, fixed carbon and ash, the determinations are the same, but a
+special distillation must be made to obtain a sufficient quantity of the
+volatile products for subsequent examination. Take 500 or 1000 grams of
+the well-sampled and powdered shale, and introduce into a cast-iron
+retort as shown in fig. 74. Lute the joint with fire-clay, place the
+cover on, and bolt it down. The bolts should have a covering of
+fire-clay to protect them from the action of the fire. Place the retort
+in a wind furnace, supporting it on a brick, and pack well around with
+coke. Build up the furnace around and over the retort with loose
+fire-bricks, and heat gradually.
+
+[Illustration: FIG. 74.]
+
+As soon as water begins to drip, the tube of the retort is cooled by
+wrapping a wet cloth around it, and keeping wet with water. The water is
+kept from running into the receiver by a ring of damp fire-clay. A
+quantity of gas first comes over and will be lost, afterwards water and
+oily matters. The retort must be red hot at the close of the
+distillation, and when nothing more distils off, which occurs in about
+two or three hours, the wet cloth is removed, and the tube heated with a
+Bunsen burner to drive forward the matter condensed in it into the
+receiver, and thus to clean the tube. It can be seen when the tube is
+clean by looking up through it into the red-hot retort. The receiver is
+then removed, and the retort, taken from the furnace, is allowed to
+cool. When cold it is opened, and the fixed carbon and ash weighed, as a
+check on the smaller assay.
+
+The distillate of water and oil is warmed, and will separate into two
+layers, the upper one of which is oil, and the lower water. These are
+measured, and if the specific gravity of the oil is taken, its weight
+may be calculated. If the two liquids do not separate well, the water
+may be filtered off, after cooling, through a damped filter. The
+separation is, however, best effected in a separator (fig. 75). The
+liquids are poured into this, allowed to settle, and the lower layer
+drained off. The volume of the water is measured and its weight
+calculated in per cents. on the amount of shale taken.
+
+[Illustration: FIG. 75.]
+
+~Examination of the Oil.~--A sufficient quantity of the oil must be got,
+so that if one distillation does not yield enough, the requisite
+quantity must be obtained by making two or more distillations. The oils
+are mixed, and the mixture, after having had its volume and specific
+gravity ascertained, is placed in a copper retort, and re-distilled with
+the aid of a current of steam. The residue in the retort is coke.
+
+The distillate is separated from the water by means of the separator,
+and shaken for ten minutes with one-twentieth of its bulk of sulphuric
+acid (sp. g. 1.70). The temperature should not be allowed to rise above
+40°. Allow to stand, and run off the "acid tar."
+
+The oil is now shaken up with from 10 c.c. to 20 c.c. of sodic hydrate
+solution (sp. g. 1.3), allowed to stand, warmed for half-an-hour, and
+the "soda-tar" run off.
+
+On mixing this soda-tar with dilute acid, the "crude shale oil creosote"
+separates, and is measured off.
+
+The purified oil is next re-distilled in fractions, which come over in
+the following order:--"Naphtha," "light oil," "heavy oil," and "still
+bottoms." For the first product, which is only got from certain shales,
+the receiver is changed when the distillate has a specific gravity of
+0.78. For the second product the process is continued till a drop of the
+distillate, caught as it falls from the neck of the retort on a cold
+spatula, shows signs of solidifying. This is "crude light oil."
+
+The receiver is changed, and the "heavy oil" comes over; towards the end
+a thick brown or yellow viscid product is got. The receiver is again
+changed, and the distillation carried to dryness.
+
+The "crude light oil" is washed cold with 2 per cent. of sulphuric acid
+(concentrated), and afterwards with excess of soda. Thus purified it is
+again distilled to dryness, three fractions being collected as before.
+Naphtha, which is added to the main portion, and measured; "light oil,"
+which is also measured; and "heavy oil," which is added to that got in
+the first distillation. This last is poured into a flat-bottom capsule,
+and allowed to cool slowly. The temperature may with advantage be
+carried below freezing-point. The cooled cake is pressed between folds
+of linen, and the paraffin scale detached and weighed.
+
+The results may be reported thus:--
+
+  Naphtha, sp. g.          ----
+  Light oil, sp. g.        ----
+  Heavy oil, sp. g.        ----
+  Paraffin scale           ----
+  Coke, &c.                ----
+
+The results are calculated in per cents. on the oil taken. Some workers
+take their fractions at each rise of 50° C. The composition of average
+shale, as given by Mills, is as follows:--Specific gravity, 1.877;
+moisture, 2.54.
+
+  Gas                             }
+  Volatile matter, water, ammonia }  23.53
+  Oil                             }
+  Fixed carbon                       12.69
+  Ash                                63.74
+                                     _____
+                                     99.96
+
+The ash is made up of silica, 55.6; ferric oxide, 12.2; alumina, 22.14;
+lime, 1.5; sulphur, 0.9; soluble salts (containing 0.92 per cent.
+sulphuric oxide), 8.3.
+
+  Total sulphur in shale      1.8 per cent.
+    "      "    in ash        1.3    "
+
+For further information on these assays, and for the assay of
+petroleums, bitumens, &c., the student is referred to Allen's
+"Commercial Organic Analysis," Vol. II.
+
+~Determination of Organic Carbon in a Limestone.~--Take 1 or 2 grams and
+dissolve with a very slight excess of dilute hydrochloric acid,
+evaporate to dryness, and determine the carbon in the residue by
+combustion with copper oxide.
+
+~Estimation of Carbon in a Sample of Graphite (Black-lead).~--Weigh up 1
+or 2 grams in a dish and calcine in the muffle till the carbon is burnt
+off. Weigh the residue, and calculate the carbon by difference.
+
+[Illustration: FIG. 76.]
+
+[Illustration: FIG. 77.]
+
+[Illustration: FIG. 78.]
+
+~Determination of Carbon in Iron.~--The carbon exists in two
+states--free (graphite) and combined. The following process estimates
+the total carbon:--The carbon existing as graphite may be separately
+estimated in another portion by the same process, but using hydrochloric
+acid to dissolve the iron instead of the copper solution:--Weigh up 2
+grams of the iron (or a larger quantity if very poor in carbon), and
+attack it with 30 grams of ammonic-cupric chloride[119] dissolved in 100
+c.c. of water. Let the reaction proceed for a quarter-of-an-hour, and
+then warm until the copper is dissolved. Allow to settle, and filter
+through a filtering-tube. This is a piece of combustion tube drawn out
+and narrowed at one end, as shown in fig. 76. The narrow part is blocked
+with a pea of baked clay, and on this is placed half-an-inch of silica
+sand (previously calcined to remove organic matter), then a small plug
+of asbestos, and then a quarter-of-an-inch of sand. The tube is
+connected with a pump working at a gentle pressure, and the solution is
+filtered through the tube with the aid of a small funnel (fig. 77). The
+residue is washed, first with dilute hydrochloric acid, and then with
+distilled water. The tube is dried by aspirating air through it, and
+gently warming with a Bunsen burner. The tube is then placed in a small
+combustion-furnace, and connected with calcium chloride and potash
+bulbs, as shown in fig. 78. The potash bulb to the right of the figure
+must be weighed. A slow stream of air is drawn through the apparatus,
+and the heat gradually raised; in from thirty minutes to one hour the
+combustion will be complete. The potash bulbs are then disconnected and
+weighed, and the increase multiplied by 0.2727 gives the weight of
+carbon.
+
+
+CARBONATES.
+
+Carbon dioxide, which is formed by the complete oxidation of carbon, is
+a gas with a sweetish odour and taste, having a strong affinity for
+alkalies, and forming a series of compounds termed carbonates. The gas
+itself occurs in nature, and is sometimes met with in quantity in
+mining. The carbonates occur largely in nature, forming mountain masses
+of limestone, &c. Carbonates of many of the metals, such as carbonate of
+lead (cerussite), carbonate of iron (chalybite), carbonates of copper
+(malachite and chessylite), and carbonate of magnesia (magnesite), are
+common.
+
+All the carbonates (those of the alkalies and alkaline earths excepted)
+are completely decomposed on ignition into the oxide of the metal and
+carbon dioxide; but the temperature required for this decomposition
+varies with the nature of the base. All carbonates are soluble with
+effervescence in dilute acids; some, such as chalybite and magnesite,
+require the aid of heat. The alkaline carbonates are soluble in water;
+the rest, with the exception of the bicarbonates, are insoluble therein.
+
+Carbonates are recognised by their effervescence with acids--a stream of
+bubbles of gas are given off which collect in the tube, and possess the
+property of extinguishing a lighted match. The most characteristic test
+for the gas is a white precipitate, which is produced by passing it into
+lime or baryta-water, or into a solution of subacetate of lead.
+
+The expulsion of carbon dioxide by the stronger acids serves for the
+separation of this body from the other acids and bases.
+
+~Dry Assay.~--There is no dry assay in use. Any method which may be
+adopted will necessarily be applicable only to special compounds.
+
+
+WET METHODS.
+
+There are several methods in use which leave little to be desired either
+in speed or accuracy. We will give (1) a gravimetric method in which the
+estimation may be made directly by weighing the carbonic acid, or,
+indirectly, by estimating the carbon dioxide from the loss; (2) a
+volumetric one, by which an indirect determination is made of the gas;
+and (3) a gasometric method, in which the volume of carbon dioxide given
+off is measured, and its weight deducted.
+
+[Illustration: FIG. 79.]
+
+[Illustration: FIG. 80.]
+
+~Direct Gravimetric Method.~--Fit up the apparatus shown in the diagram
+(fig. 79). The various tubes are supported by a fixed rod with nails and
+wire loops, and connected by short lengths of rubber-tubing. The first
+tube contains soda-lime. The small flask is fitted with a rubber-stopper
+perforated with two holes, through one of which passes the tube of a
+pipette holding 25 or 30 c.c. This pipette is to contain the acid. The
+substance to be determined is weighed out into the flask. The second
+tube contains strong sulphuric acid; the third, pumice stone, saturated
+with copper sulphate solution, and dried until nearly white (at 200° C.);
+the fourth contains recently fused calcium chloride; and the fifth,
+which is the weighed tube in which the carbonic acid is absorbed,
+contains calcium chloride and soda-lime,[120] as shown in fig. 80. The
+sixth also contains calcium chloride and soda-lime; its object is to
+prevent the access of moisture and carbonic acid to the weighed tube
+from this direction; it is connected with an aspirator.
+
+Having weighed the ~U~-tube and got the apparatus in order, weigh up 1,
+2, or 5 grams of the substance and place in the flask. Fill the pipette
+with dilute acid, close the clamp, and cork the flask. Then see that the
+apparatus is tight. Open the clamp and allow from 10 to 20 c.c. of the
+acid to run on to the assay. Carbonic acid will be evolved and will be
+driven through the tubes. The gas should bubble through the sulphuric
+acid in a moderate and regular stream. When the effervescence slackens
+the clamp is opened and the greater part of the remaining acid run in.
+When the effervescence has ceased the clamp is opened to its full extent
+and a current of air drawn through with an aspirator. A gentle heat is
+applied to the flask; but it should not be prolonged or carried to
+boiling. After the removal of the heat a gentle current of air is drawn
+through the apparatus for 30 or 40 minutes. The weighed ~U~-tube, which
+in the early part of the operation will have become warm if much
+carbonic acid was present, will by this time be cold. It is
+disconnected, plugged, and weighed. The increase in weight is due to the
+carbon dioxide of the sample.
+
+_Example._--Ore taken 1 gram.
+
+  Weight of tube, before  42.6525 grams
+     "       "    after   43.0940   "
+                          -------
+  Increase equals CO_{2}   0.4415   "
+
+[Illustration: FIG. 81.]
+
+~Indirect Gravimetric, or Determination by Loss.~--Take a Geissler's
+carbonic-acid apparatus (fig. 81) and place in the double bulb some
+strong sulphuric acid. Put into the other bulb, the stopcock being
+closed, 3 or 4 c.c. of nitric acid diluted with water. Leave the
+apparatus in the balance-box for a few minutes and weigh. Introduce into
+the flask (through A) about 1 gram of the powdered substance and again
+weigh to find the exact amount added. Allow the acid to run gradually on
+to the carbonate, and when solution is complete, heat and aspirate. Cool
+and again weigh; the loss in weight is the carbonic acid.
+
+For _Example_:--
+
+  Weight of apparatus and acids            85.494 grams
+     "           "        marble           86.879   "
+                                           ------
+  Equal to marble taken                     1.385   "
+
+  Weight of apparatus and marble           86.879  grams
+     "          "     minus carbonic acid  86.2692   "
+                                           -------
+  Equal to carbonic acid                    0.6098   "
+
+        1.385 : 100 :: 0.6098 : _x_
+                                _x_ = 44.03 per cent.
+
+The substance contains 44.03 per cent. of carbonic acid; a duplicate
+experiment gave 43.73 per cent.
+
+This method is quicker, but less exact, than the direct gravimetric
+determination.
+
+
+VOLUMETRIC METHOD.
+
+This, which is of somewhat limited application, is based upon the
+determination of the quantity of acid required to decompose the
+carbonate. It consists in adding to a weighed quantity of the mineral a
+known amount of standard solution of acid which is in excess of that
+required to effect the decomposition. The quantity of residual acid is
+then determined by titrating with standard solution of alkali. This
+method has been described under _Lime_.
+
+
+GASOMETRIC METHOD.
+
+This method is the quickest of all, and the least troublesome after the
+apparatus has been once prepared. It yields fairly accurate results when
+worked in the manner described below; but if greater precautions are
+taken the results are exact. It depends on the measurement of the volume
+of gas given off on treating the weighed sample with acid. The apparatus
+described, page 52, is used. Weigh out a portion of the mineral which
+shall contain not more than 0.15 gram of carbonic acid (or 0.4 gram of
+carbonate of lime) and put it in the bottle. Put in the inner tube 10
+c.c. of dilute hydrochloric acid (1--1), cork tightly, and read off the
+level of the liquid in the burette after adjusting the pressure. Turn
+the acid over on to the mineral. Run out the water so as to keep the
+level in the two burettes the same. When effervescence has ceased,
+rotate the contents of the bottle; finally, adjust the level in the
+burettes and read off the volume. The increase in volume is due to the
+evolved carbon dioxide. At the same time read off the "volume
+corrector."
+
+Some of the carbon dioxide remains dissolved in the acid in the
+generating bottle, and the quantity thus dissolved will depend on the
+amount of carbonate as well as on the amount of acid present.
+Consequently, a measured quantity of acid should be used in each assay
+and a comparative experiment made with a known weight of pure carbonate
+of lime which will yield about the same volume of gas. The number of
+c.c. of gas got in the assay multiplied by 4.7 will give the number of
+milligrams of pure carbonate of lime that must be taken for the
+standard. With ordinary work the error rarely exceeds half a c.c.
+
+The following example will illustrate the calculations:--
+
+One gram of a mineral was taken, and yielded 49.0 c.c. of gas. The
+"volume corrector" reading was 100.4 c.c.
+
+0.2405 gram of pure carbonate of lime was then taken, and treated in the
+same way; 50.5 c.c. of gas were got. The volume corrector still read
+100.4 c.c.
+
+0.2405 gram of carbonate of lime is equivalent to 0.1058 gram of carbon
+dioxide; then,
+
+        50.5 : 49.0 :: 0.1058 : _x_
+                                _x_ = 10.26 per cent.
+
+~Estimation of Carbonic Acid in the Air of Mines.~--According to a
+series of analyses by Angus Smith, the proportion of carbonic acid in
+the air of underground workings varied from 0.04 to 2.7 per cent. by
+volume. In places where men are working the proportion ought not to
+reach 0.25 per cent.
+
+A simple method of determining whether a sample of air reaches this
+limit (0.25 per cent.) is described by Dr. C. Le Neve Foster in the
+"Proceedings of the Mining Association and Institute of Cornwall" for
+1888. The apparatus used is an ordinary corked 8-ounce medicine bottle.
+This is filled with the air to be examined by sucking out its contents
+with a piece of rubber-tube. Half-an-ounce of dilute lime-water[121]
+(tinted with phenolphthalein) is poured in. If, on corking the bottle
+and shaking, the colour is not discharged, the air contains less than
+0.25 per cent. of carbon dioxide. "If the colour fades slowly, and does
+not finally vanish till after a great deal of shaking, it may be assumed
+that the percentage of carbon dioxide does not greatly exceed one
+quarter; whereas, if the disappearance is rapid after a very few shakes,
+the contrary, of course, is the case." The dilute lime-water is measured
+out and carried in ordinary half-ounce phials. This method does not
+pretend to great accuracy, but as a method of distinguishing between
+good and bad air it is very convenient, and will be found useful.
+
+For determining the actual proportion in the air the following plan is
+adopted:--Take a bottle which will hold about 50 ounces, and measure its
+capacity; fill the bottle with the air to be examined, pour in 100 c.c.
+of lime-water, and shake up for some time; add phenolphthalein, and
+titrate the remaining calcium hydrate with standard solution of oxalic
+acid.
+
+The solution of oxalic acid is made by dissolving 2.25 grams of
+re-crystallised oxalic acid (H_{2}C_{2}O_{4}.2H_{2}O) in water and
+diluting to 1 litre. One c.c. = 0.001 gram of lime (CaO), or 0.0007857
+gram of carbon dioxide.
+
+Take 100 c.c. of the same lime-water, to which add the same amount of
+phenolphthalein as before. Titrate. The difference between the two
+readings gives the amount of "acid" equivalent to the lime-water
+neutralised by the carbon dioxide. The number of c.c. thus used up, when
+multiplied by 0.3989, gives the number of c.c. of carbon dioxide (at
+0° C. and 760 mm.) in the volume of air taken. This volume, which is that
+of the bottle less 100 c.c., must in accurate work be reduced to the
+normal temperature and pressure.[122] The percentage by volume can then
+be calculated.
+
+
+PRACTICAL EXERCISES.
+
+1. In a gasometric determination 71.3 c.c. of gas were obtained from
+0.2055 gram of mineral. The "volume corrector" reading was 102.2 c.c.
+0.3445 gram of pure carbonate of lime gave 74.1 c.c. The "volume
+corrector" reading was 100.6. What is the percentage of carbon dioxide
+in the substance?
+
+2. What volume of dry gas at 0° C. and 760 m.m. pressure should be
+obtained from 0.3445 gram of carbonate of lime? 1 c.c. of CO_{2} under
+these conditions weighs 1.97 milligrams.
+
+3. A sample of coal is reported on as follows:--
+
+  Specific gravity      1.315
+  Moisture              1.001
+  Volatile matter      35.484
+  Fixed carbon         50.172
+  Ash                  12.028
+                      -------
+                      100.000
+
+What is there about this requiring explanation?
+
+4. Calculate the percentage of carbonic acid in a mineral from the
+following data:--
+
+  Weight of apparatus and acids                              87.0888 grams
+     "           "         "    plus mineral                 88.8858   "
+     "           "         "    after loss of carbonic acid  88.1000   "
+
+5. A sample of pig iron contains 1.43 per cent. of "combined" and 2.02
+per cent. of "free" carbon. Taking 2 grams of it for each determination,
+what weight of CO_{2} will be got on burning the residue from solution
+in ammonium cupric chloride, and what from the residue after solution in
+hydrochloric acid?
+
+
+BORON AND BORATES.
+
+Boron occurs in nature as boric acid or sassoline (H_{3}BO_{3}); borax
+or tincal (Na_{2}B_{4}O_{7}.10H_{2}O); ulexite or boronatrocalcite
+(2CaB_{4}O_{7}.Na_{2}B_{4}O_{7}); borocalcite (CaB_{4}O_{7}.4H_{2}O);
+boracite, 2Mg_{3}B_{8}O_{15}.MgCl_{2}, and some other minerals. Boric
+acid is also a constituent of certain silicates, such as tourmaline,
+axinite, and datholite.
+
+The natural borates are used in the preparation of borax, which is
+largely employed as a preservative agent, for fluxing, and for other
+purposes.
+
+There is only one series of boron compounds which have any importance.
+These are the borates in which the trioxide (B_{2}O_{3}) acts the part
+of a weak acid. The addition of any acid liberates boric acid, which
+separates out in cold solutions as a crystalline precipitate. Boric acid
+is soluble in alcohol and in hot water. On evaporating these solutions
+it is volatilised, although the anhydrous oxide is "fixed" at a red
+heat. The borates are mostly fusible compounds, and are soluble in acids
+and in solutions of ammonic salts.
+
+~Detection.~--Boron in small quantities will escape detection unless
+specially looked for, but there is no difficulty in detecting its
+presence. Heated in the Bunsen-burner flame with "Turner's test," it
+gives an evanescent yellowish-green colour, due to fluoride of boron
+(BF_{3}). "Turner's test" is a mixture of 5 parts of bisulphate of
+potash and 1 part of fluor spar. Boric acid itself imparts a
+characteristic green colour to the flame, which gives a spectrum made up
+of four well-marked and equidistant lines, three in the green and one in
+the blue. Solutions of boric acid give with "turmeric paper," which has
+been dipped into it and dried, a characteristic red tint. This is a very
+delicate test, but in trying it a blank experiment should be carried out
+alongside with a solution made up of the same re-agents which have been
+used in liberating the boric acid in the sample.
+
+~Solution and Separation.~--The solution presents no difficulty, but the
+separation is troublesome. The best method is that of Gooch; who, if
+necessary, first fuses with carbonate of soda, and after the removal of
+chlorides and fluorides (by nitrate of silver or a lime salt),
+evaporates the aqueous extract with nitric or acetic acid to dryness in
+a retort and, subsequently, with repeated doses of 10 c.c. each of
+methyl alcohol. The distillate contains the boron as boric acid. Half a
+gram of the trioxide (B_{2}O_{3}) is completely carried over by two
+evaporations, each with 10 c.c. of the alcohol; but if water or foreign
+salts are present, more than this is required. In ordinary cases six
+such evaporations are sufficient for 0.2 gram of the oxide.[123]
+
+
+GRAVIMETRIC DETERMINATION.
+
+Before the introduction of Gooch's process it was usual to determine the
+boron trioxide "by difference." If the alcoholic distillate containing
+the boric acid is digested with about 1 gram (a known weight) of lime
+for ten or fifteen minutes, the alcohol can be evaporated off without
+danger of loss. Either calcium nitrate or acetate (which will be formed
+at the same time) yields lime upon subsequent ignition. Consequently,
+the increase in weight, after ignition, upon that of the lime taken
+gives the amount of boron trioxide present. The trioxide contains 31.4
+per cent. of boron (B). Since magnesia does not form a soluble hydrate
+it cannot satisfactorily be used instead of lime.
+
+[Illustration: FIG. 82.]
+
+The apparatus required is shown in fig. 82. It consists of a small
+retort or evaporating vessel made out of a pipette of 200 c.c. capacity.
+This is heated by means of a paraffin-bath at 130° or 140° C. It is
+connected with an upright condenser, at the lower end of which is a
+small flask which serves as a receiver.
+
+The quantity of the borate taken should contain not more than 0.2 gram
+of the trioxide. Insoluble compounds are "dissolved in nitric acid at
+once, or, if necessary, first fused with sodium carbonate." With soluble
+and alkaline borates sufficient nitric acid is added to render it
+faintly acid. The solution is then introduced into the retort.
+
+"The lime, to retain the boric acid in the distillate, is ignited in the
+crucible in which the evaporation of the distillate is to be made
+subsequently." It is then cooled in the desiccator for ten minutes, and
+weighed. The lime is transferred to the receiving flask and slaked with
+a little water. The retort is lowered into the bath so that "only the
+rear dips below the surface." The evaporation is carried to dryness,
+the retort being lowered further into the bath as the evaporation
+proceeds. Ten c.c. of methyl alcohol are introduced upon the residue,
+and the evaporation again started. Six such portions of alcohol are thus
+distilled and 2 c.c. of water are introduced and evaporated between the
+second and third, as also between the fourth and fifth distillations. If
+acetic acid is used instead of nitric in the first instance this
+addition of water is unnecessary.
+
+The distillate is evaporated in the crucible ignited over the blowpipe,
+cooled in the desiccator for ten minutes and weighed. The increase in
+weight gives the boron trioxide. The results tend to be from 1 to 2
+milligrams too high.
+
+
+VOLUMETRIC METHOD.
+
+This method is applicable to the indirect determination of boric acid in
+borax and similar compounds. It is based on the measurement of the
+quantity of normal solution of acid required to replace the boric acid,
+and, consequently, is rather a measure of the soda present. The process
+is an alkalimetric one, and is carried out as follows:--Weigh up 3 grams
+of the sample and dissolve in water. Tint with methyl orange, and run in
+from an ordinary burette normal solution of sulphuric acid until a pink
+tint is got. 100 c.c. of the normal solution of acid are equal to 7.0
+grams of boron trioxide (B_{2}O_{3}), or 10.1 grams of anhydrous borax
+(Na_{2}B_{4}O_{7}).
+
+~Examination of Borax.~--In addition to the determination just given,
+the following determinations are also required:--
+
+~Water.~--Take about 2 grams and heat to tranquil fusion in a platinum
+crucible. Count the loss in weight as water.
+
+~Sulphuric Oxide.~--Take 2 grams, dissolve in water, acidify with
+hydrochloric acid, filter, and precipitate with barium chloride. Wash
+the precipitate, ignite, and weigh as barium sulphate (see _Sulphur_).
+
+~Chlorine.~--Take 2 grams, dissolve in water, acidify with nitric acid,
+filter, and add silver nitrate. Collect, wash, and weigh the precipitate
+as silver chloride.
+
+~Alumina.~--Take 5 or 10 grams, dissolve in water, boil, add ammonia in
+slight excess, and filter off the precipitate when it has settled. Wash
+with hot water, ignite, and weigh as alumina (Al_{2}O_{3}).
+
+FOOTNOTES:
+
+[113] If the dishes show a manganese stain, wash them out with a few
+drops of hydrochloric and sulphurous acids. Pass the acid liquor through
+the same small filter but collect the liquor apart. Make ammoniacal and
+again pass through the filter, this time collecting the liquid with the
+main filtrate.
+
+[114] This rarely amounts to more than 1 milligram.
+
+[115] To make this, dissolve 1 gram of titanium oxide by fusing for some
+time with an excess of bisulphate of potash and dissolve out with cold
+water and sulphuric acid. Dilute to 1 litre, having previously added not
+less than 50 c.c. of strong sulphuric acid: 1 c.c. will contain .01 gram
+of TiO_{2}. For the assay take 10 c.c. of this, add 2 c.c. of peroxide
+of hydrogen and dilute to 100 c.c. Run this from a burette into the
+flask until the colour equals that of the assay. Each c.c. equals 1
+milligram of TiO_{2}. Fluorides must be absent.
+
+[116] C + O_{2} = CO_{2}
+
+[117] For example, soluble organic acids formed by partial oxidation
+with nitric acid.
+
+[118] For coals, and other bodies containing sulphur, chromate of lead
+should be used instead of oxide of copper; and the temperature should be
+limited to dull redness.
+
+[119] This may be prepared by dissolving 534 grams of ammonium chloride
+and 854 grams of crystallized cupric chloride (CuCl_{2}.2H_{2}O) in hot
+water and crystallizing.
+
+[120] Soda-lime is made by dissolving 100 grams of "soda" in water, and
+carefully slaking 200 grams of lime with it. Evaporate to dryness in an
+iron dish and ignite at a low red heat in a crucible. Use the small
+lumps.
+
+[121] Made by diluting 1 part by measure of saturated lime-water up to
+10 with recently boiled distilled water.
+
+[122] See under _Gasometric Assays_.
+
+[123] See "A Method for the Separation and Estimation of Boric Acid," by
+F.A. Gooch, _Chemical News_, January 7, 1887.
+
+
+
+
+APPENDIX A.
+
+TABLE OF ATOMIC WEIGHTS AND OTHER CONSTANTS.
+
+  ---------+------------+----------+----------+---------
+           |            |          |          |
+   Symbols.|   Names.   |  Atomic  | Specific | Melting
+           |            | Weights. | Gravity. | Points.
+  ---------+------------+----------+----------+---------
+           |            |          |          |   C.
+      Ag   | Silver     |  107.9   |   10.5   |  1000°
+      Al   | Aluminium  |   27.0   |    2.7   |   700°
+      As   | Arsenic    |   75.0   |    5.9   |
+      Au   | Gold       |  197.3   |   19.2   |  1200°
+      B    | Boron      |   11.0   |    2.7   |
+      Ba   | Barium     |  137.0   |    4.0   |
+      Be   | Beryllium  |    9.0   |    2.1   |
+      Bi   | Bismuth    |  208.9   |    9.8   |   270°
+      Br   | Bromine    |   80.0   |    3.2   |   -25°
+      C    | Carbon     |   12.0   |          |
+      Ca   | Calcium    |   40.0   |    1.6   |
+      Cd   | Cadmium    |  112.0   |    8.6   |   315°
+      Ce   | Cerium     |  140.2   |    6.7   |
+      Cl   | Chlorine   |   35.5   |          |
+      Co   | Cobalt     |   59.0   |    8.5   |
+      Cr   | Chromium   |   52.1   |    7.3   |
+      Cs   | Caesium    |  132.9   |    1.9   |    25°
+      Cu   | Copper     |   63.4   |    8.9   |  1090°
+      Di   | Didymium   |  142.3   |    6.5   |
+      Er   | Erbium     |  166.3   |          |
+      F    | Fluorine   |   19.0   |          |
+      Fe   | Iron       |   56.0   |    7.8   |
+      Ga   | Gallium    |   69.0   |    5.9   |    30°
+      Ge   | Germanium  |   72.3   |          |
+      H    | Hydrogen   |    1.0   |          |
+      Hg   | Mercury    |  200.0   |   13.6   |   -40°
+      I    | Iodine     |  126.8   |    4.9   |   106°
+      In   | Indium     |  113.7   |    7.4   |   175°
+      Ir   | Iridium    |  193.1   |   22.4   |
+      K    | Potassium  |   39.1   |    0.86  |  62.5°
+      La   | Lanthanum  |  138.2   |    6.1   |
+      Li   | Lithium    |    7.0   |    0.59  |   180°
+      Mg   | Magnesium  |   24.3   |    1.7   |
+      Mn   | Manganese  |   55.0   |    8.0   |
+      Mo   | Molybdenum |   96.0   |    8.6   |
+      N    | Nitrogen   |   14.0   |          |
+      Na   | Sodium     |   23.0   |    0.97  |  95.6°
+      Nb   | Niobium    |   94.0   |    4.1   |
+      Ni   | Nickel     |   58.7   |    8.9   |
+      O    | Oxygen     |   16.0   |          |
+      Os   | Osmium     |  191.7   |   22.4   |
+      P    | Phosphorus |   31.0   |    1.8   |    44°
+      Pb   | Lead       |  206.9   |   11.4   |   334°
+      Pd   | Palladium  |  106.6   |   11.4   |  1350°
+      Pt   | Platinum   |  195.0   |   21.5   |  2000°
+      Rb   | Rubidium   |   85.5   |    1.5   |  38.5°
+      Rh   | Rhodium    |  103.5   |   12.1   |
+      Ru   | Ruthenium  |  101.6   |   11.4   |
+      S    | Sulphur    |   32.0   |    2.0   |   115°
+      Sb   | Antimony   |  120.0   |    6.7   |   425°
+      Se   | Selenium   |   79.0   |    4.8   |   100°
+      Si   | Silicon    |   28.4   |    2.0   |
+      Sn   | Tin        |  119.0   |    7.3   |   235°
+      Sr   | Strontium  |   87.6   |    2.5   |
+      Ta   | Tantalum   |  182.6   |          |
+      Te   | Tellurium  |  125.0   |    6.2   |   480°
+      Th   | Thorium    |  232.6   |    7.8   |
+      Ti   | Titanium   |   48.0   |    5.3   |
+      Tl   | Thallium   |  204.2   |   11.9   |   294°
+      U    | Uranium    |  239.6   |   18.4   |
+      V    | Vanadium   |   51.4   |    5.5   |
+      W    | Tungsten   |  184.0   |   19.1   |
+      Y    | Yttrium    |   89.1   |          |
+      Yb   | Ytterbium  |  173.0   |          |
+      Zn   | Zinc       |   65.3   |    6.9   |   423°
+      Zr   | Zirconium  |   90.6   |    4.1   |
+  _________|____________|__________|__________|_________
+
+The atomic weights in this table are in accord with the numbers given by
+F.W. Clarke (Dec. 6, 1890), chief chemist of the United States
+Geological Survey.
+
+[Illustration: _Table for Converting Degrees of the Centigrade
+Thermometer into Degrees of Fahrenheit's Scale._]
+
+
+Nitric Acid.
+
+_Table showing the percentage, by Weight, of Real Acid_ (HNO_{3}) _in
+Aqueous Solutions of Nitric Acid of different Specific Gravities.
+Temperature_, 15° C.
+
+  -------+-------++-------+-------++-------+-------
+   1.530 | 100.0 || 1.405 |  66.0 || 1.205 |  33.0
+   1.527 |  99.0 || 1.400 |  65.0 || 1.198 |  32.0
+   1.524 |  98.0 || 1.395 |  64.0 || 1.192 |  31.0
+   1.520 |  97.0 || 1.390 |  63.0 || 1.185 |  30.0
+   1.516 |  96.0 || 1.386 |  62.0 || 1.179 |  29.0
+   1.513 |  95.0 || 1.380 |  61.0 || 1.172 |  28.0
+   1.509 |  94.0 || 1.374 |  60.0 || 1.166 |  27.0
+   1.506 |  93.0 || 1.368 |  59.0 || 1.159 |  26.0
+   1.503 |  92.0 || 1.363 |  58.0 || 1.152 |  25.0
+   1.499 |  91.0 || 1.358 |  57.0 || 1.145 |  24.0
+   1.495 |  90.0 || 1.353 |  56.0 || 1.138 |  23.0
+   1.492 |  89.0 || 1.346 |  55.0 || 1.132 |  22.0
+   1.488 |  88.0 || 1.341 |  54.0 || 1.126 |  21.0
+   1.485 |  87.0 || 1.335 |  53.0 || 1.120 |  20.0
+   1.482 |  86.0 || 1.329 |  52.0 || 1.114 |  19.0
+   1.478 |  85.0 || 1.323 |  51.0 || 1.108 |  18.0
+   1.474 |  84.0 || 1.317 |  50.0 || 1.102 |  17.0
+   1.470 |  83.0 || 1.311 |  49.0 || 1.096 |  16.0
+   1.467 |  82.0 || 1.304 |  48.0 || 1.089 |  15.0
+   1.463 |  81.0 || 1.298 |  47.0 || 1.083 |  14.0
+   1.460 |  80.0 || 1.291 |  46.0 || 1.077 |  13.0
+   1.456 |  79.0 || 1.284 |  45.0 || 1.071 |  12.0
+   1.452 |  78.0 || 1.277 |  44.0 || 1.065 |  11.0
+   1.449 |  77.0 || 1.270 |  43.0 || 1.060 |  10.0
+   1.445 |  76.0 || 1.264 |  42.0 || 1.053 |   9.0
+   1.442 |  75.0 || 1.257 |  41.0 || 1.047 |   8.0
+   1.438 |  74.0 || 1.251 |  40.0 || 1.041 |   7.0
+   1.435 |  73.0 || 1.244 |  39.0 || 1.034 |   6.0
+   1.431 |  72.0 || 1.238 |  38.0 || 1.028 |   5.0
+   1.427 |  71.0 || 1.232 |  37.0 || 1.022 |   4.0
+   1.423 |  70.0 || 1.225 |  36.0 || 1.016 |   3.0
+   1.418 |  69.0 || 1.218 |  35.0 || 1.010 |   2.0
+   1.414 |  68.0 || 1.212 |  34.0 || 1.004 |   1.0
+   1.410 |  67.0 ||       |       ||       |
+  -------+-------++-------+-------++-------+--------
+
+
+HYDROCHLORIC ACID.
+
+_Table showing the percentage, by Weight, of Real Acid_ (HCl) _in
+Aqueous Solutions of Hydrochloric Acid of different Specific Gravities.
+Temperature_, 15° C.
+
+  -----------+---------++----------+---------++----------+---------
+  |  1.2000  |  40.78  ||  1.1410  |  28.54  ||  1.0798  |  16.31  |
+  |  1.1982  |  40.37  ||  1.1389  |  28.13  ||  1.0778  |  15.90  |
+  |  1.1964  |  39.96  ||  1.1369  |  27.72  ||  1.0758  |  15.49  |
+  |  1.1946  |  39.55  ||  1.1349  |  27.32  ||  1.0738  |  15.08  |
+  |  1.1928  |  39.14  ||  1.1328  |  26.91  ||  1.0718  |  14.68  |
+  |  1.1910  |  38.74  ||  1.1308  |  26.50  ||  1.0697  |  14.27  |
+  |  1.1893  |  38.33  ||  1.1287  |  26.10  ||  1.0677  |  13.86  |
+  |  1.1875  |  37.92  ||  1.1267  |  25.69  ||  1.0657  |  13.45  |
+  |  1.1857  |  37.51  ||  1.1247  |  25.28  ||  1.0637  |  13.05  |
+  |  1.1846  |  37.11  ||  1.1226  |  24.87  ||  1.0617  |  12.64  |
+  |  1.1822  |  36.70  ||  1.1206  |  24.46  ||  1.0597  |  12.23  |
+  |  1.1802  |  36.29  ||  1.1185  |  24.06  ||  1.0577  |  11.82  |
+  |  1.1782  |  35.88  ||  1.1164  |  23.65  ||  1.0557  |  11.41  |
+  |  1.1762  |  35.47  ||  1.1143  |  23.24  ||  1.0537  |  11.01  |
+  |  1.1741  |  35.07  ||  1.1123  |  22.83  ||  1.0517  |  10.60  |
+  |  1.1721  |  34.66  ||  1.1102  |  22.43  ||  1.0497  |  10.19  |
+  |  1.1701  |  34.25  ||  1.1082  |  22.02  ||  1.0477  |   9.78  |
+  |  1.1681  |  33.84  ||  1.1061  |  21.61  ||  1.0457  |   9.38  |
+  |  1.1661  |  33.43  ||  1.1041  |  21.20  ||  1.0437  |   8.97  |
+  |  1.1641  |  33.03  ||  1.1020  |  20.79  ||  1.0417  |   8.56  |
+  |  1.1620  |  32.62  ||  1.1000  |  20.39  ||  1.0397  |   8.15  |
+  |  1.1599  |  32.21  ||  1.0980  |  19.98  ||  1.0377  |   7.75  |
+  |  1.1578  |  31.80  ||  1.0960  |  19.57  ||  1.0357  |   7.34  |
+  |  1.1557  |  31.40  ||  1.0939  |  19.16  ||  1.0337  |   6.93  |
+  |  1.1536  |  30.99  ||  1.0919  |  18.76  ||  1.0318  |   6.52  |
+  |  1.1515  |  30.58  ||  1.0899  |  18.35  ||  1.0298  |   6.11  |
+  |  1.1494  |  30.17  ||  1.0879  |  17.94  ||  1.0279  |   5.51  |
+  |  1.1473  |  29.76  ||  1.0859  |  17.53  ||  1.0259  |   5.30  |
+  |  1.1452  |  29.36  ||  1.0838  |  17.12  ||  1.0239  |   4.89  |
+  |  1.1431  |  28.95  ||  1.0818  |  16.72  ||  1.0200  |   4.01  |
+  -----------+---------++----------+---------++----------+---------
+
+
+AMMONIA.
+
+_Table showing the percentage, by Weight, of Real Ammonia_ (NH_{3}) _in
+Aqueous Solutions of Ammonia of different Specific Gravities.
+Temperature_, 14° C.
+
+  ----------+--------++----------+--------++----------+--------
+    0.8844  |  36.0  ||  0.9145  |  23.6  ||  0.9534  |  11.6
+    0.8852  |  35.6  ||  0.9156  |  23.2  ||  0.9549  |  11.2
+    0.8860  |  35.2  ||  0.9168  |  22.8  ||  0.9563  |  10.8
+    0.8868  |  34.8  ||  0.9180  |  22.4  ||  0.9578  |  10.4
+    0.8877  |  34.4  ||  0.9191  |  22.0  ||  0.9593  |  10.0
+    0.8885  |  34.0  ||  0.9203  |  21.6  ||  0.9608  |   9.6
+    0.8894  |  33.6  ||  0.9215  |  21.2  ||  0.9623  |   9.2
+    0.8903  |  33.2  ||  0.9227  |  20.8  ||  0.9639  |   8.8
+    0.8911  |  32.8  ||  0.9239  |  20.4  ||  0.9654  |   8.4
+    0.8920  |  32.4  ||  0.9251  |  20.0  ||  0.9670  |   8.0
+    0.8929  |  32.0  ||  0.9264  |  19.6  ||  0.9685  |   7.6
+    0.8938  |  31.6  ||  0.9277  |  19.2  ||  0.9701  |   7.2
+    0.8948  |  31.2  ||  0.9289  |  18.8  ||  0.9717  |   6.8
+    0.8957  |  30.8  ||  0.9302  |  18.4  ||  0.9733  |   6.4
+    0.8967  |  30.4  ||  0.9314  |  18.0  ||  0.9749  |   6.0
+    0.8976  |  30.0  ||  0.9327  |  17.6  ||  0.9765  |   5.6
+    0.8986  |  29.6  ||  0.9340  |  17.2  ||  0.9781  |   5.2
+    0.8996  |  29.2  ||  0.9353  |  16.8  ||  0.9790  |   4.8
+    0.9006  |  28.8  ||  0.9366  |  16.4  ||  0.9807  |   4.6
+    0.9016  |  28.4  ||  0.9380  |  16.0  ||  0.9823  |   4.2
+    0.9026  |  28.0  ||  0.9393  |  15.6  ||  0.9839  |   3.8
+    0.9036  |  27.6  ||  0.9407  |  15.2  ||  0.9855  |   3.4
+    0.9047  |  27.2  ||  0.9420  |  14.8  ||  0.9873  |   3.0
+    0.9057  |  26.8  ||  0.9434  |  14.4  ||  0.9890  |   2.6
+    0.9068  |  26.4  ||  0.9449  |  14.0  ||  0.9907  |   2.2
+    0.9078  |  26.0  ||  0.9463  |  13.6  ||  0.9924  |   1.8
+    0.9089  |  25.6  ||  0.9477  |  13.2  ||  0.9941  |   1.4
+    0.9100  |  25.2  ||  0.9491  |  12.8  ||  0.9959  |   1.0
+    0.9111  |  24.8  ||  0.9505  |  12.4  ||  0.9975  |   0.6
+    0.9122  |  24.4  ||  0.9520  |  12.0  ||  0.9991  |   0.2
+    0.9133  |  24.0  ||          |        ||          |
+  ----------+--------++----------+--------++----------+--------
+
+
+SULPHURIC ACID.
+
+_Table showing the percentage, by Weight, of Real Acid_ (H_{2}SO_{4})
+_in Aqueous Solutions of Sulphuric Acid of varying Specific Gravity.
+Temperature_, 15° C.
+
+  --------+--------++--------+--------++--------+--------
+   1.838  | 100.0  || 1.568  |  66.0  || 1.247  |  33.0
+   1.840  |  99.0  || 1.557  |  65.0  || 1.239  |  32.0
+   1.841  |  98.0  || 1.545  |  64.0  || 1.231  |  31.0
+   1.841  |  97.0  || 1.534  |  63.0  || 1.223  |  30.0
+   1.840  |  96.0  || 1.523  |  62.0  || 1.215  |  29.0
+   1.838  |  95.0  || 1.512  |  61.0  || 1.206  |  28.0
+   1.836  |  94.0  || 1.501  |  60.0  || 1.198  |  27.0
+   1.834  |  93.0  || 1.490  |  59.0  || 1.190  |  26.0
+   1.831  |  92.0  || 1.480  |  58.0  || 1.182  |  25.0
+   1.827  |  91.0  || 1.469  |  57.0  || 1.174  |  24.0
+   1.822  |  90.0  || 1.458  |  56.0  || 1.167  |  23.0
+   1.816  |  89.0  || 1.448  |  55.0  || 1.159  |  22.0
+   1.809  |  88.0  || 1.438  |  54.0  || 1.151  |  21.0
+   1.802  |  87.0  || 1.428  |  53.0  || 1.144  |  20.0
+   1.794  |  86.0  || 1.418  |  52.0  || 1.136  |  19.0
+   1.786  |  85.0  || 1.408  |  51.0  || 1.129  |  18.0
+   1.777  |  84.0  || 1.398  |  50.0  || 1.121  |  17.0
+   1.767  |  83.0  || 1.388  |  49.0  || 1.113  |  16.0
+   1.756  |  82.0  || 1.379  |  48.0  || 1.106  |  15.0
+   1.745  |  81.0  || 1.370  |  47.0  || 1.098  |  14.0
+   1.734  |  80.0  || 1.361  |  46.0  || 1.091  |  13.0
+   1.722  |  79.0  || 1.351  |  45.0  || 1.083  |  12.0
+   1.710  |  78.0  || 1.342  |  44.0  || 1.075  |  11.0
+   1.698  |  77.0  || 1.333  |  43.0  || 1.068  |  10.0
+   1.686  |  76.0  || 1.324  |  42.0  || 1.061  |   9.0
+   1.675  |  75.0  || 1.315  |  41.0  || 1.053  |   8.0
+   1.663  |  74.0  || 1.306  |  40.0  || 1.046  |   7.0
+   1.651  |  73.0  || 1.297  |  39.0  || 1.039  |   6.0
+   1.639  |  72.0  || 1.289  |  38.0  || 1.032  |   5.0
+   1.627  |  71.0  || 1.281  |  37.0  || 1.025  |   4.0
+   1.615  |  70.0  || 1.272  |  36.0  || 1.019  |   3.0
+   1.604  |  69.0  || 1.264  |  35.0  || 1.013  |   2.0
+   1.592  |  68.0  || 1.256  |  34.0  || 1.006  |   1.0
+   1.580  |  67.0  ||        |        ||        |
+  --------+--------++--------+--------++--------+--------
+
+
+
+
+APPENDIX B.
+
+
+ESTIMATION OF SMALL QUANTITIES OF GOLD.[124]
+
+In the case of small buttons of gold the weight can be determined more
+easily and accurately by measuring with the help of a microscope than by
+the actual use of a balance. Moreover, the method of measurement is
+applicable to the determination of quantities of gold too minute to
+affect even the most delicate balance.
+
+For quantities of gold of from .5 to .005 milligram a microscope with
+1/2 inch objective and B eyepiece is suitable. The measurements are made
+with the help of a scale engraved (or, better, photographed) on a
+circular piece of glass which rests on the diaphragm of the eyepiece.
+This scale and the object upon the stage can be easily brought into
+focus at the same time. The button of gold obtained by cupelling is
+loosened from the cupel by gently touching with the moistened point of a
+knife; it generally adheres to the knife, and is then transferred to a
+glass slide. The slide is placed on the stage of the microscope,
+illuminated from below; and the button is brought into focus, and so
+placed that it apparently coincides with the scale. The diameters in two
+or three directions (avoiding the flattened surface) are then read off:
+the different directions being got by rotating the eyepiece. The mean
+diameter is taken. The weight of the button is arrived at by comparing
+with the mean diameter of a _standard prill_ of gold of known weight.
+The weights are in the proportion of the cubes of the diameters. For
+example, suppose a prill has been obtained which measures 12.5 divisions
+of the scale, and that a standard prill weighing 0.1 milligram measures
+11.1 divisions. The weight will be calculated as follows:
+
+  11.1^{3} : 12.5^{3} :: 0.1 : _x_
+
+             0.1×12.5×12.5×12.5
+  _x_ = -------------------- = 0.143 milligram.
+              11.1×11.1×11.1
+
+The calculations are simplified by the use of a table of cubes. The
+standard prills used in the comparison should not differ much in size
+from the prills to be determined. They are prepared by alloying known
+weights of gold and lead, so as to get an alloy of known composition,
+say one per cent. gold. Portions of the alloy containing the weight of
+gold required (say 0.1 milligram) are then weighed off and cupelled on
+small smooth cupels, made with the finest bone-ash. Care must be taken
+to remove the cupels as soon as cupellation has finished. Several
+standard prills of the same size should be made at the same time, and
+their mean diameter calculated. The lead for making the gold-lead alloy
+is prepared from litharge purified by reducing from it about 10 per
+cent. of its lead by fusion with a suitable proportion of flour; the
+purified litharge is powdered, mixed with sufficient flour and reduced
+to metal.
+
+In determining the gold contained in small buttons of silver-gold alloy
+obtained in assaying (and in which the silver is almost sure to be in
+excess of that required for parting), transfer the button from the cupel
+to a small clean porcelain crucible; pour on it a drop or two of nitric
+acid (diluted with half its bulk of water), and heat gently and
+cautiously until action has ceased. If the residual gold is broken up,
+move the crucible so as to bring the particles together, so that they
+may cohere. Wash three or four times with distilled water, about half
+filling the crucible each time and decanting off against the finger. Dry
+the crucible in a warm place; and when dry, but whilst still black, take
+the gold up on a small piece of pure lead. Half a grain of lead is
+sufficient, and it is best to hold it on the point of a blunt penknife,
+and press it on the gold in the crucible. The latter generally adheres.
+Transfer to a small smooth cupel and place in the muffle. When the
+cupellation has finished, the button of gold is measured as already
+described.
+
+
+PRACTICAL NOTES ON THE IODIDE PROCESS OF COPPER ASSAYING.
+
+For the following remarks and experiments we are indebted to Mr. J.W.
+Westmoreland, who has had considerable experience with the process.
+Having dissolved the ore he converts the metals into sulphates by
+evaporating with sulphuric acid. The copper is then separated as
+subsulphide by means of hyposulphite of soda, and the precipitate is
+washed, dried, and calcined. The resulting oxide of copper is then
+dissolved in nitric acid; and to the concentrated solution, a saturated
+solution of carbonate of soda is added in sufficient quantity to throw
+down a considerable proportion of the copper. Acetic acid is added to
+dissolve the precipitate, and when this is effected more of the acid is
+poured on so as to render the solution strongly acid. To this potassium
+iodide crystals are added in the proportion of ten parts of iodide to
+each one part of copper supposed to be present. The solution is then
+titrated with "hypo" as usual.
+
+For the examination of technical products experiments made in sulphuric
+acid solutions have no value, since arsenic acid, which is generally
+present to a greater or less extent, affects the end reaction. In such
+solutions bismuth may also interfere.
+
+The solution best suited for the assay is one containing acetate of soda
+and free acetic acid. The presence of acetate of soda counteracts the
+interference of arsenic and of bismuth.
+
+The return of the blue colour after titration is due to the excessive
+dilution of the assay, or to an insufficiency of potassium iodide, or to
+the presence of nitrous fumes. The interference of an excess of sodium
+acetate is avoided by adding more iodide crystals to the extent of
+doubling the usual amount.
+
+The interference of lead can be avoided by the addition of sulphuric
+acid or of phosphate of soda to the acid solution containing the copper,
+and before neutralising with carbonate of soda. The end reaction is,
+however, with care distinguishable without this addition. The following
+experiments, each containing .0648 gram of lead, were made by him in
+illustration:
+
+  ---------------+-------------------+---------------+---------------------
+   Copper taken. |   Reagent added.  | Copper found. |    End reaction.
+  ---------------+-------------------+---------------+---------------------
+    .2092 gram   |         --        |  .2077 gram   | fairly satisfactory
+    .2101   "    |         --        |  .2092   "    |          "
+    .2167   "    |   sulphuric acid  |  .2152   "    |          "
+    .2117   "    |         "         |  .2108   "    |          "
+    .2109   "    | phosphate of soda |  .2092   "    |  good, colourless
+    .2205   "    |         "         |  .2174   "    |    rather yellow
+  ---------------+-------------------+---------------+---------------------
+
+_Effect of Sodium Acetate._--Each solution contained .3343 gram of
+copper.
+
+                     a.b.c.       d.          e.          f.          g.
+                     grams.      grams.      grams.      grams.      grams.
+  "Acetate" added    --         16.2        16.2        16.2        16.2
+  "Iodide" added     3.5         3.5         7.0         3.5         7.0
+  Copper found        .3343       .3324       .3351       .3269       .3356
+
+In these experiments, except with the excessive quantities of acetate of
+soda and the insufficiency of potassium iodide in the cases of c and
+f, there was no difficulty with the after-blueing.
+
+
+METHOD OF SEPARATING COBALT AND NICKEL.
+
+The following method of separating and estimating cobalt and nickel has
+been described by Mr. James Hope,[125] with whom it has been in daily
+use for several years with completely satisfactory results.
+
+The quantity of ore taken should contain about .5 gram of the mixed
+metals. It is dissolved in hydrochloric acid or aqua regia, and the
+solution evaporated to dryness. The residue is taken up with dilute
+hydrochloric acid and hot water. The solution is filtered off from the
+silica, freed from second group metals by treatment with sulphuretted
+hydrogen and filtered, and after oxidation with nitric acid is separated
+from iron and alumina by the basic acetate method (page 233). The
+precipitate is redissolved in a little hydrochloric acid, and again
+precipitated by sodium acetate. The two filtrates are mixed and treated
+with a little acetic acid, and the cobalt and nickel are then
+precipitated as sulphides by a current of sulphuretted hydrogen. The
+precipitate is filtered off, washed, dried, and calcined, and the
+resulting oxides are weighed to get an idea as to the quantity of the
+two metals present.
+
+The calcined precipitate is dissolved in a small covered beaker in aqua
+regia with the help of a few drops of bromine to remove any separated
+sulphur, and the solution evaporated to dryness with a few drops of
+sulphuric acid. The residue is dissolved in hot water, diluted to about
+50 c.c., and heated to boiling. About 2 grams (four times the quantity
+of mixed metals present) of ammonium phosphate (AmH_{2}PO_{4}) are
+weighed off, dissolved in the smallest possible quantity of water, and
+boiled for a minute or two with a few c.c. of dilute sulphuric acid.
+This is added to the boiling-hot solution of cobalt and nickel, which is
+then treated cautiously with dilute ammonia until the precipitate
+partially dissolves. The addition of the ammonia is continued drop by
+drop with constant stirring, until the cobalt comes down as a pink
+precipitate of ammonium cobalt phosphate (AmCoPO_{4}). The beaker is
+placed on the top of a water bath with occasional stirring for five or
+ten minutes. The blue liquid containing the nickel is decanted through a
+small filter and the precipitate is dissolved with a few drops of dilute
+sulphuric acid. The resulting solution is treated with a small excess of
+ammonium phosphate and the cobalt again precipitated by the cautious
+addition of ammonia exactly as before. The precipitate containing the
+whole of the cobalt is filtered off and washed with small quantities of
+hot water. The filtrate is added to the previous one containing the
+greater part of the nickel.
+
+The ammonium cobalt phosphate is dried, transferred to a platinum
+crucible, and ignited over a Bunsen flame for fifteen or twenty minutes.
+A purple coloured cobalt pyrophosphate (Co_{2}P_{2}O_{7}) is thus
+formed, and is weighed. It contains 40.3 per cent. of cobalt.
+
+The mixed filtrates containing the nickel are placed in a tall beaker,
+and dilated if necessary to about 200 c.c. Ten c.c. of strong ammonia
+are added, and the solution, heated to 70° C., is ready for
+electrolysis. A battery of two 1-1/2 pint Bunsen cells is used. This is
+found capable of depositing from .15 to .20 gram of nickel per hour, and
+from two to three hours is generally sufficient for the electrolysis.
+The electrode with the deposited nickel is washed with distilled water,
+afterwards with alcohol as described under copper, and is then dried and
+weighed.
+
+The following results obtained with this method by Mr. Hope illustrate
+the accuracy of the method. They were obtained by working on solutions
+containing known weights of the two metals:
+
+  -------------------------+-------------------------
+            Taken.         |          Found.
+  ------------+------------+------------+------------
+     Cobalt.  |   Nickel.  |   Cobalt.  |   Nickel.
+  ------------+------------+------------+------------
+   .1236 gram | .1155 gram | .1242 gram | .1155 gram
+   .1236   "  | .0577   "  | .1232   "  | .0575   "
+   .2472   "  | .0577   "  | .2449   "  | .0585   "
+   .3708   "  | .0577   "  | .3701   "  | .0580   "
+   .0618   "  | .3465   "  | .0619   "  | .3454   "
+   .0618   "  | .2310   "  | .0625   "  | .2295   "
+   .0618   "  | .1155   "  | .0621   "  | .1155   "
+  ------------+------------+------------+------------
+
+FOOTNOTES:
+
+[124] For fuller information see a paper on "The Estimation of Minute
+Quantities of Gold," by Dr. George Tate; read before the Liverpool
+Polytechnic Society, Nov. 1889.
+
+[125] _Journal of the Society of Chemical Industry_, No 4, vol. ix.
+April 30, 1890.
+
+
+
+
+APPENDIX C.
+
+
+A LECTURE ON THE THEORY OF SAMPLING.
+
+The problem of the sampler is essentially the same as that of the
+student of statistics. One aims at getting a small parcel of ore, the
+other a number of data, but each hopes to obtain what shall represent a
+true average applicable to a much larger mass of material. Ignoring the
+mechanical part of the problems, the sampling errors of the one and the
+deviations from the average of the other are the same thing.
+
+It may be doubted whether many not specially trained in the study of
+statistics could answer such a question as the following:--Seven hundred
+thousand men being employed, there are, in a given year, one thousand
+deaths from accident. Assuming the conditions to remain unaltered,
+within what limits could one foretell the number of deaths by accident
+in any other year?
+
+On the other hand, there is a widespread belief in the efficacy of what
+is called the law of averages. Even the ordinary newspaper reader is
+accustomed to look on the national death-rate or birth-rate as a thing
+capable of being stated with accuracy to one or two places of decimals,
+and he knows that the annual number of suicides is practically constant.
+
+If a man played whist often and kept a record of the number of trumps n
+each hand, he would find fortune treated him quite fairly; in a year's
+play the average number would deviate very little from the theoretical
+average, _i.e._, one-quarter of thirteen. And a knowledge of this truth
+is useful, and that not merely in keeping ejaculations in due restraint.
+But every good player knows more than this: he has a sense of what
+variations in the number of trumps may reasonably be expected. For
+example, he will be prepared to risk something on neither of his
+opponents having more than five trumps, and will accept it as a
+practical certainty that no one has more than eight. Much of what is
+known as good judgment is based on a proper estimate of deviations from
+the average. The question has an important bearing on sampling, as may
+be seen from the fact that shuffling and dealing at cards are but
+modifications of the well-known mixing and quartering of the sampler.
+
+Because of this bearing on sampling and for other reasons, I became many
+years ago much interested in the question, and gave to its solution
+perhaps more labour than it was worth. In books on Medical Statistics
+the answer to the question is stated in a mathematical formula, called
+Poisson's formula, which, in a modified form, I shall give further on.
+But this did not satisfy me, because I wanted to learn what a reasonably
+safe _limit of error_ actually meant, and this could be best learnt by
+experiment; so with the help of some friends I went in for a thorough
+course of penny-tossing.
+
+Tossing a penny twenty times, an average result would be ten heads and
+ten tails. To find the deviations from this, we tossed two hundred
+twenties, _i.e._, four thousand times. Of the two hundred, thirty-three
+gave the exact average, viz.:--10 heads; sixty-four gave an error of
+one, viz.:--9 or 11 heads; forty-nine, an error of two; twenty-six, an
+error of three; twenty, an error of four; eight gave an error of five,
+and this limit was not exceeded. From these we may say that six is a
+reasonably safe limit of error. Ninety-seven cases, say one-half, gave
+an error not exceeding one; and the mean error is 1.8.
+
+In other words, in twenty tosses you will not get more than 16 nor less
+than 4 heads; you are as likely as not to get 9, 10, or 11 heads; and
+lastly, if you lost in twenty throws all heads or tails over 10 your
+average loss would be 1.8 penny, or say roughly 2d. on the twenty
+throws.
+
+It was necessary to compare these with another series containing a
+larger average, say that of 100 heads in 200 throws. I confess the
+labour of tossing pennies two hundred at a time was little to our taste.
+So from a bag of pennies borrowed from the bank, we weighed out samples
+containing two hundred, and for an evening we were busy counting heads
+and tails in these. The heads in sixty samples ranged from 80 to 114.
+One hundred heads occurred seven times. The extent and frequency of the
+errors is shown in the table.
+
+  ------+-------+------+-------+------+-------
+  Error.|No. of |Error.|No. of |Error.|No. of
+        | Times.|      | Times.|      | Times.
+  ------+-------+------+-------+------+-------
+    1   |   8   |  6   |   3   |  11  |   1
+    2   |   5   |  7   |   3   |  14  |   3
+    3   |   6   |  8   |   3   |  15  |   1
+    4   |   3   |  9   |   7   |  18  |   2
+    5   |   6   | 10   |   1   |  20  |   1
+  --------------------------------------------
+
+We may call the limit of error 21. Twenty-nine results out of sixty, say
+one-half, had an error not exceeding 4; and the mean error is 5.6. In
+comparing these with the series 10 in 20 we must, working by rule,
+divide not by 10 but by 3.16, the square root of 10; for if we multiply
+an average by any number[126] the error is also multiplied but only by
+the square root of the number. The error varies as the square root of
+the number. Now
+
+  21/3.16 = 6.6 = limit of error for 10 in 20.
+   5.6/3.16 = 1.8 = mean error    "   "     "
+   4/3.16 = 1.2 = probable error  "   "     "
+
+It will be seen that these calculated results agree fairly well with
+those actually obtained. The rule by which these calculations are made
+is important and will bear further illustration. To calculate the
+number of heads in 3200 throws, we have to find the limit of error on a
+true average of 1600 in 3200. This being 16 times the average of 100 in
+200, the corresponding errors must be multiplied by 4. This gives
+
+   21×4 = 84 = limit of error.
+  5.6×4 = 22.4 = mean error.
+    4×4 = 16 = probable error.
+
+The results I have actually obtained with these large numbers are hardly
+enough to base much on, but have a value by way of confirmation.
+Expecting 1600 heads, the actual numbers were 1560, 1596, 1643, 1557,
+1591, 1605, 1615, 1545.
+
+It will be seen that exactly half are within the probable error; but
+this, considering the small number of results, must be more or less of
+an accident; it is more to the point they are all well within the limits
+of error.
+
+I have a large number of other results which with a single exception are
+all in accord with those given; and this exception only just overstepped
+the limits. It was like a case of nine trumps, which though in a sense
+possible, is very unlikely to happen in any one's experience.
+
+But even now we are not quite in a position to answer the question with
+which we started. If you refer to it you will see that we are face to
+face with this problem: the limit of variation on the 1000 who died
+would be say 70,[127] ignoring decimals. But if we calculate on the
+number who did not die, viz.--699,000,[128] we shall get a variation 26
+times as great as this. But it is evident the variation must be the same
+in each case. I submitted this kind of problem also to the test of
+experiment, the results of which gave me great faith in Poisson's
+formula.
+
+Imagine two hundred pennies in a bag all heads up. Any shaking will
+spoil this arrangement and give a certain proportion of tails. And,
+further, the probable effect of shaking and turning will be to reduce
+the preponderance of heads or tails whichever may be in excess. This of
+course is the reason why we are so unlikely to get more than 120 of them
+in either position.
+
+But if the two hundred pennies are increased to 20,000 by adding pennies
+which have tails on both sides, then the shaking or mixing would be less
+effective. We should still expect as an average result to get the 100
+heads but in 20,000 instead of 200. The variation will be 28 or 29 on
+the 100 instead of 20. And this is a better limit in such cases. _Taking
+28 as the limit of error on 100 instances_ and proportionally increasing
+the others so that _the mean error becomes 7.8 and the probable error
+5.6_, we may now calculate the answer without gross mistake.
+
+The probable variation on the 1000 deaths by accident will be 18, the
+mean variation will be 24.6, and the limits of variation 88.5. One such
+table showing in five years a mean number of deaths of about 1120 per
+annum gives an annual deviation of about 50 up or down of this. It will
+be seen at once that an improvement of 30 or 40 in any one year would be
+without meaning, but that an improvement of from 100 to 200 would
+indicate some change for the better in the circumstances of the
+industry. Before applying these principles to the elucidation of some of
+the problems of sampling it will be well to give Poisson's formula (in a
+modified form) and to illustrate its working.
+
+Let _x_ equal the number of cases of one sort, _y_ the cases of the
+other sort, and _z_ the total. In the example, _z_ will be the 700,000
+engaged in the industry; _x_ will be the 1000 killed by accidents, and
+_y_ will be the 699,000 who did not so die. The limit of deviation or
+error calculated by Poisson's formula will be the square root of
+8_xy_/_z_. Replacing _x_, _y_ and _z_ by the figures of the example we
+get the square root of (8×1000×699000)/700,000, which works out to the
+square root of 7988.57, or 89.3. Which means that we may reasonably
+expect the number of deaths not to vary from 1000 by more than 89,
+_i.e._, they will be between 1090 and 910. It will be seen that this
+number is in very satisfactory agreement with 88.5 given by the rougher
+calculation based on my own experiments.
+
+To come to the question of sampling. Consider a powder of uniform
+fineness and fine enough to pass through an 80 sieve. For purposes of
+calculation this may be assumed to be made up of particles of about
+one-eighth of a millimetre across (say roughly 1/200 of an inch); cubed,
+this gives the content as about 1/500 (strictly 1/512) of a cubic m.m.
+Now one cubic m.m. of water weighs 1 milligram; therefore 500 such
+particles if they have the specific gravity of water weigh 1 milligram,
+and otherwise weigh 1 milligram multiplied by the sp. gr.: 500 particles
+of ruby silver (Pyrargyrite)[129] will weigh 5.8 milligrams and will
+contain nearly 3.5 milligrams of silver.
+
+Now suppose a portion of 3.2667 grams (1/10 Assay Ton) of silver ore to
+contain 500 such particles of ruby silver and no other material carrying
+silver: such an ore would contain 35 ozs. of silver to the ton. But the
+limits of variation on 500 particles would be 28[130] multiplied by the
+square root of 5, or 62 particles. Thus the limit of sampling error
+would amount to just one-eighth of the silver present, or say to rather
+more than 4 ozs. to the ton; the mean sampling error would be rather
+more than a quarter of this, or say about 1.3 ozs. to the ton.
+
+On the other hand, if one took for the assay a charge six times greater
+(say about 20 grams), the number of particles would be 3000 and the
+limits of variation would be 28 multiplied by the square root of 30, or
+153 particles, which is very closely 1/20 of the silver present, or say
+1.75 ozs. to the ton, whilst the mean error would amount to about .5
+ozs. to the ton.
+
+To work these examples by Poisson's formula let us assume the gangue to
+have a mean sp. gr. of 3. Then 500 particles would weigh 3 milligrams;
+and 3.2609[131] grams would contain 543,500 particles. There would be
+then 500 of ruby silver and 543,500 of gangue, together 544,000, and the
+formula gives the square root of (8×500×543500)/544000, which works out
+to 63 particles as against 62 by the other method.
+
+A practical conclusion from this is of course that either the ore must
+be powdered more finely or a larger portion than 3 grams must be taken
+for the assay. Moreover, it is evident that on such an ore no small
+sample must be taken containing less than several million particles.
+
+Consider now a copper ore of the same uniform fineness containing
+particles of copper pyrites (sp. gr. 4) of which 1000 particles will
+weigh 8 milligrams, mixed with gangue of which 1000 particles weigh 6
+milligrams.
+
+If one gram of such ore contain .5 gram of copper pyrites (= .1725 gram
+copper) and .5 gram of gangue, these will contain 62,500 and say 83,500
+particles respectively. Altogether 146,000 particles. With Poisson's
+formula this gives the limit of sampling error as the square root of
+(8×62500×83500)/146000 or 521 particles. But a variation of 521 on
+62,500 is a variation of .83 per cent. The percentage of copper in the
+ore is 17.25 per cent., and .83 per cent. of this is .14 per cent. The
+limits of sampling error, therefore, are 17.11 per cent. and 17.39 per
+cent. Again, it must be remembered that the mean sampling error would be
+a little over one-quarter of this, or say from 17.2 per cent. to 17.3
+per cent. The practical conclusion is that a powder of this degree of
+fineness is not fine enough. In the last place let us consider a similar
+iron ore containing 90 per cent. of hęmatite (sp. gr. 5) and 10 per
+cent. of gangue (sp. gr. 3), 1 gram of such ore will contain 90,000
+particles of hęmatite weighing .9 gram and containing .63 gram of iron
+with say 16,500 particles of gangue weighing .1 gram. Altogether 106,500
+particles.
+
+Poisson's formula then gives the limits of variation as the square root
+of (8×90000×16500)/106500 or 334 particles. But 334 on 90,000 is 0.23 on
+63.0, which is the percentage of iron present. The limits of sampling
+error then are 62.77 per cent. and 63.23 per cent. and the mean
+variation is from 62.94 per cent. to 63.06 per cent.
+
+These examples are worthy of careful consideration, and it must be
+remembered that the calculations are made on the assumption that the ore
+is made up of uniform particles of mineral of such fineness as would
+pass easily through an 80 sieve, but which does not pretend to represent
+with great exactness the fineness of the powdered ore customary in
+practice. They show that having passed through such a sieve is no proof
+of sufficient powdering, not that all ores powdered and so sifted are
+unfit for assaying. This last would be an absurd and illogical
+conclusion.
+
+If an ore be powdered to a fairly fine sand and then be passed through a
+series of sieves, say a 40, 60, and 80, in such a state that little or
+none remains on the first, but the others retain a large proportion;
+then of that which comes through the 80 sieve, perhaps two-thirds by
+weight may be even coarser than the powder I have used in the example.
+Of the rest most may be of about half this diameter; the weight of the
+really fine powder may be quite inconsiderable. On the other hand, if
+the grinding be continued until, on sifting, little or nothing that is
+powderable remains on the sieves; then in the sifted product the
+proportions will be very different. This last, of course, is the only
+right way of powdering. Also it is evident that so much depends on the
+manner of powdering that nothing precise can be stated as to the average
+coarseness of the powder. Suppose, however, by good powdering a product
+is obtained which may be represented by a uniform powder with particles
+1/20th of a millimetre in diameter (say roughly 1/500 inch). Compared
+with the previous powder, the diameter has been divided by 2.5; their
+number, therefore, in any given weight has been increased by the cube of
+2.5, which is 15.6. But the value of a sample varies as the square root
+of the number of particles. Hence the reduction in size and consequent
+increase in number has made the sample nearly four times better than
+before; and it will be seen that this brings the sampling error within
+tolerable limits.
+
+There are one or two words of warning which should be given. In the
+first place, using a 90 sieve instead of an 80 must not be too much
+relied on; the powder I took in the example would pass through it. It is
+a question of good powdering rather than of fine sifting. In the second
+place, a set of, say half-a-dozen, assays concordant within 1 oz. where
+the theory gives 4 ozs. as the limit of error does not upset the theory:
+the theory itself states this as likely. It is the error you _may_ get
+in one or two assays out of a hundred, not the error you are _likely_ to
+get in any one assay, which is considered under the heading "limit of
+error."
+
+Accepting the result just arrived at that a portion of 1 gram may be
+safely taken for an assay if the particles are 1-20th of a millimetre in
+diameter, the further question remains as to what weight of the original
+sample must be reduced to this degree of fineness. This may be answered
+on the principle that the same degree of excellence should be aimed at
+in each of a series of samplings. This principle is illustrated in the
+table on page 2.
+
+A fine sand, such as would pass a 40 sieve but be retained on a 60
+sieve, would be fairly represented by particles one-quarter of a
+millimetre in diameter. This being five times coarser, to contain the
+same number of particles must be 125 times (the cube of 5) as heavy;
+therefore 125 grams of it can be taken with the same degree of safety as
+1 gram of the finer powder. Of such a sand about this weight should be
+taken and reduced to the finer powder. If the ore were in coarse sand,
+say in particles 1 millimetre in diameter, this would be four times as
+coarse as that last considered, and we should have to take 64 times as
+much of it: 64 times 125 grams is 8 kilos, or say roughly from 15 to 20
+lbs. This should be crushed to the finer size and mixed; then from 100
+to 150 grams should be taken and ground to the finest powder.
+
+There is, however, a reason why, on the coarser stuff, a smaller
+proportion may safely be used. This becomes more evident if we consider
+a still coarser sample. A heap of ore in stones about 2 inches across
+would be 50 times coarser than the sand, and an equivalent sample would
+need to be 125,000 times heavier; this would amount to about 1000 tons.
+Experienced samplers would say that under such conditions so large a
+sample was hardly necessary.
+
+This is because I have assumed in the calculations that the grains of
+copper pyrites, for example, were all copper pyrites and the particles
+of gangue were free from copper. This would be true or nearly so for the
+very fine powder, but far from true in the case of the ore heap. In the
+heap probably few of the stones would be pure ore and still fewer would
+be free from copper. The stones would differ among themselves in their
+copper contents only within certain comparatively narrow limits. And it
+is evident that, if replacing one stone by another, instead of resulting
+in the gain or loss of all the copper one or other contained, merely
+affected the result to one-tenth of this amount, then a sample of
+1-100th of the weight (say 10 tons) would be equally safe.
+
+It should be remembered, however, that while the man who samples on a
+large scale can safely and properly reduce the size of his samples on
+this account, yet the principle is one which counts less and less as the
+stuff becomes more finely divided, and ought to be ignored in the
+working down of the smaller samples which come to the assayer.
+
+FOOTNOTES:
+
+[126] The 10 in 20 multiplied by 10 = 100 in 200.
+
+[127] Multiply the errors for 100 by the square root of 10.
+
+[128] Multiply the errors for 100 by the square root of 6990.
+
+[129] Sp. Gr. 5.8. Silver 60 per cent.
+
+[130] Taking 28 as the limit of variation on 100.
+
+[131] The weight of the ore less the weight of ruby silver in it.
+
+
+
+
+INDEX.
+
+
+Acid measures, 49
+
+Acidimetry, 323
+
+Acidity of ores, 168
+
+Acids, 54
+  strength of, 54, 75, 436
+
+Air of mines, carbonic acid in, 428
+
+Alkalies, 330
+  determination of, 331
+  Lawrence Smith's method for, 333, 412
+  separation of, 332
+
+Alkalimetry, 323
+
+Alkaline earths, 320
+
+Alumina, 314
+  determination of, 315
+  in mineral phosphates, 316
+  separation of, 314, 316
+
+Amalgamation, 126
+
+Ammonia, detection of, 341
+  determination of, 342
+  in natural waters, 353
+
+Antimony, 225
+  detection of, 227
+  dry assay for, 226
+  gravimetric assay, 228
+  separation of, 228
+  volumetric assay, 229
+
+Arsenic, 381
+  detection of, 381
+  dry assay for, 382
+  gravimetric assay, 383
+  in brimstone, 393
+  in crude arsenic, 388, 393
+  in mispickel, 125, 392
+  iodine, assay for, 386
+  separation by distilling, 384
+  uranium acetate, assay for, 389
+  Volhard's method  applied to, 124
+
+Assay book, 11
+  note, 12
+  results, 7
+  tons, 13, 131
+
+Assaying, 1
+  methods, 15
+
+Assays, check, 154
+  preliminary, 147
+
+Atomic weights, 69
+  table of, 433
+
+
+Barium, 326
+
+Baryta, 326
+
+Barytes, sulphur in, 378
+
+Base bullion, sampling of, 157
+
+Basic acetate separation, 233
+
+Baumé's hydrometer, 77
+
+Beryllia, 319
+
+Bismuth, 220
+  colorimetric assay, 223
+  detection of, 221
+  gravimetric determination of, 222
+  in commercial copper, 208
+  separation of, 222
+
+Black tin, 271
+  an analysis of, 287
+  assay of, 276
+  copper in, 204
+  examination of, 285
+  separation by vanning, 272
+
+Blank assays, 34
+
+Blende, sulphur in, 375
+  zinc in, 266
+
+Book, assay, 11
+  laboratory, 10
+  sample, 9
+
+Boracic acid. _See Boron_
+
+Borax, examination of, 431
+
+Boron, 429
+  direct determination of, 431
+
+Brass, copper in, 194
+  zinc in, 265
+
+Bromine and bromides, 361
+
+Bronze, copper in, 194
+  tin in, 281
+
+Burettes, 51
+
+Burnt ore, silver in, 116, 118
+  sulphur in, 377
+
+
+Cadmium, 269
+  gravimetric determination, 269
+  separation of, 269
+
+Caesium, 339
+
+Calcination, 22, 92, 139, 345
+
+Calcium, 320
+  detection of, 321
+  gravimetric determination, 321
+  separation of, 321
+  titration with normal acid, 322
+  titration with permanganate, 322
+
+Calculation of results, 7
+
+Calculations from formulę, 70
+
+Calorific effect of coal, 419
+
+Calorimeter, 419
+
+Calx, 345
+
+Carbon, 414
+  gravimetric determination, 416
+  in iron or steel, 423
+
+Carbonates, 424
+
+Carbonic acid in the air of mines, 428
+
+Caustic potash = potassium hydroxide, 65
+
+Caustic soda = sodium hydroxide, 66
+
+Cerium, 318
+
+Chalybite, iron in, 243
+
+Charcoal, 21, 94
+
+Check assays for gold, 154
+  for silver, 104, 113
+
+Chlorine and chlorides, 359
+
+Chromium, 307
+  gravimetric assay, 309
+  in chrome iron ore, 308
+  volumetric assay, 309
+
+Clays, examination of, 316
+
+Coals, 418
+
+Cobalt, 259
+  detection of, 259
+  dry assay for, 251
+  gravimetric determination, 260
+  in hardhead, 288
+  separation from nickel, 442, 254, 258
+
+Coke, 25
+
+Common salt, examination of, 336
+
+Concentrates, assay for gold of, 140
+
+Colorimetric assays, 44
+
+Copper, 175
+
+Copper, bismuth in, 208
+  colorimetric assay for, 190, 203
+  commercial, arsenic in, 208, 388
+  commercial, copper in, 193
+  commercial, examination of, 205
+  cyanide assay for, 194
+  dry assay of, 176
+  dry assay, loss of, in, 176
+  electrolytic assay for, 190, 203
+  gold in, 206
+  iodide assay for, 199
+  iron in, 209, 249
+  lead in, 206
+  separation of, 183
+  silver in, 205
+  sulphur in, 207
+
+Copper ores, solution of, 183
+  valuation of, 181
+
+Copper pyrites, copper in, 179, 188, 198, 202
+  sulphur in, 376
+
+Culm, 22
+
+Cupel, 23, 142
+
+Cupellation, loss, corrections for, 103
+  loss in gold, 145
+  loss in silver, 101
+  of gold lead alloys, 182
+  of silver lead alloys, 98, 110
+  temperature of, 143
+
+Cyanicides, 169
+
+Cyanide assay for copper, 194
+  for nickel, 255
+  for tin, 278
+
+Cyanides, alkalinity of, 167
+  assay of, 167
+  commercial, 160
+  double, 161
+  gold-dissolving power, 162
+  prussic acid, 162
+  volumetric determination of, 163, 165
+
+Cyanide liquors, alkalinity of, 167
+  assay of, 164, 165
+  assay of, for gold, 140
+  assay of, for zinc, &c., 169
+
+
+Daniell cells, 185
+
+Didymium, 319
+
+Dollars to the ton, 9
+
+Dry assays, 16
+
+Drying, 5, 33
+
+
+Earths, 314
+  the alkaline, 320
+
+Electrodes, 187
+
+Electrolysis for copper, 184
+  for nickel, 254
+
+Equations, 69
+
+Erbia, 319
+
+
+Ferrous and ferric salts, 231
+
+Filtration, 31
+
+Finishing point, 42
+
+Flasks, graduated, 49
+
+Flatting, 149
+
+Fluorine and fluorides, 363
+
+Fluxes, 16, 93, 136, 138, 140
+
+Formulę, 68
+
+Furnaces, 25
+
+
+Galena, lead in, 217, 218
+
+Gangue, 405
+  iron in the, 244
+
+Gas-measuring apparatus, 52
+
+Gases, measurement of, 44
+
+Gay-Lussac's assay for silver, 119
+  assay for silver modified, 123
+
+German silver, copper in, 194
+  nickel in, 255, 259
+
+Gold, 126
+  amalgamation of, 126
+  in cyanide liquor, 140
+  loss of, in cupellation, 145
+  loss of, in parting, 154
+  preparation of, 63
+  silver in, 157
+  silver in, after parting, 154
+  test for, 126
+
+Gold-lead alloys, cupellation of, 142
+  sampling of, 158
+
+Gold ores assay with cyanide solutions, 141
+  calcination of, 139
+  concentrates, 140
+  fluxing, 136, 138, 140
+  sampling of, 127
+  size of assay charges, 127
+  tailings, 140
+
+Gold-parting, 150
+  platinum in, 145, 154, 170, 171
+
+Gold-zinc slimes, 142
+
+Graduated vessels, 49
+
+Gravimetric methods, 15, 27
+
+
+Halogens, 358
+
+Hardhead, 287
+  an analysis of, 289
+
+Hot plate, 30
+
+Hydrogen, preparation of, 62
+  reduction by, 280
+
+Hydrometer, 77
+
+
+Ignition, 32
+  in hydrogen, 280
+
+Indicators, 42
+
+Inquartation, 146
+
+Iodine and iodides, 362
+
+Iridium, 171
+
+Iron, 231
+  bichromate assay for, 237, 243,
+  carbon in, 423
+  colorimetric assay for, 247
+  ferrous and ferric, 231
+  gravimetric determination, 233
+  permanganate assay for, 236, 238
+  phosphorus in, 399
+  reduction of ferric solutions, 235, 241
+  separation of, 232
+  stannous chloride assay for, 244
+  volumetric assays for, 234
+
+Iron ores, iron in, 244, 247
+  phosphates in, 399
+
+
+Laboratory books, 9
+
+Lanthanum, 319
+
+Lawrence Smith's method for alkalies, 333, 412
+
+Lead, 211
+  colorimetric assay for, 218
+  detection of, 211
+  dry assay for, 211
+  gravimetric determination  of, 213
+  in commercial copper, 206
+  in commercial zinc, 214
+  in galena, 217, 218
+  separation of, 211, 213
+  volumetric  determination of, 214
+
+Litharge, use of, in dry assays, 20, 93
+
+Lithium, 338
+
+Lime, 320
+  milk of, 321
+  volumetric assays for, 322
+
+Limestone, examination of, 329
+  lime in, 324
+
+Limewater, 321
+
+Loths, 9
+
+
+Magnesia, magnesium, 328
+  mixture, preparation of, 64
+
+Manganese, 298
+  colorimetric assay, 306
+  detection of, 299
+  gravimetric  determination  of, 300
+  separation of, 299
+  volumetric determination of, 300
+
+Manganese peroxide, ferrous sulphate assay for, 301
+  iodine assay for, 302
+  = manganese dioxide, 298
+
+Manganese ore, copper in, 204
+  manganese in, 300
+  peroxide in, 302
+
+Matte, 18
+
+Measuring, 49
+  flasks, 49
+  gases, 44, 52
+  gold buttons, 133, 440,
+  liquids, 49
+  silver buttons, 106
+
+Mechanical methods, 16
+
+Mercury, 171
+  dry assay, 172
+  wet assay, 173
+
+Metallic particles in ores, gold, 129
+  particles in ores, silver, 108
+  particles, tin, 278, 287
+
+Micrometer, 133
+
+Microscope, measuring with the, 440, 133
+
+Mispickel, arsenic in, 125, 392
+  sulphur in, 376
+
+Moisture, 7, 350
+
+Molybdate separation for phosphates, 395
+  solution, preparation of, 60
+
+Molybdenum, 311
+
+Muffle, 25
+
+
+Nessler's solution, 342
+
+Nickel, 251
+  dry assay for, 251
+  electrolytic assay, 254
+  gravimetric determination of, 254
+  in German silver, 255, 259
+  separation from cobalt, 254, 258, 442
+  separation from iron, 258
+  separation from manganese, 258
+  separation of, 253
+  volumetric assay, 255
+
+Niobium, 297
+
+Nitre, 22
+  use of, in dry assays, 95
+
+Nitrogen and nitrates, 400
+
+Nitrometer, 403
+
+Normal acid, normal solutions, 323
+
+
+Ores, determining water in, 5, 351
+  drying, 5
+  powdering, 4, 109, 130, 448
+  quantities of, for an assay, 11, 27, 127
+  sampling, 1, 127, 444
+  with metallic particles, 3, 108, 129
+
+Osmiridium, 171
+
+Osmium, 171
+
+Ounces to the ton, long, 107
+  to the ton, short, 132
+
+Oxidation, 345
+
+Oxides, 345
+  determination of oxygen in, 346
+
+Oxidising agents, 22, 95, 345
+  effect of nitre, 95
+  effect of nitric acid, 56
+
+Oxygen, 344
+  equivalent, 358
+  in natural waters, 344, 356
+  in ores, 348
+
+
+Palladium, 171
+
+Parting, 150
+  acids, 150
+  in flasks, 151
+  in glazed crucibles, 153
+  in special apparatus, 156
+  in test tubes, 152
+
+Phosphate, assay of apatite for, 399
+  assay of iron ore for, 399
+
+Phosphates, gravimetric assay, 396
+  volumetric assay, 397
+
+Phosphorus and phosphates, 394
+  in iron, 399
+
+Pipette, 50, 120
+
+Platinum, 170
+  in gold, 145, 154, 170
+
+Potash, commercial examination of, 338
+
+Potassium, 336
+  gravimetric determination, 337
+
+Potassium cyanide, 22, 65, 160
+  commercial assay of, 167
+  commercial, purity of, 161
+
+Powdering, 4, 130, 448, 109
+
+Precipitation, 30
+
+Precipitates, drying, 32
+  igniting, 32, 34
+  washing, 31
+
+Preliminary assays, 104, 147
+
+Preparation of acids, 54
+  of other reagents, 59
+
+Prill, 108, 129, 278, 287
+
+Produce, 8
+
+Pyrarsenate of magnesia, 383
+
+Pyrites, iron in, 244
+  sulphur in, 370, 376
+
+Pyrophosphate of magnesia, 397
+
+
+Quantity to be taken for an assay, 11, 27, 127
+
+Quartation, 146
+
+Quartering, 2
+
+
+Reagents, strength of, 54
+
+Red lead for dry assays, 20, 22, 94
+
+Reducing agents, 21, 94
+  effects of charcoal, &c., 94
+  effect of mineral sulphides, 95, 97, 98
+
+Reduction by hydrogen, 280
+  of ferric solutions, 235, 242, 244
+
+Regulus, 18
+
+Report form, 12
+
+Results, calculation of, 7, 13, 16, 38, 107, 131, 132
+  statement of, 7
+
+Rhodium, 171
+
+Roasting, 22, 345
+
+Rolling, 149
+
+Rubidium, 340
+
+Ruthenium, 171
+
+
+Sample book, 9
+
+Sampling, 1
+  effect of powdering on, 449
+  errors, 447
+  gold ores, 127
+  metals, 157
+  theory of, 444
+
+Scorification of silver ores, 88
+
+Scorifier, 23, 89
+
+Selenium, 379
+
+Separation, as sulphides, 57
+  basic acetate, 233
+  molybdate, 395
+
+Shales, bituminous, 420
+
+Silicon and silicates, 405
+  in iron, 414
+
+Silica in rocks, 409
+  in slags, 414
+
+Silicates, alkalies in, 333, 412
+  beryllia in, 320
+  examination of, 409
+  titanium in, 411
+
+Silver, 87
+  correction for cupellation loss, 103
+  detection of, 87
+  Gay-Lussac's assay, 119
+  Gay-Lussac's assay modified, 123
+  gravimetric determination of, 117
+  in bullion, 113
+  in burnt ore, 116, 118
+  in copper, 114, 205
+  in galena, 114
+  in lead, 113
+  in oxide of lead, 113
+  in silver precipitate, 115
+  loss in cupellation, 101
+  pure preparation of, 66
+  Volhard's assay, 121
+  volumetric methods, 119, 121, 123
+
+Silver lead alloys, cupellation of, 98
+                   sampling of, 157
+
+Silver ore, crucible assay of, 90
+  metallic particles in, 108
+  scorification of, 88
+
+Size of assay charges, 11, 27, 127
+
+Slags, 19
+
+Soda-lime, 425
+
+Sodium, 334
+
+Sodium cyanide, 160
+
+Solution, 29
+
+Solutions, normal, 323
+  standard, 36
+
+Specific gravity, 75, 436
+
+Speise, 19
+
+Standard, 37
+  solutions, 36
+
+Standardising, 37
+
+Steel, carbon in, 423
+  chromium in, 310
+  manganese in, 300
+
+Stoking, 25, 143
+
+Strength of reagents, 54
+
+Strontium, 324
+
+Sulphates and sulphur, 367
+  gravimetric determination, 369
+  volumetric determination, 370
+
+Sulphides, reducing action of, 9, 95
+
+Sulphocyanate assay for silver, 121
+
+Sulphur in blende, 375
+  in burnt ore, 377
+  in chalcocite, 376
+  in coal, 419
+  in copper, 207
+  in copper pyrites, 376
+  in mispickel, 376
+  in pyrites, 370, 376
+
+Sulphuretted hydrogen, preparation, 57
+
+Surcharge, 154
+
+System in assaying, 28
+
+
+Table, atomic weights, 433
+  comparing thermometers, 435
+  ounces to the long ton, 107
+  ounces to the short ton, 132
+  sp. g. ammonia, 438
+  sp. g. hydrochloric acid, 437
+  sp. g. minerals, 86
+  sp. g. nitric acid, 436
+  sp. g. sulphuric acid, 439
+  sp. g. water, 83
+
+Tantalum, 297
+
+Tartar, 20, 94
+
+Tellurium, 379
+  improved test for, 150
+
+Thallium, 219
+
+Thorium, 317
+
+Tin, 271 _See also Black tin_
+  assay for, by vanning, 273
+  copper in, 204
+  Cornish assay, 276
+  cyanide assay, 278
+  detection of, 279
+  gravimetric determination of, 281
+  iron in, 250
+  separation of, 280
+  volumetric assay for, 282
+
+Tin arsenide, 284
+
+Tin phosphide, 284
+
+Tin slag, 290
+  an analysis of, 292
+  tin in, 290
+
+Titanium, 292
+  detection of, 293
+  in black tin, 272, 287
+  in rocks, 411
+  separation, &c., 294
+
+Titration, 35
+  indirect, 43, 72
+
+Ton, assay, 13, 131,
+  long, 2240 lbs. = 32,666.6 oz., 107
+  short, 2000 lbs = 29,166.6 oz., 132
+
+Tungsten, 295
+
+Tungstic acid, 295
+  gravimetric determination, 296
+  in black tin, 285
+  in wolfram, 296
+
+
+Uranium, 312
+
+Valuation, of copper ores, 181
+
+Vanadium, 310
+
+Vanning, 273
+
+Volhard's assay applied to arsenic, 124
+  silver assay, 121
+
+Volume-corrector, 53
+
+Volumetric assay, 35, 38
+
+
+Water, 7, 350
+  direct determination of, 351
+  examination of, 352
+  expansion of, 83
+  solids in, 354
+
+Weighing, 47
+  small gold buttons, 131
+
+Weights, 47
+
+Wolfram, an analysis of, 296
+  tungstic acid in, 296
+
+
+Yttria, 319
+
+
+Zinc, 261
+  commercial, examination of, 268
+  commercial, iron in, 249
+  commercial, lead in, 214
+  dry assay, 261
+  gasometric assay, 266
+  gravimetric determination, 262
+  in blende, 266
+  in cyanide liquors, 169
+  in silver precipitate, 266
+  separation of, 262
+  volumetric assay, 263
+
+Zirconia, 317
+
+
+Printed by BALLANTYNE, HANSON & Co.
+
+London & Edinburgh.
+
+
+
+
+A SELECTION FROM THE SCIENTIFIC AND TECHNICAL WORKS
+
+_PUBLISHED BY_
+
+~CHARLES GRIFFIN & COMPANY, LIMITED.~
+
+[Illustration]
+
+MESSRS. CHARLES GRIFFIN & COMPANY'S PUBLICATIONS may be obtained through
+any Bookseller in the United Kingdom, or will be sent Post-free on
+receipt of a remittance to cover published price. To prevent delay,
+Orders should be accompanied by a Cheque or Postal Order crossed "UNION
+OF LONDON AND SMITH'S BANK, Chancery Lane Branch."
+
+*** _For INDEX, see next page._
+[Transcriber's Note: No index on next page.]
+
+[Illustration]
+
+COMPLETE TECHNICAL, MEDICAL, and GENERAL CATALOGUES forwarded Post-free
+on Application.
+
+~LONDON:~
+
+~EXETER STREET, STRAND.~
+
+       *       *       *       *       *
+
+THIRD EDITION, _Revised, with an Additional Chapter on Foundations.
+Numerous Diagrams, Examples, and Tables. Large 8vo. Cloth. 16s._
+
+~THE DESIGN OF STRUCTURES:~
+
+~A Practical Treatise on the Building of Bridges, Roofs, &c.~
+
+BY S. ANGLIN, C.E.,
+
+Master of Engineering, Royal University of Ireland, late Whitworth
+Scholar, &c.
+
+"Students of Engineering will find this Text-Book
+INVALUABLE."--_Architect._
+
+"The author has certainly succeeded in producing a THOROUGHLY PRACTICAL
+Text-Book."--_Builder._
+
+"We can unhesitatingly recommend this work not only to the Student, as
+the BEST TEXT-BOOK on the subject, but also to the professional engineer
+as an EXCEEDINGLY VALUABLE book of reference."--_Mechanical World._
+
+       *       *       *       *       *
+
+THIRD EDITION, _Thoroughly Revised. Royal 8vo. With numerous
+Illustrations and 13 Lithographic Plates. Handsome Cloth. Price 30s._
+
+~A PRACTICAL TREATISE ON~
+
+~BRIDGE-CONSTRUCTION:~
+
+~Being a Text-Book on the Construction of Bridges in Iron and Steel.~
+
+~FOR THE USE OF STUDENTS, DRAUGHTSMEN, AND ENGINEERS.~
+
+BY T. CLAXTON FIDLER, M. INST. C.E.,
+
+~Prof. of Engineering, University College, Dundee.~
+
+GENERAL CONTENTS.--PART I.--Elementary Statics. PART II.--General
+Principles of Bridge-Construction. PART III.--The Strength of Materials.
+PART IV.--The Design of Bridges in Detail.
+
+"The new edition of Mr. Fidler's work will again occupy the same
+CONSPICUOUS POSITION among professional text-books and treatises as has
+been accorded to its predecessors. The instruction imparted is SOUND,
+SIMPLE, AND FULL. The volume will be found valuable and useful alike to
+those who may wish to study only the theoretical principles enunciated,
+and ... to others whose object and business is ... practical."--_The
+Engineer._
+
+       *       *       *       *       *
+
+At Press. In Large 8vo. Handsome Cloth. With Copious Plates and
+Illustrations.
+
+The Principles and Practice of ~DOCK ENGINEERING.~
+
+By BRYSON CUNNINGHAM, B.E., ASSOC.M.INST.C.E., Of the Engineers'
+Department, Mersey Docks and Harbour Board.
+
+~GENERAL CONTENTS.~
+
+Historical and Discursive.--Dock Design.--Constructive
+Appliances.--Materials.--Dock and Quay Walls.--Entrance Passages and
+Locks.--Jetties, Wharves, and Piers.--Dock Gates and Caissons.--Transit
+Sheds and Warehouses.--Dock Bridges.--Graving and Repairing
+Docks.--Working Equipment of Docks.--INDEX.
+
+*** The object of the Author has been to deal fully and comprehensively
+with the problems arising out of the construction and maintenance of
+Docks and their appanages, not simply as a record of works carried out,
+but as a treatise on the principles underlying their construction and an
+investigation of the mathematical theories involved. It is primarily
+intended for the student; but it is hoped that the large amount of data
+and material collected from various sources, and in many cases
+contributed specially for this book, will render it useful to the expert
+engineer as a work of reference; while, at the same time, of general
+interest to directors and others connected with the management and
+administration of seaports.
+
+       *       *       *       *       *
+
+THIRD EDITION. In Two Parts, Published Separately.
+
+A TEXT-BOOK OF
+
+~Engineering Drawing and Design~
+
+Vol. I.--Practical Geometry, Plane, and Solid. 3s.
+
+VOL. II.--Machine and Engine Drawing and Design. 4s. 6d.
+
+by
+
+SIDNEY H. WELLS, WH.SC.,
+
+A.M.INST.C.E., A.M.INST.MECH.E.,
+
+Principal of the Battersea Polytechnic Institute, and Head of the
+Engineering Department therein; formerly of the Engineering Departments
+of the Yorkshire College, Leeds; and Dulwich College, London.
+
+_With many Illustrations, specially prepared for the Work, and numerous
+Examples, for the Use of Students in Technical Schools and Colleges._
+
+"A CAPITAL TEXT-BOOK, arranged on an EXCELLENT SYSTEM, calculated to
+give an intelligent grasp of the subject, and not the mere faculty of
+mechanical copying.... Mr. Wells shows how to make complete working
+drawings, discussing fully each step in the design."--_Electrical
+Review._
+
+"The first book leads easily and naturally towards the second, where the
+technical pupil brought into contact with large and more complex
+designs."--_The Schoolmaster._
+
+       *       *       *       *       *
+
+~Works by BRYAN DONKIN, M. Inst. C.E., M. Inst. Mech. E., &c.~
+
+THIRD EDITION, Revised and Enlarged. With additional Illustrations.
+Large 8vo, Handsome Cloth. 25s.
+
+~GAS, OIL, AND AIR ENGINES:
+
+A Practical Text-Book on Internal Combustion Motors without Boiler.~
+
+BY BRYAN DONKIN, M. INST. C.E., M. INST. MECH. E.
+
+GENERAL CONTENTS.--~Gas Engines~:--General Description--History and
+Development--British, French, and German Gas Engines--Gas Production for
+Motive Power--Theory of the Gas Engine--Chemical Composition of Gas in
+Gas Engines--Utilisation of Heat--Explosion and Combustion. ~Oil
+Motors~:--History and Development--Various Types--Priestman's and other
+Oil Engines. ~Hot-Air Engines~:--History and Development--Various Types:
+Stirling's, Ericsson's, &c., &c.
+
+"The BEST BOOK NOW PUBLISHED on Gas, Oil, and Air Engines.... Will be of
+VERY GREAT INTEREST to the numerous practical engineers who have to make
+themselves familiar with the motor of the day.... Mr. Donkin has the
+advantage of LONG PRACTICAL EXPERIENCE, combined with HIGH SCIENTIFIC
+AND EXPERIMENTAL KNOWLEDGE, and an accurate perception of the
+requirements of Engineers."--_The Engineer._
+
+"We HEARTILY RECOMMEND Mr. Donkin's work.... A monument of careful
+labour.... Luminous and comprehensive."--_Journal of Gas Lighting_.
+
+"A thoroughly RELIABLE AND EXHAUSTIVE Treatise."--_Engineering._
+
+       *       *       *       *       *
+
+In Quarto, Handsome Cloth. With Numerous Plates. 25s.
+
+THE HEAT EFFICIENCY OF STEAM BOILERS (LAND, MARINE, AND LOCOMOTIVE).
+
+~With many Tests and Experiments on different Types of Boilers, as to
+the Heating Value of Fuels, &c., with Analyses of Gases and Amount of
+Evaporation, and Suggestions for the Testing of Boilers.~
+
+BY BRYAN DONKIN, M. INST. C.E.
+
+GENERAL CONTENTS.--Classification of different Types of Boilers--425
+Experiments on English and Foreign Boilers with their Heat Efficiencies
+shown in Fifty Tables--Fire Grates of Various Types--Mechanical
+Stokers--Combustion of Fuel in Boilers--Transmission of Heat through
+Boiler Plates, and their Temperature--Feed Water Heaters, Superheaters,
+Feed Pumps, &c.--Smoke and its Prevention--Instruments used in
+Testing Boilers--Marine and Locomotive Boilers--Fuel Testing
+Stations--Discussion of the Trials and Conclusions--On the
+Choice of a Boiler, and Testing of Land, Marine, and Locomotive
+Boilers--Appendices--Bibliography--Index.
+
+_With Plates illustrating Progress made during recent years, and the
+best Modern Practice._
+
+"A WORK OF REFERENCE AT PRESENT UNIQUE. Will give an answer to almost
+any question connected with the performance of boilers that it is
+possible to ask."--_Engineer._
+
+"Probably the MOST EXHAUSTIVE _résumé_ that has ever been collected. A
+PRACTICAL BOOK by a thoroughly practical man."--_Iron and Coal Trades
+Review._
+
+       *       *       *       *       *
+
+THIRD EDITION, _Revised and Enlarged. Pocket-Size, Leather, 12s. 6d.;
+also Larger Size for Office Use, Cloth, 12s. 6d._
+
+~Boilers, Marine and Land:~ THEIR CONSTRUCTION AND STRENGTH.
+
+A HANDBOOK OF RULES, FORMULĘ, TABLES, &C., RELATIVE TO MATERIAL,
+SCANTLINGS, AND PRESSURES, SAFETY VALVES, SPRINGS, FITTINGS AND
+MOUNTINGS, &C.
+
+FOR THE USE OF ENGINEERS, SURVEYORS, BOILER-MAKERS, AND STEAM USERS.
+
+BY T.W. TRAILL, M. INST. C.E., F.E.R.N., Late Engineer Surveyor-in-Chief
+to the Board of Trade.
+
+*** To the Second and Third Editions many New Tables for Pressure, up to
+200 Lbs. per Square Inch have been added.
+
+"THE MOST VALUABLE WORK on Boilers published in England."--_Shipping
+World._
+
+"Contains an ENORMOUS QUANTITY OF INFORMATION arranged in a very
+convenient form.... A MOST USEFUL VOLUME ... supplying information to be
+had nowhere else."--_The Engineer._
+
+       *       *       *       *       *
+
+_Third Impression._ Large Crown 8vo. With numerous Illustrations. 6s.
+
+ENGINE-ROOM PRACTICE:
+
+~A Handbook for Engineers and Officers in the Royal Navy and Mercantile
+Marine, Including the Management of the Main and Auxiliary Engines on
+Board Ship.~
+
+BY JOHN G. LIVERSIDGE,
+
+Engineer, R.N., A.M.I.C.E., Instructor in Applied Mechanics at the Royal
+Naval College, Greenwich.
+
+_Contents._--General Description of Marine Machinery.--The Conditions of
+Service and Duties of Engineers of the Royal Navy.--Entry and Conditions
+of Service of Engineers of the Leading S.S. Companies.--Raising
+Steam.--Duties of a Steaming Watch on Engines and Boilers.--Shutting off
+Steam.--Harbour Duties and Watches.--Adjustments and Repairs of
+Engines.--Preservation and Repairs of "Tank" Boilers.--The Hull and its
+Fittings.--Cleaning and Painting Machinery.--Reciprocating Pumps, Feed
+Heaters, and Automatic Feed-Water Regulators.--Evaporators.--Steam
+Boats.--Electric Light Machinery.--Hydraulic Machinery.--Air-Compressing
+Pumps.--Refrigerating Machines.--Machinery of Destroyers.--The
+Management of Water-Tube Boilers.--Regulations for Entry of Assistant
+Engineers, R.N.--Questions given in Examinations for Promotion of
+Engineers, R.N.--Regulations respecting Board of Trade Examinations for
+Engineers, &c.
+
+"The contents CANNOT FAIL TO BE APPRECIATED."--_The Steamship._
+
+"This very useful book.... ILLUSTRATIONS are of GREAT IMPORTANCE in a
+work of this kind, and it is satisfactory to find that SPECIAL ATTENTION
+has been given in this respect."--_Engineers' Gazette._
+
+       *       *       *       *       *
+
+_In Crown 8vo, extra, with Numerous Illustrations_. [_Shortly._
+
+GAS AND OIL ENGINES:
+
+An Introductory Text-Book on the Theory, Design, Construction, and
+Testing of Internal Combustion Engines without Boiler.
+
+FOR THE USE OF STUDENTS.
+
+BY PROF. W.H. WATKINSON, WHIT. SCH., M. INST. MECH. E., Glasgow and West
+of Scotland Technical College.
+
+       *       *       *       *       *
+
+SECOND EDITION, Revised. With numerous Plates reduced from Working
+Drawings and 280 Illustrations in the Text. 21s.
+
+_A MANUAL OF_ LOCOMOTIVE ENGINEERING:
+
+A Practical Text-Book for the Use of Engine Builders, Designers and
+Draughtsmen, Railway Engineers, and Students.
+
+BY
+
+WILLIAM FRANK PETTIGREW, M. INST. C.E.
+
+With a Section on American and Continental Engines.
+
+BY ALBERT F. RAVENSHEAR, B.SC., Of His Majesty's Patent Office.
+
+_Contents_.--Historical Introduction, 1763-1863.--Modern Locomotives:
+Simple.--Modern Locomotives: Compound.--Primary Consideration in
+Locomotive Design.--Cylinders, Steam Chests, and Stuffing
+Boxes.--Pistons, Piston Rods, Crossheads, and Slide Bars.--Connecting
+and Coupling Rods.--Wheels and Axles, Axle Boxes, Hornblocks, and
+Bearing Springs.--Balancing.--Valve Gear.--Slide Valves and Valve
+Gear Details.--Framing, Bogies and Axle Trucks, Radial Axle
+Boxes.--Boilers.--Smokebox, Blast Pipe, Firebox Fittings.--Boiler
+Mountings.--Tenders.--Railway Brakes.--Lubrication.--Consumption
+of Fuel, Evaporation and Engine Efficiency.--American
+Locomotives.--Continental Locomotives.--Repairs, Running, Inspection,
+and Renewals.--Three Appendices.--Index.
+
+"Likely to remain for many years the STANDARD WORK for those wishing to
+learn Design."--_Engineer._
+
+"A most interesting and valuable addition to the bibliography of the
+Locomotive."--_Railway Official Gazette._
+
+"We recommend the book as THOROUGHLY PRACTICAL in its character, and
+MERITING A PLACE IN ANY COLLECTION of ... works on Locomotive
+Engineering."--_Railway News._
+
+"The work CONTAINS ALL THAT CAN BE LEARNT from a book upon such a
+subject. It will at once rank as THE STANDARD WORK UPON THIS IMPORTANT
+SUBJECT."--_Railway Magazine._
+
+       *       *       *       *       *
+
+_In Large 8vo. Handsome Cloth. With Plates and Illustrations. 16s._
+
+LIGHT RAILWAYS AT HOME AND ABROAD.
+
+BY WILLIAM HENRY COLE, M. INST. C.E., Late Deputy-Manager, North-Western
+Railway, India.
+
+_Contents._--Discussion of the Term "Light Railways."--English Railways,
+Rates, and Farmers.--Light Railways in Belgium, France, Italy, other
+European Countries, America and the Colonies, India, Ireland.--Road
+Transport as an alternative.--The Light Railways Act, 1896.--The
+Question of Gauge.--Construction and Working.--Locomotives and
+Rolling-Stock.--Light Railways in England, Scotland, and
+Wales.--Appendices and Index.
+
+"Mr. W.H. Cole has brought together ... a LARGE AMOUNT OF VALUABLE
+INFORMATION ... hitherto practically inaccessible to the ordinary
+reader."--_Times._
+
+"Will remain, for some time yet a STANDARD WORK in everything relating
+to Light Railways."--_Engineer._
+
+"The author has extended practical experience that makes the book lucid
+and useful. It is EXCEEDINGLY well done"--_Engineering._
+
+"The whole subject is EXHAUSTIVELY and PRACTICALLY considered. The work
+can be cordially recommended as INDISPENSABLE to those whose duty it is
+to become acquainted with one of the prime necessities of the immediate
+future."--_Railway Official Gazette._
+
+"THERE COULD BE NO BETTER BOOK of first reference on its subject. All
+classes of Engineers will welcome its appearance."--_Scotsman._
+
+       *       *       *       *       *
+
+THIRD EDITION, Revised and Enlarged. _With Numerous Illustrations. Price
+8s. 6d._
+
+~VALVES AND VALVE-GEARING:~
+
+_INCLUDING THE CORLISS VALVE AND TRIP GEARS._
+
+BY
+
+CHARLES HURST, Practical Draughtsman.
+
+"CONCISE explanations illustrated by 115 VERY CLEAR DIAGRAMS and
+drawings and 4 folding-plates ... the book fulfils a VALUABLE
+function."--_Athenęum._
+
+"MR. HURST'S VALVES AND VALVE-GEARING will prove a very valuable aid,
+and tend to the production of Engines of SCIENTIFIC DESIGN AND
+ECONOMICAL WORKING.... Will be largely sought after by Students and
+Designers.--_Marine Engineer._
+
+"USEFUL AND THOROUGHLY PRACTICAL. Will undoubtedly be found of GREAT
+VALUE to all concerned with the design of Valve-gearing."--_Mechanical
+World._
+
+"Almost EVERY TYPE OF VALVE and its gearing is clearly set forth, and
+illustrated in such a way as to be READILY UNDERSTOOD and PRACTICALLY
+APPLIED by either the Engineer, Draughtsman, or Student.... Should prove
+both USEFUL and VALUABLE to all Engineers seeking for RELIABLE and CLEAR
+information on the subject. Its moderate price brings it within the
+reach of all"--_Industries and Iron._
+
+"Mr. HURST'S work is ADMIRABLY suited to the needs of the practical
+mechanic.... It is free from any elaborate theoretical discussions, and
+the explanations of the various types of valve-gear are accompanied by
+diagrams which render them EASILY UNDERSTOOD."--_The Scientific
+American._
+
+       *       *       *       *       *
+
+~Hints on Steam Engine Design and Construction.~ By CHARLES HURST,
+"Author of Valves and Valve Gearing." In Paper Boards, 8vo., Cloth Back.
+Illustrated. Price 1s. 6d. net.
+
+CONTENTS.--I. Steam Pipes.--II. Valves.--III. Cylinders.--IV. Air Pumps
+and Condensers.--V. Motion Work.--VI. Crank Shafts and Pedestals.--VII.
+Valve Gear.--VIII. Lubrication.--IX. Miscellaneous Details--INDEX.
+
+"A handy volume which every practical young engineer should
+possess."--_The Model Engineer._
+
+       *       *       *       *       *
+
+JUST OUT. Strongly Bound in Super Royal 8vo. Cloth Boards.
+
+~BONUS TABLES:~
+
+For Calculating Wages on the Bonus or Premium Systems.
+
+_For Engineering, Technical and Allied Trades._
+
+BY HENRY A. GOLDING, A.M.INST.M.E.,
+
+Technical Assistant to Messrs. Bryan Donkin and Clench, Ltd., and
+Assistant Lecturer in Mechanical Engineering at the Northampton
+Institute, London, E.C.
+
+"The adoption of this system for the payment of workmen has created a
+demand for some handy table or series of tables, by means of which the
+wages may be easily found without the necessity of any calculations
+whatever. With the object of supplying this need, the author has
+compiled the following tables, which have been in practical use for some
+time past at a large engineering works in London, and have been found of
+inestimable value. Not only are they of great value as a 'time saving
+appliance,' the computation of the bonus or premiums earned by a number
+of men taking only _one-tenth_ the time by the aid of these tables
+compared with ordinary calculations, but they possess the additional
+advantage of being less liable to error, as there is practically no
+possibility of a mistake occurring."--_Extract from Preface._
+
+       *       *       *       *       *
+
+Large 8vo, Handsome Cloth. With Illustrations, Tables, &c. 21s.
+
+Lubrication & Lubricants:
+
+A TREATISE ON THE
+
+~THEORY AND PRACTICE OF LUBRICATION~
+
+AND ON THE
+
+~NATURE, PROPERTIES, AND TESTING OF LUBRICANTS.~
+
+BY LEONARD ARCHBUTT, F.I.C., F.C.S., Chemist to the Midland Railway
+Company,
+
+AND
+
+R. MOUNTFORD DEELEY, M.I.M.E., F.G.S., Midland Railway Locomotive Works'
+Manager, Derby.
+
+CONTENTS.--I. Friction of Solids.--II. Liquid Friction or Viscosity, and
+Plastic Friction.--III. Superficial Tension.--IV. The Theory of
+Lubrication.--V. Lubricants, their Sources, Preparation, and
+Properties.--VI. Physical Properties and Methods of Examination of
+Lubricants.--VII. Chemical Properties and Methods of Examination of
+Lubricants.--VIII. The Systematic Testing of Lubricants by Physical and
+Chemical Methods.--IX. The Mechanical Testing of Lubricants.--X. The
+Design and Lubrication of Bearings.--XI. The Lubrication of
+Machinery.--INDEX.
+
+"Destined to become a CLASSIC on the subject."--_Industries and Iron._
+
+"Contains practically ALL THAT IS KNOWN on the subject. Deserves the
+careful attention of all Engineers."--_Railway Official Guide._
+
+       *       *       *       *       *
+
+FOURTH EDITION. _Very fully Illustrated. Cloth_, _4s. 6d._
+
+STEAM-BOILERS: THEIR DEFECTS, MANAGEMENT, AND CONSTRUCTION.
+
+BY R.D. MUNRO, _Chief Engineer of the Scottish Boiler Insurance and
+Engine Inspection Company._
+
+GENERAL CONTENTS.--I. EXPLOSIONS caused (1) by Overheating of
+Plates--(2) By Defective and Overloaded Safety Valves--(3) By
+Corrosion, Internal or External--(4) By Defective Design
+and Construction (Unsupported Flue Tubes; Unstrengthened Manholes;
+Defective Staying; Strength of Rivetted Joints; Factor of
+Safety)--II. CONSTRUCTION OF VERTICAL BOILERS: Shells--Crown
+Plates and Uptake Tubes--Man-Holes, Mud-Holes, and
+Fire-Holes--Fireboxes--Mountings--Management--Cleaning--Table of
+Bursting Pressures of Steel Boilers--Table of Rivetted
+Joints--Specifications and Drawings of Lancashire Boiler for Working
+Pressures (a) 80 lbs.; (b) 200 lbs. per square inch respectively.
+
+"A valuable companion for workmen and engineers engaged about Steam
+Boilers, ought to be carefully studied, and ALWAYS AT HAND."--_Coll.
+Guardian._
+
+"The book is VERY USEFUL, especially to steam users, artisans, and young
+Engineers."--_Engineer._
+
+       *       *       *       *       *
+
+BY THE SAME AUTHOR.
+
+KITCHEN BOILER EXPLOSIONS: Why they Occur, and How to Prevent their
+Occurrence. A Practical Handbook based on Actual Experiment. With
+Diagram and Coloured Plate. Price 3s.
+
+       *       *       *       *       *
+
+JUST OUT. _In Crown 8vo, Handsome Cloth. With Numerous Illustrations.
+5s. net._
+
+EMERY GRINDING MACHINERY.
+
+~_A Text-Book of Workshop Practice in General Tool Grinding, and the
+Design, Construction, and Application of the Machines Employed._~
+
+BY
+
+R.B. HODGSON, A.M. INST. MECH. E., Author of "Machines and Tools
+Employed in the Working of Sheet Metals."
+
+INTRODUCTION.--Tool Grinding.--Emery Wheels.--Mounting Emery
+Wheels.--Emery Rings and Cylinders.--Conditions to Ensure Efficient
+Working.--Leading Types of Machines.--Concave and Convex Grinding.--Cup
+and Cone Machines.--Multiple Grinding.--"Guest" Universal and Cutter
+Grinding Machines.--Ward Universal Cutter Grinder.--Press.--Tool
+Grinding.--Lathe Centre Grinder.--Polishing.--INDEX.
+
+"Deals practically with every phase of his subject."--_Ironmonger._
+
+       *       *       *       *       *
+
+FIFTH EDITION. Folio, strongly half-bound, 21/.
+
+TRAVERSE TABLES:
+
+~Computed to Four Places of Decimals for every Minute of Angle up to 100
+of Distance.~
+
+~For the use of Surveyors and Engineers.~
+
+BY
+
+RICHARD LLOYD GURDEN,
+Authorised Surveyor for the Governments of New South Wales and Victoria.
+
+*** _Published with the Concurrence of the Surveyors-General for New
+South Wales and Victoria._
+
+"Those who have experience in exact SURVEY-WORK will best know how to
+appreciate the enormous amount of labour represented by this valuable
+book. The computations enable the user to ascertain the sines and
+cosines for a distance of twelve miles to within half an inch, and this
+BY REFERENCE TO BUT ONE TABLE, in place of the usual Fifteen minute
+computations required. This alone is evidence of the assistance which
+the Tables ensure to every user, and as every Surveyor in active
+practice has felt the want of such assistance FEW KNOWING OF THEIR
+PUBLICATION WILL REMAIN WITHOUT THEM."--_Engineer._
+
+       *       *       *       *       *
+
+WORKS BY
+
+ANDREW JAMIESON, M. INST. C.E., M.I.E.E., F.R.S.E.,
+
+_Formerly Professor of Electrical Engineering, The Glasgow and West of
+Scotland Technical College._
+
+       *       *       *       *       *
+
+PROFESSOR JAMIESON'S ADVANCED TEXT-BOOKS.
+
+_In Large Crown 8vo. Fully Illustrated._
+
+~STEAM AND STEAM-ENGINES (A Text-Book on).~ For the Use of Students
+preparing for Competitive Examinations. With 600 pp., over 200
+Illustrations, 6 Folding Plates, and numerous Examination Papers.
+THIRTEENTH EDITION, Revised. 8/6.
+
+"Professor Jamieson fascinates the reader by his CLEARNESS OF CONCEPTION
+AND SIMPLICITY OF EXPRESSION. His treatment recalls the lecturing of
+Faraday."--_Athenęum._
+
+"The BEST BOOK yet published for the use of Students."--_Engineer._
+
+~MAGNETISM AND ELECTRICITY (An Advanced Text-Book on).~ For Advanced and
+"Honours" Students. By Prof. Jamieson, assisted by David Robertson,
+B.Sc., Professor of Electrical Engineering in the Merchant Venturers'
+Technical College, Bristol. [_Shortly._
+
+~APPLIED MECHANICS (An Advanced Text-Book on).~
+
+Vol. I.--Comprising Part I.: The Principle of Work and its applications;
+Part II.: Gearing. Price 7s. 6d. THIRD EDITION.
+
+"FULLY MAINTAINS the reputation of the Author."--_Pract. Engineer._
+
+Vol. II.--Comprising Parts III. to VI.: Motion and Energy; Graphic
+Statics; Strength of Materials; Hydraulics and Hydraulic Machinery.
+SECOND EDITION. 8s. 6d.
+
+"WELL AND LUCIDLY WRITTEN."--_The Engineer._
+
+*** _Each of the above volumes is complete in itself, and sold
+separately._
+
+       *       *       *       *       *
+
+PROFESSOR JAMIESON'S INTRODUCTORY MANUALS.
+
+_Crown 8vo. With Illustrations and Examination Papers._
+
+~STEAM AND THE STEAM-ENGINE (Elementary Manual of).~ For First-Year
+Students. NINTH EDITION, Revised. 3/6.
+
+"Should be in the hands of EVERY engineering apprentice."--_Practical
+Engineer._
+
+~MAGNETISM AND ELECTRICITY (Elementary Manual of).~ For First-Year
+Students. FIFTH EDITION.. 3/6.
+
+"A CAPITAL TEXT-BOOK.... The diagrams are an important
+feature."--_Schoolmaster._
+
+"A THOROUGHLY TRUSTWORTHY Text-book. PRACTICAL and clear."--_Nature._
+
+~APPLIED MECHANICS (Elementary Manual of).~ Specially arranged for
+First-Year Students. FIFTH EDITION, Revised. 3/6.
+
+"The work has VERY HIGH QUALITIES, which may be condensed into the one
+word 'CLEAR.'"--_Science and Art._
+
+       *       *       *       *       *
+
+IN PREPARATION. _300 pages. Crown 8vo. Profusely Illustrated._
+
+~MODERN ELECTRIC TRAMWAY TRACTION: A Text-Book of Present-Day Practice.~
+
+_For the Use of Electrical Engineering Students and those interested in
+Electric Transmission of Power._
+
+BY PROF. ANDREW JAMIESON.
+
+       *       *       *       *       *
+
+~A POCKET-BOOK of ELECTRICAL RULES and TABLES.~ For the Use of
+Electricians and Engineers. Pocket Size. Leather, 8s. 6d. SIXTEENTH
+EDITION. [See p. 49.
+
+       *       *       *       *       *
+
+WORKS BY
+
+W.J. MACQUORN RANKINE, LL.D., F.R.S.,
+
+_Late Regius Professor of Civil Engineering in the University of
+Glasgow._
+
+THOROUGHLY REVISED BY
+
+W.J. MILLAR, C.E.,
+
+_Late Secretary to the Institute of Engineers and Shipbuilders in
+Scotland._
+
+       *       *       *       *       *
+
+~A MANUAL OF APPLIED MECHANICS:~ Comprising the Principles of Statics
+and Cinematics, and Theory of Structures, Mechanism, and Machines. With
+Numerous Diagrams. Crown 8vo, cloth. SIXTEENTH EDITION. 12s. 6d.
+
+       *       *       *       *       *
+
+~A MANUAL OF CIVIL ENGINEERING:~ Comprising Engineering Surveys,
+Earthwork, Foundations, Masonry, Carpentry, Metal Work, Roads, Railways,
+Canals, Rivers, Waterworks, Harbours, &c. With Numerous Tables and
+Illustrations. Crown 8vo. Cloth. TWENTY-FIRST EDITION. 16s.
+
+       *       *       *       *       *
+
+~A MANUAL OF MACHINERY AND MILLWORK:~ Comprising the Geometry, Motions,
+Work, Strength, Construction, and Objects of Machines, &c. Illustrated
+with nearly 300 Woodcuts, Crown 8vo, cloth. SEVENTH EDITION. 12s. 6d.
+
+       *       *       *       *       *
+
+~A MANUAL OF THE STEAM-ENGINE AND OTHER PRIME MOVERS:~ With a Section on
+GAS, OIL, and AIR ENGINES, by BRYAN DONKIN, M.Inst.C.E. With Folding
+Plates and Numerous Illustrations. Crown 8vo, cloth. FIFTEENTH EDITION.
+12s. 6d.
+
+       *       *       *       *       *
+
+~USEFUL RULES AND TABLES:~ For Architects, Builders, Engineers,
+Founders, Mechanics, Shipbuilders, Surveyors, &c. With APPENDIX for the
+use of ELECTRICAL ENGINEERS. By Professor JAMIESON, F.R.S.E. SEVENTH
+EDITION. 10s. 6d.
+
+       *       *       *       *       *
+
+~A MECHANICAL TEXT-BOOK:~ A Practical and Simple Introduction to the
+Study of Mechanics. By Professor RANKINE and E.F. BAMBER, C.E. With
+Numerous Illustrations. Crown 8vo, cloth. FIFTH EDITION. 9s.
+
+*** _The_ "MECHANICAL TEXT-BOOK" _was designed by_ Professor RANKINE _as
+an_ INTRODUCTION _to the above Series of Manuals._
+
+       *       *       *       *       *
+
+~MISCELLANEOUS SCIENTIFIC PAPERS.~
+
+Royal 8vo. Cloth, 31s. 6d.
+
+Part I. Papers relating to Temperature, Elasticity, and Expansion of
+Vapours, Liquids, and Solids. Part II. Papers on Energy and its
+Transformations. Part III. Papers on Wave-Forms, Propulsion of Vessels,
+&c.
+
+With Memoir by Professor TAIT, M.A. Edited by W.J. MILLAR, C.E. With
+fine Portrait on Steel, Plates, and Diagrams.
+
+"No more enduring Memorial of Professor Rankine could be devised than
+the publication of these papers in an accessible form.... The Collection
+is most valuable on account of the nature of his discoveries, and the
+beauty and completeness of his analysis.... The Volume exceeds in
+importance any work in the same department published in our
+time."--_Architect._
+
+       *       *       *       *       *
+
+SHELTON-BEY (W. Vincent, Foreman to the Imperial Ottoman Gun Factories,
+Constantinople):
+
+~THE MECHANIC'S GUIDE:~ A Hand-Book for Engineers and Artizans. With
+Copious Tables and Valuable Recipes for Practical Use. Illustrated.
+_Second Edition._ Crown 8vo. Cloth, 7/6.
+
+       *       *       *       *       *
+
+_SECOND EDITION, Revised and Enlarged. In Large 8vo, Handsome cloth,
+34s._
+
+HYDRAULIC POWER AND HYDRAULIC MACHINERY.
+
+BY HENRY ROBINSON, M. INST. C.E., F.G.S.,
+
+FELLOW OF KING'S COLLEGE, LONDON; PROF. OF CIVIL ENGINEERING, KING'S
+COLLEGE, ETC., ETC.
+
+With numerous Woodcuts, and Sixty-nine Plates.
+
+"A Book of great Professional Usefulness."--_Iron._
+
+       *       *       *       *       *
+
+_In Large 8vo, Handsome Cloth. With Frontispiece, several Plates, and
+over 250 Illustrations. 21s._
+
+THE PRINCIPLES AND CONSTRUCTION OF PUMPING MACHINERY (STEAM AND WATER
+PRESSURE).
+
+With Practical Illustrations of ENGINES and PUMPS applied to MINING,
+TOWN WATER SUPPLY, DRAINAGE of Lands, &c., also Economy and Efficiency
+Trials of Pumping Machinery.
+
+BY HENRY DAVEY,
+
+Member of the Institution of Civil Engineers, Member of the Institution
+of Mechanical Engineers, F.G.S., &c.
+
+CONTENTS--Early History of Pumping Engines--Steam Pumping Engines--Pumps
+and Pump Valves--General Principles of Non-Rotative Pumping Engines--The
+Cornish Engine, Simple and Compound--Types of Mining Engines--Pit
+Work--Shaft Sinking--Hydraulic Transmission of Power in Mines--Valve
+Gears of Pumping Engines--Water Pressure Pumping Engines--Water
+Works Engines--Pumping Engine Economy and Trials of Pumping
+Machinery--Centrifugal and other Low-Lift Pumps--Hydraulic Rams. Pumping
+Mains, &c.--INDEX.
+
+"By the 'one' English Engineer who probably knows more about Pumping
+Machinery than ANY OTHER.' ... A VOLUME RECORDING THE RESULTS OF LONG
+EXPERIENCE AND STUDY."--_The Engineer._
+
+"Undoubtedly THE BEST AND MOST PRACTICAL TREATISE on Pumping Machinery
+THAT HAS YET BEEN PUBLISHED."--_Mining Journal._
+
+       *       *       *       *       *
+
+_Royal 8vo, Handsome Cloth. With numerous Illustrations and Tables.
+25s._
+
+THE STABILITY OF SHIPS.
+
+BY
+
+SIR EDWARD J. REED, K.C.B., F.R.S., M.P.,
+
+KNIGHT OF THE IMPERIAL ORDERS OF ST. STANILAUS OF RUSSIA; FRANCIS JOSEPH
+OF AUSTRIA; MEDJIDIE OF TURKEY; AND RISING SUN OF JAPAN; VICE-PRESIDENT
+OF THE INSTITUTION OF NAVAL ARCHITECTS.
+
+In order to render the work complete for the purposes of the
+Shipbuilder, whether at home or abroad, the Methods of Calculation
+introduced by Mr. F.K. BARNES, Mr. GRAY, M. REECH, M. DAYMARD, and Mr.
+BENJAMIN, are all given separately, illustrated by Tables and worked-out
+examples. The book contains more than 200 Diagrams, and is illustrated
+by a large number of actual cases, derived from ships of all
+descriptions.
+
+"Sir EDWARD REED'S 'STABILITY OF SHIPS' is INVALUABLE. The NAVAL
+ARCHITECT will find brought together and ready to his hand, a mass of
+information which he would otherwise have to seek in an almost endless
+variety of publications, and some of which he would possibly not be able
+to obtain at all elsewhere."--_Steamship._
+
+       *       *       *       *       *
+
+~THE DESIGN AND CONSTRUCTION OF SHIPS.~ By JOHN HARVARD BILES,
+M.INST.N.A., Professor of Naval Architecture in the University of
+Glasgow. [_In Preparation._
+
+       *       *       *       *       *
+
+SECOND EDITION. Illustrated with Plates, Numerous Diagrams, and Figures
+in the Text. 18s. net.
+
+~STEEL SHIPS: THEIR CONSTRUCTION AND MAINTENANCE.~
+
+_A Manual for Shipbuilders, Ship Superintendents, Students, and Marine
+Engineers._
+
+BY THOMAS WALTON, NAVAL ARCHITECT, AUTHOR OF "KNOW YOUR OWN SHIP."
+
+CONTENTS.--I. Manufacture of Cast Iron, Wrought Iron, and
+Steel.--Composition of Iron and Steel, Quality, Strength, Tests, &c. II.
+Classification of Steel Ships. III. Considerations in making choice of
+Type of Vessel.--Framing of Ships. IV. Strains experienced by
+Ships.--Methods of Computing and Comparing Strengths of Ships. V.
+Construction of Ships.--Alternative Modes of Construction.--Types of
+Vessels.--Turret, Self Trimming, and Trunk Steamers, &c.--Rivets
+and Rivetting, Workmanship. VI. Pumping Arrangements. VII.
+Maintenance.--Prevention of Deterioration in the Hulls of
+Ships.--Cement, Paint, &c.--INDEX.
+
+"So thorough and well written is every chapter in the book that it is
+difficult to select any of them as being worthy of exceptional praise.
+Altogether, the work is excellent, and will prove of great value to
+those for whom it is intended."--_The Engineer._
+
+"Mr. Walton has written for the profession of which he is an ornament.
+His work will be read and appreciated, no doubt, by every M.I.N.A., and
+with great benefit by the majority of them."--_Journal of Commerce._
+
+       *       *       *       *       *
+
+SECOND EDITION, Cloth, 8s. 6d. Leather, for the Pocket, 8s. 6d.
+
+~GRIFFIN'S ELECTRICAL PRICE-BOOK:~ For Electrical, Civil, Marine, and
+Borough Engineers, Local Authorities, Architects, Railway Contractors,
+&c., &c. Edited by H.J. DOWSING.
+
+"The ELECTRICAL PRICE-BOOK REMOVES ALL MYSTERY about the cost of
+Electrical Power. By its aid the EXPENSE that will be entailed
+by utilising electricity on a large or small scale can be
+discovered."--_Architect._
+
+       *       *       *       *       *
+
+GRIFFIN'S NAUTICAL SERIES,
+
+EDITED BY EDW. BLACKMORE,
+
+Master Mariner, First Class Trinity House Certificate, Assoc. Inst.
+N.A.; AND WRITTEN, MAINLY, by SAILORS for SAILORS.
+
+"THIS ADMIRABLE SERIES."--_Fairplay_. "A VERY USEFUL SERIES."--_Nature_.
+
+"The volumes of MESSRS. GRIFFIN'S NAUTICAL SERIES may well and
+profitably be read by ALL interested in our NATIONAL MARITIME
+PROGRESS."--_Marine Engineer._
+
+"EVERY SHIP should have the WHOLE SERIES as a REFERENCE LIBRARY.
+HANDSOMELY BOUND, CLEARLY PRINTED and ILLUSTRATED."--_Liverpool Journ.
+of Commerce._
+
+~The British Mercantile Marine:~ An Historical Sketch of its Rise and
+Development. By the EDITOR, CAPT. BLACKMORE. 3s. 6d.
+
+"Captain Blackmore's SPLENDID BOOK ... contains paragraphs on every
+point of interest to the Merchant Marine. The 243 pages of this book are
+THE MOST VALUABLE to the sea captain that have EVER been
+COMPILED."--_Merchant Service Review._
+
+~Elementary Seamanship.~ By D. WILSON-BARKER, Master Mariner, F.R.S.E.,
+F.R.G.S. With numerous Plates, two in Colours, and Frontispiece. THIRD
+EDITION, Thoroughly Revised, Enlarged, and Re-set. With additional
+Illustrations. 6s.
+
+"This ADMIRABLE MANUAL, by CAPT. WILSON BARKER, of the 'Worcester',
+seems to us PERFECTLY DESIGNED. "--_Athenęum._
+
+~Know Your Own Ship~: A Simple Explanation of the Stability,
+Construction, Tonnage, and Freeboard of Ships. By THOS. WALTON, Naval
+Architect. With numerous Illustrations and additional Chapters on
+Buoyancy, Trim, and Calculations. SIXTH EDITION, Revised. 7s. 6d.
+
+"MR. WALTON'S book will be found VERY USEFUL."--_The Engineer._
+
+~Navigation: Theoretical and Practical.~ By D. WILSON-BARKER, Master
+Mariner, &c., and WILLIAM ALLINGHAM. SECOND EDITION, Revised. 8s. 6d.
+
+"PRECISELY the kind of work required for the New Certificates of
+competency. Candidates will find it INVALUABLE."--_Dundee Advertiser._
+
+~Marine Meteorology~: For Officers of the Merchant Navy. By WILLIAM
+ALLINGHAM, First Class Honours, Navigation, Science and Art Department.
+With Illustrations, Maps, and Diagrams, and _facsimile_ reproduction of
+log page. 7s. 6d.
+
+"Quite the BEST PUBLICATION on this subject."--_Shipping Gazette._
+
+~Latitude and Longitude: How to find them.~ By W.J. MILLAR, C.E., late
+Sec. to the Inst. of Engineers and Shipbuilders in Scotland. SECOND
+EDITION, Revised. 2s.
+
+"Cannot but prove an acquisition to those studying Navigation."--_Marine
+Engineer._
+
+~Practical Mechanics:~ Applied to the requirements of the Sailor. By
+THOS. MACKENZIE, Master Mariner, F.R.A.S. SECOND EDITION, Revised. 3s.
+6d.
+
+"WELL WORTH the money ... EXCEEDINGLY HELPFUL."--_Shipping World._
+
+~Trigonometry:~ For the Young Sailor, &c. By RICH. C. BUCK, of the
+Thames Nautical Training College, H.M.S. "Worcester." SECOND EDITION,
+Revised. Price 3s. 6d.
+
+"This EMINENTLY PRACTICAL and reliable volume."--_Schoolmaster_.
+
+~Practical Algebra.~ By RICH. C. BUCK. Companion Volume to the above,
+for Sailors and others. Price 3s. 6d.
+
+"It is JUST THE BOOK for the young sailor mindful of
+progress."--_Nautical Magazine._
+
+~The Legal Duties of Shipmasters.~ By BENEDICT WM. GINSBURG, M.A.,
+LL.D., of the Inner Temple and Northern Circuit; Barrister-at-Law.
+SECOND EDITION, Thoroughly Revised and Extended. Price 4s. 6d.
+
+"INVALUABLE to masters ... We can fully recommend it."--_Shipping
+Gazette._
+
+~A Medical and Surgical Help for Shipmasters.~ Including First Aid at
+Sea. By WM. JOHNSON SMITH, F.R.C.S., Principal Medical Officer, Seamen's
+Hospital, Greenwich. SECOND EDITION, Revised. 6s. "SOUND, JUDICIOUS,
+REALLY HELPFUL."--_The Lancet._
+
+       *       *       *       *       *
+
+_Introductory Volume. Price 3s. 6d._
+
+THE ~British Mercantile Marine.~
+
+BY EDWARD BLACKMORE, MASTER MARINER; ASSOCIATE OF THE INSTITUTION OF
+NAVAL ARCHITECTS; MEMBER OF THE INSTITUTION OF ENGINEERS AND
+SHIPBUILDERS IN SCOTLAND; EDITOR OF GRIFFIN'S "NAUTICAL SERIES."
+
+GENERAL CONTENTS.--HISTORICAL: From Early Times to 1486--Progress under
+Henry VIII.--To Death of Mary--During Elizabeth's Reign--Up to the Reign
+of William III.--The 18th and 19th Centuries--Institution of
+Examinations--Rise and Progress of Steam Propulsion--Development of Free
+Trade--Shipping Legislation, 1862 to 1875--"Locksley Hall"
+Case--Shipmasters' Societies--Loading of Ships--Shipping
+Legislation, 1884 to 1894--Statistics of Shipping. THE PERSONNEL:
+Shipowners--Officers--Mariners--Duties and Present Position. EDUCATION:
+A Seaman's Education: what it should be--Present Means of
+Education--Hints. DISCIPLINE AND DUTY--Postscript--The Serious Decrease
+in the Number of British Seamen, a Matter demanding the Attention of the
+Nation.
+
+"INTERESTING AND INSTRUCTIVE ... may be read WITH PROFIT AND
+ENJOYMENT."--_Glasgow Herald._
+
+"EVERY BRANCH of the subject is dealt with in a way which shows that the
+writer 'knows the ropes' familiarly."--_Scotsman._
+
+"This ADMIRABLE book ... TEEMS with useful information--Should be in the
+hands of every Sailor."--_Western Morning News._
+
+       *       *       *       *       *
+
+THIRD EDITION, _Thoroughly Revised, Enlarged, and Re-set. With
+Additional Illustrations. Price 6s._
+
+~A MANUAL OF ELEMENTARY SEAMANSHIP.~
+
+BY
+
+D. WILSON-BARKER, MASTER MARINER; F.R.S.E., F.R.G.S., &C., &C.; YOUNGER
+BROTHER OF THE TRINITY HOUSE.
+
+With Frontispiece, Numerous Plates (Two in Colours), and Illustrations
+in the Text.
+
+GENERAL CONTENTS.--The Building of a Ship; Parts of Hull, Masts,
+&c.--Ropes, Knots, Splicing, &c.--Gear, Lead and Log, &c.--Rigging,
+Anchors--Sailmaking--The Sails, &c.--Handling of Boats under
+Sail--Signals and Signalling--Rule of the Road--Keeping and Relieving
+Watch--Points of Etiquette--Glossary of Sea Terms and Phrases--Index.
+
+*** The volume contains the NEW RULES OF THE ROAD.
+
+"This ADMIRABLE MANUAL, by CAPT. WILSON-BARKER of the 'Worcester,' seems
+to us PERFECTLY DESIGNED, and holds its place excellently in GRIFFIN'S
+NAUTICAL SERIES.' ... Although intended for those who are to become
+Officers of the Merchant Navy, it will be found useful by ALL
+YACHTSMEN."--_Athenęum._
+
+*** For complete List of GRIFFIN'S NAUTICAL SERIES, see p. 39.
+
+       *       *       *       *       *
+
+SECOND EDITION, _Revised and Illustrated. Price 3s. 6d._
+
+~NAVIGATION:~
+
+~PRACTICAL AND THEORETICAL~
+
+BY DAVID WILSON-BARKER, R.N.R, F.R.S.E., &c., &c.,
+
+AND
+
+WILLIAM ALLINGHAM,
+
+FIRST-CLASS HONORS, NAVIGATION, SCIENCE AND ART DEPARTMENT.
+
+With Numerous Illustrations and Examination Questions.
+
+GENERAL CONTENTS.--Definitions--Latitude and Longitude--Instruments of
+Navigation--Correction of Courses--Plane Sailing--Traverse
+Sailing--Day's Work--Parallel Sailing--Middle Latitude
+Sailing--Mercator's Chart--Mercator Sailing--Current Sailing--Position
+by Bearings--Great Circle Sailing--The Tides--Questions--Appendix:
+Compass Error--Numerous Useful Hints, &c.--Index.
+
+"PRECISELY the kind of work required for the New Certificates of
+competency in grades from Second Mate to extra Master.... Candidates
+will find it INVALUABLE."--_Dundee Advertiser._
+
+"A CAPITAL LITTLE BOOK ... specially adapted to the New Examinations.
+The Authors are CAPT. WILSON-BARKER (Captain-Superintendent of the
+Nautical College, H.M.S. 'Worcester,' who has had great experience in
+the highest problems of Navigation), and MR. ALLINGHAM, a well-known
+writer on the Science of Navigation and Nautical Astronomy."--_Shipping
+World._
+
+       *       *       *       *       *
+
+_Handsome Cloth. Fully Illustrated. Price 7s. 6d._
+
+~MARINE METEOROLOGY, FOR OFFICERS OF THE MERCHANT NAVY.~
+
+BY WILLIAM ALLINGHAM,
+
+Joint Author of "Navigation, Theoretical and Practical."
+
+With numerous Plates, Maps, Diagrams, and Illustrations, and a facsimile
+Reproduction of a Page from an actual Meteorological Log-Book.
+
+SUMMARY OF CONTENTS.
+
+INTRODUCTORY.--Instruments Used at Sea for Meteorological
+Purposes.--Meteorological Log-Books.--Atmospheric Pressure.--Air
+Temperatures.--Sea Temperatures.--Winds.--Wind Force Scales.--History of
+the Law of Storms.--Hurricanes, Seasons, and Storm Tracks.--Solution of
+the Cyclone Problem.--Ocean Currents.--Icebergs.--Synchronous
+Charts.--Dew, Mists, Fogs, and Haze.--Clouds.--Rain, Snow, and
+Hail.--Mirage, Rainbows, Coronas, Halos, and Meteors.--Lightning,
+Corposants, and Auroras.--QUESTIONS.--APPENDIX.--INDEX.
+
+"Quite the BEST publication, AND certainly the MOST INTERESTING, on this
+subject ever presented to Nautical men."--_Shipping Gazette._
+
+*** For Complete List of GRIFFIN'S NAUTICAL SERIES, see p. 39.
+
+       *       *       *       *       *
+
+SECOND EDITION, REVISED. With Numerous Illustrations. Price ~3s. 6d.~
+
+~Practical Mechanics:~ Applied to the Requirements of the Sailor.
+
+By THOS. MACKENZIE,
+
+_Master Mariner, F.R.A.S._
+
+GENERAL CONTENTS.--Resolution and Composition of Forces--Work done by
+Machines and Living Agents--The Mechanical Powers: The Lever; Derricks
+as Bent Levers--The Wheel and Axle: Windlass; Ship's Capstan; Crab
+Winch--Tackles: the "Old Man"--The Inclined Plane; the Screw--The Centre
+of Gravity of a Ship and Cargo--Relative Strength of Rope: Steel Wire,
+Manilla, Hemp, Coir--Derricks and Shears--Calculation of
+the Cross-breaking Strain of Fir Spar--Centre of Effort of
+Sails--Hydrostatics: the Diving-bell; Stability of Floating Bodies; the
+Ship's Pump, &c.
+
+"THIS EXCELLENT BOOK ... contains a LARGE AMOUNT of
+information."--_Nature._
+
+"WELL WORTH the money ... will be found EXCEEDINGLY HELPFUL."--_Shipping
+World._
+
+"NO SHIPS' OFFICERS' BOOKCASE will henceforth be complete without
+CAPTAIN MACKENZIE'S 'PRACTICAL MECHANICS.' Notwithstanding my many
+years' experience at sea, it has told me _how much more there is to
+acquire_."--(Letter to the Publishers from a Master Mariner).
+
+"I must express my thanks to you for the labour and care you have taken
+in 'PRACTICAL MECHANICS.' ... IT IS A LIFE'S EXPERIENCE. ... What an
+amount we frequently see wasted by rigging purchases without reason and
+accidents to spars, &c., &c.! 'PRACTICAL MECHANICS' WOULD SAVE ALL
+THIS."--(Letter to the Author from another Master Mariner).
+
+       *       *       *       *       *
+
+~WORKS BY RICHARD C. BUCK,~
+
+of the Thames Nautical Training College, H.M.S. 'Worcester.'
+
+~A Manual of Trigonometry:~ _With Diagrams, Examples, and Exercises.
+Price 3s. 6d._
+
+SECOND EDITION, Revised and Corrected.
+
+*** Mr. Buck's Text-Book has been SPECIALLY PREPARED with a view to the
+New Examinations of the Board of Trade, in which Trigonometry is an
+obligatory subject.
+
+"This EMINENTLY PRACTICAL and RELIABLE VOLUME."--_Schoolmaster._
+
+       *       *       *       *       *
+
+~A Manual of Algebra.~
+
+_Designed to meet the Requirements of Sailors and others. Price 3s. 6d._
+
+*** These elementary works on ALGEBRA and TRIGONOMETRY are written
+specially for those who will have little opportunity of consulting a
+Teacher. They are books for "SELF-HELP." All but the simplest
+explanations have, therefore, been avoided, and ANSWERS to the Exercises
+are given. Any person may readily, by careful study, become master of
+their contents, and thus lay the foundation for a further mathematical
+course, if desired. It is hoped that to the younger Officers of our
+Mercantile Marine they will be found decidedly serviceable. The Examples
+and Exercises are taken from the Examination Papers set for the Cadets
+of the "Worcester."
+
+"Clearly arranged, and well got up.... A first-rate Elementary
+Algebra."--_Nautical Magazine._
+
+       *       *       *       *       *
+
+SECOND EDITION, Thoroughly Revised and Extended. In Crown 8vo. Handsome
+Cloth. Price 4s. 6d.
+
+~THE LEGAL DUTIES OF SHIPMASTERS.~
+
+BY
+
+BENEDICT WM. GINSBURG, M.A., LL.D. (CANTAB.),
+
+Of the Inner Temple and Northern Circuit; Barrister-at-Law.
+
+~General Contents.~--The Qualification for the Position of
+Shipmaster--The Contract with the Shipowner--The Master's Duty in
+respect of the Crew: Engagement; Apprentices; Discipline; Provisions,
+Accommodation, and Medical Comforts; Payment of Wages and Discharge--The
+Master's Duty in respect of the Passengers--The Master's Financial
+Responsibilities--The Master's Duty in respect of the Cargo--The
+Master's Duty in Case of Casualty--The Master's Duty to certain Public
+Authorities--The Master's Duty in relation to Pilots, Signals, Flags,
+and Light Dues--The Master's Duty upon Arrival at the Port of
+Discharge--Appendices relative to certain Legal Matters: Board of Trade
+Certificates, Dietary Scales, Stowage of Grain Cargoes, Load Line
+Regulations, Life-saving Appliances, Carriage of Cattle at Sea, &c.,
+&c.--Copious Index.
+
+"No intelligent Master should fail to add this to his list of necessary
+books. A few lines of it may SAVE A LAWYER'S FEE, BESIDES ENDLESS
+WORRY."--_Liverpool Journal of Commerce._
+
+"SENSIBLE, plainly written, in CLEAR and NON-TECHNICAL LANGUAGE, and
+will be found of much service by the Shipmaster."--_British Trade
+Review._
+
+       *       *       *       *       *
+
+SECOND EDITION, Revised. With Diagrams. Price 2s.
+
+~Latitude and Longitude: How to Find them.~
+
+By W.J. MILLAR, C.E.,
+
+_Late Secretary to the Inst. of Engineers and Shipbuilders in Scotland._
+
+"CONCISELY and CLEARLY WRITTEN ... cannot but prove an acquisition to
+those studying Navigation."--_Marine Engineer._
+
+"Young Seamen will find it HANDY and USEFUL, SIMPLE and CLEAR."--_The
+Engineer._
+
+       *       *       *       *       *
+
+~FIRST AID AT SEA.~
+
+SECOND EDITION, Revised. With Coloured Plates and Numerous
+Illustrations, and comprising the latest Regulations Respecting the
+Carriage of Medical Stores on Board Ship. Price 6s.
+
+~A MEDICAL AND SURGICAL HELP FOR SHIPMASTERS AND OFFICERS IN THE
+MERCHANT NAVY.~
+
+BY
+
+WM. JOHNSON SMITH, F.R.C.S.,
+
+Principal Medical Officer, Seamen's Hospital, Greenwich.
+
+*** The attention of all interested in our Merchant Navy is requested to
+this exceedingly useful and valuable work. It is needless to say that it
+is the outcome of many years PRACTICAL EXPERIENCE amongst Seamen.
+
+"SOUND, JUDICIOUS, REALLY HELPFUL."--_The Lancet._
+
+       *       *       *       *       *
+
+SIXTH EDITION. _Revised, with Chapters on Trim, Buoyancy, and
+Calculations. Numerous Illustrations. Handsome Cloth, Crown 8vo. Price
+7s. 6d._
+
+~KNOW YOUR OWN SHIP.~
+
+BY THOMAS WALTON, NAVAL ARCHITECT.
+
+SPECIALLY ARRANGED TO SUIT THE REQUIREMENTS OF SHIPS' OFFICERS,
+SHIPOWNERS, SUPERINTENDENTS, DRAUGHTSMEN, ENGINEERS, AND OTHERS.
+
+This work explains, in a simple manner, such important subjects as:--
+
+  Displacement,
+  Deadweight,
+  Tonnage,
+  Freeboard,
+  Moments,
+  Buoyancy,
+  Strain,
+  Structure,
+  Stability,
+  Rolling,
+  Ballasting,
+  Loading,
+  Shifting Cargoes,
+  Admission of Water,
+  Sail Area,
+  &c., &c.
+
+"The little book will be found EXCEEDINGLY HANDY by most officers and
+officials connected with shipping.... Mr. Walton's work will obtain
+LASTING SUCCESS, because of its unique fitness for those for whom it has
+been written."--_Shipping World._
+
+"An EXCELLENT WORK, full of solid instruction and INVALUABLE to every
+officer of the Mercantile Marine who has his profession at
+heart."--_Shipping._
+
+"Not one of the 242 pages could well be spared. It will admirably fulfil
+its purpose ... useful to ship owners, ship superintendents, ship
+draughtsmen, and all interested in shipping."--_Liverpool Journal of
+Commerce._
+
+"A mass of VERY USEFUL INFORMATION, accompanied by diagrams and
+illustrations, is given in a compact form."--_Fairplay._
+
+"We have found no one statement that we could have wished differently
+expressed. The matter has, so far as clearness allows, been admirably
+condensed, and is simple enough to be understood by every
+seaman."--_Marine Engineer._
+
+       *       *       *       *       *
+
+~BY THE SAME AUTHOR.~
+
+~Steel Ships: Their Construction and Maintenance.~
+
+(~See page 38.~)
+
+       *       *       *       *       *
+
+Fourteenth Edition, Revised. Price 21s.
+
+_Demy 8vo, Cloth. With Numerous Illustrations, reduced from Working
+Drawings._
+
+~A MANUAL OF MARINE ENGINEERING:~ COMPRISING THE DESIGNING,
+CONSTRUCTION, AND WORKING OF MARINE MACHINERY.
+
+By A.E. SEATON, M. Inst. C.E., M. Inst. Mech. E., M. Inst. N.A.
+
+GENERAL CONTENTS.--PART I.--Principles of Marine Propulsion. PART
+II.--Principles of Steam Engineering. PART III.--Details of Marine
+Engines: Design and Calculations for Cylinders, Pistons, Valves,
+Expansion Valves, &c. PART IV.--Propellers. PART V.--Boilers. PART
+VI.--Miscellaneous.
+
+*** This EDITION includes a Chapter on WATER-TUBE BOILERS, with
+Illustrations of the leading Types and the Revised Rules of the _Bureau
+Veritas_.
+
+"In the three-fold capacity of enabling a Student to learn how to
+design, construct, and work a Marine Steam-Engine, Mr. Seaton's Manual
+has NO RIVAL."--_Times._
+
+"By far the BEST MANUAL in existence.... Gives a complete account of the
+methods of solving, with the utmost possible economy, the problems
+before the Marine Engineer."--_Athenęum._
+
+"The Student, Draughtsman, and Engineer will find this work the MOST
+VALUABLE HANDBOOK of Reference on the Marine Engine now in
+existence."--_Marine Engineer._
+
+       *       *       *       *       *
+
+SEVENTH EDITION, Thoroughly Revised. Pocket-Size, Leather. 8s. 6d.
+
+~A POCKET-BOOK OF MARINE ENGINEERING RULES AND TABLES, FOR THE USE OF
+Marine Engineers, Naval Architects, Designers, Draughtsmen,
+Superintendents and Others.~
+
+BY
+
+A.E. SEATON, M.I.C.E., M.I.Mech.E., M.I.N.A.,
+
+AND
+
+H.M. ROUNTHWAITE, M.I.Mech.E., M.I.N.A.
+
+"ADMIRABLY FULFILS its purpose."--_Marine Engineer._
+
+       *       *       *       *       *
+
+By B. CUNNINGHAM.
+
+~DOCKS: THEIR CONSTRUCTION & MAINTENANCE.~
+
+(See page 27.)
+
+       *       *       *       *       *
+
+WORKS BY PROF. ROBERT H. SMITH, Assoc. M.I.C.E., M.I.M.E., M.I.El.B.,
+M.I. Min. E., Whit. Sch., M. Ord. Meiji.
+
+       *       *       *       *       *
+
+THE CALCULUS FOR ENGINEERS AND PHYSICISTS, Applied to Technical
+Problems.
+
+WITH EXTENSIVE CLASSIFIED REFERENCE LIST OF INTEGRALS.
+
+By PROF. ROBERT H. SMITH.
+
+ASSISTED BY
+
+R.F. MUIRHEAD, M.A., B.Sc.,
+
+Formerly Clark Fellow of Glasgow University, and Lecturer on Mathematics
+at Mason College.
+
+_In Crown 8vo, extra, with Diagrams and Folding-Plate._ 8s. 6d.
+
+"PROF. R.H. SMITH'S book will be serviceable in rendering a hard road AS
+EASY AS PRACTICABLE for the non-mathematical Student and
+Engineer."--_Athenęum._
+
+"Interesting diagrams, with practical illustrations of actual
+occurrence, are to be found here in abundance. THE VERY COMPLETE
+CLASSIFIED REFERENCE TABLE will prove very useful in saving the time of
+those who want an integral in a hurry."--_The Engineer._
+
+       *       *       *       *       *
+
+MEASUREMENT CONVERSIONS
+
+(English and French): 28 GRAPHIC TABLES OR DIAGRAMS.
+
+Showing at a glance the MUTUAL CONVERSION of MEASUREMENTS in DIFFERENT
+UNITS
+
+Of Lengths, Areas, Volumes, Weights, Stresses, Densities, Quantities of
+Work, Horse Powers, Temperatures, &c.
+
+_For the use of Engineers, Surveyors, Architects, and Contractors._
+
+_In 4to, Boards. 7s. 6d._
+
+       *       *       *       *       *
+
+*** Prof. SMITH'S CONVERSION-TABLES form the most unique and
+comprehensive collection ever placed before the profession. By their use
+much time and labour will be saved, and the chances of error in
+calculation diminished. It is believed that henceforth no Engineer's
+Office will be considered complete without them.
+
+"The work is INVALUABLE."--_Colliery Guardian._
+
+"Ought to be in EVERY office where even occasional conversions are
+required.... Prof. SMITH'S TABLES form very EXCELLENT CHECKS on
+results."--_Electrical Review._
+
+"Prof. Smith deserves the hearty thanks, not only of the ENGINEER, but
+of the COMMERCIAL WORLD, for having smoothed the way for the ADOPTION of
+the METRIC SYSTEM of MEASUREMENT, a subject which is now assuming great
+importance as a factor in maintaining our HOLD upon FOREIGN
+TRADE."--_The Machinery Market._
+
+       *       *       *       *       *
+
+In Large 8vo. Handsome Cloth. 10s. 6d.
+
+CHEMISTRY FOR ENGINEERS.
+
+BY
+
+BERTRAM BLOUNT, F.I.C., F.C.S., A.I.C.E., Consulting Chemist to the
+Crown Agents for the Colonies.
+
+AND
+
+A.G. BLOXAM, F.I.C., F.C.S., Consulting Chemist, Head of the Chemistry
+Department, Goldsmiths' Inst., New Cross.
+
+GENERAL CONTENTS.--Introduction--Chemistry of the Chief Materials of
+Construction--Sources of Energy--Chemistry of Steam-raising--Chemistry
+of Lubrication and Lubricants--Metallurgical Processes used in the
+Winning and Manufacture of Metals.
+
+"The authors have SUCCEEDED beyond all expectation, and have produced a
+work which should give FRESH POWER to the Engineer and
+Manufacturer."--_The Times._
+
+"PRACTICAL THROUGHOUT ... an ADMIRABLE TEXT-BOOK, useful not only to
+Students, but to ENGINEERS and MANAGERS OF WORKS in PREVENTING WASTE and
+IMPROVING PROCESSES."--_Scotsman._
+
+"A book worthy to take HIGH RANK ... treatment of the subject of GASEOUS
+FUEL particularly good.... WATER GAS and its production clearly worked
+out.... We WARMLY RECOMMEND the work."--_Journal of Gas Lighting._
+
+For Companion Volume by the same Authors, see "CHEMISTRY FOR
+MANUFACTURERS," p. 71.
+
+       *       *       *       *       *
+
+WORKS BY WALTER R. BROWNE, M.A., M. INST. C.E., Late Fellow of Trinity
+College, Cambridge.
+
+~THE STUDENT'S MECHANICS: An Introduction to the Study of Force and
+Motion.~
+
+With Diagrams. Crown 8vo. Cloth, 4s. 6d.
+
+"Clear in style and practical in method, 'THE STUDENT'S MECHANICS' is
+cordially to be commended from all points of view."--_Athenęum._
+
+       *       *       *       *       *
+
+FOUNDATIONS OF MECHANICS.
+
+Papers reprinted from the _Engineer._ In Crown 8vo, 1s.
+
+       *       *       *       *       *
+
+Demy 8vo, with Numerous Illustrations, 9s.
+
+FUEL AND WATER: A Manual for Users of Steam and Water.
+
+BY PROF. FRANZ SCHWACKHÖFER OF VIENNA, AND WALTER R. BROWNE, M.A., C.E.
+
+GENERAL CONTENTS.--Heat and Combustion--Fuel, Varieties of--Firing
+Arrangements: Furnace, Flues, Chimney--The Boiler, Choice
+of--Varieties--Feed-water Heaters--Steam Pipes--Water: Composition,
+Purification--Prevention of Scale, &c., &c.
+
+"The Section on Heat is one of the best and most lucid ever
+written."--_Engineer._
+
+"Cannot fail to be valuable to thousands using steam power."--_Railway
+Engineer._
+
+       *       *       *       *       *
+
+GRIFFINS LOCAL GOVERNMENT HANDBOOKS.
+
+WORKS SUITABLE FOR MUNICIPAL AND COUNTY ENGINEERS, ANALYSTS, AND OTHERS.
+
+See also Davies' _Hygiene_, p. 99, and MacLeod's _Public Health_, p.
+110.
+
+~Gas Manufacture (The Chemistry of).~ A Handbook on the Production,
+Purification, and Testing of Illuminating Gas, and the Assay of
+Bye-Products. By W.J.A. BUTTERFIELD, M.A., F.I.C., F.C.S. With
+Illustrations. THIRD EDITION, Revised (in preparation). [See page 77.
+
+~Water Supply:~ A Practical Treatise on the Selection of Sources and the
+Distribution of Water. By REGINALD E. MIDDLETON, M. Inst. C.E., M. Inst.
+Mech. E., F.S.I. With Four Plates and Numerous Diagrams. Crown 8vo. [See
+page 77.
+
+~Central Electrical Stations:~ Their Design, Organisation, and
+Management. By ~C.H. Wordingham~, A.K.C., M. Inst. C.E. Price 24s. net.
+
+_For details see opposite page._
+
+~Sewage Disposal Works:~ A Guide to the Construction of Works for the
+Prevention of the Pollution by Sewage of Rivers and Estuaries. By W.
+SANTO CRIMP, M. Inst. C.E., F.G.S. SECOND EDITION, Revised and Enlarged.
+Large 8vo, Handsome Cloth. With 37 Plates. Price 30s. [See page 76.
+
+~Trades' Waste:~ Its Treatment and Utilisation, with Special Reference
+to the Prevention of Rivers' Pollution. By W. NAYLOR, F.C.S., A.M. Inst.
+C.E. With Numerous Plates, Diagrams, and Illustrations. 21s. net. [See
+page 76.
+
+~Calcareous Cements:~ Their Nature, Preparation, and Uses. With some
+Remarks upon Cement Testing. By GILBERT REDGRAVE, Assoc. Inst. C.E. With
+Illustrations, Analytical Data, and Appendices on Costs, &c. 8s. 6d.
+[See page 76.
+
+~Road Making and Maintenance:~ A Practical Treatise for Engineers,
+Surveyors, and others. With an Historical Sketch of Ancient and Modern
+Practice. By THOMAS AITKEN, Assoc. M. Inst. C.E., M. Assoc. Municipal
+and County Engrs.; M. San. Inst. With numerous Plates, Diagrams, and
+Illustrations. 21s. [See page 79.
+
+~Light Railways at Home and Abroad.~ By WILLIAM HENRY COLE, M. Inst.
+C.E., late Deputy Manager, North-Western Railway, India. Large 8vo,
+Handsome Cloth, Plates and illustrations. 16s. [See page 30.
+
+~Practical Sanitation:~ A Handbook for Sanitary Inspectors and others
+interested in Sanitation. By GEO. REID, M.D., D.P.H., Medical Officer,
+Staffordshire County Council. With Appendix on Sanitary Law, by Herbert
+Manley, M.A., M.B., D.P.H. TENTH EDITION, Revised. 6s. [See page 78.
+
+~Sanitary Engineering~: A Practical Manual of Town Drainage and Sewage
+and Refuse Disposal. By FRANK WOOD, A.M. Inst. C.E., F.G.S., Borough
+Surveyor, Fulham. Fully Illustrated. 8s. 6d. net. [See page 78.
+
+~Dairy Chemistry:~ A Practical Handbook for Dairy Managers, Chemists,
+and Analysts. By ~H. Droop Richmond~, F.C.S., Chemist to the Aylesbury
+Dairy Company. With Tables, Illustrations, &c. Handsome Cloth, 16s. [See
+page 73.
+
+~Milk: Its Production and Uses.~ With Chapters on Dairy Farming, The
+Diseases of Cattle, and on the Hygiene and Control of Supplies. By
+EDWARD F. WILLOUGHBY, M.D. (Lond.), D.P.H. (Lond. and Camb.), Inspector
+of Farms and General Scientific Adviser to Welford & Sons, Ltd. [See
+page 73.
+
+~Flesh Foods:~ With Methods for their Chemical, Microscopical, and
+Bacteriological Examination. A Handbook for Medical Men, Inspectors,
+Analysts, and others. By C. AINSWORTH MITCHELL, B.A., F.I.C., Mem.
+Council Soc. of Public Analysts. With numerous Illustrations and a
+coloured Plate. 10s. 6d. [See page 73.
+
+~Foods:~ Their Composition and Analysis. By A. WYNTER BLYTH, M.R.C.S.,
+F.C.S., Public Analyst for the County of Devon. With Tables, Folding
+Plate, and Frontispiece. FIFTH EDITION, Thoroughly Revised. 21s. [See
+page 72.
+
+"AN ADMIRABLE DIGEST of the most recent state of knowledge."--_Chemical
+News._
+
+       *       *       *       *       *
+
+ELECTRICAL ENGINEERING.
+
+_In Large 8vo. Handsome Cloth. Profusely Illustrated with Plates,
+Diagrams, and Figures. 24s. net._
+
+CENTRAL ELECTRICAL STATIONS: Their Design, Organisation, and Management.
+
+BY CHAS. H. WORDINGHAM, A.K.C., M. INST. C.E., M. INST. MECH. E., Late
+Memb. of Council Inst. E.E., and Electrical Engineer to the City of
+Manchester.
+
+ABRIDGED CONTENTS.
+
+Introductory.--Central Station Work as a Profession.--As an
+Investment.--The Establishment of a Central Station.--Systems of
+Supply.--Site.--Architecture.--Plant.--Boilers.--Systems of Draught and
+Waste Heat Economy.--Coal Handling, Weighing, and Storing.--The
+Transmission of Steam.--Generators.--Condensing Appliances.--Switching
+Gear, Instruments, and Connections.--Distributing Mains.--Insulation,
+Resistance, and Cost.--Distributing Networks.--Service Mains and
+Feeders.--Testing Mains.--Meters and Appliances.--Standardising
+and Testing Laboratory.--Secondary Batteries.--Street
+Lighting.--Cost.--General Organisation.--Mains Department.--Installation
+Department.--Standardising Department.--Drawing Office.--Clerical
+Department.--The Consumer.--Routine and Main Laying.--INDEX.
+
+"One of the MOST VALUABLE CONTRIBUTIONS to Central Station literature we
+have had for some time."--_Electricity._
+
+       *       *       *       *       *
+
+ELECTRICITY CONTROL.
+
+A Treatise on Electricity Switchgear and Systems of Transmission.
+
+BY LEONARD ANDREWS, M.I.E.E.,
+
+Ex-Member of Council of the Incorporated Municipal Electrical
+Association; Consulting Electrical Engineer to the Hastings Corporation,
+&c., &c.
+
+General Principles of Switchgear Design.--Constructional
+Details.--Circuit Breakers or Arc Interrupting Devices.--Automatically
+Operated Circuit Breakers.--Alternating Reverse Current
+Devices.--Arrangement of 'Bus Bars, and Apparatus for Parallel
+Running.--General Arrangement of Controlling Apparatus for High Tension
+Systems.--General Arrangement of Controlling Apparatus for Low Tension
+Systems.--Examples of Complete Installations.--Long Distance
+Transmission Schemes.
+
+       *       *       *       *       *
+
+SIXTEENTH EDITION, Thoroughly Revised and Enlarged.
+
+A POCKET-BOOK OF ELECTRICAL RULES & TABLES
+
+_FOR THE USE OF ELECTRICIANS AND ENGINEERS._
+
+BY JOHN MUNRO, C.E., & PROF. JAMIESON, M. INST. C.E., F.R.S.E.
+
+With Numerous Diagrams. Pocket Size. Leather, 8s. 6d.
+
+~GENERAL CONTENTS.~
+
+Units of Measurement.--Measures.--Testing.--Conductors.--Dielectrics.--
+Submarine Cables.--Telegraphy.--Electro-Chemistry.--Electro-Metallurgy.--
+Batteries.--Dynamos and Motors.--Transformers.--Electric
+Lighting.--Miscellaneous.--Logarithms.--Appendices.
+
+"WONDERFULLY PERFECT.... Worthy of the highest commendation we can give
+it."--_Electrician._
+
+"The STERLING VALUE of Messrs. MUNRO and JAMIESON'S
+POCKET-BOOK."--_Electrical Review._
+
+       *       *       *       *       *
+
+~By PROFESSORS J.H. POYNTING & J.J. THOMSON.~
+
+In Five Volumes. Large 8vo. Sold Separately.
+
+~A TEXT-BOOK OF PHYSICS.~
+
+BY
+
+J.H. POYNTING, SC.D., F.R.S.,
+
+Late Fellow of Trinity College, Cambridge; Professor of Physics,
+Birmingham University.
+
+AND
+
+J.J. THOMSON, M.A., F.R.S.
+
+Fellow of Trinity College, Cambridge; Prof. of Experimental Physics in
+the University of Cambridge.
+
+       *       *       *       *       *
+
+Introductory Volume, fully Illustrated. SECOND EDITION, Revised.
+
+Price 10s. 6d.
+
+~PROPERTIES OF MATTER.~
+
+CONTENTS.--Gravitation.--The Acceleration of
+Gravity.--Elasticity.--Stresses and Strains.--Torsion.--Bending of
+Rods.--Spiral Springs.--Collision.--Compressibility of
+Liquids.--Pressures and Volumes of Gases.--Thermal Effects Accompanying
+Strain.--Capillarity.--Surface Tension.--Laplace's Theory of
+Capillarity.--Diffusion of Liquids.--Diffusion of Gases.--Viscosity of
+Liquids.--INDEX.
+
+       *       *       *       *       *
+
+VOLUME II. SECOND EDITION. Fully Illustrated. Price 8s. 6d.
+
+~SOUND.~
+
+CONTENTS.--The Nature of Sound and its chief Characteristics.--The
+Velocity of Sound in Air and other Media.--Reflection and Refraction of
+Sound.--Frequency and Pitch of Notes.--Resonance and Forced
+Oscillations.--Analysis of Vibrations.--The Transverse
+Vibrations of Stretched Strings or Wires.--Pipes and other Air
+Cavities.--Rods.--Plates.--Membranes.--Vibrations maintained by
+Heat.--Sensitive Flames and Jets.--Musical Sand.--The Superposition of
+Waves.--INDEX.
+
+"The work ... may be recommended to anyone desirous of possessing an
+EASY UP-TO-DATE STANDARD TREATISE on Acoustics."--_Literature._
+
+"Very clearly written.... The names of the authors are a guarantee of
+the SCIENTIFIC ACCURACY and UP-TO-DATE CHARACTER of the
+work."--_Educational Times._
+
+       *       *       *       *       *
+
+VOLUME III. At Press. Fully Illustrated.
+
+~HEAT.~
+
+Remaining Volumes in Preparation--
+
+~LIGHT; MAGNETISM AND ELECTRICITY.~
+
+       *       *       *       *       *
+
+~THE MEAN DENSITY OF THE EARTH:~ An Essay to which the Adams Prize was
+adjudged in 1893 in the University of Cambridge. By J.H. POYNTING,
+Sc.D., F.R.S., Late Fellow of Trinity College, Cambridge; Professor of
+Physics, Birmingham University. In Large 8vo, with Bibliography,
+Illustrations in the Text, and Seven Lithographed Plates. 12s. 6d.
+
+"An account of this subject cannot fail to be of GREAT and GENERAL
+INTEREST to the scientific mind. Especially is this the case when the
+account is given by one who has contributed so considerably as has Prof.
+Poynting to our present state of knowledge with respect to a very
+difficult subject.... Remarkably has Newton's estimate been verified by
+Prof. Poynting."--_Athenęum._
+
+       *       *       *       *       *
+
+~Griffin's Geological, Prospecting, Mining, and Metallurgical
+Publications.~
+
+For Works on CHEMISTRY and CHEMICAL INDUSTRIES see p. 69.
+
+                                                              PAGE
+Geology, Stratigraphical,        R. ETHERIDGE, F.R.S.,          52
+  "   Physical,                  PROF. H.G. SEELEY,             52
+  "   Practical Aids,            PROF. GRENVILLE COLE,          53
+  "   Open Air Studies,               "        "                19
+Griffin's "New Land" Series,     ED. BY PROF. COLE,             54
+  Prospecting for Minerals,      S. HERBERT COX, A.R.S.M.,      55
+  Food Supply,                   ROBT. BRUCE,                   55
+  New Lands,                     H.R. MILL, D.SC., F.R.S.E.,    54
+  Building Construction,         PROF. JAMES LYON,              54
+Ore and Stone Mining,            PROF. LE NEVE FOSTER,          56
+  Elementary Mining,               "         "                  56
+  Coal Mining,                   H.W. HUGHES, F.G.S.,           56
+  Practical Coal Mining,         G.L. KERR, M.INST.M.E.,        58
+  Elementary "                       "     "                    58
+  Electrical Coal Mining,        D. BURNS,                      58
+Mine-Surveying,                  BENNETT H. BROUGH, A.R.S.M.,   57
+Blasting and Explosives,         O. GUTTMANN, A.M.I.C.E.,       57
+Mine Accounts,                   PROF. J.G. LAWN,               57
+Mining Engineers' Pkt.-Bk.,      E.R. FIELD, M.INST.M.M.,       60
+Petroleum,                       REDWOOD AND HOLLOWAY,          61
+  A Handbook on Petroleum,       J.H. THOMSON AND DR. REDWOOD,  61
+  The Petroleum Lamp,                 "      "                  61
+Metallurgical Analysis,          MACLEOD AND WALKER,            60
+Metallurgy (General),            PHILLIPS AND BAUERMAN,         60
+  " (Elementary),                PROF. HUMBOLDT SEXTON,         66
+  Getting Gold,                  J.C.F. JOHNSON, F.G.S.,        58
+  Gold Seeking in South Africa,  THEO KASSNER,                  59
+  Cyanide Process,               JAMES PARK, F.G.S.,            59
+  Cyaniding,                     SMART AND JULIAN,              59
+  Electric Smelting,             Borchers and McMillan,         67
+  Electro-Metallurgy,            W.G. McMillan, F.I.C.,         67
+  Assaying,                      J.J. & C. BERINGER,            66
+  Metallurgical Analysis,        J.J. MORGAN, F.C.S,            66
+Griffin's Metallurgical Series   ED. BY SIR W. ROBERTS-AUSTEN,  62
+  Introduction,                  SIR W. ROBERTS-AUSTEN, K.C.B., 63
+  Gold, Metallurgy of,           DR. KIRKE ROSE, A.R.S.M.,      63
+  Lead and Silver, "             H.F. COLLINS, A.R.S.M.,        64
+  Iron, Metallurgy of,           THOS. TURNER, A.R.S.M.,        65
+  Steel, "                       F.W. HARBORD,                  65
+  Metallurgical Machinery,       H.C. JENKINS, A.R.S.M.,        64
+Goldsmith and Jeweller's Art,    THOS. B. WIGLEY,               68
+Precious Stones,                 DR. MAX BAUER,                 68
+
+       *       *       *       *       *
+
+_Demy 8vo, Handsome cloth, 18s._
+
+Physical Geology and Palęontology,
+
+_ON THE BASIS OF PHILLIPS._
+
+BY
+
+HARRY GOVIER SEELEY, F.R.S., PROFESSOR OF GEOGRAPHY IN KING'S COLLEGE,
+LONDON.
+
+With Frontispiece in Chromo-Lithography, and Illustrations.
+
+"It is impossible to praise too highly the research which PROFESSOR
+SEELEY'S 'PHYSICAL GEOLOGY' evidences. IT IS FAR MORE THAN A
+TEXT-BOOK--it is a DIRECTORY to the Student in prosecuting his
+researches."--_Presidential Address to the Geological Society, 1885, by
+Rev. Prof. Bonney, D.Sc., LL.D., F.R.S._
+
+"PROFESSOR SEELEY maintains in his 'PHYSICAL GEOLOGY' the high
+reputation he already deservedly bears as a Teacher."--_Dr. Henry
+Woodward, F.R.S., in the "Geological Magazine."_
+
+"PROFESSOR SEELEY'S work includes one of the most satisfactory Treatises
+on Lithology in the English language."--_American Journal of
+Engineering._
+
+       *       *       *       *       *
+
+_Demy 8vo, Handsome cloth, 34s._
+
+Stratigraphical Geology & Palęontology,
+
+_ON THE BASIS OF PHILLIPS._
+
+BY
+
+ROBERT ETHERIDGE, F.R.S.,
+
+OF THE NATURAL HIST. DEPARTMENT, BRITISH MUSEUM, LATE PALĘONTOLOGIST TO
+THE GEOLOGICAL SURVEY OF GREAT BRITAIN, PAST PRESIDENT OF THE GEOLOGICAL
+SOCIETY, ETC.
+
+With Map, Numerous Tables, and Thirty-six Plates.
+
+"No such compendium of geological knowledge has ever been brought
+together before."--_Westminster Review._
+
+"If PROF. SEELEY'S volume was remarkable for its originality and the
+breadth of its views, Mr. ETHERIDGE fully justifies the assertion made
+in his preface that his book differs in construction and detail from
+any known manual.... Must take HIGH RANK AMONG WORKS OF
+REFERENCE."--_Athenęum._
+
+       *       *       *       *       *
+
+OPEN-AIR STUDIES IN GEOLOGY: An Introduction to Geology Out-of-doors.
+
+BY PROFESSOR GRENVILLE COLE, M.R.I.A., F.G.S.
+
+For details, see Griffin's Introductory Science Series, p. 85.
+
+       *       *       *       *       *
+
+_Crown 8vo. Handsome Cloth, 2s. 6d._
+
+~RESEARCHES ON THE PAST AND PRESENT HISTORY OF THE EARTH'S ATMOSPHERE.~
+
+_Including the latest Discoveries and their Practical Applications._
+
+BY DR. THOMAS LAMB PHIPSON.
+
+PART I.--THE EARTH'S ATMOSPHERE IN REMOTE GEOLOGICAL PERIODS.
+
+PART II.--THE ATMOSPHERE OF OUR PRESENT PERIOD. APPENDICES; INDEX.
+
+*** Dr. Phipson's work presents, amidst much which is of interest to the
+Scientist and the General Reader alike, a short _résumé_ of his
+discovery of the origin of Atmospheric Oxygen, the existence of which he
+attributes wholly to the action of Solar Radiation upon vegetable life.
+The book will be found replete with much that is new, curious, and
+interesting, both in connection with Weather Lore, and with Scientific
+Meteorology.--_Publisher's Note._
+
+"The book should prove of interest to general readers, as well as to
+meteorologists and other students of science."--_Nature._
+
+       *       *       *       *       *
+
+By GRENVILLE A.J. COLE, M.R.I.A., F.G.S.,
+
+Professor of Geology in the Royal College of Science for Ireland, and
+Examiner in the University of London.
+
+_See also the two following pages (54, 55), and page 85._
+
+       *       *       *       *       *
+
+~AIDS IN PRACTICAL GEOLOGY:~
+
+_WITH A SECTION ON PALĘONTOLOGY._
+
+BY PROFESSOR GRENVILLE COLE, M.R.I.A., F.G.S.
+
+FOURTH EDITION, Thoroughly Revised. With Frontispiece and Illustrations.
+Cloth, 10s. 6d.
+
+  GENERAL CONTENTS.--
+    PART I.--SAMPLING OF THE EARTH'S CRUST.
+    PART II.--EXAMINATION OF MINERALS.
+    PART III.--EXAMINATION OF ROCKS.
+    PART IV.--EXAMINATION OF FOSSILS.
+
+"Prof. Cole treats of the examination of minerals and rocks in a way
+that has never been attempted before ... DESERVING OF THE HIGHEST
+PRAISE. Here indeed are 'Aids' INNUMERABLE and INVALUABLE. All
+the directions are given, with the utmost clearness and
+precision."--_Athenęum._
+
+"That the work deserves its title, that it is full of 'AIDS,' and in the
+highest degree 'PRACTICAL,' will be the verdict of all who use
+it."--_Nature._
+
+"This EXCELLENT MANUAL ... will be A VERY GREAT HELP.... The Section on
+the Examination of Fossils is probably the BEST of its kind yet
+published.... FULL of well-digested information from the newest sources
+and from personal research."--_Annals of Nat. History._
+
+       *       *       *       *       *
+
+GRIFFINS "NEW LAND" SERIES.
+
+       *       *       *       *       *
+
+_Practical Hand-Books for the Use of Prospectors, Explorers, Settlers,
+Colonists, and all Interested in the opening up and Development of New
+Lands._
+
+EDITED BY GRENVILLE A.J. COLE, M.R.I.A., F.G.S.,
+
+Professor of Geology in the Royal College of Science for Ireland, and
+Examiner in the University of London.
+
+       *       *       *       *       *
+
+_In Crown 8vo. Handsome Cloth. 5s._
+
+_With Numerous Maps Specially Drawn and Executed for this Work._
+
+NEW LANDS:
+
+THEIR RESOURCES AND PROSPECTIVE ADVANTAGES.
+
+BY HUGH ROBERT MILL, D.Sc., LL.D., F.R.S.E.,
+
+Librarian to the Royal Geographical Society.
+
+INTRODUCTORY.--The Development of New Lands.--The Dominion of
+Canada.--Canada, Eastern Provinces.--Canada, Western Provinces and
+Territories.--Newfoundland.--The United States.--Latin America,
+Mexico.--Latin America, Temperate Brazil and Chili.--Latin America,
+Argentina.--The Falkland Islands.--Victoria.--New South
+Wales.--Queensland.--South Australia.--Tasmania.--Western
+Australia.--New Zealand.--The Resources of South Africa.--Southern
+Rhodesia.--INDEX.
+
+"PAINSTAKING ... COMPLETE ... of great PRACTICAL ASSISTANCE."--_The
+Field._
+
+"A want admirably supplied.... Has the advantage of being written by a
+professed Geographer."--_Geographical Journal._
+
+       *       *       *       *       *
+
+_IN PREPARATION._
+
+~BUILDING CONSTRUCTION IN WOOD, STONE, AND CONCRETE.~ By JAMES LYON,
+M.A., Professor of Engineering in the Royal College of Science for
+Ireland; sometime Superintendent of the Engineering Department in the
+University of Cambridge; and J. Taylor, A.R.C.S.I.
+
+       *       *       *       *       *
+
+*** Other Volumes, dealing with subjects of PRIMARY IMPORTANCE in the
+EXAMINATION and UTILISATION of Lands which have not as yet been fully
+developed, are in preparation.
+
+       *       *       *       *       *
+
+THIRD EDITION, _Revised. With Illustrations. Handsome Cloth, 5s._
+
+PROSPECTING FOR MINERALS.
+
+A Practical Handbook for Prospectors, Explorers, Settlers, and all
+interested in the Opening up and Development of New Lands.
+
+BY
+
+S. HERBERT COX, Assoc. R.S.M., M. Inst. M.M., F.G.S., &c.
+
+GENERAL CONTENTS.--Introduction and Hints on Geology--The Determination
+of Minerals: Use of the Blow-pipe, &c.--Rock-forming Minerals and
+Non-Metallic Minerals of Commercial Value: Rock Salt, Borax, Marbles,
+Lithographic Stone, Quartz and Opal, &c., &c.--Precious Stones and
+Gems--Stratified Deposits: Coal and Ores--Mineral Veins and
+Lodes--Irregular Deposits--Dynamics of Lodes: Faults, &c.--Alluvial
+Deposits--Noble Metals: Gold, Platinum, Silver,
+&c.--Lead--Mercury--Copper--Tin--Zinc--Iron--Nickel, &c.--Sulphur,
+Antimony, Arsenic, &c.--Combustible Minerals--Petroleum--General Hints
+on Prospecting--Glossary--Index.
+
+     "This ADMIRABLE LITTLE WORK ... written with SCIENTIFIC
+     ACCURACY in a CLEAR and LUCID style.... An IMPORTANT ADDITION
+     to technical literature ... will be of value not only to the
+     Student, but to the experienced Prospector.... If the
+     succeeding volumes of the NEW LAND SERIES are equal in merit to
+     the First, we must congratulate the Publishers on successfully
+     filling up a gap in existing literature.--_Mining Journal._
+
+     "This EXCELLENT HANDBOOK will prove a perfect _Vade-mecum_ to
+     those engaged in the practical work of Mining and
+     Metallurgy."--_Times of Africa._
+
+       *       *       *       *       *
+
+With many Engravings and Photographs. Handsome Cloth, 4s. 6d.
+
+FOOD SUPPLY.
+
+By ROBERT BRUCE, Agricultural Superintendent to the Royal Dublin
+Society.
+
+With Appendix on Preserved Foods by C.A. Mitchell, B.A., F.L.C.
+
+GENERAL CONTENTS.--Climate and Soil--Drainage and Rotation of
+Crops--Seeds and Crops--Vegetables and Fruits--Cattle and
+Cattle-Breeding--Sheep and Sheep Rearing--Pigs--Poultry--Horses--The
+Dairy--The Farmer's Implements--The Settler's Home.
+
+"BRISTLES WITH INFORMATION."--_Farmers' Gazette._
+
+"The work is one which will appeal to those intending to become farmers
+at home or in the Colonies, and who desire to obtain a general idea of
+the true principles of farming in ALL ITS BRANCHES."--_Journal of the
+Royal Colonial Inst._
+
+"A most READABLE and VALUABLE book, and merits an EXTENSIVE
+SALE."--_Scottish Farmer._
+
+"Will prove of service in ANY PART OF THE WORLD."--_Nature._
+
+       *       *       *       *       *
+
+FOURTH EDITION, Revised, and brought thoroughly up-to-date by L.H.
+COOKE, Instructor in Mine Surveying, Royal College of Science.
+
+With Frontispiece and 716 Illustrations. Price 34s.
+
+ORE & STONE MINING.
+
+BY
+
+C. LE NEVE FOSTER, D.Sc., F.R.S.,
+
+PROFESSOR OF MINING, ROYAL COLLEGE OF SCIENCE; EXAMINER IN MINING TO THE
+BOARD OF EDUCATION.
+
+GENERAL CONTENTS.
+
+INTRODUCTION. Mode of Occurrence of
+Minerals.--Prospecting.--Boring.--Breaking Ground.--Supporting
+Excavations.--Exploitation.--Haulage or Transport.--Hoisting or
+Winding.--Drainage.--Ventilation.--Lighting.--Descent and
+Ascent.--Dressing.--Principles of Employment of Mining
+Labour.--Legislation affecting Mines and Quarries.--Condition of the
+Miner.--Accidents.--Index.
+
+"Dr. Foster's book was expected to be epoch-making, and it fully
+justifies such expectation.... A MOST ADMIRABLE account of the mode of
+occurrence of practically ALL KNOWN MINERALS. Probably stands unrivalled
+for completeness."--_The Mining Journal_.
+
+"This EPOCH-MAKING work ... appeals to MEN OF EXPERIENCE no less than to
+students."--_Berg- und Hüttenmännische Zeitung_.
+
+"This SPLENDID WORK."--_Oesterr. Ztschrft. für Berg- und Hüttenwesen_.
+
+       *       *       *       *       *
+
+ELEMENTARY MINING AND QUARRYING
+
+(An Introductory Text-book). By Prof. C. LE NEVE FOSTER, F.R.S. With
+Illustrations. [_At Press._
+
+       *       *       *       *       *
+
+FOURTH EDITION, _Revised and Greatly Enlarged. With Numerous Additional
+Illustrations, mostly reduced from Working Drawings. Price 24s. net._
+
+A TEXT-BOOK OF COAL-MINING:
+
+_FOR THE USE OF COLLIERY MANAGERS AND OTHERS ENGAGED IN COAL-MINING._
+
+BY
+
+HERBERT WILLIAM HUGHES, F.G.S.,
+
+Assoc. Royal School of Mines, General Manager of Sandwell Park Colliery.
+
+GENERAL CONTENTS.
+
+Geology.--Search for Coal.--Breaking Ground.--Sinking.--Preliminary
+Operations.--Methods of Working.--Haulage.--Winding.--Pumping.--
+Ventilation.--Lighting.--Works at Surface.--Preparation of Coal for
+Market.--INDEX.
+
+"Quite THE BEST book of its kind ... as PRACTICAL in aim as a book can
+be ... The illustrations are EXCELLENT."--_Athenęum_.
+
+"We cordially recommend the work."--_Colliery Guardian_.
+
+"Will soon come to be regarded as the STANDARD WORK of its
+kind."--_Birmingham Daily Gazette._
+
+       *       *       *       *       *
+
+TENTH EDITION, Revised and Enlarged. With Numerous Diagrams.
+
+Cloth, 7s. 6d.
+
+~A TREATISE ON MINE-SURVEYING:
+
+For the use of Managers of Mines and Collieries, Students at the Royal
+School of Mines, &c.~
+
+By BENNETT H. BROUGH, F.G.S., ASSOC.R.S.M.,
+
+Formerly Instructor of Mine-Surveying, Royal School of Mines.
+
+GENERAL CONTENTS.--General Explanations.--Measurement of
+Distances.--Miner's Dial.--Variation of the
+Magnetic-Needle.--Surveying.--German Dial.--Theodolite.--Traversing
+Underground.--Surface-Surveys.--Plotting the Survey.--Calculation of
+Areas.--Levelling.--Measuring Distances by
+Telescope.--Setting-out.--Problems.--Photographic
+Surveying.--_Appendices._
+
+"Its CLEARNESS of STYLE, LUCIDITY of DESCRIPTION, and FULNESS of DETAIL
+have long ago won for it a place unique in the literature of this branch
+of mining engineering, and the present edition fully maintains the high
+standard of its predecessors. To the student, and to the mining engineer
+alike, ITS VALUE is inestimable. The illustrations are excellent."--_The
+Mining Journal._
+
+       *       *       *       *       *
+
+_In Large 8vo._ SECOND EDITION. _Price 10s. 6d._
+
+~Mine Accounts and Mining Book-keeping.~
+
+For Students, Managers, Secretaries, and others.
+
+_With Examples taken from Actual Practice of Leading Companies._
+
+BY
+
+JAMES GUNSON LAWN, Assoc.R.S.M., Assoc. Mem. Inst. C.E., F.G.S.,
+
+Professor of Mining at the South African School of Mines.
+
+EDITED BY C. LE NEVE FOSTER, D.Sc., F.R.S.
+
+GENERAL CONTENTS.--Introduction.--Part I. Engagement and Payment of
+Workmen.--Part II. Purchases and Sales.--Part III. Working Summaries and
+Analyses.--Part IV. Ledger, Balance Sheet, and Company Books.--Part V.
+Reports and Statistics.
+
+"It seems IMPOSSIBLE to suggest how Mr. LAWN'S book could be made more
+COMPLETE or more VALUABLE, careful, and exhaustive."--_Accountants'
+Magazine_.
+
+       *       *       *       *       *
+
+_In Large 8vo, with Illustrations and Folding-Plates. 10s. 6d._
+
+~BLASTING~:
+
+AND THE USE OF EXPLOSIVES.
+
+A Handbook for Engineers and others Engaged in Mining, Tunnelling,
+Quarrying, &c.
+
+BY OSCAR GUTTMANN, ASSOC. M. INST. C.E.
+
+_Member of the Societies of Civil Engineers and Architects of Vienna and
+Budapest, Corresponding Member of the Imp. Roy. Geological Institution
+of Austria, &c._
+
+"This ADMIRABLE work."--_Colliery Guardian._
+
+"Should prove a _vade-mecum_ to Mining Engineers and all engaged in
+practical work."--_Iron and Coal Trades Review._
+
+       *       *       *       *       *
+
+_In Crown 8vo. Handsome cloth. With Numerous Illustrations. 6s. net._
+
+~ELECTRICAL PRACTICE IN COLLIERIES.~
+
+BY D. BURNS, M.E., M.INST.M.E.,
+
+Certificated Colliery Manager, and Lecturer on Mining and Geology to the
+Glasgow and West of Scotland Technical College.
+
+Units of Measurement, Conductors, &c.--The Theory of the Dynamo.--The
+Dynamo, Details of Construction and Working.--Motors.--Lighting
+Installations in Collieries.--Pumping by Electricity.--Electrical
+Haulage.--Coal Cutting.--Miscellaneous Applications of Electricity in
+Mines.--INDEX.
+
+"A clear and concise introduction to electrical practice in
+collieries."--_Mining Journal._
+
+       *       *       *       *       *
+
+SECOND EDITION. Large Crown 8vo. Handsome Cloth. With over 520
+Illustrations in the Text. 12s. 6d.
+
+~PRACTICAL COAL-MINING:~ A MANUAL FOR MANAGERS, UNDER-MANAGERS, COLLIERY
+ENGINEERS, AND OTHERS.
+
+_With Worked-out Problems on Haulage, Pumping, Ventilation, &c._
+
+BY GEORGE L. KERR, M.E., M.INST.M.E.
+
+"An ESSENTIALLY PRACTICAL WORK, and can be confidently recommended. No
+department of Coal-Mining has been overlooked."--_Engineers' Gazette._
+
+"This book JUST MEETS the wants of Students preparing for the Colliery
+Managers' Examinations. I have decided to use it for our classes
+here.... We have, I believe the largest atining class in Great
+Britain."--_The Principal of a Training College._
+
+       *       *       *       *       *
+
+ELEMENTARY COAL-MINING: For the Use of Students, Miners, and others
+preparing for Examinations. By GEORGE L. KERR, M.E., M.INST.M.E., Author
+of "Practical Coal-Mining." In Crown 8vo. Handsome Cloth. With 200
+Illustrations. 3s. 6d.
+
+"An abundance of information conveyed in a popular and attractive
+form.... Will be of great use to all who are in any way interested in
+coal mining."--_Scottish Critic._
+
+       *       *       *       *       *
+
+SECOND EDITION. _With Illustrations. Cloth, 3s. 6d._
+
+~GETTING GOLD:~
+
+A GOLD-MINING HANDBOOK FOR PRACTICAL MEN.
+
+BY J.C.F. JOHNSON, F.G.S., A.I.M.E.,
+
+Life Member Australasian Mine-Managers' Association.
+
+GENERAL CONTENTS.--Introductory: Prospecting (Alluvial and
+General)--Lode or Reef Prospecting--Genesiology of Gold--Auriferous
+Lodes--Drifts--Gold Extraction--Lixiviation--Calcination--Motor Power
+and its Transmission--Company Formation--Mining Appliances and
+Methods--Australasian Mining Regulations.
+
+"PRACTICAL from beginning to end ... deals thoroughly with the
+Prospecting, Sinking, Crushing, and Extraction of gold."--_Brit.
+Australasian._
+
+       *       *       *       *       *
+
+_With Plates and Illustrations. Handsome Cloth. At Press._
+
+~THE CYANIDE PROCESS OF GOLD EXTRACTION.~
+
+_A Text-Book for the Use of Metallurgists and Students at Schools of
+Mines, &c._
+
+BY JAMES PARK, F.G.S., M.INST.M.M.,
+
+Professor of Mining and Director of the Otago University School of
+Mines; late Director Thames School of Mines, and Geological Surveyor and
+Mining Geologist to the Government of New Zealand.
+
+THIRD ENGLISH EDITION. Thoroughly Revised and Greatly Enlarged. With
+additional details concerning the Siemens-Halske and other recent
+processes.
+
+CONTENTS.--The MacArthur Process.--Chemistry of the Process.--Laboratory
+Experiments.--Control Testing and Analysis of Solutions.--Appliances for
+Cyanide Extraction.--The Actual Extraction by Cyanide.--Application of
+the Process.--Leaching by Agitation.--Zinc Precipitation of Gold.--The
+Siemens-Halske Process.--Other Cyanide Processes.--Antidotes for Cyanide
+Poisoning.--Cyaniding in New Zealand.
+
+"Mr. Park's book deserves to be ranked as amongst the BEST OF EXISTING
+TREATISES ON THIS SUBJECT."--_Mining Journal._
+
+       *       *       *       *       *
+
+AT PRESS. _With Numerous Plates, Maps, and Illustrations._
+
+~CYANIDING GOLD & SILVER ORES.~
+
+A Practical Treatise on the Cyanide Process; its Application, Methods of
+Working, Design and Construction of Plant, and Costs.
+
+BY H. FORBES JULIAN,
+
+Mining and Metallurgical Engineer; Specialist in Gold: Late Technical
+Adviser of the Deutsche Gold und Silber Scheide Anstalt,
+Frankfort-on-Maine.
+
+AND EDGAR SMART, A.M.I.C.E.,
+
+Civil and Metallurgical Engineer.
+
+*** This book deals with the Cyanide Process from Technical, Commercial,
+and Scientific points of view. It is adapted for the Use of Directors,
+Managers, and Superintendents of Mines and Metallurgical Works, Mining
+Engineers, Metallurgists, Chemists, Assayers, Working Cyaniders, and
+Students.
+
+       *       *       *       *       *
+
+_In Crown. 8vo. Illustrated. Fancy Cloth Boards._ 4c. 6c.
+
+~GOLD SEEKING IN SOUTH AFRICA:~
+
+A Handbook of Hints for intending Explorers, Prospectors, and Settlers.
+
+BY THEO KASSNER,
+
+Mine Manager, Author of the Geological Sketch Map of the De Kaap Gold
+Fields.
+
+_With a Chapter on the Agricultural Prospects of South Africa._
+
+ABSTRACT OF CONTENTS--History.--Geology.--Prospecting.--The De Kaap
+Goldfields.--Komati and Swaziland.--Cost of Mining, Native Labour,
+&c.--Lydenberg Goldfields--Zoutspanberg.--Witwatersrand.--Other
+Goldfields.--General Considerations--Conclusions.--Agricultural
+Prospects, Tables, Index, &c.
+
+"As fascinating in its way as anything ever penned by Jules Verne. Mr.
+Kassner manages to impart his information in a way that enables him to
+be understanded even of the dullest."--_African Commerce._
+
+       *       *       *       *       *
+
+AT PRESS. Large 8vo. Handsome Cloth. With Illustrations.
+
+METALLURGICAL ANALYSIS & ASSAYING:
+
+A THREE YEARS' COURSE FOR STUDENTS OF SCHOOLS OF MINES.
+
+By W.A. MACLEOD, B.A., B.Sc., A.O.S.M. (N.Z.),
+
+Formerly Assist.-Director, Thames School of Mines (N.Z.), and Lecturer
+in Chemistry, University of Tasmania; Director of Queensland Government
+School of Mines, Charters Towers;
+
+AND CHAS. WALKER, F.C.S.,
+
+Formerly Assist.-Demonstrator in Chemistry, Sydney University; Lecturer
+in Chemistry and Metallurgy, Charters Towers School of Mines
+
+PART I.--QUALITATIVE ANALYSIS AND PREPARATION AND PROPERTIES OF GASES.
+
+PART II.--QUALITATIVE AND QUANTITATIVE ANALYSIS.
+
+PART III.--ASSAYING, TECHNICAL ANALYSIS (GAS, WATER, FUELS, OILS, &C.).
+
+*** "The aim of this work is to provide the student with a graded course
+of work leading from Simple Quantitative Analysis up to the Technical
+Quantitative Methods. It has been specially prepared to meet the
+requirements of Schools of Mines, and more especially, of those in the
+Colonies, the subject matter having been selected to cover a three
+years' laboratory course."--_Extract from Author's Preface._
+
+       *       *       *       *       *
+
+THIRD EDITION. With Folding Plates and Many Illustrations. 36s.
+
+ELEMENTS OF METALLURGY.
+
+A PRACTICAL TREATISE ON THE ART OF EXTRACTING METALS FROM THEIR ORES.
+
+BY J. ARTHUR PHILLIPS, M. INST. C.E., F.C.S., F.G.S., &c., AND H.
+BAUERMAN, V.P.G.S.
+
+GENERAL CONTENTS.--Refractory Materials.--Fire-Clays.--Fuels,
+&c.--Aluminium.--Copper.--Tin.--Antimony.--Arsenic.--Zinc.--Mercury.--
+Bismuth.--Lead.--Iron.--Cobalt.--Nickel.--Silver.--Gold.--Platinum.
+
+"Of the THIRD EDITION, we are still able to say that, as a Text-book of
+Metallurgy, it is THE BEST with which we are acquainted."--_Engineer._
+
+"A work which is equally valuable to the Student as a Text-book, and to
+the practical Smelter as a Standard Work of Reference.... The
+Illustrations are admirable examples of Wood Engraving."--_Chemical
+News._
+
+       *       *       *       *       *
+
+~THE MINING ENGINEERS' REPORT BOOK AND DIRECTORS'~ AND SHAREHOLDERS'
+GUIDE TO MINING REPORTS. By EDWIN R. FIELD, M.INST.M.M. With Notes on
+the Valuation of Mining Property and Tabulating Reports, Useful Tables,
+&c., and provided with detachable blank pages for MS. Notes.
+
+"An ADMIRABLY compiled book which Mining Engineers and Managers will
+find EXTREMELY USEFUL."--_Mining Journal._
+
+       *       *       *       *       *
+
+SECOND EDITION. _In Preparation. In Two Volumes, Large 8vo. With
+Numerous Maps, Plates, and Illustrations in the Text. Price 45s._
+
+~PETROLEUM _AND ITS PRODUCTS:_ A PRACTICAL TREATISE.~
+
+By Dr. BOVERTON REDWOOD, F.R.S.E., F.I.C., ASSOC.R.C.S.,
+
+Hon. Corr. Mem. of the Imperial Russian Technical Society; Mem. of the
+American Chemical Society; Adviser to the Home Office and to the
+Corporation of London under the Petroleum Acts, &c., &c.
+
+ASSISTED BY GEO. T. HOLLOWAY, F.I.C., ASSOC. R.C.S., And Numerous
+Contributors.
+
+GENERAL CONTENTS.--I. Historical.--II. Geological and Geographical
+Distribution of Petroleum and Natural Gas.--III. Chemical and Physical
+Properties.--IV. Origin--V. Production.--VI. Refining.--VII. The Shale
+Oil and Allied Industries.--VIII. Transport, Storage, and
+Distribution.--IX. Testing.--X. Application and Uses.--XI. Legislation
+at Home and Abroad.--XII. Statistics.--INDEX.
+
+"The MOST COMPREHENSIVE AND CONVENIENT ACCOUNT that has yet appeared of
+a gigantic Industry which has made incalculable additions to the comfort
+of civilised man."--_The Times._
+
+"A SPLENDID CONTRIBUTION to our technical literature."--_Chemical News._
+
+       *       *       *       *       *
+
+_With Plates (One Coloured) and Illustrations. Price 8s. 6d. net._
+
+~A HANDBOOK ON PETROLEUM.~
+
+_FOR INSPECTORS UNDER THE PETROLEUM ACTS,_
+
+And for those engaged in the Storage, Transport, Distribution, and
+Industrial Use of Petroleum and its Products, and of Calcium Carbide.
+With suggestions on the Construction and Use of Mineral Oil Lamps.
+
+BY CAPTAIN J.H. THOMSON, H.M. Chief Inspector of Explosives,
+
+AND
+
+DR. BOVERTON REDWOOD, Author of "Petroleum and its Products."
+
+CONTENTS.--I. Introductory.--II. Sources of Supply.--III.
+Production.--IV. Chemical Products, Shale Oil, and Coal Tar.--V. Flash
+Point and Fire Test.--VI. Testings.--VII. Existing Legislation relating
+to Petroleum.--VIII.--IX.--Precautions Necessary.--X. Petroleum Oil
+Lamps.--XI. Carbide of Calcium and Acetylene.--Appendices.--INDEX.
+
+"A volume that will enrich the world's petroleum literature, and render
+a service to the British branch of the industry.... Reliable,
+indispensable, a brilliant contribution."--_Petroleum._
+
+       *       *       *       *       *
+
+~THE PETROLEUM LAMP: Its Choice and Use.~ A Guide to the Safe Employment
+of Mineral Oil in what is commonly termed the Paraffin Lamp. By CAPT.
+J.H. THOMSON and Dr. BOVERTON REDWOOD. Popular Edition, Illustrated. 1s.
+net.
+
+"The book contains a great deal of interesting reading, much of which is
+thoroughly practical and useful. It is a work which will meet every
+purpose for which it has been written."--_Petroleum._
+
+       *       *       *       *       *
+
+Griffin's Metallurgical Series.
+
+       *       *       *       *       *
+
+_STANDARD WORKS OF REFERENCE_
+
+FOR
+
+Metallurgists, Mine-Owners, Assayers, Manufacturers, and all interested
+in the development of the Metallurgical Industries.
+
+EDITED BY Sir W. ROBERTS-AUSTEN, K.C.B., D.C.L, F.R.S.
+
+_In Large 8vo, Handsome Cloth. With Illustrations._
+
+       *       *       *       *       *
+
+~INTRODUCTION to the STUDY of METALLURGY.~ By the EDITOR. FIFTH EDITION.
+18s. (See p. 63.)
+
+~GOLD (The Metallurgy of).~ By THOS. KIRKE ROSE, D.Sc., Assoc.R.S.M.,
+F.I.C., Chemist and Assayer of the Royal Mint. FOURTH EDITION. 21s. (See
+p. 63.)
+
+~LEAD AND SILVER (The Metallurgy of).~ By H.F. COLLINS, Assoc.R.S.M.,
+M.Inst.M.M. Part I., Lead, 16s; Part II., Silver, 16s. (See p. 64.)
+
+~IRON (The Metallurgy of).~ By T. TURNER, A.R.S.M., F.I.C., F.C.S.
+SECOND EDITION, Revised. 16s. (See p. 65.)
+
+~STEEL (The Metallurgy of).~ By F.W. HARBORD, Assoc.R.S.M., F.I.C., with
+a Section on Mechanical Treatment by J.W. HALL, A.M.Inst, C.E. (See p.
+65.) [_Ready shortly._
+
+       *       *       *       *       *
+
+_Will be Published at Short Intervals._
+
+~METALLURGICAL MACHINERY:~ the Application of Engineering to
+Metallurgical Problems. By HENRY CHARLES JENKINS, Wh.Sc., Assoc.R.S.M.,
+Assoc.M.Inst.C.E., of the Royal College of Science. (See p. 64).
+
+~ALLOYS.~ By the EDITOR.
+
+*** Other Volumes in Preparation.
+
+       *       *       *       *       *
+
+FIFTH EDITION, thoroughly Revised and considerably Enlarged. Large 8vo,
+with numerous Illustrations and Micro-Photographic Plates of different
+varieties of Steel. 18s.
+
+~An Introduction to the Study of METALLURGY.~
+
+BY
+
+Sir W. ROBERTS-AUSTEN, K.C.B., D.C.L., F.R.S., A.R.S.M., Late Chemist
+and Assayer of the Royal Mint, and Professor of Metallurgy in the Royal
+College of Science.
+
+GENERAL CONTENTS.--The Relation of Metallurgy to Chemistry.--Physical
+Properties of Metals.--Alloys.--The Thermal Treatment of Metals.--Fuel
+and Thermal Measurements.--Materials and Products of
+Metallurgical Processes.--Furnaces.--Means of Supplying Air to
+Furnaces.--Thermo-Chemistry.--Typical Metallurgical Processes.--The
+Micro-Structure of Metals and Alloys.--Economic Considerations.
+
+"No English text-book at all approaches this in the COMPLETENESS with
+which the most modern views on the subject are dealt with. Professor
+Austen's volume will be INVALUABLE, not only to the student, but also to
+those whose knowledge of the art is far advanced."--_Chemical News._
+
+       *       *       *       *       *
+
+FOURTH EDITION, Revised, Considerably Enlarged, and in part Re-written.
+Including the most recent Improvements in the Cyanide Process. With
+Frontispiece and numerous Illustrations. 21s.
+
+~THE METALLURGY OF GOLD.~
+
+BY
+
+T. KIRKE ROSE, D.Sc.Lond., Assoc.R.S.M., _Chemist and Assayer of the
+Royal Mint_.
+
+GENERAL CONTENTS.--The Properties of Gold and its Alloys.--Chemistry of
+Gold.--Mode of Occurrence and Distribution.--Placer Mining.--Shallow
+Deposits.--Deep Placer Mining.--Quartz Crushing in the Stamp
+Battery.--Amalgamation.--Other Forms of Crushing and
+Amalgamating.--Concentration.--Stamp Battery Practice.--Chlorination:
+The Preparation of Ore.--The Vat Process.--The Barrel
+Process.--Chlorination Practice in Particular Mills.--The Cyanide
+Process.--Chemistry of the Process.--Pyritic Smelting.--The Refining and
+Parting of Gold Bullion--The Assay of Gold Ores.--The Assay of
+Bullion--Economic Considerations.--Bibliography.
+
+"A COMPREHENSIVE PRACTICAL TREATISE on this important subject."--_The
+Times._
+
+"The MOST COMPLETE description of the CHLORINATION PROCESS which has yet
+been published."--_Mining Journal._
+
+"Adapted for all who are interested in the Gold Mining Industry, being
+free from technicalities as far as possible, but is more particularly of
+value to those engaged in the industry."--_Cape Times._
+
+       *       *       *       *       *
+
+EDITED BY SIR W. ROBERTS-AUSTEN, K.C.B., F.R.S., D.C.L.
+
+_In Large 8vo. Handsome Cloth. With Illustrations._
+
+       *       *       *       *       *
+
+In Two Volumes, Each Complete in Itself and Sold Separately.
+
+~THE METALLURGY OF LEAD AND SILVER.~
+
+BY H.F. COLLINS, ASSOC.R.S.M., M.INST.M.M.
+
+~Part I.--LEAD:~
+
+A Complete and Exhaustive Treatise on the Manufacture of Lead, with
+Sections on Smelting and Desilverisation, and Chapters on the Assay and
+Analysis of the Materials involved. Price 16s.
+
+SUMMARY OF CONTENTS.--Sampling and Assaying Lead and Silver.--Properties
+and Compounds of Lead.--Lead Ores.--Lead
+Smelting.--Reverberatories.--Lead Smelting in Hearths.--The Roasting of
+Lead Ores.--Blast Furnace Smelting; Principles, Practice, and Examples;
+Products.--Flue Dust, its Composition, Collection and Treatment.--Costs
+and Losses, Purchase of Ores.--Treatment of Zinc, Lead Sulphides,
+Desilverisation, Softening and Refining.--The Pattinson Process.--The
+Parkes Process.--Cupellation and Refining, &c., &c.
+
+"A THOROUGHLY SOUND and useful digest. May with EVERY CONFIDENCE be
+recommended."--_Mining Journal._
+
+       *       *       *       *       *
+
+~Part II. SILVER.~
+
+Comprising Details regarding the Sources and Treatment of Silver Ores,
+together with Descriptions of Plant, Machinery, and Processes of
+Manufacture, Refining of Bullion, Cost of Working, &c. Price 16s.
+
+SUMMARY OF CONTENTS.--Properties of Silver and its Principal
+Compounds.--Silver Ores.--The Patio Process.--The Kazo,
+Fondon, Kröhnke, and Tina Processes.--The Pan Process.--Roast
+Amalgamation.--Treatment of Tailings and Concentration.--Retorting,
+Melting, and Assaying.--Chloridising-Roasting.--The Augustin,
+Claudet, and Ziervogel Processes.--The Hypo-Sulphite Leaching
+Process.--Refining.--Matte Smelting.--Pyritic Smelting.--Matte
+Smelting in Reverberatories.--Silver-Copper Smelting and Refining.--INDEX.
+
+"The author has focussed A LARGE AMOUNT OF VALUABLE INFORMATION into a
+convenient form.... The author has evidently considerable practical
+experience, and describes the various processes clearly and
+well."--_Mining Journal._
+
+       *       *       *       *       *
+
+~_IN PREPARATION._~
+
+~METALLURGICAL MACHINERY: The Application of Engineering to
+Metallurgical Problems.~
+
+BY HENRY CHARLES JENKINS,
+
+_Wh.Sc., Assoc.R.S.M., Assoc.M.Inst.C.E._
+
+       *       *       *       *       *
+
+READY SHORTLY. With Numerous Illustrations. Large 8vo. Handsome Cloth.
+
+~THE METALLURGY OF STEEL.~
+
+BY F.W. HARBORD, ASSOC.R.S.M., F.I.C., _Consulting Metallurgist and
+Analytical Chemist to the Indian Government, Royal Indian Engineering
+College, Coopers Hill._
+
+With over 40 Plates, 500 Illustrations (comprising nearly 100
+Micro-Sections of Steel), Diagrams of Plant and Machinery, reduced from
+Working Drawings, and a Section on Mill Practice.
+
+BY J.W. HALL, A.M.INST.C.E.
+
+ABRIDGED CONTENTS.--The Plant, Machinery, Methods and Chemistry of the
+Bessemer and of the Open Hearth Processes (Acid and Basic).--The
+Mechanical Treatment of Steel comprising Mill Practice, Plant and
+Machinery.--The Influence of Metalloids, Heat Treatment, Special Steels,
+Microstructure, Testing, and Specifications.
+
+       *       *       *       *       *
+
+SECOND EDITION, Revised. Price 16s.
+
+~THE METALLURGY OF IRON.~
+
+BY THOMAS TURNER, ASSOC.R.S.M., F.I.C., _Professor of Metallurgy in the
+University of Birmingham._
+
+In Large 8vo, Handsome Cloth, With Numerous Illustrations (many from
+Photographs).
+
+_General Contents._--Early History of Iron.--Modern History of
+Iron.--The Age of Steel.--Chief Iron Ores.--Preparation of Iron
+Ores.--The Blast Furnace.--The Air used in the Blast Furnace.--Reactions
+of the Blast Furnace.--The Fuel used in the Blast Furnace.--Slags and
+Fluxes of Iron Smelting.--Properties of Cast Iron.--Foundry
+Practice.--Wrought Iron.--Indirect Production of Wrought Iron.--The
+Puddling Process.--Further Treatment of Wrought Iron.--Corrosion of Iron
+and Steel.
+
+"A MOST VALUABLE SUMMARY of knowledge relating to every method and stage
+in the manufacture of cast and wrought iron ... rich in chemical
+details.... EXHAUSTIVE and THOROUGHLY UP-TO-DATE."--_Bulletin of the
+American Iron and Steel Association._
+
+"This is A DELIGHTFUL BOOK, giving, as it does, reliable information on
+a subject becoming every day more elaborate."--_Colliery Guardian._
+
+"A THOROUGHLY USEFUL BOOK, which brings the subject UP TO DATE. OF GREAT
+VALUE to those engaged in the iron industry."--_Mining Journal._
+
+       *       *       *       *       *
+
+*** For Details of WORKS ON MINING, see pages 55-59.
+
+       *       *       *       *       *
+
+~A TEXT-BOOK OF ASSAYING:~
+
+_For the use of Students, Mine Managers, Assayers, &c._
+
+BY J.J. BERINGER, F.I.C., F.C.S., Public Analyst for, and Lecturer to
+the Mining Association of, Cornwall.
+
+AND C. BERINGER, F.C.S., Late Chief Assayer to the Rio Tinto Copper
+Company, London.
+
+With numerous Tables and Illustrations. Crown 8vo. Cloth, 10s. 6d.
+EIGHTH EDITION.
+
+GENERAL CONTENTS.--PART I.--INTRODUCTORY; MANIPULATION: Sampling;
+Drying; Calculation of Results--Laboratory-books and Reports. METHODS:
+Dry Gravimetric; Wet Gravimetric--Volumetric Assays: Titrometric,
+Colorimetric, Gasometric--Weighing and Measuring--Reagents--Formulę,
+Equations, &c.--Specific Gravity.
+
+PART II.--METALS: Detection and Assay of Silver, Gold, Platinum,
+Mercury, Copper, Lead, Thallium, Bismuth, Antimony, Iron, Nickel,
+Cobalt, Zinc, Cadmium, Tin, Tungsten, Titanium, Manganese, Chromium,
+&c.--Earths, Alkalies.
+
+PART III.--NON-METALS: Oxygen and Oxides; The Halogens--Sulphur and
+Sulphates--Arsenic, Phosphorus, Nitrogen--Silicon, Carbon, Boron--Useful
+Tables.
+
+"A REALLY MERITORIOUS WORK, that may be safely depended upon either for
+systematic instruction or for reference."--_Nature._
+
+"This work is one of the best of its kind."--_Engineer._
+
+       *       *       *       *       *
+
+THIRD EDITION, _Revised. Handsome Cloth. With Numerous Illustrations.
+6s._
+
+A TEXT-BOOK OF ~ELEMENTARY METALLURGY.~
+
+Including the Author's Practical Laboratory Course.
+
+BY A. HUMBOLDT SEXTON, F.I.C., F.C.S., Professor of Metallurgy in the
+Glasgow and West of Scotland Technical College.
+
+GENERAL CONTENTS.--Introduction.--Properties of the
+Metals.--Combustion.--Fuels.--Refractory Materials.--Furnaces.--Occurrence
+of the Metals in Nature.--Preparation of the Ore for the
+Smelter.--Metallurgical Processes.--Iron.--Steel.---Copper.--Lead.--Zinc
+and Tin.--Silver.--Gold.--Mercury.--Alloys.--Applications of ELECTRICITY
+to Metallurgy.--LABORATORY COURSE.
+
+"Just the kind of work for Students commencing the study of Metallurgy,
+or for ENGINEERING Students."--_Practical Engineer._
+
+"EXCELLENTLY got-up and WELL-ARRANGED."--_Chemical Trade Journal._
+
+       *       *       *       *       *
+
+In Large 8vo. Handsome Cloth. Price 4s.
+
+~TABLES FOR QUANTITATIVE METALLURGICAL ANALYSIS.~ FOR LABORATORY USE.
+
+_ON THE PRINCIPLE OF "GROUP" SEPARATIONS._
+
+BY J. JAMES MORGAN, F.C.S., M.S.C.I.
+
+"The Author may be CONGRATULATED on the way his work has been carried
+out."--_The Engineer._
+
+"Will COMMEND ITSELF highly in Laboratory Practice. Its CLEARNESS and
+PRECISION mark the book out as a highly useful one."--_Mining Journal._
+
+       *       *       *       *       *
+
+SECOND EDITION, Revised, Enlarged, and in part Re-written. With
+Additional Sections on MODERN THEORIES OF ELECTROLYSIS COSTS, &c. Price
+10s. 6d.
+
+A TREATISE ON ~ELECTRO-METALLURGY:~
+
+Embracing the Application of Electrolysis to the Plating, Depositing,
+Smelting, and Refining of various Metals, and to the Reproduction of
+Printing Surfaces and Art-Work, &c.
+
+BY
+
+WALTER G. McMILLAN, F.I.C., F.C.S., _Secretary to the Institution of
+Electrical Engineers; late Lecturer in Metallurgy at Mason College,
+Birmingham._
+
+With numerous Illustrations. Large Crown 8vo. Cloth.
+
+"This excellent treatise, ... one of the BEST and MOST COMPLETE manuals
+hitherto published on Electro-Metallurgy."--_Electrical Review._
+
+"This work will be a STANDARD."--_Jeweller._
+
+"Any metallurgical process which REDUCES the cost of production must of
+necessity prove of great commercial importance.... We recommend this
+manual to ALL who are interested in the PRACTICAL APPLICATION of
+electrolytic processes."--_Nature._
+
+       *       *       *       *       *
+
+In large 8vo. With Numerous Illustrations and Three Folding-Plates.
+Price 21s.
+
+~ELECTRIC SMELTING & REFINING:~ A Practical Manual of the Extraction and
+Treatment of Metals by Electrical Methods.
+
+Being the "ELEKTRO-METALLURGIE" of DR. W. BORCHERS.
+
+Translated from the Second Edition by WALTER G. McMILLAN, F.I.C.,
+F.C.S
+
+       *       *       *       *       *
+
+CONTENTS.
+
+PART I.--ALKALIES AND ALKALINE EARTH METALS: Magnesium, Lithium,
+Beryllium, Sodium, Potassium, Calcium, Strontium, Barium, the Carbides
+of the Alkaline Earth Metals.
+
+PART II.--THE EARTH METALS: Aluminium, Cerium, Lanthanum, Didymium.
+
+PART III.--THE HEAVY METALS: Copper, Silver, Gold, Zinc and Cadmium,
+Mercury, Tin, Lead, Bismuth, Antimony, Chromium, Molybdenum, Tungsten,
+Uranium, Manganese, Iron, Nickel, and Cobalt, the Platinum Group.
+
+"COMPREHENSIVE and AUTHORITATIVE ... not only FULL of VALUABLE
+INFORMATION, but gives evidence of a THOROUGH INSIGHT into the technical
+VALUE and POSSIBILITIES of all the methods discussed."--_The
+Electrician._
+
+"Dr. BORCHERS' WELL-KNOWN WORK ... must of NECESSITY BE ACQUIRED by
+every one interested in the subject. EXCELLENTLY put into English with
+additional matter by Mr. MCMILLAN."--_Nature._
+
+"Will be of GREAT SERVICE to the practical man and the
+Student."--_Electric Smelting._
+
+       *       *       *       *       *
+
+_In Large 4to, Library Style. Beautifully Illustrated with 20 Plates,
+many in Colours, and 94 Figures in the Text._
+
+~PRECIOUS STONES: Their Properties, Occurrences, and Uses.~
+
+_A Treatise for Dealers, Manufacturers, Jewellers, and for all
+Collectors and others interested in Gems._
+
+BY DR. MAX BAUER, Professor in the University of Marburg,
+
+TRANSLATED BY L.J. SPENCER, M.A. (CANTAB.), F.G.S.
+
+GENERAL CONTENTS.--General Properties of Gems: Their Natural Characters,
+Occurrence, Application, and Uses.--Detailed Description of Particular
+Gems: The Diamond, Rubies, Sapphires; Emeralds, Tourmalines, and Opals;
+Felspars, Amphiboles, Malachite.--Non-mineral Gems: Amber, &c.--Optical
+Features, Transparency, Translucency, Opacity, Refraction and
+Dispersion, &c.--APPENDIX: Pearls; Coral.
+
+       *       *       *       *       *
+
+_In Large Crown 8vo. With Numerous Illustrations. 8s. 6d._
+
+~The Art of the Goldsmith and Jeweller A Manual on the Manipulation of
+Gold and the Manufacture of Personal Ornaments.~
+
+BY THOS. B. WIGLEY, Headmaster of the Jewellers and Silversmiths'
+Association Technical School, Birmingham.
+
+ASSISTED BY J.H. STANSBIE, B.SC. (LOND.), F.I.C., Lecturer at the
+Birmingham Municipal Technical School.
+
+       *       *       *       *       *
+
+GENERAL CONTENTS.--Introduction.--The Ancient Goldsmith's
+Art.--Metallurgy of Gold.--Prices, &c.--Alloys.--Melting,
+Rolling, and Slitting Gold.--The workshop and Tools.--Wire
+Drawing.--Rings.--Chains and Insignia.--Antique Jewellery
+Work.--PRECIOUS STONES.--Cutting.--Polishing and Finishing.--Chasing,
+and its Revival.--Etruscan Embossing, and Repoussé Work.--Colouring
+and Finishing.--Enamelling.--Engraving.--Moulding and
+Casting Ornaments, &c.--Fluxes. &c.--Recovery of the Precious
+Metals.--Refining and Assaying.--Gilding and Electro
+Deposition.--Hall-Marking.--Miscellaneous.--Appendix.
+
+       *       *       *       *       *
+
+~Griffin's Chemical and Technological Publications.~
+
+       *       *       *       *       *
+
+_For Metallurgy and Electro-Metallurgy, see previous Section._
+
+                                                                       PAGE
+~Inorganic Chemistry~,                     PROFS. DUPRÉ AND HAKE,        70
+~Quantitative Analysis~,                   PROF. HUMBOLDT SEXTON,        70
+~Qualitative     "~                               "          "           70
+~Chemistry for Engineers~,                 BLOUNT AND BLOXAM,            71
+     ~"     "  Manufacturers~,                 "         "               71
+~Foods, Analysis of~,                      A. WYNTER BLYTH,              72
+~Poisons, Detection of~,                       "       "                 72
+~Tables for Chemists and Manufacturers~,   PROF. CASTELL-EVANS,          79
+~Agricultural Chemistry~,                  PROF. J.M.H. MUNRO,           75
+~Dairy Chemistry~,                         H. D. RICHMOND,               73
+~Milk~,                                    E.F. WILLOUGHBY,              73
+~Flesh Foods~,                             C.A. MITCHELL,                73
+~Practical Sanitation~,                    DR. G. REID,                  78
+~Sanitary Engineering~,                    F. WOOD,                      78
+~Technical Mycology~,                      LAFAR AND SALTER,             74
+~Ferments~,                                C. OPPENHEIMER,               74
+~Brewing~,                                 DR. W.J. SYKES,               75
+~Sewage Disposal~,                         SANTO CRIMP,                  76
+~Trades' Waste~,                           W. NAYLOR,                    76
+~Cements~,                                 G.R. REDGRAVE,                76
+~Water Supply~,                            R.E. MIDDLETON,               77
+~Road Making~,                             THOS. AITKEN,                 79
+~Gas Manufacture~,                         W. ATKINSON BUTTERFIELD,      77
+~Acetylene~,                               LEEDS AND BUTTERFIELD,        77
+~Fire Risks~,                              DR. SCHWARTZ,                 77
+~Petroleum~,                               REDWOOD AND HOLLOWAY,         61
+~---- (Handbook)~,                         THOMSON AND REDWOOD,          61
+~Oils, Soaps, Candles~,                    DR. ALDER WRIGHT,             81
+~Lubrication and Lubricants~,              ARCHBUTT AND DEELEY,          32
+~India Rubber~,                            DR. CARL O. WEBER,            81
+~Painters' Colours, Oils, and Varnishes~,  G.H. HURST,                   80
+~Painters' Laboratory Guide~,               "     "                      80
+~Painting and Decorating~,                 W.J. PEARCE,                  80
+~Photography~,                             A. BROTHERS,                  21
+~Dyeing~,                                  KNECHT AND RAWSON,            82
+~Dictionary of Dyes~,                      RAWSON, GARDNER, AND LAYCOCK, 82
+~Textile Printing~,                        SEYMOUR ROTHWELL,             83
+~Textile Fibres of Commerce~,              W.I. HANNAN,                  83
+~Dyeing and Cleaning~,                     G.H. HURST,                   84
+~Bleaching and Calico-Printing~,           GEO. DUERR,                   84
+
+       *       *       *       *       *
+
+~A SHORT MANUAL OF INORGANIC CHEMISTRY.~
+
+BY A. DUPRÉ, Ph.D., F.R.S.,
+
+AND
+
+WILSON HAKE, Ph.D., F.I.C., F.C.S., Of the Westminster Hospital Medical
+School
+
+THIRD EDITION, Revised, Enlarged, and Re-issued. Price 6s. net.
+
+"A well-written, clear and accurate Elementary Manual of Inorganic
+Chemistry.... We agree heartily with the system adopted by Drs. Dupré
+and Hake. WILL MAKE EXPERIMENTAL WORK TREBLY INTERESTING BECAUSE
+INTELLIGIBLE."--_Saturday Review._
+
+"There is no question that, given the PERFECT GROUNDING of the Student
+in his Science, the remainder comes afterwards to him in a manner much
+more simple and easily acquired. The work is AN EXAMPLE OF THE
+ADVANTAGES OF THE SYSTEMATIC TREATMENT of a Science over the fragmentary
+style so generally followed. BY A LONG WAY THE BEST of the small Manuals
+for Students."--_Analyst._
+
+       *       *       *       *       *
+
+~LABORATORY HANDBOOKS BY A. HUMBOLDT SEXTON,~
+
+Professor of Metallurgy in the Glasgow and West of Scotland Technical
+College.
+
+       *       *       *       *       *
+
+~OUTLINES OF QUANTITATIVE ANALYSIS.~
+
+_FOR THE USE OF STUDENTS._
+
+With Illustrations. FOURTH EDITION. Crown 8vo, Cloth, 3s.
+
+"A COMPACT LABORATORY GUIDE for beginners was wanted, and the want has
+been WELL SUPPLIED.... A good and useful book."--_Lancet_.
+
+       *       *       *       *       *
+
+~OUTLINES OF QUALITATIVE ANALYSIS.~
+
+_FOR THE USE OF STUDENTS._
+
+With Illustrations. FOURTH EDITION, Revised. Crown 8vo, Cloth, 3s. 6d.
+
+"The work of a thoroughly practical chemist."--_British Medical
+Journal._
+
+"Compiled with great care, and will supply a want."--_Journal of
+Education._
+
+       *       *       *       *       *
+
+~ELEMENTARY METALLURGY:~ Including the Author's Practical Laboratory
+Course. With many Illustrations. [See p. 66.
+
+THIRD EDITION, Revised. Crown 8vo. Cloth, 6s.
+
+"Just the kind of work for students commencing the study of
+metallurgy."--_Practical Engineer._
+
+       *       *       *       *       *
+
+~CHEMISTRY FOR ENGINEERS AND MANUFACTURERS.~
+
+A PRACTICAL TEXT-BOOK.
+
+BY
+
+BERTRAM BLOUNT, F.I.C., F.C.S., Assoc.Inst.C.E., Consulting Chemist to
+the Crown Agents for the Colonies.
+
+AND
+
+A.G. BLOXAM, F.I.C., F.C.S., Consulting Chemist, Head of the Chemistry
+Department, Goldsmiths' Inst., New Cross.
+
+In Two Vols., Large 8vo. With Illustrations. Sold Separately.
+
+       *       *       *       *       *
+
+"The authors have SUCCEEDED beyond all expectations, and have
+produced a work which should give FRESH POWER to the Engineer and
+Manufacturer."--_The Times_.
+
+       *       *       *       *       *
+
+~VOLUME I. Price 10s. 6d.~
+
+CHEMISTRY OF ENGINEERING, BUILDING, AND METALLURGY.
+
+_General Content._--INTRODUCTION--Chemistry of the Chief Materials of
+Construction--Sources of Energy--Chemistry of Steam-raising--Chemistry
+of Lubrication and Lubricants--Metallurgical Processes used in the
+Winning and Manufacture of Metals.
+
+"PRACTICAL THROUGHOUT ... an ADMIRABLE TEXT-BOOK, useful not only to
+Students, but to ENGINEERS and MANAGERS OF WORKS in PREVENTING WASTE and
+IMPROVING PROCESSES."--_Scotsman._
+
+"EMINENTLY PRACTICAL."--_Glasgow Herald._
+
+"A book worthy of HIGH RANK ... its merit is great ... treatment of the
+subject of GASEOUS FUEL particularly good.... WATER GAS and the
+production clearly worked out.... Altogether a most creditable
+production. WE WARMLY RECOMMEND IT, and look forward with keen interest
+to the appearance of Vol. II."--_Journal of Gas Lighting._
+
+~VOLUME II. Price 16s.~
+
+THE CHEMISTRY OF MANUFACTURING PROCESSES.
+
+_General Contents._--Sulphuric Acid Manufacture--Manufacture of
+Alkali, &c.--Destructive Distillation--Artificial Manure
+Manufacture--Petroleum--Lime and Cement--Clay Industries and
+Glass--Sugar and Starch--Brewing and Distilling--Oils, Resins, and
+Varnishes--Soap and Candles--Textiles and Bleaching--Colouring Matters,
+Dyeing, and Printing--Paper and Pasteboard--Pigments and
+Paints--Leather, Glue, and Size--Explosives and Matches--Minor Chemical
+Manufactures.
+
+"Certainly a GOOD and USEFUL BOOK, constituting a PRACTICAL GUIDE for
+students by affording a clear conception of the numerous processes as a
+whole."--_Chemical Trade Journal._
+
+"We CONFIDENTLY RECOMMEND this volume as a PRACTICAL, and not
+overloaded, TEXT-BOOK, of GREAT VALUE to students."--_The Builder._
+
+       *       *       *       *       *
+
+JUST OUT. FIFTH EDITION, Thoroughly Revised, Greatly Enlarged and
+Re-written. With additional Tables, Plates, and Illustrations. 21s.
+~FOODS: THEIR COMPOSITION AND ANALYSIS.~
+
+BY A. WYNTER BLYTH, M.R.C.S., F.I.C., F.C.S.,
+
+Barrister-at-Law, Public Analyst for the County of Devon, and Medical
+Officer of Health for St. Marylebone.
+
+AND M. WYNTER BLYTH, B.A., B.SC., F.C.S.
+
+GENERAL CONTENTS.--History of
+Adulteration.--Legislation.--Apparatus.--"Ash."--Sugar.--Confectionery.--
+Honey.--Treacle.--Jams and Preserved Fruits.--Starches.--Wheaten-Flour.--
+Bread.--Oats.--Barley.--Rye.--Rice.--Maize.--Millet.--Potato.--Peas.--
+Lentils.--Beans.--Milk.--Cream.--Butter.--Oleo-Margarine.--Cheese.--
+Lard.--Tea.--Coffee.--Cocoa and Chocolate.--Alcohol.--Brandy.--Rum.--
+Whisky.--Gin.--Arrack.--Liqueurs.--Absinthe.--Yeast.---Beer.--Wine.--
+Vinegar.--Lemon and Lime Juice.--Mustard.--Pepper.--Sweet and Bitter
+Almonds.--Annatto.--Olive Oil.--Water Analysis.--Appendix: Adulteration
+Acts, &c.
+
+"Simply INDISPENSABLE in the Analyst's laboratory."--_The Lancet._
+
+"A new edition of Mr. Wynter Blyth's Standard work, ENRICHED WITH ALL
+THE RECENT DISCOVERIES AND IMPROVEMENTS, will be accepted as a
+boon."--_Chemical News._
+
+       *       *       *       *       *
+
+THIRD EDITION. In Large 8vo, Cloth, with Tables and Illustrations. Price
+21s.
+
+~POISONS: THEIR EFFECTS AND DETECTION.~
+
+BY A. WYNTER BLYTH, M.R.C.S., F.I.C., F.C.S.,
+
+Barrister-at-Law, Public Analyst for the County of Devon, and Medical
+Officer of Health for St. Marylebone.
+
+GENERAL CONTENTS.
+
+I.--Historical Introduction. II.--Classification--Statistics--Connection
+between Toxic Action and Chemical Composition--Life Tests--General
+Method of Procedure--The Spectroscope--Examination of Blood and Blood
+Stains. III.--Poisonous Gases. IV.--Acids and Alkalies. V.--More or less
+Volatile Poisonous Substances. VI.--Alkaloids and Poisonous Vegetable
+Principles. VII.--Poisons derived from Living or Dead Animal Substances.
+VIII.--The Oxalic Acid Group. IX.--Inorganic Poisons. Appendix:
+Treatment, by Antidotes or otherwise, of Cases of Poisoning.
+
+"Undoubtedly THE MOST COMPLETE WORK on Toxicology in our
+language."--_The Analyst (on the Third Edition)._
+
+"As a PRACTICAL GUIDE, we know NO BETTER work."--_The Lancet (on the
+Third Edition)._
+
+*** In the THIRD EDITION, Enlarged and partly Re-written, NEW ANALYTICAL
+METHODS have been introduced, and the CADAVERIC ALKALOIDS, or PTOMAINES,
+bodies playing so great a part in Food-poisoning and in the
+Manifestations of Disease, have received special attention.
+
+       *       *       *       *       *
+
+With Numerous Tables, and 22 Illustrations. 16s.
+
+~DAIRY CHEMISTRY FOR DAIRY MANAGERS, CHEMISTS, AND ANALYSTS~
+
+A Practical Handbook for Dairy Chemists and others having Control of
+Dairies.
+
+BY H. DROOP RICHMOND, F.C.S., CHEMIST TO THE AYLESBURY DAIRY COMPANY.
+
+_Contents._--I. Introductory.--The Constituents of Milk. II. The
+Analysis of Milk. III. Normal Milk: its Adulterations and
+and their Detection. IV. The Chemical Control of the Dairy. V.
+Alterations, Biological and Sanitary Matters. VI. Butter. VII.
+Other Milk Products. VIII. The Milk of Mammals other than the
+Cow.--Appendices.--Tables.--Index.
+
+" ... In our opinion the book is the BEST CONTRIBUTION ON THE SUBJECT
+THAT HAS YET APPEARED in the English language."--_Lancet._
+
+       *       *       *       *       *
+
+AT PRESS, Fully Illustrated.
+
+~MILK: ITS PRODUCTION & USES.~
+
+_With Chapters on Dairy Farming, The Diseases of Cattle, and on the
+Hygiene and Control of Supplies._
+
+BY EDWARD F. WILLOUGHBY, M.D. (Lond.), D.P.H. (Lond. and Camb.),
+Inspector of Farms and General Scientific Adviser to Welford and Sons,
+Ltd.
+
+       *       *       *       *       *
+
+Crown 8vo, Handsome Cloth. Fully Illustrated. 10s. 6d.
+
+~FLESH FOODS: With Methods for their Chemical, Microscopical, and
+Bacteriological Examination.~
+
+_A Practical Handbook for Medical Men, Analysts, Inspectors and others._
+
+BY C. AINSWORTH MITCHELL, B.A.(OXON), Fellow of the Institute of
+Chemistry; Member of Council, Society of Public Analysts.
+
+_With Numerous Tables, Illustrations, and a Coloured Plate._
+
+CONTENTS.--Structure and Chemical Composition of Muscular Fibre.--of
+Connective Tissue, and Blood.--The Flesh of Different Animals.--The
+Examination of Flesh.--Methods of Examining Animal Fat.--The
+Preservation of Flesh.--Composition and Analysis of Sausages.--Proteids
+of Flesh.--Meat Extracts and Flesh Peptones.--The Cooking of
+Flesh.--Poisonous Flesh.--The Animal Parasites of Flesh.--The
+Bacteriological Examination of Flesh.--The Extraction and Separation of
+Ptomaines.--INDEX.
+
+*** This work is a complete compendium of the CHEMISTRY OF ANIMAL
+TISSUES. It contains directions for the detection of morbid conditions,
+putrefactive changes, and poisonous or injurious constituents, together
+with an account of their causes and effects.--_Publishers' Note._
+
+"A compilation which will be most useful for the class for whom it is
+intended."--_Athenęum._
+
+"A book which NO ONE whose duties involve considerations of food supply
+CAN AFFORD TO BE WITHOUT."--_Municipal Journal._
+
+       *       *       *       *       *
+
+In Large 8vo. Handsome Cloth. With numerous Illustrations.
+
+_Each Volume Complete in Itself, and Sold Separately._
+
+~TECHNICAL MYCOLOGY:~ THE UTILISATION OF MICRO-ORGANISMS IN THE ARTS AND
+MANUFACTURES.
+
+_A Practical Handbook on Fermentation and Fermentative Processes for the
+Use of Brewers and Distillers, Analysts, Technical and Agricultural
+Chemists, and all interested in the Industries dependent on
+Fermentation._
+
+BY DR. FRANZ LAFAR,
+
+Professor of Fermentation-Physiology and Bacteriology in the Technical
+High School, Vienna.
+
+With an Introduction by DR. EMIL CHR. HANSEN, Principal of the Carlsberg
+Laboratory, Copenhagen.
+
+TRANSLATED BY CHARLES T.C. SALTER.
+
+~Vol. I.--SCHIZOMYCETIC FERMENTATION.~ 15s.
+
+_Including the Theory of Fermentation, the Principles of Sterilization,
+and Pure Culture Processes._
+
+~Vol. II., Part I. EUMYCETIC FERMENTATION.~ 7s. 6d.
+
+_The Morphology, Chemistry, Physiology, and Fermentative Processes of
+the Eumycetes, Zygomycetes, and Saccharomycetes._
+
+"The first work of the kind which can lay claim to completeness in the
+treatment of a fascinating subject. The plan is admirable, the
+classification simple, the style is good, and the tendency of the whole
+volume is to convey sure information to the reader."--_Lancet_.
+
+*** The publishers trust that before long they will be able to present
+English readers with the whole of the second volume, arrangements having
+been concluded whereby, upon its appearance in Germany, the English
+translation will be at once put in hand. This is now being done with
+Part I., which will be issued shortly, and which will be followed by the
+two final parts.
+
+       *       *       *       *       *
+
+In Crown 8vo, Handsome Cloth. Price 7s. 6d. net.
+
+~_FERMENTS_ AND THEIR ACTIONS.~
+
+_A Text-book on the Chemistry and Physics of Fermentative Changes._
+
+BY CARL OPPENHEIMER, PH.D., M.D., Of the Physiological Institute at
+Eilangen.
+
+TRANSLATED FROM THE GERMAN BY C. AINSWORTH MITCHELL, B.A., F.I.C.,
+F.C.S.
+
+ABRIDGED CONTENTS.--Introduction.--Definition.--Chemical Nature of
+Ferments.--Influence of External Factors.--Mode of Action.--Physiological
+Action.--Secretion.--Importance of Ferments to Vital Action.--Proteolytic
+Ferments.--Trypsin.--Bacteriolytic and Hęmolytic
+Ferments.--Vegetable Ferments.--Coagulating Ferments.--Saccharifying
+Ferments.--Diastases.--Polysaccharides.--Enzymes.--Ferments which
+decompose Glucosides.--Hydrolytic Ferments.--Lactic Acid
+Fermentation.--Alcoholic Fermentation.--Biology of Alcoholic
+Fermentation.--Oxydases.--Oxidising Fermentation.--Bibliography.--INDEX.
+
+~The present Translation embodies Notes and Additions to the Work made
+by the Author subsequent to its Publication in Germany.~
+
+"Such a veritable _multum in parvo_ has never yet appeared. The author
+has set himself the task of writing a work on Ferments that should
+embrace human erudition on the subject"--_Brewers' Journal_.
+
+       *       *       *       *       *
+
+SECOND EDITION, Revised. In Large 8vo. Handsome Cloth. With Plate and
+Illustrations. Price 21s.
+
+~THE PRINCIPLES AND PRACTICE OF BREWING.~
+
+FOR THE USE OF STUDENTS AND PRACTICAL MEN.
+
+BY
+
+WALTER J. SYKES, M.D., D.P.H., F.I.C.,
+
+EDITOR OF "THE ANALYST."
+
+ABSTRACT OF CONTENTS.
+
+  I. Physical Principles involved in Brewing Operations.
+  Chemistry with special reference to the materials used in Brewing.
+
+  II. The Microscope.
+  Vegetable Biology.
+  Fermentation.
+
+  III. Water.
+  Barley and Malting.
+  Brewery Plant.
+  Brewing.
+  Beer and its Diseases.
+
+  Appendices.
+
+  Index.
+
+"A volume of Brewing Science, which has long been awaited.... We
+consider it one of THE MOST COMPLETE in CONTENTS and NOVEL IN
+ARRANGEMENT that has yet been published.... Will command a large
+sale."--_The Brewers' Journal._
+
+"The appearance of a work such as this serves to remind us of the
+ENORMOUSLY RAPID ADVANCES made in our knowledge of the Scientific
+Principles underlying the Brewing Processes.... Dr. Sykes' work will
+undoubtedly be of the GREATEST ASSISTANCE, not merely to Brewers, but to
+all Chemists and Biologists interested in the problems which the
+Fermentation Industries present."--_The Analyst._
+
+"The publication of DR. SYKES' MASTERLY TREATISE on the art of Brewing
+is quite an event in the Brewing World.... Deserves our warmest
+praise.... A better guide than Dr. Sykes could hardly be
+found."--_County Brewers' Gazette._
+
+       *       *       *       *       *
+
+In Large 8vo. Handsome Cloth.
+
+~AGRICULTURAL CHEMISTRY AND ANALYSIS:~
+
+_A PRACTICAL HANDBOOK FOR THE USE OF AGRICULTURAL STUDENTS._
+
+BY
+
+J.M.H. MUNRO, D.Sc., F.I.C., F.C.S.,
+
+Professor of Chemistry, Downton College of Agriculture.
+
+[_In Preparation._
+
+       *       *       *       *       *
+
+SECOND EDITION, REVISED AND ENLARGED.
+
+With Tables, Illustrations in the Text, and 37 Lithographic Plates.
+Medium 8vo. Handsome Cloth. 30s.
+
+~SEWAGE DISPOSAL WORKS:~
+
+A Guide to the Construction of Works for the Prevention of the Pollution
+by Sewage of Rivers and Estuaries.
+
+BY W. SANTO CRIMP, M.INST.C.E., F.G.S., Late Assistant-Engineer, London
+County Council.
+
+PART I.--INTRODUCTORY. PART II.--SEWAGE DISPOSAL WORKS IN
+OPERATION--THEIR CONSTRUCTION, MAINTENANCE, AND COST.
+
+*** From the fact of the Author's having, for some years, had charge of
+the Main Drainage Works of the Northern Section of the Metropolis, the
+chapter on LONDON will be found to contain many important details which
+would not otherwise have been available.
+
+"All persons interested in Sanitary Science owe a debt of gratitude to
+Mr. Crimp.... His work will be especially useful to SANITARY AUTHORITIES
+and their advisers ... EMINENTLY PRACTICAL AND USEFUL."--_Lancet._
+
+"Probably the MOST COMPLETE AND BEST TREATISE on the subject which has
+appeared in our language.... Will prove of the greatest use to all who
+have the problem of Sewage Disposal to face."--_Edinburgh Medical
+Journal._
+
+       *       *       *       *       *
+
+_Beautifully Illustrated, with Numerous Plates, Diagrams, and Figures in
+the Text. 21s. net._
+
+~TRADES' WASTE: ITS TREATMENT AND UTILISATION.~
+
+A Handbook for Borough Engineers, Surveyors, Architects, and Analysts.
+
+BY W. NAYLOR, F.C.S., A.M.INST.C.E., Chief Inspector of Rivers, Ribble
+Joint Committee.
+
+CONTENTS.--I. Introduction.--II. Chemical Engineering.--III.--Wool
+De-greasing and Grease Recovery.--IV. Textile Industries; Calico
+Bleaching and Dyeing.--V. Dyeing and Calico-Printing,--VI. Tanning and
+Fellmongery.--VII. Brewery and Distillery Waste.--VIII. Paper Mill
+Refuse.--IX. General Trades' Waste.--INDEX.
+
+"There is probably no person in England to-day better fitted to deal
+rationally with such a subject."--_British Sanitarian._
+
+"The work is thoroughly practical, and will serve as a handbook in the
+future for those who have to encounter the problems
+discussed."--_Chemical Trade Journal._
+
+       *       *       *       *       *
+
+In Crown 8vo, Extra. With Illustrations. 8s. 6d.
+
+~CALCAREOUS CEMENTS: _THEIR NATURE, PREPARATION, AND USES_.~
+
+~With some Remarks upon Cement Testing.~
+
+BY GILBERT R. REDGRAVE, ASSOC. INST. C.E., Assistant Secretary for
+Technology, Board of Education, South Kensington.
+
+"INVALUABLE to the Student, Architect, and Engineer."--_Building News._
+
+"Will be useful to all interested in the MANUFACTURE, USE, and TESTING
+of Cements."--_Engineer._
+
+       *       *       *       *       *
+
+Just Out. With Four Folding Plates and Numerous Illustrations. Large
+8vo.
+
+~WATER SUPPLY:~
+
+_A Practical Treatise on the Selection of Sources and the Distribution
+of Water._
+
+BY REGINALD E. MIDDLETON, M.INST.C.E., M.INST.MECH.E., F.S.I.
+
+ABRIDGED CONTENTS.--Introductory.--Requirements as to
+Quality.--Requirements as to Quantity.--Storage
+Reservoirs.--Purification.--Service Reservoirs.--The Flow of Water
+through Pipes.--Distributing Systems.--Pumping Machines.--Special
+Requirements.
+
+       *       *       *       *       *
+
+THIRD EDITION, Revised. Fully Illustrated. _At Press._
+
+THE CHEMISTRY OF ~GAS MANUFACTURE:~
+
+_A Hand-Book on the Production, Purification, and Testing of
+Illuminating Gas, and the Assay of the Bye-Products of Gas Manufacture._
+
+BY W.J. ATKINSON BUTTERFIELD, M.A., F.I.C., F.C.S., Formerly Head
+Chemist, Gas Works, Beckton, London, E.
+
+GENERAL CONTENTS.--I. Raw Materials for Gas Manufacture.--II. Coal
+Gas.--III. Carburetted Water Gas.--IV. Oil Gas.--V. Enriching by Light
+Oils.--VI. Final Details of Manufacture.--VII. Gas Analysis.--VIII.
+Photometry.--IX. Applications of Gas.--X. Bye-Products.--XI.
+Acetylene.--INDEX.
+
+"The BEST WORK of its kind which we have ever had the pleasure of
+reviewing."--_Journal of Gas Lighting_.
+
+       *       *       *       *       *
+
+JUST OUT. With Diagrams and Illustrations. 5s. net.
+
+~ACETYLENE:~
+
+THE PRINCIPLES OF ITS GENERATION AND USE.
+
+BY F.H. LEEDS, F.I.C., F.C.S., Member of the Society of Public Analysts
+and of the Acetylene Association;
+
+AND W.J. ATKINSON BUTTERFIELD, M.A., F.I.C., F.C.S., Consulting Chemist,
+Author of "The Chemistry of Gas Manufacture."
+
+GENERAL CONTENTS.--Introductory.--Advantages of Acetylene and other
+Illuminants.--Chemistry and Physics.--General Principles of Acetylene
+Generation.--Choice of a Generator.--Statutory Regulations.--Treatment
+of Acetylene after Generation.--General Properties.--Mains and Service
+Pipes.--Subsidiary Apparatus.--Burners.--Incandescent Burners.--Heating
+Apparatus and Motors.--Carburetted, Compressed, and Dissolved
+Acetylene.--Mixtures with other Gases.--Sundry Uses.--Acetylene
+Lamps.--Valuation and Analysis of Carbide.
+
+       *       *       *       *       *
+
+READY IMMEDIATELY. Large 8vo. Handsome Cloth. Price 16s. net.
+
+~FIRE AND EXPLOSION RISKS.~
+
+_A Handbook of the Detection, Investigation, and Prevention of Fires and
+Explosion._
+
+BY DR. VON SCHWARTZ.
+
+Translated from the Revised German Edition BY C.T.C. SALTER.
+
+ABRIDGED GENERAL CONTENTS.--Fires and Explosions of a General
+Character.--Dangers arising from Sources of Light and Heat.--Dangerous
+Gases.--Risks Attending Special Industries.--Materials
+Employed.--Agricultural Products.--Fats, Oils, and Resins.--Mineral Oils
+and Tar.--Alcohol, &c.--Metals, Oxides, Acids, &c.--Lightning, Ignition
+Appliances, Fireworks.
+
+       *       *       *       *       *
+
+TENTH EDITION, Revised. Price 6s.
+
+~PRACTICAL SANITATION: _A HAND-BOOK FOR SANITARY INSPECTORS AND OTHERS
+INTERESTED IN SANITATION._~
+
+BY GEORGE REID, M.D., D.P.H., _Fellow, Mem. Council, and Examiner,
+Sanitary Institute of Great Britain, and Medical Officer to the
+Staffordshire County Council._
+
+~With an Appendix on Sanitary Law.~
+
+BY HERBERT MANLEY, M.A., M.B., D.P.H., _Medical Officer of Health for
+the County Borough of West Bromwich._
+
+GENERAL CONTENTS.--Introduction--Water Supply: Drinking Water, Pollution
+of Water--Ventilation and Warming--Principles of Sewage Removal--Details
+of Drainage; Refuse Removal and Disposal--Sanitary and Insanitary Work
+and Appliances--Details of Plumbers' Work--House Construction--Infection
+and Disinfection--Food, Inspection of; Characteristics of Good Meat;
+Meat, Milk, Fish, &c., unfit for Human Food--Appendix: Sanitary Law;
+Model Bye-Laws, &c.
+
+"Dr. Reid's very useful Manual ... ABOUNDS IN PRACTICAL
+DETAIL."--_British Medical Journal_.
+
+"A VERY USEFUL HANDBOOK, with a very useful Appendix. We recommend it
+not only to SANITARY INSPECTORS, but to HOUSEHOLDERS and ALL interested
+in Sanitary matters."--_Sanitary Record_.
+
+       *       *       *       *       *
+
+COMPANION VOLUME TO REID'S SANITATION.
+
+In Crown 8vo. Handsome Cloth. Profusely Illustrated. 8s. 6d. net.
+
+~Sanitary Engineering:~ _A Practical Manual of Town Drainage and Sewage
+and Refuse Disposal._
+
+For Sanitary Authorities, Engineers, Inspectors, Architects,
+Contractors, and Students.
+
+BY
+
+FRANCIS WOOD, A.M.INST.C.E., F.G.S., Borough Engineer and Surveyor,
+Fulham; late Borough Engineer, Bacup, Lancs.
+
+GENERAL CONTENTS.
+
+Introduction.--Hydraulics.--Velocity of Water in Pipes.--Earth
+Pressures and Retaining Walls.--Powers.--House Drainage.--Land
+Drainage.--Sewers.--Separate System.--Sewage Pumping.--Sewer
+Ventilation.--Drainage Areas.--Sewers, Manholes, &c.--Trade
+Refuse.--Sewage Disposal Works.--BACTERIOLYSIS.--Sludge
+Disposal.--Construction and Cleansing of Sewers.--Refuse
+Disposal.--Chimneys and Foundations.
+
+"The volume bristles with information which will be greedily read by
+those in need of assistance. The book is one that ought to be on the
+bookshelves of EVERY PRACTICAL ENGINEER."--_Sanitary Journal_.
+
+"A VERITABLE POCKET COMPENDIUM of Sanitary Engineering.... A work which
+may, in many respects, be considered as COMPLETE ... COMMENDABLY
+CAUTIOUS ... INTERESTING ... SUGGESTIVE."--_Public Health Engineer_.
+
+       *       *       *       *       *
+
+VOL. I. NOW READY. IN HALF MOROCCO, 24S.
+
+_In Two Volumes, each complete in itself._
+
+~PHYSICO-CHEMICAL TABLES~
+
+FOR THE USE OF ANALYSTS, PHYSICISTS, CHEMICAL MANUFACTURERS, AND
+SCIENTIFIC CHEMISTS.
+
+Volume I.--Chemical Engineering, Physical Chemistry. [_Just Out._
+
+Volume II.--Chemical Physics, Pure and Analytical Chemistry.
+
+BY JOHN CASTELL-EVANS, F.I.C., F.C.S., Superintendent of the Chemical
+Laboratories, and Lecturer on Inorganic Chemistry and Metallurgy at the
+Finsbury Technical College.
+
+The Tables may almost claim to be exhaustive, and embody and collate all
+the most recent data established by experimentalists at home and abroad.
+The volumes will be found invaluable to all engaged in research and
+experimental investigation in Chemistry and Physics.
+
+The Work comprehends as far as possible ALL RULLES AND TABLES required
+by the Analyst, Brewer, Distiller, Acid- and Alkali-Manufacturer, &c.,
+&c.; and also the principal data in THERMO-CHEMISTRY, ELECTRO-CHEMISTRY,
+and the various branches of CHEMICAL PHYSICS. Every possible care has
+been taken to ensure perfect accuracy, and to include the results of the
+most recent investigations.
+
+       *       *       *       *       *
+
+_In Large 8vo. Handsome Cloth. Beautifully Illustrated. With Plates and
+Figures in the Text._ 21s.
+
+~Road Making and Maintenance:~
+
+A PRACTICAL TREATISE FOR ENGINEERS, SURVEYORS, AND OTHERS.
+
+WITH AN HISTORICAL SKETCH OF ANCIENT AND MODERN PRACTICE.
+
+BY THOS. AITKEN, ASSOC.M.INST.C.E., Member of the Association of
+Municipal and County Engineers; Member of the Sanitary Inst.; Surveyor
+to the County Council of Fife, Cupar Division.
+
+_WITH NUMEROUS PLATES, DIAGRAMS, AND ILLUSTRATIONS._
+
+CONTENTS.--Historical Sketch.--Resistance of Traction.--Laying out New
+Roads.--Earthworks, Drainage, and Retaining Walls.--Road Materials, or
+Metal.--Quarrying.--Stone Breaking and Haulage.--Road-Rolling and
+Scarifying.--The Construction of New, and the Maintenance of existing
+Roads.--Carriage Ways and Foot Ways.
+
+"The Literary style is EXCELLENT ... A COMPREHENSIVE and EXCELLENT
+Modern Book, an UP-TO-DATE work ... Should be on the reference shelf of
+every Municipal and County Engineer or Surveyor in the United Kingdom,
+and of every Colonial Engineer."--_The Surveyor_.
+
+       *       *       *       *       *
+
+THIRD EDITION, Revised and Enlarged. With Illustrations, 12s. 6d.
+
+~Painters' Colours, Oils, & Varnishes:~
+
+~A PRACTICAL MANUAL.~
+
+BY GEORGE H. HURST, F.C.S., Member of the Society of Chemical Industry;
+Lecturer on the Technology of Painters' Colours, Oils, and Varnishes,
+the Municipal Technical School, Manchester.
+
+GENERAL CONTENTS.--Introductory--THE COMPOSITION, MANUFACTURE, ASSAY,
+and ANALYSIS of PIGMENTS, White, Red, Yellow and Orange, Green, Blue,
+Brown, and Black--LAKES--Colour and Paint Machinery--Paint Vehicles
+(Oils, Turpentine, &c., &c.)--Driers--VARNISHES.
+
+"A THOROUGHLY PRACTICAL book, ... the ONLY English work that
+satisfactorily treats of the manufacture of oils, colours, and
+pigments."--_Chemical Trades' Journal_.
+
+*** FOR MR. HURST'S GARMENT DYEING AND CLEANING, see p. 84.
+
+       *       *       *       *       *
+
+In Crown 8vo. Handsome Cloth. With Illustrations. 5s.
+
+~THE PAINTER'S LABORATORY GUIDE.~
+
+A Student's Handbook of Paints, Colours, and Varnishes.
+
+BY GEORGE H. HURST, F.C.S., M.S.C.I.
+
+ABSTRACT OF CONTENTS.--Preparation of Pigment Colours.--Chemical
+Principles Involved.--Oils and Varnishes.--Properties of Oils and
+Varnishes.--Tests and Experiments.--Plants, Methods, and Machinery of
+the Paint and Varnish Manufactures.
+
+_This Work has been designed by the Author for the Laboratory of the
+Technical School, and of the Paint and Colour Works, and for all
+interested or engaged in these industries._
+
+       *       *       *       *       *
+
+SECOND EDITION, Revised. In Crown 8vo. extra. With Numerous
+Illustrations and Plates (some in Colours), including Original Designs.
+12s. 6d.
+
+~Painting and Decorating:~
+
+_A Complete Practical Manual for House Painters and Decorators._
+
+BY WALTER JOHN PEARCE,
+
+LECTURER AT THE MANCHESTER TECHNICAL SCHOOL FOR HOUSE-PAINTING AND
+DECORATING.
+
+GENERAL CONTENTS.
+
+Introduction--Workshop and Stores--Plant and Appliances--Brushes and
+Tools--Materials: Pigments, Driers, Painters' Oils--Wall Hangings--Paper
+Hanging--Colour Mixing--Distempering--Plain Painting--Staining--Varnish
+and Varnishing--Imitative
+Painting--Graining--Marbling--Gilding--Sign-Writing and
+Lettering--Decoration: General Principles--Decoration in
+Distemper--Painted Decoration--Relievo Decoration--Colour--Measuring and
+Estimating--Coach-Painting--Ship-Painting.
+
+"A THOROUGHLY USEFUL BOOK ... GOOD, SOUND, PRACTICAL INFORMATION in a
+CLEAR and CONCISE FORM."--_Plumber and Decorator_.
+
+"A THOROUGHLY GOOD AND RELIABLE TEXT-BOOK.... So FULL and COMPLETE that
+it would be difficult to imagine how anything further could be added
+about the Painter's craft."--_Builders' Journal_.
+
+       *       *       *       *       *
+
+In Large 8vo. Handsome Cloth. With 4 Plates and Several Illustrations.
+16s. net.
+
+~THE CHEMISTRY OF INDIA RUBBER.~
+
+A Treatise on the Nature of India Rubber, its Chemical and Physical
+Examination, and the Determination and Valuation of India Rubber
+Substitutes.
+
+_Including the Outlines of a Theory on Vulcanisation._
+
+BY
+
+CARL OTTO WEBER, PH.D.
+
+ABSTRACT OF CONTENTS.--Introduction.--The Chemistry of India
+Rubber.--The Examination and Valuation of India Rubber.--Examination of
+India Rubber Substitutes.--Inorganic Filling Materials.--Vulcanisers and
+Sulphur Carriers.--India Rubber Solvents.--Colouring Matters and Pigment
+Colours.--Constructive Components of India Rubber Articles.--Analysis of
+Manufactured India Rubber.--Sanitary Conditions in India Rubber
+Works.--INDEX.
+
+"Replete with scientific and also with technical interest.... The
+sub-section on the physical properties is a complete _résumé_ of every
+thing known to-day on the subject."--_India-rubber Journal_.
+
+       *       *       *       *       *
+
+NEW EDITION. In Large 8vo. Handsome Cloth. With 144 Illustrations.
+
+~OILS, FATS, BUTTERS & WAXES:~ _THEIR PREPARATION AND PROPERTIES, AND
+MANUFACTURE THEREFROM OF CANDLES, SOAPS, AND OTHER PRODUCTS._
+
+BY
+
+C.R. ALDER WRIGHT, D.Sc., F.R.S., Late Lecturer on Chemistry, St. Mary's
+Hospital Medical School; Examiner in "Soap" to the City and Guilds of
+London Institute.
+
+Thoroughly Revised, Enlarged, and in Part Rewritten
+
+BY C. AINSWORTH MITCHELL, B.A., F.I.C.
+
+"Dr. WRIGHT'S work will be found ABSOLUTELY INDISPENSABLE by every
+Chemist. TEEMS with information valuable alike to the Analyst and the
+Technical Chemist."--_The Analyst_.
+
+"Will rank as the STANDARD ENGLISH AUTHORITY on OILS and FATS for many
+years to come."--_Industries and Iron_.
+
+       *       *       *       *       *
+
+~THE TEXTILE INDUSTRIES.~
+
+       *       *       *       *       *
+
+_In Two Large Volumes, 920 pp., with a Supplementary Volume, containing
+Specimens of Dyed Fabrics. 45s._
+
+~A MANUAL OF DYEING: _FOR THE USE OF PRACTICAL DYERS, MANUFACTURERS,
+STUDENTS, AND ALL INTERESTED IN THE ART OF DYEING._~
+
+BY
+
+E. KNECHT, Ph.D., F.I.C., Head of the Chemistry and Dyeing Department of
+the Technical College, Manchester; Editor of "The Journal of the Society
+of Dyers and Colourists;"
+
+CHR. RAWSON, F.I.C., F.C.S., Late Head of the Chemistry and Dyeing
+Department of the Technical College, Bradford; Member of Council of the
+Society of Dyers and Colourists;
+
+And RICHARD LOEWENTHAL, Ph.D.
+
+       *       *       *       *       *
+
+GENERAL CONTENTS.--Chemical Technology of the Textile
+Fabrics--Water--Washing and Bleaching--Acids, Alkalies,
+Mordants--Natural Colouring Matters--Artificial Organic Colouring
+Matters--Mineral Colours--Machinery used in Dyeing--Tinctorial
+Properties of Colouring Matters--Analysis and Valuation of Materials
+used in Dyeing, &c., &c.
+
+"The MOST VALUABLE and USEFUL WORK on Dyeing that has yet appeared in
+the English language ... likely to be the STANDARD WORK OF REFERENCE for
+years to come."--_Textile Mercury_.
+
+"This authoritative and exhaustive work ... the MOST COMPLETE we have
+yet seen on the subject."--_Textile Manufacturer._
+
+"The MOST EXHAUSTIVE AND COMPLETE WORK on the subject extant."--_Textile
+Recorder._
+
+       *       *       *       *       *
+
+_Companion Volume to Knecht & Rawson's "Dyeing." In Large 8vo. Handsome
+Cloth, Library Style. 16s. net._
+
+~A DICTIONARY OF DYES, MORDANTS, & OTHER COMPOUNDS USED IN DYEING AND
+CALICO PRINTING.~
+
+_With Formulę, Properties, and Applications of the various substances
+described, and concise directions for their Commercial Valuation. and
+for the Detection of Adulterants._
+
+BY CHRISTOPHER RAWSON, F.I.C., F.C.S., Consulting Chemist to the Behar
+Indigo Planters' Association: Co-Author of "A Manual of Dyeing;"
+
+WALTER M. GARDNER, F.C.S.,
+
+Head of the Department of Chemistry and Dyeing, Bradford Municipal
+Technical College; Editor of the "Journ. Soc. Dyers and Colourists;"
+
+AND W.F. LAYCOCK, PH.D., F.C.S., Analytical and Consulting Chemist.
+
+"Turn to the book as one may on any subject, or any substance in
+connection with the trade, and a reference is sure to be found. The
+authors have apparently left nothing out. Considering the immense amount
+of information, the book is a cheap one, and we trust it will be widely
+appreciated,"--_Textile Mercury._
+
+       *       *       *       *       *
+
+_In Large 8vo, Handsome Cloth, with Numerous Illustrations. 9s. net._
+
+~TEXTILE FIBRES OF COMMERCE.~
+
+A HANDBOOK OF The Occurrence, Distribution, Preparation, and Industrial
+Uses of the Animal, Vegetable, and Mineral Products used in Spinning and
+Weaving.
+
+BY WILLIAM I. HANNAN, Lecturer on Botany at the Ashton Municipal
+Technical School, Lecturer on Cotton Spinning at the Chorley Science and
+Art School, &c.
+
+With Numerous Photo Engravings from Nature.
+
+*** The subjects discussed in this volume are, in order to facilitate
+reference, arranged in alphabetical order under their respective heads.
+The work may thus be regarded as a Dictionary of Textile Fibres. A
+feature of the work is the wealth of botanical description which
+accompanies the Section dealing with Vegetable Fibres.--_Publishers'
+Note._
+
+"USEFUL INFORMATION.... ADMIRABLE ILLUSTRATIONS.... The information is
+not easily attainable, and in its present convenient form will be
+valuable."--_Textile Recorder._
+
+       *       *       *       *       *
+
+~TEXTILE PRINTING: A PRACTICAL MANUAL.~
+
+Including the Processes Used in the Printing of COTTON, WOOLLEN, SILK,
+and HALF-SILK FABRICS.
+
+By C.F. SEYMOUR ROTHWELL, F.C.S., _Mem. Soc. of Chemical Industries;
+late Lecturer at the Municipal Technical School, Manchester_.
+
+In Large 8vo, with Illustrations and Printed Patterns. Price 21s.
+
+GENERAL CONTENTS.--Introduction.--The Machinery Used in Textile
+Printing.--Thickeners and Mordants.--The Printing of Cotton Goods.--The
+Steam Style.--Colours Produced Directly on the Fibre.--Dyed
+Styles.--Padding Style.--Resist and Discharge Styles.--The Printing of
+Compound Colourings, &c.--The Printing of Woollen Goods.--The Printing
+of Silk Goods.--Practical Recipes for Printing.--Appendix.--Useful
+Tables.--Patterns.
+
+"BY FAR THE BEST and MOST PRACTICAL BOOK on TEXTILE PRINTING which has
+yet been brought out, and will long remain the standard work on the
+subject. It is essentially practical in character."--_Textile Mercury._
+
+"THE MOST PRACTICAL MANUAL of TEXTILE PRINTING which has yet appeared.
+We have no hesitation in recommending it."--_The Textile Manufacturer._
+
+       *       *       *       *       *
+
+Large 8vo. Handsome Cloth. 12s. 6d.
+
+~BLEACHING & CALICO-PRINTING.~
+
+A Short Manual for Students and Practical Men.
+
+BY GEORGE DUERR, Director of the Bleaching, Dyeing, and Printing
+Department at the Accrington and Bacup Technical Schools; Chemist and
+Colourist at the Irwell Print Works.
+
+ASSISTED BY WILLIAM TURNBULL (of Turnbull & Stockdale, Limited).
+
+With Illustrations and upwards of One Hundred Dyed and Printed Patterns
+designed specially to show various Stages of the Processes described.
+
+GENERAL CONTENTS.--COTTON, Composition of; BLEACHING, New Processes;
+PRINTING, Hand-Block; Flat-Press Work; Machine Printing--MORDANTS--STYLES
+OF CALICO-PRINTING: The Dyed or Madder Style, Resist Padded Style,
+Discharge and Extract Style, Chromed or Raised Colours,
+Insoluble Colours, &c.--Thickeners--Natural Organic Colouring
+Matters--Tannin Matters--Oils, Soaps, Solvents--Organic
+Acids--Salts--Mineral Colours--Coal Tar Colours--Dyeing--Water,
+Softening of--Theory of Colours--Weights and Measures, &c.
+
+"When a READY WAY out of a difficulty is wanted, it is IN BOOKS LIKE
+THIS that it is found."--_Textile Recorder._
+
+"Mr. DUERR'S WORK will be found MOST USEFUL.... The information given is
+of GREAT VALUE.... The Recipes are THOROUGHLY PRACTICAL."--_Textile
+Manufacturer._
+
+       *       *       *       *       *
+
+SECOND EDITION. Revised and Enlarged. With Numerous Illustrations. 4s.
+6d.
+
+~GARMENT DYEING AND CLEANING.~
+
+A Practical Book for Practical Men.
+
+BY GEORGE H. HURST, F.C.S., Member of the Society of Chemical Industry.
+
+GENERAL CONTENTS.--Technology of the Textile Fibres--Garment
+Cleaning--Dyeing of Textile Fabrics--Bleaching--Finishing of Dyed and
+Cleaned Fabrics--Scouring and Dyeing of Skin Rugs and Mats--Cleaning and
+Dyeing of Feathers--Glove Cleaning and Dyeing--Straw Bleaching and
+Dyeing--Glossary of Drugs and Chemicals--Useful Tables.
+
+"An UP-TO-DATE hand book has long been wanted, and Mr. Hurst has done
+nothing more complete than this. An important work, the more so that
+several of the branches of the craft here treated upon are almost
+entirely without English Manuals for the guidance of workers. The price
+brings it within the reach of all."--_Dyer and Calico-Printer._
+
+"Mr. Hurst's work DECIDEDLY FILLS A WANT ... ought to be in the hands of
+every GARMENT DYER and cleaner in the Kingdom"--_Textile Mercury._
+
+       *       *       *       *       *
+
+"Boys COULD NOT HAVE A MORE ALLURING INTRODUCTION to scientific pursuits
+than these charming-looking volumes."--Letter to the Publishers from the
+Headmaster of one of our great Public Schools.
+
+Handsome Cloth, 7s. 6d. Gilt, for Presentation, 8s. 6d.
+
+~OPEN-AIR STUDIES IN BOTANY: SKETCHES OF BRITISH WILD FLOWERS IN THEIR
+HOMES.~
+
+BY R. LLOYD PRAEGER, B.A., M.R.I.A.
+
+Illustrated by Drawings from Nature by S. Rosamond Praeger, and
+Photographs by R. Welch.
+
+GENERAL CONTENTS.--A Daisy-Starred Pasture--Under the Hawthorns--By the
+River--Along the Shingle--A Fragrant Hedgerow--A Connemara Bog--Where
+the Samphire grows--A Flowery Meadow--Among the Corn (a Study in
+Weeds)--In the Home of the Alpines--A City Rubbish-Heap--Glossary.
+
+"A FRESH AND STIMULATING book ... should take a high place.... The
+Illustrations are drawn with much skill."--_The Times._
+
+"BEAUTIFULLY ILLUSTRATED.... One of the MOST ACCURATE as well as
+INTERESTING books of the kind we have seen."--_Athenęum._
+
+"Redolent with the scent of woodland and meadow."--_The Standard._
+
+       *       *       *       *       *
+
+_With 12 Full-Page Illustrations from Photographs. Cloth. Second
+Edition, Revised. 8s. 6d._
+
+~OPEN-AIR STUDIES IN GEOLOGY: An Introduction to Geology Out-of-doors.~
+
+BY GRENVILLE A.J. COLE, F.G.S., M.R.I.A., Professor of Geology in the
+Royal College of Science for Ireland, and Examiner in the University of
+London.
+
+GENERAL CONTENTS.--The Materials of the Earth--A Mountain Hollow--Down
+the Valley--Along the Shore--Across the Plains--Dead Volcanoes--A
+Granite Highland--The Annals of the Earth--The Surrey Hills--The Folds
+of the Mountains.
+
+"The FASCINATING 'OPEN-AIR STUDIES' of PROF. COLE give the Subject a
+GLOW ANIMATION ... cannot fail to arouse keen interest in
+geology."--_Geological Magazine._
+
+"A CHARMING BOOK, beautifully illustrated."--_Athenęum._
+
+       *       *       *       *       *
+
+_Beautifully Illustrated. With a Frontispiece in Colours, and Numerous
+Specially Drawn Plates by Charles Whymper. 7s. 6d._
+
+~OPEN-AIR STUDIES IN BIRD-LIFE: SKETCHES OF BRITISH BIRDS IN THEIR
+HAUNTS.~
+
+BY CHARLES DIXON.
+
+The Spacious Air.--The Open Fields and Downs.--In the Hedgerows.--On
+Open Heath and Moor.--On the Mountains.--Amongst the Evergreens.--Copse
+and Woodland.--By Stream and Pool.--The Sandy Wastes and
+Mud-flats.--Sea-laved Rocks.--Birds of the Cities.--INDEX.
+
+"Enriched with excellent illustrations. A welcome addition to all
+libraries."--_Westminster Review._
+
+       *       *       *       *       *
+
+_Twentieth Annual Issue. Handsome cloth, 7s. 6d. (To Subscribers, 6s.)._
+
+THE OFFICIAL YEAR-BOOK OF THE SCIENTIFIC AND LEARNED SOCIETIES OF GREAT
+BRITAIN AND IRELAND.
+
+COMPILED FROM OFFICIAL SOURCES.
+
+_Comprising (together with other Official Information) LISTS of the
+PAPERS read during the Session 1902-1903 before all the LEADING
+SOCIETIES throughout the Kingdom engaged in the following Departments of
+Research_:--
+
+§ 1. Science Generally: _i.e._, Societies occupying themselves with
+several Branches of Science, or with Science and Literature jointly.
+
+§ 2. Mathematics and Physics.
+
+§ 3. Chemistry and Photography.
+
+§ 4. Geology, Geography, and Mineralogy.
+
+§ 5. Biology, including Microscopy and Anthropology.
+
+§ 6. Economic Science and Statistics.
+
+§ 7. Mechanical Science, Engineering, and Architecture.
+
+§ 8. Naval and Military Science.
+
+§ 9. Agriculture and Horticulture.
+
+§ 10. Law.
+
+§ 11. Literature.
+
+§ 12. Psychology.
+
+§ 13. Archęology.
+
+§ 14. Medicine.
+
+"FILLS A VERY REAL WANT."--_Engineering._
+
+"INDISPENSABLE to any one who may wish to keep himself abreast of the
+scientific work of the day."--_Edinburgh Medical Journal._
+
+"The YEAR-BOOK OF SOCIETIES is a Record which ought to be of the
+_greatest use for the progress of Science_."--_Lord Playfair, F.R.S.,
+K.C.B., M.P., Past-President of the British Association._
+
+"It goes almost without saying that a Handbook of this subject will be
+in time _one of the most generally useful works for the library or the
+desk_."--_The Times._
+
+"British Societies are now _well represented_ in the 'Year-Book of the
+Scientific and Learned Societies of Great Britain and Ireland'"--(Art.
+"Societies" in New Edition of "Encyclopędia Britannica," vol. xxii.)
+
+       *       *       *       *       *
+
+Copies of the FIRST ISSUE, giving an Account of the History,
+Organization, and Conditions of Membership of the various Societies, and
+forming the groundwork of the Series, may still be had, price 7/6. _Also
+Copies of the Issues following._
+
+The _YEAR-BOOK OF SOCIETIES_ forms a complete _INDEX TO THE SCIENTIFIC
+WORK_ of the sessional year in the various Departments. It is used as a
+HANDBOOK in all our great SCIENTIFIC CENTRES, MUSEUMS, and LIBRARIES
+throughout the Kingdom, and has become an _INDISPENSABLE BOOK OF
+REFERENCE_ to every one engaged in Scientific Work.
+
+_READY IN OCTOBER EACH YEAR._
+
+
+~Griffin's Metallurgical Series.~
+
+Edited by SIR W. ROBERTS-AUSTEN, K.C.B., F.R.S., D.C.L.
+
+       *       *       *       *       *
+
+_Fifth Edition, Thoroughly Revised and Considerably Enlarged._ 18s.
+
+~INTRODUCTION TO THE STUDY OF METALLURGY.~ By Sir W.C. ROBERTS-AUSTEN.
+With additional Illustrations and Micro-Photographic Plates of Different
+Varieties of Steel.
+
+_Fourth Edition, Thoroughly Revised and Enlarged._ 21s. ~THE METALLURGY
+OF GOLD.~ By T. KIRKE ROSE, D.Sc., Assayer of the Royal Mint. Including
+the most recent Improvements in the Cyanide Process. With new
+Frontispiece and additional Illustrations.
+
+_In Two Volumes, each complete in itself._
+
+~THE METALLURGY OF LEAD AND SILVER.~ By H.F. COLLINS, Assoc. R.S.M.,
+M.Inst.M.M. ~Part I.--LEAD.~ With Sections on Smelting and
+Desilverisation, and the Assay and Analysis of the Materials Involved.
+16s. ~Part II.--SILVER.~ Sources and Treatment of Ores, with
+Descriptions of Plant, Machinery, &c. 16s.
+
+_Second Edition, Revised. With numerous Illustrations._ 16s. ~THE
+METALLURGY OF IRON.~ By THOMAS TURNER, F.I.C., Assoc. R.S.M. Professor
+of Metallurgy at the University of Birmingham.
+
+_Large 8vo. Profusely Illustrated with Plates and Diagrams._ ~THE
+METALLURGY OF STEEL.~ By F.W. HARBORD. With a Section on the Mechanical
+Treatment of Steel. By J.W. HALL. 25s. net.
+
+       *       *       *       *       *
+
+~ASSAYING.~ By J.J. BERINGER, F.I.C., F.C.S., and C. BERINGER, F.C.S.
+NINTH EDITION, Revised. With Diagrams, 10s. 6d.
+
+~GETTING GOLD.~ A Practical Treatise for Prospectors and MINERS. By
+J.C.F. JOHNSON, A.I.M.E.. F.G.S., Life Member Australian Mine Managers'
+Association. Numerous Illustrations. SECOND EDITION. 3s. 6d.
+
+~GOLD SEEKING IN SOUTH AFRICA.~ A Handbook of Hints for Intending
+Explorers, Prospectors, and Settlers. By THEO. KASSNER. With a Chapter
+on Agriculture. Crown 8vo, Fancy Cloth Boards. Illustrated. 4s. 6d. net.
+
+~THE CYANIDE PROCESS OF GOLD EXTRACTION.~ By JAMES PARK, F.G.S.,
+M.Inst.M.M., late Geological Surveyor and Mining Geologist to the New
+Zealand Government. NEW EDITION, Revised and Enlarged from the last New
+Zealand Edition. With Frontispiece, Plates and Illustrations. 6s. net.
+
+~PROSPECTING FOR MINERALS.~ A Practical Handbook. By S. HERBERT COX,
+Assoc. R.S.M., M.Inst.M.M., F.G.S., &c. With Illustrations. SECOND
+EDITION, Revised. Cloth, 5s.; Leather, 6s. 6d.
+
+~TABLES FOR QUANTITATIVE METALLURGICAL ANALYSIS FOR LABORATORY USE.~ By
+J. JAMES MORGAN, F.C.S. Large 8vo, strongly bound, cloth, 4s.
+
+~ELECTRIC SMELTING AND REFINING.~ By Dr. W. BORCHERS. Translated by
+WALTER G. MCMILLAN, F.I.C., F.C.S., from the Second German Edition. With
+numerous Illustrations and Three Folding Plates. 21s.
+
+~MINE ACCOUNTS AND MINING BOOKKEEPING.~ From the ACTUAL PRACTICE of
+leading Mining Companies. By JAMES G. LAWN, Assoc. R.S.M.,
+A.M.Inst.C.E.F.G.S. Edited by Sir LE NEVE FOSTER, D.Sc., F.R.S. Large
+8vo. THIRD EDITION. 10s. 6d.
+
+       *       *       *       *       *
+
+_Large 8vo. Handsome Cloth. Illustrated, 12s. 6d. net._ ~METALLURGICAL
+ANALYSIS AND ASSAYING:~ A Three Years' Course for Students. By W.A.
+MACLEOD, B.A., B.Sc., A.O.S.M. (N.Z.), and CHAS. WALKER, F.C.S.
+
+~Part I.--Qualitative Analysis, and Preparation and Properties of
+Cases.~ ~Part II.--Qualitative and Quantitative Analysis.~ ~Part
+III.--Assaying, Technical Analysis (Gas, Water, Fuels, Oils, &c.).~
+
+       *       *       *       *       *
+
+London: Charles Griffin & Co., Ltd., Exeter Street, Strand.
+
+
+
+***END OF THE PROJECT GUTENBERG EBOOK A TEXTBOOK OF ASSAYING: FOR THE USE
+OF THOSE CONNECTED WITH MINES.***
+
+
+******* This file should be named 18751-8.txt or 18751-8.zip *******
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+<h1>The Project Gutenberg eBook, A Textbook of Assaying: For the Use of Those
+Connected with Mines., by Cornelius Beringer and John Jacob Beringer</h1>
+<pre class="pg">
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at <a href = "http://www.gutenberg.org">www.gutenberg.org</a></pre>
+<p>Title: A Textbook of Assaying: For the Use of Those Connected with Mines.</p>
+<p>Author: Cornelius Beringer and John Jacob Beringer</p>
+<p>Release Date: July 3, 2006  [eBook #18751]</p>
+<p>Language: English</p>
+<p>Character set encoding: ISO-8859-1</p>
+<p>***START OF THE PROJECT GUTENBERG EBOOK A TEXTBOOK OF ASSAYING: FOR THE USE OF THOSE CONNECTED WITH MINES.***</p>
+<p>&nbsp;</p>
+<h3>E-text prepared by Peter Yearsley, Josephine Paolucci,<br />
+    and the Project Gutenberg Online Distributed Proofreading Team<br />
+    (http://www.pgdp.net/)</h3>
+<p>&nbsp;</p>
+<p>Transcriber's Note:</p>
+
+<p>Parentheses have been added to clarify fractions.
+Letters in brackets with a = sign before it means
+that the letters have a macron over them, e.g. H[=A=c] signifies that
+the Ac has a macron over it.</p>
+
+<p>Minor typographical errors have been corrected. Footnotes have been
+moved to the end of the chapter, and all advertisements have been moved
+to the end of the book.</p>
+<p>&nbsp;</p>
+<hr class="full" />
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+
+<h1>A TEXT-BOOK OF ASSAYING:</h1>
+
+<h3><i>FOR THE USE OF THOSE CONNECTED WITH MINES.</i></h3>
+
+<h3>BY</h3>
+
+<h2>C. AND J. J. BERINGER.</h2>
+
+<h4>REVISED BY</h4>
+
+<h2>J. J. BERINGER,</h2>
+
+<p class="center">ASSOC. OF THE ROYAL SCHOOL OF MINES; FELLOW OF THE CHEMICAL SOCIETY AND
+OF THE INST. OF CHEMISTRY; PRINCIPAL OF THE CAMBORNE MINING SCHOOL; AND
+LATE PUBLIC ANALYST FOR THE COUNTY OF CORNWALL.</p>
+
+<h4><i>With numerous Diagrams and Tables.</i></h4>
+
+<h3><i>NINTH EDITION.</i></h3>
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+
+<p class ="center">
+LONDON:<br />
+CHARLES GRIFFIN AND COMPANY, <span class="smcap">Limited</span>,<br />
+EXETER STREET, STRAND.<br /><br />
+1904.</p>
+
+<h4>[<i>All rights reserved.</i>]</h4>
+<hr style="width: 65%;" />
+
+<h2><a name="PUBLISHERS_NOTE_TO_THE_NINTH_EDITION" id="PUBLISHERS_NOTE_TO_THE_NINTH_EDITION"></a>PUBLISHER'S NOTE TO THE NINTH EDITION</h2>
+
+
+<p>The continued popularity of the present work, the last edition of which
+was published only a little over a year ago, continues to be a source of
+gratification to the publishers, who have much pleasure in issuing the
+present edition.</p>
+
+<p>&nbsp;&nbsp;&nbsp;&nbsp;<i>January 1904.</i></p>
+
+<hr style="width: 45%;" />
+<h2>PREFACE TO THE SIXTH EDITION</h2>
+
+<p>The principal changes in this edition are additions to the articles on
+Gold, Cyanides, and Nickel, and a much enlarged Index. The additional
+matter covers more than forty pages.</p>
+
+<p>
+J. J. BERINGER.<br />
+<br />
+<span class="smcap">Camborne</span>,<br />
+<i>January 1900.</i><br />
+</p>
+
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_vi" id="Page_vi">[Pg vi]</a></span></p>
+<h2><a name="PREFACE" id="PREFACE"></a>PREFACE.</h2>
+
+
+<p>The Text-book now offered to the public has been prepared to meet the
+existing want of a practical "handy book" for the Assayer.</p>
+
+<p>To mining men the word "assaying" conveys a sufficiently clear meaning,
+but it is difficult to define. Some writers limit it to the
+determination of silver and gold, and others imagine that it has only to
+do with "furnace-work." These limitations are not recognised in
+practice. In fact, assaying is becoming wider in its scope, and the
+distinction between "assayers" and "analysts" will in time be difficult
+to detect. We have endeavoured rather to give what will be of use to the
+assayer than to cover the ground within the limits of a faulty
+definition.</p>
+
+<p>At first our intention was to supply a description of those substances
+only which have a commercial value, but on consideration we have added
+short accounts of the rarer elements, since they are frequently met
+with, and occasionally affect the accuracy of an assay.</p>
+
+<p>Under the more important methods we have given the results of a series
+of experiments showing the effect of varying conditions<span class='pagenum'><a name="Page_vii" id="Page_vii">[Pg vii]</a></span> on the accuracy
+of the process. Such experiments are often made by assayers, but seldom
+recorded. Statements like those generally made&mdash;that "this or that
+substance interferes"&mdash;are insufficient. It is necessary to know under
+what conditions and to what extent.</p>
+
+<p>Students learning any particular process cannot do better than repeat
+such a series of experiments. By this means they will, at the same time,
+acquire the skill necessary for performing an assay and a confidence in
+their results based upon work under different conditions.</p>
+
+<p>The electrolytic method of copper assaying given under <i>Copper</i> is a
+modification of Luckow's; it was introduced by us into the offices of
+the Rio Tinto Copper Company, and has been in use for many years with
+success. This modification is now employed in copper-works in Spain,
+Germany, and England, and is used in place of the dry assay for the
+commercial valuation of copper ores.</p>
+
+<p>We have adhered to the gram and the "c.c." as the units of weight and
+volume. Those who prefer working with grains and grain-measures can use
+the figures given, multiplied by ten. For example:&mdash;When 1 gram is
+mentioned, 10 grains should be used, and 10 grain-measures take the
+place of 1 "c.c." It is not advisable to mix the two systems, as by
+using gram weights and grain-measures.</p>
+
+<p>We have intentionally to a large extent omitted to mention the names of
+those who have originated or modified the various processes. The
+practice of naming a process after its discoverer has developed of late
+years, and is becoming objectionable. It is a graceful thing to name a
+gas-burner after Bunsen, or a condenser after Liebig; but when the
+practice has developed<span class='pagenum'><a name="Page_viii" id="Page_viii">[Pg viii]</a></span> so far that one is directed to "Finkenerise" a
+residue, or to use the "Reichert-Meissl-Wollny" process, it is time to
+stop.</p>
+
+<p>We are indebted to the standard works of Allen, Crookes, Fresenius,
+Lunge, Michell, Percy, and Sutton, and wish to express our sense of
+special indebtedness to Mr. Richard Smith, of the Royal School of Mines.
+One or two of the illustrations are taken from Mr. Sexton's excellent
+little book on <i>Qualitative Analysis</i>. Our obligation to some others is
+mentioned in the text.</p>
+
+<p>Finally, we have to thank for assistance in the experimental work
+Messrs. Bailey, Beswick, Clarke, Grant, Higgins, and Smith.</p>
+
+<p>THE AUTHORS.</p>
+
+<p><span class="smcap">Camborne</span>,&nbsp;&nbsp; <i>Nov. 1889</i>.</p>
+
+
+
+<hr style="width: 65%;" />
+
+<p><span class='pagenum'><a name="Page_ix" id="Page_ix">[Pg ix]</a></span></p>
+<h2><a name="CONTENTS" id="CONTENTS"></a>CONTENTS.</h2>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>PART I.</td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER I.</td></tr>
+<tr><td align='center'>INTRODUCTORY.</td></tr>
+<tr><td align='left'></td><td align='right'>Page</td></tr>
+<tr><td align='left'>Object of assaying</td><td align='right'><a href='#Page_1'>1</a></td></tr>
+<tr><td align='left'>Sampling</td><td align='right'><a href='#Page_1'>1</a></td></tr>
+<tr><td align='left'>Drying: determination of moisture</td><td align='right'><a href='#Page_5'>5</a></td></tr>
+<tr><td align='left'>Calculation and statement of results</td><td align='right'><a href='#Page_7'>7</a></td></tr>
+<tr><td align='left'>Laboratory books and report forms</td><td align='right'><a href='#Page_9'>9</a></td></tr>
+<tr><td align='left'>Quantity to be taken for an assay</td><td align='right'><a href='#Page_11'>11</a></td></tr>
+<tr><td align='left'>Exercises</td><td align='right'><a href='#Page_14'>14</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER II.</td></tr>
+<tr><td align='center'>METHODS OF ASSAYING.&mdash;DRY GRAVIMETRIC METHODS.</td></tr>
+<tr><td align='left'>Methods of assaying</td><td align='right'><a href='#Page_15'>15</a></td></tr>
+<tr><td align='left'>Gravimetric methods</td><td align='right'><a href='#Page_15'>15</a></td></tr>
+<tr><td align='left'>Mechanical separations</td><td align='right'><a href='#Page_16'>16</a></td></tr>
+<tr><td align='left'>Dry assays</td><td align='right'><a href='#Page_16'>16</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>a</i>) Fluxes</td><td align='right'><a href='#Page_16'>16</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>b</i>) Reducing agents</td><td align='right'><a href='#Page_21'>21</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>c</i>) Oxidising agents</td><td align='right'><a href='#Page_22'>22</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>d</i>) Apparatus</td><td align='right'><a href='#Page_24'>24</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER III.</td></tr>
+<tr><td align='center'>WET GRAVIMETRIC METHODS.</td></tr>
+<tr><td align='left'>Wet gravimetric methods</td><td align='right'><a href='#Page_27'>27</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>a</i>) Solution</td><td align='right'><a href='#Page_29'>29</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>b</i>) Precipitation</td><td align='right'><a href='#Page_30'>30</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>c</i>) Filtration</td><td align='right'><a href='#Page_31'>31</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>d</i>) Drying and igniting</td><td align='right'><a href='#Page_32'>32</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER IV.</td></tr>
+<tr><td align='center'>VOLUMETRIC ASSAYS.</td></tr>
+<tr><td align='left'>Titrometric assays</td><td align='right'><a href='#Page_35'>35</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>a</i>) Standard solutions</td><td align='right'><a href='#Page_36'>36</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>b</i>) Standardising</td><td align='right'><a href='#Page_37'>37</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>c</i>) Methods of working</td><td align='right'><a href='#Page_42'>42</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>d</i>) Indirect titration</td><td align='right'><a href='#Page_43'>43</a></td></tr>
+<tr><td align='left'>Colorimetric assays</td><td align='right'><a href='#Page_44'>44</a></td></tr>
+<tr><td align='left'>Gasometric assays</td><td align='right'><a href='#Page_44'>44</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER V.</td></tr>
+<tr><td align='center'>WEIGHING AND MEASURING.</td></tr>
+<tr><td align='left'>Weighing</td><td align='right'><a href='#Page_47'>47</a></td></tr>
+<tr><td align='left'>Measuring liquids</td><td align='right'><a href='#Page_49'>49</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>a</i>) Graduated flasks</td><td align='right'><a href='#Page_49'>49</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>b</i>) Pipettes</td><td align='right'><a href='#Page_50'>50</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>c</i>) Burettes</td><td align='right'><a href='#Page_51'>51</a></td></tr>
+<tr><td align='left'>Measuring gases</td><td align='right'><a href='#Page_52'>52</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER VI.</td></tr>
+<tr><td align='center'>REAGENTS.</td></tr>
+<tr><td align='left'>Acids, &amp;c.</td><td align='right'><a href='#Page_54'>54</a></td></tr>
+<tr><td align='left'>Bases, salts, &amp;c.</td><td align='right'><a href='#Page_59'>59</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER VII.</td></tr>
+<tr><td align='left'>Formul&aelig;, equations, &amp;c.</td><td align='right'><a href='#Page_68'>68</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER VIII.</td></tr>
+<tr><td align='center'>SPECIFIC GRAVITY.</td></tr>
+<tr><td align='left'>Introductory</td><td align='right'><a href='#Page_75'>75</a></td></tr>
+<tr><td align='left'>Determination of specific gravity&mdash;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>a</i>) Hydrometers</td><td align='right'><a href='#Page_76'>76</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;(<i>b</i>) Specific gravity bottles</td><td align='right'><a href='#Page_78'>78</a></td></tr>
+<tr><td align='left'>Calculations depending on specific gravity</td><td align='right'><a href='#Page_84'>84</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr><tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>PART II.</td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER IX.</td></tr>
+<tr><td align='center'>SILVER, GOLD, PLATINUM, CYANIDES, MERCURY.</td></tr>
+<tr><td align='left'>Silver&mdash;Detection</td><td align='right'><a href='#Page_87'>87</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_87'>87</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Scorification</td><td align='right'><a href='#Page_88'>88</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) Pot assays, average ores</td><td align='right'><a href='#Page_90'>90</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;ores with metallic oxides</td><td align='right'><a href='#Page_91'>91</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ores with metallic sulphides</td><td align='right'><a href='#Page_91'>91</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Explanatory notes on the fusion</td><td align='right'><a href='#Page_93'>93</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;The effect of charcoal, flour, &amp;c.</td><td align='right'><a href='#Page_94'>94</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;The effect of nitre</td><td align='right'><a href='#Page_95'>95</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;The effect of mineral sulphides</td><td align='right'><a href='#Page_95'>95</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) Cupellation</td><td align='right'><a href='#Page_98'>98</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The loss of silver</td><td align='right'><a href='#Page_101'>101</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Condition affecting the loss</td><td align='right'><a href='#Page_102'>102</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Methods of correction</td><td align='right'><a href='#Page_103'>103</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Lead required for cupellation</td><td align='right'><a href='#Page_105'>105</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(4) Calculation of the results in ounces to the ton of 2240 lbs. Table</td><td align='right'><a href='#Page_107'>107</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Ores with metallic particles</td><td align='right'><a href='#Page_108'>108</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(5) Explanatory notes</td><td align='right'><a href='#Page_110'>110</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(6) Examples of dry silver assays</td><td align='right'><a href='#Page_113'>113</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Wet assays</td><td align='right'><a href='#Page_116'>116</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric method</td><td align='right'><a href='#Page_117'>117</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Gay-Lussac's method</td><td align='right'><a href='#Page_119'>119</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Volhard's method</td><td align='right'><a href='#Page_121'>121</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;A modified Gay-Lussac</td><td align='right'><a href='#Page_123'>123</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Volhard's method applied to arsenic</td><td align='right'><a href='#Page_124'>124</a></td></tr>
+<tr><td align='left'>Gold&mdash;Detection</td><td align='right'><a href='#Page_126'>126</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Amalgamation assay</td><td align='right'><a href='#Page_126'>126</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_127'>127</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Size of charges</td><td align='right'><a href='#Page_127'>127</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) Sampling</td><td align='right'><a href='#Page_127'>127</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) Assay tons</td><td align='right'><a href='#Page_131'>131</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(4) Small buttons, weighing</td><td align='right'><a href='#Page_131'>131</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; measuring</td><td align='right'><a href='#Page_133'>133</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(5) Concentration in lead</td><td align='right'><a href='#Page_136'>136</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Quartz ores</td><td align='right'><a href='#Page_136'>136</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Ores with oxide of iron</td><td align='right'><a href='#Page_138'>138</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Ores with metallic sulphides</td><td align='right'><a href='#Page_139'>139</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(6) Cyanide charges, residues, &amp;c.</td><td align='right'><a href='#Page_140'>140</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(7) Cupellation</td><td align='right'><a href='#Page_142'>142</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Cupels</td><td align='right'><a href='#Page_142'>142</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Cupellation temperature</td><td align='right'><a href='#Page_143'>143</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Cupellation loss</td><td align='right'><a href='#Page_145'>145</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(8) Inquartation</td><td align='right'><a href='#Page_146'>146</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(9) Flatting</td><td align='right'><a href='#Page_149'>149</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(10) Parting, in flasks</td><td align='right'><a href='#Page_151'>151</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;   in test tubes</td><td align='right'><a href='#Page_152'>152</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;in glazed crucibles</td><td align='right'><a href='#Page_153'>153</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  Loss, &amp;c.</td><td align='right'><a href='#Page_154'>154</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(11) Check assays, surcharge</td><td align='right'><a href='#Page_154'>154</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(12) Bullion assays in special apparatus</td><td align='right'><a href='#Page_156'>156</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Silver, &amp;c., in gold bullion</td><td align='right'><a href='#Page_157'>157</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(13) Sampling of base bullion, &amp;c.</td><td align='right'><a href='#Page_157'>157</a></td></tr>
+<tr><td align='left'>Cyanides&mdash;Commercial cyanides</td><td align='right'><a href='#Page_160'>160</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Double cyanides</td><td align='right'><a href='#Page_161'>161</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Prussic acid</td><td align='right'><a href='#Page_162'>162</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gold-dissolving power of cyanide liquor</td><td align='right'><a href='#Page_162'>162</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Assay for cyanide strength</td><td align='right'><a href='#Page_163'>163</a>, 165</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Assay of commercial cyanide</td><td align='right'><a href='#Page_167'>167</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Alkalinity of cyanides</td><td align='right'><a href='#Page_167'>167</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Acidity of ores</td><td align='right'><a href='#Page_168'>168</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Metals in cyanide liquors</td><td align='right'><a href='#Page_169'>169</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Cyanicides</td><td align='right'><a href='#Page_169'>169</a></td></tr>
+<tr><td align='left'>Platinum</td><td align='right'><a href='#Page_170'>170</a></td></tr>
+<tr><td align='left'>Iridium</td><td align='right'><a href='#Page_171'>171</a></td></tr>
+<tr><td align='left'>Mercury</td><td align='right'><a href='#Page_171'>171</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_172'>172</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Wet method</td><td align='right'><a href='#Page_173'>173</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER X.</td></tr>
+<tr><td align='center'>COPPER, LEAD, THALLIUM, BISMUTH, ANTIMONY.</td></tr>
+<tr><td align='left'>Copper&mdash;Introductory</td><td align='right'><a href='#Page_175'>175</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_176'>176</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Valuation of copper ores</td><td align='right'><a href='#Page_181'>181</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Wet methods</td><td align='right'><a href='#Page_183'>183</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Electrolytic assay</td><td align='right'><a href='#Page_184'>184</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Volumetric methods</td><td align='right'><a href='#Page_194'>194</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Cyanide method</td><td align='right'><a href='#Page_194'>194</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) Iodide method</td><td align='right'><a href='#Page_199'>199</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) Colorimetric method</td><td align='right'><a href='#Page_203'>203</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Examination of commercial copper</td><td align='right'><a href='#Page_205'>205</a></td></tr>
+<tr><td align='left'>Lead</td><td align='right'><a href='#Page_211'>211</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_211'>211</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Wet assay</td><td align='right'><a href='#Page_213'>213</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Gravimetric method</td><td align='right'><a href='#Page_213'>213</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) Volumetric method</td><td align='right'><a href='#Page_214'>214</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(3) Colorimetric method</td><td align='right'><a href='#Page_218'>218</a></td></tr>
+<tr><td align='left'>Thallium</td><td align='right'><a href='#Page_219'>219</a></td></tr>
+<tr><td align='left'>Bismuth</td><td align='right'><a href='#Page_220'>220</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_221'>221</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Wet method</td><td align='right'><a href='#Page_221'>221</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Gravimetric determination</td><td align='right'><a href='#Page_222'>222</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) Colorimetric assay</td><td align='right'><a href='#Page_223'>223</a></td></tr>
+<tr><td align='left'>Antimony</td><td align='right'><a href='#Page_225'>225</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_225'>225</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Wet method</td><td align='right'><a href='#Page_227'>227</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(1) Gravimetric assay</td><td align='right'><a href='#Page_228'>228</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(2) Volumetric method</td><td align='right'><a href='#Page_229'>229</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XI.</td></tr>
+<tr><td align='center'>IRON, NICKEL, COBALT, ZINC, CADMIUM.</td></tr>
+<tr><td align='left'>Iron</td><td align='right'><a href='#Page_231'>231</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric determination</td><td align='right'><a href='#Page_233'>233</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Permanganate and bichromate methods</td><td align='right'><a href='#Page_234'>234</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Stannous chloride method</td><td align='right'><a href='#Page_244'>244</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Colorimetric determination</td><td align='right'><a href='#Page_247'>247</a></td></tr>
+<tr><td align='left'>Nickel</td><td align='right'><a href='#Page_251'>251</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_251'>251</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Electrolytic assay</td><td align='right'><a href='#Page_254'>254</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Titration by cyanide</td><td align='right'><a href='#Page_255'>255</a></td></tr>
+<tr><td align='left'>Cobalt</td><td align='right'><a href='#Page_259'>259</a></td></tr>
+<tr><td align='left'>Zinc</td><td align='right'><a href='#Page_261'>261</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric method</td><td align='right'><a href='#Page_262'>262</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Volumetric method</td><td align='right'><a href='#Page_263'>263</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gasometric method</td><td align='right'><a href='#Page_266'>266</a></td></tr>
+<tr><td align='left'>Cadmium</td><td align='right'><a href='#Page_269'>269</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XII.</td></tr>
+<tr><td align='center'>TIN, TUNGSTEN, TITANIUM.</td></tr>
+<tr><td align='left'>Tin</td><td align='right'><a href='#Page_271'>271</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Vanning</td><td align='right'><a href='#Page_273'>273</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Dry assay</td><td align='right'><a href='#Page_276'>276</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Detection, &amp;c.</td><td align='right'><a href='#Page_279'>279</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric determination</td><td align='right'><a href='#Page_281'>281</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Volumetric determination</td><td align='right'><a href='#Page_282'>282</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Examples</td><td align='right'><a href='#Page_284'>284</a></td></tr>
+<tr><td align='left'>Titanium</td><td align='right'><a href='#Page_292'>292</a></td></tr>
+<tr><td align='left'>Tungsten</td><td align='right'><a href='#Page_295'>295</a></td></tr>
+<tr><td align='left'>Niobic and Tantalic Oxides</td><td align='right'><a href='#Page_297'>297</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XIII.</td></tr>
+<tr><td align='center'>MANGANESE, CHROMIUM, ETC.</td></tr>
+<tr><td align='left'>Manganese</td><td align='right'><a href='#Page_298'>298</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric determination</td><td align='right'><a href='#Page_300'>300</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Volumetric determination</td><td align='right'><a href='#Page_300'>300</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Ferrous sulphate assay</td><td align='right'><a href='#Page_301'>301</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Iodine assay</td><td align='right'><a href='#Page_302'>302</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Colorimetric determination</td><td align='right'><a href='#Page_306'>306</a></td></tr>
+<tr><td align='left'>Chromium</td><td align='right'><a href='#Page_307'>307</a></td></tr>
+<tr><td align='left'>Vanadium</td><td align='right'><a href='#Page_310'>310</a></td></tr>
+<tr><td align='left'>Molybdenum</td><td align='right'><a href='#Page_311'>311</a></td></tr>
+<tr><td align='left'>Uranium</td><td align='right'><a href='#Page_312'>312</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XIV.</td></tr>
+<tr><td align='center'>EARTHS, ALKALINE EARTHS, ALKALIES.</td></tr>
+<tr><td align='left'>Alumina</td><td align='right'><a href='#Page_314'>314</a></td></tr>
+<tr><td align='left'>Thoria</td><td align='right'><a href='#Page_317'>317</a></td></tr>
+<tr><td align='left'>Zirconia</td><td align='right'><a href='#Page_317'>317</a></td></tr>
+<tr><td align='left'>Cerium</td><td align='right'><a href='#Page_318'>318</a></td></tr>
+<tr><td align='left'>Lanthanum and Didymium</td><td align='right'><a href='#Page_319'>319</a></td></tr>
+<tr><td align='left'>Yttria</td><td align='right'><a href='#Page_319'>319</a></td></tr>
+<tr><td align='left'>Beryllia</td><td align='right'><a href='#Page_319'>319</a></td></tr>
+<tr><td align='left'>Lime</td><td align='right'><a href='#Page_320'>320</a></td></tr>
+<tr><td align='left'>Strontia</td><td align='right'><a href='#Page_324'>324</a></td></tr>
+<tr><td align='left'>Baryta</td><td align='right'><a href='#Page_326'>326</a></td></tr>
+<tr><td align='left'>Magnesia</td><td align='right'><a href='#Page_328'>328</a></td></tr>
+<tr><td align='left'>The Alkalies</td><td align='right'><a href='#Page_330'>330</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Sodium</td><td align='right'><a href='#Page_334'>334</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Potassium</td><td align='right'><a href='#Page_336'>336</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Lithium</td><td align='right'><a href='#Page_338'>338</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;C&aelig;sium</td><td align='right'><a href='#Page_339'>339</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Rubidium</td><td align='right'><a href='#Page_340'>340</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Ammonium</td><td align='right'><a href='#Page_340'>340</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr><tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>PART III.</td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XV.</td></tr>
+<tr><td align='center'>OXYGEN AND OXIDES&mdash;THE HALOGENS.</td></tr>
+<tr><td align='left'>Oxygen</td><td align='right'><a href='#Page_344'>344</a></td></tr>
+<tr><td align='left'>Oxides</td><td align='right'><a href='#Page_345'>345</a></td></tr>
+<tr><td align='left'>Water</td><td align='right'><a href='#Page_350'>350</a></td></tr>
+<tr><td align='left'>The Halogens</td><td align='right'><a href='#Page_358'>358</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Chlorine</td><td align='right'><a href='#Page_359'>359</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Bromine</td><td align='right'><a href='#Page_361'>361</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Iodine</td><td align='right'><a href='#Page_362'>362</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Fluorine</td><td align='right'><a href='#Page_363'>363</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XVI.</td></tr>
+<tr><td align='center'>SULPHUR AND SULPHATES.</td></tr>
+<tr><td align='left'>Sulphur</td><td align='right'><a href='#Page_367'>367</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric determination</td><td align='right'><a href='#Page_369'>369</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Volumetric determination</td><td align='right'><a href='#Page_370'>370</a></td></tr>
+<tr><td align='left'>Sulphates</td><td align='right'><a href='#Page_377'>377</a></td></tr>
+<tr><td align='left'>Selenium</td><td align='right'><a href='#Page_379'>379</a></td></tr>
+<tr><td align='left'>Tellurium</td><td align='right'><a href='#Page_379'>379</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XVII.</td></tr>
+<tr><td align='center'>ARSENIC, PHOSPHORUS, NITROGEN.</td></tr>
+<tr><td align='left'>Arsenic</td><td align='right'><a href='#Page_381'>381</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Gravimetric determination</td><td align='right'><a href='#Page_383'>383</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;Volumetric method, "iodine"</td><td align='right'><a href='#Page_384'>384</a></td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;" &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"uranic acetate"</td><td align='right'><a href='#Page_389'>389</a></td></tr>
+<tr><td align='left'>Phosphorus</td><td align='right'><a href='#Page_394'>394</a></td></tr>
+<tr><td align='left'>Gravimetric determination</td><td align='right'><a href='#Page_396'>396</a></td></tr>
+<tr><td align='left'>Volumetric determination</td><td align='right'><a href='#Page_397'>397</a></td></tr>
+<tr><td align='left'>Nitrogen and Nitrates</td><td align='right'><a href='#Page_400'>400</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>CHAPTER XVIII.</td></tr>
+<tr><td align='center'>SILICON, CARBON, BORON.</td></tr>
+<tr><td align='left'>Silicon and Silicates</td><td align='right'><a href='#Page_405'>405</a></td></tr>
+<tr><td align='left'>Carbon and Carbonates</td><td align='right'><a href='#Page_414'>414</a></td></tr>
+<tr><td align='left'>Coals</td><td align='right'><a href='#Page_418'>418</a></td></tr>
+<tr><td align='left'>Shales</td><td align='right'><a href='#Page_420'>420</a></td></tr>
+<tr><td align='left'>Carbonates</td><td align='right'><a href='#Page_424'>424</a></td></tr>
+<tr><td align='left'>Boron and Borates</td><td align='right'><a href='#Page_429'>429</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>APPENDIX A.</td></tr>
+<tr><td align='left'>Table of atomic weights and other constants</td><td align='right'><a href='#Page_433'>433</a></td></tr>
+<tr><td align='left'>Table for converting degrees of the centigrade thermometer</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;into degrees of Fahrenheit's scale</td><td align='right'><a href='#Page_435'>435</a></td></tr>
+<tr><td align='left'>Tables showing strengths of aqueous solutions of nitric and hydrochloric acids,</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;of ammonia and of sulphuric acid</td><td align='right'><a href='#Page_436'>436</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>APPENDIX B.</td></tr>
+<tr><td align='left'>Estimation of small quantities of gold</td><td align='right'><a href='#Page_440'>440</a></td></tr>
+<tr><td align='left'>Practical notes on the iodide process of copper assaying</td><td align='right'><a href='#Page_441'>441</a></td></tr>
+<tr><td align='left'>Method of separating cobalt and nickel</td><td align='right'><a href='#Page_442'>442</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>APPENDIX C.</td></tr>
+<tr><td align='left'>A lecture on the theory of sampling</td><td align='right'><a href='#Page_444'>444</a></td></tr>
+<tr><td align='left'>&nbsp;</td></tr><tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='center'>Index</td><td align='right'><a href='#Page_450'>450</a></td></tr>
+</table></div>
+
+
+
+
+<hr style="width: 65%;" />
+<h2><a name="A_TEXT-BOOK_OF_ASSAYING" id="A_TEXT-BOOK_OF_ASSAYING"></a>A TEXT-BOOK OF ASSAYING.</h2>
+
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p>
+<h2><a name="CHAPTER_I" id="CHAPTER_I"></a>CHAPTER I.</h2>
+
+<h3>INTRODUCTORY.</h3>
+
+
+<p>Assaying has for its object the determination of the quantities of those
+constituents of a material which add to or detract from its value in the
+arts and manufactures. The methods of assaying are mainly those of
+analytical chemistry, and are limited by various practical
+considerations to the determination of the constituents of a small
+parcel, which is frequently only a few grains, and rarely more than a
+few ounces, in weight. From these determinations calculations are made,
+which have reference to a mass of material of, perhaps, hundreds of
+tons. But in all cases, whether the mass under consideration be large or
+small, whether the material be obtained by mining, grown, or
+manufactured, the assayer is supposed to receive a small quantity,
+called "the sample," which is, or ought to be, the exact counterpart of
+the mass of material that is being dealt with. The taking and making of
+this sample is termed "sampling"; and the men whose special work it is
+to select such samples are "the samplers."</p>
+
+<p>But although "sampling" is thus distinct from "assaying," the assayer
+should be familiar with the principles of sampling, and rigorous in the
+application of these principles in the selecting, from the sample sent
+him, that smaller portion upon which he performs his operations.</p>
+
+<p><b>Sampling.</b>&mdash;<i>In the case of gases</i>, there is absolutely no trouble in
+mixing. The only difficulty is in drawing off a fair sample where, as in
+flues, the body of the gas is in motion, and varies a little in
+composition from time to time. In this case, care must be taken to draw
+off uniformly a sufficient volume of the gas during a prolonged period;
+any portion of this larger volume may then be taken for the analytical
+operation.<span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span></p>
+
+<p><i>In the case of liquids</i>, which mix more or less easily&mdash;and this class
+includes metals, &amp;c., in the state of fusion&mdash;more or less severe
+agitation, followed by the immediate withdrawal of a portion, will yield
+a fairly representative sample.</p>
+
+<p><i>In the case of solids</i>, the whole mass must be crushed, and, if not
+already of fairly uniform quality, mixed, before sampling can take
+place. Most of the material which a sampler is called upon to deal with,
+is, however, in a more or less divided state and fairly uniform. In
+practice it is assumed that 5 per cent. of the whole (= 1/20th), if
+taken in portions of equal weight and at frequent and regular intervals,
+will represent the mass from which it was taken. Taking a heap of ore,
+A, and selecting one out of every twenty spade-, bag-, barrow-, or
+wagon-fuls, according to the quantity of stuff in the heap, there is
+obtained a second heap, B, containing one-twentieth of the stuff of the
+heap A. If we crush the stuff in B until this heap contains
+approximately the same number of stones as A did&mdash;which means, crushing
+every stone in B into about twenty pieces&mdash;B will become the counterpart
+of A. Selecting in the same manner 5 per cent. of B, there is got a
+third heap, C. This alternate reduction and pulverising must be carried
+on until a sample of suitable size is obtained. This may be expressed
+very clearly thus:&mdash;</p>
+
+<p>
+<span style="margin-left: 3em;">A&nbsp; =&nbsp; 1000 tons of rocks and lumpy ore.</span><br />
+<span style="margin-left: 3em;">B&nbsp; =&nbsp; &nbsp; 50&nbsp; &nbsp; &nbsp; " &nbsp; "&nbsp; &nbsp;  rough stones,&nbsp; 1/20th of A.</span><br />
+<span style="margin-left: 3em;">C&nbsp; =&nbsp; &nbsp;  2.5&nbsp; &nbsp; "&nbsp; &nbsp;  "&nbsp; &nbsp;  small stones,&nbsp; 1/20th of B.</span><br />
+<span style="margin-left: 3em;">D&nbsp; =&nbsp; &nbsp;  0.125&nbsp; "&nbsp; &nbsp;  "&nbsp; &nbsp;  coarse powder, 1/20th of C.</span><br />
+</p>
+
+<div class="figcenter" style="width: 358px;">
+<img src="images/fig001.jpg" width="358" height="300" alt="Fig. 1." title="" />
+
+</div>
+
+<p>If the material to be sampled is already a dry powder, 5 per cent. of it
+should be heaped in a cone; each lot being added on<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span> the apex of the
+cone already formed, so that it may distribute itself by falling evenly
+in all directions. When the cone is completed, convert it into a low
+frustrum of a cone by drawing stuff uniformly and in a direct line from
+the centre to the circumference. Draw two diameters at right angles to
+each other, and reserving any two alternate quarters, reject the others.
+Mix; and form another cone, and proceed until a sample is got of the
+bulk required.</p>
+
+<p>This is the usual plan, and all samples should be treated in this way
+when the stuff is fine enough to fall evenly down the sides of a cone.</p>
+
+<p>Samples as they reach the assay office are seldom in a fit state for the
+work of the assayer; they are generally too coarse, and ought always to
+be more than he wants for any particular determination. The portion he
+requires should never be taken at hap-hazard; the sample must be reduced
+systematically to the quantity required.</p>
+
+<p>1. <i>If the sample is a liquid:</i> it is sufficient to shake the bottle,
+and take out a measured or weighed quantity for the assay.</p>
+
+<p>2. <i>If a liquid with a solid in suspension:</i> measure the whole of it.
+Filter. Make up the filtrate with the wash-water or water to the
+original bulk. Assay it. Dry and weigh the residue, and make a separate
+assay of it.</p>
+
+<p>3. <i>If of a creamy consistency, free from heavy particles:</i> mix well;
+spread out evenly on a glazed tile. Take up equal portions at equal
+distances. Mix and assay.</p>
+
+<p>4. <i>If a mud of coarse and fine particles, or of particles of unequal
+density:</i> weigh and transfer to a porcelain dish, or weigh in the dish.
+Dry at 100&deg; C., weigh. Treat the residue as a solid capable of being
+powdered.</p>
+
+<p>5. <i>If a solid capable of being powdered, or already powdered:</i> heap up
+into a cone; flatten with a spatula; divide along two diameters at right
+angles, and carefully reject the whole of two alternate quarters,
+brushing away any fine powder. Mix the other quarters, and repeat (if
+necessary). For small quantities a fine state of division is essential.</p>
+
+<p>6. <i>If a solid with metallic particles:</i> powder and pass through a
+sieve; the metallic particles will not pass through. Weigh both portions
+and assay separately. <i>Sifting should be followed by a very thorough
+mixing.</i></p>
+
+<p>7. <i>If a metal or alloy in bar or ingot:</i> clean the upper surface of the
+bar, and bore through the bar. Use the borings. If the ingot or bar is
+small, cut it through and file the section. Filings must be freed from
+fragments of the file by means of a magnet; and from oil, if any be
+present, by washing with a suitable<span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span> solvent.<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> Where practicable,
+metals and alloys are best sampled by melting and granulating. The
+student must carefully avoid any chance of mixing dirt or particles of
+other samples with the particular sample which he is preparing. One ore
+should be done at a time, and when finished, it should be labelled and
+wrapped up, or bottled, before starting on a fresh sample.</p>
+
+<p>When an ore requires to be very finely ground in an agate mortar, it is
+often advisable to mix with a little pure alcohol and rub until free
+from grit; dry at 100&deg; C. and mix well before weighing.</p>
+
+<p>When an assay is required of a quantity of ore made up of parcels of
+different weight and quality, each parcel should be separately sampled
+and parts of each sample, bearing to each other the same proportion by
+weight as the original parcels, should be taken and mixed. For example,
+a lot of ore is made up of one parcel of A, 570 tons, one of B, 180
+tons, and another of C, 50 tons; a sample representing the whole may be
+got by mixing 57 parts of a sample of A with 18 parts of a sample of B,
+and 5 parts of a sample of C.</p>
+
+<div class="figcenter" style="width: 386px;">
+<img src="images/fig002.jpg" width="386" height="300" alt="Fig. 2." title="" />
+
+</div>
+
+<p>A bruising plate, like that in fig. 2, is convenient for general office
+work. The slab is of cast iron, about an inch thick. It is firmly
+supported on a solid block of wood, and pivoted for convenience in
+emptying. The bruising-hammer is steel-faced, about 4 inches square, and
+1-1/2 inch thick. The block is firmly fixed to a small table or tressel,
+so that the slab is about 2 feet 6 inches<span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span> from the ground. The slab is
+cleaned, and the sample collected with the help of a stiff-haired brush.</p>
+
+<p><b>Drying: Determination of Moisture.</b>&mdash;In practice, the moisture is
+generally determined by the samplers, and the proportion is specified in
+grains per pound on the label attached to the sample when it reaches the
+assay office. The method adopted is usually to dry 1 lb. = 7000 grs. of
+the ore in a frying-pan heated over a gas flame, or in an ordinary oven,
+until a cold bright piece of metal or glass is no longer damped when
+held over it. The loss of weight in grains = moisture.</p>
+
+<p>Properly, however, this work should be done by the assayer, if only for
+the following reason. It is assumed that the dry ore of the sampler and
+of the assayer are the same thing; according to the nature of the ore,
+this may or may not be the case. The assayer, however, uses the sample
+which he has dried for his moisture-determination, as the dry ore on
+which he makes his other assays, and no variation in moisture would
+influence the other and more important determinations. Some ores are
+sent to the smelter with from 5 to 15 per cent. of adherent water. In
+these cases it is best to spread out the sample, and taking equal
+portions fairly at regular intervals, weigh into a Berlin dish 20 grams.
+This should then be dried over a sand-bath, or if the ore is likely to
+be injured by excess of heat, over a water-bath until the weight is
+constant. The loss of weight multiplied by 5 gives the percentage of
+water present.</p>
+
+<p>Example:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight of dish + wolfram</td><td align='right'>32.67</td> <td align='left'>grms.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dish</td><td align='right'>12.67</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;wolfram</td><td align='right'>20.00</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dish + wolfram</td><td align='right'>32.67</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dried</td><td align='right'>30.15</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;water</td><td align='right'>2.52</td><td align='left'>"</td></tr>
+<tr><td align='left'>2.52 &times; 5 = 12.6</td><td align='right'><b>12.6%.</b></td></tr>
+</table></div>
+
+
+<p>There are other ores which are not apparently wet, but in the state
+called "air-dried." It is easier to take fair samples of these, and,
+consequently, it is not necessary to use so large a quantity as 20
+grams. But with a smaller quantity, extra precautions must be taken. All
+dry solids at ordinary temperatures absorb moisture from the air. The
+amount varies with the nature of the material and with the quantity of
+surface exposed. Light bulky powders absorb more than heavy ones,
+because of the greater condensing surface. It is on this account that it
+is well to weigh substances, which have been dried, between
+close-fitting watch-glasses. The<span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span> method of determining moisture is to
+weigh out into the glasses 5 grams of ore, and dry in the water-oven
+until there is no further loss of weight. On taking the glasses out of
+the oven, they should be at once closed, the clip put on, and after
+cooling in a desiccator weighed. If after a second trial the loss is the
+same, or only increased by a milligram, the determination is finished.</p>
+
+<p>Example:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'> Weight of glasses + pyrites</td><td align='right'>31.0470</td> <td align='left'>grms.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;glasses</td><td align='right'>26.0470</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;pyrites</td><td align='right'>5.0000</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;glasses + pyrites, dried 1 hour</td><td align='right'>30.8965</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dried 1-1/2 &nbsp;&nbsp;&nbsp;"</td><td align='right'>30.8957</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='right'>31.0470</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;dried</td><td align='right'>30.8957</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;moisture</td><td align='left'>0.1513</td><td align='left'>"</td></tr>
+<tr><td align='left'>0.1513 &times; 20 = 3.026</td><td align='right'><b>3.02%.</b></td></tr>
+</table></div>
+
+
+<div class="figcenter" style="width: 103px;">
+<img src="images/fig003.jpg" width="103" height="400" alt="Fig. 3." title="" />
+
+</div>
+
+<p>Sometimes it may be advisable to dry 10 grams, in which case multiplying
+the loss by 10 will give the percentage. The dried ore should be
+transferred to a weighing-tube (fig. 3), and reserved for the subsequent
+determinations. The weighing-tube with the ore must be marked, and kept
+in a desiccator.</p>
+
+<p>Most ores and inorganic substances can be dried, and their moisture
+determined by the loss in this way. When, however, the substance
+contains another somewhat volatile ingredient, it is exposed over
+sulphuric acid in a desiccator for two days (if <i>in vacuo</i>, all the
+better), and the loss determined. Moisture in dynamite should be
+determined in this way.</p>
+
+<p>When water is simply mechanically mixed with a substance it presents but
+little difficulty. The combined water is a different matter. Slaked
+lime, even when perfectly dry, contains much water; and if the water of
+soda crystals were separated and frozen, it would occupy a volume equal
+to that of the original crystals. Perfectly dry substances may contain
+much water, and this combined water is retained by different materials
+with very unequal vigour. Sodium sulphate and sodium phosphate crystals
+lose water even when exposed under ordinary conditions to dry air. Soda
+crystals when heated melt, and at a moderate temperature give off their
+water with ebullition. The temperature at which all the water is given
+up varies with each particular salt; the actual determination of the
+water in each case will require somewhat different treatment. Such
+determinations, however, are seldom<span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span> required; and from a practical
+point of view this combined water causes no trouble.</p>
+
+<p><i>In assaying ores</i>, we term "moisture" all water which is lost by
+exposure in a water-oven at 100&deg; C., and the "dry ore" is the ore which
+has been dried at this temperature. No advantage, but rather endless
+confusion, would be caused by varying the temperature with the object of
+estimating the whole of the water which a hydrated salt may contain. The
+results of the assay of the other components should be calculated on the
+"dry ore." One advantage of this is obvious:&mdash;The dry ore has a constant
+composition, and the results of all assays of it will be the same, no
+matter when made; the moisture, however, may vary from day to day, and
+would be influenced by a passing shower of rain. It is well to limit
+this variability to the moisture by considering it apart, and thus avoid
+having the percentage, say, of copper rising and falling under the
+influence of the weather.</p>
+
+<p>In the case of certain salts, however, such as soda crystals and
+hydrated sulphate of copper (when these constitute the bulk of the
+substance to be assayed), it is as well to perform the assay on the
+moist, or at any rate air-dried, substance.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a> It would be equally
+convenient to calculate on the substance dried at 100&deg; C.; but in this
+case it would be well, in order to avoid a somewhat shallow criticism,
+to replace the term "moisture" by the longer but equivalent phrase
+"water lost at 100&deg; C."</p>
+
+<p><b>Calculation and Statement of Results.</b>&mdash;By far the most generally
+convenient method of stating the results of an assay is that of the
+percentage or parts in a hundred, and to avoid a needlessly troublesome
+calculation it is well to take such a quantity of ore for each assay as
+by a simple multiplication will yield the percentage. In these
+calculations decimals are freely employed, and students should make
+themselves familiar with the methods of using them.</p>
+
+<p>Other methods of statement are in use, and have advantages in certain
+special cases. With bullion the parts in a thousand are given, and in
+those cases in which the percentage is very small, as in water analysis,
+it is convenient to report on parts in 100,000, or even on parts per
+1,000,000. These are easily got from the corresponding percentages by
+shifting the decimal point one, three, or four places to the right. Thus
+92.5 per cent. is 925 per thousand; and 0.0036 per cent. is 3.6 per
+100,000, or 36 per million.</p>
+
+<p>With ores of tin, silver, and gold, the result is stated as so many
+cwts., lbs., or ozs., in the ton. With dressed tin ores as they are<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span>
+sent to the smelter, the produce is given in cwts. and quarters to the
+ton. The corresponding percentage may be obtained by multiplying by
+five; or, inversely, if the percentage is given, the produce may be got
+by dividing by five. A produce of 13-1/2 equals a percentage of 13.5 &times; 5
+= 67.5; and a percentage of 70.0 equals a produce of 70 / 5 = 14. With
+tin ores as raised (in which the percentage is small) the reduction must
+be carried to pounds per ton. One per cent. equals 22.4 lbs. to the ton;
+consequently, if we multiply the percentage by 22.4, the produce will be
+given. Thus, if an ore contains 6.7 per cent. of oxide of tin, the
+produce is 6.7 &times; 22.4 = 150 lbs. (or 1 cwt., 1 quarter, and 10 lbs.) to
+the ton. With gold and silver ores, the proportion of precious metal is
+small, and it is necessary to carry the reduction to ozs. and dwts. to
+the ton; and since gold and silver are sold by troy weight, whilst the
+ton is avoirdupois, it is of importance to remember that the ounces in
+the two systems are not the same. A ton contains 15,680,000 grains,
+which equal 653,333.3 dwts. or 32,666.6 ozs. (troy). The following rules
+are useful:&mdash;</p>
+
+<p>
+<span style="margin-left: 3em;">To get ozs. (troy) per ton, multiply parts per 100,000 by 0.327;</span><br />
+<span style="margin-left: 3em;">To get dwts. per ton, multiply parts per 100,000 by 6.53;</span><br />
+<span style="margin-left: 3em;">To get grains per ton, multiply parts per 100,000 by 156.8.</span><br />
+</p>
+
+<p>Where liquids are being assayed, cubic centimetres are held to be
+equivalent to grams, and the usual method of statement is, "so many
+parts by weight in so many by measure." Where the statement is made as
+grams per litre or grains per gallon, there can be no doubt as to what
+is meant; and even if it be expressed in parts per 100,000, parts by
+weight in a measured volume must be understood unless the contrary is
+expressly stated.</p>
+
+<p>In some cases, where the density of the solution differs greatly from
+that of water, the percentage by weight may be given; and in others,
+mixtures of two or more liquids, the percentages may be given by volume
+or by weight; as so many c.c. in 100 c.c., or as so many grams in 100
+grams, or even as so many grams in 100 c.c. In such cases it must be
+distinctly shown which method of statement is adopted.</p>
+
+<p>One grain per gallon means 1 grain in 70,000 grain-measures, or one part
+in 70,000. Dividing by 7 and multiplying by 10 will convert grains per
+gallon into parts per 100,000. Inversely, dividing by 10 and multiplying
+by 7, will convert parts per 100,000 into grains per gallon.</p>
+
+<p>Grams per litre are parts per 1000; multiplying by 100 will give parts
+per 100,000, and multiplying by 70 will give grains per gallon.</p>
+
+<p>Among foreign systems of weights, the French is by far the best.
+Kilograms (2.205 lbs.) per quintal (220.5 lbs.) are parts per cent.; and
+grams (15.43 grs.) per quintal are parts per<span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span> 100,000. From the rule
+already given, grams per quintal may be converted into ounces to the ton
+by multiplying by 0.327.</p>
+
+<p>The German loths per centner (1/2 oz. (avoirdupois) to 100 lbs.) equal
+parts per 3200; they are converted into parts per cent. by dividing by
+32, or into ounces (troy) per ton by multiplying by 10.208.</p>
+
+<p>In the United States, as a sort of compromise between the avoirdupois
+and metric systems, a ton is taken as 2000 lbs. There, too, the custom
+is adopted of reporting the gold and silver contents of an ore as so
+many dollars and cents to the ton. In the case of gold, an ounce is
+considered to be worth 20.6718 dollars. With silver, the <i>nominal</i> value
+is 1.2929 dollars per ounce, but frequently in assay reports it is taken
+as one dollar. The practice is objectionable. The prices of metals vary
+with the fluctuations of the market, and if the assayer fixed the price,
+the <i>date</i> of his report would be all important; if, on the other hand,
+he takes a fixed price which does not at all times agree with the market
+one, it leaves a path open for the deception of those unacquainted with
+the custom. American "dollars on the ton of 2000 lbs." may be converted
+into "ounces in the ton of 2240 lbs." by dividing by 1.1544 in the case
+of silver, and by 18.457 in the case of gold.</p>
+
+<p><b>Laboratory Books and Report Forms.</b>&mdash;The record which the assayer makes
+of his work must be clear and neat, so that reference, even after an
+interval of years, should be certain and easy. One method should be
+adopted and adhered to. Where there are a large number of samples, three
+books are required.</p>
+
+<p><i>Sample Book.</i>&mdash;This contains particulars of the samples (marks, &amp;c.),
+which are entered by the office-clerk as they arrive. He at the same
+time puts on each sample the distinguishing number.</p>
+
+<p class="center">
+<span class="smcap">Example of Page of Sample Book</span>.<br /></p>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Date.</td><td align='left'>Number.</td><td align='left'>Sample.</td><td align='left'>Remarks.</td></tr>
+<tr><td align='left'>Feb. 1</td><td align='left'>482</td><td align='left'>Tough Copper</td><td align='left'>For Arsenic.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;" &nbsp;&nbsp;&nbsp;2</td><td align='left'>X</td><td align='left'>Piece of Metal</td><td align='left'>For Ni and Cu.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"</td><td align='left'>483</td><td align='left'>Tough Copper.</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"</td><td align='left'>73</td><td align='left'>Silver Precipitate, 4 casks, 24 cwt. 1 qr.</td><td align='left'>With Letter.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"</td><td align='left'>494</td><td align='left'>Purple Ore, 200 tons.</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"</td><td align='left'>1 J.T.</td><td align='left'>Lead Ore, 1 J.T.</td><td align='left'>From Corsica.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"</td><td align='left'>2 J.T.</td><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2 J.T.</td><td align='left'>&nbsp;</td></tr>
+</table></div>
+
+
+
+<p><i>Laboratory Book.</i> This is the Assayer's note-book, in which he enters
+clearly the particulars of his work&mdash;the results obtained, as<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> well as
+how these results were arrived at. The calculations should be done on
+scrap-paper, and should not be entered, although, of course, detail
+enough must be shown to enable the results to be recalculated.</p>
+
+<p class="center">
+<span class="smcap">Example of Page of Laboratory Book.</span><br /></p>
+
+<pre>
+____________________________________________________________
+
+Purple Ore                                     5 grams
+19/10/89          0.0042 grm.
+                      0.0021  "
+                      &mdash;&mdash;&mdash;
+       Colorimetric   0.0063 &times; 20         =  0.13% Copper
+______________________________________________________________
+
+      482
+  Tough Copper                              10 grams
+    Feb. 1/89        10.5 c.c. Uranium.
+                                          =  0.52% Arsenic
+______________________________________________________________
+
+     2082
+  Tough Copper                              10 grams
+                     12.7 c.c. Uranium.
+                                          =  0.63% Arsenic
+______________________________________________________________
+
+      491                                   10 grams
+  Tough Copper       13.7 c.c. Uranium
+    Feb. 1/89
+                                          =  0.68% Arsenic
+______________________________________________________________
+
+  Standard of Uranium acetate.
+            0.150 gram As2O3 = 23.3 c.c. Uranium.
+              &#8756; 100 cc. Uranium  =  0.5 gram As.
+______________________________________________________________
+
+     10071                                    5 grams
+   Tin Ore          Cruc. and SnO2 9.6065 grms.
+  Feb. 3/89         Cruc. and Ash     9.4235   "
+                                   &mdash;&mdash;&mdash;
+                         SnO2 = 0.1830  = 2.88% Tin
+______________________________________________________________
+</pre>
+
+<p><i>The Assay Book.</i>&mdash;This is the Official book, and is a combination of
+the Sample and Laboratory books. It corresponds with the report-forms.
+Without being loaded with detail, it should contain sufficient to
+characterise each sample.<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span></p>
+
+<p class="center">
+
+<span class="smcap">Example of Page of Assay Book.</span><br /></p>
+
+<p><b>Description of Sample.</b></p>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Date.</td><td align='left'>Material.</td><td align='left'> Weight.</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>No.</td><td align='left'> Water Lost at 100&deg; C.</td><td align='left'> Assay on the Dry Material.</td><td align='left'> Date Reported.</td></tr>
+<tr><td align='left'>1889</td><td align='left'>&nbsp;</td><td align='left'> ton</td><td align='left'> cwt</td><td align='left'> qrs</td><td align='left'> lbs</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>Feb. 1</td><td align='left'> Tough cake copper</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'> 482</td><td align='left'>...</td><td align='left'> Arsenic, 0.52%</td><td align='left'>7</td></tr>
+<tr><td align='left'>"</td><td align='left'>Tough cake copper</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>  2082</td><td align='left'>...</td><td align='left'> Arsenic, 0.63%</td><td align='left'>7</td></tr>
+<tr><td align='left'>"</td><td align='left'> Tough cake copper</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>  491</td><td align='left'>...</td><td align='left'> Arsenic, 0.68%</td><td align='left'>7</td></tr>
+<tr><td align='left'>Feb. 2</td><td align='left'> Nickel disc for C.R.</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'>  X</td><td align='left'>...</td><td align='left'> Copper, 73.75</td><td align='left'>7</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Nickel, 24.34</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Iron, 2.18</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> &mdash;&mdash;&mdash;</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> 100.27</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> &mdash;&mdash;&mdash;</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'> "</td><td align='left'> Silver precipitate, 4 casks</td><td align='left'>...</td><td align='left'>24</td><td align='left'> 1</td><td align='left'> 0</td><td align='left'> 73</td><td align='left'> Not det.</td><td align='left'> Silver, 4.851</td><td align='left'>10</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Gold, 0.0215</td><td align='left'>...</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Lead, 19.37</td><td align='left'>...</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Zinc, 2.00</td><td align='left'>...</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Silver, 1584.7 ozs. per ton</td><td align='left'>...</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Gold, 7.0 ozs. per ton</td><td align='left'>...</td></tr>
+<tr><td align='left'>"</td><td align='left'>Purple ore</td><td align='left'>...</td><td align='left'> 200</td><td align='left'>...</td><td align='left'>...</td><td align='left'>...</td><td align='left'> 494</td><td align='left'> Not det.</td><td align='left'> Copper, 0.13%</td><td align='left'> 11</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'>&nbsp;</td><td align='left'> Sulphur 0.15%</td><td align='left'>...</td></tr>
+</table></div>
+
+<p>When the number of samples is small, the Sample Book may be omitted, and
+the entries made in the Assay Book as the samples arrive.</p>
+
+<p><i>Report-forms.</i> These should entail as little writing as possible in
+making out the report. For general purposes the form given on p. 12 is
+useful.</p>
+
+<p><b>The quantity of substance</b> to be taken for any particular assay depends
+largely upon the method of assay adopted. There are, however, some
+general considerations which should be remembered, and some devices for
+simplifying the calculations which should be discussed.</p>
+
+<p>The smaller the percentage of the substance to be determined, the larger
+should be the amount of the ore taken. The following table will give a
+general idea as to this:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>Percentage of the substance to be determined.</td><td align='center'>Amount of ore, &amp;c. to be weighed.</td></tr>
+<tr><td align='center'>100-10</td><td align='center'>1 gram.</td></tr>
+<tr><td align='center'>10-5</td><td align='center'>2 grams.</td></tr>
+<tr><td align='center'>5-1</td><td align='center'>5 &nbsp;&nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='center'>1-0.1</td><td align='center'>10 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='center'>0.1-0.01</td><td align='center'>20 &nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span></p>
+
+<div class="figcenter" style="width: 490px;">
+<img src="images/assaynote.jpg" width="490" height="300" alt="ASSAY NOTE" title="" />
+<span class="caption">ASSAY NOTE</span>
+</div>
+
+<p>The rougher the method of assay adopted, the larger should be the<span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span>
+quantity of ore taken. If the degree of accuracy attainable with the
+methods and instruments at the assayer's service is known, it is easy to
+calculate what quantity should be taken for any particular case. If the
+results are good within 0.001 gram, then, taking 1 gram of ore we can
+report within 0.1 per cent., or if they are good within 0.0002 gram,
+taking 20 grams of ore, we can report within 1 part per 100,000, or very
+closely within 6-1/2 dwt. to the ton. If it is wished to be yet more
+particular in reporting, larger quantities must be taken. The difficulty
+of manipulating very small or very large precipitates, &amp;c., must be
+borne in mind. So, too, must the fact that the greater the weight of the
+final product of an assay, the less, as a rule, is the percentage error.
+The distinction between absolute and percentage error, often overlooked,
+is important. If 0.5 gram of silver be cupelled with 20 grams of lead,
+there may be obtained a button of 0.495 gram; the absolute loss is 0.005
+gram, and this equals 1 per cent. of the silver present. Similarly,
+cupelling 0.1 gram, the resulting button may be 0.098; the absolute loss
+is only 0.002 gram, but this equals 2 per cent. of the silver present.
+In the same way the student should see that the two results, 91.5 per
+cent. and 92.0 per cent., are really more concordant than the results
+9.1 per cent. and 9.2 per cent.</p>
+
+<p>A device often adopted in practice where a large number of assays of one
+kind are made, and the report is given as so many ounces or pounds to
+the ton, is that known as the <i>assay ton</i>. The assay ton may be any
+arbitrary and convenient weight, but its subdivisions must bear to it
+the same relations as pounds and ounces bear to the actual ton. On the
+other hand, in a laboratory where many kinds of work are performed,
+different sets of weights of this kind would only tend to confusion,
+even if they were not unnecessary. With a set of gram weights and its
+subdivisions anything may be done. If it is desired to report as pounds
+to the ton, then, since there are 2240 lbs. to the ton, a weight of
+2.240 grams may be taken as the assay ton, and each 0.001 gram yielded
+will equal 1 lb., or 22.4 grams may represent the ton, and each 0.01
+gram a pound. Similarly, since there are 32,666.6 ozs. troy to the ton;
+if we take 32.6667 grams as the assay ton, each 0.001 gram will equal 1
+oz. to the ton. In some cases it may be convenient to have, in addition
+to the usual gram weights, one or other of the "assay tons" mentioned
+above, but generally it is better to work on a purely decimal system,
+and convert when required into ounces per ton, &amp;c., either by actual
+calculation or by reference to a set of tables.<span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span></p>
+
+
+<p><span class="smcap">Practical Exercises.</span></p>
+
+<p>The student should practise such calculations as the following:&mdash;</p>
+
+<p>
+1. Calculate the percentages in the following cases:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Ore taken, 2 grams; copper found, 0.2155.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>)&nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  1.5 gram; iron found, 0.8340.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>)&nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  30 grams; lead found, 23.2.</span><br />
+<br />
+2. Calculate the parts per thousand in the following:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Bullion taken, 1.1 gram; silver found, 1.017.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>)&nbsp; &nbsp; &nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  1.14 gram; silver found, 1.026.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>)&nbsp; &nbsp; &nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  0.6 gram; gold found, 0.5500.</span><br />
+<br />
+3. Calculate parts per 100,000 in the following:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Ore taken, 20 grams; silver found, 0.0075.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>)&nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  50 grams; gold found, 0.0026.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>) Water taken, 500 c.c.; solids found, 0.1205.</span><br />
+<br />
+4. Calculate cwts. to the ton in the following:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Ore taken, 5 grams; tin found, 2.816.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>)&nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  5 grams; tin found, 3.128.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>) An ore with 68.2 per cent. of tin.</span><br />
+<br />
+5. Calculate lbs. to the ton in the following:&mdash;<br />
+<span style="margin-left: 1em;">(a) An ore with 3.28 per cent. oxide of tin.</span><br />
+<span style="margin-left: 1em;">(b) Ore taken, 20 grams; oxide of tin found, 1.67.</span><br />
+<br />
+6. Calculate ozs. (troy) to the ton in the following:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Ore taken, 50 grams; gold found, 0.0035.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>)&nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  20 grams; silver found, 0.0287.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>)&nbsp; &nbsp; "&nbsp; &nbsp; &nbsp;  25 grains; silver found, 0.0164.</span><br />
+<br />
+7.  Calculate in grains per gallon:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) 0.51 gram per litre.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>) 24.6 parts per 100,000.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>) Solution taken, 100 c.c.; copper found, 0.0045 gram.</span><br />
+<span style="margin-left: 1em;">(<i>d</i>)&nbsp; &nbsp; &nbsp; &nbsp;  "&nbsp; &nbsp; &nbsp; &nbsp; 50 c.c.; iron found, 0.165 gram.</span><br />
+<br />
+8. Convert into ozs. (troy) per ton:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) 7 loths per centner.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>) 30 grams per quintal.</span><br />
+<span style="margin-left: 1em;">(<i>c</i>) 15 parts per 100,000.</span><br />
+</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> Ether or carbon bisulphide.</p></div>
+
+<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> Such substances are best dried by pressing between folds of
+dry filter-paper.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<h2><a name="CHAPTER_II" id="CHAPTER_II"></a>CHAPTER II.</h2>
+<p><span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span></p>
+
+<h3>METHODS OF ASSAYING.&mdash;DRY GRAVIMETRIC METHODS.</h3>
+
+
+<p>The methods of assaying are best classed under two heads, Gravimetric
+and Volumetric, in the former of which the final results are weighed,
+whilst in the latter they are measured. A commoner and older division is
+expressed in the terms much used in practice&mdash;wet assays and dry assays.
+Wet assays include all those in which solvents, &amp;c. (liquid at the
+ordinary temperature), are mainly used; and dry assays, those in which
+solid re-agents are almost exclusively employed. Dry assays form a
+branch of gravimetric work, and we shall include under this head all
+those assays requiring the help of a wind furnace. Wet assays, as
+generally understood, would include not only those which we class as wet
+gravimetric assays, but also all the volumetric processes.</p>
+
+<p><b>Gravimetric Methods</b> aim at the separation of the substance from the
+other matters present in the ore, so that it may be weighed; and,
+therefore, they must yield the <i>whole</i> of the substance in a pure state.
+It is not necessary that a metal should be weighed as metal; it may be
+weighed in the form of a compound of definite and well known
+composition. For example, one part by weight of silver chloride contains
+(and, if pure, always contains) 0.7527 part of silver; and a quantity of
+this metal can be as exactly determined by weighing it as chloride as by
+weighing it in the metallic state. But in either case the metal or its
+chloride must be pure.</p>
+
+<p>Exact purity and complete separation are not easily obtained; and
+methods are used which are defective in one or both of these respects.
+It is well to note that an impure product increases the result, whilst a
+loss of the substance decreases it; so that if both defects exist in a
+process they tend to neutralise each other. Of dry methods generally, it
+may be said that they neither give the whole of the substance nor give
+it pure; so that they are only calculated to show the amount of metal
+that can be extracted on a manufacturing scale, and not the actual
+quantity of it present.<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> Their determinations are generally rough and
+always low. The gold and silver determinations, however, will compare
+very favourably with any of the other processes for the estimation of
+these metals in their ores.</p>
+
+<p>The calculation of the results of a gravimetric assay has already been
+referred to. If the result is to be stated as percentage, it may always
+be done by the following rule:&mdash;<i>Multiply the weight of the substance
+got by the percentage of metal it contains, and divide by the weight of
+ore taken.</i></p>
+
+<p>Gravimetric methods are divided into three groups: (1) mechanical
+separations; (2) dry methods; and (3) wet methods.</p>
+
+<p><b>Mechanical Separations.</b>&mdash;Under this head are classed the method of
+assaying tin ores, known as vanning, and the amalgamation assay for
+gold. A set of sieves to determine the relative proportion of powders of
+different degrees of fineness is sometimes useful. A set with 10, 20, 40
+and 80 meshes to the inch is convenient.</p>
+
+<p><b>Dry Assays.</b>&mdash;An important distinction between wet and dry methods of
+assaying is, that in the former the substance is got into the liquid
+state by solution, whilst in the latter fusion is taken advantage of.</p>
+
+<p>The difference between solution and fusion is easily illustrated: a lump
+of sugar heated over a candle-flame melts or fuses; suspended in water
+it dissolves. Many substances which are insoluble or infusible of
+themselves, become soluble or fusible when mixed with certain others;
+thus, in this way, solution is got with the aid of reagents, and fusion
+with the help of fluxes. For example, lead is insoluble in water, but if
+nitric acid be added, the metal rapidly disappears. It is convenient,
+but somewhat inaccurate, to say that the acid dissolves the lead. If the
+lead be acted on by nitric acid alone, without water, it is converted
+into a white powder, which does not dissolve until water is added; in
+this case it is obvious that the water is the solvent. The function of
+the acid is to convert the lead into a soluble compound.</p>
+
+<p><b>Fluxes</b> may act as true solvents. Fused carbonate of soda dissolves
+baric carbonate, and perhaps in many slags true solution occurs; but in
+the great majority of cases a flux is a solid reagent added for the
+purpose of forming a fusible <i>compound</i> with the earthy or stony
+minerals of the ore. Few of the minerals which occur in the gangue of an
+ore are fusible; and still fewer are sufficiently fusible for the
+purposes of the assayer, consequently the subject is one of importance,
+and it ought to be treated on chemical principles. An idea of the
+composition of some of the more frequently occurring rocks may be
+gathered from the following table, which represents rough averages:<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span>&mdash;</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>&nbsp;</td><td align='left'>Silica.</td><td align='left'>Alumina.</td><td align='left'>Oxide of iron</td><td align='left'>Lime and Magnesia.</td><td align='left'>Alkalies.</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>%</td><td align='left'>%</td><td align='left'>%</td><td align='left'>%</td><td align='left'>%</td></tr>
+<tr><td align='left'>Sandstone, grit, quartzite, &amp;c.</td><td align='left'>80-100</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Granite, gneiss, quartz-porphyry, fire-clay, &amp;c.</td><td align='left'>70-75</td><td align='left'>13-20</td><td align='left'>2</td><td align='left'>2</td><td align='left'>5-8 Less in fire-clay.</td></tr>
+<tr><td align='left'>Mica-schist</td><td align='left'>65</td><td align='left'>18</td><td align='left'>5</td><td align='left'>3</td><td align='left'>3</td></tr>
+<tr><td align='left'>Trachyte, syenite</td><td align='left'>60</td><td align='left'>17</td><td align='left'>7</td><td align='left'>4-7</td><td align='left'>6-9</td></tr>
+<tr><td align='left'>Clay-slate</td><td align='left'>60</td><td align='left'>18</td><td align='left'>10</td><td align='left'>8</td><td align='left'>3</td></tr>
+<tr><td align='left'>Diorite</td><td align='left'>54</td><td align='left'>17</td><td align='left'>12</td><td align='left'>9</td><td align='left'>3-4</td></tr>
+<tr><td align='left'>Horneblende-rock</td><td align='left'>50</td><td align='left'>18</td><td align='left'>15</td><td align='left'>12</td><td align='left'>3-4</td></tr>
+<tr><td align='left'>Brick-clay</td><td align='left'>50</td><td align='left'>34</td><td align='left'>8</td><td align='left'>6</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>China-clay</td><td align='left'>47</td><td align='left'>39</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Basalt, dolerite, &amp;c.</td><td align='left'>50</td><td align='left'>15</td><td align='left'>15</td><td align='left'>16</td><td align='left'>3</td></tr>
+<tr><td align='left'>Serpentine</td><td align='left'>44</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>44</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Chalk, limestone, dolomite, &amp;c.</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>45-55</td><td align='left'>&mdash;</td></tr>
+</table></div>
+
+<p>Silica itself, and the silicates of alumina, of lime, and of magnesia,
+are practically infusible; the silicates of soda, of potash, and of iron
+are easily fusible if the base (soda, potash, or oxide of iron) be
+present in sufficient quantity, and if, in the case of the iron, it is
+present mainly as lower oxide (ferrous silicate). The addition of lime,
+oxide of iron, or alkali to silicate of alumina results in the formation
+of a double silicate of alumina and lime, or of alumina and iron, &amp;c.,
+all of which are easily fusible. Similarly, if to a silicate of lime we
+add oxide of iron, or soda, or even alumina, a fusible double silicate
+will be formed. Thus lime, soda, oxide of iron, and clay, are <i>fluxes</i>
+when properly used; but since lime, clay (and oxide of iron if there be
+any tendency to form peroxide), are of themselves infusible, any excess
+of these fluxes would tend to stiffen and render pasty the resulting
+slag. So, too, soda, which is a very strong base, may act prejudicially
+if it be in sufficient excess to set free notable quantities of lime and
+magnesia, which but for that excess would exist in combination as
+complex fusible silicates. There are many minerals which with but little
+soda form a glass, but with more yield a lumpy scoriacious mass. There
+are many minerals, too, which are already basic (for example, calcite),
+and which, when present, demand either a less basic or an acid flux
+according to the proportions in which they exist. For purposes of this
+kind borax, or glass, or clay with more or less soda may be used, and of
+these borax is by far the most generally useful. An objection to too
+basic a slag (and a very important one) is the speed with which it
+corrodes<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span> ordinary crucibles. These crucibles, consisting of quartz and
+clay, are rapidly attacked by lime, soda and bases generally.</p>
+
+<div class="figcenter" style="width: 456px;">
+<img src="images/fig004.jpg" width="456" height="309" alt="Fig. 4." title="" />
+
+</div>
+
+<p>In considering what is and what is not a good slag, certain chemical
+properties are of importance. If a mixture of many substances be fused
+and allowed to solidify in a crucible, there will be found some or all
+of the following. At the bottom of the crucible (fig. 4) a button of
+metal, resting on this a speise; then a regulus, next a slag made up of
+silicates and borates and metallic oxides, and lastly, on the top
+another layer of slag, mainly made up of fusible chlorides and
+sulphates. In assaying operations the object is generally to concentrate
+the metal sought for in a button of metal, speise or regulus, and to
+leave the earthy and other impurities as far as possible in the slag;
+whether there be one or two layers of slag is a matter of
+indifference;<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> but the chemical action of the lower layer upon the
+speise, or regulus, or metal, is of great importance.</p>
+
+<p>A <i>regulus</i> is a compound of one or more of the metals with sulphur; it
+is usually brittle, often crystalline, and of a dull somewhat greasy
+lustre. It is essential that the slag, when solid, shall be so much more
+brittle than the regulus, that it shall be easy to crumble, and remove
+it without breaking the latter; and it must not be basic. The effect of
+fusing a regulus with a basic slag is well seen when <i>sulphide of lead</i>
+is fused with <i>carbonate of soda</i>; the result is a button of metal (more
+or less pure), and a slag containing sulphides of lead and sodium; and
+again, if sulphide of lead be fused with an excess of oxide of lead, a
+button of lead will be got, and a slag which is simply oxide of lead
+(with whatever it may have taken up from the crucible), or if a
+sufficient excess has not been used, oxide of lead mixed with some
+sulphide. When (as is most frequently the case) the desire is to prevent
+the formation of regulus, these reactions may be taken advantage of, but
+otherwise the use of a flux having any such tendency must be avoided. A
+good slag (from which a regulus may be easily separated) may be obtained
+by fusing, say, 20 grams of ore with borax 15 grams, powdered glass 15
+grams, fluor spar, 20 grams, and lime 20 grams; by quenching the slag in
+water as soon as it has solidified, it is rendered very brittle.</p>
+
+<p>Sulphide of iron formed during an assay will remain diffused<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span> through
+the slag, instead of fusing into a button of regulus, if the slag
+contain sulphide of sodium. The same is true of other sulphides if not
+present in too great a quantity, and if the temperature is not too high.</p>
+
+<p><i>Speises</i> are compounds of a metal or metals with arsenic. They are
+chiefly of interest in the metallurgy of nickel, cobalt, and tin. They
+are formed by heating the metal or ore in covered crucibles with arsenic
+and, if necessary, a reducing agent. The product is fused with more
+arsenic under a slag, consisting mainly of borax. They are very fusible,
+brittle compounds. On exposure to the air at a red heat the arsenic and
+the metal simultaneously oxidize. When iron, cobalt, nickel, and copper
+are present in the same speise, they are eliminated in the order
+mentioned.</p>
+
+<p><i>Slags</i> from which metals are to be separated should not be too acid; at
+least, in those cases in which the metal is to be reduced from a
+compound, as well as separated from earthy impurities. Where the object
+is simply to get a button of metal from a substance in which it is
+already in the metallic state, but mixed with dross (made up of metallic
+oxides, such as those of zinc or iron), from which it is desired to
+separate it, an acid flux like borax is best; or, if the metal is easily
+fusible, and there would be danger of loss of metal by oxidation or
+volatilising, it may be melted under a layer of resin or fat. Common
+salt is sometimes used with a similar object, and is often useful. Under
+certain conditions, however, it has a tendency to cause the formation of
+volatile chlorides with a consequent loss of metal.</p>
+
+<p>In the great majority of cases, the fusion of the metal is accompanied
+by reduction from the state of oxide; in these the slag should be basic.
+It is not easy to reduce the whole of a reducible oxide (say oxide of
+copper or of iron) from a slag in which it exists as a borate or
+silicate; there should be at least enough soda present to liberate it.
+When the object is to separate one metal, say copper, without reducing
+an unnecessary amount of another (iron) at the same time, a slag with a
+good deal of borax is a distinct advantage. The slag then will probably
+not be free from copper, so that it will be necessary to powder and mix
+the slag with some soda and a reducing agent, and to again fuse the slag
+in order to separate this residual metal. In all those cases in which
+the slag retains an oxide of a heavy metal, this cleaning of the slag is
+advisable, and in the case of rich ores necessary. Slags containing
+sulphides are especially apt to retain the more easily reducible metals.</p>
+
+<p>The following are the ordinary and most useful fluxes:&mdash;</p>
+
+<p><b>Soda.</b>&mdash;The powdered bicarbonate, sold by druggists as "carbonate<span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span> of
+soda," is generally used. It gives off its water and excess of carbonic
+acid readily and without fusion. Where the melting down is performed
+rapidly, the escaping gas is apt to cause trouble by frothing, and so
+causing waste of the material. Ordinary carbonate of soda, when hydrated
+(soda crystals), melts easily, and gives off its water with ebullition.
+It is unfit for use in assaying, but when dried it can be used instead
+of the bicarbonate. One part of the dried carbonate is equivalent to
+rather more than one and a half parts of the bicarbonate. From two to
+four parts of the flux are amply sufficient to yield a fluid slag with
+one part of earthy matter. This statement is also true of the fluxes
+which follow.</p>
+
+<p><b>Borax</b> is a hydrated biborate of soda, containing nearly half its
+weight of water. When heated it swells up, loses its water, and fuses
+into a glass. The swelling up may become a source of loss in the assay
+by pushing some of the contents out of the crucible. To avoid this,
+<i>fused</i> or <i>dried borax</i> may be used, in which case a little more than
+half the amount of borax indicated will suffice. Borax will flux almost
+anything, but it is especially valuable in fluxing lime, &amp;c., and
+metallic oxides; as also in those cases in which it is desired to keep
+certain of the latter in the slag and out of the button of metal.</p>
+
+<p><b>Oxide of Lead</b>, in the form of red lead or litharge, is a valuable
+flux; it easily dissolves those metallic oxides which are either
+infusible or difficultly fusible of themselves, such as oxides of iron
+or copper. The resulting slag is strongly basic and very corrosive; no
+crucible will long withstand the attack of a fused mixture of oxides of
+lead and copper. With silicates, also, it forms very fusible double
+silicates; but in the absence of silicates and borates it has no action
+upon lime or magnesia. Whether the lead be added as litharge or as red
+lead, it will exist in the slag as monoxide (litharge); the excess of
+oxygen of the red lead is thus available for oxidising purposes. If this
+oxidising power is prejudicial, it may be neutralised by mixing the red
+lead with 1 per cent. of charcoal.</p>
+
+<p><b>Glass</b>: broken beakers and flasks, cleaned, dried, and powdered will
+do. It should be free from lead.</p>
+
+<p><b>Fluor</b>: fluor-spar as free as possible from other minerals, powdered.
+It helps to flux phosphate of lime, &amp;c., and infusible silicates.</p>
+
+<p><b>Lime</b>: should be fresh and powdered. It must not be slaked. Powdered
+white marble (carbonate of lime) will do; but nearly double the quantity
+must be taken. One part of lime produces the same effect as 1.8 parts of
+the carbonate of lime.</p>
+
+<p><b>Tartar</b> and "black flux," are reducing agents as well as fluxes.<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span> The
+"black flux," which may be obtained by heating tartar, is a mixture of
+carbonate of potash and charcoal.</p>
+
+<p><span class="smcap">Reducing Agents.</span>&mdash;The distinction between reducing agents and
+fluxes (too often ignored) is an important one. Fluxes yield slags;
+reducing agents give buttons of regulus or of metal. The action of a
+reducing agent is the separation of the oxygen or sulphur from the metal
+with which it is combined. For example, the mineral anglesite (lead
+sulphate) is a compound of lead, sulphur, and oxygen; by carefully
+heating it with charcoal the oxygen is taken away by the charcoal, and a
+regulus of lead sulphide remains. If the regulus be then fused with
+metallic iron the sulphur is removed by the iron, and metallic lead is
+left. The charcoal and the iron are reducing agents. But in defining a
+reducing agent as one which removes oxygen, or sulphur, from a metallic
+compound so as to set the metal free, it must be remembered that sulphur
+itself will reduce metallic lead from fused litharge, and that oxygen
+will similarly set free the metal in fused lead sulphide. There is no
+impropriety in describing sulphur as a reducing agent; but it is absurd
+to call oxygen one. Some confusion will be avoided if these substances
+and those which are opposite to them in property be classed as oxidising
+and de-oxidising, sulphurising, and de-sulphurising agents. Most
+oxidising agents also act as de-sulphurisers.</p>
+
+<p><i>The de-oxidising agents</i> most in use are the following:&mdash;</p>
+
+<p><b>Charcoal.</b>&mdash;Powdered wood charcoal; it contains more or less
+hygroscopic moisture and about 3 or 4 per cent. of ash. The rest may be
+considered carbon. Carbon heated with metallic oxides takes the oxygen;
+at low temperatures it forms carbon dioxide, and at higher ones, carbon
+monoxide. Other conditions besides that of temperature have an influence
+in producing these results; and as the quantity of charcoal required to
+complete a definite reaction varies with these, it should be calculated
+from the results of immediate experience rather than from theoretical
+considerations.</p>
+
+<p><b>Flour.</b>&mdash;Ordinary wheat flour is convenient in use. On being heated it
+gives off inflammable gases which have a certain reducing effect, and a
+residue of finely divided carbon is left. It is likely to vary in the
+quantity of moisture it contains. Two parts of flour should be used
+where one part of charcoal would be otherwise required.</p>
+
+<p><b>Tartar.</b>&mdash;This is crude hydric potassic tartrate; the purified salt,
+cream of tartar, may be used. On being heated it gives off inflammable
+gases, and leaves a residue formed of potassic carbonate mixed with
+finely divided carbon. Five parts of tartar should be used in the place
+of one of charcoal.<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span></p>
+
+<p><b>Anthracite</b> or <b>Culm</b> is a kind of coal containing 90 per cent. or more
+of carbon. It gives off no inflammable gas. It is denser, and takes
+longer in burning, than charcoal. Its reducing effect is little inferior
+to that of charcoal. Almost any organic substance can be used as a
+reducing agent, but it is well not to select one which melts, swells up,
+or gives off much water and gas when heated in the furnace.</p>
+
+<p><b>Potassic Cyanide</b> is an easily fusible and somewhat volatile salt,
+which, when fused, readily removes oxygen and sulphur from metallic
+compounds, and forms potassic cyanate or sulphocyanate as the case may
+be. Commercial samples vary much in purity; some contain less than 50
+per cent. of the salt. For assaying, only the better qualities should be
+used.</p>
+
+<p><b>Iron</b> is a de-sulphurising rather than a de-oxidising agent. Iron is
+used in the form of rods, 1/2-inch in diameter, or of nails, or of hoop
+iron. In the last case it should be thin enough to be bent without
+difficulty. Wrought iron crucibles are very useful in the processes
+required for making galena assays.</p>
+
+<p><i>The chief oxidising agents (which are also de-sulphurisers)</i> are the
+following:&mdash;</p>
+
+<p><b>Nitre</b>, or Potassic Nitrate.&mdash;This salt fuses very easily to a watery
+liquid. It oxidises most combustible substances with deflagration, and
+thereby converts sulphides into sulphates, arsenides into arsenates, and
+most metals into oxides. In the presence of strong bases, such as soda,
+the whole of the sulphur is fully oxidised; but in many cases some
+arsenic is apt to escape, and to give rise to a peculiar garlic-like
+odour. The sulphates of soda and potash are thus formed, and float as a
+watery liquid on the surface of the slag.</p>
+
+<p><b>Red lead</b> is an oxide of lead. About one-quarter of its oxygen is very
+loosely held, and, hence, is available for oxidising purposes, without
+any separation of metallic lead. The rest of the oxygen is also
+available; but for each part of oxygen given off, about 13 parts of
+metallic lead are deposited. In silver assays this power of readily
+giving up oxygen is made use of. The residual oxide (litharge) acts as a
+flux.</p>
+
+<p><b>Hot air</b> is the oxidising agent in roasting operations. The sulphur and
+arsenic of such minerals as mispickel and pyrites are oxidised by the
+hot air and pass off as sulphur dioxide and "white arsenic." The metals
+generally remain in the form of oxide, mixed with more or less sulphate
+and arsenate. The residue may remain as a powdery substance (a calx), in
+which case the process of roasting is termed calcination; or it may be a
+pasty mass or liquid. In the calcination of somewhat fusible minerals,
+the roasting should be done at a low temperature to avoid clotting;<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span>
+arsenic and sulphur being with difficulty burnt off from the clotted
+mineral. A low temperature, however, favours the formation of sulphates;
+and these (if not removed) would reappear in a subsequent reduction as
+sulphides. These sulphates may be decomposed by a higher temperature
+towards the end of the operation; their removal is rendered more certain
+by rubbing up the calx with some culm and re-roasting, or by strongly
+heating the calx after the addition of solid ammonic carbonate. In
+roasting operations, as large a surface of the substance as possible
+should be exposed to the air. If done in a crucible, the crucible should
+be of the Cornish type, short and open, not long and narrow. For
+calcinations, <i>roasting dishes</i> are useful: these are broad and shallow,
+not unlike saucers, but unglazed. In those cases in which the products
+of the roasting are liquid at the temperature used, a <i>scorifier</i> (fig.
+38) is suitable if it is desired to keep the liquid; but if the liquid
+is best drained off as quickly as it is formed, a <i>cupel</i> (fig. 5)
+should be used.</p>
+
+<div class="figcenter" style="width: 340px;">
+<img src="images/fig005.jpg" width="340" height="235" alt="Fig. 5." title="" />
+
+</div>
+
+<p>A scorifier is essentially a roasting dish sufficiently thick to resist,
+for a time, the corrosive action of the fused metallic oxides it is to
+contain. The essential property of a cupel is, that it is sufficiently
+porous to allow the fused oxide to drain into it as fast as it is
+formed. It should be large enough to absorb the whole of the liquid; and
+of course must be made of a material upon which the liquid has no
+corrosive action. Cupels do not bear transport well; hence the assayer
+generally has to make them, or to supervise their making. A quantity of
+bone ash is carefully mixed with water so that no lumps are formed, and
+the mixture is then worked up by rubbing between the hands. The bone ash
+is sufficiently wet when its cohesion is such that it can be pressed
+into a lump, and yet be easily crumbled into powder. Cupel moulds should
+be purchased. They are generally made of turned iron or brass. They
+consist of three parts (1) a hollow cylinder; (2) a disc of metal; and
+(3) a piston for compressing the bone ash and shaping the top of the
+cupel. The disc forms a false bottom for the cylinder. This is put in
+its place, and the cylinder filled (or nearly so) with the moistened
+bone ash. The bone ash is then pressed into shape with the piston, and
+the cupel finished with the help of three or four smart blows from a
+mallet. Before removing the piston, turn it half-way round upon its axis
+so as to loosen and smooth the face of the cupel. The cupel is got out
+by pressing up<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span> the disc of metal forming the false bottom; the removal
+is more easily effected if the mould is somewhat conical, instead of
+cylindrical, in form. The cupels are put in a warm place to dry for two
+or three days. A conveniently sized cupel is 1-1/4 inches in diameter
+and about 3/4 inch high. The cavity of the cupel is about 1/4 inch deep,
+and something of the shape shown in fig. 5.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig006.jpg" width="300" height="414" alt="Fig. 6." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig007.jpg" width="300" height="518" alt="Fig. 7." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 522px;">
+<img src="images/fig008.jpg" width="522" height="300" alt="Fig. 8." title="" />
+
+</div><p><span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span></p>
+
+<p>There are two kinds of furnaces required, the "wind" and "muffle"
+furnaces. These are built of brick, fire-brick, of course, being used
+for the lining. They are connected with a chimney that will provide a
+good draught. Figure 6 shows a section of the wind furnace, fig. 7 a
+section of the muffle furnace, and fig. 8 a general view of a group
+comprising a muffle and two wind furnaces suitable for general work.
+When in operation, the furnaces are covered with iron-bound tiles. The
+opening under the door of the muffle is closed with a loosely fitting
+brick. The floor of the muffle is protected with a layer of bone-ash,
+which absorbs any oxide of lead that may be accidentally spilt. The fire
+bars should be easily removable.</p>
+
+<p>Few tools are wanted; the most important are some cast-iron moulds,
+tongs (fig. 9), stirrers for calcining (fig. 10), and light tongs of a
+special form for handling scorifiers and cupels (<i>see</i> <span class="smcap">Silver</span>).</p>
+
+<div class="figcenter" style="width: 746px;">
+<img src="images/fig009.jpg" width="746" height="153" alt="Fig. 9." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 500px;">
+<img src="images/fig010.jpg" width="500" height="67" alt="Fig. 10." title="" />
+
+</div>
+
+<p>The coke used should be of good quality; the formation of a fused ash
+(clinker), in any quantity, causes ceaseless trouble, and requires
+frequent removal. The coke should be broken into lumps of a uniform size
+(about 2 in. across) before being brought into the office. The furnace
+should be well packed by stirring, raising the coke and not ramming it,
+and it should be uniformly heated, not hot below and cold above. In
+lighting a furnace, a start is made with wood and charcoal, this readily
+ignites and sets fire to the coke, which of itself does not kindle
+easily.</p>
+
+<p>In commencing work, add (if necessary) fresh coke, and mix well; make
+hollows, and into these put old crucibles; pack around with coke, so
+that the surface shall be concave, sloping upwards from the mouths of
+the crucibles to the sides of the furnace; close the furnace, and, when
+uniformly heated, substitute for the empty crucibles those which contain
+the assays. It is rarely advisable to have a very hot fire at first,
+because with a gradual heat the gases and steam quietly escape through
+the unfused mass, while with too strong a heat these might make some of
+the matter in the crucible overflow. Moreover, if the heat should be too
+strong at first, the flux might melt and run to the bottom of the
+crucible, leaving the quartz, &amp;c., as a pasty mass above; with a gentler
+heat combination is completed, and the<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> subsequent fiercer heat simply
+melts the fusible compound into homogeneous slag.</p>
+
+<p>The fused material may be left in the crucible and separated from it by
+breaking when cold. It is generally more convenient to pour it into
+cast-iron moulds. These moulds should be dry and smooth. They act best
+when warmed and oiled or black-leaded.</p>
+
+<p>Air entering through the fire-bars of a furnace and coming in contact
+with hot coke combines with it, forming a very hot mixture of carbonic
+acid and nitrogen; this ascending, comes in contact with more coke, and
+the carbonic acid is reduced to carbonic oxide; at the top of the
+furnace, or in the flue, the carbonic oxide meeting fresh air, combines
+with the oxygen therein and re-forms carbonic acid. In the first and
+third of these reactions, much heat is evolved; in the second, the
+furnace is cooled a little. It must always be remembered, that the
+carbonic oxide of the furnace gases is a reducing agent. When these
+gases are likely to exert a prejudicial effect, and a strongly oxidising
+atmosphere is required, the work is best done in a <i>muffle</i>.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> There is an exception to this, as when the slag is liable
+to be acted on when exposed to the air and to the gases of the furnace.
+In this case a layer of fused common salt floating on the slag, so as to
+protect it from the air and furnace gases, is a distinct advantage.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span></p>
+<h2><a name="CHAPTER_III" id="CHAPTER_III"></a>CHAPTER III.</h2>
+
+<h3>WET GRAVIMETRIC METHODS.</h3>
+
+
+<p>In <i>dry assays</i> the metal is almost always separated and weighed as
+metal; in <i>wet</i> gravimetric assays the metal is more usually weighed in
+the form of a definite compound of known composition. The general
+methods of working resemble those of ordinary chemical analysis, and
+their successful working is greatly helped by a knowledge of, at any
+rate, those compounds of the metal which enable it to be separated, and
+of those which are the most convenient forms in which it can be weighed.
+But the work of the assayer differs from that of the analyst, inasmuch
+as the bulk of his estimations are made upon material of practically the
+same kind, varying only in richness; consequently in assaying, it is
+possible (and necessary) to work on such a definite plan as will involve
+the least amount of labour in weighing and calculating.</p>
+
+<p>The assayer connected with mining has generally two classes of material
+to deal with: those comparatively rich and those comparatively poor. For
+example, silver in bullion and in ores; copper precipitates or regulus,
+and copper ores and slags; and "black tin" and tin ores. He is only
+occasionally called on to assay the intermediate products. It is
+indispensable that he should have an approximate knowledge of the
+substance to be determined. With new ores this information is best got
+by a qualitative testing. Knowing that only certain bodies are present,
+it is evident that the number of separations can be reduced, and that
+simple methods can be devised for arriving at the results sought for.
+The best method is that which involves the least number of separations.
+The reactions must be sharp and complete, and yet not be liable to error
+under varying conditions.</p>
+
+<p>To bring the richer and poorer materials under the same conditions for
+the assay, a small weight, say 1 gram of the richer, and a larger weight
+(5 or 10 grams) of the poorer, substance is weighed up. A method is then
+adopted which will concentrate the whole of the metal (either during or
+after solution) in a product which need not necessarily be pure. The
+work on this product is comparatively easy. In separating small
+quantities of a substance from a large bulk of impurities, the group
+separations must not<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span> as a rule be too much relied on. Very large
+precipitates carry down small quantities of bodies not belonging to the
+group, more especially when there is a tendency to form weak double
+compounds. The re-dissolving and re-precipitating of bulky precipitates
+should be avoided.</p>
+
+<p>When a large number of assays of the same kind have to be carried out, a
+plan something like the following is adopted:&mdash;The samples, after having
+been dried, are placed in order on a table at the left hand of the
+assayer. He takes the first, marks it with a number, samples and weighs
+up the quantity required, and transfers it to a flask, which is
+similarly marked. As the weighings are finished, the samples are placed
+in the same order on his right hand. The assistant takes the flasks in
+batches of four or five at a time to the fume cupboard, where he adds a
+measured quantity of acid. When solution has been effected, dilution
+with a measured volume is generally necessary. The assayer sees to this
+and (whilst the funnels and filters are being prepared) makes any
+separation that is necessary. The filters are arranged in order on a
+rack (fig. 11), and need not be marked unless the precipitates or
+residues have subsequently to be dried. The filters are washed with hot
+water, and if the filtrates are wanted flasks are placed beneath, if
+not, the solution is drained off down the sink. Precipitation or
+reduction (or whatever it may be) is now made; the assistant filters the
+prepared samples, one at a time, whilst the assayer is engaged with the
+others. The same style of work is continued until the assays are
+completed. If one should be spoiled, it is better to allow it to stand
+over for assaying along with the next batch. If one filters slowly or is
+in any way less forward than the rest, it may lessen the accuracy of the
+other assays, owing to oxidation, &amp;c., it should, therefore, be put on
+one side. The assays are dealt with in batches of ten or twenty, so that
+a large quantity of work can be quickly finished.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig011.jpg" width="450" height="231" alt="Fig. 11." title="" />
+
+</div>
+
+<p>When the assays are finished, it is the duty of the assistant to clean
+the apparatus (with reagents, if necessary), and to put the<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span> vessels in
+the place set apart for them. Flasks are best kept inverted on a rack,
+so that they may be dry and clean by the next morning. Berlin crucibles
+must be cleaned and ignited.</p>
+
+<p>The amount of apparatus employed should be as little as is feasible. The
+assay should be carried out as much as possible in the same flask. The
+bench must be clean, and altogether free from apparatus not in actual
+use. Crucibles and dishes in which weighings are made should be marked
+with numbers or letters; and their weights recorded, together with the
+date of weighing, in a small ledger, which is kept in the drawer of the
+balance. By this means a record of the "wear" of each piece of apparatus
+is obtained, and, what is more important, much weighing is saved, and
+increased confidence is gained. The weight of each piece of apparatus
+need not be taken daily. It will be seen from the record in the book and
+a knowledge of the use it has been put to how often a checking of the
+weight is necessary. The entries are made in black lead as follows:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Dish, A.&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>Feb. 3&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>9.4210 grams.</td></tr>
+<tr><td align='left'></td><td align='right'>5&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>9.4225</td></tr>
+<tr><td align='left'></td><td align='right'>6&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>9.4230</td></tr>
+<tr><td align='left'></td><td align='right'>7&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>9.4200</td></tr>
+</table></div>
+
+<p>Platinum vessels and apparatus lose, and porcelain ones slightly gain,
+weight with continued use.</p>
+
+<p>The special details of the work is given under each assay; certain
+general instructions will be given here.</p>
+
+<p><b>Solution.</b>&mdash;It is not always necessary to get the whole of the mineral
+in solution, provided the body sought for is either completely dissolved
+or altogether left in the residue. It is often only by a qualitative
+examination of the solution (or residue, as the case may be) that the
+assayer can satisfy himself that it is free from the substance sought.
+But previous experience with the same kind of ore will show to what
+extent this testing is necessary.</p>
+
+<p>Solution is generally best effected in flasks; but where the resulting
+liquid has afterwards to be evaporated to dryness and ignited,
+evaporating dishes (fig. 12) are used. With them clock glasses are used
+as covers during solution to avoid loss through effervescence.
+Evaporating dishes are also best when an insoluble residue has to be
+collected, since it is difficult to wash out most residues from a flask.
+Bumping occurs less frequently in dishes than in flasks.</p>
+
+<div class="figcenter" style="width: 294px;">
+<img src="images/fig012.jpg" width="294" height="232" alt="Fig. 12." title="" />
+
+</div>
+
+<p>After the addition of the acid, and mixing by agitation, the vessel
+containing the substance is heated. This is best done on<span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> the "hot
+plate" (fig. 13). This consists of a slab of cast iron about half or
+three-quarters of an inch thick, supported on loose fire bricks, and
+heated by two or three ring burners (figs. 14 and 15). The burners are
+connected to the gas supply by means of <i>lead</i> tubing, to which they are
+soldered. Flasks and dishes after being put on the plate are not further
+handled until solution is complete or the evaporation is carried to
+dryness. The hot plate is contained in a cupboard so as to be out of the
+reach of cold draughts.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig013.jpg" width="450" height="206" alt="Fig. 13." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig014.jpg" width="450" height="149" alt="Fig. 14." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 431px;">
+<img src="images/fig015.jpg" width="431" height="300" alt="Fig. 15." title="" />
+
+</div>
+
+<p>The action of the acids and other solvents is described in the chapter
+on Reagents.</p>
+
+<p><b>Precipitation.</b>&mdash;In precipitating add sufficient of the reagent to
+complete the reaction. The student must be on his guard against adding a
+very large excess, which is the commoner error. In some reactions the
+finishing point is obvious enough; either no more precipitate is formed,
+or a precipitate is completely dissolved, or some well-marked colour or
+odour is developed or removed.</p>
+
+<p>In those cases in which there is no such indication, theoretical
+considerations should keep the use of reagents within reasonable limits.
+The solutions of the reagents (<i>see</i> <span class="smcap">Reagents</span>) are generally of
+five or ten per cent. strength. A small excess over that demanded by
+theory should be sufficient.<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span></p>
+
+<div class="figcenter" style="width: 299px;">
+<img src="images/fig016.jpg" width="299" height="328" alt="Fig. 16." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig017.jpg" width="450" height="203" alt="Fig. 17." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 339px;">
+<img src="images/fig018.jpg" width="339" height="352" alt="Fig. 18." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig019.jpg" width="450" height="207" alt="Fig. 19." title="" />
+
+</div>
+
+<p><b>Filtration.</b>&mdash;Solutions are best filtered hot whenever the assay allows
+of this being so done. The precipitate should be allowed to settle, and
+the clear liquid decanted on the filter with the aid of a glass rod if
+necessary. The filter-paper must not be too large, but at the same time
+it must not be overloaded with the precipitate. There should be ample
+room for washing. For general use three sizes of filter-paper are
+sufficient. Common quick filtering-paper (English) is best for most work
+in assaying. The specially prepared paper (Swedish or Rhenish) is used
+for collecting those precipitates which have to be weighed. The papers
+are folded as shown in fig. 16, and should not project above the funnel.
+The filter-paper works better if damped with hot water. In special cases
+filtering is hastened by means of an air-pump. The apparatus used
+consists of a water-jet (fig. 17), which is connected with the tap, as
+also with a bottle fitted as shown in fig. 18. The pump draws the air
+out from the bottle, and atmospheric pressure forces the liquid through
+the filter-paper. The bottom of the funnel is provided with a platinum
+cone, which supports the filter-paper, and prevents its breaking. The
+pump is only used in exceptional cases; nearly all the filtrations
+required by the assayer can be made without it. The usual methods of
+supporting the funnel during filtration are shown in fig. 19. Where the
+filtrate is not wanted, pickle bottles make convenient supports. After
+the precipitate has been thrown on the filter, it is washed. In washing,
+several washings with a small quantity of water are more effective than
+a few with a<span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span> larger quantity of that fluid. The upper edge of the
+filter-paper is specially liable to escape complete washing. Excessive
+washing must be avoided; the point at which the washing is complete is
+found by collecting a little of the filtrate and testing it. The
+precipitate is removed from the filter-paper for further treatment by
+opening out the paper and by washing the precipitate with a jet of water
+from a wash-bottle into a beaker, or back through the funnel into the
+flask. In some cases, when the precipitate has to be dissolved in
+anything in which it is readily soluble, solution is effected in the
+filter itself allowing the liquid to run through as it is formed.</p>
+
+<p><b>Drying and Igniting.</b>&mdash;Precipitates, as a rule, require drying before
+being ignited. With small precipitates the filter-paper may be opened
+out, and placed on a warm asbestos slab till dry; or the funnel and the
+filter with the precipitate is placed in a warm place, and supported by
+any convenient means. The heat must never be sufficient to char the
+paper. Some precipitates must be dried at a temperature not higher than
+100&deg;C. These are placed in the water-oven (fig. 20), and, when
+apparently dry, they are taken from the funnel, placed between glasses,
+and then left in the oven till they cease to lose weight. Such
+precipitates are collected on tared filters. Those precipitates which
+will stand a higher temperature are dried in the hot-air oven at a
+temperature of from 120&deg; to 150&deg;. The drying is continued until they
+appear to be free from moisture, and until the precipitate ceases to
+adhere to the filter. In drying sulphides the heat must not be raised to
+the melting point of sulphur, since, if there is any free sulphur
+present, it fuses and filters through.</p>
+
+<div class="figcenter" style="width: 321px;">
+<img src="images/fig020.jpg" width="321" height="450" alt="Fig. 20." title="" />
+
+</div>
+
+<p>The precipitate, having been dried, is transferred to a watch-glass. The
+filter-paper is opened out over a sheet of note-paper, and, with a
+camel-hair brush, the precipitate is gently brought into the glass. Most
+precipitates come away easily, and the transfer can be made without
+apparent loss. The watch-glass is covered by the funnel, and the
+filter-paper (folded into a quadrant) held by the tweezers and set fire
+to with the flame of a Bunsen burner. It is allowed to burn over the
+crucible, into which the black bulky ash is allowed to drop, and two or
+three drops of nitric acid are then added. The crucible is placed on a<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span>
+pipe-stem triangle (fig. 21), supported on a tripod. It is at first
+heated gently with a Bunsen burner, and afterwards more strongly, until
+the residue is free from carbon. It is cooled, and treated with any acid
+necessary to convert the small amount of precipitate into the state in
+which it is to be weighed; heated again, and cooled. The main
+precipitate is transferred to the crucible, and the heating repeated
+very gently at first, but more strongly towards the end of the
+operation. It is next placed in the muffle, and, after two or three
+minutes at a red heat, it is removed and allowed to cool in the
+desiccator before weighing. This is for bodies that will bear a red
+heat; for those compounds that require a lower temperature the heating
+in the muffle is omitted. The muffle used for this purpose must not be
+used at the same time for cupelling; a gas muffle (fig. 22), such as one
+of Fletcher's, is best. A desiccator (fig. 23) is an air-tight vessel
+which prevents access of moisture, &amp;c., to the substance. Usually the
+air in it is kept dry by means of a basin containing sulphuric acid.</p>
+
+<div class="figcenter" style="width: 371px;">
+<img src="images/fig021.jpg" width="371" height="377" alt="Fig. 21." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 316px;">
+<img src="images/fig022.jpg" width="316" height="300" alt="Fig. 22." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 405px;">
+<img src="images/fig023.jpg" width="405" height="397" alt="Fig. 23." title="" />
+
+</div>
+
+<p>The crucible is removed from the muffle with the tongs and carried to
+the desiccator. It is best, in an office, to have a large desiccator
+permanently fixed alongside the balance, into which all substances may
+be put before being weighed. The substance is removed from the bench or
+muffle in the small hand apparatus generally sold, and carried to the
+balance room to be transferred to the large desiccator, where it is
+allowed to become thoroughly cold before being weighed. Twenty minutes
+is generally the time allowed after ignition before it is advisable to
+weigh. Bodies allowed to cool in the air after they have been ignited
+will absorb moisture, and hot bodies placed in the balance-pan will
+disturb the equilibrium and show false results. Compounds that absorb
+moisture must be weighed quickly; they should, therefore, be<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> weighed in
+covered vessels. Such compounds are detected by their
+continually-increasing weight. They should be ignited and weighed again
+in a well-covered dish.</p>
+
+<p>Substances that have been washed with alcohol, ether, or any readily
+volatile liquid are dried in the water oven. They quickly dry if there
+is no water present, and are generally fit for weighing in less than one
+hour. Sometimes drying for a few minutes only will be sufficient.</p>
+
+<p>The weight of the crucible and precipitate having been obtained, the
+weight of the crucible and ash is deducted; for example&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Crucible and precipitate</td><td align='right'>10.183</td><td align='left'>grams.</td></tr>
+<tr><td align='left'>Crucible and ash</td><td align='right'>9.527</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>0.656</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>The weight of the ash is best added to that of the crucible. The amount
+of ash in filter-papers must not be neglected, although papers are now
+made almost free from ash, and the amount to be deducted is found by
+taking eight or ten papers and burning them until they become white, and
+then weighing the ash. The amount varies from 0.004 to 0.0005 gram for
+different papers. Having determined the ash, place in the balance-drawer
+three of the filter-papers pinned together, with the weights marked on
+them in the way shown in fig. 24, so as to be readily seen when there is
+occasion to refer to them.</p>
+
+<div class="figcenter" style="width: 294px;">
+<img src="images/fig024.jpg" width="294" height="351" alt="Fig. 24." title="" />
+
+</div>
+
+<p>It must be remembered that the determination of small quantities of
+substances generally involves the use of reagents which are often
+contaminated, as an impurity, with the body sought for. Thus, in
+assaying silver, the oxide of lead or metallic lead used is rarely free
+from silver; and in the case of arsenic, the acids, zinc or ferric
+chloride are sure to contain arsenic. The same observation applies to
+the precipitation of lead by zinc, &amp;c. The errors caused by these
+impurities are more marked in the determination of material having small
+quantities of metal than in that of ores which contain larger
+quantities. Errors of this kind are counteracted or neutralised by
+"blank" or "blind" determinations. These consist in carrying out by the
+side of and during the assay a duplicate experiment with the reagents
+only, which are thereby subjected to the same processes of solution,
+evaporation, filtration, &amp;c. The final result thus obtained is deducted
+from that given by the assay, the difference gives the corrected result.
+In some cases, where it is desired or necessary to have a tangible
+residue or precipitate, some <i>pure</i> inert material is added.</p>
+
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span></p>
+<h2><a name="CHAPTER_IV" id="CHAPTER_IV"></a>CHAPTER IV.</h2>
+
+<h3>VOLUMETRIC ASSAYS.</h3>
+
+
+<p>These have been already described as those in which the results are got
+by measuring, either&mdash;(1) the volume of a reagent required to complete
+some reaction, or (2) the volume of the resulting product. For example,
+if a permanganate of potash solution be added to a solution containing a
+weighed amount of iron, dissolved in sulphuric acid, the strong colour
+of the permanganate of potash will be removed until a certain quantity
+of it has been added. Repeating the experiment, it will be found that
+the same amount of iron decolorises the same volume of the permanganate
+solution within certain narrow limits of variation, known as "error of
+experiment." This error is due to variation in the method of working and
+to slight differences in the weighings and measurings; it is present in
+all experimental methods, although the limits of variation are wider in
+some than in others. Apart from this error of experiment, however, it is
+certain that a given volume of the permanganate of potash solution
+corresponds to a definite weight of iron, so that if either is known the
+other may be calculated. Similarly, if a known weight of zinc (or of
+carbonate of lime) be dissolved in hydrochloric acid, a gas will be
+given off which can be measured, and so long as the conditions of the
+experiment do not vary, the same weight of zinc (or of carbonate of
+lime) gives off the same volume of gas. The weight of the one can be
+determined from the volume of the other.</p>
+
+<p>Or, again, the quantity of some substances may be measured by the colour
+of their solutions, on the principle that, other things being equal, the
+colour of a solution depends upon the quantity of colouring matter
+present. So that if two solutions of the same substance are equally
+coloured they are of equal strength. In this way an unknown may be
+compared with a known strength, and a fairly accurate determination may
+be made. These three illustrations serve as types of the three chief
+classes of volumetric assays&mdash;titrometric, gasometric, and colorimetric.</p>
+
+<p><b>Titrometric Assays.</b>&mdash;Within the limits of the error of experiment, a
+definite volume of a solution or gas represents a certain weight of
+metal or other substance, hence the exact weight may be<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span> determined by
+experiment. The error of experiment may be reduced to insignificant
+dimensions by repeating the experiment, and taking the mean of three or
+four determinations. This will at the same time show the amount of
+variation. Thus, if 0.5 gram of iron were dissolved and found to require
+50.3 cubic centimetres of the solution of permanganate of potash, and if
+on repeating, 50.4, 50.2, and 50.3 c.c. were required, the experimenter
+would be justified in saying that 50.3 c.c. of the permanganate solution
+represent 0.5 gram of iron, and that his results were good within 0.2
+c.c. of the permanganate solution. So that if in an unknown solution of
+iron, 50.5 c.c. of the permanganate solution were used up, he could
+state with confidence that it contained a little more than 0.5 gram of
+iron. With a larger experience the confidence would increase, and with
+practice the experimental error will diminish.</p>
+
+<p>But supposing that the unknown solution required, say, 100.5 instead of
+50.5 c.c., he would not be justified in saying that, since 50.3 c.c. are
+equivalent to 0.5 gram, 100.6 c.c. are equivalent to twice that amount;
+and that, consequently, the unknown solution contained a little less
+than 1 gram of iron; or, at least, he could not say it except he (or
+some one else) had determined it by experiment. But if on dissolving 1
+gram of iron, he found it to require 100.6 c.c. of the solution, and in
+another experiment with 0.8 gram of iron that 80.5 c.c. of the solution
+were required, he would be justified in stating that <i>the volume of
+solution required is proportional to the quantity of metal present</i>.
+There are a large number of volumetric assays of which this is true, but
+that it is true in any particular case can only be proved by experiment.
+Even where true it is well not to rest too much weight upon it, and in
+all cases the quantity of metal taken, to determine the strength of the
+solution used, should not differ widely from that present in the assay.
+There are certain terms which should be explained here. When the
+solution of a reagent is applied under such conditions that the volume
+added can be correctly determined, the operation is called "titrating,"
+the solution of the reagent used the "standard solution," and the
+process of determining the strength of the standard solution is
+"standardising." The "standard" is the quantity of metal equivalent to
+100 c.c. of the standard solution.</p>
+
+<p><b>Standard Solutions.</b>&mdash;In making these the salt is accurately weighed
+and transferred to a litre flask, or to the graduated cylinder, and
+dissolved. The method of dissolving it varies in special cases, and
+instructions for these will be found under the respective assays.
+Generally it is dissolved in a small quantity of liquid, and then
+diluted to the mark. For those substances that require the aid of heat,
+the solution is made in a pint flask, cooled,<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> and transferred; after
+which the flask is well washed out. After dilution, the liquids in the
+measuring vessel must be thoroughly mixed by shaking. This is more
+easily and better done in the cylinder than in the litre flask. The
+solution is next transferred to a dry "Winchester" bottle and labelled.
+The label may be rendered permanent by waxing it.</p>
+
+<p>Standard solutions should not be kept in a place exposed to direct
+sunlight. Oxidising and reducing solutions, such as those of
+permanganate of potash, ferrous sulphate, iodine, hyposulphite of soda,
+&amp;c., gradually weaken in strength; the solutions of other salts are more
+stable; while those of potassium bichromate and baric chloride are
+almost permanent. Solutions of potassium permanganate may be kept for a
+month or so without much change. The solutions of hyposulphite of soda
+and of iodine should be examined weekly. Ferrous sulphate solutions, if
+acidulated with sulphuric acid, may be depended on for two or three
+weeks without fresh standardising. Before filling the burette, the
+"Winchester" bottle should be well shaken and a portion of about 50 or
+100 c.c. poured into a dry beaker or test-glass. Besides the standard
+solutions, which are required for titrating an assay, permanent
+solutions of the metal or acid of equivalent strength are very useful.
+When the finishing point of a titration has been overstepped (<i>i.e.</i>,
+the assay has been "overdone"), a measured volume, say 5 or 10 c.c., of
+a solution containing the same metal may be added. The titration can
+then be continued, but more cautiously, and the value in "c.c." for the
+quantity added be deducted from the final reading.</p>
+
+<p><b>Standardising.</b>&mdash;Suppose the object is to standardise a solution of
+permanganate similar to that referred to above. A convenient quantity of
+iron (say 0.5 gram) would be weighed out, dissolved in dilute sulphuric
+acid, and the solution titrated. Suppose 49.6 c.c. of the permanganate
+solution are required, then</p>
+
+<p>
+<span style="margin-left: 3em;">49.6 : 0.5 :: 100 : <i>x</i></span><br />
+<span style="margin-left: 11em;"><i>x</i> = 1.008 gram.</span><br />
+</p>
+
+<p>This result, 1.008 gram, is the "<i>standard</i>." When a gas is measured,
+the standard may be calculated in the same way. For example: with 0.224
+gram of zinc, 75.8 c.c. of gas were obtained. Then the quantity of zinc
+equivalent to 100 c.c. of the gas is got by the proportion.</p>
+
+<p>
+<span style="margin-left: 3em;">75.8 : 0.224 :: 100 : <i>x</i></span><br />
+<span style="margin-left: 11em;"><i>x</i> = 0.2955 gram.</span><br />
+</p>
+
+<p>Using the term "standard" in this sense, the following rules hold
+good:<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span>&mdash;</p>
+
+<p>To find the weight of metal in a given substance:&mdash;<i>Multiply the
+standard by the number of c.c. used and divide by 100.</i> For example: a
+piece of zinc was dissolved and the gas evolved measured 73.9 c.c. Then
+by the rule, 0.2955 &times; 73.9 / 100 should give the weight of the piece of
+zinc. This gives 0.2184 gram.</p>
+
+<p>To find the percentage of metal in a given substance:&mdash;<i>Multiply the
+standard by the number of c.c. used and divide by the weight of
+substance taken.</i> For example: if 2 grams of a mineral were taken, and
+if on titrating with the permanganate solution (standard 1.008) 60.4
+c.c. were required, then (1.008&times;60.4)/2 = 30.44. This is the
+percentage.</p>
+
+<p>If the standard is exactly 1 gram, and 1 gram of ore is always taken,
+these calculations become very simple. The "c.c." used give at once the
+percentage, or divided by 100 give the weight of metal.</p>
+
+<p>If it is desired to have a solution with a standard exactly 1.0 gram, it
+is best first to make one rather stronger than this, and then to
+standardise carefully. Divide 1000 by the standard thus obtained and the
+result will be the number of c.c. which must be taken and be diluted
+with water to 1 litre. For example: suppose the standard is 1.008, then
+1000/1.008 gives 992, and if 992 c.c. be taken and diluted with water to
+1000 c.c. a solution of the desired strength will be obtained. The
+standard of this should be confirmed. A simpler calculation for the same
+purpose is to multiply the standard by 1000; this will give the number
+of c.c. to which 1 litre of the solution should be diluted. In the above
+example a litre should be diluted to 1008 c.c.</p>
+
+<p>It has been assumed in these rules that the titration has yielded
+proportional results; but these are not always obtained. There can be no
+doubt that in any actual re-action the proportion between any two
+re-agents is a fixed one, and that if we double one of these then
+exactly twice as much of the other will enter into the re-action; but in
+the working it may very well be that no re-action at all will take place
+until after a certain excess of one or of both of the re-agents is
+present. In titrating lead with a chromate of potash solution, for
+example, it is possible that at the end of the titration a small
+quantity of the lead may remain unacted on; and it is certain that a
+small excess of the chromate is present in the solution. So, too, in
+precipitating a solution of silver with a standard solution of common
+salt, a point is reached at which a small quantity of each remains in
+solution; a further addition either of silver or of salt will cause a
+precipitate, and a similar phenomenon has been observed in precipitating
+a hydrochloric acid solution of a sulphate with<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> baric chloride. The
+excess of one or other of the re-agents may be large or small; or, in
+some cases, they may neutralise each other. Considerations like these
+emphasise the necessity for uniformity in the mode of working. Whether a
+process yields proportional results, or not, will be seen from a series
+of standardisings. Having obtained these, the results should be arranged
+as in the table, placing the quantities of metal used in the order of
+weight in the first column, the volumes measured in the second, and the
+standards calculated in the third. If the results are proportional,
+these standards will vary more or less, according to the delicacy of the
+process, but there will be no apparent order in the variation. The
+average of the standards should then be taken.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight.</td><td align='left'>Volume found.</td><td align='left'>Standard</td></tr>
+<tr><td align='left'> 0.2160 gram</td><td align='left'>72.9 c.c.</td><td align='left'>0.2963</td></tr>
+<tr><td align='left'> 0.2185&nbsp;&nbsp; "</td><td align='left'>73.9 &nbsp;&nbsp;"</td><td align='left'>0.2957</td></tr>
+<tr><td align='left'> 0.2365 &nbsp;&nbsp; "</td><td align='left'>79.9&nbsp;&nbsp;"</td><td align='left'>0.2959</td></tr>
+<tr><td align='left'> 0.2440 &nbsp;&nbsp; "</td><td align='left'>82.3&nbsp;&nbsp;"</td><td align='left'>0.2964</td></tr>
+<tr><td align='left'> 0.2555&nbsp;&nbsp;  "</td><td align='left'>85.9 &nbsp;&nbsp;"</td><td align='left'>0.2974</td></tr>
+</table></div>
+
+<p>Any inclination that may be felt for obtaining an appearance of greater
+accuracy by ignoring the last result must be resisted. For, although it
+would make no practical difference whether the mean standard is taken as
+0.2961 or 0.2963, it is well not to ignore the possibility that an error
+of 0.4 c.c. may arise. A result should only be ignored when the cause of
+its variation is known.</p>
+
+<p>In this series the results are proportional, but the range of weights
+(0.216-0.2555 gram) is small. All processes yield fairly proportional
+results if the quantities vary within narrow limits.</p>
+
+<p>As to results which are not proportional, it is best to take some
+imaginary examples, and then to apply the lesson to an actual one. A
+series of titrations of a copper solution by means of a solution of
+potassic cyanide gave the following results:&mdash;</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper taken.</td><td align='left'>Cyanide used.</td><td align='left'>Standard.</td></tr>
+<tr><td align='left'>0.1 gram</td><td align='left'>11.9 c.c.</td><td align='left'>0.8403</td></tr>
+<tr><td align='left'>0.2&nbsp;&nbsp;  "</td><td align='left'>23.7&nbsp;&nbsp;  "</td><td align='left'>0.8438</td></tr>
+<tr><td align='left'>0.3&nbsp;&nbsp;  "</td><td align='left'>35.6&nbsp;&nbsp;  "</td><td align='left'>0.8426</td></tr>
+<tr><td align='left'>0.4&nbsp;&nbsp;  "</td><td align='left'>47.6&nbsp;&nbsp;  "</td><td align='left'>0.8403</td></tr>
+</table></div>
+
+<p>These are proportional, but by using a larger quantity of acid and
+ammonia in the work preliminary to titration, we might have had<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> to use
+1 c.c. of cyanide solution more in each case before the finishing point
+was reached. The results would then have been:</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper taken.</td><td align='left'>Cyanide used.</td><td align='left'>Standard.</td></tr>
+<tr><td align='left'>0.1 gram</td><td align='left'>12.9 c.c.</td><td align='left'>0.7752</td></tr>
+<tr><td align='left'>0.2&nbsp;&nbsp;  "</td><td align='left'>24.7&nbsp;&nbsp;  "</td><td align='left'>0.8097</td></tr>
+<tr><td align='left'>0.3&nbsp;&nbsp;  "</td><td align='left'>36.6&nbsp;&nbsp;  "</td><td align='left'>0.8191</td></tr>
+<tr><td align='left'>0.4&nbsp;&nbsp;  "</td><td align='left'>48.6&nbsp;&nbsp;  "</td><td align='left'>0.8230</td></tr>
+</table></div>
+
+<p>It will be noted that the value of the standard increases with the
+weight of metal used; and calculations from the mean standard will be
+incorrect.</p>
+
+<p>By subtracting the lowest standardising from the highest, a third result
+is got free from any error common to the other two; thus:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>0.4</td><td align='left'>gram</td><td align='left'>=</td><td align='left'>48.6</td><td align='left'>c.c.</td><td align='left'>"cyanide."</td></tr>
+<tr><td align='left'>0.1</td><td align='center'>"</td><td align='left'>=</td><td align='left'>12.9</td><td align='center'>"</td><td align='center'>"</td></tr>
+<tr><td align='left'>&mdash;&mdash;</td><td align='left'></td><td align='left'></td><td align='left'>&mdash;&mdash;</td></tr>
+<tr><td align='left'>0.3</td><td align='center'>"</td><td align='left'>=</td><td align='left'>35.7</td><td align='center'>"</td><td align='center'>"</td></tr>
+</table></div>
+
+<p>And the standard calculated from this corrected result is 0.8404.
+Further, if 0.3 gram requires 35.7 c.c., then 0.1 gram should require
+11.9 c.c., or 1.0 c.c. less than that actually found.</p>
+
+<p>We may therefore use the following rules for working processes which do
+not yield proportional results. Make a series of two or three
+titrations, using very different quantities of metal in each. Subtract
+the lowest of these from the highest, and calculate the standard with
+the remainder. Calculate the volume required by this standard in any
+case, and find the excess or deficit, as the case may be. If an excess,
+subtract it from the result of each titration; if a deficit, add it; and
+use the standard in the usual way. The following table shows an actual
+example:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Chalk taken.</td><td align='left'>Gas obtained.</td><td align='left'>Standard.</td></tr>
+<tr><td align='left'>0.0873 gram</td><td align='left'>17.8 c.c.</td><td align='left'>0.4904</td></tr>
+<tr><td align='left'>0.1305&nbsp;&nbsp; "</td><td align='left'>27.3&nbsp;&nbsp; "</td><td align='left'>0.4780</td></tr>
+<tr><td align='left'>0.1690&nbsp;&nbsp; "</td><td align='left'>35.8&nbsp;&nbsp; "</td><td align='left'>0.4721</td></tr>
+<tr><td align='left'>0.1905&nbsp;&nbsp; "</td><td align='left'>40.4&nbsp;&nbsp; "</td><td align='left'>0.4715</td></tr>
+<tr><td align='left'>0.2460&nbsp;&nbsp; "</td><td align='left'>52.5&nbsp;&nbsp; "</td><td align='left'>0.4686</td></tr>
+<tr><td align='left'>0.3000&nbsp;&nbsp; "</td><td align='left'>64.0&nbsp;&nbsp; "</td><td align='left'>0.4687</td></tr>
+</table></div>
+
+<p>It will be seen that the standard decreases as the quantity of chalk
+increases; this points to a deficiency in the quantity of gas evolved.<span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span></p>
+
+<p>Then</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>0.3000</td><td align='left'>=</td><td align='left'>64.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>0.0873</td><td align='left'>=</td><td align='left'>17.8</td><td align='center'>"</td></tr>
+<tr><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>=</td><td align='left'>&mdash;&mdash;</td></tr>
+<tr><td align='left'>0.2127</td><td align='left'>=</td><td align='left'>46.2</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>and 0.2127&times;100/46.2 = 0.4604. Then, multiplying the weight of chalk
+taken by 100, and dividing by 0.4604, we get the calculated results of
+the following table:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Chalk taken.</td><td align='left'>Gas found.</td><td align='left'>Gas calculated.</td><td align='left'>Difference.</td></tr>
+<tr><td align='left'>0.0873 gram</td><td align='left'>17.8 c.c.</td><td align='left'>18.9 c.c.</td><td align='left'>-1.1 c.c.</td></tr>
+<tr><td align='left'>0.1305&nbsp;&nbsp; "</td><td align='left'>27.3&nbsp;&nbsp; "</td><td align='left'>28.3&nbsp;&nbsp; "</td><td align='left'>-1.0&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>0.1690&nbsp;&nbsp; "</td><td align='left'>35.8&nbsp;&nbsp; "</td><td align='left'>36.7&nbsp;&nbsp; "</td><td align='left'>-0.9&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>0.1905&nbsp;&nbsp; "</td><td align='left'>40.4&nbsp;&nbsp; "</td><td align='left'>41.4&nbsp;&nbsp; "</td><td align='left'>-1.0&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>0.2460&nbsp;&nbsp; "</td><td align='left'>52.5&nbsp;&nbsp; "</td><td align='left'>53.4&nbsp;&nbsp; "</td><td align='left'>-0.9&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>0.3000&nbsp;&nbsp; "</td><td align='left'>64.0&nbsp;&nbsp; "</td><td align='left'>65.1&nbsp;&nbsp; "</td><td align='left'>-1.1&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+<p>By adding 1 c.c. to the quantity of gas obtained, and taking 0.4604 as
+the standard, the calculated results will agree with those found with a
+variation of 0.1 c.c. When a large number of assays of the same kind are
+being made, this method of calculation is convenient; when, however,
+only one or two determinations are in question, it is easier to make a
+couple of standardisings, taking quantities as nearly as possible the
+same as those present in the assays.</p>
+
+<p>Sometimes it is necessary to draw up a table which will show, without
+calculation, the weight of substance equivalent to a given volume of gas
+or of solution. The substance used for standardising should be, whenever
+possible, a pure sample of the substance to be determined&mdash;that is, for
+copper assays pure copper should be used, for iron assays pure iron, and
+so on; but when this cannot be got an impure substance may be used,
+provided it contains a known percentage of the metal, and that the
+impurities present are not such as will interfere with the accuracy of
+the assay. Including compounds with these, the standard may be
+calculated by multiplying the standard got in the usual way, by the
+percentage of metal in the compound or impure substance, and dividing by
+100. If, for example, the standard 1.008 gram was obtained by using a
+sample of iron containing 99.7 per cent. of metal, the corrected
+standard would be 1.008&times;99.7/100 = 1.005.</p>
+
+<p>In volumetric analysis the change brought about must be one in which the
+end of the reaction is rendered prominent either by a change of colour
+or by the presence or absence of a precipitate. If the end of the
+reaction or finishing-point is not of itself visible,<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span> then it must be
+rendered visible by the use of a third reagent called an indicator.</p>
+
+<p>For example, the action of sulphuric acid upon soda results in nothing
+which makes the action conspicuous; if, however, litmus or
+phenolphthalein be added the change from blue to red in the first case,
+or from red to colourless in the second, renders the finishing-point
+evident. Some indicators cannot be added to the assay solution without
+spoiling the result; in which case portions of the assay solution must
+be withdrawn from time to time and tested. This withdrawal of portions
+of the assay solution, if rashly done, must result in loss; if, however,
+the solution is not concentrated, and if the portions are only withdrawn
+towards the end of the titration, the loss is very trifling, and will
+not show-up on the result. The usual plan adopted is to have a solution
+of the indicator placed in drops at fairly equal intervals distributed
+over a clean and dry white porcelain-plate: a drop or two of the
+solution to be tested is then brought in contact with one of these and
+the effect noted. Another plan is to have thin blotting-paper, moistened
+with a solution of the indicator and dried; a drop of the solution to be
+tested placed on this shows the characteristic change. When the assay
+solution contains a suspended solid which interferes with the test, a
+prepared paper covered with an ordinary filter-paper answers very well;
+a drop of the solution to be tested is placed on the filter-paper, and,
+sinking through, shows its effect on the paper below.</p>
+
+<p>Except when otherwise stated, all titrations should be made at the
+ordinary temperature; cooling, if necessary, by holding the flask under
+the tap. When a titration is directed to be made in a boiling solution,
+it must be remembered that the standard solution is cold, and that every
+addition lowers the temperature of the assay.</p>
+
+<p>On running the solution from the burette into the assay, do not let it
+run down the side of the flask. If a portion of the assay has to be
+withdrawn for testing, shake the flask to ensure mixing, and then take
+out a drop with the test-rod; the neglect of these precautions may give
+a finishing-point too early. This is generally indicated by a sudden
+finish, in which case on shaking the flask and again testing no reaction
+is got. Do not remove the drop on the point of the burette with the
+test-rod; let it remain where it is or drop it into the solution by
+carefully opening the clip.</p>
+
+<p>Generally the methods of working are as follows:&mdash;</p>
+
+<p>(1) <i>When the finishing-point depends on a change of colour in the
+solution.</i>&mdash;Increase the bulk of the assay up to from 100 to 150 c.c.
+with water. Boil or cool, as the case may be. Run in the standard
+solution from a burette speedily, until the re-agent appears to have a
+slower action, and shake or stir all the time.<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> Then run 1 c.c. or so at
+a time, still stirring, and finally add drops until the colour change is
+got.</p>
+
+<p>(2) <i>When an outside-indicator is used.</i>&mdash;Pour the standard solution
+from a burette into the assay until 5 or 6 c.c. from the
+finishing-point; then run in 1 c.c. at a time (stirring and testing on
+the plate between each) until the indicator shows the change wanted, and
+deduct 0.5 c.c. for excess. When greater accuracy is sought for a
+duplicate assay is made. In this case the standard solution is run in
+close up to the end, and the operation is finished off with a few drops
+at a time.</p>
+
+<p>(3) <i>Where the finishing-point depends upon the absence of a precipitate
+and no outside-indicator is used.</i>&mdash;As in the last case, run in the
+standard solution up to within a few c.c. of the end, then run in 1 c.c.
+at a time until a precipitate is no longer formed, but here 1.5 c.c.
+must be deducted for excess, since it is evident that the whole of the
+last "c.c." must have been, and a portion of the previous one may have
+been, in excess.</p>
+
+<p><b>Indirect Titration.</b>&mdash;The action of permanganate of potash upon a
+ferrous solution is one of oxidation, hence it is evident that if any
+other oxidising agent is present it will count as permanganate. In such
+a case the titration can be used (indirectly) to estimate the quantity
+of such oxidising agent, by determining how much less of the
+permanganate is used. For example, suppose that 1 gram of iron dissolved
+in sulphuric acid requires 100 c.c. of standard permanganate to fully
+oxidise it, but that the same amount of iron only requires 35.6 c.c. of
+the same standard permanganate if it has been previously heated with 0.5
+gram of black oxide of manganese. Here it is evident that 0.5 gram of
+black oxide does the work of 64.4 c.c.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> of the permanganate solution,
+and that these quantities are equivalent; moreover, if 64.4 c.c.
+correspond with 0.5 gram, then 100 c.c. correspond with 0.7764 which is
+the standard. On theoretical grounds, and by a method of calculation
+which will be explained further on (under the heading "Calculations from
+Formul&aelig;"), it can be found that if the standard for iron is 1 gram, that
+for the black oxide will be 0.7764 gram.</p>
+
+<p>The principles of these indirect titrations become clearer when
+expressed in a condensed form. Thus, in the example selected, and using
+the formul&aelig; Fe = Iron, KMnO<sub>4</sub> = permanganate of potash, and MnO<sub>2</sub> =
+oxide of manganese, we have:&mdash;</p>
+
+<p>
+(1)                1 gram Fe = 100 c.c. KMnO<sub>4</sub><br />
+<br />
+(2)                1 gram Fe = 35.6 c.c. KMnO<sub>4</sub> + 0.5 gram MnO<sub>2</sub><br />
+<span style="margin-left: 3.5em;">&#8756; 100 c.c. KMnO<sub>4</sub> = 35.6 c.c. KMnO<sub>4</sub> + 0.5 gram MnO<sub>2</sub></span><br />
+<span style="margin-left: 5em;">(100 - 35.6) c.c. KMnO<sub>4</sub> = 0.5 gram MnO<sub>2</sub></span><br />
+<span style="margin-left: 5em;">64.4 c.c. KMnO<sub>4</sub> = 0.5 gram MnO<sub>2</sub></span><br />
+<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span></p>
+
+<p>The iron does not enter into the calculation if the same quantity is
+present in the two experiments.</p>
+
+<p>An indirect titration thus requires three determinations, but if more
+than one assay is to be carried on, two of these need not be repeated.
+The standard is calculated in the usual way.</p>
+
+<p><b>Colorimetric Assays.</b>&mdash;These are assays in which the colour imparted to
+a solution by some compound of the metal to be determined is taken
+advantage of; the depth of colour depending on the quantity of metal
+present. They are generally used for the determination of such small
+quantities as are too minute to be weighed. The method of working is as
+follows:&mdash;A measured portion of the assay solution (generally 2/3, 1/2,
+1/3, or 1/4 of the whole), coloured by the substance to be estimated, is
+placed in a white glass cylinder standing on a sheet of white paper or
+glazed porcelain. Into an exactly similar cylinder is placed the same
+amount of re-agents, &amp;c., as the portion of the assay solution contains,
+and then water is added until the solutions are of nearly equal bulk.
+Next, a standard solution of the metal being estimated is run in from a
+burette, the mixture being stirred after each addition until the colour
+approaches that of the assay. The bulk of the two solutions is equalised
+by adding water. Then more standard solution is added until the tints
+are very nearly alike. Next, the amount added is read off from the
+burette, still more is poured in until the colour is slightly darker
+than that of the assay, and the burette read off again. The mean of the
+readings is taken, and gives the quantity of metal added. It equals the
+quantity of metal in the portion of the assay. If this portion was
+one-half of the whole, multiply by two; if one-third, multiply by three,
+and so on. When the quantity of metal in very dilute solutions is to be
+determined, it is sometimes necessary to concentrate the solutions by
+boiling them down before applying the re-agent which produces the
+coloured compound. Such concentration does not affect the calculations.</p>
+
+<p><b>Gasometric Assays.</b>&mdash;Gasometric methods are not much used by assayers,
+and, therefore, those students who wish to study them more fully than
+the limits of this work will permit, are recommended to consult Winkler
+and Lunge's text-book on the subject. The methods are without doubt
+capable of a more extended application. In measuring liquids, ordinary
+variations of temperature have but little effect, and variations of
+atmospheric pressure have none at all, whereas with gases it is
+different. Thus, 100 c.c. of an ordinary aqueous solution would, if
+heated from 10&deg; C. to 20&deg; C., expand to about 100.15 c.c. 100 c.c. of a
+gas similarly warmed would expand to about 103.5 c.c., and a fall of one
+inch in the barometer would have a very similar effect. And in
+measuring<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> gases we have not only to take into account variations in
+volume due to changes in temperature and atmospheric pressure, but also
+that which is observed when a gas is measured wet and dry. Water gives
+off vapour at all temperatures, but the amount of vapour is larger as
+the temperature increases.</p>
+
+<p>By ignoring these considerations, errors of 3 or 4 per cent. are easily
+made; but, fortunately, the corrections are simple, and it is easy to
+construct a piece of apparatus by means of which they may be reduced to
+a simple calculation by the rule of three.</p>
+
+<p>The volume of a gas is, in practice, usually reduced to that which it
+would be at a temperature of 0&deg; C., when the column of mercury in the
+barometer is 760 mm. high. But, although convenient, this practice is
+not always necessary. The only thing required is some way of checking
+the variations in volume, and of calculating what the corrected volume
+would be under certain fixed conditions.</p>
+
+<p>Suppose that at the time a series of standardisings is being made, 100
+c.c. of air were confined in a graduated tube over moist mercury. These
+100 c.c. would vary in volume from day to day, but it would always be
+true of them that they would measure 100 c.c. under the same conditions
+as those under which the standardisings were made. If, then, in making
+an actual assay, 35.4 c.c. of gas were obtained, and the air in the tube
+measured 105 c.c., we should be justified in saying, that if the
+conditions had been those of the standardising, the 105 c.c. would have
+measured 100 c.c., and the 35.4 c.c. would have been 33.7; for 105:
+100:: 35.4: 33.7. The rule for using such a piece of apparatus for
+correcting volumes is:&mdash;<i>Multiply the c.c. of gas obtained by 100, and
+divide by the number of c.c. of air in the apparatus.</i></p>
+
+<p>If it is desired to calculate the volumes under standard conditions
+(that is, the gas dry, at 0&deg; C. and 760 mm. barometric pressure) the
+calculations are easily performed, but the temperature and pressure must
+be known.</p>
+
+<p><i>Correction for Moisture.</i>&mdash;The "vapour tension" of water has been
+accurately determined for various temperatures, and it may be looked
+upon as counteracting the barometric pressure. For example, at 15&deg; C.
+the vapour tension equals 12.7 millimetres of mercury; if the barometer
+stood at 750 mm., the correction for moisture would be made by
+subtracting 12.7 from 750, and taking 737.3 mm. to be the true
+barometric pressure.</p>
+
+<p>The vapour tensions for temperatures from 0&deg; C. to 20&deg; C. are as
+follows:<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span>&mdash;</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temp.</td><td align='left'>Tension.</td><td align='left'>Temp.</td><td align='left'>Tension.</td><td align='left'>Temp.</td><td align='left'>Tension.</td></tr>
+<tr><td align='left'>0&deg;</td><td align='left'>4.6 mm.</td><td align='left'>7&deg;</td><td align='left'>7.5 mm.</td><td align='left'>14&deg;</td><td align='left'>11.9 mm.</td></tr>
+<tr><td align='left'>1&deg;</td><td align='left'>4.9 mm.</td><td align='left'>8&deg;</td><td align='left'>8.0 mm.</td><td align='left'>15&deg;</td><td align='left'>12.7 mm.</td></tr>
+<tr><td align='left'>2&deg;</td><td align='left'>5.3 mm.</td><td align='left'>9&deg;</td><td align='left'>8.6 mm.</td><td align='left'>16&deg;</td><td align='left'>13.5 mm.</td></tr>
+<tr><td align='left'>3&deg;</td><td align='left'>5.7 mm.</td><td align='left'>10&deg;</td><td align='left'>9.2 mm.</td><td align='left'>17&deg;</td><td align='left'>14.4 mm.</td></tr>
+<tr><td align='left'>4&deg;</td><td align='left'>6.1 mm.</td><td align='left'>11&deg;</td><td align='left'>9.8 mm.</td><td align='left'>18&deg;</td><td align='left'>15.3 mm.</td></tr>
+<tr><td align='left'>5&deg;</td><td align='left'>6.5 mm.</td><td align='left'>12&deg;</td><td align='left'>10.5 mm.</td><td align='left'>19&deg;</td><td align='left'>16.3 mm.</td></tr>
+<tr><td align='left'>6&deg;</td><td align='left'>7.0 mm.</td><td align='left'>13&deg;</td><td align='left'>11.2 mm.</td><td align='left'>20&deg;</td><td align='left'>17.4 mm.</td></tr>
+</table></div>
+
+
+
+<p>The <i>correction for pressure</i> is:&mdash;Multiply the volume by the actual
+pressure and divide by 760.</p>
+
+<p>The <i>correction for temperature</i>:&mdash;Multiply the volume by 273 and divide
+by the temperature (in degrees Centigrade) added to 273.</p>
+
+<p>For all three corrections the following rules hold good. <i>To reduce to
+0&deg; C. and 760 mm. dry.</i></p>
+
+<p>
+<span style="margin-left: 12em;">Volume &times; 0.3592 &times; (Pressure-tension)</span><br />
+<span style="margin-left: 1em;">Corrected volume = &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 15em;">Temperature + 273</span><br />
+</p>
+
+<p>To find the volume, which a given volume under standard conditions would
+assume, if those conditions are altered.</p>
+
+<p>
+<span style="margin-left: 10em;">Volume &times; 2.784 &times; (Temperature + 273)</span><br />
+Resulting volume =  &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+<span style="margin-left: 14.5em;">Pressure - tension</span><br />
+</p>
+
+<p>As an example, we will suppose that it is desired to enclose in the
+apparatus referred to on p. 45, a volume of air, which, when dry (at 0&deg;
+C. and 760 mm.), shall measure 100 c.c., whilst the actual temperature
+is 15&deg; C., and the pressure 750 mm.</p>
+
+<p>The second formula is the one to be used, and we get 108.7 c.c.</p>
+
+<p>
+<span style="margin-left: 11.5em;">100 c.c.&times;2.784&times;288</span><br />
+<span style="margin-left: 1em;">Required volume =&nbsp; &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 13.5em;">750-12.7</span><br />
+<br />
+<span style="margin-left: 11em;">80179.2</span><br />
+<span style="margin-left: 10em;">= &mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 11.5em;">737.3</span><br />
+<br />
+<span style="margin-left: 11em;">= 108.7 c.c.</span><br />
+</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> 100-35.6 = 64.4.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span></p>
+<h2><a name="CHAPTER_V" id="CHAPTER_V"></a>CHAPTER V.</h2>
+
+<h3>WEIGHING AND MEASURING.</h3>
+
+
+<p><b>Weighing.</b>&mdash;The system of weights and measures which we have adopted is
+the French or metric system; in this the gram (15.43 grains) is the unit
+of weight; the only other weight frequently referred to is the
+milligram, which is 0.001, or 1/1000 gram. The unit of volume is the
+cubic centimetre, which is approximately the volume of 1 gram of water,
+and which thus bears to the gram the same relation as grain-measures
+bear to grains. It is usual to write and even pronounce cubic centimetre
+shortly as c.c., and the only other denomination of volume we shall have
+occasion to use is the "litre," which measures 1000 c.c., and is roughly
+1-3/4 pints.</p>
+
+<p>The weights used are kept in boxes in a definite order, so that the
+weights on the balance can be counted as well by noting those which are
+absent from the box as by counting those present on the scale-pan. The
+weights run 50, 20, 10, 10, 5, 2, 1, 1 and 1 grams, and are formed of
+brass. The fractions of the gram are generally made of platinum or of
+aluminium, and are arranged in the following order:&mdash;0.5, 0.2, 0.1, 0.1,
+and 0.05, 0.02, 0.01, 0.01. These may be marked in this way, or they may
+be marked 500, 200, 100, 100, 50, 20, 10, 10; the 500 meaning 500
+milligrams.</p>
+
+<p>Some makers send out weights in the series 50, 20, 20, 10, &amp;c.</p>
+
+<p>Weights of less than 0.01 gram are generally present in a box, but it is
+much more convenient to work with a rider. This is a piece of wire which
+in the pan weighs 0.01 gram; it is made in such a form that it will ride
+on the beam, and its effective weight decreases as it approaches the
+centre. If the arm of the beam is divided into tenths, then each tenth
+counting from the centre outward equals 0.001 gram or 1 milligram, and
+if these tenths be further subdivided the fractions of a milligram are
+obtained; and these give figures in the fourth place of decimals. A
+fairly good balance should be sensitive to 0.0001 gram. The weights must
+never be touched with the fingers, and the forceps for moving them is
+used for no other purpose. When not in actual use the box is kept
+closed. The weights must not be allowed to remain on the pan of the
+balance. The balance-case must not be<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span> open without some reason. It must
+be fixed level, and, once fixed, must not be needlessly moved. The bench
+on which it stands should be used for no other purpose, and no one
+should be allowed to lean upon it.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig025.jpg" width="300" height="125" alt="Fig. 25." title="" />
+
+</div>
+
+<p>When using a balance sit directly in front of it. Ordinarily the
+substance to be weighed is best put on the pan to the user's left; the
+weights and the rider are then easily manipulated. Powders, &amp;c., should
+not be weighed directly on the balance; a counterpoised watch-glass or
+metal scoop (fig. 25) should be used. In some cases it is advisable to
+use a weighing-bottle. This is a light, well-stoppered bottle (fig. 3)
+containing the powdered ore. It is first filled and weighed; then some
+of the substance is carefully poured from it into a beaker or other
+vessel, and it is weighed again; the difference in the two weighings
+gives the weight of substance taken. A substance must always be cold
+when weighed, and large glass vessels should be allowed to stand in the
+balance-box a little while before being weighed. Always have the balance
+at rest when putting on or taking off anything from the pans. Put the
+weights on systematically. In using the rider (except you have a reason
+to the contrary), put it on at the 5; if this is too much, then try it
+at the 3; if then the weights are too little, try at the 4, if still not
+enough, the correct weight must be between the 4 and 5; try half-way
+between.</p>
+
+<p>It is best to work with the balance vibrating; equilibrium is
+established when the vibration to the left is the mean of the preceding
+and succeeding vibrations to the right. For example, if it vibrates 6
+divisions to the right on one swing, and 5 divisions on the next, the
+intermediate vibration to the left should have been 5-1/2.</p>
+
+<p>Note whether the substance increases in weight whilst on the balance. If
+it does it may be because it was put on warm, and is cooling, or it may
+be because it is taking up moisture from the air. Substances which take
+up moisture rapidly should be weighed in clipped watch-glasses or in
+light-weighing bottles or tubes.</p>
+
+<p>Students, in recording the weights, should first read off those missing
+from the box, writing down each order of figures as determined; first
+tens, then units, and so on. Remember that the first four platinum
+weights give the figures of the first place of decimals, the second four
+give the second place, and that the third and fourth places are given by
+the rider. Having taken down the figures, confirm them by reading off
+the weights as you put them<span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span> back into the box. Do not rest a weight on
+the palm of your hand for convenience in reading the mark upon it.
+Remember one weight lost from a box spoils the set. Do not take it for
+granted that the balance is in equilibrium before you start weighing:
+try it.</p>
+
+<div class="figcenter" style="width: 253px;">
+<img src="images/fig026.jpg" width="253" height="435" alt="Fig. 26." title="" />
+
+</div>
+
+<p><b>Measuring Liquids.</b>&mdash;For coarse work, such as measuring acids for
+dissolving ores, graduated glasses similar to those used by druggists
+may be used. It is well to have two sizes&mdash;a smaller graduated into
+divisions of 5 c.c. (fig. 26), and a larger with divisions equal to 10
+c.c. No measurement of importance should be made in a vessel of this
+kind, as a slight variation in level causes a serious error.</p>
+
+<p><b>Graduated flasks</b> must be used when anything has to be made up to a
+definite bulk, or when a fixed volume has to be collected. If, for
+example, a certain weight of substance has to be dissolved and diluted
+to a litre, or if the first 50 c.c. of a distillate has to be collected,
+a flask should be used. Each flask is graduated for one particular
+quantity; the most useful sizes are 1000 c.c., 500 c.c., 200 c.c., 100
+c.c., and 50 c.c. The mark should be in the narrowest part of the neck,
+and should be tangential to the curved surface of the liquid when the
+flask <i>contains</i> the exact volume specified. The level of a curved
+surface of liquid is at first somewhat difficult to read: the beginner
+is in doubt whether the surface should be taken at <span class="smcap">a</span>,
+<span class="smcap">b</span>, or <span class="smcap">c</span> (fig. 27). It is best to take the lowest
+reading <span class="smcap">c</span>. In some lights it is difficult to find this; in such
+cases a piece of white paper or card held behind and a little below, so
+as to throw light up and against the curved surface, will render it
+clear. In reading, one should look neither up at nor down upon the
+surface, but the eye should be on the same level with it. It must be
+kept in mind that flasks <i>contain</i> the quantity specified, but deliver
+less than this by the amount remaining in them and damping the sides. If
+it is desired to transfer the contents say of a 100 c.c. flask to a
+beaker, it will be necessary to complete the transfer by rinsing out the
+flask and adding the washings; otherwise there will be a sensible loss.
+Graduated cylinders (fig. 28) are convenient for preparing standard
+solutions.</p>
+
+<div class="figcenter" style="width: 319px;">
+<img src="images/fig027.jpg" width="319" height="400" alt="Fig. 27." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 228px;">
+<img src="images/fig028.jpg" width="228" height="450" alt="Fig. 28." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig029.jpg" width="300" height="344" alt="Fig. 29." title="" />
+
+</div>
+
+<p><b>Pipettes</b> and burettes are graduated to <i>deliver</i> the quantities<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span>
+specified. The principle of the pipette, and the advantages and
+disadvantages of its various forms, may be understood by considering the
+first form shown in fig. 29. It is essentially a bulbed tube drawn out
+to a jet at its lower end, and having on each side of the bulb a mark so
+placed that when the surface of the liquid falls from the upper to the
+lower mark the instrument shall deliver exactly 100 c.c. The bore of the
+jet should be of such a size as will allow the level of the liquid to
+fall at the rate of about one foot in two minutes. If it runs more
+quickly than this, an appreciable error arises from the varying amount
+of liquid remaining, and damping the sides of the bulb. The flow of
+liquid from a pipette must not be hastened by blowing into it. The lower
+tube or nose of the pipette should be long enough to reach into the
+bottle or flask containing the liquid about to be measured. The pipette
+is filled by sucking at the open end with the mouth; this method of
+filling renders the use of the instrument dangerous for such liquids as
+strong acids, ammonia, and such poisonous solutions as that of potassic
+cyanide. One attempt with a fairly strong solution of ammonia will teach
+the beginner a very useful lesson. As soon as the liquid rises above the
+upper mark in the pipette, the mouth is withdrawn, and the pipette
+quickly closed by pressing the upper aperture with the index finger of
+the right hand; it is well to have the finger slightly moist, but not
+damp. The neck of the pipette should be long enough to allow its being
+firmly grasped by the fingers and thumb of the right hand without
+inconvenience. The pipette is first held in a vertical position long
+enough to allow any moisture outside the tube to run down, and then the
+liquid is allowed to run out to the level of the upper mark; this is
+easily effected by lessening the pressure. If the finger is wet, the
+flow will be jerky, and good work impossible. The pipette is next held
+over the vessel into which the 100 c.c. are to be put, and the liquid
+allowed to run out. When the bulb is nearly empty, the flow should be
+checked by replacing the finger, and the liquid allowed to escape slowly
+until the lower mark is reached. The pipette is then withdrawn; it is in
+the withdrawing that the disadvantage of this particular form<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> makes
+itself felt. It must be withdrawn<span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span> very steadily, as the slightest shock
+causes the remaining column of liquid to vibrate, whereby air is drawn
+in and the liquid is forced out.</p>
+
+<p>This disadvantage is got rid of by making the mouth of the jet the lower
+limit, or, in other words, allowing the instrument to empty itself.
+There are two forms of such pipettes; in the one generally recommended
+in Gay-Lussac's silver assay (the last shown in fig. 29) the nose is
+replaced by a jet. This is most conveniently filled by stopping the jet
+with the finger, and allowing the liquid to flow in a fine stream into
+the neck until the pipette is filled, and then working as just
+described. The other form is the one in general use; in fact, a long
+nose to a pipette is so convenient that it may almost be said to be
+necessary. But the accuracy is slightly diminished; a long narrow tube
+makes a poor measuring instrument because of the amount of liquid it
+finally retains. A defect possessed by both forms is the retention of a
+drop of varying size in the nozzle. Whatever method is adopted for
+removing this drop must be always adhered to. The most convenient form
+is the one last described, and the most useful sizes are 100 c.c., 50
+c.c., 20 c.c., 10 c.c., and 5 c.c. Ten c.c. pipettes graduated into
+tenths of a cubic centimetre are very useful: those are best in which
+the graduation stops short of the bottom.</p>
+
+<p>All measurements should be made at the ordinary temperature; and, before
+being used, the pipette should be rinsed out with a cubic centimetre or
+so of the solution to be measured. After using, it should be washed out
+with water.</p>
+
+<p><b>Burettes</b> differ mainly from pipettes in having the flow of liquid
+controlled from below instead of from above. The best form is that known
+as Mohr's, one kind of which is provided with a glass stopcock, while
+the other has a piece of india-rubber tube compressed by a clip. The
+latter cannot be used for solutions of permanganate of potash or of
+iodine, or of any substance which acts on india-rubber; but in other
+respects there is little to choose between the two kinds. A burette
+delivering 100 c.c., and graduated into fifths (<i>i.e.</i>, each division =
+0.2 c.c.), is a very convenient size. For some kinds of work, 50 c.c.
+divided into tenths (<i>i.e.</i>, each division = 0.1 c.c.) may be selected.</p>
+
+<p>Burettes may be fixed in any convenient stand; they must be vertical and
+should be so placed that the assayer can read any part of the graduated
+scale without straining. When not in use, they should be kept full of
+water. When using a burette, the water must be run out; the burette is
+next rinsed with some of the solution to be used, and drained; and then
+it is filled with the solution. Next squeeze the india-rubber tube so as
+to disentangle air-bubbles and, by smartly opening the clip, allow the
+tube and<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span> jet to be filled; see that no bubbles of air are left. Then
+run out cautiously until the level of the liquid in the burette stands
+at zero. In reading the level with very dark-coloured liquids it is
+convenient to read from the level <span class="smcap">a</span> (fig. 27), and, provided it
+is done in each reading, there is no objection to this. The accuracy of
+the reading of a burette is sensibly increased by the use of an Erdmann
+float. This is an elongated bulb, weighted with mercury, and fitting
+(somewhat loosely) the tube of the burette. It floats in the solution,
+and is marked with a horizontal line; this line is taken as the level of
+the liquid. If the burette is filled from the top, the float rises with
+aggravating slowness, and this is its chief disadvantage. The float must
+come to rest before any reading is made.</p>
+
+<div class="figcenter" style="width: 150px;">
+<img src="images/fig030.jpg" width="150" height="450" alt="Fig. 30." title="" />
+
+</div>
+
+<p>A convenient plan for filling a burette from below is shown in fig. 30.
+The diagram explains itself. The bottle containing the standard solution
+is connected with the burette by a syphon arrangement through the glass
+tube and T-piece. The flow of liquid into the burette is controlled by
+the clip. When this clip is opened, the burette fills; and when it is
+closed, the burette is ready for use in the ordinary way.</p>
+
+<p><b>Measuring Gases.</b>&mdash;Lange's nitrometer (fig. 69) is a very convenient
+instrument for many gasometric methods. It requires the use of a fair
+quantity of mercury. In fig. 31, there is a representation of a piece of
+apparatus easily fitted up from the ordinary material of a laboratory.
+It is one which will serve some useful purposes. It consists of a
+wide-mouthed bottle fitted (by preference) with a rubber cork. The cork
+is perforated, and in the perforation is placed a glass tube which
+communicates with the burette. The burette is connected by a rubber tube
+and a Y-piece, either with another burette or with a piece of ordinary
+combustion-tube of about the same size. The wide-mouthed bottle contains
+either a short test-tube or an ordinary phial with its neck cut off. In
+working the apparatus the weighed substance is put in the bottle and the
+re-agent which<span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span> is to act on it, in the test-tube; the cork is then
+inserted. The liquid in the two burettes is next brought to the same
+level, either by pouring it in at <span class="smcap">a</span> or running it out at
+<span class="smcap">b</span>. The level of the liquid in the apparatus for correcting
+variation in volume is then read and noted. Next, after seeing that the
+level of the liquid in the burette has not changed, turn the bottle over
+on its side so that the re-agent in the test-tube shall be upset into
+the bottle. Then, as the volume of the gas increases, lower the liquid
+in the burette by running it out at <span class="smcap">b</span>, and at the same time
+keep the level in <span class="smcap">a</span> half an inch or so lower than that in the
+burette. When the action has finished bring the liquid in the two
+vessels to the same level and read off the burette. This part of the
+work must always be done in the same manner.</p>
+
+<div class="figcenter" style="width: 248px;">
+<img src="images/fig031.jpg" width="248" height="450" alt="Fig. 31." title="" />
+
+</div>
+
+<p><i>The volume corrector for gas analysis</i> is a graduated glass tube of 120
+c.c. capacity inverted over a narrow glass cylinder of mercury. It
+contains 0.2 or 0.3 c.c. of water and a volume of air, which, if dry and
+under standard conditions, would measure 100 c.c. The actual volume
+varies from day to day, and is read off at any time by bringing the
+mercury inside and outside to the same level. This is done by raising or
+lowering the tube, as may be required. Any volume of gas obtained in an
+assay can be corrected to standard temperature and pressure by
+multiplying by 100 and dividing by the number of c.c. in the corrector
+at the time the assay is made.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> It is best to use this form with a glass stopcock, or with
+an india-rubber tube and clip, after the manner of a Mohr's burette.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span></p>
+<h2><a name="CHAPTER_VI" id="CHAPTER_VI"></a>CHAPTER VI.</h2>
+
+<h3>RE-AGENTS.&mdash;ACIDS, ETC.</h3>
+
+
+<p><b>Acetic Acid</b>, H[=A=c] or C<sub>2</sub>H<sub>4</sub>O<sub>2</sub>. (sp. gr. 1.044, containing 33
+per cent. real acid).&mdash;An organic acid, forming a class of salts,
+acetates, which are for the most part soluble in water, and which, on
+ignition, leave the oxide or carbonate of the metal. It is almost always
+used in those cases where mineral acids are objectionable. To convert,
+for example, a solution of a substance in hydrochloric acid into a
+solution of the same in acetic acid, alkali should be added in excess
+and then acetic acid. Many compounds are insoluble in acetic acid, which
+are soluble in mineral acids, such as ferric phosphate, ferric arsenate,
+zinc sulphide, calcium oxalate, &amp;c., so that the use of acetic acid is
+valuable in some separations. The commercial acid is strong enough for
+most purposes, and is used without dilution.</p>
+
+<p><b>"Aqua Regia"</b> is a mixture of 1 part by measure of nitric acid and 3
+parts of hydrochloric acid. The acids react forming what is practically
+a solution of chlorine.<a name="FNanchor_6_6" id="FNanchor_6_6"></a><a href="#Footnote_6_6" class="fnanchor">[6]</a> The mixture is best made when wanted, and is
+chiefly used for the solution of gold and platinum and for "opening up"
+sulphides. When solutions in aqua regia are evaporated, chlorides are
+left.</p>
+
+<p><b>Bromine</b>, Br. (sp. gr. 3.0). Practically pure bromine.&mdash;It is a heavy
+reddish-brown liquid and very volatile. It boils at 60&deg; C., and,
+consequently, must be kept in a cool place. It gives off brown
+irritating vapours, which render its use very objectionable. Generally
+it answers the same purpose as aqua regia, and is employed where the
+addition of nitric acid to a solution has to be specially avoided. It is
+also used for dissolving metals only from ores which contain metallic
+oxides not desired in the solution.</p>
+
+<p><b>"Bromine Water"</b> is simply bromine shaken up with water till no more is
+dissolved.</p>
+
+<p><b>Carbonic Acid</b>, CO<sub>2</sub>.&mdash;A heavy gas, somewhat soluble in water; it is
+mainly used for providing an atmosphere in which substances may be
+dissolved, titrated, &amp;c., without fear of oxidation. It is also used in
+titrating arsenic assays with "iodine" when a feeble acid<span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span> is required
+to prevent the absorption of iodine by the alkaline carbonate. It is
+prepared when wanted in solution, by adding a gram or so of bicarbonate
+of soda and then as much acid as will decompose the bicarbonate
+mentioned. When a quantity of the gas is wanted, it is prepared, in an
+apparatus like that used for sulphuretted hydrogen, by acting on
+fragments of marble or limestone with dilute hydrochloric acid.</p>
+
+<p><b>Citric Acid</b> (H<sub>3</sub>[=C=i] or C<sub>6</sub>H<sub>8</sub>O<sub>7</sub>.H<sub>2</sub>O) is an organic acid
+which occurs in colourless crystals, soluble in less than their weight
+of water. The solution must be freshly prepared, as it gets mouldy when
+kept. It forms a comparatively unimportant class of salts (citrates). It
+is used in the determination of phosphoric acid, chiefly for the purpose
+of preventing the precipitation of phosphates of iron and alumina by
+ammonia, and in a few similar cases. The commercial crystals are used;
+they should be free from sulphuric acid and leave no ash on ignition.</p>
+
+<p><b>Hydrochloric Acid</b>, HCl in water, (sp. gr. 1.16. It contains 32 per
+cent. of hydrogen chloride).&mdash;It is sometimes called "muriatic acid,"
+and when impure, "spirit of salt." The acid solution should be
+colourless and free from arsenic, iron, and sulphuric acid. It forms an
+important family of salts, the chlorides. It is the best acid for
+dissolving metallic oxides and carbonates, and is always used by the
+assayer when oxidising agents are to be avoided. The acid is used
+without dilution when no directions are expressly given to dilute it. It
+has no action on the following metals: gold, platinum, arsenic, and
+mercury; it very slightly attacks antimony, bismuth, lead, silver, and
+copper. Tin is more soluble in it, but with difficulty; whilst iron,
+zinc, nickel, cobalt, cadmium, and aluminium easily dissolve with
+evolution of hydrogen and the formation of the lower chloride if the
+metal forms more than one class of salts. All the metallic oxides,
+except a few of the native and rarer oxides, are dissolved by it with
+the formation of chlorides of the metal and water.</p>
+
+<p><b>Dilute Hydrochloric Acid</b> is made by diluting the strong acid with an
+equal volume of water. This is used for dissolving precipitates obtained
+in the general course of analysis and the more easily soluble metals.</p>
+
+<p><b>Hydrofluoric Acid, HF.</b>&mdash;A solution in water may be purchased in
+gutta-percha or lead bottles. It is of variable strength and doubtful
+purity. It must always be examined quantitatively for the residue left
+on evaporation. It is used occasionally for the examination of
+silicates. It attacks silica, forming fluoride of silicon, which is a
+gas. When the introduction of another base will not interfere with the
+assay, the substance may be mixed in the platinum dish with fluoride of
+ammonium,<span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span> or of potassium, or of calcium, and hydrochloric acid,
+instead of treating it with the commercial acid. It is only required in
+special work. The fumes and acid are dangerous, and, of course, glass or
+porcelain vessels cannot be used with it.</p>
+
+<p><b>Iodine, I.</b>&mdash;This can be obtained in commerce quite pure, and is often
+used for standardising. It is very slightly soluble in water, but
+readily dissolves in potassium iodide solution. It closely resembles
+chlorine and bromine in its properties, and can be used for dissolving
+metals without, at the same time, attacking any oxide which may be
+present. It is chiefly used as an oxidizing agent in volumetric work,
+being sharp in its reactions and easily detected in minute quantities.
+It cannot be used in alkaline solutions, since it reacts with the
+hydrates, and even with the carbonates, to form iodides and iodates.
+Iodine is soluble in alcohol.</p>
+
+<p><b>Nitric Acid, HNO<sub>3</sub>.</b> (Sp. gr. 1.42; boiling point 121&deg; C.; contains
+70 per cent. by weight of hydrogen nitrate).&mdash;It is convenient to
+remember that one c.c. of this contains 1 gram of real acid. It combines
+the properties of an acid and of an oxidising agent. One c.c. contains
+0.76 gram of oxygen, most of which is very loosely held, and easily
+given up to metals and other oxidisable substances. Consequently it will
+dissolve many metals, &amp;c., upon which hydrochloric acid has no action.
+All sulphides (that of mercury excepted) are attacked by it, and for the
+most part rendered soluble. It has no action on gold or platinum, and
+very little on aluminium. The strong acid at the ordinary temperature
+does not act on iron or tin; and in most cases it acts better when
+diluted. Some nitrates being insoluble in nitric acid, form a protecting
+coat to the metal which hinders further action. Where the strong acid
+does act the action is very violent, so that generally it is better to
+use the dilute acid. When iron has been immersed in strong nitric acid
+it not only remains unacted on, but assumes a <i>passive</i> state; so that
+if, after being wiped, it is then placed in the dilute acid, it will not
+dissolve. Tin and antimony are converted into insoluble oxides, while
+the other metals (with the exception of those already mentioned)
+dissolve as nitrates. During the solution of the metal red fumes are
+given off, which mainly consist of nitrogen peroxide. The solution is
+often coloured brown or green because of dissolved oxides of nitrogen,
+which must be got rid of by boiling. Generally some ammonium nitrate is
+formed, especially in the cases of zinc, iron, and tin, when these are
+acted on by cold dilute acid. Sulphur, phosphorus, and arsenic are
+converted into sulphuric, phosphoric, and arsenic acids respectively,
+when boiled with the strong acid.<span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span></p>
+
+<p><b>Dilute Nitric Acid.</b>&mdash;Dilute 1 volume of the strong acid with 2 of
+water.</p>
+
+<p><b>Oxalic Acid</b>, H<sub>2</sub>O or (H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>.2H<sub>2</sub>O.)&mdash;This is an organic
+acid in colourless crystals. It forms a family of salts&mdash;the oxalates.
+It is used in standardising; being a crystallised and permanent acid, it
+can be readily weighed. It is also used in separations, many of the
+oxalates being insoluble. For general use make a 10 per cent. solution.
+Use the commercially pure acid. On ignition the acid should leave no
+residue.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig032.jpg" width="450" height="316" alt="Fig. 32." title="" />
+
+</div>
+
+<p><b>Sulphuretted Hydrogen.</b> Hydrosulphuric acid, SH<sub>2</sub>.&mdash;A gas largely
+used in assaying, since by its action it allows of the metals being
+conveniently classed into groups. It is soluble in water, this liquid
+dissolving at the ordinary temperature about three times its volume of
+the gas. The solution is only useful for testing. In separations, a
+current of the gas must always be used. It is best prepared in an
+apparatus like that shown in fig. 32, by acting on ferrous sulphide with
+dilute hydrochloric acid. When iron has to be subsequently determined in
+the assay solution, the gas should be washed by bubbling it through
+water in the smaller bottle; but for most purposes washing can be
+dispensed with. The gas is very objectionable, and operations with it
+must be carried out in a cupboard with a good draught. When the
+precipitation has been completed, the apparatus should always be washed
+out. The effect of this acid on solutions of the metals is to form
+sulphides. All the metallic sulphides are insoluble in water; but some
+are soluble in alkaline, and some in acid, solutions. If sulphuretted
+hydrogen is passed through an acid solution containing the metals till
+no further precipitation takes place, a precipitate will be formed
+containing sulphides insoluble in the acid. On filtering, adding ammonia
+(to render the filtrate alkaline), and again passing the gas, a further
+precipitate will be obtained, consisting of sulphides insoluble in an
+alkaline solution, but not precipitable in an acid one; the filtrate may
+also contain sulphides not precipitable in an acid solution, which are
+soluble in an alkaline one; these will be thrown down on neutralising.
+Again, the metals precipitated in the acid solution form sulphides which
+may be divided into groups, the one consisting of those which are
+soluble, and the other of those which are not soluble, in alkalies. This
+classification is shown in the following summary:<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span>&mdash;</p>
+
+<p>
+1. <i>Precipitable in an acid solution.</i><br />
+<br />
+<span style="margin-left: 1em;">(<i>a</i>) Soluble in Alkalies.&mdash;Sulphides of As, Sb, Sn, Au, Pt, Ir, Mo, Te, and Se.</span><br />
+<br />
+<span style="margin-left: 1em;">(<i>b</i>) Insoluble in Alkalies.&mdash;Sulphides of Ag, Pb, Hg, Bi, Cu, Cd, Pd, Rh, Os, and Ru.</span><br />
+<br />
+2. <i>Not precipitated in an acid solution, but thrown down in an alkaline one.</i><br />
+<br />
+<span style="margin-left: 1em;">Sulphides of Mn, Zn, Fe, Ni, Co, In, Tl, and Ga.</span><br />
+</p>
+
+<p>These can again be divided into those which are dissolved by dilute
+acids and those which are not.</p>
+
+<p>
+3. <i>Not precipitated in an acid or alkaline solution, but thrown<br />
+down on neutralising the latter.</i><br />
+<br />
+<span style="margin-left: 1em;">Sulphides of V and W.</span><br />
+</p>
+
+<p>Sulphuretted hydrogen is a strong reducing agent. Ferric salts are
+thereby quickly reduced to ferrous; in hot solutions nitric acid is
+decomposed. These changes are marked by a precipitation of sulphur, and
+the student must be careful to pass the gas sufficiently long, and not
+be too hasty in concluding that no sulphide will form because it does
+not at once make its appearance. The best indication that it has been
+passed long enough is the smell of the gas in the solution after
+shaking.</p>
+
+<p><b>Sulphurous Acid</b>, H<sub>2</sub>SO<sub>3</sub>.&mdash;The reagent used may be regarded as a
+saturated solution of sulphur dioxide in water. It may be purchased, and
+keeps for a long time. It may be made by heating copper with sulphuric
+acid and passing the gas formed into water. The heat should be withdrawn
+when the gas is coming off freely. It is used as a reducing agent, and
+should not be diluted.</p>
+
+<p><b>Sulphuric Acid</b>, H<sub>2</sub>SO<sub>4</sub>. (Sp. gr. 1.84, containing 96 per cent. of
+real acid, H<sub>2</sub>SO<sub>4</sub>.)&mdash;This acid forms insoluble sulphates with salts
+of lead, strontium, and barium. It has a high boiling point, 290&deg; C.,
+and, when evaporated with salts of the more volatile acids, converts
+them into sulphates. When nitrates or chlorides are objectionable in a
+solution, evaporation with sulphuric acid removes them. In working with
+this acid caution is necessary, since, on mixing with water, great heat
+is evolved; and, if either the acid or water has been previously heated,
+a serious accident may result. In diluting the acid it should be poured
+into cold water. Glass vessels containing boiling sulphuric acid should
+be handled as little as possible, and should not be cooled under the
+tap. The action of diluted sulphuric acid on metals closely resembles
+that of dilute hydrochloric acid. Magnesium, aluminium, iron, zinc,
+nickel, cobalt, manganese, and cadmium dissolve, with evolution of
+hydrogen, in the cold acid, or when warmed. The action of hot and strong
+sulphuric acid is<span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span> altogether different; it acts as an oxidising agent,
+and is itself reduced to sulphur dioxide or even to sulphur. The
+following metals are attacked in this way:&mdash;copper, bismuth, mercury,
+silver, antimony, tin, and lead. Gold, platinum, and arsenic are not
+affected. This property is made use of in parting silver from gold and
+platinum. Metallic sulphides are similarly attacked; but this method of
+opening up minerals has the disadvantage of giving rise to the formation
+of anhydrous sulphates of iron, &amp;c., which are not readily dissolved
+when afterwards diluted. The use of sulphuric acid in assaying is (for
+these reasons) to be avoided. Its chief use is as a drying agent, since
+it has a strong affinity for water. Air under a bell jar may be kept dry
+by means of a basin of sulphuric acid, and gases bubbled through it are
+freed from water-vapour.</p>
+
+<p><b>Dilute Sulphuric Acid.</b>&mdash;This is made by diluting 1 volume of the
+strong acid with 4 of water.</p>
+
+<p><b>Tartaric Acid</b>, H<sub>2</sub>[=T] or C<sub>4</sub>H<sub>6</sub>O<sub>6</sub>.&mdash;A crystallised organic
+acid, soluble in less than its own weight of water, or in less than
+three parts of alcohol. It is used for the same purposes as citric acid
+is. The solution is made when required.</p>
+
+
+<h4>BASES, SALTS, &amp;c.</h4>
+
+<p><b>Alcohol</b>, C<sub>2</sub>H<sub>6</sub>O. (Commercial alcohol of sp. gr. 0.838; it
+contains 84 per cent. by weight of alcohol.)&mdash;It should burn with a
+non-luminous flame and leave no residue. It is used for washing
+precipitates where water is inapplicable, and for facilitating drying.</p>
+
+<p><b>Ammonia</b>, NH<sub>3</sub>. (Commercial ammonia, a solution having a sp. gr. of
+0.88 to 0.89, and containing about 33 per cent. of ammonia.)&mdash;It is used
+as an alkali (more commonly than soda or potash), since an excess of it
+is easily removed by boiling. The salts of ammonium formed by it may be
+removed by igniting, or by evaporating in a porcelain dish with an
+excess of nitric acid. It differs in a marked way from soda or potash in
+its solvent action on the oxides or hydrates of the metals. Salts of the
+following metals are soluble in an ammoniacal solution in the presence
+of ammonic chloride:&mdash;copper, cadmium, silver, nickel, cobalt,
+manganese, zinc, magnesium, sodium, potassium, and the alkaline earths.</p>
+
+<p><b>Dilute Ammonia</b> is made by diluting 1 vol. of commercial ammonia with 2
+of water. The dilute ammonia is always used; but in assays for copper a
+stronger solution (1 of strong ammonia to 1 of water) is required.</p>
+
+<p><b>Ammonic Carbonate</b> (Am<sub>2</sub>CO<sub>3</sub>) is prepared by dissolving one part of
+the commercial sesquicarbonate of ammonia in four parts of water, and
+adding one part of strong ammonia.<span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span></p>
+
+<p><b>Ammonic Bicarbonate</b> (HAmCO<sub>3</sub>) is prepared by saturating a solution
+of the sesquicarbonate of ammonia with carbon dioxide.</p>
+
+<p><b>Ammonic Chloride</b>, AmCl.&mdash;Use the commercial salt in a 20 per cent.
+solution in water. The salt should leave no residue on ignition.</p>
+
+<p><b>Ammonic Molybdate.</b>&mdash;The solution is prepared as follows:&mdash;Dissolve 100
+grams of the powdered commercial salt in 200 c.c. of dilute ammonia, and
+pour the solution in a slow stream into 750 c.c. of dilute nitric acid;
+make up to 1 litre, and allow the mixture to settle before using. It is
+used for the purpose of separating phosphoric oxide from bases and from
+other acids, and also as a test for phosphates and arsenates. In using
+this solution the substance must be dissolved in nitric acid, and a
+considerable excess of the reagent added (50 c.c. is sufficient to
+precipitate 0.1 gram P<sub>2</sub>O<sub>5</sub>); when the phosphate is in excess no
+precipitate will be got. The precipitate is phospho-molybdate of
+ammonia.</p>
+
+<p><b>Ammonic Nitrate</b> (AmNO<sub>3</sub>) is used in the separation of phosphoric
+oxide by the molybdate method, and occasionally for destroying organic
+matter. It is soluble in less than its own weight of water. The solution
+is made when wanted.</p>
+
+<p><b>Ammonic Oxalate</b> (Am<sub>2</sub>C<sub>2</sub>O<sub>4</sub>.2H<sub>2</sub>O) is used chiefly for the
+separation of lime. The solution is made by dissolving 15 grams of the
+salt in 100 c.c. of water.</p>
+
+<p><b>Ammonic Sulphide</b> may be purchased in the state of a strong solution.
+It is yellow, and contains the disulphide, S<sub>2</sub>Am<sub>2</sub>. It serves the
+same purpose as is obtained by passing a current of sulphuretted
+hydrogen through an ammoniacal solution; but has the disadvantage of
+loading the solution with sulphur, which is precipitated when the
+solution is subsequently acidified. It is useful for dissolving the
+lower sulphide of tin (SnS).</p>
+
+<p><b>Baric Carbonate</b> (BaCO<sub>3</sub>) is sometimes used for precipitating the
+weaker bases. It should be prepared when wanted by precipitating a
+solution of baric chloride with ammonic carbonate and washing. The moist
+precipitate is used without drying.</p>
+
+<p><b>Baric Chloride</b>, BaCl<sub>2</sub>.2H<sub>2</sub>O.&mdash;A crystallised salt, soluble in
+2-1/2 parts of water. It is used for the detection and separation of
+sulphates. Make a 10 per cent. solution.</p>
+
+<p>"<b>Black Flux.</b>"&mdash;A mixture of finely divided carbon with carbonate of
+potash or with carbonates of potash and soda. It is prepared by heating
+tartar or "rochelle salt" until no more combustible gas is given off.
+One gram will reduce about 2 grams of lead from litharge.</p>
+
+<p><b>Borax</b>, Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>.10H<sub>2</sub>O.&mdash;It is chiefly used as a flux in dry
+assaying, as already described. It is also used in testing before<span class='pagenum'><a name="Page_61" id="Page_61">[Pg 61]</a></span> the
+blowpipe; many metallic oxides impart a characteristic colour to a bead
+of borax in which they have been fused.</p>
+
+<p><b>Calcium Chloride.</b>&mdash;The crystallised salt is CaCl<sub>2</sub>.6H<sub>2</sub>O; dried at
+200&deg; C. it becomes CaCl<sub>2</sub>.2H<sub>2</sub>O, and when fused it becomes
+dehydrated. The fused salt, broken into small lumps, is used for drying
+gases. It combines with water, giving off much heat; and dissolves in a
+little more than its own weight of water. Strong solutions may be used
+in baths in which temperatures above the boiling-point of water are
+required. One part of the salt and 2 of water give a solution boiling at
+112&deg;, and a solution of 2 parts of the salt in 1 of water boils at 158&deg;.
+The salt is very little used as a reagent.</p>
+
+<p><b>Calcium Fluoride</b> or "<b>Fluor Spar</b>," CaF<sub>2</sub>.&mdash;The mineral is used as a
+flux in dry assaying; it renders slags which are thick from the presence
+of phosphates, &amp;c., very fluid. Mixed with hydrochloric acid it may
+sometimes be used instead of hydrofluoric acid.</p>
+
+<p><b>Calcium Carbonate</b>, CaCO<sub>3</sub>.&mdash;It is precipitated in a pure state by
+ammonic carbonate from a solution of calcium chloride. It is used for
+standardising. In the impure state, as marble or limestone, it is used
+in the preparation of carbonic acid.</p>
+
+<p><b>Calcium Hydrate</b> or <b>"Lime Water."</b>&mdash;This is used in testing for carbon
+dioxide and in estimating the amount of that gas present in air. It may
+be made by slaking quicklime and digesting the slaked lime with water.
+One hundred c.c. of water at 15&deg; C. dissolves 0.1368 grams of the
+hydrate (CaH<sub>2</sub>O<sub>2</sub>), and hot water dissolves still less. "<i>Milk of
+lime</i>" is slaked lime suspended in water.</p>
+
+<p><b>Cobalt Nitrate</b> (Co(NO<sub>3</sub>)<sub>2</sub>.6H<sub>2</sub>O) is used in a 10 per cent.
+solution for the detection of oxides of zinc, aluminium, &amp;c.; on
+ignition with which it forms characteristically coloured compounds.</p>
+
+<p><b>Copper</b>, Cu.&mdash;Pure copper, as obtained by electrolysis, can be
+purchased. This only should be used.</p>
+
+<p><b>Copper Oxide</b>, CuO.&mdash;It occurs as a black, heavy, and gritty power, and
+is used for the oxidation of carbon and hydrogen in organic substances.
+It should be ignited and cooled out of contact with air just before
+using, since it is hygroscopic. Oxide of copper which has been used may
+be again utilised after calcination.</p>
+
+<p><b>Copper Sulphate</b> (CuSO<sub>4</sub>.5H<sub>2</sub>O) contains 25.4 per cent. of copper.
+It is used in the outer cell of a Daniell-battery. The commercial salt
+is used for this purpose. The re-crystallised and pure salt is used for
+preparing the anhydrous sulphate, which is used for detecting moisture
+in gases. For this purpose it is<span class='pagenum'><a name="Page_62" id="Page_62">[Pg 62]</a></span> dried at 200&deg; C. till no trace of
+green or blue colour remains. It must be prepared when wanted. It may be
+conveniently used in the form of pumice-stone, saturated with a solution
+of the salt and dried. Traces of moisture develop a green colour.</p>
+
+<p><b>Ferric Chloride</b>, Fe<sub>2</sub>Cl<sub>6</sub>. (When crystallised,
+Fe<sub>2</sub>Cl<sub>6</sub>.6H<sub>2</sub>O.)&mdash;The solution is prepared as described under
+iron. The commercial salt contains arsenic, and, since the chief use of
+ferric chloride is for the determination of this substance, it must be
+purified (<i>see</i> under <span class="smcap">Arsenic</span>).</p>
+
+<p><b>Ferric Sulphate</b> (Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>) is a yellowish white deliquescent
+salt. It is used as an indicator in volumetric silver assaying, and for
+the separation of iodine from bromine. It may be purchased as iron alum,
+Am<sub>2</sub>Fe<sub>2</sub>(SO<sub>4</sub>)<sub>4</sub>.24H<sub>2</sub>O. But it is best prepared by adding
+strong sulphuric acid to ferric hydrate in equivalent proportions. Use
+it as a solution containing 2 or 3 per cent. of iron.</p>
+
+<p><b>Ferrous Sulphate</b>, FeSO<sub>4</sub>.7H<sub>2</sub>O.&mdash;The granulated form is best, and
+can be purchased pure. It is used for standardising. It keeps better in
+crystals than in solution. It is readily soluble in water, but the
+solution is best made with the help of a little free acid. As a re-agent
+use a 10 per cent. solution. The crystals should be clear bluish-green;
+if their colour is dark green, brown, or blue, they should be rejected.</p>
+
+<p><b>Ferrous Sulphide</b> (FeS) is used for the preparation of sulphuretted
+hydrogen. It may be purchased and broken in small lumps, nut-size, for
+use.</p>
+
+<p>"<b>Fusion Mixture</b>" (K<sub>2</sub>CO<sub>3</sub>.Na<sub>2</sub>CO<sub>3</sub>) is a mixture of potassic
+and sodic carbonates in the proportions of 13 of the former to 10 of the
+latter, by weight. It is hygroscopic. A mixture of the bicarbonates is
+better, being purer and less apt to get damp.</p>
+
+<p><b>Gallic Acid</b> (C<sub>7</sub>H<sub>6</sub>O<sub>5</sub>.H<sub>2</sub>O) is an organic acid, occurring as
+a pale fawn-coloured crystalline powder, soluble in 100 parts of cold
+water, or in 3 parts of boiling water. It is used for the determination
+of antimony. A 10 per cent. solution in warm water is made when
+required.</p>
+
+<p><b>Hydrogen</b> (H) is a gas. It is obtained by acting on zinc with dilute
+hydrochloric or sulphuric acid. It is used as a reducing agent, and for
+providing an atmosphere free from oxygen. It reduces metallic oxides at
+a high temperature. It must be freed from water; and special precautions
+should be taken to prevent an admixture with air. It is generally
+required in a current which can be continued for an hour or more without
+interruption. The preparation can be conveniently carried out in the
+apparatus shown (fig. 33). A quart bottle is half filled with sheet
+zinc, and connected with bulbs filled with sulphuric acid, and with<span class='pagenum'><a name="Page_63" id="Page_63">[Pg 63]</a></span> a
+calcium chloride tube. The last is connected with the apparatus through
+which the gas has to be passed. Dilute hydrochloric acid mixed with a
+few cubic centimetres (20 c.c. to 1 pint) of stannous chloride sol. to
+fix any dissolved oxygen, is placed in the funnel, and let into the
+bottle by opening the stopcock when required. Care must be taken to let
+the hydrogen escape for some time before starting the reduction.</p>
+
+<div class="figcenter" style="width: 470px;">
+<img src="images/fig033.jpg" width="470" height="320" alt="Fig. 33." title="" />
+
+</div>
+
+<p><b>Gold</b>, Au.&mdash;Gold, obtained by cupelling and "parting," is for most
+purposes sufficiently pure. It is best kept in the shape of foil. When
+the purer metal is required, gold should be dissolved in aqua regia, the
+solution evaporated to a paste, diluted, allowed to stand, and filtered.
+The filtered solution is acidified with hydrochloric acid, warmed, and
+precipitated with sodium sulphite. The precipitate is collected, washed,
+and fused on charcoal.</p>
+
+<p><b>Iron</b>, Fe.&mdash;The soft wire (thin) is used for standardising. Rods are
+used in dry assays as a desulphurising agent. Steel must not be used,
+since it is not pure, and contains a variable amount of iron.</p>
+
+<p><b>Lead</b>, Pb.&mdash;Granulated lead or lead-foil is used in the dry assay for
+silver and gold, and in the preparation of lead salts. It can be
+obtained very pure, but always contains more or less silver, 1 or 2
+milligrams in 100 grams. The amount of silver it contains must be
+determined and recorded.</p>
+
+<p><b>Lead Acetate</b> (Pb[=A=c]<sub>2</sub>.3H<sub>2</sub>O, or
+Pb(C<sub>2</sub>H<sub>3</sub>O<sub>2</sub>)<sub>2</sub>.3H<sub>2</sub>O) is used as a test, specially for the
+detection and estimation of sulphuretted hydrogen. Prepare a 10 per
+cent. solution for use.</p>
+
+<p><b>Lead Nitrate</b> (Pb(NO<sub>3</sub>)<sub>2</sub>) can be purchased pure. It is used for
+standardising.</p>
+
+<p><b>Lead Dioxide</b> (PbO<sub>2</sub>) occurs as a dark-brown powder. It is used as an
+oxidizing agent and for absorbing sulphurous oxide. It can be prepared
+by digesting red lead with warm dilute nitric acid; washing and drying
+the residue.</p>
+
+<p>"<b>Litharge</b>," PbO.&mdash;It can be purchased as a yellow heavy powder. It is
+used in dry assaying as a flux, as a desulphurising agent, and also as a
+source of lead. It always contains some silver, the amount of which must
+be determined.</p>
+
+<p><b>Litmus.</b>&mdash;This is an organic colouring matter which is turned red by
+acids and blue by alkalies. For ordinary purposes it is best used as
+litmus paper, which may be purchased in small books. A solution is
+prepared by digesting 15 or 20 grams of the commercial litmus in 100
+c.c. of water on the water bath. After being allowed to settle, it is
+filtered and made just faintly red with<span class='pagenum'><a name="Page_64" id="Page_64">[Pg 64]</a></span> acetic acid. Then there is
+added a drop or two of a solution of soda and 10 c.c. of alcohol. It
+should be kept in a loosely-covered bottle.</p>
+
+<p><b>Magnesia</b>, MgO.&mdash;It may be purchased as "calcined magnesia." It is used
+for making "magnesia mixture," and should be kept in a corked
+wide-mouthed bottle.</p>
+
+<p>"<b>Magnesia Mixture.</b>"&mdash;Dissolve 22 grams of magnesia in about a quarter
+of a litre of dilute hydrochloric acid, avoiding excess. Add 5 grams of
+magnesia, boil, and filter. Add 300 grams of ammonic chloride, and 250
+c.c. of strong ammonia; and dilute with water to 2 litres. It should be
+kept in a stoppered winchester.</p>
+
+<p><b>Magnesium Sulphate</b>, MgSO<sub>4</sub>.7H<sub>2</sub>O.&mdash;It can be purchased very pure,
+and is occasionally used as a standard salt.</p>
+
+<p><b>Manganese Dioxide</b>, MnO<sub>2</sub>.&mdash;It is used in the preparation of
+chlorine. The commercial article is not pure, but is sufficiently so for
+this purpose.</p>
+
+<p><b>Marble</b>, CaCO<sub>3</sub>.&mdash;Fragments of the white crystalline variety only
+should be used. It is used as a source of lime and of carbon dioxide.</p>
+
+<p><b>Mercury</b>, Hg.&mdash;This can be purchased pure. It should have a bright
+surface, flow without a tail, and leave no residue on ignition. It is
+used as a standard; for amalgamation; and as a confining liquid in gas
+analysis.</p>
+
+<p><b>Mercuric Chloride</b> (HgCl<sub>2</sub>) may be purchased pure. Make a 5 per cent.
+solution in water. It is used for destroying an excess of stannous
+chloride; for removing sulphuretted hydrogen from solution; and as a
+test for stannous salts.</p>
+
+<p><b>Microcosmic Salt</b>, HAmNaPO<sub>4</sub>.8H<sub>2</sub>O.&mdash;When fused NaPO<sub>3</sub> is formed.
+It is used in testing for metallic oxides and silica before the
+blowpipe. The crystals are sometimes used as a standard for phosphoric
+acid.</p>
+
+<p>"<b>Nessler's Solution.</b>"&mdash;Mode of preparation: Dissolve 35 grams of
+potassium iodide in 100 c.c. of water; dissolve 17 grams of mercuric
+chloride in 300 c.c. of water, and pour this solution into that of the
+iodide till a permanent precipitate is produced; make up to 1 litre with
+a 20 per cent. solution of potash; add mercuric chloride till a
+precipitate is again formed; allow to settle and decant. It is used for
+detecting ammonia.</p>
+
+<p><b>Nitre.</b>&mdash;This is potassium nitrate.</p>
+
+<p><b>Platinum Chloride</b>, 2HCl.PtCl<sub>4</sub>. (In the crystallised form it has
+6H<sub>2</sub>O).&mdash;It may be made as follows:&mdash;Take 5 grams of clean platinum
+scrap and dissolve in a flask at a gentle heat in 50 c.c. of
+hydrochloric acid with the occasional addition of some nitric acid;
+evaporate to a paste; and then dissolve in 100 c.c. of water. It is used
+for separating and determining potassium.<span class='pagenum'><a name="Page_65" id="Page_65">[Pg 65]</a></span></p>
+
+<p><b>Phenolphthalein</b> is an organic compound used as an indicator; more
+especially in determining the weaker acids, it cannot be used in the
+presence of ammonia. Dissolve half a gram in 100 c.c. of dilute alcohol.</p>
+
+<p><b>Potassium Bicarbonate</b>, KHCO<sub>3</sub>.&mdash;It may be purchased pure; on
+ignition it leaves the carbonate, K<sub>2</sub>CO<sub>3</sub>, which may be used as a
+standard.</p>
+
+<p><b>Potassium Cyanide</b>, KCN.&mdash;It is used in the dry assay as a reducing
+agent. The commercial salt is very impure. Purchase that sold as
+potassic cyanide (gold) which contains about 95 per cent. of KCN. It is
+used for copper assaying and occasionally in separation. Make a 10 per
+cent. solution when wanted.</p>
+
+<p><b>Potassium Bichromate</b>, K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>. It may be purchased nearly
+pure. It is used as an oxidising agent, for determining iron; and as a
+test solution. For this last purpose a 10 per cent. solution is
+prepared.</p>
+
+<p><b>Potassium Chlorate</b> (KClO<sub>3</sub>) can be purchased pure. It is used with
+hydrochloric acid as a substitute for aqua regia.</p>
+
+<p><b>Potassium Ferrocyanide</b> (K<sub>4</sub>Fe(CN)<sub>6</sub>.3H<sub>2</sub>O), or "yellow prussiate
+of potash," is used as a test; as an indicator; and for the
+determination of zinc. Make a 5 per cent. solution.</p>
+
+<p><b>Potassium Ferricyanide</b> (K<sub>6</sub>Fe<sub>2</sub>(CN)<sub>12</sub>), or "red prussiate of
+potash," is used for testing; and as an indicator. Make a 5 per cent.
+solution when wanted, as it decomposes on keeping.</p>
+
+<p><b>Potassium Hydrate</b>, KHO. Purchase that purified with alcohol. It is an
+alkali, and is used for absorbing carbonic acid, &amp;c.</p>
+
+<p><b>Potassium Iodide</b>, KI. It may be purchased nearly pure. It is used as a
+test and for dissolving iodine. It should be used in a 10 per cent.
+solution freshly made. The solution decomposes on exposure to light,
+with separation of iodine.</p>
+
+<p><b>Potassium Nitrate</b> (KNO<sub>3</sub>) can be purchased pure. It is used in the
+dry way as an oxidizing agent. It is very fusible. It decomposes at a
+low temperature into potassium nitrite (KNO<sub>2</sub>) and free oxygen; and at
+a higher temperature leaves potash (K<sub>2</sub>O). It oxidizes sulphur and
+carbon with explosive violence. This action may be moderated by mixing
+the nitre with carbonate of soda, common salt, or some other inert body.</p>
+
+<p><b>Potassium Nitrite</b>, KNO<sub>2</sub>.&mdash;The commercial article is not pure, but
+is sufficiently so for the purpose required. A saturated solution is
+used in the separation of cobalt; the solution is made when wanted.</p>
+
+<p><b>Potassium Permanganate</b>, KMnO<sub>4</sub>.&mdash;This salt can be purchased
+sufficiently pure. It is much used as an oxidizing agent.</p>
+
+<p><b>Potassium Bisulphate</b> (KHSO<sub>4</sub>) is used as a dry reagent for opening
+up minerals. It fuses; and at a much higher temperature<span class='pagenum'><a name="Page_66" id="Page_66">[Pg 66]</a></span> is converted
+into potassium sulphate with loss of sulphuric acid.</p>
+
+<p><b>Potassium Sulphocyanate</b> (KCNS) is used for the detection and
+determination of traces of ferric iron; as also in the separation of
+silver and copper from some of the other metals. Make a 10 per cent.
+solution. It should show no colour on the addition of hydrochloric acid.</p>
+
+<p>"<b>Red Lead</b>" (Pb<sub>3</sub>O<sub>4</sub>) is used in the dry assay as a flux instead of
+litharge, from which it differs in containing a little more oxygen. When
+acted on by nitric acid a brown residue of lead dioxide is left, nitrate
+of lead going into solution. Like litharge it always carries silver;
+about 2 milligrams in 100 grams.</p>
+
+<p><b>Silver</b>, Ag.&mdash;Pure silver in foil is required as a standard. It may be
+prepared as follows:&mdash;Dissolve scrap silver in dilute nitric acid and
+decant off from any residue; dilute the solution with hot water and add
+hydrochloric acid until there is no further precipitate, stir; allow the
+precipitate to settle; decant and wash; dry the precipitate, mix it with
+twice its bulk of carbonate of soda and fuse the mixture in a crucible
+until tranquil; clean the button and roll or hammer it into foil.</p>
+
+<p><b>Sodium Acetate</b>, NaC<sub>2</sub>H<sub>3</sub>O<sub>2</sub>.3H<sub>2</sub>O.&mdash;The crystals may be
+purchased sufficiently pure. Make a 20 per cent. solution in water. It
+is used for replacing mineral acids by acetic acid.<a name="FNanchor_7_7" id="FNanchor_7_7"></a><a href="#Footnote_7_7" class="fnanchor">[7]</a></p>
+
+<p><b>Sodium Acetate and Acetic Acid.</b>&mdash;A solution is used in the
+determination of phosphates and arsenates; 100 grams of the salt is
+dissolved in 500 c.c. of acetic acid, and diluted with water to one
+litre.</p>
+
+<p><b>Sodium Bicarbonate</b> (NaHCO<sub>3</sub>)is used as a flux in dry methods. On
+ignition it leaves the carbonate (Na<sub>2</sub>CO<sub>3</sub>), which is used as a
+standard reagent. Make a 20 per cent. solution of the carbonate for use.
+It should be free from chlorides or sulphates, or if impure the amount
+of impurities must be determined.</p>
+
+<p><b>Sodium Hydrate</b>, NaHO. It may be purchased in sticks, which should be
+kept in a well-corked bottle. It is sometimes called "caustic soda." It
+is a strong alkali. It is used for neutralizing acid solutions and for
+separations where ammonia is unsuitable. Make a 5 per cent. solution for
+use.</p>
+
+<p><b>Sodium Hyposulphite</b>, Na<sub>2</sub>S<sub>2</sub>O<sub>8</sub>.5H<sub>2</sub>O.&mdash;It may be purchased
+pure. It is generally known as "hypo." It is used as a standard.</p>
+
+<p><b>Sodium Sulphite</b> (Na<sub>2</sub>SO<sub>3</sub>.7H<sub>2</sub>O) is used as a reducing agent.</p>
+
+<p><b>Sodium Phosphate</b>, Na<sub>2</sub>HPO<sub>4</sub>.12H<sub>2</sub>O. The crystals may be
+purchased pure, but they effloresce in dry air with loss of water.<span class='pagenum'><a name="Page_67" id="Page_67">[Pg 67]</a></span> It
+is used as a standard and for precipitating magnesia, &amp;c. Make a 10 per
+cent. solution.</p>
+
+<p><b>Stannous Chloride</b>, SnCl<sub>2</sub>.2H<sub>2</sub>O.&mdash;The crystals are best purchased.
+If kept dry and free from air they are fairly permanent. A solution is
+made by dissolving 20 grams in 10 c.c. of hydrochloric acid and diluting
+to 1 litre. The solution is not permanent. It is a strong reducing
+agent, and is chiefly used in solution for this purpose.</p>
+
+<p><b>Tin</b>, Sn.&mdash;Grain tin should be purchased. It is not pure, but contains
+99.5 per cent. of the metal. The chief impurity is copper. It can be
+used as a standard. When acted on with hot hydrochloric acid it slowly
+dissolves (more rapidly in contact with platinum) and forms stannous
+chloride.</p>
+
+<p><b>Uranium Acetate</b>, UO<sub>2</sub>(C<sub>2</sub>H<sub>3</sub>O<sub>2</sub>)<sub>2</sub>.H<sub>2</sub>O.&mdash;It is best
+purchased in crystals. The solution is used for the determination of
+phosphates and arsenates. A solution of 3 per cent. strength is
+occasionally used as an indicator.</p>
+
+<p><b>Uranium Nitrate</b>, UO<sub>2</sub>(NO<sub>3</sub>)<sub>2</sub>.6H<sub>2</sub>O.&mdash;This salt is very
+soluble in water and is sometimes used instead of the acetate, which is
+somewhat difficult to dissolve.</p>
+
+<p>"<b>Water</b>," H<sub>2</sub>O.&mdash;Spring or well water is sufficiently pure for most
+purposes, 100 c.c. will leave a residue of from 10 to 30 milligrams, so
+that where a salt has to be dissolved out, evaporated, and weighed it
+should be replaced by distilled water. Rain water, melted snow, &amp;c.,
+always leave less residue than spring water; but in other respects they
+are often dirtier. Distilled water is best prepared in the office, a
+glass or tin condenser being used.</p>
+
+<p><b>Zinc</b>, Zn.&mdash;It is sold in a granulated form or in sticks. It generally
+contains over 1 per cent. of lead, with a little iron and arsenic. It is
+used for separating metals from their solutions, and generally as a
+reducing agent. For the preparation of hydrogen, and in most other
+cases, scrap sheet zinc may be used.</p>
+
+<p><b>Zinc Oxide</b>, ZnO.&mdash;The commercial oxide sometimes contains carbonate.</p>
+
+<p><b>Zinc Sulphate</b>, ZnSO<sub>4</sub>.7H<sub>2</sub>O.&mdash;It is occasionally used as a
+standard, and can be purchased nearly pure.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_6_6" id="Footnote_6_6"></a><a href="#FNanchor_6_6"><span class="label">[6]</span></a> 3HCl + HNO<sub>3</sub> = Cl<sub>2</sub> + NOCl + 2H<sub>2</sub>O.</p></div>
+
+<div class="footnote"><p><a name="Footnote_7_7" id="Footnote_7_7"></a><a href="#FNanchor_7_7"><span class="label">[7]</span></a> NaC<sub>2</sub>H<sub>3</sub>O<sub>2</sub> + HCl = H<sub>4</sub>C<sub>2</sub>O<sub>2</sub> + NaCl.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_68" id="Page_68">[Pg 68]</a></span></p>
+<h2><a name="CHAPTER_VII" id="CHAPTER_VII"></a>CHAPTER VII.</h2>
+
+<h3>FORMUL&AElig;, EQUATIONS, ETC.</h3>
+
+
+<p>Formul&aelig; and equations are a kind of short hand for expressing briefly
+and in the language of the atomic theory the facts of chemical
+composition and reaction. The convenience of this method of expressing
+the facts justifies a short description of it here.</p>
+
+<p>On comparing the percentage composition of a series of compounds the
+proportions in which the elements combine appears to be regulated by no
+simple law. For example:</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>Realgar.</td><td align='left'>Orpiment.</td><td align='left'>Mispickel.</td><td align='left'>Pyrites.</td></tr>
+<tr><td align='left'>Arsenic</td><td align='left'>71.4</td><td align='left'>60.9</td><td align='left'>46.0</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Sulphur</td><td align='left'>28.6</td><td align='left'>39.1</td><td align='left'>19.6</td><td align='left'>53.3</td></tr>
+<tr><td align='left'>Iron</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>34.4</td><td align='left'>46.7</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.0</td><td align='left'>100.0</td><td align='left'>100.0</td><td align='left'>100.0</td></tr>
+</table></div>
+
+<p>But if in these examples the composition is calculated, not on 100
+parts, but on 107, 246, 163, and 120 parts respectively, evidence of a
+simple law becomes apparent.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>Realgar.</td><td align='left'>Orpiment.</td><td align='left'>Mispickel.</td><td align='left'>Pyrites.</td></tr>
+<tr><td align='left'>Arsenic</td><td align='left'>75.0</td><td align='left'>150.0</td><td align='left'>75.0</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Sulphur</td><td align='left'>32.0</td><td align='left'>96.0</td><td align='left'>32.0</td><td align='left'>64.0</td></tr>
+<tr><td align='left'>Iron</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>56.0</td><td align='left'>56.0</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>107.0</td><td align='left'>246.0</td><td align='left'>163.0</td><td align='left'>120.0</td></tr>
+</table></div>
+
+<p>It will be seen that the proportion of arsenic is 75 or twice 75, that
+of iron is 56, and that of sulphur 32 or some simple multiple of 32. The
+series of examples might be extended indefinitely, and it would still be
+found that the "combining proportions" held good. The number 75 is
+spoken of as the "combining weight," or, more frequently, as the "atomic
+weight" of arsenic. Similarly 56 is the atomic weight of iron, and 32
+the atomic weight of sulphur. The importance of this law of chemical
+combination is altogether independent of the atomic theory; but this
+theory furnishes the simplest explanation of the facts. According to it
+a chemical compound is made up of exactly similar groups of particles.
+The<span class='pagenum'><a name="Page_69" id="Page_69">[Pg 69]</a></span> particles of each elementary substance are all alike, but differ
+from those of other elements in weight. Ultimate particles are called
+<i>atoms</i>, and the groups of atoms are called <i>molecules</i>. The atomic
+weight of any particular element is the weight of its atom compared with
+the weight of an atom of hydrogen. The atom of sulphur, for instance, is
+32 times as heavy as the atom of hydrogen, and the atomic weight of
+sulphur is 32. The <i>molecular weight</i> is the sum of the atomic weights
+of the group. The molecule of pyrites contains two atoms of sulphur and
+one of iron: on referring to the table of atomic weights it will be seen
+that the atomic weights are&mdash;sulphur 32, and iron 56. The molecular
+weight, therefore, is 32 + 32 + 56&mdash;that is, 120. The meaning of this
+is, 120 parts by weight of iron pyrites contain 64 parts of sulphur and
+56 parts of iron; and this is true whether the "parts by weight" be
+grains or tons.</p>
+
+<p><i>The symbol or formula of an atom</i> is generally the initial letter or
+letters of the Latin or English name of the substance. The atom of
+hydrogen is written H, that of oxygen O, of sulphur S, of iron (ferrum)
+Fe, and so on. A list of these symbols is given in the table of atomic
+weights.</p>
+
+<p><i>The formula of a molecule</i> is obtained by placing together the symbols
+of the contained atoms. Thus, Fe represents an atom of iron, S an atom
+of sulphur, while FeS represents the molecule of sulphide of iron as
+containing one atom of each element.</p>
+
+<p>When more than one atom of an element is present this is shown by
+writing a figure under and after the symbol; thus, FeS<sub>2</sub> represents a
+molecule with one atom of iron and two atoms of sulphur, Fe<sub>2</sub>S<sub>3</sub>
+similarly shows one with two atoms of iron and three of sulphur. When a
+group of atoms is enclosed in brackets, a figure after and under the
+bracket multiplies all within it; for example, Pb(NO<sub>3</sub>)<sub>2</sub> is another
+way of writing PbN<sub>2</sub>O<sub>6</sub>. Sometimes it is convenient to represent the
+atoms of a molecule as divided into two or more groups; this may be done
+by writing the formul&aelig; of the groups, and separating each simple formula
+by a full stop. Slaked lime, for instance, has the formula CaH<sub>2</sub>O<sub>2</sub>;
+or, as already explained, we may write it Ca(HO)<sub>2</sub>; or, if for
+purposes of explanation we wished to look on it as lime (CaO) and water
+(H<sub>2</sub>O), we could write it CaO.H<sub>2</sub>O. A plus sign (+) has a different
+meaning; CaO + H<sub>2</sub>O indicates quantities of two substances, water and
+lime, which are separate from each other. The sign of equality (=) is
+generally used to separate a statement of the reagents used from another
+statement of the products of the reaction; it may be translated into the
+word "yields" or "becomes." The two statements form an equation.</p>
+
+<p>Ignoring the quantitative relation, the meaning of the equation<span class='pagenum'><a name="Page_70" id="Page_70">[Pg 70]</a></span> CaO +
+H<sub>2</sub>O = CaO.H<sub>2</sub>O is: "lime and water yield slaked lime." By referring
+to a table of atomic weights we can elicit the quantitative relations
+thus:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>CaO</td><td align='center'>+</td><td align='center'>H<sub>2</sub>O</td><td align='center'>=</td><td align='center'>CaH<sub>2</sub>O<sub>2</sub></td></tr>
+<tr><td align='center'>&#8595;</td><td align='left'></td><td align='center'>&#8595;</td><td align='left'></td><td align='center'>&#8595;</td></tr>
+<tr><td align='right'>Ca = 40</td><td align='left'></td><td align='left'>H<sub>2</sub> = 2</td><td align='center'> = 1&times;2</td><td align='right'>Ca = 40</td></tr>
+<tr><td align='right'>O = 16</td><td align='left'></td><td align='left'>O = 16</td><td align='left'></td><td align='right'>H<sub>2</sub> = 2</td><td align='center'> = 1&times;2</td></tr>
+<tr><td align='right'>&mdash;&mdash;</td><td align='left'></td><td align='right'>&mdash;&mdash;</td><td align='left'></td><td align='right'>O<sub>2</sub> = 32</td><td align='center'> = 16&times;2</td></tr>
+<tr><td align='right'>56</td><td align='left'></td><td align='right'>18</td><td align='left'></td><td align='right'>&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'></td><td align='right'>74</td></tr>
+</table></div>
+
+
+
+
+<p>Or, putting it in words, 56 parts of lime combine with 18 parts of water
+to form 74 parts of slaked lime. This equation enables one to answer
+such a question as this:&mdash;How much lime must be used to produce 1 cwt.
+of slaked lime? for, if 74 lbs. of slaked lime require 56 lbs. of lime,
+112 lbs. will require (56 &times; 112)/74, or about 84-3/4 lbs.</p>
+
+<p>As another example having a closer bearing on assaying take the
+following question:&mdash;"In order to assay 5 grams of 'black tin' (SnO<sub>2</sub>)
+by the cyanide process, how much potassic cyanide (KCN) will be
+required?" The reaction is</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>SnO<sub>2</sub></td><td align='left'>+</td><td align='left'>2KCN</td><td align='left'>= Sn + 2KCNO</td></tr>
+<tr><td align='center'>&#8595;</td><td align='left'></td><td align='center'>&#8595;</td></tr>
+<tr><td align='right'>Sn = 118</td><td align='left'></td><td align='left'>K = 39</td></tr>
+<tr><td align='right'>O<sub>2</sub> = 32</td><td align='left'></td><td align='left'>C = 12</td></tr>
+<tr><td align='right'>&mdash;&mdash;</td><td align='left'></td><td align='left'>N = 14</td></tr>
+<tr><td align='right'>150</td><td align='left'></td><td align='right'>&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='right'>65</td><td align='left'>&times;2 = 130</td></tr>
+</table></div>
+
+
+<p>What is sought for here is the relation between the quantities of
+SnO<sub>2</sub> and KCN. Note that a figure before a formula multiplies all that
+follows up to the next stop or plus or equality sign. The question is
+now resolved to this: if 150 grams of oxide of tin require 130 grams of
+cyanide, how much will 5 grams require?</p>
+
+<p>
+<span style="margin-left: 3em;">150 : 130 :: 5 : <i>x</i></span><br />
+<span style="margin-left: 11.5em;"><i>x</i> = 4.33 grams.</span><br />
+</p>
+
+<p>A problem of frequent occurrence is to find the percentage composition
+of a substance when its formula has been given. For example: "What
+percentage of iron is contained in a mineral having the formula
+2Fe<sub>2</sub>O<sub>3</sub>.3H<sub>2</sub>O?" Bringing this formula together we have
+Fe<sub>4</sub>H<sub>6</sub>O<sub>9</sub>. Find the molecular weight.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Fe<sub>4</sub></td><td align='right'>= 224</td><td align='left'>= 56&times;4</td></tr>
+<tr><td align='left'>H<sub>6</sub></td><td align='right'>= 6</td><td align='left'>= 1&times;6</td></tr>
+<tr><td align='left'>O<sub>9</sub></td><td align='right'>= 144</td><td align='left'>= 16&times;9</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>374</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_71" id="Page_71">[Pg 71]</a></span></p>
+
+<p>Then we get: 374 parts of the mineral contain 224 of iron. How much will
+100 contain?</p>
+
+<p>
+<span style="margin-left: 3em;">374 : 224 :: 100 : <i>x</i></span><br />
+<span style="margin-left: 12em;"><i>x</i> = 59.89.</span><br />
+</p>
+
+<p>And the answer to the question is 59.89 per cent.</p>
+
+<p>Again, suppose the question is of this kind:&mdash;"How much crystallised
+copper sulphate (CuSO<sub>4</sub>.5H<sub>2</sub>O) will be required to make 2 litres of
+a solution, 1 c.c. of which shall contain 0.0010 gram of copper?"</p>
+
+<p>A litre is 1000 c.c., so, therefore, 2 litres of the solution must
+contain 0.001 gram &times; 2000, or 2 grams. How much crystallised copper
+sulphate will contain this amount of metal?</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Cu</td><td align='right'>= 63.3</td></tr>
+<tr><td align='left'>S</td><td align='right'>= 32.0</td></tr>
+<tr><td align='left'>O<sub>4</sub></td><td align='right'>= 64.0</td><td align='left'>= 16&times;4</td></tr>
+<tr><td align='left'>5H<sub>2</sub>O</td><td align='right'> = 90.0</td><td align='left'>= 18&times;5</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>249.3</td></tr>
+</table></div>
+
+
+<p>If 63.3 grams of copper are contained in 249.3 grams of sulphate, in how
+much is 2 grams contained.</p>
+
+<p>
+<span style="margin-left: 3em;">63.3 : 249.3 :: 2 grams : <i>x</i></span><br />
+<span style="margin-left: 16em;"><i>x</i> = 7.8769 grams.</span><br />
+</p>
+
+<p>The answer is, 7.8769 grams must be taken.</p>
+
+<p>As a sample of another class of problem similar in nature to the last
+(but a little more complicated) take the following:&mdash;"What weight of
+permanganate of potash must be taken to make 2 litres of a solution, 100
+c.c. of which shall be equivalent to 1 gram of iron?" In the first place
+the 2 litres must be equivalent to 20 grams of iron, for there are 20 &times;
+100 c.c. in two litres. In the titration of iron by permanganate
+solution there are two reactions. First in dissolving the iron</p>
+
+<p>
+<span style="margin-left: 3em;">Fe + H<sub>2</sub>SO<sub>4</sub> = FeSO<sub>4</sub> + H<sub>2</sub></span><br />
+<span style="margin-left: 3em;">&#8595;</span><br />
+<span style="margin-left: 3em;">56</span><br />
+</p>
+
+<p>and second, in the actual titration,</p>
+
+<p>
+10FeSO<sub>4</sub> + 2KMnO<sub>4</sub> + 9H<sub>2</sub>SO<sub>4</sub>= 2MnSO<sub>4</sub> + 5Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 2KHSO<sub>4</sub> + 8H<sub>2</sub>O<br />
+<span style="margin-left: 7.5em;">&#8595;</span><br />
+<span style="margin-left: 6.5em;">K = 39</span><br />
+<span style="margin-left: 6em;">Mn = 55</span><br />
+<span style="margin-left: 6.5em;">O<sub>4</sub>= 64</span><br />
+<span style="margin-left: 9em;">&mdash;&mdash;</span><br />
+<span style="margin-left: 9em;">158 &times; 2 = 316</span><br />
+</p>
+
+<p>As before, attention is confined to the two substances under<span class='pagenum'><a name="Page_72" id="Page_72">[Pg 72]</a></span>
+consideration&mdash;viz., Fe and KMnO<sub>4</sub>. In the second equation, we find
+316 parts of the permanganate are required for 10 molecules of FeSO<sub>4</sub>;
+and in the first equation 56 parts of iron are equivalent to one
+molecule of FeSO<sub>4</sub>, therefore 560 of iron are equivalent to 316 of
+permanganate; and the question is, How much of the permanganate will be
+equivalent to 20 grams of iron?</p>
+
+<p>
+<span style="margin-left: 3em;">560 : 316 :: 20 grams : <i>x</i>.</span><br />
+<span style="margin-left: 10.5em;"><i>x</i> = 11.286 grams.</span><br />
+</p>
+
+<p>The answer is 11.286 grams.</p>
+
+<p>Very similar to this last problem is the question suggested under the
+head "Indirect Titration" (p. 43). "If 100 c.c. of the standard
+permanganate solution are equivalent to 1 gram of iron, how much
+peroxide of manganese will they be equivalent to?" The equation for
+dissolving the iron is already given; the second equation is</p>
+
+<p>
+2FeSO<sub>4</sub> + MnO<sub>2</sub> + 2H<sub>2</sub>SO<sub>4</sub> = Fe<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub> + MnSO<sub>4</sub> + 2H<sub>2</sub>O<br />
+<span style="margin-left: 7em;">&#8595;</span><br />
+<span style="margin-left: 5.5em;">Mn = 55</span><br />
+<span style="margin-left: 5.5em;">O<sub>2</sub> = 32</span><br />
+<span style="margin-left: 8.5em;">&mdash;&mdash;</span><br />
+<span style="margin-left: 8.5em;">87</span><br />
+</p>
+
+<p>It will be seen that 87 grams of peroxide of manganese are equivalent to
+112 grams of iron. How much then is equivalent to 1 gram of iron?</p>
+
+<p>
+<span style="margin-left: 3em;">112 : 87 :: 1 gram : <i>x</i></span><br />
+<span style="margin-left: 10em;"><i>x</i> = 0.7767 gram.</span><br />
+</p>
+
+<p>It is sometimes convenient to calculate the formula of a substance from
+its analysis. The method of calculating is shown by the following
+example. Required the formula of a mineral which gave the following
+figures on analysis:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Cupric oxide (CuO)</td><td align='right'>10.58</td></tr>
+<tr><td align='left'>Ferrous oxide (FeO)</td><td align='right'>15.69</td></tr>
+<tr><td align='left'>Zinc oxide (ZnO)</td><td align='right'>0.35</td></tr>
+<tr><td align='left'>Sulphuric oxide (SO<sub>2</sub>)</td><td align='right'>28.82</td></tr>
+<tr><td align='left'>Water (H<sub>2</sub>O)</td><td align='right'>44.71</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>100.15</td></tr>
+</table></div>
+
+<p>First find the molecular weights of CuO, FeO, &amp;c., and divide the
+corresponding percentages by these figures. Thus, CuO = 63.3+16 = 79.3
+and 10.58 divided by 79.3 gives 0.1334. Similarly FeO = 56+16 = 72 and
+15.69 divided by 72 gives 0.2179. Treated in the same way the oxide of
+zinc, sulphuric oxide and water give as results 0.0043, 0.3602 and
+2.484.</p>
+
+<p>Classify the results as follows:<span class='pagenum'><a name="Page_73" id="Page_73">[Pg 73]</a></span>&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bases.&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>Acids.&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>Water.&nbsp;&nbsp;&nbsp;&nbsp;</td></tr>
+<tr><td align='left'>CuO 0.1334&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>SO<sub>3</sub> 0.3602&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>H<sub>2</sub>O 2.484&nbsp;&nbsp;&nbsp;&nbsp;</td></tr>
+<tr><td align='left'>FeO 0.2179&nbsp;&nbsp;&nbsp;&nbsp;</td></tr>
+<tr><td align='left'>ZnO 0.0043</td></tr>
+<tr><td align='left'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'> RO 0.3556&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>RO<sub>3</sub> 0.3602&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>R<sub>2</sub>O 2.484</td></tr>
+</table></div>
+
+
+<p>The figures 0.3556, 0.3602 and 2.484 should be then divided by the
+lowest of them&mdash;<i>i.e.</i>, 0.3556; or where, as in this case, two of the
+figures are very near each other the mean of these may be taken&mdash;<i>i.e.</i>,
+0.3579. Whichever is taken the figures got will be approximately 1, 1
+and 7. The formula is then RO.SO<sub>3</sub>.7H<sub>2</sub>O in which R is nearly 2/5ths
+copper, 3/5ths iron and a little zinc.</p>
+
+<p>This formula requires the following percentage composition, which for
+the sake of comparison is placed side by side with the actual results.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='right'>Calculated.</td><td align='right'>Found.</td></tr>
+<tr><td align='left'>Cupric oxide</td><td align='right'>11.29</td><td align='right'>10.58</td></tr>
+<tr><td align='left'>Ferrous oxide</td><td align='right'>15.37</td><td align='right'>15.69</td></tr>
+<tr><td align='left'>Zinc oxide</td><td align='right'>nil</td><td align='right'>0.35</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='right'>28.47</td><td align='right'>28.82</td></tr>
+<tr><td align='left'>Water</td><td align='right'>44.84</td><td align='right'>44.71</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>99.97</td><td align='right'>100.15</td></tr>
+</table></div>
+
+<p>Trimming the results of an analysis to make them fit in more closely
+with the calculations from the formula would be foolish as well as
+dishonest. There can be no doubt that the actual analytical results
+represent the composition of the specimen much more closely than the
+formula does; although perhaps other specimens of the same mineral would
+yield results which would group themselves better around the calculated
+results than around those of the first specimen analysed. It must be
+remembered that substances are rarely found pure either in nature or in
+the arts; so that in most cases the formula only gives an approximation
+to the truth. In the case of hydrated salts there is generally a
+difficulty in getting the salt with exactly the right proportion of
+water.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>The following calculations may be made:&mdash;</p>
+
+<p>
+1. Calculate standards in the following cases&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Silver taken, 1.003 gram. Standard salt used, 100.15 c.c.</span><br />
+<span style="margin-left: 1em;">(<i>b</i>) Iron taken, 0.7 gram. Bichromate used, 69.6 c.c.</span><br />
+<br />
+2. Calculate percentages:&mdash;<br />
+<span style="margin-left: 1em;">(<i>a</i>) Ore taken, 1 gram. Solution used, 65.2 c.c. Standard, 0.987 gram.</span><br />
+<span class='pagenum'><a name="Page_74" id="Page_74">[Pg 74]</a></span>
+<br />
+<span style="margin-left: 1em;">(<i>b</i>) Ore taken, 1 gram. Barium sulphate got, 1.432 gram. Barium
+sulphate contains 13.73 per cent. of sulphur, and the percentage
+of sulphur in the ore is wanted.</span><br />
+<br />
+<span style="margin-left: 1em;">(<i>c</i>) Barium sulphate is BaSO<sub>4</sub>. Calculate the percentage of sulphur
+it contains, for use in the preceding question.</span><br />
+<br />
+3.  A method of estimating the quantity of peroxide in a manganese ore
+is based on the following reactions:&mdash;<br />
+<br />
+<span style="margin-left: 2em;">(1) MnO<sub>2</sub> + 4HCl = MnCl<sub>2</sub> + Cl<sub>2</sub> + 2H<sub>2</sub>O.</span><br />
+<br />
+<span style="margin-left: 2em;">(2) Cl + KI = KCl + I.</span><br />
+<br />
+To how much MnO<sub>2</sub> is 1 gram of Iodine (I) equivalent?<br />
+<br />
+4. A mineral has the following composition:&mdash;<br />
+<br />
+<span style="margin-left: 1em;">Carbonic acid (CO<sub>2</sub>)&nbsp; &nbsp;  19.09</span><br />
+<span style="margin-left: 1em;">Copper oxide (CuO)&nbsp; &nbsp; &nbsp;  71.46</span><br />
+<span style="margin-left: 1em;">Water (H<sub>2</sub>O)&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 9.02</span><br />
+<br />
+What is its formula?<br />
+<br />
+5. How much copper is contained in 1.5 gram of crystallized copper sulphate
+(CuSO<sub>4</sub>.5H<sub>2</sub>O)? How much of these crystals must be taken
+to give 0.4 gram of copper?<br />
+<br />
+6. How much ferrous sulphate crystals (FeSO<sub>4</sub>.7H<sub>2</sub>O) must be taken to
+yield 2 litres of a solution, 100 c.c. of which shall contain 0.56
+gram of iron?<br />
+<br />
+7. Galena is PbS, and h&aelig;matite Fe<sub>2</sub>O<sub>3</sub>. What percentages of metal do
+these minerals contain?<br />
+</p>
+
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_75" id="Page_75">[Pg 75]</a></span></p>
+<h2><a name="CHAPTER_VIII" id="CHAPTER_VIII"></a>CHAPTER VIII</h2>
+
+<h3>SPECIFIC GRAVITY.</h3>
+
+
+<p>The relation of the weight of a substance to its volume should be kept
+in mind in all cases where both weight and volume are dealt with.
+Students are apt to imagine that on mixing equal volumes of, say,
+sulphuric acid and water, an acid of half the strength must be obtained.
+If the statement of strength is in parts by weight this will lead to
+considerable error. For example, 100 c.c. of sulphuric acid containing
+98 per cent. by weight of real acid, will, if diluted with 100 c.c. of
+water, yield a solution containing not 49 per cent. by weight, but about
+63.5 per cent. of the acid. The reason is this: the 100 c.c. of
+sulphuric acid weighs 184 grams, and contains 180.32 grams of real acid,
+while the 100 c.c. of water weighs only 100 grams; the mixed water and
+acid weighs 284 grams, and contains 180.32 of real acid, which is
+equivalent to nearly 63.5 per cent. by weight. If, however, the method
+of statement be volumetric, it would be correct to say that doubling the
+volume halves the strength: if 100 c.c. of brine contains 10 grams of
+salt, and is diluted with water to 200 c.c., it would be of one-half the
+former strength, that is, 100 c.c. of the solution would contain 5 grams
+of salt.</p>
+
+<p>This confusion is avoided by always stating the strengths as so many
+grams or "c.c." in 100 c.c. of the liquid. But obviously it would be
+advantageous to be able to determine quickly the weight of any
+particular substance corresponding to 1 c.c. or some other given volume.
+Moreover, in descriptions of processes the strengths of acids and
+solutions are frequently defined neither by their gravimetric nor
+volumetric composition, but by a statement either of specific gravity or
+of the degrees registered by Twaddell's or Beaum&eacute;'s hydrometer. Thus, in
+the description of the process of gold parting, one writer gives: "The
+acid should be of 1.2 specific gravity"; and another says: "The acid
+must not be stronger than 32&deg; Beaum&eacute;."</p>
+
+<p>These considerations justify an account of the subject in such a work as
+this. And on other grounds the determination of a specific<span class='pagenum'><a name="Page_76" id="Page_76">[Pg 76]</a></span> gravity is
+one of the operations with which an assayer should be familiar.</p>
+
+<p>The meaning of "specific gravity" is present in the mind of every one
+who uses the sentence "lead is heavier than water." This is meaningless
+except some such phrase as "bulk for bulk" be added. Make the sentence
+quantitative by saying: "bulk for bulk lead is 11.36 times heavier than
+water," and one has the exact meaning of: "the specific gravity of lead
+is 11.36." A table of the specific gravities of liquids and solids shows
+how many times heavier the substances are than water.</p>
+
+<p>It is better, however, to look upon the specific gravity (written
+shortly, sp. g.) as the weight of a substance divided by its volume. In
+the metric system, 1 c.c. of water at 4&deg; C. weighs with sufficient
+exactness 1 gram; consequently, the sp. g., which states how many times
+heavier than water the substance is, also expresses the weight in grams
+of one c.c. of it. So that if a 100 c.c. flask of nitric acid weighs,
+after the weight of the flask has been deducted, 120 grams, 1 c.c. of
+the acid weighs 1.2 gram, and the sp. g. is 1.2. The specific gravity,
+then, may be determined by dividing the weight of a substance in grams
+by its volume in c.c.; but it is more convenient in practice to
+determine it by dividing <i>the weight of the substance by the weight of
+an equal volume of water</i>. And since the volumes of all substances,
+water included, vary with the temperature, the temperature at which the
+sp. g. is determined should be recorded. Even then there is room for
+ambiguity to the extent that such a statement as the following, "the
+specific gravity of the substance at 50&deg; C. is 0.9010," may mean when
+compared with water at 50&deg; C. or 4&deg; C., or even 15.5&deg; C. For practical
+purposes it should mean the first of these, for in the actual
+experiments the water and the substance are compared at the same
+temperature, and it is well to give the statement of results without any
+superfluous calculation. In the metric system the standard temperature
+is 4&deg; C., for it is at this point that 1 c.c. of water weighs exactly 1
+gram. In England, the standard temperature is 60&deg; F. (15.5&deg; C.), which
+is supposed to be an average temperature of the balance-room. The
+convenience of the English standard, however, is merely apparent; it
+demands warming sometimes and sometimes cooling. For most purposes it is
+more convenient to select a temperature sufficiently high to avoid the
+necessity of cooling at any time. Warming to the required temperature
+gives very little trouble.</p>
+
+<p><b>Determination of Specific Gravity.</b>&mdash;There is a quick and easy method
+of determining the density or sp. g. of a liquid, based upon the fact
+that a floating body is buoyed up more by a heavy liquid than by a light
+one. The method is more remarkable for<span class='pagenum'><a name="Page_77" id="Page_77">[Pg 77]</a></span> speed than accuracy, but still
+is sufficiently exact. The piece of apparatus used for the purpose is
+endowed with a variety of names&mdash;sp. g. spindle, hydrometer, areometer,
+salimeter, alcoholimeter, lactometer, and so on, according to the
+special liquid upon which it is intended to be used. It consists of a
+float with a sinker at one end and a graduated tube or rod at the other.
+It is made of metal or glass. Generally two are required, one for
+liquids ranging in sp. g. from 1.000 to 2.000, and another, which will
+indicate a sp. g. between 0.700 and 1.000. The range depends on the size
+of the instrument. For special work, in which variations within narrow
+limits are to be determined, more delicate instruments with a narrower
+range are made.</p>
+
+<div class="figcenter" style="width: 228px;">
+<img src="images/fig034.jpg" width="228" height="450" alt="Fig. 34." title="" />
+
+</div>
+
+<p>In using a hydrometer, the liquid to be tested is placed in a cylinder
+(fig. 34) tall enough to allow the instrument to float, and not too
+narrow. The temperature is taken, and the hydrometer is immersed in the
+fluid. The mark on the hydrometer stem, level with the surface of the
+liquid, is read off. With transparent liquids it is best to read the
+mark under and over the water surface and take the mean.</p>
+
+<p>The graduation of hydrometers is not made to any uniform system. Those
+marked in degrees Baum&eacute; or Twaddell, or according to specific gravity,
+are most commonly used. The degrees on Baum&eacute;'s hydrometer agree among
+themselves in being at equal distances along the stem; but they are
+proportional neither to the specific gravity, nor to the percentage of
+salt in the solution. They may be converted into an ordinary statement
+of specific gravity by the following formul&aelig;:&mdash;</p>
+
+<p>
+<span style="margin-left: 3em;">Sp. g. = 144.3/(144.3-degrees Baum&eacute;.)</span><br />
+</p>
+
+<p>or putting the rule in words, subtract the degrees Baum&eacute; from 144.3, and
+divide 144.3 with the number thus obtained. For example: 32&deg; Baum&eacute;
+equals a sp. g. of 1.285.</p>
+
+<p>
+<span style="margin-left: 3em;">144.3/(144.3-32) = 144.3/(112.3) = 1.285</span><br />
+</p>
+
+<p>This rule is for liquids heavier than water; for the lighter liquids the
+rule is as follows:&mdash;</p>
+
+<p>
+<span style="margin-left: 3em;">Sp. g. = 146/(136 + degrees Baum&eacute;.)</span><br />
+</p>
+
+<p>or in words divide 146 by the number of degrees Baum&eacute; added<span class='pagenum'><a name="Page_78" id="Page_78">[Pg 78]</a></span> to 136. For
+example: ammonia of 30&deg; Beaum&eacute; has a sp. g. of 0.880 (nearly).</p>
+
+<p>
+<span style="margin-left: 3em;">146/(136+30) = 146/166 = 0.8795</span><br />
+</p>
+
+<p>A simple series of calculations enables one to convert a Beaum&eacute;
+hydrometer into one showing the actual sp. g. Graduation, according to
+sp. g. is the most convenient for general purposes. In these instruments
+the distances between the divisions become less as the densities
+increase.</p>
+
+<p>Twaddell's hydrometer is graduated in this way: Each degree Twaddell is
+0.005 in excess of unity. To convert into sp. g. multiply the degrees
+Twaddell by 0.005, and add 1. For example: 25&deg; Twaddell equals a sp. g.
+of 1.125.</p>
+
+<p>
+<span style="margin-left: 3em;">25&times;.005 = 0.125; + 1.000 = 1.125.</span><br />
+</p>
+
+<p>There is a practice which ignores the decimal point and speaks of a sp.
+g. of 1125 instead of 1.125. In some cases it is convenient, and
+inasmuch as no substance has a real sp. g. of much over 20, it can lead
+to no confusion. The figures expressed in this way represent the weight
+of a litre in grams.</p>
+
+<p>Some hydrometers are graduated so as to show at a glance the percentage
+composition of the liquid they are intended to be used with. Gay-Lussac
+designed one to show the alcoholic strength of mixtures of alcohol and
+water; the construction of others upon the same principle is easy and
+perhaps useful. But when the principle is applied to complex liquids and
+mixed solutions, it is misleading.</p>
+
+<p>The various methods of graduation ought all to give place to one showing
+a simple statement of the sp. g.</p>
+
+<p>The method of determining sp. g. with the hydrometer is obviously
+inapplicable to the case of solids, and in the case of liquids it should
+not be used where exact figures are required. There are several other
+methods which may be used, but on the whole those with the specific
+gravity bottle are most convenient.</p>
+
+<div class="figcenter" style="width: 114px;">
+<img src="images/fig035.jpg" width="114" height="300" alt="Fig. 35." title="" />
+
+</div>
+
+<p><b>The specific gravity bottle</b> (fig. 35) is a light flask of about 25
+c.c. capacity, provided with a well-fitting perforated stopper. It is
+essentially a graduated flask, which measures a constant volume, but it
+does not much matter what the volume is.</p>
+
+<p><i>In taking the sp. g. of a liquid</i> (<i>or, what is the same thing, a fused
+solid</i>) there is wanted the weights (1) of the flaskful of water and (2)
+of the flaskful of the liquid. Dividing the second by the first gives
+the required sp. g. The actual weighings required are<span class='pagenum'><a name="Page_79" id="Page_79">[Pg 79]</a></span>&mdash;</p>
+
+<p>
+(1) of the dry and empty flask,<br />
+<br />
+(2) of the flask filled with water, and<br />
+<br />
+(3) of the flask filled with the liquid.<br />
+</p>
+
+<p>The weighing of the flask once made need not be often repeated. It is
+well to do so now and then for safety's sake; but one weighing will
+serve for a large number of determinations. The same remarks apply to
+the weighing of the bottle filled with water. The bottle is dried by
+rinsing out first with alcohol and afterwards with ether; ether is very
+volatile, and a short exposure in a warm place will soon drive off the
+little remaining about the sides. The ether vapour should be sucked out
+through a glass tube. See that the bore of the stopper is dry as well as
+the bottle. Let the dry bottle stand in the box of the balance for a
+minute or two before weighing. The weight is, strictly speaking, not
+that of the empty bottle, but of the bottle filled with air. The empty
+bottle would weigh from 20 to 30 milligrams less. Correcting for this
+would, in most cases, only make a difference in the fourth place of
+decimals,<a name="FNanchor_8_8" id="FNanchor_8_8"></a><a href="#Footnote_8_8" class="fnanchor">[8]</a> so that it is better to ignore the error.</p>
+
+<p>The weight of the flask filled with water is got by filling it with
+distilled water, and inserting the stopper. The excess of water will
+overflow at the margin and through the bore. The bottle is wiped with a
+soft, dry cloth, taking care not to squeeze or warm the bottle. The
+bottle will remain filled to the top of the stopper. It is allowed to
+stand in the balance box for a minute or two, and then weighed.</p>
+
+<p>Distilled water, as stated, should be used; the use of ordinary water
+may increase the weight by 5 or 6 milligrams. Many waters, if they have
+not previously been boiled, give off bubbles of air which render the
+weighing worthless.</p>
+
+<p>The temperature of the water is of greater importance; lowering the
+temperature 2&deg; will increase the weight by 10 or 12 milligrams. A beaker
+of water may be warmed or cooled to the required temperature; then the
+bottle is filled from it, and quickly weighed. If the balance-room is
+cooler than the water, the latter will draw back into the bottle, and a
+few small bubbles of air will enter; but even in extreme cases this will
+only increase the weight by a very small fraction of a milligram. There
+is more trouble caused when the room is warmer, for the liquid then
+expands and protrudes as a drop resting on the top of the stopper.<span class='pagenum'><a name="Page_80" id="Page_80">[Pg 80]</a></span>
+There will in this case be loss by evaporation, which in the case of the
+more volatile liquids, such as alcohol, is serious. To prevent this
+loss, as well as any that may arise by overflow, the stopper should be
+dilated above into a small cup, A (fig. 36), which may itself be
+stoppered. In a bottle of this kind the neck of the stopper is
+graduated, and the bottle is considered full when the liquid stands at
+the level of the mark in the neck. On inserting the stopper, the liquid
+rises into the cup, and is reduced to the level of the mark by
+absorption with pieces of filter-paper.</p>
+
+<div class="figcenter" style="width: 126px;">
+<img src="images/fig036.jpg" width="126" height="300" alt="Fig. 36." title="" />
+
+</div>
+
+<p>For most purposes, however, there is no need for cooling and allowing
+room for subsequent expansion. The assayer, as a rule, can select his
+own standard temperature, and may choose one which will always
+necessitate warming. It will be handier in this case to have a bottle
+with a thermometer stopper. Of the two types shown in fig. 37, that with
+the external thermometer tube (A) is more generally useful.</p>
+
+<div class="figcenter" style="width: 171px;">
+<img src="images/fig037.jpg" width="171" height="300" alt="Fig. 37." title="" />
+
+</div>
+
+<p>The bottle is filled at a lower temperature, and is then gently warmed
+so as to slowly raise the temperature to the required degree. The
+superfluous liquid is then at once wiped off, and the bottle cooled and
+weighed.</p>
+
+<p>The weight of the flask filled with the liquid whose sp. g. has to be
+determined is ascertained in a similar way. Of course the temperature
+must be the same. If the liquid does not mix with water, the bottle
+should be dried before filling, but otherwise the flask need only be
+rinsed out two or three times with the liquid.</p>
+
+<p>Having obtained the three weighings, deduct the weight of the bottle
+from each of the others to get the weights of the water and liquid
+respectively. Divide the latter by the former, the result shows the sp.
+g. As an example, take the following, in which a rather large sp. g.
+bottle was used:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1. Weight of bottle</td><td align='left'>39.299</td><td align='left'> gram</td></tr>
+<tr><td align='left'>2. Weight of bottle and water</td><td align='left'>81.884</td><td align='center'>"</td></tr>
+<tr><td align='left'>3. Weight of bottle and paraffin</td><td align='left'>73.146</td><td align='center'>"</td></tr>
+</table></div>
+
+<p>By subtracting 1 from 2 and 3 the result is as follows:<span class='pagenum'><a name="Page_81" id="Page_81">[Pg 81]</a></span>&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>81.884</td><td align='left'>grams</td><td align='left'>73.146</td><td align='left'>grams</td></tr>
+<tr><td align='left'>39.299</td><td align='left'>"</td><td align='left'>39.299</td><td align='left'>"</td></tr>
+<tr><td align='left'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>42.585</td><td align='left'>of water.</td><td align='left'>33.847</td><td align='left'>of paraffin.</td></tr>
+</table></div>
+
+
+<p>Divide the weight of the paraffin by that of the water&mdash;</p>
+
+<p>
+42.585)33.8470(0.7948<br />
+<span style="margin-left: 4.5em;">29.8095</span><br />
+<span style="margin-left: 4.5em;">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 4.5em;">.......</span><br />
+</p>
+
+<p>The sp. g. of the paraffin is 0.7948.</p>
+
+<p><i>The sp. g. of a fusible solid</i> may be obtained in the same way at a
+temperature some degrees above its fusing point.</p>
+
+<p><i>The sp. g. of a solid in powder or gravel sufficiently fine to pass
+through the neck of the bottle</i> is easily determined. If the bottle
+filled with water weighs 50 grams, and there is placed on the pan
+alongside of it 20 grams of a sand, the weight of the two together will
+of course be 70 grams. But if the sand is put in the bottle, it
+evidently displaces its own bulk of water; and if, on again weighing,
+the weight is found to be 62 instead of 70 grams, it is because the 20
+grams of sand has displaced 8 grams of water. Bulk for bulk, the sand is
+2-1/2 times as heavy.</p>
+
+<p>In practice, the weight of the bottle filled with water will probably be
+already known; if not, it must be determined. A certain quantity, say 20
+grams, of the powdered substance is then transferred carefully to the
+bottle. The bottle need not be dry inside, but its neck and outside must
+be. In making this transference a careful worker will make no loss, and
+the mode of working saves a little time. But it is better to weigh the
+dry flask; put into it 10 to 20 grams of the powder, and weigh again.
+The increase in weight gives accurately the weight of powder in the
+bottle. About two-thirds fill the bottle with distilled water, and mix
+with the powder by gentle shaking. Air bubbles will disentangle
+themselves, and rise to the surface of the water. Wash back anything
+adhering to the stopper with a jet of water, and fill the bottle almost
+to overflowing. Allow it to stand for a minute or so; replace the
+stopper; warm to the required temperature; take off the superfluous
+moisture; wipe and weigh. As an example, take the following:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.</td><td align='left'>Weight</td><td align='left'>of</td><td align='left'>bottle</td><td align='left'>12.681</td><td align='left'>grams</td></tr>
+<tr><td align='left'>2.</td><td align='center'>"</td><td align='center'>"</td><td align='left'>bottle filled with water</td><td align='left'>37.708</td><td align='center'>"</td></tr>
+<tr><td align='left'>3.</td><td align='center'>"</td><td align='center'>"</td><td align='left'>bottle with wolfram</td><td align='left'>40.821</td><td align='center'>"</td></tr>
+<tr><td align='left'>4.</td><td align='center'>"</td><td align='center'>"</td><td align='left'>bottle with wolfram and water</td><td align='left'>61.199</td><td align='center'>"</td></tr>
+</table></div>
+<p><span class='pagenum'><a name="Page_82" id="Page_82">[Pg 82]</a></span></p>
+
+<p>Subtract (1) from (3) to get the weight of wolfram taken:</p>
+
+<p>
+40.821 grams<br />
+12.681   &nbsp;&nbsp;&nbsp;"<br />
+&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+28.140   &nbsp;&nbsp;&nbsp;"<br />
+</p>
+
+<p>add the weight of the wolfram to the weight of the bottle filled with
+water:</p>
+
+<p>
+28.140 grams<br />
+37.708   &nbsp;&nbsp;&nbsp;"<br />
+&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+65.848   &nbsp;&nbsp;&nbsp;"<br />
+</p>
+
+<p>subtract (4) from this to get the weight of water displaced:</p>
+
+<p>
+65.848 grams<br />
+61.199&nbsp;&nbsp;&nbsp;   "<br />
+&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+<span style="margin-left: 0.5em;">4.649&nbsp;&nbsp;&nbsp;  "</span><br />
+</p>
+
+<p>Divide the weight of the wolfram by the weight of the water displaced to
+get sp. g.:</p>
+
+<p>
+4.649)28.140(6.053<br />
+<span style="margin-left: 3em;">27.894</span><br />
+<span style="margin-left: 3em;">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 3em;">......</span><br />
+</p>
+
+<p><i>If the solid is soluble in water, or has a tendency to float</i>, some
+liquid other than water is used. Paraffin oil or oil of turpentine will
+do. The process is as follows:&mdash;The weight of the dry and empty bottle
+having been determined, add a sufficiency of the substance and weigh
+again to find how much has been added. Fill up with paraffin oil and
+weigh again. Clean out the substance by rinsing with paraffin; fill up
+and weigh. Calculate the sp. g. as if water had been used, and multiply
+by the sp. g. of the paraffin.</p>
+
+<p>For example:</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.</td><td align='left'> Weight</td><td align='left'> of</td><td align='left'> bottle</td><td align='left'>39.299</td><td align='left'> grams</td></tr>
+<tr><td align='left'>2.</td><td align='left'>"</td><td align='left'>"</td><td align='left'> bottle and nitre</td><td align='left'>57.830</td><td align='left'>"</td></tr>
+<tr><td align='left'>3.</td><td align='left'>"</td><td align='left'>"</td><td align='left'>bottle and paraffin</td><td align='left'>73.146</td><td align='left'>"</td></tr>
+<tr><td align='left'>4.</td><td align='left'>"</td><td align='left'>"</td><td align='left'> bottle and paraffin and nitre</td><td align='left'>84.665</td><td align='left'>"</td></tr>
+<tr><td align='left'>5.</td><td align='left'>"</td><td align='left'>"</td><td align='left'> bottle and water</td><td align='left'>81.884</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>First from (1),(3), and (5), calculate the sp. g. of the paraffin as
+already shown. It will be 0.7948. Deduct (1) from (2) to get the weight
+of the nitre:</p>
+
+<p>
+57.830 grams<br />
+39.299 &nbsp;&nbsp;&nbsp;  "<br />
+&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+18.531 &nbsp;&nbsp;&nbsp;  "<br />
+<span class='pagenum'><a name="Page_83" id="Page_83">[Pg 83]</a></span></p>
+
+<p>add this to (3):</p>
+
+<p>
+<span style="margin-left: 8.5em;">18.531 grams</span><br />
+<span style="margin-left: 8.5em;">73.146&nbsp;&nbsp;&nbsp;&nbsp;  "</span><br />
+<span style="margin-left: 8.5em;">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 8.5em;">91.677&nbsp;&nbsp;&nbsp;&nbsp;  "</span><br />
+</p>
+
+<p>and deduct (4) to find the weight of the equal bulk of paraffin.</p>
+
+<p>
+<span style="margin-left: 8.5em;">91.677 grams</span><br />
+<span style="margin-left: 8.5em;">84.665&nbsp;&nbsp;&nbsp;  "</span><br />
+<span style="margin-left: 8.5em;">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 9em;">7.012&nbsp;&nbsp;&nbsp;  "</span><br />
+</p>
+
+<p>divide the weight of the nitre by the weight of the paraffin:</p>
+
+<p>
+<span style="margin-left: 5.5em;">7.012)18.531(2.6427</span><br />
+<span style="margin-left: 8.5em;">&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 8.5em;">......</span><br />
+</p>
+
+<p>The sp. g., taking paraffin as the standard instead of water, is 2.6427.
+Multiply this by the sp. g. of paraffin, 0.7948, and the result is
+2.1004 as the sp. g. of nitre compared with water.</p>
+
+<p>Similarly, a sp. g. compared with water at say 50&deg; C. can be converted
+into one compared with water at standard temperature, by multiplying by
+the sp. g. of water at 50&deg; C. The following table gives the sp. g. of
+water at various temperatures:&mdash;</p>
+
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Degrees Centigrade.</td><td align='left'>Sp. G.</td><td align='left'>Degrees Centigrade.</td><td align='left'>Sp. G.</td><td align='left'>Degrees Centigrade.</td><td align='left'>Sp. G.</td></tr>
+<tr><td align='center'>4&deg;</td><td align='left'>1.0000</td><td align='center'>20&deg;</td><td align='left'>0.9982</td><td align='center'>40&deg;</td><td align='left'>0.9923</td></tr>
+<tr><td align='center'>10&deg;</td><td align='left'>0.9997</td><td align='center'>25&deg;</td><td align='left'>0.9971</td><td align='center'>50&deg;</td><td align='left'>0.9881</td></tr>
+<tr><td align='center'>15&deg;</td><td align='left'>0.9991</td><td align='center'>30&deg;</td><td align='left'>0.9957</td><td align='center'>100&deg;</td><td align='left'>0.9586</td></tr>
+</table></div>
+
+
+<p>If, for example, a substance at 50&deg; C. has a sp. g. of 0.9010 as
+compared with water at 50&deg; C., it will have (compared with water at 4&deg;
+C.) a sp. g. of 0.9010 &times; 0.9881; or 0.8903. The figures 0.8903 represent
+the sp. g. of the substance at 50&deg; C. compared with water at 4&deg; C.
+Except in comparing the sp. gravities of the same substance at different
+temperatures, a calculation of this kind serves no useful purpose.</p>
+
+<p><i>In taking the specific gravity of a solid not in powder</i>, a lump of it
+is freed from loose particles and its exact weight determined. By means
+of a horse hair with a slip knot it is suspended to the balance, and
+beneath it is placed, out of contact with the balance pan, a beaker of
+distilled water. The horse hair must be long enough to keep the mineral
+well beneath the surface of the water so as to allow the balance to
+vibrate. Air bubbles are removed by touching with a camel-hair pencil.
+Whilst the mineral is suspended in water the weight is again taken. It
+will weigh less than before, and the difference between the two
+weighings gives<span class='pagenum'><a name="Page_84" id="Page_84">[Pg 84]</a></span> the weight of water (and consequently the volume)
+displaced by the mineral. The weight in air divided by the difference is
+the specific gravity. Thus</p>
+
+<p>
+Weight in air     3.2170 grams<br />
+Weight in water   2.7050 &nbsp;&nbsp;  "<br />
+<span style="margin-left: 9em;">&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 2em;">Difference&nbsp; &nbsp; 0.5120 gram</span><br />
+<br />
+3.2170/0.5120 equals 6.28, the sp. g.<br />
+</p>
+
+<p>The sp. g. of a substance depends mainly on its composition, but is
+affected by certain conditions. The effect of temperature has been
+already considered. Air holes and empty spaces lessen the specific
+gravity of otherwise solid bodies; and metals, which after fusion become
+imperfect solids, have their density increased by hammering or rolling.
+But metals when free from pores have their density diminished when
+rolled, without annealing. The effects of these conditions are slight
+when compared with those due to the presence of impurities.</p>
+
+<p>For simple substances, or mixtures of only two substances, a
+determination of sp. g. is a sufficient check on the composition for
+many practical purposes; and with more complex mixtures, such as slags
+and some of the products of dressing operations in which the material
+does not differ much in its nature from time to time, such a
+determination will yield information of considerable value, and afford a
+check upon the proper working of a process.</p>
+
+<p>When the mixing of two substances is accompanied by a change in volume,
+the sp. g. of the mixture can only be learnt by experiment. But when the
+substances have no such action on each other the resulting sp. g. can be
+calculated. Some of these calculations have a practical interest as well
+as an educational value. Students should practise them so as to become
+familiar with the relations between weight and volume.</p>
+
+<p><i>When substances are mixed by volume</i>, the sp. g. of the mixture is the
+mean of those of its constituents, and may be calculated in the usual
+way for obtaining averages. 1 c.c. of a substance having a sp. g. of 1.4
+mixed with 1 c.c. of another having a sp. g. of 1.0 will yield 2 c.c. of
+a substance having a sp. g. of 1.2. If, however, we write gram instead
+of c.c. in the above statement, the resulting sp. g. will be 1.16. The
+simplest plan is to remember that the sp. g. is the weight divided by
+the volume (sp. g. = w/v) and the sp. g. of a mixture is the sum of the
+weights divided by the sum of the volumes (sp. g. = (w + w' + w",
+&amp;c.)/(v + v' + v", &amp;c.)). In the above example the sum of the volumes is
+2 c.c.; the weights (got by multiplying each volume by its<span class='pagenum'><a name="Page_85" id="Page_85">[Pg 85]</a></span>
+corresponding sp. g.) are 1.4 gram and 1 gram. The sum of the weights
+divided by the sum of the volumes is 2.4/2 or 1.2.</p>
+
+<p>The sp. g. of a mixture of 10 c.c. of a substance having a sp. g. of
+1.2, with 15 c.c. of another having a sp. g. of 1.5 may be thus found:&mdash;</p>
+
+<p>
+sp. g. = (12+22.5)/(10+15) = 1.38<br />
+</p>
+
+<p>multiply each volume by its sp. g. to get its weight:</p>
+
+<p>
+10&times;1.2 = 12   15&times;1.5 = 22.5<br />
+</p>
+
+<p>add these together (12+22.5 = 34.5) and divide by the sum of the volumes
+(10+15 = 25):</p>
+
+<p>
+<span style="margin-left: 0.5em;">25)34.5(1.38</span><br />
+<span style="margin-left: 2em;">25</span><br />
+<span style="margin-left: 2em;">&mdash;</span><br />
+<span style="margin-left: 2em;">95, &amp;c.</span><br />
+</p>
+
+<p>The sp. g. will be 1.38, provided the mixture is not accompanied by any
+change of volume.</p>
+
+<p>The same formula will serve when the proportion of the ingredients is
+given by weight. A mixture of 4 parts by weight of galena (sp. g. 7.5)
+with 5 parts of blende (sp. g. 4) will have a sp. g. of 5.06:</p>
+
+<p>
+sp. g. = (4+5)/(0.53+1.25) = 9/1.78 = 5.06<br />
+</p>
+
+<p>It is necessary in this case to calculate the volumes of the galena and
+of the blende, which is done by dividing the weights by the sp.
+gravities: thus, 4 divided by 7.5 gives 0.53 and 5 divided by 4 gives
+1.25.</p>
+
+<p>The converse problem is a little more difficult. Given the sp. g. of a
+mixture and of each of the two ingredients, the percentage by weight of
+the heavier ingredient may be ascertained by the following rule, which
+is best expressed as a formula. There are three sp. gravities given; if
+the highest be written H, the lowest L and that of the mixture M, then:</p>
+
+<p>
+Percentage of heavier mineral = (100&times;H&times;(M-L))/(M&times;(H-L))<br />
+</p>
+
+<p>Suppose a sample of tailings has a sp. g. of 3.0, and is made up of
+quartz (sp. g. 2.6) and pyrites (sp. g. 5.1): then the percentage of
+pyrites is 27:</p>
+
+<p>
+(100&times;5.1&times;(3-2.6))/(3&times;(5.1-2.6)) = (510&times;0.4)/(3&times;2.5) = 204/7.5 = 27.2<br />
+</p>
+
+<p>The same problem could be solved with the help of a little algebra by
+the rule already given, as thus: the sp. g. of a mixture<span class='pagenum'><a name="Page_86" id="Page_86">[Pg 86]</a></span> equals the sum
+of the <i>weights</i> of the constituents divided by the sum of the
+<i>volumes</i>. Then 100 grams of the tailings with <i>x</i> per cent. of pyrites
+contain 100-<i>x</i> per cent. of quartz. The sum of the weights is 100. The
+volume of the pyrites is <i>x</i>/5.1 and of the quartz (100-<i>x</i>)/2.6.</p>
+
+<p>Then we have by the rule</p>
+
+<p>
+3 = 100/((<i>x</i>/5.1)+(100-<i>x</i>)/2.6)<br />
+3 = 1326/(510-2.5<i>x</i>)<br />
+204 = 7.5<i>x</i><br />
+<span style="margin-left: 1em;">and <i>x</i> = 27.2</span><br />
+</p>
+
+<p>If the percentage (P) and sp. g. (H) of one constituent and the sp. g.
+(M) of the mixture are known, the sp. g. of the other constituent may be
+calculated by the following formula, in which <i>x</i> is the required sp.
+g.:</p>
+
+<p>
+<i>x</i> = ((100-P)&times;M&times;H)/((100&times;H)-(P&times;M))<br />
+</p>
+
+<p>For example, "tailings" (sp. g. 3.0) containing 27.2 per cent. of
+pyrites (sp. g. 5.1) will contain (100-27.2), 72.8 per cent. of earthy
+matter having a mean sp. g. of <i>x</i>:</p>
+
+<p>
+<i>x</i> = ((100-27.2)&times;3&times;5.1)/((100&times;5.1)-(27.2&times;3))<br />
+&nbsp;&nbsp;&nbsp;&nbsp;= 1113.84/428.4 = 2.6<br />
+</p>
+
+<p>The differences in sp. g. corresponding to differences in strength have
+been carefully determined and tabulated in the case of the stronger
+acids and of many other liquids. Such tables are given at the end of
+this book.</p>
+
+<p><i>To Calculate the Weight of a Measured Volume of Mineral or
+Rock.</i>&mdash;Multiply the cubic feet by 62.4 and then multiply by the sp. g.
+of the stuff, the answer gives the weight in pounds. For example, 100
+cubic feet of quartz weighs 100&times;62.4&times;2.6 = 16,224 lbs. The weight of any
+mass of mineral of known extent and sp. g. is ascertained in this way.</p>
+
+<p>The following table gives the specific gravities of some of the commoner
+minerals.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Barytes</td><td align='left'>4.5</td></tr>
+<tr><td align='left'>Blende</td><td align='left'>4.0</td></tr>
+<tr><td align='left'>Calcite</td><td align='left'>2.6</td></tr>
+<tr><td align='left'>Cassiterite</td><td align='left'>6.9</td></tr>
+<tr><td align='left'>Chalybite</td><td align='left'>3.8</td></tr>
+<tr><td align='left'>Copper pyrites</td><td align='left'>4.2</td></tr>
+<tr><td align='left'>Fluor</td><td align='left'>3.1</td></tr>
+<tr><td align='left'>Galena</td><td align='left'>7.5</td></tr>
+<tr><td align='left'>H&aelig;matite</td><td align='left'>5.0</td></tr>
+<tr><td align='left'>Mispickel</td><td align='left'>6.2</td></tr>
+<tr><td align='left'>Pyrites</td><td align='left'>5.0</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>2.6</td></tr>
+</table></div>
+
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_8_8" id="Footnote_8_8"></a><a href="#FNanchor_8_8"><span class="label">[8]</span></a> The difference of 20 or 30 milligrams is disregarded here
+because it detracts equally from the actual weight of the water and
+liquid to be determined. If the liquid is a heavy one the difference
+shows itself in the third or second place of decimals. The correction
+may be made by deducting from the weight of the flask 0.0012 grams for
+each gram of water it holds.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_87" id="Page_87">[Pg 87]</a></span></p>
+<h2><a name="PART_II_THE_METALS" id="PART_II_THE_METALS"></a>PART II.&mdash;THE METALS.</h2>
+
+
+
+<hr style="width: 65%;" />
+<h2><a name="CHAPTER_IX" id="CHAPTER_IX"></a>CHAPTER IX.</h2>
+
+<h3>SILVER, GOLD, CYANIDES, PLATINUM, MERCURY.</h3>
+
+
+<h4>SILVER.</h4>
+
+<p>Silver is widely diffused, and has been found in most mining districts.
+It occurs native in sufficient quantity to constitute one of the chief
+ores of the metal. It also occurs combined with sulphur (as in
+argentite), with sulphur and antimony (as in stephanite or brittle
+silver ore, and in pyrargyrite or ruby silver), and with copper,
+sulphur, antimony, and arsenic, as in polybasite. Chloride of silver
+occurs native as horn silver or kerargyrite. Silver is found in the ores
+of other metals, such as fahlerz, which sometimes contains from two to
+ten per cent. of the metal, and galena, which is an important source of
+it; in fact, galena is never found entirely free from silver. It is
+present also in greater or less quantity in the ores of copper and zinc.</p>
+
+<p>Silver dissolves readily in nitric acid, forming silver nitrate. It only
+forms one family of salts, and of these the chloride and nitrate are of
+chief importance to the assayer. The formation of the chloride of silver
+on the addition of hydrochloric acid or a soluble chloride to the nitric
+acid solution, serves for the recognition and separation of silver. The
+precipitated chloride is white (becoming violet on exposure to light),
+insoluble in nitric acid, soluble in ammonia, hyposulphite of soda, or
+concentrated solutions of chlorides. The best confirmatory test is made
+by wrapping the precipitate in a little sheet lead, and cupelling, when
+the silver will be left in the metallic state, and is easily recognized.</p>
+
+<p><b>Dry Assay.</b>&mdash;This assay is made up of two parts: (1) the concentration
+of the silver in a button of lead; and (2) the cupellation of the
+resulting alloy. The concentration of the<span class='pagenum'><a name="Page_88" id="Page_88">[Pg 88]</a></span> button of lead may be
+effected either by scorification or by fusion in a crucible.</p>
+
+<p>The scorification assay is performed in a scorifier, which is a shallow
+open-mouthed dish about 2-1/2 inches across, with a very thick bottom to
+enable it to withstand the corrosive action of the slag. A charge of
+more than 3 or 5 grams of the ore cannot be worked in one, and with such
+small charges the unavoidable variations have a serious effect on the
+figures reported. A difference of one milligram on the weight of the
+button of silver got represents a difference of 6 or 10 ounces per ton.
+With rich ores such variation is unavoidable under any conditions, and
+the only safe plan is to take the mean of several assays. But with
+poorer ores the accuracy of the assay, as well as convenience in
+working, is much increased by working in a crucible with larger charges.</p>
+
+<p>In scorification the proportion of lead required for scorifying 1 gram
+of ore is in average cases from 10 to 15 grams, sinking in the case of
+galena to 2 grams, and rising with earthy and refractory substances to
+from 30 to 40 grams. But by fusing in a crucible with well-selected
+fluxes, a proportion of 4 of flux to 1 of ore is generally sufficient;
+and not only is the proportion of added matter less, but it is also
+easier to manipulate large quantities in crucibles, so that, although in
+some cases the crucible assay is more troublesome and less satisfactory,
+yet with poor and earthy ores it is the best method of dealing with
+them; while when properly worked it yields results as accurate as
+scorification does. As a general rule, if more than 5 grams of ore must
+be taken, the crucible assay should be adopted.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig038.jpg" width="300" height="186" alt="Fig. 38." title="" />
+
+</div>
+
+<p><b>Scorification Assay.</b>&mdash;The charge of ore is usually 3 grams, sometimes
+5; the lead varies from 30 to 70 grams, and the quantity of soda, borax,
+or powdered glass added varies from 0.3 to 3 or 4 grams. It is generally
+recommended to have the lead granulated,<a name="FNanchor_9_9" id="FNanchor_9_9"></a><a href="#Footnote_9_9" class="fnanchor">[9]</a> and to mix the ore with
+about half of it in the scorifier; then to put on the rest of the lead;
+and finally to sprinkle the borax or glass on the top. It answers just
+as well, however, to use the lead in the shape of foil, and wrap the ore
+up in it; and if the ore contains much sulphur, the borax may with
+advantage be added (wrapped in a little tissue paper) some five or ten
+minutes after the operation has started.<span class='pagenum'><a name="Page_89" id="Page_89">[Pg 89]</a></span></p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig039.jpg" width="450" height="96" alt="Fig. 39." title="" />
+
+</div>
+
+<p>The process of scorification is as follows:&mdash;A scorifier (fig. 38) of
+convenient size having been selected (one 2-1/2 inches across is most
+generally useful), it is dried at a gentle heat for about ten minutes.
+The charge is then put into it, and it is introduced, with the help of a
+scorifier tongs (fig. 39), into a muffle heated considerably above
+redness. The muffle is then closed, and when the metal has melted down,
+it is opened, but the temperature is kept up. A ring of slag will, after
+a time, form around the metal, and when this appearance (known as the
+eye) presents itself, the temperature may be lowered. When the eye has
+disappeared&mdash;that is, when the layer of slag has quite closed in&mdash;a
+pinch of powdered culm wrapped in tissue paper is added. As soon as the
+slag has again become tranquil, the scorifier is taken out, and its
+contents are poured into a mould (fig. 40), the slag is detached, and
+saved. If the button of metal weighs more than 30 grams, its size is
+reduced by another scorification in the same scorifier, which should
+have been replaced in the muffle immediately after the contents had been
+poured out. If the ore is not a very rich one, the button of lead will
+carry practically all the silver; but with rich ores it is more
+satisfactory to save the slag, and subsequently to melt it down with the
+cupel on which the lead has been treated, so as to recover the silver
+lost in the slag, together with that absorbed in the cupel, at one
+operation. Or, if the cupellation loss is neglected or calculated in
+some other manner, the slag or slags from the scorifier may be powdered
+and mixed with 20 grams of oxide of lead, 5 grams of borax, and 1 gram
+of charcoal. This should be melted down in a small crucible, and the
+resulting button of lead cupelled.</p>
+
+<div class="figcenter" style="width: 485px;">
+<img src="images/fig040.jpg" width="485" height="286" alt="Fig. 40." title="" />
+
+</div>
+
+<p>If the scorification has been unsatisfactory, the quantity of silver
+obtained from the slag will be by no means inconsiderable. The usual
+explanation is that with sulphury ores compounds of metallic oxides and
+sulphides (oxysulphides) are formed, which remain in the slag, retaining
+considerable quantities of the precious metal. It is said that under
+certain conditions such a slag may contain as much as 10 per cent. of
+silver. An excess of lead and a high temperature prevents the formation
+of these oxysulphides. But if much silver is present in the ore, the
+slag cannot be safely<span class='pagenum'><a name="Page_90" id="Page_90">[Pg 90]</a></span> thrown away, even if sulphur is absent, and the
+process has been satisfactorily performed.</p>
+
+<p>If the crust which appears on the surface of the lead does not clear,
+add a small lump of borax and 20 grams more lead; then close the muffle,
+and keep the temperature as high as possible. If the slag forms
+properly, but shows unfused or only half-fused lumps, even when the
+scorification has proceeded for some time, add more borax, and stir with
+an iron rod. The slag adhering to the rod must be detached by hammering,
+and replaced in the scorifier.</p>
+
+<p>If the ore consists largely of quartz, soda should be added instead of
+borax; or, if it contains much copper, powdered quartz may be used. If
+the scorifier at the end of an operation is more than usually corroded,
+the borax should be replaced in subsequent assays on similar ores by
+powdered glass or quartz.</p>
+
+<p>If a fairly fluid slag is formed which does not clear from the metal and
+show the eye, more lead and a higher temperature is wanted.</p>
+
+<p>As a general rule, it may be stated that when a scorification is
+unsatisfactory, what is wanted is more heat, more lead, or more borax.</p>
+
+<p>It is a safe plan when work has to be done on a strange ore, to make
+three or four assays with varying quantities of lead. The proportion of
+lead is right when a further addition does not yield a higher result.
+The proper proportion having been found, a note of it should be made for
+future use.</p>
+
+
+<h4>POT ASSAYS.</h4>
+
+<p>The object of the fusion in a crucible, like that of scorification, is
+to concentrate the silver in a button of lead which is to be
+subsequently cupelled; and to retain the earthy and waste matters in the
+slag. It is necessary to consider the quality of the slag and the weight
+and quality of the lead. The slag when fused should be liquid and
+homogeneous, and not too corrosive on the crucible. The button of lead
+should be soft, malleable, and free from a coating of regulus.<a name="FNanchor_10_10" id="FNanchor_10_10"></a><a href="#Footnote_10_10" class="fnanchor">[10]</a> In
+weight it should not differ much from the ore taken. With 20 grams of
+ore, for example, a button of lead weighing from 18 to 25 grams will be
+satisfactory: less than this would leave an undue proportion of silver
+in the slag; and more would be unnecessarily large for cupelling, and
+would increase the loss in that operation.</p>
+
+<p>With average ores, take 20 grams of the powdered ore and mix with 30
+grams of "soda," 40 grams of red-lead or litharge, 5 grams of borax, and
+from 2 to 2.5 grams of flour, and place in an E crucible<span class='pagenum'><a name="Page_91" id="Page_91">[Pg 91]</a></span> (Battersea
+round). Put these in the furnace at a red heat, cover the crucible, and
+gradually raise the temperature until the whole charge has melted down
+and is in a state of tranquil fusion. Pour into a mould, and replace the
+crucible in the furnace. As soon as the lead is solid, detach the slag
+and put it back into the crucible; and when it is again fluid, charge on
+to it with a copper scoop a mixture of 20 grams of oxide of lead, and 1
+gram of charcoal: when fusion has again become tranquil, pour and detach
+the button of lead. The lead buttons should be hammered into discs with
+rounded edges, and be freed from slag; if too big for a cupel they may
+be scorified together in a small scorifier, but it is better to cupel
+them separately.</p>
+
+<p><b>Ores containing Metallic Oxides.</b>&mdash;Peroxides of iron, manganese, and
+copper interfere by counteracting the effect of the charcoal or flour,
+and thus reducing the size of the lead button. Peroxide of iron will
+reduce the weight of lead by a little more than its own weight; and
+peroxide of manganese has about twice this effect. When these oxides are
+present an additional quantity of flour must be used, and precautions
+must be taken to prevent reoxidation of the slag by the furnace gases.
+This may best be prevented by using a layer of common salt as a cover to
+the charge. When the ores contain a good deal of quartz or stony matter,
+the fluxes just given (for average ores) will do; but the proportion of
+soda should be diminished, and that of the borax, oxide of lead, and
+flour increased as the quantity of metallic oxides become greater. If
+the ore contains practically no quartz, the soda may be altogether
+omitted, and some glass or powdered quartz added. The following charge
+may be taken as an example: weigh up 20 grams of the powdered ore, 15
+grams each of "soda" and borax, 60 grams of oxide of lead, and 5 grams
+of flour. Mix and place them in an E crucible, and cover with a layer of
+from a quarter to half an inch of common salt. Place in the furnace as
+before. The salt will give off a considerable amount of fume, which
+will, to a certain extent, conceal the state of the charge: when the
+crucible has been in the furnace for about 25 minutes remove it and pour
+out the contents immediately. With ores that produce a thick slag the
+addition of 5 grams of fluor spar will be an advantage. It may happen
+that with an unknown ore the first assay will be more or less
+unsatisfactory: but from it the necessity for adding more or less flour
+will be learnt, and a second assay, with the necessary modification of
+the charge, should give a good result.</p>
+
+<p><b>Ores containing much Sulphides.</b>&mdash;Ores of this class may be easily
+recognized, either by the appearance of the minerals they contain or by
+the odour of sulphurous oxide (SO<sub>2</sub>) which they evolve when roasted on
+a spatula. The sulphides most commonly<span class='pagenum'><a name="Page_92" id="Page_92">[Pg 92]</a></span> present, in addition to the
+sulphurized minerals of silver, are pyrites, galena, blende, and
+mispickel. When they are present in only a moderate amount, their effect
+is simply to increase the weight of the button of lead; and this is
+easily counteracted by reducing the amount of flour, or by omitting it.
+When in larger amounts, they not only yield large buttons, but also
+render the metal sulphury, sometimes even giving a button of regulus
+instead of lead. This last evil may be remedied (1) by putting in a rod
+of iron as soon as the charge has fused, or (2) it may be counteracted
+by a proper addition of nitre, or (3) when the sulphides present are
+only those of iron or copper the sulphur may be removed by calcining,
+and the ore converted into one of the class containing metallic oxides.
+The calcination is effected as follows:&mdash;Weigh up 20 grams of the
+powdered ore and place it in a wide-mouthed crucible sufficiently large
+to perform the subsequent melting down in. The roasting must be done at
+a gentle heat at first, so as to avoid clotting: the mouth of the
+crucible should project considerably above the coke, and should slope
+forward towards the worker. The charge must be occasionally stirred with
+the stirrer (fig. 10) so as to expose fresh surfaces to the action of
+the air, and to prevent adhesion to the sides of the crucible. The
+stirrer should not be removed till the calcination is finished. The
+temperature should be raised at the end to a good red heat; and (to
+ensure the decomposition of any sulphate that may be formed) the roasted
+ore should be rubbed up in a mortar with a pinch of anthracite, and
+again calcined. It is then mixed with fluxes as described, and fused in
+the same crucible.</p>
+
+<p>The calcination of an ore is a work occupying a good deal of time, and,
+in most cases, it is better to take advantage of the desulphurizing
+power of red lead or nitre. Red lead by itself will do, but a large
+quantity of it will be required; 1 part of a metallic sulphide needs
+from 20 to 50 parts of red lead to yield a button free from sulphur;
+whereas at most from 2 to 2-1/2 parts of nitre are sufficient. There is
+sometimes an advantage in having a considerable excess of oxide of lead
+in the slag, but where there is no such reason, 2 parts of red lead to 1
+of ore is enough. A charge which will do for most sulphides is the
+following: 20 grams of ore, 40 to 100 grams of red lead, 20 grams of
+"soda," 5 of borax, and sufficient nitre (or perhaps flour) to give a
+button of about 25 grams of lead. How much this must be (if not already
+known) may be approximately determined by fusing 3 grams of the ore and
+3 grams of "soda" in a small crucible (C) with 50 grams of litharge (not
+red lead) under a cover of salt, and weighing the resulting button of
+lead. Subtract 3 from the weight of lead obtained, and the difference
+multiplied by 1.3 will give the quantity in<span class='pagenum'><a name="Page_93" id="Page_93">[Pg 93]</a></span> grams of nitre required. If
+the button of lead weighs less than 3 grams flour must be added. If this
+is not satisfactory repeat the assay, adding an extra gram of nitre for
+each 4 grams of lead in excess of that required, or 1 gram of flour for
+a 12-gram deficiency.</p>
+
+<p>In the method in which iron is used as a de-sulphurising agent, only as
+much oxide of lead should be added as will give a button of lead of the
+required size. Rather a large button of lead should be got, and the slag
+should be strongly alkaline; if the ore does not already carry a large
+amount of sulphur some should be added. The fusion should be performed
+at a low temperature (similar to that for a galena assay), and should be
+continued for some time after it has become tranquil. Take 20 grams of
+the ore, 40 grams of "soda," 40 grams of oxide of lead, and 5 or 10
+grams of borax; place this mixture in a crucible (with a rod of iron, as
+in the galena assay), cover, and fuse for about half an hour. Take out
+the rod, washing it in the slag, and, in a minute or two, pour. Clean
+and cupel the button of lead.</p>
+
+<p><b>General Remarks on the Fusion.</b>&mdash;Other things being equal, the smaller
+the quantity of the slag the better, provided there is sufficient to
+cover the metal. The presence of peroxides of the heavy metals is
+prejudicial, since they tend to increase the quantity of silver retained
+in the slag. It may be given as a general rule that when iron, copper,
+manganese, &amp;c., are present, there is a more than ordinary need for
+cleaning the slags, and care must be taken to keep these metals in the
+state of lower oxide.</p>
+
+<p>In selecting the fluxes, it should be remembered that soda is the best
+for quartz, and borax for lime and metallic oxides. And that with ores
+almost free from gangue some quartz or glass should be added to protect
+the crucible. Two parts of soda are enough to flux 1 part of quartz;
+whilst of borax, or oxide of lead, 4 parts are barely sufficient. Oxide
+of lead has the advantage of being heavy and so does not occupy much
+space in the crucible; on the other hand, if the melting down be
+performed too quickly, or if oxide of lead only is used, this high
+specific gravity is a disadvantage, for the lighter earthy matter floats
+as a pasty mass on the more fluid oxide of lead, and thus escapes its
+action.</p>
+
+<p>When metallic sulphides are present in the ore, an excess of oxide of
+lead helps to keep the sulphur out of the button of metal. In addition
+to the oxide of lead required as a flux, some will be required to
+provide the lead in which the silver is to be collected. Oxide of lead,
+mixed with charcoal or flour, yields, when heated, a multitude of minute
+buttons of metal uniformly distributed through the mass of the charge;
+as the charge melts down these run together and fall to the bottom; this
+shower of lead collects<span class='pagenum'><a name="Page_94" id="Page_94">[Pg 94]</a></span> the silver more easily than a single button at
+the bottom of the crucible could do. Only that portion of the oxide of
+lead which remains in the slag can be considered as a flux; very often
+the first indication of an excessive reduction of lead is the pastiness
+of the slag rendered thick by the withdrawal of the oxide of lead which
+would have kept it fluid. If, in an assay, it is found that 5 parts of
+flux are not sufficient for 1 part of ore, the remedy lies in using a
+different flux rather than in taking a larger quantity.</p>
+
+<p><i>On the Reducing Effect of Charcoal, Flour, and Tartar.</i>&mdash;The weight to
+be got from a given charge will depend (provided sufficient oxide of
+lead is present) upon the proportion of the reducing agents in it. We
+have thought it well to illustrate this part of the subject by a series
+of experiments which the learner will do well to practise for himself
+before proceeding to the assay of actual ores. Take 80 grams of litharge
+and 20 grams of a mixture of borax and soda. Fuse three lots (1) with
+1.5 gram of charcoal, (2) with 3 grams of flour, and (3) with 7.5 grams
+of tartar. Weigh the buttons of lead obtained, and divide each by the
+weight of reducing agent used. The results will differ somewhat with the
+dryness and quality of the flour, etc., used; in one series of
+experiments they were as follows:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Gram.</td><td align='left'></td><td align='left'></td><td align='left'>Grams.</td><td align='left'></td><td align='left'></td><td align='left'>Gram.</td><td align='left'></td><td align='left'></td><td align='left'>Grams.</td></tr>
+<tr><td align='left'>1.5</td><td align='left'>charcoal</td><td align='left'>gave</td><td align='left'>34.0</td><td align='left'>lead</td><td align='left'>&#8756;</td><td align='center'> 1</td><td align='left'>charcoal</td><td align='left'>=</td><td align='left'>22.6</td><td align='left'>lead.</td></tr>
+<tr><td align='left'>3.0</td><td align='left'>flour</td><td align='center'>"</td><td align='left'>33.5</td><td align='center'>"</td><td align='left'>&#8756;</td><td align='center'>1</td><td align='left'>flour</td><td align='left'>=</td><td align='left'>11.2</td><td align='center'>"</td></tr>
+<tr><td align='left'>7.5</td><td align='left'>tartar</td><td align='center'>"</td><td align='left'>38.0</td><td align='center'>"</td><td align='left'>&#8756;</td><td align='center'>1</td><td align='left'>tartar</td><td align='left'>=</td><td align='left'>5.0</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>The use of flour as a reducing agent has many advantages, and it is well
+to remember that <i>1 gram of flour reduces about 11 grams of lead</i>; and
+that charcoal has twice, and tartar one-half, this reducing effect.</p>
+
+<p><i>On the Reducing Effect of Charcoal, &amp;c., on Red Lead.</i>&mdash;It is often
+easier to obtain red lead of good quality than it is litharge, and by a
+large number of assayers red lead is the form of oxide of lead always
+used. Red lead, however, contains an excess of oxygen which will use up
+some of the reducing agent before lead separates out. On making a series
+of experiments (similar to the last, but using 80 grams of red lead
+instead of the litharge) the results were, with the same quantities of
+the reducing agents:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>With</td><td align='left'>charcoal,</td><td align='left'>18</td><td align='left'>grams</td><td align='left'>of lead.</td></tr>
+<tr><td align='center'> "</td><td align='left'>flour,</td><td align='left'>18</td><td align='center'>"</td><td align='center'>"</td></tr>
+<tr><td align='center'> "</td><td align='left'>tartar,</td><td align='left'>22</td><td align='center'>"</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>Comparing these with the results with litharge, in the previous table it
+will be seen that the same quantity of reducing agent has in each case
+brought down 16 grams less of lead, so that a larger amount of the
+reducing agent must be added to get a button of<span class='pagenum'><a name="Page_95" id="Page_95">[Pg 95]</a></span> the same weight as that
+obtained with litharge. To get a button of a desired weight, say 22
+grams, we must add reducing agent sufficient to throw down 22 + 16 or 38
+grams of lead, which would require 3.4 grams of flour. If this amount of
+flour is fused with 80 grams of red lead, a button of lead weighing 22
+grams will be formed, the other 16 grams being kept up by the oxygen of
+the red lead.</p>
+
+<p>If the quantity of red lead differs from 80 grams, this rule must be
+modified. With 40 grams of red lead, for example, we should add an
+excess of reducing agent sufficient to throw down 8 grams of lead
+instead of 16. Similarly, with 160 grams of red lead, we should add
+enough to throw down 32 grams.</p>
+
+<p>The following rule will enable one to calculate the weight of flour
+required to produce a button of lead of any desired weight from any
+given quantity of red lead. Each 5 grams of red lead present diminishes
+the weight of the lead by 1 gram. If then we <i>divide the weight of red
+lead in a charge by 5, and add this to the weight of lead required, the
+sum divided by 11 will give the weight of flour which must be added</i>.
+Using 80 grams of red lead and wanting a button of 20 grams, we should
+add 3.3 grams of flour.</p>
+
+<p>
+80/5 = 16; 16+20 = 36; 36/11 = 3.3 nearly.<br />
+</p>
+
+<p>The following are some results obtained which will illustrate the
+rule:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Red Lead used.</td><td align='left'></td><td align='left'>Flour used.</td><td align='left'></td><td align='left'>Lead got.</td></tr>
+<tr><td align='right'>40</td><td align='center'>grams</td><td align='right'>3</td><td align='center'>grams</td><td align='right'>25.0</td><td align='center'>grams</td></tr>
+<tr><td align='right'>100</td><td align='center'>"</td><td align='right'>3</td><td align='center'>"</td><td align='right'>13.5</td><td align='center'>"</td></tr>
+<tr><td align='right'>80</td><td align='center'>"</td><td align='right'>4</td><td align='center'>"</td><td align='right'>30.0</td><td align='center'>"</td></tr>
+<tr><td align='right'>80</td><td align='center'>"</td><td align='right'>5</td><td align='center'>"</td><td align='right'>40.0</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><i>On the Reducing Effect of Metallic Sulphides, and the Counteracting
+Effect of Nitre.</i>&mdash;The sulphides found in ores will reduce a button of
+lead from oxide of lead just as flour does; and, as charcoal, flour and
+tartar differ in their reducing power, so equal weights of the different
+mineral sulphides throw down different weights of lead.</p>
+
+<p>One gram of iron pyrites yields about 11 grams of lead. One gram of
+copper pyrites, blende, fahlerz, or mispickel, yields 7 or 8 grams of
+lead, whilst 1 gram of antimonite will give 6, and 1 gram of galena only
+a little over 3 grams. It is evident that if an ore carries much of
+these sulphides, the quantity of lead reduced will be very much larger
+than that required for an assay. To counteract this effect nitre is
+added; <i>1 gram is added for each 4 grams of lead in excess of that
+required</i>. For example: with a 20-gram charge of an ore containing 50
+per cent. of pyrites, if no nitre were added, 110 grams of lead would be
+got; or, if there<span class='pagenum'><a name="Page_96" id="Page_96">[Pg 96]</a></span> was not sufficient oxide of lead to yield this
+quantity of metal, the button would be sulphury. To reduce the weight of
+the button by 80 grammes, we should add 20 grams of nitre, if litharge
+were used; or if red lead were used, we should add 16 grams of nitre,
+<i>since the oxidizing effect of 20 grams of red lead is equivalent to
+that of 1 of nitre</i>, and since 80 grams of red lead are generally used
+in a charge. Two assays of an ore of this kind with these quantities of
+nitre gave 26.0 grams of lead with litharge, and 22.5 grams with red
+lead.</p>
+
+<p>It is best to use in these assays 80 grams of red lead, 20 of soda, and
+5 of borax, with 20 grams of the ore. If the lead got by the preliminary
+fusion in a small crucible with litharge (described under "<i>ores
+containing much sulphides</i>") is known, the following table will indicate
+the quantity of nitre, or flour, to be added with this charge:&mdash;</p>
+
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Lead got in Preliminary Fusion with 3 grams of Ore.</td><td align='left'>Flour to be added to the Assay.</td><td align='left'>Nitre to be added to the Assay.</td></tr>
+<tr><td align='left'>0.0 gram</td><td align='left'>3.3 grams</td><td align='left'>none</td></tr>
+<tr><td align='left'>3.0 grams</td><td align='left'>1.3 gram</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>6.0 &nbsp;&nbsp;&nbsp;"</td><td align='left'>none</td><td align='left'>4.0 grams</td></tr>
+<tr><td align='left'>9.0&nbsp;&nbsp;&nbsp; "</td><td align='left'>&mdash;</td><td align='left'>9.0 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>12.0&nbsp;&nbsp;&nbsp; "</td><td align='left'>&mdash;</td><td align='left'>14.0 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>15.0&nbsp;&nbsp;&nbsp;&nbsp; "</td><td align='left'>&mdash;</td><td align='left'>19.0 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>18.0&nbsp;&nbsp;&nbsp; "</td><td align='left'>&mdash;</td><td align='left'>24.0 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>21.0 &nbsp;&nbsp;&nbsp;"</td><td align='left'>&mdash;</td><td align='left'>29.0&nbsp;&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+<p>If litharge is used in the assay instead of red lead 4 grams more nitre,
+or 1.5 gram less flour must be used. When more than a few grams of nitre
+are added to a charge the proportion of "soda" and borax should be
+increased, because one of the products of the reaction of nitre upon
+sulphides in the presence of soda is sulphate of soda, and because the
+"soda" thus used up no longer serves as a flux; more borax should be
+added, as it is the best flux for the metallic oxides which are formed
+in the process. If in an assay too large a button of lead is got, even
+after this calculation has been made, and the assay is repeated, add 1
+gram more nitre for each 4 grams of lead in excess. Sometimes the assay
+appears tranquil before the nitre has produced its full effect; in such
+cases it is well to seize the crucible with the tongs and mix its fused
+contents by rotating them; if this causes an effervescence, the crucible
+should be replaced in the fire and the fusion continued. The following
+experiments will illustrate the extent to which the above rules may be
+relied on. In all of them the standard flux was used, viz.:&mdash;80 grams of
+red lead, 20 of soda, and 5 of borax.<span class='pagenum'><a name="Page_97" id="Page_97">[Pg 97]</a></span></p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>Pyrites</i></td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>2.5</td><td align='left'>5</td><td align='left'>10</td><td align='left'>15</td><td align='left'>20</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>20</td><td align='left'>&mdash;</td><td align='left'>20</td><td align='left'>17.5</td><td align='left'>15</td><td align='left'>10</td><td align='left'>5</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>5</td><td align='left'>5</td><td align='left'>&mdash;</td><td align='left'>4</td><td align='left'>16</td><td align='left'>28.5</td><td align='left'>41</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>42.5</td><td align='left'>36.0</td><td align='left'>16.0</td><td align='left'>19.0</td><td align='left'>11.5</td><td align='left'>22.5</td><td align='left'>22.5</td><td align='left'>26.5</td><td align='left'>27.5</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>Copper Pyrites</i></td><td align='left'>8</td><td align='left'>8</td><td align='left'>8</td><td align='left'>8</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>12</td><td align='left'>&mdash;</td><td align='left'>12</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>4</td><td align='left'>4</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>47.5</td><td align='left'>34.0</td><td align='left'>33.0</td><td align='left'>26.0</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>Antimonite</i></td><td align='left'>8</td><td align='left'>8</td><td align='left'>8</td><td align='left'>8</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>12</td><td align='left'>&mdash;</td><td align='left'>12</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>4</td><td align='left'>4</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>29.0</td><td align='left'>26.0</td><td align='left'>13.0</td><td align='left'>13.0</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>Galena</i></td><td align='left'>10</td><td align='left'>10</td><td align='left'>10</td><td align='left'>10</td><td align='left'>15</td><td align='left'>20</td></tr>
+<tr><td align='left'>Quartz.</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>5</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>3</td><td align='left'>3</td><td align='left'>3.5</td><td align='left'>7</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>17.0</td><td align='left'>19.0</td><td align='left'>8.0</td><td align='left'>8.0</td><td align='left'>18.5</td><td align='left'>18.5</td></tr>
+</table></div>
+
+
+<p>A similar set of experiments, with 80 grams of litharge instead of 80
+grams of red lead, gave:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>Pyrites</i></td><td align='left'>4</td><td align='left'>4</td><td align='left'>4</td><td align='left'>4</td><td align='left'>7</td><td align='left'>10</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>13</td><td align='left'>10</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>5</td><td align='left'>5</td><td align='left'>12.5</td><td align='left'>20</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>46.5</td><td align='left'>40.5</td><td align='left'>25.5</td><td align='left'>24.5</td><td align='left'>27.0</td><td align='left'>26.5</td></tr>
+<tr><td align='left'><i>Copper Pyrites</i></td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>&mdash;</td><td align='left'>15</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>5</td><td align='left'>5</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>44.5</td><td align='left'>32.5</td><td align='left'>23.0</td><td align='left'>25.0</td></tr>
+<tr><td align='left'><i>Blende</i></td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>10</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>10</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>5</td><td align='left'>5</td><td align='left'>15</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>41.5</td><td align='left'>38.5</td><td align='left'>21.5</td><td align='left'>22.5</td><td align='left'>21.6</td></tr>
+<tr><td align='left'><i>Antimonite</i></td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>5</td><td align='left'>10</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>10</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>5</td><td align='left'>5</td><td align='left'>10</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>31.0</td><td align='left'>32.5</td><td align='left'>11.5</td><td align='left'>12.5</td><td align='left'>18.7</td></tr>
+<tr><td align='left'><i>Galena</i></td><td align='left'>10</td><td align='left'>10</td><td align='left'>10</td><td align='left'>10</td><td align='left'>15</td><td align='left'>20</td></tr>
+<tr><td align='left'>Quartz</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>&mdash;</td><td align='left'>15</td><td align='left'>5</td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Nitre</td><td align='left'>&mdash;</td><td align='left'>&mdash;</td><td align='left'>5</td><td align='left'>5</td><td align='left'>7.5</td><td align='left'>11</td></tr>
+<tr><td align='left'>Lead got</td><td align='left'>33.5</td><td align='left'>33.5</td><td align='left'>13.0</td><td align='left'>14.0</td><td align='left'>19.5</td><td align='left'>22.7</td></tr>
+</table></div>
+<p><span class='pagenum'><a name="Page_98" id="Page_98">[Pg 98]</a></span></p>
+
+<p>The variation in some of these experiments, in which we might have
+expected similar results, is due to the fact that the sulphur, and in
+some cases the metals, are capable of two degrees of oxidation. For
+example: theoretically 1 gram of iron pyrites (FeS<sub>2</sub>) would yield 8.6
+grams of lead if the sulphur were oxidised to sulphurous oxide (SO<sub>2</sub>),
+and the iron to ferrous oxide (FeO); whilst if the sulphur were oxidised
+to sulphate (SO<sub>3</sub>), and the iron to ferric oxide, 12.9 grams of lead
+will be thrown down. Similarly the yield with copper pyrites would be
+7.5 or 11.6; with blende, 6.4 or 8.5; with antimonite, 5.5 or 8; and
+with galena, 2.6 or 3.4. As regards the metals, the lower oxide will
+always be formed if the assay is carried out properly (fused under a
+cover, and with a sufficiency of reducing agent). But the proportion of
+sulphur oxidised completely will vary with the conditions of the assay.
+With a slag containing much soda the tendency will be to form sulphate,
+and, in consequence, a big reduction of lead; whilst with an acid slag
+containing much quartz the tendency will be for the sulphur to go off as
+sulphurous oxide (SO<sub>2</sub>). In a fusion with litharge alone all the
+sulphur will be liberated as the lower oxide, whilst with much soda it
+will be wholly converted into sulphate. For example: 3 grams of an ore
+containing a good deal of pyrites and a little galena, gave, when fused
+with litharge, 16.5 grams of lead. A similar charge, containing in
+addition 20.0 grams of soda, gave 22.5 grams of lead.</p>
+
+<p>It will be noted from the experiments that 1 gram of nitre kept up on
+the average 4 grams of lead; the range being from 3.2 with acid slags to
+5.3 with very basic ones. These facts serve to explain some apparently
+irregular results got in practice.</p>
+
+
+<h4>CUPELLATION.</h4>
+
+<p>The process is as follows:&mdash;The cupels, which should have been made some
+time before and stored in a dry place, are first cleaned by gentle
+rubbing with the finger and blowing off the loose dust; and then placed
+in a hot muffle and heated to redness for from 5 to 10 minutes before
+the alloy to be cupelled is placed on them. The reasons for this are
+sufficiently obvious: the sudden evolution of much steam will blow a
+cupel to pieces; and, if the whole of the water has not been removed
+before the cupel is filled with molten lead, the escaping steam will
+bubble through, and scatter about particles of the metal. If some
+particles of unburnt carbon remain in the bone ash, a similar result
+will be produced by the escape of bubbles of carbonic acid as soon as
+the fused litharge comes in contact with them. The cupels having been
+prepared are arranged in a definite order in the muffle, and the assay
+buttons<span class='pagenum'><a name="Page_99" id="Page_99">[Pg 99]</a></span> are arranged in a corresponding order on some suitable tray
+(cupel tray, fig. 41); the heat of the muffle being at bright redness.
+Then with the help of the tongs (fig. 42) the assay buttons should be
+placed each in its proper cupel; a note having been previously made of
+the position it is to occupy, and the door of the muffle closed.</p>
+
+<div class="figcenter" style="width: 422px;">
+<img src="images/fig041.jpg" width="422" height="195" alt="Fig. 41." title="" />
+
+</div>
+
+<p>This part of the work should be done promptly, so as not to unduly cool
+the muffle: the start requires a fairly high temperature, and is a
+critical part of the process. A black crust forms at once on the surface
+of the lead; but this ought soon to fuse and flow in greasy drops from
+off the face of the metal, so as to leave the latter fluid with a
+well-defined outline, and much brighter than the cupel. If this clearing
+does not take place, the buttons are said to be frozen; in which case
+the temperature must be raised, some pieces of charcoal put in the
+muffle, and the door closed. If they still do not clear, the heat must
+have been much too low, and it is best to reject them and repeat the
+assays.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig042.jpg" width="450" height="63" alt="Fig. 42." title="" />
+
+</div>
+
+<p>When the buttons have cleared it is well to check the draught of the
+furnace, and to partly open the door of the muffle, so as to work at as
+low a temperature as is compatible with the continuation of the
+process.<a name="FNanchor_11_11" id="FNanchor_11_11"></a><a href="#Footnote_11_11" class="fnanchor">[11]</a> Too low a temperature is indicated by the freezing of the
+buttons and the consequent spoiling of the assays. Experience soon
+enables one to judge when the heat is getting too low. A commoner error
+is to have the heat too high: it should be remembered that that which
+was high enough to clear the buttons at starting is more than sufficient
+to keep the process going. At the finish a higher temperature is again
+required: therefore the door of the muffle should be closed and the
+furnace urged. The finish is easily recognised. The drops of litharge
+which in the earlier stages flow steadily from the surface of the alloy,
+thin off later to a luminous film. At the end this film appears in
+commotion, then presents a brilliant play of colours, and, with a sudden
+extinction, the operation is finished. The metal again glows for an
+instant whilst becoming solid.</p>
+
+<p>If the button is a small one the cupel is withdrawn at once and placed
+on that square of the cupel tray which corresponds to<span class='pagenum'><a name="Page_100" id="Page_100">[Pg 100]</a></span> the position it
+occupied in the muffle. If, however, it is fairly large precautions must
+be taken to prevent spirting.</p>
+
+<p>Molten silver dissolves oxygen from the air and gives it off on
+solidifying; the escape of the gas on sudden cooling is violent and, by
+throwing off particles of the metal, may cause loss. This is called
+"vegetation" or "spirting." The silver is apparently solid when spirting
+takes place; the crust breaks suddenly and some of the metal is forced
+out. The evil is best guarded against by slow cooling and avoiding
+draughts. With large buttons of silver precautions should never be
+omitted. One plan is to allow the cupels to cool in the muffle itself,
+the mouth being closed with hot charcoal. Another is to cover the cupel
+with another cupel previously heated to redness; in this case the silver
+cools between two hot cupels, and, of course, cools slowly. A third plan
+is to withdraw the cupel to the door of the muffle, holding it until it
+begins to get solid and then immediately to put it back into the hotter
+part of the muffle.</p>
+
+<p>Silver remains after cupellation in flattened elliptical buttons,
+adhering but only slightly to the cupel. Its upper surface should show
+faint markings as if it were crystalline. The presence of platinum
+renders it still more crystalline, but removes the characteristic lustre
+and renders the metal dull and grey. Copper, if not completely removed,
+has a very marked effect on the appearance of the button: the metal is
+spread out, damping, as it were, and firmly adhering to the cupel, which
+latter in the neighbourhood of the metal is almost black with oxide of
+copper. Sometimes the silver button is globular, or even more sharply
+rounded on its under than on its upper surface; it is said that this is
+due to the presence of lead. Gold may be present even to the extent of
+50 per cent. without showing any yellow colour.</p>
+
+<p>The appearance of the cupel affords some useful information. The
+presence of cracks evidently due to shrinkage indicates a badly made
+cupel. If, however, they are accompanied by a peculiar unfolding of the
+cupel, the margin losing its distinctness, it is because of the presence
+of antimony. When lead is the only easily oxidisable metal present, the
+stained portion of cupel is yellow when cold. A greenish tint may be due
+to small quantities of copper or, perhaps, nickel, cobalt, or platinum.
+Larger quantities of copper give a greenish grey or almost black colour.
+A dark green and corroded cupel may be due to iron. Rings of
+pale-coloured scoria may be due to tin, zinc, antimony, or arsenic. When
+the cupel shows signs of the presence of these metals in objectionable
+quantity, it is well to repeat the assay and scorify so as to remove
+them before cupellation.</p>
+
+<p>The button should be detached from the cold cupel by seizing<span class='pagenum'><a name="Page_101" id="Page_101">[Pg 101]</a></span> with a
+pair of pliers: the under surface should be distorted by squeezing or
+hammering the button so as to loosen the adhering bone ash. The cleaning
+is easily completed by rubbing with a clean hard brush. After cleaning
+the buttons are best put on a tray of marked watch-glasses, and then
+taken to the balance and weighed. The weight of silver got needs a small
+correction; (1) by deducting for the amount of silver introduced by the
+lead or oxide of lead used in the assay;<a name="FNanchor_12_12" id="FNanchor_12_12"></a><a href="#Footnote_12_12" class="fnanchor">[12]</a> and (2) by adding for the
+cupellation loss.</p>
+
+<p><b>Loss in Cupellation.</b>&mdash;During the whole process of cupelling a silver
+lead alloy a more or less abundant fume may be observed rising from the
+cupel. This furnishes an evident loss of lead and a possible loss of
+silver; for although silver at the temperature of cupellation gives off
+no appreciable vapour, it is known that such fume formed on a large
+scale contains silver. It is, however, difficult to believe that the
+small amount of lead vapourised carries with it a weighable amount of
+silver. That it does not do so in the ordinary way of working is shown
+by the fact that a button of silver equal in weight to the silver lost
+in cupelling may be got by smelting the cupel and cupelling the
+resulting button of lead. The loss of silver by volatilisation is
+altogether inconsiderable, unless the temperature at which the operation
+is performed is much too high.</p>
+
+<p>Another possible source of loss is the infiltration of small particles
+of alloy into the cupel. The cupel is necessarily porous, and particles
+of metal may perhaps drain into it, more especially if the bone ash is
+not in fine powder; but if this is the main source of loss it is hard to
+see why, in cupelling equal weights of silver and gold, the loss is not
+equal in each case. It is not easy to believe that the mere filtration
+of the fused alloy will effect such a change in the proportion of the
+metals as that which actually occurs. For example: a cupel on which an
+alloy consisting of 0.80 gram of silver, 0.47 gram of gold, and 25 grams
+of lead had been cupelled, was found to contain 7-1/2 milligrams of
+silver, and rather less than half a milligram of gold. Assuming, for the
+sake of argument, that the gold present had filtered into the cupel in
+the form of small drops of alloy, it would have been accompanied by less
+than a milligram of silver, and the presence of the extra 6 or 7
+milligrams of silver must have been due to a different cause. There can,
+thus, be little doubt that the cause of the greater part of the
+"cupellation loss" is a chemical one and cannot be counteracted by a
+mechanical contrivance.<a name="FNanchor_13_13" id="FNanchor_13_13"></a><a href="#Footnote_13_13" class="fnanchor">[13]</a> In cupellation,<span class='pagenum'><a name="Page_102" id="Page_102">[Pg 102]</a></span> then, there is a loss,
+apart from imperfect working, inherent in the process itself; and as the
+amount of this loss varies under different conditions, it is necessary
+to study it somewhat in detail.</p>
+
+<p>The following experiments are taken without selection from the work of
+one student. Three experiments were made for each determination, and the
+mean result is given. By "range" is meant the difference between the
+highest and lowest result and the percentage loss is calculated on the
+silver present. The silver added in the lead used has been deducted.</p>
+
+<p><b>Effect of Varying Lead.</b>&mdash;In each experiment 0.4 gram of silver was
+taken and cupelled with the lead. The silver loss and "range" are
+expressed in milligrams.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Lead Used.</td><td align='left'>Silver Lost.</td><td align='left'>Range.</td><td align='left'>Percentage Loss.</td></tr>
+<tr><td align='left'>Grams.</td></tr>
+<tr><td align='left'>10</td><td align='left'>6.5</td><td align='left'>1.0</td><td align='left'>1.62</td></tr>
+<tr><td align='left'>20</td><td align='left'>7.0</td><td align='left'>1.0</td><td align='left'>1.75</td></tr>
+<tr><td align='left'>40</td><td align='left'>12.0</td><td align='left'>1.5</td><td align='left'>3.00</td></tr>
+<tr><td align='left'>60</td><td align='left'>12.7</td><td align='left'>0.5</td><td align='left'>3.17</td></tr>
+</table></div>
+
+
+<p>The loss increases with the lead used.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;0.4 gram of silver was cupelled with
+20 grams of lead.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature.</td><td align='left'>Silver Lost.</td><td align='left'>Range.</td><td align='left'>Percentage Loss.</td></tr>
+<tr><td align='left'>Bright red</td><td align='left'>7.0</td><td align='left'>1.0</td><td align='left'>1.75</td></tr>
+<tr><td align='left'>Clear yellow</td><td align='left'>17.3</td><td align='left'>1.7</td><td align='left'>4.32</td></tr>
+</table></div>
+
+<p>The difference in temperature in these experiments was much greater than
+would occur even with careless work.</p>
+
+<p><b>Effect of Varying Silver.</b>&mdash;20 grams of lead were used in each
+cupellation.</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Silver Taken.</td><td align='left'>Silver Lost.</td><td align='left'>Range.</td><td align='left'>Percentage Loss.</td></tr>
+<tr><td align='left'>Milligrams.</td></tr>
+<tr><td align='right'>12.5</td><td align='left'>0.7</td><td align='left'>0.2</td><td align='left'>5.6</td></tr>
+<tr><td align='right'>25.0</td><td align='left'>1.4</td><td align='left'>0.1</td><td align='left'>5.6</td></tr>
+<tr><td align='right'>50.0</td><td align='left'>1.6</td><td align='left'>0.4</td><td align='left'>3.2</td></tr>
+<tr><td align='right'>100.0</td><td align='left'>2.9</td><td align='left'>0.3</td><td align='left'>2.9</td></tr>
+<tr><td align='right'>200.0</td><td align='left'>5.6</td><td align='left'>0.5</td><td align='left'>2.8</td></tr>
+<tr><td align='right'>400.0</td><td align='left'>7.0</td><td align='left'>1.0</td><td align='left'>1.7</td></tr>
+<tr><td align='right'>800.0</td><td align='left'>9.7</td><td align='left'>1.0</td><td align='left'>1.2</td></tr>
+</table></div>
+
+
+<p>It will be seen that, although the quantity of silver lost increases<span class='pagenum'><a name="Page_103" id="Page_103">[Pg 103]</a></span>
+with the silver present, the percentage loss is greater on the smaller
+buttons.</p>
+
+<p>The following results are often quoted:&mdash;Cupelling 1 grain of silver
+with 10 grains of lead, the loss was 1.22 per cent.; 10 grains of silver
+with 100 grains of lead, loss 1.13 per cent.; 25 grains of silver
+cupelled with 250 grains of lead, lost 1.07 per cent. The proportion of
+silver to lead was the same in the three experiments, and the largest
+button gave the best result. Evidently, if the quantities of lead had
+been the same in the three experiments (say, 250 grains in each case),
+the loss on the smaller quantities of silver would appear worse in the
+comparison.</p>
+
+<p>In judging these results, it must be borne in mind that it is difficult
+to regulate the temperature, &amp;c., in consecutive experiments so as to
+get exactly similar results, so that the range in consecutive
+cupellations is greater than that in a batch cupelled side by side.</p>
+
+<p><b>Effect of Copper and Antimony.</b>&mdash;0.1 gram of silver was cupelled with
+20 grams of lead, and to one batch 0.5 gram of antimony, and to another
+0.5 gram of copper was added.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>Silver Lost.</td><td align='left'>Range.</td><td align='left'>Loss in Percentage.</td></tr>
+<tr><td align='left'>Without addition</td><td align='left'>2.9</td><td align='left'>0.3</td><td align='left'>2.9</td></tr>
+<tr><td align='left'>With antimony</td><td align='left'>3.2</td><td align='left'>0.2</td><td align='left'>3.2</td></tr>
+<tr><td align='left'>With copper</td><td align='left'>4.9</td><td align='left'>1.7</td><td align='left'>4.9</td></tr>
+</table></div>
+
+<p>Perhaps the antimony has so small an effect because it is eliminated in
+the earlier part of the process, while the silver is still alloyed with,
+and protected by, a large proportion of lead; whilst the copper on the
+other hand makes its fiercest attack towards the close, when the silver
+is least capable of resisting it. The ill effects of copper are most
+strongly felt when the quantity of lead present is not sufficient to
+remove it: the coppery button of silver got under these conditions is
+very considerably less than the weight of silver originally taken.</p>
+
+<p>Although the above is a fair statement of the loss attending average
+work, it will not do in very important and exact work to place too much
+reliance on the figures given, or, indeed, on any other set of figures,
+with the object of correcting the result of an assay. Each man must rely
+on his own work.</p>
+
+<p>It is easy to determine what allowance must be made for the loss in
+cupellation by cupelling side by side with the assay piece an alloy of
+similar and <i>known</i> composition. For, if the two pieces are very nearly
+alike, we may justly conclude that the loss on each will be the same;
+and if, further, we take the average of three or four such
+determinations we shall get results accurate within 0.1 per cent. The
+method of getting such results may be best explained<span class='pagenum'><a name="Page_104" id="Page_104">[Pg 104]</a></span> by one or two
+illustrations. This method of working is termed "assaying by checks."</p>
+
+<p>Suppose we have an alloy of silver and lead in unknown proportions and
+that by cupelling two lots of 10 grams each there is got from I. 0.1226
+gram of silver, and from II. 0.1229 gram. We should know from general
+experience that the actual quantity of silver present was from 2 to 4
+milligrams more than this. To determine more exactly what the loss is,
+the following plan is recommended:&mdash;The two silver buttons are wrapped
+up each in 10 grams of lead, and cupelled side by side with two other
+lots of 10 grams of the original alloy. If now the two buttons I. and
+II. weigh 0.1202 and 0.1203, they will have suffered in this second
+cupellation an average loss of 2.5 milligrams. Suppose the two fresh
+lots of alloy gave 0.1233 and 0.1235 of silver, the average loss on
+these would also be 2.5 milligrams. Add this loss to each result, and
+take the mean; which is in this case 0.1259.</p>
+
+<p>If copper is present in the alloy as well as silver, it is necessary to
+add about the same quantity of copper to the checks as is supposed, or
+known, to be present in the assays. If the substance to be assayed is an
+alloy of silver and copper, first cupel 0.5 gram of it, with, say, 10
+grams of lead, and weigh the resulting button of silver, in order to get
+an approximate knowledge of its composition. Suppose the button weighs
+0.3935 gram. We know that this is below the truth: for the sake of round
+numbers take it as 0.4, and assume that the rest of the alloy (0.1 gram)
+was copper. Two check pieces are then weighed out, each containing 0.4
+gram silver and 0.1 gram of copper wrapped in 5 grams of lead. Of course
+the silver must be pure. And there is also weighed out two (or better,
+four) assay pieces each containing half a gram of the alloy wrapped in 5
+grams of lead. The whole lot are then cupelled as nearly as possible
+under the same conditions. With four assay pieces, the cupels should be
+placed close together in two rows of three across the muffle; the two
+check pieces are put in the middle cupels. Suppose the buttons of silver
+got weighed as follows:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Check pieces</td><td align='left'>I.</td><td align='left'>0.3940</td><td align='left'>II.</td><td align='left'>0.3945</td></tr>
+<tr><td align='left'>Assay pieces</td><td align='left'>I.</td><td align='left'>0.3905</td><td align='left'>II.</td><td align='left'>0.3912</td></tr>
+<tr><td align='left'></td><td align='left'>III.</td><td align='left'>0.3910</td><td align='left'>IV.</td><td align='left'>0.3909</td></tr>
+</table></div>
+
+
+<p>The average loss on the two check pieces is 5.7 milligrams, and the
+average result of the four assay pieces is 0.3909. Add the average loss
+to the average result, and there is got the corrected result, 0.3966.
+And if 0.5 gram of alloy contain 0.3966 of silver, 1000 will contain
+793.2 of silver, and this is the degree of fineness.</p>
+
+<p>A correction for the loss in cupellation is always made in this<span class='pagenum'><a name="Page_105" id="Page_105">[Pg 105]</a></span> way
+when rich alloys are being assayed; and in the case of rich ores it may
+be done after the manner of the first of the above illustrations. There
+is another method of working which relies more on experiment. This is to
+smelt the cupel as described further on (p. 114), and to again cupel the
+resulting button of lead. The button of silver got in this second
+cupellation is added to that first obtained. It will sometimes, but not
+often, happen that the two buttons together will slightly exceed in
+weight the silver which was actually present. This is because of the
+retention in the buttons of a small quantity of lead. It has been stated
+that the proportion of lead thus retained may be as much as 1% of the
+silver present; this, however, can only be under exceptional conditions.
+A determination of the actual silver in the buttons got in the series of
+cupellations quoted on pages 102, 103, gave an average percentage of
+99.85, so that even with the larger buttons the effect of the retained
+lead would be only to increase the weight by about 1 milligram. In the
+method of working with checks, the retained lead has no disturbing
+influence.</p>
+
+<p><b>The proportion of lead required</b> for the cupellation of any particular
+alloy requires consideration. With too much lead the time occupied in
+the process is increased, and so is the loss of silver; on the other
+hand, too little lead is of greater disadvantage than too much. From 8
+to 16 parts of lead are required for each part of silver alloy, or, if
+gold is present, about twice as much as this must be used. For the
+cupellation of 1 gram of a silver copper alloy containing different
+percentages of copper, the following quantities of lead should be
+used:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>Percentage of Copper in Alloy.</td><td align='center'>&nbsp;&nbsp;&nbsp;Lead Required.</td></tr>
+<tr><td align='right'>5</td><td align='right'>6</td><td align='center'>grams</td></tr>
+<tr><td align='right'>10</td><td align='right'>8</td><td align='center'>"</td></tr>
+<tr><td align='right'>20</td><td align='right'>10</td><td align='center'>"</td></tr>
+<tr><td align='right'>30</td><td align='right'>12</td><td align='center'>"</td></tr>
+<tr><td align='right'>40</td><td align='right'>14</td><td align='center'>"</td></tr>
+<tr><td align='right'>50-100</td><td align='right'>16-18</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>The alloy, in not too large pieces, is wrapped in the required weight of
+lead foil and charged into the cupel at once; or the lead may be put in
+first, and, when the cupellation has fairly started, the alloy may be
+added wrapped in tissue paper; or a portion of the lead may be first
+started and the alloy wrapped in the remaining lead and subsequently
+added. The cupellation of large quantities of alloy or of alloys which
+contain tin, antimony, iron, or any substance which produces a scoria,
+or corrodes the cupel, must be preceded by a scorification. The
+advantages of this are that the slag is poorer in precious metal<span class='pagenum'><a name="Page_106" id="Page_106">[Pg 106]</a></span> than
+that found on a cupel and is more easily collected and cleaned; that
+larger quantities of metal can be treated, and that, even if the
+substance is in part infusible, or produces at the start a clinkery mass
+or scoria, the oxide of lead gradually accumulates, fluxes the solid
+matters, and produces a good final result; but if the oxide of lead by
+itself is not sufficient for the purpose, borax or some other flux can
+be easily added.</p>
+
+<p>If the button of silver got is very small its weight may be estimated
+from its size; but it must be remembered that the weight varies as the
+cube of the diameter. If one button has twice the diameter of another it
+is eight times as heavy and so on. Scales specially constructed for
+measuring silver and gold buttons may be purchased; but it is much
+better to make the measurement with the help of a microscope provided
+with an eyepiece micrometer.</p>
+
+<p>If the length of the long diameter of a silver button be taken the
+following table will give the corresponding weight in milligrams:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Diameter.</td><td align='left'>Weight.</td><td align='left'>Diameter.</td><td align='left'>Weight.</td></tr>
+<tr><td align='left'>0.04 inch</td><td align='left'>3.6</td><td align='left'>0.015 inch</td><td align='left'>0.19</td></tr>
+<tr><td align='left'>0.035&nbsp;&nbsp; "</td><td align='left'>2.4</td><td align='left'>0.014&nbsp;&nbsp; "</td><td align='left'>0.15</td></tr>
+<tr><td align='left'>0.03 &nbsp;&nbsp;"</td><td align='left'>1.5</td><td align='left'>0.013&nbsp;&nbsp; "</td><td align='left'>0.12</td></tr>
+<tr><td align='left'>0.025&nbsp;&nbsp; "</td><td align='left'>0.9</td><td align='left'>0.012&nbsp;&nbsp; "</td><td align='left'>0.097</td></tr>
+<tr><td align='left'>0.02 &nbsp;&nbsp;"</td><td align='left'>0.45</td><td align='left'>0.011&nbsp;&nbsp; "</td><td align='left'>0.075</td></tr>
+<tr><td align='left'>0.019 &nbsp;&nbsp;"</td><td align='left'>0.4</td><td align='left'>0.010 &nbsp;&nbsp;"</td><td align='left'>0.056</td></tr>
+<tr><td align='left'>0.018&nbsp;&nbsp; "</td><td align='left'>0.33</td><td align='left'>0.008&nbsp;&nbsp; "</td><td align='left'>0.028</td></tr>
+<tr><td align='left'>0.017&nbsp;&nbsp; "</td><td align='left'>0.27</td><td align='left'>0.006&nbsp;&nbsp; "</td><td align='left'>0.012</td></tr>
+<tr><td align='left'>0.016&nbsp;&nbsp; "</td><td align='left'>0.23</td><td align='left'>0.004&nbsp;&nbsp; "</td><td align='left'>0.004</td></tr>
+</table></div>
+
+<p>The weight of a corresponding button of gold is got by multiplying by
+2.25. These figures are based on those given by Plattner, and apply only
+to buttons of such shape as those left after cupellation. A sphere of
+silver 0.01 inch in diameter would weigh 0.09 milligram, and a similar
+sphere of gold weighs 0.167 milligram.</p>
+
+<p>It is safer, however, to compare with a micrometer the diameter of the
+button whose weight has to be determined with that of a standard button
+of nearly equal size whose weight is known. The weights of the two
+buttons are proportional to the cubes of their diameters. This plan of
+working is described more fully in Appendix B., page 440.</p>
+
+<p><b>Calculation of the Results.</b>&mdash;After deducting for the silver added, and
+correcting for the cupellation loss, the calculation is made in the
+usual way; reporting as so many parts per thousand in the case of rich
+alloys and as so many ounces and<span class='pagenum'><a name="Page_107" id="Page_107">[Pg 107]</a></span> pennyweights, or better as ounces and
+decimals of an ounce, in the case of poor alloys and ores.</p>
+
+<p>In this last case, however, it is less fatiguing to refer to a set of
+tables which give, either directly or by means of simple addition, the
+produce corresponding to any weight obtained from certain given weights
+of the substance. The following table gives the produce in ounces and
+decimals of an ounce per ton of 2240 pounds:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight of Metal got.</td><td align='left'>Weight of Ore taken.</td></tr>
+<tr><td align='left'>&nbsp;</td><td align='left'>3 grams.</td><td align='left'>5 grams.</td><td align='left'>20 grams.</td><td align='left'>50 grams.</td><td align='left'>100 grams.</td></tr>
+<tr><td align='left'>0.0001</td><td align='left'>1.09</td><td align='left'>0.65</td><td align='left'>0.16</td><td align='left'>0.06</td><td align='left'>0.03</td></tr>
+<tr><td align='left'>0.0002</td><td align='left'>2.18</td><td align='left'>1.31</td><td align='left'>0.33</td><td align='left'>0.13</td><td align='left'>0.06</td></tr>
+<tr><td align='left'>0.0003</td><td align='left'>3.27</td><td align='left'>1.96</td><td align='left'>0.49</td><td align='left'>0.20</td><td align='left'>0.10</td></tr>
+<tr><td align='left'>0.0004</td><td align='left'>4.36</td><td align='left'>2.61</td><td align='left'>0.65</td><td align='left'>0.26</td><td align='left'>0.13</td></tr>
+<tr><td align='left'>0.0005</td><td align='left'>5.44</td><td align='left'>3.27</td><td align='left'>0.82</td><td align='left'>0.33</td><td align='left'>0.16</td></tr>
+<tr><td align='left'>0.0006</td><td align='left'>6.53</td><td align='left'>3.92</td><td align='left'>0.98</td><td align='left'>0.39</td><td align='left'>0.19</td></tr>
+<tr><td align='left'>0.0007</td><td align='left'>7.62</td><td align='left'>4.57</td><td align='left'>1.14</td><td align='left'>0.46</td><td align='left'>0.23</td></tr>
+<tr><td align='left'>0.0008</td><td align='left'>8.71</td><td align='left'>5.23</td><td align='left'>1.31</td><td align='left'>0.52</td><td align='left'>0.26</td></tr>
+<tr><td align='left'>0.0009</td><td align='left'>9.80</td><td align='left'>5.88</td><td align='left'>1.47</td><td align='left'>0.59</td><td align='left'>0.29</td></tr>
+<tr><td align='left'>0.001</td><td align='left'>10.89</td><td align='left'>6.53</td><td align='left'>1.63</td><td align='left'>0.65</td><td align='left'>0.33</td></tr>
+<tr><td align='left'>0.002</td><td align='left'>21.78</td><td align='left'>13.07</td><td align='left'>3.27</td><td align='left'>1.31</td><td align='left'>0.65</td></tr>
+<tr><td align='left'>0.003</td><td align='left'>32.67</td><td align='left'>19.60</td><td align='left'>4.90</td><td align='left'>1.96</td><td align='left'>0.98</td></tr>
+<tr><td align='left'>0.004</td><td align='left'>43.56</td><td align='left'>26.13</td><td align='left'>6.53</td><td align='left'>2.61</td><td align='left'>1.31</td></tr>
+<tr><td align='left'>0.005</td><td align='left'>54.44</td><td align='left'>32.67</td><td align='left'>8.17</td><td align='left'>3.27</td><td align='left'>1.63</td></tr>
+<tr><td align='left'>0.006</td><td align='left'>65.33</td><td align='left'>39.20</td><td align='left'>9.80</td><td align='left'>3.92</td><td align='left'>1.96</td></tr>
+<tr><td align='left'>0.007</td><td align='left'>76.22</td><td align='left'>45.73</td><td align='left'>11.43</td><td align='left'>4.57</td><td align='left'>2.29</td></tr>
+<tr><td align='left'>0.008</td><td align='left'>87.11</td><td align='left'>52.27</td><td align='left'>13.07</td><td align='left'>5.23</td><td align='left'>2.61</td></tr>
+<tr><td align='left'>0.009</td><td align='left'>98.00</td><td align='left'>58.80</td><td align='left'>14.70</td><td align='left'>5.88</td><td align='left'>2.94</td></tr>
+<tr><td align='left'>0.01</td><td align='left'>108.89</td><td align='left'>65.33</td><td align='left'>16.33</td><td align='left'>6.53</td><td align='left'>3.27</td></tr>
+<tr><td align='left'>0.02</td><td align='left'>217.78</td><td align='left'>130.67</td><td align='left'>32.67</td><td align='left'>13.07</td><td align='left'>6.53</td></tr>
+<tr><td align='left'>0.03</td><td align='left'>326.67</td><td align='left'>196.00</td><td align='left'>49.00</td><td align='left'>19.60</td><td align='left'>9.80</td></tr>
+<tr><td align='left'>0.04</td><td align='left'>435.56</td><td align='left'>261.33</td><td align='left'>65.33</td><td align='left'>26.13</td><td align='left'>13.07</td></tr>
+<tr><td align='left'>0.05</td><td align='left'>544.44</td><td align='left'>326.67</td><td align='left'>81.67</td><td align='left'>32.67</td><td align='left'>16.33</td></tr>
+<tr><td align='left'>0.06</td><td align='left'>653.33</td><td align='left'>392.00</td><td align='left'>98.00</td><td align='left'>39.20</td><td align='left'>19.60</td></tr>
+<tr><td align='left'>0.07</td><td align='left'>762.22</td><td align='left'>457.33</td><td align='left'>114.33</td><td align='left'>45.73</td><td align='left'>22.87</td></tr>
+<tr><td align='left'>0.08</td><td align='left'>871.11</td><td align='left'>522.67</td><td align='left'>130.67</td><td align='left'>52.27</td><td align='left'>26.13</td></tr>
+<tr><td align='left'>0.09</td><td align='left'>980.00</td><td align='left'>588.00</td><td align='left'>147.00</td><td align='left'>58.80</td><td align='left'>29.40</td></tr>
+<tr><td align='left'>0.1</td><td align='left'>1088.89</td><td align='left'>653.33</td><td align='left'>163.33</td><td align='left'>65.33</td><td align='left'>32.67</td></tr>
+<tr><td align='left'>0.2</td><td align='left'>2177.78</td><td align='left'>1306.67</td><td align='left'>326.67</td><td align='left'>130.67</td><td align='left'>65.33</td></tr>
+<tr><td align='left'>0.3</td><td align='left'>3266.67</td><td align='left'>1960.00</td><td align='left'>490.00</td><td align='left'>196.00</td><td align='left'>98.00</td></tr>
+<tr><td align='left'>0.4</td><td align='left'>4355.56</td><td align='left'>2613.33</td><td align='left'>653.33</td><td align='left'>261.33</td><td align='left'>130.67</td></tr>
+<tr><td align='left'>0.5</td><td align='left'>5444.44</td><td align='left'>3266.67</td><td align='left'>816.67</td><td align='left'>326.67</td><td align='left'>163.33</td></tr>
+<tr><td align='left'>0.6</td><td align='left'>6533.33</td><td align='left'>3920.00</td><td align='left'>980.00</td><td align='left'>392.00</td><td align='left'>196.00</td></tr>
+<tr><td align='left'>0.7</td><td align='left'>7622.22</td><td align='left'>4573.33</td><td align='left'>1143.33</td><td align='left'>457.33</td><td align='left'>228.67</td></tr>
+<tr><td align='left'>0.8</td><td align='left'>8711.11</td><td align='left'>5226.67</td><td align='left'>1306.67</td><td align='left'>522.67</td><td align='left'>261.33</td></tr>
+<tr><td align='left'>0.9</td><td align='left'>9800.00</td><td align='left'>5880.00</td><td align='left'>1470.00</td><td align='left'>588.00</td><td align='left'>294.00</td></tr>
+<tr><td align='left'>1.0</td><td align='left'>10888.89</td><td align='left'>6533.33</td><td align='left'>1633.33</td><td align='left'>653.33</td><td align='left'>326.67</td></tr>
+</table></div>
+
+<p>When, as in this table, the fraction of an ounce is expressed by two
+places of decimals, it may be reduced to pennyweights (dwts.)<span class='pagenum'><a name="Page_108" id="Page_108">[Pg 108]</a></span> by
+dividing by 5. For example, 0.40 of an ounce is 8 dwts. The fraction of
+a dwt. similarly expressed may be converted into grains with sufficient
+exactness by dividing by 4. Thus, 1.63 ozs. equal 1 oz. 12.60 dwts., or
+1 oz. 12 dwts. 15 grains. In England it is usual to report in ounces and
+decimals of an ounce.</p>
+
+<p>The way to use the table is best shown by an example. Suppose a button
+of silver weighing 0.0435 gram was obtained from 20 grams of ore. Look
+down the 20-gram column of the table, and select the values
+corresponding to each figure of the weight, thus:&mdash;</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;0.04   = 65.33 ozs. to the ton<br />
+&nbsp;&nbsp;&nbsp;&nbsp;0.003  =  4.90&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;         "<br />
+&nbsp;&nbsp;&nbsp;&nbsp;0.0005 =  0.82&nbsp;&nbsp;&nbsp;&nbsp;         "<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+&nbsp;&nbsp;&nbsp;&nbsp;0.0435 = 71.05&nbsp;&nbsp;&nbsp;&nbsp;         "<br />
+</p>
+
+<p>Add these together. The produce is 71.05 ozs., or 71 ozs. 1 dwt. to the
+ton.</p>
+
+<p>Or, suppose an ore is known to contain 1.24 per cent. of silver. Look
+down the 100-gram column, select the values, and add them together as
+before.</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;1.0  = 326.67 ozs. per ton<br />
+&nbsp;&nbsp;&nbsp;&nbsp;0.2  =  65.33    &nbsp;&nbsp;&nbsp;&nbsp;  "<br />
+&nbsp;&nbsp;&nbsp;&nbsp;0.04 =  13.07    &nbsp;&nbsp;&nbsp;&nbsp;  "<br />
+&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+&nbsp;&nbsp;&nbsp;&nbsp;1.24 = 405.07  &nbsp;&nbsp;&nbsp;&nbsp;    "<br />
+</p>
+
+<p>This gives 405 ozs. 1 dwt. 10 grains to the ton.</p>
+
+<p>The calculation becomes more complicated when, as is frequently the
+case, the ore contains metallic particles. These show themselves by
+refusing to pass through the sieve when the ore is powdered. When they
+are present, a large portion, or if feasible the whole, of the sample is
+powdered and sifted. The weights of the sifted portion and of the
+"metallics," or prills, are taken; the sum of these weights gives that
+of the whole of the sample taken. It is very important that nothing be
+lost during the operation of powdering.</p>
+
+<p>Each portion has to be assayed separately. It is usual to assay a
+portion of the sifted sample, say, 20 or 50 grams, and to add to the
+produce of this its share of the "metallics." This way of calculating,
+which is more convenient than correct, is illustrated by the following
+example:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight of</td><td align='left'> whole sample</td><td align='right'>400</td><td align='left'>grams</td></tr>
+<tr><td align='left'>Made up of</td><td align='left'>sifted portions</td><td align='right'>399</td><td align='center'>"</td></tr>
+<tr><td align='left'>"</td><td align='left'>"Metallics"</td><td align='right'>1</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='right'>400</td><td align='center'>"</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_109" id="Page_109">[Pg 109]</a></span></p>
+
+<p>Twenty grams of the sifted portion, when assayed, gave 0.1050 gram of
+silver. The whole of the "metallics" scorified and cupelled gave 0.842
+gram of silver. Since the 20 grams assayed was 1-20th of the whole,
+1-20th part of the 0.842 gram of silver (from the metallics) must be
+added to its produce. We thus get 0.1471 gram (0.1050 + 0.0421).</p>
+
+<p>Referring to the 20 gram column, we get&mdash;</p>
+
+<p>
+0.1    = 163.33<br />
+0.04   =  65.33<br />
+0.007  =  11.43<br />
+0.0001 =   0.16<br />
+&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;<br />
+0.1471 = 240.25 ounces per ton.<br />
+</p>
+
+<p>A more legitimate method of calculation is as follows:&mdash;Calculate
+separately the produce of each fraction as if they were from different
+ores. Multiply each produce (best stated in per cents.) by the weight of
+the corresponding fraction. Add together the products, and divide by the
+weight of the whole sample. Taking the same example for illustration, we
+have:&mdash;</p>
+
+<p>
+<i>Metallics.</i>&mdash;Weight 1 gram.<br />
+<span style="margin-left: 3.5em;">1 gram of it yielded 0.842 grams of silver.</span><br />
+<span style="margin-left: 1.5em;">&#8756; Produce = 84.2 per cent.</span><br />
+<span style="margin-left: 3.5em;">Produce multiplied by the weight is still <b>84.2</b>.</span><br />
+<i>Sifted Portion.</i>&mdash;Weight 399 grams.<br />
+<span style="margin-left: 3.5em;">20 grams of it yielded 0.105 gram of silver.</span><br />
+<span style="margin-left: 1.5em;">&#8756; Produce = 0.525 per cent.</span><br />
+<span style="margin-left: 3.5em;">Produce multiplied by weight (0.525 &times; 399) is <b>209.475</b>.</span><br />
+</p>
+
+<p>Add together; and divide by 400, the weight of the whole sample&mdash;</p>
+
+<p>
+<span style="margin-left: 6.5em;">84.2</span><br />
+<span style="margin-left: 6em;">209.475</span><br />
+<span style="margin-left: 6em;">&mdash;&mdash;&mdash;-</span><br />
+<span style="margin-left: 3.5em;">400) 293.675 (0.7342</span><br />
+</p>
+
+
+<p>0.7342 is the total produce of the ore in per cents.</p>
+
+<p>Referring to the 100-gram column in the table we find 239.84 ounces to
+the ton as the produce.</p>
+
+<p>
+0.7    = 228.67<br />
+0.03   =   9.80<br />
+0.004  =   1.31<br />
+0.0002 =   0.06<br />
+<span style="margin-left: 4.5em;">&mdash;&mdash;&mdash;</span><br />
+<span style="margin-left: 4.5em;">239.84</span><br />
+</p>
+
+<p>Comparing this with the result calculated by the first method&mdash;viz.,
+240.26, we see that that was 0.38 oz., or between 7 and 8 dwts. too
+high.</p>
+
+<p>With ores containing "metallics" it is of great importance to powder the
+whole of the selected sample without loss during the process; and of
+even greater importance to well mix the sifted portion, of which the
+last portions to come through the sieve are<span class='pagenum'><a name="Page_110" id="Page_110">[Pg 110]</a></span> apt to be more than
+ordinarily rich through the grinding down of some portions of the
+metallic prills.</p>
+
+<p><b>Remarks on Cupellation.</b>&mdash;Cupellation is at once the neatest and the
+most important of the dry methods of assaying. Its purpose is to remove
+easily oxidisable metals, such as lead and copper, from silver and gold,
+which are oxidisable with difficulty. Metals of the first class are
+often spoken of as <i>base</i>, and gold and silver as <i>noble</i> metals.</p>
+
+<p>When lead is exposed to the action of air at a temperature a little
+above redness, it combines with the oxygen of the air to form litharge,
+an oxide of lead, which at the temperature of its formation is a
+<i>liquid</i>. Consequently, if the lead rests on a porous support, which
+allows the fused litharge to drain away as fast as it is formed, a fresh
+surface of the lead will be continually exposed to the action of the
+air, and the operation goes on until the whole of the lead has been
+removed. Silver or gold exposed to similar treatment does not oxidise,
+but retains its metallic condition; so that an alloy of lead and silver
+similarly treated would yield its lead as oxide, which would sink into
+the support, while the silver would remain as a button of metal.</p>
+
+<p>The porous support, which is called <i>a cupel</i>(fig. 5), should absorb the
+slag (oxide of lead, etc.) just as a sponge absorbs water, but must be
+sufficiently fine-grained to be impervious to the molten metal. At first
+sight it appears difficult to filter, as it were, a fluid slag from a
+fluid metal; but an ordinary filter-paper damped with oil will allow
+oils to run through and yet retain the water; but damped with water it
+will allow water to run through and retain oils. Similarly, fused slags
+damp and filter through a cupel, but the molten metal not damping it
+withdraws itself into a button, which is retained. Although, of course,
+if the cupel is very coarse-grained the metal may sink into the hollows.</p>
+
+<p>Copper, antimony, tin, and most other metals, form powdery oxides, which
+are not of themselves easily fusible, and it is necessary when these are
+present to add some solvent or flux to render the oxide sufficiently
+fluid. Fortunately, oxide of lead is sufficient for the purpose; hence,
+mixed oxides of copper and lead, provided the lead is present in proper
+proportion, form a fluid slag. In separating copper from silver or gold,
+advantage is taken of this fact; for, although we cannot cupel an alloy
+of copper and silver, it is easy to cupel an alloy of copper, silver and
+lead. If, however, the lead is not present in sufficient quantity, the
+whole of the copper will not be removed, and the button of silver, still
+retaining copper, will be found embedded in a coating of black oxide of
+copper. Copper oxidises less easily than lead does; and, consequently,
+the alloy which is being cupelled becomes relatively<span class='pagenum'><a name="Page_111" id="Page_111">[Pg 111]</a></span> richer in copper
+as the operation proceeds. It is on this account that the ill-effects of
+the copper make themselves felt at the close of the operation, and that
+the oxide of copper is found accumulated around the button of silver.
+Tin and antimony, on the other hand, are more easily oxidised; and the
+tendency of their oxides to thicken the slag makes itself felt at the
+commencement: if the button of alloy once frees itself from the ring or
+crust of unfused oxide first formed, the cupellation proceeds quietly,
+and leaves a clean button of silver in the centre. But in either case
+the cupellation is imperfect, and should be repeated with a larger
+proportion of lead. An unfused and, consequently, unabsorbed slag tends
+to retain small buttons of alloy or metal, and thus cause serious loss.</p>
+
+<p>There is a principle underlying many of the phenomena of dry silver
+assaying which the student should endeavour to understand; and which
+serves to emphasise and explain some facts which without an explanation
+may present difficulties. If a button of melted lead be covered with a
+layer of slag rich in oxide of lead, and a second metal be added, this
+other metal distributes itself between the metal and slag in proportions
+which depend mainly upon the ease with which it is oxidised, and to a
+large extent upon the relative quantities of material present. Easily
+oxidisable metals such as zinc, iron, antimony and tin, will go mainly
+into the slag, and, if the proportion of the slag is large, very little
+will go into the metal. On the other hand, with metals oxidisable with
+difficulty, such as silver, gold, and platinum, the reverse holds true;
+nearly the whole of the metals will go into the lead, and very little
+into the slag. If, however, the slag be very rich, say in antimony, the
+lead will contain antimony; and, on the other hand, if the lead be very
+rich in silver, the slag will contain silver in appreciable quantity.
+Copper, which is near lead in the facility with which it is oxidised,
+will serve for the purpose of a detailed example. The results of actual
+analyses of metal and slag formed in contact with each other are shown
+in the following table:&mdash;</p>
+
+<p class="center">Percentage Composition of the Metal.</p>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Lead.</td><td align='right'>Copper.</td></tr>
+<tr><td align='right'>6.8</td><td align='right'>93.2</td></tr>
+<tr><td align='right'>20.0</td><td align='right'>80.0</td></tr>
+<tr><td align='right'>28.0</td><td align='right'>72.0</td></tr>
+<tr><td align='right'>32.0</td><td align='right'>68.0</td></tr>
+<tr><td align='right'>85.0</td><td align='right'>15.0</td></tr>
+</table></div>
+
+<p class="center">Percentage Composition of the Slag.</p>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Lead.</td><td align='left'>Copper.</td></tr>
+<tr><td align='right'>71.4</td><td align='right'>21.4</td></tr>
+<tr><td align='right'>78.0</td><td align='right'>17.0</td></tr>
+<tr><td align='right'>80.0</td><td align='right'>12.5</td></tr>
+<tr><td align='right'>86.0</td><td align='right'>6.7</td></tr>
+<tr><td align='right'>90.0</td><td align='right'>3.6</td></tr>
+</table></div>
+
+
+
+<p>It will be seen from this table that the slag is always much richer in
+lead and poorer in copper than the metal with which it<span class='pagenum'><a name="Page_112" id="Page_112">[Pg 112]</a></span> is in contact.
+The ratio of lead to copper in these five samples is:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>In the Metal.</td><td align='left'>In the Slag.</td></tr>
+<tr><td align='left'></td><td align='left'>1 : 14</td><td align='left'>1 : 0.3</td></tr>
+<tr><td align='left'></td><td align='left'>1 : 4</td><td align='left'>1 : 0.2</td></tr>
+<tr><td align='left'></td><td align='left'>1 : 2.5</td><td align='left'>1 : 0.16</td></tr>
+<tr><td align='left'></td><td align='left'>1 : 2</td><td align='left'>1 : 0.08</td></tr>
+<tr><td align='left'></td><td align='left'>1 : 0.16</td><td align='left'>1 : 0.04</td></tr>
+</table></div>
+
+<p>Assuming these figures to be correct, the following statement is
+approximately true. On oxidising an alloy of 10 grams of copper and 10
+grams of lead, and pouring off the slag when 3 grams of lead have gone
+into it, there will be a loss of (owing to the slag carrying it off)
+about 0.2 gram of copper. On repeating the operation, the next 3 grams
+of lead will carry with them about 0.5 gram of copper; and on again
+repeating, 3 grams of lead will remove 0.8 gram of copper. Finally, the
+last gram of lead will carry with it 0.3 gram of copper, and there will
+be left a button of copper weighing 8.3 grams. The slag will have
+carried off altogether 1.7 gram of copper, which is 17 per cent. of the
+metal originally present.</p>
+
+<p>With the more perfect exposure to the air, and quicker removal of the
+slag, which results from heating on a cupel, the loss would be heavier.
+Karsten got by actual experiment on cupelling copper and lead in equal
+proportions, a loss of 21.25 per cent.</p>
+
+<p>Going back to the example: if the slag were collected and fused with a
+suitable reducing agent so as to convert, say, half of it into metal,
+that half would contain nearly the whole of the copper (such a reduction
+is called "cleaning the slag"). On reoxidising this metal, another
+button of copper is formed which, added to the first, would reduce the
+loss from 17 per cent. to, say, 7 or 8 per cent. And it is conceivable
+that by a series of similar operations, almost the whole of the 10 grams
+of copper originally taken might be recovered. In practice the problem
+is (as far as the copper is concerned) not how to save, but how most
+easily to remove it; and since the removal of this metal is quicker from
+an alloy containing not too much lead, it is evident that two or three
+operations with small quantities of lead will be more effectual than a
+single treatment with a larger quantity. With those metals (tin,
+antimony, &amp;c.) which pass quickly into the slag, the contrary is true;
+hence with these it is necessary to have enough lead present, so that
+the slag formed at the outset shall contain enough oxide of lead to make
+it fluid. As silver is so much less easily oxidised than copper, we
+should reasonably expect that the proportion of silver carried off in
+the oxide of lead would be considerably less than that of the copper
+indicated in the above<span class='pagenum'><a name="Page_113" id="Page_113">[Pg 113]</a></span> example. Indeed, there are one or two facts
+which tend to encourage the hope that the operation may be conducted
+without any loss. If a piece of pure silver foil is exposed on a cupel
+to air at the usual temperature of cupellation, it undergoes very little
+change; it does not even fuse; it loses nothing in weight, and does not
+oxidise. In fact, even if oxide of silver were formed under these
+conditions, it could not continue to exist, for it is decomposed into
+silver and oxygen at a temperature considerably below redness. On the
+other hand, oxide of silver is not reduced to metal by heat alone, when
+mixed with an excess of oxide of lead; while metallic silver is
+converted into oxide when heated with the higher oxides of lead, copper,
+and some other metals. That silver, and even gold (which is more
+difficult to oxidise than silver), may be carried off in the slag in
+this way, is in agreement with general experience. If 10 grams of silver
+are cupelled with 10 grams of lead, there will be a loss of about 50
+milligrams of silver, which is in round numbers 1-30th of the
+corresponding copper loss; with 10 grams of gold and 10 grams of lead,
+the loss will be 4 or 5 milligrams, which is about 1-12th of the
+corresponding silver loss.</p>
+
+<p><b>Determination of Silver in Assay Lead.</b>&mdash;Scorify 50 grams of the lead
+with 0.5 gram of powdered quartz or glass at not too high a temperature.
+When the eye has "closed in," pour; reject the slag, and cupel the
+button of lead. Remove the cupel from the muffle immediately the
+operation is finished. Weigh, and make a prominent note of the result in
+the assay book, as so many milligrams of silver contained in 100 grams
+of lead.</p>
+
+<p><b>Determination of Silver in Red Lead or Litharge.</b>&mdash;Fuse 100 grams of
+the oxide with from 10 to 20 grams of borax; and in the case of litharge
+with 2 grams or with red lead 4 grams of flour. Cupel the lead, and
+weigh the button of silver. Note the result as in the last case.</p>
+
+<p><b>Determination of Silver in Argentiferous Lead.</b>&mdash;Be careful in taking
+the sample, since with rich silver lead alloys the error from bad
+sampling may amount to several parts per cent. Cupel two lots of 20
+grams each, and weigh the buttons of silver. Add to these the estimated
+cupel loss, and calculate the result. Or wrap each button of silver in
+20 grams of assay lead, and re-cupel side by side with two fresh lots of
+20 grams each of the alloy. Calculate the loss incurred, and add on to
+the weight of the two fresh buttons got.</p>
+
+<p><b>Determination of Silver in Bullion.</b>&mdash;The remarks made under the last
+heading as to the importance of correct sampling apply with equal force
+here. Make a preliminary assay by cupelling 0.1 gram of the alloy with 1
+gram of assay lead; calculate<span class='pagenum'><a name="Page_114" id="Page_114">[Pg 114]</a></span> the percentage composition. Refer to the
+table on page 105 to find what weight of lead is required for cupelling
+1 gram of alloy.</p>
+
+<p>Weigh out four lots of 1 gram each, and wrap them in the required
+quantity of lead. Make two check pieces by weighing up two lots of fine
+silver equal to that which you believe to be present in the assay
+pieces; add copper to make up the weight to 1 gram, and wrap in the same
+quantity of lead as was used for the assays.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig043.jpg" width="450" height="334" alt="Fig. 43." title="" />
+
+</div>
+
+<p>Prepare six cupels and charge them in the annexed order (fig. 43), and
+cupel. Guard against spirting. Clean and weigh the buttons of silver.
+Add the mean loss on the two check pieces to the mean weight of the four
+assay pieces; this multiplied by 1000 will give the degree of fineness.</p>
+
+<p><b>Determination of Silver in Copper.</b>&mdash;The silver is best separated in
+the wet way before cupelling, but if the proportion is not too small, it
+can be found by cupellation. Weigh up 3 grams of the metal, wrap in 30
+grams of sheet lead, and cupel; when the cupellation has proceeded for
+fifteen minutes, add 20 grams more lead, and continue till finished.
+Weigh the button of silver.</p>
+
+<p>The cupellation loss will be five or six per cent. of the silver
+present. Determine it by powdering the saturated portion of the cupel
+and fusing in a large Cornish crucible with 30 grams each of soda and
+borax, 10 grams of fluor spar, and 1-1/2 gram of charcoal. Cupel the
+resulting button of lead, and add 10 grams more of lead towards the
+close of the operation. Deduct the weight of silver contained in the
+lead used from the weight of the two buttons, and calculate to ounces to
+the ton.</p>
+
+<p>In an experiment in which 0.1975 gram of silver was present, the weight
+of the button from the first cupellation was 0.1867, and that of the
+button from the second, after correcting for the lead added, was 0.0110
+gram.</p>
+
+<p><b>Determination of Silver in Galena.</b> <i>By Pot Assay.</i>&mdash;Mix 20 grams of
+the powdered ore with 30 grams of red lead, 20 grams of soda, and 5
+grams of borax, as also with from 7 to 10 grams of nitre. Fuse and pour.
+Clean the slag if the ore is rich. Cupel the buttons of lead. Make the
+usual corrections and calculate in ounces to the ton.</p>
+
+<p><i>By Scorification.</i>&mdash;Take 10 grams of the ore, 30 grams of lead,<span class='pagenum'><a name="Page_115" id="Page_115">[Pg 115]</a></span> and
+0.5 gram of borax. Scorify, clean the slag by adding anthracite after
+the "eye" has closed in: cupel the button of lead. Weigh the button of
+silver, make the necessary corrections, and calculate to ounces to the
+ton.</p>
+
+<p>The determination may also be made by cupelling the button of lead got
+in the dry lead assay.</p>
+
+<p>A sample of galena determined by the three methods gave the following
+results:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>By</td><td align='left'>pot assay</td><td align='left'>7.18 ozs.</td><td align='left'> per ton.</td></tr>
+<tr><td align='left'> "</td><td align='left'>scorification</td><td align='left'>7.02</td><td align='center'>"</td></tr>
+<tr><td align='left'> "</td><td align='left'>lead assay</td><td align='left'>6.72</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Determination of Silver in an Ore.</b> <i>By Pot Assay.</i>&mdash;Take 20 grams of
+the powdered ore and mix with 30 grams of soda, 40 grams of red lead,
+and 5 grams of borax, as also with from 2 to 3 grams of flour. Fuse:
+pour. Clean the slag by fusing with 20 grams of red lead and two grams
+of flour. Cupel the buttons of lead; weigh; make the necessary
+corrections, and calculate to ounces to the ton.</p>
+
+<p><i>By Scorification.</i>&mdash;Take 5 grams of the powdered ore, 50 grams of lead,
+and 0.5 gram of "soda" or borax. Scorify. Clean the slag by fusing in a
+crucible as in the pot assay. Cupel, &amp;c.</p>
+
+<p class="center"><i>Examples.</i>&mdash;<i>By Pot Assay.</i>&mdash;Ore taken 20 grams.<br /></p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Silver got</td><td align='left'>0.2893</td><td align='left'>gram</td></tr>
+<tr><td align='left'>Silver from slag</td><td align='left'>0.0060</td><td align='center'>"</td></tr>
+<tr><td align='left'>Silver lost in cupellation</td><td align='left'>0.0100</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>0.3053</td><td align='center'>"</td></tr>
+<tr><td align='left'>Deduct silver in red lead</td><td align='left'>0.0017</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Silver in ore</td><td align='left'>0.3036</td><td align='center'>"</td><td align='left'>= 495.9 ozs. per ton.</td></tr>
+</table></div>
+
+<p class="center"><i>By Scorification.</i>&mdash;Ore taken, 3 grams.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Silver got.</td><td align='left'>0.0425</td><td align='left'>gram</td></tr>
+<tr><td align='left'>Silver from slag</td><td align='left'>0.0022</td><td align='center'>"</td></tr>
+<tr><td align='left'>Silver lost in cupellation</td><td align='left'>0.0020</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>0.0467</td><td align='center'>"</td></tr>
+<tr><td align='left'>Deduct silver in lead</td><td align='left'>0.0015</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Silver in ore</td><td align='left'>0.0452</td><td align='center'>"</td><td align='left'>= 492.2 ozs. per ton.</td></tr>
+</table></div>
+
+
+
+<p><b>Determination of Silver in Silver Precipitate.</b>&mdash;This substance
+contains, in addition to metallic silver and gold, sulphates of lead and
+lime; oxides of zinc, copper, and iron; and more or less organic matter.
+The sample as received is generally free from "water at 100&deg; C."; and,
+since it rapidly absorbs water, care should be taken in weighing it.<span class='pagenum'><a name="Page_116" id="Page_116">[Pg 116]</a></span></p>
+
+<p>Since it contains combined water it is not suited for scorifying;
+therefore the determination of silver and gold (fine metal) is made by
+pot assay. Weigh up 5 grams of the precipitate, mix with 100 grams of
+litharge and 1 gram of charcoal. Melt in a crucible at a moderate heat
+and pour. Detach the slag, replace in the crucible, and, when fused, add
+a mixture of 20 grams of litharge and 1 gram of charcoal. When the
+fusion is again tranquil, pour; and cupel the two buttons of lead.</p>
+
+<p>In a sample worked in this manner the mean of four determinations gave
+0.6819 gram of "fine metal"; deducting 1 milligram for the silver
+contained in the oxide of lead, and adding 8 milligrams for the
+cupellation loss, there is got 0.6889 gram or 13.778 per cent. of silver
+(and gold) in the sample.</p>
+
+<p><b>Determination of Silver in Burnt Ores.</b> <i>By Pot Assay.</i>&mdash;Roasted
+cupriferous pyrites containing small quantities of gold and silver comes
+under this heading. The following mixture will give a fluid slag which
+is heavy and tough when cold:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ore.</td><td align='left'>Borax.</td><td align='left'>Sand.</td><td align='left'>Litharge.</td><td align='left'>Charcoal.</td></tr>
+<tr><td align='left'>100</td><td align='left'>50</td><td align='left'>50</td><td align='left'>100</td><td align='left'>7</td></tr>
+</table></div>
+
+<p>Mix; place in a large crucible; cover with salt; and melt down under
+cover. When fused drop in an iron rod for a few minutes, and about a
+couple of minutes after its withdrawal, pour the charge quickly into a
+large conical mould. The button of lead should weigh about 50 grams.
+Cupel and weigh the silver. The litharge may be replaced by red lead, in
+which case another gram of charcoal powder must be added.</p>
+
+<p>In our experience the results obtained by this method are about 20 per
+cent. less than the actual content of the ore. The results of two
+assays, after deducting for the silver in the litharge used, were 3.9
+and 4.1 milligrams; and a third assay, in which 5.4 milligrams of silver
+had been added, gave 9.2, which, after deducting the added silver,
+leaves 3.8 milligrams. The average of the three results is 3.9
+milligrams from the 100 grams of ore.</p>
+
+<p>Two lots of 100 grams of the same ore treated in the wet way gave 5.2
+and 5.0 milligrams of silver. Burnt ores from Spanish pyrites carry
+about 0.005 per cent. of silver.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p>Silver is got into solution from its ores by attacking with nitric acid,
+but it is best, after dissolving, to cautiously add dilute hydrochloric
+acid, and to carefully avoid excess. If the quantity of silver is very
+small the solution is allowed to stand twenty-four hours, but,
+otherwise, it is warmed and filtered as soon as it clears.<span class='pagenum'><a name="Page_117" id="Page_117">[Pg 117]</a></span> Dry the
+residue and concentrate the silver in a button of lead by pot method or
+scorification, according to the amount of stony matter present. Cupel
+the lead, and the resulting button will be free from all metals, except
+perhaps gold. It may be weighed; or dissolved in nitric acid, and the
+silver determined gravimetrically in the diluted and filtered solution.
+It is better to weigh the metal and afterwards to determine the gold in
+it, estimating the silver by difference. Silver alloys are dissolved in
+dilute nitric acid (free from chlorides), diluted, and filtered. The
+solution is then ready for gravimetric determination.</p>
+
+<p>Sulphuretted hydrogen precipitates silver (like copper), completely,
+even from fairly acid solutions.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>Add dilute hydrochloric acid in small excess to the hot dilute solution,
+which must contain free nitric acid. Heat and stir until the solution
+clears. Decant through a small filter, and wash with hot water,
+acidulated at first with a little nitric acid if bismuth is suspected to
+be present. Dry quickly, transfer as much as possible of the precipitate
+to a watch-glass; burn and ignite the filter paper, treating the ash
+first with two drops of nitric acid and then with one of hydrochloric,
+and again dry. Add the rest of the silver chloride and heat slowly over
+a Bunsen burner until it begins to fuse. Cool and weigh.</p>
+
+<p>The precipitate is silver chloride (AgCl) and contains 75.27 per cent.
+of silver. The moist precipitate is heavy and curdy; it is decomposed by
+direct sunlight, becoming violet under its influence. When heated it is
+yellowish; and, since it is volatile at a high temperature, it must not,
+in drying, be heated above its fusing point. The fused chloride can be
+removed from the crucible (to which it adheres strongly) by digesting
+with dilute acid and zinc.</p>
+
+<p>For the determination of silver in nearly pure bullion the following
+process is used:&mdash;Weigh up 1.5054 gram of the alloy. With this amount of
+alloy each 2 milligrams of silver chloride formed is equivalent to 1
+degree of fineness, so that the weight of the silver chloride obtained
+(stated in milligrams and divided by 2) will give the degree of
+fineness. Transfer to a bottle (known as "bottles for the Indian mint
+assay") and dissolve in 10 c.c. of dilute nitric acid, then make up with
+water to 200 c.c. and add 3 c.c. of dilute hydrochloric acid. Allow to
+stand a few minutes and then shake. Fill the bottle completely with
+water, allow to settle, and syphon off the clear liquid; pour on more
+water,<span class='pagenum'><a name="Page_118" id="Page_118">[Pg 118]</a></span> shake gently to break up the lumps, and again fill the bottle
+with water. Invert over the mouth of the bottle a porous Wedgwood
+crucible, somewhat similar to those used in gold parting. Take firm hold
+of the crucible and bottle, and invert promptly so that the silver
+chloride may be collected in the crucible. Allow to stand a little while
+for the precipitate to settle, and then carefully remove the crucible
+under water.<a name="FNanchor_14_14" id="FNanchor_14_14"></a><a href="#Footnote_14_14" class="fnanchor">[14]</a> Drain off most of the water and break up the silver
+chloride with the help of a well-rounded glass rod. This greatly
+facilitates the subsequent drying. Dry first on the water bath and then
+on the iron plate. Remove the dried silver chloride, by inverting the
+crucible, and weigh it.</p>
+
+<p>As an example, 3 determinations of silver in a coin carried out in this
+way gave:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>(1)</td><td align='left'>1.8500</td><td align='left'>gram AgCl</td><td align='left'>= 925.0</td><td align='left'>fineness.</td></tr>
+<tr><td align='left'>(2)</td><td align='left'>1.8498</td><td align='center'>"</td><td align='left'>= 924.9</td><td align='center'>"</td></tr>
+<tr><td align='left'>(3)</td><td align='left'>1.8502</td><td align='center'>"</td><td align='left'>= 925.1</td><td align='center'>"</td></tr>
+</table></div>
+
+<p><b>Determination of Silver in Burnt Ores.</b>&mdash;Take 100 grams of the ore and
+place in a large beaker of 2-1/2 litres capacity, and cover with 375
+c.c. of hydrochloric acid. Boil for half an hour until the oxides are
+dissolved and the residue looks like sand and pyrites; then add 20 c.c.
+of nitric acid, and boil till free from nitrous fumes. Dilute to 2
+litres with water, and pass a current of sulphuretted hydrogen till the
+iron is reduced, the copper and silver precipitated, and the liquor
+smells of the gas. This takes about one hour and a half.</p>
+
+<p>Filter off the precipitate (rejecting the solution) and wash with warm
+water. Dry and transfer to an evaporating dish, adding the ashes of the
+filter paper. Heat gently with a Bunsen burner until the sulphur burns,
+and then calcine until no more sulphurous oxide comes off. When cold add
+30 c.c. of nitric acid, boil and dilute to 100 c.c. Add 1 c.c. of very
+dilute hydrochloric acid (1 to 100),<a name="FNanchor_15_15" id="FNanchor_15_15"></a><a href="#Footnote_15_15" class="fnanchor">[15]</a> stir well, and allow to stand
+overnight. Decant on to a Swedish filter paper, dry and calcine.</p>
+
+<p>Mix the ashes with 100 grams of litharge and 1 gram of charcoal, and
+fuse in a small crucible. Detach the button of lead and cupel. Weigh and
+make the usual corrections. As an example, 100 grams of ore treated in
+this way gave 5.8 milligrams of silver; deducting 0.8 for the silver
+added in the oxide of lead leaves 5 milligrams obtained from the ore.
+Another experiment on 100 grams of the same ore to which 5 milligrams of
+silver had<span class='pagenum'><a name="Page_119" id="Page_119">[Pg 119]</a></span> been added gave 11.0 milligrams. Deduct 5.8 for the silver
+added; this leaves 5.2 milligrams as the silver obtained from the ore.
+These give, as a mean result, 0.0051 per cent., or 1.66 ounce per ton.</p>
+
+<p><b>Determination of Silver in Commercial Copper.</b>&mdash;For the method of doing
+this, with an example and experiment, see under the heading of
+<i>Examination of Commercial Copper</i>.</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>There are two of these, one adapted for the determination of silver in
+alloys of approximately known composition, and the other of more general
+application. The first of these, generally known as "Gay-Lussac's"
+method is, as regards its working, perfect in principle; but it requires
+a practically constant quantity of silver, that is, one which varies by
+a few milligrams only in each determination. It is a confirmatory method
+rather than a determinative one. The other is known as "Volhard's," and
+resembles in principle and method an ordinary volumetric process.</p>
+
+<p><b>Gay-Lussac's method</b> is based on the precipitation of silver from a
+nitric acid solution by a solution of sodium chloride. The point at
+which the whole of the silver is precipitated being recognised by the
+standard solution ceasing to give a precipitate. The process depends for
+its success upon, (1) the ease which silver chloride separates out from
+the solution leaving it clear after shaking, and, (2), the cloudiness
+produced by the reaction of very small quantities of silver nitrate and
+sodium chloride. In working, a quantity of the sodium chloride solution
+equal to 1 gram of silver is added at once to the assay; and, when the
+solution has been rendered clear by shaking, the residual silver (which
+should not exceed a few milligrams) is estimated with the help of a
+weaker solution of sodium chloride. The success in working evidently
+depends upon the accuracy with which the first addition of the salt
+solution is made. On this account the standard solution is run in from a
+special pipette capable of delivering a practically invariable volume of
+solution. It is not so important that this shall deliver exactly 100
+c.c. as that in two consecutive deliveries the volume shall not differ
+by more than 0.05 c.c. The dilute salt solution is one-tenth of the
+strength of that first run in, and 1 c.c. of it is equivalent to 1
+milligram of silver. Ordinarily it is run in 1 c.c. at a time (and an
+ordinary burette may be used for this purpose), shaking between each
+addition until it ceases to give a precipitate. If many such additions
+have to be made the operation not only becomes tedious, but the
+solution<span class='pagenum'><a name="Page_120" id="Page_120">[Pg 120]</a></span> also ceases to clear after shaking, so that it becomes
+impossible to determine the finishing point.</p>
+
+<p>If the assay contains less than one gram of silver the first addition of
+the dilute salt solution of course produces no precipitate. Five
+milligrams of silver in solution (5 c.c.) is then added, and the assay
+proceeded with in the usual way; 5 milligrams of silver being deducted
+from the amount found.</p>
+
+<p>There is required for the assay a <i>standard solution of sodium
+chloride</i>, which is prepared by dissolving 5.4162 grams of the salt
+(made by neutralizing carbonate of soda with hydrochloric acid) in water
+and diluting to one litre. 100 c.c. of this is equivalent to 1 gram of
+silver.</p>
+
+<p>The weaker solution of salt is made by diluting 100 c.c. of the stronger
+one to one litre. One c.c. of this will equal 1 milligram of silver, or
+0.1 c.c. of the stronger solution.</p>
+
+<p>A <i>standard solution of silver</i> equivalent to the dilute salt solution
+is made by dissolving 1 gram of fine silver in 10 c.c. of dilute nitric
+acid, and diluting with water to one litre.</p>
+
+<div class="figcenter" style="width: 133px;">
+<img src="images/fig044.jpg" width="133" height="450" alt="Fig. 44." title="" />
+
+</div>
+
+<p>The solution of salt is standardised as follows:&mdash;Weigh up 1.003 gram of
+fine silver and dissolve in 25 c.c. of dilute nitric acid in a bottle
+provided with a well-fitting flat-headed stopper. Heat on the water bath
+to assist solution, resting the bottle in an inclined position. When
+dissolved blow out the nitrous fumes with the help of a glass tube bent
+at right angles. Run in from a stoppered pipette (as shown in fig. 44)
+100 c.c. of the standard salt solution, and shake vigorously until the
+solution clears. Fill an ordinary burette with the weaker standard salt
+solution, and run 1 c.c. into the assay bottle, letting it run down the
+side so that it forms a layer resting on the assay solution. If any
+silver remains in solution a cloudy layer will be formed at the junction
+where the two liquids meet. This is best observed against a black
+background If a cloudiness is seen, shake, to clear the liquid, and run
+in another c.c. of salt, and continue this until a cloudiness is no
+longer visible. Deduct 1.5 c.c. from the amount of the weaker sodium
+chloride solution run in. Divide the corrected reading by 10, and add to
+the 100 c.c. This will give the volume of strong salt solution
+equivalent to the silver taken.</p>
+
+<p>If the first addition of the weaker salt solution causes no cloudiness
+add 5 c.c. of the silver solution from an ordinary pipette, shake, and
+then run in the weaker salt solution, working as before. These 5
+milligrams of silver added must be allowed<span class='pagenum'><a name="Page_121" id="Page_121">[Pg 121]</a></span> for before calculating. As
+an example:&mdash;1.0100 gram of fine silver was taken for standardising a
+solution and 4 c.c. of the weaker salt solution were run in. Deducting
+1.5 and dividing by 10 gives 0.25 c.c. to be added to the 100 c.c.</p>
+
+<p>
+<span style="margin-left: 3em;">100.25 : 1.0100 :: 100 : <i>x</i></span><br />
+<span style="margin-left: 10em;"><i>x</i> = 1.0075</span><br />
+</p>
+
+<p>which is the standard of the salt solution.</p>
+
+<p>The method of working an assay may be gathered from the following
+example:&mdash;In the determination of silver in some buttons left after
+cupellation, it was assumed that these would contain 99.5 per cent. of
+silver. For the assay it was necessary to take a quantity that should
+contain a little more than 1.0075 grams of silver; then</p>
+
+<p>
+<span style="margin-left: 3em;">99.5 : 100 :: 1.0075 : <i>x</i></span><br />
+<span style="margin-left: 10em;"><i>x</i> = 1.0125</span><br />
+</p>
+
+<p>To ensure a slight excess, there was taken 1.0150 gram of the buttons,
+which was treated in exactly the same way as for the standardising. The
+quantity of the weaker salt solution required was 7 c.c.; deducting 1.5
+c.c., and dividing by 10, gives 100.55 c.c. of strong salt solution,
+which is equivalent to 1.0130 gram of silver. This being obtained from
+1.015 gram of alloy, is equal to 99.8 per cent., or 998.0 fine.</p>
+
+<p><b>The Effect of Temperature.</b>&mdash;The standardising and the assay must be
+done at the same time, since a difference of 5&deg; C. makes a difference of
+0.1 c.c. in measuring the 100 c.c. of strong solution of salt. It is
+always best to prepare a standard with each batch of assays.</p>
+
+<p><b>SULPHOCYANATE METHOD.</b>&mdash;Volhard's process is based upon the
+precipitation of silver in nitric acid solutions with potassium
+sulphocyanate, the finishing point being the development of a
+reddish-brown colour, produced by the action of the excess of
+sulphocyanate upon ferric sulphate. The white sulphocyanate settles
+readily, leaving the liquor clear; and a persistent brown coloration in
+the liquid indicates the finish. The assay must be carried out in the
+cold; and water free from chlorides<a name="FNanchor_16_16" id="FNanchor_16_16"></a><a href="#Footnote_16_16" class="fnanchor">[16]</a> must be used.</p>
+
+<p><i>The standard sulphocyanate of potassium</i> solution is made by dissolving
+4-1/2 or 5 grams of the salt (KCyS) in water, and diluting to 1 litre.
+100 c.c. are about equivalent to 0.5 gram of silver.<span class='pagenum'><a name="Page_122" id="Page_122">[Pg 122]</a></span></p>
+
+<p><i>The standard silver nitrate solution</i> is made by dissolving 5 grams of
+fine silver in 50 c.c. of dilute nitric acid, boiling off nitrous fumes,
+and diluting to 1 litre.</p>
+
+<p>The <i>indicator</i> is a saturated solution of iron alum, or a solution of
+ferric sulphate of equivalent strength made by titrating acid ferrous
+sulphate with potassium permanganate. Use 2 c.c. for each assay.</p>
+
+<p>The sulphocyanate solution is standardised by placing 50 c.c. of the
+silver nitrate solution in a flask with 20 c.c. of dilute nitric acid,
+diluting to 100 c.c. with water, and running in the sulphocyanate until
+the greater part of the silver is precipitated; then adding 2 c.c. of
+the ferric indicator, and continuing the titration until a reddish-brown
+colour is developed, and remains permanent after shaking continuously.
+The assay is similarly performed, the silver being used in the state of
+a nitric acid solution.</p>
+
+<p>The effect of variations in the conditions of the assay may be seen from
+the following experiments, in which 20 c.c. of standard silver nitrate
+were used:&mdash;</p>
+
+<p><b>Effect of Varying Temperature</b>:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>10&deg; C.</td><td align='left'>30&deg; C.</td><td align='left'>70&deg; C.</td><td align='left'>100&deg; C.</td></tr>
+<tr><td align='left'>Sulphocyanate reqd.</td><td align='left'>19.6 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>19.0 c.c.</td><td align='left'>18.6 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Nitric Acid</b>:&mdash;Varying nitric acid has no effect,
+except that with a fairly acid solution the finishing point is somewhat
+sharper.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Nitric acid added</td><td align='left'>5 c.c.</td><td align='left'>10 c.c.</td><td align='left'>20 c.c.</td><td align='left'>50 c.c.</td></tr>
+<tr><td align='left'>Sulphocyanate reqd.</td><td align='left'>19.6 c.c.</td><td align='left'>19.5 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.6 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Bulk</b>:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td><td align='left'>200 c.c.</td><td align='left'>300 c.c.</td></tr>
+<tr><td align='left'>Sulphocyanate reqd.</td><td align='left'>19.5 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.7 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Ammonic Nitrate</b>:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ammonic nitrate</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>Sulphocyanate reqd.</td><td align='left'>19.6 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.7 c.c.</td><td align='left'>19.9 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Silver</b>:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Silver added</td><td align='left'>1 c.c.</td><td align='left'>10 c.c.</td><td align='left'>20 c.c.</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td></tr>
+<tr><td align='left'>Sulphocyanate reqd.</td><td align='left'>1.0 c.c.</td><td align='left'>9.70 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>49.4 c.c.</td><td align='left'>99.0 c.c.</td></tr>
+</table></div>
+
+<p>This method is valuable for determining silver in salts, alloys, and
+solutions, where no more than an ordinary degree of accuracy is
+demanded. It is easy, and applicable under most of the usual conditions.
+Its greatest disadvantage is the brown coloration<span class='pagenum'><a name="Page_123" id="Page_123">[Pg 123]</a></span> produced by the
+sulphocyanate when the assay is nearly, but not quite, finished; and the
+slowness with which this is removed on shaking up with the precipitate.
+This is worse with large quantities of precipitate, and if about 1 gram
+of silver is present, it gives an indefiniteness to the finish which
+lowers the precision of the process to about 1 in 500; this is useless
+for the assays of bullion. One writer states that this inconvenience is
+due to portions of liquid being entangled in the precipitate, but it
+appears much more likely to be due to the action of the precipitate
+itself. In attempting to apply the process to the assay of bullion by
+working it on the principle of a Gay-Lussac assay, it was found that a
+very considerable excess of silver was required to complete the
+reaction. In these experiments 100 c.c. of "sulphocyanate" (very
+accurately measured) was run into the solution containing the weighed
+portion of bullion (fine silver) and, after shaking the solution, was
+filtered. In the filtrate the remaining silver, if there should be any,
+was determined by the ordinary titration, but with "sulphocyanate" of
+one-tenth the strength. This final titration was quite satisfactory. The
+amount of silver precipitated by the first 100 c.c., however, varied
+with the quantity of silver present as in the following series.<a name="FNanchor_17_17" id="FNanchor_17_17"></a><a href="#Footnote_17_17" class="fnanchor">[17]</a></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Silver present.</td><td align='left'></td><td align='left'>Silver precipitated.</td></tr>
+<tr><td align='right'>1.1342</td><td align='left'> gram.</td><td align='right'>1.1322</td><td align='left'> gram.</td></tr>
+<tr><td align='right'>1.1375</td><td align='left'>"</td><td align='right'>1.1335</td><td align='left'>"</td></tr>
+<tr><td align='right'>1.1405</td><td align='left'>"</td><td align='right'>1.1351</td><td align='left'>"</td></tr>
+<tr><td align='right'>1.1484</td><td align='left'>"</td><td align='right'>1.1379</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>These, of course, preclude a method of the kind aimed at, and at the
+same time emphasise the importance of uniformity of work in the ordinary
+process. In the determination of chlorides in sea-water, Dittmar used a
+combined method: precipitating the bulk of the silver as chloride, and
+after filtering, determining the small excess of silver by
+sulphocyanate. This modification answers admirably when applied to the
+assay of bullion. In the ordinary Gay-Lussac method, the precipitation
+of the bulk of the silver by the 100 c.c. of salt solution leaves
+nothing to be desired, either as to ease in working or accuracy of
+result; the silver precipitate settles quickly, and leaves a clear
+liquor admirably fitted for the determination of the few milligrams of
+silver remaining in solution. But the method of determining this
+residual silver by adding successive small quantities of salt so long as
+they continue to give a precipitate is unsatisfactory, and,<span class='pagenum'><a name="Page_124" id="Page_124">[Pg 124]</a></span> judged on
+its own merits apart from the rest of the process, could hardly escape
+condemnation. It is clumsy in practice, for the continued adding of
+small portions of salt solution is laborious and becomes impossible with
+more than a few milligrams of silver in solution. The proposed
+modification is simple; having precipitated the silver with the 100 c.c.
+of salt solution, as described under Gay-Lussac's method (page 120),
+shake till the liquor clears, and filter into a flask, washing with a
+little distilled water. Add 2 c.c. of "ferric indicator" to the filtrate
+and titrate with a standard "sulphocyanate solution" made by diluting
+the ordinary standard solution to such an extent that 100 c.c. after
+diluting shall be equivalent to 0.1 gram of silver.<a name="FNanchor_18_18" id="FNanchor_18_18"></a><a href="#Footnote_18_18" class="fnanchor">[18]</a> Calculate the
+weight of silver found by "sulphocyanate" and add it to the weight which
+100 c.c. of the salt solution will precipitate.</p>
+
+<p>An advantage of this modification is that an excess of 15 milligrams may
+be determined as easily and exactly as 5. In standardising the salt
+solution, then, weigh up, say 1.0150 gram of pure silver, dissolve and
+titrate. Suppose 13.5 c.c. of "sulphocyanate" required; then these are
+equivalent to .0135 gram of silver, (100 c.c. = .1); the silver
+precipitated by the salt is 1.0150-.0135&mdash;<i>i.e.</i>, 1.0015 gram, which is
+the standard.</p>
+
+<p><b>Application of the Method to Assays for Arsenic.</b>&mdash;If silver nitrate be
+added to a neutral solution of an arsenate of one of the alkali metals,
+silver arsenate (Ag<sub>3</sub>AsO<sub>4</sub>), is thrown down as a dark-red
+precipitate. If, after adding excess of silver nitrate to insure a
+complete precipitation, the arsenate of silver be filtered off, the
+weight of the arsenic could be estimated from the weight of silver
+arsenate formed. But this may be done much more conveniently by
+dissolving the precipitate in nitric acid, and titrating with
+sulphocyanate; the silver found will be to the arsenic present as 324
+(108&times;3) is to 75.</p>
+
+<p>The mineral is best treated by the method given in the third paragraph
+on page 382; but the solution, after being acidified with nitric acid,
+should be made exactly neutral with ammonia. A small excess of silver
+nitrate should then be added, and since acid is liberated in the
+reaction, the liquor must again be neutralised.<a name="FNanchor_19_19" id="FNanchor_19_19"></a><a href="#Footnote_19_19" class="fnanchor">[19]</a> The precipitate must
+then be filtered off, and washed with distilled water. Then dissolve it
+in the paper by slowly running over it 20 c.c. of dilute nitric acid.
+Wash the filter with distilled water, collecting with the filtrate in a
+small flask. Add 2 c.c. of "ferric indicator" and titrate.<span class='pagenum'><a name="Page_125" id="Page_125">[Pg 125]</a></span></p>
+
+<p>If the sulphocyanate solution be made up with 11 or 12 grams of the
+potassium salt to the litre, and be then standardised and diluted, so
+that for 100 c.c. it shall equal 1.08 gram of silver, (see p. 38), then
+it will also equal .25 gram of arsenic (As). Except for ores rich in
+arsenic, it will be better to work with a solution one half this
+strength. The standard as calculated from an experiment with pure silver
+should be checked by another using pure resublimed white arsenic,
+As<sub>2</sub>O<sub>3</sub>, which contains 75.75 % of the metal. The quantity of white
+arsenic taken, .1 or .2 gram, should contain about as much arsenic as
+will be present in the assays. It is converted into sodium arsenate by
+evaporating to a small bulk with nitric acid and neutralising with soda.
+The precipitation and titration of the silver arsenate should be exactly
+as in the assays.</p>
+
+<p>The difficulty of the method is in the neutralising; which has to be
+very carefully done since silver arsenate is soluble in even faintly
+acid solutions; one drop of nitric acid in 100 c.c. of water is enough
+to produce an absolutely worthless result; and an excess of acid much
+less than this is still very prejudicial. The addition of a little
+sodium acetate to the solution after the final neutralising has a good
+effect.</p>
+
+<p><b>Arsenic in Mispickel.</b>&mdash;Weigh up .250 gram of the finely-powdered ore,
+and place in a Berlin crucible about 1-1/4 or 1-1/2 inch in diameter.
+Treat with 10 or 12 drops, one drop at a time, of strong nitric acid,
+warm very gently, but avoid much heating. Put on a thin layer of nitre,
+and rather more than half fill the crucible with a mixture of equal
+parts of soda and nitre. Heat quickly in the blow-pipe flame, and when
+the mass is fused and effervescing, withdraw and allow to cool. Boil out
+with water, filter and wash. Insert a piece of litmus paper and
+cautiously neutralise with nitric acid, using ammonia to neutralise any
+accidental excess of the acid. Add a gram or so of ammonium nitrate and
+silver nitrate in excess, neutralise again with ammonia and add two or
+three grams of sodium acetate. Filter off the precipitate, wash and
+titrate. In the fusion care should be taken to avoid much effervescence
+(an excess of the soda mitigates this) and the operation should be
+stopped as soon as the whole has entered into fusion.</p>
+
+
+<h4>COLORIMETRIC DETERMINATION.</h4>
+
+<p>There is, properly speaking, no colorimetric method, but the following,
+which is sometimes used, is based on similar principles.<span class='pagenum'><a name="Page_126" id="Page_126">[Pg 126]</a></span> It is useful
+for the determination of small quantities of silver in substances which
+yield clear solutions with nitric acid.</p>
+
+<p>Dissolve a weighed quantity of the substance in nitric acid, and dilute
+to a definite bulk. Divide into two equal parts. To one, add a drop or
+two of dilute hydrochloric acid, stir and filter. To the other, add a
+similar amount of dilute acid, and then to the filtered portion run in
+from a burette standard silver nitrate (1 c.c. = 0.5 milligram silver)
+until the solutions are equally turbid. Calculate in the usual way.</p>
+
+
+<h4>GOLD.</h4>
+
+<p>Gold occurs in nature chiefly as metal. It always contains more or less
+silver, and, in alluvial sands, &amp;c., may be associated with platinum and
+iridium.</p>
+
+<p>Gold is insoluble in hydrochloric or nitric acid, but is dissolved by
+aqua regia or by solutions of iodine, bromine, or chlorine. It is taken
+up by mercury, forming an amalgam, from which the mercury may be driven
+off by heat.</p>
+
+<p>When gold occurs in particles of any size, it is readily detected by its
+appearance, but when finely disseminated through a large quantity of
+rock, it is separated and detected by the amalgamation assay&mdash;described
+below&mdash;or by a process of washing somewhat similar to vanning, or by the
+following test:&mdash;Powder and, if necessary, roast 50 to 100 grams of the
+ore, put on it three or four crystals of iodine and enough alcohol to
+cover it; allow to stand for half an hour; a piece of filter paper
+moistened with the liquid and burnt leaves an ash with a distinctly
+purple tint if any gold is present. It is better, however, to filter off
+the solution, evaporate, and ignite. Then, either take up with mercury,
+and ignite the amalgam so as to get a speck of the metallic gold; or
+treat with a few drops of aqua regia, and test the solution with
+stannous chloride: a purple coloration indicates gold.</p>
+
+<p><b>AMALGAMATION ASSAY.</b>&mdash;This does not attempt to give the total produce
+of gold, but rather the quantity which can be extracted on a large
+scale; therefore it should imitate as closely as possible the process
+adopted in the mine or district for extracting the metal.</p>
+
+<p>Take 2 lbs of the ore in powder and roast; make into a stiff paste with
+hot water and rub up for an hour or so with a little mercury. Wash off
+the sand carefully, and collect the amalgam. Drive off the mercury by
+heat, and weigh the residual gold. It is best to cupel it with lead
+before weighing.<span class='pagenum'><a name="Page_127" id="Page_127">[Pg 127]</a></span></p>
+
+<p>In an experiment on a lot of ore which contained 0.189 gram of gold,
+0.179 gram was obtained by the above process, equal to about 94-1/2 per
+cent. recovered. With ores generally, the yield may be from 80 to 90 per
+cent. of the actual gold present.</p>
+
+
+<h4>DRY ASSAY.</h4>
+
+<p>The dry assay of gold ores resembles in its main particulars the dry
+assay for silver by the crucible method; and for much that is of
+importance in its discussion the student is referred to what is written
+under Silver on pp. 90-113.</p>
+
+<p><b>Size of Assay Charges.</b>&mdash;Gold ores rarely contain more than a few
+ounces, often only a few pennyweights of gold to the ton; consequently,
+the button of gold obtainable from such quantities of ore as may be
+conveniently worked by assaying methods is often so small as to require
+more than ordinary care in its manipulation. One milligram of gold forms
+a button of about the size of one of the full-stops on this page, and
+compared with a million similar particles of quartz (about four ounces),
+represents a produce of a quarter of an ounce to the ton: a proportion
+such as the assayer is frequently called on to determine. It is evident,
+therefore, that a charge of half an ounce or less of the ore, such as is
+usual with silver ores, would demand of the worker both skill and care
+in the handling of the minute quantity of gold to be obtained from it.
+Fortunately the work is simple and precise, so that in practised hands
+and with only a 5-gram charge the assay of a 5-dwt. ore is practicable;
+with so small a charge, however, the result is barely perceptible on a
+sensitive balance: the button of gold should be measured under a
+microscope. It follows, therefore, that larger charges of say 50, 100,
+or even 200 grams, have an advantage in that they lessen the strain on
+the worker's attention, and, except in the case of the poorest mineral,
+bring the button of gold within the scope of the balance. On the other
+hand, the inconvenience of the larger charges lies in the amount of
+fluxes and consequent size of the crucibles required to flux them.</p>
+
+<p><b>Sampling.</b>&mdash;A further consideration in favour of the larger charges is
+the matter of sampling. In preparing his ore, the student should ask
+himself what reasonable expectation he has that the portion he puts in
+the furnace will be of average richness. The larger charges are likely
+to be nearer than the smaller ones to the average of the parcel of ore
+from which they are taken. In explanation of this, let us suppose a
+large<span class='pagenum'><a name="Page_128" id="Page_128">[Pg 128]</a></span> heap of 5-dwt. ore, in sand of the coarseness of full-stops, and
+containing all its gold in particles of 1 milligram, as uniformly
+distributed as care and labour in the mixing can accomplish. Such a heap
+could not possibly occur in practice, but it will serve for purposes of
+illustration. Now, one ton of the sand, however taken, would contain
+appreciably the same quantity of gold as any other ton. For a ton would
+contain about 8000 particles of gold; and even if two separate tons
+differed by as much as 100 particles (which they are just likely to do),
+this would mean only a difference of 1 or 2 grains to the ton. On the
+other hand, two portions of 14 lbs., which should contain on the average
+50 particles of gold, are likely enough to differ by 10 particles, and
+this, calculated on a ton, means a difference of 1 dwt. It is easy to
+see that something like this should be true; for on calculating the
+14-lb. lot up to a ton, the deviation from the average, whatever it may
+be, is multiplied by 160; whereas, if the ton were made up by adding
+14-lb. lot to 14-lb. lot, up to the full tale, then a large proportion
+of the errors (some being in excess and some in defect) would neutralise
+each other. An average which is practically true when dealing with
+thousands, and perhaps sufficiently exact with hundreds, would be merely
+misleading when applied to tens and units. Reasonable safety in
+sampling, then, is dependent largely on the number of particles of gold
+in the charge taken, and the risk of an abnormal result is less, the
+larger the charge taken.</p>
+
+<p>By doubling the charge, however, we merely double the number of
+particles. Powdering finely is much more effective; for, since the
+weight of a particle varies as the cube of the diameter, halving the
+diameter of the particles increases their number eight-fold. If, now, we
+modify our illustration by assuming the particles to have only one-sixth
+the diameter of a full-stop (which would represent a powder of a
+fineness not unusual in ores prepared for assaying), we should multiply
+the number of particles by 200 (6 &times; 6 &times; 6 = 216). We should then
+reasonably expect a 14-lb. parcel of the powder to give as safe a sample
+as a ton of the sand would give; and portions of a size fit for crucible
+work, say 50 or 100 grams, would be as safe as 10 or 20-lb. samples of
+the coarser stuff. For example, 60 grams of such powder would contain,
+for a 5-dwt. ore, about 100 particles; and in the majority of cases the
+error due to sampling would be less than 10 or 12 grains to the ton, and
+would only occasionally exceed a pennyweight. With richer ores the
+actual deviation stated as so much to the ton of ore might be greater,
+but it would represent a smaller proportion, stated in percentage of
+the<span class='pagenum'><a name="Page_129" id="Page_129">[Pg 129]</a></span> gold actually present, and would ultimately fall within the limits
+of unavoidable error.</p>
+
+<p>It will be seen that the size of the quartz particles has no direct
+bearing on the argument; and, in fact, the coarseness of the quartz only
+interferes by preventing the uniform mixing of the sand and by binding
+together several particles of gold; in this last case, particles so
+united must, of course, count as one larger particle. Now, there are
+some natural ores in which the gold particles are all very small; with
+these fine powdering and mixing yields a product from which a sample may
+be safely taken. Then, again, in "tailings," before or after treatment
+with cyanide, we have a similar material, inasmuch as the coarser gold
+has been removed by previous amalgamation. With these, it is not unusual
+to take the portion for assay without any further powdering, since they
+are poor in gold, and have already been stamped and passed through a
+sieve of say thirty holes to the inch (linear).</p>
+
+<p>But there are other ores, in lump showing no visible gold, which contain
+the gold in all possible degrees of fineness, from say prills of a
+milligram or so down to a most impalpable powder. The treatment of these
+cannot be so simple and straightforward. Suppose a parcel of 1000 grams
+(say 2 lbs.) of such ore in fine powder, containing on an average 1
+particle of 1 milligram (the presence or absence of which makes a
+difference of .6 dwt. on the ton), 10 others of about .5 milligram (each
+representing .3 dwt.), and 100 others, which are too coarse to pass
+through an 80 sieve, and having an average weight of .1 milligram (each
+.06 dwt.), and that the rest of the gold, equivalent altogether to 2
+ounces to the ton, is so finely divided that a charge of 50 grams may be
+taken without any considerable risk of its interfering with the
+sampling. Then in a 50-gram charge there would be one chance in twenty
+of getting the milligram particle, in which case the result would be
+12.35 dwts. too high; on the other hand, if it were not present the
+result would on this account be .65 dwt. too low. Of the ten
+.5-milligram particles, it is as likely as not that one will be present,
+and its presence or absence would cause an error of 3.3 dwts., more or
+less. Of the 100 particles of .1 milligram, there would probably be from
+3 to 7, instead of 5, the proper number; this would mean a variation of
+2.6 dwts. from the true proportion. So that the probable result would
+range about 5 dwts. more or less than the 2-1/2 ozs., which is the true
+produce, and there are possibilities of astounding results. It is true
+that the majority of the results would be well within these limits, and
+now and again the heart of the student would be gladdened by a beautiful
+concordance in<span class='pagenum'><a name="Page_130" id="Page_130">[Pg 130]</a></span> duplicate assays; nevertheless, there can be no
+reasonable expectation of a good assay, and to work in this way, on a
+50-gram charge, would be to court failure. The coarse gold must ruin the
+assay.</p>
+
+<p>The difficulty may be met by concentrating the whole of the coarse gold
+in a small fraction of the ore, by sifting and making a separate assay
+of this fraction. A portion of the ore, of about 1000 grams, is ground
+to a very fine powder and passed through an 80 sieve, re-grinding when
+necessary, until only 20 or 30 grams is left of the coarser powder. This
+is mixed with fluxes and carried through as a separate assay. The sifted
+portion is <i>thoroughly mixed</i>, and a portion of it, say 30 or 50 grams,
+taken for assay. The weights of the two portions must be known, and care
+must be taken that nothing is lost in the powdering. The method of
+calculating the mean result from the two assays is shown on page 109. In
+this way of working there is no advantage in continuing the grinding
+until the coarser fraction is reduced to a gram or so&mdash;rather the
+contrary; and rubbing on until all the gold is sent through the sieve is
+to be distinctly avoided. The student must bear in mind that what he is
+aiming at is the exclusion of all coarse gold from the portion of ore of
+which he is going to take only a fraction.</p>
+
+<p>The question of the smaller sampling of gold ores has been dwelt on at
+considerable length, as befits its importance, in order that the student
+may be impressed with a sense of its true meaning. Sampling is not a
+mystery, nor does the art lie in any subtle manner of division. It is,
+of course, absolutely necessary that the stuff to be sampled shall be
+well mixed, and the fractions taken, so that each part of the little
+heap shall contribute its share to the sample. Moreover, it must be
+remembered that tossing about is a poor sort of mixing, and that
+everything tending to separate the large from the small, the light from
+the heavy, or the soft from the hard (as happens in sifting), must be
+avoided, or, if unavoidable, must be remedied by subsequent mixing.</p>
+
+<p>With a well-taken sample, we may rely on a great majority of our results
+falling within normal limits of error; but nothing can be more certain
+than that, in a moderately large experience we shall get, now and again,
+deviations much more considerable. These erratic assays can only be met
+by the method of working duplicates, which call attention to the fault
+by discordant results. Such faulty assays should be repeated in
+duplicate, so that we may rest the decision on three out of four
+determinations.</p>
+
+<p>The likelihood of two very faulty assays being concordant is<span class='pagenum'><a name="Page_131" id="Page_131">[Pg 131]</a></span> remote;
+but with very important work, as in selling parcels of ore, even this
+risk should be avoided, as concordance in these cases is demanded in the
+reports of two or more assayers. The following actual reports on a
+disputed assay will illustrate this: (<i>a</i>) 5 ozs. 1 dwt.; (<i>b</i>) 5 ozs.
+10 dwts. 12 grains; (<i>c</i>) 5 ozs. 11 dwts.; (<i>d</i>) 5 ozs. 11 dwts. 12 grs.
+The mean result of several assays, unless there be some fault in the
+method, will be very fairly exact; and individual assays, with an
+uncertainty of 1 in 20, may, by repetition, have this reduced to 1 in
+100 or less.</p>
+
+<p><b>Assay Tons, etc.</b>&mdash;Having decided on taking a larger or smaller
+portion, the exact quantity to be used will be either some round number
+of grams, such as 50 or 100, easily calculable into percentage; or it
+will be that known as the "Assay Ton" (see page 13) or some simple
+multiple or fraction of it, which is easily calculable into ounces. The
+reports, too, are at least as often made as ounces in the short ton of
+2000 lbs., as on the more orthodox ton of 2240 lbs. Now the short ton is
+equal to 29,166.6 troy ounces; and the corresponding "assay ton" is got
+from it by replacing ounces by milligrams. The advantage of its use is
+that if one assay ton of ore has been taken, the number of milligrams of
+gold obtained is also the number of ounces of gold in a ton of the ore,
+and there is absolutely no calculation. Even if half an assay ton has
+been taken the only calculation needed is multiplying the milligrams by
+two. On the other hand with a charge of two assay tons the milligrams
+need halving. Where weights of this kind (<i>i.e.</i>, assay tons) are not at
+hand they may be easily extemporised out of buttons of tin or some
+suitable metal, and it is better to do this than to array out the grams
+and its fractions at each weighing. The sets of "assay tons," however,
+are easily purchased. As stated on page 13, the assay ton for 2240 lbs.
+is 32.6667 grams; and for the short ton, 29.1667 grams. If, however, the
+round number of grams be used and the result brought by calculation to
+the produce on 100 grams, the conversion to ounces to the ton may be
+quickly effected by the help of the table on page 107. As this table
+only deals with the ton of 2240 lbs., it is supplemented here by a
+shortened one dealing only with <i>the produce of 100 grams</i> and stating
+the result in <i>ounces troy to the short ton of 2000 lbs</i>.</p>
+
+<p><b>Estimation of Small Quantities of Gold.</b>&mdash;<i>By the Balance.</i> In
+estimating minute quantities of gold there are one or two points, of
+importance to an assayer only in this assay, where they will often allow
+one to avoid the working of inconveniently large charges. One of these
+is known as "weighing by the method of<span class='pagenum'><a name="Page_132" id="Page_132">[Pg 132]</a></span></p>
+
+<p class="center"> TABLE FOR CALCULATING OUNCES TO THE SHORT TON FROM THE
+                    YIELD OF GOLD FROM 100 GRAMS OF ORE.</p>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Milligram.</td><td align='left'>Ounces to the Ton.</td><td align='left'>Milligram.</td><td align='left'>Ounces to the Ton.</td><td align='left'>Milligram.</td><td align='left'>Ounces to the Ton.</td></tr>
+<tr><td align='left'>0.01</td><td align='left'>0.003</td><td align='left'>0.4</td><td align='left'>0.117</td><td align='left'>7.0</td><td align='left'>2.042</td></tr>
+<tr><td align='left'>0.02</td><td align='left'>0.006</td><td align='left'>0.5</td><td align='left'>0.145</td><td align='left'>8.0</td><td align='left'>2.333</td></tr>
+<tr><td align='left'>0.03</td><td align='left'>0.009</td><td align='left'>0.6</td><td align='left'>0.175</td><td align='left'>9.0</td><td align='left'>2.625</td></tr>
+<tr><td align='left'>0.04</td><td align='left'>0.012</td><td align='left'>0.7</td><td align='left'>0.204</td><td align='left'>10.0</td><td align='left'>2.916</td></tr>
+<tr><td align='left'>0.05</td><td align='left'>0.014</td><td align='left'>0.8</td><td align='left'>0.233</td><td align='left'>20.0</td><td align='left'>5.833</td></tr>
+<tr><td align='left'>0.06</td><td align='left'>0.017</td><td align='left'>0.9</td><td align='left'>0.262</td><td align='left'>30.0</td><td align='left'>8.750</td></tr>
+<tr><td align='left'>0.07</td><td align='left'>0.020</td><td align='left'>1.0</td><td align='left'>0.292</td><td align='left'>40.0</td><td align='left'>11.666</td></tr>
+<tr><td align='left'>0.08</td><td align='left'>0.023</td><td align='left'>2.0</td><td align='left'>0.583</td><td align='left'>50.0</td><td align='left'>14.583</td></tr>
+<tr><td align='left'>0.09</td><td align='left'>0.026</td><td align='left'>3.0</td><td align='left'>0.875</td><td align='left'>60.0</td><td align='left'>17.500</td></tr>
+<tr><td align='left'>0.10</td><td align='left'>0.029</td><td align='left'>4.0</td><td align='left'>1.167</td><td align='left'>70.0</td><td align='left'>20.416</td></tr>
+<tr><td align='left'>0.20</td><td align='left'>0.058</td><td align='left'>5.0</td><td align='left'>1.458</td><td align='left'>80.0</td><td align='left'>23.333</td></tr>
+<tr><td align='left'>0.30</td><td align='left'>0.087</td><td align='left'>6.0</td><td align='left'>1.750</td><td align='left'>90.0</td><td align='left'>26.250</td></tr>
+</table></div>
+
+
+<p>vibrations." Suppose a balance at rest in perfect equilibrium, with the
+pointer exactly over the middle point of the scale. Let the scale be a
+series of points at equal distances along a horizontal line; then, if a
+small weight be placed on one pan, the pointer will deviate from its
+vertical position and come to rest opposite some definite part of the
+scale, which will depend upon the magnitude of the weight added. The law
+determining this position is a very simple one; the deviation as
+measured along the points of the scale varies directly as the weight
+added. For example, with an ordinarily sensitive balance, such as is
+used for general purposes, one milligram will move the pointer along,
+say, three divisions of the scale; then two milligrams will move it six
+divisions; half a milligram, one and a half divisions; and so on. Of
+course, with a more sensitive balance the deviations will be greater.
+Now the point at which the needle comes to rest is also the middle point
+about which it vibrates when swinging. For example, if the needle swings
+from the third to the seventh division on the right then [(7+3)/2] it
+will come to rest on the fifth. In working by this method the following
+conventions are useful: Always place the button to be weighed on the
+left pan of the balance, the weights on the right; count the divisions
+of the scale from the centre to right and left, marking the former + and
+the latter -; thus -5 is the fifth division to the left. Then the
+position of rest is half the algebraic sum of two readings. For example,
+let the readings be 7 to the right and 3 to the left, then (+7-3)/2 =
++2. The mean division is the second division<span class='pagenum'><a name="Page_133" id="Page_133">[Pg 133]</a></span> to the right. If the
+student will place himself in front of a balance and repeat the
+following observations and replace the figures here given by his own, he
+will have no difficulty in grasping the method. First determine the
+<i>bias</i> of the balance; suppose the unloaded balance swings +1.25 and -1;
+the bias then is (1.25-1)/2 = +.125 or one-eighth of a division to the
+right. Now having put on the button to be weighed let the readings be
++7.5 and +9.25, and (7.5+9.25)/2 = +8.375. Then the effect of the button
+has been to move the pointer from +.125 to +8.375, or 8.25 divisions to
+the right; we should, therefore, add the weight equivalent of 8.25
+divisions to the weights, whatever they may be on the right hand pan of
+the balance; if the divisions were to the left (- divisions) we should
+subtract. The value of 1 division is easily determined. Suppose the
+button in the example were a 1 milligram weight, then we should have
+found that 1 milligram = 8.25 divisions &#8756; 1 division = .121 milligram.
+This method of working adds very considerably to the power of a balance
+in distinguishing small quantities.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig044a.jpg" width="300" height="380" alt="Fig. 44a." title="" />
+
+</div>
+
+<p><i>By the Microscope</i>.&mdash;The use of the microscope also is a real advantage
+in estimating the weights of minute buttons of gold where there is no
+undue risk in sampling, and where an error of say 1 in 20 on the
+quantity of gold is tolerable. For ores with copper, lead, zinc, &amp;c., as
+well as for tailings rather poor in gold, this leaves a wide field of
+usefulness. The method is described on page 440, but the description
+needs supplementing for those who are not accustomed to the use of a
+microscope. The eye-piece of a microscope (fig. 44<i>a</i>, A) unscrews at
+<i>a</i>, showing a diaphragm at <i>b</i>, which will serve as a support for an
+eye-piece micrometer. This last, B, is a scale engraved on glass, and
+may be purchased of any optical instrument maker, though it may be
+necessary to send the eye-piece to have it properly fitted. When resting
+on the diaphragm it is in focus for the upper lens, so that on looking
+through the microscope, the scale is clearly seen in whatever position
+the instrument may be as regards the object being looked at. Suppose
+this to be a small button of gold on a shallow, flat watch-glass, on the
+stage of the microscope. Bring the button under the "objective" (<i>i.e.</i>,
+the nose of the microscope), which should be about a quarter of an inch
+above the watch-glass; then looking through the instrument, raise the
+tube until the button of gold, or at least some dust on the glass, comes
+into focus. If the button is not in the field, rest the thumbs and index
+fingers, using both hands, on the edge of the watch-glass, pressing
+lightly but steadily, and give the glass a slow, short, sweeping motion;
+the button will perhaps appear as an ill-defined blackness, because<span class='pagenum'><a name="Page_134" id="Page_134">[Pg 134]</a></span> not
+quite in focus. Bring this into the centre of the field. Raise or lower
+the microscope until the button appears with sharp outlines. If the
+scale does not cover the button, rotate the eye-piece; this will bring
+the scale into a new position. Since the divisions over the button are
+less distinct than the others, it is best to read the latter. Thus, in
+fig. 44<i>b</i>, there are 36 divisions on one side of the button, and 35 on
+the other, making altogether 71. The whole scale is 80, therefore the
+diameter of the button is 9 divisions. The value of each division
+obviously varies with the magnifying power employed. With most
+microscopes there is a telescopic arrangement whereby the tube may be
+lengthened; if this be done and the button again brought in focus, it
+will be seen that, as measured on the scale, the button is much larger
+than before. It is evident, therefore, the micrometer must always be
+used in the same way. The method given in the appendix (page 440), for
+finding the value of the scale when gold buttons are to be measured is
+easy and satisfactory. When the button of gold is so small that there is
+considerable risk of losing<span class='pagenum'><a name="Page_135" id="Page_135">[Pg 135]</a></span> it in transferring to a watch-glass, it may
+be measured on the cupel, but for this purpose it must be well
+illuminated; this is best done by concentrating light on it with a lens,
+or with what comes to the same thing, a clean flask filled with water.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig044b.jpg" width="300" height="350" alt="Fig. 44b." title="" />
+
+</div>
+
+<p>Most assayers, however, using a micrometer in this way, would like to
+know its absolute value. To do this, a stage micrometer must be
+purchased. This is like an ordinary microscope slide (fig. 44<i>a</i>, C),
+and when looked at through a microscope it shows (fig. 44<i>c</i>) lines
+ruled on the glass at distances of tenths and hundredths of a
+millimetre, ten of each, so that the full scale is 1.1 mm. In the case
+illustrated, 60 divisions of the scale in the eye-piece are just equal
+to the 1.1 mm., therefore 1 division equals .0183 mm. A cube of this
+diameter would contain (.0183&times;.0183&times;.0183) .0000061285 cubic mm. The
+corresponding sphere is got by multiplying by .5236; this gives
+.000003209 cb. mm. The weight of 1 cb. mm. of water is 1 milligram; and,
+since gold is 19.2 times as heavy as water (sp. g. = 19.2), the contents
+in cb. mm. must be multiplied by 19.2. This gives .0000616 milligram as
+the weight of a sphere of gold measuring 1 division.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig044c.jpg" width="300" height="329" alt="Fig. 44c." title="" />
+
+</div>
+
+<p>If every result had to be calculated in this way the method would be
+very laborious; but, having the figures for the first division, those of
+the others may be calculated by multiplying by the cube of<span class='pagenum'><a name="Page_136" id="Page_136">[Pg 136]</a></span> the
+corresponding number. Thus, for the third division (3&times;3&times;3 = 27), the
+content of the cube (.0000061285&times;27) is .0001655 cb. mm.; the content of
+the sphere (.000003209&times;27) is .0000866 cb. mm.; and the corresponding
+sphere of gold (.0000616&times;27) is .00166 milligram. With the help of a
+table of cubes the whole calculation for 25 or 30 divisions may be made
+in half an hour, and the results preserved in the form of a table will
+simplify all future work.</p>
+
+<p><b>Assay Operations.</b>&mdash;The actual work of the assay resolves itself into
+three operations:&mdash;(1) The fusion of the ore and concentration of the
+"fine metal" (<i>i.e.</i>, gold and silver) in a button of lead; (2) The
+cupellation of the lead, whereby a button of fine metal is obtained; and
+(3) the "parting" of the gold which separates it from the accompanying
+silver. The following description takes the order as here given, but the
+student, in learning the method, should first practise cupellation if he
+has not already done so; next he should practise the separation of gold
+from silver, taking known weights of fine gold (p. 63), varying from .5
+or .3 gram down to quite minute quantities, and not resting satisfied
+until a sensitive balance can barely distinguish between the weights of
+gold taken and found. It may be noted here that if he has not a flatting
+mill at his disposal, then for large buttons it is better to make an
+alloy with eight or nine parts of silver to one of gold, and attack it
+with acid without previous flattening, rather than accept the risk and
+labour of beating out a less easily attacked alloy to the necessary
+thinness with a hammer. It is only after a sense of security in gold
+parting has been acquired, that the attack of an ore can be profitably
+accomplished, and even then simple and easy ores should be first taken,
+passing on to others more difficult, either because of a more complex
+mineral composition or a difficulty in sampling.</p>
+
+<p><b>Concentration of the fine Metal in Lead.</b>&mdash;The best flux for quartz,
+which makes up the earthy matter of most gold ores, is soda, and this is
+best added as carbonate or bicarbonate. By theory,<a name="FNanchor_20_20" id="FNanchor_20_20"></a><a href="#Footnote_20_20" class="fnanchor">[20]</a> 50 grams of
+quartz will require 88.5 grams of the carbonate, or 140 grams of the
+bicarbonate, to form sodium silicate, which is a glassy, easily-fusible
+substance, making a good slag. If the bicarbonate is used, and heat is
+applied gradually, steam and carbonic acid are given off at a
+comparatively low temperature, and the carbonate is left; at a higher
+temperature (about 800&deg; C., or a cherry-red heat) the carbonate fuses
+attacking<span class='pagenum'><a name="Page_137" id="Page_137">[Pg 137]</a></span> the quartz, and giving off more carbonic acid; as the heat
+increases, and the attack on the quartz (which of itself is infusible)
+becomes complete, the whole mass settles down to a liquid sodium
+silicate, which is sufficiently fluid to allow the gold and lead to
+settle to the bottom. The fluid slag does to a certain extent dissolve
+some of the crucible, but not seriously. In a perfect working of this
+experiment, the first evolution of gases (steam and carbonic acid)
+should be gentle, so as to run no risk of its blowing the fine powder
+out of the crucible; and the heat at which the second evolution of
+carbonic acid is produced should be maintained until the reaction is
+completed, so that there may be little or no formation of gas in the
+fused mass to cause an effervescence which may force some of the charge
+over the edges of the crucible. Of course, in practice the ideal fusion
+is not attained, but there is no difficulty in approaching it closely
+enough to prevent the charge at any time rising above the level it
+reached at first in the crucible, and this should be accomplished. It is
+usual with quartzose ores to rely mainly on the action of carbonate of
+soda, but not entirely. Litharge is also used; it forms, on fusion with
+quartz, a silicate of lead, which is a yellow glass, easily fusible, and
+more fluid in the furnace than silicate of soda is. By theory, 50 grams
+of quartz would require 186 grams of litharge.<a name="FNanchor_21_21" id="FNanchor_21_21"></a><a href="#Footnote_21_21" class="fnanchor">[21]</a> The reaction takes
+place without evolution of gas, and in its working the only point is to
+so regulate the heat that the litharge shall not fuse and drain under
+the unattacked quartz, leaving it as a pasty mass on the surface. Now,
+if in making up a charge for 50 grams of ore, we took 100 grams of
+bicarbonate of soda (equivalent to about 63 grams of the carbonate),
+this being five-sevenths of 140 grams (which by itself would be
+sufficient), leaves two-sevenths of the quartz to be fluxed by other
+reagents: two-sevenths of 186 grams (say 52 grams) of litharge would
+serve for this purpose. But if we used 10 grams of borax, which has a
+fluxing action about equal to that of the litharge, then 40 grams of the
+latter, or (making an allowance for the quartz being not quite pure) say
+35 grams, will suffice. The fluxes, then, for the 50 grams of ore would
+be: bicarbonate of soda 100 grams, litharge 35 grams, and borax 10
+grams; we could decrease any of these, and proportionately increase
+either or both of the others, and still rely on getting a fusible slag,
+which is the whole of the function of a flux, considered simply as a
+flux. It should be remembered, however, that the slag is a bi-silicate
+or acid slag, and that its acid character is increased by increasing the
+proportion of borax.</p>
+
+<p><span class='pagenum'><a name="Page_138" id="Page_138">[Pg 138]</a></span></p><p>But in addition to the fluxes there is required about 30 or 40 grams of
+lead to collect the silver and gold. This is best added as litharge (say
+40 grams) and flour (4 grams), or charcoal powder (2 grams). See pages
+93 and 94. The full charge, then, would be:</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ore</td><td align='left'>50</td><td align='left'>grams.</td></tr>
+<tr><td align='left'>Bicarbonate of soda</td><td align='left'>100</td><td align='left'>"</td></tr>
+<tr><td align='left'>Litharge</td><td align='left'>75</td><td align='left'>"</td></tr>
+<tr><td align='left'>Borax</td><td align='left'>10</td><td align='left'>"</td></tr>
+<tr><td align='left'>Flour</td><td align='left'>4</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>These should be mixed, placed in a suitable crucible (a G Battersea,
+round, will do), and heated, at first at a red heat, but finally much
+hotter, so as to get a fluid and clean slag. When the charge has been in
+tranquil fusion for some little time, take it out and pour it into an
+iron mould. When cold, detach the button of lead. The slag should be
+glassy, all through alike, and easily separable from the metal. With
+ordinary ores, this slag may be considered as free from gold. In an
+experiment in which 90 milligrams of gold were added, the full amount
+was obtained from the lead produced by the first fusion. But in certain
+cases, more especially where large amounts of metallic oxides are
+present, the slag is not so clean, and with these the slag should be
+powdered, mixed with 40 grams of litharge and 4 of flour, and melted
+again; it is an advantage to add a small prill of say 2 or 3 milligrams
+of silver to the charge, as it insures a visible product in the
+cupellation. Indeed, this last precaution is a good one to be taken
+wherever there is reason to expect very small buttons. It has the
+further advantage, that, if the quantity of silver necessary for
+inquartation is known, the right quantity may be added here, so as to
+save a subsequent operation.</p>
+
+<p><b>Ores containing Oxides of Iron.</b>&mdash;Of the metallic oxides likely to be
+present in a slag, oxide of iron is the most important. Gold is
+occasionally found in a matrix of this substance, and in the assay of
+"concentrates" largely made up of pyrites, this oxide will be formed in
+the preliminary calcination. Now, the lower oxide of iron (ferrous
+oxide, FeO) is easy to deal with; fused borax will dissolve about its
+own weight of it, and a silicate of soda (such as makes up the bulk of a
+slag in a gold assay) will take up at least half as much. But the higher
+oxide (ferric oxide, Fe<sub>2</sub>O<sub>3</sub>) is more refractory; even 6 parts of
+borax yields a poor product, and slags with any considerable percentage
+of it are not satisfactory. A student attempting to recover gold from
+some h&aelig;matite (in which there was about half an ounce of the metal),
+found in the slag nearly a gram of gold, although in the first<span class='pagenum'><a name="Page_139" id="Page_139">[Pg 139]</a></span> fusion
+the slag appeared perfectly fluid. There is, however, no difficulty in
+getting good slags, even with large quantities of iron. For example,
+with 50 grams of ferric oxide, 10 of quartz, 30 of borax, 30 of
+soda,<a name="FNanchor_22_22" id="FNanchor_22_22"></a><a href="#Footnote_22_22" class="fnanchor">[22]</a> 50 of litharge, and 7 of flour, the result was quite
+satisfactory. So, too, was 25 of quartz, 50 of soda, 50 of litharge, and
+7 of flour. It is well, however, in such cases to have an ample
+proportion of flux and to aim at a larger button of lead than usual by
+increasing the proportion of flour or charcoal (see also page 91). A
+charge used on the Randt for roasted "concentrates" (which we may
+roughly speak of as quartz and ferric oxide), is one assay ton (about 30
+grams) each of ore, soda, and borax, and one and a half assay ton of
+litharge and 2 grams of charcoal. Whilst, for the same material, from
+which most of the gold has been extracted by "chloridising," 2.5 tons
+each of ore, borax, and soda, 4 of litharge, and 4 grams of charcoal are
+needed. This quantity requires a large crucible (I Battersea, round). In
+this the proportion of silicate of soda and borax counted together is to
+the oxide of iron as 4 to 1, on the supposition that the quartz and
+oxide of iron of the ore are in about equal quantities; but, in the
+larger charge especially, much oxide of lead would also remain as a
+flux.</p>
+
+<p><b>Ores containing Sulphides.</b>&mdash;In assaying ores containing a large
+proportion of pyrites or mispickel, or both, the best plan is to take a
+portion and calcine so as to convert it into a product of the kind just
+considered. The weighed portion of ore should be placed in a clean
+crucible and be heated to incipient redness: with pyrites the first
+effect is to drive off about half the sulphur as vapour which burns as
+flame over the ore. At this stage care should be taken that there is no
+great increase of temperature, otherwise there may be more or less
+fusion, which would spoil the operation. When the sulphur flame ceases
+the solid sulphide of iron burns with visible incandescence and the
+charge should now be stirred with a flattened iron rod so as to expose
+fresh portions to the air. The top of the furnace must be open, so that
+air may have free access to the crucible. When stirring is no longer
+followed by visible burning the heat may be raised to full redness. The
+crucible is then lifted out (the stirrer still resting in it) and if the
+charge gives off no odour of burning sulphur it is shaken out into an
+iron mortar and mixed with the fluxes, taking care to clean the stirrer
+in the mixture. The charge is then replaced in the crucible in which the
+roasting was done and fused in the furnace. The resulting button of lead
+is cupelled for fine metal. Ores rich in sulphides requiring this
+treatment are frequently<span class='pagenum'><a name="Page_140" id="Page_140">[Pg 140]</a></span> "concentrates." For their assay take 1 assay
+ton (30 grams), calcine and mix with an equal weight of soda and of
+borax (30 grams each), and half as much again of litharge (1.5 tons or
+45 grams), and with 2 grams of charcoal or 5 grams of flour.</p>
+
+<p>Where the sulphides are present in smaller proportion (10 per cent. or
+less), they may be taken as serving the purpose of flour or charcoal
+(see page 95); the sulphur and iron are oxidised at the expense of the
+litharge with a consequent separation of lead as metal. If the
+proportion of sulphides is not sufficient to give a large enough button
+of lead, some charcoal or flour should be added. On the other hand, if
+they are in small excess and give a button of lead somewhat sulphury,
+<i>i.e.</i>, hard and brittle, it may be remedied by the judicious addition
+of nitre; this last reagent, however, should not be used in large
+quantity. A plan much used to prevent sulphury buttons is to insert an
+iron rod or a nail in the charge in the crucible; the iron takes the
+sulphur forming sulphide of iron which in moderate quantity does not
+form a separate layer of matte but dissolves in the slag. A slag formed
+of 50 grams of quartz, 100 soda, and some borax, may take up in this way
+some 10 or 12 grams of sulphide of iron. If, however, an ore gives a
+layer of matte or speise, it is best to repeat the assay by the method
+of calcining before fusion.</p>
+
+<p><b>Cyanide Charges, etc.</b>&mdash;In assaying the "tailings" which are to be
+treated in a cyaniding plant the following charge is used:</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Tailings</td><td align='left'>3</td><td align='left'>assay tons or</td><td align='left'>100</td><td align='left'>grams.</td></tr>
+<tr><td align='left'>Litharge</td><td align='left'>4.5</td><td align='center'>"</td><td align='left'>150</td><td align='center'>"</td></tr>
+<tr><td align='left'>Soda</td><td align='left'>4.5</td><td align='center'>"</td><td align='left'>150</td><td align='center'>"</td></tr>
+<tr><td align='left'>Borax</td><td align='left'>.75</td><td align='center'>"</td><td align='left'>25</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>The sand is assayed without any further crushing and the assay is made
+in duplicate.</p>
+
+<p>The residues after treatment with cyanide, differing from the tailings
+merely in being poorer in gold because of the extraction by the solution
+of cyanide, are run down with the same fluxes in the same relative
+proportions. But four charges of 2.5 assay tons (say 75 grams) are
+worked, and two of the resulting buttons are scorified together and then
+cupelled, etc., so as to give duplicate assays on charges of 5 assay
+tons. This is one of the cases in which it is desirable to add a small
+portion of silver before cupelling.</p>
+
+<p>In assaying the "cyanide liquors" for gold, 2 assay tons of the liquor
+are measured out (58.3 c.c. for the ton of 2000 lbs., 65.3 c.c.<span class='pagenum'><a name="Page_141" id="Page_141">[Pg 141]</a></span> for the
+other) and are evaporated to dryness in a lead dish weighing about 35
+grams. Such a dish is easily extemporised out of a piece of lead foil,
+if the ordinary vessel is not at hand; but care must be taken that the
+lead is free from gold. The dish with the dried residue is then
+scorified and the resulting button of lead is cupelled.</p>
+
+<div class="figcenter" style="width: 248px;">
+<img src="images/fig044d.jpg" width="248" height="450" alt="Fig. 44d." title="" />
+
+</div>
+
+<p>In some cases the fusion of the ore may be replaced by a treatment with
+solution of cyanide of potassium and the gold recovered from the
+solution in the way just described. For this purpose the ore should be
+in not too fine powder, otherwise there will be great difficulty in
+filtering; a sand which will pass a 30 sieve and having no large
+proportion of very fine stuff will do. Not less than 200 grams should be
+taken; and as an extraction apparatus a bell jar capable of holding half
+as much again may be used. Such a jar may be extemporised by cutting off
+the bottom of a bottle by leading a crack around it with a red hot
+poker; or a lamp chimney will serve the purpose. The smaller mouth of
+the jar is closed by a perforated cork provided with a clipped tube
+after the manner of a burette (see fig. 44<i>d</i>). In the jar, just over
+the cork, put a plug of loose asbestos or glass wool, or a piece of
+sponge to act as a filter; a layer of broken glass, coarse at the bottom
+and fine at the top, will serve the same purpose. On this, place the
+charge of ore to be extracted. Prepare a solution of cyanide of
+potassium in water, with 5 or 10 grams of the salt to the litre. It may
+be that the whole point of the assay depends on the solution being of a
+definite strength; as, for example, where the relative efficiency of
+solutions of different strengths is being determined, when it will be
+best to estimate the quantity of cyanide of potassium in the dilute
+solution by the method given at the end of this article (page 160). Pour
+the cyanide solution on to the ore, letting the first portions to come
+through run into the beaker, but as soon as the ore is thoroughly wetted
+close the clip and allow to stand for several hours. Then, opening the
+clip, run through more cyanide solution and then water, so as to wash
+the gold-carrying liquor thoroughly into the beaker. It is no matter if
+the liquor is a little bit turbid; transfer it to a lead dish,
+evaporate, scorify, and cupel in the usual fashion.<span class='pagenum'><a name="Page_142" id="Page_142">[Pg 142]</a></span></p>
+
+<p>The assay of gold-zinc slimes, which is the precipitate formed by zinc
+acting on cyanide solutions of gold, may be made by wrapping 2 or 3
+grams in 40 grams of sheet lead and scorifying, cupelling, &amp;c. The
+amount of impurity in the stuff varies greatly; it is usually calcined
+and mixed thoroughly with soda 40 per cent., borax 30 per cent., and
+sand 10 per cent., and melted in graphite pots. The buttons of bullion
+obtained are afterwards remelted with borax and run into bars, the
+fineness of which varies from 600 to 830 thousandths. The bars are
+sampled by chipping off diagonally opposite corners: or better, by
+drilling, the drillings being freed from pieces of steel with the help
+of a magnet.</p>
+
+<p><b>Cupellation.</b><a name="FNanchor_23_23" id="FNanchor_23_23"></a><a href="#Footnote_23_23" class="fnanchor">[23]</a>&mdash;The cupellation of lead for gold differs very little
+from that of lead carrying silver. When the gold is accompanied by a
+larger proportion of silver, and both have to be determined, the
+cupellation must be conducted exactly as in a silver assay, the usual
+precautions being taken to moderate the temperature so as to lessen the
+cupellation loss and to promote a slow and undisturbed solidification in
+order to avoid spirting. If, however, the gold predominates the finish
+should be effected at a higher heat, as the melting-point of gold is
+100&deg; higher than that of silver. The bad effect of a higher temperature
+in increasing the cupellation loss need hardly be considered in the case
+of such small buttons of gold as are obtained in assaying gold ores, as
+any loss there may be is hardly appreciable by the balance. With larger
+quantities of gold, however (as in assaying gold bullion), this loss
+becomes important; and it is therefore necessary to very carefully
+regulate the temperature of the muffle so as to minimise the loss.</p>
+
+<p><b>The cupels</b> are made of well-burnt bone-ash, of the fineness of coarse
+wheat flour, moistened with one-twelfth its weight of water and
+compressed into shape in suitable moulds. The moulds sold for this
+purpose are often of unsuitable shape. Since lead has a specific gravity
+of over 11, a cup to hold from 15 to 25 grams of molten lead need not
+have a capacity of more than about 2 c.c. A hollow about 1 inch across
+and 1/4 inch deep is sufficient; and the body of the cupel to absorb
+this weight of lead should itself weigh from 20 to 25 grams. The button
+of lead in a gold assay may be twice as heavy as this. For these larger
+buttons a hollow 1-1/3 inch across and 1/3 inch deep will be sufficient.
+If these larger cupels are not at hand the larger buttons will have to
+be reduced in size by a scorification before cupelling. In some cases
+this preliminary scorification is advantageous or even necessary: this
+may be because the lead is hard and impure, or it may be that a very
+small button of gold is expected. In the latter case it is best to<span class='pagenum'><a name="Page_143" id="Page_143">[Pg 143]</a></span>
+scorify the lead down to something less than 1 gram, and to perform the
+cupellation on a specially prepared small fine cupel. These small cupels
+are best made by grinding the unsaturated portion of a used cupel to a
+fine powder, and compressing the dry powder into a small Berlin crucible
+or scorifier; the face should be made quite smooth by pressure from a
+pestle. On such cupels a small speck of gold (less than .01 milligram)
+will be left in a good shape and easily visible; but the cupel must be
+withdrawn from the muffle as soon as the cupellation is finished to make
+sure of always getting the button in good condition. In places, such as
+Mints, where large numbers of bullion assays are regularly made a
+special form of cupel is used so that not less than six dozen assays may
+all be cupelled at the same time in a muffle of ordinary size. These
+cupels are square blocks, a little less than 2 inches across, and a
+little more than three quarters of an inch deep. Each block carries four
+hollows of about .7 inch across and .3 inch deep. A muffle, on a floor
+space of 6 inches by 12, would take 3 of these blocks abreast and 6
+deep, and thus provide the means for 72 assays.<a name="FNanchor_24_24" id="FNanchor_24_24"></a><a href="#Footnote_24_24" class="fnanchor">[24]</a></p>
+
+<p>Cupels made with wet bone-ash should be slowly dried; and if in the
+muffle they can be slowly brought to an orange-red heat it is all the
+better. Under no circumstances must the lead be placed on the cupel
+before the latter has been so thoroughly heated that it can no longer
+give off steam or gas of any kind. For this gas bubbling through the
+molten metal spatters it, thus spoiling one assay and throwing doubt on
+all the rest. Again, the risk of freezing at the start is much greater
+with a cupel which has not been properly heated.</p>
+
+<p>The best plan is to do all the cupellations in batches. After the muffle
+has cooled down for the withdrawal of the last batch, and the old cupels
+have been taken out, the new cupels for the next batch should be put in
+their place. The furnace should then be stoked and made ready for the
+next cupellations; by the time the furnace is ready the cupels will be
+ready also. There should be no unnecessary handling of the cupels once
+they have been placed in the muffle.</p>
+
+<p><b>The cupellation temperature for gold</b> is an orange-red heat or perhaps
+a little hotter. Beginners, who are apt to overheat their furnace,
+should avoid a heat which can properly be called yellow. Dr. T.K.
+Rose<a name="FNanchor_25_25" id="FNanchor_25_25"></a><a href="#Footnote_25_25" class="fnanchor">[25]</a> has determined the temperature of a muffle during the
+cupellation of gold-silver alloys at the Royal Mint. In one muffle the
+temperature ranged from 1065&deg; to<span class='pagenum'><a name="Page_144" id="Page_144">[Pg 144]</a></span> 1095&deg; C.; the lower temperature was of
+course in the front of the muffle. In another it ranged from 1022&deg; to
+1062&deg;, and here the muffle appeared to the eye "decidedly cooler than
+usual." The alloy left after cupelling was made up of 1 part of gold to
+2-1/2 parts of silver, and was fused at 952&deg;; hence the usual
+temperature of cupellation was, say, 120&deg; or 130&deg; above the
+melting-point of the residual metal. To obtain some real knowledge as to
+the meaning of these figures, the student should prepare pointed pieces
+of the following metals: silver, which melts at 945&deg;; gold, which melts
+at 1035&deg;; and an alloy, half silver, half gold, which melts at 990&deg;.
+These should be placed on clean cupels in a muffle almost entirely
+closed; the temperature should be very slowly raised, and the appearance
+of the muffle when each metal begins to melt should be carefully noted.
+The cupelling temperature in Dr. Rose's experiment was as much above the
+melting-point of gold as this is above that of the silver-gold alloy.
+The <i>finish of the cupellation</i> of gold or gold-silver alloys is
+practically the same as with pure silver; there is the same thinning out
+of the litharge into a luminous film which becomes iridescent before the
+brightening. But the danger of spirting decreases as the proportion of
+gold becomes greater, and disappears when the gold is much over 30 per
+cent. Nevertheless it is well to let such buttons become solid
+undisturbed and protected from draughts in the body of the muffle. This
+means closing the muffle and allowing the furnace to cool down somewhat
+before withdrawing the cupels. Buttons solidified in this way are more
+malleable than when they are withdrawn promptly on the finish of the
+cupellation. This is important with large buttons, as in a bullion
+assay. On the other hand, very small buttons, especially such as have to
+be measured rather than weighed, should be withdrawn as soon as the
+luminous film has disappeared. For when this is done the button can be
+loosened from the cupel by merely touching it with the point of a pin,
+and is then safely and easily transferred to a watch glass by touching
+it with the head of a pin which has been moistened. It adheres to this,
+and if the pin is not too wet comes off at once on touching the glass,
+or in any case will do so on gentle warming.</p>
+
+<p>Molten gold, with little or no silver, has a peculiar colour which is
+easy to recognise; it is more globular than a button of silver of the
+same size would be, and it shows less adhesion to the cupel. Just after
+becoming solid it glows beautifully, and this is so marked that it is a
+valuable help in finding the position of a button when it is more than
+ordinarily minute.</p>
+
+<p>If the button left from cupellation is yellow it is at least half gold,
+and a rough guess as to the proportion of gold may be made from its
+yellowness; the rest of the metal is generally silver. The<span class='pagenum'><a name="Page_145" id="Page_145">[Pg 145]</a></span> presence of
+platinum or one of the platinum group of metals makes the surface of the
+button dull and crystalline. The native alloy of osmium and iridium does
+not alloy with gold, however, but falls to the bottom of the molten
+metal. It shows itself in the subsequent parting as a black spot or
+streak on the under surface.</p>
+
+<p>The buttons are removed from the cupel with a pair of pliers and then
+brushed to remove adherent litharge and bone-ash. Some assayers advise
+cleaning by dipping in warm dilute hydrochloric acid followed by washing
+in water and drying. The button is next weighed. When the quantity of
+silver obtained is not required to be known the weighing may sometimes
+be omitted. The next operation in either case is parting either with or
+without a previous inquartation.</p>
+
+<p><i>The loss of gold in cupellation</i> is by no means always inconsiderable.
+In three cupellations of 1 gram of gold with 20 grams of lead made
+purposely at a very high temperature the cupel absorbed 6.04, 6.20, and
+6.45 milligrams of gold. Hence at a high temperature there may easily be
+a loss of more than half a per cent. of the gold. In ten cupellations
+with the same quantities of gold and lead, but at an ordinary
+temperature, the gold recovered from the cupels varied from 1.37 to 1.92
+milligrams, and gave an average of 1.59 milligrams. In round numbers the
+cupellation loss of pure gold is .15 per cent.</p>
+
+<p>But if the gold be alloyed with <i>silver</i> the loss is diminished, as is
+shown by the following experiments. Gold, .3 gram, was cupelled with 10
+grams of lead and varying amounts of silver, and the cupels were assayed
+for gold with the following results:</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Silver in the alloy</td><td align='left'>.3 gram</td><td align='left'>.6 gram</td><td align='left'>.9 gram</td></tr>
+<tr><td align='left'>Gold in the cupel</td><td align='left'>.47 milligram</td><td align='left'>.32 milligram</td><td align='left'>.17 milligram</td></tr>
+</table></div>
+
+<p>These, calculated on the .3 gram of gold, give the loss as .157, .107
+and .057 per cent. respectively. The effect of <i>copper</i>, on the other
+hand, is to increase the cupellation loss, which, silver being absent,
+may from this cause rise to .3 per cent., even when the temperature is
+not excessive.</p>
+
+<p>In the ordinary assay of gold-copper alloys a constant weight of the
+alloy is always taken; hence as the weight of copper in a cupel charge
+increases, the weight of gold decreases. The silver, on the other hand,
+is always very nearly two and a half times as much as the gold, whatever
+its quantity may be. But the cupellation loss is smaller with less gold
+and greater with more copper, and it so happens in these assays that
+these two opposites nearly neutralise one another. Mr. W.F. Lowe<a name="FNanchor_26_26" id="FNanchor_26_26"></a><a href="#Footnote_26_26" class="fnanchor">[26]</a>
+found the gold recoverable<span class='pagenum'><a name="Page_146" id="Page_146">[Pg 146]</a></span> from the cupels on which 20 grains of gold
+bullion had been treated varied only between .014 and .015 grain (<i>i.e.</i>
+from .07 to .075 per cent. of the bullion treated), although the quality
+of the bullion varied from 9 to 22 carat.<a name="FNanchor_27_27" id="FNanchor_27_27"></a><a href="#Footnote_27_27" class="fnanchor">[27]</a> But in the poorest bullion
+there was only 7.5 grains of pure gold, while in the richest there were
+18.3 grains; yet each lost on the cupel the same weight of gold, viz.,
+.014 grain. When reckoned in percentages of the actual gold present the
+losses are .187 per cent. and .076 per cent. respectively. The heavier
+percentage loss is mainly due to the increased quantity of copper.</p>
+
+<p>As with silver so with gold the predominant cause of the cupellation
+loss is the solution of the metal in the molten litharge which passes
+into the cupel. Three lots of 1 gram of gold cupelled each with 20 grams
+of lead repeatedly, so as to make 13 cupellations in all, lost in actual
+weight 35.72 milligrams. The gold recovered from the cupels amounted
+altogether to 34.56 milligrams. This shows that, compared with the
+absorption by the cupel, the other causes of loss are inconsiderable.</p>
+
+<p>The loss of gold by <i>volatilisation</i> is, however, a real one. The dust
+from the flues of assay furnaces has been tested on several occasions
+and found to contain gold, though in small quantity. Thus Mr. Lowe found
+.073 per cent. of silver and .00033 per cent. of gold in such a
+material. The lead volatilised from a gold bullion assay would need to
+be ten times as rich as this to account for a loss of gold equal to the
+hundredth part of a milligram. Dr. Rose, in the paper already quoted,
+believes that on a .5 gram charge of standard bullion the loss from
+volatilisation is not less than .025 nor more than .05 milligram of
+gold.</p>
+
+<p>By way of conclusion it may be said that the cupellation loss of gold is
+about .07 per cent., and that it is largely met or even over corrected
+by a compensating error due to silver retained in the gold after
+parting.</p>
+
+<p><b>Inquartation.</b>&mdash;The method of separating the gold from the silver in
+gold-silver alloys by boiling with nitric acid does not act equally well
+in all cases. An alloy half silver half gold, rolled to thin sheet and
+boiled for half an hour with nitric acid, may still retain more than
+two-thirds of its silver. An alloy of 1 part gold and 1.7 parts of
+silver gives up practically the whole of its silver under similar
+treatment. The gold is left in a coherent, though easily broken, sheet
+retaining the shape of the original alloy. The gold thus left is quite
+spongy and porous, so that the acid can penetrate into its innermost
+portions. But if the silver is in<span class='pagenum'><a name="Page_147" id="Page_147">[Pg 147]</a></span> large excess in the alloy, the
+removal of the silver is less complete, and the residual gold, instead
+of holding together in a form easy to manipulate, falls to a powder
+which requires care and time in its treatment. The older assayers,
+therefore, added silver to their gold in such proportion that the alloy
+for parting should be one quarter gold to three quarters silver. This
+operation they called <i>inquartation</i>.</p>
+
+<p>The modern practice is to aim at getting an alloy with 2-1/2 parts of
+silver and 1 part of gold. In gold bullion assays this proportion should
+be obtained with fair exactness. And in the parting of such gold buttons
+as are obtained in assaying ores it is well to aim at this proportion,
+though absolute precision is not a matter of importance.</p>
+
+<p>If the button left on cupelling the lead from an assay of an ore appears
+white, it is best to assume that it already contains at least a
+sufficiency of silver, in the absence of any knowledge to the contrary.
+This will be true in almost all cases. But if, on parting, it does not
+lose at least two-thirds of its weight, this indicates that the
+assumption was not justified; and also what quantity of silver must be
+added to the button before again attempting to part. Generally the fault
+will be in the other direction; the silver will be in excess and the
+gold will break up and demand very careful treatment.</p>
+
+<p>If, however, such a button is yellow, then, from its weight and depth of
+colour, a rough estimate can be made of how much gold is contained in
+it. Silver must be added to make the total weight 3-1/2 times as much as
+that of the gold supposed to be present. Thus, if the button weighs 10
+milligrams and is supposed to contain 8 milligrams of gold, then 8
+multiplied by 3-1/2 is 28; the button must, in such case, be made up to
+28 milligrams by adding 18 milligrams of silver. In judging of the
+quality of the gold button, no ordinary error will very seriously affect
+the result. If, in the example just given, the quantity of gold present
+was really 7 or even 9 milligrams of gold, the resulting alloy would
+still have been suitable for such partings. In fact, in routine assays,
+where the quantity as well as the quality of the gold is known within
+fair limits, it is often the custom to add the silver for inquartation
+to the lead during the first cupellation.</p>
+
+<p>But in the assay of rich gold alloys such approximate work will not do.
+If the composition is not already known with a fair degree of accuracy
+<i>preliminary assays</i> must be made. Weigh up two lots of 100 milligrams
+of the alloy and wrap each in 3 grams of lead. To one add 300 milligrams
+of silver. Cupel both. The button containing the added silver must be
+flattened and boiled with 15 c.c. of nitric acid; and the resulting
+gold<span class='pagenum'><a name="Page_148" id="Page_148">[Pg 148]</a></span> must be washed, dried, ignited and weighed. This, in milligrams,
+gives directly the percentage of gold. The weight of the other button
+gives the percentage of gold and silver; the difference between the two
+gives the percentage of silver. The rest will, perhaps, be copper.</p>
+
+<p>The composition of the alloy being known, or having been determined as
+just described, the calculation of how much silver must be added is
+fairly simple. The following is an example. Suppose the bullion contains
+92 per cent. of gold, 1 per cent. of silver and 7 per cent. of copper,
+and that .5 gram of it is to be taken for an assay. The .5 gram, then,
+will contain</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Gold</td><td align='left'>.460</td><td align='left'> gram</td></tr>
+<tr><td align='left'>Silver</td><td align='left'>.005</td><td align='left'>"</td></tr>
+<tr><td align='left'>Copper</td><td align='left'>.035</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>But the total silver required is .46 gram &times; 2.5. This equals 1.15.
+Allowing for the .005 gram of silver already present, 1.145 gram of
+silver must be added.</p>
+
+<p>The silver is incorporated with the gold, and at the same time the
+copper is eliminated, by cupelling with sheet lead. How much sheet lead
+must be used will depend partly on how much bullion is taken, partly on
+how much copper it contains. Four grams of lead will do for a .5 gram
+charge; and for a .3 gram charge, 3 grams may be used. But with 20 per
+cent. of copper these amounts should be doubled; with 40 per cent. of
+copper they should be trebled; and with over 60 per cent. of copper four
+times as much lead should be used. For small buttons of gold as little
+lead as may be relied on to start cupelling may be taken; the lead may
+conveniently be in the form of little cups made by folding lead foil on
+a piece of glass rod. With a large number of bullion assays
+systematically worked and checked a simple plan would be to always use
+the quantity of lead required by the alloy containing most copper which
+turns up for assay. This weight, cut out of lead foil, would be kept in
+stock folded into little bags ready to receive the bullion and silver.</p>
+
+<p>The silver used for inquartation must, of course, be free from gold and
+is best prepared by the assayer who is to use it (see p. 66). It should
+not be in long strips or angular pieces likely to perforate the lead in
+which it is folded. When wrapped in the lead it should be in the middle
+and should make as compact a parcel as possible.</p>
+
+<p>Each little parcel, as completed, should be placed on a tray in its
+properly numbered compartment. Its position here should correspond to
+that it will occupy in the muffle and eventually in the cupel tray. The
+cupellation must be made with all the<span class='pagenum'><a name="Page_149" id="Page_149">[Pg 149]</a></span> requisite precautions. A good
+smooth malleable button is needed for the next operation, which is known
+as flatting.</p>
+
+<div class="figcenter" style="width: 301px;">
+<img src="images/fig045.jpg" width="301" height="300" alt="Fig. 45." title="" />
+
+</div>
+
+<p><b>Flatting.</b>&mdash;Small buttons, such as are got in assaying most gold ores,
+are placed on a polished steel anvil and flattened by one or two blows
+with a hammer. The flattened discs are heated to dull redness on a clean
+cupel and are then ready for parting. Somewhat larger buttons may be
+similarly treated, but they should be annealed (<i>i.e.</i> heated to redness
+and allowed to cool) during the flattening. The silver-gold alloy left
+from the cupellation is soft and bends like lead; but after hammering or
+rolling it becomes harder, gets a spring in it like a piece of
+mainspring and cracks or splits somewhat easily. There should be no
+cracks or stripping or even roughness on the flattened metal, since such
+defects may cause the loss of small particles either during the
+flattening or in the subsequent treatment with acid. The softness of the
+metal is restored by heating. In bullion assays the flatting of the
+buttons requires care and practice for its skilful working. The strips
+of alloy for parting should be of uniform thickness and condition so
+that the action of the acid shall be equal in all cases. The button is
+taken from the cupel, cleaned and placed on the anvil: it is then struck
+a heavy blow which widens it to about 3/4 inch in diameter; this blow is
+followed by two others, one a little in front, the other behind, which
+lengthen the disc and give a very blunt roof-like slope to its upper
+face. It should then be annealed. This may be done by putting it in a
+just red-hot scorifier heated in a muffle: it very soon attains the
+right heat and may then be transferred to a cold scorifier; the hot
+scorifier should be put back into the muffle. The softened disc is then
+taken to the rolls (Fig. 45). The rolls are loosened until the disc can
+be pressed between them. Looking through the interval between them the
+rolls should appear exactly parallel; if they are not, one adjusting
+screw should be loosened and the other tightened until parallelism is
+obtained. The rolls are now turned and the disc should be drawn through
+without any great effort. Beginners are apt to err by trying to do too
+much with one turn of the handle. It is easy to stop whilst the rolls
+are only just gripping the metal and then to bring the disc back by
+reversing the action. If the disc was originally level<span class='pagenum'><a name="Page_150" id="Page_150">[Pg 150]</a></span> and the rolls
+are parallel, the metal will appear as a strip which has been merely
+lengthened. If the rolls are tighter on one side the strip will be
+bowed; the tighter side will correspond with the outer curve of the
+crescent. A mistake of this kind may be amended by passing the strip
+through the rolls the other way, so as to reverse the irregularity and
+so straighten the strip. The screw on the looser side should then be
+tightened until parallelism is obtained; after which more care should be
+taken to tighten the two screws equally. The rolling should be stopped
+when the strip is 3 or 4 inches long and of the thickness of an ordinary
+visiting card. The strip should be annealed during the rolling and again
+at the finish.</p>
+
+<p><b>Parting.</b>&mdash;The thin sheet of metal is dropped into hot dilute nitric
+acid and boiled for five or six minutes after the brisk action of the
+acid on the metal has ceased. At this stage nearly all the silver has
+gone into solution as nitrate of silver and the acid is charged with
+this salt. This acid is poured off and the residual metal is again
+boiled for from 20 to 30 minutes with a second lot of stronger acid.
+This leaves the gold almost pure, though it may still retain from .05 to
+.1 per cent. of silver. Treatment with the first acid only would
+probably leave three or four times as much.</p>
+
+<p>The <i>nitric acid</i> used should be free from hydrochloric, sulphuric,
+iodic and telluric acids. In testing it for the first of these add
+nitrate of silver and dilute with distilled water; there should be no
+turbidity. In testing for the others evaporate three lots in dishes over
+a water-bath. Test one for sulphates by adding water and barium
+chloride. Test another for iodates by taking up with a little water,
+adding a few drops of starch paste and then dilute sulphurous acid
+solution a little at a time; there should be no blue colour. Test the
+third for tellurium by heating with 1 c.c. of strong sulphuric acid
+until dense fumes come off; allow to cool considerably; a piece of tin
+foil added to the warm acid develops a fine purple colour if only a
+trace of tellurium is present.</p>
+
+<p>The presence of lower oxides of nitrogen, which impart a brown colour to
+the acid, is objectionable; they, however, are removed by boiling the
+diluted acid before using it for parting. It is usual to keep a stock of
+the acid suitably diluted to the two strengths required for the parting.
+These are known as the parting acids. The <i>first parting acid</i> is the
+weaker and is used in the first attack on the metal. The specific
+gravity generally recommended for it is about 1.2. It may be prepared
+either by diluting the strong acid with about its own volume of
+distilled water, or by suitably diluting the second parting acid which
+has been<span class='pagenum'><a name="Page_151" id="Page_151">[Pg 151]</a></span> already used in an assay; the small proportion of silver this
+contains is not harmful for this purpose. The <i>second parting acid</i> has
+a specific gravity of about 1.3, and may be made by diluting the strong
+acid with half its volume of distilled water.</p>
+
+<p><i>Parting in Flasks.</i>&mdash;Flasks are most convenient for the larger
+partings, as in bullion assays; and should always be used for this
+purpose unless some of the special parting apparatus, like that used in
+Mints, is available. Many assayers use flasks, though of a smaller size,
+for the ordinary partings in assaying gold ores. The flasks are either
+bulbs with long necks (Fig. 46) which ought to be heated on rose burners
+of special construction; or they are small flat-bottomed conical flasks
+which may be conveniently heated on a hot-plate and are, in this
+respect, much easier to deal with in general work. The following
+instructions apply to the parting of an alloy containing a few decigrams
+of gold together with the proper proportion of silver.</p>
+
+<div class="figcenter" style="width: 118px;">
+<img src="images/fig046.jpg" width="118" height="400" alt="Fig. 46." title="" />
+
+</div>
+
+<p>The strip from the rolls, after being softened by annealing, is folded
+on itself on a glass rod into a roll or cornet. It should be so plastic
+that it will retain the shape thus given it and not spring open on
+removing the pressure of the fingers. About 50 c.c. of the first parting
+acid are placed in a 6-ounce conical flask and heated to boiling; the
+flask is then withdrawn, and tilted a little to one side, whilst the
+cornet is cautiously dropped into it; there will be a sudden issue of
+hot vapours and a prompt withdrawal of the hand is advisable. The flask
+is replaced on the hot plate and the acid is kept boiling for 10 or 15
+minutes. The flask is then withdrawn and the acid diluted with about an
+equal volume of distilled water. If the flask has a thick glass band
+around its neck, a little way down,<a name="FNanchor_28_28" id="FNanchor_28_28"></a><a href="#Footnote_28_28" class="fnanchor">[28]</a> care must be taken to use hot
+water, for any sudden chill will certainly crack the flask where it is
+thus thickened. The liquor is carefully decanted into a clean beaker and
+is then thrown into a jar marked "waste silver." About 40 c.c. of the
+second parting acid, heated to boiling, is then poured into the flask,
+which is then replaced on the hot plate. The boiling is continued for 15
+or 20 minutes or even longer. At this stage bumping has to be specially
+guarded against; after a little experience it is easy to see when this
+is imminent and the flask should be withdrawn to a cooler part of the
+plate; it is better to prolong the heating at a temperature below
+boiling than to run the risk of disaster. Some of the older writers,
+however, are<span class='pagenum'><a name="Page_152" id="Page_152">[Pg 152]</a></span> rather insistent on vigorous boiling with large bubbles.
+The addition of a small ball of well-burnt clay of about the size of a
+pea has been recommended, as it lessens the tendency to irregular and
+dangerous boiling. At the end of the treatment with the second acid the
+flask is withdrawn from the plate and the acid is diluted with an equal
+volume of distilled water. The liquor is carefully decanted into a
+beaker, and then poured into a jar or Winchester marked "acid waste"; it
+serves for making the first parting acid. The flask is then washed twice
+with hot distilled water; the washings must be carefully decanted from
+the gold. The flask is then filled with water. A parting cup (size B) is
+then placed over its mouth, like a thimble on the tip of a finger. This
+cup is of unglazed porous earthenware of such texture that it absorbs
+the last few drops of water left on drying; and with a surface to which
+the gold does not adhere even on ignition. The gold should fall out
+cleanly and completely on merely inverting the cup over the pan of the
+balance. The flask and cup are then inverted so that the flask stands
+mouth down in the cup; a little of the water from the flask flows into
+the cup, but only a little. The gold falls steadily through the water
+into the cup. When time has been allowed for even the finest of the gold
+to have settled into the cup, the flask is removed. This is easiest done
+under water. The cup, with the flask still resting in it, is dipped
+under water in a basin; as soon as the neck of the flask is immersed the
+crucible can safely be drawn away from under it and then lifted out of
+the water. The flask should not be taken away first, for the rush of
+water from it may easily sweep the gold out of the cup. The water in the
+cup is then drained off and the cup is dried at not too high a
+temperature; for if the last drop or two of water should boil there is
+danger of spattering the gold out of the crucible. When it is dry, the
+cup is heated on a pipe-clay triangle over a Bunsen burner, or on a slab
+of asbestos in a muffle, to a dull-red heat. This brings the gold to
+"colour"; that is, the loose tender dark coloured gold becomes bright
+yellow and coherent; and is in a state fit to be transferred to the
+balance and weighed. All unnecessary transferences must be avoided. As
+soon as the cup is cool it may be inverted over the pan of the balance,
+when the gold will fall out cleanly or, at the worst, a gentle tap with
+the finger will be sufficient to detach it.</p>
+
+<p><i>Parting in test-tubes</i>, or in the smaller conical flasks, is used in
+the assay of gold ores of ordinary richness. The work is exactly like
+that just described in all its main features. Generally speaking much
+less acid will be used; for example, in test-tubes and for small
+buttons, 3 or 4 c.c. of each acid is quite enough. Again,<span class='pagenum'><a name="Page_153" id="Page_153">[Pg 153]</a></span> the action
+need not be so prolonged; 10 or 15 minutes in each acid is sufficient.
+So, too, the heating may be less; it is very convenient to support the
+test-tubes in a water-bath, or merely to rest them in a beaker of
+boiling water; and there is no serious objection to doing this. A
+smaller parting cup should be used; the A size is suitable. The button,
+on the other hand, should be beaten thinner than is needed for the
+larger partings. If the silver should be in excess and the gold becomes
+much broken up, ample time should be given for subsidence from the
+test-tube or flask into the parting cup.</p>
+
+<p><i>Parting in glazed crucibles or dishes.</i>&mdash;This method of working has the
+advantage that there is no transference of the gold until it is placed
+on the pan of the balance. On the other hand, in the boiling more care
+is required in adjusting the temperature. The following instructions
+apply to the treatment of very small buttons, to which the method is
+more particularly applicable; but very little modification is needed for
+the treatment of larger buttons. The smallest sized Berlin crucibles
+answer admirably. They should be cleaned by treatment with hot and
+strong sulphuric acid, followed by washing in distilled water; the
+comfort and ease of working mainly depends on the thoroughness of this
+cleaning. The crucible, one-third full with the first parting acid, is
+heated on the hot plate until the acid is almost boiling. The flattened
+and annealed button is dropped into it and the heating continued with,
+at most, gentle boiling for a few minutes. The crucible is then filled
+with distilled water, which cools it enough for easy handling; and when
+the gold has settled the liquor is poured off along a glass rod into a
+clean beaker. Any greasiness of the crucible makes itself felt here and
+is very objectionable. The crucible is then one-third filled with the
+second parting acid and the heating resumed, care being taken not to
+raise the temperature too high; this should be continued much longer
+than before, say for five or ten minutes or even longer according to the
+size of the button. Distilled water is again added and, when it is
+drained off, the washing with distilled water is twice repeated. It will
+not be possible to drain off the last drop of water; but if the gold is
+coherent, the crucible can be so inclined that this drop drains away
+from the gold, in which case the drying can be done rapidly; the boiling
+of the water will do no harm. But when the gold is much broken up, it
+will collect in the middle of this drop and the drying must be done
+gently; best by putting the crucible in a warm place. When dry, the
+crucible is heated till the gold changes colour, but the heat must be
+kept well below redness. When cold, the gold is transferred directly to
+the pan of the balance. With minute specks of gold which will require<span class='pagenum'><a name="Page_154" id="Page_154">[Pg 154]</a></span>
+measuring, it is best to put a small piece of lead foil (say .1 gram) in
+the crucible over the gold, and then heat the crucible to above redness
+over a blowpipe. Whilst the lead is oxidising it is easily swept round
+in a bath of molten litharge by merely tilting the crucible. In this way
+any separated specks of gold can be taken up with certainty. When the
+worker is satisfied that the lead has had ample opportunity for taking
+up the gold, the lead must be kept in one place and the heat slowly
+lowered. By this means the button becomes supported in comparatively
+pure litharge and when solid can be picked out quite easily with a pair
+of pliers and in a very clean condition. The lead button is then
+cupelled on a very fine cupel, as already described. The method of
+working last described destroys the crucible. If the gold is not quite
+so small this may be avoided. A small piece of lead foil should be
+hammered out until it is perfectly flexible. It is then shaped into a
+tray and the gold is transferred to it. The lead is then folded over,
+with the help of two pins; and cupelled.</p>
+
+<p>If the crucible shows a black stain on heating it is because some silver
+remains through bad washing. It shows poor work and the assay should be
+repeated.</p>
+
+<p><i>The silver retained in the gold after parting</i> is, in bullion assays,
+an important matter; it is roughly equal to the loss of gold due to
+absorption by the cupel. Mr. Lowe working on .5 oz. of gold, obtained by
+parting in assaying bullion, found it to contain .123 per cent. of
+silver. Dr. Rose in some special assay pieces found by a less direct
+method of assaying, from .06 to .09 per cent. of silver. The proportion
+of silver retained varies in a marked way with the proportion of gold to
+silver in the alloy before parting. It is generally stated that the
+retained silver is least when this proportion is 1 to 2-1/2, and more or
+less silver than this leads to a less pure gold after parting.</p>
+
+<p><i>Platinum</i> in an alloy being parted is dissolved along with the silver
+either altogether or in part. It imparts a straw yellow colour to the
+parting acid. <i>Palladium</i> gives an orange colour to the acid.</p>
+
+<p><i>The loss of gold by solution in the acid during parting</i> is small, but
+easily demonstrable. On a 500-milligram charge of bullion it may amount
+to from .05 to .15 milligram; <i>i.e.</i> from .01 to .03 per cent. It is due
+to gold actually dissolved and not merely held in suspension.</p>
+
+<p><b>Assaying with checks. Surcharge.</b>&mdash;It will be seen from what has been
+stated that the errors in gold parting are of two kinds: viz. (1) a loss
+of gold on the cupel and to a less extent by solution in the acid, and
+(2) an apparent gain of gold due to the retention of silver in the
+parted material. Both errors are small,<span class='pagenum'><a name="Page_155" id="Page_155">[Pg 155]</a></span> and as they are of an opposite
+character they tend to neutralise each other. Hence they are altogether
+without effect on the accuracy of the assays of ores when the total gold
+is reckoned in milligrams. And even with the larger amounts present in
+bullion assays their influence is so small that an uncorrected result is
+still fairly accurate; the resultant error would not be more than one
+part in two or three thousand.</p>
+
+<p>It is customary to report the purity of bullion, or its fineness as it
+is called, in parts per thousand of bullion. The sum of the errors of an
+assay, which is called the <i>surcharge</i>, is reported in the same way.
+Thus a surcharge of + .3 means that the gold as weighed was .3 part per
+1000 more than the gold actually present. But a surcharge - .3 means
+that on the whole there was a loss of .3 part per 1000 in the assay.</p>
+
+<p>Speaking roughly the retained silver will vary with the weight of gold
+present; if one alloy contains twice as much gold as another the
+retained silver will be about twice as much also. On the other hand, as
+already explained, the cupellation loss on the poorer alloy is as much
+as, or even more than, with the richer one, because of the copper, &amp;c.
+present. With rich gold alloys the silver more than compensates for the
+loss and the surcharge is positive; but with poorer alloys the loss is
+greater and the surcharge is negative.</p>
+
+<p>In Mints and places where bullion assays must be made with the highest
+attainable accuracy, the surcharge is determined by experiment, and the
+proper correction is made in the reports on the bullion. This is done by
+making assays of gold of the highest degree of purity alongside of those
+of the bullion whose quality has to be determined. These "checks" are so
+made that they do not differ from the actual assays in any material
+point. Thus, being of the same quality and weight and undergoing exactly
+the same treatment, they may reasonably be expected to have the same
+surcharge as the assays they imitate. Suppose the bullion being assayed
+varies only a little, up or down, from 900 gold and 100 copper in the
+thousand, and that .5 gram of it is used in each assay. A quantity of
+gold differing only a little from .450 gram would be very exactly
+weighed and placed with .050 gram of copper in the same weight of lead
+as is being used in the other assays. It would be cupelled, parted, &amp;c.,
+as nearly as possible under the same conditions as the actual assays.
+Suppose the pure gold weighed .45016 gram and the parted gold weighed
+.45025 gram, the gain in weight, .00009 gram, would be deducted from the
+actual assays. A surcharge correction is never applied except to bullion
+of the same quality as that represented by the "check assay" it was
+calculated from.<span class='pagenum'><a name="Page_156" id="Page_156">[Pg 156]</a></span></p>
+
+<p>It is evident that unless the gold is of the highest degree of purity
+these check assays will introduce an error almost equal to that which it
+is designed to remedy. Moreover, to work the checks to the greatest
+advantage, a very systematic and uniform method of working must be
+adopted.</p>
+
+<p><b>Parting in special apparatus.</b>&mdash;One plan for obtaining greater
+uniformity is to stamp each cornet with a number for purposes of
+identification, and to treat several, including one or more check assays
+in the same acid contained in a beaker; all the assays under these
+conditions evidently receive precisely the same acid treatment. Such a
+plan can of course only be adopted where there is no risk of the gold
+breaking up during the parting. An improvement on this is to have a
+porcelain basin<a name="FNanchor_29_29" id="FNanchor_29_29"></a><a href="#Footnote_29_29" class="fnanchor">[29]</a> about 8-1/2 inches in diameter and with a capacity
+of about 1-1/2 litres. It is provided with a porcelain cover with 30
+numbered holes through which tubes dip into the acid. The cover is
+removable. The tubes are like test-tubes and are supported by the cover;
+their bottoms are perforated with holes or slits. The acid is placed in
+the basin and boiled over a flat burner; it enters the tubes through the
+slits. The cornets are placed each in its proper tube. When the boiling
+is finished, the cover with the tubes is lifted and at the same time the
+acid drains back into the basin. A dip into a basin of distilled water
+washes at one operation all 30 assays. The cover is then put on a basin
+containing the stronger parting acid which is already boiling. This
+boiling is continued for half an hour. The cover with the 30 cornets is
+then lifted out from the acid and dipped two or three times in distilled
+water to wash off the last traces of acid. To transfer the cornets from
+the tubes to the porous cups the whole of the tube must be dipped under
+the water; otherwise the operation is exactly as when working with
+test-tubes.</p>
+
+<p>A still simpler method of working is to use small platinum cups<a name="FNanchor_30_30" id="FNanchor_30_30"></a><a href="#Footnote_30_30" class="fnanchor">[30]</a>
+provided with fine slits which admit the acid but retain the gold. A
+number of these, say 60, are supported on a platinum tray. The parting
+acids are boiled in platinum dishes under a hood; and the 60 cornets
+(each in its proper cup) are placed in the acid all at once: the tray
+carrying the cups is provided with a handle suitable for this purpose.
+After a proper boiling the tray is lifted out of the weaker acid into
+the stronger one, where it undergoes the second boiling. It is next
+dipped several times in distilled water and lastly, after a gentle
+drying, it is raised to an annealing temperature which must not be too<span class='pagenum'><a name="Page_157" id="Page_157">[Pg 157]</a></span>
+high for fear of the gold sticking to the platinum. After cooling, the
+cornets are transferred from the platinum cups directly to the pan of
+the balance. Here all 60 cornets have exactly the same treatment and the
+"checks" may be compared with great exactness with the other assays
+accompanying them. There is, too, a great saving of labour.<a name="FNanchor_31_31" id="FNanchor_31_31"></a><a href="#Footnote_31_31" class="fnanchor">[31]</a></p>
+
+<p><b>Silver, &amp;c., in gold bullion.</b>&mdash;The base metals are generally
+determined by cupelling .5 gram of the alloy with 5 grams of lead. The
+loss in cupellation having been allowed for by any of the usual methods
+(see p. 104) the gold and silver contents are given. By deducting the
+gold the proportion of silver is obtained. The silver is generally
+determined by difference in this way. If it is desired to dissolve out
+the copper, silver, &amp;c., and to determine them in the wet way, the gold
+must first be alloyed with a sufficiency of some other metal to render
+it amenable to the attack by acid. Cadmium is the metal generally
+recommended, and the alloy is made by melting together a weighed portion
+of the gold with five or six times its weight of cadmium in a Berlin
+crucible and under a thin layer of potassium cyanide.</p>
+
+<p><b>Lead with gold or silver.</b>&mdash;Large quantities of lead carrying gold and
+silver are sold to refiners in bars weighing about 100 lbs. each. The
+assay of these alloys presents no special difficulties, but the sampling
+of them is a question which may be profitably discussed.<a name="FNanchor_32_32" id="FNanchor_32_32"></a><a href="#Footnote_32_32" class="fnanchor">[32]</a></p>
+
+<p>A molten metal may be conceived to have all the physical states observed
+in ordinary liquids, although these cannot be actually seen owing to its
+opaqueness. There is no doubt that <i>pure</i> lead at a temperature only a
+little above its melting-point can contain a large proportion of gold in
+such a manner that it may in a figurative way be spoken of as a clear
+solution. Any small portion withdrawn from the molten metal would afford
+a perfect sample. The same would be true of any pure alloy of lead and
+silver in which the silver does not exceed the proportion of 2-1/2 per
+cent.<a name="FNanchor_33_33" id="FNanchor_33_33"></a><a href="#Footnote_33_33" class="fnanchor">[33]</a> On the other hand, if the molten metal contains much more than
+.5 per cent. of zinc, more than .1 per cent. of copper, or a larger
+quantity of silver, it may be likened to a turbid liquor. The
+resemblance holds good so far that if the molten lead be further heated,
+whereby its solvent power on the added metal is increased, the turbidity
+will disappear, or at least<span class='pagenum'><a name="Page_158" id="Page_158">[Pg 158]</a></span> be considerably diminished. A portion taken
+at random from such a molten metal may, or may not, give a good sample.
+The suspended insoluble matter will tend to concentrate itself in the
+upper or lower parts of the liquid according to whether it is heavier or
+lighter than it; and this separation may occur with extreme slowness or
+with fair rapidity. However, it is generally agreed that in the case of
+such alloys as occur in practice, samples taken in this way are quite
+satisfactory and are the best obtainable. The precautions insisted on
+are that the lead shall be made as hot as practicable; that it shall be
+stirred up at the time of taking the sample; and that the portion
+withdrawn shall be taken out with a ladle at least as hot as the molten
+metal. The further precaution that if any dross be on the surface of the
+metal it shall be skimmed off and separately sampled and assayed is
+almost too obvious to require mention. An alternative and, perhaps,
+better way of taking the sample is to withdraw portions at equal
+intervals from the stream of metal whilst the pot is being emptied;
+equal weights taken from these portions and mixed (by melting or in some
+other way) give a fair sample of the whole. In addition, separate assays
+of each portion will show to what extent the metal lacks uniformity in
+composition For example, samples taken at the beginning, middle, and end
+of a run gave the following results in ozs. of silver per ton: 475, 472,
+466, showing an average result of 471 ozs. Fifteen fractions taken at
+regular intervals during the same pouring ranged from 475 ozs. to 464
+ozs.: the average result was 469.8 ozs. The same lead cast into bars and
+sampled by sawing gave an average of 470 ozs.<a name="FNanchor_34_34" id="FNanchor_34_34"></a><a href="#Footnote_34_34" class="fnanchor">[34]</a> In another case<a name="FNanchor_35_35" id="FNanchor_35_35"></a><a href="#Footnote_35_35" class="fnanchor">[35]</a>
+samples drawn at the beginning, middle, and end of a run gave 1345 ozs.,
+1335 ozs. and 1331 ozs. The mean result in such cases is always a
+reasonably safe one, but evidently where the metal varies a good deal it
+is safer to take more than three dips.</p>
+
+<p>Imagine such lead run into moulds and allowed to become solid as bars;
+the difference between bar and bar would not be greater than that
+between corresponding dip samples. But in each bar the distribution of
+the silver and gold is very seriously affected during solidification.
+Chips taken from the same bar of auriferous lead may show in one place
+23 ozs. of gold to the ton, in another 39 ozs.; similarly with silver
+they may vary as much as from 900 ozs. to 1500 ozs. to the ton.</p>
+
+<p>This rearrangement of the constituents of a bar takes place whilst the
+lead is partly solid, partly liquid. The most useful conception of such
+half-solidified metal is that of a felted spongy<span class='pagenum'><a name="Page_159" id="Page_159">[Pg 159]</a></span> mass of skeleton
+crystals of comparatively pure lead saturated with a still fluid
+enriched alloy. If the solidification of an ingot of impure tin be
+watched it will be evident that the frosted appearance of the surface is
+due to the withdrawal of the fluid portion from a mat of crystals of
+purer tin which have been for some time solid and a contraction of the
+mass. The shrinking of the last part to become solid is further shown by
+the collapse of the surface of the ingot where weakest; that is, a
+furrow is formed on the flat surface. In other cases of fused metal
+there is expansion instead of contraction in this final stage of the
+solidification, and the enriched alloy then causes the upper face of the
+ingot to bulge outwards. There are other causes effecting the
+redistribution of the metals through the ingot. There can be no general
+rule of wide application showing which part of a bar is richest and
+which poorest in the precious metals. This will depend on the quantities
+of gold or silver, on the quantities and kinds of other metals present
+and on the manner of casting. The student is advised to consult Mr.
+Claudet's paper which has been already referred to.</p>
+
+<p>The best method of sampling such bars is to melt them all down and to
+take a dip sample of the molten metal in one or other of the methods
+already described. According to Mr. Claudet this should be done in all
+cases where the gold exceeds one or two ounces or where the silver
+exceeds 200 ozs. to the ton. If during the melting down some dross has
+formed this must be skimmed off, weighed and separately sampled and
+assayed. The clean lead also must be weighed, sampled and assayed. The
+mean result must be calculated. Thus 14 tons 5 cwts. of clean lead
+assaying 32 ozs. to the ton will contain 456 ozs. of silver; 15 cwt.
+dross assaying 20 ozs. to the ton will contain 15 ozs. of silver. The 15
+tons of lead and dross will contain 471 ozs. of silver or 31.4 ozs. per
+ton.</p>
+
+<p>Of the methods of sampling which avoid melting the bars, that known as
+sawing is the only one which is thoroughly satisfactory. In it the bars
+are brought to a circular saw having fine teeth and are sawn across
+either completely or halfway through; in this way a quantity of lead
+sawdust is obtained (say 1 lb. or so from a bar) which represents
+exactly the average of the bar along the particular cross section taken
+and approximately that of the whole bar. A bar of lead, which by dip
+assay gave 334 ozs. to the ton, gave on three transverse sections 333
+ozs., 335 ozs. and 331 ozs. The variation may be greater than this, but
+with a large number of bars, where each bar is cut across in as far as
+possible a different place, these variations tend to neutralise each
+other and a good sample is obtained. Two or three cwt. of sawdust may be
+obtained<span class='pagenum'><a name="Page_160" id="Page_160">[Pg 160]</a></span> in this way; this is thoroughly mixed and reduced by
+quartering in the usual way or by a mechanical sampler. A sample of 2 or
+3 lbs. is sent to the assayer. This being contaminated with the oil used
+in lubricating the saw is freed from it by washing with carbon
+bisulphide, ether or benzene and dried. Then, after mixing, 100 to 200
+grams of it are carefully weighed and placed in a hot crucible, the heat
+of which should be sufficient to melt all the lead. The molten lead
+should not be overheated and should show no loss due to the melting. The
+removal of the oil may have decreased the weight by perhaps one half per
+cent. If the lead gives dross on heating it may be melted under 10 or 20
+grams of potassium cyanide, which prevents the formation of dross.
+Samples are sometimes taken with a drill, gouge or chisel, though no
+method of this kind is quite satisfactory. One plan adopted is to use a
+punch which, when driven into the bar, gives a core or rod of metal
+about half as long as the bar is thick and about one-eighth of an inch
+across. With five bars side by side it is customary to drive in the
+punch at one end on the first bar, and at the opposite end on the last
+one, and on the others in intermediate positions in such a manner that
+all the holes will be along a diagonal of the rectangle enclosing the
+bars. The bars are then turned over and similar portions punched out
+through the bottoms of the bars and along the other diagonal. Or one set
+of five may be sampled along the top and the next set along the bottom
+of the bars.</p>
+
+<p>Silver and gold present in bars of copper are subject to the same
+irregularity of distribution as in lead. The sampling of such bars is
+guided by the same principles.<a name="FNanchor_36_36" id="FNanchor_36_36"></a><a href="#Footnote_36_36" class="fnanchor">[36]</a></p>
+
+
+<h4>CYANIDES.</h4>
+
+<p>The cyanides ought perhaps to be considered along with chlorides,
+bromides and iodides in Chapter XV. But they are treated here because
+they owe their importance to their use in the extraction of gold and
+because their determination has become a part of the ordinary work of an
+assayer of gold ores.</p>
+
+<p>Formerly, the cyanide most easily obtained in commerce was potassium
+cyanide; and it was generally sold in cakes which might contain as
+little as 40 per cent. or as much as 95 per cent. of the pure salt. It
+became customary to express the quality of a sample of commercial
+cyanide by saying it contained so much per cent. of potassium cyanide.
+The commercial product now made<span class='pagenum'><a name="Page_161" id="Page_161">[Pg 161]</a></span> by improved methods of manufacture is
+actually sodium cyanide, but is called "potassium cyanide" (probably
+with the words "double salt" on the label); it contains cyanide
+equivalent to something over 100 per cent. of potassium cyanide in
+addition to a large proportion of sodium carbonate and other impurities.
+What is wanted in most cases is merely a soluble cyanide, and it is a
+matter of indifference whether the base be sodium or potassium. But
+since 49 parts of sodium cyanide (NaCN = 49) are equivalent to 65 parts
+of potassium cyanide (KCN = 65) it is evident that a pure sample of
+sodium cyanide would contain cyanide equivalent to little less than 133
+per cent. of potassium cyanide. Therefore a sample of cyanide reported
+on in this way may be rich in cyanide, and yet have much impurity.</p>
+
+<p>The commonest impurity in commercial cyanide is carbonate of sodium or
+potassium. This may be tested for by dissolving, say, 2 grams in a
+little water and adding barium chloride. There may be formed a white
+precipitate of barium carbonate, which if filtered off, washed and
+treated with acid, will dissolve with effervescence. Cyanate may be
+tested for in the solution from which the barium carbonate has been
+filtered by adding a little soda and boiling; if cyanates are present
+they decompose, giving off ammonia (which may be tested for in the
+steam) and yielding a further precipitate of barium carbonate.<a name="FNanchor_37_37" id="FNanchor_37_37"></a><a href="#Footnote_37_37" class="fnanchor">[37]</a> If
+the soda alone gave a further precipitate of barium carbonate, this may,
+perhaps, be due to the presence of bicarbonates. Alkaline sulphides may
+be present in small quantity in commercial cyanide. Their presence is
+shown at once when the sample is being tested for its strength in
+cyanide, inasmuch as the first few drops of silver nitrate solution
+produce at once a darkening of the liquor. A special test for sulphide
+may be made by adding a drop or two of solution of acetate of lead to
+four or five c.c. of soda solution and adding this to a clear solution
+of the suspected cyanide. This will cause a black precipitate or colour,
+if any sulphide is present.</p>
+
+<p>The cyanides of the heavier metals combine with the alkaline cyanides to
+form double cyanides. Some of these, ferrocyanide and ferricyanide of
+potassium for example, have such characteristic properties that the fact
+that they are cyanides may be overlooked. Others, such as potassium zinc
+cyanide (K<sub>2</sub>ZnCy<sub>4</sub>), have much less distinctiveness: they behave
+more or less as a mixture of two cyanides and are, moreover, so easily
+decomposed that it may be doubted if they can exist in dilute alkaline
+solutions. In reporting the cyanide strength of a cyanide liquor as
+equivalent to so much<span class='pagenum'><a name="Page_162" id="Page_162">[Pg 162]</a></span> per cent. of potassium cyanide, there is a
+question as to whether the cyanide present in the form of any of these
+double cyanides should be taken into account. It must be remembered that
+the object of the assay is not to learn how much of the cyanide exists
+in the solution as actual potassium cyanide; reporting the strength in
+terms of this salt is a mere matter of convenience; what is really
+desired is to know how much of the cyanide present in the liquor is
+"free" or "available" for the purposes of dissolving gold. Every one is
+agreed as to the exclusion of such cyanides as the following: potassium
+ferrocyanide (K<sub>4</sub>FeCy<sub>6</sub>), potassium ferricyanide (K<sub>3</sub>FeCy<sub>6</sub>),
+potassium silver cyanide (KAgCy<sub>2</sub>), and potassium aurocyanide
+(KAuCy<sub>2</sub>); and the double cyanides with copper or nickel. But with
+cyanide liquors containing zinc the position is less satisfactory. One
+method of assay gives a lower proportion of cyanide when this metal is
+present; and the loss of available cyanide thus reported depends, though
+in a fitful and uncertain way, upon the quantity of zinc present. The
+other method of assay reports as full a strength in cyanide as if no
+zinc were present. Unfortunately, using both methods and accepting the
+difference in the results as a measure of the quantity of zinc present,
+or at any rate of the zinc present as cyanide, is not satisfactory. It
+appears best to use the method which ignores the zinc; and to determine
+the amount of zinc by a special assay of the liquor for this metal.</p>
+
+<p>The cyanide present as hydrogen cyanide or prussic acid (HCy) is
+practically useless as a gold solvent. Hence any report on the strength
+of a cyanide liquor which assigned to this the same value as its
+equivalent of alkaline cyanide would be misleading. On the other hand,
+it is "available cyanide" inasmuch as a proper addition of sodium
+hydrate<a name="FNanchor_38_38" id="FNanchor_38_38"></a><a href="#Footnote_38_38" class="fnanchor">[38]</a> would restore its value. The question of the presence or
+absence of free prussic acid is involved in the larger one as to whether
+the cyanide solution has the right degree of alkalinity. The assay for
+"cyanide" should include the hydrogen cyanide with the rest.</p>
+
+<p>A rough test of the power of a cyanide liquor for dissolving gold may be
+made by floating a gold leaf on its surface and noting the time required
+for its solution. This test might, perhaps, be improved by taking, say,
+20 c.c. of the liquor and adding three or four gold leaves so that the
+gold shall always be in considerable excess. The liquor should not be
+diluted as this will affect the result. It should be allowed to stand
+for a definite time, say at least two or three hours, or better, that
+corresponding to the time the liquor is left in contact with the ore in
+actual practice. The<span class='pagenum'><a name="Page_163" id="Page_163">[Pg 163]</a></span> liquor should then be filtered off and, with the
+washings, be evaporated in a lead dish as in the assay of cyanide
+liquors for gold (p. 141). The gold obtained on cupelling, less any gold
+and silver originally present in the liquor, would be the measure of the
+gold dissolving power.</p>
+
+
+<h4>THE ASSAY FOR CYANIDE BY TITRATION WITH SILVER NITRATE.</h4>
+
+<p>The determination of the quantity of a cyanide is made by finding how
+much silver nitrate is required to convert the whole of the cyanide into
+potassium silver cyanide<a name="FNanchor_39_39" id="FNanchor_39_39"></a><a href="#Footnote_39_39" class="fnanchor">[39]</a> or one of the allied compounds. It will be
+seen from the equation that 170 parts by weight of silver nitrate are
+required for 130 parts by weight of potassium cyanide. As already
+explained it is customary to report the cyanide-strength in terms of
+potassium cyanide, even when only the sodium salt is present. One gram
+of potassium cyanide will require 1.3076 gram of silver nitrate. <i>The
+standard solution of silver nitrate</i> is made by dissolving 13.076 grams
+of silver nitrate in distilled water and diluting to 1 litre; 100 c.c.
+of such a solution are equivalent to 1 gram of potassium cyanide.<a name="FNanchor_40_40" id="FNanchor_40_40"></a><a href="#Footnote_40_40" class="fnanchor">[40]</a></p>
+
+<p>The titration is performed in the usual way, running the standard
+solution of silver nitrate into a solution containing a known weight or
+volume of the material containing the cyanide. The <i>finishing point</i> is
+determined in one of two ways, both of which are largely used. In the
+first place, as long as there remains any free cyanide in the solution
+the silver nitrate will combine with it forming the double cyanide and
+yielding a clear solution; but as soon as all the free cyanide is used
+up the silver nitrate will react with the double cyanide<a name="FNanchor_41_41" id="FNanchor_41_41"></a><a href="#Footnote_41_41" class="fnanchor">[41]</a> forming
+silver cyanide, which separates as a white precipitate and renders the
+solution turbid. But, in the second place, if potassium iodide is
+present in the solution the excess of silver nitrate will react with
+it,<a name="FNanchor_42_42" id="FNanchor_42_42"></a><a href="#Footnote_42_42" class="fnanchor">[42]</a> rather than with the double cyanide; and silver iodide will
+separate as a yellowish turbidity which is easily recognised.</p>
+
+<p>In working with pure solutions, the two finishing points give the same
+results; and this is true even when there is much difference in the
+degree of dilution. The finishing point with the iodide,<span class='pagenum'><a name="Page_164" id="Page_164">[Pg 164]</a></span> however, has
+an advantage in precision. Moreover, it is but little affected by
+variations in alkalinity, which render the other finishing point quite
+useless. The great difference between the two is shown when zinc is
+present in the solution. In this case, when working without the iodide,
+the first appearance of a turbidity is less distinct; the turbidity
+increases on standing and as a finishing point is unsatisfactory. It can
+be determined with precision only by very systematic working and after
+some experience. The turbidity is due to the separation of an insoluble
+zinc compound. A most important point (to which reference has already
+been made) is that less silver nitrate is required to give this
+turbidity and, consequently, a lower strength in cyanide is reported. On
+the other hand, as much silver nitrate is required to give the yellow
+turbidity due to silver iodide as would be required if no zinc were
+present.</p>
+
+<p>Unfortunately the difference in the two titrations does not depend
+merely on the quantity of zinc present; as it is also influenced by the
+extent of dilution, the degree of alkalinity of the solution, and the
+quantity of cyanide present. In an experiment with .055 gram of zinc
+sulphate and .1 gram of potassium cyanide the difference in the two
+finishing points was only .1 c.c.; whereas with .4 gram of potassium
+cyanide, the other conditions being the same, the difference was 1.5
+c.c. of standard silver nitrate. On the assumption that all the zinc was
+present as potassium zinc cyanide (K<sub>2</sub>ZnCy<sub>4</sub>) the difference should
+have been 5 c.c. in each case. Again, repeating the experiment with .4
+gram of potassium cyanide, but with .11 gram of crystallised zinc
+sulphate, the difference was 6.5 c.c.: that is, merely doubling the
+quantity of zinc increased the difference by more than four times. Hence
+it would appear better to use the method with the iodide and make a
+separate assay for the zinc. But since the student may be called on to
+use the other method, he is advised to practice it also.</p>
+
+<p><b>The assay without iodide.</b>&mdash;The standard solution of silver nitrate is
+placed in a small burette divided into tenths of a c.c. Ten c.c. of the
+cyanide solution to be assayed is transferred to a small flask and
+diluted with water to about 70 c.c. The silver solution is then run in
+from the burette (with constant shaking of the flask), a little at a
+time but somewhat rapidly, until a permanent turbidity appears. Since 1
+c.c. of the silver nitrate solution corresponds to .01 gram of potassium
+cyanide, it also corresponds to .1 per cent. of this salt counted on the
+10 c.c. of cyanide solution taken. The titration should be performed in
+a fairly good uniform light. The learner should practice on a fairly
+pure solution of potassium cyanide at first, and this may<span class='pagenum'><a name="Page_165" id="Page_165">[Pg 165]</a></span> conveniently
+have a strength of about 1 per cent. For practice with solutions
+containing zinc make a solution containing 1.1 gram of crystallised zinc
+sulphate in 100 c.c. and slowly add measured quantities of from 1 to 5
+c.c. of this to the 10 c.c. of cyanide liquor before diluting for the
+titration.</p>
+
+<p>If a cyanide solution blackens on the addition of the silver nitrate it
+contains sulphide. In this case, shake up a considerable bulk of the
+liquor with a few grams of lead carbonate, allow to settle and make the
+assay on 10 c.c. of the clear liquor.</p>
+
+<p>If the cyanide liquor be suspected to contain free prussic acid, take 10
+c.c. for the assay as usual; but, before titrating, add .1 or .2 gram of
+sodium carbonate. On no condition must caustic soda or ammonia be added.
+The difference between the results, with and without the addition of
+carbonate of soda, is supposed to measure the quantity of free prussic
+acid. If this has to be reported it is best done as "prussic acid
+equivalent to ... per cent. of potassium cyanide." Suppose, for example,
+the difference in the two titrations equals 1 c.c. of standard silver
+nitrate; the prussic acid found would be equivalent to .1 per cent. of
+potassium cyanide.</p>
+
+<p><b>The assay with iodide.</b>&mdash;The standard solution of silver nitrate is
+placed in a burette divided into tenths of a c.c. Take 10 c.c. of the
+cyanide liquor, which should previously have been treated with white
+lead for the removal of sulphides if these happened to be present.
+Transfer to a small flask, add 3 or 4 drops of a solution of potassium
+iodide and 2 or 3 c.c. of a solution of sodium hydrate; dilute to 60 or
+70 c.c. with water. If much zinc is present the soda may be increased to
+20 or 30 c.c. with advantage. The standard solution should be run in
+somewhat rapidly, but a little at a time, so that the precipitate at
+first formed shall be small and have only a momentary existence. The
+titration is continued until there is a permanent yellowish turbidity.
+The most satisfactory and exact finish is got by ignoring any faint
+suspicion of a turbidity and accepting the unmistakable turbidity which
+the next drop of silver nitrate is sure to produce. This finishing point
+gives results which are exactly proportional to the quantity of cyanide
+present; and it can be recognised with more than ordinary precision even
+in solutions which are not otherwise perfectly clear.</p>
+
+<p>Each c.c. of the standard silver nitrate solution corresponds to .01
+gram of potassium cyanide; and if 10 c.c. of the liquor are taken for
+assay this corresponds to .1 per cent. or 2 lbs. to the short ton or
+2.24 lbs. to the long ton. As already explained the result should be
+reported as "cyanide equivalent to so much per cent. of potassium
+cyanide."<span class='pagenum'><a name="Page_166" id="Page_166">[Pg 166]</a></span></p>
+
+<p>The following experimental results were obtained with a solution of
+potassium cyanide made up to contain about 1.2 per cent. of the salt.</p>
+
+<p><b>Effect of varying cyanide.</b>&mdash;The bulk before titration was in each case
+60 c.c.; 2 c.c. of soda and 3 drops of potassium iodide were used in
+each case.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Cyanide added</td><td align='left'>40 c.c.</td><td align='left'>30 c.c.</td><td align='left'>20 c.c.</td><td align='left'>10 c.c.</td><td align='left'>5 c.c.</td><td align='left'>1 c.c.</td></tr>
+<tr><td align='left'>Silver required</td><td align='left'>47.0 c.c.</td><td align='left'>35.25 c.c.</td><td align='left'>23.5 c.c.</td><td align='left'>11.7 c.c.</td><td align='left'>5.8 c.c.</td><td align='left'>1.15 c.c.</td></tr>
+</table></div>
+
+
+<p>Accepting the result for 40 c.c. as correct, the others are in very
+satisfactory agreement.</p>
+
+<p><b>Effect of varying dilution.</b>&mdash;The conditions were those of the 40 c.c.
+experiment in the last series; but varying amounts of water were used in
+diluting.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Water added</td><td align='left'>none</td><td align='left'>100 c.c.</td><td align='left'>200 c.c.</td><td align='left'>400 c.c.</td></tr>
+<tr><td align='left'>Silver required</td><td align='left'>47.0 c.c.</td><td align='left'>47.0 c.c.</td><td align='left'>47.0 c.c.</td><td align='left'>47.05 c.c.</td></tr>
+</table></div>
+
+<p>Very considerable dilution therefore has no effect.</p>
+
+<p><b>Effect of varying soda.</b>&mdash;The conditions were those of the 40 c.c.
+experiment in the first series, except that varying amounts of soda
+solution were used.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Soda added</td><td align='left'>none</td><td align='left'>10 c.c.</td><td align='left'>30 c.c.</td></tr>
+<tr><td align='left'>Silver required</td><td align='left'>46.95 c.c.</td><td align='left'>47.0 c.c.</td><td align='left'>47.0 c.c.</td></tr>
+</table></div>
+
+<p>This alkali therefore has no prejudicial effect.</p>
+
+<p><b>Effect of ammonia.</b>&mdash;Soda causes turbidity in some cyanide liquors;
+with these it should be replaced by 2 or 3 c.c. of dilute ammonia with a
+gram or so of ammonium chloride. The following experiments with dilute
+ammonia show that larger quantities of this reagent must be avoided.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ammonia added</td><td align='left'>none</td><td align='left'>10 c.c.</td><td align='left'>30 c.c.</td><td align='left'>60 c.c.</td></tr>
+<tr><td align='left'>Silver required</td><td align='left'>46.95 c.c.</td><td align='left'>47.15 c.c.</td><td align='left'>47.7 c.c.</td><td align='left'>49.5 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of sodium bicarbonate.</b>&mdash;In this experiment 1 gram of
+bicarbonate of soda was used instead of the soda or ammonia of the other
+experiments. The silver nitrate required was only 46.45 c.c. instead of
+the 47.0 c.c. which is the normal result. This is probably due to the
+liberation of prussic acid and shows the importance of having the
+solution alkaline.</p>
+
+<p><b>Effect of zinc.</b>&mdash;In each experiment 40 c.c. of the cyanide solution
+and .5 gram of zinc sulphate crystals were used and the bulk was made up
+to 100 c.c. before titrating.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Soda added</td><td align='left'>1 c.c.</td><td align='left'>5 c.c.</td><td align='left'>10 c.c.</td><td align='left'>25 c.c.</td></tr>
+<tr><td align='left'>Silver required</td><td align='left'>47.1 c.c.</td><td align='left'>47.0 c.c.</td><td align='left'>46.9 c.c.</td><td align='left'>46.9 c.c.</td></tr>
+</table></div>
+
+<p>The work was easier with the more alkaline solutions. The titration in
+the presence of zinc is comparatively easy, but, in<span class='pagenum'><a name="Page_167" id="Page_167">[Pg 167]</a></span> learning it, it is
+well to have a burette with cyanide so that if a titration be overdone
+it can be brought back by the addition of 1 or 2 c.c. more cyanide and
+the finish repeated; a quarter of an hour's work in this way will ensure
+confidence in the method.</p>
+
+<p><b>Effect of other substances.</b>&mdash;It was found that an alkaline cyanate,
+sulphocyanate, ferrocyanide, nitrite, borate, silicate or carbonate has
+no effect. The ferricyanide had a small influence and, as might be
+expected, hyposulphite is fatal to the assay. The addition of salts of
+lead and cadmium was without effect. On the other hand, nickel produces
+its full effect; and the quantity of nickel added can be calculated with
+accuracy from the extent of its interference with the titration.</p>
+
+<p><b>Assay of commercial cyanide of potassium.</b>&mdash;Break off 20 or 30 grams of
+the cyanide in clean fresh pieces, weigh accurately to the nearest
+centigram. Dissolve in water containing a little sodium hydroxide;
+transfer to a 2-litre flask: dilute to 2 litres; add a few grams of
+white lead; shake up and allow to settle. Run 50 c.c. of the clear
+liquor from a burette into an 8 oz. flask; add 2 or 3 c.c. of soda
+solution and 3 drops of potassium iodide. Titrate with the standard
+solution of silver nitrate. The percentage may be calculated by
+multiplying the number of c.c. used by 40 (50 c.c. is one fortieth of
+the 2 litres) and dividing by the weight of commercial cyanide
+originally taken.</p>
+
+<p><b>Alkalinity of commercial potassium cyanide and of cyanide
+solutions.</b>&mdash;Hydrocyanic acid like carbonic acid has no action on
+methyl-orange;<a name="FNanchor_43_43" id="FNanchor_43_43"></a><a href="#Footnote_43_43" class="fnanchor">[43]</a> hence the alkaline cyanides may be titrated with
+"normal acid" as easily as the carbonates or hydrates. 100 c.c. of
+normal acid will neutralise 6.5 grams of pure potassium cyanide.<a name="FNanchor_44_44" id="FNanchor_44_44"></a><a href="#Footnote_44_44" class="fnanchor">[44]</a> A
+solution of commercial cyanide prepared as for the assay last described,
+but best without the addition of white lead, may be used for the test.
+Take 50 c.c. of it; tint faintly yellow with methyl-orange and titrate
+with normal acid till the liquor acquires a permanent reddish tint. In
+the case of the purer samples of cyanide the quantity of acid used will
+correspond exactly with that required to neutralise the actual quantity
+of cyanide present as determined by the assay with nitrate of silver.
+The less pure samples will show an excess of alkalinity because of the
+presence of sodium carbonate or of potassium carbonate.</p>
+
+<p>In comparing the alkalinity and cyanide strength of a solution the
+simplest plan is to take 65 c.c. of the solution and titrate<span class='pagenum'><a name="Page_168" id="Page_168">[Pg 168]</a></span> with
+normal acid; for in this case each c.c. of normal acid corresponds to .1
+per cent. of potassium cyanide. In systematic assays of this kind, the
+alkalinity would no doubt be generally in excess of that required by the
+cyanide present: there would be no inconvenience in recording such
+excess in terms of potassium cyanide.</p>
+
+<p><b>Determination of the acidity of an ore.</b>&mdash;Most ores have the power of
+destroying more or less of the alkalinity of a cyanide solution and in a
+proportionate degree of damaging its efficiency. An assay is needed to
+determine how much lime or soda must be added for each ton of ore in
+order to counteract this. Whether this acidity should be reported in
+terms of the lime or of the soda required to neutralise it will depend
+on which of these reagents is to be used in the actual practice. Again,
+if the ore is washed with water before treating with cyanide on the
+large scale, then the assay should be made of the acidity of the ore
+after a similar washing.</p>
+
+<p>The <i>standard solutions of acid and alkali</i> used for this determination
+may be one-fifth normal. 200 c.c. of the normal solution should be
+diluted to 1 litre in each case, 1 c.c. of the resulting solutions would
+be equivalent to 8 milligrams of soda (NaHO) or 5.6 milligrams of lime,
+CaO. It must be remembered this refers to the pure bases in each case.
+Suppose it is desired to report as so many lbs. of lime to the short ton
+(2000 lbs.) of ore. Since 1 c.c. of the standard solution is equivalent
+to 5.6 milligrams of lime, if we take 2000 times this weight of ore
+(<i>i.e.</i> 11,200 milligrams or 11.2 grams) for the assay, each c.c. of
+standard solution will be equivalent to 1 lb. of lime to the short
+ton.<a name="FNanchor_45_45" id="FNanchor_45_45"></a><a href="#Footnote_45_45" class="fnanchor">[45]</a></p>
+
+<p><b>Total acidity.</b>&mdash;Weigh out 11.2 grams of the ore, place them in a
+four-inch evaporating dish and measure on to it from a burette 10 or 20
+c.c. of the standard solution of soda. Stir the soda solution into the
+ore and allow to stand for 15 or 20 minutes with occasional stirring.
+Stir up with 30 or 40 c.c. of water, float a piece of litmus paper on
+the liquid and titrate with the standard solution of acid. If the ore is
+strictly neutral the quantity of "acid" required to redden the litmus
+will be the same as the quantity of "soda" originally used. If the ore
+is acid, less acid will be used. For example, if 10 c.c. of soda were
+used and only 7 c.c. of acid were required, the ore will have done the
+work of the remaining 3 c.c. of acid. And the ton of ore will require 3
+lbs. of lime to neutralise its acidity.<span class='pagenum'><a name="Page_169" id="Page_169">[Pg 169]</a></span></p>
+
+<p><b>Acidity after washing.</b>&mdash;Take 11.2 grams of the ore; wash thoroughly
+with water and immediately treat the residue, without drying, exactly as
+just described.</p>
+
+<p><b>Examination of cyanide solutions for metals, &amp;c.</b>&mdash;Take a measured
+quantity of the solution, say 20 c.c.<a name="FNanchor_46_46" id="FNanchor_46_46"></a><a href="#Footnote_46_46" class="fnanchor">[46]</a> and evaporate in a small dish
+with, say, half a c.c. of strong sulphuric acid. Evaporate at first, on
+a water-bath in a well ventilated place, but finish off with a naked
+Bunsen flame, using a high temperature at the end in order to completely
+decompose the more refractory double cyanides. Allow to cool; moisten
+with strong hydrochloric acid; warm with a little water and test for the
+metals in the solution by the ordinary methods. Since the quantities of
+the metals likely to be present may be given in milligrams the work must
+be carefully performed. It may be worth while to determine the
+proportions of lime and magnesia as well as those of the metals proper.</p>
+
+<p>Or the 20 c.c. of cyanide liquor may be evaporated with 5 c.c. of strong
+nitric acid to dryness and gently ignited and the residue taken up with
+2 or 3 c.c. of strong hydrochloric acid.</p>
+
+<p>Copper, iron, and zinc can be rapidly determined in such a solution, as
+follows. Dilute with water to 10 or 15 c.c., add an excess of ammonia,
+and filter. The precipitate will contain the iron as ferric hydrate;
+dissolve it in a little hot dilute sulphuric acid: reduce with
+sulphuretted hydrogen; boil off the excess of gas, cool and titrate with
+standard potassium permanganate (p. 236). Determine the copper in the
+filtrate colorimetrically (p. 203); but avoid further dilution. Then add
+dilute hydrochloric acid, so as to have an excess of 4 or 5 c.c. after
+neutralising the ammonia; add some clean strips of lead foil, and boil
+until the solution has for some time become colourless. Titrate with
+standard potassium ferrocyanide (p. 263) without further dilution, and
+bearing in mind that at most only one or two c.c. will be required.</p>
+
+<p><b>Examination of an ore for "cyanicides."</b>&mdash;Place 100 grams of the ore
+with 200 c.c. of a cyanide solution of known strength (say .1 or .2 per
+cent.) in a bottle and agitate for a definite time, such as one or two
+days. Filter off some of the liquor and assay for cyanide, using say 20
+c.c. Calculate how much cyanide has been destroyed in the operation.
+Evaporate 20 c.c. with sulphuric or nitric acid and examine for metal.
+Test another portion for sulphides, &amp;c.</p>
+
+<p>The student who has mastered the methods of assaying can greatly improve
+himself by working out such problems as the above.<span class='pagenum'><a name="Page_170" id="Page_170">[Pg 170]</a></span></p>
+
+
+<h4>PLATINUM.</h4>
+
+<p>Platinum occurs in nature in alluvial deposits associated with gold and
+some rare metals, generally in fine metallic grains, and, occasionally,
+in nuggets. It is a grey metal with a high specific gravity, 21.5 when
+pure and about 18.0 in native specimens. It is fusible only at the
+highest temperature, and is not acted on by acids.</p>
+
+<p>It is dissolved by warm aqua regia, forming a solution of "platinic
+chloride," H<sub>2</sub>PtCl<sub>6</sub>. This substance on evaporation remains as a
+brownish red deliquescent mass; on drying at 300&deg; C. it is converted
+into platinous chloride, PtCl<sub>2</sub>, and becomes insoluble, and at a
+higher temperature it is converted into platinum. All platinum compounds
+yield the metal in this way. Platinic chloride combines with other
+chlorides to form double salts, of which the ammonic and potassic
+platino-chlorides are the most important.</p>
+
+<p>Platinum alone is not soluble in nitric acid; but when alloyed with
+other metals which dissolve in this acid it too is dissolved; so that in
+gold parting, for example, if platinum was present, some, or perhaps the
+whole of it would go into solution with the silver. Such alloys,
+however, when treated with hot sulphuric acid leave the platinum in the
+residue with the gold.</p>
+
+<p>Platinum is detected when in the metallic state by its physical
+characters and insolubility in acids. In alloys it may be found by
+dissolving them in nitric acid or in aqua regia, evaporating with
+hydrochloric acid, and treating the filtrate with ammonic chloride and
+alcohol. A heavy yellow precipitate marks its presence.</p>
+
+<p>The assay of bullion, or of an alloy containing platinum, may be made as
+follows: Take 0.2 gram of the alloy and an equal weight of fine silver,
+cupel with sheet lead, and weigh. The loss in weight, after deducting
+that of the silver added, gives the weight of the base metals, copper,
+lead, &amp;c. Flatten the button and part by boiling with strong sulphuric
+acid for several minutes. <i>When cold</i>, wash, anneal, and weigh. The
+weight is that of the platinum and gold. The silver may be got by
+difference. Re-cupel the metal thus got with 12 or 15 times its weight
+of silver, flatten and part the gold with nitric acid in the usual way
+(see under <i>Gold</i>), and the platinum will dissolve. The gold may contain
+an alloy of osmium and iridium; if so, it should be weighed and treated
+with aqua regia. The osmiridium will remain as an insoluble residue,
+which can be separated and weighed. Its weight deducted from that
+previously ascertained will give the weight of the gold.<span class='pagenum'><a name="Page_171" id="Page_171">[Pg 171]</a></span></p>
+
+<p>When the platinum only is required, the alloy must be dissolved by
+prolonged treatment with aqua regia, the solution evaporated to dryness,
+and the residue extracted with water. The solution thus obtained is
+treated with ammonic chloride in large excess and with some alcohol. A
+sparingly soluble<a name="FNanchor_47_47" id="FNanchor_47_47"></a><a href="#Footnote_47_47" class="fnanchor">[47]</a> yellow ammonic platinum chloride is thrown down,
+mixed, perhaps, with the corresponding salts of other metals of the
+platinum group. Gold will be in solution. The solution is allowed to
+stand for some time, and then the precipitate is filtered off, washed
+with alcohol, dried, and transferred (wrapped in the filter paper) to a
+weighed crucible. It is ignited, gently at first, as there is danger of
+volatilising some of the platinum chloride, and afterwards intensely.
+With large quantities of platinum the ignition should be performed in an
+atmosphere of hydrogen. Cool and weigh as metallic platinum.</p>
+
+
+<h4>IRIDIUM</h4>
+
+<p>Occurs in nature alloyed with osmium as osmiridium or iridosmine, which
+is "rather abundant in the auriferous beach sands of Northern
+California" (Dana). It occurs in bright metallic scales, which do not
+alloy with lead, and are insoluble in aqua regia. Iridium also occurs in
+most platinum ores, and forms as much as two per cent. of some
+commercial platinum. In chemical properties it resembles platinum, but
+the ammonic irido-chloride has a dark red colour, and on ignition leaves
+metallic iridium, which does not dissolve in aqua regia diluted with
+four or five times its volume of water and heated to a temperature of
+40&deg; or 50&deg; C.</p>
+
+<p>The other metals of the platinum group are Palladium, Rhodium, Osmium,
+and Ruthenium. They differ from gold, platinum, and iridium by the
+insolubility of their sulphides in a solution of sodium sulphide.
+Palladium is distinguished by the insolubility of its iodide; and Osmium
+by the volatility of its oxide on boiling with nitric acid.</p>
+
+
+<h4>MERCURY.</h4>
+
+<p>Mercury occurs native and, occasionally, alloyed with gold or silver in
+natural amalgams; but its chief ore is the sulphide, cinnabar. It is
+comparatively rare, being mined for only in a few districts. It is
+chiefly used in the extraction of gold and silver from their ores
+(amalgamation); for silvering mirrors, &amp;c.</p>
+
+<p>Mercury forms two series of salts, mercurous and mercuric, but for the
+purposes of the assayer the most important property<span class='pagenum'><a name="Page_172" id="Page_172">[Pg 172]</a></span> is the ease with
+which it can be reduced to the metallic state from either of these.
+Mercury itself is soluble in nitric acid, forming, when the acid is hot
+and strong, mercuric nitrate. Cinnabar is soluble only in aqua regia.
+Mercurous salts are generally insoluble, and may be converted into
+mercuric salts by prolonged boiling with oxidising agents (nitric acid
+or aqua regia). The salts of mercury are volatile, and, if heated with a
+reducing agent or some body capable of fixing the acid, metallic mercury
+is given off, which may be condensed and collected.</p>
+
+<p>Mercury is separated from its solutions by zinc or copper, or it may be
+thrown down by stannous chloride, which, when in excess, gives a grey
+powder of metallic mercury, or, if dilute, a white crystalline
+precipitate of mercurous chloride. Nitric acid solutions of mercury
+yield the metal on electrolysis; and, if the pole on which the metal
+comes down be made of gold or copper, or is coated with these, the
+separated mercury will adhere thereto. It may then be washed and
+weighed.</p>
+
+<p>The best tests for mercury next to obtaining globules of the metal are:
+(1) a black precipitate with sulphuretted hydrogen from acid solutions,
+which is insoluble in nitric acid; and (2) a white precipitate with
+stannous chloride.</p>
+
+
+<h4>DRY METHOD.</h4>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig047.jpg" width="450" height="139" alt="Fig. 47." title="" />
+
+</div>
+
+<p>Weigh up 5 grams, if the ore is rich, or 10 grams, if a poorer mineral.
+Take a piece of combustion tube from 18 inches to 2 feet long, closed at
+one end, and place in it some powdered magnesite, so as to fill it to a
+depth of 2 or 3 inches, and on that a layer of an equal quantity of
+powdered lime (not slaked). Mix the weighed sample of ore in a mortar
+with 10 grams of finely powdered lime and transfer to the tube; rinse
+out the mortar with a little more lime, and add the rinsings. Cover with
+a layer of six or seven inches more lime and a loosely fitting plug of
+asbestos. Draw out the tube before the blowpipe to the shape shown in
+fig. 47, avoiding the formation of a ridge or hollow at the bend which
+might collect the mercury. Tap gently, holding the tube nearly
+horizontal, so as to allow sufficient space above the mixture for the
+passage of the gases and vapours which are formed. Place the tube in a
+"tube furnace," and, when in position, place a small beaker of water so
+that it shall just close the opening of the tube. The point of the tube
+should not more than touch<span class='pagenum'><a name="Page_173" id="Page_173">[Pg 173]</a></span> the surface of the water. Bring the tube
+gradually to a red heat, commencing by heating the lime just behind the
+asbestos plug, and travelling slowly backwards. When the portion of the
+tube containing the ore has been heated to redness for some time the
+heat is carried back to the end of the tube. The magnesite readily gives
+up carbonic acid, which fills the tube and sweeps the mercury vapour
+before it. Some of the mercury will have dropped into the beaker, and
+some will remain as drops adhering to the upper part of the neck. Whilst
+the tube is still hot cut off the neck of the tube just in front of the
+asbestos plug (a drop of water from the wash bottle will do this), and
+wash the mercury from the neck into the beaker. The mercury easily
+collects into a globule, which must be transferred, after decanting off
+the bulk of the water, to a weighed Berlin crucible. The water is
+removed from the crucible, first by the help of filter paper, and then
+by exposing in a desiccator over sulphuric acid, where it should be left
+until its weight remains constant. It should not be warmed.</p>
+
+<p><i>Example</i>:&mdash;5 grams of an ore treated in this way gave 4.265 grams of
+mercury, equivalent to 85.3 per cent. Pure cinnabar contains 86.2 per
+cent.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p><i>Solution.</i>&mdash;Since solutions of chloride of mercury cannot be boiled
+without risk of loss,<a name="FNanchor_48_48" id="FNanchor_48_48"></a><a href="#Footnote_48_48" class="fnanchor">[48]</a> nitric acid solutions should be used wherever
+possible. No mercury-containing minerals are insoluble in acids; but
+cinnabar requires aqua regia for solution. In dissolving this mineral
+nitric acid should be used, with just as much hydrochloric acid as will
+suffice to take it up.</p>
+
+<p>To separate the mercury, pass sulphuretted hydrogen in considerable
+excess through the somewhat dilute solution. The precipitate should be
+black, although it comes down at first very light coloured. It is
+filtered, washed, and transferred back to the beaker, and then digested
+with warm ammonic sulphide. The residue, filtered, washed, and boiled
+with dilute nitric acid, will, in the absence of much lead, be pure
+mercuric sulphide. If much lead is present, a portion may be
+precipitated as sulphate, but can be removed by washing with ammonic
+acetate. To get the mercury into solution, cover with nitric acid and a
+few drops of hydrochloric, and warm till solution is effected. Dilute
+with water to 50 or 100 c.c.<span class='pagenum'><a name="Page_174" id="Page_174">[Pg 174]</a></span></p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>This may be made by <i>electrolysis</i>. The same apparatus as is used for
+the electrolytic copper assay may be employed, but instead of a cylinder
+of platinum one cut out of sheet copper should be taken, or the platinum
+one may be coated with an evenly deposited layer of copper. Fix the
+spiral and weighed copper cylinder in position, couple up the battery,
+<i>and when this has been done</i> put the nitric acid solution of the
+mercury in its place.<a name="FNanchor_49_49" id="FNanchor_49_49"></a><a href="#Footnote_49_49" class="fnanchor">[49]</a> The student had better refer to the
+description of the <i>Electrolytic Copper Assay</i>.</p>
+
+<p>The mercury comes down readily, and the precipitation is complete in a
+few hours: it is better to leave it overnight to make sure of complete
+reduction. Disconnect the apparatus, and wash the cylinder, first with
+cold water, then with alcohol. Dry by placing in the water oven for two
+or three minutes. Cool and weigh: the increase in weight gives the
+amount of metallic mercury.</p>
+
+<p>It must be remembered that copper will precipitate mercury without the
+aid of the battery; but in this case copper will go into solution with a
+consequent loss in the weight of the cylinder: this must be avoided by
+connecting the battery before immersing the electrodes in the assay
+solution. The electrolysed solution should be treated with an excess of
+ammonia, when a blue coloration will indicate copper, in which case the
+electrolysis is unsatisfactory. With a little care this need not happen.
+Gold cylinders may preferably be used instead of copper; but on platinum
+the deposit of mercury is grey and non-adherent, so that it cannot be
+washed and weighed.</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>Several methods have been devised: for the details of these the student
+is referred to Sutton's "Handbook of Volumetric Analysis."</p>
+
+
+<h4>QUESTIONS.</h4>
+
+<p>1. The specific gravity of mercury is 13.596. What volume would 8 grams
+occupy?</p>
+
+<p>2. If 3.169 grams of cinnabar gave 2.718 grams of mercury, what would be
+the percentage of the metal in the ore?</p>
+
+<p>3. Pour solution of mercuric chloride on mercury and explain what
+happens.</p>
+
+<p>4. On dissolving 0.3 gram of mercury in hot nitric acid, and passing
+sulphuretted hydrogen in excess through the diluted solution, what
+weight of precipitate will be got?</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_9_9" id="Footnote_9_9"></a><a href="#FNanchor_9_9"><span class="label">[9]</span></a> Lead may be granulated by heating it to a little above the
+melting point, pouring it into a closed wooden box, and rapidly
+agitating it as it solidifies.</p></div>
+
+<div class="footnote"><p><a name="Footnote_10_10" id="Footnote_10_10"></a><a href="#FNanchor_10_10"><span class="label">[10]</span></a> A rod of iron placed in the crucible with the assays will
+decompose any regulus that may be formed.</p></div>
+
+<div class="footnote"><p><a name="Footnote_11_11" id="Footnote_11_11"></a><a href="#FNanchor_11_11"><span class="label">[11]</span></a> With buttons poor in silver the lowering of the
+temperature at this stage is not a matter of importance.</p></div>
+
+<div class="footnote"><p><a name="Footnote_12_12" id="Footnote_12_12"></a><a href="#FNanchor_12_12"><span class="label">[12]</span></a> 100 grams of the lead, or of its oxide, will contain from
+1.5 to 2.5 milligrams.</p></div>
+
+<div class="footnote"><p><a name="Footnote_13_13" id="Footnote_13_13"></a><a href="#FNanchor_13_13"><span class="label">[13]</span></a> Still the precautions of having cupels well made from bone
+ash in fine powder, and of working the cupellation at as low a
+temperature as possible are very proper ones, provided they are not
+carried to an absurd excess.</p></div>
+
+<div class="footnote"><p><a name="Footnote_14_14" id="Footnote_14_14"></a><a href="#FNanchor_14_14"><span class="label">[14]</span></a> Be careful to remove the crucible before taking the bottle
+out of the basin of water; if this is not done the chloride may be
+washed out of it.</p></div>
+
+<div class="footnote"><p><a name="Footnote_15_15" id="Footnote_15_15"></a><a href="#FNanchor_15_15"><span class="label">[15]</span></a> 1 c.c. of this dilute acid will precipitate 8 or 9
+milligrams of silver.</p></div>
+
+<div class="footnote"><p><a name="Footnote_16_16" id="Footnote_16_16"></a><a href="#FNanchor_16_16"><span class="label">[16]</span></a> Chlorides interfere not merely by removing silver as
+insoluble silver chloride, but also by making it difficult to get a good
+finishing point, owing to the silver chloride removing the colour from
+the reddened solution.</p></div>
+
+<div class="footnote"><p><a name="Footnote_17_17" id="Footnote_17_17"></a><a href="#FNanchor_17_17"><span class="label">[17]</span></a> These results were obtained when using ammonium
+sulphocyanate, and cannot be explained by the presence of such
+impurities as chlorides, &amp;c.</p></div>
+
+<div class="footnote"><p><a name="Footnote_18_18" id="Footnote_18_18"></a><a href="#FNanchor_18_18"><span class="label">[18]</span></a> Multiply the <i>standard</i> by 1000, and dilute 100 c.c. of
+the standard solution to the resulting number of c.c. Thus, with a
+solution of a standard .495, dilute 100 c.c. to 495 c.c., using, of
+course, distilled water.</p></div>
+
+<div class="footnote"><p><a name="Footnote_19_19" id="Footnote_19_19"></a><a href="#FNanchor_19_19"><span class="label">[19]</span></a> HNa<sub>2</sub>AsO<sub>4</sub> + 3AgNO<sub>3</sub> = Ag<sub>3</sub>AsO<sub>4</sub> + HNO<sub>3</sub> +
+2NaNO<sub>3</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_20_20" id="Footnote_20_20"></a><a href="#FNanchor_20_20"><span class="label">[20]</span></a>
+<br />
+SiO<sub>2</sub> + Na<sub>2</sub>CO<sub>3</sub> = CO<sub>2</sub> + Na<sub>2</sub>SiO<sub>3</sub><br />
+SiO<sub>2</sub> + 2NaHCO<sub>3</sub> = 2CO<sub>2</sub> + Na<sub>2</sub>SiO<sub>3</sub> + H<sub>2</sub>O.<br />
+</p></div>
+
+<div class="footnote"><p><a name="Footnote_21_21" id="Footnote_21_21"></a><a href="#FNanchor_21_21"><span class="label">[21]</span></a> PbO + SiO<sub>2</sub> = PbSiO<sub>3</sub></p></div>
+
+<div class="footnote"><p><a name="Footnote_22_22" id="Footnote_22_22"></a><a href="#FNanchor_22_22"><span class="label">[22]</span></a> Here and elsewhere in this article when a flux is spoken
+of as soda the bicarbonate is meant.</p></div>
+
+<div class="footnote"><p><a name="Footnote_23_23" id="Footnote_23_23"></a><a href="#FNanchor_23_23"><span class="label">[23]</span></a> See the description of the process commencing on p. 98 and
+the explanatory remarks on p. 110.</p></div>
+
+<div class="footnote"><p><a name="Footnote_24_24" id="Footnote_24_24"></a><a href="#FNanchor_24_24"><span class="label">[24]</span></a> Percy, <i>Metallurgy of Silver and Gold</i>, p. 258.</p></div>
+
+<div class="footnote"><p><a name="Footnote_25_25" id="Footnote_25_25"></a><a href="#FNanchor_25_25"><span class="label">[25]</span></a> "Limits of Accuracy attained in Gold-bullion Assay,"
+<i>Trans. Chem. Soc.</i>, 1893.</p></div>
+
+<div class="footnote"><p><a name="Footnote_26_26" id="Footnote_26_26"></a><a href="#FNanchor_26_26"><span class="label">[26]</span></a> "Assaying and Hall-marking at the Chester Assay Office."
+W.F. Lowe. <i>Journ. Soc. Chem. Industry</i>, Sept. 1889.</p></div>
+
+<div class="footnote"><p><a name="Footnote_27_27" id="Footnote_27_27"></a><a href="#FNanchor_27_27"><span class="label">[27]</span></a> Fine or pure gold is 24 carat. Nine carat gold therefore
+contains 9 parts of gold in 24 of the alloy; eighteen carat gold
+contains 18 parts of gold in 24; and so on.</p></div>
+
+<div class="footnote"><p><a name="Footnote_28_28" id="Footnote_28_28"></a><a href="#FNanchor_28_28"><span class="label">[28]</span></a> The mouth of the flask must not have a rim around it.</p></div>
+
+<div class="footnote"><p><a name="Footnote_29_29" id="Footnote_29_29"></a><a href="#FNanchor_29_29"><span class="label">[29]</span></a> See "Assaying and Hall-marking at the Chester Assay
+Office," by W.F. Lowe. <i>Journ. Soc. Chem. Industry</i>, Sept. 1889.</p></div>
+
+<div class="footnote"><p><a name="Footnote_30_30" id="Footnote_30_30"></a><a href="#FNanchor_30_30"><span class="label">[30]</span></a> Percy, <i>Metallurgy of Silver and Gold</i>, p. 263.</p></div>
+
+<div class="footnote"><p><a name="Footnote_31_31" id="Footnote_31_31"></a><a href="#FNanchor_31_31"><span class="label">[31]</span></a> See also "The Assaying of Gold Bullion," by C. Whitehead
+and T. Ulke. <i>Eng. and Mining Journal</i>, New York, Feb. 12, 1898.</p></div>
+
+<div class="footnote"><p><a name="Footnote_32_32" id="Footnote_32_32"></a><a href="#FNanchor_32_32"><span class="label">[32]</span></a> Consult Percy's <i>Metallurgy of Silver and Gold</i>, p. 172;
+A.C. Claudet, <i>Trans. Inst. Mining and Metallurgy</i>, vol. vi. p. 29; G.M.
+Roberts <i>Trans. Amer. Inst. Mining Engineers</i>, Buffalo Meeting, 1898; J.
+and H.S. Pattinson, <i>Journ. Soc. Chem. Industry</i>, vol. xi. p. 321.</p></div>
+
+<div class="footnote"><p><a name="Footnote_33_33" id="Footnote_33_33"></a><a href="#FNanchor_33_33"><span class="label">[33]</span></a> Heycock and Neville, <i>Journ. Chem. Soc.</i>, 1892, p. 907.</p></div>
+
+<div class="footnote"><p><a name="Footnote_34_34" id="Footnote_34_34"></a><a href="#FNanchor_34_34"><span class="label">[34]</span></a> G.M. Roberts.</p></div>
+
+<div class="footnote"><p><a name="Footnote_35_35" id="Footnote_35_35"></a><a href="#FNanchor_35_35"><span class="label">[35]</span></a> A.C. Claudet.</p></div>
+
+<div class="footnote"><p><a name="Footnote_36_36" id="Footnote_36_36"></a><a href="#FNanchor_36_36"><span class="label">[36]</span></a> "The Sampling of Argentiferous and Auriferous Copper," by
+A.R. Ledoux. <i>Journ. Canadian Mining Institute</i>, 1899.</p></div>
+
+<div class="footnote"><p><a name="Footnote_37_37" id="Footnote_37_37"></a><a href="#FNanchor_37_37"><span class="label">[37]</span></a> NaCNO + BaCl<sub>2</sub> + NaHO + H<sub>2</sub>O = NH<sub>3</sub> + BaCO<sub>3</sub> + 2
+NaCl.</p></div>
+
+<div class="footnote"><p><a name="Footnote_38_38" id="Footnote_38_38"></a><a href="#FNanchor_38_38"><span class="label">[38]</span></a> HCy + NaHO = NaCy + H<sub>2</sub>O.</p></div>
+
+<div class="footnote"><p><a name="Footnote_39_39" id="Footnote_39_39"></a><a href="#FNanchor_39_39"><span class="label">[39]</span></a> 2KCN + AgNO<sub>3</sub> = KAg(CN)<sub>2</sub> + KNO<sub>3</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_40_40" id="Footnote_40_40"></a><a href="#FNanchor_40_40"><span class="label">[40]</span></a> If it be desired to make a solution so that 100 c.c. shall
+be equivalent to 1 gram of sodium cyanide, then 18.085 grams of silver
+nitrate should be taken for each litre.</p></div>
+
+<div class="footnote"><p><a name="Footnote_41_41" id="Footnote_41_41"></a><a href="#FNanchor_41_41"><span class="label">[41]</span></a> AgNO<sub>3</sub> + KAgCy<sub>2</sub> = 2 AgCy + KNO<sub>3</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_42_42" id="Footnote_42_42"></a><a href="#FNanchor_42_42"><span class="label">[42]</span></a> AgNO<sub>3</sub> + KI = AgI + KNO<sub>3</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_43_43" id="Footnote_43_43"></a><a href="#FNanchor_43_43"><span class="label">[43]</span></a> See pp. 322, 323, and 324 for a description of the methods
+for measuring the quantity of acid or alkali.</p></div>
+
+<div class="footnote"><p><a name="Footnote_44_44" id="Footnote_44_44"></a><a href="#FNanchor_44_44"><span class="label">[44]</span></a> KCN + HCl = KCl + HCN</p></div>
+
+<div class="footnote"><p><a name="Footnote_45_45" id="Footnote_45_45"></a><a href="#FNanchor_45_45"><span class="label">[45]</span></a> Taking 16.0 grams of ore, each c.c. = 1 lb. of soda to the
+short ton. The corresponding figures for the long ton are 12.544 grams
+for lime and 17.92 grams for soda.</p></div>
+
+<div class="footnote"><p><a name="Footnote_46_46" id="Footnote_46_46"></a><a href="#FNanchor_46_46"><span class="label">[46]</span></a> In which case each .01 gram of metal found equals 1 lb to
+the short ton of solution.</p></div>
+
+<div class="footnote"><p><a name="Footnote_47_47" id="Footnote_47_47"></a><a href="#FNanchor_47_47"><span class="label">[47]</span></a> 100 c.c. of water dissolves 0.66 gram of the salt; it is
+almost insoluble in alcohol or in solutions of ammonic chloride.</p></div>
+
+<div class="footnote"><p><a name="Footnote_48_48" id="Footnote_48_48"></a><a href="#FNanchor_48_48"><span class="label">[48]</span></a> According to Personne mercuric chloride is not volatilised
+from boiling solutions when alkaline chlorides are present.</p></div>
+
+<div class="footnote"><p><a name="Footnote_49_49" id="Footnote_49_49"></a><a href="#FNanchor_49_49"><span class="label">[49]</span></a> The solution should contain about 0.25 gram of mercury,
+and a large excess of nitric acid must be avoided.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_175" id="Page_175">[Pg 175]</a></span></p>
+<h2><a name="CHAPTER_X" id="CHAPTER_X"></a>CHAPTER X.</h2>
+
+<h3>COPPER&mdash;LEAD&mdash;THALLIUM&mdash;BISMUTH&mdash;ANTIMONY.</h3>
+
+
+<h4>COPPER.</h4>
+
+
+<p>Copper occurs native in large quantities, especially in the Lake
+Superior district; in this state it is generally pure. More frequently
+it is found in combination. The ores of copper may be classed as oxides
+and sulphides. The most abundant oxidised ores are the carbonates,
+malachite and chessylite; the silicates, as also the red and black
+oxides, occur less abundantly. All these yield their copper in solution
+on boiling with hydrochloric acid.</p>
+
+<p>The sulphides are more abundant. Copper pyrites (or yellow ore),
+erubescite (or purple ore), and chalcocite (or grey ore) are the most
+important. Iron pyrites generally carries copper and is frequently
+associated with the above-mentioned minerals. These are all attacked by
+nitric acid. They nearly all contain a small quantity of organic matter,
+and frequently considerable quantities of lead, zinc, silver, gold,
+arsenic, bismuth, &amp;c.</p>
+
+<p>The copper ores are often concentrated on the mine before being sent
+into the market, either by smelting, when the product is a regulus or
+matte, or by a wet method of extraction, yielding cement copper or
+precipitate. A regulus is a sulphide of copper and iron, carrying from
+30 to 40 per cent. of copper. A precipitate, which is generally in the
+form of powder, consists mainly of metallic copper. Either regulus or
+precipitate may be readily dissolved in nitric acid.</p>
+
+<p>Copper forms two classes of salts, cuprous and cupric. The former are
+pale coloured and of little importance to the assayer. They are easily
+and completely converted into cupric by oxidising agents. Cupric
+compounds are generally green or blue, and are soluble in ammonia,
+forming deep blue solutions.<span class='pagenum'><a name="Page_176" id="Page_176">[Pg 176]</a></span></p>
+
+
+<h4>DRY ASSAY.</h4>
+
+<p>That, for copper, next after those for gold and silver, holds a more
+important position than any other dry assay. The sale of copper ores has
+been regulated almost solely in the past by assays made on the Cornish
+method. It is not pretended that this method gives the actual content of
+copper, but it gives the purchaser an idea of the quantity and quality
+of the metal that can be got by smelting. The process is itself one of
+smelting on a small scale. As might be expected, however, the assay
+produce and the smelting produce are not the same, there being a smaller
+loss of copper in the smelting. The method has worked very well, but
+when applied to the purchase of low class ores (from which the whole of
+the copper is extracted by wet methods) it is unsatisfactory. The
+following table, which embodies the results of several years' experience
+with copper assays, shows the loss of copper on ores of varying produce.
+The figures in the fourth column show how rapidly the proportion of
+copper lost increases as the percentage of copper in the ore falls below
+30 per cent. For material with more than 30 per cent. the proportion
+lost is in inverse proportion to the copper present.</p>
+
+
+<h4>LOSS OF COPPER.</h4>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper present.</td><td align='left'>Dry Assay.</td><td align='left'>Margin.</td><td align='left'>Loss on 100 Parts of Copper.</td></tr>
+<tr><td align='left'>Per cent.</td><td align='left'>Per cent.</td><td align='left'>Per cent.</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>100</td><td align='left'>98</td><td align='left'>2.0</td><td align='left'>2.0</td></tr>
+<tr><td align='left'>95</td><td align='left'>92-1/2</td><td align='left'>2.5</td><td align='left'>2.6</td></tr>
+<tr><td align='left'>90</td><td align='left'>87-3/8</td><td align='left'>2.6</td><td align='left'>2.9</td></tr>
+<tr><td align='left'>85</td><td align='left'>82-3/8</td><td align='left'>2.6</td><td align='left'>3.0</td></tr>
+<tr><td align='left'>80</td><td align='left'>77-3/8</td><td align='left'>2.6</td><td align='left'>3.2</td></tr>
+<tr><td align='left'>75</td><td align='left'>72-3/8</td><td align='left'>2.6</td><td align='left'>3.5</td></tr>
+<tr><td align='left'>70</td><td align='left'>67-1/2</td><td align='left'>2.5</td><td align='left'>3.6</td></tr>
+<tr><td align='left'>65</td><td align='left'>62-1/2</td><td align='left'>2.5</td><td align='left'>3.8</td></tr>
+<tr><td align='left'>60</td><td align='left'>57-5/8</td><td align='left'>2.4</td><td align='left'>4.0</td></tr>
+<tr><td align='left'>55</td><td align='left'>52-3/4</td><td align='left'>2.3</td><td align='left'>4.2</td></tr>
+<tr><td align='left'>50</td><td align='left'>47-3/4</td><td align='left'>2.2</td><td align='left'>4.4</td></tr>
+<tr><td align='left'>45</td><td align='left'>43</td><td align='left'>2.0</td><td align='left'>4.5</td></tr>
+<tr><td align='left'>40</td><td align='left'>38-1/8</td><td align='left'>1.8</td><td align='left'>4.6</td></tr>
+<tr><td align='left'>35</td><td align='left'>33-1/4</td><td align='left'>1.7</td><td align='left'>4.8</td></tr>
+<tr><td align='left'>30</td><td align='left'>28-1/2</td><td align='left'>1.50</td><td align='left'>5.0</td></tr>
+<tr><td align='left'>25</td><td align='left'>23-1/2</td><td align='left'>1.50</td><td align='left'>6.0</td></tr>
+<tr><td align='left'>20</td><td align='left'>18-1/2</td><td align='left'>1.56</td><td align='left'>7.8</td></tr>
+<tr><td align='left'>18</td><td align='left'>16-1/2</td><td align='left'>1.53</td><td align='left'>8.5</td></tr>
+<tr><td align='left'>16</td><td align='left'>14-1/2</td><td align='left'>1.48</td><td align='left'>9.3</td></tr>
+<tr><td align='left'>14</td><td align='left'>12-5/8</td><td align='left'>1.40</td><td align='left'>10.0</td></tr>
+<tr><td align='left'>12</td><td align='left'>10-5/8</td><td align='left'>1.37</td><td align='left'>11.4</td></tr>
+<tr><td align='left'>10</td><td align='left'>8-3/4</td><td align='left'>1.28</td><td align='left'>12.8</td></tr>
+<tr><td align='left'>8</td><td align='left'>6-7/8</td><td align='left'>1.14</td><td align='left'>14.3</td></tr>
+<tr><td align='left'>6</td><td align='left'>5</td><td align='left'>1.05</td><td align='left'>17.5</td></tr>
+<tr><td align='left'>5</td><td align='left'>4</td><td align='left'>1.00</td><td align='left'>20.0</td></tr>
+<tr><td align='left'>4</td><td align='left'>3</td><td align='left'>1.00</td><td align='left'>25.0</td></tr>
+<tr><td align='left'>3.75</td><td align='left'>2-3/4</td><td align='left'>0.97</td><td align='left'>26.0</td></tr>
+<tr><td align='left'>3.50</td><td align='left'>2-9/16</td><td align='left'>0.94</td><td align='left'>27.0</td></tr>
+<tr><td align='left'>3.25</td><td align='left'>2-5/16</td><td align='left'>0.91</td><td align='left'>28.0</td></tr>
+<tr><td align='left'>3.00</td><td align='left'>2-1/8</td><td align='left'>0.87</td><td align='left'>29.0</td></tr>
+<tr><td align='left'>2.75</td><td align='left'>1-15/16</td><td align='left'>0.82</td><td align='left'>30.0</td></tr>
+<tr><td align='left'>2.50</td><td align='left'>1-3/4</td><td align='left'>0.77</td><td align='left'>31.0</td></tr>
+<tr><td align='left'>2.25</td><td align='left'>1-1/2</td><td align='left'>0.72</td><td align='left'>32.0</td></tr>
+<tr><td align='left'>2.00</td><td align='left'>1-5/16</td><td align='left'>0.66</td><td align='left'>33.0</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_177" id="Page_177">[Pg 177]</a></span></p>
+
+<p>The wet assay being known, the dry assay can be calculated with the help
+of the above table by deducting the amount in the column headed "margin"
+opposite the corresponding percentage. For example, if the wet assay
+gives a produce of 17.12 per cent., there should be deducted 1.5; the
+dry assay would then be 15.62, or, since the fractions are always
+expressed in eighths, 15-5/8. With impure ores, containing from 25 to 50
+per cent. of copper, the differences may be perhaps 1/4 greater.</p>
+
+<p>Wet methods are gradually replacing the dry assay, and it is probable
+that in the future they will supersede it; for stock-taking, and the
+various determinations required in smelting works and on mines, they are
+generally adopted, because they give the actual copper contents, and
+since it is obvious that a knowledge of this is more valuable to the
+miner and smelter. Moreover, the working of the dry method has been
+monopolised by a small ring of assayers, with the double result of
+exciting outside jealousy and, worse still, of retarding the development
+and improvement of the process.</p>
+
+<p>The principal stages of the dry assay are: (1) the concentration of the
+copper in a regulus; (2) the separation of the sulphur by calcining; (3)
+the reduction of the copper by fusion; and (4) the refining of the metal
+obtained.</p>
+
+<p>The whole of these operations are not necessary with all copper
+material. Ores are worked through all the stages; with mattes, the
+preliminary fusion for regulus is omitted; precipitates are simply fused
+for coarse copper, and refined; and blister or bar coppers are refined,
+or, if very pure, subjected merely to washing.</p>
+
+<p>The quantity of ore generally taken is 400 grains, and is known as "a
+full trial"; but for rich material, containing more than 50 per cent. of
+copper, "a half trial," or 200 grains, is used.<span class='pagenum'><a name="Page_178" id="Page_178">[Pg 178]</a></span></p>
+
+<p><b>Fusion for Regulus.</b>&mdash;The ore (either with or without a previous
+imperfect roasting to get rid of any excess of sulphur) is mixed with
+borax, glass, lime, and fluor spar; and, in some cases, with nitre, or
+iron pyrites, according to the quality of the ore. The mixture is placed
+in a large Cornish crucible, and heated as uniformly as possible in the
+wind furnace, gradually raising the temperature so as to melt down the
+charge in from 15 to 20 minutes. The crucible is removed and its
+contents poured into an iron mould. When the slag is solid, it is taken
+up with tweezers and quenched in water. The regulus is easily detached
+from the slag. It should be convex above and easily broken, have a
+reddish brown colour, and contain from 40 to 60 per cent. of copper. A
+regulus with more than this is "too fine," and with less "too coarse." A
+regulus which is too fine is round, compact, hard, and of a dark bluish
+grey on the freshly broken surface. A coarse regulus is flat and coarse
+grained, and more nearly resembles sulphide of iron in fracture and
+colour.</p>
+
+<p>If an assay yields a regulus "too coarse," a fresh determination is made
+with more nitre added, or the roasting is carried further. With low
+class ores a somewhat coarse regulus is an advantage. If, on the other
+hand, the regulus is too fine, less nitre or less roasting is the
+remedy. With grey copper ores and the oxidised ores, iron pyrites is
+added.</p>
+
+<p><b>Calcining the Regulus.</b>&mdash;It is powdered in an iron mortar and
+transferred to a small Cornish crucible, or (if the roasting is to be
+done in the muffle) to a roasting dish or scorifier. The calcining is
+carried out at a dull red heat, which is gradually increased. The charge
+requires constant stirring at first to prevent clotting, but towards the
+end it becomes sandy and requires less attention. If the temperature
+during calcination has been too low sulphates are formed, which are
+again reduced to sulphides in the subsequent fusion. To prevent this the
+roasted regulus is recalcined at a higher temperature, after being
+rubbed up with a little anthracite. The roasted substance must not smell
+of burning sulphur when hot. It is practically a mixture of the oxides
+of copper and iron.</p>
+
+<p><b>Fusion for Coarse Copper.</b>&mdash;The calcined regulus is mixed with a flux
+consisting of borax and carbonate of soda, with more or less tartar
+according to its weight. Some "assayers" use both tartar and nitre, the
+former of course being in excess. The charge is returned to the crucible
+in which it was calcined, and is melted down at a high temperature, and,
+as soon as tranquil, poured. When solid it is quenched and the button of
+metal separated.<span class='pagenum'><a name="Page_179" id="Page_179">[Pg 179]</a></span></p>
+
+<p>The slag is black and glassy. The small quantity of copper which it
+retains is recovered by a subsequent "cleaning," together with the slags
+from the next operation.</p>
+
+<p>The button of "coarse copper" obtained must be free from a coating of
+regulus. It will vary somewhat in appearance according to the nature and
+quantity of the impurities.</p>
+
+<p><b>Refining the Coarse Copper.</b>&mdash;The same crucible is put back in the
+furnace, deep down and under the crevice between the two bricks. When it
+has attained the temperature of the furnace the coarse copper is dropped
+into it and the furnace closed. The copper will melt almost at once with
+a dull surface, which after a time clears, showing an "eye." Some
+refining flux is then shot in from the scoop (fig. 48), and, when the
+assay is again fluid, it is poured. When cold the button of metal is
+separated.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig048.jpg" width="450" height="212" alt="Fig. 48." title="" />
+
+</div>
+
+<p>The button of "fine" copper is flat or pitted on its upper surface, and
+is coated with a thin orange film; it must have the appearance of good
+copper. If it is covered with a red or purple film, it is overdone or
+"burnt." If, on the other hand, it has a rough, dull appearance, it is
+not sufficiently refined. Assays that have been "burnt" are rejected.
+Those not sufficiently fine are treated as "coarse copper," and again
+put through the refining operation.</p>
+
+<p><b>Cleaning the Slags.</b>&mdash;These are roughly powdered and re-fused with
+tartar, etc., as in the fusion for coarse copper. The button of metal
+got is separated (if big enough refined) and weighed.</p>
+
+<p>The details of the process are slightly varied by different assayers:
+the following will be good practice for the student.</p>
+
+<p><b>Determination of Copper in Copper Pyrites.</b>&mdash;Powder, dry, and weigh up
+20 grams of the ore. Mix with 20 grams each of powdered lime and fluor,
+15 grams each of powdered glass and borax, and 5 or 10 grams of nitre.
+Transfer to a large Cornish crucible and fuse under a loose cover at a
+high temperature for from 15 to 20 minutes. When fluid and tranquil pour
+into a mould. When the slag has solidified, but whilst still hot, quench
+by dipping two or three times in cold water. Avoid leaving it in the
+water so long that it does not dry after removal. When cold separate the
+button, or perhaps buttons, of regulus by crumbling the slag between the
+fingers. See that the slag is<span class='pagenum'><a name="Page_180" id="Page_180">[Pg 180]</a></span> free from regulus. It should be light
+coloured when cold and very fluid when hot. Reject the slag.</p>
+
+<p>Powder the regulus in a mortar and transfer to a small crucible.
+Calcine, with occasional stirring, until no odour of sulphurous oxide
+can be detected. Shake back into the mortar, rub up with about 1 gram of
+powdered anthracite, and re-calcine for 10 minutes longer.</p>
+
+<p>Mix the calcined regulus with 10 grams of tartar, 20 grams of soda, and
+3 grams of borax; and replace in the crucible used for calcining. Fuse
+at a bright red heat for 10 or 15 minutes. Pour, when tranquil.</p>
+
+<p>As soon as solid, quench in water, separate the button of copper, and
+save the slag.</p>
+
+<p>To refine the copper a very hot fire is wanted, and the fuel should not
+be too low down in the furnace. Place the crucible well down in the fire
+and in the middle of the furnace. The same crucible is used, or, if a
+new one is taken, it must be glazed with a little borax. When the
+crucible is at a good red heat, above the fusing point of copper, drop
+the button of copper into it, and close the furnace. Watch through the
+crevice, and, as soon as the button has melted and appears clear showing
+an eye, shoot in 10 grams of refining flux, close the furnace, and, in a
+few minutes, pour; then separate the button of copper. Add the slag to
+that from the coarse copper fusion, and powder. Mix with 5 grams of
+tartar, 0.5 gram of powdered charcoal, and 2 grams of soda. Fuse in the
+same crucible, and, when tranquil, pour; quench, and pick out the prills
+of metal.</p>
+
+<p>If the copper thus got from the slags is coarse looking and large in
+amount, it must be refined; but, if small in quantity, it may be taken
+as four-fifths copper. The combined results multiplied by five give the
+percentage of copper.</p>
+
+<p>The refining flux is made by mixing 3 parts (by measure) of powdered
+nitre, 2-1\2 of tartar, and 1 of salt. Put in a large crucible, and stir
+with a red-hot iron until action has ceased. This operation should be
+carried out in a well-ventilated spot.</p>
+
+<p>For pure ores in which the copper is present, either as metal or oxide,
+and free from sulphur, arsenic, &amp;c., the concentration of the copper in
+a regulus may be omitted, and the metal obtained in a pure state by a
+single fusion.<a name="FNanchor_50_50" id="FNanchor_50_50"></a><a href="#Footnote_50_50" class="fnanchor">[50]</a> It is necessary to get a fluid neutral slag with the
+addition of as small an amount of flux as possible. The fusion should be
+made at a high temperature, so as not to occupy more than from 20 to 25
+minutes. Thirty grams of ore is taken for a charge, mixed with 20 grams
+of cream of<span class='pagenum'><a name="Page_181" id="Page_181">[Pg 181]</a></span> tartar, and 10 grams each of dried borax and soda. If the
+gangue of the ore is basic, carrying much oxide of iron or lime, silica
+is added, in quantity not exceeding 10 grams. If, on the other hand, the
+gangue is mainly quartz, oxide of iron up to 7 grams must be added.</p>
+
+<p><i>Example.</i>&mdash;Twenty grams of copper pyrites, known to contain 27.6 per
+cent. of copper, gave by the method first described 5.22 grams of
+copper, equalling 26-1/8 per cent. Another sample of 20 grams of the
+same ore, calcined, fused with 40 grams of nitre, and washed to ensure
+the removal of arsenic and sulphur, and treated according to the second
+method, gave a button weighing 5.27 grams, equalling 26-3/8 per cent.
+The ore contained a considerable quantity of lead. Lead renders the
+assay more difficult, since after calcination it remains as lead
+sulphate, and in the fusion for coarse copper reappears as a regulus on
+the button.</p>
+
+<p><b>The Estimation of Moisture.</b>&mdash;The Cornish dry assayer very seldom makes
+a moisture determination. He dries the samples by placing the papers
+containing them on the iron plate of the furnace.</p>
+
+<p>It is well known that by buying the copper contents of pyrites by
+Cornish assay, burning off the sulphur, and converting the copper into
+precipitate, a large excess is obtained.</p>
+
+
+<h4>NOTES ON THE VALUATION OF COPPER ORES.</h4>
+
+<p>Closely bound up with the practice of dry copper assaying is that of
+valuing a parcel of copper ore. The methods by which the valuation is
+made have been described by Mr. Westmoreland,<a name="FNanchor_51_51" id="FNanchor_51_51"></a><a href="#Footnote_51_51" class="fnanchor">[51]</a> and are briefly as
+follows:&mdash;The produce of the parcel is settled by two assayers, one
+acting for the buyer, the other for the seller; with the help, in case
+of non-agreement, of a third, or referee, whose decision is final. The
+dry assayers who do this are in most cases helped, and sometimes,
+perhaps, controlled, by wet assays made for one or both of the parties
+in the transaction.</p>
+
+<p>In the case of "ticketing," the parcels are purchased by the smelters by
+tender, and the value of any particular parcel is calculated from the
+average price paid, as follows:&mdash;The "standard," or absolute value of
+each ton of fine copper in the ore, is the price the smelters have paid
+for it, plus the returning charges or cost of smelting the quantity of
+ore in which it is contained. The value of any particular parcel of ore
+is that of the quantity of fine copper it contains, calculated on this
+standard, minus the returning charges. The ton consists of 21 cwts.,
+and<span class='pagenum'><a name="Page_182" id="Page_182">[Pg 182]</a></span> it is assumed that the "settled" produce is the actual yield of the
+ore.</p>
+
+<p>If at a ticketing in Cornwall 985 tons of ore containing 63.3 tons of
+fine copper (by dry assay) brought &pound;2591 12<i>s.</i>, the standard would be
+&pound;83 15<i>s.</i> This is calculated as follows:&mdash;The returning charge is fixed
+at 55<i>s.</i> per ton of ore. This on 985 tons will amount to &pound;2708 15<i>s.</i>
+Add this to the actual price paid, and there is got &pound;5300 as the value
+of the fine copper present. The weight of copper in these 985 tons being
+63.3 tons, the standard is &pound;5300/63.3, or &pound;83 15<i>s.</i> (nearly).</p>
+
+<p>The value of a parcel of 150 tons of a 6 per cent. ore on the same
+standard would be arrived at as follows:&mdash;The 150 tons at 6 per cent.
+would contain 9 tons (150&times;6/100) of fine copper. This, at &pound;83 15<i>s.</i>
+per ton, would give &pound;753 15<i>s.</i> From this must be deducted the returning
+charges on 150 tons of ore at 55<i>s.</i> per ton, or &pound;412 10<i>s.</i> This leaves
+&pound;341 5<i>s.</i> as the value of the parcel.</p>
+
+<p>At Swansea the returning charge is less than in Cornwall, and varies
+with the quality of the ore. This appears equitable, since in smelting
+there are some costs which are dependent simply on the number of tons
+treated, and others which increase with the richness. The returning
+charge then is made up of two parts, one fixed at so much (12<i>s.</i> 2<i>d.</i>)
+per ton of ore treated, and the other so much (3<i>s.</i> 9<i>d.</i>) per unit of
+metal in the ore. In this way the returning charge on a ton of ore of
+8-3/4 produce would be 12<i>s.</i> 2<i>d.</i>+(8-3/4&times;3<i>s.</i> 9<i>d.</i>), or &pound;2 5<i>s</i>.</p>
+
+<p>If, for example, Chili bars, containing 96 per cent. of copper, bring
+&pound;50 per ton, the standard is &pound;71 9<i>s.</i> 4<i>d.</i> It is got at in this way.
+The returning charge on a 96 per cent. ore is 12<i>s.</i> 2<i>d.</i>+(96&times;3<i>s.</i>
+9<i>d.</i>), or &pound;18 12<i>s.</i> 2<i>d.</i> This added to &pound;50 gives &pound;68 12<i>s.</i> 2<i>d.</i>,
+and this multiplied by 100 and divided by 96 (100 tons of the bars will
+contain 96 tons of fine copper) will give &pound;71 9<i>s.</i> 4<i>d.</i></p>
+
+<p>The price of 100 tons of pyrites, containing 2-1/4 per cent. of copper
+by dry assay, would be got on this standard as follows:&mdash;The parcel of
+ore would contain 2-1/4 tons of copper. This multiplied by the standard
+gives &pound;160 16<i>s.</i> 0<i>d.</i> From this must be deducted the returning charge,
+which for 1 ton of ore of this produce would be 12<i>s.</i> 2<i>d.</i> + (2-1/4 &times;
+3<i>s.</i> 9<i>d.</i>) or &pound;1 0<i>s.</i> 7<i>d.</i>, and on the 100 tons is &pound;102 18<i>s.</i> 4<i>d.</i>
+This would leave &pound;57 17<i>s.</i> 10<i>d.</i> as the price of the parcel, or 11<i>s.</i>
+7<i>d.</i> per ton. This would be on the standard returning charge of 45<i>s.</i>
+(for 8-3/4 per cent. ore); if a smaller returning charge was agreed on,
+say 38<i>s.</i>, the difference in this case, 7<i>s.</i>, would be added to the
+price per ton.<span class='pagenum'><a name="Page_183" id="Page_183">[Pg 183]</a></span></p>
+
+
+<h4>WET METHODS.</h4>
+
+<p>The solubility of the ores of copper in acid has already been described,
+but certain furnace products, such as slags, are best opened up by
+fusion with fusion mixture and a little nitre.</p>
+
+<p>The method of dissolving varies with the nature of the ore. With 5 grams
+of pyrites, a single evaporation with 20 c.c. of nitric acid will give a
+residue completely soluble in 30 c.c. of hydrochloric acid. If the ore
+carries oxide of iron or similar bodies, these are first dissolved up by
+boiling with 20 c.c. of hydrochloric acid, and the residue attacked by
+an addition of 5 c.c. of nitric. When silicates decomposable by acid are
+present, the solution is evaporated to dryness to render the silica
+insoluble; the residue extracted with 30 c.c. of hydrochloric acid, and
+diluted with water to 150 c.c. It is advisable to have the copper in
+solution as chloride. To separate the copper, heat the solution nearly
+to boiling (best in a pint flask), and pass a rapid current of
+sulphuretted hydrogen for four or five minutes until the precipitate
+settles readily and the liquid smells of the gas. When iron is present
+it will be reduced to the ferrous state before the copper sulphide
+begins to separate. The copper appears as a brown coloration or black
+precipitate according to the quantity present. Filter through a coarse
+filter, wash with hot water containing sulphuretted hydrogen, if
+necessary. Wash the precipitate back into the flask, boil with 10 c.c.
+of nitric acid, add soda till alkaline, and pass sulphuretted hydrogen
+again. Warm and filter, wash and redissolve in nitric acid, neutralise
+with ammonia, add ammonic carbonate, boil and filter. The copper freed
+from impurities will be in the solution. Acidulate and reprecipitate
+with sulphuretted hydrogen. When the nature of the impurities will allow
+it, this process may be shortened to first filtering off the gangue,
+then precipitating with sulphuretted hydrogen and washing the
+precipitate on the filter first with water and then with ammonium
+sulphide.</p>
+
+<p>Having separated the copper as sulphide, its weight is determined as
+follows. Dry and transfer to a weighed porcelain crucible, mix with a
+little pure sulphur, and ignite at a red heat for 5 or 10 minutes in a
+current of hydrogen. Allow to cool while the hydrogen is still passing.
+Weigh. The subsulphide of copper thus obtained contains 79.85 per cent.
+of copper; it is a greyish-black crystalline mass, which loses no weight
+on ignition if air is excluded.</p>
+
+<p>Copper may be separated from its solutions by means of sodium
+hyposulphite. The solution is freed from hydrochloric and nitric acids
+by evaporation with sulphuric acid; diluted to about<span class='pagenum'><a name="Page_184" id="Page_184">[Pg 184]</a></span> a quarter of a
+litre; heated nearly to boiling; and treated with a hot solution of
+sodium hyposulphite (added a little at a time) until the precipitate
+settles and leaves the solution free from colour. The solution contains
+suspended sulphur. The precipitate is easily washed, and under the
+proper conditions the separation is complete, but the separation with
+sulphuretted hydrogen is more satisfactory, since the conditions as to
+acidity, &amp;c., need not be so exact.</p>
+
+<p>Zinc or iron is sometimes used for separating copper from its solutions,
+but they are not to be recommended.</p>
+
+
+<h4>ELECTROLYTIC ASSAY.</h4>
+
+<p>The separation of copper by means of a current of electricity is largely
+made use of, and forms the basis of the most satisfactory method for the
+determination of this metal. If the wire closing an electric circuit be
+broken, and the two ends immersed in a beaker of acidulated water or
+solution of any salt, the electricity will pass through the liquid,
+bringing about some remarkable changes. Hydrogen and the metals will be
+liberated around that part of the wire connected with the zinc end of
+the battery, and oxygen, chlorine, and the acid radicals will be set
+free around the other. Different metals are deposited in this way with
+varying degrees of ease, and whether or not any particular metal will be
+deposited depends&mdash;(1) on the conditions of the solution as regards acid
+and other substances present, and (2) on the <i>intensity</i> of the current
+of electricity used. For analytical purposes the metal should be
+deposited not only free from the other metals present, but also as a
+firm coherent film, which may afterwards be manipulated without fear of
+loss. This is, in the case of copper and many other metals, effected by
+a simple control of the conditions. It is necessary that the electrodes,
+or wires which bring the electricity into the solution, should be made
+of a material to which the deposited metal will adhere, and which will
+not be attacked by substances originally present or set free in the
+solution. They are generally made of platinum. There are various
+arrangements of apparatus used for this purpose, but the following plan
+and method of working is simple and effective, and has been in daily use
+with very satisfactory results for the last five or six years.</p>
+
+<p>The battery used is made up of two Daniell cells, coupled up for
+intensity as shown in fig. 49&mdash;that is, with the copper of one connected
+with the zinc of the other. For eight or ten assays daily the quart size
+should be used, but for four or five two pint cells will be sufficient.<span class='pagenum'><a name="Page_185" id="Page_185">[Pg 185]</a></span></p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig049.jpg" width="300" height="294" alt="Fig. 49." title="" />
+
+</div>
+
+<p>The outer pot of each cell is made of sheet copper, and must be clean
+and free from solder on the inside. It is provided near the top with a
+perforated copper shelf in the shape of a ring, into which the inner or
+porous cell loosely fits. It is charged with a saturated solution of
+copper sulphate, and crystals of this salt must be added, and always
+kept in excess. When the battery is at work copper is being deposited on
+the inner surface of this pot.</p>
+
+<p>The inner or porous pot contains the zinc rod, and is charged with a
+dilute acid, made by diluting one volume of sulphuric acid up to ten
+with water. The object of the porous pot is to prevent the mixing of the
+acid and copper sulphate solutions, without interrupting the flow of
+electricity. The copper sulphate solution will last for months, but the
+acid must be emptied out and recharged daily.</p>
+
+<p>The zinc rods must be well amalgamated by rubbing with mercury under
+dilute acid until they show a uniformly bright surface. They should not
+produce a brisk effervescence when placed in the acid in the porous pot
+before coupling up.</p>
+
+<p>The battery when working is apt to become dirty from the "creeping" of
+the copper and zinc sulphate solution. It must be kept away from the
+working bench, and is best kept in a box on the floor.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig050.jpg" width="450" height="198" alt="Fig. 50." title="" />
+
+</div>
+
+<p>The connection of the battery with, and the fixing of, the electrodes
+may be made by any suitable arrangement, but the following is a very
+convenient plan. The wire from the zinc is connected by means of a
+binding screw with a piece of stout copper wire, which, at a distance
+sufficiently great to allow of easy coupling with the battery, is led
+along the back of a piece<span class='pagenum'><a name="Page_186" id="Page_186">[Pg 186]</a></span> of hard wood. This is fixed horizontally
+about one foot above the working bench. The general arrangement is shown
+in fig. 50, in which, however, for the sake of economy of space, the
+battery is placed on the working bench instead of on the floor. The
+piece of wood is one inch square and three or four feet long. It is
+perforated from front to back at distances of six inches by a<span class='pagenum'><a name="Page_187" id="Page_187">[Pg 187]</a></span> number of
+small holes, in which are inserted screws like that shown in fig. 51.
+These are known as "terminals," and may be obtained of any electrician.
+The head of each screw is soldered to the wire mentioned above as
+running along the back and as being connected with the zinc end of the
+battery. These terminals serve to fix the electrodes on which the copper
+is to be deposited. The wire from the copper end of the battery is
+similarly connected by a connecting screw (fig. 52) with another wire (H
+in fig. 53), which runs along the top of the rod and has soldered to it,
+at distances of six inches, cylindrical spirals of copper wire. These
+should project from the rod at points about half-way between the
+terminals already described. They may be made by wrapping copper wire
+around a black-lead pencil for a length of about three inches.</p>
+
+<div class="figcenter" style="width: 428px;">
+<img src="images/fig051.jpg" width="428" height="265" alt="Fig. 51." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 315px;">
+<img src="images/fig052.jpg" width="315" height="235" alt="Fig. 52." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 348px;">
+<img src="images/fig053.jpg" width="348" height="450" alt="Fig. 53." title="" />
+
+</div>
+
+<p>The rod is perforated from top to bottom with a series of small holes,
+one in advance of each terminal but as near it as possible. Into these
+short pieces of glass tube are inserted to ensure insulation. These
+receive the other electrodes, which are connected with the wire leading
+to the copper end of the battery, through the spirals, with the help of
+a binding screw. The figure will make this clear. (Fig. 53.)</p>
+
+<div class="figcenter" style="width: 278px;">
+<img src="images/fig054.jpg" width="278" height="450" alt="Fig. 54" title="" />
+
+</div>
+
+<p><b>The electrodes</b> consist of a platinum spiral and cylinder. The spiral
+should have the shape shown in A, fig. 54. When in work it is passed
+through one of the holes fitted with glass tubes and connected with the
+copper end of the battery. The thickness of the wire of which it is made
+is unimportant, provided it is stout enough to keep its form and does
+not easily bend. The spiral will weigh about 8 grams. The cylinder (C,
+fig. 54) will weigh about 12 grams. It should have the shape shown in
+the figure. In working it is clamped to one of the terminals, and on it
+the copper is deposited. A cylinder will serve for the deposition of
+from 1 to 1.5 gram of copper. It is made by rivetting a square piece of
+foil on to a stiff piece of wire, and then bending into shape over a
+glass tube or piece of rounded wood. Each cylinder carries a distinctive
+number, and is marked by impressing<span class='pagenum'><a name="Page_188" id="Page_188">[Pg 188]</a></span> Roman numerals on the foil with the
+blade of a knife. The weight of each is carefully taken and recorded.
+They lose slightly in weight when in use, but the loss is uniform, and
+averages half a milligram per month when in daily use. The cylinders are
+cleaned from deposited copper by dissolving off with nitric acid and
+washing with water; and from grease by igniting.</p>
+
+<p>The <b>beakers</b>, to contain the solution of copper to be electrolysed, are
+ordinary tall beakers of about 200 c.c. capacity, and are marked off at
+100 c.c. and 150 c.c. They are supported on movable stands, consisting
+of wooden blocks about six inches high and three inches across. The bar
+of wood which carries the connecting wires and electrodes is permanently
+fixed over the working bench, at such a height that, with the beakers
+resting on these blocks, the electrodes shall be in position for
+working.</p>
+
+<p>To fix the electrodes to the rod, remove the stand and beaker and pass
+the long limb of the spiral up through one of the glass tubes. Connect
+it with the free end of the copper spiral by means of a connecting screw
+(fig. 52), and then draw out and bend the copper spiral so that the
+platinum one may hang freely. Screw the wire of the cylinder to the
+terminal, and, if necessary, bend it so that the cylinder itself may be
+brought to encircle the rod of the spiral in the manner shown in fig.
+53.</p>
+
+<p>The <b>general method of working</b> is as follows:&mdash;The quantity of ore to
+be taken for an assay varies with the richness of the ore, as is shown
+in the following table:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Percentage of Copper in the Ore.</td><td align='left'>Quantity of Ore to be taken.</td></tr>
+<tr><td align='center'>1 to 5</td><td align='center'>5 grams</td></tr>
+<tr><td align='center'>5 to 10</td><td align='center'>3&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='center'>10 to 30</td><td align='center'>2&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='center'>30 to 50</td><td align='center'>1.5&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='center'>50 to 100</td><td align='center'>1&nbsp;&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<p>The weighed quantity of ore is dissolved by evaporating with nitric acid
+and taking up with hydrochloric, as already described. Any coloured
+residue which may be left is generally organic matter: it is filtered
+off, calcined, and any copper it contains is estimated colorimetrically.
+Nearly always, however, the residue is white and sandy. The copper is
+separated from the solution as sulphide by means of a rapid current of
+sulphuretted hydrogen. The liquid is decanted off through a filter, the
+precipitate washed once with hot water and then rinsed back into the
+flask (the filter paper being opened out) with a jet of water from a
+wash bottle. Fifteen c.c. of nitric acid are added to the contents of
+the flask, which are then briskly boiled until the bulk is reduced to<span class='pagenum'><a name="Page_189" id="Page_189">[Pg 189]</a></span>
+less than 10 c.c. The boiling down is carried out in a cupboard free
+from cold draughts, so as to prevent the condensation of acid and steam
+in the neck of the flask. Twenty c.c. of water are next added, and the
+solution is warmed, and filtered into one of the beakers for
+electrolysis. The filtrate and washings are diluted with water to the
+100 c.c. mark, and the solution is then ready for the battery. It must
+not contain more than 10 per cent. by volume of nitric acid.</p>
+
+<p>The number and weight of the platinum cylinder having been recorded,
+both electrodes are fixed in position and the wooden block removed from
+under them. The beaker containing the copper solution is then brought up
+into its place with one hand, and the block replaced with the other so
+as to support it. All the assays having been got into position, the
+connecting wires are joined to the battery. If everything is right
+bubbles of oxygen at once stream off from the spiral, and the cylinder
+becomes tarnished by a deposit of copper. If the oxygen comes off but no
+copper is deposited, it is because the assay solution contains too much
+nitric acid. If no action whatever takes place, it is because the
+current is not passing. In this case examine the connections to see that
+they are clean and secure, and the connecting wires to see that they are
+not touching each other.</p>
+
+<p>The action is allowed to go on for sixteen or seventeen hours, so that
+it is best to let the current act overnight. In the morning the
+solutions will appear colourless, and a slow stream of oxygen will still
+be coming off from the spiral.</p>
+
+<p>A wash-bottle with cold distilled water and two beakers, one with
+distilled water and the other with alcohol, are got ready. The block is
+then removed, the spiral loosened and lowered with the beaker. The
+cylinder is next detached and washed with a stream of water from the
+wash-bottle, the washings being added to the original solution. The
+current from the battery is not stopped until all the cylinders are
+washed. After being dipped in the beaker of water and once or twice in
+that with the alcohol, it is dried in the water-oven for about three
+minutes, and then weighed. The increase in weight is due to deposited
+copper. This should be salmon-red in colour, satin-like or crystalline
+in appearance, and in an even coherent deposit, not removed by rubbing.
+It is permanent in air when dry, but sulphuretted hydrogen quickly
+tarnishes it, producing coloured films. With ores containing even very
+small proportions of bismuth, the deposited copper has a dark grey
+colour, and when much of this metal is present the copper is coated with
+a grey shaggy deposit.</p>
+
+<p>It still remains to determine any copper left undeposited in the
+solution. This does not generally exceed four or five milligrams,<span class='pagenum'><a name="Page_190" id="Page_190">[Pg 190]</a></span> and
+is estimated colorimetrically. Thirty c.c. of dilute ammonia (one of
+strong ammonia mixed with one of water) are added to the electrolysed
+solution, which is then diluted up to the 150 c.c. mark with water. It
+is mixed, using the spiral as stirrer, and, after standing a few minutes
+to allow the precipitate to settle, 100 c.c. of it are filtered off
+through a dry filter for the colorimetric determination. Since only
+two-thirds of the solution are taken for this, the quantity of copper
+found must be increased by one-half to get the quantity actually
+present.</p>
+
+<div class="figcenter" style="width: 204px;">
+<img src="images/fig055.jpg" width="204" height="400" alt="Fig. 55." title="" />
+
+</div>
+
+<p>The <b>colorimetric determination</b> may be made in the manner described
+under that head, but where a number of assays are being carried out it
+is more convenient to have a series of standard phials containing known
+amounts of copper in ammoniacal solution. By comparing the measured
+volume of the assay solution with these, the amount of copper present is
+determined at a glance. These standard bottles, however, can only be
+economically used where a large number of assays are being made daily.</p>
+
+<p>A convenient plan is to get a quantity of white glass four-ounce phials,
+like that in fig. 55, and to label them so that they shall contain 100
+c.c. when filled up to the bottom of the labels. The labels should be
+rendered permanent by coating with wax, and be marked with numbers
+indicating the milligrams of copper present. The bottles are stopped
+with new clean corks, and contain, in addition to the specified quantity
+of copper, 6 c.c. of nitric acid and 10 c.c. of strong ammonia, with
+sufficient water to make up the bulk to 100 c.c. The copper is best
+added by running in the requisite amount of a standard solution of
+copper, each c.c. of which contains 0.001 gram of the metal.</p>
+
+<p>The standard bottles should be refilled once every three or four months,
+since their colorimetric value becomes slowly less on keeping. The
+following determinations of a set which had been in use for three months
+will illustrate this. The figures indicate milligrams of copper in 100
+c.c.: the first row gives the nominal and the second row the actual
+colorimetric value of the standards. The difference between the two
+shows the deterioration.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'> 1&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>2&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>3&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>4&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>6&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>8&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>10&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>12&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>14&nbsp;&nbsp;&nbsp;&nbsp;</td></tr>
+<tr><td align='left'> 1&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>2&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>3&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>3.7&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>5.5&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>7.5&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>9&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>11&nbsp;&nbsp;&nbsp;&nbsp;</td><td align='left'>13&nbsp;&nbsp;&nbsp;&nbsp;</td></tr>
+</table></div>
+
+
+<p>The amount of copper in the assay is got by increasing that found
+colorimetrically by one-half and adding to that found on the platinum
+cylinder. The percentage is calculated in the usual<span class='pagenum'><a name="Page_191" id="Page_191">[Pg 191]</a></span> way. The following
+examples will illustrate this, as well as the method of recording the
+work in the laboratory book:&mdash;</p>
+
+<pre>
+_____________________________________________
+Cylinder I. + Cu                       9.5410
+Cylinder I.                            9.5170
+                                       &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
+                                       0.0240
+By colour 100 c.c. = 0.0015}
+                     0.0007}           0.0022
+                     &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;            &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
+                     0.0022            0.0262
+IX. Sample.    Took 5 grams.
+                              Copper = 0.52%
+_____________________________________________
+Cylinder VI. + Cu                     10.5705
+Cylinder VI.                          10.0437
+                                      &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
+                                       0.5268
+By colour, 100 c.c. = 0.0070}
+                      0.0035}          0.0105
+                      &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;           &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
+                      0.0105           0.5373
+Matte, No. 1070. Took 1.5 gram.
+                             Copper = 35.82%
+_____________________________________________
+Cylinder XIII. + Cu                   12.0352
+Cylinder XIII.                        11.0405
+                                      &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
+                                       0.9947
+By colour 100 c.c. = 0.0005}
+                     0.0002}           0.0007
+                     &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;            &mdash;&mdash;&mdash;&mdash;&mdash;&mdash;
+                     0.0007            0.9954
+X. Sample, Cake copper. Took 1.0053 gram.
+                             Copper = 99.00%
+____________________________________________
+</pre>
+
+<p>In the electrolytic assay of metals, alloys, precipitates, and other
+bodies rich in copper, the preliminary separation of the copper by
+sulphuretted hydrogen is unnecessary. It is sufficient to dissolve the
+weighed sample in 10 c.c. of nitric acid, boil off nitrous fumes, dilute
+to 100 c.c. with water, and then electrolyse.</p>
+
+<p><b>General Considerations.</b>&mdash;In the preliminary work with the copper
+sulphide there is a small loss owing to its imperfect removal in washing
+the filter paper, and another small loss in dissolving in nitric acid
+owing to the retention of particles in the fused globules of sulphur. To
+determine its amount the filter-papers and sulphur were collected from
+forty assays, and the copper in them determined. The average amount of
+copper in each assay was 0.175 gram; that left on the filter paper was
+0.00067 gram; and that retained by the sulphur 0.00003 gram; thus
+showing an<span class='pagenum'><a name="Page_192" id="Page_192">[Pg 192]</a></span> average loss from both sources of 0.00070 gram. The
+determinations from another lot of forty-two similar assays gave on an
+average</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper left on filter paper</td><td align='left'>0.00070</td><td align='left'>gram</td></tr>
+<tr><td align='left'>Copper retained by sulphur.</td><td align='left'>0.00004</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>The loss from these sources is trifling, and need only be considered
+when great accuracy is required.</p>
+
+<p>The deposition of the copper under the conditions given is satisfactory,
+but, as already stated, if the solution contain more than 10 per cent.
+of nitric acid it is not thrown down at all; or if a stronger current is
+used, say that from three Bunsen cells, it will be precipitated in an
+arborescent brittle form, ill adapted for weighing. It may be noted here
+that increasing the size of the cells does not necessarily increase the
+intensity of the current.</p>
+
+<p>In two determinations on pure electrotype copper the following results
+were obtained:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper Taken.</td><td align='left'>Copper Found.</td></tr>
+<tr><td align='left'>0.8988 gram</td><td align='left'>0.8985 gram</td></tr>
+<tr><td align='left'>0.8305&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.8303&nbsp;&nbsp;&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<p>The presence of salts of ammonia, &amp;c., somewhat retards the deposition,
+but has no other ill effect.</p>
+
+<p>The organic matter generally present in copper ores interferes more
+especially in the colorimetric determination of the residual copper. It
+can be detected on dissolving the ore as a light black residue insoluble
+in nitric acid. It is filtered off at once, or, if only present in small
+amount, it is carried on in the ordinary process of the assay and
+separated in the last filtration before electrolysis.</p>
+
+<p>The following experiments were made to test the effect of the presence
+of salts of foreign metals in the solution during the precipitation of
+copper by electrolysis:&mdash;</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper Taken.</td><td align='left'>Other Metal Added.</td><td align='left'>Copper Found.</td></tr>
+<tr><td align='left'>0.1000 gram</td><td align='left'>0.1000 gram of silver</td><td align='left'>0.1800</td></tr>
+<tr><td align='left'>0.1050&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000 &nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.2000</td></tr>
+<tr><td align='left'>0.1030 &nbsp;&nbsp;&nbsp;"</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; mercury</td><td align='left'>0.2010</td></tr>
+<tr><td align='left'>0.1037&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.2015</td></tr>
+<tr><td align='left'>0.1020&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lead</td><td align='left'>0.1020</td></tr>
+<tr><td align='left'>0.1030&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>0.1028</td></tr>
+<tr><td align='left'>0.1010&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; arsenic</td><td align='left'>0.1010</td></tr>
+<tr><td align='left'>0.1007&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1022</td></tr>
+<tr><td align='left'>0.1030&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; antimony</td><td align='left'>0.1050</td></tr>
+<tr><td align='left'>0.1034&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1057</td></tr>
+<tr><td align='left'>0.0990&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1200&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; tin</td><td align='left'>0.0990</td></tr>
+<tr><td align='left'>0.1014&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000 &nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1015</td></tr>
+<tr><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; bismuth</td><td align='left'>0.1662</td></tr>
+<tr><td align='left'>0.1040&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; of cadmium</td><td align='left'>0.1052</td></tr>
+<tr><td align='left'>0.1009&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1300&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; zinc</td><td align='left'>0.1017</td></tr>
+<tr><td align='left'>0.1014&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; nickel</td><td align='left'>0.1007</td></tr>
+<tr><td align='left'>0.1079&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1200&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; iron</td><td align='left'>0.1089</td></tr>
+<tr><td align='left'>0.1054&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; chromium (Cr<sub>2</sub>O<sub>3</sub>)</td><td align='left'>0.1035</td></tr>
+<tr><td align='left'>0.1034&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(K<sub>2</sub>CrO<sub>4</sub>)</td><td align='left'>0.1010</td></tr>
+<tr><td align='left'>0.1075&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; aluminium</td><td align='left'>0.1078</td></tr>
+<tr><td align='left'>0.1010&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.1000&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; manganese</td><td align='left'>0.0980</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_193" id="Page_193">[Pg 193]</a></span></p>
+
+<p>It will be seen from these that mercury, silver, and bismuth are the
+only metals which are precipitable<a name="FNanchor_52_52" id="FNanchor_52_52"></a><a href="#Footnote_52_52" class="fnanchor">[52]</a> along with the copper under the
+conditions of the assay. Mercury, which if present would interfere, is
+separated because of the insolubility of its sulphide in nitric acid.</p>
+
+<p>Bismuth is precipitated only after the main portion of the copper is
+thrown down. It renders the copper obviously unsuitable for weighing. It
+darkens, or forms a greyish coating on, the copper; and this darkening
+is a delicate test for bismuth. In assaying ores containing about three
+and a half per cent. of copper, and known to contain bismuth in
+quantities scarcely detectable in ordinary analysis, the metal deposited
+was distinctly greyish in colour, and would not be mistaken for pure
+copper. Ten grams of this impure copper were collected and analysed,
+with the following results:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper</td><td align='right'>99.46</td><td align='left'>per cent.</td></tr>
+<tr><td align='left'>Bismuth</td><td align='right'>00.30</td><td align='center'>"</td></tr>
+<tr><td align='left'>Iron</td><td align='right'>00.14</td><td align='center'>"</td></tr>
+<tr><td align='left'>Arsenic</td><td align='right'>00.10</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>100.00</td></tr>
+</table></div>
+
+
+<p>The quantity of copper got in each assay was 0.175 gram, and
+consequently the bismuth averaged 0.00053 gram.</p>
+
+<p>To separate the bismuth in such a case the deposit is dissolved off by
+warming it in the original solution. The bismuth is precipitated by the
+addition of ammonic carbonate, and the solution, after filtering and
+acidifying with nitric acid, is re-electrolysed.</p>
+
+<p><b>Determination of Copper in Commercial Copper.</b>&mdash;Take from 1 to 1.5
+gram, weigh carefully, and transfer to a beaker; add 20 c.c. of water
+and 10 c.c. of nitric acid; cover with a clock<span class='pagenum'><a name="Page_194" id="Page_194">[Pg 194]</a></span> glass, and allow to
+dissolve with moderate action; boil off nitrous fumes, dilute to 100
+c.c., and electrolyse. The cylinder must be carefully weighed, and the
+electrolysis allowed to proceed for 24 hours. The weight found will be
+that of the copper and silver. The silver in it must be determined<a name="FNanchor_53_53" id="FNanchor_53_53"></a><a href="#Footnote_53_53" class="fnanchor">[53]</a>
+and deducted.</p>
+
+<p><b>Determination of Copper in Brass, German Silver, or Bronze.</b>&mdash;Treat in
+the same manner as commercial copper. If nickel is present, the few
+milligrams of copper remaining in the electrolysed solution should be
+separated with sulphuretted hydrogen, the precipitated sulphide
+dissolved in nitric acid, and determined colorimetrically.</p>
+
+
+<h4>VOLUMETRIC PROCESSES.</h4>
+
+<p>There are two of these in use, one based on the decolorising effect of
+potassic cyanide upon an ammoniacal copper solution, and the other upon
+the measurement of the quantity of iodine liberated from potassic iodide
+by the copper salt. The cyanide process is the more generally used, and
+when carefully worked, "on certain understood and orthodox conditions,"
+yields good results; but probably there is no method of assaying where a
+slight deviation from these conditions so surely leads to error. An
+operator has no difficulty in getting concordant results with duplicate
+assays; yet different assayers, working, without bias, on the same
+material, get results uniformly higher or lower; a difference evidently
+due to variations in the mode of working. Where a large number of
+results are wanted quickly it is a very convenient method. The iodide
+process is very satisfactory when worked under the proper conditions.</p>
+
+
+<h4>CYANIDE METHOD.</h4>
+
+<p>The process is based upon the facts&mdash;(1) that when ammonia is added in
+excess to a solution containing cupric salts, ammoniacal copper
+compounds are formed which give to the solution a deep blue colour; and
+(2) that when potassic cyanide is added in sufficient quantity to such a
+solution the colour is removed, double cyanides of copper and potassium
+or ammonium being formed.<a name="FNanchor_54_54" id="FNanchor_54_54"></a><a href="#Footnote_54_54" class="fnanchor">[54]</a> In the explanation generally given the
+formation of cuprous cyanide is supposed<a name="FNanchor_55_55" id="FNanchor_55_55"></a><a href="#Footnote_55_55" class="fnanchor">[55]</a>; but in practice it is
+found that one part of copper requires rather more than four parts of
+cyanide, which agrees with the former, rather than the latter,
+explanation.</p>
+
+<p><span class='pagenum'><a name="Page_195" id="Page_195">[Pg 195]</a></span></p><p>Reliance on the accuracy of the process cannot rest upon the
+supposition that the cyanide required for decoloration is proportional
+to the copper present, for varying quantities of ammonia salts, ammonia
+and water, and differences of temperature have an important effect. The
+results are concordant and exact only when the cyanide is standardised
+under the same conditions as it is used. It is best to have the assay
+solution and that used for standardising as nearly as possible alike,
+and to titrate the two solutions side by side. This demands an
+approximate knowledge of the quantity of copper contained in the ore and
+a separation of the bulk of the impurities.</p>
+
+<p>For the titration there is required a standard solution of potassium
+cyanide made by dissolving 42 grams of the salt, known to dealers as
+Potassium Cyanide (Gold), in water and diluting to one litre: 100 c.c.
+of this will be about equivalent to one gram of copper. For poor ores
+the solution may conveniently be made half this strength.</p>
+
+<p>The solution of the ore and the separation of the copper as sulphide are
+effected in the same ways as have been already described for
+electrolysis. Similarly, too, the sulphide is attacked with 15 c.c. of
+nitric acid and the assay boiled down to 10 c.c. Add 20 c.c. of water
+and warm, filter into a pint flask, wash well with water, and dilute to
+about 150 c.c.; add 30 c.c. of dilute ammonia, and cool.</p>
+
+<p>Prepare a standard by dissolving a quantity of electrotype copper
+(judged to be about the same as that contained in the assay) in 20 c.c.
+of water and 10 c.c. of nitric acid, boil off the nitrous fumes, and
+dilute to 150 c.c.: add 30 c.c. of dilute ammonia and cool.</p>
+
+<p>Fill a burette with the standard cyanide solution. The burette with
+syphon arrangement, figured on page 52, is used. A number of titrations
+can be carried on at the same time provided the quantity of copper
+present in each is about the same. This is regulated in weighing up the
+ore. The flasks must of course be marked, and should be arranged in
+series on a bench in front of a good light and at such a height that the
+liquid can be looked through without stooping. Supposing about 50 c.c.
+of cyanide will be required, 30 c.c. should be run into each, and each
+addition be recorded as soon as made; then run 15 c.c. into each. The
+solutions will now probably show marked differences of tint: add 1 c.c.
+of cyanide to the lighter ones and more to the darker, so as to bring
+the colours to about the same depth of tint. They should all be of
+nearly equal tint just before finishing. At the end add half a c.c. at a
+time until the colours are completely discharged. A piece of damp filter
+paper held between the light<span class='pagenum'><a name="Page_196" id="Page_196">[Pg 196]</a></span> and the flask assists in judging the
+colour when nearly finished. Overdone assays show a straw yellow colour
+which deepens on standing.</p>
+
+<p>The following will illustrate the notes recorded of five such assays and
+one standard:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>(1)</td><td align='left'>30</td><td align='left'>c.c.</td><td align='left'>15</td><td align='left'>c.c.</td><td align='left'>5</td><td align='left'>c.c.</td><td align='left'>2</td><td align='left'>c.c.</td><td align='left'>1</td><td align='left'>c.c.</td><td align='left'>1/2</td><td align='left'>c.c.</td><td align='left'>&mdash;</td><td align='left'>c.c.</td><td align='left'> =</td><td align='left'>53-1/2</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>(2)</td><td align='left'> 30</td><td align='left'>"</td><td align='left'>15</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>&mdash;</td><td align='left'>"</td><td align='left'>=</td><td align='left'>48-1/2</td><td align='left'>"</td></tr>
+<tr><td align='left'>(3)</td><td align='left'> 30</td><td align='left'>"</td><td align='left'>15</td><td align='left'>"</td><td align='left'>3</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>&mdash;</td><td align='left'>"</td><td align='left'>=</td><td align='left'>50-1/2</td><td align='left'>"</td></tr>
+<tr><td align='left'>(4)</td><td align='left'> 30</td><td align='left'>"</td><td align='left'>15</td><td align='left'>"</td><td align='left'>5</td><td align='left'>"</td><td align='left'>2</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>=</td><td align='left'>54</td><td align='left'>"</td></tr>
+<tr><td align='left'>(5)</td><td align='left'> 30</td><td align='left'>"</td><td align='left'>15</td><td align='left'>"</td><td align='left'>2</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>&mdash;</td><td align='left'>"</td><td align='left'>=</td><td align='left'>49-1/2</td><td align='left'>"</td></tr>
+<tr><td align='left'>(6)</td><td align='left'> 30</td><td align='left'>"</td><td align='left'>15</td><td align='left'>"</td><td align='left'>2</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>1/2</td><td align='left'>"</td><td align='left'>=</td><td align='left'>50</td><td align='left'>standard</td></tr>
+</table></div>
+
+
+<p>Three grams of ore were taken, and the standard contained 0.480 gram of
+copper.</p>
+
+<p>In this series the difference of half a c.c. means about 0.15 per cent.
+on the ore; with a little practice it is easy to estimate whether the
+whole or half of the last addition should be counted.</p>
+
+<p>To get satisfactory results, the manner of finishing once adopted must
+be adhered to.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of the assay:&mdash;Use <i>a solution of copper nitrate</i>, made by dissolving 10
+grams of copper in 50 c.c. of water and 35 c.c. of nitric acid, and
+diluting to a litre. 100 c.c. = 1 gram of copper.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;In these experiments 20 c.c. of copper
+nitrate were used, with 10 c.c. of nitric acid, 30 c.c. of dilute
+ammonia, and water to 200 c.c. The results were&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg;</td><td align='left'>30&deg;</td><td align='left'>70&deg;</td><td align='left'>100&deg;</td></tr>
+<tr><td align='left'>Cyanide required</td><td align='left'>21.5 c.c.</td><td align='left'>20.8 c.c.</td><td align='left'>19.7 c.c.</td><td align='left'>18.8 c.c.</td></tr>
+</table></div>
+
+<p>The temperature is that of the solution <i>before</i> titrating. These show
+the importance of always cooling before titrating, and of titrating the
+assay and standard at the same temperature.</p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;The quantities of copper, acid, and ammonia
+were the same as in the last-mentioned experiments. The results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td><td align='left'>300.0</td><td align='left'>c.c.</td><td align='left'>400.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Cyanide required</td><td align='left'>23.3</td><td align='left'>"</td><td align='left'>21.7</td><td align='left'>"</td><td align='left'>21.4</td><td align='left'>"</td><td align='left'>21.4</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>These show that large variations in bulk must be avoided.</p>
+
+<p><b>Effect of Varying Ammonia.</b>&mdash;The quantities of copper and acid were the
+same as in the series of experiments last noticed. The bulk was 200 c.c.
+The results were:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Dilute ammonia</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>30.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Cyanide required</td><td align='left'>20.9</td><td align='left'>"</td><td align='left'>21.7</td><td align='left'>"</td><td align='left'>22.3</td><td align='left'>"</td><td align='left'>24.6</td><td align='left'>"</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Acid.</b>&mdash;The quantities of copper and water were the
+same as in the last-noticed set of experiments: 30 c.c. of dilute
+ammonia were used.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Nitric acid</td><td align='left'>5.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>15.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Cyanide required</td><td align='left'>21.6</td><td align='left'>"</td><td align='left'>21.7</td><td align='left'>"</td><td align='left'>21.5</td><td align='left'>"</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_197" id="Page_197">[Pg 197]</a></span></p>
+
+<p>On adding nitric acid to the solution it combines with a portion of the
+ammonia to form ammonic nitrate; it will be seen from the last series of
+experiments that the lessening of the amount of free ammonia will
+decrease the quantity of cyanide required; but, on the other hand, the
+ammonic nitrate which is at the same time formed will increase the
+amount required; under the conditions of the assay these two effects
+neutralise each other, and such differences in the quantity of acid as
+are likely to occur are unimportant.</p>
+
+<p><b>Effect of Varying Ammonic Salts.</b>&mdash;The quantities of copper, water, and
+ammonia were the same as in the last mentioned set of experiments, but
+no nitric acid was used.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ammonic nitrate added</td><td align='left'>1 gram</td><td align='left'>5 grams</td><td align='left'>10 grams</td><td align='left'>20 grams</td></tr>
+<tr><td align='left'>Cyanide required</td><td align='left'>21.2 c.c.</td><td align='left'>22.1 c.c.</td><td align='left'>23.1 c.c.</td><td align='left'>24.1 c.c.</td></tr>
+</table></div>
+
+
+<p>These show that combined ammonia seriously affects the titration, and
+that the principle sometimes recommended of neutralising the acid with
+ammonia, and then adding a constant quantity of ammonia, is not a good
+one, because there is then an interference both by the ammonia and by
+the variable quantity of ammonic salts.</p>
+
+<p>The same quantity of combined ammonia has the same effect, whether it is
+present as sulphate, nitrate, chloride, or acetate, as the following
+experiments show. Four lots of 20 c.c. of "copper nitrate" were taken,
+and 20 c.c. of dilute ammonia added to each. These were carefully
+neutralised with the respective acids, rendered alkaline with 30 c.c.
+more of ammonia, cooled, diluted to bulk, and titrated. The results
+were:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>With</td><td align='left'>sulphuric acid</td><td align='left'>22.5</td><td align='left'>c.c. of</td><td align='left'>cyanide</td></tr>
+<tr><td align='center'>"</td><td align='left'>nitric acid</td><td align='left'>22.6</td><td align='center'>"</td><td align='center'>"</td></tr>
+<tr><td align='center'>"</td><td align='left'>hydrochloric acid</td><td align='left'>22.6</td><td align='center'>"</td><td align='center'>"</td></tr>
+<tr><td align='center'>"</td><td align='left'>acetic acid</td><td align='left'>22.5</td><td align='center'>"</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Foreign Salts.</b>&mdash;Sulphates, nitrates and chlorides of sodium
+or potassium have no action, whilst the hydrates, carbonates,
+bicarbonates, sulphites, and nitrites have an important effect. The
+interference of ammonic salts has already been shown.</p>
+
+<p>Salts of silver, zinc, and nickel react with cyanide just as copper
+does, and consequently interfere. Ferrous salts are sure to be absent,
+and ferric salts yield ferric hydrate with the ammonia, which is not
+acted on by the cyanide, but, owing to its bulkiness, it settles slowly;
+this lengthens the time required for titration, and so modifies the
+manner of working. <i>An assay should not be worked with ferric hydrate
+present, unless the standard contains about the same amount of it.</i> On
+mines it is often inconvenient to separate the copper by means of
+sulphuretted hydrogen; hence it is customary to titrate without
+previous<span class='pagenum'><a name="Page_198" id="Page_198">[Pg 198]</a></span> separation. In this case, instead of standardising the cyanide
+with electrotype copper, a standard ore should be used. This should be
+an ore (of the same kind as those being assayed) in which the copper has
+been carefully determined.</p>
+
+<p><b>Effect of Varying Copper.</b>&mdash;In these experiments 10 c.c. of nitric
+acid, 30 c.c. of ammonia, and water to 200 c.c. were used.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper nitrate present</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'> 100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Cyanide required</td><td align='left'>0.7</td><td align='left'>"</td><td align='left'>11.2</td><td align='left'>"</td><td align='left'>21.7</td><td align='left'>"</td><td align='left'>54.5</td><td align='left'> "</td><td align='left'>108.1</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>These results show that under the conditions laid down the various
+causes of disturbance nearly neutralise one another, and the results
+within a fair range are practically proportional.</p>
+
+<p><b>Determination of Copper in Copper Pyrites.</b>&mdash;Weigh up 2 grams of the
+dried and powdered ore, and place in an evaporating dish about four
+inches in diameter. Cover with 20 c.c. of nitric acid and put on a hot
+plate. Evaporate to dryness without further handling. Allow to cool and
+take up with 30 c.c. of hydrochloric acid, boil, dilute, and transfer to
+a pint flask, filtering if necessary. Make up the bulk with the washings
+to about 150 c.c. Precipitate with sulphuretted hydrogen, filter, and
+wash back the precipitate into the flask. Add 15 c.c. of nitric acid,
+and boil down rapidly to 10 c.c. Dilute, add 30 c.c. of dilute ammonia,
+make up to 150 c.c., and cool. For the standard, weigh up 0.5 gram of
+copper, more or less, according to the quantity judged to be present in
+the assay. Dissolve in 20 c.c. of dilute nitric acid, boil off nitrous
+fumes, add 30 c.c. of dilute ammonia, make up to the same bulk as that
+of the assay, and cool. Titrate the two solutions side by side and as
+nearly as possible in the same manner.</p>
+
+<p>Since the assay solution is often turbid from the presence of small
+quantities of lead and of iron from incomplete washing, and since this
+slight precipitate is very slow in settling, the standard can hardly be
+compared strictly with the assay. This can be counteracted by
+precipitating in both solutions a mixture of ferric and aluminic
+hydrates, which settles readily and leaves the supernatant liquor clear.
+To effect this, boil the nitric acid solutions with 30 c.c. of a
+solution containing 15 grams each of alum and ferrous sulphate to the
+litre. In an actual determination 2 grams of the ore were taken and
+compared with 0.5 gram of copper. The assay required 57.7 c.c. of
+cyanide and the standard 52.5 c.c.</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;52.5 : 0.5 :: 57.7 : 0.5495<br />
+</p>
+
+<p>This on 2 grams of ore = 27.47 per cent.; the same sample by
+electrolysis gave 27.60 per cent. of copper.<span class='pagenum'><a name="Page_199" id="Page_199">[Pg 199]</a></span></p>
+
+<p><b>Determination without Previous Separation.</b>&mdash;Dissolve up 2 grams as
+before, but, instead of passing sulphuretted hydrogen, add 30 c.c. of
+dilute ammonia, shake well, and cool. Prepare a standard by dissolving
+0.5 gram of copper in 1 c.c. of nitric acid, add 0.6 gram of iron in the
+form of ferric chloride and 20 c.c. of hydrochloric acid, dilute to
+about 150 c.c., add 30 c.c. of dilute ammonia, and cool. Titrate the two
+solutions side by side. In a determination on the sample last used, 58
+c.c. were required for the assay and 53 c.c. for the standard, which
+indicates 27.3 per cent. of copper.</p>
+
+<p>This method of working is somewhat rough.</p>
+
+
+<h4>IODIDE METHOD.</h4>
+
+<p>This is based upon the fact that when potassic iodide in excess is added
+to a strong solution of a cupric salt in a faintly acid solution,
+cuprous iodide is formed and an equivalent of iodine liberated.<a name="FNanchor_56_56" id="FNanchor_56_56"></a><a href="#Footnote_56_56" class="fnanchor">[56]</a> The
+iodine is measured by titrating with a solution of sodium
+hyposulphite,<a name="FNanchor_57_57" id="FNanchor_57_57"></a><a href="#Footnote_57_57" class="fnanchor">[57]</a> using starch paste as indicator. The iodine is soluble
+in the excess of potassium iodide, forming a deep brown solution; the
+hyposulphite is added until this brown colour is almost removed. Starch
+paste is then added, and strikes with the remaining iodine a dirty blue
+colour. The addition of the "hypo" is continued until the blue colour is
+discharged. The end reaction is sharp; a drop is sufficient to complete
+it.</p>
+
+<p>As regards the titration, the process leaves little to be desired; the
+quantity of "hypo" required is strictly proportional to the copper
+present, and ordinary variations in the conditions of working are
+without effect. The presence of salts of bismuth masks the end reaction
+because of the strong colour imparted to the solution by the iodide of
+bismuth. Under certain conditions there is a return of the blue colour
+in the assay solution after the finishing point has apparently been
+reached, which is a heavy tax on the patience and confidence of the
+operator. This is specially apt to occur when sodium acetate is present,
+although it may also be due to excessive dilution.</p>
+
+<p><b>The standard "hypo" solution</b> is made by dissolving 39.18 grams of the
+crystallised salt (Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub>.5H<sub>2</sub>O) in water and diluting to
+one litre. One hundred c.c. will equal one gram of copper.</p>
+
+<p>The starch solution is made by mixing 1 gram of starch into a thin paste
+with cold water, pouring it into 200 c.c. of boiling<span class='pagenum'><a name="Page_200" id="Page_200">[Pg 200]</a></span> water, and
+continuing the boiling for a minute or so. The solution must be cold
+before use, and about 2 c.c. is used for each assay. It should not be
+added until the bulk of the iodine has been reduced.</p>
+
+<p>To standardise the "hypo," weigh up 0.3 or 0.4 gram of pure copper,
+dissolve in 5 c.c. of dilute nitric acid, boil off nitrous fumes, and
+dilute with an equal bulk of cold water. Add "soda" solution until a
+permanent precipitate is obtained, and then 1 c.c. of acetic acid. This
+should yield a clear solution. Fill an ordinary burette with the "hypo."
+Add 3 grams of potassium iodide crystals to the copper solution, and,
+when these are dissolved, dilute to 100 c.c. with water. Run in the
+"hypo" solution rather quickly until the brown colour is nearly
+discharged&mdash;<i>i.e.</i>, to within 3 or 4 c.c. of the finish. Add 2 c.c. of
+the starch solution, and continue the addition of the "hypo" a few drops
+at a time until the tint suddenly changes to a cream colour. The blue
+colour must not return on standing three or four minutes. Calculate the
+standard in the usual way.</p>
+
+<p>In assaying ores, the copper is dissolved and separated with
+sulphuretted hydrogen as in the other processes, but the sulphide should
+be washed more completely to ensure the absence of iron salts.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of the assay. Use a solution of copper sulphate containing 39.38 grams
+of copper sulphate crystals (CuSO<sub>4</sub>.5H<sub>2</sub>O) in the litre. 100 c.c.
+equal 1.00 gram of copper.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The assay after the addition of the
+potassic iodide must be kept cold, else iodine may be volatilised.</p>
+
+<p><b>Effect of Varying Potassium Iodide.</b>&mdash;In various descriptions of the
+process the amount of iodide required is variously stated at from "a few
+crystals" to as much as 10 grams. The proportion required by theory for
+1 gram of copper is a little over 5 grams: an excess, however, is
+required to keep the liberated iodine in solution. On economic grounds
+this excess should not be extravagant; if the student uses 10 parts of
+the iodide for each part of copper in the assay he will have sufficient.
+In the experiments there were used 20 c.c. of the copper sulphate, with
+varying amounts of potassic iodide, and the following results were
+got:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Potassic iodide added</td><td align='left'>1.5 gram</td><td align='left'>3 grams</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+</table></div>
+
+<p>In these the iodide was added direct to the solution containing the
+copper, which was afterwards diluted to 100 c.c. and titrated.<span class='pagenum'><a name="Page_201" id="Page_201">[Pg 201]</a></span> In
+another series the iodide was added after the dilution to 100 c.c., and
+the results were:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Potassic iodide added</td><td align='left'>1.5 gram</td><td align='left'>3 grams</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.1 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;In these experiments, 20 c.c. of copper
+sulphate were taken, 3 grams of potassic iodide added, and also water to
+the required bulk.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td><td align='left'>500.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>19.9</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>In the last of these experiments the colour was discharged at 18 c.c.,
+but gradually returned until 19.9 c.c. had been run in. It will be seen
+that considerable variation in bulk does not interfere.</p>
+
+<p><b>Effect of Acetic Acid.</b>&mdash;These experiments were like the last series
+mentioned, but the bulk was 100 c.c., and varying amounts of acetic acid
+were added.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acetic acid added</td><td align='right'>0</td><td align='left'>c.c.</td><td align='right'>1.0</td><td align='left'>c.c.</td><td align='right'>5.0</td><td align='left'>c.c.</td><td align='right'>10.0</td><td align='left'>c.c.</td><td align='right'>20.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='right'>20.0</td><td align='left'>"</td><td align='right'>20.1</td><td align='left'>"</td><td align='right'>20.1</td><td align='left'>"</td><td align='right'>20.0</td><td align='left'>"</td><td align='right'>20.2</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>Acetic acid, then, does not interfere to any serious extent.</p>
+
+<p><b>Effect of Varying Sodium Acetate.</b>&mdash;These experiments were like those
+last mentioned, but without acetic acid, and with varying amounts of
+sodium acetate.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodium acetate added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>2 grams</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.2 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>18.2 c.c.</td></tr>
+</table></div>
+
+
+<p>In the 5 grams experiment, when the finishing point had been apparently
+reached the colour slowly returned; but as the results generally on
+titrating were not satisfactory a repetition of the experiment was made
+with the addition of 5 c.c. of acetic acid, which gave an equally bad
+result.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;The conditions of these experiments were the
+same as before. The salts were added and dissolved before the addition
+of the potassium iodide. Using 5 grams (or in the case of the acids, 5
+c.c.), the results were as follows:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt added</td><td align='left'>&mdash;</td><td align='left'>dilute H<sub>2</sub>SO<sub>4</sub></td><td align='left'>Acetic acid</td><td align='left'>NaAc</td><td align='left'>NaCl</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.1 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>20.1 c.c.</td></tr>
+<tr><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'>Salt added</td><td align='left'>KNO<sub>3</sub></td><td align='left'>Na<sub>2</sub>SO<sub>4</sub></td><td align='left'>AmCl</td><td align='left'>Am<sub>2</sub>SO<sub>4</sub></td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.2 c.c.</td><td align='left'>18.7 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>19.9 c.c.</td></tr>
+</table></div>
+
+<p>The low result with the sulphate of soda was evidently due to the
+formation of a sparingly soluble double salt, which removed copper from
+the solution; on adding a little acetic acid the full amount of "hypo"
+was required. The effect of the presence of certain metals is important.
+The method of determining it was to add the substance to the solution
+containing the copper, and<span class='pagenum'><a name="Page_202" id="Page_202">[Pg 202]</a></span> partly precipitate with soda solution; then
+treating with 1 c.c. of acetic acid, adding the iodide, and proceeding
+as before.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Substance Added.</td><td align='left'>"Hypo" Required,</td></tr>
+<tr><td align='center'>-</td><td align='left'>20. c.c</td></tr>
+<tr><td align='left'>0.050 gram arsenic as As<sub>2</sub>O<sub>5</sub></td><td align='left'>20.0 "</td></tr>
+<tr><td align='left'>0.050&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; antimony as SbCl<sub>5</sub></td><td align='left'>19.8 "</td></tr>
+<tr><td align='left'>0.050&nbsp;&nbsp;&nbsp;&nbsp; "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; lead as Pb(NO<sub>3</sub>)<sub>2</sub></td><td align='left'>20.1 "</td></tr>
+</table></div>
+
+
+<p>A similar experiment with 0.050 gram of bismuth nitrate could not be
+determined, the end-reaction being masked. Bismuth iodide is soluble in
+potassic iodide, forming a brown solution, the colour of which is very
+similar to that produced by iodine; and although it does not strike a
+blue colour with starch, "hypo" has an action on it.</p>
+
+<p>A similar experiment with 0.050 gram of iron as ferric chloride required
+22.3 c.c. of "hypo," and the colour returned on standing. This shows
+that ferric acetate liberates iodine under the conditions of the assay.
+Trying to counteract this, by adding to a similar solution 0.5 gram of
+phosphate of soda dissolved in a little water, 19.7 c.c. of "hypo" were
+required instead of 20.0, but the assay showed signs of returning
+colour.</p>
+
+<p>In standardising, the same result was obtained, whether the copper was
+present as nitrate or sulphate before neutralising.</p>
+
+<p><b>Effect of Varying Copper.</b>&mdash;With the same conditions as before, but
+with varying amounts of copper and a proportionally increasing quantity
+of iodide, the results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper present</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>1.0</td><td align='left'>"</td><td align='left'>10.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>50.0</td><td align='left'>"</td><td align='left'>100.0</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>showing the results to be exactly proportional.<a name="FNanchor_58_58" id="FNanchor_58_58"></a><a href="#Footnote_58_58" class="fnanchor">[58]</a></p>
+
+<p><b>Determination of Copper in Copper Pyrites.</b>&mdash;Take 2 grams of the dried
+and powdered ore and treat in a porcelain dish with 20 c.c. of nitric
+acid, and evaporate to dryness. Take up with 30 c.c. of hydrochloric
+acid, dilute, and transfer to a pint flask; make up with water to 200
+c.c., warm, and pass sulphuretted hydrogen to excess. Filter, and wash
+the precipitate with water acidified with sulphuric acid. Wash the
+precipitate back into the flask, and dissolve with 15 c.c. of nitric
+acid. Evaporate almost to dryness; add 20 c.c. of water, and boil till
+free from nitrous fumes; filter off the sulphur and gangue; neutralise
+with soda, avoiding excess; add 1 or 2 c.c. of acetic acid, and shake
+till clear. Add 5 grams of potassium iodide, dilute to 100 c.c., and
+titrate. The following is an example:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>0.5 gram of copper required</td><td align='left'>50.5</td><td align='left'> c.c.</td><td align='left'> "hypo."</td></tr>
+<tr><td align='left'>The assay required</td><td align='left'>55.6</td><td align='left'>"</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>which is equal to 27.5 per cent. of copper.<span class='pagenum'><a name="Page_203" id="Page_203">[Pg 203]</a></span></p>
+
+
+<h4>COLORIMETRIC PROCESS.</h4>
+
+<p>This is based on the blue coloration of ammoniacal copper solutions. The
+quantity of copper in 100 c.c. of the assay solution should not be more
+than 15 milligrams, or less than half a milligram. It is not so delicate
+as most other colorimetric methods, but nevertheless is a very useful
+one.</p>
+
+<p>The manner of working is the same as that described under iron.</p>
+
+<p><b>Standard Copper Solution.</b>&mdash;Weigh up 0.5 gram of electrotype copper,
+dissolve in 10 c.c. of nitric acid, boil off nitrous fumes, and dilute
+to 1 litre. 1 c.c. = 0.5 milligram.</p>
+
+<p>In nearly all cases it will be necessary to separate the copper with
+sulphuretted hydrogen from a solution of about 5 grams of the material
+to be assayed. The filter paper containing the sulphide (and, probably,
+much sulphur) is dried and burnt. The ashes are dissolved in 5 c.c. of
+dilute nitric acid, 10 c.c. of dilute ammonia added, and the solution
+filtered through a coarse filter into a Nessler tube, washing the paper
+with a little dilute ammonia.</p>
+
+<p>The estimation of the colour and calculation of the result are made in
+the way described on page 44.</p>
+
+<p>The effect of varying conditions on the assay may be seen from the
+following experiments.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The effect of increased temperature is
+to slightly decrease the colour, but this can only be observed when a
+fair quantity of copper is present.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.0</td><td align='left'>c.c. at 15&deg;</td><td align='left'>showed the</td><td align='left'>colour of</td><td align='left'>1.0</td><td align='left'>c.c. at 70&deg;</td></tr>
+<tr><td align='left'>2.5</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>2.7</td><td align='center'>"</td></tr>
+<tr><td align='left'>5.0</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>5.0</td><td align='center'>"</td></tr>
+<tr><td align='left'>10.0</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>9.0</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Ammonia.</b>&mdash;The solution must, of course, contain free
+ammonia; about 5 c.c. of dilute ammonia in 50 c.c. bulk is the quantity
+to be used in the experiments. A larger quantity affects the results,
+giving lower readings and altering the tint. With small quantities of
+ammonia the colour approaches a violet; with larger, a sky-blue.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'> 2.5</td><td align='left'>c.c. with</td><td align='left'>25</td><td align='left'>c.c. of</td><td align='left'>strong ammonia</td><td align='left'>read</td><td align='left'>2.2</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'> 5.0</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>"</td><td align='left'>4.0</td><td align='center'>"</td></tr>
+<tr><td align='left'>10.0</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>"</td><td align='left'>8.0</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Ammonic Salts.</b>&mdash;The following table shows the results after
+addition of ammonic salts:<span class='pagenum'><a name="Page_204" id="Page_204">[Pg 204]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>C.c. Present.</td><td align='center'>With 10 grams Ammonic Nitrate.</td><td align='left'>With 10 grams Ammonic Chloride.</td><td align='center'>With 10 grams Ammonic Sulphate.</td></tr>
+<tr><td align='center'>2.5</td><td align='center'>2.5</td><td align='center'>2.5</td><td align='center'>2.0</td></tr>
+<tr><td align='center'>5.0</td><td align='center'>5.0</td><td align='center'>5.3</td><td align='center'>4.3</td></tr>
+<tr><td align='center'>10.0</td><td align='center'>10.0</td><td align='center'>10.0</td><td align='center'>8.5</td></tr>
+</table></div>
+
+<p>These show that sulphates should be avoided, and either nitrate or
+chloride solutions be used in the standard as well as in the assay.</p>
+
+<p><b>Determination of Copper in a Manganese Ore.</b>&mdash;Treat 3 grams of the ore
+with 20 c.c. of hydrochloric acid, and evaporate to dryness. Take up
+with 10 c.c. of hydrochloric acid; dilute to about 200 c.c., and pass
+sulphuretted hydrogen until the solution smells of the gas; filter,
+burn, take up with 5 c.c. of dilute nitric acid, add 10 c.c. of dilute
+ammonia, and filter into the Nessler tube, and make up with the washings
+to 50 c.c. Into the "standard" tube put 5 c.c. of dilute nitric acid and
+10 c.c. of dilute ammonia. Make up to nearly 50 c.c. with water, and run
+in the standard copper until the colours are equal. In a determination 4
+c.c. (= 2.0 milligrams of copper) were required; this in 3 grams of ore
+= 0.07 per cent.</p>
+
+<p><b>Determination of Copper in "Black Tin."</b>&mdash;Weigh up 3 grams of the dried
+ore, boil with 10 c.c. of hydrochloric acid, and afterwards add 1 c.c.
+of nitric; boil off nitrous fumes, evaporate to about 5 c.c., dilute to
+50 c.c., add 20 c.c. of dilute ammonia; stir, and filter. If much iron
+is present, dissolve the precipitate of ferric hydrate in acid, and
+reprecipitate with ammonia. Mix the two filtrates, and dilute to 100
+c.c. Take 50 c.c. for the test. A sample of 3 grams of an ore treated in
+this way required 5.2 c.c. of standard copper to produce equality of
+tint. This gives 0.35 per cent.</p>
+
+<p><b>Determination of Copper in Tin.</b>&mdash;Weigh up 1 gram of the sample,
+transfer to an evaporating dish, and cover with 30 c.c. of aqua regia.
+Warm until the metal has dissolved, then evaporate almost to dryness.
+Take up with a few c.c. of hydrochloric acid and again evaporate.</p>
+
+<p>Dissolve the residue in 10 c.c. of dilute hydrochloric acid and transfer
+to a 100 c.c. flask. Add 10 c.c. of dilute ammonia and make up with
+water to the containing mark.</p>
+
+<p>Filter off 50 c.c. of the solution into a Nessler glass and determine
+the copper in it colorimetrically.<span class='pagenum'><a name="Page_205" id="Page_205">[Pg 205]</a></span></p>
+
+
+<h4>EXAMINATION OF COMMERCIAL COPPER.</h4>
+
+<p>Very pure copper can be obtained in commerce, owing to the demand for
+metal of "high conductivity" for electrical purposes, which practically
+means for metal free from impurities.</p>
+
+<p>Much of the metal sold contains as much as one per cent. of foreign
+substances, of which arsenic is the most important. The other elements
+to be looked for are bismuth, lead, antimony, silver, gold, iron,
+nickel, cobalt, sulphur, and oxygen. In "blister copper" (which is the
+unrefined metal), aluminium, silicon, and phosphorus may be met with.</p>
+
+<p><b>Oxygen.</b>&mdash;All commercial copper carries oxygen; most of it is present
+as cuprous oxide, which is dissolved by molten copper. The estimation of
+oxygen is often made "by difference." The copper and the other
+impurities being determined, the rest is assumed to be oxygen. Probably
+this is nearly correct, but the whole of the oxygen should not be
+ascribed to cuprous oxide; for any arsenic the metal contained would be
+present as cuprous arsenite, since arsenide of copper and cuprous oxide
+could not exist together at the temperature of fusion without
+interacting. In the report of the analysis, it is best to state the
+proportion of oxygen thus:&mdash;</p>
+
+<p>
+<span style="margin-left: 1em;">Oxygen &mdash;&mdash;&mdash; per cent. by difference.</span><br />
+</p>
+
+<p>There is a method of determination by fusing 5 or 10 grams in a brasqued
+crucible, and counting the loss as oxygen; and another method for the
+determination of cuprous oxide based on the reaction of this substance
+with nitrate of silver.<a name="FNanchor_59_59" id="FNanchor_59_59"></a><a href="#Footnote_59_59" class="fnanchor">[59]</a> About 2 grams of silver nitrate, dissolved
+in 100 c.c. of water, is allowed to act upon 1 gram of the copper in the
+cold. The precipitate is filtered off, washed thoroughly with water, and
+the basic salt dissolved and determined colorimetrically.</p>
+
+<p>One part of copper found represents 1.68 part of cuprous oxide, or 0.19
+part of oxygen. Copper generally carries from 0.1 to 0.2 per cent. of
+oxygen.</p>
+
+<p><b>Silver</b> is found in most samples, but occurs in variable proportions;
+when it amounts to 30 ounces per ton it has a commercial value. To
+determine its amount, dissolve 10 grams of the copper in 35 c.c. of
+nitric acid and 50 c.c. of water, boil off nitrous fumes, and dilute to
+about 100 c.c. One or two c.c. of dilute hydrochloric<span class='pagenum'><a name="Page_206" id="Page_206">[Pg 206]</a></span> acid (one to 100
+of water) are added, stirred in, and the precipitate allowed to settle
+for twenty-four hours. Filter through a double Swedish paper, dry, burn,
+and cupel the ashes with one gram of sheet lead.</p>
+
+<p>Ten grams of a sample of copper gave in this way 4.7 milligrams of
+silver. Ten grams of the same copper, to which 24 milligrams of silver
+had been added gave 28.2 milligrams.</p>
+
+<p><b>Gold.</b>&mdash;To determine it, dissolve 10, 20, or 50 grams of the sample in
+35, 70, or 175 c.c. of nitric acid and an equal volume of water, boil
+till free from nitrous fumes, and dilute to double its volume. Allow to
+stand for some time, decant on to a filter, dry, burn, and cupel the
+ashes with 1 gram of sheet lead. If silver is present, owing to traces
+of chlorides in the re-agents used, "parting" will be necessary. (See
+<i>Gold</i>.)</p>
+
+<p>Working in this way on 20 grams of copper, to which 1.8 milligram of
+gold had been added, a button weighing 2.0 milligrams was obtained.</p>
+
+<p><b>Antimony</b> is not a frequent impurity of copper: it can be detected in
+quantities over 0.1 per cent. by a white residue of Sb<sub>2</sub>O<sub>4</sub>,
+insoluble in nitric acid. With material containing only small quantities
+of antimony the white oxide does not show itself for some time, but on
+long-continued boiling it separates as a fine powder. It is best (when
+looking for it) to evaporate the nitric acid solution to the
+crystallising point, to add a little fresh nitric acid and water, and
+then to filter off the precipitate. After weighing it should be examined
+for arsenic and bismuth.</p>
+
+<p><b>Lead.</b>&mdash;Refined coppers are often free from lead, anything more than
+traces being seldom found; in coarse coppers it is sometimes present in
+considerable quantities.</p>
+
+<p>Its presence may be detected in the estimation of the copper
+electrolytically, the platinum spiral becoming coated with a brown or
+black deposit of lead dioxide. The depth of colour varies with the lead
+present, and obviously could be made the basis of an approximate
+estimation. The colour shows itself within an hour or so, but is best
+observed when all the copper has been deposited.</p>
+
+<p>Electrolysing a solution of one gram of pure copper, to which 0.5
+milligram of lead had been added, the deposit was dark brown; in a
+similar solution with 1 milligram of lead it was much darker, and with 2
+milligrams it was black. Under the conditions of the assay the dioxide
+cannot be weighed, as it partly dissolves on breaking the current. When
+lead has been found, its quantity may be estimated by evaporating to
+dryness the nitric acid solution to which an excess of sulphuric acid
+has been added, taking up with water, and filtering off and weighing the
+lead sulphate.<span class='pagenum'><a name="Page_207" id="Page_207">[Pg 207]</a></span></p>
+
+<p>The separation of traces of lead as chromate is a fairly good one.
+Dissolve 5 grams of the copper in 17 c.c. of nitric acid and an equal
+volume of water; boil off nitrous fumes, neutralise with soda, and
+afterwards acidulate with acetic acid; and dilute to a litre. Add 20
+grams of sodium acetate, warm, and precipitate the lead with a dilute
+solution of potassium chromate. Copper chromate (yellow) may be at the
+same time thrown down, but it is readily soluble on diluting. Filter off
+the precipitate; wash it into a beaker and pass sulphuretted hydrogen;
+oxidise the sulphide and weigh as lead sulphate. Treated in this way 5
+grams of copper yielded sulphate of lead equal to 2.0 milligrams of
+lead. Five grams of the same sample to which 10 milligrams of lead were
+added gave 11.4 milligrams.</p>
+
+<p><b>Nickel and Cobalt.</b>&mdash;Nickel is always present in larger or smaller
+quantities in commercial copper, and, perhaps, has an influence on the
+properties of the metal. It is determined as follows:&mdash;Dissolve 10 grams
+of the copper in 35 c.c. of nitric acid and an equal bulk of water, boil
+off nitrous fumes and neutralise with soda, add 2 grams of carbonate of
+soda dissolved in water, boil, and filter. Acidify the filtrate with 2
+or 3 c.c. of dilute nitric acid and dilute to 1 or 1-1/2 litres. Pass
+sulphuretted hydrogen through the cold solution till the copper is all
+down and the liquid smells of the gas. Filter and evaporate the filtrate
+to a small bulk, and determine the nickel by electrolysing the solution
+rendered ammoniacal, or by precipitating as sulphide and weighing as
+sulphate. (See under <i>Nickel</i>.) The precipitate, after weighing, should
+be tested for cobalt. If present it is separated with potassium nitrite
+as described under <i>Cobalt</i>. Ten grams of copper gave 6.0 milligrams of
+nickel; and another lot of 10 grams of the same copper, to which 10.0
+milligrams of nickel had been added, gave 17.2 milligrams.</p>
+
+<p><b>Sulphur.</b>&mdash;The amount of sulphur in refined copper is very small,
+seldom exceeding 0.005 per cent. In coarse copper, as might be expected,
+it is found in larger quantities.</p>
+
+<p>In determining it, it is first converted into sulphuric acid, and then
+precipitated and weighed as barium sulphate. The precipitation cannot be
+effected from a nitric acid solution. Ten grams of copper are dissolved
+in nitric acid, as for the other determinations, and then boiled with
+excess of hydrochloric acid till the nitric acid is completely removed.
+There is then added a few drops of a dilute solution of baric chloride,
+and the solution is allowed to stand for some hours. The baric sulphate
+is filtered off and weighed.</p>
+
+<p>The necessity for precipitating from a hydrochloric acid solution is
+seen from the following determinations. In each experiment<span class='pagenum'><a name="Page_208" id="Page_208">[Pg 208]</a></span> 10 grams of
+copper was used, and a known weight of sulphur, in the form of copper
+sulphate, added.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>Sulphur added.</td><td align='center'>Sulphur found in Hydrochloric Acid Solution.</td><td align='center'>Sulphur found in Nitric Acid Solution.</td></tr>
+<tr><td align='center'>5 milligrams</td><td align='center'>8 milligrams</td><td align='center'>0.03 milligrams</td></tr>
+<tr><td align='center'>10 &nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='center'>11 &nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='center'>0.03 &nbsp;&nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='center'>15 &nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='center'>17 &nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='center'>12.00 &nbsp;&nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+<p><b>Bismuth.</b>&mdash;Nearly all samples of copper contain bismuth, but only in
+small quantities. It is best determined colorimetrically as described
+under <i>Bismuth</i>. The method of concentrating and preparing the solution
+for colorimetric assay is as follows. Dissolve 10 grams of copper in
+nitric acid, as in the other determinations; neutralise with soda; add 1
+or 1.5 grams of bicarbonate of soda and boil for ten minutes; filter,
+dissolve the precipitate in hot dilute sulphuric acid; add sulphurous
+acid and potassium iodide in excess, and boil till free from iodine.
+Filter and dilute to 500 c.c. Take 50 c.c. of the yellow solution for
+the determination. A few c.c. of a dilute solution of sulphurous acid (1
+in 100) will prevent the liberation of iodine. The following experiments
+test the method of separation. Ten grams of copper were treated as above
+and precipitated with 1.5 gram of "soda;" the precipitate contained 0.6
+milligram of bismuth (= 0.006 per cent.). The filtrate treated with
+another 1.5 gram of "soda" gave a precipitate which was free from
+bismuth. To the filtrate from this was added 1.0 milligram of bismuth,
+and another fraction was precipitated with 1.5 gram of "soda." In this
+precipitate was found 1.0 milligram of bismuth. To the filtrate another
+milligram of bismuth was added and the separation with "soda" repeated.
+The bismuth was separated from this precipitate with ammonic carbonate
+before determination, and 0.9 milligram was found.</p>
+
+<p><b>Arsenic.</b>&mdash;The proportion of arsenic in copper varies from 0.01 to 0.75
+per cent. whilst in coarse copper it may amount to 2 or even 3 per cent.
+To determine it, dissolve 5, 10, or 20 grams of the copper (according to
+the amount of arsenic present) in 18 c.c., 35 c.c., or 70 c.c. of nitric
+acid, and an equal volume of water. Boil off the nitrous fumes, dilute
+to 100 c.c. and neutralise with soda; add 1.5 or 2 grams of carbonate of
+soda dissolved in a little water, and boil. Filter (washing is
+unnecessary) and dissolve back into the flask with a little dilute
+hydrochloric acid; add 30 c.c. of dilute ammonia and 25 c.c. of
+"magnesia mixture," and allow to stand overnight. The whole of the
+arsenic is precipitated as ammonic-magnesic arsenate in one hour, but it
+is<span class='pagenum'><a name="Page_209" id="Page_209">[Pg 209]</a></span> advisable to leave it longer. The precipitate may be dried and
+weighed, or, better, titrated with uranium acetate. (See <i>Arsenic.</i>) To
+test this method of separation 10 grams of pure copper were taken and
+0.200 gram of arsenic dissolved with it. The arsenic was determined by
+titration with uranium acetate, and 0.200 gram was found. Two other
+similar experiments with 0.080 and 0.010 gram of arsenic added, gave
+0.079 and 0.012 gram respectively.</p>
+
+<p>Antimony or bismuth may be present without interfering with the
+titration. With 0.100 gram of antimony and 0.100 gram of arsenic, 0.100
+gram of arsenic was found; and in another case, with 0.100 gram of
+bismuth and 0.060 gram of arsenic, 0.060 gram was found. In these
+experiments the antimony and bismuth were present in the assay solution
+when titrated. For a gravimetric determination they would require to be
+removed before precipitating with "magnesia mixture."</p>
+
+<p>Phosphorus, if present, counts as arsenic in the proportion of 1 to 2.4;
+but, except in the case of coarse coppers, it is always absent.</p>
+
+<p>Iron, if present, interferes by forming a white flocculent precipitate
+of ferric arsenate after the addition of the sodium acetate and
+preliminary to the titration. Each milligram of iron abstracts, in this
+way, 1.3 milligrams of arsenic.</p>
+
+<p><b>Iron.</b>&mdash;Refined coppers carry traces of iron, varying from 0.001 to
+0.01 per cent. It is best determined during the arsenic estimation. The
+precipitate of the ammonic-magnesic arsenate will contain the whole of
+the iron as ferric hydrate. On dissolving in hydrochloric acid,
+neutralising with ammonia, adding 5 c.c. of sodic acetate, diluting, and
+boiling, it reappears as a white precipitate of ferric arsenate. It is
+filtered off (the arsenic being estimated in the filtrate), dissolved in
+warm hydrochloric acid, and determined colorimetrically as described
+under <i>Iron</i>. A series of experiments testing the separation is there
+given.</p>
+
+<p><b>Phosphorus.</b>&mdash;Refined coppers do not carry phosphorus, although it may
+be present in "coarse copper" up to 1 per cent. or more. In such samples
+the following method is adopted for the estimation of both phosphorus
+and arsenic. Dissolve 10 grams of copper and 0.1, 0.2, or 0.3 gram of
+iron wire (according to the amount of arsenic and phosphorus present) in
+35 c.c. of nitric acid and an equal volume of water. Add soda till the
+free acid is nearly neutralised. Next add a strong solution of sodium
+acetate, until the solution ceases to darken on further addition, then
+dilute with water to half a litre. The solution is best contained in a
+large beaker; it is next heated to the boiling point, and at once
+removed and allowed to settle. If the precipitate is<span class='pagenum'><a name="Page_210" id="Page_210">[Pg 210]</a></span> light coloured it
+is evidence that sufficient iron has not been added, or, if it is green,
+from basic copper salts, it shows that the solution was not sufficiently
+acid. In either case start afresh. Filter off the precipitate and wash
+with hot water containing a little sodium acetate, dissolve it off the
+filter with hot dilute hydrochloric acid, add ammonia in excess, and
+pass sulphuretted hydrogen for five minutes. Warm at about 70&deg; C. for a
+quarter of an hour. Filter. The clear yellow filtrate contains the
+arsenic and phosphorus. Add dilute sulphuric acid in excess; filter off
+the yellow precipitate of sulphide of arsenic, dissolve it in nitric
+acid, and titrate with uranium acetate, as described under <i>Arsenic</i>.</p>
+
+<p>The filtrate from the sulphide of arsenic is rendered alkaline with
+ammonia and "magnesia mixture" added. The solution is stirred, and
+allowed to stand overnight. The precipitate of ammonic-magnesic
+phosphate is filtered off, dissolved, and titrated with uranium acetate,
+using the same standard solution as is used in the arsenic assay: 0.5
+gram of arsenic equals 0.207 gram of phosphorus.</p>
+
+<p><b>Copper.</b>&mdash;The method of determining this has been described under
+<i>Electrolytic Assay</i>.</p>
+
+<p>In the method of concentration by fractional precipitation with sodic
+carbonate (which is adopted in most of these determinations) the
+precipitate will contain all the bismuth, iron, and alumina; the arsenic
+and phosphorus as cupric arsenate and phosphate; and the greater part of
+the lead, antimony, and silver. The nickel and cobalt, and the sulphur
+as sulphuric acid, will remain in solution with the greater part of the
+copper.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. According to a wet assay 2 grams of a certain ore contained 0.3650
+gram of copper. What would you expect the dry assay produce to be?</p>
+
+<p>2. A standard solution is made by dissolving 25 grams of potassic
+cyanide and diluting to a litre. Assuming the salt to be 98 per cent.
+real cyanide, what would 100 c.c. of the solution be equivalent to in
+grams of copper?</p>
+
+<p>3. How would you make a solution of "hypo" of such strength that 100
+c.c. shall equal 0.633 gram of copper?</p>
+
+<p>4. What weight of ore, containing 17.0 per cent. of copper, would you
+take in order to get about 0.5 gram of copper in solution for
+electrolysis?</p>
+
+<p>5. The solution of copper in nitric acid is effected by the following
+reaction:&mdash;</p>
+
+<p>3Cu + 8HNO<sub>3</sub> = 3Cu(NO<sub>3</sub>)<sub>2</sub> + 4H<sub>2</sub>O + 2NO.</p>
+
+<p>What volume of nitric acid will be required to dissolve 1 gram of
+copper?<span class='pagenum'><a name="Page_211" id="Page_211">[Pg 211]</a></span></p>
+
+
+<h4>LEAD.</h4>
+
+<p>The chief ore of lead is galena, a sulphide of lead, common in most
+mining districts, and frequently associated with blende and
+copper-pyrites. It always carries more or less silver; so that in the
+assay of the ore a silver determination is always necessary. Carbonate
+(cerussite), sulphate (anglesite), and phosphate (pyromorphite) of lead
+also occur as ores, but in much smaller quantities.</p>
+
+<p>Lead ores are easily concentrated (owing to their high specific gravity,
+&amp;c.) by mechanical operations, so that the mineral matter sent to the
+smelter is comparatively pure.</p>
+
+<p>Lead is readily soluble in dilute nitric acid. The addition of sulphuric
+acid to this solution throws down heavy, white, and insoluble lead
+sulphate.</p>
+
+<p>Galena is soluble in hot hydrochloric acid, sulphuretted hydrogen being
+evolved; but the action is retarded by the separation of the sparingly
+soluble lead chloride. If a rod of zinc is placed in this solution,
+metallic lead is precipitated on it as a spongy mass, the lead chloride
+being decomposed as fast as it is formed. The opening up of the ore is
+thus easily effected, the sulphur going off as sulphuretted hydrogen,
+and the lead remaining in a form easily soluble in dilute nitric acid.
+Galena itself is readily attacked by nitric acid, part of the lead going
+into solution, and the rest remaining as insoluble lead sulphate. The
+sulphate is due to the oxidation of the sulphur by nitric acid; its
+amount will vary with the quantity and concentration of the acid used.
+Sulphate of lead is soluble in solutions of ammonium or sodium acetate;
+or it may be converted into carbonate by boiling with carbonate of soda.
+The carbonate, after washing off the sulphate of soda, dissolves easily
+in nitric acid. The precipitation of lead from acid solutions with
+sulphuric acid, and the solubility of the precipitate in ammonium
+acetate, distinguishes it from all other metals. The addition of
+potassium chromate to the acetate solution reprecipitates the lead as a
+yellow chromate.</p>
+
+
+<h4>DRY ASSAY.</h4>
+
+<p>The dry assay of lead is largely used, but it is only applicable to rich
+or concentrated ores, and even with these only gives approximate
+results. Both lead and lead sulphide are sensibly volatile at a
+moderately-high temperature; hence it is necessary to obtain a slag
+which is easily fusible. As a reducing agent iron is almost always used,
+and this is added either in the form of an iron rod, or the crucible
+itself is made of this metal. The flux used is carbonate of soda.<span class='pagenum'><a name="Page_212" id="Page_212">[Pg 212]</a></span></p>
+
+<p>When a clay crucible is used, the method of working is as
+follows:&mdash;Weigh up 25 grams of the dry and powdered ore, mix with an
+equal weight of "soda" and 2 grams of tartar; place in a crucible (E.
+Battersea round), and then insert a piece of iron rod about half an inch
+in diameter, and of such a length that it will just allow the crucible
+to be covered. The rod should be pushed down so as to touch the bottom
+of the crucible, and the mixture should be covered with a sprinkling of
+borax. Place in a furnace heated to, but not above, redness, and cover
+the crucible. In about twenty minutes the charge will be fused: the
+fusion is complete when bubbles of gas are no longer being evolved; and
+then, but not till then, the iron is withdrawn, any adhering buttons of
+lead being washed off by dipping the rod a few times in the slag. Cover
+the crucible, leave it for a minute or two, and then pour. Detach the
+slag, when cold, by hammering. The weight of the button multiplied by 4
+gives the percentage. The commoner errors of students in working the
+process are too high a temperature and too quick a withdrawal.</p>
+
+<p>A sample of ore treated in this manner gave on duplicate assay 17.5 and
+17.6 grams of lead, equalling 70.0 and 70.4 per cent. respectively. By
+wet assay the sample gave 73.3 per cent. Using an iron crucible, the
+results will be 1 per cent. or so higher. The crucible must be made of
+wrought iron; and, if it has been previously used, should be cleaned by
+heating to dull redness and scraping the scale off with a stirrer. Take
+30 grams of the ore, mix with 30 grams of "soda" and 3 grams of tartar;
+put the mixture in the crucible, and cover with a sprinkling of borax;
+heat for about twenty minutes at not too high a temperature, and then
+scrape down the slag adhering to the side with a stirrer. Leave in the
+furnace till action has ceased. Before pouring, tap the pot gently, and
+then tilt it so as to make the slag wash over the part of the crucible
+along which the charge is to be poured. Pour; and, when cold, clean and
+weigh the button of metal. A crucible may be used from ten to twenty
+times.</p>
+
+<p>These assays are for ores containing the lead chiefly as sulphide. For
+oxidised ores, charcoal or tartar is employed as the reducing agent. The
+student may practise on red lead as follows:&mdash;Take 30 grams of red lead;
+mix with 10 grams each of borax and "soda" and about 1.5 gram of
+powdered charcoal; place in a small clay crucible with a cover (C.
+Battersea round), fuse at a gentle heat, and pour when action ceases.
+This assay will only take a few minutes.</p>
+
+<p>Where lead is present as phosphate (as in the case of pyromorphite), or
+mixed with phosphates (as sometimes happens), carbonate of soda is a
+suitable flux; but the phosphate of soda<span class='pagenum'><a name="Page_213" id="Page_213">[Pg 213]</a></span> which is formed makes a thick
+tenacious slag, which is very apt to be carried out of the pot by the
+escaping gas. A wide-mouthed clay pot is taken and a little fluor spar
+added. For the assay of pyromorphite the following charge may be
+used:&mdash;Ore, 20 grams; "soda," 25 grams; tartar, 7 grams; and fluor spar,
+5 grams; and 2 grams of borax as a cover. This will melt down in about
+ten minutes, and should be poured as soon as tranquil.</p>
+
+
+<h4>WET ASSAY.</h4>
+
+<p>In the case of galena the best method of getting the lead into solution
+is to treat with hydrochloric acid and zinc. Put 1 gram of the ore in an
+evaporating dish 4 inches across, and cover with 10 c.c. of dilute
+hydrochloric acid. Heat till the evolution of sulphuretted hydrogen
+becomes sluggish, and then drop in a piece of zinc rod. If the solution
+effervesces too strongly, dilute it. Continue the heating until the
+sulphide is seen to be all dissolved; when the lead is all precipitated,
+pour off the liquid and wash twice with cold water. Peel off the
+precipitated lead with the help of a glass rod, and then clean the zinc.
+Cover the lead with 20 c.c. of water and 5 c.c. of dilute nitric acid,
+and heat gently till dissolved; all the lead will be in solution, and,
+when filtered off from the gangue, will be ready for a gravimetric
+determination. For volumetric work this filtering is unnecessary.</p>
+
+<p>The chief objection to this method is that commercial zinc carries
+considerable quantities of lead. Although this can be determined and
+allowed for, the correction required is in most cases too large to be
+satisfactory. The following method is applicable in all cases, but is
+more troublesome:&mdash;Treat 1 gram of the ore with 10 c.c. of dilute nitric
+acid in an evaporating dish covered with a clock-glass, and evaporate
+till nearly dry. Take up with 50 c.c. of water, and add 10 c.c. of
+dilute sulphuric acid. Filter. The residue contains the lead as
+sulphate, together with the insoluble matter of the ore and globules of
+sulphur. Warm with a solution of ammonium acetate, and filter. The lead
+will be in the filtrate, and is recovered in a state fit for direct
+gravimetric estimation by the addition of dilute sulphuric acid. If the
+volumetric method is to be used, the lead sulphate should be dissolved
+out with a solution of sodium acetate instead of with the ammonium salt
+solution.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The lead is separated and precipitated as sulphate, as already
+described. The solution must be allowed to stand, and the clear<span class='pagenum'><a name="Page_214" id="Page_214">[Pg 214]</a></span> liquid
+be decanted through a filter. Transfer the precipitate, and wash with
+very dilute sulphuric acid (1 or 2 c.c. in 100 c.c. of water). The acid
+must be completely removed with one or two washes with cold water, and
+then with alcohol. The volume of liquid required for washing is small,
+as the precipitate is dense and easily cleaned; but the washing must be
+carefully done, since if any acid remains it will, on drying, char the
+paper, and render the subsequent work troublesome. Dry, transfer to a
+watch-glass, and burn the filter paper, collecting its ash in a weighed
+porcelain crucible. The filter paper must be freed as much as possible
+from the lead sulphate before burning, and the ash treated with a drop
+or two of nitric and sulphuric acids. Transfer the lead sulphate to the
+crucible; ignite gently, keeping the temperature below redness; cool,
+and weigh. The precipitate will contain 73.6 per cent. of lead oxide or
+68.3 per cent. of lead.</p>
+
+<p><b>Determination of Lead in Commercial Zinc.</b>&mdash;Take 10 grams of zinc, and
+treat (without heating) with 60 c.c. of dilute hydrochloric acid. When
+the zinc is nearly all dissolved, decant off the clear liquid, and
+dissolve the residue in 2 c.c. of dilute nitric acid. Evaporate till
+most of the acid is removed; dilute to 20 or 30 c.c. with water, and add
+10 c.c. of dilute sulphuric acid. Filter off, and weigh the lead
+sulphate. Ten grams treated in this way gave&mdash;0.1610 gram of lead
+sulphate, equivalent to 1.10 per cent. of lead.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This is based upon the reaction between chromate of potash and soluble
+lead salts in neutral solutions, whereby an insoluble yellow chromate of
+lead is produced.<a name="FNanchor_60_60" id="FNanchor_60_60"></a><a href="#Footnote_60_60" class="fnanchor">[60]</a> An excess of the chromate is required to complete
+the reaction, so that the point at which an indicator shows the presence
+of undecomposed chromate cannot be satisfactorily taken as the finish.
+Therefore an excess of the standard chromate must be run in, and such
+excess determined.</p>
+
+
+<p>Chromate of lead is not precipitated from strong nitric acid solutions,
+and only incompletely from dilute ones. Acids generally are detrimental
+to the precipitation, and must be neutralised before titrating. If the
+lead is present as sulphate in sodic acetate solution, it is well to
+render it distinctly alkaline with ammonia.</p>
+
+<p>Lead chromate precipitated in the cold is a lemon-yellow, light
+precipitate, very difficult to filter: on heating to 40&deg; C. the colour
+becomes orange; at 60&deg; C. it assumes a deeper hue, and becomes<span class='pagenum'><a name="Page_215" id="Page_215">[Pg 215]</a></span>
+flocculent; and at a boiling temperature it still further darkens and
+settles readily. These changes in colour are not due to any chemical
+change, as will be seen by testing the filtrate for chromium or lead:
+this is an advantage to the assay, since it is only at the higher
+temperature that the precipitate can be easily filtered. The lead is not
+completely precipitated, but the amount remaining in solution is only 2
+or 3 milligrams, which is just sufficient to give a dark coloration with
+sulphuretted hydrogen.</p>
+
+<p><i>The standard chromate of potash solution</i> is made by dissolving 7.13
+grams of bichromate of potash and 2.0 grams of caustic soda in water,
+and diluting to 1 litre; or 9.40 grams of the neutral chromate
+(K<sub>2</sub>CrO<sub>4</sub>) may be dissolved and diluted to 1 litre: 100 c.c. will be
+equivalent to 1.000 gram of lead.</p>
+
+<p><i>Standard Lead Solution.</i>&mdash;16 grams of nitrate of lead (Pb(NO<sub>3</sub>)<sub>2</sub>)
+are dissolved in water and diluted to 1 litre; 100 c.c. will contain
+1.000 gram of lead.</p>
+
+<p><i>Acetate of Soda Solution.</i>&mdash;250 grams of the crystallised salt
+(NaAc.3H<sub>2</sub>O) are dissolved, and diluted to 1 litre. Use 40 c.c. for
+each assay.</p>
+
+<p>In the titration the assay solution should measure 150 to 200 c.c., and
+should be boiling or nearly so. It is best contained in a pint flask,
+and the standard chromate solution used with an ordinary burette. Run in
+the chromate solution in a steady stream until the whole of the lead has
+been precipitated. The amount required for this may be calculated: for
+example, 1 gram of an 80 per cent. ore would require 80 c.c. A little of
+the assay may be filtered off, and if it does not show a yellow colour
+in the filtrate run in 2 c.c. more of the standard solution and continue
+this addition till a colour is shown. After this run in another c.c. to
+ensure an excess, dilute to 250 c.c., and heat to boiling; allow to
+settle for three or four minutes, filter off 50 c.c. into a Nessler
+glass, and determine the excess of chromate colorimetrically. The excess
+found in the 50 c.c. must, of course, be multiplied by five, and then be
+deducted from the quantity of chromate originally run into the assay
+solution. The quantity to be deducted should not exceed 3 c.c. Where a
+number of determinations are made the colorimetric estimation is
+facilitated by using a series of standard phials similar to those
+described under the <i>Electrolytic Copper Assay</i>. The determination is
+rendered sharper and less liable to error by the addition of a few drops
+of acetic acid to convert the chromate into bichromate. The same
+chromate solution must be used in this determination as was used in the
+precipitation.</p>
+
+<p>In standardising the chromate solution, the standard lead nitrate
+solution is used. A quantity containing about as much<span class='pagenum'><a name="Page_216" id="Page_216">[Pg 216]</a></span> lead as the assay
+is supposed to contain is measured off, rendered alkaline with dilute
+ammonia, and then neutralised with acetic acid, using a small piece of
+litmus paper dropped into the solution as indicator. Then dilute, boil,
+and titrate. When the lead in the assay has been separated as sulphate
+and dissolved in sodic acetate, less chromate is apparently required,
+and in this case it will be necessary to precipitate the lead in the
+standard with an equivalent of sodic sulphate and redissolve in sodic
+acetate just as in the assay. In these solutions (although there is
+considerable chromate in excess) a further addition of 5 or 6 c.c. of
+the chromate solution will cause a further precipitate. The following
+experiments show the effect of variation in the conditions of the
+assay:&mdash;</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;Twenty c.c. of lead nitrate solution
+and 10 grams of sodium acetate were used; diluted to 200 c.c., heated to
+the desired temperature, and titrated. The results were:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg;</td><td align='left'>30&deg;</td><td align='left'>50&deg;</td><td align='left'>100&deg;</td></tr>
+<tr><td align='left'>"Chromate" required</td><td align='left'>19.8 c.c.</td><td align='left'>19.5 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>19.2 c.c.</td></tr>
+</table></div>
+
+
+<p>The first two of these filtered badly, the precipitate coming through
+the filter; the last was very satisfactory in the working.</p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;Using 20 c.c. of lead nitrate, and 10 grams
+of sodium acetate as before, diluting to the required bulk, heating to
+boiling, and titrating, the results were:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td><td align='left'>500.0</td><td align='left'>c.c.</td><td align='left'>1000.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Chromate" required</td><td align='left'>19.6</td><td align='left'>"</td><td align='left'>19.3</td><td align='left'>"</td><td align='left'>19.4</td><td align='left'>"</td><td align='left'>19.4</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Acetic Acid.</b>&mdash;Since the experiments are carried out
+in the presence of sodic acetate, acetic acid is the only acid whose
+effect need be considered. Working as before, but with 200 c.c. bulk and
+varying amounts of the acid, the results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acid present</td><td align='left'>&mdash;</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>40.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Chromate" required</td><td align='left'>19.7 c.c.</td><td align='left'>19.1</td><td align='left'>"</td><td align='left'>18.5</td><td align='left'>"</td><td align='left'>17.3</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>These experiments show that only slight quantities of acid are
+admissible.</p>
+
+<p><b>Effect of Varying Sodium Acetate.</b>&mdash;With the same conditions as before,
+but with varying weights of sodium acetate, the results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodium acetate present</td><td align='left'>&mdash;</td><td align='left'>5 grams</td><td align='left'>10 grams</td><td align='left'>25 grams</td><td align='left'>50 grams</td></tr>
+<tr><td align='left'>"Chromate" required</td><td align='left'>19.7 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>18.8 c.c.</td><td align='left'>17.8 c.c.</td></tr>
+</table></div>
+
+<p>These experiments show that excessive quantities of sodium acetate must
+be avoided. Ammonium acetate interferes to a<span class='pagenum'><a name="Page_217" id="Page_217">[Pg 217]</a></span> greater extent, and if
+both acetic acid and this salt are present, each exerts its disturbing
+influence. With 10 grams of ammonium acetate, 19.4 c.c. of the chromate
+solution were required instead of 19.7 c.c. in the absence of this salt;
+with 10 grams of the acetate and 10 c.c. of acetic acid, only 18.6 c.c.
+were required.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;As already stated, sulphates interfere.
+Twenty c.c. of the lead nitrate solution were taken, precipitated with
+sulphate of soda, and the precipitate dissolved in 10 grams of sodium
+acetate and titrated as before. Duplicate experiments required 18.6 c.c.
+and 18.7 c.c. of the chromate solution. A similar experiment with 40
+c.c. of lead nitrate required 37.4 c.c. of chromate. If the sulphate had
+not been present, the results would have been 19.7 c.c. and 39.4 c.c.
+respectively.</p>
+
+<p><b>Effect of Varying Lead.</b>&mdash;In these experiments the conditions were as
+before, but with varying amounts of lead.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Lead nitrate solution present</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Chromate solution required.</td><td align='left'>9.4</td><td align='left'>"</td><td align='left'>19.7</td><td align='left'>"</td><td align='left'>48.8</td><td align='left'>"</td><td align='left'>98.2</td><td align='left'>"</td></tr>
+</table></div>
+
+<p><b>Determination of Lead in Galena.</b>&mdash;Weigh up 1 gram of the powdered and
+dried ore, and boil in an evaporating dish with 10 c.c. of dilute
+hydrochloric acid. When the action becomes sluggish, dilute with an
+equal bulk of water, and add a weighed piece of zinc rod about 1 inch
+long and quarter-inch across. Keep up a moderate action by warming till
+the ore is seen to be completely attacked and the lead precipitated.
+Decant off the solution, wash once, strip off the lead, wash and weigh
+the remaining zinc. Dissolve the lead in 5 c.c. of dilute nitric acid,
+and 5 c.c. of water with the aid of heat. Dilute and transfer to a pint
+flask; add a slight excess of dilute ammonia, and render faintly acid
+with acetic acid. Dilute to 150 c.c., heat to boiling, and run in the
+standard chromate in slight excess, noting the amount required, and make
+up to 250 c.c. with water. Boil the solution, allow to settle for a
+minute or so, filter off 50 c.c., and determine the excess of chromate
+colorimetrically. As an example, 1 gram of an impure galena was
+precipitated with 75 c.c. of standard chromate (100 c.c. = 1.020 gram
+lead). The excess found in 50 c.c. was 0.3 c.c., which, multiplied by 5,
+gives 1.5 c.c. as the excess in the whole solution. The remaining 73.5
+c.c. of "chromate" required by the assay, are equivalent to 0.7497 gram
+of lead. The zinc used up weighed 1.5 grams, and contained 0.0165 gram
+of lead. Thus we get&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Lead in the assay</td><td align='left'>0.7497</td><td align='left'>gram</td></tr>
+<tr><td align='left'>Lead from the zinc</td><td align='left'>0.0165</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>&#8756; Lead in the galena</td><td align='left'>0.7332</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>Equivalent to 73.3 per cent.</p>
+
+<p><span class='pagenum'><a name="Page_218" id="Page_218">[Pg 218]</a></span></p>
+
+<p>Another sample, in which the galena was accompanied with a large
+quantity of pyrites, gave the following results:&mdash;Three grams were
+treated with 30 c.c. of dilute hydrochloric acid and a rod of zinc. The
+zinc and lead were carefully transferred to another vessel, the zinc
+cleaned, and the lead (dissolved in 5 c.c. of dilute nitric acid and 20
+c.c. of water) treated as before.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>14.5 c.c. of the chromate were required</td><td align='left'>= 0.1479</td><td align='left'>gram lead</td></tr>
+<tr><td align='left'>Lead in 2 grams of zinc</td><td align='left'>= 0.0220</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>&#8756; Lead in 3 grams of the ore</td><td align='left'>= 0.1259</td><td align='center'>"</td></tr>
+</table></div>
+
+<p>Equivalent to 4.20 per cent.</p>
+
+<p>The same ore gave by separation of the lead with sulphuretted hydrogen,
+and conversion into sulphate, 4.16 per cent.</p>
+
+<p>With fairly pure ores, free from sulphate, the assay may be made more
+quickly as follows: Dissolve 1 gram of the finely powdered ore by
+boiling gently with 40 c.c. of dilute hydrochloric acid for 15 minutes;
+cool; add a few drops of permanganate; neutralise with ammonia, add
+acetic acid and a little sodium acetate. Titrate with standard chromate.</p>
+
+
+<h4>COLORIMETRIC PROCESS.</h4>
+
+<p>This is based upon the brown coloration produced in very dilute
+solutions of lead by the action of a solution of sulphuretted hydrogen.
+The quantity of lead in the 50 c.c. of the assay solution must not much
+exceed 0.5 milligram, nor be less than 0.01. The sulphuretted hydrogen
+is used in the form of a solution, and is not bubbled through the assay.
+The principle of working is the same as previously described.</p>
+
+<p><i>Standard Lead Solution.</i>&mdash;Each c.c. of this should contain 0.1
+milligram of lead. It is made by diluting 10 c.c. of the solution of
+lead nitrate, described under the volumetric process, to 1 litre.</p>
+
+<p><i>Sulphuretted hydrogen water</i> is made by passing a current of the washed
+gas into water till the latter is saturated.</p>
+
+<p>Five c.c. of the sulphuretted hydrogen water are put into a Nessler
+tube, the measured portion of the assay solution added, and the whole
+diluted with water to the 50 c.c. mark. Into the standard Nessler tube
+the same amount of the sulphuretted hydrogen water is put, and diluted
+to nearly 50 c.c. The standard lead solution is then run in till the
+tints are equal. The assay solution must not contain much free acid, and
+if the conditions will allow it, may with advantage be rendered alkaline
+with ammonia. The chief cause of disturbance is the precipitation of
+lead sulphide forming a black turbid solution instead of a<span class='pagenum'><a name="Page_219" id="Page_219">[Pg 219]</a></span> brown clear
+one. This may be caused by using hot solutions or an excess of acid.
+Other metals precipitable by sulphuretted hydrogen must be absent as
+well as strong oxidising agents.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The effect of increased temperature is
+to change the colour from brown to black, and to render the estimation
+difficult.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1</td><td align='left'>c.c.</td><td align='left'> at 15&deg; C.</td><td align='left'>showed the</td><td align='left'>colour of</td><td align='left'>0.5</td><td align='left'>c.c.</td><td align='left'>at 60&deg; C.</td></tr>
+<tr><td align='left'>2</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>1.5</td><td align='center'>"</td><td align='left'>at 60&deg; C.</td></tr>
+<tr><td align='left'>3</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>5.0</td><td align='center'>"</td><td align='left'>at 50&deg; C.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Time.</b>&mdash;The colour becomes lighter on standing: 2
+c.c. on standing 10, 20, and 40 minutes became equal in colour to 1.7
+c.c.</p>
+
+<p><b>Effect of Acids and Ammonia.</b>&mdash;Two c.c. of the solution with 2 c.c. of
+dilute hydrochloric acid became cloudy and equivalent to about 2.5 c.c.;
+and a similar result was got with 2 c.c. of dilute sulphuric acid. With
+2 c.c. of dilute ammonia the solution became somewhat darker, or equal
+to 2.3 c.c.; but gave a very clear solution easy to compare.</p>
+
+<p><b>Determination of Lead in Commercial Zinc.</b>&mdash;Dissolve 0.1 gram of the
+metal in 1 c.c. of dilute nitric acid evaporates till a solid separates
+out, dilute to 100 c.c. with water, and take 20 c.c. for assay. A sample
+treated in this way required 2.4 c.c.; this multiplied by 5 gives 12.0
+c.c., equivalent to 1.2 milligram of lead, or 1.2 per cent. By
+gravimetric assay the sample gave 1.10 per cent.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. Thirty grams of galena gave on dry assay 21 grams of lead; and this,
+on cupellation, gave 15 milligrams of silver. Calculate the results in
+per cents. of lead and in ounces of silver to the ton of ore.</p>
+
+<p>2. How many ounces of silver to the ton would be contained in the lead
+got from this ore if the loss in smelting is equal to that of the assay?</p>
+
+<p>3. Having given you a sample of white lead freed from oil by washing
+with ether, how would you proceed to determine the percentage of lead in
+it?</p>
+
+
+<h4>THALLIUM.</h4>
+
+<p>Thallium is a rare metal, found in small quantities in some varieties of
+iron and copper pyrites, and in some lithia micas. It resembles lead in
+appearance. Its compounds resemble the salts of the alkalies in some
+respects; and, in others, those of the heavy metals.</p>
+
+<p>It is detected by the green colour which its salts impart to the flame.
+This, when examined with the spectroscope, shows only one bright green
+line.<span class='pagenum'><a name="Page_220" id="Page_220">[Pg 220]</a></span></p>
+
+<p>It is separated and estimated by dissolving in aqua regia; converting
+into sulphate by evaporation with sulphuric acid; separating the second
+group of metals with sulphuretted hydrogen in the acid solution, boiling
+off the excess of the gas; nearly neutralising with carbonate of soda;
+and precipitating the thallium with an excess of potassic iodide. On
+allowing the liquid to stand for some time a bright yellow precipitate
+of thallous iodide separates out. This is collected on a weighed filter;
+washed with cold water, finishing off with alcohol; dried at 100&deg; C.,
+and weighed. The precipitate is thallous iodide TlI, and contains 61.6
+per cent. of thallium.</p>
+
+
+<h4>BISMUTH.</h4>
+
+<p>Bismuth is nearly always found in nature in the metallic state; but
+occasionally it is met with as sulphide in bismuthine and as carbonate
+in bismutite. It is also found in some comparatively rare minerals, such
+as tetradymite, combined with tellurium, and associated with gold. In
+minute quantities it is widely distributed: it is a common constituent
+of most copper ores; hence it finds its way into refined copper, which
+is seldom free from it. It is occasionally met with in silver in
+sufficient quantity to interfere with the working qualities of that
+metal.</p>
+
+<p>Bismuth compounds are used in medicine and in the manufacture of alloys.
+Bismuth possesses many useful properties. It has considerable commercial
+value, and sells at a high price.</p>
+
+<p>The metal is brittle, breaks with a highly crystalline fracture, and has
+a characteristic reddish-yellow colour. It is almost insoluble in
+hydrochloric, but readily dissolves in nitric, acid; and gives, if the
+acid is in excess, a clear solution. Bismuth salts have a strong
+tendency to separate out as insoluble basic compounds; this is more
+especially true of the chloride which, on diluting with a large volume
+of water, becomes milky; the whole of the bismuth separating out. The
+nitrate, carbonate, and hydrate yield the oxide (Bi<sub>2</sub>O<sub>3</sub>) on
+ignition. This oxide closely resembles litharge. It combines with
+silica, forming fluid slags; and at a red heat is liquid enough to be
+absorbed by a cupel; in fact, bismuth may take the place of lead in
+cupellation. The metal itself is easily fusible, and may be separated
+from its ores by liquation.</p>
+
+<p>The assay of bismuth by wet methods presents little difficulty, and is
+fairly accurate. The price of the metal is such that only methods which
+yield good results should be adopted; and, since bismuth is volatile at
+the temperature of the furnace, and is found mixed with ores not easy to
+flux, as also with metals which are not easily separated by the dry
+method, the dry assay can only be considered as having a qualitative
+value.<span class='pagenum'><a name="Page_221" id="Page_221">[Pg 221]</a></span></p>
+
+
+<h4>DRY ASSAY.</h4>
+
+<p><b>By Liquation.</b>&mdash;This is adapted to ores containing the bismuth as
+metal. Take 20 grams of the powdered ore and place in a crucible with a
+perforated bottom, put this crucible into another of about the same size
+and lute the joint. Lute on a cover, place in the furnace and heat to
+redness. The bismuth melts readily and drains into the lower crucible
+from which, when cold, it is taken and weighed.</p>
+
+<p><b>By Fusion.</b>&mdash;For fairly pure ores the process is as follows:&mdash;Take 20
+grams of the ore and mix with 20 grams of fusion mixture, 10 grams of
+salt and 5 or 10 grams of potassium cyanide; place in a crucible, cover,
+and fuse at a moderate temperature for about fifteen minutes; pour; when
+cold detach the metal and weigh.</p>
+
+<p>For coppery ores in which the metals are present as sulphides use the
+fluxes just given with 2 grams of charcoal (instead of the cyanide) and
+a little sulphur.</p>
+
+<p>For coppery ores in which the metals are present as oxides, mix 20 grams
+of the ore with 10 grams of fusion mixture, 4 grams of salt, 4 grams of
+sulphur and 2 grams of charcoal; and fuse.</p>
+
+<p>A considerable percentage of bismuth is lost in these assays; it is
+stated as being nearly 8 per cent. of the metal present.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p><b>Detection.</b>&mdash;Bismuth is detected by dissolving the substance in nitric
+or hydrochloric acid and precipitating the diluted solution with
+sulphuretted hydrogen. The precipitated sulphides, after digesting with
+soda and washing, are dissolved in nitric acid and the solution boiled
+with ammonium carbonate. The precipitate is washed and then warmed with
+dilute sulphuric acid. The solution will contain the bismuth. Add a
+solution of potassium iodide in excess, and boil; a yellow or dark brown
+solution proves that bismuth is present. Another good test for small
+quantities of bismuth is to add tartaric acid to the solution to be
+tested, and then to make it alkaline with potash. Add a few c.c. of
+Schneider's liquid,<a name="FNanchor_61_61" id="FNanchor_61_61"></a><a href="#Footnote_61_61" class="fnanchor">[61]</a> and heat. A brownish-black colour is produced by
+as little as one part of bismuth in 200,000 of solution. The test is not
+applicable in the presence of mercury, copper, or manganese.<span class='pagenum'><a name="Page_222" id="Page_222">[Pg 222]</a></span></p>
+
+<p>Compounds of bismuth fused with cyanide of potassium in a Berlin
+crucible readily give a globule of bismuth which is recognised by its
+appearance and fracture.</p>
+
+<p><b>Solution and Separation.</b>&mdash;The solution of bismuth compounds presents
+no difficulty. They are soluble in nitric acid or aqua regia, and,
+provided the solution is sufficiently acid, they remain dissolved. In
+separating it from other metals the solution is made up to about 100
+c.c. and treated with a current of sulphuretted hydrogen. The bismuth
+comes down in a tolerably strong acid solution. The sulphide is decanted
+on to a filter and washed. It is next digested with ammonic sulphide;
+or, better (especially when other metals are present), dissolved in
+nitric acid, and treated with an excess of ammonia and a current of
+sulphuretted hydrogen. The precipitate is filtered off and evaporated to
+dryness with nitric acid. It is taken up with a few drops of sulphuric
+acid and a little water; and warmed and filtered, if necessary. The
+filtrate is nearly neutralised with ammonia; ammonium carbonate added in
+slight excess; and the liquid heated to boiling and filtered. The
+bismuth will be contained in the precipitate with perhaps traces of
+lead, antimony, tin, or sometimes iron from incomplete separation or
+washing. When only traces of a precipitate are got it must be tested.
+The bismuth precipitate is readily soluble in dilute nitric acid.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The bismuth having been separated and dissolved in nitric acid<a name="FNanchor_62_62" id="FNanchor_62_62"></a><a href="#Footnote_62_62" class="fnanchor">[62]</a> is
+precipitated (after dilution) by the addition of carbonate of ammonium
+in slight excess, and boiling. The precipitate is filtered off, washed
+with hot water, dried, ignited, and weighed. The ignition should be
+performed carefully at not above a low red heat. The oxide which is
+formed has, at this temperature, a dark yellow or brown colour, and
+becomes yellow on cooling. It is bismuthic oxide (Bi<sub>2</sub>O<sub>3</sub>) and
+contains 89.65 per cent. of bismuth. Fusion with potassium cyanide at a
+temperature just sufficient to melt the salt reduces it to the metal
+which falls to the bottom and runs into a globule. The button of metal
+may be weighed, but it often sticks tenaciously to the bottom of the
+crucible. The precipitation with ammonic carbonate must not be made in a
+sulphate or chloride solution; since basic compounds would then be
+thrown down, and the result on weighing would either be too low (because
+of the volatilisation of the chloride), or too high (because of the
+retention of sulphuric acid).<span class='pagenum'><a name="Page_223" id="Page_223">[Pg 223]</a></span></p>
+
+<p>Bismuth compounds in a nitric acid solution are readily decomposed by
+the electric current, but the deposited bismuth is not coherent. It
+comes down in shaggy tufts which are difficult to wash and easy to
+oxidise.</p>
+
+
+<h4>VOLUMETRIC ASSAY.</h4>
+
+<p>There are two methods which have been proposed; one based on the
+precipitation as chromate and the estimation of the chromic acid; and
+the other on the precipitation as oxalate and subsequent titration with
+permanganate of potash. These offer little advantage over the easy
+gravimetric determination.</p>
+
+
+<h4>COLORIMETRIC METHOD.</h4>
+
+<p>Bismuth iodide dissolves in excess of potassium iodide, forming a
+yellow-coloured solution, indistinguishable in colour from that given by
+iodine. The colour, however, is not removed by boiling or by sulphurous
+acid. Since none of the commoner metals give such a colour, and free
+iodine is easily separated by boiling, this method is specially suited
+for small determinations of bismuth.</p>
+
+<p>It requires a <i>solution of bismuth</i>, made by dissolving 0.1 gram of
+bismuth in a drop or so of nitric acid, evaporating with a little
+sulphuric acid and diluting with water to 1 litre. 1 c.c. will contain
+0.1 milligram of bismuth. And a <i>solution of sulphurous acid</i>, made by
+diluting 10 c.c. of the commercial acid to 1 litre with water.</p>
+
+<p>The determination is made in the usual way: 50 c.c. of the prepared
+solution, which should not carry more than 0.75 milligram nor less than
+0.01 milligram of bismuth, are placed in a Nessler tube and the colour
+compared with that observed in a similar tube containing water and
+potassium iodide on adding the standard solution of bismuth.</p>
+
+<p>The assay solution is prepared by separating the bismuth with
+sulphuretted hydrogen, boiling the precipitate with nitric acid, and
+evaporating with sulphuric acid. Take up with water, add 10 or 20 c.c.
+of solution of potassium iodide, boil off any iodine liberated, dilute,
+filter, and make up to 100 c.c. According to the depth of colour take
+10, 20, or 50 c.c. and transfer to the Nessler tube. Add a few c.c. of
+the solution of sulphurous acid. Into the other Nessler tube put as much
+potassium iodide solution as is contained in the assay tube, with
+sulphurous acid and water to within a few c.c. of the bulk. Then add the
+standard bismuth solution till the tints are equal.<span class='pagenum'><a name="Page_224" id="Page_224">[Pg 224]</a></span></p>
+
+<p>The student must be careful not to confuse the colour of the bismuth
+iodide with that of free iodine. If the yellow colour is removed by
+boiling and returns on standing it is due altogether to iodine; if it is
+lessened by the addition of a few drops of the dilute sulphurous acid,
+it is in part due to it. Hence the necessity of having a little free
+sulphurous acid in each tube. A strong solution must not be used, since
+it liberates iodine from potassium iodide.</p>
+
+<p>The following experiments illustrate the effect of variation in the
+conditions of the assay:&mdash;</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;At a higher temperature the colour is
+somewhat lessened.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>at 15&deg; C.</td><td align='left'>showed the colour of</td><td align='left'>0.8 c.c.</td><td align='left'> at 70&deg; C.</td></tr>
+<tr><td align='left'>2.5</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>2.0</td><td align='center'>"</td></tr>
+<tr><td align='left'>5.0</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>5.0</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Free Acid.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>2.5</td><td align='left'>c.c. with</td><td align='left'>5 c.c. of</td><td align='left'>nitric acid</td><td align='left'>equalled</td><td align='left'>2.5</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>5.0</td><td align='center'>"</td><td align='center'>"</td><td align='left'>sulphuric acid</td><td align='center'>"</td><td align='left'>5.0</td><td align='center'>"</td></tr>
+</table></div>
+
+<p>Hydrochloric acid almost completely removes the colour, which, however,
+is restored by the addition of a few crystals of potassium iodide.</p>
+
+<p><b>Effect of Alkalies.</b>&mdash;Ammonia, soda, or potash destroys the colour, but
+it is restored on acidifying with nitric or sulphuric acid.</p>
+
+<p><b>Effect of Ammonic Salts.</b>&mdash;The following table shows the results after
+addition of ammonic salts:&mdash;</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>C.c. present.</td><td align='center'>With 10 grams Ammonic Nitrate.</td><td align='center'>With 10 grams Ammonic Sulphate.</td><td align='center'>With 10 grams Ammonic Chloride.</td></tr>
+<tr><td align='center'>1.0 c.c.</td><td align='center'>0.9 c.c.</td><td align='center'>1.1 c.c.</td><td align='center'>&mdash;</td></tr>
+<tr><td align='center'>2.5&nbsp;&nbsp; "</td><td align='center'>2.5&nbsp;&nbsp; "</td><td align='center'>2.7 &nbsp;&nbsp;"</td><td align='center'>&mdash;</td></tr>
+<tr><td align='center'>5.0 &nbsp;&nbsp;"</td><td align='center'>5.0&nbsp;&nbsp; "</td><td align='center'>5.5&nbsp;&nbsp; "</td><td align='center'>&mdash;</td></tr>
+</table></div>
+
+<p>Ammonic chloride, like hydrochloric acid, removes the colour, which may
+be restored on the addition of more potassium iodide. Nitrates and
+sulphates do not thus interfere.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;Sodic hyposulphite almost completely removes
+the colour. Copper salts liberate iodine; but when this has been removed
+by boiling and the cuprous iodide has been filtered off there is no
+further interference. Dilute solutions of lead salts give no colour.<span class='pagenum'><a name="Page_225" id="Page_225">[Pg 225]</a></span></p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. A fusible alloy is made up of 8 parts of bismuth, 5 of lead, and 3 of
+tin. What weight of oxide of bismuth, Bi<sub>2</sub>O<sub>3</sub>, would you get on the
+analysis of 1 gram of it?</p>
+
+<p>2. What weight of bismuth can be got from 2 grams of the subnitrate
+BiONO<sub>3</sub>.H<sub>2</sub>O?</p>
+
+<p>3. How would you detect and separate arsenic, lead, and copper in a
+sample of bismuth?</p>
+
+
+<h4>ANTIMONY.</h4>
+
+<p>Antimony occurs in the native state, but is rare; its common ore is
+antimonite, the sulphide (Sb<sub>2</sub>S<sub>3</sub>). Jamesonite and other sulphides
+of lead and antimony are frequently met with. Sulphide of antimony is
+also a constituent of fahlerz and of many silver ores.</p>
+
+<p>Antimonite occurs generally in fibrous masses, has a lead-like metallic
+lustre, is easily cut with a knife, and melts in the flame of a candle.</p>
+
+<p>Antimony itself has a very crystalline fracture, is brittle, and has a
+bluish-white colour. It is used in the preparation of alloys with lead
+and tin for the manufacture of type-metal. It is readily fusible, and
+imparts hardness and the property of taking a sharp cast to its alloys.
+It is practically insoluble in hydrochloric acid. On boiling with strong
+nitric acid it is converted into antimonic oxide (Sb<sub>2</sub>O<sub>5</sub>), which is
+a powder almost insoluble in this acid or in water, but which may be got
+into solution with difficulty by the prolonged action of hydrochloric
+and tartaric acids. Antimonic oxide is converted on ignition into the
+tetroxide (Sb<sub>2</sub>O<sub>4</sub>) with loss of oxygen. Antimony forms two series
+of salts, antimonious and antimonic; and advantage is taken of this in
+its determination volumetrically. Either sulphide of antimony yields
+antimonious chloride on boiling with hydrochloric acid, sulphuretted
+hydrogen being given off; and, in the case of antimonic sulphide,
+sulphur is deposited. Antimonious is converted into antimonic chloride
+by treatment with permanganate of potash in an acid solution. Antimonic
+chloride and potassium iodide react, forming antimonious chloride and
+free iodine. This latter may be got rid of by boiling. Sulphide of
+antimony is separated from the ore by liquation; this regulus is met
+with in commerce as "crude antimony."</p>
+
+
+<h4>DRY ASSAY.</h4>
+
+<p>An approximate determination of the amount of sulphide of antimony in an
+ore may be made by fusing and liquating in a luted double crucible in
+the manner described under bismuth.<span class='pagenum'><a name="Page_226" id="Page_226">[Pg 226]</a></span> This is unsatisfactory. The
+determination of metallic antimony in an ore is made either by fusion
+with potassium cyanide or by fusion with iron, as in the galena assay.
+Both methods yield poor results; and, where iron is used, it must be
+added in quantity only sufficient for desulphurising; this amounts to
+about 40 per cent. in pure ores. If the iron is in excess it alloys with
+the reduced antimony. If, on the other hand, it is insufficient, the
+metal will contain sulphur; or sulphide of antimony will be lost in the
+slag.</p>
+
+<p>The following note, for which we are indebted to Mr. Bedford McNeill,
+A.R.S.M., gives a description of the method adopted in the commercial
+valuation of a parcel of antimony ore:&mdash;</p>
+
+<p>The antimony smelter, when he wishes to determine the value of any
+parcel of ore&mdash;usually the sulphide&mdash;that may be offered for sale,
+practically has recourse to the smelting operation. That is, a quantity
+of 2 or 3 cwts. taken by his sampler having been obtained, he treats it
+under the immediate supervision of the foreman smelter as if it formed
+part of the ore in process of daily reduction at his works. He thus
+determines by actual trial the output which it may fairly be anticipated
+will be yielded by the bulk, and upon the result of this trial or assay,
+and the knowledge gained of the actual behaviour of the ore under
+treatment, he bases his tender, knowing that, should he secure the
+parcel, he may confidently expect a similar return.</p>
+
+<p>Briefly, the process consists of the three ordinary operations of&mdash;</p>
+
+<p>
+(<i>a</i>) Singling or removing most of the antimony from the ore;<br />
+(<i>b</i>) Doubling;<br />
+(<i>c</i>) Refining or "starring."<br />
+</p>
+
+<p>But in the assay sufficient information is generally given by the first
+two of these.</p>
+
+<p>A new pot having been taken and made hot in the furnace, 40 or 45 lbs.
+of the ore is weighed in (the mineral from the necessities of sampling
+not exceeding walnut size); 1 to 3 lbs. of salt cake is now added to
+render the separation of the resulting sulphide of iron more easy, as
+also to assist in the fusion of the gangue; 20 to 25 lbs. of tin-plate
+scrap, beaten more or less into ball shape, is weighed, placed on the
+top of the ore and salt cake, and the whole brought to a state of
+fusion. The foreman from time to time takes notice of the behaviour of
+the ore under the working conditions. Ores that manifest a tendency to
+"boil" or "froth " require the admixture of other more sluggish mineral
+in order to render their reduction economically practicable.</p>
+
+<p>After 1-1/4 to 1-1/2 hours (the time depending mainly on the
+temperature), the contents of the crucible are usually in a state of
+tranquil fusion. The pot is now lifted from the fire, and its<span class='pagenum'><a name="Page_227" id="Page_227">[Pg 227]</a></span> contents
+transferred to a conical iron mould, the empty pot being immediately put
+back into the fire, and the latter "mended" with sufficient coke for
+another run. The conical mould (when dealing with a "strange" ore, and
+the possibility of insufficient iron being present to satisfy the
+sulphur contents) is wiped inside with clay previous to pouring in the
+molten charge. Otherwise the mould itself will be attacked, and the
+contents after solidifying will require to be chiselled out piecemeal.</p>
+
+<p>A further 40 lbs. of the ore is now charged into the crucible with iron
+as above; but before this second charge is ready to be drawn an
+inspection of the first may suggest the addition of either 3 or 5 lbs.
+more iron, or 5 or 10 lbs. more ore.</p>
+
+<p>It is a good fault rather to aim at an excess of iron as tending to
+clean the ore from antimony, any of the latter that (from an
+insufficiency of iron) may be left in the slag from the first process
+being irretrievably lost; whereas, if the iron be in excess, that which
+is combined with the crude antimony resulting from the first process is
+easily got rid of by adding 3 to 5 lbs. or so of ore in the second
+process.</p>
+
+<p>This latter, as practised for the determination of the value of a parcel
+of ore, consists in selecting two of the best quality singles, resulting
+from perhaps four or five trials as above, and running them down with a
+few pounds of salt cake, or a mixture of salt cake with American potash,
+and (as is generally necessary) a small addition of ore.</p>
+
+<p>Upon the final result (confirmed perhaps on another pair of singles,
+and, judging from the total weight or output of the metal as calculated
+from the ore used in "singling," plus any added in the "doubling," the
+crystalline fracture and face of the metal, its colour, etc.) the price
+to be offered for the parcel of ore is fixed.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p><b>Detection.</b>&mdash;The antimony, if any, being got into solution by treating
+the ore with hydrochloric acid or aqua regia may be detected by
+evaporating with hydrochloric acid, diluting, and filtering into the
+cover of a platinum crucible or (better) a platinum dish. A small lump
+of zinc is then added, and, if antimony is present, <i>the dish</i> will in a
+minute or so be stained black with a deposit of metallic antimony. This
+stain is removed by nitric, but not by hydrochloric, acid. The reaction
+is delicate and characteristic; arsenic under like conditions is evolved
+as arseniuretted hydrogen, and tin is deposited as metal <i>on the zinc</i>.</p>
+
+<p><b>Solution.</b>&mdash;Ores, &amp;c., containing antimony are best opened up by
+boiling with hydrochloric acid or aqua regia; treatment with<span class='pagenum'><a name="Page_228" id="Page_228">[Pg 228]</a></span> nitric
+acid should be avoided wherever possible, since it forms antimonic acid,
+which is subsequently dissolved only with difficulty. Salts of antimony
+in solution have a tendency to form insoluble basic salts; so that care
+must be exercised in diluting. Compounds such as antimonite which are
+soluble in hydrochloric should be dissolved at once in that acid.</p>
+
+<p><b>Separation.</b>&mdash;To the solution add potash in excess and a little free
+sulphur, and pass a current of sulphuretted hydrogen for some minutes;
+allow to digest for an hour or so on a hot plate; filter; and wash the
+residue. Acidulate the filtrate with hydrochloric acid: the precipitate
+will contain the antimony (as Sb<sub>2</sub>S<sub>5</sub>), and possibly arsenic or tin.
+The precipitate is transferred to a beaker and boiled with hydrochloric
+acid; the solution is filtered off and diluted. Add a few crystals of
+tartaric acid, and pass a current of sulphuretted hydrogen for some
+time. The first flocculent precipitate will become denser, and render
+the filtering more easy. Transfer the precipitate (after washing free
+from chlorides) to a Berlin dish, and treat cautiously with fuming
+nitric acid. The action of this acid on the sulphide is very violent.
+Evaporate and ignite, transfer to a silver dish, and fuse with four or
+five times its weight of caustic soda, cool and extract with a little
+water, then add an equal volume of alcohol, and allow to stand
+overnight. Filter, wash with dilute alcohol. (The filtrate will contain
+the tin.) The residue contains the antimony as antimonate of soda, and
+is dissolved off the filter with hot dilute hydrochloric, with the help
+of a little tartaric, acid. The filtrate is now ready for the
+gravimetric determination.</p>
+
+
+<h4>GRAVIMETRIC ASSAY.</h4>
+
+<p>Pass a current of sulphuretted hydrogen through the solution containing
+the antimony to which a little tartaric acid has been previously added.
+Pass the gas till the precipitate becomes dense, and the antimony is all
+down. The solution must not be too strongly acid. Filter off the
+precipitate, wash with hot water, dry in the water oven, transfer to a
+weighed porcelain dish, and cautiously treat with fuming nitric acid.
+Continue the action on the water bath till the sulphur and antimony are
+completely oxidised. Evaporate; ignite, gently at first, then strongly
+over the blast; cool, and weigh. The residue is a white infusible
+powder, and consists of antimony tetroxide, Sb<sub>2</sub>O<sub>4</sub>, containing
+78.94 per cent. of the metal.</p>
+
+<p><b>Determination of Antimony as Bigallate.</b>&mdash;What appears to be a very
+good method has been worked out by M.A. Guyard, and is described in
+Crookes' <i>Select Methods</i>, p. 398.<span class='pagenum'><a name="Page_229" id="Page_229">[Pg 229]</a></span></p>
+
+<p>The antimony must be in solution as antimonious chloride, and must not
+be accompanied by an excess of hydrochloric acid. To ensure these
+conditions, the solution is treated with potassium iodide until no more
+iodine is evolved, and is then evaporated to remove the excess of
+hydrochloric acid. To the concentrated, and nearly neutral, solution a
+freshly-prepared solution of gallic acid is added in slight excess. A
+bulky white precipitate is formed that settles rapidly. The solution is
+diluted with hot water and washed by decantation. Then the precipitate
+is collected on a weighed double filter, washed once or twice with hot
+water, and dried at 100&deg; C. The dried substance is antimony bigallate,
+and contains 40.85 per cent. of antimony. It should be completely
+soluble in ammonium sulphide. The solution in which the antimony is
+precipitated need not be quite free from other metals.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This is based on the reduction of antimonic chloride (SbCl<sub>5</sub>) to
+antimonious (SbCl<sub>3</sub>) by the action of potassium iodide in strong
+hydrochloric acid solution.<a name="FNanchor_63_63" id="FNanchor_63_63"></a><a href="#Footnote_63_63" class="fnanchor">[63]</a> Iodine is at the same time liberated,
+and the amount of antimony reduced is got at by titrating with sodium
+hyposulphite, which measures the iodine set free.</p>
+
+<p>The standard solution of sodium hyposulphite is made by dissolving 41.32
+grams of the salt (Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub>.5H<sub>2</sub>O) in water, and diluting to 1
+litre. One hundred c.c. will be equivalent to about 1 gram of antimony.</p>
+
+<p>It is standardised with the help of a solution of antimony made as
+follows:&mdash;Weigh up 5 grams of powdered antimony, transfer to a flask,
+and cover with 50 c.c. of hydrochloric acid; boil, and add nitric acid
+(5 or 10 drops at a time) until the metal is dissolved. Allow the action
+of the nitric acid to cease before adding more. Boil down to a small
+bulk, add 250 c.c. of hydrochloric acid, and dilute to nearly 1 litre.
+Warm until any precipitate which has formed is redissolved; allow to
+cool slowly, and run in from a pipette a weak solution of permanganate
+until a faint brown colour is produced. Dilute to exactly 1 litre; 100
+c.c. contain 0.5 gram of antimony as antimonic chloride.</p>
+
+<p>In standardising, take 50 c.c. of the antimony solution, and transfer to
+a flask; add 2 grams of potassium iodide crystals, and when dissolved,
+after standing a few minutes, run in the solution of "hypo" from an
+ordinary burette until the greater part of the iodine has been reduced.
+Add a few drops of starch solution, and continue the addition of the
+"hypo" until the muddy-green colour<span class='pagenum'><a name="Page_230" id="Page_230">[Pg 230]</a></span> changes to a clear brownish-yellow.
+The solution must be shaken after each addition of the "hypo."</p>
+
+<p>In determining antimony in ore, weigh up 0.5 to 1 gram, and dissolve in
+hydrochloric acid with, if necessary, the help of chlorate of potash.
+The antimony is separated as sulphide, redissolved in hydrochloric acid,
+and oxidised with a crystal of chlorate of potash. Chlorine is boiled
+off, and the solution diluted with an equal bulk of water. To the clear
+cold solution potassium iodide is added, and after a few minutes the
+liberated iodine is titrated with "hypo," as already described. The
+method only yields satisfactory results when the standard and assay are
+carried out alike.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_50_50" id="Footnote_50_50"></a><a href="#FNanchor_50_50"><span class="label">[50]</span></a> "Modern American Methods of Copper Smelting" (Dr.
+Peters).</p></div>
+
+<div class="footnote"><p><a name="Footnote_51_51" id="Footnote_51_51"></a><a href="#FNanchor_51_51"><span class="label">[51]</span></a> "Journal of the Society of Chemical Industry," vol. v. No.
+2.</p></div>
+
+<div class="footnote"><p><a name="Footnote_52_52" id="Footnote_52_52"></a><a href="#FNanchor_52_52"><span class="label">[52]</span></a> Lead when present is precipitated on the <i>spiral</i> in the
+form of a dark powder of dioxide (PbO<sub>2</sub>). Manganese is also thrown
+down on the spiral as dioxide (MnO<sub>2</sub>), the solution at the same time
+becomes violet from the formation of permanganic acid.</p></div>
+
+<div class="footnote"><p><a name="Footnote_53_53" id="Footnote_53_53"></a><a href="#FNanchor_53_53"><span class="label">[53]</span></a> See the method given under <i>Examination of Commercial
+Copper</i>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_54_54" id="Footnote_54_54"></a><a href="#FNanchor_54_54"><span class="label">[54]</span></a> CuSO<sub>4</sub> + 4KCy = 2KCy.CuCy<sub>2</sub> + K<sub>2</sub>SO<sub>4</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_55_55" id="Footnote_55_55"></a><a href="#FNanchor_55_55"><span class="label">[55]</span></a> 2CuSO<sub>4</sub> + 3KCy + Am<sub>2</sub>O = Cu<sub>2</sub>Cy<sub>2</sub> + Am<sub>2</sub>SO<sub>4</sub> +
+K<sub>2</sub>SO<sub>4</sub> + KCyO.</p></div>
+
+<div class="footnote"><p><a name="Footnote_56_56" id="Footnote_56_56"></a><a href="#FNanchor_56_56"><span class="label">[56]</span></a> 2CuSO<sub>4</sub> + 4KI = Cn<sub>2</sub>I<sub>2</sub> + 2I + 2K<sub>2</sub>SO<sub>4</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_57_57" id="Footnote_57_57"></a><a href="#FNanchor_57_57"><span class="label">[57]</span></a> 2Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub> + 2I = 2NaI + Na<sub>2</sub>S<sub>4</sub>O<sub>6</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_58_58" id="Footnote_58_58"></a><a href="#FNanchor_58_58"><span class="label">[58]</span></a> For further information, see Appendix B., and a paper by
+J.W. Westmoreland, <i>Journal of the Society of Chemical Industry</i>, vol.
+v. p. 48.</p></div>
+
+<div class="footnote"><p><a name="Footnote_59_59" id="Footnote_59_59"></a><a href="#FNanchor_59_59"><span class="label">[59]</span></a>
+<br />
+3Cu<sub>2</sub>O + 6AgNO<sub>3</sub> + 3H<sub>2</sub>O<br />
+<span style="margin-left: 1.5em;">= 2Cu<sub>2</sub>H<sub>3</sub>O<sub>3</sub>NO<sub>3</sub> + 2Cu(NO<sub>3</sub>)<sub>2</sub> + 6Ag.</span><br />
+<span style="margin-left: 2.5em;">(Insoluble basic salt.)</span><br />
+</p></div>
+
+<div class="footnote"><p><a name="Footnote_60_60" id="Footnote_60_60"></a><a href="#FNanchor_60_60"><span class="label">[60]</span></a> K<sub>2</sub>CrO<sub>4</sub> + Pb(NO<sub>3</sub>)<sub>2</sub> = PbCrO<sub>4</sub> + 2KNO<sub>3</sub></p></div>
+
+<div class="footnote"><p><a name="Footnote_61_61" id="Footnote_61_61"></a><a href="#FNanchor_61_61"><span class="label">[61]</span></a> Made by dissolving 12 grams of tartaric acid and 4 grams
+of stannous chloride in water, and adding potash solution till it is
+alkaline. The solution should remain clear on heating to 60&deg; or 70&deg; C.</p></div>
+
+<div class="footnote"><p><a name="Footnote_62_62" id="Footnote_62_62"></a><a href="#FNanchor_62_62"><span class="label">[62]</span></a> It must be remembered that arsenate of bismuth is
+completely insoluble in this acid.</p></div>
+
+<div class="footnote"><p><a name="Footnote_63_63" id="Footnote_63_63"></a><a href="#FNanchor_63_63"><span class="label">[63]</span></a> SbCl<sub>5</sub> + 2KI = I<sub>2</sub> + SbCl<sub>3</sub> + 2KCl.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_231" id="Page_231">[Pg 231]</a></span></p>
+<h2><a name="CHAPTER_XI" id="CHAPTER_XI"></a>CHAPTER XI.</h2>
+
+<h3>IRON&mdash;NICKEL&mdash;COBALT&mdash;ZINC&mdash;CADMIUM.</h3>
+
+
+<h4>IRON.</h4>
+
+<p>Iron rusts or oxidises very readily, and, consequently, is rarely found
+in the metallic state in nature; such native iron as is found being
+generally of meteoric origin or imbedded in basalt and other igneous
+rocks. It chiefly occurs as oxide, as in magnetite, h&aelig;matite, and in the
+brown iron ores and ochres. Chalybite, which is carbonate of iron, is an
+ore of great importance. Iron is found combined with sulphur in
+pyrrhotine and pyrites, and together with arsenic in mispickel. It is a
+common constituent of most rocks, imparting to them a green, black, or
+brown colour; and is present, either as an essential part or as an
+impurity, in most substances.</p>
+
+<p>The chemistry of iron is somewhat complicated by the existence of two
+oxides, each of which gives rise to a well-marked series of compounds.
+Those derived from the lower oxide, known as ferrous salts, are
+generally pale and greenish. Ferric salts are derived from the higher
+oxide, and are generally red, brown, or yellow. The existence of these
+two well-marked families of salts renders the assay of iron
+comparatively easy, for the quantity of iron present in a solution can
+be readily measured by the amount of oxidising or reducing agent
+required to convert it from the one state into the other&mdash;that is, from
+ferrous to ferric, or from ferric to ferrous, as the case may be.</p>
+
+<p>In the red and brown iron ores and ochres ferric iron is present; in
+chalybite the iron is in the ferrous state; and in magnetite it is
+present in both forms. Traces of iron in the ferrous state may be found
+(even in the presence of much ferric iron) by either of the following
+tests:&mdash;</p>
+
+<div class="blockquot"><p>1. Ferricyanide of potassium gives a blue precipitate or green
+coloration; with ferric salts a brown colour only is produced.</p>
+
+<p>2. A solution of permanganate of potassium is decolorised by a
+ferrous salt, but not by a ferric one.</p></div><p><span class='pagenum'><a name="Page_232" id="Page_232">[Pg 232]</a></span></p>
+
+<p>Traces of ferric iron can be detected (even in the presence of much
+ferrous iron) by the following tests:&mdash;</p>
+
+<div class="blockquot"><p>(1) By the brown or yellow colour of the solution, especially
+when hot.</p>
+
+<p>(2) By giving a pink or red coloration with sulphocyanide of
+potassium.</p></div>
+
+<p>Substances containing oxide of iron yield the whole of the iron as metal
+when fused at a high temperature with charcoal and suitable fluxes. The
+metal, however, will contain varying proportions of carbon and other
+impurities, and its weight can only afford a rough knowledge of the
+proportion of the metal in the ore. There are two or three methods of
+dry assay for iron, but they are not only inexact, but more troublesome
+than the wet methods, and need not be further considered. Chalybite and
+the hydrated oxides dissolve very readily in hydrochloric acid; h&aelig;matite
+and magnetite dissolve with rather more difficulty. Iron itself, when
+soft, is easily soluble in dilute hydrochloric, or sulphuric, acid.
+Pyrites, mispickel, &amp;c., are insoluble in hydrochloric acid, but they
+are readily attacked by nitric acid. Certain minerals, such as chrome
+iron ore, titaniferous iron ore, and some silicates containing iron,
+remain in the residue insoluble in acids. Some of these yield their iron
+when attacked with strong sulphuric acid, or when fused with the acid
+sulphate of potash. Generally, however, it is better in such stubborn
+cases to fuse with carbonate of soda, and then attack the "melt" with
+hydrochloric acid.</p>
+
+<p>When nitric acid, or the fusion method, has been used, the metal will be
+in solution in the ferric state, no matter in what condition it existed
+in the ore. But with dilute hydrochloric or sulphuric acid it will
+retain its former degree of oxidation. Hydrochloric acid, for example,
+with chalybite (ferrous carbonate) will give a solution of <i>ferrous</i>
+chloride; with h&aelig;matite (ferric oxide) it will yield <i>ferric</i> chloride;
+and with magnetite (ferrous and ferric oxides) a mixture of ferrous and
+ferric chlorides. Metallic iron yields solutions of <i>ferrous</i> salts. It
+is convenient to speak of the iron in a ferrous salt as ferrous iron,
+and when in the ferric state as ferric iron. Frequently it is required
+to determine how much of the iron exists in an ore in each condition. In
+such cases it is necessary to keep off the air whilst dissolving; the
+operation should, therefore, be performed in an atmosphere of carbonic
+acid.</p>
+
+<p><b>Separation.</b>&mdash;The separation of the iron from the other substances is
+as follows:&mdash;Silica is removed by evaporating the acid solution, and
+taking up with acid, as described under <i>Silica</i>; the whole of the iron
+will be in solution. The metals of Groups I. and II. are removed by
+passing sulphuretted hydrogen,<span class='pagenum'><a name="Page_233" id="Page_233">[Pg 233]</a></span> and at the same time the iron will be
+reduced to the ferrous state. The solution should be filtered into a 16
+oz. flask, boiled to get rid of the gas, and treated (whilst boiling)
+with a few drops of nitric acid, in order to convert the whole of the
+iron into the ferric state. When this condition is arrived at, an
+additional drop of nitric acid causes no dark coloration. The boiling
+must be continued to remove nitrous fumes. Next add caustic soda
+solution until the colour of the solution changes from yellow to red.
+The solution must be free from a precipitate; if the soda be
+incautiously added a permanent precipitate will be formed, in which case
+it must be redissolved with hydrochloric acid, and soda again, but more
+cautiously, added. After cooling, a solution of sodium acetate is added
+until the colour of the solution is no longer darkened. The solution,
+diluted to two-thirds of the flaskful with water, is heated to boiling.
+Long-continued boiling must be avoided. The precipitate is filtered
+quickly through a large filter, and washed with hot water containing a
+little acetate of soda.</p>
+
+<p>The precipitate will contain all the iron and may also contain alumina,
+chromium, titanium, as well as phosphoric, and, perhaps, arsenic
+acids.<a name="FNanchor_64_64" id="FNanchor_64_64"></a><a href="#Footnote_64_64" class="fnanchor">[64]</a></p>
+
+<p>Dissolve the precipitate off the filter with dilute sulphuric acid,
+avoiding excess, add tartaric acid and then ammonia in excess. Pass
+sulphuretted hydrogen, warm, and allow the precipitate to settle. Filter
+and wash with water containing a little ammonic sulphide.</p>
+
+
+<h4>GRAVIMETRIC METHOD.</h4>
+
+<p>Dissolve the precipitate in dilute hydrochloric acid; peroxidise with a
+few drops of nitric acid and boil, dilute to about 200 c.c., add ammonia
+(with constant stirring) till the liquid smells of it, and heat to
+boiling. Wash as much as possible by decantation with hot water.
+Transfer to the filter, and wash till the filtrate gives no indication
+of soluble salts coming through. The filtrate must be colourless and
+clear. The wet precipitate is very bulky, of a dark-brown colour and
+readily soluble in dilute acids, but insoluble in ammonia and dilute
+alkalies. When thrown down from a solution containing other metals it is
+very apt to carry portions of these with it, even when they are by
+themselves very soluble in ammoniacal solutions. It must be dried and
+ignited, the filter paper being burnt separately and its ash added. When
+further ignition ceases to cause a loss of weight, the residue is ferric
+oxide (Fe<sub>2</sub>O<sub>3</sub>), which contains 70 per cent. of iron. The weight of
+iron therefore can be calculated by multiplying the weight of oxide
+obtained by 0.7.<span class='pagenum'><a name="Page_234" id="Page_234">[Pg 234]</a></span></p>
+
+<p>The presence of ammonic chloride causes loss of iron during the
+ignition, and organic matter causes an apparent loss by reducing the
+iron to a lower state of oxidation. When the iron in the solution much
+exceeds 0.2 gram the volumetric determination is generally adopted, as
+the bulkiness of the precipitate of ferric hydrate makes the gravimetric
+method very inconvenient.</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>As already explained these are based on the measurement of the volume of
+a reagent required to bring the whole of the iron from the ferrous to
+the ferric state (oxidation), or from the ferric to the ferrous
+(reduction). Ferrous compounds are converted into ferric by the action
+of an oxidising agent in the presence of an acid. Either permanganate or
+bichromate of potash is generally used for this purpose.<a name="FNanchor_65_65" id="FNanchor_65_65"></a><a href="#Footnote_65_65" class="fnanchor">[65]</a></p>
+
+<p>Ferric compounds are reduced to ferrous by the action of:&mdash;</p>
+
+<p>
+(1)  Stannous chloride;<br />
+(2)  Sulphuretted hydrogen;<br />
+(3)  Sodium sulphite; or<br />
+(4)  Zinc.<a name="FNanchor_66_66" id="FNanchor_66_66"></a><a href="#Footnote_66_66" class="fnanchor">[66]</a><br />
+</p>
+
+<p>The processes, then, may be divided into two kinds, one based on
+oxidation and the other on reduction. In each case the titration must be
+preceded by an exact preparation of the solution to be assayed in order
+that the iron may be in the right state of oxidation.</p>
+
+
+<h4>PERMANGANATE AND BICHROMATE METHODS.</h4>
+
+<p>These consist of three operations:&mdash;</p>
+
+<p>
+(1) Solution of the ore;<br />
+(2) Reduction of the iron to the ferrous state; and<br />
+(3) Titration.<br />
+</p>
+
+<p><b>Solution.</b>&mdash;The only point to be noticed concerning the first operation
+(in addition to those already mentioned) is that nitric acid must be
+absent. If nitric acid has been used, evaporate to dryness, of course
+without previous dilution; add hydrochloric or sulphuric acid, and boil
+for five or ten minutes. Dilute with water to about 100 c.c., and warm
+until solution is complete.</p>
+
+<p>The reduction is performed by either of the following methods:<span class='pagenum'><a name="Page_235" id="Page_235">[Pg 235]</a></span>&mdash;</p>
+
+<p>1. <i>With Stannous Chloride.</i>&mdash;Fill a burette with a solution of stannous
+chloride,<a name="FNanchor_67_67" id="FNanchor_67_67"></a><a href="#Footnote_67_67" class="fnanchor">[67]</a> and cautiously run the liquid into the hot assay solution
+(in which the iron is present as <i>chloride</i>) until the colour is
+discharged. A large excess of the stannous chloride must be avoided.
+Then add 5 c.c. of a 2-1/2 per cent. solution of mercuric chloride, this
+will cause a white precipitate (or a grey one if too large an excess of
+the stannous chloride has been added). Boil till the solution clears,
+cool, dilute, and titrate.</p>
+
+<p>2. <i>With Sulphuretted Hydrogen.</i>&mdash;Cool the solution and pass through it
+a current of washed sulphuretted hydrogen till the liquid smells
+strongly of the gas after withdrawal and shaking. A white precipitate of
+sulphur will be formed, this will not interfere with the subsequent
+titration provided it is precipitated in the cold. If, however, the
+precipitate is coloured (showing the presence of the second group
+metals), or if the precipitation has been carried out in a hot solution,
+it should be filtered off. Boil the solution until the sulphuretted
+hydrogen is driven off; this may be tested by holding a strip of filter
+paper dipped in lead acetate solution in the steam issuing from the
+flask. The presence of sulphuretted hydrogen should be looked for rather
+than its absence. It is well to continue the boiling for a few minutes
+after the gas has been driven off. Cool and titrate.</p>
+
+<p>3. <i>With Sodium Sulphite.</i>&mdash;Add ammonia (a few drops at a time) until
+the precipitate first formed redissolves with difficulty. If a permanent
+precipitate is formed, redissolve with a few drops of acid. To the warm
+solution add from 2 to 3 grams of sodium sulphite crystals. The solution
+will become strongly coloured, but the colour will fade away on standing
+for a few minutes in a warm place. When the colour is quite removed, add
+20 c.c. of dilute sulphuric acid, and boil until the steam is quite free
+from the odour of sulphurous acid. Cool and titrate.</p>
+
+<p>4. <i>With Zinc.</i>&mdash;Add about 10 grams of granulated zinc; if the hydrogen
+comes off violently add water; if, on the other hand, the action is very
+slow, add sufficient dilute sulphuric acid to keep up a brisk
+effervescence. The reduction is hastened by warming, and is complete
+when the solution is quite colourless and a drop of the liquid tested
+with sulphocyanate of potassium gives no reaction for ferric iron.
+Filter through "glass wool" or quick filtering paper. The zinc should be
+still giving off gas rapidly, indicating a freely acid solution; if not,
+acid must be added. Wash with water rendered acid. Cool and titrate.</p>
+
+<p>With regard to the relative advantages of the different methods they may
+be roughly summed up as follows:&mdash;The stannous<span class='pagenum'><a name="Page_236" id="Page_236">[Pg 236]</a></span> chloride method has the
+advantage of immediately reducing the ferric iron whether in hot or cold
+solution and under varied conditions in regard to acidity, but has the
+disadvantage of similarly reducing salts of copper and antimony, which,
+in a subsequent titration, count as iron. Moreover, there is no
+convenient method of eliminating any large excess of the reagent that
+may have been used; and, consequently, it either leaves too much to the
+judgment of the operator, or entails as much care as a titration.
+Students generally get good results by this method.</p>
+
+<p>The sulphuretted hydrogen method also has the advantage of quick
+reduction under varying conditions, and the further one of adding
+nothing objectionable to the solution; in fact it removes certain
+impurities. The disadvantages are the necessity for boiling off the
+excess of the gas, and of filtering off the precipitated sulphur,
+although this last is not necessary if precipitated cold. The tendency
+with students is to get high results. The sodium sulphite method has the
+advantages of being clean and neat, and of requiring no nitration. On
+the other hand it requires practice in obtaining the best conditions for
+complete reduction; and, as with sulphuretted hydrogen, there is the
+necessity for boiling off the gas, while there is no simple and delicate
+test for the residual sulphurous acid. In addition, if an excess of
+sodium sulphite has been used and enough acid not subsequently added,
+the excess will count as iron. Students generally get low results by
+this method.</p>
+
+<p>The advantages of the zinc method are, that it is easily worked and that
+the excess of zinc is readily removed by simply filtering. The
+disadvantages are the slowness<a name="FNanchor_68_68" id="FNanchor_68_68"></a><a href="#Footnote_68_68" class="fnanchor">[68]</a> with which the last portions of
+ferric iron are reduced, the danger of loss by effervescence, the
+precipitation of basic salts, and, perhaps, of iron, and the loading of
+the solution with salts of zinc, which in the titration with bichromate
+have a prejudicial effect. The tendency in the hands of students is to
+get variable results, sometimes low and sometimes high.</p>
+
+<p>Generally speaking, the sulphuretted hydrogen and sodium sulphite
+methods are to be preferred. Carefully worked each method will yield
+good results.</p>
+
+<p>The titration may be done with a standard solution of (1) permanganate
+of potash, or (2) bichromate of potash.</p>
+
+<p>1. <i>With Permanganate of Potash.</i>&mdash;Prepare a standard solution by
+dissolving 2.82 grams of the salt and diluting to one litre. The
+strength of this should be 100 c.c. = 0.5 gram of iron, but it varies
+slightly, and should be determined (and afterwards<span class='pagenum'><a name="Page_237" id="Page_237">[Pg 237]</a></span> checked every two or
+three weeks) by weighing up 0.2 gram of iron wire, dissolving in 10 c.c.
+of dilute sulphuric acid, diluting to about 100 c.c., and titrating.</p>
+
+<p>The standard solution must be put in a burette with a glass stopcock, as
+it attacks india-rubber. The assay should be contained in a pint flask,
+and be cooled before titrating. The standard solution must be run in
+until a pinkish tinge permeates the whole solution; this must be taken
+as the finishing point. When certain interfering bodies are present this
+colour quickly fades, but the fading must be ignored. With pure
+solutions the colour is fairly permanent, and a single drop of the
+potassium permanganate solution is sufficient to determine the finishing
+point.</p>
+
+<p>2. <i>With Bichromate of Potash.</i>&mdash;Prepare a standard solution by
+dissolving 4.39 grams of the powdered and dried salt in water, and
+diluting to 1 litre. This solution is permanent, its strength is
+determined by dissolving 0.2 gram of iron wire in 10 c.c. of dilute
+sulphuric acid, diluting to about a quarter of a litre, and titrating.</p>
+
+<p>Also prepare a test solution by dissolving 0.1 gram of ferricyanide of
+potassium in 100 c.c. of water. This solution does not keep well and
+must be freshly prepared.</p>
+
+<p>An ordinary burette is used. The assay is best contained in a glazed
+earthenware dish, and may be titrated hot or cold. To determine the
+finishing point, place a series of drops of the ferricyanide solution on
+a dry white glazed plate. The drops should be of about the same size and
+be placed in lines at fairly equal distances. The bichromate is run in,
+in a steady stream, the assay solution being continuously stirred until
+the reaction is sensibly slackened. Then bring a drop of the assay with
+the stirrer in contact with one of the test drops on the plate. The
+standard can be safely run in 1 c.c. at a time, so long as the test drop
+shows signs of a precipitate. When only a coloration is produced run in
+cautiously a few drops at a time so long as two drops of the assay gives
+with the test a colour which is even faintly greener than two drops of
+the assay solution placed alongside. The finishing point is decided and
+practically permanent, although it demands a little practice to
+recognise it. The titration with permanganate of potassium has the
+advantage of a more distinct finishing point and easier mode of working;
+its application, however, is somewhat limited by the disturbing effects
+of hydrochloric acid. The bichromate method has the advantage of a
+standard solution which does not alter in strength, and the further one
+of being but little affected by altering conditions of assay.
+Hydrochloric acid has practically no effect on it. Both methods give
+accurate results and are good examples of volumetric methods.<span class='pagenum'><a name="Page_238" id="Page_238">[Pg 238]</a></span></p>
+
+<p>The following results illustrate the extent to which the methods may be
+relied on; and the influence which the various conditions of experiment
+have on the assay.</p>
+
+<p>Solutions of ferrous sulphate and of ferrous chloride were made
+containing 0.5 gram of iron in each 100 c.c., thus corresponding to the
+standard solutions of permanganate and bichromate of potassium. These
+last were prepared in the way already described. The solution of ferrous
+sulphate was made by dissolving 5.01 grams of iron wire in 100 c.c. of
+dilute sulphuric acid and diluting to 1 litre. A similar solution may be
+made by dissolving 24.82 grams of pure ferrous sulphate crystals in
+water, adding 100 c.c. of dilute sulphuric acid, and diluting to 1
+litre.</p>
+
+<p><b>Rate of Oxidation by Exposure to Air.</b>&mdash;This is an important
+consideration, and if the rate were at all rapid would have a serious
+influence on the manner of working, since exclusion of air in the
+various operations would be troublesome. 20 c.c. of the solution of
+ferrous sulphate were taken in each experiment, acidified with 10 c.c.
+of dilute sulphuric acid, and diluted to 100 c.c. The solution was
+exposed, cold, in an open beaker for varying lengths of time, and
+titrated with permanganate of potassium.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Time exposed</td><td align='left'>1 hour</td><td align='left'>1 day</td><td align='left'>2 days</td><td align='left'>3 days</td></tr>
+<tr><td align='left'>c.c. required</td><td align='left'>19.2</td><td align='left'>19.1</td><td align='left'>19.0</td><td align='left'>19.0</td></tr>
+</table></div>
+
+<p>These results show that the atmospheric oxidation in cold solutions is
+unimportant. With boiling solutions the results are somewhat different;
+a solution which at the outset required 20 c.c. of permanganate of
+potassium, after boiling for an hour in an open beaker (without any
+precautions to prevent oxidation), water being added from time to time
+to replace that lost by evaporation, required 19.2 c.c. If the solution
+be evaporated to dryness the oxidising power of concentrated sulphuric
+acid comes into play, so that very little ferrous iron will be left. A
+solution evaporated in this way required only 2.2 c.c. of permanganate
+of potassium.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;In these experiments the bulk was in
+each case 100 c.c., and 10 c.c. of dilute sulphuric acid were present.
+The permanganate required by</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='right'>1</td><td align='left'>c.c.</td><td align='left'>of ferrous sulphate was,</td><td align='left'>at 15&deg;</td><td align='right'>1.0 c.c.,</td><td align='left'>and at 70&deg;</td><td align='left'>1.1</td><td align='left'>c.c.</td></tr>
+<tr><td align='right'>10</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>9.7</td><td align='center'>"</td><td align='left'>9.8</td><td align='center'>"</td></tr>
+<tr><td align='right'>100</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>97.7</td><td align='center'>"</td><td align='left'>96.8</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>The lower result with the 100 c.c. may be due to oxidation from
+exposure.<span class='pagenum'><a name="Page_239" id="Page_239">[Pg 239]</a></span></p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;The following experiments show that
+considerable variations in bulk have no practical effect. In each case
+20 c.c. of ferrous sulphate solution and 10 c.c. of dilute acid were
+used.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk of assay</td><td align='right'>30</td><td align='left'>c.c.</td><td align='right'>100</td><td align='left'>c.c.</td><td align='right'>500</td><td align='left'>c.c.</td><td align='right'>1000</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='right'>20.0</td><td align='left'>"</td><td align='right'>20.0</td><td align='left'>"</td><td align='right'>20.2</td><td align='left'>"</td><td align='right'>20.5</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Free Sulphuric Acid.</b>&mdash;Free acid is necessary for these
+assays; if there is an insufficiency, the assay solution, instead of
+immediately decolorising the permanganate, assumes a brown colour. The
+addition of 10 c.c. of dilute sulphuric acid suffices to meet
+requirements and keep the assay clear throughout. The following
+experiments show that a considerable excess of acid may be used without
+in the least affecting the results. In each case 20 c.c. of ferrous
+sulphate were used.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Dilute sulphuric acid</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>5.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.3</td><td align='left'>"</td><td align='left'>19.3</td><td align='left'>"</td><td align='left'>19.3</td><td align='left'>"</td><td align='left'>19.3</td><td align='left'>"</td><td align='left'>19.3</td><td align='left'>"</td><td align='left'>19.3</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Foreign Salts.</b>&mdash;When the assay has been reduced with zinc
+varying quantities of salts of this metal pass into solution, the amount
+depending on the quantity of acid and iron present. Salts of sodium or
+ammonium may similarly be introduced. It is essential to know by
+experiment that these salts do not exert any effect on the titration.
+The following series of experiments show that as much as 50 grams of
+zinc sulphate may be present without interfering.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Zinc sulphate present</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>10 grams</td><td align='left'>50 grams</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td></tr>
+</table></div>
+
+<p>Magnesium, sodium, and ammonium salts, are equally without effect.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ammonic sulphate present</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.3 c.c.</td><td align='left'>19.2 c.c.</td><td align='left'>19.3 c.c.</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodic sulphate present</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Magnesic sulphate present</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td><td align='left'>19.3 c.c.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Amounts of Iron.</b>&mdash;It is important to know within
+what limits the quantity of iron in an assay may safely vary from that
+used in standardising. In the following experiments the conditions as to
+bulk, acidity, and mode of working were the same as before:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ferrous sulphate solution taken</td><td align='left'>1</td><td align='left'>c.c.</td><td align='left'>10</td><td align='left'>c.c.</td><td align='left'>20</td><td align='left'>c.c.</td><td align='left'>50</td><td align='left'>c.c.</td><td align='left'>100</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>1.0</td><td align='left'>"</td><td align='left'>9.7</td><td align='left'>"</td><td align='left'>19.6</td><td align='left'>"</td><td align='left'>48.9</td><td align='left'>"</td><td align='left'>97.7</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_240" id="Page_240">[Pg 240]</a></span></p>
+
+<p>The ferrous sulphate solution is here a little weaker than that of the
+permanganate of potassium, but the results show that the permanganate
+required is proportional to the iron present.</p>
+
+<p><b>Titrations in Hydrochloric Solutions.</b>&mdash;These are less satisfactory
+than those in sulphuric solutions, since an excess of hydrochloric acid
+decomposes permanganate of potassium, evolving chlorine, and since the
+finishing point is indicated, not by the persistence of the pink colour
+of the permanganate, but by a brown coloration probably due to
+perchloride of manganese. Nevertheless, if the solution contains only
+from 5 to 10 per cent. of free hydrochloric acid (sp. g. 1.16) the
+results are the same as those obtained in a sulphuric acid solution.
+Equal weights (0.1 gram) of the same iron wire required exactly the same
+quantity of the permanganate of potassium solution (20 c.c.) whether the
+iron was dissolved in dilute sulphuric or dilute hydrochloric acid. The
+following series of experiments are on the same plan as those given
+above with sulphuric acid solutions. A solution of ferrous chloride was
+made by dissolving 5.01 grams of iron wire in 50 c.c. of dilute
+hydrochloric acid and diluting to 1 litre. The dilute hydrochloric acid
+was made by mixing equal volumes of the acid (sp. g. 1.16) and water.</p>
+
+<p><b>Rate of Atmospheric Oxidation.</b>&mdash;20 c.c. of the ferrous chloride
+solution were acidified with 10 c.c. of the dilute hydrochloric acid and
+diluted to 100 c.c. This solution was exposed cold in open beakers.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Time exposed</td><td align='left'>&mdash;</td><td align='left'>1 hour</td><td align='left'>1 day</td><td align='left'>2 days</td><td align='left'>3 days</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.6 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.5 c.c.</td><td align='left'>19.4 c.c.</td><td align='left'>19.5 c.c.</td></tr>
+</table></div>
+
+<p>Similar solutions boiled required, before boiling, 20 c.c.; after
+boiling for one hour, replacing the water as it evaporated, 19.3 c.c.;
+and after evaporation to a paste and redissolving, 17.0 c.c.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;Solutions similar to the last were
+titrated and gave the following results:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg;</td><td align='left'>30&deg;</td><td align='left'>50&deg;</td><td align='left'>70&deg;</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>19.8 c.c.</td><td align='left'>19.6 c.c.</td><td align='left'>19.5 c.c.</td><td align='left'>19.4 c.c.</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;As before, 20 c.c. of the iron solution, and
+10 c.c. of the dilute acid were diluted to the required volumes and
+titrated.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>30 c.c.</td><td align='left'>100 c.c.</td><td align='left'>500 c.c.</td><td align='left'>1000 c.c.</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>20.4 "</td><td align='left'>20.3 "</td><td align='left'>20.8 "</td><td align='left'>21.5 "</td></tr>
+</table></div>
+
+<p>The variation due to difference in bulk here, although only equal to an
+excess of 0.7 milligram of iron for each 100 c.c. of dilution, are about
+three times as great as those observed in a sulphuric acid solution.<span class='pagenum'><a name="Page_241" id="Page_241">[Pg 241]</a></span></p>
+
+<p><b>Effect of Free Hydrochloric Acid.</b>&mdash;In these experiments 20 c.c. of the
+ferrous chloride solution were used with varying quantities of acid, the
+bulk of the assay in each case being 100 c.c.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Dilute acid present</td><td align='left'>5 c.c.</td><td align='left'>10 c.c.</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>20.2 "</td><td align='left'>20.2 "</td><td align='left'>20.5 "</td><td align='left'>21.0 "</td></tr>
+</table></div>
+
+<p>The last had a very indistinct finishing point, the brown coloration
+being very evanescent. The effect of the acid is modified by the
+presence of alkaline and other sulphates, but not by sulphuric acid.
+Repeating the last experiment we got&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Without further addition</td><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>21.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='right'>With</td><td align='left'>100</td><td align='left'> c.c.</td><td align='left'>of dilute sulphuric acid</td><td align='left'>22.0</td><td align='left'>"</td></tr>
+<tr><td align='right'> "</td><td align='left'>10</td><td align='left'>grams</td><td align='left'> ammonic sulphate</td><td align='left'>20.5</td><td align='left'>"</td></tr>
+<tr><td align='right'> "</td><td align='left'>10</td><td align='left'>"</td><td align='left'>sodic sulphate</td><td align='left'>20.0</td><td align='left'>"</td></tr>
+<tr><td align='right'> "</td><td align='left'>10</td><td align='left'>"</td><td align='left'>magnesium sulphate</td><td align='left'>20.4</td><td align='left'>"</td></tr>
+<tr><td align='right'> "</td><td align='left'>10</td><td align='left'>"</td><td align='left'>manganese sulphate</td><td align='left'>20.2</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>The results with these salts, in counteracting the interference of the
+acid, however, were not a complete success, since the end-reactions were
+all indistinct, with the exception, perhaps, of that with the manganese
+sulphate.</p>
+
+<p><b>Effect of Varying Amounts of Iron.</b>&mdash;In these experiments the bulk of
+the assay was 100 c.c., and 10 c.c. of acid were present.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ferrous chloride used</td><td align='left'>1 c.c.</td><td align='left'>10 c.c.</td><td align='left'>20 c.c.</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td></tr>
+<tr><td align='left'>Permanganate required</td><td align='left'>1.1 "</td><td align='left'>10.3 "</td><td align='left'>20.3 "</td><td align='left'>50.4 "</td><td align='left'>100.1 "</td></tr>
+</table></div>
+
+<p>In making himself familiar with the permanganate of potassium titration,
+the student should practise by working out a series of experiments
+similar to the above, varying his conditions one at a time so as to be
+certain of the cause of any variation in his results. He may then
+proceed to experiment on the various methods of reduction.</p>
+
+<p><i>A solution of ferric chloride</i> is made by dissolving 5.01 grams of iron
+wire in 50 c.c. of hydrochloric acid (sp. g. 1.16), and running from a
+burette nitric acid diluted with an equal volume of water into the
+boiling iron solution, until the liquid changes from a black to a
+reddish-yellow. About 4.5 c.c. of the nitric acid will be required, and
+the finishing point is marked by a brisk effervescence. The solution of
+iron should be contained in an evaporating dish, and boiled briskly,
+with constant stirring. There should be no excess of nitric acid. Boil
+down to about half its bulk; then cool, and dilute to one litre with
+water. Twenty c.c. of this solution diluted to 100 c.c. with water, and
+acidified with 10 c.c. of dilute hydrochloric acid, should not
+decolorise any of the permanganate of potassium solution; this shows the
+absence of ferrous salts. And 20 c.c. of the same solution, boiled with<span class='pagenum'><a name="Page_242" id="Page_242">[Pg 242]</a></span>
+20 c.c. of the ferrous sulphate solution, should not decrease the
+quantity of "permanganate" required for the titration of the ferrous
+sulphate added. In a series of experiments on the various methods of
+reduction, the following results were got. The modes of working were
+those already described.</p>
+
+<p>(1) <i>With Stannous Chloride.</i>&mdash;Twenty c.c. of the ferric chloride
+solution required, after reduction with stannous chloride, 20 c.c. of
+"permanganate." Fifty c.c. of a solution of ferrous chloride, which
+required on titration 49.8 c.c. of "permanganate," required for
+re-titration (after subsequent reduction with stannous chloride) 50 c.c.
+of the permanganate solution.</p>
+
+<p>(2) <i>With Sulphuretted Hydrogen.</i>&mdash;Two experiments with this gas, using
+in each 20 c.c. of the ferric chloride solution, and 10 c.c. of
+hydrochloric acid, required (after reduction) 20.2 c.c. and 20.1 c.c. of
+"permanganate." Repeating the experiments by passing the gas through a
+nearly boiling solution, but in other respects working in the same way,
+21.3 c.c. and 21.6 c.c. of the permanganate solution were required. The
+sulphur was not filtered off in any of these. In another experiment, in
+which 50 c.c. of the ferrous sulphate solution were titrated with
+"permanganate," 48 c.c. of the latter were required. The titrated
+solution was next reduced with sulphuretted hydrogen, brought to the
+same bulk as before, and again titrated; 47.9 c.c. of the permanganate
+of potassium solution were required.</p>
+
+<p>(3) <i>With Sodium Sulphite.</i>&mdash;Twenty c.c. of the ferric chloride
+solution, reduced with sodium sulphite, required 19.9 c.c. of
+"permanganate." In one experiment 50 c.c. of the ferrous sulphate
+solution were titrated with "permanganate"; 49.3 c.c. of the
+last-mentioned solution were required. The titrated solution was reduced
+with sodium sulphite, and again titrated; it required 49.2 c.c. of the
+permanganate of potassium solution.</p>
+
+<p>(4) <i>With Zinc.</i>&mdash;Twenty c.c. of the ferric chloride solution, reduced
+with zinc and titrated, required 20.8 c.c. of "permanganate." Fifty c.c.
+of a solution of ferrous sulphate which required 49.7 c.c. of
+"permanganate," required for re-titration, after reduction with zinc,
+49.7 c.c.</p>
+
+<p>The student should next practise the titration with bichromate, which is
+more especially valuable in the estimation of hydrochloric acid
+solutions. The following experiments are on the same plan as those
+already given. In each experiment (except when otherwise stated) there
+were present 20 c.c. of the ferrous chloride solution, and 10 c.c. of
+dilute hydrochloric acid, and the bulk was 300 c.c.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The quantities of the bichromate of
+potassium solution required were as follows:<span class='pagenum'><a name="Page_243" id="Page_243">[Pg 243]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg;</td><td align='left'>30&deg;</td><td align='left'>70&deg;</td><td align='left'>100&deg;</td></tr>
+<tr><td align='left'>Bichromate required</td><td align='left'>20.2 c.c.</td><td align='left'>20.3 c.c.</td><td align='left'>20.3 c.c.</td><td align='left'>20.4 c.c.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Bulk.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td><td align='left'>200 c.c.</td><td align='left'>500 c.c.</td><td align='left'>1000 c.c.</td></tr>
+<tr><td align='left'>Bichromate required</td><td align='left'>20.4 "</td><td align='left'>20.4 "</td><td align='left'>20.4 "</td><td align='left'>20.5 "</td><td align='left'>20.8 "</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Acid.</b>&mdash;In these, variable quantities of dilute
+hydrochloric acid were used.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acid present</td><td align='left'>10 c.c.</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td></tr>
+<tr><td align='left'>Bichromate required</td><td align='left'>20.3 "</td><td align='left'>20.3 "</td><td align='left'>20.2 "</td></tr>
+</table></div>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;The effect of the addition of 10 grams of
+crystallized zinc sulphate was to decrease the quantity of "bichromate"
+required from 20.3 c.c. to 20.1 c.c., but the colour produced with the
+test-drop was very slight at 18.5 c.c., and with incautious work the
+finishing point might have been taken anywhere between these extremes.
+Zinc should not be used as a reducing agent preliminary to a
+"bichromate" titration. Ten grams of ammonic sulphate had the effect of
+rendering the finishing point faint for about 0.5 c.c. before the
+titration was finished, but there was no doubt about the finishing point
+when allowed to stand for a minute. The student should note that a
+titration is not completed if a colour is developed on standing for five
+or ten minutes. Ten grams of sodic sulphate had no effect; 20.3 c.c.
+were required.</p>
+
+<p><b>Effect of Varying Iron.</b>&mdash;The results are proportional, as will be seen
+from the following details:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ferrous chloride present</td><td align='left'>1.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td></tr>
+<tr><td align='left'>Bichromate required</td><td align='left'>1.0 "</td><td align='left'>10.2 "</td><td align='left'>20.3 "</td><td align='left'>51.0 "</td><td align='left'>102.3 "</td></tr>
+</table></div>
+
+
+<p>The student may now apply these titrations to actual assays of minerals.
+The following examples will illustrate the mode of working and of
+calculating the results:&mdash;</p>
+
+<p><b>Determination of Iron in Chalybite.</b>&mdash;Weigh up 1 gram of the dry
+powdered ore, and dissolve in 10 c.c. of dilute sulphuric acid and an
+equal volume of water with the aid of heat. Avoid evaporating to
+dryness. Dilute and titrate. The result will give the percentage of iron
+existing in the ore in the ferrous state. Some ferric iron may be
+present. If it is wished to determine this also, add (in dissolving
+another portion) 10 c.c. of dilute hydrochloric acid to the sulphuric
+acid already ordered, and reduce the resulting solution before
+titrating. By dissolving and titrating (without previous reduction) one
+has a measure of the ferrous iron present; by dissolving, reducing, and
+then titrating, one can<span class='pagenum'><a name="Page_244" id="Page_244">[Pg 244]</a></span> measure the total iron; and as the iron exists
+in only two conditions, the total iron, less the ferrous iron, is the
+measure of the ferric iron.</p>
+
+<p><b>Determination of Iron in Brown or Red Ores or Magnetite.</b>&mdash;Weigh up 0.5
+gram of the ore (powdered and dried at 100&deg; C.), and dissolve in from 10
+to 20 c.c. of strong hydrochloric acid, boiling until all is dissolved,
+or until no coloured particles are left. Dilute, reduce, and titrate.</p>
+
+<p><b>Determination of Iron in Pyrites.</b>&mdash;Weigh up 1 gram of the dry powdered
+ore, and place in a beaker. Cover with 10 c.c. of strong sulphuric acid,
+mix well by shaking, and place on the hot plate without further handling
+for an hour or so until the action has ceased. <i>Allow to cool</i>, and
+dilute to 100 c.c. Warm until solution is complete. Reduce and titrate.</p>
+
+<p><b>Determination of Iron in Substances Insoluble in Acids.</b>&mdash;Weigh up 1
+gram of the ore, mix with 5 or 6 grams of carbonate of soda and 0.5 gram
+of nitre by rubbing in a small mortar, and transfer to a platinum
+crucible. Clean out the mortar by rubbing up another gram or so of soda,
+and add this to the contents of the crucible as a cover. Fuse till
+tranquil. Cool. Extract with water. If the ore carries much silica,
+evaporate to dryness with hydrochloric acid to separate it. Re-dissolve
+in hydrochloric acid, and separate the iron by precipitating with
+ammonia and filtering. If only a small quantity of silica is present,
+the aqueous extract of the "melt" must be filtered, and the insoluble
+residue washed and dissolved in dilute hydrochloric acid. Reduce and
+titrate.</p>
+
+<p>A convenient method of at once separating iron from a solution and
+reducing it, is to add ammonia, pass sulphuretted hydrogen through it,
+filter, and dissolve the precipitate in dilute sulphuric acid. The
+solution, when boiled free from sulphuretted hydrogen, is ready for
+titrating.</p>
+
+
+<h4>STANNOUS CHLORIDE PROCESS.</h4>
+
+<p>The colour imparted to hot hydrochloric acid solutions by a trace of a
+ferric compound is so strong, and the reducing action of stannous
+chloride is so rapid, that a method of titration is based upon the
+quantity of a standard solution of stannous chloride required to
+completely decolorise a solution containing ferric iron. This method is
+more especially adapted for the assay of liquors containing much ferric
+iron and of those oxidised ores which are completely soluble in
+hydrochloric acid. It must be remembered, however, that it only measures
+the ferric iron present, and when (as is generally the case) the total
+iron is wanted,<span class='pagenum'><a name="Page_245" id="Page_245">[Pg 245]</a></span> it is well to calcine the weighed portion of ore
+previous to solution in order to get the whole of the iron into the
+higher state of oxidation, since many ores which are generally supposed
+to contain only ferric iron carry a considerable percentage of ferrous.</p>
+
+<p><i>The stannous chloride solution</i> is made by dissolving 20 grams of the
+commercial salt (SnCl<sub>2</sub>.2H<sub>2</sub>O) in 100 c.c. of water with the help of
+20 c.c. of dilute hydrochloric acid, and diluting to a litre. The
+solution may be slightly opalescent, but should show no signs of a
+precipitate. The strength of this is about equivalent to 1 gram of iron
+for each 100 c.c. of the solution, but it is apt to lessen on standing,
+taking up oxygen from the air, forming stannic chloride. A larger
+proportion of hydrochloric acid than is ordered above would remove the
+opalescence, but at the same time increase this tendency to atmospheric
+oxidation, as the following experiments show. The stannous chloride
+solution (20 c.c.) was mixed with varying amounts of strong hydrochloric
+acid (sp. g. 1.16), diluted to 100 c.c., and exposed in open beakers for
+varying lengths of time; and the residual stannous chloride measured by
+titration with permanganate. The quantities required were as follows:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Time Exposed.</td><td align='left'>50 per cent. Acid.</td><td align='left'>10 per cent. Acid.</td><td align='left'>1 per cent. Acid.</td></tr>
+<tr><td align='left'>1 hour</td><td align='left'>33.2 c.c.</td><td align='left'>34.4 c.c.</td><td align='left'>34.5 c.c.</td></tr>
+<tr><td align='left'>1 day</td><td align='left'>5.0 "</td><td align='left'>24.0 "</td><td align='left'>27.6 "</td></tr>
+<tr><td align='left'>2 days</td><td align='left'>3.0 "</td><td align='left'>14.5 "</td><td align='left'>21.3 "</td></tr>
+</table></div>
+
+
+<p>These indicate very clearly the increased susceptibility to oxidation in
+strongly acid solutions.</p>
+
+<p><i>A standard solution of ferric chloride</i> is prepared in the same manner
+as that described under the experiments on the methods of reduction; but
+it should be of twice the strength, so that 100 c.c. may contain 1 gram
+of iron. This solution is used for standardising the stannous chloride
+when required; and must be carefully prepared; and tested for the
+presence of nitric acid.</p>
+
+<p>The titration is more limited in its application than either of the
+oxidising processes because of the restrictions as to bulk, quality and
+quantity of free acid present, and other conditions of the solution to
+be assayed. The following experiments show the conditions necessary for
+a successful titration.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;Twenty c.c. of ferric chloride
+solution with 20 c.c. of strong hydrochloric acid, diluted to 50 c.c.,
+gave the following results when titrated:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg;</td><td align='left'>30&deg;</td><td align='left'>70&deg;</td><td align='left'>100&deg;</td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>22.8 c.c.</td><td align='left'>22.0 c.c.</td><td align='left'>22.1 c.c.</td><td align='left'>22.0 c.c.</td></tr>
+</table></div>
+
+
+<p>The finishing point, however, is more distinct the hotter the<span class='pagenum'><a name="Page_246" id="Page_246">[Pg 246]</a></span> solution;
+so that it is best in all cases to run the standard into the boiling
+solution.</p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;Solutions containing the same quantity of
+iron and acid as the last, but diluted to various bulks, and titrated
+while boiling, gave the following results:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>30 c.c.</td><td align='left'>100 c.c.</td><td align='left'>500 c.c.</td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>21.5 "</td><td align='left'>21.7 "</td><td align='left'>24.3 "</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Quantities of Hydrochloric Acid.</b>&mdash;In these
+experiments the bulk before titration was 50 c.c. except in the last, in
+which it was 70 c.c. With less than 5 c.c. of strong hydrochloric acid
+the finishing point is indistinct and prolonged.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Strong hydrochloric acid present</td><td align='left'>5 c.c.</td><td align='left'>10 c.c.</td><td align='left'>20 c.c.</td><td align='left'>30 c.c.</td><td align='left'>50 c.c.</td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>21.1 "</td><td align='left'>21.1 "</td><td align='left'>21.2 "</td><td align='left'>21.8 "</td><td align='left'>22.2 "</td></tr>
+</table></div>
+
+
+<p><b>Effect of Free Sulphuric Acid.</b>&mdash;In these experiments 20 c.c. of
+hydrochloric acid were present, and the bulk was 50 c.c.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Strong sulphuric acid present</td><td align='left'>&mdash; c.c.</td><td align='left'>3 c.c.</td><td align='left'>5 c.c.</td><td align='left'>10 c.c.</td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>21.6 "</td><td align='left'>22.3 "</td><td align='left'>22.9 "</td><td align='left'>23.1 "</td></tr>
+</table></div>
+
+<p>This interference of strong sulphuric acid may be completely
+counteracted by somewhat modifying the mode of working. Another
+experiment, like the last of this series, required 21.6 c.c.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;Experiments in which 10 grams of various
+salts were added showed them to be without effect. The results were as
+follows:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt present</td><td align='left'>&mdash;</td><td align='left'>AmCl</td><td align='left'>Am<sub>2</sub>SO<sub>4</sub></td><td align='left'>MgCl<sub>2</sub></td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>21.6 c.c.</td><td align='left'>21.6 c.c.</td><td align='left'>21.6 c.c.</td><td align='left'>21.6 c.c.</td></tr>
+<tr><td align='left'>Salt present</td><td align='left'>CaCl<sub>2</sub></td><td align='left'>FeCl<sub>2</sub></td><td align='left'>Al<sub>2</sub>Cl<sub>6</sub></td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>21.8 c.c.</td><td align='left'>21.6 c.c.</td><td align='left'>21.6 c.c.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Iron.</b>&mdash;Titrating a solution (with 20 c.c. of
+hydrochloric acid) measuring 50 c.c., and kept boiling, the quantity of
+stannous chloride solution required is practically proportional to the
+iron present.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ferric chloride added</td><td align='left'>1 c.c.</td><td align='left'>10 c.c.</td><td align='left'>20 c.c.</td><td align='left'>50 c.c.</td><td align='left'>100 c.c.</td></tr>
+<tr><td align='left'>Stannous chloride required</td><td align='left'>1.1 "</td><td align='left'>10.5 "</td><td align='left'>20.6 "</td><td align='left'>51.4 "</td><td align='left'>102.6 "</td></tr>
+</table></div>
+
+<p>The student, having practised some of the above experiments, may proceed
+to the assay of an iron ore.</p>
+
+<p><b>Determination of Iron in Brown Iron Ore.</b>&mdash;Weigh up 1 gram of the dried
+and powdered ore, calcine in the cover of a<span class='pagenum'><a name="Page_247" id="Page_247">[Pg 247]</a></span> platinum crucible, and
+dissolve up in an evaporating dish<a name="FNanchor_69_69" id="FNanchor_69_69"></a><a href="#Footnote_69_69" class="fnanchor">[69]</a> with 20 c.c. of strong
+hydrochloric acid. When solution is complete, dilute to 50 c.c. after
+replacing any acid that may have been evaporated. Boil, and run in the
+stannous chloride solution until the colour is faintly yellow; boil
+again, and continue the addition of the stannous chloride solution,
+stirring continuously until the solution appears colourless. Note the
+quantity of the stannous chloride solution required. Suppose this to be
+59 c.c. Take 60 c.c. of the standard ferric chloride solution, add 20
+c.c. of hydrochloric acid, boil and titrate in the same way as before.
+Suppose this to require 61 c.c. Then as 61 is equivalent to 60 of the
+iron solution, 59 is equivalent to 58.13.<a name="FNanchor_70_70" id="FNanchor_70_70"></a><a href="#Footnote_70_70" class="fnanchor">[70]</a> This gives the percentage.
+It is not necessary to standardise the stannous chloride solution in
+this way with each sample assayed, the ratio 61: 60 would serve for a
+whole batch of samples; but the standardising should be repeated at
+least once each day.</p>
+
+
+<h4>COLORIMETRIC METHOD.</h4>
+
+<p>This method is valuable for the determination of small quantities of
+iron present as impurities in other metals or ores. It is based on the
+red coloration developed by the action of potassic sulphocyanate on acid
+solutions of ferric salts.</p>
+
+<p><i>Standard Ferric Chloride Solution.</i>&mdash;Take 1 c.c. of the ferric chloride
+solution used for standardising the stannous chloride solution, add 2
+c.c. of dilute hydrochloric acid, and dilute to 1 litre with water. 1
+c.c. = 0.01 milligram.</p>
+
+<p><i>Solution of Potassic Sulphocyanate.</i>&mdash;Dissolve 60 grams of the salt in
+water, and dilute to a litre. It should be colourless. Use 10 c.c. for
+each test.</p>
+
+<p>The quantity of the substance to be weighed for the assay should not
+contain more than a milligram of iron; consequently, if the ore contain
+more than 0.1 per cent. of that metal, less than a gram of it must be
+taken.</p>
+
+<p>The method is as follows:&mdash;Weigh up 1 gram of the substance and dissolve
+in a suitable acid; dilute; and add permanganate of potash solution
+until tinted. Boil for some time and dilute to 100 c.c. Take a couple of
+Nessler tubes, holding over 100 c.c., but marked at 50 c.c.; label them
+"1" and "2"; and into each<span class='pagenum'><a name="Page_248" id="Page_248">[Pg 248]</a></span> put 10 c.c. of the potassic sulphocyanate
+solution and 2 c.c. of dilute hydrochloric acid. The solutions should be
+colourless. To "1" add 10 c.c. of the assay solution, and dilute to the
+50 c.c. mark. To the other add water, but only to within 5 or 10 c.c. of
+this mark. Now run in the standard ferric chloride solution from a small
+burette, 1 c.c. at a time, stirring after each addition till the colour
+is nearly equal to that of the assay (No. 1). At this stage bring the
+solution to the same level by diluting, and make a further addition of
+the standard ferric chloride solution till the colours correspond. The
+amount of iron will be the same in each tube; that in the standard may
+be known by reading off the volume from the burette and multiplying by
+0.01 milligram.</p>
+
+<p>If the 10 c.c. of the assay solution gave a colour requiring more than 5
+or 6 c.c. of the standard ferric chloride solution, repeat the
+determination, taking a smaller proportion.</p>
+
+<p>The effect of varying conditions on the assay will be seen from the
+following experiments:&mdash;</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The effect of increase of temperature
+is to lessen the colour; in fact, by boiling, the colour can be entirely
+removed. All assays are best carried out in the cold.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1</td><td align='left'>c.c. at 15&deg;</td><td align='left'>would only show</td><td align='left'>the colour of</td><td align='left'>0.75</td><td align='left'>c.c. at 45&deg;</td></tr>
+<tr><td align='left'>2</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>1.75</td><td align='center'>"</td></tr>
+<tr><td align='left'>5</td><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>4.0</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Time.</b>&mdash;The effect of increase of time is to increase the
+colour, as will be seen from the following experiments:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>2</td><td align='left'>c.c. on standing</td><td align='left'>10 minutes</td><td align='left'>became equal to</td><td align='left'>2.25</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>2</td><td align='center'>"</td><td align='left'>20</td><td align='center'>"</td><td align='left'>2.75</td><td align='left'>"</td></tr>
+<tr><td align='left'>2</td><td align='center'>"</td><td align='left'>40</td><td align='center'>"</td><td align='left'>3.00</td><td align='left'>"</td></tr>
+</table></div>
+
+<p><b>Effect of Free Acid.</b>&mdash;If no acid at all be present, the sulphocyanate
+of potassium solution removes the colour it first produces, so that a
+certain amount of acid is necessary to develop the colour. The use of a
+large excess has a tendency to increase the colour produced.</p>
+
+
+<p>5 c.c. nitric acid (sp. g. 1.4) read 3.7 c.c. instead of 2 c.c. with the dilute acid.</p>
+
+<p>5 c.c. sulphuric acid (sp. g. 1.32) read 2.2 c.c. instead of 2 c.c. with the dilute acid.</p>
+
+<p>5 c.c. hydrochloric acid (sp. g. 1.16) read 2.5 c.c. instead of 2 c.c. with the dilute acid.</p>
+
+
+<p><b>Effect of Foreign Metals.</b>&mdash;Lead, mercury, cadmium, bismuth, arsenic,
+tin, antimony, nickel, cobalt, manganese, aluminium, zinc, strontium,
+barium, calcium, magnesium, sodium, or potassium, when separately
+present in quantities of from 100 to 200 times the weight of iron
+present, do not interfere if they have previously<span class='pagenum'><a name="Page_249" id="Page_249">[Pg 249]</a></span> been brought to their
+highest oxidised condition by boiling with nitric acid or by treating
+with permanganate. Arsenic and phosphoric acids interfere unless an
+excess of free hydrochloric or other acid is present. Oxalic acid (but
+not tartaric acid) in minute quantities destroys the colour. Nitrous
+acid strikes a red colour with the sulphocyanate of potassium;
+consequently, when nitric acid has been used in excess, high results may
+be obtained. Copper and some other metals interfere, so that in most
+cases it is advisable to concentrate the iron before estimating it. A
+blank experiment should always be made with the reagents used in order
+to determine the iron, if any, introduced during the solution, &amp;c., of
+the substance assayed.</p>
+
+<p><b>Determination of Iron in Metallic Copper.</b>&mdash;This may be most
+conveniently done during the estimation of the arsenic. The small
+quantity of white flocculent precipitate which may be observed in the
+acetic acid solution before titrating, contains the whole of the iron as
+ferric arsenate. It should be filtered off, dissolved in 10 c.c. of
+dilute hydrochloric acid, and diluted to 100 c.c.; 10 c.c. of this may
+be taken for the estimation. For example: 10 grams of copper were taken,
+and the iron estimated; 3.0 c.c. of standard ferric chloride solution
+were used, equivalent to 0.03 milligram of iron; this multiplied by 10
+(because only 1/10th of the sample was taken) gives 0.3 milligram as the
+iron in 10 grams of copper. This equals 0.003 per cent.</p>
+
+<p>In a series of experiments with this method working on 10-gram lots of
+copper, to which known quantities of iron had been added, the following
+were the results:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Iron present</td><td align='left'>0.015%</td><td align='left'>0.070%</td><td align='left'>0.100%</td><td align='left'>0.495%</td></tr>
+<tr><td align='left'>Iron found</td><td align='left'>0.015"</td><td align='left'>0.061"</td><td align='left'>0.087"</td><td align='left'>0.522"</td></tr>
+</table></div>
+
+
+<p>When no arsenic is present in the copper, the iron can be separated by
+fractionally precipitating with sodic carbonate, dissolving in ammonia,
+and filtering off the ferric hydrate. Coppers generally carry more iron
+the less arsenic they contain.</p>
+
+<p><b>Determination of Iron in Metallic Zinc.</b>&mdash;Dissolve 1 gram of zinc in 10
+c.c. of dilute hydrochloric acid, adding a drop or two of nitric acid
+towards the end to effect complete solution. Boil, dilute, and tint with
+the permanganate of potassium solution; boil till colourless, and dilute
+to 100 c.c. Take 10 c.c. for the determination. Make a blank experiment
+by boiling 10 c.c. of dilute hydrochloric acid with a drop or two of
+nitric acid; add a similar quantity of the permanganate of potassium
+solution, boiling, &amp;c., as before. The quantity of iron in zinc varies
+from less than 0.005 to more than 2.0 per cent. When 1 gram is taken
+and<span class='pagenum'><a name="Page_250" id="Page_250">[Pg 250]</a></span> worked as above, each c.c. of ferric chloride solution required
+indicates 0.01 per cent. of iron.</p>
+
+<p><b>Determination of Iron in Metallic Tin.</b>&mdash;Cover 1 gram of tin with 5
+c.c. of hydrochloric acid, add 1 c.c. of nitric acid, and evaporate to
+dryness. Take up with 2 c.c. of dilute hydrochloric acid, add 10 c.c. of
+the potassic sulphocyanate solution, and make up to 50 c.c. Probably the
+colour developed will be brown instead of red owing to the presence of
+copper; in this case, add to the standard as much copper as the assay is
+known to contain (which must have previously been determined; see
+<i>Copper</i>); the titration is then carried out in the usual way.</p>
+
+<p>Or the iron may be separated from the copper in the tin by the following
+process:&mdash;Dissolve 5 grams of metal in 30 c.c. of hydrochloric acid and
+5 c.c. of nitric acid, and evaporate to dryness. Take up with 5 c.c. of
+dilute hydrochloric acid, add 10 grams of potash dissolved in 30 c.c. of
+water, and warm till the tin is dissolved. Pass sulphuretted hydrogen,
+boil, cool, and filter. The iron and copper will be in the precipitate.
+They are separated in the ordinary manner.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. Calculate from the following determinations the percentages of
+ferrous, ferric, and total iron in the sample of ore used.</p>
+
+<p>1 gram of ore dissolved and titrated required 26.7 c.c. of bichromate of
+potassium solution.</p>
+
+<p>1 gram of ore dissolved, reduced, and titrated required 43.5 c.c. of
+bichromate of potassium solution.</p>
+
+<p>Standard = 1.014.</p>
+
+<p>2. One gram of an ore contained 0.307 gram of ferrous iron and 0.655
+gram of total iron. The iron existing as oxide, what are the percentages
+of ferrous oxide (FeO) and ferric oxide (Fe<sub>2</sub>O<sub>3</sub>) in the ore?</p>
+
+<p>3. One gram of brown iron ore dissolved in hydrochloric acid required
+59.2 c.c. of stannous chloride (standard = 0.930). Another gram
+dissolved in acid and titrated with "permanganate" required 8.2 c.c.
+(standard = 0.4951). Calculate the percentages of ferrous, ferric, and
+total iron.</p>
+
+<p>4. Another gram of the same ore, roasted, dissolved and titrated with
+stannous chloride, required 63.5 c.c. To what extent does this result
+confirm the others?</p>
+
+<p>5. Two grams of a metal were dissolved and diluted to 100 c.c. Five c.c.
+were taken for a colorimetric determination, and required 4.5 c.c. of
+the standard ferric chloride solution. What is the percentage of iron in
+the metal?<span class='pagenum'><a name="Page_251" id="Page_251">[Pg 251]</a></span></p>
+
+
+<h4>NICKEL.</h4>
+
+<p>Nickel and cobalt are closely related in their chemical properties, and
+may best be considered together. Nickel is the commoner of the two, and
+is met with in commerce alloyed with copper and zinc as German silver;
+as also in the coinage of the United States and on the Continent. It is
+used for plating polished iron and steel goods, forming a coating little
+liable to rust and taking a good polish. The ores of nickel are not very
+common. Kupfernickel and chloanthite are arsenides of nickel with,
+generally, more or less iron and cobalt. Noumeite and garnierite are
+hydrated silicates of nickel and magnesia. The chief sources of nickel
+are these silicates, which are found in large quantity in New Caledonia;
+and a pyrites found in Norway, containing three or four per cent. of the
+metal. In smaller quantities it is more widely distributed, being
+frequently met with in copper ores; consequently, commercial copper is
+rarely free from it.</p>
+
+<p>Nickel is readily soluble in moderately concentrated nitric acid. Its
+salts are mostly green, and soluble in excess of ammonia, forming blue
+solutions; in these respects it resembles copper. The acid solutions,
+however, are not precipitated by sulphuretted hydrogen, although in
+alkaline solutions a black sulphide is formed which is insoluble in
+dilute hydrochloric acid. If the sulphide is formed in a solution
+containing much free ammonia, the precipitation is incomplete, some
+sulphide remaining in the solution and colouring it dark brown. These
+reactions serve to distinguish and separate nickel from other metals,
+except cobalt. If the separated sulphide be heated in a borax bead, the
+colour obtained will be a sherry brown in the outer flame, and grey or
+colourless in the inner flame if nickel only is present. In the presence
+of cobalt these colours are masked by the intense and characteristic
+blue yielded in both flames by that metal.</p>
+
+
+<h4>DRY ASSAY.</h4>
+
+<p>The dry assay of nickel (cobalt being at the same time determined) is
+based on the formation of a speise which will carry the cobalt, nickel,
+copper, and some of the iron of the ore in combination with arsenic. A
+speise of this kind, fused and exposed at a red heat to air, first loses
+arsenide of iron by oxidation. It is only when the iron has been
+oxidised that the arsenide of cobalt begins to be attacked; and when the
+removal of the cobalt is complete, the nickel commences to pass into the
+slag, the copper being left till last. The changes are rendered evident
+by fusion<span class='pagenum'><a name="Page_252" id="Page_252">[Pg 252]</a></span> in contact with borax. The process is as follows:&mdash;Weigh up 5
+grams of the ore, and calcine thoroughly on a roasting dish in the
+muffle. Rub up with some anthracite, and re-roast. Mix intimately with
+from 3 to 5 grams of metallic arsenic, and heat in a small covered clay
+crucible at dull redness in a muffle until no more fumes of arsenic come
+off (about 15 minutes). Take out the crucible, and inject a mixture of
+20 grams of carbonate of soda, 5 grams of flour, and 2 grams of fused
+borax. Place in the wind furnace, and raise the temperature gradually
+until the charge is in a state of tranquil fusion. Pour; when cold,
+detach the button of speise, and weigh.</p>
+
+<p>Weigh out carefully a portion of about 1 gram of it. Place a shallow
+clay dish in the muffle, and heat it to bright redness; then add about
+1.5 gram of borax glass wrapped in a piece of tissue paper; when this
+has fused, drop the piece of speise into it. Close the muffle until the
+speise has melted, which should be almost at once. The arsenide of iron
+will oxidise first, and when this has ceased the surface of the button
+brightens. Remove it from the muffle, and quench in water as soon as the
+button has solidified. The borax should be coloured slightly blue.
+Weigh: the loss is the arsenide of iron. Repeat the operation with the
+weighed button on another dish, using rather less borax. Continue the
+scorification until a film, green when cold, floating on the surface of
+the button shows that the nickel is beginning to oxidise. Cool,
+separate, and weigh the button as before. The loss is the arsenide of
+cobalt.</p>
+
+<p>If copper is absent, the speise is now arsenide of nickel.</p>
+
+<p>The weight of nickel corresponding to the arsenide got is calculated by
+multiplying by 0.607; and, similarly, the weight of the cobalt is
+ascertained by multiplying the loss in the last scorification by
+0.615.<a name="FNanchor_71_71" id="FNanchor_71_71"></a><a href="#Footnote_71_71" class="fnanchor">[71]</a> It must be remembered that the nickel and cobalt so obtained
+are derived from a fraction only of the speise yielded by the ore taken,
+so that the results must be multiplied by the weight of the whole of the
+speise, and divided by the weight of the fragment used in the
+determination. As an example, suppose 5 grams of ore gave 3.3 grams of
+speise, and 1.1 gram of this gave 0.8 gram of nickel arsenide. Then&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='right'>0.8&times;0.607</td><td align='left'>=</td><td align='right'>0.4856</td><td align='left'>gram of nickel</td></tr>
+<tr><td align='right'>0.4856&times;3.3/1.1</td><td align='left'>=</td><td align='right'>1.456</td><td align='left'>gram of nickel</td></tr>
+</table></div>
+
+
+<p>And this being obtained from 5 grams of ore is equivalent to 29.12 per
+cent.</p>
+
+<p>When copper is also present, weigh up accurately about 0.5 gram of gold,
+and place it on the scorifier with the button of nickel and copper
+arsenide, using borax as before. Scorify until<span class='pagenum'><a name="Page_253" id="Page_253">[Pg 253]</a></span> the button shows the
+bluish-green colour of a fused gold-copper alloy. Then cool, and weigh
+the button of copper and gold. The increase in weight of the gold button
+gives the copper as metal. The weight of the copper multiplied by 1.395
+is the weight of the copper arsenide (Cu<sub>3</sub>As) present. The difference
+will be the nickel arsenide.</p>
+
+<p>The student should enter the weighings in his book as follows:</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ore taken</td><td align='left'>&mdash;</td><td align='left'>grams</td></tr>
+<tr><td align='left'>Speise got</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>Speise taken</td><td align='left'>&mdash;</td><td align='left'>grams</td></tr>
+<tr><td align='left'>Arsenides of</td><td align='left'>cobalt, nickel, and copper</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+<tr><td align='center'>"</td><td align='left'>nickel and copper</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>Gold added</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>Gold and copper got</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>Showing Cobalt</td><td align='left'>&mdash;</td><td align='left'>per cent.</td></tr>
+<tr><td align='left'></td><td align='left'>Nickel</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>Copper</td><td align='left'>&mdash;</td><td align='left'>"</td></tr>
+</table></div>
+
+
+
+<h4>WET METHODS.</h4>
+
+<p><b>Solution and Separation.</b>&mdash;Two or three grams of a rich ore, or 5 to 10
+grams if poor, are taken for the assay. If much arsenic is present (as
+is usually the case), the ore must be calcined before attacking with
+acids. Transfer to a flask; and boil, first with hydrochloric acid until
+the oxides are dissolved, and then with the help of nitric acid, until
+nothing metalliferous is left. Dilute, nearly neutralise with soda, and
+separate the iron as basic acetate,<a name="FNanchor_72_72" id="FNanchor_72_72"></a><a href="#Footnote_72_72" class="fnanchor">[72]</a> as described in page 233.
+Through the filtrate pass sulphuretted hydrogen till saturated. Allow to
+settle (best overnight), filter, and wash. Transfer the precipitate to a
+beaker, and dissolve in nitric acid. Dilute with water, pass
+sulphuretted hydrogen, and filter off the precipitate, if any. Boil off
+the gas, add ammonia until a precipitate is formed, and then acidify
+somewhat strongly with acetic acid. Pass sulphuretted hydrogen in a slow
+stream until any white precipitate of zinc sulphide, there may be,
+begins to darken. Filter; to the filtrate add ammonia, and pass
+sulphuretted hydrogen. The precipitate will contain the nickel and
+cobalt as sulphides.</p>
+
+<p>Where small quantities of nickel and cobalt are present, and an
+approximate determination is sufficient, they can be concentrated as
+follows:&mdash;Remove the copper, &amp;c., by passing sulphuretted hydrogen
+through the acid solution and filtering; add ammonia<span class='pagenum'><a name="Page_254" id="Page_254">[Pg 254]</a></span> to the filtrate,
+and again pass sulphuretted hydrogen; then heat nearly to boiling, and
+filter. Dissolve the precipitate off the filter with dilute hydrochloric
+acid; the residue will contain nearly all the nickel and cobalt as
+sulphides.</p>
+
+<p><b>Separation of Nickel and Cobalt.</b>&mdash;Dissolve the sulphides separated as
+above in nitric acid; render alkaline with a solution of potash, then
+acidify with acetic acid; add a concentrated solution of <i>nitrite</i> of
+potash. The liquid after this addition must have an acid reaction. Allow
+to stand for 24 hours in a warm place. Filter off the yellow precipitate
+of nitrite of potash and cobalt, and wash with a 10 per cent. solution
+of acetate of potash. The cobalt is determined in the precipitate in the
+way described under <i>Cobalt</i>. The nickel is separated from the solution
+by boiling with sodic hydrate, filtering, and dissolving the precipitate
+in nitric acid. The solution will contain the nickel.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution, which contains the nickel free from other metals, is
+heated, and a solution of sodic hydrate added in slight excess. The
+precipitate is filtered off, washed with boiling water, dried, ignited
+at a red heat, and weighed when cold. The ignited substance is nickel
+oxide (NiO), and contains 78.67 per cent. of nickel. The oxide is a
+green powder, readily and completely soluble in hydrochloric acid, and
+without action on litmus paper. It is very easily reduced by ignition in
+hydrogen to metallic nickel.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig056.jpg" width="450" height="286" alt="Fig. 56." title="" />
+
+</div>
+
+<p>Nickel is also determined by electrolysis, as follows:&mdash;The nitric acid
+solution is rendered strongly ammoniacal, and placed under the
+electrolytic apparatus used for the copper assay. Three cells (fig. 56),
+however, must be used, coupled up for intensity, that is, with the zinc
+of one connected with the copper of the next. The electrolysis is
+allowed to go on overnight, and in the morning the nickel will be
+deposited as a bright and coherent film. A portion of the solution is
+drawn off with a pipette; if it smells of ammonia, has no blue colour,
+and gives no precipitate with ammonic sulphide, the separation is
+complete. Wash the cylinder containing the deposited metal, first with
+water and then with alcohol, as in the copper assay. Dry in the water
+oven, and weigh. The increase in weight is metallic nickel.<span class='pagenum'><a name="Page_255" id="Page_255">[Pg 255]</a></span></p>
+
+<p>As an example:&mdash;There was taken 1 gram of a nickel alloy used for
+coinage. It was dissolved in 10 c.c. of nitric acid, and diluted to 100
+c.c. with water. The copper was then precipitated by electrolysis. It
+weighed 0.734 gram. The solution, after electrolysis, was treated with
+sulphuretted hydrogen, and the remaining copper was thrown down as
+sulphide, and estimated colorimetrically. This amounted to 3-1/2
+milligrams. The filtrate was evaporated, treated with ammonia, warmed,
+and filtered. The ferric hydrate was dissolved in dilute acid, and
+reprecipitated, dried, ignited, and weighed. Its weight was 0.0310 gram.
+The two filtrates were mixed, and reduced in bulk to about 50 c.c.; a
+considerable excess of ammonia was added, and the nickel precipitated by
+electrolysis. It weighed 0.2434 gram. These quantities are equivalent
+to:</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Copper</td><td align='left'>73.75</td><td align='left'>per cent.</td></tr>
+<tr><td align='left'>Nickel</td><td align='left'>24.34</td><td align='left'>"</td></tr>
+<tr><td align='left'>Iron</td><td align='left'>2.17</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.26</td></tr>
+</table></div>
+
+
+
+<h4>VOLUMETRIC DETERMINATION.</h4>
+
+<p>An alkaline solution of potassium cyanide, to which a little potassium
+iodide has been added, can be assayed for its strength in cyanide by
+titrating with a standard solution of silver nitrate. Nickel interferes
+with this assay, doing the work of its equivalent of silver; and the
+quantity of nickel present can be calculated from the amount of its
+interference in the titration. A volumetric assay for nickel is based on
+this. It has the disadvantage of all indirect titrations in that it
+requires two standard solutions. On the other hand it gives good results
+even under unfavourable conditions, and is applicable in the presence of
+much zinc. Small quantities of cobalt will count as so much nickel, but
+larger quantities make the assay unworkable. Some of the other
+metals&mdash;lead for example&mdash;have no appreciable effect; but practically
+the solution demands a preliminary treatment which would result in their
+removal. Nevertheless it is a very satisfactory method and makes the
+determination of nickel quick and comparatively easy in most cases.</p>
+
+<p><i>The standard solution of silver nitrate</i> is made by dissolving 14.48
+grams of recrystallised silver nitrate in distilled water and diluting
+to 1 litre: 100 c.c. of this solution are equivalent to 0.25 gram of
+nickel.<a name="FNanchor_73_73" id="FNanchor_73_73"></a><a href="#Footnote_73_73" class="fnanchor">[73]</a></p>
+<p><span class='pagenum'><a name="Page_256" id="Page_256">[Pg 256]</a></span></p>
+<p><i>The standard solution of potassium cyanide</i> should be made so as to be
+exactly equal to the silver nitrate solution. This can be done as
+follows: Weigh up 12 grams of good potassium cyanide (95 per cent.),
+dissolve in water, add 50 c.c. of a 10 per cent. solution of sodium
+hydrate and dilute to 1 litre. Fill one burette with this and another
+with the solution of silver nitrate. Run 50 c.c. of the cyanide into a
+flask; add a few drops of potassium iodide solution and titrate with the
+standard silver nitrate until there is a distinct permanent yellowish
+turbidity. The titration is more fully described under <i>Cyanide</i>, p.
+165. The cyanide solution will be found rather stronger than the silver
+nitrate; dilute it so as to get the two solutions of equal value. For
+example, 51.3 c.c. of silver nitrate may have been required: then add
+1.3 c.c. of water to each 50 c.c. of the cyanide solution remaining. If
+the full 950 c.c. are available, then add to them 24.7 c.c. of water.
+After mixing, take another 50 c.c. and titrate with the silver nitrate;
+the two solutions should now be exactly equal. The cyanide solution,
+being strongly alkaline with soda, keeps very well; but its strength
+should be checked from time to time by titrating with silver nitrate;
+should there be any slight inequality in the strengths of the two
+solutions it is easily allowed for in the calculations.</p>
+
+<p><b>The titration.</b>&mdash;The solution, containing not much more than 0.1 gram
+of nickel, and free from the interfering metals, must be cooled. It is
+next neutralised and then made strongly alkaline with a solution of soda
+(NaHO); an excess of 20 or 30 c.c. suffices. This will produce a
+precipitate. The cyanide solution is now run in from a burette until the
+solution clears, after which an excess of about 20 c.c. is added. It is
+well to use some round number of c.c. to simplify the calculation. Add a
+few drops of potassium iodide solution, and run in the standard solution
+of silver nitrate from a burette. This should be done a little at a
+time, though somewhat rapidly, and with constant shaking, till a
+permanent yellow precipitate appears. If the addition of the cyanide did
+not result in a perfectly clear solution, this is because something
+besides nickel is present. The residue may be filtered off, though with
+a little practice the finishing-point may be detected with certainty in
+the presence of a small precipitate. If the student has the slightest
+doubt about a finish he should run in another 5 c.c. of the cyanide and
+again finish with silver nitrate. The second result will be the same as
+the first. For example, if 40 c.c. of cyanide and 30 c.c. of silver
+nitrate were required at the first titration, then the 45 c.c. of
+cyanide in the second titration will require 35 c.c. of silver nitrate.
+The difference between the quantities<span class='pagenum'><a name="Page_257" id="Page_257">[Pg 257]</a></span> of the two solutions used in each
+case will be 10 c.c. It is this difference in the readings of the two
+burettes which measures the quantity of nickel present. Each c.c. of the
+difference is equal to .0025 gram of nickel. But if the cyanide solution
+is not exactly equal in strength to the silver nitrate, the quantity of
+cyanide used should be calculated to its equivalent in silver nitrate
+before making the subtraction.</p>
+
+<p>The following experimental results illustrate the accuracy of the assay
+and the effect upon it of varying conditions. A solution containing 1
+gram of nickel sulphate (NiSO<sub>4</sub>.6H<sub>2</sub>O) in 100 c.c. was used. By a
+separate assay the sulphate was found to contain 22.25 per cent. of
+nickel. For the sake of simplicity the results of the experiments are
+stated in weights of nickel in grams.</p>
+
+<p><b>Effect of varying excess of Cyanide Solution.</b>&mdash;In each experiment
+there was 20 c.c. of the nickel solution, equal to .0445 gram of nickel.
+There were also 10 c.c. of soda solution, 3 or 4 drops of potassium
+iodide and sufficient water to bring the bulk to 100 c.c. before
+titrating.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Cyanide in excess</td><td align='left'>6 c.c.</td><td align='left'>4 c.c.</td><td align='left'>8 c.c.</td><td align='left'>12 c.c.</td><td align='left'>25 c.c.</td></tr>
+<tr><td align='left'>Nickel found</td><td align='left'>.0434</td><td align='left'>.0436</td><td align='left'>.0440</td><td align='left'>.0442</td><td align='left'>.0444</td></tr>
+</table></div>
+
+<p>Although the difference between the highest and lowest of these results
+is only 1 milligram, their meaning is quite obvious. The excess of
+cyanide should not be less than 20 c.c.</p>
+
+<p><b>Effect of varying the quantity of Soda.</b>&mdash;There were two series of
+experiments, one with 2 c.c. of nickel solution (= .0044 gram of
+nickel), the other with 20 c.c. The conditions were as before, except
+that the quantity of soda was varied.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Soda added</td><td align='left'></td><td align='left'>5 c.c.</td><td align='left'>15 c.c.</td><td align='left'>30 c.c.</td></tr>
+<tr><td align='left'>Nickel found,</td><td align='left'>1st series</td><td align='left'>.0037</td><td align='left'>.0042</td><td align='left'>.0045</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>2nd series</td><td align='left'>.0444</td><td align='left'>.0444</td><td align='left'>.0442</td></tr>
+</table></div>
+
+
+<p>These show that the presence of much soda, though it has only a small
+effect, is beneficial rather than otherwise. Ammonia has a bad effect,
+if present in anything like the same quantities.</p>
+
+<p><b>Effect of varying the Nickel.</b>&mdash;In experiments with 10, 20, and 40 c.c.
+of the nickel solution, the results were:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Nickel present</td><td align='left'>.0222</td><td align='left'>.0445</td><td align='left'>.0890</td></tr>
+<tr><td align='left'>Nickel found</td><td align='left'>.0220</td><td align='left'>.0442</td><td align='left'>.0884</td></tr>
+</table></div>
+
+<p><b>Effect of Zinc.</b>&mdash;In these experiments 20 c.c. of nickel solution (=
+.0445 gram of nickel), 10 c.c. of soda, 6 drops of potassium iodide and
+water to 100 c.c. were used. The excess of cyanide was purposely kept at
+from 10 to 15 c.c., which is hardly sufficient.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Zinc added</td><td align='left'>0</td><td align='left'>.25 gram.</td><td align='left'>.5 gram.</td></tr>
+<tr><td align='left'>Nickel found</td><td align='left'>.0442</td><td align='left'>.0440</td><td align='left'>.0407</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_258" id="Page_258">[Pg 258]</a></span></p>
+
+<p>On increasing the excess of cyanide to over 20 c.c. and doubling the
+quantity of soda, the experiment with 0.5 gram of zinc gave 0.441 gram
+of nickel. Hence the titration is satisfactory in the presence of zinc
+provided that not fewer than 20 or 30 c.c. of soda are used, and that
+the excess of cyanide is such that not fewer than 20 or 30 c.c. of
+silver nitrate are required in the titration. Moreover, these
+precautions should be taken whether zinc is present or not.</p>
+
+<p><b>Effect of other Metals.</b>&mdash;If metals of the first and second groups are
+present they should be removed by passing sulphuretted hydrogen and
+filtering. If <i>iron</i> is present it must be removed, since ferrous salts
+use up much cyanide, forming ferrocyanides, and ferric salts yield
+ferric hydrate, which obscures the end reaction. Hence the sulphuretted
+hydrogen must be boiled off and the iron removed as basic ferric acetate
+by the method described on p. 233. If the precipitate is bulky it should
+be dissolved in a little dilute acid, neutralised and again precipitated
+as basic acetate. The nickel will be in the two filtrates. In the
+absence of manganese and cobalt the titration may be made without
+further separation.</p>
+
+<p><i>Manganese</i> does not directly interfere, but the precipitated hydrate,
+which rapidly darkens through atmospheric oxidation, obscures the end
+reaction. It may be removed by passing sulphuretted hydrogen through the
+filtrate from the acetate separation: sulphides of nickel, cobalt and
+zinc will be precipitated, whilst manganese remains in solution: the
+addition of more sodium acetate may assist the precipitation. The
+precipitate must be filtered off and dissolved in nitric acid: the
+solution should be evaporated to dryness. The filtrate may retain a
+little nickel; if so, add ammonia till alkaline, then acidify with
+acetic acid and again filter; any small precipitate obtained here should
+be added to that first obtained.</p>
+
+<p>It is only when <i>cobalt</i> is present that any further separation is
+required. Cobalt hydrate takes up oxygen from the air, and on adding
+potassium cyanide some may refuse to dissolve; and the solution itself
+acquires a brown colour, which becomes deeper on standing. At this stage
+the cobalt is easily separated. The solution containing the nickel and
+cobalt with no great excess of acid, is made alkaline by adding 20 c.c.
+of soda exactly as in preparing for a titration. So, too, the solution
+of cyanide is added so as to have an excess of 20 or 30 c.c.; the
+solution may have a brown colour, but if it is not quite clear it <i>must</i>
+be filtered. Then warm (boiling is not needed) and add from 50 to 100
+c.c. of bromine water. This throws down all the nickel as black
+peroxide<span class='pagenum'><a name="Page_259" id="Page_259">[Pg 259]</a></span> in a condition easy to filter. Filter it off and wash with
+water. The precipitate can be dissolved off the filter with the greatest
+ease by a little warm sulphurous acid. The filtrate and washings, boiled
+till free from sulphurous acid, yield the nickel as sulphate in a clean
+condition.</p>
+
+<p><b>Determination of Nickel in Nickel Sulphate Crystals.</b>&mdash;Take 0.5 gram of
+the salt, dissolve in 50 c.c. of water and add 25 c.c. of solution of
+soda. Run in from a burette, say, 60 c.c. "cyanide." Add a few drops of
+potassium iodide and titrate back with "silver nitrate." Suppose 15.5
+c.c. of the latter is required. Then 15.5 c.c. subtracted from 60 c.c.
+leaves 44.5 c.c., and since 100 c.c. = 0.25 gram of nickel, 44.5 c.c.
+will equal 0.11125 gram of nickel. This in 0.5 gram of the salt equals
+22.25 per cent.</p>
+
+<p><b>Determination of Nickel in German Silver.</b>&mdash;Weigh up 0.5 gram of the
+alloy, and dissolve in a dish with 5 or 10 c.c. of dilute nitric acid.
+Add 5 c.c. of dilute sulphuric acid and evaporate till all the nitric
+acid is removed. Cool, take up with 50 c.c. of water, and when dissolved
+pass sulphuretted hydrogen through the solution. Filter off the
+precipitate and wash with water containing sulphuretted hydrogen and
+dilute sulphuric acid. Boil down the filtrate and washings to get rid of
+the excess of the gas; add some nitric acid and continue the boiling.
+Cool, neutralise the excess of acid with soda, add 1 gram of sodium
+acetate and boil. Filter off the precipitate which contains the iron.
+The filtrate, cooled and rendered alkaline with soda, is ready for the
+titration.</p>
+
+
+<h4>COBALT</h4>
+
+<p>Occurs less abundantly than nickel. Its chief ores are smaltite and
+cobaltite, which are arsenides of cobalt, with more or less iron,
+nickel, and copper. It also occurs as arseniate in erythrine, and as
+oxide in asbolan or earthy cobalt, which is essentially a wad carrying
+cobalt.</p>
+
+<p>It is mainly used in the manufacture of smalts for imparting a blue
+colour to glass and enamels. The oxide of cobalt forms coloured
+compounds with many other metallic oxides. With oxide of zinc it forms
+"Rinman's green"; with aluminia, a blue; with magnesia, a pink. This
+property is taken advantage of in the detection of substances before the
+blow-pipe.</p>
+
+<p>The compounds of cobalt in most of their properties closely resemble
+those of nickel, and the remarks as to solution and separation given for
+the latter metal apply here. Solutions of cobalt are pink, whilst those
+of nickel are green.<span class='pagenum'><a name="Page_260" id="Page_260">[Pg 260]</a></span></p>
+
+<p>The detection of cobalt, even in very small quantity, is rendered easy
+by the strong blue colour which it gives to the borax bead, both in the
+oxidising and in the reducing flame. It is concentrated from the ore in
+the same way as nickel, and should be separated from that metal by means
+of potassic nitrite in the way described. The dry assay of cobalt has
+been given under <i>Nickel</i>.</p>
+
+
+<h4>GRAVIMETRIC METHOD.</h4>
+
+<p>The yellow precipitate from the potassium nitrite, after being washed
+with the acetate of potash, is washed with alcohol, dried, transferred
+to a weighed porcelain crucible, and cautiously ignited with an excess
+of strong sulphuric acid. The heat must not be sufficient to decompose
+the sulphate of cobalt, which decomposition is indicated by a blackening
+of the substance at the edges. The salt bears a low red heat without
+breaking up. If blackening has occurred, moisten with sulphuric acid,
+and ignite again. Cool and weigh. The substance is a mixture of the
+sulphates of cobalt and potash (2CoSO<sub>4</sub> + 3K<sub>2</sub>SO<sub>4</sub>), and contains
+14.17 per cent. of cobalt.</p>
+
+<p>Cobalt is also gravimetrically determined, like nickel, by electrolysis,
+or by precipitation with sodic hydrate. In the latter case, the ignited
+oxide will be somewhat uncertain in composition, owing to its containing
+an excess of oxygen. Consequently, it is better to reduce it by igniting
+at a red heat in a current of hydrogen and to weigh it as metallic
+cobalt.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. In the dry assay of an ore containing cobalt, nickel, and copper, the
+following results were obtained. Calculate the percentages. Ore taken, 5
+grams. Speise formed, 0.99 gram. Speise taken. 0.99 gram. Arsenides of
+cobalt, nickel, and copper got, 0.75 gram. Arsenide of nickel and copper
+got, 0.54 gram. Gold added, 0.5 gram. Gold and copper got, 0.61 gram.</p>
+
+<p>2. Calculate the percentage composition of the following compounds:
+Co<sub>2</sub>As, Ni<sub>2</sub>As, and Cu<sub>2</sub>As.</p>
+
+<p>3. A sample of mispickel contains 7 per cent. cobalt. What weight of the
+mixed sulphates of potash and cobalt will be obtained in a gravimetric
+determination on 1 gram of the ore?</p>
+
+<p>4. 0.3157 gram of metal was deposited by the electrolysis of a nickel
+and cobalt solution. On dissolving in nitric acid and determining the
+cobalt 0.2563 gram of potassium and cobalt sulphates were got. Find the
+weights of cobalt and nickel present in the deposit.</p>
+
+<p>5. What should be the percentage composition of pure cobaltite, its
+formula being CoAsS?<span class='pagenum'><a name="Page_261" id="Page_261">[Pg 261]</a></span></p>
+
+
+<h4>ZINC.</h4>
+
+<p>Zinc occurs in nature most commonly as sulphide (blende); it also occurs
+as carbonate (calamine) and silicate (smithsonite). Each of these is
+sufficiently abundant to be a source of the metal.</p>
+
+<p>The metal is known in commerce as "spelter" when in ingots, and as sheet
+zinc when rolled. It is chiefly used in the form of alloys with copper,
+which are known as brasses. It is also used in the form of a thin film,
+to protect iron goods from rusting&mdash;galvanised iron.</p>
+
+<p>Ores of zinc, more especially blende, are met with in most lead, copper,
+gold, and silver mines, in larger or small quantities scattered through
+the lodes. Those ores which generally come under the notice of the
+assayer are fairly rich in zinc; but alloys and metallurgical products
+contain it in very varying proportions.</p>
+
+<p>Zinc itself is readily soluble in dilute acids; any residue which is
+left after boiling with dilute hydrochloric or sulphuric acid consists
+simply of the impurities of the metal; this is generally lead.</p>
+
+<p>All zinc compounds are either soluble in, or are decomposed by, boiling
+with acids, the zinc going into solution. Zinc forms only one series of
+salts, and these are colourless. Their chief characteristic is
+solubility in an alkaline solution, from which sulphuretted hydrogen
+produces a white precipitate of zinc sulphide. Zinc is detected by
+dissolving the substance in hydrochloric or nitric acid, boiling, and
+adding sodic hydrate in excess, filtering, and adding ammonic sulphide
+to the filtrate. The precipitate contains the zinc, which can be
+dissolved out by boiling with dilute sulphuric acid, and detected by the
+formation of a white precipitate on the addition of potassic
+ferrocyanide.</p>
+
+<p>The dry assay of zinc can only be made indirectly, and is
+unsatisfactory. Zinc is volatile, and at the temperature of its
+reduction is a gas. It is impracticable to condense the vapour so as to
+weigh the metal, consequently its amount is determined by loss. The
+following method gives approximate results: Take 10 grams of the dried
+and powdered ore and roast, first at a low temperature and afterwards at
+a higher one, with the help of carbonate of ammonia to decompose the
+sulphates formed; cool and weigh. The metals will be present as oxides.
+Mix with 2 grams of powdered charcoal and charge into a black-lead
+crucible heated to whiteness, cover loosely, and leave in the furnace
+for about a quarter of an hour. Uncover and calcine the residue, cool
+and weigh. The loss in weight multiplied by 8.03 gives the percentage of
+zinc in the ore.<span class='pagenum'><a name="Page_262" id="Page_262">[Pg 262]</a></span></p>
+
+
+<h4>WET METHODS.</h4>
+
+<p>Solution and separation may be effected as follows: Treat 1 or 3 grams
+of the substance with 10 or 30 c.c. of hydrochloric acid or aqua regia;
+evaporate to dryness; take up with 10 c.c. of hydrochloric acid and
+dilute to 100 c.c.; heat nearly to boiling; saturate with sulphuretted
+hydrogen; filter, and wash with water acidulated with hydrochloric acid.
+Boil off the sulphuretted hydrogen and peroxidise with a few drops of
+nitric acid. Cool; add caustic soda till nearly, but not quite,
+neutralised, and separate the iron as basic acetate by the method
+described under <i>Iron</i>. To the filtrate add ammonia till alkaline, and
+pass sulphuretted hydrogen. Allow to settle and decant on to a filter.
+Dissolve off the precipitate from the filter with hot dilute
+hydrochloric acid. The solution will contain the zinc, together with any
+manganese the ore contained, and, perhaps, traces of nickel and cobalt.
+If the zinc is to be determined volumetrically, and manganese is
+present, this latter is separated with carbonate of ammonia, as
+described further on; but if a gravimetric method is used, and only
+small quantities of manganese are present, it is better to proceed as if
+it were absent, and to subsequently determine its amount, which should
+be deducted.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution containing the zinc is contained in an evaporating dish,
+and freed from sulphuretted hydrogen by boiling, and, if necessary, from
+an excess of acid by evaporation. The evaporating dish must be a large
+one. Cautiously add sodium carbonate to the hot, moderately dilute
+solution, until the liquid is distinctly alkaline, and boil. Allow the
+precipitate to settle, decant on to a filter, and wash with hot water.
+Dry, transfer to a porcelain crucible (cleaning the paper as much as
+possible), add the ash, ignite, and weigh. The substance weighed is
+oxide of zinc, which contains 80.26 per cent. of the metal. It is a
+white powder, becoming yellow when heated. It must not show an alkaline
+reaction when moistened. If it contains manganese this metal will be
+present as sesquioxide (Mn<sub>2</sub>O<sub>3</sub>). Its amount can be determined by
+dissolving in dilute acid and boiling with an excess of sodic hydrate.
+The oxide of manganese will be precipitated, and can be ignited and
+weighed. Its weight multiplied by 1.035 must be deducted from the weight
+of oxide of zinc previously obtained. The results yielded by the
+gravimetric determination are likely to be high, since the basic
+carbonate of<span class='pagenum'><a name="Page_263" id="Page_263">[Pg 263]</a></span> zinc frequently carries down with it more or less soda
+which is difficult to wash off.</p>
+
+
+<h4>VOLUMETRIC DETERMINATION</h4>
+
+<p>This method is based on the facts that zinc salts in an acid solution
+decompose potassium ferrocyanide, forming a white insoluble zinc
+compound; and that an excess of the ferrocyanide can be detected by the
+brown coloration it strikes with uranium acetate. The method resembles
+in its working the bichromate iron assay. The standard solution of
+potassium ferrocyanide is run into a hot hydrochloric acid solution of
+the zinc until a drop of the latter brought in contact with a drop of
+the indicator (uranium acetate) on a white plate strikes a brown colour.
+The quantity of zinc in the solution must be approximately known; run in
+a little less of the ferrocyanide than is expected will be necessary;
+test a drop or two of the assay, and then run in, one or two c.c. at a
+time, until the brown colour is obtained. Add 5 c.c. of a standard zinc
+solution, equivalent in strength to the standard "ferrocyanide,"
+re-titrate, and finish off cautiously. Of course 5 c.c. must be deducted
+from the reading on the burette. The precipitate of zinc ferrocyanide
+formed in the assay solution is white; but if traces of iron are
+present, it becomes bluish. If the quantity of ferrocyanide required is
+known within a few c.c., the finishing point is exactly determined in
+the first titration without any addition of the standard zinc solution.
+Unfortunately this titration serves simply to replace the gravimetric
+determination, and does not, as many volumetric processes do, lessen the
+necessity for a complete separation of any other metals which are
+present. Most metals give precipitates with ferrocyanide of potassium in
+acid solutions. If the conditions are held to, the titration is a fairly
+good one, and differences in the results of an assay will be due to
+error in the separation. Ferric hydrate precipitated in a fairly strong
+solution of zinc will carry with it perceptible quantities of that
+metal. Similarly, large quantities of copper precipitated as sulphide by
+means of sulphuretted hydrogen will carry zinc with it, except under
+certain nicely drawn conditions. When much copper is present it is best
+separated in a nitric acid solution by electrolysis. The titration of
+the zinc takes less time, and, with ordinary working, is more
+trustworthy than the gravimetric method.</p>
+
+<p><i>The standard ferrocyanide solution</i> is made by dissolving 43.2 grams of
+potassium ferrocyanide (K<sub>4</sub>FeCy<sub>6</sub>.3H<sub>2</sub>O) in water, and diluting to
+a litre. One hundred c.c. are equal to 1 gram of zinc.<span class='pagenum'><a name="Page_264" id="Page_264">[Pg 264]</a></span></p>
+
+<p><i>The standard zinc solution</i> is made by dissolving 10 grams of pure zinc
+in 50 c.c. of hydrochloric acid and 100 or 200 c.c. of water, and
+diluting to 1 litre, or by dissolving 44.15 grams of zinc sulphate
+(ZnSO<sub>4</sub>.7H<sub>2</sub>O) in water with 30 c.c. of hydrochloric acid, and
+diluting to 1 litre. One hundred c.c. will contain 1 gram of zinc.</p>
+
+<p><i>The uranium acetate solution</i> is made by dissolving 0.2 gram of the
+salt in 100 c.c. of water.</p>
+
+<p>To standardise the "ferrocyanide" measure off 50 c.c. of the standard
+zinc solution into a 10 oz. beaker, dilute to 100 c.c., and heat to
+about 50&deg; C. (not to boiling). Run in 47 or 48 c.c. of the
+"ferrocyanide" solution from an ordinary burette, and finish off
+cautiously. Fifty divided by the quantity of "ferrocyanide" solution
+required gives the standard.</p>
+
+<p>In assaying ores, &amp;c., take such quantity as shall contain from 0.1 to 1
+gram of zinc, separate the zinc as sulphide, as already directed.
+Dissolve the sulphide off the filter with hot dilute hydrochloric acid,
+which is best done by a stream from a wash bottle. Evaporate the
+filtrate to a paste, add 5 c.c. of dilute hydrochloric acid, dilute to
+100 c.c. or 150 c.c., heat to about 50&deg; C., and titrate. Manganese, if
+present, counts as so much zinc, and must be specially separated, since
+it is not removed by the method already given. The following method will
+effect its removal. To the hydrochloric acid solution of the zinc and
+manganese add sodium acetate in large excess and pass sulphuretted
+hydrogen freely. Allow to settle, filter off the zinc sulphide and wash
+with sulphuretted hydrogen water. The precipitate, freed from manganese,
+is then dissolved in hydrochloric acid and titrated.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of the assay:&mdash;</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;Using 20 c.c. of the standard zinc
+solution, 5 c.c. of dilute hydrochloric acid, and diluting to 100 c.c.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg; C.</td><td align='left'>30&deg; C.</td><td align='left'>70&deg; C.</td><td align='left'>100&deg; C.</td></tr>
+<tr><td align='left'>"Ferrocyanide" required</td><td align='left'>20.6 c.c.</td><td align='left'>20.3 c.c.</td><td align='left'>20.3 c.c.</td><td align='left'>20.3 c.c.</td></tr>
+</table></div>
+
+
+<p>The solution can be heated to boiling before titrating without
+interfering with the result; but it is more convenient to work with the
+solution at about 50&deg; C. Cold solutions must not be used.</p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;These were all titrated at about 50&deg; C., and
+were like the last, but with varying bulk.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>25.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Ferrocyanide" required</td><td align='left'>20.2</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.3</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td></tr>
+</table></div>
+
+<p>Any ordinary variation in bulk has no effect.<span class='pagenum'><a name="Page_265" id="Page_265">[Pg 265]</a></span></p>
+
+<p><b>Effect of Varying Hydrochloric Acid.</b>&mdash; With 100 c.c. bulk and varying
+dilute hydrochloric acid the results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acid added</td><td align='left'>0.0</td><td align='left'>c.c.</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>5.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Ferrocyanide" required</td><td align='left'>24.4</td><td align='left'>"</td><td align='left'>20.2</td><td align='left'>"</td><td align='left'>20.3</td><td align='left'>"</td><td align='left'>20.3</td><td align='left'>"</td><td align='left'>20.7</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Foreign Salts.</b>&mdash;The experiments were carried out under the
+same conditions as the others. Five grams each of the following salts
+were added:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt added</td><td align='left'>Ammonic chloride.</td><td align='left'>Ammonic sulphate.</td><td align='left'>Sodium chloride.</td><td align='left'>Sodium sulphate.</td></tr>
+<tr><td align='left'>"Ferrocyanide" required</td><td align='left'>20.3 c.c.</td><td align='left'>20.5 c.c.</td><td align='left'>20.6 c.c.</td><td align='left'>20.4 c.c.</td></tr>
+<tr><td align='left'>Salt added</td><td align='left'>Potassium Nitrate.</td><td align='left'>Magnesium sulphate.</td><td align='left'>Nil.</td></tr>
+<tr><td align='left'>"Ferrocyanide" required</td><td align='left'>20.2 c.c.</td><td align='left'>20.4 c.c.</td><td align='left'>20.4 c.c.</td></tr>
+</table></div>
+
+<p>In a series of experiments in which foreign metals were present to the
+extent of 0.050 gram in each, with 20 c.c. of zinc solution and 5 c.c.
+of dilute hydrochloric acid, those in which copper sulphate, ferrous
+sulphate, and ferric chloride were used, gave (as might be expected) so
+strongly coloured precipitates that the end reaction could not be
+recognised. The other results were:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>"Ferrocyanide" required.</td></tr>
+<tr><td align='center'>With</td><td align='left'></td><td align='left'>nothing added.</td><td align='left'></td><td align='left'>20.3 c.c.</td></tr>
+<tr><td align='center'> "</td><td align='left'>0.050</td><td align='center'>gram</td><td align='left'>lead (as chloride)</td><td align='left'>20.9 "</td></tr>
+<tr><td align='center'> "</td><td align='left'>0.050</td><td align='center'>"</td><td align='left'>manganese (as sulphate)</td><td align='left'>25.5 "</td></tr>
+<tr><td align='center'> "</td><td align='left'>0.050</td><td align='center'>"</td><td align='left'>cadmium (as sulphate)</td><td align='left'>23.5 "</td></tr>
+<tr><td align='center'> "</td><td align='left'>0.050</td><td align='center'>"</td><td align='left'>nickel (as sulphate)</td><td align='left'>26.2 "</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Zinc.</b>&mdash;These were titrated under the usual
+conditions, and gave the following results:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Zinc added</td><td align='left'>1.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td></tr>
+<tr><td align='left'>"Ferrocyanide" required</td><td align='left'>1.1 "</td><td align='left'>10.2 "</td><td align='left'>20.3 "</td><td align='left'>50.6 "</td><td align='left'>101.0 "</td></tr>
+</table></div>
+
+
+<p><b>Determination of Zinc in a Sample of Brass.</b>&mdash;Take the solution from
+which the copper has been separated by electrolysis and pass
+sulphuretted hydrogen until the remaining traces of copper and the lead
+are precipitated, filter, boil the solution free from sulphuretted
+hydrogen, put in a piece of litmus paper, and add sodic hydrate solution
+in slight excess; add 10 c.c. of dilute hydrochloric acid (which should
+render the solution acid and clear); warm, and titrate.</p>
+
+<p>A sample of 0.5 gram of brass treated in this manner required 16.4 c.c.
+of "ferrocyanide" (standard 100 c.c. = 0.9909 zinc), which equals 0.1625
+gram of zinc or 32.5 per cent.<span class='pagenum'><a name="Page_266" id="Page_266">[Pg 266]</a></span></p>
+
+<p><b>Determination of Zinc in Blende.</b>&mdash;Dissolve 1 gram of the dried and
+powdered sample in 25 c.c. of nitric acid with the help of two or three
+grams of potassium chlorate dissolved in the acid. Evaporate to complete
+dryness, taking care to avoid spirting. Add 7 grams of powdered ammonium
+chloride, 15 c.c. of strong ammonia and 25 c.c. of boiling water; boil
+for one minute and see that the residue is all softened. Filter through
+a small filter, and wash thoroughly with small quantities of a hot one
+per cent. solution of ammonium chloride. Add 25 c.c. of hydrochloric
+acid to the filtrate. Place in the solution some clean lead foil, say 10
+or 20 square inches. Boil gently until the solution has been colourless
+for three or four minutes. Filter, wash with a little hot water; and
+titrate with standard ferrocyanide.</p>
+
+<p><b>Determination of Zinc in Silver Precipitate.</b>&mdash;This precipitate
+contains lead sulphate, silver, copper, iron, zinc, lime, &amp;c. Weigh up 5
+grams of the sample, and extract with 30 c.c. of dilute sulphuric acid
+with the aid of heat. Separate the copper with sulphuretted hydrogen,
+peroxidise the iron with a drop or two of nitric acid, and separate as
+acetate. Render the filtrate ammoniacal, pass sulphuretted hydrogen;
+warm, and filter. Dissolve the precipitated zinc sulphide in dilute
+hydrochloric acid, evaporate, dilute, and titrate. Silver precipitates
+carry about 2.5 per cent. of zinc.</p>
+
+
+<h4>GASOMETRIC METHOD.</h4>
+
+<p>Metallic zinc is readily soluble in dilute hydrochloric or sulphuric
+acid, hydrogen being at the same time evolved.<a name="FNanchor_74_74" id="FNanchor_74_74"></a><a href="#Footnote_74_74" class="fnanchor">[74]</a> The volume of the
+hydrogen evolved is obviously a measure of the amount of zinc present in
+the metallic state. The speed with which the reaction goes on (even in
+the cold) and the insolubility of hydrogen renders this method of assay
+a convenient one. It is especially applicable to the determination of
+the proportion of zinc in zinc dust. The apparatus described in the
+chapter on gasometric method is used. The method of working is as
+follows: Fill the two burettes with cold water to a little above the
+zero mark, place in the bottle about 0.25 gram of the substance to be
+determined, and in the inner phial or test tube 5 c.c. of dilute
+sulphuric acid; cork the apparatus tightly and allow to stand for a few
+minutes; then bring the water to the same level in the two burettes by
+running out through the clip at the bottom. Read off the level of the
+liquid in the graduated burette. Turn the<span class='pagenum'><a name="Page_267" id="Page_267">[Pg 267]</a></span> bottle over sufficiently to
+spill the acid over the zinc, and then run water out of the apparatus so
+as to keep the liquid in the two burettes at the same level, taking care
+not to run it out more quickly than the hydrogen is being generated.
+When the volume of gas ceases to increase, read off the level of the
+liquid, deduct the reading which was started with; the difference gives
+the volume of hydrogen evolved. At the same time read off the volume of
+air in the "volume corrector," which must be fixed alongside the gas
+burettes. Make the correction. For example: A piece of zinc weighing
+0.2835 gram was found to give 99.9 c.c. of gas at a time when the
+corrector read 104 c.c.<a name="FNanchor_75_75" id="FNanchor_75_75"></a><a href="#Footnote_75_75" class="fnanchor">[75]</a> Then the corrected volume is</p>
+
+<p>
+<span style="margin-left: 4em;">104 : 100 :: 99.9 : <i>x</i>.</span><br />
+<span style="margin-left: 14em;"><i>x</i> = 96.0 c.c.</span><br />
+</p>
+
+
+<p>100 c.c. of hydrogen at 0&deg; C. and 760 mm. is equivalent to 0.2912 gram
+of zinc; therefore the quantity of zinc found is</p>
+
+<p>
+<span style="margin-left: 4em;">100 : 96 :: 0.2912 : <i>x</i>.</span><br />
+<span style="margin-left: 14.5em;"><i>x</i> = 0.2795 gram of zinc.</span><br />
+</p>
+
+<p>This being contained in 0.2835 gram of metal is equivalent to 98.5 per
+cent.</p>
+
+<p>As an example of a determination in which reducing the volume of
+liberated hydrogen to 0&deg; C. and 760 mm. is avoided, the following may be
+taken:&mdash;</p>
+
+<p>
+<span style="margin-left: 4em;">0.2315 gram of pure zinc gave 82.1 c.c. of gas;</span><br />
+<span style="margin-left: 4em;">and the volume of air in the corrector was 103.6 c.c.</span><br />
+<br />
+<span style="margin-left: 4em;">0.2835 gram of the assay gave 99.9 c.c. of gas;</span><br />
+<span style="margin-left: 4em;">and the volume of air in the corrector was 104.0 c.c.;</span><br />
+<br />
+<span style="margin-left: 4em;">104 : 103.6 :: 99.9 : <i>x</i>.</span><br />
+<span style="margin-left: 14.5em;"><i>x</i> = 99.5 c.c.</span><br />
+</p>
+
+<p>This is the volume of gas got in the assay if measured under the same
+conditions as the standard,</p>
+
+<p>
+<span style="margin-left: 4em;">82.1 : 99.5 :: 0.2315 : <i>x</i>.</span><br />
+<span style="margin-left: 14.5em;"><i>x</i> = 0.2806.</span><br />
+<span style="margin-left: 4em;">Then 0.2835 : 0.2806 :: 100: <i>x</i>.</span><br />
+<span style="margin-left: 14.5em;"><i>x</i> = 98.9 per cent.</span><br />
+</p>
+
+<p>As these assays can be made quickly, it is well for the sake of greater
+accuracy to make them in duplicate, and to take the mean of the
+readings. One set of standardisings will do for any number of assays.
+The student must carefully avoid unnecessary handling of the bottle in
+which the zinc is dissolved.</p>
+
+<p><b>Colorimetric Method.</b>&mdash;Zinc salts being colourless, there is no
+colorimetric determination.<span class='pagenum'><a name="Page_268" id="Page_268">[Pg 268]</a></span></p>
+
+
+<h4>EXAMINATION OF COMMERCIAL ZINC.</h4>
+
+<p>Take 20 grams of zinc, and dissolve them in dilute nitric acid; boil,
+allow to settle; filter; wash, dry; ignite the precipitate, if any, and
+weigh as oxide of tin. Examine this for arsenic.</p>
+
+<p><b>Lead.</b>&mdash;Add ammonia and carbonate of ammonia to the liquid, and boil,
+filter off the precipitate, wash with hot water. Digest the precipitate
+with dilute sulphuric acid; filter, wash, and weigh the sulphate of
+lead.</p>
+
+<p><b>Iron.</b>&mdash;To the filtrate from the sulphate of lead add ammonia, and pass
+sulphuretted hydrogen; digest, and filter. (Save the filtrate.) Dissolve
+the precipitate in hydrochloric acid, oxidise with nitric acid, and
+precipitate with ammonia. Wash, ignite, and weigh as ferric oxide.
+Calculate to iron.</p>
+
+<p><b>Arsenic.</b>&mdash;To the filtrate from the sulphide of iron add hydrochloric
+acid in slight excess; filter off, and wash the precipitate. Rinse it
+back into the beaker, dissolve in nitric acid, filter from the sulphur,
+and add ammonia, in excess, and magnesia mixture. Filter off the
+ammonic-magnesic arsenate, and wash with dilute ammonia. Dry, ignite
+with nitric acid, and weigh as magnesic pyrarsenate. Calculate to
+arsenic, and add to that found with the tin.</p>
+
+<p><b>Copper.</b>&mdash;To the filtrate from the ammonia and ammonic carbonate add
+sulphuric acid in small excess, and pass sulphuretted hydrogen. Allow to
+settle, filter, and wash. Rinse the precipitate into a beaker, boil with
+dilute sulphuric acid, and filter. (Save the filtrate.) Dry, burn the
+paper with the precipitate, treat with a drop or two of nitric acid,
+ignite, and weigh as copper oxide. Calculate to copper.</p>
+
+<p><b>Cadmium.</b>&mdash;To the filtrate from the sulphide of copper add ammonia, so
+as to nearly neutralise the excess of acid, and pass sulphuretted
+hydrogen. Collect and weigh the precipitate as cadmium sulphide, as
+described under <i>Cadmium</i>.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. What weight of hydrogen will be evolved in dissolving 1 gram of zinc
+in dilute sulphuric acid?</p>
+
+<p>2. How many c.c. would this quantity of hydrogen measure at 0&deg; C. and
+760 m.m.? (1 litre weighs 0.0896 gram).</p>
+
+<p>3. 0.23 gram of zinc are found to give 77.9 c.c. of hydrogen. In another
+experiment under the same conditions 80.2 c.c. are got. What weight of
+zinc was used for the second experiment?<span class='pagenum'><a name="Page_269" id="Page_269">[Pg 269]</a></span></p>
+
+<p>4. A sample of blende is found to contain 55 per cent. of zinc. What
+percentage of zinc sulphide did the sample contain?</p>
+
+<p>5. How much metallic lead would be precipitated from a solution of lead
+acetate by 1 gram of zinc?</p>
+
+
+<h4>CADMIUM.</h4>
+
+<p>Cadmium occurs in nature as cadmium sulphide in greenockite, CdS, which
+is very rare. It is widely diffused in calamine, blende, and other zinc
+ores, forming, in some cases, as much as 2 or 3 per cent. of the ore.
+Oxide of cadmium forms the "brown blaze" of the zinc smelters.</p>
+
+<p>Sulphide of cadmium is used as a pigment (cadmium yellow); and the metal
+and some of its salts are useful reagents.</p>
+
+<p>The salts of cadmium closely resemble those of zinc. The hydrate,
+however, is insoluble in excess of potash, and the sulphide is insoluble
+in dilute acids. It forms only one series of salts.</p>
+
+<p>Cadmium is detected by giving with sulphuretted hydrogen in solutions,
+not too strongly acid, a yellow precipitate, which is insoluble in
+solutions of the alkalies, alkaline sulphides, or cyanide of potassium.</p>
+
+<p><b>Solution and Separation.</b>&mdash;Substances containing cadmium are soluble in
+acids. The solution is evaporated to dryness (to render any silica that
+may be present insoluble) and taken up with 10 c.c. of dilute
+hydrochloric acid. Dilute to 100 c.c., and pass sulphuretted hydrogen.
+Filter, digest the precipitate with soda, wash, and boil with dilute
+sulphuric acid. Filter; the filtrate contains the cadmium and, possibly,
+a small quantity of zinc, from which it is best separated by
+reprecipitating with sulphuretted hydrogen.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution containing the cadmium freed from the other metals is
+precipitated with sulphuretted hydrogen in a moderately-acid solution.
+The precipitate is collected on a weighed filter, and washed, first with
+an acid solution of sulphuretted hydrogen, and afterwards with water. It
+is dried at 100&deg; C. and weighed. If free sulphur is suspected to be
+present, extract with bisulphide of carbon, and again weigh. The residue
+is cadmium sulphide, which contains 77.78 per cent. of cadmium. It is a
+yellow powder insoluble in solutions of the alkalies, alkaline
+sulphides, or cyanide of potassium. It dissolves readily in acid. It
+cannot be ignited in a current of hydrogen without loss.<span class='pagenum'><a name="Page_270" id="Page_270">[Pg 270]</a></span></p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>The solution containing the cadmium is concentrated by evaporation, and
+mixed with an excess of oxalic acid and alcohol. The precipitate is
+filtered, washed with alcohol, dissolved in hot hydrochloric acid, and
+titrated with permanganate of potassium.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_64_64" id="Footnote_64_64"></a><a href="#FNanchor_64_64"><span class="label">[64]</span></a> When chromium is present some of the iron may escape
+precipitation but it can be recovered from the solution by means of
+ammonic sulphide.</p></div>
+
+<div class="footnote"><p><a name="Footnote_65_65" id="Footnote_65_65"></a><a href="#FNanchor_65_65"><span class="label">[65]</span></a>
+</p><p>
+(1) 10FeSO<sub>4</sub> + 2KMnO<sub>4</sub> + 8H<sub>2</sub>SO<sub>4</sub> = 5Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 2MnSO<sub>4</sub> +
+K<sub>2</sub>SO<sub>4</sub> + 8H<sub>2</sub>O.
+(2) 6FeCl<sub>2</sub> + K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> + 14HCl = 3Fe<sub>2</sub>Cl<sub>6</sub> + Cr<sub>2</sub>Cl<sub>6</sub> + 2KCl +
+7H<sub>2</sub>O.</p></div>
+
+<div class="footnote"><p><a name="Footnote_66_66" id="Footnote_66_66"></a><a href="#FNanchor_66_66"><span class="label">[66]</span></a>
+</p><p><br />
+<span style="margin-left: 1em;">(1) Fe<sub>2</sub>Cl<sub>6</sub> + SnCl<sub>2</sub> = 2FeCl<sub>2</sub> + SnCl<sub>4</sub>.</span><br />
+<span style="margin-left: 1em;">(2) Fe<sub>2</sub>Cl<sub>6</sub> + SH<sub>2</sub> = 2FeCl<sub>2</sub> + 2HCl + S.</span><br />
+<span style="margin-left: 1em;">(3) Fe<sub>2</sub>Cl<sub>6</sub> + Na<sub>2</sub>SO<sub>3</sub> + H<sub>2</sub>O = 2FeCl<sub>2</sub> + Na<sub>2</sub>SO<sub>4</sub> + 2HCl.</span><br />
+<span style="margin-left: 1em;">(4) Fe<sub>2</sub>Cl<sub>6</sub> + Zn = 2FeCl<sub>2</sub> + ZnCl<sub>2</sub>.</span><br /></p></div>
+
+<div class="footnote"><p><a name="Footnote_67_67" id="Footnote_67_67"></a><a href="#FNanchor_67_67"><span class="label">[67]</span></a> 20 grams of stannous chloride and 20 c.c. of dilute
+hydrochloric acid are diluted to one litre.</p></div>
+
+<div class="footnote"><p><a name="Footnote_68_68" id="Footnote_68_68"></a><a href="#FNanchor_68_68"><span class="label">[68]</span></a> The maximum reducing effect of zinc is obtained by
+exposing as large a surface as possible of the metal in a hot
+concentrated solution containing but little free acid (Thorpe).</p></div>
+
+<div class="footnote"><p><a name="Footnote_69_69" id="Footnote_69_69"></a><a href="#FNanchor_69_69"><span class="label">[69]</span></a> About 5 inches in diameter.</p></div>
+
+<div class="footnote"><p><a name="Footnote_70_70" id="Footnote_70_70"></a><a href="#FNanchor_70_70"><span class="label">[70]</span></a> 61: 60:: 59: 58.13.
+</p><p>
+The iron in the ore is, then, the same in amount as that in 58.13 c.c.
+of the ferric chloride solution; and since 100 c.c. of the latter
+contain 1 gram of iron, 58.13 c.c. of the same contains 0.5813 gram of
+iron; and, further, if 1 gram of ore carries this amount of iron, 100
+grams of ore will obviously give 58.13 grams of iron.</p></div>
+
+<div class="footnote"><p><a name="Footnote_71_71" id="Footnote_71_71"></a><a href="#FNanchor_71_71"><span class="label">[71]</span></a> These compounds are Ni<sub>2</sub>As and Co<sub>2</sub>As.</p></div>
+
+<div class="footnote"><p><a name="Footnote_72_72" id="Footnote_72_72"></a><a href="#FNanchor_72_72"><span class="label">[72]</span></a> With large quantities of iron the ferric precipitate
+should be re-dissolved and re-precipitated. The filtrate must be added
+to the original filtrate.</p></div>
+
+<div class="footnote"><p><a name="Footnote_73_73" id="Footnote_73_73"></a><a href="#FNanchor_73_73"><span class="label">[73]</span></a>
+<br />
+4KCy + NiSO<sub>4</sub> = K<sub>2</sub>NiCy<sub>4</sub> + K<sub>2</sub>SO<sub>4</sub><br />
+2KCy + AgNO<sub>3</sub> = KAgCy<sub>2</sub> + KNO<sub>3</sub><br />
+<span style="margin-left: 0.5em;">&#8756;&nbsp; 2AgNO<sub>3</sub> = Ni</span><br />
+</p></div>
+
+<div class="footnote"><p><a name="Footnote_74_74" id="Footnote_74_74"></a><a href="#FNanchor_74_74"><span class="label">[74]</span></a> Zn + H<sub>2</sub>SO<sub>4</sub> = H<sub>2</sub> + ZnSO<sub>4</sub>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_75_75" id="Footnote_75_75"></a><a href="#FNanchor_75_75"><span class="label">[75]</span></a> These 104 c.c. are equivalent to 100 c.c. of dry air at 0&deg;
+C. and 760 mm.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_271" id="Page_271">[Pg 271]</a></span></p>
+<h2><a name="CHAPTER_XII" id="CHAPTER_XII"></a>CHAPTER XII.</h2>
+
+<h3>TIN&mdash;TUNGSTEN&mdash;TITANIUM.</h3>
+
+
+<h4>TIN.</h4>
+
+<p>Tin occurs in nature as cassiterite (containing from 90 to 95 per cent.
+of oxide of tin), which mineral is the source from which the whole of
+the tin of commerce is derived. Tin also occurs as sulphide combined
+with sulphides of copper and iron in the mineral stannine or bell-metal
+ore. It is a constituent of certain rare minerals, such as tantalite.</p>
+
+<p>The methods of assaying tin in actual use are remarkable when compared
+with those of other metals. The more strictly chemical methods are
+rendered troublesome by the oxide being insoluble in acids, resembling
+in this respect the gangue with which it is associated. Moreover, it is
+not readily decomposed by fusion with alkalies. The oxide has first to
+be reduced to metal before the tin can be dissolved. The reduction may
+be performed by fusing with potassic cyanide, by heating to moderate
+redness in a current of hydrogen or coal gas, or by heating to a higher
+temperature with carbon. The reduced metal is only slowly dissolved by
+hydrochloric acid, and although it is readily soluble in aqua regia, the
+solution cannot be evaporated or freed from the excess of acids, by
+boiling, without loss of tin, because of the volatility of stannic
+chloride. There has long been a difficulty in getting a quick wet
+method.</p>
+
+<p>The process of assaying tin ores adopted in the mines of Cornwall is a
+mechanical one known as "vanning," the object of which is to find the
+percentage of "black tin," which, it is well to remember, is not pure
+cassiterite, much less pure oxide of tin. Tin ore, as taken from the
+lode, contains from 2 to 5 per cent. of cassiterite, and is mainly made
+up of quartz, felspar, chlorite, schorl, and other stony minerals,
+together with more or less mispickel, iron and copper pyrites, oxide of
+iron, and wolfram. The cassiterite has a specific gravity (6.4 to 7.1)
+considerably higher than that of the vein-stuff (2.5 to 3.0), and is
+concentrated by a series of washings till it is free from the lighter
+material. Those minerals which have a specific gravity approaching that
+of<span class='pagenum'><a name="Page_272" id="Page_272">[Pg 272]</a></span> the cassiterite are not completely removed. The mispickel and copper
+and iron pyrites are converted into oxides by roasting, and are in great
+part removed by a subsequent washing. The concentrated product is known
+as "black tin," and in this condition is sold to the smelter. The chief
+foreign matters in the black tin are silica, oxides of iron and copper,
+and wolfram, with traces of manganese and niobic acid; and in certain
+stream ores there may be as much as 6 or 7 per cent. of titaniferous
+iron. The black tin from the mines contains from 5 to 12 per cent. of
+water, and is sold and assayed wet. A series of typical samples of black
+tin ranged as follows:&mdash;</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Source of Material.</td><td align='center'>Percentage of Metal in Dry Ore.</td><td align='center'>Specific Gravity.</td></tr>
+<tr><td align='left'>Good mine ore</td><td align='center'>72.0</td><td align='center'>6.39</td></tr>
+<tr><td align='left'>Inferior do.</td><td align='center'>71.5</td><td align='center'>6.64</td></tr>
+<tr><td align='left'>Titaniferous stream ore</td><td align='center'>67.0</td><td align='center'>6.39</td></tr>
+<tr><td align='left'>Mine ore with wolfram</td><td align='center'>64.5</td><td align='center'>6.67</td></tr>
+<tr><td align='left'>Ore from stream works</td><td align='center'>58.5</td><td align='center'>5.99</td></tr>
+</table></div>
+
+<p>It will be seen from these figures that black tin is a very variable
+substance; and that the specific gravity is largely influenced by the
+impurities; hence, it is only an indication of the percentage of metal
+when the same kind of ore is dealt with.</p>
+
+<p>As already pointed out, the object of vanning is to determine the
+proportion of black tin in the lode stuff. The relation between the
+actual content in oxide of tin and the produce got by vanning has been
+tested on several occasions with results which show a fair degree of
+approximation.</p>
+
+<p>The following are some published results of assays of the same batch of
+ore. The vanning results were obtained by a Cornish vanner of recognised
+ability, and the wet assays by two London firms of the highest
+standing:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Vanning results:</td></tr>
+<tr><td align='center'>(Average)</td><td align='left'>91 lbs.</td><td align='left'>of "black tin."</td></tr>
+<tr><td align='left'>Wet Assay results:</td></tr>
+<tr><td align='center'>A</td><td align='left'>83.7 lbs.</td><td align='left'>of stannic oxide.</td></tr>
+<tr><td align='center'>B</td><td align='left'>79.7 lbs.</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>The vanner reported his black tin as containing 70 per cent. of tin.
+This will bring his result, if calculated as stannic oxide, to 80.9 lbs.
+to the ton; which agrees with the others.</p>
+
+<p>According to our experience the "van" assay agrees fairly well with the
+"wet" one, if the black tin is assumed to contain 92.5 per cent. of
+stannic oxide (SnO<sub>2</sub>).</p>
+
+<p>Vanners are, as a rule, skilful men, and show remarkable dexterity in
+separating the black tin, with the help of their<span class='pagenum'><a name="Page_273" id="Page_273">[Pg 273]</a></span> apparatus, which
+consists simply of a shovel and a kieve of water. An account of the
+process is given below. But different vanners, all good men, will get
+different results working on material new to them. The black tin weighed
+by the vanner is supposed to correspond in quality with the black tin
+returned from the floors of the mine for which he is assaying, but this
+differs materially in different mines with the nature of the gangue. The
+process leaves too much to the judgment of the vanner. It is more than
+probable that in practice the returns from the dressing-floors check the
+assayer, instead of, as should properly be the case, the assayer
+checking the returns. It is only when this last is done that any control
+is had over the system of dressing. A correct assay of this ore is a
+matter of some importance, because of the high price of the metal.</p>
+
+<p>The method of assaying the black tin is a dry one, and consists of
+mixing it with "culm," and submitting it in a black-lead crucible to the
+highest temperature of a wind furnace. The sample is taken wet as it
+arrives at the smelting house, and is assayed direct. The product of the
+assay is examined, and a deduction of a considerable percentage is very
+properly made for impurities, since the assay really determines the
+percentage, not merely of tin, but of the bodies present which are
+reducible at a white heat. The judgment as to how much is to be deducted
+is assisted partly by an examination of the metal got from the assay,
+and partly by the experience acquired in smelting similar ores. The
+produce, which is that of the impure tin, is stated in parts in twenty;
+thus a produce of 14 is equivalent to 70 per cent., or to 14 cwt. per
+ton.</p>
+
+<div class="figcenter" style="width: 364px;">
+<img src="images/fig057.jpg" width="364" height="300" alt="Fig. 57." title="" />
+
+</div>
+
+<h4>MECHANICAL SEPARATION.&mdash;VANNING.</h4>
+
+<p>This process, which has already been referred to, is carried out as
+follows:&mdash;After sampling the ore in the ordinary way, a quantity
+(varying with its richness) is weighed out. Special weights are
+generally used. The standard weight, marked 200, weighs about an ounce;
+with poor ores this quantity is taken for an assay, but with richer ores
+100 or even 50 is sufficient. The unit of weight has no special name,
+but the parts in 200 are spoken of as the produce; thus, if 200 of ore
+were taken and 9.5 of black tin were separated, the produce would be
+9-1/2: obviously half the "produce" will give the percentage. The
+weighed portion of the ore is placed on the vanning shovel. The vanner
+stands in front of a tub of water (kieve) and allows 30 or 40 c.c. of
+water to flow on to the ore. He then raises the shovel a little above
+the surface of the water, and, holding it nearly horizontal, briskly<span class='pagenum'><a name="Page_274" id="Page_274">[Pg 274]</a></span>
+rotates the water by imparting to the shovel a slight circular motion,
+passing into an elliptical one (front to back). This causes the finer
+mud to be suspended in the liquid, which is then run off, leaving the
+body of the ore in the centre of the shovel. This is repeated until the
+water after standing a moment is fairly clear. About half as much water
+as before is brought on; then, with a motion which is similar to the
+previous one, but with a jerk added in one direction, the heavier
+minerals are thrown up, and the stony matter brought back. The jerk is
+produced just as the wave of water is returning. The descending wave of
+water draws with it the bulkier and lighter particles of the ore, whilst
+the heavier matter lying on the bottom is scarcely affected by it. The
+jerky motion, however, carries it to the front of the shovel. The
+lighter stuff is washed off, and the residue dried by holding the shovel
+over the furnace. It now corresponds, more or less, to the stuff which
+on the mine is sent to the calciner. It is swept from the shovel into a
+scoop, and transferred to a hot crucible; in which it is calcined until
+free from sulphur. Some vanners calcine their samples before commencing
+to van. The calcined ore is shaken out of the crucible on to the shovel;
+rubbed up with a hammer; and washed (as at first) to get rid of the
+finer and lighter "waste." The separating motions are again gone
+through; and the "head" of the best of the black tin is thrown well up
+on one side of the shovel in the form of a crescent, so as to leave room
+on the shovel to work with the "tailings." The quantity of water used is
+kept low, to prevent this "crop" tin from being washed back again. The
+tailings are then crushed to free the tin from adherent oxide of iron;
+and again washed to throw up the remaining tin ore. As this tin is
+finely divided, it is more difficult to bring it up, so that a vigorous
+and rapid motion is required. The tailings are now washed off, and the
+whole of the black tin is brought into the centre of the shovel. It
+requires two or three washings more to free it from the waste it
+contains. Very small quantities of water are used. The purity of the
+black tin can be seen by its appearance on the shovel. The cleaned ore
+is dried as before, freed from particles of iron with the aid of a
+magnet, and weighed. The weighings are carried to 1/8th of the<span class='pagenum'><a name="Page_275" id="Page_275">[Pg 275]</a></span> unit
+used. The following example illustrates the method of calculation
+adopted on the mine. A parcel of 1 ton 2 cwt. 3 qrs. of tin ore with a
+produce of 45 (equal to 22-1/2 per cent.) contains 5 cwt. 0 qrs. 12 lbs.
+of black tin. This result is obtained as follows:&mdash;</p>
+
+<pre>
+ton   cwt.   qrs.
+  1     2     3
+              9   }
+----------------- }
+ 10     4     3   } equivalent to multiplying by 45.
+              5   }
+----------------  }
+  5.1   3     3     strike off the first figure to the right.
+              4      multiply by 4 to reduce to quarters.
+---------
+  4    12
+        3
+---------
+  4    15
+ 28                  multiply by 28 to reduce to pounds.
+-----
+112
+ 15
+-----
+ 12.7                strike off the first figure to the right.
+</pre>
+
+<p>Similarly, a parcel of 20 tons 10 cwt. with a produce of 9-1/2 contains
+19 cwt. 1 qr. 25 lbs. of black tin. For the following information, as
+well as for much of that already given about vanning, we are indebted to
+Captain Reynolds, of Cook's Kitchen Mine. "To have a complete set of
+tools for all vanning purposes, it will be necessary to get the
+following:&mdash;A vanning shovel 14 inches long and 13 inches wide, weighing
+not over 2-3/4 pounds. It is made of hammered sheet iron of the shape
+shown in fig. 57. It must have a light wooden handle (preferably of
+deal) 3 feet long. A bruising hammer, weighing 2-1/2 pounds, with a
+handle 1 foot long. A pair of tongs (furnace) 2-1/2 feet long, made of
+1/2-inch round iron. And a set of ordinary clay crucibles for calcining.
+There ought to be two sets of scales and weights: the first should be
+confined to weighing the powdered tin stuff, and the second ought to be
+a much higher class one, for weighing the black tin obtained. The
+furnace for roasting the sample should be 10 inches square and 12 inches
+deep, with the fire-bars at the bottom three-quarters of an inch apart.
+The water-box for vanning in should be at least 4 feet long, 2 feet 6
+inches wide, and 8 inches deep."<span class='pagenum'><a name="Page_276" id="Page_276">[Pg 276]</a></span></p>
+
+
+<h4>DRY METHODS.</h4>
+
+<p>For the following description of the process adopted in Cornwall we are
+indebted to Mr. A.K. Barnett, F.G.S., of Chyandour.</p>
+
+<p><b>Cornish Method.</b>&mdash;<i>Tin Ore Assay.</i>&mdash;The ore to be smelted or assayed
+should be concentrated to say not less than 50 per cent. of metallic
+tin; though to obtain satisfactory results it should be brought nearer
+70 per cent., as with ore containing less than 40 to 50 per cent. of
+metal there will be a considerable loss both in the assaying and in the
+smelting. If the ore to be operated on does not contain this quantity of
+metal, then the sample (if coarse) must be reduced to a fine state, the
+gangue being removed by vanning, and the ore saved for the fire assay.</p>
+
+<p>The method adopted for the determination of tin in the ore is as
+follows:&mdash;About 2-1/2 ounces troy (1200 grains, or about 80 grams) of
+the ore to be assayed is weighed out and mixed on a flat copper pan
+(shaped with a long lip) with one-fifth of its weight (240 grains, or
+15.5 grams) of powdered culm (anthracite). The mixture of ore and culm
+is either transferred to a black-lead crucible before the latter is put
+into the furnace, or, as some prefer, it is carefully swept into a
+crucible which has been imbedded in the fire. Some assayers cover their
+pots with a flat cover placed loosely on, while others leave the mixture
+in the open pot. The furnace, which has been previously fired to a
+strong heat, is then covered, and the sample is subjected to a sharp
+fire for a period of from twelve to twenty minutes. No definite time can
+be stated, as, besides the strength of the fire, the quality and
+condition of the ore, and the impurities associated with it, greatly
+affects the time required for the complete reduction of the ore. As soon
+as the mixture in the crucible has settled down to a uniform white heat,
+and any very slight ebullition which may have taken place has subsided,
+the crucible is gently shaken, removed from the fire (the culm-ash or
+slag which covers the metal being carefully drawn aside with an iron
+scraper), and the metal is poured quickly into an iron ingot-mould,
+which is usually placed on a copper pan to save the culm-slag and the
+adherent metal which comes out with it. The crucible is then carefully
+scraped, and the scrapings, together with the contents of the mould and
+pan, are transferred to a mortar. There the ingot of tin is freed from
+slag and then taken to the scales. The rest, after being finely
+powdered, is passed through a sieve. The flattened particles of tin
+which remain on the sieve are weighed with the ingot (the <i>lump</i>, as it
+is called); whilst the siftings are vanned on a shovel, and (the slag
+being washed off) the fine tin is collected, dried, and weighed with the
+rest: the whole gives the<span class='pagenum'><a name="Page_277" id="Page_277">[Pg 277]</a></span> produce or percentage of metal in the ore.
+The results of the assays are expressed in cwts. of metal in the ton of
+ore. The percentage is rarely given and never used in Cornwall.
+Thus&mdash;"13-1/2 Produce" would mean that the assay yielded results at the
+rate of 13-1/2 cwts. of metal for one ton of the ore. Some assayers use
+a little powdered fluor-spar to assist the fusion of refractory slags. A
+small quantity of borax will also occasionally be of service for ores
+containing silica in excess of any iron that may be present. The borax
+renders the slag more fusible, and assists the formation of a larger
+lump (with less fine tin in the slag) than would be obtained by the use
+of culm alone.</p>
+
+<p>The quality and the percentage of <i>pure tin</i> in the metal will vary
+considerably, according to the impurities that are associated with the
+ore to be assayed.</p>
+
+<p>The crude lump is then remelted in a small iron ladle at as low a
+temperature as possible, and the fused metal is poured into a shallow
+trench about 4 inches long by 3/4 of an inch wide cut in a block of
+white marble. The metal will be silvery-white if the temperature
+employed be correct; if too hot, the surface will show a yellow, red, or
+blue colour (according to the heat employed); in such case the metal
+should be remelted at a lower temperature. If the metal on cooling
+remains perfectly clear and bright, then it may be assumed that the tin
+is of good quality and commercially pure. A crystallised or frosted
+appearance of the metal indicates the presence of some alloy, say of
+iron, copper, zinc, lead, antimony, &amp;c. The assayer who has had much
+practice can readily distinguish the metal or metals that are associated
+with the ore by noting the appearance of the tin on cooling; and can
+fairly judge the quantity of impurity present by the amount of the
+crystallisation or stain.</p>
+
+<p>Whilst the foregoing method of assaying cannot lay claim to scientific
+accuracy, it is by no means so imperfect as some writers would have us
+believe, who state that a loss of 5 to 10 per cent. arises in the
+operation. It is certainly the most ready and expeditious mode of
+determining the commercial value of a parcel of tin ore, which, after
+all, is the main object of all assaying operations.</p>
+
+<p>The difficulty which beginners find in obtaining satisfactory results,
+and any loss of metal which those not accustomed to the process may
+incur, will invariably occur in the vanning of the powdered slag for the
+fine tin, the rest of the operations being easy of execution, and
+requiring only the ordinary care necessary for all metallurgical work.</p>
+
+<p>There is no doubt that if low percentage ores containing silica are
+assayed in this manner, low results are obtained, as it is impossible<span class='pagenum'><a name="Page_278" id="Page_278">[Pg 278]</a></span>
+to reduce the whole of the tin in the presence of free silica; with this
+class of ores, care should be taken to remove some of the silica by
+preliminary vanning, or some flux should be added which will combine
+with the silica, and so prevent its entering into combination with the
+tin. Low quality tin ores containing iron, copper, lead, zinc, antimony,
+etc., combined with arsenic, sulphur, or oxygen, will give very much
+higher results than the actual percentage of tin in the sample. The
+other metals (being readily reduced in the presence of tin) alloy with
+it, and give a hard lump difficult to fuse in the iron ladle; where the
+quantity of foreign metals is large, the metal can only be melted to a
+stiff pasty mass; so that (in determining the value of a ton of tin ore,
+or even reporting on the percentage of tin it contains) not only must
+the weight of the assay be the basis for calculation, but the quality
+and character of the metal obtained must also be considered. Thus two
+ores of tin might be assayed both yielding a similar <i>produce</i>, say
+13-1/2 (67-1/2 per cent.), and yet one might contain 5 per cent. less
+tin than the other.</p>
+
+<p>If it be required to obtain the pure metal from tin ores containing the
+ores of other metals associated with them, the latter must be removed by
+digesting in strong hydrochloric acid, and washing. The assay may then
+be conducted in the usual way, and a fairly pure lump will be obtained.</p>
+
+<p>If wolfram be present in any appreciable quantity in the ore, it
+considerably reduces the proportion of lump, and at the same time it
+increases the fine tin (or <i>prillion</i>, as it is termed) in the assay.
+This may be got rid of by boiling in aqua regia, and dissolving out the
+tungstic acid which has been liberated by means of ammonia.</p>
+
+<p>It will be seen that this method of assaying tin has its advantages and
+its drawbacks. It is quickly performed; with ores of good quality it
+gives results not to be excelled by any other process; and it gives the
+smelter the actual alloy and quality of metal he may expect to get in
+the smelting of the ore, which no other mode of assaying will do:
+against which may be set the skill required to obtain accurate results
+with the vanning shovel; the loss of metal in poor ores containing an
+excess of silica; and the high results from ores containing a large
+quantity of metallic impurities.</p>
+
+<p><b>Cyanide Method.</b>&mdash;Weigh up 20 grams of the ore and dry it on a scoop
+over the Bunsen flame. When dry, weigh, and calculate the percentage of
+water from the loss in weight. Transfer the dried ore to an evaporating
+dish, and cover with 30 c.c. of hydrochloric acid; boil for 10 or 12
+minutes, and then add 5 c.c.<span class='pagenum'><a name="Page_279" id="Page_279">[Pg 279]</a></span> of nitric acid and boil again. Dilute with
+water, and filter. Transfer the filter and its contents to an E
+Battersea crucible, and calcine it for a few minutes. Cool, and weigh
+the residue. The loss equals the oxides soluble in acid. Transfer the
+residue to the crucible and mix it with its own weight of cyanide of
+potassium; add a similar amount of "cyanide" as a cover. Place in the
+furnace, and when the charge has attained the temperature of the furnace
+(in from 3 to 6 minutes), remove it at once; tap the pot <i>vigorously</i>
+several times, and then pour its contents quietly into a mould. Dissolve
+the slag in water, clean, dry, and weigh the button of tin.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p><b>Detection.</b>&mdash;Tin ore is detected by its insolubility in acids, high
+specific gravity, and characteristic appearance in water. The powder is
+separated from the lighter gangue by washing. It is fused in a Berlin
+crucible with five times its weight of potassic cyanide at a moderately
+high temperature in a muffle, or over the blowpipe. The slag is washed
+off with water, and the metallic buttons or residue treated with
+hydrochloric acid (not aqua regia), for some time. One portion of the
+solution strikes a purple colour with chloride of gold, another portion
+gives a white or grey precipitate or cloudiness with mercuric chloride.
+These reactions are characteristic of tin as stannous chloride.</p>
+
+<p>Metallic tin treated with nitric acid becomes converted into a white
+insoluble powder (metastannic acid). Aqua regia dissolves tin readily,
+forming stannic chloride, and in this solution the metal is detected by
+precipitation with sulphuretted hydrogen, which gives a yellow
+precipitate. Tin in solution as stannic or stannous chloride is
+precipitated as metal by means of zinc.</p>
+
+<p>The fact that tin forms two well-defined series of compounds is taken
+advantage of in assaying (just as in the case of iron), by determining
+how much of an oxidising agent is required to convert it from the
+stannous into the stannic state. For example, on the addition of a
+solution of permanganate of potash to a solution of stannous chloride
+the oxidation goes on rapidly, and the finishing point is sharp and
+distinct; but acid solutions of stannous chloride quickly take up oxygen
+from that dissolved in the water used and from the air. Unfortunately,
+there is no obvious sign that such oxidation has taken place, except
+that (fatal to the assay) a smaller volume of the permanganate is
+required. Great care is required with such solutions, both before and
+during titration. The addition of an excess of ferric chloride to the
+stannous<span class='pagenum'><a name="Page_280" id="Page_280">[Pg 280]</a></span> solution, as soon as the whole of the tin has been dissolved,
+will lessen this liability to oxidation.</p>
+
+<p><b>Separation.</b>&mdash;If the tin is present in an alloy, the substance is
+boiled in an evaporating dish with dilute nitric acid until the whole of
+the material is attacked. Evaporate nearly to dryness, dilute, boil for
+a few minutes, and filter off the white insoluble residue. Under certain
+circumstances this residue will be nearly free from other metals, in
+which case it is ignited and weighed. If not known to be pure it must be
+ignited, reduced in a current of hydrogen, and treated as subsequently
+described.</p>
+
+<p>When the tin is present as insoluble oxide in an ore, the substance is
+finely powdered, and from 1 to 5 grams of it (according to its richness)
+boiled with 30 c.c. of hydrochloric acid in an evaporating dish till the
+oxide of iron is seen to be dissolved. Then add 1 c.c. of nitric acid
+(or more if much pyrites, &amp;c., is present) and continue the boiling till
+these are decomposed; dilute and filter off, washing first with dilute
+acid and afterwards with a little dilute ammonia, dry, ignite, and place
+in a combustion tube (together with the filter-ash) and heat to redness
+for about thirty minutes in a current of dried hydrogen.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig058.jpg" width="450" height="115" alt="Fig. 58." title="" />
+
+</div>
+
+<p>The oxide of tin is placed in a porcelain boat (fig. 58), which is then
+introduced into a piece of combustion tube. The latter, wrapped in a
+piece of wire gauze, is supported on a couple of iron rings, and heated
+by one or two Bunsen burners in a furnace fitted up with loose
+fire-brick tiles, as shown in fig. 59.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig059.jpg" width="450" height="136" alt="Fig. 59." title="" />
+
+</div>
+
+<p>When the reduction is complete the tube is allowed to cool; the boat is
+removed and the tin dissolved. Add a rod of zinc to the freely-acid hot
+solution, and in a few minutes decant through a filter and wash with
+water, after having removed the zinc. Wash the precipitated metal back
+into the beaker, and dissolve in 10 c.c. of dilute nitric acid,
+evaporate off the excess of acid;<span class='pagenum'><a name="Page_281" id="Page_281">[Pg 281]</a></span> dilute, boil, and filter. Wash, dry,
+ignite strongly in a porcelain crucible, and weigh.</p>
+
+<p>In the absence of antimony the above separation works very well, but if
+this metal is present in quantity the metals precipitated on the zinc
+must be covered with hydrochloric acid and treated with a few drops of
+nitric. It is then warmed with iron wire until no more of the latter
+dissolves. The antimony is precipitated as metal, and the tin remains in
+solution as stannous chloride. The antimony is filtered off, and may be
+washed with alcohol, and weighed, whilst the tin in the filtrate is
+precipitated with zinc, and treated as already described.</p>
+
+<h4>GRAVIMETRIC METHOD.</h4>
+
+<p>If the tin is not already in the metallic state it is reduced to this
+condition by the method given (precipitation by zinc). Treat the
+finely-divided metal (washed free from chlorides) in a four-inch
+evaporating dish with 10 c.c. of dilute nitric acid, cover with a
+clock-glass, and apply a gentle heat until the precipitate appears of a
+white colour and the metal is completely attacked. Evaporate nearly to
+dryness on a water-bath; then add 50 c.c. of water, heat to boiling, and
+filter. Wash with hot water, dry, transfer to a weighed porcelain
+crucible, add the filter-ash, ignite strongly, and weigh. The
+precipitate after ignition is stannic oxide (SnO<sub>2</sub>). It is a
+yellowish-white powder (darker whilst hot), insoluble in acids, and
+contains 78.67 per cent. of tin. Cold dilute nitric acid dissolves tin
+to a clear solution, which becomes a white enamel-like jelly on heating;
+this (filtered off, washed, and dried) forms an opal-like substance,
+which is converted on ignition into stannic oxide with evolution of
+nitrous fumes. Stannic oxide when ignited with chlorides is more or less
+completely converted into stannic chloride, which volatilises. The
+presence of chlorides during the evaporation with nitric acid causes a
+similar loss.</p>
+
+<p><b>Determination of Tin in an Alloy.</b>&mdash;(<i>Bronze.</i>)&mdash;Take 2 grams, and
+attack with 20 c.c. of dilute nitric acid in a covered beaker with the
+aid of heat. Boil till the bulk is reduced by one-half, dilute with 50
+c.c. of water, allow to settle for a few minutes, and filter; wash well
+first with water acidulated with a little nitric acid, and afterwards
+with water; dry, ignite, and weigh as stannic oxide.</p>
+
+<p><b>Determination of Tin in Tin Ore.</b>&mdash;Treat 5 grams of the dried and
+finely-powdered ore with 30 c.c. of hydrochloric acid in a four-inch
+evaporating dish. After the soluble oxides have been dissolved add 1 or
+2 c.c. of nitric acid, boil off nitrous fumes,<span class='pagenum'><a name="Page_282" id="Page_282">[Pg 282]</a></span> dilute, and filter. Dry
+the filter, transfer the cleaned ore to a piece of combustion tube ten
+or twelve inches long and narrowed at one end. Pass a current of
+hydrogen through the tube and heat to redness for 30 minutes; cool
+whilst the gas is still passing. Dissolve in 20 c.c. of dilute
+hydrochloric acid and keep the solution tinted with permanganate of
+potassium. When the colour of the permanganate becomes permanent dilute
+to a bulk of 50 c.c. with water, filter, and wash. Heat; add a rod of
+zinc weighing about 3 grams; allow to stand for a few minutes; decant
+through a filter; and wash, removing the remaining zinc and returning
+the tin to the beaker. Treat with 5 c.c. of dilute nitric acid, boil for
+some time, take up with water, filter, wash, dry, ignite, and weigh as
+stannic oxide.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p><b>Titration with Solution of Permanganate of Potassium.</b>&mdash;This titration
+may be made either directly on the solution of stannous chloride
+(prepared by dissolving the precipitated metal in hydrochloric acid), or
+indirectly, on a solution of ferrous chloride (produced by the reducing
+action of the precipitated metal on ferric chloride). The standard
+solution of permanganate of potassium is made by dissolving 5.356 grams
+of the salt in water and diluting to one litre. 100 c.c. are equivalent
+to 1.00 gram of tin.</p>
+
+<p>The precipitated tin is transferred to a flask; and dissolved in 10 c.c.
+hydrochloric acid, with the aid of heat and in an atmosphere of carbonic
+acid. The acid and metal are placed in the flask; which is then filled
+with the gas, and stopped with a cork provided with a rubber valve. When
+solution is complete the flask is again filled with carbonic acid. Fifty
+c.c. of water freed from air and saturated with carbonic acid are then
+added. This water is made by adding a gram of bicarbonate of soda and 2
+c.c. of hydrochloric acid to 100 c.c. of water: the effervescence sweeps
+out the dissolved oxygen. The permanganate of potassium solution is then
+run in from a stop-cock burette in the usual way until a faint pink
+tinge is obtained.</p>
+
+<p>The following experiments show the effect of variations in the
+conditions of the assay. A solution of stannous chloride equivalent in
+strength to the "permanganate" was made by dissolving 19.06 grams of the
+crystallised salt (SnCl<sub>2</sub>.2H<sub>2</sub>O.) in 50 c.c. of water and 10 c.c. of
+hydrochloric acid and diluting to 1 litre with water freed from
+dissolved oxygen. 100 c.c. contain 1 gram of tin. In the first
+experiments tap water was used and no precautions were taken for
+excluding air. Except when otherwise<span class='pagenum'><a name="Page_283" id="Page_283">[Pg 283]</a></span> stated, 20 c.c. of the stannous
+chloride were used in each experiment with 10 c.c. of hydrochloric acid,
+and were diluted to 100 c.c. with water before titration.</p>
+
+<p><b>Effect of Varying Hydrochloric Acid.</b></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acid added</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Permanganate" required</td><td align='left'>18.8</td><td align='left'>"</td><td align='left'>18.9</td><td align='left'>"</td><td align='left'>18.8</td><td align='left'>"</td><td align='left'>18.8</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>The only effect of the increase in quantity of acid was to give the
+brown of perchloride of manganese instead of the pink of permanganic
+acid to mark the finishing point.</p>
+
+<p><b>Effect of Varying Temperature.</b></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg; C.</td><td align='left'>50&deg; C.</td><td align='left'>70&deg; C.</td><td align='left'>100&deg; C.</td></tr>
+<tr><td align='left'>"Permanganate" required</td><td align='left'>18.8 c.c.</td><td align='left'>18.7 c.c.</td><td align='left'>18.6 c.c.</td><td align='left'>18.4 c.c.</td></tr>
+</table></div>
+
+<p><b>Rate of Atmospheric Oxidation.</b>&mdash;Solutions ready for titration were
+exposed to air at the ordinary temperature for varying lengths of time
+and then titrated.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Time exposed</td><td align='left'>0 min.</td><td align='left'>5 min.</td><td align='left'>10 min.</td><td align='left'>20 min.</td><td align='left'>60 min.</td></tr>
+<tr><td align='left'>"Permanganate" required</td><td align='left'>18.8 c.c.</td><td align='left'>18.8 c.c.</td><td align='left'>18.8 c.c.</td><td align='left'>18.8 c.c.</td><td align='left'>18.6 c.c.</td></tr>
+</table></div>
+
+<p>It is best to titrate at once, although the loss by oxidation is only
+small after one hour's exposure.</p>
+
+<p><b>Effect of Varying Tin.</b></p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Stannous chloride added</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Permanganate" required</td><td align='left'>0.7</td><td align='left'>"</td><td align='left'>8.8</td><td align='left'>"</td><td align='left'>18.0</td><td align='left'>"</td><td align='left'>47.4</td><td align='left'>"</td><td align='left'>95.4</td><td align='left'>"</td></tr>
+</table></div>
+
+<p><b>Effect of Varying Bulk.</b></p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td><td align='left'>500.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Permanganate" required.</td><td align='left'>9.0</td><td align='left'>"</td><td align='left'>18.3</td><td align='left'>"</td><td align='left'>17.4</td><td align='left'>"</td><td align='left'>15.1</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>The two last series show an interference, which is due to the oxygen
+dissolved in the water, as may be seen from the following similar
+experiments, which were, however, performed with water freed from oxygen
+and in which the titrations were effected in an atmosphere of carbonic
+acid.</p>
+
+<p><b>Effect of Varying Tin.</b>&mdash;A new solution of stannous chloride was used.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Stannous chloride added</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Permanganate" required</td><td align='left'>1.0</td><td align='left'>"</td><td align='left'>10.0</td><td align='left'>"</td><td align='left'>19.8</td><td align='left'>"</td><td align='left'>49.6</td><td align='left'>"</td><td align='left'>99.3</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Bulk.</b></p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>30.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td><td align='left'>500.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Permanganate" required</td><td align='left'>19.8</td><td align='left'>"</td><td align='left'>19.8</td><td align='left'>"</td><td align='left'>19.8</td><td align='left'>"</td><td align='left'>19.8</td><td align='left'>"</td><td align='left'>19.8</td><td align='left'>"</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_284" id="Page_284">[Pg 284]</a></span></p>
+
+<p>It will be seen that in working under these conditions the results are
+proportional and the method satisfactory.</p>
+
+<p><b>Examination of Tin Phosphide.</b>&mdash;(<i>Phosphor Tin</i>.)&mdash;This substance is
+used in the manufacture of "phosphor bronze" and similar alloys. It is a
+crystalline, imperfectly-malleable, metallic substance. It is soluble in
+hydrochloric acid with effervescence; phosphoretted hydrogen, which
+inflames on the addition of a drop or two of nitric acid, being evolved.
+It is attacked by nitric acid, yielding a white powder of stannic
+phosphate; this is not easily decomposed by ammonium sulphide or readily
+soluble in hydrochloric acid.</p>
+
+<p>"Phosphor-tin" is made up only of tin and phosphorus. For the estimation
+weigh up 1 gram. Place in a weighed Berlin dish; and cover with 10 c.c.
+of nitric acid and 3 or 4 c.c. of water. Let the reaction proceed (under
+a clock-glass) on the water-bath till complete. Remove the glass;
+evaporate to dryness, and ignite, at first gently over a Bunsen burner,
+and afterwards in the muffle at a red heat. Cool in the desiccator, and
+weigh as quickly as possible when cold. The substance contains the tin
+as stannic oxide, SnO<sub>2</sub>, and the phosphorus as phosphoric oxide,
+P<sub>2</sub>O<sub>5</sub>. The increase in weight on the gram of substance taken gives
+the weight of the oxygen taken up by the phosphorus and tin, and since 1
+gram of tin takes up only 0.271 gram of oxygen, and 1 gram of phosphorus
+takes up 1.29 gram, the proportion of tin to phosphorus can be
+calculated from the increase in weight. For example, 1 gram of a sample
+gave 1.3410 gram of mixed oxides, which is 0.070 gram in excess of that
+which would be got with pure tin. If the substance was all phosphorus
+the excess would be 1.0190 gram; consequently the proportion of
+phosphorus in the substance is 0.070 / 1.019, or 6.87 per cent. The tin
+is calculated by difference, 93.13 per cent.</p>
+
+<p>Another method of separating and determining the phosphorus is as
+follows:&mdash;Take 1 gram of the substance and add to it 15 c.c. of hot aqua
+regia. Boil till dissolved, dilute, and precipitate the tin with
+sulphuretted hydrogen. To the filtrate add ammonia and "magnesia
+mixture." Filter; wash the precipitate with dilute ammonia; dry, ignite,
+and weigh as magnesic pyrophosphate. Calculate the phosphorus, and take
+the tin by difference.</p>
+
+<p>A sample of phosphor tin gave&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Tin</td><td align='left'>93.1</td><td align='left'>per cent. (by difference)</td></tr>
+<tr><td align='left'>Phosphorus</td><td align='left'>6.9</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;-</td></tr>
+<tr><td align='left'></td><td align='left'>100.0</td></tr>
+</table></div>
+
+
+<p><b>Tin Arsenide.</b>&mdash;This is met with in tin-smelting; it closely resembles
+the phosphide, but the crystals have a duller grey<span class='pagenum'><a name="Page_285" id="Page_285">[Pg 285]</a></span> appearance. It
+contains simply tin and arsenic. The determination is made by treating 1
+gram of the substance with nitric acid and weighing the mixed oxides of
+tin and arsenic in the same manner as in the case of the phosphide. One
+gram of arsenic will give 1.533 gram of arsenic oxide, As<sub>2</sub>O<sub>5</sub>;
+consequently the excess of weight of the mixed oxides over 1.271 gram
+must be divided by 0.262; the result multiplied by 100 gives the
+percentage of arsenic. In consequence of the higher atomic weight of
+arsenic the results by this method are not so close as with the
+phosphide. Each milligram of excess weight (over 1.271) represents 0.38
+per cent. of arsenic, As. Both in this and in the corresponding
+phosphide determination care must be taken to avoid absorption of
+moisture, by allowing the oxides to cool in a desiccator and weighing
+quickly.</p>
+
+<p>The percentage of arsenic is better determined as follows:&mdash;Weigh up 1
+gram of the substance, dissolve in aqua regia, dilute, and pass
+sulphuretted hydrogen. Render alkaline with ammonia, and add ammonium
+sulphide till the precipitate is dissolved. Add "magnesia mixture."
+Filter off the precipitate, wash with dilute ammonia, ignite with a few
+drops of nitric acid, and weigh as magnesic pyrarsenate. Calculate the
+arsenic and take the tin by difference. A sample treated in this way
+gave&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Tin</td><td align='left'>96.8</td><td align='left'>per cent. by difference</td></tr>
+<tr><td align='left'>Arsenic</td><td align='left'>3.2</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;-</td></tr>
+<tr><td align='left'></td><td align='left'>100.0</td></tr>
+</table></div>
+
+
+<p><b>Examination of Black Tin.</b>&mdash;Dry the ore, and reduce it to a fine
+powder. Weigh up 2 grams, and boil with 20 c.c. of hydrochloric acid and
+2 c.c. of nitric for ten or fifteen minutes. Filter, and reserve the
+filtrate.</p>
+
+<p><b>Tungstic Acid.</b>&mdash;Digest the residue with about 50 c.c. of water and a
+few c.c. of dilute ammonia for a few minutes, and filter; collect the
+filtrate in a weighed porcelain dish, evaporate to dryness, ignite, and
+weigh as tungstic acid, WO<sub>3</sub>.</p>
+
+<p><b>Stannic Oxide.</b>&mdash;Dry, ignite, and weigh the insoluble residue. Transfer
+to a porcelain boat, and reduce in a current of hydrogen at a red heat
+for half an hour. Allow to cool whilst the hydrogen is still passing.
+Transfer the boat to a beaker, and dissolve up the tin in 10 c.c. of
+hydrochloric acid and a c.c. or so of nitric. Wash out the combustion
+tube with some acid and add the washing to the contents of the beaker.
+Warm gently, dilute with water, and filter. Collect, dry, ignite, and
+weigh the insoluble residue. Through the filtrate pass a rapid current
+of sulphuretted hydrogen, allow to settle, and filter. Wash the
+precipitate with hot water, dry, calcine gently; ignite with ammonium
+<span class='pagenum'><a name="Page_286" id="Page_286">[Pg 286]</a></span>carbonate, and weigh as stannic oxide, SnO<sub>2</sub>. The insoluble residue
+will in most cases retain some tin. Fuse it with fusion mixture, take up
+with hydrochloric acid, filter, pass sulphuretted hydrogen through the
+filtrate, collect and wash the sulphide of tin. Ignite and weigh as
+stannic oxide, and add it to that previously obtained.</p>
+
+<p><b>Copper.</b>&mdash;Pass sulphuretted hydrogen through the acid filtrate obtained
+in the first cleaning of the ore, collect the precipitate, and wash
+first with soda solution and then with hot water. Dry, ignite, and weigh
+as cupric oxide, CuO. Mix the filtrate with that from the main portion
+of the sulphide of tin.</p>
+
+<p><b>Ferric Oxide.</b>&mdash;Boil off the sulphuretted hydrogen from the mixed
+filtrates and peroxidise with nitric acid. Add ammonia in slight excess,
+boil, filter, dry, ignite, and weigh the precipitate as ferric oxide.
+This will be practically pure, but the iron in it must be determined by
+dissolving and titrating. The filtrate from the iron may contain zinc,
+lime, and magnesia, but rarely in quantities sufficient to be
+determined.</p>
+
+<p><b>Silica, &amp;c.</b>&mdash;-The silica may be calculated from the weight of the
+residue insoluble in acid, after the reduction of the tin in hydrogen,
+by deducting from it the weight of the oxide of tin subsequently found.
+Or it may be determined as follows:&mdash;The insoluble portion is fused with
+fusion mixture, and taken up with hydrochloric acid, as already
+described. On filtering, the filter will retain a portion of the silica.
+The rest is recovered, after the removal of the stannous sulphide, by
+evaporating to dryness, taking up with hydrochloric acid, and filtering
+through the same filter. It is washed, dried, ignited, and weighed as
+silica. The filtrate from the silica is boiled with a little nitric acid
+and precipitated with ammonia. The precipitate is collected, washed,
+ignited, and weighed as ferric oxide and alumina (but it frequently
+contains oxide of titanium). When the last is present it is determined
+by fusing with bisulphate of potash and extracting with cold water. The
+solution is nearly neutralised with ammonia, charged with sulphurous
+acid, and boiled. The precipitate is collected, washed, dried, ignited,
+and weighed as oxide of titanium, TiO<sub>2</sub>. The difference between this
+weight and that of the combined oxides gives the ferric oxide and
+alumina. The filtrate from the mixed oxides is examined for lime and
+magnesia.</p>
+
+<p><b>Sulphur.</b>&mdash;Rub up 5 grams of the ore with 5 grams of nitre, transfer to
+a porcelain dish, and fuse over a Bunsen burner for fifteen minutes.
+When cold, extract with water, and determine the sulphur volumetrically
+with standard barium chloride. The sulphur may be present as sulphide or
+sulphate.</p>
+
+<p><b>Arsenic.</b>&mdash;Take 5 grams, and evaporate with nitric acid; dilute, add
+ammonia, pass sulphuretted hydrogen, and filter.<span class='pagenum'><a name="Page_287" id="Page_287">[Pg 287]</a></span></p>
+
+<p>To the filtrate add "magnesia mixture." Collect the precipitate, ignite
+with nitric acid, and weigh as magnesic pyrarsenate.</p>
+
+<p>The following may be taken as an example of the composition of an impure
+black tin:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Tungstic acid</td><td align='right'>1.8%</td></tr>
+<tr><td align='left'>Stannic oxide</td><td align='right'>79.0</td></tr>
+<tr><td align='left'>Silica</td><td align='right'>2.6</td></tr>
+<tr><td align='left'>Titanic oxide</td><td align='right'>0.8</td></tr>
+<tr><td align='left'>Copper oxide</td><td align='right'>0.9</td></tr>
+<tr><td align='left'>Ferric oxide</td><td align='right'>13.4</td></tr>
+<tr><td align='left'>Sulphur</td><td align='right'>0.4</td></tr>
+<tr><td align='left'>Arsenic</td><td align='right'>0.3</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>99.2</td></tr>
+</table></div>
+
+<p><b>Examination of Hardhead.</b>&mdash;In the smelting of tin ores a quantity of
+speise, known as "hardhead," is produced. It is essentially an arsenide
+of iron, carrying a considerable quantity of tin. Much of this last is
+present in the form of small buttons of metal distributed through the
+mass. The buttons can be seen on careful inspection, and become evident
+on powdering.</p>
+
+<p>In assaying the substance, a variation in the usual method of sampling
+is required, because of the quantity of metal present which cannot be
+powdered. After powdering as finely as possible, the coarse particles
+are sifted off and weighed. The weight of the powder is also taken. The
+method of working is best illustrated by an example. A sample of
+hardhead weighed 155.1 grams, and gave 21.0 grams of coarse particles,
+equivalent to 13.5 per cent. of the whole. The fine portion weighed 134
+grams, which is equivalent to 86.5 per cent.</p>
+
+<p>Thirteen and a half grams of the coarse material were dissolved in aqua
+regia, and diluted with water to 1 litre. Ten c.c. of this contain 0.135
+gram of the metallic portion, which is the amount contained in 1 gram of
+the original hardhead. If, in a determination, 1 gram of the substance
+is wanted, weigh up 0.865 gram of the powdered portion, and add to it 10
+c.c. of the solution. It will be seen that these together make up 1 gram
+of the original sample. The solution of the metallic portion must be
+saved until the analysis is finished.</p>
+
+<p><b>Tin and Copper.</b>&mdash;Weigh up the portion of the powdered stuff equivalent
+to 1 gram of the sample. Transfer to a flask, and cover with 10 c.c. of
+the solution of the metallic portion and 10 c.c. of aqua regia. Boil
+gently till oxidation is complete and the nitric acid for the greater
+part driven off. Dilute to 100 c.c. with water, and pass sulphuretted
+hydrogen for some time. Filter, wash with hot water, and rinse through
+the funnel back into the flask. Digest with yellow sodium sulphide until
+only a<span class='pagenum'><a name="Page_288" id="Page_288">[Pg 288]</a></span> light, flocculent, black precipitate is left. Filter this off,
+wash with hot water, dry, calcine, treat with a little nitric acid,
+ignite, and weigh as copper oxide, CuO. The weight multiplied by 0.7983
+gives the weight of copper.</p>
+
+<p>The filtrate containing the tin is rendered acid with hydrochloric acid,
+and filtered. The precipitate is rinsed into a half-pint beaker, covered
+with 20 c.c. of hydrochloric acid, and boiled down to about 20 c.c. The
+solution is filtered off from the sulphur and sulphide of arsenic,
+which, after washing with hot water, is transferred to a flask labelled
+"arsenic." A strip of sheet zinc (2 in. by 1 in.) is placed in the
+solution. The evolution of hydrogen should be brisk. In five or ten
+minutes decant off a few c.c. of the liquid, and test with sulphuretted
+hydrogen for tin. If no yellowish precipitate is formed, decant off the
+rest of the liquid, and wash the precipitated metal with hot water two
+or three times by decantation. The metal should be in a lump; if there
+are any floating particles they must be made to sink by compression with
+a glass rod. Transfer the washed metal to an evaporating dish 3 or 4 in.
+across, and cover with a few c.c. of hot water. Add nitric acid drop by
+drop till the tin is completely attacked. Evaporate nearly to dryness,
+and add a drop or two more of nitric acid and 20 c.c. of water. Boil and
+filter. Wash with hot water, dry, ignite, and weigh as stannic oxide,
+SnO<sub>2</sub>. Calculate to metallic tin by multiplying by 0.7867.<a name="FNanchor_76_76" id="FNanchor_76_76"></a><a href="#Footnote_76_76" class="fnanchor">[76]</a></p>
+
+<p>The filtrate from the first treatment with sulphuretted hydrogen will
+probably no longer smell of the gas. Warm and pass the gas for a few
+minutes longer. Filter off any precipitate of sulphide of arsenic, and
+transfer it to the flask for "arsenic." Boil the filtrate (ignoring any
+signs of a further precipitation of arsenic) with a few c.c. of nitric
+acid, and separate the iron as basic acetate. Wash; reserve the filtrate
+for cobalt.</p>
+
+<p><b>Iron.</b>&mdash;Rinse back the "basic acetate," precipitate into the flask, add
+ammonia, dilute with water to about 100 c.c., and pass sulphuretted
+hydrogen for a few minutes. Filter, and wash with hot water. Collect the
+filtrate in the flask labelled "arsenic." Boil the precipitate with
+dilute sulphuric acid, filter, and titrate the filtrate with the
+permanganate of potassium solution after boiling off the sulphuretted
+hydrogen. Report the result as iron. The sulphuric acid will not effect
+complete solution, a light black residue will remain, chiefly sulphur;
+this must be rinsed into the filtrate from the acetate separation. It
+contains cobalt.</p>
+
+<p><b>Cobalt.</b>&mdash;The filtrate from the acetate separation will have a pink
+colour. Render it ammoniacal and pass sulphuretted<span class='pagenum'><a name="Page_289" id="Page_289">[Pg 289]</a></span> hydrogen. Collect
+the precipitate on a filter, dry, and ignite. Dissolve in hydrochloric
+acid, and evaporate nearly to dryness with an excess of nitric acid.
+Dilute with 10 or 20 c.c. of water and add potash solution in slight
+excess. Add acetic acid until the solution is acid and the precipitate
+is quite dissolved. Add 20 or 30 c.c. of a strong solution of potassium
+nitrite, and determine the cobalt, as described on pp. 254, 256. Boil
+the filtrate from the cobalt, precipitate with hydrochloric acid, render
+ammoniacal, and test for zinc, nickel, and manganese.</p>
+
+<p><i>The remainder of the tin</i> will be contained in the flask labelled
+"arsenic." Acidify with hydrochloric acid and filter. Rinse into a
+beaker, and evaporate to a small bulk with 10 c.c. of nitric acid.
+Dilute and filter. Dry the precipitate, consisting of stannic arsenate
+(2SnO<sub>2</sub>.As<sub>2</sub>O<sub>5</sub>), ignite, and weigh. Calculate the tin it contains
+by multiplying by 0.4453, and add to that already found.</p>
+
+<p><b>Arsenic.</b>&mdash;This is determined in a separate portion. Weigh up a portion
+of the powder equivalent to 1 gram of the hardhead, place in a pint
+flask, and boil with 10 c.c. of nitric acid. When action has ceased add
+10 c.c. of the solution of the metallic portion and then hydrochloric
+acid (a few drops at a time) till solution is complete. Warm gently in
+dissolving, but do not boil. Dilute to about 100 c.c., render alkaline
+with ammonia, and add 20 c.c. of yellow ammonium sulphide. Digest at a
+gentle heat for about thirty minutes, filter, and wash. Add 50 c.c. of
+magnesia mixture, shake well, allow to stand for an hour, filter, and
+wash with dilute ammonia. The precipitate is dissolved and then titrated
+with uranium acetate, or it is evaporated with nitric acid, ignited, and
+weighed as pyrarsenate of magnesia. Calculate the result to arsenic, As.</p>
+
+<p><b>Sulphur.</b>&mdash;Weigh up a portion of the powder equivalent to 2 or 3 grams
+of the hardhead. Rub up in a mortar with 5 grams of nitre and fuse in a
+porcelain dish for ten minutes. Extract with water, add 20 or 30 c.c.
+(as the case may be) of the solution of the "metallics." Add 10 grams of
+sodic acetate, and ferric chloride until the precipitate turns brown;
+dilute with water to half a litre, boil, and titrate with standard baric
+chloride, as described under <i>Sulphur</i>. Report as sulphur.</p>
+
+<p>A sample of hardhead examined in this way gave&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sulphur</td><td align='right'>3.00%</td></tr>
+<tr><td align='left'>Arsenic</td><td align='right'>27.10</td></tr>
+<tr><td align='left'>Tin</td><td align='right'>22.2</td></tr>
+<tr><td align='left'>Copper</td><td align='right'>1.64</td></tr>
+<tr><td align='left'>Iron</td><td align='right'>43.2</td></tr>
+<tr><td align='left'>Cobalt</td><td align='right'>2.6</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>99.74</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_290" id="Page_290">[Pg 290]</a></span></p>
+
+<p><b>Examination of Tin Slags.</b>&mdash;In tin smelting works the term "slag" is
+applied to the unfused portion of the charge. It is made up of unburnt
+anthracite and small lumps of slag proper together with some buttons of
+metallic tin. This is rarely, if ever, assayed. The slag proper (or, as
+it is generally called, "glass") is a silicate of iron, alumina, and
+lime, containing from 3 to 7 per cent. of tin. It is thus examined:&mdash;The
+sample after bruising on an iron plate, is reduced to a very fine powder
+by grinding in an agate mortar. In this state it is in most cases
+readily decomposed by hydrochloric acid.</p>
+
+<p><b>Determination of Tin.</b>&mdash;Where the percentage of tin only is required,
+take 2 grams of the powdered slag and well mix with it 20 c.c. of
+hydrochloric acid, and heat to boiling. Add 1 c.c. of nitric acid, allow
+to stand for fifteen minutes, dilute with water, and filter. Pass a
+rapid current of sulphuretted hydrogen for some time. Allow to settle,
+and filter. The precipitate, after washing with hot water, is dried, and
+gently calcined until the greater part of the sulphur is burnt off. It
+is then strongly ignited in the muffle (or over the blowpipe) with the
+addition of a small lump of ammonic carbonate. The residue is weighed as
+stannic oxide (SnO<sub>2</sub>); and is calculated to metallic tin by
+multiplying by 0.787. The percentage on the slag is calculated in the
+usual way.</p>
+
+<p>The tin is always best determined in the examination of slags by a
+separate assay carried out in this way. The determination of the other
+constituents is thus made:&mdash;</p>
+
+<p><b>Silica.</b>&mdash;Take 2 grams of the powdered slag and cover them, in a small
+evaporating dish, with 20 c.c. of hydrochloric acid; mix well by
+stirring with a glass rod; and evaporate to dryness. If (as is generally
+the case) tungsten is present the solution will be blue. Take up with 20
+c.c. of hydrochloric acid. Add 1 c.c. of nitric acid; and reduce by
+boiling to about half the bulk. Add about 20 c.c. of water, boil, and
+filter. Wash the residue with hot dilute hydrochloric acid. It consists
+of silica with the tungstic acid. Wash it back into the dish; and digest
+with 5 or 10 c.c. of a cold solution of ammonic carbonate. Filter; and
+collect the filtrate and washings in a weighed porcelain dish. Dry the
+residue, ignite strongly, and weigh as silica, SiO<sub>2</sub>. In certain
+exceptional cases this may contain some unaltered cassiterite, which is
+easily recognised by its appearance.</p>
+
+<p><b>Tungsten.</b>&mdash;The ammonic carbonate filtrate from the silica is
+evaporated to dryness, ignited strongly over the blowpipe, and weighed.
+The residue is tungstic acid, WO<sub>3</sub>. The tungsten may be conveniently
+reported in this form, although it is probably present as a lower
+oxide.<span class='pagenum'><a name="Page_291" id="Page_291">[Pg 291]</a></span></p>
+
+<p><b>Tin.</b>&mdash;The acid filtrate from the silica and tungstic acid is treated
+with sulphuretted hydrogen. The sulphide of tin is filtered off. Since
+the percentage of tin has been already determined, this precipitate may
+be neglected; or may be treated in the same way as the previous one, so
+as to check the result. Since some stannic chloride will have been lost
+in the evaporation, a low result may be expected. The tin should be
+reported as stannous oxide; and is calculated by multiplying the
+percentage of tin by 1.136.</p>
+
+<p>The filtrate from the tin is boiled rapidly down to remove sulphuretted
+hydrogen; and then peroxidised with 1 or 2 c.c. of nitric acid. It is
+cooled, transferred to a graduated flask, and diluted with water to 200
+c.c.</p>
+
+<p><b>Ferrous Oxide and Alumina.</b>&mdash;Half the filtrate from the tin (that is,
+100 c.c.) is taken, nearly neutralised with soda, and treated with
+sodium acetate. The basic acetate precipitate obtained on boiling is
+filtered off and washed. Reserve the filtrate. The precipitate is
+dissolved off the filter with hot dilute hydrochloric acid; and the
+solution thus formed is treated with a slight excess of ammonia, and
+boiled. The precipitate is filtered off, washed with hot water, dried,
+ignited, and weighed as mixed ferric oxide and alumina. The ignited
+precipitate is then dissolved with sulphuric and hydrochloric acids; and
+the iron determined in the solution by titration with the solution of
+stannous chloride. The iron found is calculated to and reported as
+ferrous oxide, FeO (factor = 1.286). To find the alumina, which is best
+estimated by difference, multiply the iron by 1.428 to get the weight of
+ferric oxide, and deduct this from the weight of alumina and ferric
+oxide found. This, of course, gives the alumina. A direct determination
+may be made by removing the tin from the titrated solution with
+sulphuretted hydrogen, filtering, nearly neutralising with ammonia, and
+boiling with a few grams of hyposulphite of soda. The precipitate,
+filtered, washed, and ignited, is the alumina, which is weighed. The
+direct determination gives a slightly low result.</p>
+
+<p><b>Oxides of Zinc and Manganese.</b>&mdash;These are determined in the filtrate
+from the basic acetate precipitate by rendering alkaline with ammonia,
+and passing a current of sulphuretted hydrogen. Generally a small, but
+decided, precipitate of alumina comes down, together with sulphides of
+any zinc or manganese which is present. The precipitate is allowed to
+settle, dried, ignited, and weighed. The metals are separately
+determined in it; and the residue is counted as alumina, and added to
+that already found. The mixed precipitate amounts to from 1 to 2 per
+cent. of the sample.<span class='pagenum'><a name="Page_292" id="Page_292">[Pg 292]</a></span></p>
+
+<p><b>Lime.</b>&mdash;The filtrate from the last is treated with ammonic oxalate,
+boiled for a few minutes, allowed to settle, and filtered. The
+precipitate is washed with hot water; dried; ignited; and weighed as
+carbonate, after gentle ignition; or as lime, after strong ignition in
+the muffle.</p>
+
+<p><b>Magnesia.</b>&mdash;The filtrate from the lime is treated with sodic phosphate
+and ammonia. It is well mixed by stirring, and allowed to stand
+overnight. The precipitate is washed with dilute ammonia, dried,
+ignited, and weighed as pyrophosphate.</p>
+
+<p><b>Soda and Potash.</b>&mdash;These are determined in the remaining half of the
+filtrate from the tin. The solution is rendered ammoniacal with ammonia;
+and treated, first with sulphuretted hydrogen, and then with ammonium
+oxalate. The precipitate is filtered off and rejected. The filtrate is
+evaporated in a small porcelain dish over a Bunsen burner, or on the
+sand bath; and towards the close (or earlier if the evaporation is not
+proceeding well) nitric acid is added. The evaporation is carried to
+dryness; and the residue heated nearly to redness. The residue, which
+consists of magnesia with carbonates and chlorides of the alkalies, is
+extracted with water; and filtered. The filtrate is evaporated with
+hydrochloric acid in a weighed platinum dish, ignited gently, and
+weighed. This gives the weight of the mixed chlorides of sodium and
+potassium; which are then separated and determined as described under
+<i>Potash</i>.</p>
+
+<p>It must be remembered when calculating the percentage that (with the
+exception of the silica, tungstic acid, and tin) the determinations have
+been made on 1 gram of the sample.</p>
+
+<p>The following analysis will illustrate the composition of such a slag:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Tungstic acid</td><td align='right'>1.3%</td></tr>
+<tr><td align='left'>Silica</td><td align='right'>39.4</td></tr>
+<tr><td align='left'>Stannous oxide</td><td align='right'>8.1</td></tr>
+<tr><td align='left'>Ferrous oxide</td><td align='right'>26.2</td></tr>
+<tr><td align='left'>Alumina</td><td align='right'>14.8</td></tr>
+<tr><td align='left'>Oxide of manganese</td><td align='right'>traces</td></tr>
+<tr><td align='left'>Lime</td><td align='right'>7.9</td></tr>
+<tr><td align='left'>Magnesia</td><td align='right'>0.5</td></tr>
+<tr><td align='left'>Alkalies calculated as soda</td><td align='right'>1.7</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>99.9</td></tr>
+</table></div>
+
+
+
+<h4>TITANIUM.</h4>
+
+<p>Titanium only occurs as a mineral in its oxidised state, or as titanic
+oxide (TiO<sub>2</sub>). It is a substance which has little commercial value,
+and is generally recognised as one of the rare bodies; although, in
+small quantities, it is widely disseminated. It occurs in granite,
+basalt, and other igneous rocks in quantities up to as<span class='pagenum'><a name="Page_293" id="Page_293">[Pg 293]</a></span> much as 1 per
+cent. It is also met with in clays and iron ores, and in river sands, in
+which it is often associated with stream tin. The proper minerals of
+titanium are rutile (TiO<sub>2</sub>), titaniferous iron (titanate of iron), and
+sphene (titanate and silicate of lime).</p>
+
+<p>The oxide of titanium (like cassiterite and quartz) is undecomposed by
+hydrochloric or nitric acid; so that it is generally found in the
+residue insoluble in acids. The titanates, however, are attacked, and a
+portion of the titanium dissolves; so that it must be looked for in both
+the filtrate and residue. Oxide of titanium in its native form, or after
+ignition, may be made soluble by fusing the finely-divided substance
+with fusion mixture in a platinum dish. The resulting titanate is
+dissolved out of the "melt" by cold hydrochloric acid.</p>
+
+<p>The method most commonly used is fusion with bisulphate of potash. This
+renders the oxide of titanium soluble in cold water. The process is as
+follows:&mdash;The substance is extracted with hydrochloric and nitric acids,
+and the solution reserved for further treatment; the residue is dried,
+moistened with sulphuric acid, and evaporated once or twice to dryness
+with hydrofluoric acid. It is then fused with bisulphate of potash, and
+the "melt" extracted with cold water until all soluble matter is
+removed. The solution is filtered. The residue may consist of unremoved
+silica, and oxides of tantalum, niobium, and, perhaps, chromium. On the
+prolonged boiling of the filtrate, the oxide of titanium (and oxide of
+zirconium, if any) is precipitated.</p>
+
+<p>Any titanium dissolved by the first extraction with acids is recovered
+in the following way:&mdash;Sulphuretted hydrogen is passed into the acid
+solution, and any precipitate that may be formed is filtered off. The
+filtrate is oxidised, and the iron, aluminium, and titanium are
+separated as basic acetates (see under <i>Iron</i>). The precipitate is dried
+and fused with bisulphate of potash. The "melt" is extracted with cold
+water, filtered if necessary, and the solution rendered first faintly
+alkaline with ammonia, then very slightly acid with sulphuric acid. 30
+or 40 c.c. of a saturated solution of sulphurous acid is added, and the
+oxide of titanium precipitated by prolonged boiling. It is filtered off,
+added to the precipitate previously got, ignited with ammonic carbonate
+towards the end, and then weighed.</p>
+
+<p><b>Detection.</b>&mdash;Titanium is detected in an insoluble residue by fusing the
+residue for some time in a bead of microcosmic salt. In the reducing
+flame it gives a violet colour, which becomes reddish-brown if much iron
+is present. In the oxidising flame it gives a colourless or whitish
+bead. It is best detected in acid solutions by the deep brown or iodine
+colour developed on adding hydroxyl. A solution of this can be prepared
+<span class='pagenum'><a name="Page_294" id="Page_294">[Pg 294]</a></span>by pouring peroxide of barium (BaO<sub>2</sub>) diffused in water into dilute
+hydrochloric acid (a little at a time), and keeping the acid in excess.</p>
+
+<p><b>Separation.</b>&mdash;In the usual course of an analytical separation the
+hydrate of titanium will be thrown down with ferric hydrate, &amp;c., on the
+addition of ammonic chloride and ammonia. It is best separated from this
+precipitate by fusion with bisulphate of potash, as already described,
+but it must be remembered that the presence of much mineral acid
+prevents complete precipitation when the solution is boiled. Further, if
+phosphates are present, the precipitate will contain phosphoric oxide;
+it may be freed from this by fusion with sodium carbonate. A very good
+method of separating titanium from iron is to add tartaric acid and
+ammonia to the solution, and then precipitate the iron (as sulphide)
+with sulphuretted hydrogen. The filtrate contains the titanium, which is
+recovered by evaporating and igniting. It may be separated from zirconia
+by the action of sodium carbonate, which precipitates both; but when
+concentrated, redissolves the zirconia. The separation from large
+quantities of silica is best effected by evaporating with hydrofluoric
+acid, which volatilises the silicon; but sulphuric acid must be present,
+otherwise some titanium also will be lost, as may be seen from the
+following experiments,<a name="FNanchor_77_77" id="FNanchor_77_77"></a><a href="#Footnote_77_77" class="fnanchor">[77]</a> in which oxide of titanium (pure, ignited)
+was evaporated to dryness with a quantity of hydrofluoric acid known by
+experiment to be sufficient to volatilise 1 gram of silica.</p>
+
+<p><i>Without sulphuric acid</i>, 0.0466 gram of titanic oxide left 0.0340 gram,
+showing a loss of about 25 per cent.</p>
+
+<p><i>With sulphuric acid</i> the following results were obtained:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Oxide taken.</td><td align='left'>Left after Evaporation and Ignition.</td></tr>
+<tr><td align='left'>0.0340 gram</td><td align='left'>0.0340 gram</td></tr>
+<tr><td align='left'>0.0414&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.0413&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>0.0520 &nbsp;&nbsp;&nbsp;"</td><td align='left'>0.0520 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>0.0352&nbsp;&nbsp;&nbsp; "</td><td align='left'>0.0352&nbsp;&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The titanic hydrate thrown down by ammonia (or on boiling the solution
+from the bisulphate) is collected, washed, dried, ignited strongly with
+the addition of a little ammonic carbonate, and weighed. The substance
+is titanic oxide (TiO<sub>2</sub>), and is generally reported as such. It
+contains 60.98 per cent. of titanium. It should be white, if pure
+(Holland), white, yellow, or brown (Fresenius), or black (Tidy).<span class='pagenum'><a name="Page_295" id="Page_295">[Pg 295]</a></span></p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>A method has been proposed based on the reduction of titanic oxide by
+zinc in hydrochloric acid solutions to the sesquioxide. The reduction is
+marked by the development of a violet or green colour, the former with
+chlorides and the latter when fluorides are present. The quantity of
+titanium reduced is measured by titrating with permanganate of potassium
+solution. The water used must be free from dissolved oxygen.</p>
+
+
+<h4>TUNGSTEN AND TUNGSTATES.</h4>
+
+<p>Tungsten occurs in nature only in the oxidised state, or as tungstic
+acid (WO<sub>3</sub>), either free, as in wolframine, or combined with oxides of
+manganese and iron, as in wolfram, or with lime, as in scheelite.
+Wolfram occurs associated with tin ores, the value of which is
+consequently lowered. Both wolfram and scheelite are of considerable
+importance as a source of tungstic acid for the manufacture of sodium
+tungstate, which is used as a mordant and for some other purposes, and
+as a source of metallic tungsten, which is used in steel-making.</p>
+
+<p>The tungsten minerals have a high specific gravity (6 to 7.5). On
+treatment with hydrochloric acid or aqua regia they are decomposed; the
+yellow tungstic acid separates and remains insoluble.</p>
+
+<p>Tungsten itself is insoluble in nitric acid or aqua regia; but is
+converted into tungstic acid (WO<sub>3</sub>) by prolonged and strong ignition
+in air. Alloys containing tungsten leave tungstic acid after treatment
+with nitric acid or aqua regia. Tungstic acid may be got into solution
+after fusion with alkalies or alkaline carbonates. This solution gives
+with hydrochloric acid a white precipitate of tungstic acid, which
+becomes yellow on boiling, but the separation is not complete. Fusion
+with bisulphate of potash gives a residue, which does not dissolve in
+water, but is soluble in ammonic carbonate. For the assay of minerals
+containing tungsten these reactions are only occasionally taken
+advantage of for testing or purifying the separated tungstic acid.</p>
+
+<p><b>Detection.</b>&mdash;The minerals are easily recognised by their physical
+characters, and the yellow tungstic acid separated by boiling with acids
+is the best test for its presence; this, after decanting and washing,
+immediately dissolves in a few drops of dilute ammonia. A solution of
+tungstate acidulated with hydrochloric acid becomes intensely blue on
+the addition of stannous chloride and warming. Fused in a bead of
+microcosmic salt it<span class='pagenum'><a name="Page_296" id="Page_296">[Pg 296]</a></span> gives a clear blue colour (reddish-brown if iron is
+also present) in the reducing flame, but is colourless in the oxidising
+flame.</p>
+
+<p><b>Solution and Separation.</b>&mdash;The decomposition and solution of natural
+tungstates is difficult to effect owing to the separation of tungstic
+acid; the method of treatment is as follows:&mdash;Boil the finely-powdered
+substance with hydrochloric acid or aqua regia till it apparently ceases
+to be attacked; dilute, filter, and wash with dilute hydrochloric acid.
+Cover with dilute ammonia, and filter the solution, which contains
+ammonic tungstate, into an evaporating dish. Treat the residue again
+with acid, and again dissolve out the separated tungstic acid with
+ammonia, and repeat this operation until decomposition is complete. By
+this means there will be obtained&mdash;(1) a solution containing tungstate
+of ammonia; (2) an insoluble residue with silicates, and oxides of tin,
+niobium, tantalum, &amp;c.; and (3) an acid solution containing the soluble
+bases. The tungstate of ammonia requires simple evaporation on the
+water-bath and gentle ignition in order to cause the tungstic acid to be
+left in an almost pure state; possibly, it may carry a little silica.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The tungstic acid is dissolved, and separated as ammonic tungstate, and,
+after evaporation, is gently ignited, the heat being increased towards
+the end. The residual tungstic acid is fixed, so that when the ammonia
+has been driven off it may be strongly heated without loss. It is a dark
+yellow or brown powder whilst hot, which becomes a light yellow on
+cooling. If any reduction has taken place it will be more or less
+greenish. It is weighed when cold, and is the trioxide or "tungstic
+acid" (WO<sub>3</sub>), which contains 79.31 per cent. of tungsten. After its
+weight has been taken its purity is checked by fusing with hydric
+potassic sulphate, extracting with water, and treating the residue with
+ammonic carbonate. Any silica present will be left undissolved; it
+should be separated and weighed, and its weight deducted from that of
+the tungstic acid found.</p>
+
+<p><b>Determination of Tungstic Acid in Wolfram.</b>&mdash;Take 2 grams of the
+finely-powdered sample and boil with 50 c.c. of hydrochloric acid for
+half an hour, adding 5 c.c. of nitric acid towards the end. Allow to
+stand overnight and boil again for 15 or 20 minutes; dilute with an
+equal volume of water, and filter. Wash with dilute hydrochloric acid,
+dissolve in a few c.c. of warm dilute ammonia, and dilute to 200 c.c.
+with distilled water; allow to settle, and filter. Evaporate in a
+weighed dish, ignite, and weigh.<span class='pagenum'><a name="Page_297" id="Page_297">[Pg 297]</a></span></p>
+
+<p>The following analysis will illustrate the composition of a sample of
+Cornish wolfram as brought into the market:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Tungstic acid</td><td align='right'>50.1%</td></tr>
+<tr><td align='left'>Cassiterite</td><td align='right'>10.9</td></tr>
+<tr><td align='left'>Ferrous oxide</td><td align='right'>24.6</td></tr>
+<tr><td align='left'>Manganous oxide</td><td align='right'>5.4</td></tr>
+<tr><td align='left'>Niobic oxide, alumina, &amp;c.</td><td align='right'>3.5</td></tr>
+<tr><td align='left'>Silica</td><td align='right'>1.2</td></tr>
+<tr><td align='left'>Copper oxide</td><td align='right'>2.7</td></tr>
+<tr><td align='left'>Zinc oxide</td><td align='right'>0.22</td></tr>
+<tr><td align='left'>Arsenic</td><td align='right'>0.51</td></tr>
+<tr><td align='left'>Sulphur</td><td align='right'>0.20</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>99.33</td></tr>
+</table></div>
+
+
+
+<h4>NIOBIC AND TANTALIC OXIDES.</h4>
+
+<p>These oxides are commonly met with in samples of wolfram and tinstone,
+especially niobic. They are probably present in the form of columbite, a
+niobate of iron and manganese; and tantalite, a tantalate of the same
+metals.</p>
+
+<p>On boiling with hydrochloric acid they are both liberated, and remain
+for the greater part (all the niobic) in the insoluble residue with the
+tungstic acid. On removing the latter with dilute ammonia they remain as
+a white insoluble precipitate, very prone to run through the filter on
+washing. They may be dissolved in hydrofluoric acid either at once or
+after fusion with bisulphate of potash, and extraction with cold water.
+To the solution in hydrofluoric acid gradually add a boiling solution of
+acid potassium fluoride (HF, KF.). Potassic fluotantalate (soluble in
+200 parts of water) separates out first, and afterwards potassic
+fluoniobate (soluble in 12 parts of water). The separated salts (after
+heating with sulphuric acid and washing out the potassium sulphate
+formed) are ignited with ammonic carbonate, and weighed as tantalic
+oxide (Ta<sub>2</sub>O<sub>5</sub>) and niobic oxide (Nb<sub>2</sub>O<sub>5</sub>) respectively.</p>
+
+<p>They are both white powders. The oxide of niobium dissolved in a bead of
+microcosmic salt gives a bluish colour in the reducing flame. The oxide
+of tantalum dissolves in the bead, but gives no colour.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_76_76" id="Footnote_76_76"></a><a href="#FNanchor_76_76"><span class="label">[76]</span></a> This will give almost the whole of the tin; a further
+portion will be got in subsequent work, and must be added to this
+result.</p></div>
+
+<div class="footnote"><p><a name="Footnote_77_77" id="Footnote_77_77"></a><a href="#FNanchor_77_77"><span class="label">[77]</span></a> Published by P. Holland, in the <i>Chemical News</i>, vol. lix.
+p. 27.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_298" id="Page_298">[Pg 298]</a></span></p>
+<h2><a name="CHAPTER_XIII" id="CHAPTER_XIII"></a>CHAPTER XIII.</h2>
+
+<h3>MANGANESE, CHROMIUM, &amp;c.</h3>
+
+
+<h4>MANGANESE.</h4>
+
+<p>Manganese occurs mainly as black oxide (MnO<sub>2</sub>) in the mineral
+pyrolusite; and, in a less pure form, in psilomelane and wad. The value
+of the ore depends rather on the percentage of available oxygen than on
+the proportion of metal present. The results of assays are generally
+reported as so much per cent. of the dioxide (MnO<sub>2</sub>). In smaller
+quantities it is very widely distributed. Manganese itself has a value
+for steel-making; or, rather, for the making of spiegeleisen and
+ferro-manganese, which are used in the Bessemer and Siemens processes.
+For this purpose the percentage of the metal (Mn) is required.
+Consequently the minerals of manganese may be considered in two
+aspects&mdash;(1) as a source of oxygen; and (2) as a source of manganese.
+These will require separate consideration.</p>
+
+<p>The black oxide is mainly used in the preparation of chlorine,
+liberation of which it brings about when treated with hot hydrochloric
+acid, or with a mixture of common salt and sulphuric acid. The quantity
+of chlorine which is obtained depends upon the proportion of dioxide
+present;<a name="FNanchor_78_78" id="FNanchor_78_78"></a><a href="#Footnote_78_78" class="fnanchor">[78]</a> and in assaying may either be measured by its equivalent of
+iodine liberated, or by the oxidising effect on an acid solution of
+ferrous sulphate. When the ore also carries substances which have a
+reducing effect (such as ferrous compounds), such assays will give, not
+the total dioxide (MnO<sub>2</sub>), but less, by the amount required to oxidise
+these impurities; and this is exactly what is required in valuing such
+an ore for commercial purposes. Manganese compounds are characterised by
+the readiness with which they may be converted into highly-oxidised
+bodies. Solution of manganese in hydrochloric acid, rendered alkaline
+with ammonia, yields a clear solution,<a name="FNanchor_79_79" id="FNanchor_79_79"></a><a href="#Footnote_79_79" class="fnanchor">[79]</a> which rapidly takes up oxygen
+from the air, forming a brown precipitate of the oxide (Mn<sub>2</sub>O<sub>3</sub>).
+The addition of<span class='pagenum'><a name="Page_299" id="Page_299">[Pg 299]</a></span> bromine or chlorine to such a solution determines the
+precipitation of a still higher oxide (approximately MnO<sub>2</sub>). On
+treating a compound containing manganese with nitric acid and dioxide of
+lead (PbO<sub>2</sub>), the oxidation is carried still further, a
+purple-coloured solution of permanganic acid (HMnO<sub>4</sub> or
+H<sub>2</sub>O.Mn<sub>2</sub>O<sub>7</sub>) being formed. On fusing minerals containing (even
+traces of) manganese with sodium carbonate in an open crucible, a green
+"melt" is obtained which owes its colour to sodium manganate
+(Na<sub>2</sub>MnO<sub>4</sub> or Na<sub>2</sub>O.MnO<sub>3</sub>). This salt is soluble in water,
+forming a green solution; which, when rendered acid, rapidly changes
+into the permanganate with the characteristic purple colour.
+Permanganate of potash is a salt much used in assaying, with some
+properties of which the student will have already become familiar.</p>
+
+
+<p>Compounds of manganese, on boiling with strong hydrochloric acid, yield
+manganous chloride<a name="FNanchor_80_80" id="FNanchor_80_80"></a><a href="#Footnote_80_80" class="fnanchor">[80]</a> (MnCl<sub>2</sub>).</p>
+
+<p>The properties given above serve for the detection of manganese; the
+higher oxides are distinguished by causing the evolution of chlorine
+(with its peculiarly suffocating smell) when acted on with hydrochloric
+acid; while the green "melt," with sodium carbonate, can be relied on
+for the recognition of manganese itself. There is no dry assay of
+manganese ores.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p>Strong hydrochloric acid is the best solvent for ores of manganese; but
+where the proportion of dioxide (MnO<sub>2</sub>) is required, the solution is
+effected during the assay. The ore should be in a very fine state of
+division before treatment with acids.</p>
+
+<p>The separation of manganese from other metals is thus effected: Ignite,
+in order to destroy any organic matter which may be present; dissolve in
+hydrochloric acid, and evaporate to dryness, to separate silica. Take up
+with hydrochloric acid, dilute, pass sulphuretted hydrogen, and filter.
+Boil off the excess of gas, peroxidise the iron with a drop or two of
+nitric acid, and separate the iron as basic acetate (as described under
+<i>Iron</i>).<a name="FNanchor_81_81" id="FNanchor_81_81"></a><a href="#Footnote_81_81" class="fnanchor">[81]</a> If the iron precipitate is bulky, it is dissolved in a
+little hydrochloric acid, reprecipitated, and the filtrate added to the
+original one. Neutralise with soda, and add bromine in excess; heat
+gradually to boiling, allow to settle, and filter. The precipitate is
+impure dioxide of manganese (containing alkalies and, possibly, cobalt
+or nickel).<span class='pagenum'><a name="Page_300" id="Page_300">[Pg 300]</a></span></p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>Dissolve the precipitate in hydrochloric acid, and boil; add a slight
+excess of carbonate of soda, warm, and filter. Wash with hot water, dry,
+carefully ignite in an open Berlin crucible, and weigh. The substance is
+the brown oxide (Mn<sub>3</sub>O<sub>4</sub>), and contains 72.05 per cent. of
+manganese. If the percentage of dioxide is required it may be calculated
+by multiplying the percentage of manganese by 1.582. It must be borne in
+mind that the manganese should never be calculated to dioxide except
+when it is known to exist in the ore only in that form.</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>The two methods are based on the oxidising effect of manganese dioxide;
+and if the metal does not already exist in this form it will require a
+preliminary treatment to convert it. The following method due to Mr. J.
+Pattinson<a name="FNanchor_82_82" id="FNanchor_82_82"></a><a href="#Footnote_82_82" class="fnanchor">[82]</a> effects this: A quantity of the ore containing not more
+than .25 grams of the metal (Mn), is dissolved in hydrochloric acid in a
+pint beaker, and, if necessary, 3 or 4 c.c. of nitric acid are added to
+peroxidise the iron, and ferric chloride is added if required, so that
+there may be at least as much iron as manganese. Calcium carbonate is
+added till the solution is slightly red; and next the redness is removed
+by the cautious addition of acid; 30 c.c. of zinc chloride solution
+(containing 15 grams of zinc per litre) are added, the liquid is brought
+to boil and diluted to about 300 c.c. with boiling water; 60 c.c. of a
+solution of bleaching powder (33 grams to the litre and filtered),
+rendered slightly greenish by acid, are then run in and are followed by
+3 grams of calcium carbonate suspended in 15 c.c. of boiling water.
+During effervescence the beaker is covered, the precipitate is stirred,
+and 2 c.c. of methylated spirit are mixed in. The precipitate is
+collected on a large filter, washed with cold water, and then with hot,
+till free from chlorine, which is tested for with starch and potassium
+iodide. The acid ferrous sulphate solution (presently described) is then
+measured into the beaker, and the precipitate, still in the paper,
+added; more acid is added (if necessary), and the solution is diluted
+and titrated. In place of bleaching powder solution, 90 c.c. of bromine
+water (containing 22 grams per litre) may be used.<span class='pagenum'><a name="Page_301" id="Page_301">[Pg 301]</a></span></p>
+
+
+<h4>FERROUS SULPHATE ASSAY.</h4>
+
+<p>This method, which is the one commonly used, is based on the
+determination of the amount of ferrous iron oxidised by a known weight
+of the ore. It is known that 87 parts of the dioxide will oxidise 112
+parts of ferrous iron;<a name="FNanchor_83_83" id="FNanchor_83_83"></a><a href="#Footnote_83_83" class="fnanchor">[83]</a> therefore 1 gram will oxidise 1.287 gram of
+ferrous iron, or 1 gram of ferrous iron oxidised will be equivalent to
+0.7768 gram of the dioxide. The finely-divided substance containing the
+dioxide is digested in a solution of a known quantity of iron in
+sulphuric acid. The iron, of course, must be in excess, which excess is
+determined when the ore is dissolved by titrating with standard
+permanganate or bichromate of potash solution. The assay resolves itself
+into one for the determination of ferrous iron, for which the standard
+solutions and method of working described under <i>Iron</i> are used.</p>
+
+<p>The assay is as follows:&mdash;For rich ores, 2 grams of clean soft iron wire
+are treated, in a pint flask, with 100 c.c. of dilute sulphuric acid and
+warmed till dissolved. Carefully sample the ore, and in one portion
+determine the "moisture at 100&deg; C.;" grind the rest in a Wedgwood mortar
+with a little pure alcohol until free from grit. This reduces the
+substance to a finely-divided state and assists solution. Evaporate off
+the alcohol and dry at 100&deg; C., mix well, and keep in a weighing-bottle.
+Weigh up 2 grams and add them to the solution of iron in the flask;
+carefully wash it all down into the acid liquid. On rotating the flask
+the ore will rapidly dissolve, but gentle heat may be used towards the
+end to complete the solution. When the residue is clean and
+sandy-looking, and free from black particles, the flask is cooled, and
+the residual ferrous iron is determined by titration with
+"permanganate." The iron thus found, deducted from the 2 grams taken,
+will give the amount of iron peroxidised by the dioxide contained in the
+2 grams of ore. This divided by 2 and multiplied by 77.68 will give the
+percentage of dioxide in the sample, or multiplied by 49.41 will give
+that of metallic manganese.</p>
+
+<p>When the quantity of manganese or of the dioxide to be determined is
+small, it is not necessary to use 2 grams of iron; 1 gram, or even less,
+may be taken. The iron may be used in the form of a standard solution of
+ferrous sulphate and portions measured off, thus saving the labour of
+weighing.<span class='pagenum'><a name="Page_302" id="Page_302">[Pg 302]</a></span></p>
+
+<p><b>Determination of Dioxide in a Manganese Ore.</b>&mdash;Weigh up 1 or 2 grams of
+the finely-powdered ore<a name="FNanchor_84_84" id="FNanchor_84_84"></a><a href="#Footnote_84_84" class="fnanchor">[84]</a> and an equal weight of pure iron wire,
+dissolve the wire in 50 or 100 c.c. of dilute sulphuric acid, and, when
+solution is complete, add the ore and warm till it too is dissolved.
+Cool and titrate the remaining ferrous iron with the permanganate or
+bichromate of potassium solution.</p>
+
+<p>For example, 0.7560 gram of pyrolusite and 1.000 gram of iron were taken
+and treated as above; 13.9 c.c. of "permanganate" (standard 100 c.c. =
+0.4920 gram iron) were required; this indicates that 0.0684 gram of iron
+was left unoxidised by the ore. The iron oxidised, then, was 0.9316 gram
+(1.000 - 0.0684); multiplying this by 0.7768, we find that 0.7237 gram
+is the quantity of manganese dioxide which was present. This is
+equivalent to 95.77 per cent.;</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;0.7560 : 0.7237 :: 100 : 95.77.<br />
+</p>
+
+
+<h4>IODINE METHOD.</h4>
+
+<p>It has been already stated that when dioxide of manganese is boiled with
+strong hydrochloric acid chlorine is given off, and that the amount of
+chlorine so liberated is a measure of the dioxide present. If the
+chlorine is passed into a solution of potassium iodide, an equivalent of
+iodine will be set free.<a name="FNanchor_85_85" id="FNanchor_85_85"></a><a href="#Footnote_85_85" class="fnanchor">[85]</a> This is apparently a very indirect way of
+determining how much of the dioxide is present; but the reactions are
+very sharp, and the final determination of the iodine is an easy one.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig060.jpg" width="300" height="308" alt="Fig. 60." title="" />
+
+</div>
+
+<p>The finely-powdered sample of dioxide is placed in a small flask
+provided with an exit tube leading into a solution of potassic iodide
+(fig. 60). On adding hydrochloric acid and boiling, the chlorine evolved
+is driven into the iodide solution and there absorbed; the boiling is
+continued till the steam and hydrochloric acid fumes have driven the
+last portions of the chlorine out of the flask and into the solution. In
+this experiment there is a strong tendency for the iodide solution<span class='pagenum'><a name="Page_303" id="Page_303">[Pg 303]</a></span> to
+rush back into the flask. This tendency is overcome by avoiding draughts
+and regulating the heat; or by placing a lump of magnesite in the flask,
+which acts by evolving carbonic acid and so producing a steady outward
+pressure. When the distillation is finished the tube containing the
+iodine is detached and washed out into a beaker. If the solution is
+strongly acid it should be almost neutralised by the cautious addition
+of dilute ammonia. If crystals of iodine have separated, potassium
+iodide must be added in quantity sufficient to dissolve them. The
+condenser must be kept cool whilst the chlorine is passing into it.</p>
+
+<p>The solution, transferred to a beaker, is titrated with a standard
+solution of sodic hyposulphite (100 c.c. = 1.27 gram iodine or 0.435
+gram of dioxide of manganese). In titrating, the solution should be
+cold, or not warmer than 30&deg; C. The bulk may vary from 100 to 200 c.c.;
+but it is best always to work with the same volume. The "hypo" is run in
+with constant agitation until the brown colour has been reduced to a
+light yellow; 5 c.c. of starch solution are then added and the titration
+cautiously continued until the end is reached; the finish is indicated
+by a change from blue to colourless.</p>
+
+<p>The assay solution may be acidified with acetic, sulphuric, or
+hydrochloric acid before titrating with "hypo;" but it must be only
+faintly so. An excess of acid may be nearly neutralised with ammonia
+without interference, but excess of alkali is fatal. Bicarbonate of soda
+must not be used in excess; it is best to avoid it altogether. The assay
+solution should be titrated at once, as it weakens on standing; and the
+"hypo" solution should be standardised every two or three days, as its
+strength is not constant.</p>
+
+<p><i>The standard solution of hyposulphite of soda</i> is made by dissolving 25
+grams of the salt (Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub>.5H<sub>2</sub>O) in water and diluting to 1
+litre. 100 c.c. are equivalent to 1.27 gram of iodine.</p>
+
+<p>This solution is standardised by weighing, in a small beaker, about half
+a gram of iodine, to which is added a crystal or two of potassium iodide
+and a few drops of water. When dissolved, the solution is diluted to 100
+c.c., and titrated in the manner described. The starch solution is made
+in the manner described under the iodide copper assay. 5 c.c. are used
+for each titration.</p>
+
+<p>In determining the effects of variations in the condition of the assay a
+solution of iodine was used, which was equivalent in strength to the
+"hypo" solution. It was made by dissolving 12.7 grams of iodine with 25
+grams of potassium iodide in a little water and diluting to 1 litre. 100
+c.c. of this solution were found (at the time of the experiments) to be
+equivalent to 102.0 c.c. of the "hypo."<span class='pagenum'><a name="Page_304" id="Page_304">[Pg 304]</a></span></p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The bulk of the solution was 100 c.c.;
+20 c.c. of iodine were taken, and 5 c.c. of starch solution were added
+towards the end as indicator. These conditions are also those of the
+other experiments, except where otherwise stated. Iodine being volatile,
+it is to be expected that with hot solutions low results will be
+obtained.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg;</td><td align='left'>20&deg;</td><td align='left'>40&deg;</td><td align='left'>60&deg;</td><td align='left'>80&deg;</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>20.4 c.c.</td><td align='left'>20.1 c.c.</td><td align='left'>19.2 c.c.</td><td align='left'>15.5 c.c.</td></tr>
+</table></div>
+
+
+<p>These show that the temperature should not much exceed 20&deg;.</p>
+
+<p><b>Effect of Exposure of the Iodine Solution.</b>&mdash;Twenty c.c. of the iodine
+were diluted to 100 c.c., and exposed for varying lengths of time in
+open beakers at the ordinary temperature, and then titrated.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Time exposed</td><td align='left'>&mdash;</td><td align='left'>1 day</td><td align='left'>2 days</td><td align='left'>3 days</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>16.1 c.c.</td><td align='left'>13.6 c.c.</td><td align='left'>9.4 c.c.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Bulk.</b>&mdash;These experiments were carried out in the
+usual way, bulk only varying.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>100.0</td><td align='left'>c.c.</td><td align='left'>200.0</td><td align='left'>c.c.</td><td align='left'>300.0</td><td align='left'>c.c.</td><td align='left'>500.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Acid.</b>&mdash;These experiments were under the usual
+conditions, the bulk being 100 c.c. The results were&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acetic acid</td><td align='left'>&mdash;</td><td align='left'>1.5</td><td align='left'>c.c.</td><td align='left'>30.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>20.7</td><td align='left'>"</td><td align='left'>20.7</td><td align='left'>"</td></tr>
+<tr><td align='left'>Hydrochloric acid</td><td align='left'>&mdash;</td><td align='left'>1.5</td><td align='left'>c.c.</td><td align='left'>15.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>20.6</td><td align='left'>"</td><td align='left'>20.9</td><td align='left'>"</td></tr>
+<tr><td align='left'>Sulphuric acid</td><td align='left'>&mdash;</td><td align='left'>0.5</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>20.7</td><td align='left'>"</td><td align='left'>15.2</td><td align='left'>"<a name="FNanchor_86_86" id="FNanchor_86_86"></a><a href="#Footnote_86_86" class="fnanchor">[86]</a> </td></tr>
+<tr><td align='left'>Nitric acid</td><td align='left'>&mdash;</td><td align='left'>0.5</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'> c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>21.5</td><td align='left'>"</td><td align='left'></td><td align='left'>could not be titrated.</td></tr>
+</table></div>
+
+
+<p>In the application of this titration to the assay of manganese ores,
+hydrochloric and hydriodic acids are the only ones likely to be present.</p>
+
+<p><b>Effect of Alkalies.</b>&mdash;On theoretical grounds the presence of these is
+known to be inadmissible. A solution rendered faintly alkaline with
+ammonia required only 11.2 c.c. of "hypo;" and another, with 0.5 gram of
+caustic soda, required 4.0 c.c. instead of 20.4 c.c. as in neutral
+solutions.</p>
+
+<p><b>Effect of nearly Neutralising Hydrochloric Acid Solutions with
+Ammonia.</b>&mdash;Provided care is taken not to add<span class='pagenum'><a name="Page_305" id="Page_305">[Pg 305]</a></span> excess of ammonia, this
+has a good effect, counteracting the interference of excess of acid.
+Thus 20 c.c. of iodine (as before) required 20.4 c.c. of "hypo;" with 15
+c.c. of hydrochloric acid 20.7 c.c. were required, but with 15 c.c. of
+acid, nearly neutralised with dilute ammonia 20.4 c.c. were used.</p>
+
+<p><b>Effect of the Addition of Starch.</b>&mdash;The addition of varying quantities
+of starch has no effect, provided it is added when the titration is
+nearly finished, as the following experiments show:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Starch added</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>5.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>20.5</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>But if the starch is added before the titration, the results are liable
+to error.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Starch added</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>24.0</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>The starch should be used fresh, and is best made on the day it is used;
+after four days the finishing point is not so good.</p>
+
+<p><b>Effect of Varying Potassium Iodide.</b>&mdash;An excess of iodide is always
+required to keep the iodine in solution; a larger excess has little
+effect.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Iodide added</td><td align='left'>&mdash;</td><td align='left'>1 gram</td><td align='left'>20 grams</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>20.5 c.c.</td><td align='left'>20.6 c.c.</td></tr>
+</table></div>
+
+
+<p>The 20 c.c. of iodine used, itself contained 0.5 gram of potassium
+iodide.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bicarbonate of soda added</td><td align='left'>&mdash;</td><td align='left'>0.5 gram</td><td align='left'>1.5 gram</td><td align='left'>5.0 grams</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>18.2 c.c.</td><td align='left'>17.1 c.c.</td><td align='left'>16.0 c.c.</td></tr>
+</table></div>
+
+
+<p>The solution obviously must be free from bicarbonate of soda. This
+should be remembered, since when titrating arsenic assays with iodine it
+must be present; and students must avoid confounding the two titrations.</p>
+
+<p>In some other experiments, in which 10 grams each of the salts were
+taken, the following results were obtained:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt added</td><td align='left'>&mdash;</td><td align='left'>AmCl</td><td align='left'>AmNO<sub>3</sub></td><td align='left'>Am<sub>2</sub>SO<sub>4</sub></td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.4 c.c.</td><td align='left'>20.5 c.c.</td><td align='left'>20.3 c.c.</td><td align='left'>20.2 c.c.</td></tr>
+</table></div>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt added</td><td align='left'>NaCl</td><td align='left'>NaNO<sub>3</sub></td><td align='left'>Na<sub>2</sub>SO<sub>4</sub></td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>20.3 c.c.</td><td align='left'>20.4 c.c.</td><td align='left'>20.4 c.c.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Iodine.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Iodine added</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>10.0</td><td align='left'>c.c.</td><td align='left'>20.0</td><td align='left'>c.c.</td><td align='left'>50.0</td><td align='left'>c.c.</td><td align='left'>100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Hypo" required</td><td align='left'>1.3</td><td align='left'>"</td><td align='left'>10.2</td><td align='left'>"</td><td align='left'>20.4</td><td align='left'>"</td><td align='left'>51.0</td><td align='left'>"</td><td align='left'>102.0</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p><b>Determination of Dioxide in a Manganese Ore.</b>&mdash;Weigh up 0.25 to 0.3
+gram of the powdered ore; place in a flask, cover<span class='pagenum'><a name="Page_306" id="Page_306">[Pg 306]</a></span> with 10 c.c. of
+hydrochloric acid, and close the flask with a paraffined cork, and bulbs
+(as shown in fig. 60), having previously charged the bulb with 5 grams
+of potassium iodide in strong solution. Heat the flask, and boil
+cautiously for about fifteen minutes. Wash the contents of the bulbs
+into a large beaker, nearly (but not quite) neutralise with dilute
+ammonia, and titrate with the standard "hypo."</p>
+
+<p>As an example, 0.2675 gram of pyrolusite was taken, and required 60.3
+c.c. of standard "hypo" (100 c.c. equal 1.185 gram iodine, or 0.4042
+gram MnO<sub>2</sub>), which equals 0.2437 gram of the dioxide or 91.1 per cent.</p>
+
+
+<h4>COLORIMETRIC METHOD.</h4>
+
+<p>When compounds of manganese free from chlorides are boiled with nitric
+acid and dioxide of lead,<a name="FNanchor_87_87" id="FNanchor_87_87"></a><a href="#Footnote_87_87" class="fnanchor">[87]</a> the manganese is converted into
+permanganic acid, which is soluble and tints the solution violet. The
+depth of colour depends on the amount of manganese present, and this
+should not much exceed 10 milligrams. A quantity of substance containing
+not more than this amount of manganese should be boiled for a few
+minutes with 25 c.c. of a solution containing 5 c.c. of nitric acid, and
+10 or 20 c.c. of dilute sulphuric acid, with 2 or 3 grams of lead
+dioxide. Filter through asbestos, wash by decantation with dilute
+sulphuric acid, make up with distilled water<a name="FNanchor_88_88" id="FNanchor_88_88"></a><a href="#Footnote_88_88" class="fnanchor">[88]</a> to a definite bulk, and
+take a measured portion for the colorimetric determination.</p>
+
+<p>The standard solution of manganese is made by dissolving 0.1435 gram of
+permanganate of potash (KMnO<sub>4</sub>) in a little water acidulated with
+nitric acid, and diluting to 1 litre. One c.c. will contain 0.05
+milligram of manganese.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. What percentage of manganese (Mn) is contained in permanganate of
+potash (KMnO<sub>4</sub>)?</p>
+
+<p>2. Ten c.c. of a solution of permanganate of potash is found to oxidise
+10 c.c. of an acid solution of ferrous sulphate. The manganese is
+determined in the titrated solution by precipitation as dioxide and
+titrating. How much of the ferrous solution will be oxidised in the
+second titration?</p>
+
+<p>3. What weight of potassium iodide would be just sufficient to absorb
+the chlorine evolved by 0.5 gram of pure dioxide of manganese?<span class='pagenum'><a name="Page_307" id="Page_307">[Pg 307]</a></span></p>
+
+<p>4. What weight of iron must be dissolved up so as to have an excess of
+0.25 gram after oxidation by 1 gram of pure dioxide?</p>
+
+<p>5. What weight of the brown oxide, Mn<sub>2</sub>O<sub>4</sub> will be left on igniting
+1 gram of the pure dioxide?</p>
+
+
+<h4>CHROMIUM.</h4>
+
+<p>Chromium occurs in nature chiefly as chromite or chrome iron ore (FeO<sub>2</sub>Cr<sub>2</sub>O<sub>3</sub>, with more or less MgO and Al<sub>2</sub>O<sub>3</sub>), which is the chief
+ore. It is a constituent of some silicates, and is frequently met with
+in very small quantities in iron ores. It occurs as chromate in
+crocoisite (PbCrO<sub>4</sub>), and some other rare minerals.</p>
+
+<p>The metal is used in steel-making. Steel containing about 0.5 per cent.
+of it is rendered very hard; but its chief value is in its salts, the
+chromates. These are highly-coloured compounds, generally red or yellow.
+Some of the insoluble chromates are used as pigments; chromate of lead
+or chrome-yellow is the most important. The soluble chromates, those of
+soda and potash, are valuable chemicals, and are largely used in the
+preparation of pigments, dyeing and tanning, and as oxidising agents.</p>
+
+<p>Chromium forms two important classes of compounds&mdash;chromic salts,
+corresponding to the oxide Cr<sub>2</sub>O<sub>3</sub>, and chromates, which contain the
+trioxide CrO<sub>3</sub>. Solutions of chromic salts are green, whilst those of
+the chromates are yellow. Chromates are reduced to chromic salts by the
+action of most reducing agents in the presence of an acid; and this
+property is used in assaying for the volumetric determination of ferrous
+iron, &amp;c. The chromates in solution are more stable than other similar
+oxidising agents, and consequently are generally used in the laboratory
+as one of the standard oxidising agents for volumetric analysis. They
+have the disadvantage of requiring an outside indicator. Bichromate of
+potash (K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>) is the salt generally used for this purpose.</p>
+
+<p>Chromic salts are oxidised to chromate by fusion with "fusion mixture"
+and nitre, or by treating with chlorine in an alkaline solution.</p>
+
+<p>Chromic salts closely resemble those of ferric iron, and in the ordinary
+course of analysis chromic hydrate (green) is precipitated together with
+ferric hydrate, alumina, &amp;c., on the addition of ammonic chloride and
+ammonia. The ignited oxide, Cr<sub>2</sub>O<sub>3</sub>, however, is not reduced on
+heating to redness in a current of hydrogen.</p>
+
+<p><b>Detection.</b>&mdash;Chromium is detected by fusing the powdered substance with
+"fusion mixture" and nitre. The melt is extracted with water and
+filtered. The filtrate is acidified with acetic acid, and treated with a
+few drops of a solution of lead<span class='pagenum'><a name="Page_308" id="Page_308">[Pg 308]</a></span> acetate. A yellow precipitate indicates
+chromium. Substances containing chromium impart a green colour to the
+borax bead in both flames. Small quantities of chromate in neutral
+solution can be found by the dark or violet-red colouration imparted
+thereto on boiling with a dilute decoction of logwood.</p>
+
+<p><b>Solution and Separation.</b>&mdash;Chromates and chromic salts are generally
+soluble in water or dilute acids. Chrome iron ore, however, and ignited
+chromic oxide are insoluble; and the former presents considerable
+difficulty on attempting to open up by the usual methods. A large number
+of mixtures have been tried in order to get all the chromium in a
+soluble form. Among these are the following. One part of the very
+finely-powdered ore is fused with any of these mixtures.</p>
+
+<p>
+(1) 10 parts of bisulphate of potash.<br />
+(2)  5 parts of bisulphate of potash and 5 parts of potassium fluoride.<br />
+(3)  5 parts of hydric potassic fluoride.<br />
+(4) 12 parts of bisulphate of potash; and, afterwards, with 6 parts of<br />
+carbonate of soda and 6 parts of nitre.<br />
+(5)  8 parts of borax; afterwards, with carbonate of soda till it ceases<br />
+to effervesce; then, with 3 parts of carbonate of soda and 3 of<br />
+nitre.<br />
+(6)  4 parts of borax and 6 parts of fusion mixture.<br />
+(7) 12 parts of caustic potash.<br />
+(8) 10 parts of caustic soda and 30 of magnesia.<br />
+(9)  5 parts of caustic soda and 3 of magnesia.<br />
+(10)  2 parts of carbonate of soda and 1 of lime.<br />
+(11)  6 parts of soda-lime and 2 of chlorate of potash.<br />
+(12) Sodium peroxide.<br />
+</p>
+
+<p>Of these, numbers 1, 2, and 3 yield the chromium in a form soluble in
+dilute acids, as chromic salt. The rest in a form soluble in water, as
+potassium or sodium chromate.</p>
+
+<p>On boiling an insoluble chromium compound with chlorate of potash and
+nitric acid, the chromium passes into solution as chromate. This method,
+however, does not answer for chrome iron ore. In the fusion methods the
+ore must be very finely powdered, well mixed with the fluxes, and
+subjected to a prolonged fusion in a platinum vessel at a high
+temperature. Undecomposed particles require re-fusion.</p>
+
+<p>The aqueous extract containing the chromate is ready for volumetric
+work, except in those cases where nitre has been used. For gravimetric
+work the solution is acidified with hydrochloric acid, then mixed with
+ammonia in slight excess, boiled, and filtered. The filtrate is
+acidified with hydrochloric acid, and treated with sulphuretted
+hydrogen, warmed, rendered slightly alkaline with ammonia, and the gas
+again passed. The chromium is precipitated as chromic hydrate mixed with
+sulphur from the<span class='pagenum'><a name="Page_309" id="Page_309">[Pg 309]</a></span> reduction with sulphuretted hydrogen. It is filtered
+off, washed with hot water, and ignited. It is weighed as chromic oxide.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution containing the chromium, freed from other metals and earths
+and in the form of (green) chromic salt, is heated to boiling. If any
+chromate is present reduce it with sodium sulphite or sulphuretted
+hydrogen. Add ammonia in slight excess, boil till the liquid is free
+from a red tint, and allow to settle for a few minutes. Filter, wash
+with hot water, dry, and ignite strongly in a loosely-covered crucible.
+Cool, and weigh. The substance is chromic oxide, Cr<sub>2</sub>O<sub>3</sub>, and
+contains 68.62 per cent. of chromium. It is a dark-green powder
+insoluble in acids.</p>
+
+<p>When, as is generally the case, the chromium exists altogether as
+chromate (phosphates and arsenates being absent) it is best to proceed
+as follows:&mdash;Render the solution acid with acetic acid, then add sodium
+acetate to the solution and heat nearly to boiling; next treat with a
+slight excess of acetate of lead, and boil. Allow to settle, and filter.
+Wash the precipitate with hot water, dry in the water-oven or at a low
+temperature. Transfer the precipitate to a weighed Berlin crucible, burn
+the filter separately, ignite below redness, cool in the desiccator, and
+weigh. The substance is lead chromate, PbCrO<sub>4</sub>, and contains 16.1 per
+cent. of chromium, or 23.53 per cent. of chromic oxide (Cr<sub>2</sub>O<sub>3</sub>).</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This is based on the oxidation of ferrous iron by the solution
+containing the chromium as chromate. A known weight of iron (0.5, 1, or
+1.5 gram, according to the quantity of chromate) is dissolved in 50 c.c.
+of dilute sulphuric acid. The solution containing the chromate is added,
+and the remaining ferrous iron titrated with the permanganate or
+bichromate of potassium solution, as described under <i>Iron</i>. The iron
+thus found is deducted from that taken, and the difference gives the
+iron oxidised by the chromate. This multiplied by 0.3101 gives the
+chromium, Cr, and when multiplied by 0.4529 gives the chromic oxide,
+Cr<sub>2</sub>O<sub>3</sub>.</p>
+
+
+<h4>COLORIMETRIC METHOD.</h4>
+
+<p>Small quantities of chromium may be determined, after conversion into
+chromate, colorimetrically. The solution, which should not contain more
+than a few milligrams in 100 c.c., is acidified with acetic acid and
+compared against an equal volume<span class='pagenum'><a name="Page_310" id="Page_310">[Pg 310]</a></span> of water rendered acid with acetic
+acid and tinted with a standard bichromate of potassium solution. This
+standard bichromate is made by dissolving 2.827 grams of the salt in
+water and diluting to 1 litre. One c.c. will contain 1 milligram of
+chromium, Cr. The manner of working this assay is the same as that
+adopted in the other colorimetric processes.</p>
+
+<p><b>Determination of Chromium in Steel.</b><a name="FNanchor_89_89" id="FNanchor_89_89"></a><a href="#Footnote_89_89" class="fnanchor">[89]</a>&mdash;Weigh up 2.4 grams, dissolve
+in hydrochloric acid, and evaporate to dryness. Fuse with sodium
+carbonate and nitre, extract with water, and make up to 301 c.c. Take
+250 c.c. of the clear liquor, boil with hydrochloric acid, add sodium
+phosphate, and then ammonia in slight excess. Heat till clear. Filter
+off the precipitate, dissolve it in hydrochloric acid, and evaporate to
+dryness. Take up with a little acid, filter, and precipitate with a
+slight excess of ammonia. Wash, ignite, and weigh as chromium phosphate
+(3Cr<sub>2</sub>O<sub>3</sub>,2P<sub>2</sub>O<sub>5</sub>), which contains 42.2 per cent. of chromium.</p>
+
+
+<h4>VANADIUM.</h4>
+
+<p>Vanadium occurs in certain rare minerals, such as vanadinite
+(3Pb<sub>3</sub>(VO<sub>4</sub>)<sub>2</sub>.PbCl<sub>2</sub>), a vanadate of lead; mottramite, a
+vanadate of copper and lead; and dechenite, a vanadate of lead and zinc.
+It is occasionally found in iron and copper ores and in the slags from
+them. In Spanish copper-precipitates it is found along with chromium,
+and is probably derived from the iron used for precipitating. The
+vanadates, like the chromates, are coloured compounds, generally yellow
+or red. On reduction, blue solutions are got. In their general reactions
+vanadates resemble phosphates.</p>
+
+<p>Vanadium is detected by the red colouration produced by passing
+sulphuretted hydrogen into ammoniacal solutions for some time. On adding
+an acid to the filtered solution a brown precipitate of the sulphide is
+produced. This gives with borax a colourless bead in the oxidising, and
+a green one in the reducing, flame.</p>
+
+<p>It is separated by fusing the ore with potassic nitrate, extracting with
+water and precipitating with baric chloride. The precipitate is boiled
+with dilute sulphuric acid, filtered, neutralised with ammonia, and
+saturated with ammonic chloride. Ammonium vanadate separates out. It is
+filtered off, ignited, and weighed as vanadic oxide, V<sub>2</sub>O<sub>5</sub>,
+containing 56.18 per cent. of vanadium.<span class='pagenum'><a name="Page_311" id="Page_311">[Pg 311]</a></span></p>
+
+
+<h4>MOLYBDENUM.</h4>
+
+<p>Molybdenum occurs in nature chiefly as molybdenite (MoS<sub>2</sub>); it also
+occurs in wulfenite, a molybdate of lead (PbMoO<sub>4</sub>), and in molybdic
+ochre (MoO<sub>3</sub>).</p>
+
+<p>Molybdate of ammonia is an important reagent in the determination of
+phosphates, the manufacture of which compound is the chief purpose to
+which molybdenum is applied.</p>
+
+<p>Iron and copper ores frequently contain molybdenum, sometimes in
+quantity; consequently it is met with in slags and pig-iron.</p>
+
+<p>Molybdenum forms several series of salts. In those corresponding to the
+lower oxides it is basic; but the trioxide (MoO<sub>3</sub>) is the acid oxide
+which forms a series of salts called the molybdates. All molybdenum
+compounds are converted into the trioxide by boiling with nitric acid.
+The trioxide is a white powder readily dissolved by ammonia. It fuses at
+a red heat, and volatilises freely in contact with air. It is slightly
+soluble in water.</p>
+
+<p>Molybdates are easily reduced, with the production of coloured
+solutions, by most reducing agents. Sulphuretted hydrogen first produces
+a blue tint, and then precipitates a brown sulphide. The precipitation
+as sulphide is only complete on prolonged treatment; a green colour
+indicates that some molybdenum still remains in solution. The
+precipitated sulphide is soluble in ammonium sulphide.</p>
+
+<p><b>Detection.</b>&mdash;Molybdenum is detected by its behaviour with sulphuretted
+hydrogen. Molybdenite can only be mistaken for graphite, from which it
+is easily distinguished by yielding sulphur dioxide on roasting, and by
+giving, on charcoal, a yellowish white incrustation, which becomes blue
+on touching it for a moment with the reducing flame. The borax-bead is
+colourless in the oxidising, and dark-brown in the reducing, flame.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution containing the molybdate is neutralised and treated with an
+excess of mercurous nitrate. The precipitate is allowed to settle for
+some time, filtered, and washed with a dilute solution of mercurous
+nitrate. Then it is dried, transferred to a weighed Berlin crucible
+containing ignited oxide of lead, mixed, ignited, and weighed. The
+increase in weight gives the amount of trioxide, MoO<sub>3</sub>. This contains
+66.7 per cent. of molybdenum.<span class='pagenum'><a name="Page_312" id="Page_312">[Pg 312]</a></span></p>
+
+
+<h4>URANIUM.</h4>
+
+<p>Uranium occurs chiefly as pitchblende, which is an impure oxide
+(U<sub>3</sub>O<sub>8</sub>). It is also found as sulphate in uranochre, johannite, &amp;c.;
+and as phosphate in the uranites, torbernite (hydrated phosphate of
+uranium and copper), and autunite (hydrated phosphate of uranium and
+lime). It also occurs in some rarer minerals.</p>
+
+<p>The oxide is used for colouring glass; and the nitrate and acetate are
+used as reagents. "Uranium yellow," used for enamel painting, is sodium
+uranate. The uranates, in which the oxide of uranium acts as an acid,
+are mostly insoluble and of secondary importance.</p>
+
+<p>Uranium forms two families of salts, uranous and uranic; corresponding
+to the oxides UO<sub>2</sub> and UO<sub>3</sub> respectively. The former are generally
+green and the latter yellow. Uranous salts are converted into uranic by
+boiling with nitric acid or other oxidising agents. Uranic salts, on the
+other hand, are easily reduced by sulphuretted hydrogen, stannous
+chloride or zinc. This property is made use of in determining the
+quantity of uranium in pure solutions by titrating with permanganate of
+potassium solution as in the case with iron.</p>
+
+<p><b>Detection.</b>&mdash;The most characteristic reaction of the uranium compounds
+is their behaviour in the presence of alkaline carbonates in which they
+are freely soluble; even ammonium sulphide will not precipitate uranium
+from these solutions. On neutralising the carbonate with an acid a
+uranate of the alkali is precipitated. Ammonia or sodic hydrate (free
+from carbonates) give yellow precipitates, which are insoluble in excess
+of the reagent, but are soluble in acids. Ferrocyanide of potassium
+gives a reddish-brown precipitate. Uranium colours the borax-bead
+yellowish-green in the oxidising, and green in the reducing, flame.</p>
+
+<p><b>Solution and Separation.</b>&mdash;The compounds of uranium are soluble in
+acids. Powder the substance and evaporate with an excess of nitric acid.
+Take up with hydrochloric acid, dilute, pass sulphuretted hydrogen, and
+filter. Peroxidise the filtrate with a little nitric acid, add an excess
+of ammonic carbonate and some ammonium sulphide, and filter. Render the
+solution acid, boil; and precipitate the uranium by means of ammonia.
+Filter off, and wash it with dilute ammonic chloride. Ignite, and weigh
+<span class='pagenum'><a name="Page_313" id="Page_313">[Pg 313]</a></span>as protosesqui-oxide, U<sub>3</sub>O<sub>8</sub>.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution containing the uranium free from other metals is, if
+required, first peroxidised by boiling with nitric acid. Ammonia in
+slight excess is added to the nearly-boiling solution. A yellow
+precipitate is formed, which is filtered off hot and washed with a
+dilute solution of ammonium chloride. The precipitate is dried and
+ignited; and weighed as U<sub>3</sub>O<sub>8</sub>, which contains 84.8 per cent. of
+uranium.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This is based on the precipitation of uranium as phosphate from acetic
+acid solutions and the recognition of complete precipitation by testing
+with potassic ferrocyanide; it is the converse of the process for the
+volumetric determination of phosphate.</p>
+
+<p><i>The standard solution of phosphate</i> is prepared by dissolving 29.835
+grams of hydric sodic phosphate (Na<sub>2</sub>HPO<sub>4</sub>.12H<sub>2</sub>O) in water and
+diluting to 1 litre. 100 c.c. will be equivalent to 2 grams of uranium.</p>
+
+<p>Take 1 gram of the sample (or, if poor in uranium, 2 grams) and separate
+the uranium as described. Dissolve the precipitate in nitric acid and
+evaporate to a small bulk, add 2 grams of sodium acetate, dilute with
+water to 100 c.c., and boil. Titrate the boiling solution with the
+sodium phosphate till it ceases to give a brown colouration with
+potassium ferrocyanide. Calculate the percentage in the usual way.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_78_78" id="Footnote_78_78"></a><a href="#FNanchor_78_78"><span class="label">[78]</span></a> MnO<sub>2</sub> + 4HCl = MnCl<sub>2</sub> + Cl<sub>2</sub> + 2H<sub>2</sub>O.</p></div>
+
+<div class="footnote"><p><a name="Footnote_79_79" id="Footnote_79_79"></a><a href="#FNanchor_79_79"><span class="label">[79]</span></a> Provided a sufficiency of ammonic chloride is present.</p></div>
+
+<div class="footnote"><p><a name="Footnote_80_80" id="Footnote_80_80"></a><a href="#FNanchor_80_80"><span class="label">[80]</span></a> With some silicates, &amp;c., a preliminary fusion with sodium
+carbonate will be necessary.</p></div>
+
+<div class="footnote"><p><a name="Footnote_81_81" id="Footnote_81_81"></a><a href="#FNanchor_81_81"><span class="label">[81]</span></a> Instead of sodium acetate, ammonium succinate can be
+used.</p></div>
+
+<div class="footnote"><p><a name="Footnote_82_82" id="Footnote_82_82"></a><a href="#FNanchor_82_82"><span class="label">[82]</span></a> <i>Journ. Soc. Chem. Industry</i>, vol. x. p. 333.</p></div>
+
+<div class="footnote"><p><a name="Footnote_83_83" id="Footnote_83_83"></a><a href="#FNanchor_83_83"><span class="label">[83]</span></a> MnO<sub>2</sub> + 2FeSO<sub>4</sub> + 2H<sub>2</sub>SO<sub>4</sub> = Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> +
+MnSO<sub>4</sub> + 2H<sub>2</sub>O.</p></div>
+
+<div class="footnote"><p><a name="Footnote_84_84" id="Footnote_84_84"></a><a href="#FNanchor_84_84"><span class="label">[84]</span></a> If the ore is very rich, a smaller quantity (0.75 or 1.5
+gram) must be taken; otherwise the iron will be insufficient.</p></div>
+
+<div class="footnote"><p><a name="Footnote_85_85" id="Footnote_85_85"></a><a href="#FNanchor_85_85"><span class="label">[85]</span></a>
+<br />
+MnO<sub>2</sub> + 4HCl = MnCl<sub>2</sub> + 2H<sub>2</sub>O + Cl<sub>2</sub>.<br />
+Cl<sub>2</sub> + 2KI = 2KCl + I<sub>2</sub>.<br />
+</p></div>
+
+<div class="footnote"><p><a name="Footnote_86_86" id="Footnote_86_86"></a><a href="#FNanchor_86_86"><span class="label">[86]</span></a> Iodine probably lost by volatilisation.</p></div>
+
+<div class="footnote"><p><a name="Footnote_87_87" id="Footnote_87_87"></a><a href="#FNanchor_87_87"><span class="label">[87]</span></a> Obtained as a brown powder by digesting red lead with
+nitric acid and filtering.</p></div>
+
+<div class="footnote"><p><a name="Footnote_88_88" id="Footnote_88_88"></a><a href="#FNanchor_88_88"><span class="label">[88]</span></a> The water for dilution and the dilute sulphuric acid used
+for washing should be previously tested, to see they have no reducing
+action, with dilute permanganate of potassium solution.</p></div>
+
+<div class="footnote"><p><a name="Footnote_89_89" id="Footnote_89_89"></a><a href="#FNanchor_89_89"><span class="label">[89]</span></a> Arnold and Hardy, <i>Chemical News</i>, vol. lvii. p. 153.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_314" id="Page_314">[Pg 314]</a></span></p>
+<h2><a name="CHAPTER_XIV" id="CHAPTER_XIV"></a>CHAPTER XIV.</h2>
+
+<h3>EARTHS, ALKALINE EARTHS, ALKALIES.</h3>
+
+
+<h4>ALUMINA.</h4>
+
+<p>Alumina, the oxide of aluminium (Al<sub>2</sub>O<sub>3</sub>), is found in nature fairly
+pure in the mineral corundum; transparent and coloured varieties of
+which form the gems sapphire and ruby. A coarser compact variety
+contaminated with oxide of iron constitutes emery. Compounded with
+silica, alumina forms the base of clays and many rock-forming minerals.
+China clay (or kaolin) is used as a source of alumina. Bauxite, hydrated
+alumina, is also used for the same purpose&mdash;that is, for the preparation
+of sulphate of alumina. The mineral cryolite is a fluoride of aluminium
+and sodium.</p>
+
+<p>Corundum is characterised by a high specific gravity (4.0) and extreme
+hardness. By these it is distinguished from felspar and similar
+minerals, which it somewhat resembles in general appearance.</p>
+
+<p>Aluminium is used for a variety of small purposes: it is white, light,
+and very tenacious; but owing to the difficulty of its reduction it is
+expensive.</p>
+
+<p>Aluminium forms one series of salts which closely resemble those of
+ferric iron. It forms an interesting series of double sulphates, known
+as the alums. Common potash alum is
+Al<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>,K<sub>2</sub>SO<sub>4</sub>,24H<sub>2</sub>O.</p>
+
+<p><b>Detection.</b>&mdash;Alumina is not precipitated from its acid solution by
+sulphuretted hydrogen, but it is thrown down by ammonia (with the other
+earths) as a white hydrate, soluble in soda and insoluble in ammonic
+carbonate. Filtered off and ignited, it assumes, after treatment with
+nitrate of cobalt before the blowpipe, a blue colour which is
+characteristic. With natural compounds containing metallic oxides this
+colour is masked. It is more satisfactory to make a separation in the
+wet way and to test the ignited oxide.</p>
+
+<p><b>Separation and Solution.</b>&mdash;If the substance is insoluble in
+hydrochloric acid it is finely powdered and fused with "fusion mixture"
+with the help, in the case of corundum (which is very refractory) of a
+little caustic soda or potash. The method of<span class='pagenum'><a name="Page_315" id="Page_315">[Pg 315]</a></span> working is the same as
+that described for opening up silicates. See under <i>Silica</i>. Corundum
+cannot be powdered in Wedgwood, or even agate, mortars; since it rapidly
+wears these away and becomes contaminated with their powder. It is best
+to use a hard steel mortar and to extract the metallic particles from
+the bruised sample with a magnet or dilute acid.</p>
+
+<p>When the substance has been completely attacked and dissolved, it is
+evaporated to dryness with an excess of hydrochloric acid on the
+water-bath to render any silica present insoluble. The residue is
+extracted with hydrochloric acid and freed from the second group of
+metals by means of sulphuretted hydrogen. The filtrate from this (after
+removing the sulphuretted hydrogen by boiling) is nearly neutralised,
+and treated with 8 or 10 grams of hyposulphite of soda<a name="FNanchor_90_90" id="FNanchor_90_90"></a><a href="#Footnote_90_90" class="fnanchor">[90]</a> in solution.
+It is then boiled till the sulphurous oxide is driven off. The
+precipitate is filtered off, ignited, and weighed as alumina.</p>
+
+<p>It is sometimes more convenient to proceed as follows:&mdash;After boiling
+off the sulphuretted hydrogen peroxidise the iron with a little nitric
+acid, add a solution of ammonic chloride, and then ammonia in very
+slight excess; boil, filter, wash, ignite, and weigh the oxides. These
+generally consist of ferric oxide and alumina. It is a common practice
+to determine the iron, calculate it to ferric oxide, and so to estimate
+the alumina indirectly. This may be done either by igniting in a current
+of hydrogen and estimating the iron by the weight of oxygen lost; or, by
+dissolving with sulphuric and hydrochloric acids, and determining the
+iron volumetrically. It should be borne in mind that these oxides will
+also contain any phosphoric oxide that happened to be in the mineral.</p>
+
+<p>In general analyses of samples containing alumina, it may be contained
+in both the soluble and insoluble portions. In these cases it is better
+to fuse the sample with "fusion mixture" before treatment with acids.
+The alumina in the fused mass will exist in a state soluble in acids.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>Solutions containing alumina free from the other metals are diluted to a
+convenient bulk and heated nearly to boiling. Add chloride of ammonium,
+and then ammonia in slight excess; boil, allow to settle, filter, and
+wash with hot water. Dry the precipitate, and ignite in a platinum or
+porcelain crucible at the strongest heat. Cool, and weigh. The substance
+<span class='pagenum'><a name="Page_316" id="Page_316">[Pg 316]</a></span>is alumina, Al<sub>2</sub>O<sub>3</sub>, which contains 52.94 per cent. of aluminium.
+It is only in special cases, such as the analysis of metals and alloys,
+that it is reported as aluminium. The percentage of alumina is generally
+given.</p>
+
+<p>Ignited alumina is difficultly soluble in acids; it is not reduced by
+hydrogen at a red heat. Ignited with ammonium chloride portions are
+volatilised.</p>
+
+<p><b>Direct Determination of Alumina in the Presence of Iron.</b>&mdash;The iron and
+alumina are precipitated as hydrates by ammonia. The precipitate is
+dissolved in hydrochloric acid and the iron reduced to the ferrous
+state. It is then added to a hot solution of potash or soda. The
+solution is boiled till the precipitate settles readily, filtered, and
+washed with hot water. The alumina is contained in the filtrate, which
+is acidified with hydrochloric acid and the alumina precipitated
+therefrom as hydrate with ammonia, as just described.</p>
+
+<p><b>Determination of Alumina in the Presence of Phosphates and Iron.</b>&mdash;For
+details, see a paper by R.T. Thomson in the "Journal of the Society of
+Chemical Industry," v. p. 152. The principles of the method are as
+follows:&mdash;If the substance does not already contain sufficient
+phosphoric oxide to saturate the alumina, some phosphate is added. The
+iron is reduced to the ferrous state and phosphate of alumina
+precipitated in an acetic acid solution. It is purified by
+reprecipitation, ignited, and weighed as phosphate
+(Al<sub>2</sub>O<sub>3</sub>,P<sub>2</sub>O<sub>5</sub>), which contains 41.8 per cent. of alumina,
+Al<sub>2</sub>O<sub>3</sub>.</p>
+
+
+<h4>EXAMINATION OF CLAYS.</h4>
+
+<p><b>Moisture.</b>&mdash;Take 5 grams of the carefully-prepared sample and dry in
+the water-oven till the weight is constant.</p>
+
+<p><b>Loss on Ignition.</b>&mdash;Weigh up 2 grams of the sample used for the
+moisture determination, and ignite in a platinum-crucible to redness,
+cool, and weigh.</p>
+
+<p><b>Silica and Insoluble Silicates.</b>&mdash;Weigh up another 2 grams of the dried
+sample, and place them in a platinum dish; moisten with water, and cover
+with 20 c.c. of sulphuric acid. Evaporate and heat gently to drive off
+the greater portion of the free acid. Allow to cool; and repeat the
+operation. Extract by boiling with dilute hydrochloric acid, filter,
+wash, dry, ignite, and weigh. The quantity of insoluble silicates is
+determined by dissolving out the separated silica with a strong boiling
+solution of sodium carbonate. The residue (washed, dried, and ignited)
+is weighed, and reported as "sand."</p>
+
+<p><b>Alumina and Ferrous Oxide.</b>&mdash;To the filtrate from the silica add "soda"
+solution till nearly neutral, and then sodium<span class='pagenum'><a name="Page_317" id="Page_317">[Pg 317]</a></span> acetate. Boil and filter
+off the precipitate. Reserve the filtrate. Dissolve the precipitate in
+hydrochloric acid, and dilute to exactly 200 c.c. Divide into two parts
+of 100 c.c. each. In one determine the iron by reducing and titrating in
+the way described under volumetric iron. Calculate the percentage as
+ferrous oxide, unless there are reasons to the contrary, also calculate
+its weight as ferric oxide. To the other portion add ammonia in slight
+excess, and boil. Filter, wash with hot water, dry, ignite, and weigh as
+mixed alumina and ferric oxide. The weight of the ferric oxide has
+already been determined in the first portion: deduct it, and the
+difference is the weight of alumina.</p>
+
+<p><b>Lime.</b>&mdash;To the reserved filtrate, concentrated by evaporation, add
+ammonium oxalate and ammonia; boil, filter, ignite strongly, and weigh
+as lime.</p>
+
+<p><b>Magnesia</b> is separated from the filtrate by adding sodium phosphate. It
+is weighed as magnesium pyrophosphate.</p>
+
+<p><b>Potash and Soda.</b>&mdash;These are determined in a fresh portion of the
+sample by Lawrence Smith's method, as described on page 333.</p>
+
+
+<h4>THORIA.</h4>
+
+<p>This is an oxide of thorium, ThO<sub>2</sub>. It is only found in a few rare
+minerals. It is a heavy oxide, having, when strongly ignited, a specific
+gravity of 9.2. In the ordinary course of analysis it will be separated
+and weighed as alumina. It is separated from this and other earths by
+the following method. The solution in hydrochloric acid is nearly
+neutralised and then boiled with sodium hyposulphite. The thoria will be
+in the precipitate. It is dissolved, and the solution heated with
+ammonium oxalate in excess. The precipitate is thorium oxalate, which is
+washed with hot water, dried, and ignited. It is then weighed as thoria,
+ThO<sub>2</sub>. Thoria which has been ignited is not readily soluble in acids.</p>
+
+
+<h4>ZIRCONIA.</h4>
+
+<p>The oxide of zirconium, ZrO<sub>2</sub>, is found in the mineral zircon, a
+silicate of zirconia, ZrSiO<sub>4</sub>. When heated intensely it becomes very
+luminous, and is used on this account for incandescent lights.</p>
+
+<p>In the ordinary course it is thrown down by ammonia with the other
+earths, from which it is thus separated:&mdash;The hydrates precipitated in
+the cold, and washed with cold water, are dissolved<span class='pagenum'><a name="Page_318" id="Page_318">[Pg 318]</a></span> in hydrochloric
+acid, nearly neutralised with soda, and precipitated by boiling with
+hyposulphite of soda. Dissolve; and from the hydrochloric acid solution
+precipitate the thoria (if any) with ammonium oxalate. To the filtrate
+add carbonate of ammonia, which will precipitate any titanium present.
+The zirconia will be in solution, and is recovered by precipitating with
+potassium sulphate, or by evaporating the solution and igniting. It is
+separated from alumina by taking advantage of its insolubility in
+potassic hydrate.</p>
+
+<p>It is estimated in zircons in the following way:&mdash;The powdered substance
+is fused with bisulphate of potash, and extracted with dilute sulphuric
+acid. The residue is fused with caustic soda and extracted with water.
+The portion not dissolved, consisting of zirconate of soda, is dissolved
+in hydrochloric acid. The solution is diluted, filtered if necessary,
+and treated with ammonia in excess. The precipitate is filtered off,
+washed with hot water, dried, ignited, and weighed as zirconia, ZrO<sub>2</sub>.
+This is a white powder, which is insoluble in acids; even in
+hydrofluoric acid it is only slightly attacked.</p>
+
+
+<h4>CERIUM.</h4>
+
+<p>Cerium occurs as silicate (together with the oxides of lanthanum,
+didymium, iron and calcium) in the mineral cerite, which is its chief
+source. It also occurs as phosphate in monazite, and as fluoride in
+fluocerite. The oxalate is used in medicine. Cerium forms two classes of
+salts corresponding to the oxides, cerous oxide (Ce<sub>2</sub>O<sub>3</sub>) and ceric
+oxide (CeO<sub>2</sub>). Compounds of cerium with volatile acids yield dioxide
+on ignition; and this, on solution in hydrochloric acid, yields cerous
+chloride and chlorine.</p>
+
+<p>In the ordinary course cerium is thrown down along with alumina and the
+other earths by ammonia. It is separated by dissolving the hydrates in
+hydrochloric acid, and oxidizing with chlorine water. On treating with
+oxalic acid, cerium, lanthanum, and didymium are precipitated as
+oxalates, which on ignition are converted into oxides. These are soluble
+in acids. Their solution in hydrochloric acid is nearly neutralised;
+acetate of soda is then added, and an excess of sodium hypochlorite. On
+boiling, the cerium is precipitated as dioxide, which is filtered off,
+ignited, and weighed.</p>
+
+<p>Cerium is detected by giving with borax a bead which is yellow in the
+oxidising, and colourless in the reducing flame. Traces of cerium
+compounds boiled with dioxide of lead and nitric acid will give a yellow
+solution.<span class='pagenum'><a name="Page_319" id="Page_319">[Pg 319]</a></span></p>
+
+
+<h4>LANTHANUM AND DIDYMIUM</h4>
+
+<p>occur together with cerium in cerite, and are separated with that metal
+as oxalates, as described under <i>Cerium</i>.</p>
+
+<p>Didymium salts have a rose or violet colour, and impart (when in
+sufficient quantity) the same colour to the borax bead. Solutions have a
+characteristic absorption-spectrum.</p>
+
+<p>The separation of lanthanum and didymium in the solution from which the
+cerium has been precipitated is effected by precipitating them together
+as oxalates, igniting, and dissolving in dilute nitric acid. This
+solution is then evaporated to dryness and ignited, for a few minutes,
+just below redness. A subnitrate of didymium is formed, and remains as
+an insoluble residue on extracting with hot water. The separated salts
+are treated with ammonia and ignited, and weighed as oxides (La<sub>2</sub>O<sub>3</sub>
+and Di<sub>2</sub>O<sub>3</sub>).</p>
+
+
+<h4>YTTRIA.</h4>
+
+<p>Yttria is found in gadolinite and some other rare minerals. It is
+precipitated along with the other earths by ammonia. It is distinguished
+by the insolubility of its hydrate in potash, by the insolubility of its
+oxalate in oxalic acid, and by not being precipitated by hyposulphite of
+soda or potassium sulphate. Further, it is precipitated by potash in the
+presence of tartaric acid as an insoluble tartrate. This reaction
+distinguishes the members of the yttria group from most of the other
+earths. The other members of the group closely resemble it, and amongst
+them are erbia, terbia, ytterbia, scandia, &amp;c.</p>
+
+
+<h4>BERYLLIA.</h4>
+
+<p>The oxide of beryllium, BeO (also known as glucina), occurs in nature
+mainly as silicate. Beryl, the green transparent variety of which is the
+emerald, is the best known of these. It is a silicate of alumina and
+beryllia.<a name="FNanchor_91_91" id="FNanchor_91_91"></a><a href="#Footnote_91_91" class="fnanchor">[91]</a> Some other minerals in which it occurs are phenakite,
+euclase, and chrysoberyl.</p>
+
+<p>In the ordinary course of analysis, beryllia will be precipitated with
+alumina, &amp;c., by ammonic hydrate. It is distinguished by the solubility
+of its hydrate in ammonic carbonate, by not being precipitated by
+boiling with sodium hyposulphite, and by not being precipitated by
+ammonic sulphide from an ammonic carbonate solution.</p>
+
+<p>The analysis of silicates containing beryllia is thus effected.<span class='pagenum'><a name="Page_320" id="Page_320">[Pg 320]</a></span> The
+finely powdered substance is fused with twice its weight of potassium
+carbonate; and the "melt" is extracted with water, and evaporated with a
+slight excess of sulphuric acid to render the silica insoluble. Treat
+with water, filter, and evaporate the filtrate until a crust is formed.
+Potash alum crystallises out. The liquor is poured off into a warm
+strong solution of ammonium carbonate. Ferric hydrate and alumina will
+be precipitated. They are filtered off, re-dissolved, and again
+precipitated in ammonic carbonate solution; the combined filtrates are
+boiled for some time, and acidified slightly with hydrochloric acid. The
+carbon dioxide is boiled off, and the beryllia is then precipitated as
+hydrate with ammonia. The hydrate is washed with hot water, dried,
+ignited, and weighed as beryllia, BeO.</p>
+
+<p>Beryllia has a specific gravity of 3.08. It is white, infusible, and
+insoluble in water. After ignition, it is insoluble in acids, except
+sulphuric, but is rendered soluble by fusion with alkalies.</p>
+
+<p>Beryllia, in a solution of carbonate of ammonia, is precipitated as
+carbonate on boiling in proportion as the carbonate of ammonia is
+volatilised. The hydrate is dissolved by a boiling solution of ammonic
+chloride, ammonia being evolved.</p>
+
+
+<h3>THE ALKALINE EARTHS.</h3>
+
+
+<h4>LIME.</h4>
+
+<p>Lime is an oxide of calcium, CaO. It occurs abundantly in nature, but
+only in a state of combination. The carbonate (CaCO<sub>3</sub>), found as
+limestone, chalk, and other rocks, and as the minerals calcite and
+arragonite, is the most commonly occurring compound. The hydrated
+sulphate, gypsum (CaSO<sub>4</sub>.2H<sub>2</sub>O), is common, and is used in making
+"plaster of Paris." Anhydrite (CaSO<sub>4</sub>) also occurs in rock masses, and
+is often associated with rock salt. Phosphate of lime, in the forms of
+apatite, phosphorite, coprolite, &amp;c., is largely mined. Lime is a
+component of most natural silicates. Calcium also occurs, combined with
+fluorine, in the mineral fluor (CaF<sub>2</sub>). In most of these the acid is
+the important part of the mineral; it is only the carbonate which is
+used as a source of lime.</p>
+
+<p>Lime, in addition to its use in mortars and cements, is valuable as a
+flux in metallurgical operations, and as a base in chemical work on a
+large scale. A mixture of lime and magnesia is used in the manufacture
+of basic fire-bricks.</p>
+
+<p>Carbonate of lime on ignition, especially when in contact with reducing
+substances, loses carbonic acid, and becomes lime. This<span class='pagenum'><a name="Page_321" id="Page_321">[Pg 321]</a></span> is known as
+"quicklime"; on treatment with water it becomes hot, expands, and falls
+to a powder of "slaked lime" or calcium hydrate (CaH<sub>2</sub>O<sub>2</sub>). The
+hydrate is slightly soluble in water (0.1368 gram in 100 c.c.), forming
+an alkaline solution known as lime-water. Calcium hydrate is more
+generally used suspended in water as "milk of lime."</p>
+
+<p>As a flux it is used either as limestone or as quicklime. Silica forms
+with lime a compound, calcium silicate, which is not very fusible; but
+when alumina and other oxides are present, as in clays and in most rocky
+substances, the addition of lime gives a very fusible slag.</p>
+
+<p><b>Detection.</b>&mdash;Calcium is detected by the reddish colour which its salts
+impart to the flame. It is best to moisten with hydrochloric acid (or,
+in the case of some silicates, to treat with ammonium fluoride) before
+bringing the substance into the flame. When seen through a spectroscope,
+it shows a large number of lines, of which a green and an orange are
+most intense and characteristic. Calcium is detected in solution (after
+removal of the metals by treatment with sulphuretted hydrogen and
+ammonium sulphide) by boiling with ammonium oxalate and ammonia. The
+lime is completely thrown down as a white precipitate. Lime is
+distinguished from the other alkaline earths by forming a sulphate
+insoluble in dilute alcohol, but completely soluble in a boiling
+solution of ammonium sulphate.</p>
+
+<p>Lime compounds are for the most part soluble in water or in dilute
+hydrochloric acid. Calcium fluoride must be first converted into
+sulphate by evaporation in a platinum dish with sulphuric acid.
+Insoluble silicates are opened up by fusion with "fusion mixture," as
+described under <i>Silica</i>.</p>
+
+<p><b>Separation.</b>&mdash;The separation of lime is effected by evaporating with
+hydrochloric acid, to separate silica; and by treating with sulphuretted
+hydrogen, to remove the second group of metals. If the substance
+contains much iron, the solution is next oxidised by boiling with a
+little nitric acid; and the iron, alumina, &amp;c., are removed as basic
+acetates. The filtrate is treated with ammonia and sulphuretted
+hydrogen, and allowed to settle. The filtrate from this is heated to
+boiling, treated with a solution of ammonium oxalate in excess, boiled
+for five or ten minutes, allowed to settle for half an hour, and
+filtered. The precipitate contains all the lime as calcium oxalate.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The precipitate of calcium oxalate is washed with hot water, dried,
+transferred to a weighed platinum crucible, and ignited at<span class='pagenum'><a name="Page_322" id="Page_322">[Pg 322]</a></span> a
+temperature not above incipient redness. This ignition converts the
+oxalate into carbonate, with evolution of carbonic oxide, which burns at
+the mouth of the crucible with a blue flame.<a name="FNanchor_92_92" id="FNanchor_92_92"></a><a href="#Footnote_92_92" class="fnanchor">[92]</a> Generally a small
+quantity of the carbonate is at the same time converted into lime. To
+reconvert it into carbonate, moisten with a few drops of ammonic
+carbonate solution, and dry in a water-oven. Heat gently over a Bunsen
+burner, cool, and weigh. The substance is calcium carbonate (CaCO<sub>3</sub>),
+and contains 56 per cent. of lime (CaO). It is a white powder, and
+should show no alkaline reaction with moistened litmus-paper.</p>
+
+<p>Where the precipitate is small, it is better to ignite strongly over the
+blowpipe, and weigh directly as lime. With larger quantities, and when
+many determinations have to be made, it is easier to make the
+determination volumetrically.</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>These are carried out either by dissolving the oxalate at once in dilute
+sulphuric acid, and titrating with permanganate of potassium solution;
+or by calcining it to a mixture of lime and carbonate, and determining
+its neutralising power with the standard solutions of acid and alkali.</p>
+
+<p><b>Titration with Permanganate of Potassium Solution.</b>&mdash;This solution is
+made by dissolving 5.643 grams of the salt in water, and by diluting to
+1 litre; 100 c.c. are equivalent to 0.5 gram of lime. The solution is
+standardised by titrating a quantity of oxalic acid about equivalent to
+the lime present in the assay; 0.5 gram of lime is equivalent to 1.125
+gram of crystallised oxalic acid. The standardising may be done with
+iron. The standard found for iron multiplied by 0.5 gives that for lime.</p>
+
+<p>The process is as follows:&mdash;The calcium oxalate (having been
+precipitated and washed, as in the gravimetric process) is washed
+through the funnel into a flask with hot dilute sulphuric acid, boiled
+till dissolved, diluted to 200 c.c. with water, and heated to about 80&deg;
+C. The standard solution of "permanganate" is then run in, (not too
+quickly, and with constant shaking) until a permanent pink tinge is
+produced. The c.c. used multiplied by the standard, and divided by the
+weight of the substance taken, will give the percentage of lime.</p>
+
+<p><b>Estimation of Lime by Alkalimetry.</b>&mdash;The methods of determining the
+amount of an alkali or base by means of a standard acid solution, or,
+conversely, of determining an acid by means of a standard alkaline
+solution, are so closely related that<span class='pagenum'><a name="Page_323" id="Page_323">[Pg 323]</a></span> they are best considered under
+one head. The same standard solution is applicable for many purposes,
+and, consequently, it is convenient to make it of such strength that one
+litre of it shall equal an equivalent in grams of any of the substances
+to be determined. Such solutions are termed <i>normal</i>. For example, a
+solution of hydrochloric acid (HCl = 36.5) containing 36.5 grams of real
+acid per litre, would be normal and of equivalent strength to a solution
+containing either 17 grams of ammonia (NH<sub>3</sub> = 17) or 40 grams of sodic
+hydrate (NaHO = 40) per litre. It will be seen in these cases that the
+normal solution contains the molecular weight in grams per litre; and,
+if solutions of these strengths be made, it will be found that they
+possess equal neutralising value.</p>
+
+<p>If, now, a solution containing 98 grams of sulphuric acid (H<sub>2</sub>SO<sub>4</sub> =
+98) per litre be made, it will be found to have twice the strength of
+the above solution, that is, 100 c.c. of the soda would only require 50
+c.c. of the acid to neutralise it. The reason for this will be seen on
+inspecting the equations:&mdash;</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;NaHO + HCl = NaCl + H<sub>2</sub>O.<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2NaHO + H<sub>2</sub>SO<sub>4</sub> = Na<sub>2</sub>SO<sub>4</sub> + 2H<sub>2</sub>O.<br />
+</p>
+
+<p>Acids like sulphuric acid are termed bibasic, and their equivalent is
+only half the molecular weight. Thus, a normal solution of sulphuric
+acid would contain 49 grams (98/2) of real acid per litre. Similarly,
+lime and most of the bases are bibasic, as may be seen from the
+following equations; hence their equivalent will be half the molecular
+weight.</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2HCl + CaO = CaCl<sub>2</sub> + H<sub>2</sub>O.<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2HCl + MgO = MgCl<sub>2</sub> + H<sub>2</sub>O.<br />
+</p>
+
+<p><i>The standard normal solution of hydrochloric acid</i> is made by diluting
+100 c.c. of the strong acid to one litre with water. This will be
+approximately normal. In order to determine its exact strength, weigh up
+3 grams of recently ignited pure sodium carbonate or of the ignited
+bicarbonate. Transfer to a flask and dissolve in 200 c.c. of water; when
+dissolved, cool, tint faintly yellow with a few drops of a solution of
+methyl orange, and run in the standard "acid " from a burette till the
+yellow changes to a pink. Read off the number of c.c. used, and
+calculate to how much sodium carbonate 100 c.c. of the "acid" are
+equivalent. If the "acid" is strictly normal, this will be 5.3 grams. It
+will probably be equivalent to more than this. Now calculate how much
+strictly normal "acid" would be equivalent to the standard<span class='pagenum'><a name="Page_324" id="Page_324">[Pg 324]</a></span> found. For
+example: suppose the standard found is 5.5 gram of sodium carbonate,
+then&mdash;</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;5.3 : 5.5 :: 100 : <i>x</i><br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(where <i>x</i> is the quantity of normal "acid" required).<br />
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<i>x</i> = 103.8 c.c.<br />
+</p>
+
+<p>To get the "acid" of normal strength, we should then add 3.8 c.c. of
+water to each 100 c.c. of the standard solution remaining. Suppose there
+were left 930 c.c. of the approximate "acid," 35.3 c.c. of water must be
+added and mixed. It should then be checked by another titration with
+pure sodium carbonate.</p>
+
+<p><i>The standard solution of semi-normal "alkali."</i> The best alkali for
+general purposes is ammonia, but, since it is volatile (especially in
+strong solutions), it is best to make it of half the usual strength, or
+<i>semi-normal</i>. One litre of this will contain 8.5 grams of ammonia
+(NH<sub>3</sub>), and 100 c.c. of it will just neutralise 50 c.c. of the normal
+"acid." Take 100 c.c. of dilute ammonia and dilute with water to one
+litre. Run into a flask 50 c.c. of the standard "acid," tint with methyl
+orange, and run in from a burette the solution of ammonia till
+neutralised. Less than 100 c.c. will probably be used. Suppose 95 c.c.
+were required, there should have been 100, hence there is a deficiency
+of five. Then, for each 95 c.c. of standard "ammonia" left, add 5 c.c.
+of water, and mix well. 100 c.c. will now be equivalent to 50 c.c. of
+the "acid."</p>
+
+<p>As an example of the application of this method, we may take the
+determination of lime in limestone, marble, and similar substances.</p>
+
+<p><b>Determination of Lime in Limestone.</b>&mdash;Weigh up 1 gram of the dried
+sample, and dissolve in 25 c.c. of normal acid, cool, dilute to 100
+c.c., and titrate with the semi-normal solution of alkali (using
+methyl-orange as an indicator). Divide the c.c. of alkali used by 2,
+subtract from 25, and multiply by 0.028 to find the weight of lime. This
+method is not applicable in the presence of other carbonates or oxides,
+unless the weight of these substances be afterwards determined and due
+correction be made.</p>
+
+
+<h4>STRONTIA.</h4>
+
+<p>Strontia, the oxide of strontium (SrO), occurs in nature as sulphate, in
+the mineral celestine (SrSO<sub>4</sub>), and as carbonate in strontianite
+(SrCO<sub>3</sub>). It is found in small quantities in limestones, chalk, &amp;c.</p>
+
+<p>Strontia is used in sugar-refining, and for the preparation of coloured
+lights.</p>
+
+<p><b>Detection.</b>&mdash;It is detected by the crimson colour which its<span class='pagenum'><a name="Page_325" id="Page_325">[Pg 325]</a></span> compounds
+(when moistened with hydrochloric acid) impart to the flame. The
+spectrum shows a large number of lines, of which a red, an orange, and a
+blue are most characteristic.</p>
+
+<p>It resembles lime in many of its compounds, but is distinguished by the
+insolubility of its sulphate in a boiling solution of ammonium sulphate,
+and by the insolubility of its nitrate in alcohol. From baryta, which it
+also resembles, it is distinguished by not yielding an insoluble
+chromate in an acetic acid solution, by the solubility of its chloride
+in alcohol, and by the fact that its sulphate is converted into
+carbonate on boiling with a solution formed of 3 parts of potassium
+carbonate and 1 of potassium sulphate.</p>
+
+<p>It is got into solution in the same manner as lime. The sulphate should
+be fused with "fusion mixture," extracted with water, and thoroughly
+washed. The residue will contain the strontia as carbonate, which is
+readily soluble in dilute hydrochloric or nitric acid.</p>
+
+<p><b>Separation.</b>&mdash;It is separated (after removal of the silica and metals,
+as described under <i>Lime</i>) by adding ammonia and ammonia carbonate, and
+allowing to stand for some hours in a warm place. In the absence of
+baryta or lime it is filtered off, and weighed as strontium carbonate,
+which contains 70.17 per cent. of strontia. It is separated from baryta
+by dissolving in a little hydrochloric acid, adding ammonia in excess,
+and then acidifying with acetic acid, and precipitating the baryta with
+potassium bichromate, as described under <i>Baryta</i>. The strontia is
+precipitated from the filtrate by boiling for some time with a strong
+solution of ammonic sulphate and a little ammonia. Fifty parts of
+ammonic sulphate are required for each part of strontia or lime present.
+The precipitate is filtered off, and washed first with a solution of
+ammonic sulphate, and then with alcohol. It is dried, ignited and
+weighed as strontium sulphate.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The determination of strontia in pure solutions is best made by adding
+sulphuric acid in excess and alcohol in volume equal to that of the
+solution. Allow to stand overnight, filter, wash with dilute alcohol,
+dry, ignite at a red heat, and weigh as sulphate (SrSO<sub>4</sub>). This
+contains 56.4 per cent. of strontia (SrO); or 47.7 per cent. of
+strontium.<span class='pagenum'><a name="Page_326" id="Page_326">[Pg 326]</a></span></p>
+
+
+<h4>BARYTA.</h4>
+
+<p>Baryta, oxide of barium (BaO), commonly occurs in combination with
+sulphuric oxide in the mineral barytes or heavy spar (BaSO<sub>4</sub>), and in
+combination with carbon dioxide in witherite (BaCO<sub>3</sub>). These minerals
+are not unfrequently found in large quantity (associated with galena and
+other metallic sulphides) in lodes. Small isolated crystals of these are
+frequently found in mining districts. Barium is a constituent of certain
+mineral waters. The minerals are recognised by their high specific
+gravity and their crystalline form.</p>
+
+<p>Compounds of barium are often used by the assayer, more especially the
+chloride and hydrate. The salts are, with the exception of the sulphate,
+generally soluble in water or hydrochloric acid. In such solutions
+sulphuric acid produces a white precipitate of baric sulphate, which is
+practically insoluble in all acids.</p>
+
+<p>The dioxide (BaO<sub>2</sub>) is used for the preparation of oxygen. On strong
+ignition it gives up oxygen, and is converted into baryta (BaO), which,
+at a lower temperature, takes up oxygen from the air, re-forming the
+dioxide.</p>
+
+<p><b>Detection.</b>&mdash;Barium is detected by the green colour its salts,
+especially the chloride, give to the flame. This, viewed through the
+spectroscope, shows a complicated spectrum, of which two lines in the
+green are most easily recognised and characteristic. The salts of barium
+give no precipitate with sulphuretted hydrogen in either acid or
+alkaline solution, but with sulphuric acid they at once give a
+precipitate, which is insoluble in acetate of soda. In solutions
+rendered faintly acid with acetic acid, they give a yellow precipitate
+with bichromate of potash. These reactions are characteristic of barium.</p>
+
+<p>Baryta is got into solution in the manner described under <i>Lime</i>; but in
+the case of the sulphate the substance is fused with three or four times
+its weight of "fusion mixture." The "melt" is extracted with water,
+washed, and the residue dissolved in dilute hydrochloric acid.</p>
+
+<p><b>Separation.</b>&mdash;The separation is thus effected:&mdash;The solution in
+hydrochloric acid is evaporated to dryness, re-dissolved in hot dilute
+hydrochloric acid, and sulphuric acid is added to the solution till no
+further precipitate is formed. The precipitate is filtered off, and
+digested with a solution of ammonium acetate or of sodium hyposulphite
+at 50&deg; or 60&deg; C. to dissolve out any lead sulphate. The residue is
+filtered off, washed, dried, and ignited. The ignited substance is mixed
+with four or five times its weight of "fusion mixture," and fused in a
+platinum-dish over the blowpipe<span class='pagenum'><a name="Page_327" id="Page_327">[Pg 327]</a></span> for a few minutes. When cold, it is
+extracted with cold water, filtered, and washed. The residue is
+dissolved in dilute hydrochloric acid, and (if necessary) filtered. The
+solution contains the barium as baric chloride mixed, perhaps, with
+salts of strontium or lime. To separate these, ammonia is added till the
+solution is alkaline, and then acetic acid in slight excess. Chromate of
+baryta is then thrown down, by the addition of bichromate of potash, as
+a yellow precipitate. It is allowed to settle, filtered and washed with
+a solution of acetate or of nitrate of ammonia. It is dried, ignited
+gently, and weighed. It is BaCrO<sub>4</sub>, and contains 60.47 per cent. of
+baryta.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The gravimetric determination of baryta, when lime and strontia are
+absent, is as follows:&mdash;The solution, if it contains much free acid, is
+nearly neutralised with ammonia, and then diluted to 100 or 200 c.c. It
+is heated to boiling, and dilute sulphuric acid is added till no further
+precipitation takes place. The precipitate is allowed to settle for a
+few minutes, decanted through a filter, and washed with hot water; and,
+afterwards, dried, transferred to a porcelain crucible, and strongly
+ignited in the muffle or over the blowpipe for a few minutes. It is then
+cooled, and weighed as sulphate of baryta (BaSO<sub>4</sub>). It contains 65.67
+per cent. of baryta (BaO).</p>
+
+<p>In determining the baryta in minerals which are soluble in acid, it is
+precipitated direct from the hydrochloric acid solution (nearly
+neutralised with ammonia) by means of sulphuric acid. The precipitated
+baric sulphate is digested with a solution of ammonic acetate; and
+filtered, washed, ignited, and weighed.</p>
+
+
+<h4>VOLUMETRIC DETERMINATION.</h4>
+
+<p>The principle and mode of working of this is the same as that given
+under the Sulphur Assay; but using a standard solution of sulphuric acid
+instead of one of barium chloride. The standard solution of sulphuric
+acid is made to contain 32.02 grams of sulphuric acid (H<sub>2</sub>SO<sub>4</sub>), or
+an equivalent of a soluble alkaline sulphate, per litre. 100 c.c. will
+be equal to 5 grams of baryta.</p>
+
+<p>Five grams of the substance are taken, and the baryta they contain
+converted into carbonate (if necessary). The carbonate is dissolved in
+dilute hydrochloric acid. Ten grams of sodium acetate are added, and the
+solution, diluted to 500 c.c., is boiled, and titrated in the manner
+described.<span class='pagenum'><a name="Page_328" id="Page_328">[Pg 328]</a></span></p>
+
+<p>Lead salts must be absent in the titration, and so must strontia and
+lime. Ferrous salts should be peroxidised by means of permanganate or
+chlorate of potash. Other salts do not interfere.</p>
+
+
+<h4>MAGNESIA.</h4>
+
+<p>Magnesia, the oxide of magnesium (MgO) occurs in nature in the rare
+mineral periclase (MgO); and hydrated, as brucite (MgH<sub>2</sub>O<sub>2</sub>). As
+carbonate it occurs in large quantity as magnesite (MgCO<sub>3</sub>), which is
+the chief source of magnesia. Mixed with carbonate of lime, it forms
+magnesian limestone and dolomite. It is present in larger or smaller
+quantity in most silicates; and the minerals, serpentine, talc, steatite
+and meerschaum are essentially hydrated silicates of magnesia. Soluble
+magnesian salts occur in many natural waters; more especially the
+sulphate and the chloride. Kieserite (MgSO<sub>4</sub>.H<sub>2</sub>O) occurs in
+quantity at Stassfurt, and is used in the manufacture of Epsom salts.</p>
+
+<p><b>Detection.</b>&mdash;Magnesia is best detected in the wet way. Its compounds
+give no colour to the flame, and the only characteristic dry reaction is
+its yielding a pink mass when ignited before the blowpipe (after
+treatment with a solution of cobalt nitrate). In solution, it is
+recognised by giving no precipitate with ammonia or ammonic carbonate in
+the presence of ammonic chloride, and by giving a white crystalline
+precipitate on adding sodium phosphate or arsenate to the ammoniacal
+solution.</p>
+
+<p>Magnesia differs from the other alkaline earths by the solubility of its
+sulphate in water.</p>
+
+<p>Magnesia is dissolved by boiling with moderately strong acids; the
+insoluble compounds are fused with "fusion mixture," and treated as
+described under <i>Silicates</i>.</p>
+
+<p><b>Separation.</b>&mdash;It is separated by evaporating the acid solution to
+dryness to render silica insoluble, and by taking up with dilute
+hydrochloric acid. The solution is freed from the second group of metals
+by means of sulphuretted hydrogen, and the iron, alumina, &amp;c., are
+removed with ammonic chloride, ammonia, and ammonic sulphide. The
+somewhat diluted filtrate is treated, first, with ammonia, and then with
+carbonate of ammonia in slight excess. It is allowed to stand for an
+hour in a warm place, and then filtered. The magnesia is precipitated
+from the filtrate by the addition of an excess of sodium phosphate and
+ammonia. It is allowed to stand overnight, filtered, and washed with
+dilute ammonia. The precipitate contains the magnesia as
+ammonic-magnesic phosphate.</p>
+
+<p>In cases where it is not desirable to introduce sodium salts or
+phosphoric acid into the assay solution, the following method is<span class='pagenum'><a name="Page_329" id="Page_329">[Pg 329]</a></span>
+adopted. The solution (freed from the other alkaline earths by ammonium
+carbonate) is evaporated in a small porcelain dish with nitric acid. The
+residue (after removing the ammonic salts by ignition) is taken up with
+a little water and a few crystals of oxalic acid, transferred to a
+platinum dish, evaporated to dryness, and ignited. The residue is
+extracted with small quantities of boiling water and filtered off; while
+the insoluble magnesia is washed. The filtrate contains the alkalies.
+The residue is ignited, and weighed as magnesia. It is MgO.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution containing the magnesia is mixed with chloride of ammonium
+and ammonia in excess. If a precipitate should form, more ammonic
+chloride is required. Add sodium phosphate solution in excess, stir and
+allow to stand overnight. Filter and wash the precipitate with dilute
+ammonia. Dry, transfer to a platinum or porcelain crucible, and ignite
+(finally at intense redness); cool, and weigh. The substance is magnesic
+pyrophosphate (Mg<sub>2</sub>P<sub>2</sub>O<sub>7</sub>), and contains 36.04 per cent. of
+magnesia.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>The magnesia having been precipitated as ammonic-magnesic phosphate,
+which is the usual separation, its weight can be determined
+volumetrically by the method of titration described under <i>Phosphates</i>.</p>
+
+<p>The same standard solution of uranium acetate is used. Its standard for
+magnesia is got by multiplying the standard for phosphoric oxide by
+0.5493. For example, if one hundred c.c. are equivalent to 0.5 gram of
+phosphoric oxide, they will be equivalent to (0.5 &times; .5493) 0.2746 gram
+of magnesia. The method of working and the conditions of the titration
+are the same as for the phosphate titration. The quantity of substance
+taken for assay must not contain more than 0.1 or 0.2 gram of magnesia.
+After precipitating as ammonic-magnesic phosphate with sodium phosphate,
+and well washing with ammonia, it is dissolved in dilute hydrochloric
+acid, neutralised with ammonia, and sodic acetate and acetic acid are
+added in the usual quantity. The solution is boiled and titrated.</p>
+
+
+<h4>EXAMINATION OF A LIMESTONE.</h4>
+
+<p><b>Silica and Insoluble Silicates.</b>&mdash;Take one gram of the dried sample and
+dissolve it in 10 c.c. of dilute hydrochloric acid; filter; wash, dry,
+and ignite the residue.<span class='pagenum'><a name="Page_330" id="Page_330">[Pg 330]</a></span></p>
+
+<p><b>Organic Matter.</b>&mdash;If the residue insoluble in hydrochloric acid shows
+the presence of organic matter, it must be collected on a weighed filter
+and dried at 100&deg;. On weighing, it gives the combined weights of organic
+and insoluble matter. The latter is determined by igniting and weighing
+again. The organic matter is calculated by difference.</p>
+
+<p><b>Lime.</b>&mdash;Where but little magnesia is present, this is determined by
+titration with standard acid. Take one gram, and dissolve it in 25 c.c.
+of normal hydrochloric acid. Tint with methyl-orange and titrate with
+semi-normal ammonia. Divide the quantity of ammonia used by 2, deduct
+this from 25, and multiply the remainder by 2.8. This gives the
+percentage of lime. Where magnesia is present, the same method is
+adopted, and the magnesia (which is separately determined) is afterwards
+deducted. The percentage of magnesia found is multiplied by 1.4, and the
+result is deducted from the apparent percentage of lime got by
+titrating.</p>
+
+<p><b>Magnesia.</b>&mdash;Dissolve 2 grams of the limestone in hydrochloric acid, and
+separate the lime with ammonia and ammonium oxalate. The filtrate is
+treated with sodium phosphate, and the magnesia is weighed as
+pyrophosphate, or titrated with uranium acetate.</p>
+
+<p><b>Iron.</b>&mdash;Dissolve 2 grams in hydrochloric acid, reduce, and titrate with
+standard permanganate of potassium solution. This gives the total iron.
+The ferrous iron is determined by dissolving another 2 grams in
+hydrochloric acid and at once titrating with the permanganate of
+potassium solution.</p>
+
+<p><b>Manganese.</b>&mdash;Dissolve 20 grams in hydrochloric acid, nearly neutralise
+with soda, add sodium acetate, boil, and filter. To the filtrate add
+bromine; boil, and determine the manganese in the precipitate. See page
+300.</p>
+
+<p><b>Phosphoric Oxide.</b>&mdash;This is determined by dissolving the ferric acetate
+precipitate from the manganese separation in hydrochloric acid, adding
+ammonia in excess, and passing sulphuretted hydrogen. Filter and add to
+the filtrate "magnesia mixture." The precipitate is collected, washed
+with ammonia, ignited, and weighed as pyrophosphate.</p>
+
+
+<h4>THE ALKALIES.</h4>
+
+<p>The oxides of sodium, potassium, lithium, c&aelig;sium, and rubidium and
+ammonia are grouped under this head. Of these c&aelig;sia and rubidia are
+rare, and lithia comparatively so. They are easily distinguished by
+their spectra. They are characterised by the solubility of almost all
+their salts in water, and, consequently, are found in the solutions from
+which the earths and oxides of the metals have been separated by the
+usual group re-agents.<span class='pagenum'><a name="Page_331" id="Page_331">[Pg 331]</a></span></p>
+
+<p>The solution from which the other substances have been separated is
+evaporated to dryness, and the product ignited to remove the ammonic
+salts added for the purpose of separation. The residue contains the
+alkali metals generally, as chlorides or sulphates. Before determining
+the quantities of the particular alkali metals present, it is best to
+convert them altogether, either into chloride or sulphate, and to take
+the weight of the mixed salts. It is generally more convenient to weigh
+them as chlorides. They are converted into this form, if none of the
+stronger acids are present, by simply evaporating with an excess of
+hydrochloric acid. Nitrates are converted into chlorides by this
+treatment. When sulphates or phosphates are present, the substance is
+dissolved in a little water, and the sulphuric or phosphoric acid
+precipitated with a slight excess of acetate of lead in the presence of
+alcohol. The solution is filtered, and the excess of lead precipitated
+with sulphuretted hydrogen. The filtrate from this is evaporated to
+dryness with an excess of hydrochloric acid, and the residue, consisting
+of the mixed chlorides, is gently ignited and weighed. In many cases
+(such as the analysis of slags and of some natural silicates where the
+percentage of alkalies is small) the percentage of soda and potash
+(which most commonly occur) need not be separately determined. It is
+sufficient to report the proportion of mixed alkalies; which is thus
+ascertained:&mdash;Dissolve the ignited and weighed chlorides in 100 c.c. of
+distilled water, and titrate with the standard solution of silver
+nitrate (using potassic chromate as indicator) in the manner described
+under <i>Chlorine</i>. The c.c. of silver nitrate used gives the weight in
+milligrams of the chlorine present. Multiply this by 0.775, and deduct
+the product from the weight of the mixed chlorides. This will give the
+combined weight of the alkalies (Na<sub>2</sub>O and K<sub>2</sub>O) present. For
+example, 0.0266 gram of mixed chlorides required on titrating 14.2 c.c.
+of silver nitrate, which is equivalent to 0.0142 gram of chlorine. This
+multiplied by 0.775 gives 0.0110 to be deducted from the weight of the
+mixed chlorides.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Mixed chlorides</td><td align='left'>0.0266 gram</td></tr>
+<tr><td align='left'>Deduction</td><td align='left'>0.0110&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Mixed alkalies</td><td align='left'>0.0156&nbsp;&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<p>Assuming this to have been got from 1 gram of a rock, it would amount to
+1.56 per cent. of "potash and soda."</p>
+
+<p>The relative proportions of the potash and soda can be ascertained from
+the same determination. Sodium and potassium chlorides have the
+following composition:<span class='pagenum'><a name="Page_332" id="Page_332">[Pg 332]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodium</td><td align='left'>39.38</td><td align='left'>Potassium</td><td align='left'>52.46</td></tr>
+<tr><td align='left'>Chlorine</td><td align='left'>60.62</td><td align='left'>Chlorine</td><td align='left'>47.54</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.00</td><td align='left'></td><td align='left'>100.00</td></tr>
+</table></div>
+
+
+<p>The percentage of chlorine in the mixed chlorides is calculated. It
+necessarily falls somewhere between 47.5 and 60.6 per cent., and
+approaches the one or the other of these numbers as the proportion of
+the sodium or potassium preponderates. Each per cent. of chlorine in
+excess of 47.5 represents 7.63 per cent. of sodium chloride in the mixed
+chlorides. The percentage of potash and soda in the substance can be
+calculated in the usual way. Sodium chloride multiplied by 0.5302 gives
+its equivalent of soda (Na<sub>2</sub>O), and potassium chloride multiplied by
+0.6317 gives its equivalent of potash (K<sub>2</sub>O).</p>
+
+<p>The weight of sodium chloride in the mixed chlorides is also calculated
+thus:&mdash;Take the same example for illustration. Multiply the chlorine
+found by 2.103. This gives&mdash;</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(0.0142&times;2.103) = 0.02987.<br />
+</p>
+
+<p>From the product deduct the weight of the mixed chlorides found&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Product</td><td align='left'>0.02987</td></tr>
+<tr><td align='left'>Mixed chlorides</td><td align='left'>0.02660</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Difference</td><td align='left'>0.00327</td></tr>
+</table></div>
+
+
+<p>The difference multiplied by 3.6288 gives the weight of sodium chloride
+in the mixture. In this case it equals 0.0118 gram. The potassium
+chloride is indicated by the difference between this and the weight of
+the mixed chlorides. It equals 0.0148 gram. We have now got&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodium chloride</td><td align='left'>0.0118 gram</td></tr>
+<tr><td align='left'>Potassium chloride</td><td align='left'>0.0148 &nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+
+<p>from 1 gram of the rock taken. Multiplying these by their factors we
+have (Soda = 0.0118&times;0.5302; Potash 0.0148&times;0.6317)&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Soda</td><td align='left'>= 0.625 per cent.</td></tr>
+<tr><td align='left'>Potash</td><td align='left'>= 0.935&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<p><b>Concentration of the Alkalies.</b>&mdash;With the exception of magnesia, all
+the other bases are separated from the alkalies in the ordinary course
+of work without the addition of any re-agent which cannot be removed by
+simple evaporation and ignition. Consequently, with substances soluble
+in acids, successive treatment of the solution with sulphuretted
+hydrogen, ammonia,<span class='pagenum'><a name="Page_333" id="Page_333">[Pg 333]</a></span> ammonic sulphide, and ammonic carbonate, filtering,
+where necessary, will yield a filtrate containing the whole of the
+alkalies with ammonic salts and, perhaps, magnesia.</p>
+
+<p>The filtrate is evaporated in a small porcelain dish, with the addition
+of nitric acid towards the finish. It is carried to dryness and ignited.
+The residue is taken up with a little water, treated with a few crystals
+of oxalic acid, and again evaporated and ignited. The alkaline salts are
+extracted with water, and filtered from the magnesia into a weighed
+platinum dish. The solution is then evaporated with an excess of
+hydrochloric acid, ignited at a low red heat, and weighed. The residue
+consists of the mixed alkaline chlorides.</p>
+
+<p>For substances (such as most silicates and similar bodies) not
+completely decomposed by acids, Lawrence Smith's method is generally
+used. This is as follows:&mdash;Take from 0.5 to 1 gram of the finely
+powdered mineral, and mix, by rubbing in the mortar, with an equal
+weight of ammonium chloride. Then mix with eight times as much pure
+calcium carbonate, using a part of it to rinse out the mortar. Transfer
+to a platinum crucible, and heat gently over a Bunsen burner until the
+ammonic chloride is decomposed (five or ten minutes). Raise the heat to
+redness, and continue at this temperature for about three quarters of an
+hour. The crucible must be kept covered. Cool, and turn out the mass
+into a 4-inch evaporating dish; wash the crucible and cover with
+distilled water, and add the washings to the dish; dilute to 60 or 80
+c.c., and heat to boiling. Filter and wash. Add to the filtrate about
+1.5 gram of ammonium carbonate; evaporate to about 40 c.c., and add a
+little more ammonic carbonate and some ammonia. Filter into a weighed
+platinum dish, and evaporate to dryness. Heat gently, to drive off the
+ammonic chloride, and ignite to a little below redness. Cool and weigh.
+The residue consists of the mixed alkaline chlorides.</p>
+
+<p><b>Separation of the Alkali-Metals from each other.</b>&mdash;Sodium and lithium
+are separated from the other alkali-metals by taking advantage of the
+solubility of their chlorides in the presence of platinic chloride; and
+from one another by the formation of an almost insoluble lithic
+phosphate on boiling with a solution of sodium phosphate in a slightly
+alkaline solution. C&aelig;sium, rubidium, and potassium yield precipitates
+with platinic chloride, which are somewhat soluble, and must be
+precipitated from concentrated solutions. C&aelig;sium and rubidium are
+separated from potassium by fractional precipitation with platinum
+chloride. Their platino-chlorides, being less soluble than that of
+potassium, are precipitated first. One hundred parts of boiling water
+dissolve 5.18 of the potassium platino-chloride, 0.634 of the rubidium<span class='pagenum'><a name="Page_334" id="Page_334">[Pg 334]</a></span>
+salt, and 0.377 of the corresponding c&aelig;sium compound. The separation of
+lithium, c&aelig;sium, and rubidium is seldom called for, owing to their
+rarity. The details of the separation of potassium from sodium are
+described under <i>Potassium</i>. Ammonia compounds are sharply marked off
+from the rest by their volatility, and it is always assumed that they
+have been removed by ignition; if left in the solution, they would count
+as potassium compounds. They will be considered under <i>Ammonia</i>.</p>
+
+
+<h4>SODIUM.</h4>
+
+<p>Sodium is the commonest of the alkali metals. It is found in nature
+chiefly combined with chlorine as "common salt" (NaCl). This mineral is
+the source from which the various compounds of sodium in use are
+prepared. Sodium occurs abundantly as nitrate (NaNO<sub>3</sub>) in Chili
+saltpetre, and as silicate in various minerals, such as albite (or
+soda-felspar).</p>
+
+<p>It occurs as fluoride in cryolite (Na<sub>3</sub>AlF<sub>6</sub>), and as carbonate in
+natron, &amp;c. Sulphates are also found. Sodium is very widely diffused,
+few substances being free from it.</p>
+
+<p>The detection of sodium is easy and certain, owing to the strong yellow
+colour its salts impart to the flame; this, when viewed by the
+spectroscope, shows a single yellow line.<a name="FNanchor_93_93" id="FNanchor_93_93"></a><a href="#Footnote_93_93" class="fnanchor">[93]</a> The extreme delicacy of
+this test limits its value, because of the wide diffusion of sodium
+salts. It is more satisfactory to separate the chloride, which may be
+recognised by its taste, flame coloration, fusibility, and negative
+action with reagents. The chloride dissolved in a few drops of water
+gives with potassium metantimoniate, a white precipitate of the
+corresponding sodium salt.</p>
+
+<p>Sodium salts are dissolved out from most compounds on treatment with
+water or dilute acids. Insoluble silicates are decomposed and the alkali
+rendered soluble by Lawrence Smith's method, which has just been
+described. The separation of the sodium from the mixed chlorides is
+effected in the following way:&mdash;The chlorides are dissolved in a little
+water and the potassium separated as platino-chloride. The soluble
+sodium platino-chloride, with the excess of platinum, is boiled, mixed
+with sulphuric acid, evaporated to dryness, and ignited. On extracting
+with water, filtering, evaporating, and igniting, sodium sulphate is
+left, and is weighed as such.</p>
+
+<p>It is more usual, and quite as satisfactory, to calculate the weight of
+the sodium chloride by difference from that of the mixed chlorides, by
+subtracting that of the potassium chloride,<span class='pagenum'><a name="Page_335" id="Page_335">[Pg 335]</a></span> which is separately
+determined. For example, 1 gram of a rock gave&mdash;Mixed chlorides, 0.0266
+gram, and 0.0486 gram of potassic platino-chloride. This last is
+equivalent to 0.0149 gram of potassium chloride.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Mixed chlorides found</td><td align='left'>0.0266</td></tr>
+<tr><td align='left'>Deduct potassium chloride</td><td align='left'>0.0149</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Leaves sodium chloride</td><td align='left'>0.0117</td></tr>
+</table></div>
+
+<p>The weight of sodium chloride found, multiplied by 0.5302, gives the
+weight of the soda (Na<sub>2</sub>O).</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The solution, which must contain no other metal than sodium, is
+evaporated in a weighed platinum crucible or dish. Towards the finish an
+excess, not too great, of sulphuric acid is added, and the evaporation
+is continued under a loosely fitting cover. The residue is ignited over
+the blowpipe, a fragment of ammonic carbonate being added towards the
+end, when fumes of sulphuric acid cease to be evolved. This ensures the
+removal of the excess of acid. The crucible is cooled in the desiccator,
+and weighed. The substance is sulphate of soda (Na<sub>2</sub>SO<sub>4</sub>), and
+contains 43.66 per cent. of soda (Na<sub>2</sub>O), or 32.38 per cent. of sodium
+(Na).</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>There are various methods used for the different compounds of sodium.
+There is no one method of general application. Thus with "common salt"
+the chlorine is determined volumetrically; and the sodium, after
+deducting for the other impurities, is estimated by difference.</p>
+
+<p>With sodic carbonate and caustic soda, a given weight of the sample is
+titrated with standard acid, and the equivalent of soda estimated from
+the alkalinity of the solution.</p>
+
+<p>With sodium sulphate, a modification of the same method is used. To a
+solution of 3.55 grams of the salt contained in a half-litre flask, 250
+c.c. of a solution of baryta water is added. The volume is made up to
+500 c.c. with water. The solution is mixed and filtered. Half of the
+filtrate is measured off, treated with a current of carbonic acid, and
+then boiled. It is transferred to a half-litre flask, diluted to the
+mark, shaken up, and filtered. 250 c.c. of the filtrate, representing a
+quarter of the sample taken, is then titrated with standard acid. The
+standard acid is made by diluting 250 c.c. of the normal acid to 1
+litre. The c.c. of<span class='pagenum'><a name="Page_336" id="Page_336">[Pg 336]</a></span> acid used multiplied by 2 gives the percentage. A
+correction must be made to counteract the effect of impurities in the
+baryta as well as errors inherent in the process. This is small, and its
+amount is determined by an experiment with 3.55 grams of pure sodium
+sulphate.</p>
+
+
+<h4>EXAMINATION OF COMMON SALT.</h4>
+
+<p><b>Moisture.</b>&mdash;Powder and weigh up 10 grams of the sample into a platinum
+dish. Dry in a water oven for an hour, and afterwards heat to bare
+redness over a Bunsen burner. Cool, and weigh. The loss gives the water.</p>
+
+<p><b>Chlorine.</b>&mdash;Weigh up two separate lots of 1 gram each; dissolve in 100
+c.c. of water, and determine the chlorine by titrating with the standard
+silver nitrate solution, using chromate of potash as indicator. See
+<i>Chlorine</i>.</p>
+
+<p><b>Insoluble Matter.</b>&mdash;Dissolve 10 grams of the salt in water with the
+help of a little hydrochloric acid. Filter off the sediment, wash,
+ignite, and weigh. This residue is chiefly sand. Dilute the nitrate to
+500 c.c.</p>
+
+<p><b>Lime.</b>&mdash;Take 250 c.c. of the filtrate, render ammoniacal and add
+ammonium oxalate; wash, dry, and ignite the precipitate. Weigh as lime
+(CaO).</p>
+
+<p><b>Magnesia.</b>&mdash;To the filtrate from the lime add phosphate of soda. Allow
+to stand overnight, filter, wash with dilute ammonia, dry, ignite, and
+weigh as pyrophosphate.</p>
+
+<p><b>Sulphuric Oxide.</b>&mdash;To the remaining 250 c.c. of the filtrate from the
+"insoluble," add an excess of barium chloride. Collect, wash, dry,
+ignite, and weigh the barium sulphate.</p>
+
+<p><b>Sodium.</b>&mdash;It is estimated by difference.</p>
+
+<p>The following may be taken as an example:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Moisture</td><td align='left'>0.35</td></tr>
+<tr><td align='left'>Insoluble matter</td><td align='left'>0.40</td></tr>
+<tr><td align='left'>Lime</td><td align='left'>0.40</td></tr>
+<tr><td align='left'>Magnesia</td><td align='left'>0.05</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='left'>0.60</td></tr>
+<tr><td align='left'>Chlorine</td><td align='left'>59.60</td></tr>
+<tr><td align='left'>Sodium</td><td align='left'>38.60</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.00</td></tr>
+</table></div>
+
+
+<h4>POTASSIUM.</h4>
+
+<p>Potassium occurs in nature as chloride, in the mineral sylvine (KCl),
+and more abundantly combined with magnesium chloride, in earnallite
+<span class='pagenum'><a name="Page_337" id="Page_337">[Pg 337]</a></span>(KCl.MgCl<sub>2</sub>.6H<sub>2</sub>O). It occurs as nitrate in nitre (KNO<sub>3</sub>), and as
+silicate in many minerals, such as orthoclase (or potash-felspar) and
+muscovite (or potash-mica).</p>
+
+<p>Potassium compounds are detected by the characteristic violet colour
+they impart to the flame. The presence of sodium salts masks this tint,
+but the interference can be neutralised by viewing the flame through a
+piece of blue glass. Viewed through the spectroscope, it shows a
+characteristic line in the red and another in the violet. These,
+however, are not so easy to recognise or obtain as the sodium one.
+Concentrated solutions of potassium salts give a yellow crystalline
+precipitate with platinum chloride, and a white crystalline one with the
+acid tartrate of soda. For these tests the solution is best neutral.
+These tests are only applicable in the absence of compounds other than
+those of potassium and sodium.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>This process serves for its separation from sodium. Take 1 gram of the
+sample and dissolve it in an evaporating dish with 50 c.c. of water.
+Acidify with hydrochloric acid in quantity sufficient (if the metals are
+present as chlorides) to make it acid, or, if other acids are present,
+in at least such quantity as will provide the equivalent of chlorine.
+Add 3 grams of platinum, in solution as platinum chloride, and evaporate
+on a water-bath to a stiff paste, but not to dryness. Moisten with a few
+drops of platinic chloride solution without breaking up the paste by
+stirring. Cover with 20 c.c. of strong alcohol, and wash the crystals as
+much as possible by rotating the dish. Allow to settle for a few
+moments, and decant through a filter. Wash in the same way two or three
+times until the colour of the filtrate shows that the excess of the
+platinum chloride used is removed. Wash the precipitate on to the filter
+with a jet of alcohol from the wash-bottle; clean the filter-paper,
+using as little alcohol as possible. Dry in the water-oven for an hour.
+Brush the precipitate into a weighed dish, and weigh it. It is potassium
+platino-chloride (K<sub>2</sub>PtCl<sub>6</sub>), and contains 16.03 per cent. of
+potassium, or 30.56 per cent. of potassium chloride (KCl), which is
+equivalent to 19.3 per cent. of potash (K<sub>2</sub>O).</p>
+
+<p>If the filter-paper is not free from precipitate, burn it and weigh
+separately. The excess of weight over that of the ash will be due to
+platinum and potassic chloride (Pt and 2KCl). This multiplied by 1.413
+will give the weight of the potassic platino-chloride from which it was
+formed. It must be added to the weight of the main precipitate.</p>
+
+<p>The mixed alkaline chlorides obtained in the usual course of<span class='pagenum'><a name="Page_338" id="Page_338">[Pg 338]</a></span> analysis
+are treated in this manner; the quantity of platinum added must be about
+three times as much as the mixed chlorides weigh.</p>
+
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>These are the same as with soda.</p>
+
+<p><b>Examination of Commercial Carbonate of Potash.</b>&mdash;The impurities to be
+determined are moisture, silica, and insoluble matter, chlorine,
+sulphuric oxide, and oxide of iron. These determinations are made in the
+ways described under the examination of common salt.</p>
+
+<p>The <b>potassium</b> is determined by converting it into chloride and
+precipitating with platinum chloride, &amp;c., as just described.</p>
+
+<p><b>Available Alkali.</b>&mdash;Weigh up 23.5 grams of the sample, dissolve in
+water, and make up to 500 c.c. Take 50 c.c., tint with methyl orange,
+and titrate with the normal solution of acid. The c.c. of acid used
+multiplied by 2 gives the percentage of available alkali calculated as
+potash (K<sub>2</sub>O).</p>
+
+<p><b>Soda.</b>&mdash;This is calculated indirectly in the following way:&mdash;Deduct
+from the potassium found the quantity required for combination with the
+chlorine and sulphuric oxide present, and calculate the remainder to
+potash (K<sub>2</sub>O). The apparent surplus excess of available alkali is the
+measure of the soda present.</p>
+
+<p><b>Carbon Dioxide.</b>&mdash;The c.c. of acid used in the available alkali
+determination, multiplied by 2.2 and divided by 2.35, gives the
+percentage of carbon dioxide.</p>
+
+
+<h4>LITHIUM.</h4>
+
+<p>Lithia, the oxide of lithium (Li<sub>2</sub>O), occurs in quantities of 3 or 4
+per cent. in various silicates, such as lepidolite (or lithia-mica),
+spodumene, and petalite. It also occurs as phosphate in triphyline. It
+is a constituent of the water of certain mineral springs. A spring at
+Wheal Clifford contained as much as 0.372 gram of lithium chloride per
+litre. In small quantities, lithia is very widely diffused.</p>
+
+<p>The <b>Detection</b> of lithia is rendered easy by the spectroscope; its
+spectrum shows a red line lying about midway between the yellow sodium
+line and the red one of potassium. It also shows a faint yellow line.
+The colour of the flame (a crimson) is characteristic.</p>
+
+<p>The reactions of the lithium compounds lie between those of the alkalies
+and of the alkaline earths. Solutions are not precipitated by tartaric
+acid nor by platinic chloride. The oxide is<span class='pagenum'><a name="Page_339" id="Page_339">[Pg 339]</a></span> slowly soluble in water.
+The carbonate is not freely soluble. Lithia is completely precipitated
+by sodic phosphate, especially in hot alkaline solutions.</p>
+
+<p>In its determination the mixed alkaline chlorides obtained in the
+separation of the alkalies are dissolved in water, a solution of soda is
+added in slight excess, and the lithia precipitated with <i>sodic</i>
+phosphate. Before filtering, it is evaporated to dryness and extracted
+with hot water rendered slightly ammoniacal. The residue is transferred
+to a filter, dried, ignited, and weighed. The precipitate is lithium
+phosphate (3Li<sub>2</sub>O, P<sub>2</sub>O<sub>5</sub>), and contains 38.8 per cent. of lithia.
+The separation of lithia from magnesia is not given by the usual
+authorities. Wohler recommends evaporating the solution to dryness with
+carbonate of soda. On extracting the residue with water, the lithia
+dissolves out and is determined in the filtrate. One hundred parts of
+water dissolve, at the ordinary temperature, 0.769 parts of lithium
+carbonate (Li<sub>2</sub>CO<sub>3</sub>); the basic magnesia compound is almost
+insoluble in the absence of carbon dioxide and ammonium salts.</p>
+
+
+<h4>CAESIUM.</h4>
+
+<p>The oxide of caesium, caesia (Cs<sub>2</sub>O), is found associated with lithia
+in lepidolite, &amp;c., and, together with rubidium, in many mineral waters.
+The mineral pollux is essentially a silicate of alumina and caesia; it
+contains 34.0 per cent. of the latter oxide.</p>
+
+<p>Caesium is best detected by the spectroscope, its spectrum being
+characterised by two lines in the blue and one in the red; the latter is
+about midway between the lithium and sodium lines.</p>
+
+<p>If not detected by the spectroscope, or specially looked for, caesia
+would, in the ordinary course of work, be separated with the potash and
+weighed as potassium platino-chloride.</p>
+
+<p>Caesia is separated from all the other alkalies by adding to the acid
+solution of the mixed chlorides a strongly acid cold solution of
+antimonious chloride. The acid used must be hydrochloric. The caesium is
+precipitated as a white crystalline precipitate (CsCl.SbCl<sub>3</sub>), which
+is filtered off, and washed, when cold, with strong hydrochloric acid;
+since it is decomposed by water or on warming. The precipitate is washed
+into a beaker, and treated with sulphuretted hydrogen; after filtering
+off the sulphide of antimony, the solution leaves, on evaporation, the
+caesium as chloride.<span class='pagenum'><a name="Page_340" id="Page_340">[Pg 340]</a></span></p>
+
+
+<h4>RUBIDIUM.</h4>
+
+<p>Rubidium occurs widely diffused in nature, but in very small quantities.
+It is generally associated with caesium.</p>
+
+<p>It is detected by the spectroscope, which shows two violet lines and two
+dark red ones. Like caesium, it is precipitated with platinic chloride,
+and in the ordinary course of work would be weighed as potassium. It is
+separated from potassium by fractional precipitation with platinic
+chloride. Rubidium platino-chloride is much less soluble than the
+potassium salt.</p>
+
+
+<h4>AMMONIUM.</h4>
+
+<p>It is usual to look upon the salts of ammonia as containing a compound
+radical (NH<sub>4</sub> = Am), which resembles in many respects the metals of
+the alkalies. Ammonium occurs in nature as chloride in sal ammoniac
+(AmCl), as sulphate in mascagnine (Am<sub>2</sub>SO<sub>4</sub>), as phosphate in
+struvite (AmMgPO<sub>4</sub>.12H<sub>2</sub>O). Minerals containing ammonium are rare,
+and are chiefly found either in volcanic districts or associated with
+guano. Ammonia and ammonium sulphide occur in the waters of certain
+Tuscan lagoons, which are largely worked for the boracic acid they
+contain. The crude boracic acid from this source contains from 5 to 10
+per cent. of ammonium salts. It is from these that the purer forms of
+ammonium compounds of commerce known as "from volcanic ammonia" are
+derived. But the bulk of the ammonia of commerce is prepared from the
+ammoniacal liquors obtained as bye-products in the working of certain
+forms of blast furnaces and coke ovens, and more especially in
+gas-making.</p>
+
+<p>Ammonia hardly comes within the objects of assaying; but it is largely
+used in the laboratory, and the assayer is not unfrequently called on to
+determine it. Ammonium salts are mostly soluble in water. In strong
+solutions they give a yellow precipitate of ammonium platino-chloride on
+the addition of chloride of platinum; and with the acid tartrate of soda
+yield a white precipitate of hydric ammonic tartrate. These reactions
+are similar to those produced with potassium compounds.</p>
+
+<p>Heated with a base, such as lime or sodic hydrate, ammonium salts are
+decomposed, yielding ammonia gas (NH<sub>3</sub>), which is readily soluble in
+water. The solution of this substance is known as ammonic hydrate or
+"ammonia."</p>
+
+<p>They are volatilised on ignition; either with, or without, decomposition
+according to the acid present. This fact is of importance in analytical
+work; since it allows of the use of alkaline<span class='pagenum'><a name="Page_341" id="Page_341">[Pg 341]</a></span> solutions and reagents
+which leave nothing behind on heating. It must be remembered, however,
+that, although ammonic chloride is volatile, it cannot be volatilised in
+the presence of substances which form volatile chlorides without loss of
+the latter. For example: ferric oxide and alumina are thus lost,
+volatilising as chlorides; and there are some other compounds (notably
+ammonic magnesic arsenate) which on heating to redness suffer reduction.
+The presence of ammonic chloride in such cases must be avoided.</p>
+
+<p><b>Detection.</b>&mdash;Compounds of ammonium are detected by their evolving
+ammonia when mixed or heated with any of the stronger bases. The ammonia
+is recognised by its odour, by its alkaline reaction with litmus paper,
+and by yielding white fumes, when brought in contact with fuming acid.
+In consequence of the use of ammonium salts and ammonia as reagents, it
+is necessary to make a special test for and determination of
+ammonium.<a name="FNanchor_94_94" id="FNanchor_94_94"></a><a href="#Footnote_94_94" class="fnanchor">[94]</a> In the ordinary course of work it will be "lost on
+ignition." The determination presents little difficulty, and is based on
+the method used for its detection.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig061.jpg" width="300" height="341" alt="Fig. 61." title="" />
+
+</div>
+
+<p><b>Solution and Separation.</b>&mdash;Although ammonium salts are soluble in
+water, there is no necessity for dissolving them. The compound
+containing the ammonia is boiled with an alkaline solution; and the
+liberated ammonia condensed and collected. The substance is weighed out
+into a flask of about 200 c.c. capacity. The flask is closed with a
+rubber cork perforated to carry a 20 c.c. pipette and a bulb exit tube.
+The latter is connected with a receiver, which is a small flask
+containing dilute hydrochloric acid (fig. 61). The flask containing the
+substance is corked, and the greater part of the soda solution is run in
+from the pipette. The solution is then boiled. The ammonia volatilises,
+and is carried over into the hydrochloric acid, with which it combines
+to form ammonic chloride. The distillation is carried on gently until
+the bulk of the liquid is driven over. The ammonia in the receiver will
+be mixed only with the excess of hydrochloric acid. This separation is
+used in all determinations.<span class='pagenum'><a name="Page_342" id="Page_342">[Pg 342]</a></span></p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>The contents of the flask are transferred to a weighed platinum dish,
+and evaporated on the water-bath. It is dried until the weight is
+constant. The chloride of ammonium remains as a white mass which, after
+cooling in a desiccator, is weighed. It contains 33.72 per cent. of
+ammonium (NH<sub>4</sub>), or 31.85 per cent. of ammonia (NH<sub>3</sub>). On heating
+over the Bunsen burner it is completely volatilised, leaving no residue.</p>
+
+
+<h4>VOLUMETRIC DETERMINATION.</h4>
+
+<p>Weigh up 1.7 gram of the substance and place it in the flask. Measure
+off 50 c.c. of the normal solution of acid, place them in the receiver,
+and dilute with an equal volume of water. Run in through the pipette (by
+opening the clip) 20 c.c. of a strong solution of soda, boil until the
+ammonia has passed over, and then aspirate a current of air through the
+apparatus. Disconnect the receiver, and tint its contents with methyl
+orange. Titrate the residual acid with a semi-normal solution of alkali.
+Divide the c.c. of the "alkali" solution used by 2, and deduct from the
+50 c.c. The difference will give the number of c.c. of the normal acid
+solution neutralised by the ammonia distilled over. Each c.c. of "acid"
+so neutralised, represents 1 per cent. of ammonia in the sample. If the
+results are to be reported as ammonium, 1.8 gram of the sample is taken
+instead of 1.7 gram.</p>
+
+
+<h4>COLORIMETRIC DETERMINATION.</h4>
+
+<p>This is effected by means of "Nessler's" reagent, which strikes a brown
+colour with traces of ammonia, even with a few hundredths of a milligram
+in 100 c.c. of liquid. With larger quantities of ammonia the reagent
+gives a precipitate. This reagent is a strongly alkaline solution of
+potassic mercuric iodide; and is thus made:&mdash;</p>
+
+
+<p><i>Nessler's solution</i>: Dissolve 17 grams of mercuric chloride in 300 c.c.
+of water; and add the solution to one of 35 grams of potassium iodide in
+100 c.c. of water until a permanent precipitate is produced. Both
+solutions must be cold. Then make up to a litre by adding a 20 per cent.
+solution of potash. Add more of the mercuric chloride (a little at a
+time) until a permanent precipitate is again formed. Allow to settle,
+decant, and use the clear liquor. Four or five c.c. are used for each
+100 c.c. of liquid to be tested.</p>
+
+<p><i>A Standard Solution of Ammonia</i> is made by dissolving 0.315<span class='pagenum'><a name="Page_343" id="Page_343">[Pg 343]</a></span> gram of
+ammonic chloride in water, and diluting to 100 c.c. Ten c.c. of this are
+taken and diluted to 1 litre. One c.c. contains 0.01 milligram of
+ammonia (NH<sub>3</sub>).</p>
+
+<p>In working, the solution containing the ammonia is diluted to a definite
+volume, and to such an extent that 50 c.c. of it shall not contain more
+than 0.02 or 0.03 milligram of ammonia. Fifty c.c. of it are transferred
+to a Nessler glass and mixed with 2 c.c. of Nessler's reagent. The
+colour is noted, and an estimate made as to the amount of ammonia it
+indicates. A measured quantity of the standard ammonia, judged to
+contain about as much ammonia as that in the assay, is then put into
+another Nessler glass. It is diluted to 50 c.c. with water, and mixed
+with 2 c.c. of "Nessler." After standing a minute or two, the colours in
+the two glasses are compared. If the tints are equal, the assay is
+finished; but if the standard is weaker or stronger than the assay,
+another standard, containing more or less ammonia, as the case may be,
+must be prepared and compared with the assay. Two such experiments will
+generally be sufficient; but, if not, a third must be made. The addition
+of more standard ammonia to the solution to which the "Nessler" has
+already been added does not give a satisfactory result.</p>
+
+<p>When the ammonia in 50 c.c. has been determined, that in the whole
+solution is ascertained by a suitable multiplication. By 10, for
+example, if the bulk was 500 c.c., or by 20 if it was a litre.</p>
+
+<p>Distilled water is used throughout. It must be free from ammonia; and is
+best prepared by distilling an ammonia-free spring water.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_90_90" id="Footnote_90_90"></a><a href="#FNanchor_90_90"><span class="label">[90]</span></a> Al<sub>2</sub>Cl<sub>6</sub> + 3Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub> + 3H<sub>2</sub>O =
+Al<sub>2</sub>(HO)<sub>6</sub> + 6NaCl + 3S + 3SO<sub>2</sub></p></div>
+
+<div class="footnote"><p><a name="Footnote_91_91" id="Footnote_91_91"></a><a href="#FNanchor_91_91"><span class="label">[91]</span></a> 3BeO,Al<sub>2</sub>O<sub>3</sub>,6SiO<sub>2</sub></p></div>
+
+<div class="footnote"><p><a name="Footnote_92_92" id="Footnote_92_92"></a><a href="#FNanchor_92_92"><span class="label">[92]</span></a> CaC<sub>2</sub>O<sub>4</sub> = CaCO<sub>3</sub>+CO.</p></div>
+
+<div class="footnote"><p><a name="Footnote_93_93" id="Footnote_93_93"></a><a href="#FNanchor_93_93"><span class="label">[93]</span></a> Resolved into two with a powerful spectroscope.</p></div>
+
+<div class="footnote"><p><a name="Footnote_94_94" id="Footnote_94_94"></a><a href="#FNanchor_94_94"><span class="label">[94]</span></a> Ammonium compounds are frequently produced when dissolving
+metals in nitric acid; or when nitrates are heated in the presence of
+the metals.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<h2><a name="PART_III_NON-METALS" id="PART_III_NON-METALS"></a>PART III&mdash;NON-METALS.</h2>
+
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_344" id="Page_344">[Pg 344]</a></span></p>
+<h2><a name="CHAPTER_XV" id="CHAPTER_XV"></a>CHAPTER XV.</h2>
+
+<h3>OXYGEN AND OXIDES.&mdash;THE HALOGENS.</h3>
+
+
+<h4>OXYGEN.</h4>
+
+<p>Oxygen occurs in nature in the free state, forming 23 per cent. by
+weight, or 21 per cent. by volume of the atmosphere; but, since it is a
+gas, its presence is easily overlooked and its importance
+underestimated. Except in the examination of furnace-gases, &amp;c., the
+assayer is not often called upon to determine its quantity, but it forms
+one of his most useful reagents, and there are many cases where he
+cannot afford to disregard its presence. It occurs not only in the air,
+but also dissolved in water; ordinary waters containing on an average
+0.00085 per cent. by weight, or 0.85 parts per 100,000.</p>
+
+<p>Chemically, it is characterised by its power of combining, especially at
+high temperatures, with the other elements, forming an important class
+of compounds called oxides. This combination, when rapid, is accompanied
+by the evolution of light and heat; hence oxygen is generally called the
+supporter of combustion. This property is taken advantage of in the
+operation of calcining, scorifying, cupelling, &amp;c. The importance of a
+free access of air in all such work is seen when it is remembered that 1
+litre of air contains 0.2975 gram of oxygen, and this quantity will only
+oxidise 0.1115 gram of carbon, 0.2975 gram of sulphur, or 3.849 grams of
+lead.</p>
+
+<p>Oxidation takes place at the ordinary temperature with many substances.
+Examples of such action are seen in the weathering of pyrites, rusting
+of iron, and (in the assay office) the weakening of solutions of many
+reducing agents.</p>
+
+<p>For methods of determining the percentage of oxygen in gases, for
+technical purposes, the student is referred to Winkler &amp; Lunge's
+"Technical Gas Analysis."<span class='pagenum'><a name="Page_345" id="Page_345">[Pg 345]</a></span></p>
+
+
+<h4>OXIDES.</h4>
+
+<p>Oxides are abundant in nature, almost all the commonly occurring bodies
+being oxidised. Water (H<sub>2</sub>O) contains 88.8 per cent. of oxygen;
+silica, lime, alumina, magnesia, and the other earths are oxides, and
+the oxides of the heavier metals are in many cases important ores; as,
+for example, cassiterite (SnO<sub>2</sub>), h&aelig;matite (Fe<sub>2</sub>O<sub>3</sub>), magnetite
+(Fe<sub>3</sub>O<sub>4</sub>), and pyrolusite (MnO<sub>2</sub>). In fact, the last-named mineral
+owes its value to the excess of oxygen it contains, and may be regarded
+as an ore of oxygen rather than of manganese.</p>
+
+<p>Most of the metals, when heated to redness in contact with air, lose
+their metallic lustre and become coated with, or (if the heating be
+prolonged) altogether converted into, oxide. This oxide was formerly
+termed a "calx," and has long been known to weigh more than the metal
+from which it was obtained. For example, one part by weight of tin
+becomes, on calcining, 1.271 parts of oxide (putty powder). The student
+will do well to try the following experiments:&mdash;Take 20 grams of tin and
+heat them in a muffle on a scorifier, scraping back the dross as it
+forms, and continuing the operation until the whole of the metal is
+burnt to a white powder and ceases to increase in weight.<a name="FNanchor_95_95" id="FNanchor_95_95"></a><a href="#Footnote_95_95" class="fnanchor">[95]</a> Take care
+to avoid loss, and, when cold, weigh the oxide formed. The oxide should
+weigh 25.42 grams, which increase in weight is due to the oxygen
+absorbed from the air and combined with the metal. It can be calculated
+from this experiment (if there has been no loss) that oxide of tin
+contains 21.33 per cent. of oxygen and 78.67 per cent. of tin. Oxidation
+is performed with greater convenience by wet methods, using reagents,
+such as nitric acid, which contain a large proportion of oxygen loosely
+held. Such reagents are termed oxidising agents. Besides nitric acid,
+permanganate of potash, bichromate of potash, and peroxide of hydrogen
+are largely used for this purpose. One c.c. of nitric acid contains as
+much oxygen as 2.56 litres of air, and the greater part of this is
+available for oxidising purposes. Try the following experiment:&mdash;Take 2
+grams of tin and cover in a weighed Berlin dish with 20 c.c. of dilute
+nitric acid, heat till decomposed, evaporate to dryness, ignite, and
+weigh. The 2 grams of tin should yield 2.542 grams of oxide. The
+increase in weight will be proportionally the same as in the previous
+experiment by calcination, and is due to oxygen, which in this case has
+been derived from the nitric acid.<span class='pagenum'><a name="Page_346" id="Page_346">[Pg 346]</a></span></p>
+
+<p>The percentage of oxygen in this oxide of tin (or in any of the oxides
+of the heavier metals) may be directly determined by heating such oxides
+in a current of hydrogen, and collecting and weighing the water formed.</p>
+
+<p>It is found by experiment that 88.86 parts by weight of oxygen,
+combining with 11.14 parts of hydrogen, form 100 parts of water; so that
+from the weight of water formed it is easy to calculate the amount of
+oxygen the oxide contained.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig062.jpg" width="450" height="151" alt="Fig. 62." title="" />
+
+</div>
+
+<p>Take 1 gram of the dried and powdered oxide and place it in a warm dry
+combustion tube. Place the tube in a furnace, and connect at one end
+with a hydrogen apparatus provided with a sulphuric acid bulb for drying
+the gas, and at the other with a weighed sulphuric acid tube for
+collecting the water formed. The apparatus required is shown in fig. 62.
+Pass hydrogen through the apparatus, and, when the air has been cleared
+out, light the furnace. Continue the heat and current of hydrogen for
+half an hour (or longer, if necessary). Allow to cool. Draw a current of
+dry air through the weighed tube. Weigh. The increase in weight gives
+the amount of water formed, and this, multiplied by 0.8886, gives the
+weight of the oxygen. The percentage of oxygen thus determined should be
+compared with that got by the oxidation of the metal. It will be
+practically the same. The following results can be taken as examples:&mdash;</p>
+
+<p>Twenty grams of tin, calcined as described, gave 25.37 grams of oxide.</p>
+
+<p>Two grams of tin, oxidised with nitric acid and ignited, gave 2.551
+grams of oxide.</p>
+
+<p>One gram of the oxide of tin, on reduction in a current of hydrogen,
+gave 0.2360 gram of water (equivalent to 0.2098 gram of oxygen), and
+left 0.7900 gram of metal.</p>
+
+<p>Ten grams of ferrous sulphate gave, on strong ignition, 2.898 grams of
+ferric oxide (Fe<sub>2</sub>O<sub>3</sub>)<a name="FNanchor_96_96" id="FNanchor_96_96"></a><a href="#Footnote_96_96" class="fnanchor">[96]</a> instead of 2.877.</p>
+
+<p>The student should similarly determine the percentage of oxygen in
+oxides of copper and iron. The former oxide may be prepared by
+dissolving 5 grams of copper in 50 c.c. of dilute nitric<span class='pagenum'><a name="Page_347" id="Page_347">[Pg 347]</a></span> acid,
+evaporating to dryness, and strongly igniting the residue. The oxide of
+iron may be made by weighing up 10 grams of powdered ferrous sulphate (=
+to 2.014 grams of iron) and heating, at first gently, to drive off the
+water, and then at a red heat, until completely decomposed. The weight
+of oxide, in each case, should be determined; and the percentage of
+oxygen calculated. Compare the figures arrived at with those calculated
+from the formula of the oxides, CuO and Fe<sub>2</sub>O<sub>3</sub>.</p>
+
+<p>It would be found in a more extended series of experiments that the same
+metal will, under certain conditions, form two or more oxides differing
+among themselves in the amount of oxygen they contain. These oxides are
+distinguished from one another by such names as "higher" and "lower
+oxides," "peroxides," "protoxides," "dioxides," &amp;c.</p>
+
+<p>The oxides may be conveniently classified under three heads:&mdash;</p>
+
+<p>(1) <i>Those that are reduced to metal by heat alone</i>, such as the oxides
+of mercury, silver, platinum, gold, &amp;c.;</p>
+
+<p>(2) <i>Those which are reduced by hydrogen at a red heat</i>, which includes
+the oxides of the heavy metals;</p>
+
+<p>(3) <i>Those which are not reduced by these means</i>, good examples of which
+are silica, alumina, the alkalies, and the alkaline earths.</p>
+
+<p>Another important classification is into acid, basic and neutral oxides.
+The oxides of the non-metallic elements, such as sulphur, carbon,
+phosphorus, &amp;c., are, as a rule, acid; and the more oxygen they contain,
+the more distinctly acid they are. The oxides of the metals are nearly
+all basic; and, as a rule, the less oxygen they contain, the more
+distinctly basic they are.</p>
+
+<p>The basic oxides, which are soluble in acids, give rise to the formation
+of salts when dissolved therein. During the solution, water is formed,
+but no gas is evolved. The oxide dissolved in each case neutralizes an
+equivalent of the acid used for solution.<a name="FNanchor_97_97" id="FNanchor_97_97"></a><a href="#Footnote_97_97" class="fnanchor">[97]</a> The basic properties of
+many of these can be taken advantage of for their determination. This is
+done in the case of soda, potash, lime, &amp;c., by finding the quantity of
+acid required to neutralize a given weight of the substance.</p>
+
+<p>There are some oxides which, under certain conditions, are acid to one
+substance (a stronger base) and basic to another (a stronger acid). For
+example, the oxides of lead and of tin, as also alumina, dissolve in
+caustic soda, acting as acids; whilst, on<span class='pagenum'><a name="Page_348" id="Page_348">[Pg 348]</a></span> the other hand, they combine
+with sulphuric or hydrochloric acid, playing the part of bases.</p>
+
+<p>The oxides known as "earths," when ignited, are many of them insoluble
+in acids, although easily dissolved before ignition.</p>
+
+<p>It is common in complete analyses of minerals to meet with cases in
+which the sum total of the elements found falls short of the amount of
+ore taken; and here oxygen must be looked for. For example, this occurs
+in the case of a mixture of pyrites with oxide of iron, or in a mixture
+of sulphides and sulphates. The state in which the elements are present,
+and the percentage (say of sulphides and sulphates) can in many cases be
+determined; but this is not always required. When the difference between
+the sum total and the elements found is small, it is reported as "oxygen
+and loss." When, however, it is considerable, the oxygen may be reported
+as such; and its amount be either determined directly in the way already
+described, or calculated from the best determination that can be made of
+the relative amounts of oxides, sulphides, sulphates, &amp;c., present. Such
+cases require a careful qualitative analysis to find out that the
+substance is present; and then the separation of each constituent is
+made as strictly as possible. These remarks apply especially to ores of
+the heavy metals. The separation of the constituents is effected with
+suitable solvents applied in proper order. The soluble sulphates, for
+example, are extracted with water; the oxides by the dilute acids or
+alkalies in which they are known to be soluble. The oxygen in the
+sulphates and oxides thus obtained is estimated by determining the
+sulphur and metals in the solutions, and calculating the amount of
+oxygen with which they combine. The metals of the earths and alkalies
+are almost invariably present as oxides, and are reported as such;
+except it is known that they are present in some other form, such as
+fluoride or chloride. Thus, silica, alumina, lime, water, &amp;c., appear in
+an analysis; even in those cases where "oxygen and loss" is also
+mentioned. As an example of such a report, take the following analysis
+of Spanish pyrites:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sulphur</td><td align='right'>49.00</td></tr>
+<tr><td align='left'>Iron</td><td align='right'>43.55</td></tr>
+<tr><td align='left'>Copper</td><td align='right'>3.20</td></tr>
+<tr><td align='left'>Arsenic</td><td align='right'>0.47</td></tr>
+<tr><td align='left'>Lead</td><td align='right'>0.93</td></tr>
+<tr><td align='left'>Zinc</td><td align='right'>0.35</td></tr>
+<tr><td align='left'>Lime</td><td align='right'>0.10</td></tr>
+<tr><td align='left'>Silica, &amp;c.</td><td align='right'>0.63</td></tr>
+<tr><td align='left'>Water</td><td align='right'>0.70</td></tr>
+<tr><td align='left'>Oxygen and loss</td><td align='right'>1.07</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>100.00</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_349" id="Page_349">[Pg 349]</a></span></p>
+
+<p>The following example will illustrate the mode of calculating and
+reporting. A mineral, occurring as blue crystals soluble in water, and
+found on testing to be a mixed sulphate of iron and copper, gave on
+analysis the following results:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Water</td><td align='left'>44.51</td><td align='left'>per cent.</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='left'>28.82</td><td align='left'>"</td></tr>
+<tr><td align='left'>Copper</td><td align='left'>8.44</td><td align='left'>"</td></tr>
+<tr><td align='left'>Ferrous iron</td><td align='left'>11.81</td><td align='left'>"</td></tr>
+<tr><td align='left'>Ferric iron</td><td align='left'>0.38</td><td align='left'>"</td></tr>
+<tr><td align='left'>Zinc</td><td align='left'>0.28</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>94.24</td></tr>
+</table></div>
+
+
+<p>There is here a deficiency of 5.76 per cent. due to oxygen. Nothing else
+could be found, and it is known that in the sulphates the metals exist
+as oxides. By multiplying the weight of the copper by 1.252, the weight
+of copper oxide (CuO) will be ascertained; in this case it equals 10.57
+per cent. The ferrous iron multiplied by 1.286 will give the ferrous
+oxide (FeO); in this case 15.19 per cent. The ferric iron multiplied by
+1.428 will give the ferric oxide (Fe<sub>2</sub>O<sub>3</sub>); in this case 0.54 per
+cent. The zinc multiplied by 1.246 will give the zinc oxide (ZnO); in
+this case it equals 0.35 per cent. The analysis will be reported as&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Water</td><td align='right'>44.51</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='right'>28.82</td></tr>
+<tr><td align='left'>Copper oxide</td><td align='right'>10.57</td><td align='left'>equal to copper 8.44%</td></tr>
+<tr><td align='left'>Ferrous oxide</td><td align='right'>15.19</td></tr>
+<tr><td align='left'>Ferric oxide</td><td align='right'>0.54</td></tr>
+<tr><td align='left'>Zinc oxide</td><td align='right'>0.35</td></tr>
+<tr><td align='left'></td><td align='right'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='right'>99.98</td></tr>
+</table></div>
+
+
+<p>The following (A) is an analysis of a sample of South American copper
+ore, which will serve as a further illustration. The analysis showed the
+presence of 6.89 per cent. of ferrous oxide, and some oxide of copper.</p>
+
+<p>The analysis (B) is that of an ore from the same mine after an imperfect
+roasting. It will be seen that the carbonates have been converted into
+sulphates. If the total sulphur simply had been determined, and the
+sulphate overlooked, the "oxygen and loss" would have been 5.65 per
+cent., an amount which would obviously require an explanation.<span class='pagenum'><a name="Page_350" id="Page_350">[Pg 350]</a></span></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>A.</td><td align='left'></td><td align='left'>B.</td></tr>
+<tr><td align='left'>Water</td><td align='left'>0.25</td><td align='left'></td><td align='left'>0.59</td></tr>
+<tr><td align='left'>Organic matter</td><td align='left'>0.54</td><td align='left'></td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>Sulphur</td><td align='left'>29.50</td><td align='left'></td><td align='left'>21.33</td></tr>
+<tr><td align='left'>Copper</td><td align='left'>10.92</td><td align='left'></td><td align='left'>9.80</td><td align='left'>{Copper</td><td align='left'>9.57</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>{Copper oxide</td><td align='left'>0.28</td></tr>
+<tr><td align='left'>Iron</td><td align='left'>32.09</td><td align='left'></td><td align='left'>39.73</td><td align='left'>{Iron</td><td align='left'>34.32</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>{Ferric oxide</td><td align='left'>7.73</td></tr>
+<tr><td align='left'>Lead</td><td align='left'>0.35</td><td align='left'></td><td align='left'>0.12</td></tr>
+<tr><td align='left'>Zinc</td><td align='left'>0.86</td><td align='left'></td><td align='left'>0.69</td></tr>
+<tr><td align='left'>Cobalt</td><td align='left'>0.06</td><td align='left'></td><td align='left'>0.11</td></tr>
+<tr><td align='left'>Lime</td><td align='left'>5.25</td><td align='left'></td><td align='left'>7.69</td></tr>
+<tr><td align='left'>Magnesia</td><td align='left'>2.33</td><td align='left'></td><td align='left'>2.55</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='left'>1.00</td><td align='left'></td><td align='left'>5.30</td></tr>
+<tr><td align='left'>Carbon dioxide</td><td align='left'>8.87</td><td align='left'></td><td align='left'>&mdash;</td></tr>
+<tr><td align='left'>"Insoluble silicates"</td><td align='left'>5.12</td><td align='left'></td><td align='left'>8.38</td></tr>
+<tr><td align='left'>Oxygen and loss</td><td align='left'>2.86</td><td align='left'></td><td align='left'>2.47</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td><td align='left'>Potash</td><td align='left'>0.15</td></tr>
+<tr><td align='left'></td><td align='left'>100.00</td><td align='left'>Soda</td><td align='left'>1.09</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>100.00</td></tr>
+</table></div>
+
+
+<h4>WATER.</h4>
+
+<p>Water occurs in minerals in two forms, free and combined. The term
+"moisture" ought, strictly, to be limited to the first, although, as has
+already been explained, it is more convenient in assaying to apply the
+term to all water which is driven off on drying at 100&deg; C. The combined
+water is really a part of the mineral itself, although it may be driven
+off at a high temperature, which varies with the base. In some cases a
+prolonged red heat is required; whilst with crystallised salts it is
+sometimes given off at the ordinary temperatures. This latter
+phenomenon, known as efflorescence, is mostly confined to artificial
+salts.</p>
+
+<p>The determination of the combined water may often be made by simply
+igniting the substance from which the moisture has been removed. The
+quantity of water may be determined, either indirectly by the loss, or
+directly by collecting it in a calcium chloride tube, and weighing. In
+some cases, in which the loss on ignition does not give simply the
+proportion of combined water, it can be seen from the analysis to what
+else the loss is due; and, after a proper deduction, the amount of water
+can be estimated. For example, 1 gram of crystallised iron sulphate was
+found to contain on analysis 0.2877 gram of sulphuric oxide; and on
+igniting another gram, 0.2877 gram of ferric oxide was left. As the salt
+is known to be made up of ferrous oxide, sulphuric oxide, and combined
+water, the combined water can be thus calculated: 0.2877 gram of ferric
+oxide is equal to 0.2589 gram of ferrous<span class='pagenum'><a name="Page_351" id="Page_351">[Pg 351]</a></span> oxide,<a name="FNanchor_98_98" id="FNanchor_98_98"></a><a href="#Footnote_98_98" class="fnanchor">[98]</a> and consequently,
+the loss on ignition has been diminished by 0.0288 gram, which is the
+weight of oxygen absorbed by the ferrous oxide during calcining. The
+loss on ignition was 0.7123 gram, to which must be added 0.0288 gram;
+hence 0.7411 gram is the weight of the combined sulphuric oxide and
+water present. Deducting the weight of sulphuric oxide found, 0.2877
+gram, there is left for combined water 0.4534 gram. The composition of 1
+gram of the dry salt is then:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Water</td><td align='left'>0.4534</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='left'>0.2877</td></tr>
+<tr><td align='left'>Ferrous oxide</td><td align='left'>0.2589</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>1.0000</td></tr>
+</table></div>
+
+<p>The following is another example:&mdash;A sample of malachite lost on
+ignition 28.47 per cent., leaving a residue which was found on analysis
+to be made up of oxide of copper (equal to 70.16 per cent. on the
+mineral), and silica and oxide of iron (equal to 1.37 per cent.). Carbon
+dioxide and water (but nothing else) was found to be present, and the
+carbon dioxide amounted to 19.64 per cent.; deducting this from the loss
+on ignition, we have 8.82 as the percentage of water present. The
+analysis was then reported as follows:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Cupric oxide</td><td align='left'>70.16</td><td align='left'>equal to 56.0% copper.</td></tr>
+<tr><td align='left'>Silica and ferric oxide</td><td align='left'>1.37</td></tr>
+<tr><td align='left'>Carbon dioxide</td><td align='left'>19.64</td></tr>
+<tr><td align='left'>Water</td><td align='left'>8.82</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>99.99</td></tr>
+</table></div>
+
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig063.jpg" width="450" height="226" alt="Fig. 63." title="" />
+
+</div>
+
+<p><b>Direct Determination of Combined Water.</b>&mdash;Transfer about 3 grams of the
+substance to a piece of combustion tube (8 or 10 inches long), attached
+(as in fig. 63) at one end to a <b>U</b>-tube containing sulphuric acid, and
+at the other end to a calcium<span class='pagenum'><a name="Page_352" id="Page_352">[Pg 352]</a></span> chloride tube. The last is weighed
+previous to the determination. The tube should be warmed to ensure
+complete dryness, and must be free from a misty appearance. Aspirate a
+current of air through the apparatus, heat the mineral by means of a
+Bunsen burner, cautiously at first, and afterwards to redness (if
+necessary). The water is driven off and condenses in the calcium
+chloride tube, which is afterwards cooled and weighed. The increase in
+weight is due to the water. If the substance gives off acid products on
+heating, it is previously mixed with some dry oxide of lead or pure
+calcined magnesia.</p>
+
+
+<h4>EXAMINATION OF WATERS.</h4>
+
+<p>The assayer is occasionally called on to test water for the purpose of
+ascertaining the nature and quantity of the salts contained in it, and
+whether it is or is not fit for technical and drinking purposes.</p>
+
+<p>In mineral districts the water is generally of exceptional character,
+being more or less charged, not only with earthy salts, but also
+frequently with those of the metals. Distilled water is only used by
+assayers in certain exceptional cases, so that by many it would be
+classed among the rarer oxides. Water of ordinary purity will do for
+most purposes, but the nature and quantity of the impurities must be
+known.</p>
+
+<p>The following determinations are of chief importance:&mdash;</p>
+
+<p><b>Total Solids at 100&deg; C.</b>&mdash;Where simply the amount is required, take 100
+c.c. and evaporate on the water-bath in a weighed dish; then dry in the
+water-oven, and weigh.</p>
+
+<p><b>Total Solids Ignited.</b>&mdash;The above residue is very gently ignited
+(keeping the heat well below redness), and again weighed. A larger loss
+than 4 or 5 parts per 100,000 on the water requires an explanation.</p>
+
+<p><b>Chlorine.</b>&mdash;Take 100 c.c. of the water in a porcelain dish, add 2 c.c.
+of a 5 per cent. solution of neutral potassic chromate, and titrate with
+a neutral standard solution of nitrate of silver, made by dissolving
+4.789 grams of crystallised silver nitrate in distilled water, and
+diluting to 1 litre. The addition of the nitrate of silver is continued
+until the yellow of the solution assumes a reddish tint. The reaction is
+very sharp. Each c.c. of nitrate of silver used is equal to 1 part by
+weight of chlorine in 100,000 of water. At inland places this rarely
+amounts to more than 1 in 100,000; but near the sea it may amount to 3
+or 5. More than this requires explanation, and generally indicates
+sewage pollution.</p>
+
+<p><b>Nitric Pentoxide (N<sub>2</sub>O<sub>5</sub>).</b>&mdash;It is more generally reported under
+the heading, "nitrogen as nitrates." Take 250 c.c. of the<span class='pagenum'><a name="Page_353" id="Page_353">[Pg 353]</a></span> water and
+evaporate to 2 or 3 c.c.; acidulate with a few drops of dilute sulphuric
+acid, and transfer to a nitrometer (using strong sulphuric acid to wash
+in the last traces). The sulphuric acid must be added to at least twice
+the bulk of the liquid. Shake up with mercury. The mercury rapidly
+flours, and nitric oxide is given off (if any nitrate is present). The
+volume of the nitric oxide (corrected to normal temperature and
+pressure), multiplied by 0.25, gives the parts of nitrogen per 100,000;
+or, multiplied by 0.965, will give the nitric pentoxide in parts per
+100,000. In well and spring waters the nitrogen may amount to 0.3 or 0.4
+parts per 100,000; or in richly cultivated districts 0.7 or 0.8 parts
+per 100,000. An excess of nitrates is a suspicious feature, and is
+generally due to previous contamination.</p>
+
+<p><b>Ammonia.</b>&mdash;Take 500 c.c. of the water and place them in a retort
+connected with a Liebig's condenser. Add a drop or two of a solution of
+carbonate of soda and distil over 100 c.c.; collect another 50 c.c.
+separately. Determine the ammonia in the distillate colorimetrically
+(with Nessler's solution, as described under <i>Ammonia</i>) and compare with
+a standard solution of ammonic chloride containing 0.0315 gram of
+ammonic chloride in 1 litre of water. One c.c. contains 0.01 milligram
+of ammonia. The second distillate will show little, if any, ammonia in
+ordinary cases. The amounts found in both distillates are added
+together, and expressed in parts per 100,000.</p>
+
+<p>Waters (other than rain and tank waters) which contain more than 0.003
+per 100,000 are suspicious.</p>
+
+<p><b>Organic Matter.</b>&mdash;The organic matter cannot be determined directly; but
+for ordinary purposes it may be measured by the amount of permanganate
+of potassium which it reduces, or by the amount of ammonia which it
+evolves on boiling with an alkaline permanganate of potassium solution.</p>
+
+<p>A. <i>Albuminoid Ammonia.</i>&mdash;To the residue left after distilling the
+ammonia add 50 c.c. of a solution made by dissolving 200 grams of potash
+and 8 grams of potassium permanganate in 1100 c.c. of water, and rapidly
+boiling till the volume is reduced to 1 litre (this should be kept in a
+well stoppered bottle, and be occasionally tested to see that it is free
+from ammonia). Continue the distillation, collecting 50 c.c. at a time,
+until the distillate is free from ammonia. Three or four fractions are
+generally sufficient. Determine the ammonia colorimetrically as before.
+If the total albuminoid ammonia does not exceed 0.005 in 100,000, the
+water may be regarded as clean as regards organic matter; if it amounts
+to more than 0.015, it is dirty.</p>
+
+<p>B. <i>Oxygen Consumed.</i>&mdash;A standard solution of permanganate of potash is
+made by dissolving 0.395 gram of the salt in water<span class='pagenum'><a name="Page_354" id="Page_354">[Pg 354]</a></span> and diluting to 1
+litre. Each c.c. equals 0.1 milligram of available oxygen. The following
+are also required:&mdash;1. A solution of sodium hyposulphite containing 1
+gram of the salt (Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub>.5H<sub>2</sub>O) in 1 litre of water. 2.
+Dilute sulphuric acid, made by adding one part of the acid to three of
+water, and titrating with the permanganate solution till a faint pink
+persists after warming for several hours. 3. Starch paste. 4. Potassium
+iodide solution.</p>
+
+<p>Take 250 c.c. of the water in a stoppered bottle, add 10 c.c. of
+sulphuric acid and 10 c.c. of the permanganate, and allow to stand in a
+warm place for four hours. Then add a few drops of the solution of
+potassium iodide, and titrate the liberated iodine with "hypo," using
+starch paste towards the end as an indicator. To standardise the
+hyposulphite, take 250 c.c. of water and 10 c.c. of sulphuric acid, and
+a few drops of potassium iodide; then run in 10 c.c. of the
+"permanganate" solution, and again titrate; about 30 c.c. of the "hypo"
+will be used. The difference in the two titrations, divided by the last
+and multiplied by 10, will give the c.c. of permanganate solution used
+in oxidising the organic matter in the 250 c.c. of water. Each c.c.
+represents 0.04 parts of oxygen in 100,000.</p>
+
+<p><b>Metals.</b>&mdash;These may for the most part be estimated colorimetrically.</p>
+
+<p><b>Lead.</b>&mdash;Take 100 c.c. of the water in a Nessler tube, and add 10 c.c.
+of sulphuretted hydrogen water, and compare the tint, if any, against a
+standard lead solution, as described under <i>Colorimetric Lead</i>. Report
+in parts per 100,000.</p>
+
+<p><b>Copper.</b>&mdash;Proceed as with the last-mentioned metal; but, if lead is
+also present, boil down 500 c.c. to about 50 c.c., then add ammonia,
+filter, and estimate the copper in the blue solution, as described under
+<i>Colorimetric Copper</i>.</p>
+
+<p><b>Iron.</b>&mdash;Take 50 c.c., or a smaller quantity (if necessary), dilute up
+to the mark with distilled water, and determine with potassium
+sulphocyanate, as described under <i>Colorimetric Iron</i>.</p>
+
+<p><b>Zinc.</b>&mdash;Zinc is the only other metal likely to be present; and, since
+it cannot be determined colorimetrically, it must be separately
+estimated during the examination of the "total solids."</p>
+
+<p><b>Examination of "Total Solids."</b>&mdash;Evaporate 500 c.c. to dryness with a
+drop or two of hydrochloric acid. Take up with hydrochloric acid,
+filter, ignite, and weigh the residue as "silica." To the filtrate add a
+little ammonic chloride and ammonia, boil and filter, ignite, and weigh
+the precipitate as "oxide of iron and alumina." Collect the filtrate in
+a small flask, add a few drops of ammonium sulphide or pass sulphuretted
+hydrogen, cork the flask, and allow to stand overnight; filter, wash,
+and determine the zinc gravimetrically as oxide of zinc. If copper or
+lead were<span class='pagenum'><a name="Page_355" id="Page_355">[Pg 355]</a></span> present, they should have been previously removed with
+sulphuretted hydrogen in the acid solution. To the filtrate add ammonic
+oxalate and ammonia, boil for some time, allow to stand, filter, wash,
+ignite, and weigh as "lime." Evaporate the filtrate with nitric acid,
+and ignite. Take up with a few drops of dilute hydrochloric acid, add
+baric hydrate in excess, evaporate, and extract with water. The residue
+contains the magnesia; boil with dilute sulphuric acid, filter,
+precipitate it with phosphate of soda and ammonia, and weigh as
+pyrophosphate. The aqueous extract contains the alkalies with the excess
+of barium. Add sulphuric acid in slight excess, filter, evaporate, and
+ignite strongly. The residue consists of the sulphates of the alkalies
+(which are separately determined, as described under <i>Potash</i>).</p>
+
+<p><b>Sulphuric Oxide (SO<sub>3</sub>).</b>&mdash;Take 200 c.c. and boil to a small bulk with
+a little hydrochloric acid, filter (if necessary), add baric chloride
+solution in slight excess to the hot solution, filter, ignite, and weigh
+as baric sulphate.</p>
+
+<p><b>Carbon Dioxide (free).</b>&mdash;Carbon dioxide exists in waters in two forms,
+free and combined. The latter generally occurs as bicarbonate, although
+on analysis it is more convenient to consider it as carbonate, and to
+count the excess of carbon dioxide with the free. The method is as
+follows:&mdash;To determine the free carbon dioxide, take 100 c.c. of the
+water, place them in a flask with 3 c.c. of a strong solution of calcium
+chloride and 2 c.c. of a solution of ammonic chloride, next add 50 c.c.
+of lime-water. The strength of the lime-water must be known. Make up to
+200 c.c. with distilled water, stop the flask, and allow the precipitate
+to settle. Take out 100 c.c. of the clear solution with a pipette, and
+titrate with the standard solution of acid.<a name="FNanchor_99_99" id="FNanchor_99_99"></a><a href="#Footnote_99_99" class="fnanchor">[99]</a> The number of c.c.
+required, multiplied by two, and deducted from that required for the 50
+c.c. of lime-water, and then multiplied by 0.0045, will give the carbon
+dioxide present other than as normal carbonates.</p>
+
+<p><b>Carbon Dioxide combined</b> as normal carbonate.&mdash;100 c.c. of the water
+are tinted with phenacetolin or lacmoid; then heated to near boiling,
+and titrated with standard acid. The number of c.c. used, multiplied by
+0.0045, will give the weight in grams of the combined carbon dioxide.</p>
+
+<p><b>Free Acid.</b>&mdash;In some waters (especially those from mining districts)
+there will be no carbonates. On the contrary, there may be free mineral
+acid or acid salts. In these cases it is necessary to determine the
+amount of acid (other than carbon dioxide) present in excess of that
+required to form normal salts. This is done in the following way:&mdash;Make
+an ammoniacal copper<span class='pagenum'><a name="Page_356" id="Page_356">[Pg 356]</a></span> solution by taking 13 grams of copper sulphate
+(CuSO<sub>4</sub>.5H<sub>2</sub>O), dissolving in water, adding solution of ammonia
+until the precipitate first formed has nearly dissolved, and diluting to
+1 litre. Allow to settle, and decant off the clear liquid. The strength
+of this solution is determined by titrating against 10 or 20 c.c. of the
+standard solution of sulphuric acid (100 c.c. = 1 gram H<sub>2</sub>SO<sub>4</sub>). The
+finishing point is reached as soon as the solution becomes turbid from
+precipitated cupric hydrate. At first, as each drop falls into the acid
+solution, the ammonia and cupric hydrate combine with the free acid to
+form ammonic and cupric sulphates; but as soon as the free acid is used
+up, the ammonia in the next drop not only precipitates an equivalent of
+cupric hydrate from the solution, but also throws down that carried by
+itself. This method is applicable in the presence of metallic sulphates
+<i>other than ferric</i>. The standardising and titration should be made
+under the same conditions. Since sulphuric acid and sulphates are
+predominant in waters of this kind, it is most convenient to report the
+acidity of the water as equivalent to so much sulphuric acid.</p>
+
+<p><b>Dissolved Oxygen.</b>&mdash;For the gasometric method of analysing for
+dissolved oxygen, and for the Sch&uuml;tzenberger's volumetric method, the
+student is referred to Sutton's "Volumetric Analysis." The following is
+an easy method of estimating the free oxygen in a water:&mdash;Take 20 c.c.
+of a stannous chloride solution (about 20 grams of the salt with 10 c.c.
+of hydrochloric acid to the litre); add 10 c.c. of hydrochloric acid,
+and titrate in an atmosphere of carbon dioxide with standard
+permanganate of potassium solution (made by dissolving 1.975 gram of the
+salt in 1 litre of water: 1 c.c. equals 0.5 milligram of oxygen). A
+similar titration is made with the addition of 100 c.c. of the water to
+be tested. Less permanganate will be required in the second titration,
+according to the amount of oxygen in the water; and the difference,
+multiplied by 0.5, will give the weight of the oxygen in milligrams.
+Small quantities of nitrates do not interfere.</p>
+
+<p>In <span class="smcap">reporting</span> the results of the analysis, it is customary to
+combine the acids and bases found on some such principle as the
+following:&mdash;The sulphuric oxide is calculated as combined with the
+potash, and reported as potassic sulphate (K<sub>2</sub>SO<sub>4</sub>); the balance of
+the sulphuric oxide is then apportioned to the soda, and reported as
+sulphate of soda (Na<sub>2</sub>SO<sub>4</sub>); if any is still left, it is reported as
+calcium sulphate (CaSO<sub>4</sub>), and after that as magnesic sulphate
+(MgSO<sub>4</sub>). When the sulphuric oxide has been satisfied, the chlorine is
+distributed, taking the bases in the same order, then the nitric
+pentoxide, and lastly the carbon dioxide. But any method for thus
+combining the bases and acids must be arbitrary and inaccurate. It is
+extremely improbable that any<span class='pagenum'><a name="Page_357" id="Page_357">[Pg 357]</a></span> simple statement can represent the manner
+in which the bases and acids are distributed whilst in solution; and,
+since different chemists are not agreed as to any one system, it is
+better to give up the attempt, and simply state the results of the
+analysis. This has only one inconvenience. The bases are represented as
+oxides; and, since some of them are present as chlorides, the sum total
+of the analysis will be in excess of the actual amount present by the
+weight of the oxygen equivalent to the chlorine present as chloride. The
+following is an example of such a statement:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>Parts per 100,000.</td></tr>
+<tr><td align='left'>Total solids, dried at 100&deg; C.</td><td align='left'>28.73</td></tr>
+<tr><td align='left'>Chlorine</td><td align='left'>1.70</td></tr>
+<tr><td align='left'>Nitrogen as nitrate</td><td align='left'>0.03</td></tr>
+<tr><td align='left'>Ammonia</td><td align='left'>0.001</td></tr>
+<tr><td align='left'>Albuminoid ammonia</td><td align='left'>0.004</td></tr>
+<tr><td align='left'>"Oxygen consumed" in 4 hours</td><td align='left'>0.01</td></tr>
+</table></div>
+
+<p>The solids were made up as under:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>Per 100,000 of the Water.</td></tr>
+<tr><td align='left'>Potash</td><td align='left'>0.38</td></tr>
+<tr><td align='left'>Soda</td><td align='left'>2.01</td></tr>
+<tr><td align='left'>Magnesia</td><td align='left'>1.44</td></tr>
+<tr><td align='left'>Lime</td><td align='left'>10.55</td></tr>
+<tr><td align='left'>Ferric oxide</td><td align='left'>0.01</td></tr>
+<tr><td align='left'>Silica</td><td align='left'>0.30</td></tr>
+<tr><td align='left'>Sulphuric oxide</td><td align='left'>3.69</td></tr>
+<tr><td align='left'>Nitrogen pentoxide</td><td align='left'>0.11</td></tr>
+<tr><td align='left'>Carbon dioxide</td><td align='left'>8.38</td></tr>
+<tr><td align='left'>Chlorine</td><td align='left'>1.70</td></tr>
+<tr><td align='left'>Volatile and organic matter</td><td align='left'>0.66</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>29.23</td></tr>
+<tr><td align='left'>Less oxygen equivalent to chlorine found</td><td align='left'>0.39</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>28.84</td></tr>
+</table></div>
+
+
+<p>For the preparation of distilled water, the apparatus shown in fig. 64
+is convenient for laboratory use. It consists of a copper retort heated
+by a ring gas-burner, and connected with a worm-condenser.</p>
+
+<div class="figcenter" style="width: 382px;">
+<img src="images/fig064.jpg" width="382" height="300" alt="Fig. 64" title="" />
+
+</div>
+
+
+<h4>PRACTICAL EXERCISE.</h4>
+
+<p>A mineral, on analysis, gave the following results:&mdash;Water, 44.94 per
+cent.; sulphuric oxide, 28.72 per cent.; ferrous iron, 13.92 per cent.;
+ferric iron, 0.35 per cent.; copper, 6.1 per cent. The mineral was
+soluble in water, and showed nothing else on testing. How would you
+report the analysis? Calculate the formula for the salt.<span class='pagenum'><a name="Page_358" id="Page_358">[Pg 358]</a></span></p>
+
+
+<h4>THE HALOGENS.</h4>
+
+<p>There is a group of closely allied elements to which the name halogen
+(salt-producer) has been given. It comprises chlorine, bromine, iodine,
+and fluorine. These elements combine directly with metals, forming as
+many series of salts (chlorides, bromides, iodides, and fluorides),
+corresponding to the respective oxides, but differing in their formul&aelig;
+by having two atoms of the halogen in the place of one atom of oxygen.
+For example, ferrous oxide is FeO and ferrous chloride is FeCl<sub>2</sub>, and,
+again, ferric oxide is Fe<sub>2</sub>O<sub>3</sub>, whilst ferric chloride is
+Fe<sub>2</sub>Cl<sub>6</sub>. These salts differ from the carbonates, nitrates, &amp;c., in
+containing no oxygen. Consequently, it is incorrect to speak of such
+compounds as chloride of potash, fluoride of lime, &amp;c., since potash and
+lime are oxides. It is important to bear this in mind in reporting
+analyses in which determinations have been made, say, of chlorine,
+magnesia, and potash, or of fluorine, silica, and alumina. It is
+necessary in all such cases to deduct from the total an amount of oxygen
+equivalent to the halogen found, except, of course, where the base has
+been determined and recorded as metal. Compounds containing oxides and
+fluorides, &amp;c., do not lend themselves to the method of determining the
+halogen by difference. For example, topaz, which, according to Dana, has
+the formula Al<sub>2</sub>SiO<sub>4</sub>F<sub>2</sub>, would yield in the ordinary course of
+analysis&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Alumina</td><td align='left'>55.4%</td></tr>
+<tr><td align='left'>Silica</td><td align='left'>32.6</td></tr>
+<tr><td align='left'>Fluorine</td><td align='left'>20.6</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>108.6</td></tr>
+</table></div>
+
+<p>The oxygen equivalent to 20.6 per cent. fluorine may be found by
+multiplying the percentage of fluorine by 0.421; it is 8.7 per cent.,
+and must be deducted. The analysis would then be reported thus:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Alumina</td><td align='left'>55.4%</td></tr>
+<tr><td align='left'>Silica</td><td align='left'>32.6</td></tr>
+<tr><td align='left'>Fluorine</td><td align='left'>20.6</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>108.6</td></tr>
+<tr><td align='left'>Less oxygen equivalent to fluorine</td><td align='left'>8.7</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>99.9</td></tr>
+</table></div>
+
+
+<p>Take as an illustration the following actual analysis by F.W. Clarke and
+J.S. Diller:<span class='pagenum'><a name="Page_359" id="Page_359">[Pg 359]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Alumina</td><td align='left'>57.38%</td></tr>
+<tr><td align='left'>Silica</td><td align='left'>31.92</td></tr>
+<tr><td align='left'>Fluorine</td><td align='left'>16.99</td></tr>
+<tr><td align='left'>Potash</td><td align='left'>0.15</td></tr>
+<tr><td align='left'>Soda</td><td align='left'>1.33</td></tr>
+<tr><td align='left'>Water</td><td align='left'>0.20</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>107.97</td></tr>
+<tr><td align='left'>Deduct oxygen equivalent</td><td align='left'>7.16</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.81</td></tr>
+</table></div>
+
+<p>In calculating the factor for the "oxygen equivalent," divide the weight
+of one atom of oxygen (16) by the weight of two atoms of the halogen;
+for example, with chlorine it would be 16/71 or 0.2253; with bromine,
+16/160 or 0.1000; with iodine, 16/254 or 0.063; and with fluorine, 16/38
+or 0.421.</p>
+
+
+<h4>CHLORINE AND CHLORIDES.</h4>
+
+<p>Chlorine occurs in nature chiefly combined with sodium, as halite or
+rock salt (NaCl). With potassium it forms sylvine (KCl), and, together
+with magnesium, carnallite (KCl.MgCl<sub>2</sub>.6H<sub>2</sub>O). Of the metalliferous
+minerals containing chlorine, kerargyrite, or horn silver (AgCl), and
+atacamite, an oxychloride of copper (CuCl<sub>2</sub>.3Cu(HO)<sub>2</sub>.) are the most
+important. Apatite (phosphate of lime) and pyromorphite (phosphate of
+lead) contain a considerable amount of it. Chlorine is a gas of a
+greenish colour, possessing a characteristic odour, and moderately
+soluble in water. It does not occur native, and is generally prepared by
+the action of an oxidising agent on hydrochloric acid. It combines
+directly with metals at the ordinary temperature (even with platinum and
+gold), forming chlorides, which (except in the case of silver) are
+soluble.</p>
+
+<p>It is important in metallurgy, because of the extensive use of it in
+extracting gold by "chloridising" processes. It is also used in refining
+gold.</p>
+
+<p><b>Detection.</b>&mdash;Compounds containing the oxides of chlorine are not found
+in nature, because of the readiness with which they lose oxygen. By
+reduction they yield a chloride; the form in which chlorine is met with
+in minerals. In testing, the compound supposed to contain a chloride is
+boiled with water, or, in some cases, dilute nitric acid. To the clear
+solution containing nitric acid a few drops of nitrate of silver
+solution are added. If, on shaking, a white curdy precipitate, soluble
+in ammonia, separates out, it is sufficiently satisfactory evidence of
+the presence of chlorides.<span class='pagenum'><a name="Page_360" id="Page_360">[Pg 360]</a></span></p>
+
+<p><b>Solution and Separation.</b>&mdash;The chlorides are generally soluble in
+water, and are got into solution by extracting with warm dilute nitric
+acid. Or, if insoluble, the substance is fused with carbonate of soda,
+extracted with water, and the filtrate acidified with nitric acid. For
+the determination, it is not necessary to obtain the solution of the
+chloride free from other acids or metals. If tin, antimony, mercury, or
+platinum is present, it is best to separate by means of sulphuretted
+hydrogen. The chloride is determined in the solution after removal of
+the excess of the gas. Where traces of chlorides are being looked for, a
+blank experiment is made to determine the quantity introduced with the
+reagents. One hundred c.c. of ordinary water contains from 1 to 3
+milligrams of chlorine. On the addition of nitrate of silver to the
+nitric acid solution, chloride of silver separates out. This is free
+from other substances, except, perhaps, bromide and iodide.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>Freely mix the solution containing the chloride with dilute nitric acid,
+filter (if necessary), and treat with nitrate of silver. Heat nearly to
+boiling, and, when the precipitate has settled, filter, and wash with
+hot distilled water. Dry, and transfer to a weighed Berlin crucible.
+Burn the filter-paper separately, and convert any reduced silver into
+chloride by alternate treatment with drops of nitric and of hydrochloric
+acid. Add the main portion to this, and heat cautiously till the edges
+of the mass show signs of fusing (about 260&deg;). Cool in the desiccator
+and weigh. The substance is chloride of silver (AgCl), and contains
+24.73 per cent. of chlorine.</p>
+
+<p>The precipitated chloride is filtered and washed as soon as possible
+after settling, since on exposure to light it becomes purple, and loses
+a small amount of chlorine.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>There are several volumetric methods; but that based on the
+precipitation of silver chloride in neutral solution, by means of a
+standard solution of silver nitrate (using potassium chromate as
+indicator), is preferred. Silver chromate is a red-coloured salt; and,
+when silver nitrate is added to a solution containing both chloride and
+chromate, the development of the red colour marks off sharply the point
+at which the chloride is used up. Silver chromate is decomposed and
+consequently decolorised by solution of any chloride. The solution for
+this method must be neutral,<span class='pagenum'><a name="Page_361" id="Page_361">[Pg 361]</a></span> since free acid prevents the formation of
+the red silver chromate. If not already neutral, it is neutralised by
+titrating cautiously with a solution of soda. In a neutral solution,
+other substances (such as phosphates and arsenates) also yield a
+precipitate with a solution of nitrate of silver; and will count as
+chloride if they are not removed.</p>
+
+<p><i>The Standard Solution of Nitrate of Silver</i> is made by dissolving 23.94
+grams of the salt (AgNO<sub>3</sub>) in distilled water, and diluting to 1
+litre; 100 c.c. are equal to 0.5 gram of chlorine.</p>
+
+<p>The <i>indicator</i> is made by adding silver nitrate to a strong neutral
+solution of yellow chromate of potash (K<sub>2</sub>CrO<sub>4</sub>), till a permanent
+red precipitate is formed. The solution is allowed to settle, and the
+clear liquid decanted into a stoppered bottle labelled "chromate
+indicator for chlorine."</p>
+
+<p>Standardise the silver nitrate by weighing up 0.5 gram of pure sodium
+chloride (or potassium chloride). Transfer to a flask and dissolve in
+distilled water; dilute to 100 c.c. Fill an ordinary burette with the
+standard silver solution, and (after adjusting) run into the flask a
+quantity sufficient to throw down the greater part of the chlorine. Add
+a few drops of the chromate indicator and continue the addition of the
+silver nitrate until the yellow colour of the solution becomes
+permanently tinted red, after shaking. This shows that the chlorine is
+all precipitated, and that the chromate is beginning to come down. The
+further addition of a couple of drops of the silver solution will cause
+a marked difference in the tint. Read off the quantity run in, and
+calculate the standard. One gram of sodium chloride contains 0.6062 gram
+of chlorine; and 1 gram of potassium chloride contains 0.4754 gram.</p>
+
+<p>For the determination of small quantities of chloride (a few
+milligrams), the same method is used; but the standard solution is
+diluted so that each c.c. is equal to 1 milligram of chlorine; and the
+chromate indicator is added before titrating. The standard solution is
+made by measuring off 200 c.c. of the solution described above, and
+diluting with distilled water to 1 litre.</p>
+
+
+<h4>BROMINE AND BROMIDES.</h4>
+
+<p>Bromine closely resembles chlorine in the nature of its compounds. It
+does not occur free in nature, but is occasionally found in combination
+with silver as bromargyrite (AgBr) and, together with chloride, in
+embolite. It mainly occurs as alkaline bromides in certain natural
+waters. Nearly all the bromine of commerce is derived from the mother
+liquors of salt-works&mdash;<i>i.e.</i>,<span class='pagenum'><a name="Page_362" id="Page_362">[Pg 362]</a></span> the liquors from which the common salt
+has been crystallised out. Bromine combines directly with the metals,
+forming a series of salts&mdash;the bromides. In ordinary work they are
+separated with, and (except when specially tested for) counted as,
+chlorides. They are detected by adding chlorine water to the suspected
+solution and shaking up with carbon bisulphide. Bromine colours the
+latter brown.</p>
+
+
+<h4>IODINE AND IODIDES.</h4>
+
+<p>Iodine does not occur in nature in the free state; and iodides are rare,
+iodargyrite or iodide of silver (AgI) being the only one which ranks as
+a mineral species. Iodates are found associated with Chili saltpetre,
+which is an important source of the element.</p>
+
+<p>Iodine and Iodides are largely used in the laboratory, and have already
+been frequently referred to. It is used as an oxidising agent in a
+similar manner as permanganate and bichromate of potash, especially in
+the determinations of copper, arsenic, antimony, and manganese.</p>
+
+<p>Iodine is not readily soluble in water; but dissolves easily in a
+concentrated solution of potassium iodide. Its solutions are strongly
+coloured; a drop of a dilute solution colours a large volume of water
+decidedly yellow; on the addition of starch paste, this becomes blue.
+The delicacy of this reaction is taken advantage of in titrations to
+determine when free iodine is present. The blue colour may be
+alternately developed and removed by the addition of iodine (or an
+oxidising agent) and hyposulphite of soda (or some other reducing
+agent). In decolorising, the solution changes from blue or black to
+colourless or pale yellow according to circumstances. Sometimes the
+solution, instead of remaining colourless, gradually develops a blue
+which recurs in spite of the further addition of the reducing agent. In
+these cases the conditions of the assay have been departed from, or (and
+this is more often the case) there is some substance present capable of
+liberating iodine.</p>
+
+<p>Iodine forms a series of salts&mdash;the iodides&mdash;resembling in many respects
+the chlorides. These can be obtained by direct combination of the metals
+with iodine.</p>
+
+<p><b>Detection.</b>&mdash;Free iodine is best recognised by the violet vapours
+evolved from the solution on heating, and by the blue or black colour
+which it strikes on the addition of starch paste. Iodides are detected
+by boiling with strong solutions of ferric sulphate or chloride. Iodine
+is liberated, distilled over, and collected. Chlorine also liberates
+iodine from iodides; and this reaction is frequently made use of in
+assaying. A process based on this is<span class='pagenum'><a name="Page_363" id="Page_363">[Pg 363]</a></span> described under <i>Manganese</i>. All
+substances which liberate chlorine on boiling with hydrochloric acid
+(dioxides, bichromates, permanganates, &amp;c.) are determined in a similar
+way.</p>
+
+<p><b>Solution and Separation.</b>&mdash;Most iodides are soluble in water or dilute
+acids. The separation is effected by distilling the substance with
+solution of ferric sulphate, and collecting the vapour in a dilute
+solution of sulphurous acid or arsenite of soda. On the completion of
+the distillation, the iodine will be in the distillate as iodide; and
+the gravimetric determination is made on this.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>To the solution containing the iodine, as iodide, and which is free from
+chlorides (and bromides), add a little dilute nitric acid and nitrate of
+silver till no further precipitate is produced. Filter off, wash with
+hot water, and dry. Clean the filter-paper as much as possible, and burn
+it. Collect the ash in a weighed porcelain crucible, add the main
+portion, and heat to incipient fusion; cool, and weigh. The substance is
+silver iodide, and contains 54.03 per cent. of iodine.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This is for the titration of free iodine, and is practically that which
+is described under <i>Manganese</i>. The substance to be determined is
+distilled with ferric sulphate, and the iodine is collected in a
+solution of potassium iodide, in which it readily dissolves. If flaky
+crystals separate out in the receiver, more potassium iodide crystals
+are added. When the distillation is finished, the receiver is
+disconnected, and its contents washed out into a beaker and titrated
+with "hypo." The standard solution of "hypo" is made by dissolving 19.58
+grams of hyposulphite of soda (Na<sub>2</sub>S<sub>2</sub>O<sub>3</sub>.5H<sub>2</sub>O) in water and
+diluting to 1 litre; 100 c.c. are equal to 1 gram of iodine. To
+standardise the solution, weigh up 0.25 gram of pure iodine in a small
+beaker. Add 2 or 3 crystals of potassium iodide; cover with water; and,
+when dissolved, dilute to 50 or 100 c.c. Titrate, and calculate the
+standard.</p>
+
+
+<h4>FLUORINE AND FLUORIDES.</h4>
+
+<p>Fluorine is frequently met with as calcium fluoride or fluor-spar
+(CaF<sub>2</sub>). It occurs less abundantly as cryolite (Na<sub>3</sub>AlF<sub>6</sub>), a
+fluoride of aluminium and sodium, which is used in glass-making. Certain
+other rarer fluorides are occasionally met with. Fluorine is also<span class='pagenum'><a name="Page_364" id="Page_364">[Pg 364]</a></span> found
+in apatite, and in some silicates, such as topaz, tourmaline, micas, &amp;c.</p>
+
+<p>Hydrofluoric acid is used for etching glass and opening up silicates. It
+attacks silica, forming fluoride of silicon (SiF<sub>4</sub>), which is
+volatile. Silica is by this means eliminated from other oxides, which,
+in the presence of sulphuric acid, are fixed. The commercial acid is
+seldom pure, and generally weak; and the acid itself is dangerously
+obnoxious. The use of ammonium fluoride (or sodium fluoride) and a
+mineral acid is more convenient. Determinations of this kind are made in
+platinum dishes enclosed in lead or copper vessels in a well-ventilated
+place. Fluor-spar is useful as a flux in dry assaying; it renders slags,
+which would otherwise be pasty, quite fluid. Fluorides generally are
+fusible, and impart fusibility to substances with which they form weak
+compounds. Their fluxing action does not depend on the removal of
+silicon as fluoride.</p>
+
+<p><b>Detection.</b>&mdash;Fluorides in small quantity are easily overlooked unless
+specially sought for. In larger amounts they are recognised by the
+property hydrofluoric acid has of etching glass. A watch-glass is
+warmed, and a layer of wax is melted over the convex side. When cold,
+some lines are engraved on the waxed surface with any sharp-pointed
+instrument. The substance to be tested is powdered; and moistened, in a
+platinum dish, with sulphuric acid. The watch-glass is filled with cold
+water and supported over the dish. The dish is then carefully warmed,
+but not sufficiently to melt the wax. After a minute or two, the glass
+is taken off, and the wax removed. If the substance contained fluorine,
+the characters will be found permanently etched on the glass. An equally
+good, but more rapid, test is to mix the powdered substance with some
+silica, and to heat the mixture in a test tube with sulphuric acid.
+Silicon fluoride is evolved, and, if a moistened glass rod is held in
+the tube, it becomes coated with a white deposit of silica, formed by
+the decomposition of the silicon fluoride by the water. This is also
+used as a test for silica; but in this case the substance is mixed with
+a fluoride, and the experiment must obviously be carried out in a
+platinum vessel.</p>
+
+<p><b>Separation and Determination.</b>&mdash;The determination of fluorine is
+difficult. In the case of fluorides free from silicates (such as
+fluor-spar), it is determined indirectly by decomposing a weighed
+portion with sulphuric acid, evaporating, igniting, and weighing the
+residual sulphate. The increase in weight multiplied by 0.655 gives the
+weight of fluorine.</p>
+
+<p>In the presence of silica this method does not answer, because of the
+volatilisation of silicon fluoride. In these cases W&ouml;hler<span class='pagenum'><a name="Page_365" id="Page_365">[Pg 365]</a></span> adopted the
+following plan, which resembles that for the indirect determination of
+carbon dioxide. Mix the weighed substance in a small flask with powdered
+silica and sulphuric acid. The mouth of the flask is closed with a cork
+carrying a tube which is filled, the first half with calcium chloride
+and the second half with pumice coated with dried copper sulphate. The
+apparatus is weighed quickly, and then warmed till decomposition is
+complete. A current of dry air is aspirated for a minute or two; and the
+apparatus again weighed. The loss in weight gives that of the silicon
+fluoride (SiF<sub>4</sub>), which, multiplied by 0.7307, gives the weight of
+fluorine.</p>
+
+<p>Fresenius uses the same reaction; but collects and weighs the silicon
+fluoride. The finely powdered and dried substance is mixed with ten or
+fifteen times its weight of ignited and powdered silica. The mixture is
+introduced into a small dry flask connected on one side with a series of
+drying-tubes, and on the other with an empty tube (to condense any
+sulphuric acid). To this last is joined a drying-tube containing
+chloride of calcium and anhydrous copper sulphate. This is directly
+connected with a series of three weighed tubes in which the fluoride of
+silicon is collected. The last of these is joined to another
+drying-tube. The first weighed tube contains pumice and cotton wool,
+moistened with water; the second tube contains soda-lime as well as (in
+the upper half of the second limb) fused calcium chloride between plugs
+of wool; the third tube is filled half with soda-lime and half with
+fused calcium chloride. The distilling-flask containing the substance
+mixed with silica is charged with 40 or 50 c.c. of sulphuric acid, and
+placed on the hot plate. Alongside it is placed a similar dry flask
+containing a thermometer, and the temperature in this is kept at 150&deg; or
+160&deg; C. A current of air is sent through the tubes during the operation,
+which takes from one to three hours for from 0.1 to 1 gram of the
+substance. A correction is made by deducting 0.001 gram for every hour
+the dried air has been passed through. The increase in weight of the
+three tubes gives the weight of the silicon fluoride.</p>
+
+<p>Penfield uses a similar arrangement, but passes his silicon fluoride
+into an alcoholic solution of potassium chloride. Silica and potassium
+silico-fluoride are precipitated, and hydrochloric acid is set
+free.<a name="FNanchor_100_100" id="FNanchor_100_100"></a><a href="#Footnote_100_100" class="fnanchor">[100]</a> The acid thus liberated is titrated, with a standard solution
+of alkali, in the alcoholic solution, and from the amount of free acid
+found the fluorine is calculated. The weight of hydrochloric acid (HCl)
+found, multiplied by 1.562, gives the weight of the fluorine. With this
+method of working, fewer <b>U</b>-tubes<span class='pagenum'><a name="Page_366" id="Page_366">[Pg 366]</a></span> are required. The exit tube from the
+flask is bent so as to form a small <b>V</b>, which is kept cool in water;
+this is directly connected with the <b>U</b>-tube containing the alcoholic
+solution of potassium chloride. The flask with the assay is heated for
+about two hours, and a current of dry air is aspirated throughout the
+determination. Fluoride of silicon is a gas not easily condensed to a
+liquid: but is immediately decomposed by water or moist air.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_95_95" id="Footnote_95_95"></a><a href="#FNanchor_95_95"><span class="label">[95]</span></a> This will require two or three hours to thoroughly
+complete. It is best to powder the oxide first produced, and recalcine.</p></div>
+
+<div class="footnote"><p><a name="Footnote_96_96" id="Footnote_96_96"></a><a href="#FNanchor_96_96"><span class="label">[96]</span></a> No magnetic oxide was formed.</p></div>
+
+<div class="footnote"><p><a name="Footnote_97_97" id="Footnote_97_97"></a><a href="#FNanchor_97_97"><span class="label">[97]</span></a> For example:&mdash;
+</p><p>
+CaO + 2HCl = CaCl<sub>2</sub> + H<sub>2</sub>O.
+</p><p>
+PbO + H<sub>2</sub>SO<sub>4</sub> = PbSO<sub>4</sub> + H<sub>2</sub>O.
+</p><p>
+MgO + 2HNO<sub>3</sub> = Mg(NO<sub>3</sub>)<sub>2</sub> + H<sub>2</sub>O.
+</p><p>
+Al<sub>2</sub>O<sub>3</sub> + 6HCl = Al<sub>2</sub>Cl<sub>6</sub> + 3H<sub>2</sub>O.
+</p><p>
+Fe<sub>2</sub>O<sub>3</sub> + 3H<sub>2</sub>SO<sub>4</sub> = Fe<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub> + 3H<sub>2</sub>O.</p></div>
+
+<div class="footnote"><p><a name="Footnote_98_98" id="Footnote_98_98"></a><a href="#FNanchor_98_98"><span class="label">[98]</span></a> Fe<sub>2</sub>O<sub>3</sub>: 2FeO:: 0.2877: 0.2589.</p></div>
+
+<div class="footnote"><p><a name="Footnote_99_99" id="Footnote_99_99"></a><a href="#FNanchor_99_99"><span class="label">[99]</span></a> 100 c.c. contain 1 gram of sulphuric acid.</p></div>
+
+<div class="footnote"><p><a name="Footnote_100_100" id="Footnote_100_100"></a><a href="#FNanchor_100_100"><span class="label">[100]</span></a> 3SiF<sub>4</sub> + 4KCl + 2H<sub>2</sub>O = 2K<sub>2</sub>SiF<sub>6</sub> + SiO<sub>2</sub> +
+4HCl.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_367" id="Page_367">[Pg 367]</a></span></p>
+<h2><a name="CHAPTER_XVI" id="CHAPTER_XVI"></a>CHAPTER XVI.</h2>
+
+<h3>SULPHUR AND SULPHATES.</h3>
+
+
+<p>Sulphur occurs native in volcanic districts, and is mined in Sicily,
+Italy, and California in considerable quantities. Combined with metals
+(sulphides), it is common in all mineral districts. Iron pyrites
+(FeS<sub>2</sub>) is the most abundant source of this element. Sulphates, such
+as gypsum, are fairly common, but have no value so far as the sulphur in
+them is concerned. In coal it exists as an impurity, occurring partly as
+a constituent of organic compounds.</p>
+
+<p>Sulphur, whether free or combined with metals, forms, on burning,
+sulphurous oxide (SO<sub>2</sub>), which by the action of oxidising agents and
+water is converted into sulphuric acid. It forms two oxides, sulphurous
+(SO<sub>2</sub>) and sulphuric (SO<sub>3</sub>), which combine with bases to form
+sulphites and sulphates. Sulphites are of little importance to the
+assayer, and are converted into sulphates by the action of nitric acid
+and other oxidising agents.</p>
+
+<p>The native sulphides, when acted on with hydrochloric acid, give off
+sulphuretted hydrogen; with nitric acid or aqua regia, sulphates are
+formed, and more or less sulphur separated.</p>
+
+<p>Sulphur is detected in sulphides by the irritating odour of sulphurous
+oxide given off on roasting, by the evolution of sulphuretted hydrogen
+when treated with hydrochloric acid, or by a white precipitate of barium
+sulphate formed when barium chloride is added to the aqua regia
+solution.</p>
+
+<p><b>Dry Assay.</b>&mdash;There is no method of general application. Free or native
+sulphur may be volatilised, condensed, and weighed, but pyrites only
+gives up a portion of its sulphur when heated in a closed vessel, while
+most sulphides, and all sulphates, give up none at all.</p>
+
+<p>In the determination of sulphur in brimstone, 10 grams of the substance
+are taken, placed in a small porcelain dish, heated over a Bunsen burner
+in a well-ventilated place, and ignited. When the sulphur has been
+completely burnt off, the residue (which consists chiefly of sand) is
+collected and weighed. In a separate portion the moisture and arsenic
+are determined; the amounts of<span class='pagenum'><a name="Page_368" id="Page_368">[Pg 368]</a></span> these are deducted from the loss in the
+first experiment. The difference, multiplied by 10, gives the percentage
+of sulphur.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p><b>Solution.</b>&mdash;All sulphates, excepting those of lead, barium, strontium,
+and lime, are soluble in water or dilute acid. All sulphides, except
+cinnabar, are converted into sulphates by the action of nitric acid at a
+gentle heat; or, better, by the action of a mixture of three volumes of
+nitric acid and one volume of hydrochloric acid. This last attacks
+cinnabar as well. With most substances it is difficult to convert the
+whole of the sulphur into sulphuric acid. The sulphur separates out at
+first as a dark spongy mass, which (on continued treatment) changes to
+light-coloured flakes. When the solution becomes concentrated and the
+temperature rises sufficiently, the sulphur fuses into one or more
+honey-coloured globules which, owing to the small surface they oppose to
+the acid, are very slowly oxidised. It is not desirable to assist the
+formation of these globules; therefore, the temperature is kept as low
+as possible, and strong nitric acid is used. When such globules form, it
+is best to allow the solution to cool, when the globules will solidify.
+They can then be filtered off and picked out from the insoluble residue,
+dried, weighed, ignited, and again weighed, the loss being counted as
+sulphur. With iron pyrites this difficulty seldom occurs.</p>
+
+<p>Metallic sulphides when fused with an excess of nitre are completely
+oxidised. If the ore is rich in sulphur, some inert body (such as sodium
+chloride, or, better, sodium carbonate) is added to dilute the action.
+With pure sulphur, the action is so energetic as to cause an explosion,
+so that care should be taken. With burnt ores (incompletely calcined
+pyrites), there is sufficient oxide of iron present to prevent too rapid
+action.</p>
+
+<p>These fusions with nitre are best conducted in a platinum dish covered
+with a piece of platinum foil. The ore is ground with the nitre to
+ensure complete mixing. The heat need not be excessive, so that a single
+Bunsen burner placed beneath the dish will suffice; if the bottom of the
+dish is seen to be red-hot, it is sufficient. On cooling and extracting
+with water, the sulphur will pass into solution as potassium sulphate,
+which is then filtered off from the insoluble oxides of iron, copper,
+&amp;c. The filtrate, after having been treated with a large excess of
+hydrochloric acid, evaporated to dryness, and re-dissolved in water, is
+ready for the determination.</p>
+
+<p>Lead sulphate may be dissolved by boiling with ammonium acetate. The
+insoluble sulphates of barium, strontium, and lime,<span class='pagenum'><a name="Page_369" id="Page_369">[Pg 369]</a></span> are decomposed by
+fusing with 4 or 5 times their weight of "fusion mixture." The alkaline
+sulphates are then dissolved out with water, and filtered off from the
+insoluble residue. The filtrate is rendered acid with hydrochloric acid.</p>
+
+<p><b>Separation.</b>&mdash;The determination of the sulphuric acid in these
+solutions by precipitation with barium chloride also serves as a
+separation; but in hot acid solutions containing copper, and more
+especially iron salts, the baric sulphate has a strong tendency to carry
+down amounts of those bodies, varying, no doubt, with the conditions of
+the precipitation. Boiling hydrochloric acid fails to completely extract
+them. Moreover, the use of hot concentrated hydrochloric acid causes a
+loss by dissolving barium sulphate. Nitric acid and nitrates must be
+decomposed by prolonged boiling and evaporation with hydrochloric acid.
+The iron may be removed by adding a slight excess of ammonia to the
+faintly acid solution, filtering off, and washing the precipitated
+ferric hydrate with hot water. By slightly acidulating the filtrate with
+hydrochloric acid, it will be rendered ready for the determination.</p>
+
+
+<h4>GRAVIMETRIC METHOD.</h4>
+
+<p>This assay is one of those which strikingly shows the necessity of
+getting the assay solution under proper conditions, in order to obtain
+satisfactory results. The method has been repeatedly investigated, and
+the conclusion arrived at, "that it can be correct only by accident."
+Yet there are many chemists who get good results, and place considerable
+faith in its accuracy. This can only be due to differences in the manner
+of working. It is generally understood that nitric acid or nitrates must
+be absent; and our experience fully confirms this. Precipitations in
+nitrate solutions are worthless, as the following experiments show. In
+each experiment the bulk of the solution was 150 c.c. The solutions
+contained 10 grams of nitre, were freely acid with hydrochloric acid,
+and were precipitated (while boiling) with slight excess of baric
+chloride.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sulphuric acid</td><td align='left'>taken</td><td align='left'>0.020</td><td align='left'>gram</td><td align='left'>0.050</td><td align='left'>gram</td><td align='left'>0.100</td><td align='left'>gram</td></tr>
+<tr><td align='center'>"</td><td align='left'>found</td><td align='left'>0.019</td><td align='left'>"</td><td align='left'>0.047</td><td align='left'>"</td><td align='left'>0.098</td><td align='left'>"</td></tr>
+<tr><td align='center'>"</td><td align='left'>taken</td><td align='left'>0.500</td><td align='left'>"</td><td align='left'>1.004</td><td align='left'>"</td><td align='left'>1.000</td><td align='left'>"</td></tr>
+<tr><td align='center'>"</td><td align='left'>found</td><td align='left'>0.526</td><td align='left'>"</td><td align='left'>1.126</td><td align='left'>"</td><td align='left'>1.126</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>All the precipitates were boiled with hydrochloric acid, and thoroughly
+washed before weighing. The results of some other experiments on this
+subject are given under "sulphur" in the "examination of commercial
+copper," page 207.</p>
+
+<p>The solution having been obtained free from nitrates and chlorates<span class='pagenum'><a name="Page_370" id="Page_370">[Pg 370]</a></span> (and
+containing but little free hydrochloric acid), is largely diluted,
+heated to boiling, and precipitated with a moderate excess of a solution
+of chloride of barium (8 parts of the crystallized barium chloride are
+sufficient for 1 of sulphur). It is allowed to settle for half-an-hour,
+and then decanted through a filter. The precipitate is shaken up with
+boiling water, rendered slightly acid, filtered, washed, dried, ignited,
+and weighed. The ignited precipitate, when pure, is white, and is not
+decomposed at a red heat; it is barium sulphate (BaSO<sub>4</sub>), and contains
+13.73 per cent. of sulphur, or 34.33 per cent. of sulphuric oxide
+(SO<sub>3</sub>).</p>
+
+<p><b>Determination of Sulphur in Pyrites.</b>&mdash;Weigh up half a gram of the
+dried and powdered sample, and treat with 10 c.c. of a mixture of 3
+volumes of nitric acid and 1 volume of hydrochloric acid, occasionally
+heating. Evaporate to dryness, treat with 5 c.c. of hydrochloric acid,
+and again evaporate; take up with 1 c.c. of hydrochloric acid and 100
+c.c. of hot water, filter through a small filter, and wash. The residue
+may contain sulphates of lead, barium, or lime; it must be separately
+examined, if the total sulphur is wanted. The filtrate is heated, and
+rendered slightly alkaline with ammonia. Filter off the precipitated
+ferric hydrate through a quick filter, and wash with hot water. If
+necessary, evaporate the bulk to about 200 c.c., render faintly acid
+with hydrochloric acid, and add 20 c.c. of solution of barium chloride;
+allow to stand for half-an-hour, and decant through a filter. Wash with
+hot water, dry, ignite, and weigh. Pure pyrites contains 53.33 per cent.
+of sulphur.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This is based upon the easy conversion of all sulphur compounds into
+sulphates by fusion with nitre or by oxidation with nitric acid; and on
+the determination of the sulphate formed by titration in an acetic acid
+solution with baric chloride.<a name="FNanchor_101_101" id="FNanchor_101_101"></a><a href="#Footnote_101_101" class="fnanchor">[101]</a> The finishing point is determined by
+filtering off portions of the assay solution, and testing with sulphuric
+acid. A slight excess of baric chloride will cause a precipitate.</p>
+
+<p>The process may be divided into&mdash;(1) the preparation of the solution,
+and (2) the titration.</p>
+
+<p><b>Preparation of the Solution.</b>&mdash;Weigh up from 1 to 5 grams of the dried
+and powdered substance, and mix intimately with 4 grams of powdered
+nitre; clean out the mortar with another gram of nitre, and add this as
+a cover. Heat in a platinum crucible for fifteen minutes at a low
+temperature; cool, and extract<span class='pagenum'><a name="Page_371" id="Page_371">[Pg 371]</a></span> with water in an evaporating-dish about
+9 inches across, and holding 700 or 800 c.c. Add 10 grams of sodium
+acetate and 10 c.c. of acetic acid, and dilute to half a litre. Boil.
+The solution is ready for titrating. Substances which lose sulphur on
+heating (such as pyrites) are thus treated:&mdash;Weigh up 1 gram, and
+evaporate nearly to dryness with 10 c.c. each of nitric and hydrochloric
+acids. Take up with 10 c.c. of hydrochloric acid, and again boil down to
+a small bulk; dilute and transfer to a 9-inch evaporating-dish; add 10
+grams of sodium acetate and 5 c.c. of acetic acid, dilute to half a
+litre, and boil. The solution is ready for titrating. Sulphates may be
+dissolved up in the dish itself with the help of a c.c. or so of
+hydrochloric acid; sodium acetate and acetic acid are then added; and,
+after dilution and boiling, the solutions are at once titrated.</p>
+
+<p>The solution before titration must contain no free mineral acid, but 5
+or 10 c.c. of acetic acid should be present. It must contain 10 grams of
+sodium acetate, or sufficient to convert any free mineral acid into its
+corresponding sodic salt; or, if chlorides, nitrates or sulphates of the
+metals are present, sufficient to decompose them. If a precipitation
+occurs, as is the case with ferric salts, &amp;c., the solution is titrated
+with the precipitate in it.</p>
+
+<p><b>The Titration.</b>&mdash;<i>The standard solution of barium chloride</i> is made by
+dissolving 76.25 grams of the crystallized salt (BaCl<sub>2</sub>.2H<sub>2</sub>O) in
+distilled water, and diluting to 1 litre. 100 c.c. will equal 1 gram of
+sulphur. As indicator, use dilute sulphuric acid. The strength of the
+solution may be checked by the titration of 5 grams of ferrous sulphate
+(oxidized with permanganate of potassium or a few drops of nitric acid),
+which should require 57.5 c.c. of the barium chloride solution; or any
+pure sulphate of known composition can be used; anhydrous salts should
+be preferred.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig065.jpg" width="450" height="190" alt="Fig. 65." title="" />
+
+</div>
+
+<p>Fill an ordinary 100 c.c. burette with the solution of barium chloride.
+The evaporating dish containing the assay solution is placed on a round
+burner (as shown in fig. 65), and the solution is kept steadily boiling.
+An ordinary Bunsen-burner flame will cause bumping, and should not be
+used. Run in the standard<span class='pagenum'><a name="Page_372" id="Page_372">[Pg 372]</a></span> solution in quantity known to be
+insufficient; then withdraw a portion of about 2 c.c., with a pipette,
+and filter through a fine filter-paper into a test tube. Run in another
+0.5 c.c. of the standard solution, and withdraw and filter into a test
+tube another portion of 2 c.c.; and continue this operation until
+half-a-dozen or more portions have been drawn off. The test tubes should
+be arranged in order in a stand resting on a piece of paper, so that
+each test tube representing 0.5 c.c. of the standard baric chloride may
+have its value recorded beneath it (fig. 66). Add to each test tube 3
+drops of dilute sulphuric acid; that which shows the first appearance of
+a precipitate marks the point at which the titration is complete.
+Suppose, for example, that the test tube marked 48.5 c.c. shows no
+precipitate, while that at 49.0 c.c. shows one, it is evident that the
+finishing point lies between these readings. With a little practice, one
+can judge from the appearance of the precipitate in the 49 c.c. tube,
+whether 1/4 c.c. should be deducted or not.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig066.jpg" width="450" height="213" alt="Fig. 66." title="" />
+
+</div>
+
+<p>It is better to add dilute sulphuric acid, and to watch for the
+appearance of a precipitate in the test tube, than to add baric chloride
+and to look for its non-appearance; besides, baric chloride is much less
+likely to be present in a test tube as impurity than sulphates are. In
+this way the chance of error from what are termed "accidental causes" is
+diminished.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of titration:&mdash;</p>
+
+<p>Make <i>a standard solution of sulphuric acid</i> by diluting 43.65 grams of
+sulphuric acid (sp. g. 1.6165) to 1 litre: 100 c.c. will contain 1 gram
+of sulphur. An equivalent solution may be made by dissolving 100.62
+grams of sodium sulphate crystals (Na<sub>2</sub>SO<sub>4</sub>.10H<sub>2</sub>O), or 86.88
+grams of ferrous sulphate (FeSO<sub>4</sub>.7H<sub>2</sub>O), in water (oxidising the
+latter), and diluting to 1 litre.</p>
+
+<p>The order in which these experiments are given is that in which they
+were made in an investigation into the conditions under which the
+titration could most accurately be effected.</p>
+
+<p><b>Effect of Hydrochloric and Nitric Acids.</b>&mdash;The titrations were
+performed in the manner already described, but sodic acetate<span class='pagenum'><a name="Page_373" id="Page_373">[Pg 373]</a></span> and acetic
+acid were absent. Twenty c.c. of the standard solution of sulphuric acid
+were used.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Hydrochloric acid present</td><td align='left'>0.0</td><td align='left'>c.c.</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>2.0</td><td align='left'>c.c.</td><td align='left'>5.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>19.7</td><td align='left'>"</td><td align='left'>12.5</td><td align='left'>"</td></tr>
+<tr><td align='left'>Nitric acid present</td><td align='left'>0.0</td><td align='left'>c.c.</td><td align='left'>1.0</td><td align='left'>c.c.</td><td align='left'>2.0</td><td align='left'>c.c.</td><td align='left'>5.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>19.5</td><td align='left'>"</td><td align='left'>18.0</td><td align='left'>"</td><td align='left'>10.0</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>These show clearly the interference of free mineral acids, although very
+dilute hydrochloric acid (1 c.c. in 500 of water) has no effect.</p>
+
+<p><b>Effect of Acetic and Citric Acids.</b>&mdash;A similar series of experiments
+with these acids gave the following results:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Acetic acid present</td><td align='left'>0.0</td><td align='left'>c.c.</td><td align='left'>5.0</td><td align='left'>c.c. 50.0</td><td align='left'>c.c. 100.0</td><td align='left'>c.c.</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td><td align='left'>20.0</td><td align='left'>"</td></tr>
+</table></div>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Citric acid present</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+</table></div>
+
+
+<p>These acids do not interfere.</p>
+
+<p><b>Effect of Sodic Acetate and Acetic Acid.</b>&mdash;In each of these experiments
+5 c.c. of acetic acid was present.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodium acetate added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>10 grams</td><td align='left'>50 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+</table></div>
+
+
+<p>As sodic acetate and acetic acid did not interfere, it became desirable
+to make some experiments on the <i>finishing point</i>. The first object
+sought for was the smallest amount of the standard baric chloride in 500
+c.c. of water, required to give an indication when tested in the manner
+already described.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Conditions of Assay Solution.</td><td align='left'>Baric Chloride required.</td></tr>
+<tr><td align='left'>Water only</td><td align='left'>0.05 c.c.</td></tr>
+<tr><td align='left'>With 10 grams of sodium acetate and 5 c.c. of acetic acid</td><td align='left'>0.05 "</td></tr>
+<tr><td align='left'>The same with 5 grams of nitre</td><td align='left'>0.10 "</td></tr>
+<tr><td align='left'>Like the last, but with 5 grams of salt instead of nitre</td><td align='left'>0.10 "</td></tr>
+</table></div>
+
+
+<p>These show that as small an amount of baric chloride solution as is
+equal to only 0.000002 gram of sulphur in the 2 c.c. of solution tested
+yields a decided precipitate on the addition of 3 drops of sulphuric
+acid.</p>
+
+<p>To determine whether the same finishing point is obtained on testing the
+filtered portions in the test tubes with baric chloride as is obtained
+on testing with sulphuric acid, a titration was made with 20 c.c. of
+standard solution of sulphuric acid, together with the usual quantities
+of sodic acetate and acetic<span class='pagenum'><a name="Page_374" id="Page_374">[Pg 374]</a></span> acid; and two lots of 2 c.c. each were
+filtered into two sets of test tubes after each addition of the standard
+baric chloride. To one series 3 drops of baric chloride solution were
+added, and to the other 3 drops of sulphuric acid. The results were&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>"Baric Chloride" added.</td><td align='left'>With Dilute Sulphuric Acid.</td><td align='left'>With Baric Chloride Solution.</td></tr>
+<tr><td align='left'>19.5 c.c.</td><td align='left'>Clear</td><td align='left'>Cloudy</td></tr>
+<tr><td align='left'>19.75 "</td><td align='left'>Clear</td><td align='left'>Cloudy</td></tr>
+<tr><td align='left'>20.0 "</td><td align='left'>Finished</td><td align='left'>Finished</td></tr>
+<tr><td align='left'>20.25 "</td><td align='left'>Cloudy</td><td align='left'>Clear</td></tr>
+<tr><td align='left'>20.5 "</td><td align='left'>Cloudy</td><td align='left'>Clear</td></tr>
+</table></div>
+
+
+<p>The two methods of testing give the same result. But this balance is
+disturbed in the presence of much nitre, the indications with baric
+chloride being disturbed by an opalescence for some c.c. beyond the
+finishing point. In solutions containing free hydrochloric or nitric
+acid, a precipitate is obtained with either baric chloride or sulphuric
+acid.</p>
+
+<p><b>Effect of Varying Sulphur.</b>&mdash;In these and the subsequent experiments
+the titrations were performed in the presence of 10 grams of sodic
+acetate and 10 c.c. of acetic acid in the manner already described.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Standard sulphuric acid used</td><td align='left'>5.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>50.0 c.c.</td><td align='left'> 100.0 c.c.</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>5.0 "</td><td align='left'>10.0 "</td><td align='left'>20.0 "</td><td align='left'>50.0 "</td><td align='left'>100.0 "</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Temperature.</b>&mdash;With 5 c.c. of standard sulphuric acid
+titrated at 15&deg; C., 5 c.c. of baric chloride were required; but with
+larger quantities the results were altogether unsatisfactory when
+titrated cold.</p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>100.0 c.c.</td><td align='left'>200.0 c.c.</td><td align='left'>500.0 c.c.</td><td align='left'>1000.0 c.c.</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 "</td><td align='left'>20.0 "</td><td align='left'>20.0 "</td><td align='left'>20.5 "</td></tr>
+</table></div>
+
+
+<p>Considerable variation in bulk has no effect, but 500 c.c. is the most
+convenient volume to work with. It is well to occasionally replace the
+water boiled off during titration.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;In all these experiments 20 c.c. of
+"sulphuric acid" were used, and the titration was performed in the
+ordinary way.</p>
+
+
+<p><span class='pagenum'><a name="Page_375" id="Page_375">[Pg 375]</a></span></p>
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'><i>Sodic chloride</i> added</td><td align='left'>0 gram</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>19.7 c.c.</td></tr>
+<tr><td align='left'><i>Ammonic chloride</i> added</td><td align='left'>0 gram</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>19.5 c.c.</td></tr>
+<tr><td align='left'><i>Calcic chloride</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>2 grams</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>19.2 c.c.</td><td align='left'>19.0 c.c.</td></tr>
+<tr><td align='left'><i>Zinc chloride</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>3 grams</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+<tr><td align='left'><i>Ferrous chloride</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>3 grams</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>19.7 c.c.</td><td align='left'>19.5 c.c.</td><td align='left'>19.0 c.c.</td></tr>
+<tr><td align='left'><i>Ferric chloride</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>3 grams</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+<tr><td align='left'><i>Copper chloride</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>3 grams</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+<tr><td align='left'><i>Potassic Nitrate</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>19.0 c.c.</td></tr>
+<tr><td align='left'><i>Potassic Nitrite</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>5 grams</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+<tr><td align='left'><i>Sodic phosphate</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>22.5 c.c.</td></tr>
+<tr><td align='left'><i>Sodic arsenate</i> added</td><td align='left'>0 gram</td><td align='left'>1 gram</td></tr>
+<tr><td align='left'>"Baric chloride" required</td><td align='left'>20.0 c.c.</td><td align='left'>20.5 c.c.</td></tr>
+</table></div>
+
+
+<p>In the absence of ferric salts, phosphates and arsenates count as
+sulphur.</p>
+
+<p>In two series of experiments for determining the effect of varying
+amounts of sulphur in the form of ferrous sulphate, we obtained the
+following results:&mdash;In the first series the assay solution was prepared
+in the manner we have described for <i>Pyrites</i>; and in the second series,
+by fusion with nitre.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sulphur added</td><td align='left'></td><td align='left'></td><td align='left'>0.050 gram</td><td align='left'>0.100 gram</td><td align='left'>0.200 gram</td></tr>
+<tr><td align='left'>"Baric chloride"</td><td align='left'>required</td><td align='left'>(1)</td><td align='left'>5.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='left'>(2)</td><td align='left'>4.7 "</td><td align='left'>10.0 "</td><td align='left'>20.0 "</td></tr>
+<tr><td align='left'>Sulphur added</td><td align='left'></td><td align='left'></td><td align='left'>0.500 gram</td><td align='left'>1.000 gram</td></tr>
+<tr><td align='left'>"Baric chloride"</td><td align='left'>required</td><td align='left'>(1)</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='left'>(2)</td><td align='left'>50.0 "</td><td align='left'>100.0 "</td></tr>
+</table></div>
+
+<p>More than 5 grams of nitre must not be used in an assay; and, since the
+requisite amount of nitre considerably exceeds that sufficient to
+oxidise the sulphur, not more than 0.5 gram of unoxidised sulphur should
+be present in the portion of the sample weighed up for determination.
+When the amount of sulphur present is not known within reasonable
+limits, the test portions may be tried with a drop of baric chloride
+solution instead of sulphuric acid, so that the diminishing quantity of
+precipitate may give warning of an approach to the finishing point.</p>
+
+<p><b>Determination of Sulphur in Blende.</b>&mdash;Weigh up 1 gram<span class='pagenum'><a name="Page_376" id="Page_376">[Pg 376]</a></span> of dried and
+powdered blende, and mix and fuse with 5 grams of nitre in the manner
+described. Place the dish and its contents in the titrating-dish,
+extract with water, add 10 grams of sodium acetate and 10 c.c. of acetic
+acid, remove and wash the platinum-dish, and dilute to 500 c.c.; boil
+and titrate. In the example, duplicate determinations required (<i>a</i>)
+32.0 c.c., (<i>b</i>) 32.25 c.c., giving an average of 32.1 per cent. of
+sulphur.</p>
+
+<p><b>Determination of Sulphur in Chalcopyrite</b> (Yellow Copper Ore).&mdash;Take 1
+gram of the finely-powdered sample, and 5 grams of nitre. Sprinkle a
+little of the nitre in a small Wedgwood mortar, place the ore on it, and
+cover with 2 or 3 grams more of the nitre. Rub up together, and transfer
+to a small porcelain dish; clean out the mortar with the rest of the
+nitre, and add to the contents of the dish. Cover with a piece of
+platinum foil, and heat gently with a Bunsen burner till the nitre melts
+and the stuff shows signs of deflagrating; remove the heat, and allow
+the action to go on by itself for a minute or so, then heat over the
+Bunsen burner for 10 minutes. Cool; transfer the whole to the
+titrating-dish; boil with 500 c.c. of water; remove the small dish and
+foil; add sodic acetate and acetic acid, and titrate.</p>
+
+<p>For example, 1 gram required 34.5 c.c. of "barium chloride" (standard =
+1.005 gram S), which is equivalent to 34.7 per cent. sulphur. The
+theoretical percentage is 34.8.</p>
+
+<p><b>Determination of Sulphur in Chalcocite</b> (Grey Copper Ore).&mdash;Proceed as
+in the last experiment but, since the action with nitre is more
+moderate, no special precautions need be taken on heating. A platinum
+dish may be used.</p>
+
+<p>An example which was heated for 30 minutes required 20.5 c.c. of the
+barium chloride solution. This is equivalent to 20.6 per cent. of
+sulphur. The theoretical yield is 20.2 per cent.</p>
+
+<p><b>Determination of Sulphur in Pyrites.</b>&mdash;Take 1 gram of the
+finely-powdered sample, cover with 10 c.c. of nitric acid, and, when
+action has ceased, evaporate to a small bulk. Add 3 or 4 c.c. of
+hydrochloric acid, and again evaporate to a paste. Take up with 1 or 2
+c.c. of dilute hydrochloric acid, dilute with water, transfer to a
+titrating-dish, add 10 grams of sodic acetate and 5 c.c. of acetic acid,
+and dilute with water to 500 c.c. Boil and titrate.</p>
+
+<p>An example with 1 gram of a pure crystallized pyrites required 52.7 c.c.
+of the barium chloride solution, which is equivalent to 53.0 per cent.
+of sulphur. Theory requires 53.3 per cent. of sulphur.</p>
+
+<p><b>Determination of Sulphur in Mispickel.</b>&mdash;Take 1 gram of the powdered
+ore and evaporate with 10 c.c. of nitric acid, and take up with 3 or 4
+c.c. of hydrochloric acid. If any globules of<span class='pagenum'><a name="Page_377" id="Page_377">[Pg 377]</a></span> sulphur remain, again
+evaporate with nitric acid. Dilute, and transfer to the titrating-dish.
+Add 10 grams of sodic acetate, dilute with water, boil, and titrate. The
+mispickel carries (according to theory) exactly sufficient iron to
+precipitate the arsenic as ferric arsenate in an acetic acid solution,
+so no more iron need be added. The ferric arsenate will separate out as
+a yellowish-white flocculent precipitate.</p>
+
+<p>An example required, in duplicate experiment, 18.5 c.c. and 18.7 c.c. of
+barium chloride, equivalent to 18.7 per cent. of sulphur. The formula,
+FeS<sub>2</sub>.FeAs<sub>2</sub>, requires 19.6 percent., but the sulphur generally
+varies considerably from this amount.</p>
+
+<p><b>Determination of Sulphur in Burnt Ores.</b>&mdash;Take 5 grams of the dried and
+powdered ore, and rub up with 4 grams of nitre; transfer to the
+platinum-dish; clean out the mortar with another gram of nitre, and add
+this as a cover. Heat, and extract with water as before; add the sodium
+acetate and acetic acid; and titrate. Burnt ores carry from 2.5 to 5 per
+cent. of sulphur. A series of four determinations gave:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>"Baric Chloride" Required.</td><td align='left'>Percentage of Sulphur.</td><td align='left'>Gravimetric Results.</td></tr>
+<tr><td align='left'>12.6 c.c.</td><td align='left'>2.52 %</td><td align='left'>2.45 %</td></tr>
+<tr><td align='left'>29.9 "</td><td align='left'>5.98 "</td><td align='left'>5.84 "</td></tr>
+<tr><td align='left'>18.1 "</td><td align='left'>3.62 "</td><td align='left'>3.53 "</td></tr>
+<tr><td align='left'>22.0 "</td><td align='left'>4.40 "</td><td align='left'>4.43 "</td></tr>
+</table></div>
+
+
+<p>For ores carrying less than 1 per cent. of sulphur, take 10 grams for
+the assay.</p>
+
+<p><b>Determination of Sulphuric Oxide (SO<sub>3</sub>) in Sulphates.</b>&mdash;When the
+sulphur exists in the sample received by the assayer in an oxidised
+state as sulphate, it is usual to report it in terms of sulphuric oxide
+(SO<sub>3</sub>). In this case, the metal must also be reported as oxide. For
+example, an analysis of copper sulphate would be thus reported:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Oxide of copper (CuO)</td><td align='left'>31.8 %</td></tr>
+<tr><td align='left'>Sulphuric oxide (SO3)</td><td align='left'>32.1 "</td></tr>
+<tr><td align='left'>Water</td><td align='left'>36.1 "</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.0</td></tr>
+</table></div>
+
+
+<p>The percentage of sulphur multiplied by 2.5 gives the percentage of
+sulphuric oxide. Thus a sample of copper sulphate containing 12.85 per
+cent. of sulphur will contain 12.85 &times; 2.5 or 32.12 per cent. of
+sulphuric oxide.</p>
+
+<p>In minerals and metallurgical products, it is common to find the sulphur
+in both conditions&mdash;<i>i.e.</i>, as sulphate and sulphide. Generally in these
+the percentage of sulphur only is wanted; but this will depend entirely
+on commercial requirements, and not on<span class='pagenum'><a name="Page_378" id="Page_378">[Pg 378]</a></span> the fancy of the assayer.
+Soluble sulphates are determined separately by extracting with small
+quantities of cold water, so as to avoid the separation of basic
+sulphates, or, if the sulphides present are not at the same time
+attacked, by dilute hydrochloric acid. Lead sulphate may be extracted by
+boiling with ammonic acetate; whilst barium, strontium, and, perhaps,
+calcium sulphate, will be mainly found in the residue insoluble in
+acids.</p>
+
+<p>Weigh up from 2 to 5 grams of the material according to the amount of
+sulphur judged to be present, and dissolve them in the titrating-dish
+with 1 c.c. of hydrochloric acid and 50 c.c. of water. Add 10 grams of
+sodic acetate, and 10 c.c. of acetic acid; dilute, boil, and titrate. In
+the case of ferric salts, half the quantity of acetic acid will be
+better, as then the ferric iron will be precipitated, and a colourless
+solution will be left, in which the end reaction is more readily
+distinguished.</p>
+
+<p>Determined in this way, 5 gram samples of the following salts gave the
+results indicated below:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt.</td><td align='left'>"Barium Chloride" Required.</td><td align='left'>Sulphuric Oxide.</td></tr>
+<tr><td align='left'>Copper sulphate</td><td align='left'>64.25 c.c.</td><td align='left'>32.12 %</td></tr>
+<tr><td align='left'>Magnesium sulphate</td><td align='left'>65.25 "</td><td align='left'>32.62 "</td></tr>
+<tr><td align='left'>Zinc sulphate</td><td align='left'>56.25 "</td><td align='left'>28.12 "</td></tr>
+<tr><td align='left'>Ferrous sulphate</td><td align='left'>58.25 "</td><td align='left'>29.12 "</td></tr>
+<tr><td align='left'>Sodium sulphate</td><td align='left'>51.25 "</td><td align='left'>25.60 "</td></tr>
+</table></div>
+
+
+<p><b>Determination of Sulphuric Oxide in Barytes</b> (Heavy spar).&mdash;Fuse 2
+grams of the powdered mineral with 5 grams of "fusion mixture" for five
+minutes; and, when cold, extract with water. Filter, acidulate the
+filtrate with an excess of 10 c.c. of acetic acid, dilute, boil, and
+titrate. For example, a transparent crystallised sample required 27.0
+c.c. of barium chloride, which is equivalent to 13.6 per cent. of
+sulphur, or 34.0 per cent. of sulphuric oxide. Theory requires 34.3 per
+cent. of the latter. Since both carbonate of soda and potash are liable
+to contain sulphates, a blank determination should be made on 5 grams of
+the "fusion mixture," and the amount found be deducted from that got in
+the assay.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. The price of sulphur in an ore being 4-1/2<i>d.</i> per unit in the
+northern markets, what would be the price of a ton of ore containing 49
+per cent. of sulphur? What would be the effect on the price of an error
+of 0.25 per cent. in the assay?</p>
+
+<p>2. Pyrites carries 50 per cent. of sulphur, and on calcining yields 70
+per cent. of its weight of burnt ore. Supposing the burnt ore carries
+3.5 per cent. of sulphur, what proportion of the sulphur will have been
+removed in the calcining?<span class='pagenum'><a name="Page_379" id="Page_379">[Pg 379]</a></span></p>
+
+<p>3. How would blende compare with pyrites as a source of sulphur for
+sulphuric acid making?</p>
+
+<p>4. How would you determine the percentage of sulphuric oxide in a sample
+of gypsum? What is sulphuric oxide, and what relation does it bear to
+sulphur?</p>
+
+<p>5. A mineral contains 20.7 per cent. of water, 32.4 per cent. of lime,
+and 18.6 per cent. of sulphur. What is its probable composition? What
+experiment would you try to determine the accuracy of your conclusion?</p>
+
+
+<h4>SELENIUM</h4>
+
+<p>occurs in nature combined with copper, mercury, and lead, in certain
+rare minerals. In small quantities it is found in many ores. It is
+detected in solution by the red precipitate produced on boiling the acid
+solution with sodium sulphite. This reaction is used for its
+determination.</p>
+
+<p><b>Solution.</b>&mdash;The solution is effected by boiling with nitric acid or
+aqua regia, or by fusing with nitre. To separate the selenium, the
+solution is evaporated with an excess of hydrochloric acid and a little
+sodium or potassium chloride. This destroys any nitric acid that may be
+present, and reduces selenic acid (H<sub>2</sub>SeO<sub>4</sub>) to selenious
+(H<sub>2</sub>SeO<sub>3</sub>). The solution is diluted with water, and treated with a
+solution of sulphite of soda. It is warmed, and at last boiled. The
+selenium separates as a red precipitate, which (on boiling) becomes
+denser and black. It is collected on a weighed filter, washed with hot
+water, dried at 100&deg; C., and weighed as pure selenium.</p>
+
+<p>Selenium can be precipitated with sulphuretted hydrogen as a sulphide,
+which is readily soluble in ammonium sulphide. This sulphide may be
+oxidised with hydrochloric acid and chlorate of potash; and the selenium
+separated in the manner described.</p>
+
+
+<h4>TELLURIUM.</h4>
+
+<p>Tellurium occurs in nature, native, and in combination with gold,
+silver, bismuth and lead. It is sometimes met with in assaying gold
+ores. It may be detected by the purple colour it imparts to strong
+sulphuric acid when dissolved in the cold, and by the black precipitate
+of metallic tellurium which its solutions yield on treatment with a
+reducing agent. Telluric acid is reduced to tellurous (with evolution of
+chlorine) on boiling with hydrochloric acid.</p>
+
+<p><b>Solution</b> is effected by boiling with aqua regia, or by fusing with
+nitre and sodium carbonate.</p>
+
+<p><b>Separation.</b>&mdash;Tellurium closely resembles selenium in its reactions. It
+is separated and determined in the same way. Like<span class='pagenum'><a name="Page_380" id="Page_380">[Pg 380]</a></span> it, it forms a
+sulphide soluble in ammonium sulphide. It is distinguished from selenium
+by the insolubility, in a solution of cyanide of potassium, of the metal
+precipitated by sodium sulphite; whereas selenium dissolves, forming a
+soluble potassic seleno-cyanide.<a name="FNanchor_102_102" id="FNanchor_102_102"></a><a href="#Footnote_102_102" class="fnanchor">[102]</a></p>
+
+<p>For the determination, solution is effected by fusing with nitre and
+sodium carbonate, dissolving out the tellurate of potash with water, and
+boiling with hydrochloric acid. Tellurous compounds are formed, with
+evolution of chlorine; and the solution, on treating with a reducing
+agent (such as sulphurous acid or stannous chloride), yields metallic
+tellurium; which is washed, dried at 100&deg; C., and weighed.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_101_101" id="Footnote_101_101"></a><a href="#FNanchor_101_101"><span class="label">[101]</span></a> BaCl<sub>2</sub> + Na<sub>2</sub>SO<sub>4</sub> = BaSO<sub>4</sub> + 2NaCl.</p></div>
+
+<div class="footnote"><p><a name="Footnote_102_102" id="Footnote_102_102"></a><a href="#FNanchor_102_102"><span class="label">[102]</span></a> Se + KCy = KCySe.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_381" id="Page_381">[Pg 381]</a></span></p>
+<h2><a name="CHAPTER_XVII" id="CHAPTER_XVII"></a>CHAPTER XVII.</h2>
+
+<h3>ARSENIC, PHOSPHORUS, NITROGEN.</h3>
+
+
+<h4>ARSENIC.</h4>
+
+<p>The chief source of the arsenic of commerce is arsenical pyrites, or
+mispickel, which contains about 45 per cent. of arsenic (As). Arsenic
+also occurs as a constituent of several comparatively rare minerals;
+and, as an impurity, it is very widely distributed. White arsenic is an
+oxide of arsenic, and is obtained by roasting arsenical ores, and
+refining the material (crude arsenic), which condenses in the flues.
+Arsenic itself is volatile, and many of its compounds have the same
+property. It forms two well-defined series of salts, corresponding to
+the oxides: arsenious oxide (As<sub>2</sub>O<sub>3</sub>), and arsenic oxide
+(As<sub>2</sub>O<sub>5</sub>). These combine with bases to form arsenites and arsenates
+respectively. Boiling with nitric acid converts the lower into the
+higher oxide; and powerful reducing-agents, such as cuprous chloride,
+have the opposite effect.</p>
+
+<p>Arsenic may be detected by dissolving the substance in hydrochloric
+acid, or in aqua regia (avoiding an excess of nitric acid), and adding a
+little of this solution to the contents of a small flask in which
+hydrogen is being made by the action of zinc and hydrochloric acid. The
+ignited jet of hydrogen assumes a blue colour if arsenic is present, and
+a cold porcelain dish held in the flame (fig. 67) becomes coated with a
+dark deposit of metallic arsenic. Antimony produces a similar effect,
+but is distinguished by the insolubility of its deposit in a cold
+solution of bleaching-powder.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig067.jpg" width="450" height="296" alt="Fig. 67." title="" />
+
+</div>
+
+<p>Arsenites are distinguished by the volatility of the chloride; by
+decolorising a solution of permanganate of potassium, and by immediately
+giving a yellow precipitate with sulphuretted hydrogen. Arsenates are
+distinguished (after converting into soda salts by<span class='pagenum'><a name="Page_382" id="Page_382">[Pg 382]</a></span> boiling with
+carbonate of soda and neutralising) by giving with nitrate of silver a
+red precipitate, and with "magnesia mixture" a white crystalline one.</p>
+
+<p><b>Dry Assay.</b>&mdash;There is no dry assay which is trustworthy. The following
+method is sometimes used to find the proportion of arsenious oxide in
+"crude arsenic":&mdash;Weigh up 5 grams of the dried sample, and place them
+in a clean dry test-tube about 6 inches long. Tie a small filter-paper
+over the mouth of the tube, so as to prevent air-currents. Heat the tube
+cautiously so as to sublime off the white arsenic into the upper part of
+the tube. Cut off the bottom of the test-tube by wetting whilst hot.
+Scrape out the arsenic and weigh it. The weight gives an approximate
+idea of the quantity, and the colour of the quality, of the white
+arsenic obtainable from the sample. Some workers (sellers) weigh the
+residue, and determine the white arsenic by difference. In determining
+the percentage of moisture in these samples, the substance is dried on a
+water-bath or in a water-oven.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p><b>Solution.</b>&mdash;Where, as in crude arsenic, the substance is arsenious
+oxide (As<sub>2</sub>O<sub>3</sub>) mixed with impurities, the arsenic is best got into
+solution by warming with caustic soda, and neutralising the excess with
+hydrochloric acid; it will be present as sodium arsenite. Metals and
+alloys are acted on by means of nitric acid; or the arsenic may be at
+the same time dissolved and separated by distilling with a strongly-acid
+solution of ferric chloride, in the way described under <i>Volumetric
+Methods</i>.</p>
+
+<p>With minerals, mattes, &amp;c., solution is thus effected:&mdash;The
+finely-powdered substance is mixed (in a large platinum or porcelain
+crucible) with from six to ten times its weight of a mixture of equal
+parts of carbonate of soda and nitre. The mass is then heated gradually
+to fusion, and kept for a few minutes in that state. When cold, it is
+extracted with warm water, and filtered from the insoluble residue. The
+solution, acidified with nitric acid and boiled, contains the arsenic as
+sodium arsenate. With mispickel, and those substances which easily give
+off arsenic on heating, the substance is first treated with nitric acid,
+evaporated to dryness, and then the residue is treated in the way just
+described.</p>
+
+<p>When the arsenic is present as arsenite or arsenide, distillation with
+an acid solution of ferric chloride will give the whole of the arsenic
+in the distillate free from any metal except, perhaps, tin as stannic
+chloride. With arsenates, dissolve the substance in acid and then add an
+excess of soda. Pass sulphuretted hydrogen into the solution; warm, and
+filter. Acidulate the<span class='pagenum'><a name="Page_383" id="Page_383">[Pg 383]</a></span> filtrate, and pass sulphuretted hydrogen. Decant
+off the liquid through a filter, and digest the precipitate with ammonic
+carbonate; filter, and re-precipitate with hydrochloric acid and
+sulphuretted hydrogen. Allow to stand in a warm place, and filter off
+the yellow sulphide of arsenic. Wash it into a beaker, clean the
+filter-paper (if necessary) with a drop or two of dilute ammonia;
+evaporate with 10 c.c. of dilute nitric acid to a small bulk; dilute;
+and filter off the globules of sulphur. The filtrate contains the
+arsenic as arsenic acid.</p>
+
+
+<h4>GRAVIMETRIC METHOD.</h4>
+
+<p>Having got the arsenic into solution as arsenic acid, and in a volume
+not much exceeding 50 c.c., add about 20 c.c. of dilute ammonia and 20
+c.c. of "magnesia mixture." Stir with a glass rod, and allow to settle
+overnight. Filter, and wash with dilute ammonia, avoiding the use of
+large quantities of wash water. Dry, transfer the precipitate to a
+Berlin crucible, and clean the filter-paper thoroughly. Burn this paper
+carefully and completely; and add the ash to the contents of the
+crucible, together with 4 or 5 drops of nitric acid. Evaporate with a
+Bunsen burner, and slowly ignite, finishing off with the blow-pipe or
+muffle. Cool, and weigh. The ignited precipitate is pyrarsenate of
+magnesia (Mg<sub>2</sub>As<sub>2</sub>O<sub>7</sub>), and contains 48.4 per cent. of arsenic
+(As).</p>
+
+<p>Instead of igniting the precipitate with nitric acid, it may be
+collected on a weighed filter-paper, dried at 100&deg; C., and weighed as
+ammonic-magnesic arsenate (2AmMgAsO<sub>4</sub>.H<sub>2</sub>O), which contains 39.5 per
+cent. of arsenic. The results in this case are likely to be a little
+higher. The drying is very tedious, and is likely to leave behind more
+water than is allowed for in the formula. In a series of determinations
+in which the arsenic was weighed in both forms, the results were:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Ammonic-magnesic Arsenate in grams.</td><td align='left'>Arsenic in grams.</td><td align='left'>Magnesium Pyrarsenate in grams.</td><td align='left'>Arsenic in grams.</td></tr>
+<tr><td align='left'>0.0080</td><td align='left'>0.0032</td><td align='left'>0.0065</td><td align='left'>0.0031</td></tr>
+<tr><td align='left'>0.0400</td><td align='left'>0.0158</td><td align='left'>0.0330</td><td align='left'>0.0160</td></tr>
+<tr><td align='left'>0.0799</td><td align='left'>0.0316</td><td align='left'>0.0633</td><td align='left'>0.0306</td></tr>
+<tr><td align='left'>0.1600</td><td align='left'>0.0632</td><td align='left'>0.1287</td><td align='left'>0.0623</td></tr>
+<tr><td align='left'>0.4000</td><td align='left'>0.1580</td><td align='left'>0.3205</td><td align='left'>0.1551</td></tr>
+<tr><td align='left'>0.7990</td><td align='left'>0.3156</td><td align='left'>0.6435</td><td align='left'>0.3114</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_384" id="Page_384">[Pg 384]</a></span> </p>
+
+<h4>VOLUMETRIC METHODS.</h4>
+
+<p>There are two methods: one for determining the arsenic in the lower, and
+the other in the higher state of oxidation. In the first-mentioned
+method this is done by titrating with a standard solution of iodine; and
+in the latter with a solution of uranium acetate. Where the arsenic
+already exists as arsenious oxide, or where it is most conveniently
+separated by distillation as arsenious chloride, the iodine method
+should be used; but when the arsenic is separated as ammonic-magnesic
+arsenate or as sulphide, the uranium acetate titration should be
+adopted.</p>
+
+
+<h4>IODINE PROCESS.</h4>
+
+<p>This is based on the fact that sodium arsenite in a solution containing
+an excess of bicarbonate of soda is indirectly oxidised by iodine to
+sodium arsenate,<a name="FNanchor_103_103" id="FNanchor_103_103"></a><a href="#Footnote_103_103" class="fnanchor">[103]</a> and that an excess of iodine may be recognised by
+the blue colour it strikes with starch. The process is divided into two
+parts&mdash;(1) the preparation of the solution, and (2) the titration.</p>
+
+<p><b>Preparation of the Solution.</b>&mdash;For substances like crude arsenic, in
+which the arsenic is present as arsenious oxide, the method is as
+follows:&mdash;Take a portion which shall contain from 0.25 to 0.5 gram of
+the oxide, place in a beaker, and cover with 10 c.c. of sodic hydrate
+solution; warm till dissolved, put a small piece of litmus paper in the
+solution, and render acid with dilute hydrochloric acid. Add 2 grams of
+bicarbonate of soda in solution, filter (if necessary), and dilute to
+100 c.c. The solution is now ready for titrating.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig068.jpg" width="300" height="338" alt="Fig. 68." title="" />
+
+</div>
+
+<p>Where the arsenic has to be separated as arsenious chloride, the process
+is as follows:<a name="FNanchor_104_104" id="FNanchor_104_104"></a><a href="#Footnote_104_104" class="fnanchor">[104]</a>&mdash;Weigh up 1 gram of the finely-powdered ore (metals
+should be hammered out into a thin foil or be used as filings), and
+place in a 16-ounce flask provided with a well-fitting cork, and
+connected with a <b>U</b>-tube, as shown in the drawing (fig. 68). The
+<b>U</b>-tube should contain 2 or 3 c.c. of water, and is cooled by being<span class='pagenum'><a name="Page_385" id="Page_385">[Pg 385]</a></span>
+placed in a jar or large beaker of cold water. The water used for
+cooling should be renewed for each assay.</p>
+
+<p>Pour on the assay in the flask 50 c.c. of a "ferric chloride mixture,"
+made by dissolving 600 grams of calcium chloride and 300 grams of ferric
+chloride in 600 c.c. of hydrochloric acid, and making up to 1 litre with
+water.</p>
+
+<p>Firmly cork up the apparatus, and boil over a small Bunsen-burner flame
+for fifteen or twenty minutes, but avoid evaporating to dryness.
+Disconnect the flask, and pour away its contents at once to prevent
+breakage of the flask by their solidification. The arsenic will be
+condensed in the <b>U</b>-tube, together with the greater part of the
+hydrochloric acid; transfer the distillate to a beaker washing out the
+tube two or three times with water; add a small piece of litmus paper;
+neutralise with ammonia; render faintly <i>acid</i> with dilute hydrochloric
+acid; add 2 grams of bicarbonate of soda in solution; and dilute to 250
+c.c. The solution is now ready for titrating.</p>
+
+<p>The arsenic comes over in the early part of the distillation, as will be
+seen from the following experiment, made on 1 gram of copper
+precipitate; in which experiment the distillate was collected in
+separate portions at equal intervals, and the arsenic in each portion
+determined:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Time Distilling.</td><td align='left'>Iodine Required.</td><td align='left'>Equivalent to Arsenic in the Distillate.</td></tr>
+<tr><td align='left'>5 minutes</td><td align='left'>12.0 c.c.</td><td align='left'>0.0450 gram</td></tr>
+<tr><td align='left'>5 "</td><td align='left'>0.17 "</td><td align='left'>0.0005&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>5 "</td><td align='left'>0.0 "</td></tr>
+<tr><td align='left'>5 "</td><td align='left'>0.0 "</td></tr>
+<tr><td align='left'>To dryness</td><td align='left'>0.0 "</td></tr>
+</table></div>
+
+
+<p>The volume of each distillate was about 5 c.c.</p>
+
+<p>In this operation the metals are converted into chlorides by the action
+of ferric chloride, which gives up a part of its chlorine, and becomes
+reduced to the ferrous salt. The calcium chloride does not enter into
+the chemical reaction, but raises the temperature at which the solution
+boils, and is essential for the completion of the distillation.<a name="FNanchor_105_105" id="FNanchor_105_105"></a><a href="#Footnote_105_105" class="fnanchor">[105]</a> Two
+experiments with material containing 3.48 per cent. of arsenic gave&mdash;(1)
+with ferric chloride alone, 2.74 per cent.; and (2) with the addition of
+calcium chloride, 3.48 per cent.</p>
+
+<p>It is always necessary to make a blank determination with 1 gram of
+electrotype copper, to find out the amount of arsenic in the ferric
+chloride mixture.<a name="FNanchor_106_106" id="FNanchor_106_106"></a><a href="#Footnote_106_106" class="fnanchor">[106]</a> Unfortunately, a correction is<span class='pagenum'><a name="Page_386" id="Page_386">[Pg 386]</a></span> always required.
+This amounts to about 0.15 per cent. of arsenic on each assay, even when
+the mixture has been purified; and this constitutes the weakness of the
+method, since, in some cases, the correction is as much as, or even
+greater than, the percentage to be determined.</p>
+
+<p>The acid distillate containing the arsenious chloride may be left for an
+hour or so without much fear of oxidation; but it is safer to neutralise
+and then to add the bicarbonate of soda, as the following experiments
+show. Several portions of a solution, each having a bulk of 100 c.c.,
+were exposed for varying lengths of time, and the arsenic in each
+determined.</p>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td></tr>
+<tr><td align='left'>Time Exposed.</td><td align='left'>Acid Solutions.<br />"Iodine" Required.&nbsp;&nbsp; Arsenic Found.</td><td align='left'>Neutralised Solutions.<br /> "Iodine"Required.&nbsp;&nbsp; Arsenic Found.</td></tr>
+<tr><td align='left'>&mdash;</td><td align='left'>18.2 c.c.&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = 0.0136 gram</td><td align='left'>18.1 c.c. &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0136 gram</td></tr>
+<tr><td align='left'>1 hour</td><td align='left'>18.2&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0136 &nbsp;&nbsp;"</td><td align='left'>18.2&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0136&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>2 hours</td><td align='left'>17.7 &nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = 0.0133&nbsp;&nbsp; "</td><td align='left'>18.0&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0135&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'>4 &nbsp;&nbsp;&nbsp;"</td><td align='left'>17.5&nbsp;&nbsp;&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0131 "</td><td align='left'>18.4 &nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; = 0.0138 &nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>5 &nbsp;&nbsp;&nbsp;"</td><td align='left'>17.0&nbsp;&nbsp;&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0127 "</td><td align='left'>18.3&nbsp; " &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;= 0.0137 &nbsp;&nbsp;"</td></tr>
+</table></div>
+
+
+<p><b>The Titration.</b>&mdash;Make a <i>standard solution of iodine</i> by weighing up in
+a beaker 16.933 grams of iodine and 30 grams of potassium iodide in
+crystals; add a few c.c. of water, and, when dissolved, dilute to 1
+litre: 100 c.c. will equal 0.500 gram of arsenic.</p>
+
+<p>A solution of starch similar to that used in the iodide-copper assay
+will be required. Use 2 c.c. for each assay. Variations in the quantity
+of starch used do not interfere; but the solution must be freshly
+prepared, as after seven or eight days it becomes useless.</p>
+
+<p>To standardise the iodine solution, weigh up 0.3 gram of white arsenic;
+dissolve in caustic soda; neutralise; after acidulating, add 2 grams of
+bicarbonate of soda and 2 c.c. of the starch solution, and dilute to 200
+c.c. with cold water. Fill a burette having a glass stop-cock with the
+iodine solution, and run it into the solution of arsenic, rapidly at
+first, and then more cautiously, till a final drop produces a blue
+colour throughout the solution. Calculate the standard in the usual way.
+White arsenic contains 75.76 per cent. of arsenic.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of the titration:<span class='pagenum'><a name="Page_387" id="Page_387">[Pg 387]</a></span>&mdash;</p>
+
+<p>Make a solution of arsenic by dissolving 6.60 grams of white arsenic in
+100 c.c. of sodic hydrate solution; render slightly acid with
+hydrochloric acid; add 10 grains of bicarbonate of soda, and dilute to 1
+litre: 100 c.c. will contain 0.50 gram of arsenic.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The reaction goes on very quickly in
+the cold, and, since there is no occasion for heating, all titrations
+should therefore be carried out cold.</p>
+
+<p><b>Effect of Varying Bulk.</b>&mdash;In these experiments, 20 c.c. of arsenic
+solution were taken, 2 grams of bicarbonate of soda and 2 c.c. of starch
+solution added, and water supplied to the required bulk. The results
+were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td><td align='left'>250.0 c.c.</td><td align='left'>500.0 c.c.</td></tr>
+<tr><td align='left'>"Iodine" required</td><td align='left'>20.0 "</td><td align='left'>20.0 "</td><td align='left'>20.0 "</td><td align='left'>20.0 "</td></tr>
+</table></div>
+
+
+<p>Considerable variation in bulk does not interfere.</p>
+
+<p><b>Effect of Varying Bicarbonate of Soda.</b>&mdash;This salt must be present in
+each titration in considerable excess, to prevent the interference of
+free acid. The bicarbonate must be dissolved without heating, as neutral
+carbonates should be avoided.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bicarbonate added</td><td align='left'>1 gram</td><td align='left'>2 grams</td><td align='left'>5 grams</td><td align='left'>10 grams</td></tr>
+<tr><td align='left'>"Iodine" required</td><td align='left'>20.1 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>20.1 c.c.</td><td align='left'>20.0 c.c.</td></tr>
+</table></div>
+
+
+<p>These results show that large variation in the quantity of bicarbonate
+has no effect.</p>
+
+<p><b>Effect of Free Acid.</b>&mdash;In these experiments, the arsenic taken, the
+starch, and the bulk were as before, but no bicarbonate was added. In
+one case the solution was rendered acid with 5 c.c. of acetic acid, and
+in the other with 5 c.c. of hydrochloric acid; in both cases the
+interference was strongly marked, and no satisfactory finishing point
+could be obtained. This was much more marked with the hydrochloric acid.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;The process for getting the arsenic into
+solution will exclude all metals except tin, but the solution will be
+charged with sodium or ammonium salts in the process of neutralising, so
+that it is only necessary to see if these cause any interference. The
+alkaline hydrates, including ammonia, are plainly inadmissible, since no
+free iodine can exist in their presence. Monocarbonates similarly
+interfere, but to a much less extent; hence the necessity for rendering
+the assay distinctly acid before adding the bicarbonate of soda.</p>
+
+<p>With 20 c.c. of arsenic solution; and with bulk, soda, and starch as
+before, the results obtained were:<span class='pagenum'><a name="Page_388" id="Page_388">[Pg 388]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>"Iodine" required.</td></tr>
+<tr><td align='left'>With 20 grams of ammonic chloride</td><td align='left'>20.0 c.c.</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp; 20 grams of sodium chloride</td><td align='left'>20.0 "</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp; 20 grams of sodium acetate</td><td align='left'>20.0 "</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;" &nbsp;&nbsp;&nbsp;&nbsp;0.050 gram of tin, as stannic chloride</td><td align='left'>19.6 "</td></tr>
+<tr><td align='left'>Without any addition</td><td align='left'>20.0 "</td></tr>
+</table></div>
+
+
+<p>The interference of the stannic salt is probably mechanical, the
+precipitate carrying down some arsenious acid.</p>
+
+<p><b>Effect of Varying Arsenic.</b>&mdash;With bulk, starch, and soda as before, but
+with varying arsenic, the results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Arsenic added</td><td align='left'>1.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td></tr>
+<tr><td align='left'>"Iodine" required</td><td align='left'>1.1 "</td><td align='left'>9.9 "</td><td align='left'>20.0 "</td><td align='left'>50.0 "</td><td align='left'>100.0 "</td></tr>
+</table></div>
+
+
+<p><b>Determination of Arsenic in Metallic Copper.</b>&mdash;Put 1 gram of the copper
+filings, freed from particles of the file with a magnet, into a
+16-oz.-flask; and distil with the ferric chloride mixture, as above
+described. Neutralise the distillate; acidify; add bicarbonate of soda
+and starch; dilute; and titrate with the standard solution of
+iodine.<a name="FNanchor_107_107" id="FNanchor_107_107"></a><a href="#Footnote_107_107" class="fnanchor">[107]</a> Make a blank determination with 1 gram of electrotype
+copper, proceeding exactly as with the assay; and deduct the amount of
+arsenic found in this experiment from that previously obtained.</p>
+
+<p>Working in this way on a copper containing 0.38 per cent. of arsenic and
+0.80 per cent. of antimony, 0.38 per cent. of arsenic was found.</p>
+
+<p><b>Determination of White Arsenic in Crude Arsenic.</b>&mdash;Weigh out 1 gram of
+the dried and powdered substance (or 0.5 gram if rich), and digest with
+10 c.c. of a 10 per cent. solution of soda; dilute to about 50 c.c., and
+filter. Render faintly acid with hydrochloric acid, and filter (if
+necessary); add 2 or 3 grams of bicarbonate of soda in solution, then 5
+c.c. of starch, and titrate the cold solution with the standard solution
+of iodine.</p>
+
+<p>The following is an example:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1 gram of crude arsenic required 53.7 c.c. "Iodine;"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;100 c.c. "Iodine" = 0.6000 gram white arsenic;</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;100 : 53.7 :: 0.6 : 0.3222, or 32.2 per cent.</td></tr>
+</table></div>
+
+
+<p>With the test-tube method of dry assaying, this same sample gave results
+varying from 33 to 35 per cent. of white arsenic, which (judging from
+its appearance) was impure.<span class='pagenum'><a name="Page_389" id="Page_389">[Pg 389]</a></span></p>
+
+
+<h4>URANIC ACETATE PROCESS.</h4>
+
+<p>This may be looked upon as an alternative to the gravimetric method. It
+is applicable in all cases where the arsenic exists in solution as
+arsenic acid or as arsenate of soda. The process may be considered in
+two parts: (1) the preparation of the solution, and (2) the titration.</p>
+
+<p><b>Preparation of the Solution.</b>&mdash;If the arsenic has been separated as
+sulphide, it is sufficient to attack it with 10 or 15 c.c. of nitric
+acid, and to heat gently till dissolved, avoiding too high a temperature
+at first. Afterwards continue the heat till the separated sulphur runs
+into globules, and the bulk of the acid has been reduced to 3 or 4 c.c.
+Dilute with 20 or 30 c.c. of water; put in a piece of litmus paper; and
+add dilute ammonia until just alkaline. Then add 5 c.c. of the sodium
+acetate and acetic acid solution (which should make the solution
+distinctly acid); dilute to 150 c.c., and heat to boiling. The solution
+is ready for titrating.</p>
+
+<p>When the arsenic exists in a nitric acid solution mixed with much
+copper, it is separated in the way described under <i>Examination of
+Commercial Copper</i> (Arsenic and Phosphorus), pages 208, 209.</p>
+
+<p>If the arsenic has been separated as ammonium-magnesium arsenate, and
+phosphates are known to be absent; dissolve the precipitate (after
+filtering, but without washing) in dilute hydrochloric acid. Add dilute
+ammonia till a slight precipitate is formed, and then 5 c.c. of the
+sodium acetate and acetic acid solution; dilute to 150 c.c., and heat to
+boiling. Titrate.</p>
+
+<p>If phosphates are present (which will always be the case if they were
+present in the original substance, and no separation with sulphuretted
+hydrogen has been made), the phosphorus will count in the subsequent
+titration as arsenic (one part of phosphorus counting as 2.4 parts of
+arsenic). It will be necessary to dissolve the mixed arsenate and
+phosphate of magnesia in hydrochloric acid. Add about four or five times
+as much iron (as ferric chloride) as the combined phosphorus and arsenic
+present will unite with, and separate by the "basic acetate" process as
+described under <span class="smcap">Phosphorus</span> in the <i>Examination of Commercial
+Copper</i>, page 209. Obviously, when phosphates are present, it is easier
+to separate the arsenic as sulphide than to precipitate it with the
+"magnesia mixture."</p>
+
+<p><b>The Titration.</b>&mdash;The <i>standard solution of uranium acetate</i> is made by
+dissolving 34.1 grams of the salt (with the help of 25 c.c.<span class='pagenum'><a name="Page_390" id="Page_390">[Pg 390]</a></span> of acetic
+acid) in water; and diluting to 1 litre. The water and acid are added a
+little at a time, and warmed till solution is effected; then cooled, and
+diluted to the required volume: 100 c.c. will equal 0.50 gram of
+arsenic.</p>
+
+<p>The <i>sodic acetate and acetic acid solution</i> is made by dissolving 100
+grams of sodic acetate in 500 c.c. of acetic acid, and diluting with
+water to 1 litre. Five c.c. are used for each assay.</p>
+
+<p>The solution of potassic ferrocyanide used as <i>indicator</i> is made by
+dissolving 10 grams of the salt in 100 c.c. of water.</p>
+
+<p>To standardise the solution of uranium acetate, weigh up a quantity of
+white arsenic (As<sub>2</sub>O<sub>3</sub>) which shall be about equivalent to the
+arsenic contained in the assay (0.1 or 0.2 gram); transfer to a flask,
+and dissolve in 10 c.c. of nitric acid with the aid of heat. Evaporate
+to a small bulk (taking care to avoid the presence of hydrochloric
+acid); dilute with water; add a small piece of litmus paper; render
+faintly alkaline with ammonia; then add 5 c.c. of the sodic acetate
+mixture; dilute to 150 c.c.; and heat to boiling.</p>
+
+<p>Fill an ordinary burette with the uranium acetate solution, and run into
+the assay a quantity known to be insufficient. Again heat for a minute
+or two. Arrange a series of drops of the solution of ferrocyanide of
+potassium on a porcelain slab, and, with the help of a glass rod, bring
+a drop of the assay solution in contact with one of these. If no colour
+is produced, run in the uranium acetate, 1 c.c. at a time, testing after
+each addition, till a brown colour is developed. It is best to overdo
+the assay, and to count back. It is not necessary to filter off a
+portion of the assay before testing with the "ferrocyanide," since the
+precipitate (uranic arsenate) has no effect.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of titration. Make a solution of arsenic acid by dissolving 4.95 grams
+of arsenious acid (As<sub>2</sub>O<sub>3</sub>) in a covered beaker with 35 c.c. of
+nitric acid; evaporate down to 7 or 8 c.c.; and dilute with water to 1
+litre: 100 c.c. will contain 0.375 gram of arsenic. Use 20 c.c. for each
+experiment.</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;It is generally recommended to titrate
+the boiling solution, since it is possible that the precipitation is
+only complete on boiling. Low results are obtained in a cold solution,
+the apparent excess of uranium acetate striking a colour at once; on
+boiling, however, it ceases to do so; consequently, the solution should
+always be boiled directly before testing.</p>
+
+<p>In four experiments made in the way described, but with 20 c.c<span class='pagenum'><a name="Page_391" id="Page_391">[Pg 391]</a></span>. of a
+solution of arsenic acid stronger than that given (100 c.c. = 0.5 gram
+As), the results at varying temperatures were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg; C.</td><td align='left'>30&deg; C.</td><td align='left'>70&deg; C.</td><td align='left'>100&deg; C.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>18.0 c.c.</td><td align='left'>18.5 c.c.</td><td align='left'>18.5 c.c.</td><td align='left'>18.7 c.c.</td></tr>
+</table></div>
+<p><b>Effect of Varying Bulk.</b>&mdash;These experiments were like those last
+mentioned, but were titrated boiling, and the volume was varied:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td><td align='left'>200.0 c.c.</td><td align='left'>300.0 c.c.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>14.0 "</td><td align='left'>14.0 "</td><td align='left'>14.5 "</td><td align='left'>15.0 "</td></tr>
+</table></div>
+
+
+<p>Considerable variations in bulk are to be avoided.</p>
+
+<p><b>Effect of Varying Sodium Acetate.</b>&mdash;These experiments were carried out
+like those last noticed, but the bulk was 150 c.c., and varying amounts
+of sodic acetate were added in excess of the quantity used in the
+experiments previously described:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodic acetate added</td><td align='left'>0 gram</td><td align='left'>1 gram</td><td align='left'>10 grams</td><td align='left'>20 grams</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>14.5 c.c.</td><td align='left'>14.5 c.c.</td><td align='left'>16.0 c.c.</td><td align='left'>18.0 c.c.</td></tr>
+</table></div>
+
+<p>It is evidently important that the quantity of this salt present in each
+titration be measured out, so as to avoid variation.</p>
+
+<p><b>Effect of Varying the Sodium Acetate and Acetic Acid Solution.</b>&mdash;Acetic
+Acid also affects the results, but in the opposite direction, by
+preventing the precipitation of uranium arsenate. With varying volumes
+of the solution now under notice, the results were:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Solution added</td><td align='left'>0.0 c.c.</td><td align='left'>5.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'>15.0 c.c.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>14.5 "</td><td align='left'>14.5 "</td><td align='left'>14.5 "</td><td align='left'>14.0 "</td></tr>
+<tr><td align='left'>Solution added</td><td align='left'>20.0 "</td><td align='left'>30.0 "</td><td align='left'>40.0 "</td><td align='left'>50.0 "</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>13.2 "</td><td align='left'>10.0 "</td><td align='left'>6.0 "</td><td align='left'>2.0 "</td></tr>
+</table></div>
+
+
+<p>These show that the quantity ordered (5 c.c.) must be adhered to.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;In these experiments, 10 grams of the salt
+(the effect of which it was desired to determine) were added to a
+solution in other respects resembling those previously used:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Salt added</td><td align='left'>Ammonic sulphate</td><td align='left'>Ammonic nitrate</td><td align='left'>Ammonic chloride</td><td align='left'>Magnesium sulphate</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='center'>15.5 c.c.</td><td align='center'>15.5 c.c.</td><td align='center'>15.3 c.c.</td><td align='center'>15.3 c.c.</td></tr>
+</table></div>
+
+
+<p>Without any addition, 15.0 c.c. were required; and in another
+experiment, in which 30 grams of ammonic salts were present,<span class='pagenum'><a name="Page_392" id="Page_392">[Pg 392]</a></span> 15.6 c.c.
+of uranium solution were required. Such variations in the amount of
+ammonic salts as occur in ordinary working are unimportant.</p>
+
+<p>Phosphates, of course, interfere. In fact, the uranium acetate solution
+can be standardised by titrating with a known weight of phosphate, and
+calculating its equivalent of arsenic. Thus, in an experiment with 0.6
+gram of hydric sodic phosphate (Na<sub>2</sub>HPO<sub>4</sub>.12H<sub>2</sub>O), equivalent to
+0.05195 gram of phosphorus, or 0.1256 gram of arsenic, 23.25 c.c. of a
+solution of uranium acetate were required. The same solution
+standardised with white arsenic gave a standard of which 100 c.c. =
+0.5333 gram arsenic. On this standard the 0.6 gram of sodic phosphate
+should have required 23.5 c.c.</p>
+
+<p>Experiments in which 0.1 gram of bismuth and 0.1 gram of antimony were
+present with 0.1 gram of arsenic, showed no interference on the
+titration. Ferric or aluminic salts would remove their equivalent of
+arsenic, and, consequently, must be removed before titrating.</p>
+
+<p><b>Effect of Varying Arsenic.</b>&mdash;Varying amounts of metallic arsenic were
+weighed up and dissolved in nitric acid, &amp;c., and titrated:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Arsenic taken</td><td align='left'>0.010 gram</td><td align='left'>0.050 gram</td><td align='left'>0.100 gram</td><td align='left'>0.200 gram</td></tr>
+<tr><td align='left'>Arsenic found</td><td align='left'>0.010&nbsp;&nbsp;&nbsp;"</td><td align='left'>0.050&nbsp;&nbsp;&nbsp;"</td><td align='left'>0.100&nbsp;&nbsp;&nbsp;"</td><td align='left'>0.197&nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+<p>These experiments show that the method yields good results within these
+limits.</p>
+
+<p><b>Determination of Arsenic in Mispickel.</b>&mdash;Weigh up 1 gram of the dried
+and powdered ore, and evaporate to near dryness with 20 c.c. of dilute
+nitric acid. Make up to 100 c.c. with water, and pass sulphuretted
+hydrogen to reduce the ferric iron to the ferrous state, then add 20
+c.c. of dilute ammonia, and again pass sulphuretted hydrogen. Warm,
+filter, and evaporate the filtrate to drive off the excess of ammonia;
+then add 10 c.c. of nitric acid, and boil down till the sulphide of
+arsenic at first precipitated is dissolved; neutralise; add 5 c.c. of
+sodium acetate and acetic acid solution; transfer to a pint flask, boil,
+and titrate.</p>
+
+<p>For example, an impure sample of ore required, in duplicate assay of
+half a gram each, when treated in the above-mentioned way, 39.6 and 39.5
+c.c. of the uranium acetate solution (100 c.c. = 0.537 gram of arsenic),
+equivalent to 0.2114 gram of arsenic, or 42.3 per cent.</p>
+
+<p>An alternative method is as follows. Powder the ore very finely and
+weigh up .5 gram. Place in a 2-3/4 inch berlin dish and add strong
+nitric acid, one drop at a time until the action ceases; with care there
+need be no very violent reaction. Dry over a<span class='pagenum'><a name="Page_393" id="Page_393">[Pg 393]</a></span> water bath. Cover with 2
+grams of nitre and over this spread 5 grams of a mixture of equal parts
+of nitre and carbonate of soda. Fuse in a muffle or over a large gentle
+blow-pipe flame for 4 or 5 minutes. This will spoil the dish. Allow to
+cool and boil out in a larger dish with 100 c.c. of water. Filter and
+wash into an 8 oz. flask. Acidify the liquor with nitric and boil down
+to about 100 c.c. The acid should not be in too large excess, but an
+excess is needed to destroy nitrites. Neutralise with soda or ammonia.
+Add 5 c.c. of the mixture of sodium acetate and acetic acid. Titrate
+with uranium acetate.</p>
+
+<p><b>Determination of Arsenic (As) in Crude Arsenic.</b>&mdash;The method given
+under the iodine titration simply determines that portion of the arsenic
+which is present in the substance as arsenious oxide or white arsenic.
+The following method will give the total arsenic in the sample. It would
+be incorrect to report this as so much per cent. of arsenious oxide,
+although it may be reported as so much per cent. of arsenic equivalent
+to so much per cent. of white arsenic, thus:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Arsenic</td><td align='left'>30.0 per cent.</td></tr>
+<tr><td align='left'>Equivalent to white arsenic</td><td align='left'>39.6&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+<p>The equivalent of white arsenic is calculated by multiplying the
+percentage of arsenic by 1.32. The method of determining the percentage
+of arsenic is as follows:&mdash;-Boil 1 gram of the sample with 10 c.c. of
+nitric acid. When the bulk of the solution has been reduced to one-half,
+and red fumes are no longer evolved, dilute with a little water, and
+filter into a flask. Neutralise the filtrate, add 5 c.c. of sodic
+acetate solution, boil and filter. The precipitate (ferric arsenate) is
+transferred to a small beaker, treated with 5 c.c. of dilute ammonia,
+and sulphuretted hydrogen passed through it. The iron sulphide is
+filtered off, and the filtrate evaporated with an excess of nitric acid.
+When the solution is clear, it is neutralised, and 1 or 2 c.c. of sodic
+acetate solution having been added, is then mixed with the first
+filtrate. The solution is boiled and titrated.</p>
+
+<p>A sample treated in this way required 49.2 c.c. of the uranium acetate
+solution (100 c.c. = 0.537 gram of arsenic), equivalent to 26.4 per
+cent.</p>
+
+<p><b>Determination of Arsenic in Brimstone.</b>&mdash;Take 10 grams of the
+substance, and powder in a mortar; rub up with 10 c.c. of dilute ammonia
+and a little water; rinse into a pint flask; pass a current of
+sulphuretted hydrogen; and warm on a hot plate for a few minutes.
+Filter, acidulate the filtrate with sulphuric acid; filter off the
+precipitate; attack it with 10 c.c. of nitric acid; and proceed as in
+the other determinations.<span class='pagenum'><a name="Page_394" id="Page_394">[Pg 394]</a></span></p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. Mispickel contains 45.0 per cent. of arsenic, to how much white
+arsenic will this be equivalent?</p>
+
+<p>2. How would you make a standard solution of iodine so that 100 c.c.
+shall be equivalent to 1 gram of white arsenic?</p>
+
+<p>3. What weight of arsenic is contained in 1 gram of pyrarsenate of
+magnesia, and what weight of ammonic-magnesic arsenate would it be
+equivalent to?</p>
+
+<p>4. The residue, after heating 10 grams of crude arsenic, weighed 0.62
+gram. What information does this give as to the composition of the
+substance? If another 10 grams of the substance, heated on a water-bath,
+lost 0.43 gram, what conclusions would you draw, and how would you
+report your results?</p>
+
+<p>5. If a sample of copper contained 0.5 per cent. of arsenic, and 1 gram
+of it were taken for an assay, how much standard uranium acetate
+solution would be required in the titration?</p>
+
+
+<h4>PHOSPHORUS AND PHOSPHATES.</h4>
+
+<p>Phosphorus rarely occurs among minerals except in its highest oxidized
+state, phosphoric oxide (P<sub>2</sub>O<sub>5</sub>), in which it occurs abundantly as
+"rock phosphate," a variety of apatite which is mainly phosphate of
+lime. Phosphates of most of the metallic oxides are found. Phosphoric
+oxide in small quantities is widely diffused, and is a constituent of
+most rocks. Its presence in varying amounts in iron ores is a matter of
+importance, since it affects the quality of the iron obtainable from
+them.</p>
+
+<p>Phosphorus occurs in alloys in the unoxidized state. It is directly
+combined with the metal, forming a phosphide. In this manner it occurs
+in meteoric iron. The alloy phosphor-bronze is made up of copper, tin,
+zinc, and phosphorus.</p>
+
+<p>Phosphates are mined in large quantities for the use of manure
+manufacturers, and for making phosphorus.</p>
+
+<p>Phosphorus and arsenic closely resemble each other in their chemical
+properties, more especially those which the assayer makes use of for
+their determination. Phosphorus forms several series of salts; but the
+phosphates are the only ones which need be considered. Pyrophosphate of
+magnesia, which is the form in which phosphoric oxide is generally
+weighed, differs from the ordinary phosphate in the proportion of base
+to acid. Metaphosphates differ in the same way. If these are present, it
+must be remembered they act differently with some reagents from the
+ordinary phosphates, which are called orthophosphates. They are,
+however, all convertible into orthophosphates by some means<span class='pagenum'><a name="Page_395" id="Page_395">[Pg 395]</a></span> which will
+remove their base, such as fusion with alkaline carbonates, boiling with
+strong acids, &amp;c.<a name="FNanchor_108_108" id="FNanchor_108_108"></a><a href="#Footnote_108_108" class="fnanchor">[108]</a></p>
+
+<p>Phosphides are converted into phosphates by the action of nitric acid or
+other oxidizing agents. Dilute acids, when they act on the substance,
+evolve phosphuretted hydrogen (PH<sub>3</sub>). The student should be on his
+guard against losing phosphorus in this manner.</p>
+
+<p>There is no dry assay for phosphorus. All assays for it are made either
+gravimetrically or volumetrically.</p>
+
+<p>The separation of phosphoric oxide is made as follows:&mdash;The ore or metal
+is dissolved in acid and evaporated, to render the silica insoluble. It
+is taken up with hydrochloric acid, diluted with water, and treated with
+sulphuretted hydrogen. The filtrate is boiled, to get rid of the excess
+of gas, and treated with nitric acid, to peroxidize the iron present. If
+the iron is not present in more than sufficient quantity to form ferric
+phosphate with all the phosphorus present, some ferric chloride is
+added. The iron is then separated as basic acetate. The precipitate will
+contain the phosphorus, together with any arsenic acid not reduced by
+the sulphuretted hydrogen. The precipitate should have a decided brown
+colour. The precipitate is washed, transferred to a flask, and treated
+first with ammonia, and then with a current of sulphuretted hydrogen.
+The filtrate from this (acidulated with hydrochloric acid, and, if
+necessary, filtered) contains the phosphorus as phosphoric acid. This
+method is not applicable in the presence of alumina, chromium, titanium,
+or tin, if the solution is effected with nitric acid. The precipitate
+obtained by the action of nitric acid on tin retains any phosphoric or
+arsenic oxide that may be present.</p>
+
+<p>A method of separation more generally applicable and more convenient to
+work is based on the precipitation of a yellow phospho-molybdate of
+ammonia,<a name="FNanchor_109_109" id="FNanchor_109_109"></a><a href="#Footnote_109_109" class="fnanchor">[109]</a> by the action of an excess of ammonic molybdate upon a
+solution of a phosphate in nitric acid. Dissolve the substance by
+treatment with acid, and evaporate to dryness. Take up with 10 c.c. of
+nitric acid, and add 20 grams of ammonic nitrate, together with a little
+water. Next put in the solution of ammonium molybdate solution in the
+proportion of about 50 c.c. for each 0.1 gram of phosphoric oxide judged
+to be present. Warm to about 80&deg; C., and allow to stand for an hour.
+Filter, and wash<span class='pagenum'><a name="Page_396" id="Page_396">[Pg 396]</a></span> with a 10 per cent. solution of ammonic nitrate. It is
+not necessary that the whole of the precipitate be placed on the filter;
+but the beaker must be completely cleaned. Dissolve the precipitate off
+the filter with dilute ammonia, and run the solution into the original
+beaker. Run in from a burette, slowly and with stirring, "magnesia
+mixture," using about 15 c.c. for each 0.1 gram of phosphoric oxide.
+Allow to stand for one hour. The white crystalline precipitate contains
+the phosphorus as ammonium-magnesium phosphate.</p>
+
+<p>Phosphate of lead is decomposed by sulphuric acid; the lead is converted
+into the insoluble lead sulphate, and the phosphoric acid is dissolved.
+Phosphate of copper and phosphate of iron may be treated with
+sulphuretted hydrogen; the former in an acid, and the latter in an
+alkaline, solution. Phosphate of alumina is generally weighed without
+separation of the alumina, since this requires a fusion. In all cases
+the aim is to get the phosphoric oxide either free, or combined with
+some metal whose phosphate is soluble in ammonia.</p>
+
+<p>Joulie's method of separation is as follows:&mdash;One to ten grams of the
+sample are treated with hydrochloric acid, and evaporated to dryness
+with the addition (if any pyrites is present) of a little nitric acid.
+The residue is taken up with hydrochloric acid, cooled, transferred to a
+graduated flask, and diluted to the mark. It is then shaken up, filtered
+through a dry filter, and a measured portion (containing about 0.05 gram
+of phosphoric acid) transferred to a small beaker. Ten c.c. of a
+citric-acid solution of magnesia<a name="FNanchor_110_110" id="FNanchor_110_110"></a><a href="#Footnote_110_110" class="fnanchor">[110]</a> is added, and then an excess of
+ammonia. If an immediate precipitate is formed, a fresh portion must be
+measured out and treated with 20 c.c. of the citrate of magnesia
+solution and with ammonia as before. The beaker is put aside for from
+two to twelve hours. The precipitate is then filtered off and washed
+with weak ammonia; it contains the phosphorus as ammonium-magnesium
+phosphate.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>If the phosphate is not already in the form of ammonic-magnesic
+phosphate, it is converted into this by the addition to its solution of
+an excess of ammonia and "magnesia mixture." In order to get the
+precipitate pure, the "magnesia mixture" is run in<span class='pagenum'><a name="Page_397" id="Page_397">[Pg 397]</a></span> gradually (by drops)
+from a burette, with constant stirring. A white crystalline precipitate
+at once falls, if much phosphorus is present; but, if there is only a
+small quantity, it may be an hour or two before it shows itself. The
+solution is best allowed to rest for twelve or fifteen hours (overnight)
+before filtering. The presence of tartaric acid should be avoided; and
+the appearance of the precipitate should be crystalline. The solution is
+decanted through a filter, and the precipitate washed with dilute
+ammonia, using as little as may be necessary. The precipitate is dried,
+transferred to a weighed Berlin or platinum crucible; the filter-paper
+is carefully burnt, and its ash added to the precipitate, which is then
+ignited, at first gently over a Bunsen burner, and then more strongly
+over the blowpipe or in the muffle. The residue is a white mass of
+magnesium pyrophosphate containing 27.92 per cent. of phosphorus, or
+63.96 per cent. of phosphoric oxide.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>Instead of separating and weighing this compound, the phosphoric oxide
+in it can be determined by titration. In many cases the ore may be
+dissolved and immediately titrated without previous separation. It is
+better, however, to carry the separation so far as to get phosphoric
+acid, an alkaline phosphate, or the magnesia precipitate. It may then be
+prepared for titration in the following way:&mdash;The precipitate in the
+last case (without much washing) is dissolved in a little hydrochloric
+acid, and the solution in any case rendered fairly acid. Dilute ammonia
+is added till it is just alkaline, and then 5 c.c. of the sodic acetate
+and acetic acid mixture (as described under the Arsenic Assay). This
+should yield a clear distinctly-acid solution. It is diluted to 100 or
+150 c.c., heated to boiling, and titrated with the uranium acetate
+solution, using that of potassic ferrocyanide as indicator.</p>
+
+<p>The <i>standard solution</i> required is made by dissolving 35 grams of
+uranium acetate in water with the aid of 25 c.c. of acetic acid, and
+diluting to 1 litre.</p>
+
+<p>An <i>equivalent solution of phosphoric oxide</i> is made by dissolving 25.21
+grams of crystallised hydric disodic phosphate (HNa<sub>2</sub>PO<sub>4</sub>.12H<sub>2</sub>O)
+in water, and making up to 1 litre. 100 c.c. will contain 0.5 gram of
+phosphoric oxide (P<sub>2</sub>O<sub>5</sub>), or 0.2183 gram of phosphorus. In making
+this solution, transparent crystals only must be used. The uranium
+acetate solution is only approximately equivalent to this, so that its
+exact standard must be determined.<span class='pagenum'><a name="Page_398" id="Page_398">[Pg 398]</a></span></p>
+
+<p><i>Sodic Acetate and Acetic Acid Solution.</i>&mdash;It is the same as that
+described under <i>Arsenic</i>.<a name="FNanchor_111_111" id="FNanchor_111_111"></a><a href="#Footnote_111_111" class="fnanchor">[111]</a> Use 5 c.c. for each assay.</p>
+
+<p>The following experiments show the effect of variation in the conditions
+of the titration:&mdash;</p>
+
+<p><b>Effect of Varying Temperature.</b>&mdash;The solution should be titrated while
+boiling. This is especially necessary for the last few c.c. in order to
+get a decided and fixed finishing point.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature</td><td align='left'>15&deg; C.</td><td align='left'>30&deg; C.</td><td align='left'>70&deg; C.</td><td align='left'>100&deg; C.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>18.0 c.c.</td><td align='left'>19.2 c.c.</td><td align='left'>19.0 c.c.</td><td align='left'>18.9 c.c.</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Bulk.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Bulk</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td><td align='left'>200.0 c.c.</td><td align='left'>300.0 c.c.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>18.8&nbsp;&nbsp; "</td><td align='left'>18.9 &nbsp;&nbsp;"</td><td align='left'>19.0 &nbsp;&nbsp;"</td><td align='left'>19.3&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<p>Variation in bulk affects the results; therefore, a constant bulk should
+be adhered to.</p>
+
+<p><b>Effect of Varying Sodium Acetate and Acetic Acid Solution.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Sodium acetate and acetic acid solution</td><td align='left'>0.0 c.c.</td><td align='left'>1.0 c.c.</td><td align='left'>5.0 c.c.</td><td align='left'>10.0 c.c.</td><td align='left'> 20.0 c.c.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>18.9 &nbsp;&nbsp;"</td><td align='left'>18.9 &nbsp;&nbsp;"</td><td align='left'>19.0 &nbsp;&nbsp;"</td><td align='left'>18.8 &nbsp;&nbsp;"</td><td align='left'>17.5&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+<p>As in the titration with arsenates, an excess is dangerous to the assay;
+a definite quantity (5 c.c.) should, therefore, be used.</p>
+
+<p><b>Effect of Foreign Salts.</b>&mdash;Besides the sodium acetate, &amp;c., added, the
+only salts likely to be present are those of ammonia and magnesia. In
+three experiments, in one of which no foreign salts were introduced,
+while in the other two 5 grams of ammonic chloride and of magnesium
+sulphate respectively were added, there were required:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>With ammonic chloride</td><td align='left'>18.8 c.c.</td><td align='left'>"Uranium" solution</td></tr>
+<tr><td align='left'>With magnesium sulphate</td><td align='left'>19.0 &nbsp;&nbsp;"</td><td align='center'>"</td></tr>
+<tr><td align='left'>Without foreign salts</td><td align='left'>18.9&nbsp;&nbsp; "</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p><b>Effect of Varying Phosphate.</b>&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>"Phosphate" solution added</td><td align='left'>10.0 c.c.</td><td align='left'>20.0 c.c.</td><td align='left'>50.0 c.c.</td><td align='left'>100.0 c.c.</td></tr>
+<tr><td align='left'>"Uranium" required</td><td align='left'>9.8&nbsp;&nbsp; "</td><td align='left'>18.9&nbsp;&nbsp; "</td><td align='left'>47.6&nbsp;&nbsp; "</td><td align='left'>94.5&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+<p>The quantity of phosphoric oxide in the assay solution for the
+conditions of titration should not be much less than 0.05 gram.<span class='pagenum'><a name="Page_399" id="Page_399">[Pg 399]</a></span> For
+smaller quantities the uranium solution should be diluted to half its
+strength, and the assay solution concentrated by reducing its bulk to 50
+c.c. and using 2.5 c.c. of the sodium acetate and acetic acid solution.</p>
+
+<p><b>Determination of Phosphoric Oxide in Apatite.</b>&mdash;Weigh up 0.5 gram of
+the dried and powdered sample, and dissolve it in 5 c.c. of hydrochloric
+acid. Evaporate to a paste, add 5 c.c. of the sodic acetate and acetic
+acid solution, dilute to 100 c.c. with water, boil, and titrate with
+uranium acetate solution.</p>
+
+<p>In an example, 0.5 gram of apatite required 37.4 c.c. of uranium acetate
+solution (standard equal to 0.5291 gram of phosphoric oxide). The sample
+therefore contained 0.1979 gram of P<sub>2</sub>O<sub>5</sub>, equal to 39.58 per cent.</p>
+
+<p><b>Determination of Phosphoric Oxide in an Iron Ore.</b>&mdash;Take 10 grams, boil
+with 50 c.c. of hydrochloric acid, and evaporate to a paste; take up
+with 10 c.c. of dilute hydrochloric acid, and dilute with water to 400
+c.c. Pass sulphuretted hydrogen for nearly a quarter of an hour; warm,
+and filter. Boil off the excess of gas; cool, add ammonia till nearly
+neutral, and then a few drops of ferric chloride solution, and 4 or 5
+grams of sodium acetate, with a drop or two of acetic acid. Boil and
+filter. Dissolve the precipitate in hot dilute hydrochloric acid, and
+add citro-magnesia mixture and ammonia; allow to stand overnight;
+filter, ignite, and weigh.</p>
+
+<p>In an example, 10 grams of ore gave 28.5 milligrams of magnesic
+pyrophosphate, which is equivalent to 0.18 per cent. of phosphoric
+oxide.</p>
+
+<p><b>Determination of Phosphorus in Iron.</b>&mdash;Take from 2 to 10 grams
+(according to the amount of phosphorus present), and dissolve in aqua
+regia, keeping the nitric acid in excess; evaporate to dryness and take
+up with hydrochloric acid, boil, dilute, and filter. Add 10 c.c. of
+nitric acid, nearly neutralise with ammonia, render acid with 3 or 4
+c.c. of nitric acid, and add 10 or 20 c.c. of ammonic molybdate
+solution. Heat for some time, allow to settle, filter, and wash the
+precipitate with a solution of ammonic nitrate. Dissolve the precipitate
+in dilute ammonia, nearly neutralise with dilute hydrochloric acid, and
+add first "magnesia mixture," and then ammonia; allow to stand
+overnight; filter, wash with dilute ammonia, dry, ignite, and weigh as
+magnesic pyrophosphate. Calculate to phosphorus.<span class='pagenum'><a name="Page_400" id="Page_400">[Pg 400]</a></span></p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. Ten grams of an iron yielded 12 milligrams of pyrophosphate of
+magnesia. What percentage of phosphorus did the metal contain?</p>
+
+<p>2. Ten grams of an iron ore gave 12 milligrams of pyrophosphate. What
+percentage of phosphoric oxide did it contain?</p>
+
+<p>3. What weight of apatite 3Ca<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub>.CaClF would require 50
+c.c. of standard uranium solution (100 c.c. equal to 0.5 gram of
+P<sub>2</sub>O<sub>5</sub>)?</p>
+
+<p>4. You have reason to believe that a precipitate which has been weighed
+as magnetic pyrophosphate contains some arsenate. How would you
+determine the amount of phosphate really present?</p>
+
+<p>5. Twenty c.c. of a solution of sodic phosphate containing 0.100 gram of
+P<sub>2</sub>O<sub>5</sub> was found to require a solution containing 0.700 gram of
+hydrated uranium acetate in a titration. The precipitate contains 80.09
+per cent. uranium oxide and 19.91 per cent. of phosphoric oxide. What
+percentage of uranium oxide was contained in the uranic acetate?</p>
+
+
+<h4>NITROGEN AND NITRATES.</h4>
+
+<p>Nitrogen occurs in nature in the free state, and forms about four-fifths
+of the atmosphere. In combination, as nitrate, it is found in nitre
+(KNO<sub>3</sub>), and Chili saltpetre (NaNO<sub>3</sub>), minerals which have a
+commercial importance. The latter occurs in beds, and is extensively
+worked for use as a manure and in the preparation of nitric acid.</p>
+
+<p>Nitrogen is mainly characterised by negative properties, although many
+of its compounds are very energetic bodies. It is a gas, present
+everywhere, but so inactive that the assayer can always afford to ignore
+its presence, and, except in testing furnace gases, &amp;c., he is never
+called on to determine its quantity.</p>
+
+<p>The nitrates are an important class of salts, and may be looked on as
+compounds of the bases with nitric pentoxide (N<sub>2</sub>O<sub>5</sub>). They are,
+with the exception of a few basic compounds, soluble in water, and are
+remarkable for the ease with which they give up their oxygen. The
+alkaline nitrates fuse readily, and lose oxygen with effervescence
+forming nitrites; while at a higher temperature they yield more oxygen
+and lose their nitrogen, either as a lower oxide or as nitrogen. The
+nitrates of the metals, on heating, leave the oxide of the metal. It is
+as yielders of oxygen that nitrates are so largely used in the
+manufacture of explosives. Gunpowder contains from 65 to 75 per cent. of
+potassium nitrate (nitre).</p>
+
+<p>Nitrates are best detected and determined by their yielding nitric oxide
+when treated with sulphuric acid and a suitable reducing agent, such as
+ferrous sulphate, mercury, or copper. Nitric oxide is a colourless gas
+very slightly soluble in water. It<span class='pagenum'><a name="Page_401" id="Page_401">[Pg 401]</a></span> combines at once with oxygen, on
+mixing with the air, to form brown "nitrous fumes," and dissolves in a
+solution of ferrous sulphate, producing a characteristic blackish-brown
+colour. It is this colour which affords the best and most easily-applied
+test for nitrates. The substance suspected to contain nitrates is
+dissolved in about 1 c.c. of water, and treated with an equal volume of
+strong sulphuric acid. After cooling, a solution of ferrous sulphate is
+poured on its surface, so as to form a layer resting on it. On standing,
+a brown or black ring is developed where the liquids join, if any
+nitrate or nitrite is present. Nitrites are distinguished from nitrates
+by effervescing and yielding brown fumes when treated with a little
+dilute sulphuric acid.</p>
+
+<p>The separation of nitrates is in many cases difficult. Generally, on
+treating the substance with water, the nitrate will be in the solution,
+and is filtered off from any insoluble matter. In the exceptional cases
+it is got into solution by treating with a boiling solution of sodium
+carbonate; the nitrate will contain it as an alkaline nitrate.</p>
+
+<p>Since, however, in their determination, nitrates are never separated and
+weighed as such, the difficulty of separating them has little
+importance. Usually, the determination can be made on the original
+aqueous solution, and it is never necessary to do more than remove any
+special substance which has a bad effect; and this is easily done by the
+usual reagents.</p>
+
+
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>It follows from what has been said that there is no direct gravimetric
+determination. The percentage of nitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) in a
+comparatively pure nitrate is sometimes determined indirectly in the
+following way:&mdash;Place in a platinum-crucible 4 or 5 grams of powdered
+and cleaned quartz. Ignite, cool in a desiccator, and weigh with the
+cover. Mix 1 gram of the dried and powdered salt with the quartz in the
+crucible by stirring with a stout platinum-wire. Cover the crucible, and
+heat in a Bunsen-burner flame at scarcely visible redness for
+half-an-hour. Cool and weigh. The loss in weight gives the amount of
+nitrogen pentoxide. Sulphates and chlorides in moderate quantity do not
+interfere. The following is an example of the process:<span class='pagenum'><a name="Page_402" id="Page_402">[Pg 402]</a></span>&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Crucible and sand</td><td align='left'>26.6485 grams</td></tr>
+<tr><td align='left'>Nitre taken</td><td align='left'>1.0000&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>27.6485 &nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'>Weight after ignition</td><td align='left'>27.1160&nbsp;&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Loss on ignition</td><td align='left'>0.5325 &nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+<p>This is equal to 53.25 per cent. of nitrogen pentoxide.</p>
+
+
+<h4>VOLUMETRIC DETERMINATION.</h4>
+
+<p>This is based on the oxidising action of nitric acid, or of nitrates in
+acid solutions on ferrous salts. The pentoxide (N<sub>2</sub>O<sub>5</sub>) of the
+nitrate is reduced to nitric oxide (NO), so that 336 parts of iron
+peroxidised represent 108 parts of nitric pentoxide as oxidising
+agent.<a name="FNanchor_112_112" id="FNanchor_112_112"></a><a href="#Footnote_112_112" class="fnanchor">[112]</a> The quantity of iron peroxidised is determined by taking a
+known quantity of ferrous salt, oxidizing with a weighed sample of
+nitrate, and then determining the residual ferrous iron by titration
+with bichromate or permanganate of potassium solution. The difference
+between the ferrous iron taken and that found, gives the amount oxidized
+by the nitrate. The speed with which nitric oxide takes up oxygen from
+the air, and thus becomes capable of oxidising more iron, renders some
+precautions necessary; ferrous chloride should, therefore, be used,
+since it is easier to expel nitric oxide (by boiling) from solutions of
+a chloride than it is from those of a sulphate. The process is as
+follows:&mdash;Dissolve 2 grams of thin soft iron wire in 50 c.c. of
+hydrochloric acid in a flask provided with an arrangement for
+maintaining an atmosphere of carbon dioxide. When the iron has
+dissolved, allow the solution to cool, and add 0.5 gram of the nitrate.
+Heat gently for a few minutes, and then boil until the nitric oxide is
+expelled. An atmosphere of carbon dioxide must be kept up. Dilute with
+water, and titrate the residual iron with standard solution of
+bichromate of potassium. The standard "bichromate" is made by dissolving
+17.5 grams of the salt (K<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub>) in water, and diluting to 1
+litre: 100 c.c. equal 2 grams of iron. Deduct the weight of iron found
+from the 2 grams originally taken, and multiply by 0.3214. This gives
+the weight of the pentoxide in the sample. In an example, 0.5 gram of
+nitre was taken, and 59.4 c.c. of the "bichromate" solution were
+required. The 59.4 c.c. thus used are equivalent to 1.198 gram of iron.
+This leaves 0.822 gram as the quantity oxidised by the nitre, which,
+multiplied by 0.3214, gives 0.2642 gram for the nitrogen pentoxide, or
+52.8 per cent.<span class='pagenum'><a name="Page_403" id="Page_403">[Pg 403]</a></span></p>
+
+
+<h4>GASOMETRIC METHOD.</h4>
+
+<p>This is based upon the measurement of the nitric oxide evolved on
+shaking up a weighed quantity of the nitrate with sulphuric acid over
+mercury in a nitrometer. Each c.c. of nitric oxide obtained, when
+reduced to normal temperature and pressure, is equivalent to:&mdash;</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>0.627</td><td align='left'>milligram</td><td align='left'>of nitrogen.</td></tr>
+<tr><td align='left'>1.343</td><td align='center'>"</td><td align='left'>of nitric oxide.</td></tr>
+<tr><td align='left'>2.418</td><td align='center'>"</td><td align='left'>of nitric pentoxide.</td></tr>
+<tr><td align='left'>2.820</td><td align='center'>"</td><td align='left'>of nitric acid.</td></tr>
+<tr><td align='left'>3.805</td><td align='center'>"</td><td align='left'>of sodium nitrate.</td></tr>
+<tr><td align='left'>4.523</td><td align='center'>"</td><td align='left'>of potassium nitrate.</td></tr>
+</table></div>
+
+
+<p>In working on substances not rich in nitrates, an ordinary nitrometer
+(fig. 69) is used; but in the assay of sodium nitrate, nitroglycerine,
+&amp;c., an instrument provided with a bulb having a capacity of 100 c.c. is
+employed.</p>
+
+<div class="figcenter" style="width: 278px;">
+<img src="images/fig069.jpg" width="278" height="450" alt="Fig. 69." title="" />
+
+</div>
+
+<p>The plan of working is as follows:&mdash;The "measuring tube" is filled with
+mercury until it reaches up into the tap, and the levelling-tube is
+placed so that it contains an inch or two of mercury. If the nitrate is
+in solution, 2 or 3 c.c. of the liquid (dilute liquids are brought to
+this bulk by evaporation) are measured into the cup. The levelling-tube
+is lowered a little, and the tap cautiously opened until all but the
+last drop of the liquid has run in. The cup is then rinsed with 2 or 3
+c.c. of sulphuric acid, which is run in in the same way, and the
+operation is repeated with another lot of acid. The measuring-tube is
+now taken from the clamp, and shaken for two or three minutes, until no
+more gas is given off. It is replaced, and the mercury-level in the two
+tubes adjusted. Then it is allowed to stand until the froth has
+subsided, and the gas has cooled to the temperature of the room. The
+volume of the gas is then read off. In adjusting the level, account must
+be taken of the sulphuric acid in the measuring-tube; this is allowed
+for by having the mercury higher in the other tube by,<span class='pagenum'><a name="Page_404" id="Page_404">[Pg 404]</a></span> say, 1 mm. for
+each 6.5 mm. of sulphuric acid, or it is counterpoised by an equal
+height of sulphuric acid in the levelling-tube, in which case the two
+mercury-levels are made to correspond. On opening the tap after reading
+off the volume, there should be no change in the level of the mercury.
+If it should rise or fall a little, a slight increase or decrease (say
+0.1 c.c.) is made to the volume previously read off.</p>
+
+<p>In working with nitrate of soda, &amp;c., in the bulb nitrometer, it is
+necessary to take a quantity of the substance which will yield more than
+100 and less than 150 c.c. of the gas.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_103_103" id="Footnote_103_103"></a><a href="#FNanchor_103_103"><span class="label">[103]</span></a> Na<sub>3</sub>AsO<sub>3</sub> + H<sub>2</sub>O + 2I = Na<sub>3</sub>AsO<sub>4</sub> + 2HI. The
+acid is at once neutralised.</p></div>
+
+<div class="footnote"><p><a name="Footnote_104_104" id="Footnote_104_104"></a><a href="#FNanchor_104_104"><span class="label">[104]</span></a> Mr. Thomas Gibb is the originator of this ingenious
+process.</p></div>
+
+<div class="footnote"><p><a name="Footnote_105_105" id="Footnote_105_105"></a><a href="#FNanchor_105_105"><span class="label">[105]</span></a> By taking hold of the water present, it may prevent the
+dissociation of arsenious chloride.</p></div>
+
+<div class="footnote"><p><a name="Footnote_106_106" id="Footnote_106_106"></a><a href="#FNanchor_106_106"><span class="label">[106]</span></a> It is difficult to get ferric chloride free from arsenic;
+but the following treatment will remove 80 or 90 per cent. of the
+arsenic contained in the commercial material:&mdash;Dissolve 2 or 3 lbs. of
+ferric chloride with the smallest amount of water that will effect
+solution with the addition of 100 c.c. of hydrochloric acid; add a
+solution of sulphurous acid in quantity sufficient to reduce 2 or 3 per
+cent. of the iron to the ferrous state; allow to stand a week; and then
+boil, to remove the hydrochloric acid added. Nitric acid, which is
+prejudicial, is also removed by this treatment.</p></div>
+
+<div class="footnote"><p><a name="Footnote_107_107" id="Footnote_107_107"></a><a href="#FNanchor_107_107"><span class="label">[107]</span></a> When the amount of arsenic to be estimated is small (as
+in refined coppers), it is better to use a weaker solution of iodine.
+This is made by diluting 200 c.c. of the standard solution with water to
+1 litre. Each c.c. will equal 0.1 per cent., if 1 gram of the metal has
+been taken for the assay.</p></div>
+
+<div class="footnote"><p><a name="Footnote_108_108" id="Footnote_108_108"></a><a href="#FNanchor_108_108"><span class="label">[108]</span></a> The constitution of these phosphates may be thus
+illustrated&mdash;<br />
+</p>
+<p>Magnesic meta-phosphate&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; MgO.P<sub>2</sub>O<sub>5</sub>.<br />
+Magnesic pyro-phosphate &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2MgO.P<sub>2</sub>O<sub>5</sub>.<br />
+Magnesic ortho-phosphate&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 3MgO.P<sub>2</sub>O<sub>5</sub>.<br />
+</p></div>
+
+<div class="footnote"><p><a name="Footnote_109_109" id="Footnote_109_109"></a><a href="#FNanchor_109_109"><span class="label">[109]</span></a> The composition of which is&mdash;
+<br />
+MoO<sub>2</sub> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;90.74,<br />
+P<sub>2</sub>O<sub>5</sub> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;3.14,<br />
+(NH<sub>4</sub>)<sub>2</sub>O &nbsp;&nbsp;&nbsp;&nbsp;3.57,<br />
+H<sub>2</sub>O &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2.55=100.00.<br />
+</p></div>
+
+<div class="footnote"><p><a name="Footnote_110_110" id="Footnote_110_110"></a><a href="#FNanchor_110_110"><span class="label">[110]</span></a> This is made by adding 27 grams of magnesium carbonate (a
+little at a time) to a solution of 270 grams of citric acid in 350 c.c.
+of warm water; and, when dissolved, adding 400 c.c. of dilute ammonia,
+and making up the bulk to 1 litre; 20 c.c. of the solution is sufficient
+for 0.1 gram of P<sub>2</sub>O<sub>5</sub>, although more will be required if much iron
+or alumina is present.</p></div>
+
+<div class="footnote"><p><a name="Footnote_111_111" id="Footnote_111_111"></a><a href="#FNanchor_111_111"><span class="label">[111]</span></a> For the details of the titration, the student is referred
+to the same place.</p></div>
+
+<div class="footnote"><p><a name="Footnote_112_112" id="Footnote_112_112"></a><a href="#FNanchor_112_112"><span class="label">[112]</span></a> N<sub>2</sub>O<sub>5</sub> + 6FeO = 3Fe<sub>2</sub>O<sub>3</sub> + 2NO.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_405" id="Page_405">[Pg 405]</a></span></p>
+<h2><a name="CHAPTER_XVIII" id="CHAPTER_XVIII"></a>CHAPTER XVIII.</h2>
+
+<h3>SILICON, CARBON, BORON.</h3>
+
+
+<h4>SILICON AND SILICATES.</h4>
+
+<p>In assaying, more especially products direct from the mine, there is
+always found, when the rock is siliceous, a quantity of white
+sandy-looking substance, insoluble in acids, which is sometimes
+accompanied by a light gelatinous material very difficult to filter.
+This is variously described as "insoluble," "sand," "insoluble
+silicates," "gangue," or "rocky matter." It may be pure quartz; but
+oftener it is mixed with silicates from the rock containing the mineral.
+Some silicates, but not many, are completely decomposed by boiling with
+hydrochloric acid or aqua regia; and others are partly so, they yield a
+gelatinous precipitate of silica which greatly interferes with the
+filtering. It is a common practice with assayers to carry the first
+attack of the sample with acids to dryness, and to take up with a fresh
+portion of acid. By this means the separated silica becomes granular and
+insoluble, and capable of being filtered off and washed with comparative
+ease.</p>
+
+<p>This residue may be ignited and weighed; and be reported as so much per
+cent. of "silica and silicates insoluble in acids." Unless specially
+wanted, a determination of its constituents need not be made. When
+required, the analysis is best made on the ignited residue, and
+separately reported as "analysis of the insoluble portion."</p>
+
+<p>Silicon only occurs in nature in the oxidised state; but the oxide
+generally known as silica (SiO<sub>2</sub>) is common, being represented by the
+abundant minerals&mdash;quartz, flint, &amp;c. Silica, combined with alumina,
+lime, oxide of iron, magnesia and the alkalies, forms a large number of
+rock-forming minerals. Most rock masses, other than limestones, contain
+over 50 per cent. of silica. The following are analyses of some of the
+commoner silicates; but it must be noted that these minerals often show
+great variation in composition. This is more especially true of
+chlorite, schorl, hornblende and augite.<span class='pagenum'><a name="Page_406" id="Page_406">[Pg 406]</a></span></p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'></td><td align='center'>Silica, SiO<sub>2</sub>.</td><td align='center'>Alumina, Al<sub>2</sub>O<sub>3</sub>.</td><td align='center'>Ferric Oxide, Fe<sub>2</sub>O<sub>3</sub>.</td><td align='center'>Ferrous Oxide, FeO.</td><td align='center'>Lime, CaO.</td><td align='center'>Magnesia, MgO.</td><td align='center'>Potash, K<sub>2</sub>O.</td><td align='center'>Soda, Na<sub>2</sub>O.</td><td align='center'>Fluorine, Water &amp;c.</td></tr>
+<tr><td align='center'>Potash-felspar</td><td align='center'>65.2</td><td align='center'>18.2</td><td align='center'>0.2</td><td align='left'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>14.7</td><td align='center'>1.5</td></tr>
+<tr><td align='center'>Soda-felspar</td><td align='center'>67.0</td><td align='center'>19.2</td><td align='center'>&mdash;</td><td align='center'>0.3</td><td align='center'>1.2</td><td align='center'>1.8</td><td align='center'>2.2</td><td align='center'>7.2</td></tr>
+<tr><td align='center'>Lime-felspar</td><td align='center'>43.3</td><td align='center'>35.4</td><td align='center'>&mdash;</td><td align='center'>1.3</td><td align='center'>17.4</td><td align='center'>0.35</td><td align='center'>0.5</td><td align='center'>0.9</td></tr>
+<tr><td align='center'>Potash-mica</td><td align='center'>45.7</td><td align='center'>33.7</td><td align='center'>3.1</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>1.1</td><td align='center'>7.5</td><td align='center'>2.8</td><td align='center'>F (0.8)<br /> H<sub>2</sub>O (4.9)</td></tr>
+<tr><td align='center'>Magnesia-mica</td><td align='center'>39.1</td><td align='center'>15.4</td><td align='center'>7.1</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>23.6</td><td align='center'>7.5</td><td align='center'>2.6</td><td align='center'>F (0.7)</td></tr>
+<tr><td align='center'>Hornblende</td><td align='center'>40.6</td><td align='center'>14.3</td><td align='center'>5.8</td><td align='center'>7.2</td><td align='center'>12.5</td><td align='center'>14.0</td><td align='center'>1.5</td><td align='center'>1.6</td></tr>
+<tr><td align='center'>Augite</td><td align='center'>50.0</td><td align='center'>3.7</td><td align='center'>2.4</td><td align='center'>6.6</td><td align='center'>22.8</td><td align='center'>13.5</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>MnO (0.1)</td></tr>
+<tr><td align='center'>Almandine (Garnet)</td><td align='center'>39.7</td><td align='center'>19.7</td><td align='center'>&mdash;</td><td align='center'>39.7</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>MnO (1.8)</td></tr>
+<tr><td align='center'>Chlorite (Peach)</td><td align='center'>32.1</td><td align='center'>18.5</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>36.7</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>H<sub>2</sub>O (12.1)</td></tr>
+<tr><td align='center'>Schorl</td><td align='center'>37.0</td><td align='center'>33.1</td><td align='center'>9.3</td><td align='center'>6.2</td><td align='center'>0.5</td><td align='center'>2.6</td><td align='center'>0.7</td><td align='center'>1.4</td><td align='center'>B<sub>2</sub>O<sub>3</sub> (7.7)<br /> F (1.5)</td></tr>
+<tr><td align='center'>China-clay</td><td align='center'>46.7</td><td align='center'>39.6</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>H<sub>2</sub>O (13.4)</td></tr>
+<tr><td align='center'>Talc</td><td align='center'>61.7</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>1.7</td><td align='center'>&mdash;</td><td align='center'>31.7</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>H<sub>2</sub>O (3.8)</td></tr>
+<tr><td align='center'>Serpentine</td><td align='center'>42.9</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>3.8</td><td align='center'>&mdash;</td><td align='center'>40.5</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>H<sub>2</sub>O (12.6)</td></tr>
+<tr><td align='center'>Olivine</td><td align='center'>39.3</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td><td align='center'>14.8</td><td align='center'>&mdash;</td><td align='center'>45.8</td><td align='center'>&mdash;</td><td align='center'>&mdash;</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_407" id="Page_407">[Pg 407]</a></span></p>
+
+<p>Silicon, from a chemical point of view, is an interesting body. It
+combines with iron to form a silicide; and is present in this condition
+in cast iron. Only in the case of the analysis of this and similar
+substances is the assayer called on to report the percentage of
+<i>silicon</i>. Silicon is readily converted into silica by the action of
+oxidizing agents. Silica forms only one series of salts&mdash;the
+silicates&mdash;which have in many cases a complex constitution; thus there
+are a large number of double silicates, which vary among themselves, not
+only in the relation of base to acid (which is the essential
+difference), but also in the ratio of the bases between themselves
+(which varies with almost every specimen).</p>
+
+<p>Silica is detected by heating the substance with a fluoride and
+sulphuric acid in a platinum-crucible. On holding a rod, moistened with
+a drop of water, over the escaping fumes, the white crust of silica
+formed on the drop of water shows its presence. The insolubility of a
+fragment of the mineral in a bead of microcosmic salt, is also a very
+good test; the fragment, on prolonged heating, does not lose its angular
+form.</p>
+
+<p>There is no dry assay for this substance, nor volumetric method; when
+the determination is required, it is carried out gravimetrically and,
+generally, by the following plan.</p>
+
+<p>If the sample contains oxides, sulphides, &amp;c., in any quantity, these
+are first dissolved out by treatment with acid, evaporated to dryness,
+taken up with hydrochloric acid, and filtered. The dried residue is
+treated in the same way as the silicates. Some silicates are completely
+decomposed by such treatment; but it saves time (unless one is sure that
+no undecomposable silicate is present) to treat these in the same way as
+the others. On the other hand, there are some silicates which are only
+attacked with difficulty even by fusion with alkaline carbonates;
+consequently, it is always well to have the substance reduced to the
+finest state of division by careful powdering, as this greatly assists
+the subsequent action. With very hard silicates, the grinding away of
+the mortar in this operation will be perceptible; the foreign matter
+thus introduced must not be ignored. Previously igniting the substance
+sometimes assists the powdering; but it is best to use a steel mortar.
+The particles of steel can be removed by a magnet, or, where the nature
+of the substance will allow it, by boiling with a little dilute
+hydrochloric acid.</p>
+
+<p>The dried and powdered material is intimately mixed with four times its
+weight of "fusion mixture" in a platinum-crucible or dish. It is then
+moderately heated over a Bunsen burner, and afterwards more strongly
+fused over a blast, or enclosed in a clay crucible in the wind-furnace.
+The action is continued until the fused mass is perfectly tranquil. With
+very refractory substances,<span class='pagenum'><a name="Page_408" id="Page_408">[Pg 408]</a></span> the action must be long continued at a high
+temperature. When sufficiently cold, the crucible is examined to see
+that no particles of foreign matter are adhering to its outer surface.
+It is then transferred to a five- or six-inch evaporating-dish, where
+its contents are acted upon with warm water for some time. The "melt"
+will slowly dissolve, but the solution should be hastened by keeping the
+liquid moderately acid with hydrochloric acid. When the "melt" has
+dissolved, clean and remove the platinum-dish, and evaporate the
+solution to a paste. Continue the evaporation to dryness on a water-bath
+(not on the hot plate), and whilst drying stir with a glass rod, feeling
+at the bottom of the dish for any unfused particles, which, if present,
+can be detected by their grittiness. If there is much grit, it will be
+necessary to repeat the assay; but with a small quantity it will only be
+necessary to refuse the grit and silica after ignition.</p>
+
+<p>During solution of the "melt" and evaporation (which may be carried on
+together), a clear solution will not be obtained, a flocculent silica
+will separate out, and towards the end of the evaporation the mass will
+get gelatinous. The drying of the jelly must be finished on the
+water-bath; first, because at this temperature the silica is rendered
+insoluble in hydrochloric acid, whilst the solubility of the alumina,
+iron, &amp;c., is unaffected, which would not be the case at a much higher
+temperature; and second, because the gelatinous residue requires very
+cautious drying to prevent loss from spirting.</p>
+
+<p>When dry, the substance is moistened, and heated with strong
+hydrochloric acid, and the sides of the dish are washed down with water.
+The silica is washed by decantation two or three times with hydrochloric
+acid and hot water, before being thrown on to the filter. The filtrate
+is again evaporated to dryness, taken up with a little hydrochloric acid
+and water and again filtered. The residue on the filter is silica. The
+two lots of silica are washed free from chlorides with hot water, dried
+on an air-bath, transferred to a platinum-crucible, ignited gently at
+first, at last strongly over the blast or in a muffle, cooled in a
+desiccator, and weighed.</p>
+
+<p>The white powdery precipitate is silica (SiO<sub>2</sub>), and its weight,
+multiplied by 100, and divided by the weight of ore taken, gives the
+percentage of silica in the sample. Where the percentage of silicon is
+wanted, which is very rarely the case, it is got by multiplying this
+result by 0.4667. It is always necessary to examine the purity of the
+body weighed as silica. This is done by re-fusing the material weighed,
+and re-determining the silica in it; or, better, by mixing a weighed
+portion in a platinum-dish with a little strong sulphuric acid, covering
+with hydrofluoric acid, and<span class='pagenum'><a name="Page_409" id="Page_409">[Pg 409]</a></span> evaporating. In the latter case, the silica
+will be converted into fluoride, which will be driven off, and the
+impurities will be left behind as sulphates of barium, phosphate and
+oxide of tin, titanium, &amp;c. This must be weighed and deducted from the
+weight of the silica. In a complete examination of a silicate it should
+be treated with the precipitate containing alumina, ferric oxide, &amp;c.</p>
+
+
+<h4>EXAMINATION OF SILICATES.</h4>
+
+<p>The student interested in the analysis of rocks and rock-forming
+minerals is advised to consult a valuable paper by Dr. W.F. Hillebrand
+in the <i>Bulletin of the United States Geological Survey</i>, <i>No.</i> 148, to
+which I am very largely indebted in the revision of the following pages.</p>
+
+<p><b>Moisture.</b>&mdash;Five grams of the powdered sample is dried between
+watch-glasses in the water-oven for two hours, or till its weight is
+constant; and the loss is reported as water lost at 100&deg; C. The rest of
+the determinations are made on this dried mineral.</p>
+
+<p><b>Combined Water, &amp;c.</b>&mdash;Weigh up 1 gram of the substance, and ignite
+over the blowpipe for some time in a platinum-crucible, cool in a
+desiccator, and weigh. Record the loss as "loss on ignition," not as
+"combined water."</p>
+
+<p><b>Silica.</b>&mdash;The ignition should have been performed in an oxidising
+atmosphere in a muffle or over a slanting blowpipe flame; this will
+ensure the oxidation of any pyrites or other sulphide present, which if
+unoxidised would injure the crucible in the next operation. The ignited
+residue is mixed with 6 or 7 grams of anhydrous sodium carbonate. This
+reagent should be the purest obtainable, but its purity should be
+checked, or rather its impurities should be determined by running a
+"check" or "blank" assay with 10 grams of it through the stages of the
+analysis; the impurities will be chiefly silica, alumina and lime, and
+altogether they ought not to exceed 1 milligram. The crucible with the
+mixture is heated at first gently over a Bunsen and afterwards more
+strongly in an oxidising atmosphere in a muffle or over the blowpipe.
+The fused mass is allowed to cool in the crucible, and is then dissolved
+out in a basin with water and a small excess of hydrochloric acid. After
+the removal and cleaning of the crucible, the liquor is evaporated
+almost to dryness. Dr. Hillebrand advises stopping short of complete
+dryness. The residue is taken up with a little hydrochloric acid and
+water and filtered and washed. The liquor, including the washings, is
+again<span class='pagenum'><a name="Page_410" id="Page_410">[Pg 410]</a></span> evaporated and taken up with water and a little acid. Usually
+about 1 per cent. of silica will be thus recovered. It is to be filtered
+off and washed and added to the main silica. The filtrate is reserved.
+The silica, thoroughly washed, is dried and ignited at a high
+temperature for twenty or thirty minutes. It is then weighed in a
+platinum crucible. After weighing it is treated with hydrofluoric acid
+and a little sulphuric, carefully evaporated and ignited strongly. The
+residue, which in extreme cases may amount to 2 or 3 per cent. of the
+rock, is weighed and deducted from the weight of the impure silica. It
+is retained in the crucible.</p>
+
+<p><b>Alumina, &amp;c.</b>&mdash;The filtrate from silica is treated by the basic acetate
+method. That is, it is first treated by a cautious addition of a
+solution of soda, almost to the point of producing a precipitate, in
+order to neutralise the excess of acid; 2 or 3 grams of sodium acetate
+are added, and the whole boiled for a minute or so. The precipitate is
+filtered off and washed only slightly. Save the filtrate. The
+precipitate is dissolved in hydrochloric, or, perhaps better, in nitric
+acid; and is reprecipitated by adding an excess of ammonia and boiling.
+The precipitate is filtered and washed with water containing 2 per cent.
+of ammonium nitrate. Both filtrates are evaporated separately to a small
+bulk, a drop or two of ammonia being added to the second towards the
+finish. They are next filtered into a 6 or 8-ounce flask through a small
+filter, the second filtrate coming after, and serving in a manner as
+wash water for the first<a name="FNanchor_113_113" id="FNanchor_113_113"></a><a href="#Footnote_113_113" class="fnanchor">[113]</a>. The two washed alumina precipitates are
+dried and placed in the platinum crucible containing the residue from
+silica after treatment with hydrofluoric acid. They are then ignited in
+an oxidising atmosphere at a high temperature for about 10 minutes. The
+weight, including that of the residue from the silica, is noted as that
+of "alumina, &amp;c."</p>
+
+<p>The weighed oxides are next fused with bisulphate of potash for some
+hours. The bisulphate should have been first fused, apart, until the
+effervescence from the escape of steam has stopped. The melt is
+dissolved out with cold water and dilute sulphuric acid, and any
+insoluble residue is filtered off, washed, ignited and weighed. The
+filtrate is reserved for determinations of iron and titanium. The
+residue, after weighing, may be treated<span class='pagenum'><a name="Page_411" id="Page_411">[Pg 411]</a></span> with hydrofluoric and sulphuric
+acids for any silica,<a name="FNanchor_114_114" id="FNanchor_114_114"></a><a href="#Footnote_114_114" class="fnanchor">[114]</a> which would be determined by loss. It may be
+tested for barium sulphate by treatment with hot strong sulphuric acid;
+in which this salt dissolves, but is again insoluble (and so comes out
+as a white precipitate) on diluting with cold water; the acid also must
+be cold before adding the water. The filtrate containing the iron is
+reduced with sulphuretted hydrogen, boiled till free from that gas,
+filtered and titrated with a standard solution of permanganate of
+potassium. The iron found is calculated to ferric oxide by dividing by
+.7. The iron solution after titration serves for the determination of
+titanium oxide (TiO<sub>2</sub>). This is done colorimetrically, by adding
+peroxide of hydrogen free from hydrofluoric acid, and comparing the
+brown colour produced with that produced by the addition of a standard
+solution of titanium to an equal volume of water containing sulphuric
+acid.<a name="FNanchor_115_115" id="FNanchor_115_115"></a><a href="#Footnote_115_115" class="fnanchor">[115]</a> The alumina is determined by difference. From the weight of
+the combined precipitate which has been recorded as "Alumina, &amp;c.,"
+deduct (1) the residue, insoluble, after fusion with bisulphate; (2) the
+ferric oxide; (3) the titanium oxide; and (4) the phosphoric oxide
+(P<sub>2</sub>O<sub>5</sub>), the amount of which is subsequently determined in a
+separate portion. This gives the alumina.</p>
+
+<p><b>Manganous oxide, &amp;c.</b>&mdash;The filtrate from the "alumina, &amp;c." contained
+in a 6 or 8-ounce flask, which it nearly fills, is made slightly
+alkaline with ammonia and treated with a small excess of ammonium
+sulphide; the flask is then corked and placed on one side for some time
+(a day or so) so that the manganese sulphide may separate. The
+precipitate is filtered off and washed with water containing ammonium
+chloride and a few drops of ammonium sulphide. The filtrate is reserved
+for lime, &amp;c. The precipitate is digested with sulphuretted hydrogen
+water, to which one-fifth of its volume of strong hydrochloric acid has
+been added; this dissolves the sulphides of zinc and manganese; any
+black residue should be tested for copper and perhaps nickel. The
+solution is evaporated to dryness, taken up with a little water and
+treated with a small excess of solution of carbonate of soda. It is
+boiled and again evaporated, washed<span class='pagenum'><a name="Page_412" id="Page_412">[Pg 412]</a></span> out with hot water and filtered on
+to a small filter, dried, ignited, and weighed as Mn<sub>3</sub>O<sub>4</sub>. It is
+calculated to MnO. It may contain, and should be tested for oxide of
+zinc, which, if present, must be deducted. If the dish becomes stained
+during evaporation, take up with a few drops of hydrochloric and
+sulphurous acids, evaporate, and then treat with carbonate of soda.</p>
+
+<p><b>Lime, &amp;c.</b>&mdash;The filtrate from the manganese sulphide is boiled, and
+without cooling, treated with ammonium oxalate in solution, which also
+should be heated to boiling. The liquid is filtered off and reserved for
+magnesia. The precipitate is dissolved in very little hydrochloric acid
+and reprecipitated by adding ammonium oxalate and ammonia to the boiling
+solution. The filtrate and washings from this are reserved for magnesia.
+The precipitate is either dissolved in dilute sulphuric and titrated
+with permanganate of potash as described under Lime (p. 322); or it is
+ignited and weighed as oxide. In this last case it may be examined for
+barium and strontium, the former of which will rarely be present.</p>
+
+<p><b>Magnesia.</b>&mdash;The filtrate from the first lime precipitate is treated
+with sodium phosphate and ammonia, and allowed to stand overnight. It is
+then filtered. The precipitate is dissolved in hydrochloric acid; the
+solution is filtered into the beaker containing the solution from the
+second lime precipitate. Ammonia and sodium phosphate are again added,
+and the precipitate, after standing, is filtered off, washed with water
+containing ammonia; it is then dried, ignited and weighed as magnesium
+pyrophosphate. This is calculated into magnesia.</p>
+
+<p><b>Potash and Soda.</b>&mdash;Weigh out .5 gram of the dried ore, and mix with an
+equal quantity of ammonic chloride; and to the mixture add gradually 4
+grams of calcium carbonate ("precipitated"). Introduce into a
+platinum-crucible and cover loosely. Heat, at first, gently; and then at
+a red heat for from forty to sixty minutes. Transfer to a porcelain
+dish, and digest with 60 or 80 c.c. of water; warm and filter: to the
+filtrate add ammonic carbonate and ammonia, and filter; evaporate the
+filtrate to dryness, adding a few drops more of ammonic carbonate
+towards the end; when dry, heat gently, and then raise the temperature
+to a little below redness. Dissolve in a small quantity of water, add a
+drop of ammonic carbonate, and filter through a small filter into a
+weighed platinum dish. Evaporate, ignite gently, and weigh. The residue
+contains the soda and potash of the mineral as chlorides.</p>
+
+<p>To determine the proportion of potassium, dissolve this residue in a
+little water, add platinum chloride in excess, evaporate to a<span class='pagenum'><a name="Page_413" id="Page_413">[Pg 413]</a></span> paste,
+extract with alcohol, decant through a small weighed filter, wash with
+alcohol, and dry at 100&deg; C. Weigh. The substance is potassium platinic
+chloride (2KCl.PtCl<sub>4</sub>). Its weight, multiplied by 0.1941, will give
+the weight of potash (K<sub>2</sub>O).</p>
+
+<p>To find the proportion of soda, multiply the weight of the potassium
+platinic chloride by 0.306; this gives the weight of potassium chloride.
+Deduct this from the weight of the mixed chlorides first got; the
+difference will be the sodium chloride, which weight, multiplied by
+0.53, will give the weight of soda (Na<sub>2</sub>O).</p>
+
+<p><b>Ferrous Oxide.</b>&mdash;When a qualitative test shows both ferric and ferrous
+oxide to be present, the proportion of the ferrous oxide must be
+separately determined. The finely ground mineral mixed with dilute
+sulphuric acid is treated on a water bath with hydrofluoric acid.
+Solution is best effected in an atmosphere of carbonic acid. In about an
+hour the decomposition is complete, and the solution is diluted with
+cold water, and titrated with the solution of bichromate or of
+permanganate of potassium. The iron found is multiplied by 1.286, and
+reported as ferrous oxide. To find the proportion of ferric oxide, the
+ferrous iron found is multiplied by 1.428, and this is deducted from the
+weight of ferric oxide obtained by precipitation with ammonia. The
+ammonia precipitate contains the whole of the iron as ferric oxide;
+hence the necessity for calculating the ferrous oxide as ferric, and
+deducting it.</p>
+
+<p><b>Phosphoric Oxide (P<sub>2</sub>O<sub>5</sub>).</b>&mdash;Weigh up 5 grams of the finely-divided
+and dry sample, and digest with 10 or 20 c.c. of nitric acid; evaporate
+to dryness on the water-bath; take up with a little dilute nitric acid;
+dilute with water; and filter. Add a few grams of ammonic nitrate and 10
+c.c. of ammonium molybdate solution, heat nearly to boiling, and allow
+to settle; filter off, and wash the yellow precipitate. Dissolve with
+dilute ammonia, add "magnesia mixture," and allow to stand overnight.
+Filter, wash with dilute ammonia, dry, ignite, and weigh as
+pyrophosphate of magnesia. The weight, multiplied by 0.6396, gives the
+weight of phosphoric oxide.</p>
+
+<p><b>Soluble Silica.</b>&mdash;Some silicates are acted on by hydrochloric acid, and
+leave on evaporation a residue; which, when the soluble salts have been
+washed out, consists generally of the separated silica with perhaps
+quartz and unattacked silicates. It should be ignited, weighed and
+boiled with a solution containing less than 10 per cent. of caustic
+soda: this dissolves the separated silica. The liquor is diluted,
+rendered faintly acid, and filtered. The residue is washed, ignited and
+weighed. The loss gives the soluble silica.<span class='pagenum'><a name="Page_414" id="Page_414">[Pg 414]</a></span></p>
+
+<p><b>Estimation of Silica in Slags</b> (Ferrous silicates).&mdash;Take 1 gram of the
+powdered slag, treat with aqua regia, evaporate to dryness, extract with
+hydrochloric acid, filter, dry, ignite, and fuse the ignited residue
+with "fusion mixture," then separate and weigh the silica in the usual
+way. Slags are for the most part decomposed by boiling with aqua regia,
+but it will be found more convenient and accurate to first extract with
+acids and then to treat the residue as an insoluble silicate.</p>
+
+<p><b>Estimation of "Silica and Insoluble Silicates" in an Ore.</b>&mdash;Take 2
+grams of the powdered mineral, evaporate with nitric acid (if sulphides
+are present), treat the dried residue (or the original substance if
+sulphides are absent) with 10 or 20 c.c. of hydrochloric acid; again
+evaporate to dryness, take up with dilute hydrochloric acid, filter,
+wash, ignite, and weigh.</p>
+
+<p><b>Estimation of Silicon in Iron.</b>&mdash;Place 2 grams of the metal (borings or
+filings) in a four-inch evaporating dish, and dissolve (with aid of
+heat) in 25 c.c. of dilute nitric acid. Evaporate to complete dryness,
+take up with 20 c.c. of hydrochloric acid, and allow to digest for one
+hour. Boil down to a small bulk, dilute with a 5 per cent. solution of
+hydrochloric acid, boil, and filter. Wash with acid and water, dry,
+ignite in a platinum crucible, and weigh the SiO<sub>2</sub>. This, multiplied
+by 0.4673, gives the weight of the silicon. The percentage is calculated
+in the usual way.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. A certain rock is a mixture of 70 per cent. of quartz, 25 per cent.
+of potash-felspar, and 5 per cent. of potash-mica. What per cent. of
+silica will it contain?</p>
+
+<p>2. Two grams of a mixture of silica and cassiterite left, after
+reduction in hydrogen, 1.78 grams. Assuming all the oxide of tin to have
+been reduced, what will be the percentage of silica?</p>
+
+<p>3. The formula of a compound is 2FeO.SiO<sub>2</sub>. What percentage of silica
+will it contain?</p>
+
+<p>4. Two grams of a sample of cast-iron gave 0.025 gram of silica. Find
+the percentage of silicon in the metal.</p>
+
+<p>5. What weights of quartz and marble (CaCO<sub>3</sub>) would you take to make
+30 grams of a slag having the formula CaO.SiO<sub>2</sub>?</p>
+
+
+<h4>CARBON AND CARBONATES.</h4>
+
+<p>Carbon compounds enter so largely into the structure of organised bodies
+that their chemistry is generally considered apart from that of the
+other elements under the head of <i>Organic Chemistry</i>. Carbon occurs,
+however, among minerals not only in the oxidised state (as carbonates),
+but also in the elementary form (as in diamond and graphite), and
+combined with hydrogen,<span class='pagenum'><a name="Page_415" id="Page_415">[Pg 415]</a></span> oxygen, &amp;c. (as in petroleums, bitumens,
+lignites, shales, and coals). In small quantities "organic matter" is
+widely diffused in minerals and rocks. In shales and clays it may amount
+to as much as 10 or 20 per cent. (mainly as bituminous and coaly
+matters).</p>
+
+<p>The assayer has only to take account of the organic matter when it is of
+commercial importance, so that in assays it is generally included under
+"loss on ignition."</p>
+
+<p>In coals, shales, lignites, &amp;c., the carbon compounds are, on heating,
+split up into oils and similar compounds. The products of distillation
+may be classified as water, gas, tars, coke, and ash. The assay of these
+bodies generally resolves itself into a distillation, and, in the case
+of the shales, an examination of the distillates for the useful oils,
+paraffin, creosote, &amp;c., contained in them.</p>
+
+<p>Elementary carbon is found in nature in three different forms, but these
+all re-act chemically in the same way. They combine with oxygen to form
+the dioxide.<a name="FNanchor_116_116" id="FNanchor_116_116"></a><a href="#Footnote_116_116" class="fnanchor">[116]</a> The weight of oxygen required to burn a given weight
+of any form of carbon is the same, and the resulting product from all
+three has the same characteristic properties. Carbon dioxide is the
+common oxide of carbon. A lower oxide exists, but on burning it is
+converted into the dioxide. Wherever the oxidation of carbon takes
+place, if there is sufficient oxygen, carbon dioxide (carbonic acid) is
+formed; this re-action is the one used for the determination of carbon
+in bodies generally. The dioxide has acid properties, and combines with
+lime and other bases forming a series of salts called carbonates.</p>
+
+<p>The carbon-compounds (other than carbonates, which will be subsequently
+considered) occurring in minerals are generally characterised by their
+sparing solubility in acids. The diamond is distinguished from other
+crystals by its hardness, lustre, and specific gravity. It may be
+subjected to a red heat without being apparently affected, but at a
+higher temperature it slowly burns away. Graphite, also, burns slowly,
+but at a lower temperature. The other bodies (coals, shales, &amp;c.) differ
+considerably among themselves in the temperature at which they commence
+to burn. Some, such as anthracite, burn with little or no flame, but
+most give off gases, which burn with a luminous flame. They deflagrate
+when sprinkled on fused nitre, forming carbonate of potash. In making
+this test the student must remember that sulphur and, in fact, all
+oxidisable bodies similarly deflagrate, but it is only in the case of
+carbon compounds that carbonate of potash is formed. Carbon unites with
+iron and some of the metals to form carbides;<span class='pagenum'><a name="Page_416" id="Page_416">[Pg 416]</a></span> combined carbon of this
+kind is detected by the odour of the carburetted hydrogen evolved when
+the metal is treated with hydrochloric acid; for example, on dissolving
+steel in acid.</p>
+
+<p>The natural carbon compounds, although, speaking generally, insoluble in
+hydrochloric or nitric acids, are more or less attacked by aqua regia.
+The assayer seldom requires these compounds to be in solution. The
+presence of "organic matter"<a name="FNanchor_117_117" id="FNanchor_117_117"></a><a href="#Footnote_117_117" class="fnanchor">[117]</a> interferes with most of the reactions
+which are used for the determination of the metals. Consequently, in
+such cases, it should be removed by calcination unless it is known that
+its presence will not interfere. When calcination is not admissible it
+may be destroyed by heating with strong sulphuric acid and bichromate or
+permanganate of potash or by fusion with nitre.</p>
+
+<p>Carbon may be separated from other substances by conversion into carbon
+dioxide by burning. In most cases substances soluble in acids are first
+removed, and the insoluble residue dried, weighed, and then calcined or
+burned in a current of air. The quantity of "organic matter" may be
+determined indirectly by the loss the substance undergoes, but it is
+better to determine the "organic carbon" by confining the calcination in
+a tube, and collecting and weighing the carbon dioxide formed. Each gram
+of carbon dioxide is equivalent to 0.2727 gram of carbon.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig070.jpg" width="450" height="131" alt="Fig. 70." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 378px;">
+<img src="images/fig071.jpg" width="378" height="300" alt="Fig. 71." title="" />
+
+</div>
+
+<p>Instead of a current of oxygen or air, oxide of copper may be more
+conveniently used. The operation is as follows:&mdash;Take a clean and dry
+piece of combustion tube drawn out and closed at one end, as shown in
+the figure (fig. 70), and about eighteen inches long. Fit it with a
+perforated cork connected with a <b>U</b>-tube (containing freshly-fused
+calcium chloride in coarse grains) and a set of potash bulbs (fig. 71)
+(containing a strong solution of potash), the exit of which last is
+provided with a small tube containing calcium chloride or a stick of
+potash. Both the <b>U</b>-tube and bulbs should have a loop of fine wire, by
+which they may be suspended on the hook of the balance for convenience<span class='pagenum'><a name="Page_417" id="Page_417">[Pg 417]</a></span>
+in weighing. They must both be weighed before the combustion is
+commenced; to prevent absorption of moisture during weighing, &amp;c., the
+ends are plugged with pieces of tube and glass rod.</p>
+
+<p>Fill the combustion tube to a depth of about eight inches with some
+copper oxide, which has been recently ignited and cooled in a close
+vessel. Put in the weighed portion for assay and a little fresh copper
+oxide, and mix in the tube by means of an iron wire shaped at the end
+after the manner of a corkscrew. Put in some more oxide of copper, and
+clean the stirrer in it. Close loosely with a plug of recently ignited
+asbestos, place in the furnace, and connect the <b>U</b>-tube and bulbs in
+the way shown in the sketch (fig. 72).</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig072.jpg" width="450" height="237" alt="Fig. 72." title="" />
+
+</div>
+
+<p>See that the joints are tight, and then commence the combustion by
+lighting the burners nearest the <b>U</b>-tube; make the first three or four
+inches red hot, and gradually extend the heat backwards the length of
+the tube, but avoid too rapid a disengagement of gas. When gas ceases to
+come off, open the pointed end of the tube and draw a current of dried
+air through the apparatus.</p>
+
+<p>The carbon dioxide is absorbed in the potash bulbs, and their increase
+in weight multiplied 0.2727 gives the amount of carbon in the substance
+taken.</p>
+
+<p>The increase in weight in the calcium chloride tube will be due to the
+water formed by the oxidation of the combined hydrogen. If this last is
+required the increase in weight multiplied by 0.111 gives its amount.<span class='pagenum'><a name="Page_418" id="Page_418">[Pg 418]</a></span></p>
+
+
+<h4>COALS.</h4>
+
+<p>The determination of the actual carbon in coals and shales is seldom
+called for; if required, it would be performed in the way just
+described.<a name="FNanchor_118_118" id="FNanchor_118_118"></a><a href="#Footnote_118_118" class="fnanchor">[118]</a> The ordinary assay of a sample of coal involves the
+following determinations&mdash;moisture, volatile matter, fixed carbon, ash,
+and sulphur. These are thus carried out:&mdash;</p>
+
+<p><b>Determination of Moisture.</b>&mdash;Take 3 grams of the powdered sample and
+dry in a water-bath for an hour or so. The loss is reported as moisture.
+Coals carry from 1 to 2 per cent. If the drying is carried too far,
+coals gain a little in weight owing to oxidation, so that it is not
+advisable to extend it over more than one or two hours.</p>
+
+<p><b>Determination of Volatile Matter.</b>&mdash;This determination is an
+approximate one, and it is only when working under the same conditions
+with regard to time, amount of coal taken, and degree of heat used, that
+concordant results can be arrived at. It is a matter of importance
+whether the coal has been previously dried before heating or not, since
+a difference of 2 per cent. may be got by working on the dried or
+undried sample. Take 2 grams of the powdered, but undried, sample of
+coal, place in a weighed platinum crucible, and support this over a good
+Bunsen burner by means of a thin platinum-wire triangle. The heat is
+continued until no further quantity of gas comes off and burns at the
+mouth. This takes only a few minutes. The cover is tightly fitted on,
+and when cold the crucible is weighed. The loss in weight, after
+deducting the moisture, gives the "volatile matter," and the residue
+consists of "fixed carbon" and "ash."</p>
+
+<p><b>Determination of Ash.</b>&mdash;The coke produced in the last operation is
+turned out into a porcelain dish and ignited over a Bunsen burner till
+the residue is free from particles of carbon. Calcination is hastened by
+stirring with a platinum wire. The operation may be done in a muffle,
+but this gives results a few tenths of a per cent. too low. The dish is
+cooled in a dessicator, and weighed. The increase in weight gives the
+amount of "ash," and the difference between this and the weight of the
+coke gives the "fixed carbon."</p>
+
+<p>The assay is reported as follows:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Moisture at 100&deg; C.</td><td align='center'>__</td><td align='center'>per cent.</td></tr>
+<tr><td align='left'>Volatile matter</td><td align='center'>__</td><td align='center'>"</td></tr>
+<tr><td align='left'>Fixed carbon</td><td align='center'>__</td><td align='center'>"</td></tr>
+<tr><td align='left'>Ash</td><td align='center'>__</td><td align='center'>"</td></tr>
+<tr><td align='left'>contains sulphur __ per cent.</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_419" id="Page_419">[Pg 419]</a></span></p>
+
+<p><b>Determination of Sulphur.</b>&mdash;The sulphur exists in the coal partly in
+organic combination, partly as metallic sulphide (iron pyrites,
+marcasite, &amp;c.), and, perhaps, as sulphate. So that the sulphur
+determination must be separately reported, since a portion will go off
+with the volatile matter, and the remainder would be retained and
+weighed with the coke.</p>
+
+<p>The sulphur is thus determined:&mdash;Take 1 gram of the coal and mix with
+1.5 gram of a mixture of 2 parts of calcined magnesia and 1 part of
+carbonate of soda, and heat in a platinum crucible for one hour or until
+oxidation is complete. Turn out the mass and extract it with water and
+bromine, filter, acidulate with hydrochloric acid, boil off the bromine,
+and precipitate with baric chloride (estimating gravimetrically as given
+under <i>Sulphur</i>). Another method is as follows:&mdash;Take 1 gram of the coal
+and drop it gradually from a sheet of note paper on to 5 grams of fused
+nitre contained in a platinum dish. Extract with water, acidify with
+acetic acid, and estimate volumetrically as described under <i>Sulphur</i>.</p>
+
+<div class="figcenter" style="width: 300px;">
+<img src="images/fig073.jpg" width="300" height="450" alt="Fig. 73" title="" />
+
+</div>
+
+<p><b>Calorific Effect of Coals.</b>&mdash;The heat-giving value of a coal is best
+expressed in the number of pounds of water, previously heated to the
+boiling point, which it will convert into steam. This is generally
+termed its evaporative-power. It may be determined by means of the
+calorimeter (fig. 73). This consists of a glass cylinder marked to hold
+29.010 grains of water. The instrument consists of a perforated copper
+stand, provided with a socket and three springs. The socket holds a
+copper cylinder which is charged with 30 grains of the dried coal mixed
+with 300 grains of a mixture of 3 parts of potassium chlorate and 1 part
+of nitre. The charge is well packed in the cylinder and provided with a
+small fuse of cotton saturated with nitre. Fill the glass cylinder to
+its mark with water and take the temperature with a thermometer marked
+in degrees Fahrenheit. Ignite the fuse and immediately cover with the
+outer copper cylinder (extinguisher-fashion), which will be held in its
+place by the springs. The stop-cock should be closed before this is
+done. Place the apparatus quickly in the cylinder of water. When the
+action is over open the stop-cock and agitate the water by raising and
+lowering the instrument a few times. Again take the temperature. The<span class='pagenum'><a name="Page_420" id="Page_420">[Pg 420]</a></span>
+rise in temperature, plus 10 per cent. for the heat used in warming the
+apparatus and lost by radiation, gives the evaporative-power.</p>
+
+<p>The following is an example:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Temperature before experiment</td><td align='left'>67.0&deg;</td><td align='left'>F.</td></tr>
+<tr><td align='left'>Temperature after&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>79.0&deg;</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Rise</td><td align='left'>12.0&deg;</td><td align='left'>"</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;+ 1/10th</td><td align='left'>1.2&deg;</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Gives</td><td align='left'>13.2&deg;</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>One pound of the coal will evaporate 13.2 pounds of water.</p>
+
+
+<h4>SHALES, ETC.</h4>
+
+<p>The assay of these is carried out in the same way as that of coals, but
+the volatile matters are separately examined, and, in consequence, a
+larger quantity of material must be used. For the moisture, volatile
+matter, fixed carbon and ash, the determinations are the same, but a
+special distillation must be made to obtain a sufficient quantity of the
+volatile products for subsequent examination. Take 500 or 1000 grams of
+the well-sampled and powdered shale, and introduce into a cast-iron
+retort as shown in fig. 74. Lute the joint with fire-clay, place the
+cover on, and bolt it down. The bolts should have a covering of
+fire-clay to protect them from the action of the fire. Place the retort
+in a wind furnace, supporting it on a brick, and pack well around with
+coke. Build up the furnace around and over the retort with loose
+fire-bricks, and heat gradually.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig074.jpg" width="450" height="219" alt="Fig. 74." title="" />
+
+</div>
+
+<p>As soon as water begins to drip, the tube of the retort is cooled by
+wrapping a wet cloth around it, and keeping wet with water. The water is
+kept from running into the receiver by a ring of damp fire-clay. A
+quantity of gas first comes over and will be lost, afterwards water and
+oily matters. The retort must be red hot at the close of the
+distillation, and when nothing more distils off, which occurs in about
+two or three hours, the wet cloth is removed, and the tube heated with a
+Bunsen burner to drive<span class='pagenum'><a name="Page_421" id="Page_421">[Pg 421]</a></span> forward the matter condensed in it into the
+receiver, and thus to clean the tube. It can be seen when the tube is
+clean by looking up through it into the red-hot retort. The receiver is
+then removed, and the retort, taken from the furnace, is allowed to
+cool. When cold it is opened, and the fixed carbon and ash weighed, as a
+check on the smaller assay.</p>
+
+<p>The distillate of water and oil is warmed, and will separate into two
+layers, the upper one of which is oil, and the lower water. These are
+measured, and if the specific gravity of the oil is taken, its weight
+may be calculated. If the two liquids do not separate well, the water
+may be filtered off, after cooling, through a damped filter. The
+separation is, however, best effected in a separator (fig. 75). The
+liquids are poured into this, allowed to settle, and the lower layer
+drained off. The volume of the water is measured and its weight
+calculated in per cents. on the amount of shale taken.</p>
+
+<div class="figcenter" style="width: 100px;">
+<img src="images/fig075.jpg" width="100" height="400" alt="Fig. 75." title="" />
+
+</div>
+
+<p><b>Examination of the Oil.</b>&mdash;A sufficient quantity of the oil must be got,
+so that if one distillation does not yield enough, the requisite
+quantity must be obtained by making two or more distillations. The oils
+are mixed, and the mixture, after having had its volume and specific
+gravity ascertained, is placed in a copper retort, and re-distilled with
+the aid of a current of steam. The residue in the retort is coke.</p>
+
+<p>The distillate is separated from the water by means of the separator,
+and shaken for ten minutes with one-twentieth of its bulk of sulphuric
+acid (sp. g. 1.70). The temperature should not be allowed to rise above
+40&deg;. Allow to stand, and run off the "acid tar."</p>
+
+<p>The oil is now shaken up with from 10 c.c. to 20 c.c. of sodic hydrate
+solution (sp. g. 1.3), allowed to stand, warmed for half-an-hour, and
+the "soda-tar" run off.</p>
+
+<p>On mixing this soda-tar with dilute acid, the "crude shale oil creosote"
+separates, and is measured off.</p>
+
+<p>The purified oil is next re-distilled in fractions, which come over in
+the following order:&mdash;"Naphtha," "light oil," "heavy oil," and "still
+bottoms." For the first product, which is only got from certain shales,
+the receiver is changed when the distillate has a specific gravity of
+0.78. For the second product the process is continued till a drop of the
+distillate, caught as it falls from the neck of the retort on a cold
+spatula, shows signs of solidifying. This is "crude light oil."<span class='pagenum'><a name="Page_422" id="Page_422">[Pg 422]</a></span></p>
+
+<p>The receiver is changed, and the "heavy oil" comes over; towards the end
+a thick brown or yellow viscid product is got. The receiver is again
+changed, and the distillation carried to dryness.</p>
+
+<p>The "crude light oil" is washed cold with 2 per cent. of sulphuric acid
+(concentrated), and afterwards with excess of soda. Thus purified it is
+again distilled to dryness, three fractions being collected as before.
+Naphtha, which is added to the main portion, and measured; "light oil,"
+which is also measured; and "heavy oil," which is added to that got in
+the first distillation. This last is poured into a flat-bottom capsule,
+and allowed to cool slowly. The temperature may with advantage be
+carried below freezing-point. The cooled cake is pressed between folds
+of linen, and the paraffin scale detached and weighed.</p>
+
+<p>The results may be reported thus:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Naphtha, sp. g.</td><td align='left'>&mdash;&mdash;</td></tr>
+<tr><td align='left'>Light oil, sp. g.</td><td align='left'>&mdash;&mdash;</td></tr>
+<tr><td align='left'>Heavy oil, sp. g.</td><td align='left'>&mdash;&mdash;</td></tr>
+<tr><td align='left'>Paraffin scale</td><td align='left'>&mdash;&mdash;</td></tr>
+<tr><td align='left'>Coke, &amp;c.</td><td align='left'>&mdash;&mdash;</td></tr>
+</table></div>
+
+<p>The results are calculated in per cents. on the oil taken. Some workers
+take their fractions at each rise of 50&deg; C. The composition of average
+shale, as given by Mills, is as follows:&mdash;Specific gravity, 1.877;
+moisture, 2.54.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Gas</td><td align='left'>}</td></tr>
+<tr><td align='left'>Volatile matter, water, ammonia</td><td align='left'>}</td><td align='left'>23.53</td></tr>
+<tr><td align='left'>Oil</td><td align='left'>}</td></tr>
+<tr><td align='left'>Fixed carbon</td><td align='left'></td><td align='left'>12.69</td></tr>
+<tr><td align='left'>Ash</td><td align='left'></td><td align='left'>63.74</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'>_____</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'>99.96</td></tr>
+</table></div>
+
+
+<p>The ash is made up of silica, 55.6; ferric oxide, 12.2; alumina, 22.14;
+lime, 1.5; sulphur, 0.9; soluble salts (containing 0.92 per cent.
+sulphuric oxide), 8.3.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Total</td><td align='left'>sulphur</td><td align='left'>in shale</td><td align='left'>1.8</td><td align='left'>per cent.</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='left'>in ash</td><td align='left'>1.3</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<p>For further information on these assays, and for the assay of
+petroleums, bitumens, &amp;c., the student is referred to Allen's
+"Commercial Organic Analysis," Vol. II.</p>
+
+<p><b>Determination of Organic Carbon in a Limestone.</b>&mdash;Take 1 or 2 grams and
+dissolve with a very slight excess of dilute hydrochloric acid,
+evaporate to dryness, and determine the carbon in the residue by
+combustion with copper oxide.<span class='pagenum'><a name="Page_423" id="Page_423">[Pg 423]</a></span></p>
+
+<p><b>Estimation of Carbon in a Sample of Graphite (Black-lead).</b>&mdash;Weigh up 1
+or 2 grams in a dish and calcine in the muffle till the carbon is burnt
+off. Weigh the residue, and calculate the carbon by difference.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig076.jpg" width="450" height="86" alt="Fig. 76." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 240px;">
+<img src="images/fig077.jpg" width="240" height="380" alt="Fig. 77." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig078.jpg" width="450" height="202" alt="Fig. 78." title="" />
+
+</div>
+
+<p><b>Determination of Carbon in Iron.</b>&mdash;The carbon exists in two
+states&mdash;free (graphite) and combined. The following process estimates
+the total carbon:&mdash;The carbon existing as graphite may be separately
+estimated in another portion by the same process, but using hydrochloric
+acid to dissolve the iron instead of the copper solution:&mdash;Weigh up 2
+grams of the iron (or a larger quantity if very poor in carbon), and
+attack it with 30 grams of ammonic-cupric chloride<a name="FNanchor_119_119" id="FNanchor_119_119"></a><a href="#Footnote_119_119" class="fnanchor">[119]</a> dissolved in 100
+c.c. of water. Let the reaction proceed for a quarter-of-an-hour, and
+then warm until the copper is dissolved. Allow to settle, and filter
+through a filtering-tube. This is a piece of combustion tube drawn out
+and narrowed at one end, as shown in fig. 76. The narrow part is blocked
+with a pea of baked clay, and on this is placed half-an-inch of silica
+sand (previously calcined to remove organic matter), then a small plug
+of asbestos, and then a quarter-of-an-inch of sand. The tube is
+connected with a pump working at a gentle pressure, and the solution is
+filtered through the tube with the aid of a small funnel (fig. 77). The
+residue is washed, first with dilute hydrochloric acid, and then with
+distilled water. The tube is dried by aspirating air through it, and
+gently warming with a Bunsen burner. The tube is then placed in a small
+combustion-furnace, and connected with calcium chloride and potash
+bulbs, as shown in fig. 78. The<span class='pagenum'><a name="Page_424" id="Page_424">[Pg 424]</a></span> potash bulb to the right of the figure
+must be weighed. A slow stream of air is drawn through the apparatus,
+and the heat gradually raised; in from thirty minutes to one hour the
+combustion will be complete. The potash bulbs are then disconnected and
+weighed, and the increase multiplied by 0.2727 gives the weight of
+carbon.</p>
+
+
+<h4>CARBONATES.</h4>
+
+<p>Carbon dioxide, which is formed by the complete oxidation of carbon, is
+a gas with a sweetish odour and taste, having a strong affinity for
+alkalies, and forming a series of compounds termed carbonates. The gas
+itself occurs in nature, and is sometimes met with in quantity in
+mining. The carbonates occur largely in nature, forming mountain masses
+of limestone, &amp;c. Carbonates of many of the metals, such as carbonate of
+lead (cerussite), carbonate of iron (chalybite), carbonates of copper
+(malachite and chessylite), and carbonate of magnesia (magnesite), are
+common.</p>
+
+<p>All the carbonates (those of the alkalies and alkaline earths excepted)
+are completely decomposed on ignition into the oxide of the metal and
+carbon dioxide; but the temperature required for this decomposition
+varies with the nature of the base. All carbonates are soluble with
+effervescence in dilute acids; some, such as chalybite and magnesite,
+require the aid of heat. The alkaline carbonates are soluble in water;
+the rest, with the exception of the bicarbonates, are insoluble therein.</p>
+
+<p>Carbonates are recognised by their effervescence with acids&mdash;a stream of
+bubbles of gas are given off which collect in the tube, and possess the
+property of extinguishing a lighted match. The most characteristic test
+for the gas is a white precipitate, which is produced by passing it into
+lime or baryta-water, or into a solution of subacetate of lead.</p>
+
+<p>The expulsion of carbon dioxide by the stronger acids serves for the
+separation of this body from the other acids and bases.</p>
+
+<p><b>Dry Assay.</b>&mdash;There is no dry assay in use. Any method which may be
+adopted will necessarily be applicable only to special compounds.</p>
+
+
+<h4>WET METHODS.</h4>
+
+<p>There are several methods in use which leave little to be desired either
+in speed or accuracy. We will give (1) a gravimetric method in which the
+estimation may be made directly by weighing the carbonic acid, or,
+indirectly, by estimating the carbon dioxide from the loss; (2) a
+volumetric one, by which an indirect determination<span class='pagenum'><a name="Page_425" id="Page_425">[Pg 425]</a></span> is made of the gas;
+and (3) a gasometric method, in which the volume of carbon dioxide given
+off is measured, and its weight deducted.</p>
+
+<div class="figcenter" style="width: 450px;">
+<img src="images/fig079.jpg" width="450" height="209" alt="Fig. 79." title="" />
+
+</div>
+
+<div class="figcenter" style="width: 358px;">
+<img src="images/fig080.jpg" width="358" height="300" alt="Fig. 80." title="" />
+
+</div>
+
+<p><b>Direct Gravimetric Method.</b>&mdash;Fit up the apparatus shown in the diagram
+(fig. 79). The various tubes are supported by a fixed rod with nails and
+wire loops, and connected by short lengths of rubber-tubing. The first
+tube contains soda-lime. The small flask is fitted with a rubber-stopper
+perforated with two holes, through one of which passes the tube of a
+pipette holding 25 or 30 c.c. This pipette is to contain the acid. The
+substance to be determined is weighed out into the flask. The second
+tube contains strong sulphuric acid; the third, pumice stone, saturated
+with copper sulphate solution, and dried until nearly white (at 200&deg;
+C.); the fourth contains recently fused calcium chloride; and the fifth,
+which is the weighed tube in which the carbonic acid is absorbed,
+contains calcium chloride and soda-lime,<a name="FNanchor_120_120" id="FNanchor_120_120"></a><a href="#Footnote_120_120" class="fnanchor">[120]</a> as shown in fig. 80. The
+sixth also contains calcium chloride and soda-lime; its object is to
+prevent the access of moisture and carbonic acid to the weighed tube
+from this direction; it is connected with an aspirator.</p>
+
+<p>Having weighed the <b>U</b>-tube and got the apparatus in order, weigh up 1,
+2, or 5 grams of the substance and place in the flask. Fill the pipette
+with dilute acid, close the clamp, and cork the flask. Then see that the
+apparatus is tight. Open the clamp<span class='pagenum'><a name="Page_426" id="Page_426">[Pg 426]</a></span> and allow from 10 to 20 c.c. of the
+acid to run on to the assay. Carbonic acid will be evolved and will be
+driven through the tubes. The gas should bubble through the sulphuric
+acid in a moderate and regular stream. When the effervescence slackens
+the clamp is opened and the greater part of the remaining acid run in.
+When the effervescence has ceased the clamp is opened to its full extent
+and a current of air drawn through with an aspirator. A gentle heat is
+applied to the flask; but it should not be prolonged or carried to
+boiling. After the removal of the heat a gentle current of air is drawn
+through the apparatus for 30 or 40 minutes. The weighed <b>U</b>-tube, which
+in the early part of the operation will have become warm if much
+carbonic acid was present, will by this time be cold. It is
+disconnected, plugged, and weighed. The increase in weight is due to the
+carbon dioxide of the sample.</p>
+
+<p><i>Example.</i>&mdash;Ore taken 1 gram.</p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight</td><td align='left'>of tube,</td><td align='left'>before</td><td align='left'>42.6525</td><td align='left'> grams</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='left'>after</td><td align='left'>43.0940</td><td align='center'>"</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;-</td></tr>
+<tr><td align='left'>Increase</td><td align='left'>equals CO<sub>2</sub></td><td align='left'></td><td align='left'>0.4415</td><td align='center'>"</td></tr>
+</table></div>
+
+
+<div class="figcenter" style="width: 283px;">
+<img src="images/fig081.jpg" width="283" height="430" alt="Fig. 81." title="" />
+
+</div>
+
+<p><b>Indirect Gravimetric, or Determination by Loss.</b>&mdash;Take a Geissler's
+carbonic-acid apparatus (fig. 81) and place in the double bulb some
+strong sulphuric acid. Put into the other bulb, the stopcock being
+closed, 3 or 4 c.c. of nitric acid diluted with water. Leave the
+apparatus in the balance-box for a few minutes and weigh. Introduce into
+the flask (through A) about 1 gram of the powdered substance and again
+weigh to find the exact amount added. Allow the acid to run gradually on
+to the carbonate, and when solution is complete, heat and aspirate. Cool
+and again weigh; the loss in weight is the carbonic acid.</p>
+
+<p>For <i>Example</i>:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight</td><td align='left'>of apparatus</td><td align='left'>and acids</td><td align='left'>85.494</td><td align='left'>grams</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='left'>marble</td><td align='left'>86.879</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Equal</td><td align='left'> to marble taken</td><td align='left'></td><td align='left'>1.385</td><td align='left'>"</td></tr>
+<tr><td align='left'>Weight</td><td align='left'> of apparatus</td><td align='left'>and marble</td><td align='left'>86.879</td><td align='left'>grams</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='left'>minus carbonic acid</td><td align='left'>86.2692</td><td align='left'>"</td></tr>
+<tr><td align='left'></td><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'>Equal</td><td align='left'> to carbonic acid</td><td align='left'></td><td align='left'>0.6098</td><td align='left'>"</td></tr>
+</table></div>
+
+
+
+<p><span style="margin-left: 2.5em;">1.385 : 100 :: 0.6098 : <i>x</i></span><br />
+<span style="margin-left: 12.5em;"><i>x</i> = 44.03 per cent.</span><br /></p>
+
+
+<p><span class='pagenum'><a name="Page_427" id="Page_427">[Pg 427]</a></span></p>
+
+<p>The substance contains 44.03 per cent. of carbonic acid; a duplicate
+experiment gave 43.73 per cent.</p>
+
+<p>This method is quicker, but less exact, than the direct gravimetric
+determination.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This, which is of somewhat limited application, is based upon the
+determination of the quantity of acid required to decompose the
+carbonate. It consists in adding to a weighed quantity of the mineral a
+known amount of standard solution of acid which is in excess of that
+required to effect the decomposition. The quantity of residual acid is
+then determined by titrating with standard solution of alkali. This
+method has been described under <i>Lime</i>.</p>
+
+
+<h4>GASOMETRIC METHOD.</h4>
+
+<p>This method is the quickest of all, and the least troublesome after the
+apparatus has been once prepared. It yields fairly accurate results when
+worked in the manner described below; but if greater precautions are
+taken the results are exact. It depends on the measurement of the volume
+of gas given off on treating the weighed sample with acid. The apparatus
+described, page 52, is used. Weigh out a portion of the mineral which
+shall contain not more than 0.15 gram of carbonic acid (or 0.4 gram of
+carbonate of lime) and put it in the bottle. Put in the inner tube 10
+c.c. of dilute hydrochloric acid (1&mdash;1), cork tightly, and read off the
+level of the liquid in the burette after adjusting the pressure. Turn
+the acid over on to the mineral. Run out the water so as to keep the
+level in the two burettes the same. When effervescence has ceased,
+rotate the contents of the bottle; finally, adjust the level in the
+burettes and read off the volume. The increase in volume is due to the
+evolved carbon dioxide. At the same time read off the "volume
+corrector."</p>
+
+<p>Some of the carbon dioxide remains dissolved in the acid in the
+generating bottle, and the quantity thus dissolved will depend on the
+amount of carbonate as well as on the amount of acid present.
+Consequently, a measured quantity of acid should be used in each assay
+and a comparative experiment made with a known weight of pure carbonate
+of lime which will yield about the same volume of gas. The number of
+c.c. of gas got in the assay multiplied by 4.7 will give the number of
+milligrams of pure carbonate of lime that must be taken for the
+standard. With ordinary work the error rarely exceeds half a c.c.<span class='pagenum'><a name="Page_428" id="Page_428">[Pg 428]</a></span></p>
+
+<p>The following example will illustrate the calculations:&mdash;</p>
+
+<p>One gram of a mineral was taken, and yielded 49.0 c.c. of gas. The
+"volume corrector" reading was 100.4 c.c.</p>
+
+<p>0.2405 gram of pure carbonate of lime was then taken, and treated in the
+same way; 50.5 c.c. of gas were got. The volume corrector still read
+100.4 c.c.</p>
+
+<p>0.2405 gram of carbonate of lime is equivalent to 0.1058 gram of carbon
+dioxide; then,</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>50.5 : 49.0 :: 0.1058 : <i>x</i></td></tr>
+<tr><td align='left'><i>x</i> = 10.26 per cent.</td></tr>
+</table></div>
+
+<p><b>Estimation of Carbonic Acid in the Air of Mines.</b>&mdash;According to a
+series of analyses by Angus Smith, the proportion of carbonic acid in
+the air of underground workings varied from 0.04 to 2.7 per cent. by
+volume. In places where men are working the proportion ought not to
+reach 0.25 per cent.</p>
+
+<p>A simple method of determining whether a sample of air reaches this
+limit (0.25 per cent.) is described by Dr. C. Le Neve Foster in the
+"Proceedings of the Mining Association and Institute of Cornwall" for
+1888. The apparatus used is an ordinary corked 8-ounce medicine bottle.
+This is filled with the air to be examined by sucking out its contents
+with a piece of rubber-tube. Half-an-ounce of dilute lime-water<a name="FNanchor_121_121" id="FNanchor_121_121"></a><a href="#Footnote_121_121" class="fnanchor">[121]</a>
+(tinted with phenolphthalein) is poured in. If, on corking the bottle
+and shaking, the colour is not discharged, the air contains less than
+0.25 per cent. of carbon dioxide. "If the colour fades slowly, and does
+not finally vanish till after a great deal of shaking, it may be assumed
+that the percentage of carbon dioxide does not greatly exceed one
+quarter; whereas, if the disappearance is rapid after a very few shakes,
+the contrary, of course, is the case." The dilute lime-water is measured
+out and carried in ordinary half-ounce phials. This method does not
+pretend to great accuracy, but as a method of distinguishing between
+good and bad air it is very convenient, and will be found useful.</p>
+
+<p>For determining the actual proportion in the air the following plan is
+adopted:&mdash;Take a bottle which will hold about 50 ounces, and measure its
+capacity; fill the bottle with the air to be examined, pour in 100 c.c.
+of lime-water, and shake up for some time; add phenolphthalein, and
+titrate the remaining calcium hydrate with standard solution of oxalic
+acid.</p>
+
+<p>The solution of oxalic acid is made by dissolving 2.25 grams of
+re-crystallised oxalic acid (H<sub>2</sub>C<sub>2</sub>O<sub>4</sub>.2H<sub>2</sub>O) in water and
+diluting to 1 litre. One c.c. = 0.001 gram of lime (CaO), or 0.0007857
+gram of carbon dioxide.<span class='pagenum'><a name="Page_429" id="Page_429">[Pg 429]</a></span></p>
+
+<p>Take 100 c.c. of the same lime-water, to which add the same amount of
+phenolphthalein as before. Titrate. The difference between the two
+readings gives the amount of "acid" equivalent to the lime-water
+neutralised by the carbon dioxide. The number of c.c. thus used up, when
+multiplied by 0.3989, gives the number of c.c. of carbon dioxide (at
+0&deg; C. and 760 mm.) in the volume of air taken. This volume, which is that
+of the bottle less 100 c.c., must in accurate work be reduced to the
+normal temperature and pressure.<a name="FNanchor_122_122" id="FNanchor_122_122"></a><a href="#Footnote_122_122" class="fnanchor">[122]</a> The percentage by volume can then
+be calculated.</p>
+
+
+<h4>PRACTICAL EXERCISES.</h4>
+
+<p>1. In a gasometric determination 71.3 c.c. of gas were obtained from
+0.2055 gram of mineral. The "volume corrector" reading was 102.2 c.c.
+0.3445 gram of pure carbonate of lime gave 74.1 c.c. The "volume
+corrector" reading was 100.6. What is the percentage of carbon dioxide
+in the substance?</p>
+
+<p>2. What volume of dry gas at 0&deg; C. and 760 m.m. pressure should be
+obtained from 0.3445 gram of carbonate of lime? 1 c.c. of CO<sub>2</sub> under
+these conditions weighs 1.97 milligrams.</p>
+
+<p>3. A sample of coal is reported on as follows:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Specific gravity</td><td align='left'>1.315</td></tr>
+<tr><td align='left'>Moisture</td><td align='left'>1.001</td></tr>
+<tr><td align='left'>Volatile matter</td><td align='left'>35.484</td></tr>
+<tr><td align='left'>Fixed carbon</td><td align='left'>50.172</td></tr>
+<tr><td align='left'>Ash</td><td align='left'>12.028</td></tr>
+<tr><td align='left'></td><td align='left'>&mdash;&mdash;&mdash;</td></tr>
+<tr><td align='left'></td><td align='left'>100.000</td></tr>
+</table></div>
+
+
+<p>What is there about this requiring explanation?</p>
+
+<p>4. Calculate the percentage of carbonic acid in a mineral from the
+following data:&mdash;</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Weight</td><td align='left'>of apparatus</td><td align='left'>and acids</td><td align='left'></td><td align='left'>87.0888</td><td align='left'>grams</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>plus mineral</td><td align='left'>88.8858</td><td align='left'>"</td></tr>
+<tr><td align='center'>"</td><td align='center'>"</td><td align='center'>"</td><td align='left'>after loss of carbonic acid</td><td align='left'>88.1000</td><td align='left'>"</td></tr>
+</table></div>
+
+
+<p>5. A sample of pig iron contains 1.43 per cent. of "combined" and 2.02
+per cent. of "free" carbon. Taking 2 grams of it for each determination,
+what weight of CO<sub>2</sub> will be got on burning the residue from solution
+in ammonium cupric chloride, and what from the residue after solution in
+hydrochloric acid?</p>
+
+
+<h4>BORON AND BORATES.</h4>
+
+<p>Boron occurs in nature as boric acid or sassoline (H<sub>3</sub>BO<sub>3</sub>); borax
+or tincal (Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>.10H<sub>2</sub>O); ulexite or boronatrocalcite
+(2CaB<sub>4</sub>O<sub>7</sub>.Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>); borocalcite (CaB<sub>4</sub>O<sub>7</sub>.4H<sub>2</sub>O);
+boracite, 2Mg<sub>3</sub>B<sub>8</sub>O<sub>15</sub>.MgCl<sub>2</sub>, and some other minerals. Boric
+acid is also a<span class='pagenum'><a name="Page_430" id="Page_430">[Pg 430]</a></span> constituent of certain silicates, such as tourmaline,
+axinite, and datholite.</p>
+
+<p>The natural borates are used in the preparation of borax, which is
+largely employed as a preservative agent, for fluxing, and for other
+purposes.</p>
+
+<p>There is only one series of boron compounds which have any importance.
+These are the borates in which the trioxide (B<sub>2</sub>O<sub>3</sub>) acts the part
+of a weak acid. The addition of any acid liberates boric acid, which
+separates out in cold solutions as a crystalline precipitate. Boric acid
+is soluble in alcohol and in hot water. On evaporating these solutions
+it is volatilised, although the anhydrous oxide is "fixed" at a red
+heat. The borates are mostly fusible compounds, and are soluble in acids
+and in solutions of ammonic salts.</p>
+
+<p><b>Detection.</b>&mdash;Boron in small quantities will escape detection unless
+specially looked for, but there is no difficulty in detecting its
+presence. Heated in the Bunsen-burner flame with "Turner's test," it
+gives an evanescent yellowish-green colour, due to fluoride of boron
+(BF<sub>3</sub>). "Turner's test" is a mixture of 5 parts of bisulphate of
+potash and 1 part of fluor spar. Boric acid itself imparts a
+characteristic green colour to the flame, which gives a spectrum made up
+of four well-marked and equidistant lines, three in the green and one in
+the blue. Solutions of boric acid give with "turmeric paper," which has
+been dipped into it and dried, a characteristic red tint. This is a very
+delicate test, but in trying it a blank experiment should be carried out
+alongside with a solution made up of the same re-agents which have been
+used in liberating the boric acid in the sample.</p>
+
+<p><b>Solution and Separation.</b>&mdash;The solution presents no difficulty, but the
+separation is troublesome. The best method is that of Gooch; who, if
+necessary, first fuses with carbonate of soda, and after the removal of
+chlorides and fluorides (by nitrate of silver or a lime salt),
+evaporates the aqueous extract with nitric or acetic acid to dryness in
+a retort and, subsequently, with repeated doses of 10 c.c. each of
+methyl alcohol. The distillate contains the boron as boric acid. Half a
+gram of the trioxide (B<sub>2</sub>O<sub>3</sub>) is completely carried over by two
+evaporations, each with 10 c.c. of the alcohol; but if water or foreign
+salts are present, more than this is required. In ordinary cases six
+such evaporations are sufficient for 0.2 gram of the oxide.<a name="FNanchor_123_123" id="FNanchor_123_123"></a><a href="#Footnote_123_123" class="fnanchor">[123]</a></p>
+
+<p><span class='pagenum'><a name="Page_431" id="Page_431">[Pg 431]</a></span></p>
+<h4>GRAVIMETRIC DETERMINATION.</h4>
+
+<p>Before the introduction of Gooch's process it was usual to determine the
+boron trioxide "by difference." If the alcoholic distillate containing
+the boric acid is digested with about 1 gram (a known weight) of lime
+for ten or fifteen minutes, the alcohol can be evaporated off without
+danger of loss. Either calcium nitrate or acetate (which will be formed
+at the same time) yields lime upon subsequent ignition. Consequently,
+the increase in weight, after ignition, upon that of the lime taken
+gives the amount of boron trioxide present. The trioxide contains 31.4
+per cent. of boron (B). Since magnesia does not form a soluble hydrate
+it cannot satisfactorily be used instead of lime.</p>
+
+<div class="figcenter" style="width: 275px;">
+<img src="images/fig082.jpg" width="275" height="400" alt="Fig. 82." title="" />
+
+</div>
+
+<p>The apparatus required is shown in fig. 82. It consists of a small
+retort or evaporating vessel made out of a pipette of 200 c.c. capacity.
+This is heated by means of a paraffin-bath at 130&deg; or 140&deg; C. It is
+connected with an upright condenser, at the lower end of which is a
+small flask which serves as a receiver.</p>
+
+<p>The quantity of the borate taken should contain not more than 0.2 gram
+of the trioxide. Insoluble compounds are "dissolved in nitric acid at
+once, or, if necessary, first fused with sodium carbonate." With soluble
+and alkaline borates sufficient nitric acid is added to render it
+faintly acid. The solution is then introduced into the retort.</p>
+
+<p>"The lime, to retain the boric acid in the distillate, is ignited in the
+crucible in which the evaporation of the distillate is to be made
+subsequently." It is then cooled in the desiccator for ten minutes, and
+weighed. The lime is transferred to the receiving flask and slaked with
+a little water. The retort is lowered into the bath so that "only the
+rear dips below the surface." The<span class='pagenum'><a name="Page_432" id="Page_432">[Pg 432]</a></span> evaporation is carried to dryness,
+the retort being lowered further into the bath as the evaporation
+proceeds. Ten c.c. of methyl alcohol are introduced upon the residue,
+and the evaporation again started. Six such portions of alcohol are thus
+distilled and 2 c.c. of water are introduced and evaporated between the
+second and third, as also between the fourth and fifth distillations. If
+acetic acid is used instead of nitric in the first instance this
+addition of water is unnecessary.</p>
+
+<p>The distillate is evaporated in the crucible ignited over the blowpipe,
+cooled in the desiccator for ten minutes and weighed. The increase in
+weight gives the boron trioxide. The results tend to be from 1 to 2
+milligrams too high.</p>
+
+
+<h4>VOLUMETRIC METHOD.</h4>
+
+<p>This method is applicable to the indirect determination of boric acid in
+borax and similar compounds. It is based on the measurement of the
+quantity of normal solution of acid required to replace the boric acid,
+and, consequently, is rather a measure of the soda present. The process
+is an alkalimetric one, and is carried out as follows:&mdash;Weigh up 3 grams
+of the sample and dissolve in water. Tint with methyl orange, and run in
+from an ordinary burette normal solution of sulphuric acid until a pink
+tint is got. 100 c.c. of the normal solution of acid are equal to 7.0
+grams of boron trioxide (B<sub>2</sub>O<sub>3</sub>), or 10.1 grams of anhydrous borax
+(Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub>).</p>
+
+<p><b>Examination of Borax.</b>&mdash;In addition to the determination just given,
+the following determinations are also required:&mdash;</p>
+
+<p><b>Water.</b>&mdash;Take about 2 grams and heat to tranquil fusion in a platinum
+crucible. Count the loss in weight as water.</p>
+
+<p><b>Sulphuric Oxide.</b>&mdash;Take 2 grams, dissolve in water, acidify with
+hydrochloric acid, filter, and precipitate with barium chloride. Wash
+the precipitate, ignite, and weigh as barium sulphate (see <i>Sulphur</i>).</p>
+
+<p><b>Chlorine.</b>&mdash;Take 2 grams, dissolve in water, acidify with nitric acid,
+filter, and add silver nitrate. Collect, wash, and weigh the precipitate
+as silver chloride.</p>
+
+<p><b>Alumina.</b>&mdash;Take 5 or 10 grams, dissolve in water, boil, add ammonia in
+slight excess, and filter off the precipitate when it has settled. Wash
+with hot water, ignite, and weigh as alumina (Al<sub>2</sub>O<sub>3</sub>).</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_113_113" id="Footnote_113_113"></a><a href="#FNanchor_113_113"><span class="label">[113]</span></a> If the dishes show a manganese stain, wash them out with
+a few drops of hydrochloric and sulphurous acids. Pass the acid liquor
+through the same small filter but collect the liquor apart. Make
+ammoniacal and again pass through the filter, this time collecting the
+liquid with the main filtrate.</p></div>
+
+<div class="footnote"><p><a name="Footnote_114_114" id="Footnote_114_114"></a><a href="#FNanchor_114_114"><span class="label">[114]</span></a> This rarely amounts to more than 1 milligram.</p></div>
+
+<div class="footnote"><p><a name="Footnote_115_115" id="Footnote_115_115"></a><a href="#FNanchor_115_115"><span class="label">[115]</span></a> To make this, dissolve 1 gram of titanium oxide by fusing
+for some time with an excess of bisulphate of potash and dissolve out
+with cold water and sulphuric acid. Dilute to 1 litre, having previously
+added not less than 50 c.c. of strong sulphuric acid: 1 c.c. will
+contain .01 gram of TiO<sub>2</sub>. For the assay take 10 c.c. of this, add 2
+c.c. of peroxide of hydrogen and dilute to 100 c.c. Run this from a
+burette into the flask until the colour equals that of the assay. Each
+c.c. equals 1 milligram of TiO<sub>2</sub>. Fluorides must be absent.</p></div>
+
+<div class="footnote"><p><a name="Footnote_116_116" id="Footnote_116_116"></a><a href="#FNanchor_116_116"><span class="label">[116]</span></a> C + O<sub>2</sub> = CO<sub>2</sub></p></div>
+
+<div class="footnote"><p><a name="Footnote_117_117" id="Footnote_117_117"></a><a href="#FNanchor_117_117"><span class="label">[117]</span></a> For example, soluble organic acids formed by partial
+oxidation with nitric acid.</p></div>
+
+<div class="footnote"><p><a name="Footnote_118_118" id="Footnote_118_118"></a><a href="#FNanchor_118_118"><span class="label">[118]</span></a> For coals, and other bodies containing sulphur, chromate
+of lead should be used instead of oxide of copper; and the temperature
+should be limited to dull redness.</p></div>
+
+<div class="footnote"><p><a name="Footnote_119_119" id="Footnote_119_119"></a><a href="#FNanchor_119_119"><span class="label">[119]</span></a> This may be prepared by dissolving 534 grams of ammonium
+chloride and 854 grams of crystallized cupric chloride
+(CuCl<sub>2</sub>.2H<sub>2</sub>O) in hot water and crystallizing.</p></div>
+
+<div class="footnote"><p><a name="Footnote_120_120" id="Footnote_120_120"></a><a href="#FNanchor_120_120"><span class="label">[120]</span></a> Soda-lime is made by dissolving 100 grams of "soda" in
+water, and carefully slaking 200 grams of lime with it. Evaporate to
+dryness in an iron dish and ignite at a low red heat in a crucible. Use
+the small lumps.</p></div>
+
+<div class="footnote"><p><a name="Footnote_121_121" id="Footnote_121_121"></a><a href="#FNanchor_121_121"><span class="label">[121]</span></a> Made by diluting 1 part by measure of saturated
+lime-water up to 10 with recently boiled distilled water.</p></div>
+
+<div class="footnote"><p><a name="Footnote_122_122" id="Footnote_122_122"></a><a href="#FNanchor_122_122"><span class="label">[122]</span></a> See under <i>Gasometric Assays</i>.</p></div>
+
+<div class="footnote"><p><a name="Footnote_123_123" id="Footnote_123_123"></a><a href="#FNanchor_123_123"><span class="label">[123]</span></a> See "A Method for the Separation and Estimation of Boric
+Acid," by F.A. Gooch, <i>Chemical News</i>, January 7, 1887.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_433" id="Page_433">[Pg 433]</a></span></p>
+<h2><a name="APPENDIX_A" id="APPENDIX_A"></a>APPENDIX A.</h2>
+
+<h4><span class="smcap">Table of Atomic Weights and other Constants.</span></h4>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'> Symbols.</td><td align='center'>Names.</td><td align='center'>Atomic Weights.</td><td align='center'>Specific Gravity.</td><td align='center'>Melting Points. C.</td></tr>
+<tr><td align='center'>Ag</td><td align='center'>Silver</td><td align='right'>107.9</td><td align='right'>10.5</td><td align='right'>1000&deg;</td></tr>
+<tr><td align='center'>Al</td><td align='center'>Aluminium</td><td align='right'>27.0</td><td align='right'>2.7</td><td align='right'>700&deg;</td></tr>
+<tr><td align='center'>As</td><td align='center'>Arsenic</td><td align='right'>75.0</td><td align='right'>5.9</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Au</td><td align='center'>Gold</td><td align='right'>197.3</td><td align='right'>19.2</td><td align='right'>1200&deg;</td></tr>
+<tr><td align='center'>B</td><td align='center'>Boron</td><td align='right'>11.0</td><td align='right'>2.7</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ba</td><td align='center'>Barium</td><td align='right'>137.0</td><td align='right'>4.0</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Be</td><td align='center'>Beryllium</td><td align='right'>9.0</td><td align='right'>2.1</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Bi</td><td align='center'>Bismuth</td><td align='right'>208.9</td><td align='right'>9.8</td><td align='right'>270&deg;</td></tr>
+<tr><td align='center'>Br</td><td align='center'>Bromine</td><td align='right'>80.0</td><td align='right'>3.2</td><td align='right'>-25&deg;</td></tr>
+<tr><td align='center'>C</td><td align='center'>Carbon</td><td align='right'>12.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ca</td><td align='left'>Calcium</td><td align='right'>40.0</td><td align='right'>1.6</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Cd</td><td align='center'>Cadmium</td><td align='right'>112.0</td><td align='right'>8.6</td><td align='right'>315&deg;</td></tr>
+<tr><td align='center'>Ce</td><td align='center'>Cerium</td><td align='right'>140.2</td><td align='right'>6.7</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Cl</td><td align='center'>Chlorine</td><td align='right'>35.5</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Co</td><td align='center'>Cobalt</td><td align='right'>59.0</td><td align='right'>8.5</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Cr</td><td align='center'>Chromium</td><td align='right'>52.1</td><td align='right'>7.3</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Cs</td><td align='center'>Caesium</td><td align='right'>132.9</td><td align='right'>1.9</td><td align='right'>25&deg;</td></tr>
+<tr><td align='center'>Cu</td><td align='center'>Copper</td><td align='right'>63.4</td><td align='right'>8.9</td><td align='right'>1090&deg;</td></tr>
+<tr><td align='center'>Di</td><td align='center'>Didymium</td><td align='right'>142.3</td><td align='right'>6.5</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Er</td><td align='center'>Erbium</td><td align='right'>166.3</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>F</td><td align='center'>Fluorine</td><td align='right'>19.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Fe</td><td align='center'>Iron</td><td align='right'>56.0</td><td align='right'>7.8</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ga</td><td align='center'>Gallium</td><td align='right'>69.0</td><td align='right'>5.9</td><td align='right'>30&deg;</td></tr>
+<tr><td align='center'>Ge</td><td align='center'>Germanium</td><td align='right'>72.3</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>H</td><td align='center'>Hydrogen</td><td align='right'>1.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Hg</td><td align='center'>Mercury</td><td align='right'>200.0</td><td align='right'>13.6</td><td align='right'>-40&deg;</td></tr>
+<tr><td align='center'>I</td><td align='center'>Iodine</td><td align='right'>126.8</td><td align='right'>4.9</td><td align='right'>106&deg;</td></tr>
+<tr><td align='center'>In</td><td align='center'>Indium</td><td align='right'>113.7</td><td align='right'>7.4</td><td align='right'>175&deg;</td></tr>
+<tr><td align='center'>Ir</td><td align='center'>Iridium</td><td align='right'>193.1</td><td align='right'>22.4</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>K</td><td align='center'>Potassium</td><td align='right'>39.1</td><td align='right'>0.86</td><td align='right'>62.5&deg;</td></tr>
+<tr><td align='center'>La</td><td align='center'>Lanthanum</td><td align='right'>138.2</td><td align='right'>6.1</td><td align='right'>&nbsp;</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_434" id="Page_434">[Pg 434]</a></span></p>
+
+
+<h4><span class="smcap">Table of Atomic Weights and other Constants.</span>&mdash;<i>continued.</i></h4>
+
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>Symbols.</td><td align='center'>Names.</td><td align='center'>Atomic Weights.</td><td align='center'>Specific Gravity.</td><td align='center'>Melting Points. C.</td></tr>
+<tr><td align='center'>Li</td><td align='center'>Lithium</td><td align='right'>7.0</td><td align='right'>0.59</td><td align='right'>180&deg;</td></tr>
+<tr><td align='center'>Mg</td><td align='center'>Magnesium</td><td align='right'>24.3</td><td align='right'>1.7</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Mn</td><td align='center'>Manganese</td><td align='right'>55.0</td><td align='right'>8.0</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Mo</td><td align='center'>Molybdenum</td><td align='right'>96.0</td><td align='right'>8.6</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>N</td><td align='center'>Nitrogen</td><td align='right'>14.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Na</td><td align='center'>Sodium</td><td align='right'>23.0</td><td align='right'>0.97</td><td align='right'>95.6&deg;</td></tr>
+<tr><td align='center'>Nb</td><td align='center'>Niobium</td><td align='right'>94.0</td><td align='right'>4.1</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ni</td><td align='center'>Nickel</td><td align='right'>58.7</td><td align='right'>8.9</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>O</td><td align='center'>Oxygen</td><td align='right'>16.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Os</td><td align='center'>Osmium</td><td align='right'>191.7</td><td align='right'>22.4</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>P</td><td align='center'>Phosphorus</td><td align='right'>31.0</td><td align='right'>1.8</td><td align='right'>44&deg;</td></tr>
+<tr><td align='center'>Pb</td><td align='center'>Lead</td><td align='right'>206.9</td><td align='right'>11.4</td><td align='right'>334&deg;</td></tr>
+<tr><td align='center'>Pd</td><td align='center'>Palladium</td><td align='right'>106.6</td><td align='right'>11.4</td><td align='right'>1350&deg;</td></tr>
+<tr><td align='center'>Pt</td><td align='center'>Platinum</td><td align='right'>195.0</td><td align='right'>21.5</td><td align='right'>2000&deg;</td></tr>
+<tr><td align='center'>Rb</td><td align='center'>Rubidium</td><td align='right'>85.5</td><td align='right'>1.5</td><td align='right'>38.5&deg;</td></tr>
+<tr><td align='center'>Rh</td><td align='center'>Rhodium</td><td align='right'>103.5</td><td align='right'>12.1</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ru</td><td align='center'>Ruthenium</td><td align='right'>101.6</td><td align='right'>11.4</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>S</td><td align='center'>Sulphur</td><td align='right'>32.0</td><td align='right'>2.0</td><td align='right'>115&deg;</td></tr>
+<tr><td align='center'>Sb</td><td align='center'>Antimony</td><td align='right'>120.0</td><td align='right'>6.7</td><td align='right'>425&deg;</td></tr>
+<tr><td align='center'>Se</td><td align='center'>Selenium</td><td align='right'>79.0</td><td align='right'>4.8</td><td align='right'>100&deg;</td></tr>
+<tr><td align='center'>Si</td><td align='center'>Silicon</td><td align='right'>28.4</td><td align='right'>2.0</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Sn</td><td align='center'>Tin</td><td align='right'>119.0</td><td align='right'>7.3</td><td align='right'>235&deg;</td></tr>
+<tr><td align='center'>Sr</td><td align='center'>Strontium</td><td align='right'>87.6</td><td align='right'>2.5</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ta</td><td align='center'>Tantalum</td><td align='right'>182.6</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Te</td><td align='center'>Tellurium</td><td align='right'>125.0</td><td align='right'>6.2</td><td align='right'>480&deg;</td></tr>
+<tr><td align='center'>Th</td><td align='center'>Thorium</td><td align='right'>232.6</td><td align='right'>7.8</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Ti</td><td align='center'>Titanium</td><td align='right'>48.0</td><td align='right'>5.3</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Tl</td><td align='center'>Thallium</td><td align='right'>204.2</td><td align='right'>11.9</td><td align='right'>294&deg;</td></tr>
+<tr><td align='center'>U</td><td align='center'>Uranium</td><td align='right'>239.6</td><td align='right'>18.4</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>V</td><td align='center'>Vanadium</td><td align='right'>51.4</td><td align='right'>5.5</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>W</td><td align='center'>Tungsten</td><td align='right'>184.0</td><td align='right'>19.1</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Y</td><td align='center'>Yttrium</td><td align='right'>89.1</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Yb</td><td align='center'>Ytterbium</td><td align='right'>173.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+<tr><td align='center'>Zn</td><td align='center'>Zinc</td><td align='right'>65.3</td><td align='right'>6.9</td><td align='right'>423&deg;</td></tr>
+<tr><td align='center'>Zr</td><td align='center'>Zirconium</td><td align='right'>90.6</td><td align='right'>4.1</td><td align='right'>&nbsp;</td></tr>
+</table></div>
+
+
+<p>The atomic weights in this table are in accord with the numbers given by
+F.W. Clarke (Dec. 6, 1890), chief chemist of the United States
+Geological Survey.<span class='pagenum'><a name="Page_435" id="Page_435">[Pg 435]</a></span></p>
+
+<div class="figcenter" style="width: 400px;">
+<img src="images/ctoftable-appendixa.jpg" width="400" height="471" alt="Table for Converting Degrees of the Centigrade
+Thermometer into Degrees of Fahrenheit&#39;s Scale." title="" />
+<span class="caption">Table for Converting Degrees of the Centigrade
+Thermometer into Degrees of Fahrenheit&#39;s Scale.</span>
+</div>
+
+<p><span class='pagenum'><a name="Page_436" id="Page_436">[Pg 436]</a></span></p>
+
+
+<p>Nitric Acid.</p>
+
+<p><i>Table showing the percentage, by Weight, of Real Acid</i> (HNO<sub>3</sub>) <i>in
+Aqueous Solutions of Nitric Acid of different Specific Gravities.
+Temperature</i>, 15&deg; C.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.530</td><td align='left'>100.0</td><td align='right'>&nbsp;</td><td align='left'>1.405</td><td align='left'>66.0</td><td align='right'>&nbsp;</td><td align='left'>1.205</td><td align='left'>33.0</td></tr>
+<tr><td align='left'>1.527</td><td align='left'>99.0</td><td align='right'>&nbsp;</td><td align='left'>1.400</td><td align='left'>65.0</td><td align='right'>&nbsp;</td><td align='left'>1.198</td><td align='left'>32.0</td></tr>
+<tr><td align='left'>1.524</td><td align='left'>98.0</td><td align='right'>&nbsp;</td><td align='left'>1.395</td><td align='left'>64.0</td><td align='right'>&nbsp;</td><td align='left'>1.192</td><td align='left'>31.0</td></tr>
+<tr><td align='left'>1.520</td><td align='left'>97.0</td><td align='right'>&nbsp;</td><td align='left'>1.390</td><td align='left'>63.0</td><td align='right'>&nbsp;</td><td align='left'>1.185</td><td align='left'>30.0</td></tr>
+<tr><td align='left'>1.516</td><td align='left'>96.0</td><td align='right'>&nbsp;</td><td align='left'>1.386</td><td align='left'>62.0</td><td align='right'>&nbsp;</td><td align='left'>1.179</td><td align='left'>29.0</td></tr>
+<tr><td align='left'>1.513</td><td align='left'>95.0</td><td align='right'>&nbsp;</td><td align='left'>1.380</td><td align='left'>61.0</td><td align='right'>&nbsp;</td><td align='left'>1.172</td><td align='left'>28.0</td></tr>
+<tr><td align='left'>1.509</td><td align='left'>94.0</td><td align='right'>&nbsp;</td><td align='left'>1.374</td><td align='left'>60.0</td><td align='right'>&nbsp;</td><td align='left'>1.166</td><td align='left'>27.0</td></tr>
+<tr><td align='left'>1.506</td><td align='left'>93.0</td><td align='right'>&nbsp;</td><td align='left'>1.368</td><td align='left'>59.0</td><td align='right'>&nbsp;</td><td align='left'>1.159</td><td align='left'>26.0</td></tr>
+<tr><td align='left'>1.503</td><td align='left'>92.0</td><td align='right'>&nbsp;</td><td align='left'>1.363</td><td align='left'>58.0</td><td align='right'>&nbsp;</td><td align='left'>1.152</td><td align='left'>25.0</td></tr>
+<tr><td align='left'>1.499</td><td align='left'>91.0</td><td align='right'>&nbsp;</td><td align='left'>1.358</td><td align='left'>57.0</td><td align='right'>&nbsp;</td><td align='left'>1.145</td><td align='left'>24.0</td></tr>
+<tr><td align='left'>1.495</td><td align='left'>90.0</td><td align='right'>&nbsp;</td><td align='left'>1.353</td><td align='left'>56.0</td><td align='right'>&nbsp;</td><td align='left'>1.138</td><td align='left'>23.0</td></tr>
+<tr><td align='left'>1.492</td><td align='left'>89.0</td><td align='right'>&nbsp;</td><td align='left'>1.346</td><td align='left'>55.0</td><td align='right'>&nbsp;</td><td align='left'>1.132</td><td align='left'>22.0</td></tr>
+<tr><td align='left'>1.488</td><td align='left'>88.0</td><td align='right'>&nbsp;</td><td align='left'>1.341</td><td align='left'>54.0</td><td align='right'>&nbsp;</td><td align='left'>1.126</td><td align='left'>21.0</td></tr>
+<tr><td align='left'>1.485</td><td align='left'>87.0</td><td align='right'>&nbsp;</td><td align='left'>1.335</td><td align='left'>53.0</td><td align='right'>&nbsp;</td><td align='left'>1.120</td><td align='left'>20.0</td></tr>
+<tr><td align='left'>1.482</td><td align='left'>86.0</td><td align='right'>&nbsp;</td><td align='left'>1.329</td><td align='left'>52.0</td><td align='right'>&nbsp;</td><td align='left'>1.114</td><td align='left'>19.0</td></tr>
+<tr><td align='left'>1.478</td><td align='left'>85.0</td><td align='right'>&nbsp;</td><td align='left'>1.323</td><td align='left'>51.0</td><td align='right'>&nbsp;</td><td align='left'>1.108</td><td align='left'>18.0</td></tr>
+<tr><td align='left'>1.474</td><td align='left'>84.0</td><td align='right'>&nbsp;</td><td align='left'>1.317</td><td align='left'>50.0</td><td align='right'>&nbsp;</td><td align='left'>1.102</td><td align='left'>17.0</td></tr>
+<tr><td align='left'>1.470</td><td align='left'>83.0</td><td align='right'>&nbsp;</td><td align='left'>1.311</td><td align='left'>49.0</td><td align='right'>&nbsp;</td><td align='left'>1.096</td><td align='left'>16.0</td></tr>
+<tr><td align='left'>1.467</td><td align='left'>82.0</td><td align='right'>&nbsp;</td><td align='left'>1.304</td><td align='left'>48.0</td><td align='right'>&nbsp;</td><td align='left'>1.089</td><td align='left'>15.0</td></tr>
+<tr><td align='left'>1.463</td><td align='left'>81.0</td><td align='right'>&nbsp;</td><td align='left'>1.298</td><td align='left'>47.0</td><td align='right'>&nbsp;</td><td align='left'>1.083</td><td align='left'>14.0</td></tr>
+<tr><td align='left'>1.460</td><td align='left'>80.0</td><td align='right'>&nbsp;</td><td align='left'>1.291</td><td align='left'>46.0</td><td align='right'>&nbsp;</td><td align='left'>1.077</td><td align='left'>13.0</td></tr>
+<tr><td align='left'>1.456</td><td align='left'>79.0</td><td align='right'>&nbsp;</td><td align='left'>1.284</td><td align='left'>45.0</td><td align='right'>&nbsp;</td><td align='left'>1.071</td><td align='left'>12.0</td></tr>
+<tr><td align='left'>1.452</td><td align='left'>78.0</td><td align='right'>&nbsp;</td><td align='left'>1.277</td><td align='left'>44.0</td><td align='right'>&nbsp;</td><td align='left'>1.065</td><td align='left'>11.0</td></tr>
+<tr><td align='left'>1.449</td><td align='left'>77.0</td><td align='right'>&nbsp;</td><td align='left'>1.270</td><td align='left'>43.0</td><td align='right'>&nbsp;</td><td align='left'>1.060</td><td align='left'>10.0</td></tr>
+<tr><td align='left'>1.445</td><td align='left'>76.0</td><td align='right'>&nbsp;</td><td align='left'>1.264</td><td align='left'>42.0</td><td align='right'>&nbsp;</td><td align='left'>1.053</td><td align='left'>9.0</td></tr>
+<tr><td align='left'>1.442</td><td align='left'>75.0</td><td align='right'>&nbsp;</td><td align='left'>1.257</td><td align='left'>41.0</td><td align='right'>&nbsp;</td><td align='left'>1.047</td><td align='left'>8.0</td></tr>
+<tr><td align='left'>1.438</td><td align='left'>74.0</td><td align='right'>&nbsp;</td><td align='left'>1.251</td><td align='left'>40.0</td><td align='right'>&nbsp;</td><td align='left'>1.041</td><td align='left'>7.0</td></tr>
+<tr><td align='left'>1.435</td><td align='left'>73.0</td><td align='right'>&nbsp;</td><td align='left'>1.244</td><td align='left'>39.0</td><td align='right'>&nbsp;</td><td align='left'>1.034</td><td align='left'>6.0</td></tr>
+<tr><td align='left'>1.431</td><td align='left'>72.0</td><td align='right'>&nbsp;</td><td align='left'>1.238</td><td align='left'>38.0</td><td align='right'>&nbsp;</td><td align='left'>1.028</td><td align='left'>5.0</td></tr>
+<tr><td align='left'>1.427</td><td align='left'>71.0</td><td align='right'>&nbsp;</td><td align='left'>1.232</td><td align='left'>37.0</td><td align='right'>&nbsp;</td><td align='left'>1.022</td><td align='left'>4.0</td></tr>
+<tr><td align='left'>1.423</td><td align='left'>70.0</td><td align='right'>&nbsp;</td><td align='left'>1.225</td><td align='left'>36.0</td><td align='right'>&nbsp;</td><td align='left'>1.016</td><td align='left'>3.0</td></tr>
+<tr><td align='left'>1.418</td><td align='left'>69.0</td><td align='right'>&nbsp;</td><td align='left'>1.218</td><td align='left'>35.0</td><td align='right'>&nbsp;</td><td align='left'>1.010</td><td align='left'>2.0</td></tr>
+<tr><td align='left'>1.414</td><td align='left'>68.0</td><td align='right'>&nbsp;</td><td align='left'>1.212</td><td align='left'>34.0</td><td align='right'>&nbsp;</td><td align='left'>1.004</td><td align='left'>1.0</td></tr>
+<tr><td align='left'>1.410</td><td align='left'>67.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_437" id="Page_437">[Pg 437]</a></span></p>
+
+
+<h4><span class="smcap">Hydrochloric Acid.</span></h4>
+
+<p><i>Table showing the percentage, by Weight, of Real Acid</i> (HCl) <i>in
+Aqueous Solutions of Hydrochloric Acid of different Specific Gravities.
+Temperature</i>, 15&deg; C.</p>
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.2000</td><td align='left'>40.78</td><td align='right'>&nbsp;</td><td align='left'>1.1410</td><td align='left'>28.54</td><td align='right'>&nbsp;</td><td align='left'>1.0798</td><td align='left'>16.31</td></tr>
+<tr><td align='left'>1.1982</td><td align='left'>40.37</td><td align='right'>&nbsp;</td><td align='left'>1.1389</td><td align='left'>28.13</td><td align='right'>&nbsp;</td><td align='left'>1.0778</td><td align='left'>15.90</td></tr>
+<tr><td align='left'>1.1964</td><td align='left'>39.96</td><td align='right'>&nbsp;</td><td align='left'>1.1369</td><td align='left'>27.72</td><td align='right'>&nbsp;</td><td align='left'>1.0758</td><td align='left'>15.49</td></tr>
+<tr><td align='left'>1.1946</td><td align='left'>39.55</td><td align='right'>&nbsp;</td><td align='left'>1.1349</td><td align='left'>27.32</td><td align='right'>&nbsp;</td><td align='left'>1.0738</td><td align='left'>15.08</td></tr>
+<tr><td align='left'>1.1928</td><td align='left'>39.14</td><td align='right'>&nbsp;</td><td align='left'>1.1328</td><td align='left'>26.91</td><td align='right'>&nbsp;</td><td align='left'>1.0718</td><td align='left'>14.68</td></tr>
+<tr><td align='left'>1.1910</td><td align='left'>38.74</td><td align='right'>&nbsp;</td><td align='left'>1.1308</td><td align='left'>26.50</td><td align='right'>&nbsp;</td><td align='left'>1.0697</td><td align='left'>14.27</td></tr>
+<tr><td align='left'>1.1893</td><td align='left'>38.33</td><td align='right'>&nbsp;</td><td align='left'>1.1287</td><td align='left'>26.10</td><td align='right'>&nbsp;</td><td align='left'>1.0677</td><td align='left'>13.86</td></tr>
+<tr><td align='left'>1.1875</td><td align='left'>37.92</td><td align='right'>&nbsp;</td><td align='left'>1.1267</td><td align='left'>25.69</td><td align='right'>&nbsp;</td><td align='left'>1.0657</td><td align='left'>13.45</td></tr>
+<tr><td align='left'>1.1857</td><td align='left'>37.51</td><td align='right'>&nbsp;</td><td align='left'>1.1247</td><td align='left'>25.28</td><td align='right'>&nbsp;</td><td align='left'>1.0637</td><td align='left'>13.05</td></tr>
+<tr><td align='left'>1.1846</td><td align='left'>37.11</td><td align='right'>&nbsp;</td><td align='left'>1.1226</td><td align='left'>24.87</td><td align='right'>&nbsp;</td><td align='left'>1.0617</td><td align='left'>12.64</td></tr>
+<tr><td align='left'>1.1822</td><td align='left'>36.70</td><td align='right'>&nbsp;</td><td align='left'>1.1206</td><td align='left'>24.46</td><td align='right'>&nbsp;</td><td align='left'>1.0597</td><td align='left'>12.23</td></tr>
+<tr><td align='left'>1.1802</td><td align='left'>36.29</td><td align='right'>&nbsp;</td><td align='left'>1.1185</td><td align='left'>24.06</td><td align='right'>&nbsp;</td><td align='left'>1.0577</td><td align='left'>11.82</td></tr>
+<tr><td align='left'>1.1782</td><td align='left'>35.88</td><td align='right'>&nbsp;</td><td align='left'>1.1164</td><td align='left'>23.65</td><td align='right'>&nbsp;</td><td align='left'>1.0557</td><td align='left'>11.41</td></tr>
+<tr><td align='left'>1.1762</td><td align='left'>35.47</td><td align='right'>&nbsp;</td><td align='left'>1.1143</td><td align='left'>23.24</td><td align='right'>&nbsp;</td><td align='left'>1.0537</td><td align='left'>11.01</td></tr>
+<tr><td align='left'>1.1741</td><td align='left'>35.07</td><td align='right'>&nbsp;</td><td align='left'>1.1123</td><td align='left'>22.83</td><td align='right'>&nbsp;</td><td align='left'>1.0517</td><td align='left'>10.60</td></tr>
+<tr><td align='left'>1.1721</td><td align='left'>34.66</td><td align='right'>&nbsp;</td><td align='left'>1.1102</td><td align='left'>22.43</td><td align='right'>&nbsp;</td><td align='left'>1.0497</td><td align='left'>10.19</td></tr>
+<tr><td align='left'>1.1701</td><td align='left'>34.25</td><td align='right'>&nbsp;</td><td align='left'>1.1082</td><td align='left'>22.02</td><td align='right'>&nbsp;</td><td align='left'>1.0477</td><td align='left'>9.78</td></tr>
+<tr><td align='left'>1.1681</td><td align='left'>33.84</td><td align='right'>&nbsp;</td><td align='left'>1.1061</td><td align='left'>21.61</td><td align='right'>&nbsp;</td><td align='left'>1.0457</td><td align='left'>9.38</td></tr>
+<tr><td align='left'>1.1661</td><td align='left'>33.43</td><td align='right'>&nbsp;</td><td align='left'>1.1041</td><td align='left'>21.20</td><td align='right'>&nbsp;</td><td align='left'>1.0437</td><td align='left'>8.97</td></tr>
+<tr><td align='left'>1.1641</td><td align='left'>33.03</td><td align='right'>&nbsp;</td><td align='left'>1.1020</td><td align='left'>20.79</td><td align='right'>&nbsp;</td><td align='left'>1.0417</td><td align='left'>8.56</td></tr>
+<tr><td align='left'>1.1620</td><td align='left'>32.62</td><td align='right'>&nbsp;</td><td align='left'>1.1000</td><td align='left'>20.39</td><td align='right'>&nbsp;</td><td align='left'>1.0397</td><td align='left'>8.15</td></tr>
+<tr><td align='left'>1.1599</td><td align='left'>32.21</td><td align='right'>&nbsp;</td><td align='left'>1.0980</td><td align='left'>19.98</td><td align='right'>&nbsp;</td><td align='left'>1.0377</td><td align='left'>7.75</td></tr>
+<tr><td align='left'>1.1578</td><td align='left'>31.80</td><td align='right'>&nbsp;</td><td align='left'>1.0960</td><td align='left'>19.57</td><td align='right'>&nbsp;</td><td align='left'>1.0357</td><td align='left'>7.34</td></tr>
+<tr><td align='left'>1.1557</td><td align='left'>31.40</td><td align='right'>&nbsp;</td><td align='left'>1.0939</td><td align='left'>19.16</td><td align='right'>&nbsp;</td><td align='left'>1.0337</td><td align='left'>6.93</td></tr>
+<tr><td align='left'>1.1536</td><td align='left'>30.99</td><td align='right'>&nbsp;</td><td align='left'>1.0919</td><td align='left'>18.76</td><td align='right'>&nbsp;</td><td align='left'>1.0318</td><td align='left'>6.52</td></tr>
+<tr><td align='left'>1.1515</td><td align='left'>30.58</td><td align='right'>&nbsp;</td><td align='left'>1.0899</td><td align='left'>18.35</td><td align='right'>&nbsp;</td><td align='left'>1.0298</td><td align='left'>6.11</td></tr>
+<tr><td align='left'>1.1494</td><td align='left'>30.17</td><td align='right'>&nbsp;</td><td align='left'>1.0879</td><td align='left'>17.94</td><td align='right'>&nbsp;</td><td align='left'>1.0279</td><td align='left'>5.51</td></tr>
+<tr><td align='left'>1.1473</td><td align='left'>29.76</td><td align='right'>&nbsp;</td><td align='left'>1.0859</td><td align='left'>17.53</td><td align='right'>&nbsp;</td><td align='left'>1.0259</td><td align='left'>5.30</td></tr>
+<tr><td align='left'>1.1452</td><td align='left'>29.36</td><td align='right'>&nbsp;</td><td align='left'>1.0838</td><td align='left'>17.12</td><td align='right'>&nbsp;</td><td align='left'>1.0239</td><td align='left'>4.89</td></tr>
+<tr><td align='left'>1.1431</td><td align='left'>28.95</td><td align='right'>&nbsp;</td><td align='left'>1.0818</td><td align='left'>16.72</td><td align='right'>&nbsp;</td><td align='left'>1.0200</td><td align='left'>4.01</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_438" id="Page_438">[Pg 438]</a></span></p>
+
+
+<h4>AMMONIA.</h4>
+
+<p><i>Table showing the percentage, by Weight, of Real Ammonia</i> (NH<sub>3</sub>) <i>in
+Aqueous Solutions of Ammonia of different Specific Gravities.
+Temperature</i>, 14&deg; C.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>0.8844</td><td align='left'>36.0</td><td align='right'>&nbsp;</td><td align='left'>0.9145</td><td align='left'>23.6</td><td align='right'>&nbsp;</td><td align='left'>0.9534</td><td align='left'>11.6</td></tr>
+<tr><td align='left'>0.8852</td><td align='left'>35.6</td><td align='right'>&nbsp;</td><td align='left'>0.9156</td><td align='left'>23.2</td><td align='right'>&nbsp;</td><td align='left'>0.9549</td><td align='left'>11.2</td></tr>
+<tr><td align='left'>0.8860</td><td align='left'>35.2</td><td align='right'>&nbsp;</td><td align='left'>0.9168</td><td align='left'>22.8</td><td align='right'>&nbsp;</td><td align='left'>0.9563</td><td align='left'>10.8</td></tr>
+<tr><td align='left'>0.8868</td><td align='left'>34.8</td><td align='right'>&nbsp;</td><td align='left'>0.9180</td><td align='left'>22.4</td><td align='right'>&nbsp;</td><td align='left'>0.9578</td><td align='left'>10.4</td></tr>
+<tr><td align='left'>0.8877</td><td align='left'>34.4</td><td align='right'>&nbsp;</td><td align='left'>0.9191</td><td align='left'>22.0</td><td align='right'>&nbsp;</td><td align='left'>0.9593</td><td align='left'>10.0</td></tr>
+<tr><td align='left'>0.8885</td><td align='left'>34.0</td><td align='right'>&nbsp;</td><td align='left'>0.9203</td><td align='left'>21.6</td><td align='right'>&nbsp;</td><td align='left'>0.9608</td><td align='left'>9.6</td></tr>
+<tr><td align='left'>0.8894</td><td align='left'>33.6</td><td align='right'>&nbsp;</td><td align='left'>0.9215</td><td align='left'>21.2</td><td align='right'>&nbsp;</td><td align='left'>0.9623</td><td align='left'>9.2</td></tr>
+<tr><td align='left'>0.8903</td><td align='left'>33.2</td><td align='right'>&nbsp;</td><td align='left'>0.9227</td><td align='left'>20.8</td><td align='right'>&nbsp;</td><td align='left'>0.9639</td><td align='left'>8.8</td></tr>
+<tr><td align='left'>0.8911</td><td align='left'>32.8</td><td align='right'>&nbsp;</td><td align='left'>0.9239</td><td align='left'>20.4</td><td align='right'>&nbsp;</td><td align='left'>0.9654</td><td align='left'>8.4</td></tr>
+<tr><td align='left'>0.8920</td><td align='left'>32.4</td><td align='right'>&nbsp;</td><td align='left'>0.9251</td><td align='left'>20.0</td><td align='right'>&nbsp;</td><td align='left'>0.9670</td><td align='left'>8.0</td></tr>
+<tr><td align='left'>0.8929</td><td align='left'>32.0</td><td align='right'>&nbsp;</td><td align='left'>0.9264</td><td align='left'>19.6</td><td align='right'>&nbsp;</td><td align='left'>0.9685</td><td align='left'>7.6</td></tr>
+<tr><td align='left'>0.8938</td><td align='left'>31.6</td><td align='right'>&nbsp;</td><td align='left'>0.9277</td><td align='left'>19.2</td><td align='right'>&nbsp;</td><td align='left'>0.9701</td><td align='left'>7.2</td></tr>
+<tr><td align='left'>0.8948</td><td align='left'>31.2</td><td align='right'>&nbsp;</td><td align='left'>0.9289</td><td align='left'>18.8</td><td align='right'>&nbsp;</td><td align='left'>0.9717</td><td align='left'>6.8</td></tr>
+<tr><td align='left'>0.8957</td><td align='left'>30.8</td><td align='right'>&nbsp;</td><td align='left'>0.9302</td><td align='left'>18.4</td><td align='right'>&nbsp;</td><td align='left'>0.9733</td><td align='left'>6.4</td></tr>
+<tr><td align='left'>0.8967</td><td align='left'>30.4</td><td align='right'>&nbsp;</td><td align='left'>0.9314</td><td align='left'>18.0</td><td align='right'>&nbsp;</td><td align='left'>0.9749</td><td align='left'>6.0</td></tr>
+<tr><td align='left'>0.8976</td><td align='left'>30.0</td><td align='right'>&nbsp;</td><td align='left'>0.9327</td><td align='left'>17.6</td><td align='right'>&nbsp;</td><td align='left'>0.9765</td><td align='left'>5.6</td></tr>
+<tr><td align='left'>0.8986</td><td align='left'>29.6</td><td align='right'>&nbsp;</td><td align='left'>0.9340</td><td align='left'>17.2</td><td align='right'>&nbsp;</td><td align='left'>0.9781</td><td align='left'>5.2</td></tr>
+<tr><td align='left'>0.8996</td><td align='left'>29.2</td><td align='right'>&nbsp;</td><td align='left'>0.9353</td><td align='left'>16.8</td><td align='right'>&nbsp;</td><td align='left'>0.9790</td><td align='left'>4.8</td></tr>
+<tr><td align='left'>0.9006</td><td align='left'>28.8</td><td align='right'>&nbsp;</td><td align='left'>0.9366</td><td align='left'>16.4</td><td align='right'>&nbsp;</td><td align='left'>0.9807</td><td align='left'>4.6</td></tr>
+<tr><td align='left'>0.9016</td><td align='left'>28.4</td><td align='right'>&nbsp;</td><td align='left'>0.9380</td><td align='left'>16.0</td><td align='right'>&nbsp;</td><td align='left'>0.9823</td><td align='left'>4.2</td></tr>
+<tr><td align='left'>0.9026</td><td align='left'>28.0</td><td align='right'>&nbsp;</td><td align='left'>0.9393</td><td align='left'>15.6</td><td align='right'>&nbsp;</td><td align='left'>0.9839</td><td align='left'>3.8</td></tr>
+<tr><td align='left'>0.9036</td><td align='left'>27.6</td><td align='right'>&nbsp;</td><td align='left'>0.9407</td><td align='left'>15.2</td><td align='right'>&nbsp;</td><td align='left'>0.9855</td><td align='left'>3.4</td></tr>
+<tr><td align='left'>0.9047</td><td align='left'>27.2</td><td align='right'>&nbsp;</td><td align='left'>0.9420</td><td align='left'>14.8</td><td align='right'>&nbsp;</td><td align='left'>0.9873</td><td align='left'>3.0</td></tr>
+<tr><td align='left'>0.9057</td><td align='left'>26.8</td><td align='right'>&nbsp;</td><td align='left'>0.9434</td><td align='left'>14.4</td><td align='right'>&nbsp;</td><td align='left'>0.9890</td><td align='left'>2.6</td></tr>
+<tr><td align='left'>0.9068</td><td align='left'>26.4</td><td align='right'>&nbsp;</td><td align='left'>0.9449</td><td align='left'>14.0</td><td align='right'>&nbsp;</td><td align='left'>0.9907</td><td align='left'>2.2</td></tr>
+<tr><td align='left'>0.9078</td><td align='left'>26.0</td><td align='right'>&nbsp;</td><td align='left'>0.9463</td><td align='left'>13.6</td><td align='right'>&nbsp;</td><td align='left'>0.9924</td><td align='left'>1.8</td></tr>
+<tr><td align='left'>0.9089</td><td align='left'>25.6</td><td align='right'>&nbsp;</td><td align='left'>0.9477</td><td align='left'>13.2</td><td align='right'>&nbsp;</td><td align='left'>0.9941</td><td align='left'>1.4</td></tr>
+<tr><td align='left'>0.9100</td><td align='left'>25.2</td><td align='right'>&nbsp;</td><td align='left'>0.9491</td><td align='left'>12.8</td><td align='right'>&nbsp;</td><td align='left'>0.9959</td><td align='left'>1.0</td></tr>
+<tr><td align='left'>0.9111</td><td align='left'>24.8</td><td align='right'>&nbsp;</td><td align='left'>0.9505</td><td align='left'>12.4</td><td align='right'>&nbsp;</td><td align='left'>0.9975</td><td align='left'>0.6</td></tr>
+<tr><td align='left'>0.9122</td><td align='left'>24.4</td><td align='right'>&nbsp;</td><td align='left'>0.9520</td><td align='left'>12.0</td><td align='right'>&nbsp;</td><td align='left'>0.9991</td><td align='left'>0.2</td></tr>
+<tr><td align='left'>0.9133</td><td align='left'>24.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+</table></div>
+
+
+<p><span class='pagenum'><a name="Page_439" id="Page_439">[Pg 439]</a></span></p>
+
+
+<h4>SULPHURIC ACID.</h4>
+
+<p><i>Table showing the percentage, by Weight, of Real Acid</i> (H<sub>2</sub>SO<sub>4</sub>)
+<i>in Aqueous Solutions of Sulphuric Acid of varying Specific Gravity.
+Temperature</i>, 15&deg; C.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>1.838</td><td align='left'>100.0</td><td align='right'>&nbsp;</td><td align='left'>1.568</td><td align='left'>66.0</td><td align='right'>&nbsp;</td><td align='left'>1.247</td><td align='left'>33.0</td></tr>
+<tr><td align='left'>1.840</td><td align='left'>99.0</td><td align='right'>&nbsp;</td><td align='left'>1.557</td><td align='left'>65.0</td><td align='right'>&nbsp;</td><td align='left'>1.239</td><td align='left'>32.0</td></tr>
+<tr><td align='left'>1.841</td><td align='left'>98.0</td><td align='right'>&nbsp;</td><td align='left'>1.545</td><td align='left'>64.0</td><td align='right'>&nbsp;</td><td align='left'>1.231</td><td align='left'>31.0</td></tr>
+<tr><td align='left'>1.841</td><td align='left'>97.0</td><td align='right'>&nbsp;</td><td align='left'>1.534</td><td align='left'>63.0</td><td align='right'>&nbsp;</td><td align='left'>1.223</td><td align='left'>30.0</td></tr>
+<tr><td align='left'>1.840</td><td align='left'>96.0</td><td align='right'>&nbsp;</td><td align='left'>1.523</td><td align='left'>62.0</td><td align='right'>&nbsp;</td><td align='left'>1.215</td><td align='left'>29.0</td></tr>
+<tr><td align='left'>1.838</td><td align='left'>95.0</td><td align='right'>&nbsp;</td><td align='left'>1.512</td><td align='left'>61.0</td><td align='right'>&nbsp;</td><td align='left'>1.206</td><td align='left'>28.0</td></tr>
+<tr><td align='left'>1.836</td><td align='left'>94.0</td><td align='right'>&nbsp;</td><td align='left'>1.501</td><td align='left'>60.0</td><td align='right'>&nbsp;</td><td align='left'>1.198</td><td align='left'>27.0</td></tr>
+<tr><td align='left'>1.834</td><td align='left'>93.0</td><td align='right'>&nbsp;</td><td align='left'>1.490</td><td align='left'>59.0</td><td align='right'>&nbsp;</td><td align='left'>1.190</td><td align='left'>26.0</td></tr>
+<tr><td align='left'>1.831</td><td align='left'>92.0</td><td align='right'>&nbsp;</td><td align='left'>1.480</td><td align='left'>58.0</td><td align='right'>&nbsp;</td><td align='left'>1.182</td><td align='left'>25.0</td></tr>
+<tr><td align='left'>1.827</td><td align='left'>91.0</td><td align='right'>&nbsp;</td><td align='left'>1.469</td><td align='left'>57.0</td><td align='right'>&nbsp;</td><td align='left'>1.174</td><td align='left'>24.0</td></tr>
+<tr><td align='left'>1.822</td><td align='left'>90.0</td><td align='right'>&nbsp;</td><td align='left'>1.458</td><td align='left'>56.0</td><td align='right'>&nbsp;</td><td align='left'>1.167</td><td align='left'>23.0</td></tr>
+<tr><td align='left'>1.816</td><td align='left'>89.0</td><td align='right'>&nbsp;</td><td align='left'>1.448</td><td align='left'>55.0</td><td align='right'>&nbsp;</td><td align='left'>1.159</td><td align='left'>22.0</td></tr>
+<tr><td align='left'>1.809</td><td align='left'>88.0</td><td align='right'>&nbsp;</td><td align='left'>1.438</td><td align='left'>54.0</td><td align='right'>&nbsp;</td><td align='left'>1.151</td><td align='left'>21.0</td></tr>
+<tr><td align='left'>1.802</td><td align='left'>87.0</td><td align='right'>&nbsp;</td><td align='left'>1.428</td><td align='left'>53.0</td><td align='right'>&nbsp;</td><td align='left'>1.144</td><td align='left'>20.0</td></tr>
+<tr><td align='left'>1.794</td><td align='left'>86.0</td><td align='right'>&nbsp;</td><td align='left'>1.418</td><td align='left'>52.0</td><td align='right'>&nbsp;</td><td align='left'>1.136</td><td align='left'>19.0</td></tr>
+<tr><td align='left'>1.786</td><td align='left'>85.0</td><td align='right'>&nbsp;</td><td align='left'>1.408</td><td align='left'>51.0</td><td align='right'>&nbsp;</td><td align='left'>1.129</td><td align='left'>18.0</td></tr>
+<tr><td align='left'>1.777</td><td align='left'>84.0</td><td align='right'>&nbsp;</td><td align='left'>1.398</td><td align='left'>50.0</td><td align='right'>&nbsp;</td><td align='left'>1.121</td><td align='left'>17.0</td></tr>
+<tr><td align='left'>1.767</td><td align='left'>83.0</td><td align='right'>&nbsp;</td><td align='left'>1.388</td><td align='left'>49.0</td><td align='right'>&nbsp;</td><td align='left'>1.113</td><td align='left'>16.0</td></tr>
+<tr><td align='left'>1.756</td><td align='left'>82.0</td><td align='right'>&nbsp;</td><td align='left'>1.379</td><td align='left'>48.0</td><td align='right'>&nbsp;</td><td align='left'>1.106</td><td align='left'>15.0</td></tr>
+<tr><td align='left'>1.745</td><td align='left'>81.0</td><td align='right'>&nbsp;</td><td align='left'>1.370</td><td align='left'>47.0</td><td align='right'>&nbsp;</td><td align='left'>1.098</td><td align='left'>14.0</td></tr>
+<tr><td align='left'>1.734</td><td align='left'>80.0</td><td align='right'>&nbsp;</td><td align='left'>1.361</td><td align='left'>46.0</td><td align='right'>&nbsp;</td><td align='left'>1.091</td><td align='left'>13.0</td></tr>
+<tr><td align='left'>1.722</td><td align='left'>79.0</td><td align='right'>&nbsp;</td><td align='left'>1.351</td><td align='left'>45.0</td><td align='right'>&nbsp;</td><td align='left'>1.083</td><td align='left'>12.0</td></tr>
+<tr><td align='left'>1.710</td><td align='left'>78.0</td><td align='right'>&nbsp;</td><td align='left'>1.342</td><td align='left'>44.0</td><td align='right'>&nbsp;</td><td align='left'>1.075</td><td align='left'>11.0</td></tr>
+<tr><td align='left'>1.698</td><td align='left'>77.0</td><td align='right'>&nbsp;</td><td align='left'>1.333</td><td align='left'>43.0</td><td align='right'>&nbsp;</td><td align='left'>1.068</td><td align='left'>10.0</td></tr>
+<tr><td align='left'>1.686</td><td align='left'>76.0</td><td align='right'>&nbsp;</td><td align='left'>1.324</td><td align='left'>42.0</td><td align='right'>&nbsp;</td><td align='left'>1.061</td><td align='left'>9.0</td></tr>
+<tr><td align='left'>1.675</td><td align='left'>75.0</td><td align='right'>&nbsp;</td><td align='left'>1.315</td><td align='left'>41.0</td><td align='right'>&nbsp;</td><td align='left'>1.053</td><td align='left'>8.0</td></tr>
+<tr><td align='left'>1.663</td><td align='left'>74.0</td><td align='right'>&nbsp;</td><td align='left'>1.306</td><td align='left'>40.0</td><td align='right'>&nbsp;</td><td align='left'>1.046</td><td align='left'>7.0</td></tr>
+<tr><td align='left'>1.651</td><td align='left'>73.0</td><td align='right'>&nbsp;</td><td align='left'>1.297</td><td align='left'>39.0</td><td align='right'>&nbsp;</td><td align='left'>1.039</td><td align='left'>6.0</td></tr>
+<tr><td align='left'>1.639</td><td align='left'>72.0</td><td align='right'>&nbsp;</td><td align='left'>1.289</td><td align='left'>38.0</td><td align='right'>&nbsp;</td><td align='left'>1.032</td><td align='left'>5.0</td></tr>
+<tr><td align='left'>1.627</td><td align='left'>71.0</td><td align='right'>&nbsp;</td><td align='left'>1.281</td><td align='left'>37.0</td><td align='right'>&nbsp;</td><td align='left'>1.025</td><td align='left'>4.0</td></tr>
+<tr><td align='left'>1.615</td><td align='left'>70.0</td><td align='right'>&nbsp;</td><td align='left'>1.272</td><td align='left'>36.0</td><td align='right'>&nbsp;</td><td align='left'>1.019</td><td align='left'>3.0</td></tr>
+<tr><td align='left'>1.604</td><td align='left'>69.0</td><td align='right'>&nbsp;</td><td align='left'>1.264</td><td align='left'>35.0</td><td align='right'>&nbsp;</td><td align='left'>1.013</td><td align='left'>2.0</td></tr>
+<tr><td align='left'>1.592</td><td align='left'>68.0</td><td align='right'>&nbsp;</td><td align='left'>1.256</td><td align='left'>34.0</td><td align='right'>&nbsp;</td><td align='left'>1.006</td><td align='left'>1.0</td></tr>
+<tr><td align='left'>1.580</td><td align='left'>67.0</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td><td align='right'>&nbsp;</td></tr>
+</table></div>
+
+<p><span class='pagenum'><a name="Page_440" id="Page_440">[Pg 440]</a></span></p>
+
+
+
+<hr style="width: 65%;" />
+<h2><a name="APPENDIX_B" id="APPENDIX_B"></a>APPENDIX B.</h2>
+
+
+<h4>ESTIMATION OF SMALL QUANTITIES OF GOLD.<a name="FNanchor_124_124" id="FNanchor_124_124"></a><a href="#Footnote_124_124" class="fnanchor">[124]</a></h4>
+
+<p>In the case of small buttons of gold the weight can be determined more
+easily and accurately by measuring with the help of a microscope than by
+the actual use of a balance. Moreover, the method of measurement is
+applicable to the determination of quantities of gold too minute to
+affect even the most delicate balance.</p>
+
+<p>For quantities of gold of from .5 to .005 milligram a microscope with
+1/2 inch objective and B eyepiece is suitable. The measurements are made
+with the help of a scale engraved (or, better, photographed) on a
+circular piece of glass which rests on the diaphragm of the eyepiece.
+This scale and the object upon the stage can be easily brought into
+focus at the same time. The button of gold obtained by cupelling is
+loosened from the cupel by gently touching with the moistened point of a
+knife; it generally adheres to the knife, and is then transferred to a
+glass slide. The slide is placed on the stage of the microscope,
+illuminated from below; and the button is brought into focus, and so
+placed that it apparently coincides with the scale. The diameters in two
+or three directions (avoiding the flattened surface) are then read off:
+the different directions being got by rotating the eyepiece. The mean
+diameter is taken. The weight of the button is arrived at by comparing
+with the mean diameter of a <i>standard prill</i> of gold of known weight.
+The weights are in the proportion of the cubes of the diameters. For
+example, suppose a prill has been obtained which measures 12.5 divisions
+of the scale, and that a standard prill weighing 0.1 milligram measures
+11.1 divisions. The weight will be calculated as follows:</p>
+
+<p>
+&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;11.1<sup>3</sup> : 12.5<sup>3</sup> :: 0.1 : <i>x</i><br /></p>
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'>0.1&times;12.5&times;12.5&times;12.5</td></tr>
+<tr><td align='left'><i>x = </i></td><td align='left'>&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;&mdash;</td><td align='left'>= 0.143 milligram.</td></tr>
+<tr><td align='left'></td><td align='left'>11.1&times;11.1&times;11.1</td></tr>
+</table></div>
+
+
+<p>The calculations are simplified by the use of a table of cubes. The
+standard prills used in the comparison should not differ much in size
+from<span class='pagenum'><a name="Page_441" id="Page_441">[Pg 441]</a></span> the prills to be determined. They are prepared by alloying known
+weights of gold and lead, so as to get an alloy of known composition,
+say one per cent. gold. Portions of the alloy containing the weight of
+gold required (say 0.1 milligram) are then weighed off and cupelled on
+small smooth cupels, made with the finest bone-ash. Care must be taken
+to remove the cupels as soon as cupellation has finished. Several
+standard prills of the same size should be made at the same time, and
+their mean diameter calculated. The lead for making the gold-lead alloy
+is prepared from litharge purified by reducing from it about 10 per
+cent. of its lead by fusion with a suitable proportion of flour; the
+purified litharge is powdered, mixed with sufficient flour and reduced
+to metal.</p>
+
+<p>In determining the gold contained in small buttons of silver-gold alloy
+obtained in assaying (and in which the silver is almost sure to be in
+excess of that required for parting), transfer the button from the cupel
+to a small clean porcelain crucible; pour on it a drop or two of nitric
+acid (diluted with half its bulk of water), and heat gently and
+cautiously until action has ceased. If the residual gold is broken up,
+move the crucible so as to bring the particles together, so that they
+may cohere. Wash three or four times with distilled water, about half
+filling the crucible each time and decanting off against the finger. Dry
+the crucible in a warm place; and when dry, but whilst still black, take
+the gold up on a small piece of pure lead. Half a grain of lead is
+sufficient, and it is best to hold it on the point of a blunt penknife,
+and press it on the gold in the crucible. The latter generally adheres.
+Transfer to a small smooth cupel and place in the muffle. When the
+cupellation has finished, the button of gold is measured as already
+described.</p>
+
+
+<h4>PRACTICAL NOTES ON THE IODIDE PROCESS OF COPPER ASSAYING.</h4>
+
+<p>For the following remarks and experiments we are indebted to Mr. J.W.
+Westmoreland, who has had considerable experience with the process.
+Having dissolved the ore he converts the metals into sulphates by
+evaporating with sulphuric acid. The copper is then separated as
+subsulphide by means of hyposulphite of soda, and the precipitate is
+washed, dried, and calcined. The resulting oxide of copper is then
+dissolved in nitric acid; and to the concentrated solution, a saturated
+solution of carbonate of soda is added in sufficient quantity to throw
+down a considerable proportion of the copper. Acetic acid is added to
+dissolve the precipitate, and when this is effected more of the acid is
+poured on so as to render the solution strongly acid. To this potassium
+iodide crystals are added in the proportion of ten parts of iodide to
+each one part of copper supposed to be present. The solution is then
+titrated with "hypo" as usual.</p>
+
+<p>For the examination of technical products experiments made in sulphuric
+acid solutions have no value, since arsenic acid, which is generally
+present to a greater or less extent, affects the end reaction. In such
+solutions bismuth may also interfere.</p>
+
+<p>The solution best suited for the assay is one containing acetate of soda
+and free acetic acid. The presence of acetate of soda counteracts the
+interference of arsenic and of bismuth.</p>
+
+<p>The return of the blue colour after titration is due to the excessive<span class='pagenum'><a name="Page_442" id="Page_442">[Pg 442]</a></span>
+dilution of the assay, or to an insufficiency of potassium iodide, or to
+the presence of nitrous fumes. The interference of an excess of sodium
+acetate is avoided by adding more iodide crystals to the extent of
+doubling the usual amount.</p>
+
+<p>The interference of lead can be avoided by the addition of sulphuric
+acid or of phosphate of soda to the acid solution containing the copper,
+and before neutralising with carbonate of soda. The end reaction is,
+however, with care distinguishable without this addition. The following
+experiments, each containing .0648 gram of lead, were made by him in
+illustration:</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='center'>Copper taken.</td><td align='center'>Reagent added.</td><td align='center'>Copper found.</td><td align='center'>End reaction.</td></tr>
+<tr><td align='center'>.2092 gram</td><td align='center'>&mdash;</td><td align='center'>.2077 gram</td><td align='center'>fairly satisfactory</td></tr>
+<tr><td align='center'>.2101 &nbsp;&nbsp;"</td><td align='center'>&mdash;</td><td align='center'>.2092 "</td><td align='center'>"</td></tr>
+<tr><td align='center'>.2167&nbsp;&nbsp; "</td><td align='center'>sulphuric acid</td><td align='center'>.2152 "</td><td align='center'>"</td></tr>
+<tr><td align='center'>.2117 &nbsp;&nbsp;"</td><td align='center'>"</td><td align='center'>.2108 "</td><td align='center'>"</td></tr>
+<tr><td align='center'>.2109&nbsp;&nbsp; "</td><td align='center'>phosphate of soda</td><td align='center'>.2092 "</td><td align='center'>good, colourless</td></tr>
+<tr><td align='center'>.2205&nbsp;&nbsp; "</td><td align='center'>"</td><td align='center'>.2174 "</td><td align='center'>rather yellow</td></tr>
+</table></div>
+
+
+<p><i>Effect of Sodium Acetate.</i>&mdash;Each solution contained .3343 gram of
+copper.</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'><i>a.b.c.</i></td><td align='left'><i>d.</i></td><td align='left'><i>e.</i></td><td align='left'><i>f.</i></td><td align='left'><i>g.</i></td></tr>
+<tr><td align='left'></td><td align='left'>grams.</td><td align='left'>grams.</td><td align='left'>grams.</td><td align='left'>grams.</td><td align='left'>grams.</td></tr>
+<tr><td align='left'>"Acetate" added</td><td align='left'>&mdash;</td><td align='left'>16.2</td><td align='left'>16.2</td><td align='left'>16.2</td><td align='left'>16.2</td></tr>
+<tr><td align='left'>"Iodide" added</td><td align='left'>3.5</td><td align='left'>3.5</td><td align='left'>7.0</td><td align='left'>3.5</td><td align='left'>7.0</td></tr>
+<tr><td align='left'>Copper found</td><td align='left'>.3343</td><td align='left'>.3324</td><td align='left'>.3351</td><td align='left'>.3269</td><td align='left'>.3356</td></tr>
+</table></div>
+
+
+<p>In these experiments, except with the excessive quantities of acetate of
+soda and the insufficiency of potassium iodide in the cases of <i>d</i> and
+<i>f</i>, there was no difficulty with the after-blueing.</p>
+
+
+<h4>METHOD OF SEPARATING COBALT AND NICKEL.</h4>
+
+<p>The following method of separating and estimating cobalt and nickel has
+been described by Mr. James Hope,<a name="FNanchor_125_125" id="FNanchor_125_125"></a><a href="#Footnote_125_125" class="fnanchor">[125]</a> with whom it has been in daily
+use for several years with completely satisfactory results.</p>
+
+<p>The quantity of ore taken should contain about .5 gram of the mixed
+metals. It is dissolved in hydrochloric acid or aqua regia, and the
+solution evaporated to dryness. The residue is taken up with dilute
+hydrochloric acid and hot water. The solution is filtered off from the
+silica, freed from second group metals by treatment with sulphuretted
+hydrogen and filtered, and after oxidation with nitric acid is separated
+from iron and alumina by the basic acetate method (page 233). The
+precipitate is redissolved in a little hydrochloric acid, and again
+precipitated by sodium acetate. The two filtrates are mixed and treated
+with a little acetic acid, and the cobalt and nickel are then
+precipitated as sulphides by a current of sulphuretted hydrogen. The
+precipitate is filtered off, washed, dried,<span class='pagenum'><a name="Page_443" id="Page_443">[Pg 443]</a></span> and calcined, and the
+resulting oxides are weighed to get an idea as to the quantity of the
+two metals present.</p>
+
+<p>The calcined precipitate is dissolved in a small covered beaker in aqua
+regia with the help of a few drops of bromine to remove any separated
+sulphur, and the solution evaporated to dryness with a few drops of
+sulphuric acid. The residue is dissolved in hot water, diluted to about
+50 c.c., and heated to boiling. About 2 grams (four times the quantity
+of mixed metals present) of ammonium phosphate (AmH<sub>2</sub>PO<sub>4</sub>) are
+weighed off, dissolved in the smallest possible quantity of water, and
+boiled for a minute or two with a few c.c. of dilute sulphuric acid.
+This is added to the boiling-hot solution of cobalt and nickel, which is
+then treated cautiously with dilute ammonia until the precipitate
+partially dissolves. The addition of the ammonia is continued drop by
+drop with constant stirring, until the cobalt comes down as a pink
+precipitate of ammonium cobalt phosphate (AmCoPO<sub>4</sub>). The beaker is
+placed on the top of a water bath with occasional stirring for five or
+ten minutes. The blue liquid containing the nickel is decanted through a
+small filter and the precipitate is dissolved with a few drops of dilute
+sulphuric acid. The resulting solution is treated with a small excess of
+ammonium phosphate and the cobalt again precipitated by the cautious
+addition of ammonia exactly as before. The precipitate containing the
+whole of the cobalt is filtered off and washed with small quantities of
+hot water. The filtrate is added to the previous one containing the
+greater part of the nickel.</p>
+
+<p>The ammonium cobalt phosphate is dried, transferred to a platinum
+crucible, and ignited over a Bunsen flame for fifteen or twenty minutes.
+A purple coloured cobalt pyrophosphate (Co<sub>2</sub>P<sub>2</sub>O<sub>7</sub>) is thus
+formed, and is weighed. It contains 40.3 per cent. of cobalt.</p>
+
+<p>The mixed filtrates containing the nickel are placed in a tall beaker,
+and dilated if necessary to about 200 c.c. Ten c.c. of strong ammonia
+are added, and the solution, heated to 70&deg; C., is ready for
+electrolysis. A battery of two 1-1/2 pint Bunsen cells is used. This is
+found capable of depositing from .15 to .20 gram of nickel per hour, and
+from two to three hours is generally sufficient for the electrolysis.
+The electrode with the deposited nickel is washed with distilled water,
+afterwards with alcohol as described under copper, and is then dried and
+weighed.</p>
+
+<p>The following results obtained with this method by Mr. Hope illustrate
+the accuracy of the method. They were obtained by working on solutions
+containing known weights of the two metals:</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'> Taken.</td><td align='left'>&nbsp;</td><td align='left'> Found.</td><td align='left'>&nbsp;</td></tr>
+<tr><td align='left'> Cobalt.</td><td align='left'> Nickel.</td><td align='left'> Cobalt.</td><td align='left'> Nickel.</td></tr>
+<tr><td align='left'> .1236 gram </td><td align='left'>.1155 gram</td><td align='left'> .1242 gram</td><td align='left'> .1155 gram</td></tr>
+<tr><td align='left'> .1236&nbsp;&nbsp; "</td><td align='left'> .0577&nbsp;&nbsp; "</td><td align='left'> .1232&nbsp;&nbsp; "</td><td align='left'> .0575&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'> .2472&nbsp;&nbsp; "</td><td align='left'> .0577&nbsp;&nbsp; "</td><td align='left'> .2449&nbsp;&nbsp; "</td><td align='left'> .0585&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'> .3708&nbsp;&nbsp; "</td><td align='left'> .0577&nbsp;&nbsp; "</td><td align='left'> .3701&nbsp;&nbsp; "</td><td align='left'> .0580&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'> .0618&nbsp;&nbsp; "</td><td align='left'> .3465&nbsp;&nbsp; "</td><td align='left'> .0619&nbsp;&nbsp; "</td><td align='left'> .3454&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'> .0618&nbsp;&nbsp; "</td><td align='left'> .2310&nbsp;&nbsp; "</td><td align='left'> .0625&nbsp;&nbsp; "</td><td align='left'> .2295&nbsp;&nbsp; "</td></tr>
+<tr><td align='left'> .0618&nbsp;&nbsp; "</td><td align='left'> .1155&nbsp;&nbsp; "</td><td align='left'> .0621&nbsp;&nbsp; "</td><td align='left'> .1155&nbsp;&nbsp; "</td></tr>
+</table></div>
+
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_124_124" id="Footnote_124_124"></a><a href="#FNanchor_124_124"><span class="label">[124]</span></a> For fuller information see a paper on "The Estimation of
+Minute Quantities of Gold," by Dr. George Tate; read before the
+Liverpool Polytechnic Society, Nov. 1889.</p></div>
+
+<div class="footnote"><p><a name="Footnote_125_125" id="Footnote_125_125"></a><a href="#FNanchor_125_125"><span class="label">[125]</span></a> <i>Journal of the Society of Chemical Industry</i>, No 4, vol.
+ix. April 30, 1890.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_444" id="Page_444">[Pg 444]</a></span></p>
+<h2><a name="APPENDIX_C" id="APPENDIX_C"></a>APPENDIX C.</h2>
+
+
+<h3>A LECTURE ON THE THEORY OF SAMPLING.</h3>
+
+<p>The problem of the sampler is essentially the same as that of the
+student of statistics. One aims at getting a small parcel of ore, the
+other a number of data, but each hopes to obtain what shall represent a
+true average applicable to a much larger mass of material. Ignoring the
+mechanical part of the problems, the sampling errors of the one and the
+deviations from the average of the other are the same thing.</p>
+
+<p>It may be doubted whether many not specially trained in the study of
+statistics could answer such a question as the following:&mdash;Seven hundred
+thousand men being employed, there are, in a given year, one thousand
+deaths from accident. Assuming the conditions to remain unaltered,
+within what limits could one foretell the number of deaths by accident
+in any other year?</p>
+
+<p>On the other hand, there is a widespread belief in the efficacy of what
+is called the law of averages. Even the ordinary newspaper reader is
+accustomed to look on the national death-rate or birth-rate as a thing
+capable of being stated with accuracy to one or two places of decimals,
+and he knows that the annual number of suicides is practically constant.</p>
+
+<p>If a man played whist often and kept a record of the number of trumps n
+each hand, he would find fortune treated him quite fairly; in a year's
+play the average number would deviate very little from the theoretical
+average, <i>i.e.</i>, one-quarter of thirteen. And a knowledge of this truth
+is useful, and that not merely in keeping ejaculations in due restraint.
+But every good player knows more than this: he has a sense of what
+variations in the number of trumps may reasonably be expected. For
+example, he will be prepared to risk something on neither of his
+opponents having more than five trumps, and will accept it as a
+practical certainty that no one has more than eight. Much of what is
+known as good judgment is based on a proper estimate of deviations from
+the average. The question has an important bearing on sampling, as may
+be seen from the fact that shuffling and dealing at cards are but
+modifications of the well-known mixing and quartering of the sampler.</p>
+
+<p>Because of this bearing on sampling and for other reasons, I became many
+years ago much interested in the question, and gave to its solution
+perhaps more labour than it was worth. In books on Medical Statistics<span class='pagenum'><a name="Page_445" id="Page_445">[Pg 445]</a></span>
+the answer to the question is stated in a mathematical formula, called
+Poisson's formula, which, in a modified form, I shall give further on.
+But this did not satisfy me, because I wanted to learn what a reasonably
+safe <i>limit of error</i> actually meant, and this could be best learnt by
+experiment; so with the help of some friends I went in for a thorough
+course of penny-tossing.</p>
+
+<p>Tossing a penny twenty times, an average result would be ten heads and
+ten tails. To find the deviations from this, we tossed two hundred
+twenties, <i>i.e.</i>, four thousand times. Of the two hundred, thirty-three
+gave the exact average, viz.:&mdash;10 heads; sixty-four gave an error of
+one, viz.:&mdash;9 or 11 heads; forty-nine, an error of two; twenty-six, an
+error of three; twenty, an error of four; eight gave an error of five,
+and this limit was not exceeded. From these we may say that six is a
+reasonably safe limit of error. Ninety-seven cases, say one-half, gave
+an error not exceeding one; and the mean error is 1.8.</p>
+
+<p>In other words, in twenty tosses you will not get more than 16 nor less
+than 4 heads; you are as likely as not to get 9, 10, or 11 heads; and
+lastly, if you lost in twenty throws all heads or tails over 10 your
+average loss would be 1.8 penny, or say roughly 2d. on the twenty
+throws.</p>
+
+<p>It was necessary to compare these with another series containing a
+larger average, say that of 100 heads in 200 throws. I confess the
+labour of tossing pennies two hundred at a time was little to our taste.
+So from a bag of pennies borrowed from the bank, we weighed out samples
+containing two hundred, and for an evening we were busy counting heads
+and tails in these. The heads in sixty samples ranged from 80 to 114.
+One hundred heads occurred seven times. The extent and frequency of the
+errors is shown in the table.</p>
+
+
+<div class='center'>
+<table border="1" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>Error.</td><td align='left'>No. of Times.</td><td align='left'>Error.</td><td align='left'>No. of Times.</td><td align='left'>Error.</td><td align='left'>No. of Times.</td></tr>
+<tr><td align='left'> 1</td><td align='left'> 8</td><td align='left'> 6</td><td align='left'> 3</td><td align='left'> 11</td><td align='left'> 1</td></tr>
+<tr><td align='left'> 2</td><td align='left'> 5</td><td align='left'> 7</td><td align='left'> 3</td><td align='left'> 14</td><td align='left'> 3</td></tr>
+<tr><td align='left'> 3</td><td align='left'> 6</td><td align='left'> 8</td><td align='left'> 3</td><td align='left'> 15</td><td align='left'> 1</td></tr>
+<tr><td align='left'> 4</td><td align='left'> 3</td><td align='left'> 9</td><td align='left'> 7</td><td align='left'> 18</td><td align='left'> 2</td></tr>
+<tr><td align='left'> 5</td><td align='left'> 6</td><td align='left'> 10</td><td align='left'> 1</td><td align='left'> 20</td><td align='left'> 1</td></tr>
+</table></div>
+
+
+<p>We may call the limit of error 21. Twenty-nine results out of sixty, say
+one-half, had an error not exceeding 4; and the mean error is 5.6. In
+comparing these with the series 10 in 20 we must, working by rule,
+divide not by 10 but by 3.16, the square root of 10; for if we multiply
+an average by any number<a name="FNanchor_126_126" id="FNanchor_126_126"></a><a href="#Footnote_126_126" class="fnanchor">[126]</a> the error is also multiplied but only by
+the square root of the number. The error varies as the square root of
+the number. Now</p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'>21/3.16 = 6.6 = limit of error for 10 in 20.</td></tr>
+<tr><td align='left'> 5.6/3.16 = 1.8 = mean error&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td></tr>
+<tr><td align='left'> 4/3.16 = 1.2 = probable error&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td></tr>
+</table></div>
+
+<p>It will be seen that these calculated results agree fairly well with
+those actually obtained. The rule by which these calculations are made
+is important<span class='pagenum'><a name="Page_446" id="Page_446">[Pg 446]</a></span> and will bear further illustration. To calculate the
+number of heads in 3200 throws, we have to find the limit of error on a
+true average of 1600 in 3200. This being 16 times the average of 100 in
+200, the corresponding errors must be multiplied by 4. This gives</p>
+
+<p class="center">
+21&times;4 = 84 = limit of error.<br />
+5.6&times;4 = 22.4 = mean error.<br />
+4&times;4 = 16 = probable error.<br />
+</p>
+
+<p>The results I have actually obtained with these large numbers are hardly
+enough to base much on, but have a value by way of confirmation.
+Expecting 1600 heads, the actual numbers were 1560, 1596, 1643, 1557,
+1591, 1605, 1615, 1545.</p>
+
+<p>It will be seen that exactly half are within the probable error; but
+this, considering the small number of results, must be more or less of
+an accident; it is more to the point they are all well within the limits
+of error.</p>
+
+<p>I have a large number of other results which with a single exception are
+all in accord with those given; and this exception only just overstepped
+the limits. It was like a case of nine trumps, which though in a sense
+possible, is very unlikely to happen in any one's experience.</p>
+
+<p>But even now we are not quite in a position to answer the question with
+which we started. If you refer to it you will see that we are face to
+face with this problem: the limit of variation on the 1000 who died
+would be say 70,<a name="FNanchor_127_127" id="FNanchor_127_127"></a><a href="#Footnote_127_127" class="fnanchor">[127]</a> ignoring decimals. But if we calculate on the
+number who did not die, viz.&mdash;699,000,<a name="FNanchor_128_128" id="FNanchor_128_128"></a><a href="#Footnote_128_128" class="fnanchor">[128]</a> we shall get a variation 26
+times as great as this. But it is evident the variation must be the same
+in each case. I submitted this kind of problem also to the test of
+experiment, the results of which gave me great faith in Poisson's
+formula.</p>
+
+<p>Imagine two hundred pennies in a bag all heads up. Any shaking will
+spoil this arrangement and give a certain proportion of tails. And,
+further, the probable effect of shaking and turning will be to reduce
+the preponderance of heads or tails whichever may be in excess. This of
+course is the reason why we are so unlikely to get more than 120 of them
+in either position.</p>
+
+<p>But if the two hundred pennies are increased to 20,000 by adding pennies
+which have tails on both sides, then the shaking or mixing would be less
+effective. We should still expect as an average result to get the 100
+heads but in 20,000 instead of 200. The variation will be 28 or 29 on
+the 100 instead of 20. And this is a better limit in such cases. <i>Taking
+28 as the limit of error on 100 instances</i> and proportionally increasing
+the others so that <i>the mean error becomes 7.8 and the probable error
+5.6</i>, we may now calculate the answer without gross mistake.</p>
+
+<p>The probable variation on the 1000 deaths by accident will be 18, the
+mean variation will be 24.6, and the limits of variation 88.5. One such
+table showing in five years a mean number of deaths of about 1120 per
+annum gives an annual deviation of about 50 up or down of this. It will
+be seen at once that an improvement of 30 or 40 in any one year would be
+without meaning, but that an improvement of from 100 to 200 would
+indicate some change for the better in the circumstances of the
+industry. Before applying these principles to the elucidation of some of
+the problems of sampling it will be well to give Poisson's formula (in a
+modified form) and to illustrate its working.</p>
+
+<p><span class='pagenum'><a name="Page_447" id="Page_447">[Pg 447]</a></span></p><p>Let <i>x</i> equal the number of cases of one sort, <i>y</i> the cases of the
+other sort, and <i>z</i> the total. In the example, <i>z</i> will be the 700,000
+engaged in the industry; <i>x</i> will be the 1000 killed by accidents, and
+<i>y</i> will be the 699,000 who did not so die. The limit of deviation or
+error calculated by Poisson's formula will be the square root of
+8<i>xy</i>/<i>z</i>. Replacing <i>x</i>, <i>y</i> and <i>z</i> by the figures of the example we
+get the square root of (8&times;1000&times;699000)/700,000, which works out to the
+square root of 7988.57, or 89.3. Which means that we may reasonably
+expect the number of deaths not to vary from 1000 by more than 89,
+<i>i.e.</i>, they will be between 1090 and 910. It will be seen that this
+number is in very satisfactory agreement with 88.5 given by the rougher
+calculation based on my own experiments.</p>
+
+<p>To come to the question of sampling. Consider a powder of uniform
+fineness and fine enough to pass through an 80 sieve. For purposes of
+calculation this may be assumed to be made up of particles of about
+one-eighth of a millimetre across (say roughly 1/200 of an inch); cubed,
+this gives the content as about 1/500 (strictly 1/512) of a cubic m.m.
+Now one cubic m.m. of water weighs 1 milligram; therefore 500 such
+particles if they have the specific gravity of water weigh 1 milligram,
+and otherwise weigh 1 milligram multiplied by the sp. gr.: 500 particles
+of ruby silver (Pyrargyrite)<a name="FNanchor_129_129" id="FNanchor_129_129"></a><a href="#Footnote_129_129" class="fnanchor">[129]</a> will weigh 5.8 milligrams and will
+contain nearly 3.5 milligrams of silver.</p>
+
+<p>Now suppose a portion of 3.2667 grams (1/10 Assay Ton) of silver ore to
+contain 500 such particles of ruby silver and no other material carrying
+silver: such an ore would contain 35 ozs. of silver to the ton. But the
+limits of variation on 500 particles would be 28<a name="FNanchor_130_130" id="FNanchor_130_130"></a><a href="#Footnote_130_130" class="fnanchor">[130]</a> multiplied by the
+square root of 5, or 62 particles. Thus the limit of sampling error
+would amount to just one-eighth of the silver present, or say to rather
+more than 4 ozs. to the ton; the mean sampling error would be rather
+more than a quarter of this, or say about 1.3 ozs. to the ton.</p>
+
+<p>On the other hand, if one took for the assay a charge six times greater
+(say about 20 grams), the number of particles would be 3000 and the
+limits of variation would be 28 multiplied by the square root of 30, or
+153 particles, which is very closely 1/20 of the silver present, or say
+1.75 ozs. to the ton, whilst the mean error would amount to about .5
+ozs. to the ton.</p>
+
+<p>To work these examples by Poisson's formula let us assume the gangue to
+have a mean sp. gr. of 3. Then 500 particles would weigh 3 milligrams;
+and 3.2609<a name="FNanchor_131_131" id="FNanchor_131_131"></a><a href="#Footnote_131_131" class="fnanchor">[131]</a> grams would contain 543,500 particles. There would be
+then 500 of ruby silver and 543,500 of gangue, together 544,000, and the
+formula gives the square root of (8&times;500&times;543500)/544000, which works out
+to 63 particles as against 62 by the other method.</p>
+
+<p>A practical conclusion from this is of course that either the ore must
+be powdered more finely or a larger portion than 3 grams must be taken
+for the assay. Moreover, it is evident that on such an ore no small
+sample must be taken containing less than several million particles.</p>
+
+<p>Consider now a copper ore of the same uniform fineness containing<span class='pagenum'><a name="Page_448" id="Page_448">[Pg 448]</a></span>
+particles of copper pyrites (sp. gr. 4) of which 1000 particles will
+weigh 8 milligrams, mixed with gangue of which 1000 particles weigh 6
+milligrams.</p>
+
+<p>If one gram of such ore contain .5 gram of copper pyrites (= .1725 gram
+copper) and .5 gram of gangue, these will contain 62,500 and say 83,500
+particles respectively. Altogether 146,000 particles. With Poisson's
+formula this gives the limit of sampling error as the square root of
+(8&times;62500&times;83500)/146000 or 521 particles. But a variation of 521 on
+62,500 is a variation of .83 per cent. The percentage of copper in the
+ore is 17.25 per cent., and .83 per cent. of this is .14 per cent. The
+limits of sampling error, therefore, are 17.11 per cent. and 17.39 per
+cent. Again, it must be remembered that the mean sampling error would be
+a little over one-quarter of this, or say from 17.2 per cent. to 17.3
+per cent. The practical conclusion is that a powder of this degree of
+fineness is not fine enough. In the last place let us consider a similar
+iron ore containing 90 per cent. of h&aelig;matite (sp. gr. 5) and 10 per
+cent. of gangue (sp. gr. 3), 1 gram of such ore will contain 90,000
+particles of h&aelig;matite weighing .9 gram and containing .63 gram of iron
+with say 16,500 particles of gangue weighing .1 gram. Altogether 106,500
+particles.</p>
+
+<p>Poisson's formula then gives the limits of variation as the square root
+of (8&times;90000&times;16500)/106500 or 334 particles. But 334 on 90,000 is 0.23 on
+63.0, which is the percentage of iron present. The limits of sampling
+error then are 62.77 per cent. and 63.23 per cent. and the mean
+variation is from 62.94 per cent. to 63.06 per cent.</p>
+
+<p>These examples are worthy of careful consideration, and it must be
+remembered that the calculations are made on the assumption that the ore
+is made up of uniform particles of mineral of such fineness as would
+pass easily through an 80 sieve, but which does not pretend to represent
+with great exactness the fineness of the powdered ore customary in
+practice. They show that having passed through such a sieve is no proof
+of sufficient powdering, not that all ores powdered and so sifted are
+unfit for assaying. This last would be an absurd and illogical
+conclusion.</p>
+
+<p>If an ore be powdered to a fairly fine sand and then be passed through a
+series of sieves, say a 40, 60, and 80, in such a state that little or
+none remains on the first, but the others retain a large proportion;
+then of that which comes through the 80 sieve, perhaps two-thirds by
+weight may be even coarser than the powder I have used in the example.
+Of the rest most may be of about half this diameter; the weight of the
+really fine powder may be quite inconsiderable. On the other hand, if
+the grinding be continued until, on sifting, little or nothing that is
+powderable remains on the sieves; then in the sifted product the
+proportions will be very different. This last, of course, is the only
+right way of powdering. Also it is evident that so much depends on the
+manner of powdering that nothing precise can be stated as to the average
+coarseness of the powder. Suppose, however, by good powdering a product
+is obtained which may be represented by a uniform powder with particles
+1/20th of a millimetre in diameter (say roughly 1/500 inch). Compared
+with the previous powder, the diameter has been divided by 2.5; their
+number, therefore, in any given weight has been increased by the cube of
+2.5, which is 15.6. But the value of a sample varies as the square root
+of the number of particles. Hence the reduction in size and consequent
+increase in number has made the sample<span class='pagenum'><a name="Page_449" id="Page_449">[Pg 449]</a></span> nearly four times better than
+before; and it will be seen that this brings the sampling error within
+tolerable limits.</p>
+
+<p>There are one or two words of warning which should be given. In the
+first place, using a 90 sieve instead of an 80 must not be too much
+relied on; the powder I took in the example would pass through it. It is
+a question of good powdering rather than of fine sifting. In the second
+place, a set of, say half-a-dozen, assays concordant within 1 oz. where
+the theory gives 4 ozs. as the limit of error does not upset the theory:
+the theory itself states this as likely. It is the error you <i>may</i> get
+in one or two assays out of a hundred, not the error you are <i>likely</i> to
+get in any one assay, which is considered under the heading "limit of
+error."</p>
+
+<p>Accepting the result just arrived at that a portion of 1 gram may be
+safely taken for an assay if the particles are 1-20th of a millimetre in
+diameter, the further question remains as to what weight of the original
+sample must be reduced to this degree of fineness. This may be answered
+on the principle that the same degree of excellence should be aimed at
+in each of a series of samplings. This principle is illustrated in the
+table on page 2.[** PP: page reference]</p>
+
+<p>A fine sand, such as would pass a 40 sieve but be retained on a 60
+sieve, would be fairly represented by particles one-quarter of a
+millimetre in diameter. This being five times coarser, to contain the
+same number of particles must be 125 times (the cube of 5) as heavy;
+therefore 125 grams of it can be taken with the same degree of safety as
+1 gram of the finer powder. Of such a sand about this weight should be
+taken and reduced to the finer powder. If the ore were in coarse sand,
+say in particles 1 millimetre in diameter, this would be four times as
+coarse as that last considered, and we should have to take 64 times as
+much of it: 64 times 125 grams is 8 kilos, or say roughly from 15 to 20
+lbs. This should be crushed to the finer size and mixed; then from 100
+to 150 grams should be taken and ground to the finest powder.</p>
+
+<p>There is, however, a reason why, on the coarser stuff, a smaller
+proportion may safely be used. This becomes more evident if we consider
+a still coarser sample. A heap of ore in stones about 2 inches across
+would be 50 times coarser than the sand, and an equivalent sample would
+need to be 125,000 times heavier; this would amount to about 1000 tons.
+Experienced samplers would say that under such conditions so large a
+sample was hardly necessary.</p>
+
+<p>This is because I have assumed in the calculations that the grains of
+copper pyrites, for example, were all copper pyrites and the particles
+of gangue were free from copper. This would be true or nearly so for the
+very fine powder, but far from true in the case of the ore heap. In the
+heap probably few of the stones would be pure ore and still fewer would
+be free from copper. The stones would differ among themselves in their
+copper contents only within certain comparatively narrow limits. And it
+is evident that, if replacing one stone by another, instead of resulting
+in the gain or loss of all the copper one or other contained, merely
+affected the result to one-tenth of this amount, then a sample of
+1-100th of the weight (say 10 tons) would be equally safe.</p>
+
+<p>It should be remembered, however, that while the man who samples on a
+large scale can safely and properly reduce the size of his samples on
+this account, yet the principle is one which counts less and less as the
+stuff becomes more finely divided, and ought to be ignored in the
+working down of the smaller samples which come to the assayer.</p>
+
+<div class="footnotes"><h3>FOOTNOTES:</h3>
+
+<div class="footnote"><p><a name="Footnote_126_126" id="Footnote_126_126"></a><a href="#FNanchor_126_126"><span class="label">[126]</span></a> The 10 in 20 multiplied by 10 = 100 in 200.</p></div>
+
+<div class="footnote"><p><a name="Footnote_127_127" id="Footnote_127_127"></a><a href="#FNanchor_127_127"><span class="label">[127]</span></a> Multiply the errors for 100 by the square root of 10.</p></div>
+
+<div class="footnote"><p><a name="Footnote_128_128" id="Footnote_128_128"></a><a href="#FNanchor_128_128"><span class="label">[128]</span></a> Multiply the errors for 100 by the square root of 6990.</p></div>
+
+<div class="footnote"><p><a name="Footnote_129_129" id="Footnote_129_129"></a><a href="#FNanchor_129_129"><span class="label">[129]</span></a> Sp. Gr. 5.8. Silver 60 per cent.</p></div>
+
+<div class="footnote"><p><a name="Footnote_130_130" id="Footnote_130_130"></a><a href="#FNanchor_130_130"><span class="label">[130]</span></a> Taking 28 as the limit of variation on 100.</p></div>
+
+<div class="footnote"><p><a name="Footnote_131_131" id="Footnote_131_131"></a><a href="#FNanchor_131_131"><span class="label">[131]</span></a> The weight of the ore less the weight of ruby silver in
+it.</p></div>
+</div>
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_450" id="Page_450">[Pg 450]</a></span></p>
+<h2><a name="INDEX" id="INDEX"></a>INDEX.</h2>
+
+
+<p>
+Acid measures, <a href='#Page_49'>49</a><br />
+<br />
+Acidimetry, <a href='#Page_323'>323</a><br />
+<br />
+Acidity of ores, <a href='#Page_168'>168</a><br />
+<br />
+Acids, <a href='#Page_54'>54</a><br />
+<span style="margin-left: 1em;">strength of, <a href='#Page_54'>54</a>, <a href='#Page_75'>75</a>, <a href='#Page_436'>436</a></span><br />
+<br />
+Air of mines, carbonic acid in, <a href='#Page_428'>428</a><br />
+<br />
+Alkalies, <a href='#Page_330'>330</a><br />
+<span style="margin-left: 1em;">determination of, <a href='#Page_331'>331</a></span><br />
+<span style="margin-left: 1em;">Lawrence Smith's method for, <a href='#Page_333'>333</a>, <a href='#Page_412'>412</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_332'>332</a></span><br />
+<br />
+Alkalimetry, <a href='#Page_323'>323</a><br />
+<br />
+Alkaline earths, <a href='#Page_320'>320</a><br />
+<br />
+Alumina, <a href='#Page_314'>314</a><br />
+<span style="margin-left: 1em;">determination of, <a href='#Page_315'>315</a></span><br />
+<span style="margin-left: 1em;">in mineral phosphates, <a href='#Page_316'>316</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_314'>314</a>, <a href='#Page_316'>316</a></span><br />
+<br />
+Amalgamation, <a href='#Page_126'>126</a><br />
+<br />
+Ammonia, detection of, <a href='#Page_341'>341</a><br />
+<span style="margin-left: 1em;">determination of, <a href='#Page_342'>342</a></span><br />
+<span style="margin-left: 1em;">in natural waters, <a href='#Page_353'>353</a></span><br />
+<br />
+Antimony, <a href='#Page_225'>225</a><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_227'>227</a></span><br />
+<span style="margin-left: 1em;">dry assay for, <a href='#Page_226'>226</a></span><br />
+<span style="margin-left: 1em;">gravimetric assay, <a href='#Page_228'>228</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_228'>228</a></span><br />
+<span style="margin-left: 1em;">volumetric assay, <a href='#Page_229'>229</a></span><br />
+<br />
+Arsenic, <a href='#Page_381'>381</a><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_381'>381</a></span><br />
+<span style="margin-left: 1em;">dry assay for, <a href='#Page_382'>382</a></span><br />
+<span style="margin-left: 1em;">gravimetric assay, <a href='#Page_383'>383</a></span><br />
+<span style="margin-left: 1em;">in brimstone, <a href='#Page_393'>393</a></span><br />
+<span style="margin-left: 1em;">in crude arsenic, <a href='#Page_388'>388</a>, <a href='#Page_393'>393</a></span><br />
+<span style="margin-left: 1em;">in mispickel, <a href='#Page_125'>125</a>, <a href='#Page_392'>392</a></span><br />
+<span style="margin-left: 1em;">iodine, assay for, <a href='#Page_386'>386</a></span><br />
+<span style="margin-left: 1em;">separation by distilling, <a href='#Page_384'>384</a></span><br />
+<span style="margin-left: 1em;">uranium acetate, assay for, <a href='#Page_389'>389</a></span><br />
+<span style="margin-left: 1em;">Volhard's method&nbsp; applied to, <a href='#Page_124'>124</a></span><br />
+<br />
+Assay book, <a href='#Page_11'>11</a><br />
+<span style="margin-left: 1em;">note, <a href='#Page_12'>12</a></span><br />
+<span style="margin-left: 1em;">results, <a href='#Page_7'>7</a></span><br />
+<span style="margin-left: 1em;">tons, <a href='#Page_13'>13</a>, <a href='#Page_131'>131</a></span><br />
+<br />
+Assaying, <a href='#Page_1'>1</a><br />
+<span style="margin-left: 1em;">methods, <a href='#Page_15'>15</a></span><br />
+<br />
+Assays, check, <a href='#Page_154'>154</a><br />
+<span style="margin-left: 1em;">preliminary, <a href='#Page_147'>147</a></span><br />
+<br />
+Atomic weights, <a href='#Page_69'>69</a><br />
+<span style="margin-left: 1em;">table of, <a href='#Page_433'>433</a></span><br />
+<br />
+<br />
+Barium, <a href='#Page_326'>326</a><br />
+<br />
+Baryta, <a href='#Page_326'>326</a><br />
+<br />
+Barytes, sulphur in, <a href='#Page_378'>378</a><br />
+<br />
+Base bullion, sampling of, <a href='#Page_157'>157</a><br />
+<br />
+Basic acetate separation, <a href='#Page_233'>233</a><br />
+<br />
+Baum&eacute;'s hydrometer, <a href='#Page_77'>77</a><br />
+<br />
+Beryllia, <a href='#Page_319'>319</a><br />
+<br />
+Bismuth, <a href='#Page_220'>220</a><br />
+<span style="margin-left: 1em;">colorimetric assay, <a href='#Page_223'>223</a></span><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_221'>221</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination of, <a href='#Page_222'>222</a></span><br />
+<span style="margin-left: 1em;">in commercial copper, <a href='#Page_208'>208</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_222'>222</a></span><br />
+<br />
+Black tin, <a href='#Page_271'>271</a><br />
+<span style="margin-left: 1em;">an analysis of, <a href='#Page_287'>287</a></span><br />
+<span style="margin-left: 1em;">assay of, <a href='#Page_276'>276</a></span><br />
+<span style="margin-left: 1em;">copper in, <a href='#Page_204'>204</a></span><br />
+<span style="margin-left: 1em;">examination of, <a href='#Page_285'>285</a></span><br />
+<span style="margin-left: 1em;">separation by vanning, <a href='#Page_272'>272</a></span><br />
+<br />
+Blank assays, <a href='#Page_34'>34</a><br />
+<br />
+Blende, sulphur in, <a href='#Page_375'>375</a><br />
+<span style="margin-left: 1em;">zinc in, <a href='#Page_266'>266</a></span><br />
+<br />
+Book, assay, <a href='#Page_11'>11</a><br />
+<span style="margin-left: 1em;">laboratory, <a href='#Page_10'>10</a></span><br />
+<span style="margin-left: 1em;">sample, <a href='#Page_9'>9</a></span><br />
+<br />
+<span class='pagenum'><a name="Page_451" id="Page_451">[Pg 451]</a></span>Boracic acid. <i>See Boron</i><br />
+<br />
+Borax, examination of, <a href='#Page_431'>431</a><br />
+<br />
+Boron, <a href='#Page_429'>429</a><br />
+<span style="margin-left: 1em;">direct determination of, <a href='#Page_431'>431</a></span><br />
+<br />
+Brass, copper in, <a href='#Page_194'>194</a><br />
+<span style="margin-left: 1em;">zinc in, <a href='#Page_265'>265</a></span><br />
+<br />
+Bromine and bromides, <a href='#Page_361'>361</a><br />
+<br />
+Bronze, copper in, <a href='#Page_194'>194</a><br />
+<span style="margin-left: 1em;">tin in, <a href='#Page_281'>281</a></span><br />
+<br />
+Burettes, <a href='#Page_51'>51</a><br />
+<br />
+Burnt ore, silver in, <a href='#Page_116'>116</a>, <a href='#Page_118'>118</a><br />
+<span style="margin-left: 1em;">sulphur in, <a href='#Page_377'>377</a></span><br />
+<br />
+<br />
+Cadmium, <a href='#Page_269'>269</a><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_269'>269</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_269'>269</a></span><br />
+<br />
+Caesium, <a href='#Page_339'>339</a><br />
+<br />
+Calcination, <a href='#Page_22'>22</a>, <a href='#Page_92'>92</a>, <a href='#Page_139'>139</a>, <a href='#Page_345'>345</a><br />
+<br />
+Calcium, <a href='#Page_320'>320</a><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_321'>321</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_321'>321</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_321'>321</a></span><br />
+<span style="margin-left: 1em;">titration with normal acid, <a href='#Page_322'>322</a></span><br />
+<span style="margin-left: 1em;">titration with permanganate, <a href='#Page_322'>322</a></span><br />
+<br />
+Calculation of results, <a href='#Page_7'>7</a><br />
+<br />
+Calculations from formul&aelig;, <a href='#Page_70'>70</a><br />
+<br />
+Calorific effect of coal, <a href='#Page_419'>419</a><br />
+<br />
+Calorimeter, <a href='#Page_419'>419</a><br />
+<br />
+Calx, <a href='#Page_345'>345</a><br />
+<br />
+Carbon, <a href='#Page_414'>414</a><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_416'>416</a></span><br />
+<span style="margin-left: 1em;">in iron or steel, <a href='#Page_423'>423</a></span><br />
+<br />
+Carbonates, <a href='#Page_424'>424</a><br />
+<br />
+Carbonic acid in the air of mines, <a href='#Page_428'>428</a><br />
+<br />
+Caustic potash = potassium hydroxide, <a href='#Page_65'>65</a><br />
+<br />
+Caustic soda = sodium hydroxide, <a href='#Page_66'>66</a><br />
+<br />
+Cerium, <a href='#Page_318'>318</a><br />
+<br />
+Chalybite, iron in, <a href='#Page_243'>243</a><br />
+<br />
+Charcoal, <a href='#Page_21'>21</a>, <a href='#Page_94'>94</a><br />
+<br />
+Check assays for gold, <a href='#Page_154'>154</a><br />
+<span style="margin-left: 1em;">for silver, <a href='#Page_104'>104</a>, <a href='#Page_113'>113</a></span><br />
+<br />
+Chlorine and chlorides, <a href='#Page_359'>359</a><br />
+<br />
+Chromium, <a href='#Page_307'>307</a><br />
+<span style="margin-left: 1em;">gravimetric assay, <a href='#Page_309'>309</a></span><br />
+<span style="margin-left: 1em;">in chrome iron ore, <a href='#Page_308'>308</a></span><br />
+<span style="margin-left: 1em;">volumetric assay, <a href='#Page_309'>309</a></span><br />
+<br />
+Clays, examination of, <a href='#Page_316'>316</a><br />
+<br />
+Coals, <a href='#Page_418'>418</a><br />
+<br />
+Cobalt, <a href='#Page_259'>259</a><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_259'>259</a></span><br />
+<span style="margin-left: 1em;">dry assay for, <a href='#Page_251'>251</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_260'>260</a></span><br />
+<span style="margin-left: 1em;">in hardhead, <a href='#Page_288'>288</a></span><br />
+<span style="margin-left: 1em;">separation from nickel, <a href='#Page_442'>442</a>, <a href='#Page_254'>254</a>, <a href='#Page_258'>258</a></span><br />
+<br />
+Coke, <a href='#Page_25'>25</a><br />
+<br />
+Common salt, examination of, <a href='#Page_336'>336</a><br />
+<br />
+Concentrates, assay for gold of, <a href='#Page_140'>140</a><br />
+<br />
+Colorimetric assays, <a href='#Page_44'>44</a><br />
+<br />
+Copper, <a href='#Page_175'>175</a><br />
+<br />
+Copper, bismuth in, <a href='#Page_208'>208</a><br />
+<span style="margin-left: 1em;">colorimetric assay for, <a href='#Page_190'>190</a>, <a href='#Page_203'>203</a></span><br />
+<span style="margin-left: 1em;">commercial, arsenic in, <a href='#Page_208'>208</a>, <a href='#Page_388'>388</a></span><br />
+<span style="margin-left: 1em;">commercial, copper in, <a href='#Page_193'>193</a></span><br />
+<span style="margin-left: 1em;">commercial, examination of, <a href='#Page_205'>205</a></span><br />
+<span style="margin-left: 1em;">cyanide assay for, <a href='#Page_194'>194</a></span><br />
+<span style="margin-left: 1em;">dry assay of, <a href='#Page_176'>176</a></span><br />
+<span style="margin-left: 1em;">dry assay, loss of, in, <a href='#Page_176'>176</a></span><br />
+<span style="margin-left: 1em;">electrolytic assay for, <a href='#Page_190'>190</a>, <a href='#Page_203'>203</a></span><br />
+<span style="margin-left: 1em;">gold in, <a href='#Page_206'>206</a></span><br />
+<span style="margin-left: 1em;">iodide assay for, <a href='#Page_199'>199</a></span><br />
+<span style="margin-left: 1em;">iron in, <a href='#Page_209'>209</a>, <a href='#Page_249'>249</a></span><br />
+<span style="margin-left: 1em;">lead in, <a href='#Page_206'>206</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_183'>183</a></span><br />
+<span style="margin-left: 1em;">silver in, <a href='#Page_205'>205</a></span><br />
+<span style="margin-left: 1em;">sulphur in, <a href='#Page_207'>207</a></span><br />
+<br />
+Copper ores, solution of, <a href='#Page_183'>183</a><br />
+<span style="margin-left: 1em;">valuation of, <a href='#Page_181'>181</a></span><br />
+<br />
+Copper pyrites, copper in, <a href='#Page_179'>179</a>, <a href='#Page_188'>188</a>, <a href='#Page_198'>198</a>, <a href='#Page_202'>202</a><br />
+<span style="margin-left: 1em;">sulphur in, <a href='#Page_376'>376</a></span><br />
+<br />
+Culm, <a href='#Page_22'>22</a><br />
+<br />
+Cupel, <a href='#Page_23'>23</a>, <a href='#Page_142'>142</a><br />
+<br />
+Cupellation, loss, corrections for, <a href='#Page_103'>103</a><br />
+<span style="margin-left: 1em;">loss in gold, <a href='#Page_145'>145</a></span><br />
+<span style="margin-left: 1em;">loss in silver, <a href='#Page_101'>101</a></span><br />
+<span style="margin-left: 1em;">of gold lead alloys, <a href='#Page_182'>182</a></span><br />
+<span style="margin-left: 1em;">of silver lead alloys, <a href='#Page_98'>98</a>, <a href='#Page_110'>110</a></span><br />
+<span style="margin-left: 1em;">temperature of, <a href='#Page_143'>143</a></span><br />
+<br />
+Cyanicides, <a href='#Page_169'>169</a><br />
+<br />
+Cyanide assay for copper, <a href='#Page_194'>194</a><br />
+<span style="margin-left: 1em;">for nickel, <a href='#Page_255'>255</a></span><br />
+<span style="margin-left: 1em;">for tin, <a href='#Page_278'>278</a></span><br />
+<br />
+Cyanides, alkalinity of, <a href='#Page_167'>167</a><br />
+<span style="margin-left: 1em;">assay of, <a href='#Page_167'>167</a></span><br />
+<span style="margin-left: 1em;">commercial, <a href='#Page_160'>160</a></span><br />
+<span style="margin-left: 1em;">double, <a href='#Page_161'>161</a></span><br />
+<span style="margin-left: 1em;">gold-dissolving power, <a href='#Page_162'>162</a></span><br />
+<span style="margin-left: 1em;">prussic acid, <a href='#Page_162'>162</a></span><br />
+<span class='pagenum'><a name="Page_452" id="Page_452">[Pg 452]</a></span><span style="margin-left: 1em;">volumetric determination of, <a href='#Page_163'>163</a>, <a href='#Page_165'>165</a></span><br />
+<br />
+Cyanide liquors, alkalinity of, <a href='#Page_167'>167</a><br />
+<span style="margin-left: 1em;">assay of, <a href='#Page_164'>164</a>, <a href='#Page_165'>165</a></span><br />
+<span style="margin-left: 1em;">assay of, for gold, <a href='#Page_140'>140</a></span><br />
+<span style="margin-left: 1em;">assay of, for zinc, &amp;c., <a href='#Page_169'>169</a></span><br />
+<br />
+<br />
+Daniell cells, <a href='#Page_185'>185</a><br />
+<br />
+Didymium, <a href='#Page_319'>319</a><br />
+<br />
+Dollars to the ton, <a href='#Page_9'>9</a><br />
+<br />
+Dry assays, <a href='#Page_16'>16</a><br />
+<br />
+Drying, <a href='#Page_5'>5</a>, <a href='#Page_33'>33</a><br />
+<br />
+<br />
+Earths, <a href='#Page_314'>314</a><br />
+<span style="margin-left: 1em;">the alkaline, <a href='#Page_320'>320</a></span><br />
+<br />
+Electrodes, <a href='#Page_187'>187</a><br />
+<br />
+Electrolysis for copper, <a href='#Page_184'>184</a><br />
+<span style="margin-left: 1em;">for nickel, <a href='#Page_254'>254</a></span><br />
+<br />
+Equations, <a href='#Page_69'>69</a><br />
+<br />
+Erbia, <a href='#Page_319'>319</a><br />
+<br />
+<br />
+Ferrous and ferric salts, <a href='#Page_231'>231</a><br />
+<br />
+Filtration, <a href='#Page_31'>31</a><br />
+<br />
+Finishing point, <a href='#Page_42'>42</a><br />
+<br />
+Flasks, graduated, <a href='#Page_49'>49</a><br />
+<br />
+Flatting, <a href='#Page_149'>149</a><br />
+<br />
+Fluorine and fluorides, <a href='#Page_363'>363</a><br />
+<br />
+Fluxes, <a href='#Page_16'>16</a>, <a href='#Page_93'>93</a>, <a href='#Page_136'>136</a>, <a href='#Page_138'>138</a>, <a href='#Page_140'>140</a><br />
+<br />
+Formul&aelig;, <a href='#Page_68'>68</a><br />
+<br />
+Furnaces, <a href='#Page_25'>25</a><br />
+<br />
+<br />
+Galena, lead in, <a href='#Page_217'>217</a>, <a href='#Page_218'>218</a><br />
+<br />
+Gangue, <a href='#Page_405'>405</a><br />
+<span style="margin-left: 1em;">iron in the, <a href='#Page_244'>244</a></span><br />
+<br />
+Gas-measuring apparatus, <a href='#Page_52'>52</a><br />
+<br />
+Gases, measurement of, <a href='#Page_44'>44</a><br />
+<br />
+Gay-Lussac's assay for silver, <a href='#Page_119'>119</a><br />
+<span style="margin-left: 1em;">assay for silver modified, <a href='#Page_123'>123</a></span><br />
+<br />
+German silver, copper in, <a href='#Page_194'>194</a><br />
+<span style="margin-left: 1em;">nickel in, <a href='#Page_255'>255</a>, <a href='#Page_259'>259</a></span><br />
+<br />
+Gold, <a href='#Page_126'>126</a><br />
+<span style="margin-left: 1em;">amalgamation of, <a href='#Page_126'>126</a></span><br />
+<span style="margin-left: 1em;">in cyanide liquor, <a href='#Page_140'>140</a></span><br />
+<span style="margin-left: 1em;">loss of, in cupellation, <a href='#Page_145'>145</a></span><br />
+<span style="margin-left: 1em;">loss of, in parting, <a href='#Page_154'>154</a></span><br />
+<span style="margin-left: 1em;">preparation of, <a href='#Page_63'>63</a></span><br />
+<span style="margin-left: 1em;">silver in, <a href='#Page_157'>157</a></span><br />
+<span style="margin-left: 1em;">silver in, after parting, <a href='#Page_154'>154</a></span><br />
+<span style="margin-left: 1em;">test for, <a href='#Page_126'>126</a></span><br />
+<br />
+Gold-lead alloys, cupellation of, <a href='#Page_142'>142</a><br />
+<span style="margin-left: 1em;">sampling of, <a href='#Page_158'>158</a></span><br />
+<br />
+Gold ores assay with cyanide solutions, <a href='#Page_141'>141</a><br />
+<span style="margin-left: 1em;">calcination of, <a href='#Page_139'>139</a></span><br />
+<span style="margin-left: 1em;">concentrates, <a href='#Page_140'>140</a></span><br />
+<span style="margin-left: 1em;">fluxing, <a href='#Page_136'>136</a>, <a href='#Page_138'>138</a>, <a href='#Page_140'>140</a></span><br />
+<span style="margin-left: 1em;">sampling of, <a href='#Page_127'>127</a></span><br />
+<span style="margin-left: 1em;">size of assay charges, <a href='#Page_127'>127</a></span><br />
+<span style="margin-left: 1em;">tailings, <a href='#Page_140'>140</a></span><br />
+<br />
+Gold-parting, <a href='#Page_150'>150</a><br />
+<span style="margin-left: 1em;">platinum in, <a href='#Page_145'>145</a>, <a href='#Page_154'>154</a>, <a href='#Page_170'>170</a>, <a href='#Page_171'>171</a></span><br />
+<br />
+Gold-zinc slimes, <a href='#Page_142'>142</a><br />
+<br />
+Graduated vessels, <a href='#Page_49'>49</a><br />
+<br />
+Gravimetric methods, <a href='#Page_15'>15</a>, <a href='#Page_27'>27</a><br />
+<br />
+<br />
+Halogens, <a href='#Page_358'>358</a><br />
+<br />
+Hardhead, <a href='#Page_287'>287</a><br />
+<span style="margin-left: 1em;">an analysis of, <a href='#Page_289'>289</a></span><br />
+<br />
+Hot plate, <a href='#Page_30'>30</a><br />
+<br />
+Hydrogen, preparation of, <a href='#Page_62'>62</a><br />
+<span style="margin-left: 1em;">reduction by, <a href='#Page_280'>280</a></span><br />
+<br />
+Hydrometer, <a href='#Page_77'>77</a><br />
+<br />
+<br />
+Ignition, <a href='#Page_32'>32</a><br />
+<span style="margin-left: 1em;">in hydrogen, <a href='#Page_280'>280</a></span><br />
+<br />
+Indicators, <a href='#Page_42'>42</a><br />
+<br />
+Inquartation, <a href='#Page_146'>146</a><br />
+<br />
+Iodine and iodides, <a href='#Page_362'>362</a><br />
+<br />
+Iridium, <a href='#Page_171'>171</a><br />
+<br />
+Iron, <a href='#Page_231'>231</a><br />
+<span style="margin-left: 1em;">bichromate assay for, <a href='#Page_237'>237</a>, <a href='#Page_243'>243</a>,</span><br />
+<span style="margin-left: 1em;">carbon in, <a href='#Page_423'>423</a></span><br />
+<span style="margin-left: 1em;">colorimetric assay for, <a href='#Page_247'>247</a></span><br />
+<span style="margin-left: 1em;">ferrous and ferric, <a href='#Page_231'>231</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_233'>233</a></span><br />
+<span style="margin-left: 1em;">permanganate assay for, <a href='#Page_236'>236</a>, <a href='#Page_238'>238</a></span><br />
+<span style="margin-left: 1em;">phosphorus in, <a href='#Page_399'>399</a></span><br />
+<span style="margin-left: 1em;">reduction of ferric solutions, <a href='#Page_235'>235</a>, <a href='#Page_241'>241</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_232'>232</a></span><br />
+<span style="margin-left: 1em;">stannous chloride assay for, <a href='#Page_244'>244</a></span><br />
+<span style="margin-left: 1em;">volumetric assays for, <a href='#Page_234'>234</a></span><br />
+<br />
+Iron ores, iron in, <a href='#Page_244'>244</a>, <a href='#Page_247'>247</a><br />
+<span style="margin-left: 1em;">phosphates in, <a href='#Page_399'>399</a></span><br />
+<br />
+<br />
+Laboratory books, <a href='#Page_9'>9</a><br />
+<br />
+Lanthanum, <a href='#Page_319'>319</a><br />
+<br />
+<span class='pagenum'><a name="Page_453" id="Page_453">[Pg 453]</a></span>Lawrence Smith's method for alkalies, <a href='#Page_333'>333</a>, <a href='#Page_412'>412</a><br />
+<br />
+Lead, <a href='#Page_211'>211</a><br />
+<span style="margin-left: 1em;">colorimetric assay for, <a href='#Page_218'>218</a></span><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_211'>211</a></span><br />
+<span style="margin-left: 1em;">dry assay for, <a href='#Page_211'>211</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination&nbsp; of, <a href='#Page_213'>213</a></span><br />
+<span style="margin-left: 1em;">in commercial copper, <a href='#Page_206'>206</a></span><br />
+<span style="margin-left: 1em;">in commercial zinc, <a href='#Page_214'>214</a></span><br />
+<span style="margin-left: 1em;">in galena, <a href='#Page_217'>217</a>, <a href='#Page_218'>218</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_211'>211</a>, <a href='#Page_213'>213</a></span><br />
+<span style="margin-left: 1em;">volumetric&nbsp; determination of, <a href='#Page_214'>214</a></span><br />
+<br />
+Litharge, use of, in dry assays, <a href='#Page_20'>20</a>, <a href='#Page_93'>93</a><br />
+<br />
+Lithium, <a href='#Page_338'>338</a><br />
+<br />
+Lime, <a href='#Page_320'>320</a><br />
+<span style="margin-left: 1em;">milk of, <a href='#Page_321'>321</a></span><br />
+<span style="margin-left: 1em;">volumetric assays for, <a href='#Page_322'>322</a></span><br />
+<br />
+Limestone, examination of, <a href='#Page_329'>329</a><br />
+<span style="margin-left: 1em;">lime in, <a href='#Page_324'>324</a></span><br />
+<br />
+Limewater, <a href='#Page_321'>321</a><br />
+<br />
+Loths, <a href='#Page_9'>9</a><br />
+<br />
+<br />
+Magnesia, magnesium, <a href='#Page_328'>328</a><br />
+<span style="margin-left: 1em;">mixture, preparation of, <a href='#Page_64'>64</a></span><br />
+<br />
+Manganese, <a href='#Page_298'>298</a><br />
+<span style="margin-left: 1em;">colorimetric assay, <a href='#Page_306'>306</a></span><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_299'>299</a></span><br />
+<span style="margin-left: 1em;">gravimetric&nbsp; determination&nbsp; of, <a href='#Page_300'>300</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_299'>299</a></span><br />
+<span style="margin-left: 1em;">volumetric determination of, <a href='#Page_300'>300</a></span><br />
+<br />
+Manganese peroxide, ferrous sulphate assay for, <a href='#Page_301'>301</a><br />
+<span style="margin-left: 1em;">iodine assay for, <a href='#Page_302'>302</a></span><br />
+<span style="margin-left: 1em;">= manganese dioxide, <a href='#Page_298'>298</a></span><br />
+<br />
+Manganese ore, copper in, <a href='#Page_204'>204</a><br />
+<span style="margin-left: 1em;">manganese in, <a href='#Page_300'>300</a></span><br />
+<span style="margin-left: 1em;">peroxide in, <a href='#Page_302'>302</a></span><br />
+<br />
+Matte, <a href='#Page_18'>18</a><br />
+<br />
+Measuring, <a href='#Page_49'>49</a><br />
+<span style="margin-left: 1em;">flasks, <a href='#Page_49'>49</a></span><br />
+<span style="margin-left: 1em;">gases, <a href='#Page_44'>44</a>, <a href='#Page_52'>52</a></span><br />
+<span style="margin-left: 1em;">gold buttons, <a href='#Page_133'>133</a>, <a href='#Page_440'>440</a>,</span><br />
+<span style="margin-left: 1em;">liquids, <a href='#Page_49'>49</a></span><br />
+<span style="margin-left: 1em;">silver buttons, <a href='#Page_106'>106</a></span><br />
+<br />
+Mechanical methods, <a href='#Page_16'>16</a><br />
+<br />
+Mercury, <a href='#Page_171'>171</a><br />
+<span style="margin-left: 1em;">dry assay, <a href='#Page_172'>172</a></span><br />
+<span style="margin-left: 1em;">wet assay, <a href='#Page_173'>173</a></span><br />
+<br />
+Metallic particles in ores, gold, <a href='#Page_129'>129</a><br />
+<span style="margin-left: 1em;">particles in ores, silver, <a href='#Page_108'>108</a></span><br />
+<span style="margin-left: 1em;">particles, tin, <a href='#Page_278'>278</a>, <a href='#Page_287'>287</a></span><br />
+<br />
+Micrometer, <a href='#Page_133'>133</a><br />
+<br />
+Microscope, measuring with the, <a href='#Page_440'>440</a>, <a href='#Page_133'>133</a><br />
+<br />
+Mispickel, arsenic in, <a href='#Page_125'>125</a>, <a href='#Page_392'>392</a><br />
+<span style="margin-left: 1em;">sulphur in, <a href='#Page_376'>376</a></span><br />
+<br />
+Moisture, <a href='#Page_7'>7</a>, <a href='#Page_350'>350</a><br />
+<br />
+Molybdate separation for phosphates, <a href='#Page_395'>395</a><br />
+<span style="margin-left: 1em;">solution, preparation of, <a href='#Page_60'>60</a></span><br />
+<br />
+Molybdenum, <a href='#Page_311'>311</a><br />
+<br />
+Muffle, <a href='#Page_25'>25</a><br />
+<br />
+<br />
+Nessler's solution, <a href='#Page_342'>342</a><br />
+<br />
+Nickel, <a href='#Page_251'>251</a><br />
+<span style="margin-left: 1em;">dry assay for, <a href='#Page_251'>251</a></span><br />
+<span style="margin-left: 1em;">electrolytic assay, <a href='#Page_254'>254</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination of, <a href='#Page_254'>254</a></span><br />
+<span style="margin-left: 1em;">in German silver, <a href='#Page_255'>255</a>, <a href='#Page_259'>259</a></span><br />
+<span style="margin-left: 1em;">separation from cobalt, <a href='#Page_254'>254</a>, <a href='#Page_258'>258</a>, <a href='#Page_442'>442</a></span><br />
+<span style="margin-left: 1em;">separation from iron, <a href='#Page_258'>258</a></span><br />
+<span style="margin-left: 1em;">separation from manganese, <a href='#Page_258'>258</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_253'>253</a></span><br />
+<span style="margin-left: 1em;">volumetric assay, <a href='#Page_255'>255</a></span><br />
+<br />
+Niobium, <a href='#Page_297'>297</a><br />
+<br />
+Nitre, <a href='#Page_22'>22</a><br />
+<span style="margin-left: 1em;">use of, in dry assays, <a href='#Page_95'>95</a></span><br />
+<br />
+Nitrogen and nitrates, <a href='#Page_400'>400</a><br />
+<br />
+Nitrometer, <a href='#Page_403'>403</a><br />
+<br />
+Normal acid, normal solutions, <a href='#Page_323'>323</a><br />
+<br />
+<br />
+Ores, determining water in, <a href='#Page_5'>5</a>, <a href='#Page_351'>351</a><br />
+<span style="margin-left: 1em;">drying, <a href='#Page_5'>5</a></span><br />
+<span style="margin-left: 1em;">powdering, <a href='#Page_4'>4</a>, <a href='#Page_109'>109</a>, <a href='#Page_130'>130</a>, <a href='#Page_448'>448</a></span><br />
+<span style="margin-left: 1em;">quantities of, for an assay, <a href='#Page_11'>11</a>, <a href='#Page_27'>27</a>, <a href='#Page_127'>127</a></span><br />
+<span style="margin-left: 1em;">sampling, <a href='#Page_1'>1</a>, <a href='#Page_127'>127</a>, <a href='#Page_444'>444</a></span><br />
+<span style="margin-left: 1em;">with metallic particles, <a href='#Page_3'>3</a>, <a href='#Page_108'>108</a>, <a href='#Page_129'>129</a></span><br />
+<br />
+Osmiridium, <a href='#Page_171'>171</a><br />
+<br />
+Osmium, <a href='#Page_171'>171</a><br />
+<br />
+Ounces to the ton, long, <a href='#Page_107'>107</a><br />
+<span style="margin-left: 1em;">to the ton, short, <a href='#Page_132'>132</a></span><br />
+<br />
+Oxidation, <a href='#Page_345'>345</a><br />
+<br />
+Oxides, <a href='#Page_345'>345</a><br />
+<span class='pagenum'><a name="Page_454" id="Page_454">[Pg 454]</a></span><span style="margin-left: 1em;">determination of oxygen in, <a href='#Page_346'>346</a></span><br />
+<br />
+Oxidising agents, <a href='#Page_22'>22</a>, <a href='#Page_95'>95</a>, <a href='#Page_345'>345</a><br />
+<span style="margin-left: 1em;">effect of nitre, <a href='#Page_95'>95</a></span><br />
+<span style="margin-left: 1em;">effect of nitric acid, <a href='#Page_56'>56</a></span><br />
+<br />
+Oxygen, <a href='#Page_344'>344</a><br />
+<span style="margin-left: 1em;">equivalent, <a href='#Page_358'>358</a></span><br />
+<span style="margin-left: 1em;">in natural waters, <a href='#Page_344'>344</a>, <a href='#Page_356'>356</a></span><br />
+<span style="margin-left: 1em;">in ores, <a href='#Page_348'>348</a></span><br />
+<br />
+<br />
+Palladium, <a href='#Page_171'>171</a><br />
+<br />
+Parting, <a href='#Page_150'>150</a><br />
+<span style="margin-left: 1em;">acids, <a href='#Page_150'>150</a></span><br />
+<span style="margin-left: 1em;">in flasks, <a href='#Page_151'>151</a></span><br />
+<span style="margin-left: 1em;">in glazed crucibles, <a href='#Page_153'>153</a></span><br />
+<span style="margin-left: 1em;">in special apparatus, <a href='#Page_156'>156</a></span><br />
+<span style="margin-left: 1em;">in test tubes, <a href='#Page_152'>152</a></span><br />
+<br />
+Phosphate, assay of apatite for, <a href='#Page_399'>399</a><br />
+<span style="margin-left: 1em;">assay of iron ore for, <a href='#Page_399'>399</a></span><br />
+<br />
+Phosphates, gravimetric assay, <a href='#Page_396'>396</a><br />
+<span style="margin-left: 1em;">volumetric assay, <a href='#Page_397'>397</a></span><br />
+<br />
+Phosphorus and phosphates, <a href='#Page_394'>394</a><br />
+<span style="margin-left: 1em;">in iron, <a href='#Page_399'>399</a></span><br />
+<br />
+Pipette, <a href='#Page_50'>50</a>, <a href='#Page_120'>120</a><br />
+<br />
+Platinum, <a href='#Page_170'>170</a><br />
+<span style="margin-left: 1em;">in gold, <a href='#Page_145'>145</a>, <a href='#Page_154'>154</a>, <a href='#Page_170'>170</a></span><br />
+<br />
+Potash, commercial examination of, <a href='#Page_338'>338</a><br />
+<br />
+Potassium, <a href='#Page_336'>336</a><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_337'>337</a></span><br />
+<br />
+Potassium cyanide, <a href='#Page_22'>22</a>, <a href='#Page_65'>65</a>, <a href='#Page_160'>160</a><br />
+<span style="margin-left: 1em;">commercial assay of, <a href='#Page_167'>167</a></span><br />
+<span style="margin-left: 1em;">commercial, purity of, <a href='#Page_161'>161</a></span><br />
+<br />
+Powdering, <a href='#Page_4'>4</a>, <a href='#Page_130'>130</a>, <a href='#Page_448'>448</a>, <a href='#Page_109'>109</a><br />
+<br />
+Precipitation, <a href='#Page_30'>30</a><br />
+<br />
+Precipitates, drying, <a href='#Page_32'>32</a><br />
+<span style="margin-left: 1em;">igniting, <a href='#Page_32'>32</a>, <a href='#Page_34'>34</a></span><br />
+<span style="margin-left: 1em;">washing, <a href='#Page_31'>31</a></span><br />
+<br />
+Preliminary assays, <a href='#Page_104'>104</a>, <a href='#Page_147'>147</a><br />
+<br />
+Preparation of acids, <a href='#Page_54'>54</a><br />
+<span style="margin-left: 1em;">of other reagents, <a href='#Page_59'>59</a></span><br />
+<br />
+Prill, <a href='#Page_108'>108</a>, <a href='#Page_129'>129</a>, <a href='#Page_278'>278</a>, <a href='#Page_287'>287</a><br />
+<br />
+Produce, <a href='#Page_8'>8</a><br />
+<br />
+Pyrarsenate of magnesia, <a href='#Page_383'>383</a><br />
+<br />
+Pyrites, iron in, <a href='#Page_244'>244</a><br />
+<span style="margin-left: 1em;">sulphur in, <a href='#Page_370'>370</a>, <a href='#Page_376'>376</a></span><br />
+<br />
+Pyrophosphate of magnesia, <a href='#Page_397'>397</a><br />
+<br />
+<br />
+Quantity to be taken for an assay, <a href='#Page_11'>11</a>, <a href='#Page_27'>27</a>, <a href='#Page_127'>127</a><br />
+<br />
+Quartation, <a href='#Page_146'>146</a><br />
+<br />
+Quartering, <a href='#Page_2'>2</a><br />
+<br />
+<br />
+Reagents, strength of, <a href='#Page_54'>54</a><br />
+<br />
+Red lead for dry assays, <a href='#Page_20'>20</a>, <a href='#Page_22'>22</a>, <a href='#Page_94'>94</a><br />
+<br />
+Reducing agents, <a href='#Page_21'>21</a>, <a href='#Page_94'>94</a><br />
+<span style="margin-left: 1em;">effects of charcoal, &amp;c., <a href='#Page_94'>94</a></span><br />
+<span style="margin-left: 1em;">effect of mineral sulphides, <a href='#Page_95'>95</a>, <a href='#Page_97'>97</a>, <a href='#Page_98'>98</a></span><br />
+<br />
+Reduction by hydrogen, <a href='#Page_280'>280</a><br />
+<span style="margin-left: 1em;">of ferric solutions, <a href='#Page_235'>235</a>, <a href='#Page_242'>242</a>, <a href='#Page_244'>244</a></span><br />
+<br />
+Regulus, <a href='#Page_18'>18</a><br />
+<br />
+Report form, <a href='#Page_12'>12</a><br />
+<br />
+Results, calculation of, <a href='#Page_7'>7</a>, <a href='#Page_13'>13</a>, <a href='#Page_16'>16</a>, <a href='#Page_38'>38</a>, <a href='#Page_107'>107</a>, <a href='#Page_131'>131</a>, <a href='#Page_132'>132</a><br />
+<span style="margin-left: 1em;">statement of, <a href='#Page_7'>7</a></span><br />
+<br />
+Rhodium, <a href='#Page_171'>171</a><br />
+<br />
+Roasting, <a href='#Page_22'>22</a>, <a href='#Page_345'>345</a><br />
+<br />
+Rolling, <a href='#Page_149'>149</a><br />
+<br />
+Rubidium, <a href='#Page_340'>340</a><br />
+<br />
+Ruthenium, <a href='#Page_171'>171</a><br />
+<br />
+<br />
+Sample book, <a href='#Page_9'>9</a><br />
+<br />
+Sampling, <a href='#Page_1'>1</a><br />
+<span style="margin-left: 1em;">effect of powdering on, <a href='#Page_449'>449</a></span><br />
+<span style="margin-left: 1em;">errors, <a href='#Page_447'>447</a></span><br />
+<span style="margin-left: 1em;">gold ores, <a href='#Page_127'>127</a></span><br />
+<span style="margin-left: 1em;">metals, <a href='#Page_157'>157</a></span><br />
+<span style="margin-left: 1em;">theory of, <a href='#Page_444'>444</a></span><br />
+<br />
+Scorification of silver ores, <a href='#Page_88'>88</a><br />
+<br />
+Scorifier, <a href='#Page_23'>23</a>, <a href='#Page_89'>89</a><br />
+<br />
+Selenium, <a href='#Page_379'>379</a><br />
+<br />
+Separation, as sulphides, <a href='#Page_57'>57</a><br />
+<span style="margin-left: 1em;">basic acetate, <a href='#Page_233'>233</a></span><br />
+<span style="margin-left: 1em;">molybdate, <a href='#Page_395'>395</a></span><br />
+<br />
+Shales, bituminous, <a href='#Page_420'>420</a><br />
+<br />
+Silicon and silicates, <a href='#Page_405'>405</a><br />
+<span style="margin-left: 1em;">in iron, <a href='#Page_414'>414</a></span><br />
+<br />
+Silica in rocks, <a href='#Page_409'>409</a><br />
+<span style="margin-left: 1em;">in slags, <a href='#Page_414'>414</a></span><br />
+<br />
+Silicates, alkalies in, <a href='#Page_333'>333</a>, <a href='#Page_412'>412</a><br />
+<span style="margin-left: 1em;">beryllia in, <a href='#Page_320'>320</a></span><br />
+<span style="margin-left: 1em;">examination of, <a href='#Page_409'>409</a></span><br />
+<span style="margin-left: 1em;">titanium in, <a href='#Page_411'>411</a></span><br />
+<br />
+Silver, <a href='#Page_87'>87</a><br />
+<span style="margin-left: 1em;">correction for cupellation loss, <a href='#Page_103'>103</a></span><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_87'>87</a></span><br />
+<span style="margin-left: 1em;">Gay-Lussac's assay, <a href='#Page_119'>119</a></span><br />
+<span style="margin-left: 1em;">Gay-Lussac's assay modified, <a href='#Page_123'>123</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination of, <a href='#Page_117'>117</a></span><br />
+<span class='pagenum'><a name="Page_455" id="Page_455">[Pg 455]</a></span><span style="margin-left: 1em;">in bullion, <a href='#Page_113'>113</a></span><br />
+<span style="margin-left: 1em;">in burnt ore, <a href='#Page_116'>116</a>, <a href='#Page_118'>118</a></span><br />
+<span style="margin-left: 1em;">in copper, <a href='#Page_114'>114</a>, <a href='#Page_205'>205</a></span><br />
+<span style="margin-left: 1em;">in galena, <a href='#Page_114'>114</a></span><br />
+<span style="margin-left: 1em;">in lead, <a href='#Page_113'>113</a></span><br />
+<span style="margin-left: 1em;">in oxide of lead, <a href='#Page_113'>113</a></span><br />
+<span style="margin-left: 1em;">in silver precipitate, <a href='#Page_115'>115</a></span><br />
+<span style="margin-left: 1em;">loss in cupellation, <a href='#Page_101'>101</a></span><br />
+<span style="margin-left: 1em;">pure preparation of, <a href='#Page_66'>66</a></span><br />
+<span style="margin-left: 1em;">Volhard's assay, <a href='#Page_121'>121</a></span><br />
+<span style="margin-left: 1em;">volumetric methods, <a href='#Page_119'>119</a>, <a href='#Page_121'>121</a>, <a href='#Page_123'>123</a></span><br />
+<br />
+Silver lead alloys, cupellation of, <a href='#Page_98'>98</a><br />
+<span style="margin-left: 9.5em;">sampling of, <a href='#Page_157'>157</a></span><br />
+<br />
+Silver ore, crucible assay of, <a href='#Page_90'>90</a><br />
+<span style="margin-left: 1em;">metallic particles in, <a href='#Page_108'>108</a></span><br />
+<span style="margin-left: 1em;">scorification of, <a href='#Page_88'>88</a></span><br />
+<br />
+Size of assay charges, <a href='#Page_11'>11</a>, <a href='#Page_27'>27</a>, <a href='#Page_127'>127</a><br />
+<br />
+Slags, <a href='#Page_19'>19</a><br />
+<br />
+Soda-lime, <a href='#Page_425'>425</a><br />
+<br />
+Sodium, <a href='#Page_334'>334</a><br />
+<br />
+Sodium cyanide, <a href='#Page_160'>160</a><br />
+<br />
+Solution, <a href='#Page_29'>29</a><br />
+<br />
+Solutions, normal, <a href='#Page_323'>323</a><br />
+<span style="margin-left: 1em;">standard, <a href='#Page_36'>36</a></span><br />
+<br />
+Specific gravity, <a href='#Page_75'>75</a>, <a href='#Page_436'>436</a><br />
+<br />
+Speise, <a href='#Page_19'>19</a><br />
+<br />
+Standard, <a href='#Page_37'>37</a><br />
+<span style="margin-left: 1em;">solutions, <a href='#Page_36'>36</a></span><br />
+<br />
+Standardising, <a href='#Page_37'>37</a><br />
+<br />
+Steel, carbon in, <a href='#Page_423'>423</a><br />
+<span style="margin-left: 1em;">chromium in, <a href='#Page_310'>310</a></span><br />
+<span style="margin-left: 1em;">manganese in, <a href='#Page_300'>300</a></span><br />
+<br />
+Stoking, <a href='#Page_25'>25</a>, <a href='#Page_143'>143</a><br />
+<br />
+Strength of reagents, <a href='#Page_54'>54</a><br />
+<br />
+Strontium, <a href='#Page_324'>324</a><br />
+<br />
+Sulphates and sulphur, <a href='#Page_367'>367</a><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_369'>369</a></span><br />
+<span style="margin-left: 1em;">volumetric determination, <a href='#Page_370'>370</a></span><br />
+<br />
+Sulphides, reducing action of, <a href='#Page_9'>9</a>, <a href='#Page_95'>95</a><br />
+<br />
+Sulphocyanate assay for silver, <a href='#Page_121'>121</a><br />
+<br />
+Sulphur in blende, <a href='#Page_375'>375</a><br />
+<span style="margin-left: 1em;">in burnt ore, <a href='#Page_377'>377</a></span><br />
+<span style="margin-left: 1em;">in chalcocite, <a href='#Page_376'>376</a></span><br />
+<span style="margin-left: 1em;">in coal, <a href='#Page_419'>419</a></span><br />
+<span style="margin-left: 1em;">in copper, <a href='#Page_207'>207</a></span><br />
+<span style="margin-left: 1em;">in copper pyrites, <a href='#Page_376'>376</a></span><br />
+<span style="margin-left: 1em;">in mispickel, <a href='#Page_376'>376</a></span><br />
+<span style="margin-left: 1em;">in pyrites, <a href='#Page_370'>370</a>, <a href='#Page_376'>376</a></span><br />
+<br />
+Sulphuretted hydrogen, preparation, <a href='#Page_57'>57</a><br />
+<br />
+Surcharge, <a href='#Page_154'>154</a><br />
+<br />
+System in assaying, <a href='#Page_28'>28</a><br />
+<br />
+<br />
+Table, atomic weights, <a href='#Page_433'>433</a><br />
+<span style="margin-left: 1em;">comparing thermometers, <a href='#Page_435'>435</a></span><br />
+<span style="margin-left: 1em;">ounces to the long ton, <a href='#Page_107'>107</a></span><br />
+<span style="margin-left: 1em;">ounces to the short ton, <a href='#Page_132'>132</a></span><br />
+<span style="margin-left: 1em;">sp. g. ammonia, <a href='#Page_438'>438</a></span><br />
+<span style="margin-left: 1em;">sp. g. hydrochloric acid, <a href='#Page_437'>437</a></span><br />
+<span style="margin-left: 1em;">sp. g. minerals, <a href='#Page_86'>86</a></span><br />
+<span style="margin-left: 1em;">sp. g. nitric acid, <a href='#Page_436'>436</a></span><br />
+<span style="margin-left: 1em;">sp. g. sulphuric acid, <a href='#Page_439'>439</a></span><br />
+<span style="margin-left: 1em;">sp. g. water, <a href='#Page_83'>83</a></span><br />
+<br />
+Tantalum, <a href='#Page_297'>297</a><br />
+<br />
+Tartar, <a href='#Page_20'>20</a>, <a href='#Page_94'>94</a><br />
+<br />
+Tellurium, <a href='#Page_379'>379</a><br />
+<span style="margin-left: 1em;">improved test for, <a href='#Page_150'>150</a></span><br />
+<br />
+Thallium, <a href='#Page_219'>219</a><br />
+<br />
+Thorium, <a href='#Page_317'>317</a><br />
+<br />
+Tin, <a href='#Page_271'>271</a> <i>See also Black tin</i><br />
+<span style="margin-left: 1em;">assay for, by vanning, <a href='#Page_273'>273</a></span><br />
+<span style="margin-left: 1em;">copper in, <a href='#Page_204'>204</a></span><br />
+<span style="margin-left: 1em;">Cornish assay, <a href='#Page_276'>276</a></span><br />
+<span style="margin-left: 1em;">cyanide assay, <a href='#Page_278'>278</a></span><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_279'>279</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination of, <a href='#Page_281'>281</a></span><br />
+<span style="margin-left: 1em;">iron in, <a href='#Page_250'>250</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_280'>280</a></span><br />
+<span style="margin-left: 1em;">volumetric assay for, <a href='#Page_282'>282</a></span><br />
+<br />
+Tin arsenide, <a href='#Page_284'>284</a><br />
+<br />
+Tin phosphide, <a href='#Page_284'>284</a><br />
+<br />
+Tin slag, <a href='#Page_290'>290</a><br />
+<span style="margin-left: 1em;">an analysis of, <a href='#Page_292'>292</a></span><br />
+<span style="margin-left: 1em;">tin in, <a href='#Page_290'>290</a></span><br />
+<br />
+Titanium, <a href='#Page_292'>292</a><br />
+<span style="margin-left: 1em;">detection of, <a href='#Page_293'>293</a></span><br />
+<span style="margin-left: 1em;">in black tin, <a href='#Page_272'>272</a>, <a href='#Page_287'>287</a></span><br />
+<span style="margin-left: 1em;">in rocks, <a href='#Page_411'>411</a></span><br />
+<span style="margin-left: 1em;">separation, &amp;c., <a href='#Page_294'>294</a></span><br />
+<br />
+Titration, <a href='#Page_35'>35</a><br />
+<span style="margin-left: 1em;">indirect, <a href='#Page_43'>43</a>, <a href='#Page_72'>72</a></span><br />
+<br />
+Ton, assay, <a href='#Page_13'>13</a>, <a href='#Page_131'>131</a>,<br />
+<span style="margin-left: 1em;">long, 2240 lbs. = 32,666.6 oz., <a href='#Page_107'>107</a></span><br />
+<span style="margin-left: 1em;">short, 2000 lbs = 29,166.6 oz., <a href='#Page_132'>132</a></span><br />
+<br />
+Tungsten, <a href='#Page_295'>295</a><br />
+<br />
+Tungstic acid, <a href='#Page_295'>295</a><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_296'>296</a></span><br />
+<span style="margin-left: 1em;">in black tin, <a href='#Page_285'>285</a></span><br />
+<span style="margin-left: 1em;">in wolfram, <a href='#Page_296'>296</a></span><br />
+<br />
+<br />
+<span class='pagenum'><a name="Page_456" id="Page_456">[Pg 456]</a></span>Uranium, <a href='#Page_312'>312</a><br />
+<br />
+Valuation, of copper ores, <a href='#Page_181'>181</a><br />
+<br />
+Vanadium, <a href='#Page_310'>310</a><br />
+<br />
+Vanning, <a href='#Page_273'>273</a><br />
+<br />
+Volhard's assay applied to arsenic, <a href='#Page_124'>124</a><br />
+<span style="margin-left: 1em;">silver assay, <a href='#Page_121'>121</a></span><br />
+<br />
+Volume-corrector, <a href='#Page_53'>53</a><br />
+<br />
+Volumetric assay, <a href='#Page_35'>35</a>, <a href='#Page_38'>38</a><br />
+<br />
+<br />
+Water, <a href='#Page_7'>7</a>, <a href='#Page_350'>350</a><br />
+<span style="margin-left: 1em;">direct determination of, <a href='#Page_351'>351</a></span><br />
+<span style="margin-left: 1em;">examination of, <a href='#Page_352'>352</a></span><br />
+<span style="margin-left: 1em;">expansion of, <a href='#Page_83'>83</a></span><br />
+<span style="margin-left: 1em;">solids in, <a href='#Page_354'>354</a></span><br />
+<br />
+Weighing, <a href='#Page_47'>47</a><br />
+<span style="margin-left: 1em;">small gold buttons, <a href='#Page_131'>131</a></span><br />
+<br />
+Weights, <a href='#Page_47'>47</a><br />
+<br />
+Wolfram, an analysis of, <a href='#Page_296'>296</a><br />
+<span style="margin-left: 1em;">tungstic acid in, <a href='#Page_296'>296</a></span><br />
+<br />
+<br />
+Yttria, <a href='#Page_319'>319</a><br />
+<br />
+<br />
+Zinc, <a href='#Page_261'>261</a><br />
+<span style="margin-left: 1em;">commercial, examination of, <a href='#Page_268'>268</a></span><br />
+<span style="margin-left: 1em;">commercial, iron in, <a href='#Page_249'>249</a></span><br />
+<span style="margin-left: 1em;">commercial, lead in, <a href='#Page_214'>214</a></span><br />
+<span style="margin-left: 1em;">dry assay, <a href='#Page_261'>261</a></span><br />
+<span style="margin-left: 1em;">gasometric assay, <a href='#Page_266'>266</a></span><br />
+<span style="margin-left: 1em;">gravimetric determination, <a href='#Page_262'>262</a></span><br />
+<span style="margin-left: 1em;">in blende, <a href='#Page_266'>266</a></span><br />
+<span style="margin-left: 1em;">in cyanide liquors, <a href='#Page_169'>169</a></span><br />
+<span style="margin-left: 1em;">in silver precipitate, <a href='#Page_266'>266</a></span><br />
+<span style="margin-left: 1em;">separation of, <a href='#Page_262'>262</a></span><br />
+<span style="margin-left: 1em;">volumetric assay, <a href='#Page_263'>263</a></span><br />
+<br />
+Zirconia, <a href='#Page_317'>317</a><br />
+</p>
+
+
+<p>Printed by <span class="smcap">Ballantyne, Hanson</span> &amp; Co.</p>
+
+<p>London &amp; Edinburgh.</p>
+
+
+
+<hr style="width: 65%;" />
+<p><span class='pagenum'><a name="Page_xxv" id="Page_xxv">[Pg xxv]</a></span></p>
+<h2><a name="A_SELECTION" id="A_SELECTION"></a>A SELECTION</h2>
+
+<h4>FROM THE</h4>
+
+<h3>SCIENTIFIC AND TECHNICAL WORKS</h3>
+
+<h4><i>PUBLISHED BY</i></h4>
+
+<h3><b>CHARLES GRIFFIN &amp; COMPANY, LIMITED.</b></h3>
+
+<div class="figcenter" style="width: 403px;">
+<img src="images/advertsbooks.jpg" width="403" height="300" alt="" title="" />
+</div>
+
+<p>MESSRS. CHARLES GRIFFIN &amp; COMPANY'S PUBLICATIONS may be obtained through
+any Bookseller in the United Kingdom, or will be sent Post-free on
+receipt of a remittance to cover published price. To prevent delay,
+Orders should be accompanied by a Cheque or Postal Order crossed
+"<span class="smcap">Union of London and Smith's Bank</span>, Chancery Lane Branch."</p>
+
+<p>*** <i>For INDEX, see next page.</i></p>
+
+<div class="figcenter" style="width: 155px;">
+<img src="images/advertsstamp.jpg" width="155" height="150" alt="" title="" />
+</div>
+
+<p>COMPLETE TECHNICAL, MEDICAL, and GENERAL CATALOGUES forwarded Post-free
+on Application.</p>
+
+<p class="center"><b>LONDON:</b></p>
+
+<p class="center"><b>EXETER STREET, STRAND.</b></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxvi" id="Page_xxvi">[Pg xxvi]</a></span></p>
+
+<p><span class="smcap">Third Edition</span>, <i>Revised, with an Additional Chapter on
+Foundations. Numerous Diagrams, Examples, and Tables. Large 8vo. Cloth.
+16s.</i></p>
+
+<h3><b>THE DESIGN OF STRUCTURES:</b></h3>
+
+<h5>A Practical Treatise on the Building of Bridges, Roofs, &amp;c.</h5>
+
+<h4>BY S. ANGLIN, C.E.,</h4>
+
+<h6>Master of Engineering, Royal University of Ireland, late Whitworth
+Scholar, &amp;c.</h6>
+
+<p>"Students of Engineering will find this Text-Book
+<span class="smcap">invaluable</span>."&mdash;<i>Architect.</i></p>
+
+<p>"The author has certainly succeeded in producing a <span class="smcap">thoroughly
+practical</span> Text-Book."&mdash;<i>Builder.</i></p>
+
+<p>"We can unhesitatingly recommend this work not only to the Student, as
+the <span class="smcap">best Text-Book</span> on the subject, but also to the professional
+engineer as an <span class="smcap">exceedingly valuable</span> book of
+reference."&mdash;<i>Mechanical World.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition</span>, <i>Thoroughly Revised. Royal 8vo. With numerous
+Illustrations and 13 Lithographic Plates. Handsome Cloth. Price 3Os.</i></p>
+
+<h4>A PRACTICAL TREATISE ON</h4>
+
+<h3>BRIDGE-CONSTRUCTION:</h3>
+
+<h5>Being a Text-Book on the Construction of Bridges in Iron and Steel.</h5>
+
+<h5>FOR THE USE OF STUDENTS, DRAUGHTSMEN, AND ENGINEERS.</h5>
+
+<h4><span class="smcap">By T. CLAXTON FIDLER, M. INST</span>. C.E.,</h4>
+
+<h6>Prof. of Engineering, University College, Dundee.</h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;<span class="smcap">Part I.</span>&mdash;Elementary Statics.
+<span class="smcap">Part II.</span>&mdash;General Principles of Bridge-Construction. <span class="smcap">Part
+III.</span>&mdash;The Strength of Materials. <span class="smcap">Part IV.</span>&mdash;The Design of
+Bridges in Detail.</p>
+
+<p>"The new edition of Mr. Fidler's work will again occupy the same
+<span class="smcap">conspicuous position</span> among professional text-books and
+treatises as has been accorded to its predecessors. The instruction
+imparted is <span class="smcap">sound, simple, and full</span>. The volume will be found
+valuable and useful alike to those who may wish to study only the
+theoretical principles enunciated, and ... to others whose object and
+business is ... practical."&mdash;<i>The Engineer.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxvii" id="Page_xxvii">[Pg xxvii]</a></span></p>
+
+<p>At Press. In Large 8vo. Handsome Cloth. With Copious Plates and
+Illustrations.</p>
+
+<h4>The Principles and Practice of</h4> <h5>DOCK ENGINEERING.</h5>
+
+<h4>By BRYSON CUNNINGHAM, B.E., <span class="smcap">Assoc.M.Inst.C.E.</span>,</h4> <h6>Of the
+Engineers' Department, Mersey Docks and Harbour Board.</h6>
+
+<h5>GENERAL CONTENTS.</h5>
+
+<p>Historical and Discursive.&mdash;Dock Design.&mdash;Constructive
+Appliances.&mdash;Materials.&mdash;Dock and Quay Walls.&mdash;Entrance Passages and
+Locks.&mdash;Jetties, Wharves, and Piers.&mdash;Dock Gates and Caissons.&mdash;Transit
+Sheds and Warehouses.&mdash;Dock Bridges.&mdash;Graving and Repairing
+Docks.&mdash;Working Equipment of Docks.&mdash;<span class="smcap">Index</span>.</p>
+
+<p> *** The object of the Author has been to deal fully and comprehensively
+with the problems arising out of the construction and maintenance of
+Docks and their appanages, not simply as a record of works carried out,
+but as a treatise on the principles underlying their construction and an
+investigation of the mathematical theories involved. It is primarily
+intended for the student; but it is hoped that the large amount of data
+and material collected from various sources, and in many cases
+contributed specially for this book, will render it useful to the expert
+engineer as a work of reference; while, at the same time, of general
+interest to directors and others connected with the management and
+administration of seaports.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition.</span> In Two Parts, Published Separately.</p>
+
+<h4>A TEXT-BOOK OF</h4>
+
+<h3>Engineering Drawing and Design</h3>
+
+<h4><span class="smcap">Vol. I.&mdash;Practical Geometry, Plane, and Solid. 3s.</span></h4>
+
+<h4><span class="smcap">VOL. II.&mdash;Machine and Engine Drawing and Design. 4s. 6d.</span></h4>
+
+<h6>BY</h6>
+
+<h4>SIDNEY H. WELLS, <span class="smcap">Wh.Sc.</span>,</h4>
+
+<h6>A.M.INST.C.E., A.M.INST.MECH.E.,</h6>
+
+<p>Principal of the Battersea Polytechnic Institute, and Head of the
+Engineering Department therein; formerly of the Engineering Departments
+of the Yorkshire College, Leeds; and Dulwich College, London.</p>
+
+<p><i>With many Illustrations, specially prepared for the Work, and numerous
+Examples, for the Use of Students in Technical Schools and Colleges.</i></p>
+
+<p>"<span class="smcap">A capital text-book</span>, arranged on an <span class="smcap">EXCELLENT SYSTEM</span>,
+calculated to give an intelligent grasp of the subject, and not the mere
+faculty of mechanical copying.... Mr. Wells shows how to make complete
+working drawings, discussing fully each step in the
+design."&mdash;<i>Electrical Review.</i></p>
+
+<p>"The first book leads easily and naturally towards the second, where the
+technical pupil brought into contact with large and more complex
+designs."&mdash;<i>The Schoolmaster.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxviii" id="Page_xxviii">[Pg xxviii]</a></span></p>
+
+<h4>Works by BRYAN DONKIN, M. Inst. C.E., M. Inst. Mech. E., &amp;c.</h4>
+
+<p><span class="smcap">Third Edition</span>, Revised and Enlarged. With additional
+Illustrations. Large 8vo, Handsome Cloth. 25s.</p>
+
+<h3>GAS, OIL, AND AIR ENGINES:</h3>
+
+<h4>A Practical Text-Book on Internal Combustion Motors without Boiler.</h4>
+
+<h5><span class="smcap">By BRYAN DONKIN, M. Inst. C.E., M. Inst. Mech. E.</span></h5>
+
+<p><span class="smcap">General Contents</span>.&mdash;<b>Gas Engines</b>:&mdash;General Description&mdash;History
+and Development&mdash;British, French, and German Gas Engines&mdash;Gas Production
+for Motive Power&mdash;Theory of the Gas Engine&mdash;Chemical Composition of Gas
+in Gas Engines&mdash;Utilisation of Heat&mdash;Explosion and Combustion. <b>Oil
+Motors</b>:&mdash;History and Development&mdash;Various Types&mdash;Priestman's and other
+Oil Engines. <b>Hot-Air Engines</b>:&mdash;History and Development&mdash;Various Types:
+Stirling's, Ericsson's, &amp;c., &amp;c.</p>
+
+<p>"The <span class="smcap">best book now published</span> on Gas, Oil, and Air Engines....
+Will be of <span class="smcap">very great interest</span> to the numerous practical
+engineers who have to make themselves familiar with the motor of the
+day.... Mr. Donkin has the advantage of <span class="smcap">long practical
+experience</span>, combined with <span class="smcap">high scientific and experimental
+knowledge</span>, and an accurate perception of the requirements of
+Engineers."&mdash;<i>The Engineer.</i></p>
+
+<p>"We <span class="smcap">heartily recommend</span> Mr. Donkin's work.... A monument of
+careful labour.... Luminous and comprehensive."&mdash;<i>Journal of Gas
+Lighting</i>.</p>
+
+<p>"A thoroughly <span class="smcap">reliable and exhaustive</span>
+Treatise."&mdash;<i>Engineering.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>In Quarto, Handsome Cloth. With Numerous Plates. 25s.</p>
+
+<h3>THE HEAT EFFICIENCY OF STEAM BOILERS (LAND, MARINE, AND LOCOMOTIVE).</h3>
+
+<p><b>With many Tests and Experiments on different Types of Boilers, as to
+the Heating Value of Fuels, &amp;c., with Analyses of Gases and Amount of
+Evaporation, and Suggestions for the Testing of Boilers.</b></p>
+
+<h4><span class="smcap">By BRYAN DONKIN, M. Inst. C.E.</span></h4>
+
+<p><span class="smcap">General Contents</span>.&mdash;Classification of different Types of
+Boilers&mdash;425 Experiments on English and Foreign Boilers with their Heat
+Efficiencies shown in Fifty Tables&mdash;Fire Grates of Various
+Types&mdash;Mechanical Stokers&mdash;Combustion of Fuel in Boilers&mdash;Transmission
+of Heat through Boiler Plates, and their Temperature&mdash;Feed Water
+Heaters, Superheaters, Feed Pumps, &amp;c.&mdash;Smoke and its
+Prevention&mdash;Instruments used in Testing Boilers&mdash;Marine and Locomotive
+Boilers&mdash;Fuel Testing Stations&mdash;Discussion of the Trials and
+Conclusions&mdash;On the Choice of a Boiler, and Testing of Land, Marine, and
+Locomotive Boilers&mdash;Appendices&mdash;Bibliography&mdash;Index.</p>
+
+<p><i>With Plates illustrating Progress made during recent years, and the
+best Modern Practice.</i></p>
+
+<p>"<span class="smcap">A work of reference at present unique</span>. Will give an answer to
+almost any question connected with the performance of boilers that it is
+possible to ask."&mdash;<i>Engineer.</i></p>
+
+<p>"Probably the <span class="smcap">most exhaustive</span> <i>r&eacute;sum&eacute;</i> that has ever been
+collected. <span class="smcap">A practical Book</span> by a thoroughly practical
+man."&mdash;<i>Iron and Coal Trades Review.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxix" id="Page_xxix">[Pg xxix]</a></span></p>
+
+<p><span class="smcap">Third Edition</span>, <i>Revised and Enlarged. Pocket-Size, Leather,
+12s. 6d.; also Larger Size for Office Use, Cloth, 12s. 6d.</i></p>
+
+<h3>Boilers, Marine and Land:</h3> <h4>THEIR CONSTRUCTION AND STRENGTH.</h4>
+
+<p><span class="smcap">A Handbook of Rules, Formul&aelig;, Tables, &amp;c., relative to Material,
+Scantlings, and Pressures, Safety Valves, Springs, Fittings and
+Mountings, &amp;c.</span></p>
+
+<p>FOR THE USE OF ENGINEERS, SURVEYORS, BOILER-MAKERS, AND STEAM USERS.</p>
+
+<h4><span class="smcap">By T.W. TRAILL, M. Inst. C.E., F.E.R.N.</span>,</h4><h6> Late Engineer
+Surveyor-in-Chief to the Board of Trade.</h6>
+
+<p>*** To the Second and Third Editions many New Tables for Pressure, up to
+200 Lbs. per Square Inch have been added.</p>
+
+<p>"<span class="smcap">The most valuable work</span> on Boilers published in
+England."&mdash;<i>Shipping World.</i></p>
+
+<p>"Contains an <span class="smcap">Enormous Quantity of Information</span> arranged in a
+very convenient form.... <span class="smcap">A most useful volume</span> ... supplying
+information to be had nowhere else."&mdash;<i>The Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Third Impression.</i> Large Crown 8vo. With numerous Illustrations. 6s.</p>
+
+<h3>ENGINE-ROOM PRACTICE:</h3>
+
+<h5>A Handbook for Engineers and Officers in the Royal Navy and Mercantile
+Marine, Including the Management of the Main and Auxiliary Engines on
+Board Ship.</h5>
+
+<h4>BY JOHN G. LIVERSIDGE,</h4>
+
+<h6>Engineer, R.N., A.M.I.C.E., Instructor in Applied Mechanics at the Royal
+Naval College, Greenwich.</h6>
+
+<p><i>Contents.</i>&mdash;General Description of Marine Machinery.&mdash;The Conditions of
+Service and Duties of Engineers of the Royal Navy.&mdash;Entry and Conditions
+of Service of Engineers of the Leading S.S. Companies.&mdash;Raising
+Steam.&mdash;Duties of a Steaming Watch on Engines and Boilers.&mdash;Shutting off
+Steam.&mdash;Harbour Duties and Watches.&mdash;Adjustments and Repairs of
+Engines.&mdash;Preservation and Repairs of "Tank" Boilers.&mdash;The Hull and its
+Fittings.&mdash;Cleaning and Painting Machinery.&mdash;Reciprocating Pumps, Feed
+Heaters, and Automatic Feed-Water Regulators.&mdash;Evaporators.&mdash;Steam
+Boats.&mdash;Electric Light Machinery.&mdash;Hydraulic Machinery.&mdash;Air-Compressing
+Pumps.&mdash;Refrigerating Machines.&mdash;Machinery of Destroyers.&mdash;The
+Management of Water-Tube Boilers.&mdash;Regulations for Entry of Assistant
+Engineers, R.N.&mdash;Questions given in Examinations for Promotion of
+Engineers, R.N.&mdash;Regulations respecting Board of Trade Examinations for
+Engineers, &amp;c.</p>
+
+<p>"The contents <span class="smcap">cannot fail to be appreciated</span>."&mdash;<i>The Steamship.</i></p>
+
+<p>"This very useful book.... <span class="smcap">Illustrations</span> are of <span class="smcap">great
+importance</span> in a work of this kind, and it is satisfactory to find
+that <span class="smcap">special attention</span> has been given in this
+respect."&mdash;<i>Engineers' Gazette.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Crown 8vo, extra, with Numerous Illustrations</i>. [<i>Shortly.</i></p>
+
+<h3>GAS AND OIL ENGINES:</h3>
+
+<h5>An Introductory Text-Book on the Theory, Design, Construction, and
+Testing of Internal Combustion Engines without Boiler.</h5>
+
+<h4>FOR THE USE OF STUDENTS.</h4>
+
+<h4><span class="smcap">By Prof. W.H. WATKINSON, Whit. Sch., M. Inst. Mech. E.</span>,</h4> <h6>Glasgow
+and West of Scotland Technical College.</h6>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxx" id="Page_xxx">[Pg xxx]</a></span></p>
+
+<p><span class="smcap">Second Edition</span>, Revised. With numerous Plates reduced from
+Working Drawings and 280 Illustrations in the Text. 21s.</p>
+
+<h4><i>A MANUAL OF</i></h4><h3> LOCOMOTIVE ENGINEERING:</h3>
+
+<h5>A Practical Text-Book for the Use of Engine Builders, Designers and
+Draughtsmen, Railway Engineers, and Students.</h5>
+
+<h6>BY</h6>
+
+<h4><span class="smcap">WILLIAM FRANK PETTIGREW, M. Inst. C.E.</span></h4>
+
+<h5>With a Section on American and Continental Engines.</h5>
+
+<h4><span class="smcap">By ALBERT F. RAVENSHEAR, B.Sc.</span>,</h4> <h6>Of His Majesty's Patent Office.</h6>
+
+<p><i>Contents</i>.&mdash;Historical Introduction, 1763-1863.&mdash;Modern Locomotives:
+Simple.&mdash;Modern Locomotives: Compound.&mdash;Primary Consideration in
+Locomotive Design.&mdash;Cylinders, Steam Chests, and Stuffing
+Boxes.&mdash;Pistons, Piston Rods, Crossheads, and Slide Bars.&mdash;Connecting
+and Coupling Rods.&mdash;Wheels and Axles, Axle Boxes, Hornblocks, and
+Bearing Springs.&mdash;Balancing.&mdash;Valve Gear.&mdash;Slide Valves and Valve Gear
+Details.&mdash;Framing, Bogies and Axle Trucks, Radial Axle
+Boxes.&mdash;Boilers.&mdash;Smokebox, Blast Pipe, Firebox Fittings.&mdash;Boiler
+Mountings.&mdash;Tenders.&mdash;Railway Brakes.&mdash;Lubrication.&mdash;Consumption of
+Fuel, Evaporation and Engine Efficiency.&mdash;American
+Locomotives.&mdash;Continental Locomotives.&mdash;Repairs, Running, Inspection,
+and Renewals.&mdash;Three Appendices.&mdash;Index.</p>
+
+<p>"Likely to remain for many years the <span class="smcap">Standard Work</span> for those
+wishing to learn Design."&mdash;<i>Engineer.</i></p>
+
+<p>"A most interesting and valuable addition to the bibliography of the
+Locomotive."&mdash;<i>Railway Official Gazette.</i></p>
+
+<p>"We recommend the book as <span class="smcap">thoroughly practical</span> in its
+character, and <span class="smcap">meriting a place in any collection</span> of ... works
+on Locomotive Engineering."&mdash;<i>Railway News.</i></p>
+
+<p>"The work <span class="smcap">contains all that can be learnt</span> from a book upon such
+a subject. It will at once rank as <span class="smcap">the standard work upon this
+important subject</span>."&mdash;<i>Railway Magazine.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 8vo. Handsome Cloth. With Plates and Illustrations. 16s.</i></p>
+
+<h3>LIGHT RAILWAYS AT HOME AND ABROAD.</h3>
+
+<h4><span class="smcap">By WILLIAM HENRY COLE, M. Inst. C.E.</span>,</h4><h6> Late Deputy-Manager,
+North-Western Railway, India.</h6>
+
+<p><i>Contents.</i>&mdash;Discussion of the Term "Light Railways."&mdash;English Railways,
+Rates, and Farmers.&mdash;Light Railways in Belgium, France, Italy, other
+European Countries, America and the Colonies, India, Ireland.&mdash;Road
+Transport as an alternative.&mdash;The Light Railways Act, 1896.&mdash;The
+Question of Gauge.&mdash;Construction and Working.&mdash;Locomotives and
+Rolling-Stock.&mdash;Light Railways in England, Scotland, and
+Wales.&mdash;Appendices and Index.</p>
+
+<p>"Mr. W.H. Cole has brought together ... a <span class="smcap">large amount of valuable
+information</span> ... hitherto practically inaccessible to the ordinary
+reader."&mdash;<i>Times.</i></p>
+
+<p>"Will remain, for some time yet a <span class="smcap">Standard Work</span> in everything
+relating to Light Railways."&mdash;<i>Engineer.</i></p>
+
+<p>"The author has extended practical experience that makes the book lucid
+and useful. It is <span class="smcap">exceedingly</span> well done"&mdash;<i>Engineering.</i></p>
+
+<p>"The whole subject is <span class="smcap">exhaustively</span> and <span class="smcap">practically</span>
+considered. The work can be cordially recommended as
+<span class="smcap">indispensable</span> to those whose duty it is to become acquainted
+with one of the prime necessities of the immediate future."&mdash;<i>Railway
+Official Gazette.</i></p>
+
+<p>"<span class="smcap">There could be no better book</span> of first reference on its
+subject. All classes of Engineers will welcome its
+appearance."&mdash;<i>Scotsman.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxi" id="Page_xxxi">[Pg xxxi]</a></span></p>
+
+<p><span class="smcap">Third Edition</span>, Revised and Enlarged. <i>With Numerous
+Illustrations. Price 8s. 6d.</i></p>
+
+<h3><b>VALVES AND VALVE-GEARING:</b></h3>
+
+<h5><i>INCLUDING THE CORLISS VALVE AND TRIP GEARS.</i></h5>
+
+<h6>BY</h6>
+
+<h4>CHARLES HURST,</h4><h6> Practical Draughtsman.</h6>
+
+<p>"<span class="smcap">Concise</span> explanations illustrated by 115 <span class="smcap">very clear
+diagrams</span> and drawings and 4 folding-plates ... the book fulfils a
+<span class="smcap">valuable</span> function."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"<span class="smcap">Mr. Hurst's valves and valve-gearing</span> will prove a very
+valuable aid, and tend to the production of Engines of <span class="smcap">scientific
+design and economical working</span>.... Will be largely sought after by
+Students and Designers.&mdash;<i>Marine Engineer.</i></p>
+
+<p>"<span class="smcap">Useful and thoroughly practical.</span> Will undoubtedly be found of
+<span class="smcap">GREAT VALUE</span> to all concerned with the design of
+Valve-gearing."&mdash;<i>Mechanical World.</i></p>
+
+<p>"Almost <span class="smcap">every type of valve</span> and its gearing is clearly set
+forth, and illustrated in such a way as to be <span class="smcap">readily
+understood</span> and <span class="smcap">practically applied</span> by either the Engineer,
+Draughtsman, or Student.... Should prove both <span class="smcap">USEFUL</span> and
+<span class="smcap">valuable</span> to all Engineers seeking for <span class="smcap">reliable</span> and
+<span class="smcap">clear</span> information on the subject. Its moderate price brings it
+within the reach of all"&mdash;<i>Industries and Iron.</i></p>
+
+<p>"Mr. <span class="smcap">Hurst's</span> work is <span class="smcap">admirably</span> suited to the needs of
+the practical mechanic.... It is free from any elaborate theoretical
+discussions, and the explanations of the various types of valve-gear are
+accompanied by diagrams which render them <span class="smcap">easily
+understood</span>."&mdash;<i>The Scientific American.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><b>Hints on Steam Engine Design and Construction.</b> By <span class="smcap">Charles
+Hurst</span>, "Author of Valves and Valve Gearing." In Paper Boards, 8vo.,
+Cloth Back. Illustrated. Price 1s. 6d. net.</p>
+
+<p><span class="smcap">Contents</span>.&mdash;I. Steam Pipes.&mdash;II. Valves.&mdash;III. Cylinders.&mdash;IV.
+Air Pumps and Condensers.&mdash;V. Motion Work.&mdash;VI. Crank Shafts and
+Pedestals.&mdash;VII. Valve Gear.&mdash;VIII. Lubrication.&mdash;IX. Miscellaneous
+Details&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"A handy volume which every practical young engineer should
+possess."&mdash;<i>The Model Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>JUST OUT. Strongly Bound in Super Royal 8vo. Cloth Boards.</p>
+
+<h2><b>BONUS TABLES:</b></h2>
+
+<h4>For Calculating Wages on the Bonus or Premium Systems.</h4>
+
+<h5><i>For Engineering, Technical and Allied Trades.</i></h5>
+
+<h4><span class="smcap">By HENRY A. GOLDING, A.M.Inst.M.E.</span>,</h4>
+
+<p>Technical Assistant to Messrs. Bryan Donkin and Clench, Ltd., and
+Assistant Lecturer in Mechanical Engineering at the Northampton
+Institute, London, E.C.</p>
+
+<p>"The adoption of this system for the payment of workmen has created a
+demand for some handy table or series of tables, by means of which the
+wages may be easily found without the necessity of any calculations
+whatever. With the object of supplying this need, the author has
+compiled the following tables, which have been in practical use for some
+time past at a large engineering works in London, and have been found of
+inestimable value. Not only are they of great value as a 'time saving
+appliance,' the computation of the bonus or premiums earned by a number
+of men taking only <i>one-tenth</i> the time by the aid of these tables
+compared with ordinary calculations, but they possess the additional
+advantage of being less liable to error, as there is practically no
+possibility of a mistake occurring."&mdash;<i>Extract from Preface.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxii" id="Page_xxxii">[Pg xxxii]</a></span></p>
+
+<p>Large 8vo, Handsome Cloth. With Illustrations, Tables, &amp;c. 21s.</p>
+
+<h3>Lubrication &amp; Lubricants:</h3>
+
+<h5>A TREATISE ON THE</h5>
+
+<h4><b>THEORY AND PRACTICE OF LUBRICATION</b></h4>
+
+<h6>AND ON THE</h6>
+
+<h5><b>NATURE, PROPERTIES, AND TESTING OF LUBRICANTS.</b></h5>
+
+<h4><span class="smcap">By</span> LEONARD ARCHBUTT, F.I.C., F.C.S., </h4><h6>Chemist to the Midland
+Railway Company,</h6>
+
+<h6>AND</h6>
+
+<h4>R. MOUNTFORD DEELEY, M.I.M.E., F.G.S., </h4><h6>Midland Railway Locomotive Works'
+Manager, Derby.</h6>
+
+<p><span class="smcap">Contents</span>.&mdash;I. Friction of Solids.&mdash;II. Liquid Friction or
+Viscosity, and Plastic Friction.&mdash;III. Superficial Tension.&mdash;IV. The
+Theory of Lubrication.&mdash;V. Lubricants, their Sources, Preparation, and
+Properties.&mdash;VI. Physical Properties and Methods of Examination of
+Lubricants.&mdash;VII. Chemical Properties and Methods of Examination of
+Lubricants.&mdash;VIII. The Systematic Testing of Lubricants by Physical and
+Chemical Methods.&mdash;IX. The Mechanical Testing of Lubricants.&mdash;X. The
+Design and Lubrication of Bearings.&mdash;XI. The Lubrication of
+Machinery.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"Destined to become a <span class="smcap">classic</span> on the subject."&mdash;<i>Industries and
+Iron.</i></p>
+
+<p>"Contains practically <span class="smcap">all that is known</span> on the subject.
+Deserves the careful attention of all Engineers."&mdash;<i>Railway Official
+Guide.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Fourth Edition</span>. <i>Very fully Illustrated. Cloth</i>, <i>4s. 6d.</i></p>
+
+<h3>STEAM-BOILERS: THEIR DEFECTS, MANAGEMENT, AND CONSTRUCTION.</h3>
+
+<h4><span class="smcap">By R.D. MUNRO</span>, </h4><h6><i>Chief Engineer of the Scottish Boiler Insurance
+and Engine Inspection Company.</i></h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;I. <span class="smcap">Explosions</span> caused (1) by
+Overheating of Plates&mdash;(2) By Defective and Overloaded Safety
+Valves&mdash;(3) By Corrosion, Internal or External&mdash;(4) By Defective Design
+and Construction (Unsupported Flue Tubes; Unstrengthened Manholes;
+Defective Staying; Strength of Rivetted Joints; Factor of Safety)&mdash;II.
+<span class="smcap">Construction of Vertical Boilers</span>: Shells&mdash;Crown Plates and
+Uptake Tubes&mdash;Man-Holes, Mud-Holes, and
+Fire-Holes&mdash;Fireboxes&mdash;Mountings&mdash;Management&mdash;Cleaning&mdash;Table of
+Bursting Pressures of Steel Boilers&mdash;Table of Rivetted
+Joints&mdash;Specifications and Drawings of Lancashire Boiler for Working
+Pressures (<i>a</i>) 80 lbs.; (<i>b</i>) 200 lbs. per square inch respectively.</p>
+
+<p>"A valuable companion for workmen and engineers engaged about Steam
+Boilers, ought to be carefully studied, and <span class="smcap">always at
+hand</span>."&mdash;<i>Coll. Guardian.</i></p>
+
+<p>"The book is <span class="smcap">very useful</span>, especially to steam users, artisans,
+and young Engineers."&mdash;<i>Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">By the same Author.</span></p>
+
+<h3>KITCHEN BOILER EXPLOSIONS:</h3> <p>Why they Occur, and How to Prevent their
+Occurrence. A Practical Handbook based on Actual Experiment. With
+Diagram and Coloured Plate. Price 3s.</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxiii" id="Page_xxxiii">[Pg xxxiii]</a></span></p>
+
+<p><span class="smcap">Just Out</span>. <i>In Crown 8vo, Handsome Cloth. With Numerous
+Illustrations. 5s. net.</i></p>
+
+<h3>EMERY GRINDING MACHINERY.</h3>
+
+<h5><b><i>A Text-Book of Workshop Practice in General Tool Grinding, and the
+Design, Construction, and Application of the Machines Employed.</i></b></h5>
+
+<h6>BY</h6>
+
+<h4>R.B. HODGSON, <span class="smcap">A.M. Inst. Mech. E.</span>,</h4> <h6>Author of "Machines and
+Tools Employed in the Working of Sheet Metals."</h6>
+
+<p><span class="smcap">Introduction</span>.&mdash;Tool Grinding.&mdash;Emery Wheels.&mdash;Mounting Emery
+Wheels.&mdash;Emery Rings and Cylinders.&mdash;Conditions to Ensure Efficient
+Working.&mdash;Leading Types of Machines.&mdash;Concave and Convex Grinding.&mdash;Cup
+and Cone Machines.&mdash;Multiple Grinding.&mdash;"Guest" Universal and Cutter
+Grinding Machines.&mdash;Ward Universal Cutter Grinder.&mdash;Press.&mdash;Tool
+Grinding.&mdash;Lathe Centre Grinder.&mdash;Polishing.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"Deals practically with every phase of his subject."&mdash;<i>Ironmonger.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Fifth Edition</span>. Folio, strongly half-bound, 21/.</p>
+
+<h3>TRAVERSE TABLES:</h3>
+
+<h5><b>Computed to Four Places of Decimals for every Minute of Angle up to 100
+of Distance.</b></h5>
+
+<h5><b>For the use of Surveyors and Engineers.</b></h5>
+
+<h6>BY</h6>
+
+<h4>
+RICHARD LLOYD GURDEN,</h4>
+<h6>Authorised Surveyor for the Governments of New South Wales and Victoria.</h6>
+
+<h6>*** <i>Published with the Concurrence of the Surveyors-General for New
+South Wales and Victoria.</i></h6>
+
+<p>"Those who have experience in exact <span class="smcap">Survey-work</span> will best know
+how to appreciate the enormous amount of labour represented by this
+valuable book. The computations enable the user to ascertain the sines
+and cosines for a distance of twelve miles to within half an inch, and
+this <span class="smcap">by Reference To But One Table</span>, in place of the usual
+Fifteen minute computations required. This alone is evidence of the
+assistance which the Tables ensure to every user, and as every Surveyor
+in active practice has felt the want of such assistance <span class="smcap">few knowing
+of their publication will remain without them</span>."&mdash;<i>Engineer.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxiv" id="Page_xxxiv">[Pg xxxiv]</a></span></p>
+<h4>WORKS BY</h4>
+
+<h3><span class="smcap">ANDREW JAMIESON, M. Inst. C.E., M.I.E.E., F.R.S.E.</span>,</h3>
+
+<h5><i>Formerly Professor of Electrical Engineering, The Glasgow and West of
+Scotland Technical College.</i></h5>
+
+<hr style='width: 45%;' />
+
+<h4>PROFESSOR JAMIESON'S ADVANCED TEXT-BOOKS.</h4>
+
+<h5><i>In Large Crown 8vo. Fully Illustrated.</i></h5>
+
+<h3><b>STEAM AND STEAM-ENGINES (A Text-Book on).</b></h3>
+<p>For the Use of Students
+preparing for Competitive Examinations. With 600 pp., over 200
+Illustrations, 6 Folding Plates, and numerous Examination Papers.
+<span class="smcap">Thirteenth Edition</span>, Revised. 8/6.</p>
+
+<p>"Professor Jamieson fascinates the reader by his <span class="smcap">clearness of
+conception and simplicity of expression</span>. His treatment recalls the
+lecturing of Faraday."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"The <span class="smcap">Best Book</span> yet published for the use of
+Students."&mdash;<i>Engineer.</i></p>
+
+<h4><b>MAGNETISM AND ELECTRICITY (An Advanced Text-Book on).</b> </h4><p>For Advanced and
+"Honours" Students. By Prof. Jamieson, assisted by David Robertson,
+B.Sc., Professor of Electrical Engineering in the Merchant Venturers'
+Technical College, Bristol. [<i>Shortly.</i></p>
+
+<h4><b>APPLIED MECHANICS (An Advanced Text-Book on).</b></h4>
+
+<p>Vol. I.&mdash;Comprising Part I.: The Principle of Work and its applications;
+Part II.: Gearing. Price 7s. 6d. <span class="smcap">Third Edition.</span></p>
+
+<p>"<span class="smcap">Fully maintains</span> the reputation of the Author."&mdash;<i>Pract.
+Engineer.</i></p>
+
+<p>Vol. II.&mdash;Comprising Parts III. to VI.: Motion and Energy; Graphic
+Statics; Strength of Materials; Hydraulics and Hydraulic Machinery.
+<span class="smcap">Second Edition.</span> 8s. 6d.</p>
+
+<p>"<span class="smcap">Well and lucidly written.</span>"&mdash;<i>The Engineer.</i></p>
+
+<p>*** <i>Each of the above volumes is complete in itself, and sold
+separately.</i></p>
+
+<hr style='width: 45%;' />
+
+<h5>PROFESSOR JAMIESON'S INTRODUCTORY MANUALS.</h5>
+
+<p><i>Crown 8vo. With Illustrations and Examination Papers.</i></p>
+
+<h4><b>STEAM AND THE STEAM-ENGINE (Elementary Manual of).</b></h4> <p>For First-Year
+Students. <span class="smcap">Ninth Edition</span>, Revised. 3/6.</p>
+
+<p>"Should be in the hands of <span class="smcap">every</span> engineering
+apprentice."&mdash;<i>Practical Engineer.</i></p>
+
+<h4><b>MAGNETISM AND ELECTRICITY (Elementary Manual of).</b></h4> <p>For First-Year
+Students. <span class="smcap">Fifth Edition.</span>. 3/6.</p>
+
+<p>"<span class="smcap">A capital text-book....</span> The diagrams are an important
+feature."&mdash;<i>Schoolmaster.</i></p>
+
+<p>"<span class="smcap">A thoroughly trustworthy</span> Text-book. <span class="smcap">Practical</span> and
+clear."&mdash;<i>Nature.</i></p>
+
+<h4><b>APPLIED MECHANICS (Elementary Manual of).</b></h4><p> Specially arranged for
+First-Year Students. <span class="smcap">Fifth Edition</span>, Revised. 3/6.</p>
+
+<p>"The work has <span class="smcap">very high qualities</span>, which may be condensed into
+the one word '<span class="smcap">clear</span>.'"&mdash;<i>Science and Art.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">In Preparation.</span> <i>300 pages. Crown 8vo. Profusely Illustrated.</i></p>
+
+<h4><b><span class="smcap">Modern Electric Tramway Traction</span>: A Text-Book of Present-Day
+Practice.</b></h4>
+
+<p><i>For the Use of Electrical Engineering Students and those interested in
+Electric Transmission of Power.</i></p>
+
+<h4><span class="smcap">By Prof. ANDREW JAMIESON.</span></h4>
+
+<hr style='width: 45%;' />
+
+<h4><b>A POCKET-BOOK of ELECTRICAL RULES and TABLES.</b></h4> <p>For the Use of
+Electricians and Engineers. Pocket Size. Leather, 8s. 6d. <span class="smcap">Sixteenth
+Edition.</span> [See p. 49.</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxv" id="Page_xxxv">[Pg xxxv]</a></span></p>
+
+<h5>WORKS BY</h5>
+
+<h3>W.J. MACQUORN RANKINE, LL.D., F.R.S.,</h3>
+
+<h5><i>Late Regius Professor of Civil Engineering in the University of
+Glasgow.</i></h5>
+
+<h6>THOROUGHLY REVISED BY</h6>
+
+<h3>W.J. MILLAR, C.E.,</h3>
+
+<h6><i>Late Secretary to the Institute of Engineers and Shipbuilders in
+Scotland.</i></h6>
+
+<hr style='width: 45%;' />
+
+<p><b>A MANUAL OF APPLIED MECHANICS:</b> Comprising the Principles of Statics
+and Cinematics, and Theory of Structures, Mechanism, and Machines. With
+Numerous Diagrams. Crown 8vo, cloth. <span class="smcap">Sixteenth Edition.</span> 12s.
+6d.</p>
+
+<hr style='width: 45%;' />
+
+<p><b>A MANUAL OF CIVIL ENGINEERING:</b> Comprising Engineering Surveys,
+Earthwork, Foundations, Masonry, Carpentry, Metal Work, Roads, Railways,
+Canals, Rivers, Waterworks, Harbours, &amp;c. With Numerous Tables and
+Illustrations. Crown 8vo. Cloth. <span class="smcap">Twenty-First Edition.</span> 16s.</p>
+
+<hr style='width: 45%;' />
+
+<p><b>A MANUAL OF MACHINERY AND MILLWORK:</b> Comprising the Geometry, Motions,
+Work, Strength, Construction, and Objects of Machines, &amp;c. Illustrated
+with nearly 300 Woodcuts, Crown 8vo, cloth. <span class="smcap">Seventh Edition.</span>
+12s. 6d.</p>
+
+<hr style='width: 45%;' />
+
+<p><b>A MANUAL OF THE STEAM-ENGINE AND OTHER PRIME MOVERS:</b> With a Section on
+<span class="smcap">Gas, Oil</span>, and <span class="smcap">Air Engines</span>, by <span class="smcap">Bryan Donkin</span>,
+M.Inst.C.E. With Folding Plates and Numerous Illustrations. Crown 8vo,
+cloth. <span class="smcap">Fifteenth Edition.</span> 12s. 6d.<span class='pagenum'><a name="Page_xxxvi" id="Page_xxxvi">[Pg xxxvi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><b>USEFUL RULES AND TABLES:</b> For Architects, Builders, Engineers,
+Founders, Mechanics, Shipbuilders, Surveyors, &amp;c. With <span class="smcap">Appendix</span>
+for the use of <span class="smcap">Electrical Engineers</span>. By Professor <span class="smcap">Jamieson,
+F.R.S.E.</span> <span class="smcap">Seventh Edition.</span> 10s. 6d.</p>
+
+<hr style='width: 45%;' />
+
+<p><b>A MECHANICAL TEXT-BOOK:</b> A Practical and Simple Introduction to the
+Study of Mechanics. By Professor <span class="smcap">Rankine</span> and <span class="smcap">E.F. Bamber,
+C.E.</span> With Numerous Illustrations. Crown 8vo, cloth. <span class="smcap">Fifth
+Edition.</span> 9s.</p>
+
+<p>*** <i>The</i> "<span class="smcap">Mechanical Text-Book</span>" <i>was designed by</i> Professor
+<span class="smcap">Rankine</span> <i>as an</i> <span class="smcap">Introduction</span> <i>to the above Series of
+Manuals.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>MISCELLANEOUS SCIENTIFIC PAPERS.</b></h3>
+
+<p>Royal 8vo. Cloth, 31s. 6d.</p>
+
+<p>Part I. Papers relating to Temperature, Elasticity, and Expansion of
+Vapours, Liquids, and Solids. Part II. Papers on Energy and its
+Transformations. Part III. Papers on Wave-Forms, Propulsion of Vessels,
+&amp;c.</p>
+
+<p>With Memoir by Professor <span class="smcap">Tait, M.A.</span> Edited by <span class="smcap">W.J. Millar,
+C.E.</span> With fine Portrait on Steel, Plates, and Diagrams.</p>
+
+<p>"No more enduring Memorial of Professor Rankine could be devised than
+the publication of these papers in an accessible form.... The Collection
+is most valuable on account of the nature of his discoveries, and the
+beauty and completeness of his analysis.... The Volume exceeds in
+importance any work in the same department published in our
+time."&mdash;<i>Architect.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3>SHELTON-BEY (W. Vincent, Foreman to the Imperial Ottoman Gun Factories,
+Constantinople):</h3>
+
+<p><b>THE MECHANIC'S GUIDE:</b> A Hand-Book for Engineers and Artizans. With
+Copious Tables and Valuable Recipes for Practical Use. Illustrated.
+<i>Second Edition.</i> Crown 8vo. Cloth, 7/6.<span class='pagenum'><a name="Page_xxxvii" id="Page_xxxvii">[Pg xxxvii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><i>SECOND EDITION, Revised and Enlarged. In Large 8vo, Handsome cloth,
+34s.</i></p>
+
+<h3>HYDRAULIC POWER AND HYDRAULIC MACHINERY.</h3>
+
+<h4>BY <span class="smcap">HENRY ROBINSON, M. Inst. C.E., F.G.S.</span>,</h4>
+
+<h6>FELLOW OF KING'S COLLEGE, LONDON; PROF. OF CIVIL ENGINEERING, KING'S
+COLLEGE, ETC., ETC.</h6>
+
+<p>With numerous Woodcuts, and Sixty-nine Plates.</p>
+
+<p>"A Book of great Professional Usefulness."&mdash;<i>Iron.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 8vo, Handsome Cloth. With Frontispiece, several Plates, and
+over 250 Illustrations. 21s.</i></p>
+
+<h3>THE PRINCIPLES AND CONSTRUCTION OF PUMPING MACHINERY (STEAM AND WATER
+PRESSURE).</h3>
+
+<h5>With Practical Illustrations of <span class="smcap">Engines</span> and <span class="smcap">Pumps</span>
+applied to <span class="smcap">Mining</span>, <span class="smcap">Town Water Supply</span>,
+<span class="smcap">Drainage</span> of Lands, &amp;c., also Economy and Efficiency Trials of
+Pumping Machinery.</h5>
+
+<h4><span class="smcap">By HENRY DAVEY</span>,</h4>
+
+<h6>Member of the Institution of Civil Engineers, Member of the Institution
+of Mechanical Engineers, F.G.S., &amp;c.</h6>
+
+<p><span class="smcap">Contents</span>&mdash;Early History of Pumping Engines&mdash;Steam Pumping
+Engines&mdash;Pumps and Pump Valves&mdash;General Principles of Non-Rotative
+Pumping Engines&mdash;The Cornish Engine, Simple and Compound&mdash;Types of
+Mining Engines&mdash;Pit Work&mdash;Shaft Sinking&mdash;Hydraulic Transmission of Power
+in Mines&mdash;Valve Gears of Pumping Engines&mdash;Water Pressure Pumping
+Engines&mdash;Water Works Engines&mdash;Pumping Engine Economy and Trials of
+Pumping Machinery&mdash;Centrifugal and other Low-Lift Pumps&mdash;Hydraulic Rams.
+Pumping Mains, &amp;c.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"By the 'one' English Engineer who probably knows more about Pumping
+Machinery than <span class="smcap">any other</span>.' ... <span class="smcap">A volume recording the
+results of long experience and study.</span>"&mdash;<i>The Engineer.</i></p>
+
+<p>"Undoubtedly <span class="smcap">the best and most practical treatise</span> on Pumping
+Machinery <span class="smcap">that has yet been published</span>."&mdash;<i>Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxviii" id="Page_xxxviii">[Pg xxxviii]</a></span></p>
+<p><i>Royal 8vo, Handsome Cloth. With numerous Illustrations and Tables.
+25s.</i></p>
+
+<h3>THE STABILITY OF SHIPS.</h3>
+
+<h6>BY</h6>
+
+<h4>SIR EDWARD J. REED, K.C.B., F.R.S., M.P.,</h4>
+
+<h6>KNIGHT OF THE IMPERIAL ORDERS OF ST. STANILAUS OF RUSSIA; FRANCIS JOSEPH
+OF AUSTRIA; MEDJIDIE OF TURKEY; AND RISING SUN OF JAPAN; VICE-PRESIDENT
+OF THE INSTITUTION OF NAVAL ARCHITECTS.</h6>
+
+<p>In order to render the work complete for the purposes of the
+Shipbuilder, whether at home or abroad, the Methods of Calculation
+introduced by Mr. <span class="smcap">F.K. Barnes</span>, Mr. <span class="smcap">Gray</span>, M.
+<span class="smcap">Reech</span>, M. <span class="smcap">Daymard</span>, and Mr. <span class="smcap">Benjamin</span>, are all
+given separately, illustrated by Tables and worked-out examples. The
+book contains more than 200 Diagrams, and is illustrated by a large
+number of actual cases, derived from ships of all descriptions.</p>
+
+<p>"Sir <span class="smcap">Edward Reed's 'Stability of Ships'</span> is <span class="smcap">invaluable</span>.
+The <span class="smcap">Naval Architect</span> will find brought together and ready to his
+hand, a mass of information which he would otherwise have to seek in an
+almost endless variety of publications, and some of which he would
+possibly not be able to obtain at all elsewhere."&mdash;<i>Steamship.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>THE DESIGN AND CONSTRUCTION OF SHIPS.</b></h3> <h4>By <span class="smcap">John Harvard Biles,
+M.Inst.N.A.</span>, </h4><h6>Professor of Naval Architecture in the University of
+Glasgow. [<i>In Preparation.</i></h6>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition.</span> Illustrated with Plates, Numerous Diagrams, and
+Figures in the Text. 18s. net.</p>
+
+<h3><b>STEEL SHIPS: THEIR CONSTRUCTION AND MAINTENANCE.</b></h3>
+
+<h5><i>A Manual for Shipbuilders, Ship Superintendents, Students, and Marine
+Engineers.</i></h5>
+
+<h4><span class="smcap">By THOMAS WALTON, Naval Architect</span>, </h4><h6>AUTHOR OF "KNOW YOUR OWN
+SHIP."</h6>
+
+<p><span class="smcap">Contents.</span>&mdash;I. Manufacture of Cast Iron, Wrought Iron, and
+Steel.&mdash;Composition of Iron and Steel, Quality, Strength, Tests, &amp;c. II.
+Classification of Steel Ships. III. Considerations in making choice of
+Type of Vessel.&mdash;Framing of Ships. IV. Strains experienced by
+Ships.&mdash;Methods of Computing and Comparing Strengths of Ships. V.
+Construction of Ships.&mdash;Alternative Modes of Construction.&mdash;Types of
+Vessels.&mdash;Turret, Self Trimming, and Trunk Steamers, &amp;c.&mdash;Rivets and
+Rivetting, Workmanship. VI. Pumping Arrangements. VII.
+Maintenance.&mdash;Prevention of Deterioration in the Hulls of
+Ships.&mdash;Cement, Paint, &amp;c.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"So thorough and well written is every chapter in the book that it is
+difficult to select any of them as being worthy of exceptional praise.
+Altogether, the work is excellent, and will prove of great value to
+those for whom it is intended."&mdash;<i>The Engineer.</i></p>
+
+<p>"Mr. Walton has written for the profession of which he is an ornament.
+His work will be read and appreciated, no doubt, by every M.I.N.A., and
+with great benefit by the majority of them."&mdash;<i>Journal of Commerce.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition</span>, Cloth, 8s. 6d. Leather, for the Pocket, 8s. 6d.</p>
+
+<p><b>GRIFFIN'S ELECTRICAL PRICE-BOOK:</b> For Electrical, Civil, Marine, and
+Borough Engineers, Local Authorities, Architects, Railway Contractors,
+&amp;c., &amp;c. Edited by <span class="smcap">H.J. Dowsing</span>.</p>
+
+<p>"The <span class="smcap">Electrical Price-Book removes all mystery</span> about the cost
+of Electrical Power. By its aid the <span class="smcap">expense</span> that will be
+entailed by utilising electricity on a large or small scale can be
+discovered."&mdash;<i>Architect.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xxxix" id="Page_xxxix">[Pg xxxix]</a></span></p>
+
+<h3>GRIFFIN'S NAUTICAL SERIES,</h3>
+
+<h4><span class="smcap">Edited by</span> EDW. BLACKMORE,</h4>
+
+<h6>Master Mariner, First Class Trinity House Certificate, Assoc. Inst.
+N.A.; <span class="smcap">And Written, mainly</span>, by <span class="smcap">Sailors</span> for
+<span class="smcap">Sailors</span>.</h6>
+
+<p>"<span class="smcap">This admirable series</span>."&mdash;<i>Fairplay</i>. "<span class="smcap">A very useful
+series</span>."&mdash;<i>Nature</i>.</p>
+
+<p>"The volumes of <span class="smcap">Messrs. Griffin's Nautical Series</span> may well and
+profitably be read by <span class="smcap">all</span> interested in our <span class="smcap">national
+maritime progress</span>."&mdash;<i>Marine Engineer.</i></p>
+
+<p>"<span class="smcap">Every Ship</span> should have the <span class="smcap">whole Series</span> as a
+<span class="smcap">Reference Library. Handsomely bound, clearly printed</span> and
+<span class="smcap">illustrated</span>."&mdash;<i>Liverpool Journ. of Commerce.</i></p>
+
+<p><b>The British Mercantile Marine:</b> An Historical Sketch of its Rise and
+Development. By the <span class="smcap">Editor, Capt. Blackmore</span>. 3s. 6d.</p>
+
+<p>"Captain Blackmore's <span class="smcap">splendid book</span> ... contains paragraphs on
+every point of interest to the Merchant Marine. The 243 pages of this
+book are <span class="smcap">the most valuable</span> to the sea captain that have
+<span class="smcap">ever</span> been <span class="smcap">compiled</span>."&mdash;<i>Merchant Service Review.</i></p>
+
+<p><b>Elementary Seamanship.</b> By <span class="smcap">D. Wilson-Barker</span>, Master Mariner,
+F.R.S.E., F.R.G.S. With numerous Plates, two in Colours, and
+Frontispiece. <span class="smcap">Third Edition</span>, Thoroughly Revised, Enlarged, and
+Re-set. With additional Illustrations. 6s.</p>
+
+<p>"This <span class="smcap">admirable manual</span>, by <span class="smcap">Capt. Wilson Barker</span>, of the
+'Worcester', seems to us <span class="smcap">perfectly designed</span>. "&mdash;<i>Athen&aelig;um.</i></p>
+
+<p><b>Know Your Own Ship</b>: A Simple Explanation of the Stability,
+Construction, Tonnage, and Freeboard of Ships. By <span class="smcap">Thos. Walton</span>,
+Naval Architect. With numerous Illustrations and additional Chapters on
+Buoyancy, Trim, and Calculations. <span class="smcap">Sixth Edition</span>, Revised. 7s.
+6d.</p>
+
+<p>"<span class="smcap">Mr. Walton's</span> book will be found <span class="smcap">very useful</span>."&mdash;<i>The
+Engineer.</i></p>
+
+<p><b>Navigation: Theoretical and Practical.</b> By <span class="smcap">D. Wilson-Barker</span>,
+Master Mariner, &amp;c., and <span class="smcap">William Allingham</span>. <span class="smcap">Second
+Edition</span>, Revised. 8s. 6d.</p>
+
+<p>"<span class="smcap">Precisely</span> the kind of work required for the New Certificates
+of competency. Candidates will find it <span class="smcap">Invaluable</span>."&mdash;<i>Dundee
+Advertiser.</i></p>
+
+<p><b>Marine Meteorology</b>: For Officers of the Merchant Navy. By <span class="smcap">William
+Allingham</span>, First Class Honours, Navigation, Science and Art
+Department. With Illustrations, Maps, and Diagrams, and <i>facsimile</i>
+reproduction of log page. 7s. 6d.</p>
+
+<p>"Quite the <span class="smcap">best publication</span> on this subject."&mdash;<i>Shipping
+Gazette.</i></p>
+
+<p><b>Latitude and Longitude: How to find them.</b> By <span class="smcap">W.J. Millar</span>,
+C.E., late Sec. to the Inst. of Engineers and Shipbuilders in Scotland.
+<span class="smcap">Second Edition</span>, Revised. 2s.</p>
+
+<p>"Cannot but prove an acquisition to those studying Navigation."&mdash;<i>Marine
+Engineer.</i></p>
+
+<p><b>Practical Mechanics:</b> Applied to the requirements of the Sailor. By
+<span class="smcap">Thos. Mackenzie</span>, Master Mariner, F.R.A.S. <span class="smcap">Second
+Edition</span>, Revised. 3s. 6d.</p>
+
+<p>"<span class="smcap">Well worth</span> the money ... <span class="smcap">exceedingly
+helpful</span>."&mdash;<i>Shipping World.</i></p>
+
+<p><b>Trigonometry:</b> For the Young Sailor, &amp;c. By <span class="smcap">Rich. C. Buck</span>, of
+the Thames Nautical Training College, H.M.S. "Worcester." <span class="smcap">Second
+Edition</span>, Revised. Price 3s. 6d.</p>
+
+<p>"This <span class="smcap">eminently practical</span> and reliable
+volume."&mdash;<i>Schoolmaster</i>.</p>
+
+<p><b>Practical Algebra.</b> By <span class="smcap">Rich. C. Buck</span>. Companion Volume to the
+above, for Sailors and others. Price 3s. 6d.</p>
+
+<p>"It is <span class="smcap">just the book</span> for the young sailor mindful of
+progress."&mdash;<i>Nautical Magazine.</i></p>
+
+<p><b>The Legal Duties of Shipmasters.</b> By <span class="smcap">Benedict Wm. Ginsburg</span>,
+M.A., LL.D., of the Inner Temple and Northern Circuit; Barrister-at-Law.
+<span class="smcap">Second Edition</span>, Thoroughly Revised and Extended. Price 4s. 6d.</p>
+
+<p>"<span class="smcap">Invaluable</span> to masters ... We can fully recommend
+it."&mdash;<i>Shipping Gazette.</i></p>
+
+<p><b>A Medical and Surgical Help for Shipmasters.</b> Including First Aid at
+Sea. By <span class="smcap">Wm. Johnson Smith</span>, F.R.C.S., Principal Medical Officer,
+Seamen's Hospital, Greenwich. <span class="smcap">Second Edition</span>, Revised. 6s.
+"<span class="smcap">Sound, judicious, really helpful</span>."&mdash;<i>The Lancet.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xl" id="Page_xl">[Pg xl]</a></span></p>
+<p><i>Introductory Volume. Price 3s. 6d.</i></p>
+
+<h6>THE</h6> <h3><b>British Mercantile Marine.</b></h3>
+
+<h4><span class="smcap">By EDWARD BLACKMORE</span>, </h4><h6>MASTER MARINER; ASSOCIATE OF THE
+INSTITUTION OF NAVAL ARCHITECTS; MEMBER OF THE INSTITUTION OF ENGINEERS
+AND SHIPBUILDERS IN SCOTLAND; EDITOR OF GRIFFIN'S "NAUTICAL SERIES."</h6>
+
+<p><span class="smcap">General Contents.</span>&mdash;<span class="smcap">Historical</span>: From Early Times to
+1486&mdash;Progress under Henry VIII.&mdash;To Death of Mary&mdash;During Elizabeth's
+Reign&mdash;Up to the Reign of William III.&mdash;The 18th and 19th
+Centuries&mdash;Institution of Examinations&mdash;Rise and Progress of Steam
+Propulsion&mdash;Development of Free Trade&mdash;Shipping Legislation, 1862 to
+1875&mdash;"Locksley Hall" Case&mdash;Shipmasters' Societies&mdash;Loading of
+Ships&mdash;Shipping Legislation, 1884 to 1894&mdash;Statistics of Shipping.
+<span class="smcap">The Personnel</span>: Shipowners&mdash;Officers&mdash;Mariners&mdash;Duties and
+Present Position. <span class="smcap">Education</span>: A Seaman's Education: what it
+should be&mdash;Present Means of Education&mdash;Hints. <span class="smcap">Discipline and
+Duty</span>&mdash;Postscript&mdash;The Serious Decrease in the Number of British
+Seamen, a Matter demanding the Attention of the Nation.</p>
+
+<p>"<span class="smcap">Interesting and Instructive</span> ... may be read <span class="smcap">with profit
+and enjoyment</span>."&mdash;<i>Glasgow Herald.</i></p>
+
+<p>"<span class="smcap">Every Branch</span> of the subject is dealt with in a way which shows
+that the writer 'knows the ropes' familiarly."&mdash;<i>Scotsman.</i></p>
+
+<p>"This <span class="smcap">admirable</span> book ... <span class="smcap">teems</span> with useful
+information&mdash;Should be in the hands of every Sailor."&mdash;<i>Western Morning
+News.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition</span>, <i>Thoroughly Revised, Enlarged, and Re-set. With
+Additional Illustrations. Price 6s.</i></p>
+
+<h3><b>A MANUAL OF ELEMENTARY SEAMANSHIP.</b></h3>
+
+<h6>BY</h6>
+
+<h4><span class="smcap">D. WILSON-BARKER, Master Mariner; F.R.S.E., F.R.G.S., &amp;c., &amp;c.;</span></h4>
+<h6>YOUNGER BROTHER OF THE TRINITY HOUSE.</h6>
+
+<p>With Frontispiece, Numerous Plates (Two in Colours), and Illustrations
+in the Text.</p>
+
+<p><span class="smcap">General Contents.</span>&mdash;The Building of a Ship; Parts of Hull,
+Masts, &amp;c.&mdash;Ropes, Knots, Splicing, &amp;c.&mdash;Gear, Lead and Log,
+&amp;c.&mdash;Rigging, Anchors&mdash;Sailmaking&mdash;The Sails, &amp;c.&mdash;Handling of Boats
+under Sail&mdash;Signals and Signalling&mdash;Rule of the Road&mdash;Keeping and
+Relieving Watch&mdash;Points of Etiquette&mdash;Glossary of Sea Terms and
+Phrases&mdash;Index.</p>
+
+<p>*** The volume contains the <span class="smcap">new rules of the road</span>.</p>
+
+<p>"This <span class="smcap">admirable manual</span>, by <span class="smcap">Capt. Wilson-Barker</span> of the
+'Worcester,' seems to us <span class="smcap">perfectly designed</span>, and holds its
+place excellently in <span class="smcap">Griffin's Nautical Series</span>.' ... Although
+intended for those who are to become Officers of the Merchant Navy, it
+will be found useful by <span class="smcap">all yachtsmen</span>."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>*** For complete List of <span class="smcap">Griffin's Nautical Series</span>, see p. 39.</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xli" id="Page_xli">[Pg xli]</a></span></p>
+
+<p><span class="smcap">Second Edition</span>, <i>Revised and Illustrated. Price 3s. 6d.</i></p>
+
+<h3><b>NAVIGATION:</b></h3>
+
+<h5><b>PRACTICAL AND THEORETICAL</b></h5>
+
+<h4><span class="smcap">By</span> DAVID WILSON-BARKER, R.N.R, F.R.S.E., &amp;c., &amp;c.,</h4>
+
+<h6>AND</h6>
+
+<h4>WILLIAM ALLINGHAM,</h4>
+
+<h6>FIRST-CLASS HONORS, NAVIGATION, SCIENCE AND ART DEPARTMENT.</h6>
+
+<p>With Numerous Illustrations and Examination Questions.</p>
+
+<p><span class="smcap">General Contents.</span>&mdash;Definitions&mdash;Latitude and
+Longitude&mdash;Instruments of Navigation&mdash;Correction of Courses&mdash;Plane
+Sailing&mdash;Traverse Sailing&mdash;Day's Work&mdash;Parallel Sailing&mdash;Middle Latitude
+Sailing&mdash;Mercator's Chart&mdash;Mercator Sailing&mdash;Current Sailing&mdash;Position
+by Bearings&mdash;Great Circle Sailing&mdash;The Tides&mdash;Questions&mdash;Appendix:
+Compass Error&mdash;Numerous Useful Hints, &amp;c.&mdash;Index.</p>
+
+<p>"<span class="smcap">Precisely</span> the kind of work required for the New Certificates
+of competency in grades from Second Mate to extra Master.... Candidates
+will find it <span class="smcap">invaluable</span>."&mdash;<i>Dundee Advertiser.</i></p>
+
+<p>"<span class="smcap">A capital little book</span> ... specially adapted to the New
+Examinations. The Authors are <span class="smcap">Capt. Wilson-Barker</span>
+(Captain-Superintendent of the Nautical College, H.M.S. 'Worcester,' who
+has had great experience in the highest problems of Navigation), and
+<span class="smcap">Mr. Allingham</span>, a well-known writer on the Science of Navigation
+and Nautical Astronomy."&mdash;<i>Shipping World.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Handsome Cloth. Fully Illustrated. Price 7s. 6d.</i></p>
+
+<h3><b>MARINE METEOROLOGY, FOR OFFICERS OF THE MERCHANT NAVY.</b></h3>
+
+<h4><span class="smcap">By</span> WILLIAM ALLINGHAM,</h4>
+
+<h6>Joint Author of "Navigation, Theoretical and Practical."</h6>
+
+<p>With numerous Plates, Maps, Diagrams, and Illustrations, and a facsimile
+Reproduction of a Page from an actual Meteorological Log-Book.</p>
+
+<h4>SUMMARY OF CONTENTS.</h4>
+
+<p><span class="smcap">Introductory.</span>&mdash;Instruments Used at Sea for Meteorological
+Purposes.&mdash;Meteorological Log-Books.&mdash;Atmospheric Pressure.&mdash;Air
+Temperatures.&mdash;Sea Temperatures.&mdash;Winds.&mdash;Wind Force Scales.&mdash;History of
+the Law of Storms.&mdash;Hurricanes, Seasons, and Storm Tracks.&mdash;Solution of
+the Cyclone Problem.&mdash;Ocean Currents.&mdash;Icebergs.&mdash;Synchronous
+Charts.&mdash;Dew, Mists, Fogs, and Haze.&mdash;Clouds.&mdash;Rain, Snow, and
+Hail.&mdash;Mirage, Rainbows, Coronas, Halos, and Meteors.&mdash;Lightning,
+Corposants, and
+Auroras.&mdash;<span class="smcap">Questions.</span>&mdash;<span class="smcap">Appendix.</span>&mdash;<span class="smcap">Index.</span></p>
+
+<p>"Quite the <span class="smcap">best</span> publication, AND certainly the <span class="smcap">most
+interesting</span>, on this subject ever presented to Nautical
+men."&mdash;<i>Shipping Gazette.</i></p>
+
+<p>*** For Complete List of <span class="smcap">Griffin's Nautical Series</span>, see p. 39.</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xlii" id="Page_xlii">[Pg xlii]</a></span></p>
+
+<p><span class="smcap">Second Edition, Revised.</span> With Numerous Illustrations. Price
+<b>3s. 6d.</b></p>
+
+<h3><b>Practical Mechanics:</b> Applied to the Requirements of the Sailor.</h3>
+
+<h4>By THOS. MACKENZIE,</h4>
+
+<h6><i>Master Mariner, F.R.A.S.</i></h6>
+
+<p><span class="smcap">General Contents.</span>&mdash;Resolution and Composition of Forces&mdash;Work
+done by Machines and Living Agents&mdash;The Mechanical Powers: The Lever;
+Derricks as Bent Levers&mdash;The Wheel and Axle: Windlass; Ship's Capstan;
+Crab Winch&mdash;Tackles: the "Old Man"&mdash;The Inclined Plane; the Screw&mdash;The
+Centre of Gravity of a Ship and Cargo&mdash;Relative Strength of Rope: Steel
+Wire, Manilla, Hemp, Coir&mdash;Derricks and Shears&mdash;Calculation of the
+Cross-breaking Strain of Fir Spar&mdash;Centre of Effort of
+Sails&mdash;Hydrostatics: the Diving-bell; Stability of Floating Bodies; the
+Ship's Pump, &amp;c.</p>
+
+<p>"<span class="smcap">This Excellent Book</span> ... contains a LARGE AMOUNT of
+information."&mdash;<i>Nature.</i></p>
+
+<p>"<span class="smcap">Well worth</span> the money ... will be found EXCEEDINGLY
+HELPFUL."&mdash;<i>Shipping World.</i></p>
+
+<p>"<span class="smcap">No Ships' Officers' bookcase</span> will henceforth be complete
+without <span class="smcap">Captain Mackenzie's 'Practical Mechanics.'</span>
+Notwithstanding my many years' experience at sea, it has told me <i>how
+much more there is to acquire</i>."&mdash;(Letter to the Publishers from a
+Master Mariner).</p>
+
+<p>"I must express my thanks to you for the labour and care you have taken
+in '<span class="smcap">Practical Mechanics</span>.' ... <span class="smcap">It is a life's
+experience.</span> ... What an amount we frequently see wasted by rigging
+purchases without reason and accidents to spars, &amp;c., &amp;c.!
+<span class="smcap">'Practical Mechanics' would save all this.</span>"&mdash;(Letter to the
+Author from another Master Mariner).</p>
+
+<hr style='width: 45%;' />
+
+<h4><b>WORKS BY RICHARD C. BUCK,</b></h4>
+
+<h6>of the Thames Nautical Training College, H.M.S. 'Worcester.'</h6>
+
+<h3><b>A Manual of Trigonometry:</b> <i>With Diagrams, Examples, and Exercises.
+Price 3s. 6d.</i></h3>
+
+<h5><span class="smcap">Second Edition</span>, Revised and Corrected.</h5>
+
+<p>*** Mr. Buck's Text-Book has been <span class="smcap">specially prepared</span> with a
+view to the New Examinations of the Board of Trade, in which
+Trigonometry is an obligatory subject.</p>
+
+<p>"This <span class="smcap">eminently practical</span> and <span class="smcap">reliable
+volume</span>."&mdash;<i>Schoolmaster.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>A Manual of Algebra.</b></h3>
+
+<h5><i>Designed to meet the Requirements of Sailors and others. Price 3s. 6d.</i></h5>
+
+<p>*** These elementary works on <span class="smcap">algebra</span> and <span class="smcap">trigonometry</span>
+are written specially for those who will have little opportunity of
+consulting a Teacher. They are books for "<span class="smcap">self-help</span>." All but
+the simplest explanations have, therefore, been avoided, and
+<span class="smcap">answers</span> to the Exercises are given. Any person may readily, by
+careful study, become master of their contents, and thus lay the
+foundation for a further mathematical course, if desired. It is hoped
+that to the younger Officers of our Mercantile Marine they will be found
+decidedly serviceable. The Examples and Exercises are taken from the
+Examination Papers set for the Cadets of the "Worcester."</p>
+
+<p>"Clearly arranged, and well got up.... A first-rate Elementary
+Algebra."&mdash;<i>Nautical Magazine.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xliii" id="Page_xliii">[Pg xliii]</a></span></p>
+
+<p><span class="smcap">Second Edition</span>, Thoroughly Revised and Extended. In Crown 8vo.
+Handsome Cloth. Price 4s. 6d.</p>
+
+<h3><b>THE LEGAL DUTIES OF SHIPMASTERS.</b></h3>
+
+<h6>BY</h6>
+
+<h4>BENEDICT WM. GINSBURG, M.A., LL.D. (<span class="smcap">Cantab.</span>),</h4>
+
+<h6>Of the Inner Temple and Northern Circuit; Barrister-at-Law.</h6>
+
+<p><b>General Contents.</b>&mdash;The Qualification for the Position of
+Shipmaster&mdash;The Contract with the Shipowner&mdash;The Master's Duty in
+respect of the Crew: Engagement; Apprentices; Discipline; Provisions,
+Accommodation, and Medical Comforts; Payment of Wages and Discharge&mdash;The
+Master's Duty in respect of the Passengers&mdash;The Master's Financial
+Responsibilities&mdash;The Master's Duty in respect of the Cargo&mdash;The
+Master's Duty in Case of Casualty&mdash;The Master's Duty to certain Public
+Authorities&mdash;The Master's Duty in relation to Pilots, Signals, Flags,
+and Light Dues&mdash;The Master's Duty upon Arrival at the Port of
+Discharge&mdash;Appendices relative to certain Legal Matters: Board of Trade
+Certificates, Dietary Scales, Stowage of Grain Cargoes, Load Line
+Regulations, Life-saving Appliances, Carriage of Cattle at Sea, &amp;c.,
+&amp;c.&mdash;Copious Index.</p>
+
+<p>"No intelligent Master should fail to add this to his list of necessary
+books. A few lines of it may <span class="smcap">save a lawyer's fee, besides endless
+worry</span>."&mdash;<i>Liverpool Journal of Commerce.</i></p>
+
+<p>"<span class="smcap">Sensible</span>, plainly written, in <span class="smcap">CLEAR</span> and
+<span class="smcap">non-technical language</span>, and will be found of much service by
+the Shipmaster."&mdash;<i>British Trade Review.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition</span>, Revised. With Diagrams. Price 2s.</p>
+
+<h3><b>Latitude and Longitude: How to Find them.</b></h3>
+
+<h4>By W.J. MILLAR, C.E.,</h4>
+
+<h6><i>Late Secretary to the Inst. of Engineers and Shipbuilders in Scotland.</i></h6>
+
+<p>"<span class="smcap">Concisely</span> and <span class="smcap">clearly written</span> ... cannot but prove an
+acquisition to those studying Navigation."&mdash;<i>Marine Engineer.</i></p>
+
+<p>"Young Seamen will find it <span class="smcap">handy</span> and <span class="smcap">useful, simple</span>
+and <span class="smcap">clear</span>."&mdash;<i>The Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>FIRST AID AT SEA.</b></h3>
+
+<h5><span class="smcap">Second Edition</span>, Revised. With Coloured Plates and Numerous
+Illustrations, and comprising the latest Regulations Respecting the
+Carriage of Medical Stores on Board Ship. Price 6s.</h5>
+
+<h3><b>A MEDICAL AND SURGICAL HELP FOR SHIPMASTERS AND OFFICERS IN THE
+MERCHANT NAVY.</b></h3>
+
+<h6>BY</h6>
+
+<h4>WM. JOHNSON SMITH, F.R.C.S.,</h4>
+
+<h6>Principal Medical Officer, Seamen's Hospital, Greenwich.</h6>
+
+<p>*** The attention of all interested in our Merchant Navy is requested to
+this exceedingly useful and valuable work. It is needless to say that it
+is the outcome of many years <span class="smcap">practical experience</span> amongst
+Seamen.</p>
+
+<p>"<span class="smcap">Sound, judicious, really helpful</span>."&mdash;<i>The Lancet.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xliv" id="Page_xliv">[Pg xliv]</a></span></p>
+<p><span class="smcap">Sixth Edition.</span> <i>Revised, with Chapters on Trim, Buoyancy, and
+Calculations. Numerous Illustrations. Handsome Cloth, Crown 8vo. Price
+7s. 6d.</i></p>
+
+<h3><b>KNOW YOUR OWN SHIP.</b></h3>
+
+<h4><span class="smcap">By</span> THOMAS WALTON, <span class="smcap">Naval Architect</span>.</h4>
+
+<h5>SPECIALLY ARRANGED TO SUIT THE REQUIREMENTS OF SHIPS' OFFICERS,
+SHIPOWNERS, SUPERINTENDENTS, DRAUGHTSMEN, ENGINEERS, AND OTHERS.</h5>
+
+<p>This work explains, in a simple manner, such important subjects as:&mdash;</p>
+
+<p>
+Displacement,<br />
+Deadweight,<br />
+Tonnage,<br />
+Freeboard,<br />
+Moments,<br />
+Buoyancy,<br />
+Strain,<br />
+Structure,<br />
+Stability,<br />
+Rolling,<br />
+Ballasting,<br />
+Loading,<br />
+Shifting Cargoes,<br />
+Admission of Water,<br />
+Sail Area,<br />
+&amp;c., &amp;c.<br />
+</p>
+
+<p>"The little book will be found <span class="smcap">exceedingly handy</span> by most
+officers and officials connected with shipping.... Mr. Walton's work
+will obtain <span class="smcap">lasting success</span>, because of its unique fitness for
+those for whom it has been written."&mdash;<i>Shipping World.</i></p>
+
+<p>"An <span class="smcap">excellent work</span>, full of solid instruction and
+<span class="smcap">invaluable</span> to every officer of the Mercantile Marine who has
+his profession at heart."&mdash;<i>Shipping.</i></p>
+
+<p>"Not one of the 242 pages could well be spared. It will admirably fulfil
+its purpose ... useful to ship owners, ship superintendents, ship
+draughtsmen, and all interested in shipping."&mdash;<i>Liverpool Journal of
+Commerce.</i></p>
+
+<p>"A mass of <span class="smcap">very useful information</span>, accompanied by diagrams and
+illustrations, is given in a compact form."&mdash;<i>Fairplay.</i></p>
+
+<p>"We have found no one statement that we could have wished differently
+expressed. The matter has, so far as clearness allows, been admirably
+condensed, and is simple enough to be understood by every
+seaman."&mdash;<i>Marine Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<h4><b>BY THE SAME AUTHOR.</b></h4>
+
+<h3><b>Steel Ships: Their Construction and Maintenance.</b></h3>
+
+<p>(<b>See page 38.</b>)</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xlv" id="Page_xlv">[Pg xlv]</a></span></p>
+
+<p>Fourteenth Edition, Revised. Price 21s.</p>
+
+<p><i>Demy 8vo, Cloth. With Numerous Illustrations, reduced from Working
+Drawings.</i></p>
+
+<h3><b>A MANUAL OF MARINE ENGINEERING:</b> COMPRISING THE DESIGNING,
+CONSTRUCTION, AND WORKING OF MARINE MACHINERY.</h3>
+
+<h4>By A.E. SEATON, M. Inst. C.E., M. Inst. Mech. E., M. Inst. N.A.</h4>
+
+<p><span class="smcap">General Contents.</span>&mdash;<span class="smcap">Part I.</span>&mdash;Principles of Marine
+Propulsion. <span class="smcap">Part II.</span>&mdash;Principles of Steam Engineering. <span class="smcap">Part
+III.</span>&mdash;Details of Marine Engines: Design and Calculations for
+Cylinders, Pistons, Valves, Expansion Valves, &amp;c. <span class="smcap">Part
+IV.</span>&mdash;Propellers. <span class="smcap">Part V.</span>&mdash;Boilers. <span class="smcap">Part
+VI</span>.&mdash;Miscellaneous.</p>
+
+<p>*** This <span class="smcap">Edition</span> includes a Chapter on <span class="smcap">Water-Tube
+Boilers</span>, with Illustrations of the leading Types and the Revised
+Rules of the <i>Bureau Veritas</i>.</p>
+
+<p>"In the three-fold capacity of enabling a Student to learn how to
+design, construct, and work a Marine Steam-Engine, Mr. Seaton's Manual
+has <span class="smcap">no rival</span>."&mdash;<i>Times.</i></p>
+
+<p>"By far the <span class="smcap">best Manual</span> in existence.... Gives a complete
+account of the methods of solving, with the utmost possible economy, the
+problems before the Marine Engineer."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"The Student, Draughtsman, and Engineer will find this work the <span class="smcap">most
+valuable Handbook</span> of Reference on the Marine Engine now in
+existence."&mdash;<i>Marine Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Seventh Edition</span>, Thoroughly Revised. Pocket-Size, Leather. 8s.
+6d.</p>
+
+<h3>A POCKET-BOOK OF MARINE ENGINEERING RULES AND TABLES, FOR THE USE OF</h3><h4>
+Marine Engineers, Naval Architects, Designers, Draughtsmen,
+Superintendents and Others.</h4>
+
+<h6>BY</h6>
+
+<h4>A.E. SEATON, M.I.C.E., M.I.Mech.E., M.I.N.A.,</h4>
+
+<h6>AND</h6>
+
+<h4>H.M. ROUNTHWAITE, M.I.Mech.E., M.I.N.A.</h4>
+
+<p>"<span class="smcap">Admirably fulfils</span> its purpose."&mdash;<i>Marine Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<h4>By B. CUNNINGHAM.</h4>
+
+<h3><b>DOCKS: THEIR CONSTRUCTION &amp; MAINTENANCE.</b></h3>
+
+<p>(See page 27.)</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xlvi" id="Page_xlvi">[Pg xlvi]</a></span></p>
+
+<h4>WORKS BY PROF. ROBERT H. SMITH, Assoc. M.I.C.E., M.I.M.E., M.I.El.B.,
+M.I. Min. E., Whit. Sch., M. Ord. Meiji.</h4>
+
+<hr style='width: 45%;' />
+
+<h3>THE CALCULUS FOR ENGINEERS AND PHYSICISTS,</h3><h5> Applied to Technical
+Problems.</h5>
+
+<h5>WITH EXTENSIVE CLASSIFIED REFERENCE LIST OF INTEGRALS.</h5>
+
+<h4>By PROF. ROBERT H. SMITH.</h4>
+
+<h6>ASSISTED BY</h6>
+
+<h4>R.F. MUIRHEAD, M.A., B.Sc.,</h4>
+
+<h6>Formerly Clark Fellow of Glasgow University, and Lecturer on Mathematics
+at Mason College.</h6>
+
+<p><i>In Crown 8vo, extra, with Diagrams and Folding-Plate.</i> 8s. 6d.</p>
+
+<p>"<span class="smcap">Prof. R.H. Smith's</span> book will be serviceable in rendering a
+hard road <span class="smcap">as easy as practicable</span> for the non-mathematical
+Student and Engineer."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"Interesting diagrams, with practical illustrations of actual
+occurrence, are to be found here in abundance. <span class="smcap">The very complete
+classified reference table</span> will prove very useful in saving the
+time of those who want an integral in a hurry."&mdash;<i>The Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3>MEASUREMENT CONVERSIONS</h3>
+
+<h5>(English and French): 28 GRAPHIC TABLES OR DIAGRAMS.</h5>
+
+<p>Showing at a glance the <span class="smcap">Mutual Conversion</span> of
+<span class="smcap">Measurements</span> in <span class="smcap">Different Units</span></p>
+
+<p>Of Lengths, Areas, Volumes, Weights, Stresses, Densities, Quantities of
+Work, Horse Powers, Temperatures, &amp;c.</p>
+
+<p><i>For the use of Engineers, Surveyors, Architects, and Contractors.</i></p>
+
+<p><i>In 4to, Boards. 7s. 6d.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>*** Prof. <span class="smcap">Smith's Conversion-Tables</span> form the most unique and
+comprehensive collection ever placed before the profession. By their use
+much time and labour will be saved, and the chances of error in
+calculation diminished. It is believed that henceforth no Engineer's
+Office will be considered complete without them.</p>
+
+<p>"The work is <span class="smcap">invaluable</span>."&mdash;<i>Colliery Guardian.</i></p>
+
+<p>"Ought to be in <span class="smcap">every</span> office where even occasional conversions
+are required.... Prof. <span class="smcap">Smith's Tables</span> form very <span class="smcap">excellent
+checks</span> on results."&mdash;<i>Electrical Review.</i></p>
+
+<p>"Prof. Smith deserves the hearty thanks, not only of the
+<span class="smcap">Engineer</span>, but of the <span class="smcap">Commercial World</span>, for having
+smoothed the way for the <span class="smcap">adoption</span> of the <span class="smcap">Metric System</span>
+of <span class="smcap">Measurement</span>, a subject which is now assuming great
+importance as a factor in maintaining our <span class="smcap">hold</span> upon <span class="smcap">foreign
+trade</span>."&mdash;<i>The Machinery Market.</i><span class='pagenum'><a name="Page_xlvii" id="Page_xlvii">[Pg xlvii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p>In Large 8vo. Handsome Cloth. 10s. 6d.</p>
+
+<h3>CHEMISTRY FOR ENGINEERS.</h3>
+
+<h6>BY</h6>
+
+<h4>BERTRAM BLOUNT, F.I.C., F.C.S., A.I.C.E., </h4><h6>Consulting Chemist to the
+Crown Agents for the Colonies.</h6>
+
+<h6>AND</h6>
+
+<h4>A.G. BLOXAM, F.I.C., F.C.S.,</h4> <h6>Consulting Chemist, Head of the Chemistry
+Department, Goldsmiths' Inst., New Cross.</h6>
+
+<p>GENERAL CONTENTS.&mdash;Introduction&mdash;Chemistry of the Chief Materials of
+Construction&mdash;Sources of Energy&mdash;Chemistry of Steam-raising&mdash;Chemistry
+of Lubrication and Lubricants&mdash;Metallurgical Processes used in the
+Winning and Manufacture of Metals.</p>
+
+<p>"The authors have <span class="smcap">succeeded</span> beyond all expectation, and have
+produced a work which should give <span class="smcap">fresh power</span> to the Engineer
+and Manufacturer."&mdash;<i>The Times.</i></p>
+
+<p>"<span class="smcap">Practical throughout</span> ... an <span class="smcap">admirable text-book</span>,
+useful not only to Students, but to <span class="smcap">Engineers</span> and <span class="smcap">Managers
+of works</span> in <span class="smcap">preventing waste</span> and <span class="smcap">improving
+processes</span>."&mdash;<i>Scotsman.</i></p>
+
+<p>"A book worthy to take <span class="smcap">high rank</span> ... treatment of the subject
+of <span class="smcap">gaseous fuel</span> particularly good.... <span class="smcap">Water gas</span> and
+its production clearly worked out.... We <span class="smcap">warmly recommend</span> the
+work."&mdash;<i>Journal of Gas Lighting.</i></p>
+
+<p>For Companion Volume by the same Authors, see "<span class="smcap">Chemistry for
+Manufacturers</span>," p. 71.</p>
+
+<hr style='width: 45%;' />
+
+<h4><span class="smcap">Works by</span> WALTER R. BROWNE, M.A., <span class="smcap">M. Inst. C.E.</span>,</h4><h6> Late
+Fellow of Trinity College, Cambridge.</h6>
+
+<h3><b>THE STUDENT'S MECHANICS: An Introduction to the Study of Force and
+Motion.</b></h3>
+
+<h5>With Diagrams. Crown 8vo. Cloth, 4s. 6d.</h5>
+
+<p>"Clear in style and practical in method, '<span class="smcap">The Student's
+Mechanics</span>' is cordially to be commended from all points of
+view."&mdash;<i>Athen&aelig;um.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3>FOUNDATIONS OF MECHANICS.</h3>
+
+<h5>Papers reprinted from the <i>Engineer.</i> In Crown 8vo, 1s.</h5>
+
+<hr style='width: 45%;' />
+
+<p>Demy 8vo, with Numerous Illustrations, 9s.</p>
+
+<h3>FUEL AND WATER: A Manual for Users of Steam and Water.</h3>
+
+<h4><span class="smcap">By Prof.</span> FRANZ SCHWACKH&Ouml;FER <span class="smcap">of Vienna, and</span> WALTER R.
+BROWNE, M.A., C.E.</h4>
+
+<p><span class="smcap">General Contents.</span>&mdash;Heat and Combustion&mdash;Fuel, Varieties
+of&mdash;Firing Arrangements: Furnace, Flues, Chimney&mdash;The Boiler, Choice
+of&mdash;Varieties&mdash;Feed-water Heaters&mdash;Steam Pipes&mdash;Water: Composition,
+Purification&mdash;Prevention of Scale, &amp;c., &amp;c.</p>
+
+<p>"The Section on Heat is one of the best and most lucid ever
+written."&mdash;<i>Engineer.</i></p>
+
+<p>"Cannot fail to be valuable to thousands using steam power."&mdash;<i>Railway
+Engineer.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xlviii" id="Page_xlviii">[Pg xlviii]</a></span></p>
+
+<h4>GRIFFINS LOCAL GOVERNMENT HANDBOOKS.</h4>
+
+<h3>WORKS SUITABLE FOR MUNICIPAL AND COUNTY ENGINEERS, ANALYSTS, AND OTHERS.</h3>
+
+<h5>See also Davies' <i>Hygiene</i>, p. 99, and MacLeod's <i>Public Health</i>, p.
+110.</h5>
+
+<p><b>Gas Manufacture (The Chemistry of).</b> A Handbook on the Production,
+Purification, and Testing of Illuminating Gas, and the Assay of
+Bye-Products. By <span class="smcap">W.J.A. Butterfield</span>, M.A., F.I.C., F.C.S. With
+Illustrations. <span class="smcap">Third Edition</span>, Revised (in preparation). [See
+page 77.</p>
+
+<p><b>Water Supply:</b> A Practical Treatise on the Selection of Sources and the
+Distribution of Water. By <span class="smcap">Reginald E. Middleton</span>, M. Inst. C.E.,
+M. Inst. Mech. E., F.S.I. With Four Plates and Numerous Diagrams. Crown
+8vo. [See page 77.</p>
+
+<p><b>Central Electrical Stations:</b> Their Design, Organisation, and
+Management. By <b>C.H. Wordingham</b>, A.K.C., M. Inst. C.E. Price 24s. net.</p>
+
+<p><i>For details see opposite page.</i></p>
+
+<p><b>Sewage Disposal Works:</b> A Guide to the Construction of Works for the
+Prevention of the Pollution by Sewage of Rivers and Estuaries. By <span class="smcap">W.
+Santo Crimp</span>, M. Inst. C.E., F.G.S. <span class="smcap">Second Edition</span>, Revised
+and Enlarged. Large 8vo, Handsome Cloth. With 37 Plates. Price 30s. [See
+page 76.</p>
+
+<p><b>Trades' Waste:</b> Its Treatment and Utilisation, with Special Reference
+to the Prevention of Rivers' Pollution. By <span class="smcap">W. Naylor</span>, F.C.S.,
+A.M. Inst. C.E. With Numerous Plates, Diagrams, and Illustrations. 21s.
+net. [See page 76.</p>
+
+<p><b>Calcareous Cements:</b> Their Nature, Preparation, and Uses. With some
+Remarks upon Cement Testing. By <span class="smcap">Gilbert Redgrave</span>, Assoc. Inst.
+C.E. With Illustrations, Analytical Data, and Appendices on Costs, &amp;c.
+8s. 6d. [See page 76.</p>
+
+<p><b>Road Making and Maintenance:</b> A Practical Treatise for Engineers,
+Surveyors, and others. With an Historical Sketch of Ancient and Modern
+Practice. By <span class="smcap">Thomas Aitken</span>, Assoc. M. Inst. C.E., M. Assoc.
+Municipal and County Engrs.; M. San. Inst. With numerous Plates,
+Diagrams, and Illustrations. 21s. [See page 79.</p>
+
+<p><b>Light Railways at Home and Abroad.</b> By <span class="smcap">William Henry Cole</span>, M.
+Inst. C.E., late Deputy Manager, North-Western Railway, India. Large
+8vo, Handsome Cloth, Plates and illustrations. 16s. [See page 30.</p>
+
+<p><b>Practical Sanitation:</b> A Handbook for Sanitary Inspectors and others
+interested in Sanitation. By <span class="smcap">Geo. Reid</span>, M.D., D.P.H., Medical
+Officer, Staffordshire County Council. With Appendix on Sanitary Law, by
+Herbert Manley, M.A., M.B., D.P.H. <span class="smcap">Tenth Edition</span>, Revised. 6s.
+[See page 78.</p>
+
+<p><b>Sanitary Engineering</b>: A Practical Manual of Town Drainage and Sewage
+and Refuse Disposal. By <span class="smcap">Frank Wood</span>, A.M. Inst. C.E., F.G.S.,
+Borough Surveyor, Fulham. Fully Illustrated. 8s. 6d. net. [See page 78.</p>
+
+<p><b>Dairy Chemistry:</b> A Practical Handbook for Dairy Managers, Chemists,
+and Analysts. By <b>H. Droop Richmond</b>, F.C.S., Chemist to the Aylesbury
+Dairy Company. With Tables, Illustrations, &amp;c. Handsome Cloth, 16s. [See
+page 73.</p>
+
+<p><b>Milk: Its Production and Uses.</b> With Chapters on Dairy Farming, The
+Diseases of Cattle, and on the Hygiene and Control of Supplies. By
+<span class="smcap">Edward F. Willoughby</span>, M.D. (Lond.), D.P.H. (Lond. and Camb.),
+Inspector of Farms and General Scientific Adviser to Welford &amp; Sons,
+Ltd. [See page 73.</p>
+
+<p><b>Flesh Foods:</b> With Methods for their Chemical, Microscopical, and
+Bacteriological Examination. A Handbook for Medical Men, Inspectors,
+Analysts, and others. By <span class="smcap">C. Ainsworth Mitchell</span>, B.A., F.I.C.,
+Mem. Council Soc. of Public Analysts. With numerous Illustrations and a
+coloured Plate. 10s. 6d. [See page 73.</p>
+
+<p><b>Foods:</b> Their Composition and Analysis. By <span class="smcap">A. Wynter Blyth</span>,
+M.R.C.S., F.C.S., Public Analyst for the County of Devon. With Tables,
+Folding Plate, and Frontispiece. <span class="smcap">Fifth Edition</span>, Thoroughly
+Revised. 21s. [See page 72.</p>
+
+<p>"<span class="smcap">An admirable digest</span> of the most recent state of
+knowledge."&mdash;<i>Chemical News.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_xlix" id="Page_xlix">[Pg xlix]</a></span></p>
+
+<h3>ELECTRICAL ENGINEERING.</h3>
+
+<h5><i>In Large 8vo. Handsome Cloth. Profusely Illustrated with Plates,
+Diagrams, and Figures. 24s. net.</i></h5>
+
+<h3>CENTRAL ELECTRICAL STATIONS: Their Design, Organisation, and Management.</h3>
+
+<h4><span class="smcap">By</span> CHAS. H. WORDINGHAM, A.K.C., <span class="smcap">M. Inst. C.E.</span>, <span class="smcap">M.
+Inst. Mech. E.</span>,</h4> <h6>Late Memb. of Council Inst. E.E., and Electrical
+Engineer to the City of Manchester.</h6>
+
+<h4>ABRIDGED CONTENTS.</h4>
+
+<p>Introductory.&mdash;Central Station Work as a Profession.&mdash;As an
+Investment.&mdash;The Establishment of a Central Station.&mdash;Systems of
+Supply.&mdash;Site.&mdash;Architecture.&mdash;Plant.&mdash;Boilers.&mdash;Systems of Draught and
+Waste Heat Economy.&mdash;Coal Handling, Weighing, and Storing.&mdash;The
+Transmission of Steam.&mdash;Generators.&mdash;Condensing Appliances.&mdash;Switching
+Gear, Instruments, and Connections.&mdash;Distributing Mains.&mdash;Insulation,
+Resistance, and Cost.&mdash;Distributing Networks.&mdash;Service Mains and
+Feeders.&mdash;Testing Mains.&mdash;Meters and Appliances.&mdash;Standardising and
+Testing Laboratory.&mdash;Secondary Batteries.&mdash;Street
+Lighting.&mdash;Cost.&mdash;General Organisation.&mdash;Mains Department.&mdash;Installation
+Department.&mdash;Standardising Department.&mdash;Drawing Office.&mdash;Clerical
+Department.&mdash;The Consumer.&mdash;Routine and Main Laying.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"One of the <span class="smcap">most valuable contributions</span> to Central Station
+literature we have had for some time."&mdash;<i>Electricity.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3>ELECTRICITY CONTROL.</h3>
+
+<h5>A Treatise on Electricity Switchgear and Systems of Transmission.</h5>
+
+<h4><span class="smcap">By</span> LEONARD ANDREWS, M.I.E.E.,</h4>
+
+<h6>Ex-Member of Council of the Incorporated Municipal Electrical
+Association; Consulting Electrical Engineer to the Hastings Corporation,
+&amp;c., &amp;c.</h6>
+
+<p>General Principles of Switchgear Design.&mdash;Constructional
+Details.&mdash;Circuit Breakers or Arc Interrupting Devices.&mdash;Automatically
+Operated Circuit Breakers.&mdash;Alternating Reverse Current
+Devices.&mdash;Arrangement of 'Bus Bars, and Apparatus for Parallel
+Running.&mdash;General Arrangement of Controlling Apparatus for High Tension
+Systems.&mdash;General Arrangement of Controlling Apparatus for Low Tension
+Systems.&mdash;Examples of Complete Installations.&mdash;Long Distance
+Transmission Schemes.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Sixteenth Edition</span>, Thoroughly Revised and Enlarged.</p>
+
+<h3>A POCKET-BOOK OF ELECTRICAL RULES &amp; TABLES</h3>
+
+<h5><i>FOR THE USE OF ELECTRICIANS AND ENGINEERS.</i></h5>
+
+<h4><span class="smcap">By</span> JOHN MUNRO, C.E., &amp; <span class="smcap">Prof.</span> JAMIESON, <span class="smcap">M. Inst.
+C.E.</span>, F.R.S.E.</h4>
+
+<p>With Numerous Diagrams. Pocket Size. Leather, 8s. 6d.</p>
+
+<h4><b>GENERAL CONTENTS.</b></h4>
+
+<p>Units of
+Measurement.&mdash;Measures.&mdash;Testing.&mdash;Conductors.&mdash;Dielectrics.&mdash;Submarine
+Cables.&mdash;Telegraphy.&mdash;Electro-Chemistry.&mdash;Electro-Metallurgy.&mdash;Batteries.&mdash;Dynamos
+and Motors.&mdash;Transformers.&mdash;Electric
+Lighting.&mdash;Miscellaneous.&mdash;Logarithms.&mdash;Appendices.</p>
+
+<p>"<span class="smcap">Wonderfully Perfect</span>.... Worthy of the highest commendation we
+can give it."&mdash;<i>Electrician.</i></p>
+
+<p>"The <span class="smcap">Sterling Value</span> of Messrs. <span class="smcap">Munro</span> and
+<span class="smcap">Jamieson's Pocket-Book</span>."&mdash;<i>Electrical Review.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_l" id="Page_l">[Pg l]</a></span></p>
+
+<h4><b>By PROFESSORS J.H. POYNTING &amp; J.J. THOMSON.</b></h4>
+
+<p>In Five Volumes. Large 8vo. Sold Separately.</p>
+
+<h3><b>A TEXT-BOOK OF PHYSICS.</b></h3>
+
+<h6>BY</h6>
+
+<h4>J.H. POYNTING, SC.D., F.R.S.,</h4>
+
+<h6>Late Fellow of Trinity College, Cambridge; Professor of Physics,
+Birmingham University.</h6>
+
+<h6>AND</h6>
+
+<h4>J.J. THOMSON, M.A., F.R.S.</h4>
+
+<h6>Fellow of Trinity College, Cambridge; Prof. of Experimental Physics in
+the University of Cambridge.</h6>
+
+<hr style='width: 45%;' />
+
+<p>Introductory Volume, fully Illustrated. <span class="smcap">Second Edition</span>,
+Revised.</p>
+
+<p>Price 10s. 6d.</p>
+
+<h3><b>PROPERTIES OF MATTER.</b></h3>
+
+<p><span class="smcap">Contents.</span>&mdash;Gravitation.&mdash;The Acceleration of
+Gravity.&mdash;Elasticity.&mdash;Stresses and Strains.&mdash;Torsion.&mdash;Bending of
+Rods.&mdash;Spiral Springs.&mdash;Collision.&mdash;Compressibility of
+Liquids.&mdash;Pressures and Volumes of Gases.&mdash;Thermal Effects Accompanying
+Strain.&mdash;Capillarity.&mdash;Surface Tension.&mdash;Laplace's Theory of
+Capillarity.&mdash;Diffusion of Liquids.&mdash;Diffusion of Gases.&mdash;Viscosity of
+Liquids.&mdash;<span class="smcap">Index.</span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Volume II. Second Edition.</span> Fully Illustrated. Price 8s. 6d.</p>
+
+<h3><b>SOUND.</b></h3>
+
+<p><span class="smcap">Contents.</span>&mdash;The Nature of Sound and its chief
+Characteristics.&mdash;The Velocity of Sound in Air and other
+Media.&mdash;Reflection and Refraction of Sound.&mdash;Frequency and Pitch of
+Notes.&mdash;Resonance and Forced Oscillations.&mdash;Analysis of Vibrations.&mdash;The
+Transverse Vibrations of Stretched Strings or Wires.&mdash;Pipes and other
+Air Cavities.&mdash;Rods.&mdash;Plates.&mdash;Membranes.&mdash;Vibrations maintained by
+Heat.&mdash;Sensitive Flames and Jets.&mdash;Musical Sand.&mdash;The Superposition of
+Waves.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"The work ... may be recommended to anyone desirous of possessing an
+<span class="smcap">easy up-to-date Standard Treatise</span> on Acoustics."&mdash;<i>Literature.</i></p>
+
+<p>"Very clearly written.... The names of the authors are a guarantee of
+the <span class="smcap">scientific accuracy</span> and <span class="smcap">up-to-date character</span> of
+the work."&mdash;<i>Educational Times.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Volume III.</span> At Press. Fully Illustrated.</p>
+
+<h3><b>HEAT.</b></h3>
+
+<p>Remaining Volumes in Preparation&mdash;</p>
+
+<p><b>LIGHT; MAGNETISM AND ELECTRICITY.</b></p>
+
+<hr style='width: 45%;' />
+
+<p><b>THE MEAN DENSITY OF THE EARTH:</b> An Essay to which the Adams Prize was
+adjudged in 1893 in the University of Cambridge. By <span class="smcap">J.H.
+Poynting</span>, Sc.D., F.R.S., Late Fellow of Trinity College, Cambridge;
+Professor of Physics, Birmingham University. In Large 8vo, with
+Bibliography, Illustrations in the Text, and Seven Lithographed Plates.
+12s. 6d.</p>
+
+<p>"An account of this subject cannot fail to be of <span class="smcap">great</span> and
+<span class="smcap">general interest</span> to the scientific mind. Especially is this the
+case when the account is given by one who has contributed so
+considerably as has Prof. Poynting to our present state of knowledge
+with respect to a very difficult subject.... Remarkably has Newton's
+estimate been verified by Prof. Poynting."&mdash;<i>Athen&aelig;um.</i><span class='pagenum'><a name="Page_li" id="Page_li">[Pg li]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h4><b>Griffin's Geological, Prospecting, Mining, and Metallurgical
+Publications.</b></h4>
+
+<p>For Works on <span class="smcap">Chemistry</span> and <span class="smcap">Chemical Industries</span> see p.
+69.</p>
+
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'></td><td align='left'>PAGE</td></tr>
+<tr><td align='left'>Geology, Stratigraphical,</td><td align='left'>R. Etheridge, F.R.S.,</td><td align='left'>52</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Physical,</td><td align='left'>Prof. H.G. Seeley,</td><td align='left'>52</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Practical Aids,</td><td align='left'>Prof. Grenville Cole,</td><td align='left'>53</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Open Air Studies,</td><td align='left'>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>19</td></tr>
+<tr><td align='left'>Griffin's "New Land" Series,</td><td align='left'>Ed. by Prof. Cole,</td><td align='left'>54</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Prospecting for Minerals,</td><td align='left'>S. Herbert Cox, A.R.S.M.,</td><td align='left'>55</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Food Supply,</td><td align='left'>Robt. Bruce,</td><td align='left'>55</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;New Lands,</td><td align='left'>H.R. Mill, D.Sc., F.R.S.E.,</td><td align='left'>54</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Building Construction,</td><td align='left'>Prof. James Lyon,</td><td align='left'>54</td></tr>
+<tr><td align='left'>Ore and Stone Mining,</td><td align='left'>Prof. Le Neve Foster,</td><td align='left'>56</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Elementary Mining,</td><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>56</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Coal Mining,</td><td align='left'>H.W. Hughes, F.G.S.,</td><td align='left'>56</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Practical Coal Mining,</td><td align='left'>G.L. Kerr, M.Inst.M.E.,</td><td align='left'>58</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Elementary &nbsp;&nbsp;&nbsp;"</td><td align='left'>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>58</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Electrical Coal Mining,</td><td align='left'>D. Burns,</td><td align='left'>58</td></tr>
+<tr><td align='left'>Mine-Surveying,</td><td align='left'>Bennett H. Brough, A.R.S.M.,</td><td align='left'>57</td></tr>
+<tr><td align='left'>Blasting and Explosives,</td><td align='left'>O. Guttmann, A.M.I.C.E.,</td><td align='left'>57</td></tr>
+<tr><td align='left'>Mine Accounts,</td><td align='left'>Prof. J.G. Lawn,</td><td align='left'>57</td></tr>
+<tr><td align='left'>Mining Engineers' Pkt.-Bk.,</td><td align='left'>E.R. Field, M.Inst.M.M.,</td><td align='left'>60</td></tr>
+<tr><td align='left'>Petroleum,</td><td align='left'>Redwood and Holloway,</td><td align='left'>61</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;A Handbook on Petroleum,</td><td align='left'>J.H. Thomson and Dr. Redwood,</td><td align='left'>61</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;The Petroleum Lamp,</td><td align='left'>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>61</td></tr>
+<tr><td align='left'>Metallurgical Analysis,</td><td align='left'>Macleod and Walker,</td><td align='left'>60</td></tr>
+<tr><td align='left'>Metallurgy (General),</td><td align='left'>Phillips and Bauerman,</td><td align='left'>60</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp; (Elementary),</td><td align='left'>Prof. Humboldt Sexton,</td><td align='left'>66</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Getting Gold,</td><td align='left'>J.C.F. Johnson, F.G.S.,</td><td align='left'>58</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Gold Seeking in South Africa,</td><td align='left'>Theo Kassner,</td><td align='left'>59</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Cyanide Process,</td><td align='left'>James Park, F.G.S.,</td><td align='left'>59</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Cyaniding,</td><td align='left'>Smart and Julian,</td><td align='left'>59</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Electric Smelting,</td><td align='left'>Borchers and McMillan,</td><td align='left'>67</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Electro-Metallurgy,</td><td align='left'>W.G. McMillan, F.I.C.,</td><td align='left'>67</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Assaying,</td><td align='left'>J.J. &amp; C. Beringer,</td><td align='left'>66</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Metallurgical Analysis,</td><td align='left'>J.J. Morgan, F.C.S,</td><td align='left'>66</td></tr>
+<tr><td align='left'>Griffin's Metallurgical Series</td><td align='left'>Ed. by Sir W. Roberts-Austen,</td><td align='left'>62</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Introduction,</td><td align='left'>Sir W. Roberts-Austen, K.C.B.,,</td><td align='left'>63</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Gold, Metallurgy of,</td><td align='left'>Dr. Kirke Rose, A.R.S.M.,</td><td align='left'>63</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Lead and Silver,&nbsp;&nbsp;&nbsp; "</td><td align='left'>H.F. Collins, A.R.S.M.,</td><td align='left'>64</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Iron, Metallurgy of,</td><td align='left'>Thos. Turner, A.R.S.M.,</td><td align='left'>65</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Steel, &nbsp;&nbsp;&nbsp;"</td><td align='left'>F.W. Harbord,</td><td align='left'>65</td></tr>
+<tr><td align='left'>&nbsp;&nbsp;&nbsp;Metallurgical Machinery,</td><td align='left'>H.C. Jenkins, A.R.S.M.,</td><td align='left'>64</td></tr>
+<tr><td align='left'>Goldsmith and Jeweller's Art,</td><td align='left'>Thos. B. Wigley,</td><td align='left'>68</td></tr>
+<tr><td align='left'>Precious Stones,</td><td align='left'>Dr. Max Bauer,</td><td align='left'>68</td></tr>
+</table></div>
+
+
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_lii" id="Page_lii">[Pg lii]</a></span></p>
+<p><i>Demy 8vo, Handsome cloth, 18s.</i></p>
+
+<h3>Physical Geology and Pal&aelig;ontology,</h3>
+
+<h4><i>ON THE BASIS OF PHILLIPS.</i></h4>
+
+<h6>BY</h6>
+
+<h4>HARRY GOVIER SEELEY, F.R.S.,</h4> <h6>PROFESSOR OF GEOGRAPHY IN KING'S COLLEGE,
+LONDON.</h6>
+
+<h4>With Frontispiece in Chromo-Lithography, and Illustrations.</h4>
+
+<p>"It is impossible to praise too highly the research which <span class="smcap">Professor
+Seeley's</span> '<span class="smcap">Physical Geology</span>' evidences. <span class="smcap">It is far more
+than a Text-book</span>&mdash;it is a <span class="smcap">Directory</span> to the Student in
+prosecuting his researches."&mdash;<i>Presidential Address to the Geological
+Society, 1885, by Rev. Prof. Bonney, D.Sc., LL.D., F.R.S.</i></p>
+
+<p>"<span class="smcap">Professor Seeley</span> maintains in his '<span class="smcap">Physical Geology</span>'
+the high reputation he already deservedly bears as a Teacher."&mdash;<i>Dr.
+Henry Woodward, F.R.S., in the "Geological Magazine."</i></p>
+
+<p>"<span class="smcap">Professor Seeley's</span> work includes one of the most satisfactory
+Treatises on Lithology in the English language."&mdash;<i>American Journal of
+Engineering.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Demy 8vo, Handsome cloth, 34s.</i></p>
+
+<h3>Stratigraphical Geology &amp; Pal&aelig;ontology,</h3>
+
+<h5><i>ON THE BASIS OF PHILLIPS.</i></h5>
+
+<h6>BY</h6>
+
+<h4>ROBERT ETHERIDGE, F.R.S.,</h4>
+
+<h6>OF THE NATURAL HIST. DEPARTMENT, BRITISH MUSEUM, LATE PAL&AElig;ONTOLOGIST TO
+THE GEOLOGICAL SURVEY OF GREAT BRITAIN, PAST PRESIDENT OF THE GEOLOGICAL
+SOCIETY, ETC.</h6>
+
+<h4>With Map, Numerous Tables, and Thirty-six Plates.</h4>
+
+<p>"No such compendium of geological knowledge has ever been brought
+together before."&mdash;<i>Westminster Review.</i></p>
+
+<p>"If <span class="smcap">Prof. Seeley's</span> volume was remarkable for its originality
+and the breadth of its views, Mr. <span class="smcap">Etheridge</span> fully justifies the
+assertion made in his preface that his book differs in construction and
+detail from any known manual.... Must take <span class="smcap">high rank among works of
+reference</span>."&mdash;<i>Athen&aelig;um.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3>OPEN-AIR STUDIES IN GEOLOGY: </h3><h5>An Introduction to Geology Out-of-doors.</h5>
+
+<h4><span class="smcap">By</span> PROFESSOR GRENVILLE COLE, M.R.I.A., F.G.S.</h4>
+
+<p>For details, see Griffin's Introductory Science Series, p. 85.</p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_liii" id="Page_liii">[Pg liii]</a></span></p>
+<p><i>Crown 8vo. Handsome Cloth, 2s. 6d.</i></p>
+
+<h3><b>RESEARCHES ON THE PAST AND PRESENT HISTORY OF THE EARTH'S ATMOSPHERE.</b></h3>
+
+<h5><i>Including the latest Discoveries and their Practical Applications.</i></h5>
+
+<h4><span class="smcap">By</span> DR. THOMAS LAMB PHIPSON.</h4>
+
+<p>PART I.&mdash;<span class="smcap">The Earth's Atmosphere in Remote Geological Periods.</span></p>
+
+<p>PART II.&mdash;<span class="smcap">The Atmosphere of Our Present Period.</span> <span class="smcap">Appendices;
+Index.</span></p>
+
+<p>*** Dr. Phipson's work presents, amidst much which is of interest to the
+Scientist and the General Reader alike, a short <i>r&eacute;sum&eacute;</i> of his
+discovery of the origin of Atmospheric Oxygen, the existence of which he
+attributes wholly to the action of Solar Radiation upon vegetable life.
+The book will be found replete with much that is new, curious, and
+interesting, both in connection with Weather Lore, and with Scientific
+Meteorology.&mdash;<i>Publisher's Note.</i></p>
+
+<p>"The book should prove of interest to general readers, as well as to
+meteorologists and other students of science."&mdash;<i>Nature.</i></p>
+
+<hr style='width: 45%;' />
+
+<h4>By GRENVILLE A.J. COLE, M.R.I.A., F.G.S.,</h4>
+
+<h6>Professor of Geology in the Royal College of Science for Ireland, and
+Examiner in the University of London.</h6>
+
+<p><i>See also the two following pages (54, 55), and page 85.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>AIDS IN PRACTICAL GEOLOGY:</b></h3>
+
+<h5><i>WITH A SECTION ON PAL&AElig;ONTOLOGY.</i></h5>
+
+<h4><span class="smcap">By</span> PROFESSOR GRENVILLE COLE, M.R.I.A., F.G.S.</h4>
+
+<h5><span class="smcap">Fourth Edition</span>, Thoroughly Revised. With Frontispiece and
+Illustrations. Cloth, 10s. 6d.</h5>
+
+<p>
+GENERAL   CONTENTS.&mdash;<br />
+PART I.&mdash;<span class="smcap">Sampling of the Earth's Crust.</span><br />
+PART II.&mdash;<span class="smcap">Examination of Minerals.</span><br />
+PART III.&mdash;<span class="smcap">Examination of Rocks.</span><br />
+PART IV.&mdash;<span class="smcap">Examination of Fossils.</span><br />
+</p>
+
+<p>"Prof. Cole treats of the examination of minerals and rocks in a way
+that has never been attempted before ... <span class="smcap">deserving of the highest
+praise</span>. Here indeed are 'Aids' <span class="smcap">innumerable</span> and
+<span class="smcap">invaluable</span>. All the directions are given, with the utmost
+clearness and precision."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"That the work deserves its title, that it is full of '<span class="smcap">Aids</span>,'
+and in the highest degree '<span class="smcap">practical</span>,' will be the verdict of
+all who use it."&mdash;<i>Nature.</i></p>
+
+<p>"This <span class="smcap">excellent Manual</span> ... will be <span class="smcap">a very great
+help</span>.... The Section on the Examination of Fossils is probably the
+<span class="smcap">best</span> of its kind yet published.... <span class="smcap">Full</span> of
+well-digested information from the newest sources and from personal
+research."&mdash;<i>Annals of Nat. History.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_liv" id="Page_liv">[Pg liv]</a></span></p>
+<h3>GRIFFINS "NEW LAND" SERIES.</h3>
+
+<hr style='width: 45%;' />
+
+<p class="center"><i>Practical Hand-Books for the Use of Prospectors, Explorers, Settlers,
+Colonists, and all Interested in the opening up and Development of New
+Lands.</i></p>
+
+<h4><span class="smcap">Edited by</span> GRENVILLE A.J. COLE, M.R.I.A., F.G.S.,</h4>
+
+<h6>Professor of Geology in the Royal College of Science for Ireland, and
+Examiner in the University of London.</h6>
+
+<hr style='width: 45%;' />
+
+<p><i>In Crown 8vo. Handsome Cloth. 5s.</i></p>
+
+<h5><i>With Numerous Maps Specially Drawn and Executed for this Work.</i></h5>
+
+<h3>NEW LANDS:</h3>
+
+<h5>THEIR RESOURCES AND PROSPECTIVE ADVANTAGES.</h5>
+
+<h4><span class="smcap">By</span> HUGH ROBERT MILL, D.Sc., LL.D., F.R.S.E.,</h4>
+
+<h6>Librarian to the Royal Geographical Society.</h6>
+
+<p><span class="smcap">Introductory</span>.&mdash;The Development of New Lands.&mdash;The Dominion of
+Canada.&mdash;Canada, Eastern Provinces.&mdash;Canada, Western Provinces and
+Territories.&mdash;Newfoundland.&mdash;The United States.&mdash;Latin America,
+Mexico.&mdash;Latin America, Temperate Brazil and Chili.&mdash;Latin America,
+Argentina.&mdash;The Falkland Islands.&mdash;Victoria.&mdash;New South
+Wales.&mdash;Queensland.&mdash;South Australia.&mdash;Tasmania.&mdash;Western
+Australia.&mdash;New Zealand.&mdash;The Resources of South Africa.&mdash;Southern
+Rhodesia.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"<span class="smcap">Painstaking</span> ... <span class="smcap">complete</span> ... of great <span class="smcap">practical
+assistance</span>."&mdash;<i>The Field.</i></p>
+
+<p>"A want admirably supplied.... Has the advantage of being written by a
+professed Geographer."&mdash;<i>Geographical Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<h5><i>IN PREPARATION.</i></h5>
+
+<p><b>BUILDING CONSTRUCTION <span class="smcap">in</span> WOOD, STONE, <span class="smcap">and</span> CONCRETE.</b>
+By <span class="smcap">James Lyon</span>, M.A., Professor of Engineering in the Royal
+College of Science for Ireland; sometime Superintendent of the
+Engineering Department in the University of Cambridge; and J. Taylor,
+A.R.C.S.I.</p>
+
+<hr style='width: 45%;' />
+
+<p>*** Other Volumes, dealing with subjects of <span class="smcap">Primary Importance</span>
+in the <span class="smcap">Examination</span> and <span class="smcap">Utilisation</span> of Lands which have
+not as yet been fully developed, are in preparation.<span class='pagenum'><a name="Page_lv" id="Page_lv">[Pg lv]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition</span>, <i>Revised. With Illustrations. Handsome Cloth,
+5s.</i></p>
+
+<h3>PROSPECTING FOR MINERALS.</h3>
+
+<h5>A Practical Handbook for Prospectors, Explorers, Settlers, and all
+interested in the Opening up and Development of New Lands.</h5>
+
+<h6>BY</h6>
+
+<h4>S. HERBERT COX, Assoc. R.S.M., M. Inst. M.M., F.G.S., &amp;c.</h4>
+
+<p><span class="smcap">General Contents.</span>&mdash;Introduction and Hints on Geology&mdash;The
+Determination of Minerals: Use of the Blow-pipe, &amp;c.&mdash;Rock-forming
+Minerals and Non-Metallic Minerals of Commercial Value: Rock Salt,
+Borax, Marbles, Lithographic Stone, Quartz and Opal, &amp;c., &amp;c.&mdash;Precious
+Stones and Gems&mdash;Stratified Deposits: Coal and Ores&mdash;Mineral Veins and
+Lodes&mdash;Irregular Deposits&mdash;Dynamics of Lodes: Faults, &amp;c.&mdash;Alluvial
+Deposits&mdash;Noble Metals: Gold, Platinum, Silver,
+&amp;c.&mdash;Lead&mdash;Mercury&mdash;Copper&mdash;Tin&mdash;Zinc&mdash;Iron&mdash;Nickel, &amp;c.&mdash;Sulphur,
+Antimony, Arsenic, &amp;c.&mdash;Combustible Minerals&mdash;Petroleum&mdash;General Hints
+on Prospecting&mdash;Glossary&mdash;Index.</p>
+
+<div class="blockquot"><p>"This <span class="smcap">admirable little work</span> ... written with
+<span class="smcap">scientific accuracy</span> in a <span class="smcap">clear</span> and
+<span class="smcap">lucid</span> style.... An <span class="smcap">important addition</span> to
+technical literature ... will be of value not only to the
+Student, but to the experienced Prospector.... If the
+succeeding volumes of the <span class="smcap">New Land Series</span> are equal in
+merit to the First, we must congratulate the Publishers on
+successfully filling up a gap in existing literature.&mdash;<i>Mining
+Journal.</i></p>
+
+<p>"This <span class="smcap">excellent handbook</span> will prove a perfect
+<i>Vade-mecum</i> to those engaged in the practical work of Mining
+and Metallurgy."&mdash;<i>Times of Africa.</i></p></div>
+
+<hr style='width: 45%;' />
+
+<p>With many Engravings and Photographs. Handsome Cloth, 4s. 6d.</p>
+
+<h3>FOOD SUPPLY.</h3>
+
+<h4>By ROBERT BRUCE, Agricultural Superintendent to the Royal Dublin
+Society.</h4>
+
+<h5>With Appendix on Preserved Foods by C.A. Mitchell, B.A., F.L.C.</h5>
+
+<p><span class="smcap">General Contents.</span>&mdash;Climate and Soil&mdash;Drainage and Rotation of
+Crops&mdash;Seeds and Crops&mdash;Vegetables and Fruits&mdash;Cattle and
+Cattle-Breeding&mdash;Sheep and Sheep Rearing&mdash;Pigs&mdash;Poultry&mdash;Horses&mdash;The
+Dairy&mdash;The Farmer's Implements&mdash;The Settler's Home.</p>
+
+<p>"<span class="smcap">Bristles With Information.</span>"&mdash;<i>Farmers' Gazette.</i></p>
+
+<p>"The work is one which will appeal to those intending to become farmers
+at home or in the Colonies, and who desire to obtain a general idea of
+the true principles of farming in <span class="smcap">all its branches</span>."&mdash;<i>Journal
+of the Royal Colonial Inst.</i></p>
+
+<p>"A most <span class="smcap">readable</span> and <span class="smcap">valuable</span> book, and merits an
+<span class="smcap">extensive sale</span>."&mdash;<i>Scottish Farmer.</i></p>
+
+<p>"Will prove of service in <span class="smcap">any part of the world</span>."&mdash;<i>Nature.</i><span class='pagenum'><a name="Page_lvi" id="Page_lvi">[Pg lvi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Fourth Edition</span>, Revised, and brought thoroughly up-to-date by
+<span class="smcap">L.H. Cooke</span>, Instructor in Mine Surveying, Royal College of
+Science.</p>
+
+<h5>With Frontispiece and 716 Illustrations. Price 34s.</h5>
+
+<h3>ORE &amp; STONE MINING.</h3>
+
+<h6>BY</h6>
+
+<h4>C. LE NEVE FOSTER, D.Sc., F.R.S.,</h4>
+
+<h6>PROFESSOR OF MINING, ROYAL COLLEGE OF SCIENCE; EXAMINER IN MINING TO THE
+BOARD OF EDUCATION.</h6>
+
+<h4>GENERAL CONTENTS.</h4>
+
+<p>INTRODUCTION. Mode of Occurrence of
+Minerals.&mdash;Prospecting.&mdash;Boring.&mdash;Breaking Ground.&mdash;Supporting
+Excavations.&mdash;Exploitation.&mdash;Haulage or Transport.&mdash;Hoisting or
+Winding.&mdash;Drainage.&mdash;Ventilation.&mdash;Lighting.&mdash;Descent and
+Ascent.&mdash;Dressing.&mdash;Principles of Employment of Mining
+Labour.&mdash;Legislation affecting Mines and Quarries.&mdash;Condition of the
+Miner.&mdash;Accidents.&mdash;Index.</p>
+
+<p>"Dr. Foster's book was expected to be epoch-making, and it fully
+justifies such expectation.... <span class="smcap">A most admirable</span> account of the
+mode of occurrence of practically <span class="smcap">all known minerals</span>. Probably
+stands unrivalled for completeness."&mdash;<i>The Mining Journal</i>.</p>
+
+<p>"This <span class="smcap">epoch-making</span> work ... appeals to <span class="smcap">men of
+experience</span> no less than to students."&mdash;<i>Berg- und H&uuml;ttenm&auml;nnische
+Zeitung</i>.</p>
+
+<p>"This <span class="smcap">splendid work</span>."&mdash;<i>Oesterr. Ztschrft. f&uuml;r Berg- und
+H&uuml;ttenwesen</i>.</p>
+
+<hr style='width: 45%;' />
+
+<h3>ELEMENTARY MINING AND QUARRYING</h3>
+
+<h5>(An Introductory Text-book).</h5> <h4>By Prof. <span class="smcap">C. Le Neve Foster</span>, F.R.S.</h4>
+<h6>With Illustrations. [<i>At Press.</i></h6>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Fourth Edition</span>, <i>Revised and Greatly Enlarged. With Numerous
+Additional Illustrations, mostly reduced from Working Drawings. Price
+24s. net.</i></p>
+
+<h3>A TEXT-BOOK OF COAL-MINING:</h3>
+
+<h5><i>FOR THE USE OF COLLIERY MANAGERS AND OTHERS ENGAGED IN COAL-MINING.</i></h5>
+
+<h6>BY</h6>
+
+<h4>HERBERT WILLIAM HUGHES, F.G.S.,</h4>
+
+<h6>Assoc. Royal School of Mines, General Manager of Sandwell Park Colliery.</h6>
+
+<h4>GENERAL CONTENTS.</h4>
+
+<p>Geology.&mdash;Search for Coal.&mdash;Breaking Ground.&mdash;Sinking.&mdash;Preliminary
+Operations.&mdash;Methods of
+Working.&mdash;Haulage.&mdash;Winding.&mdash;Pumping.&mdash;Ventilation.&mdash;Lighting.&mdash;Works
+at Surface.&mdash;Preparation of Coal for Market.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"Quite <span class="smcap">the best</span> book of its kind ... as <span class="smcap">practical</span> in
+aim as a book can be ... The illustrations are
+<span class="smcap">excellent</span>."&mdash;<i>Athen&aelig;um</i>.</p>
+
+<p>"We cordially recommend the work."&mdash;<i>Colliery Guardian</i>.</p>
+
+<p>"Will soon come to be regarded as the <span class="smcap">standard work</span> of its
+kind."&mdash;<i>Birmingham Daily Gazette.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_lvii" id="Page_lvii">[Pg lvii]</a></span></p>
+<p><span class="smcap">Tenth Edition</span>, Revised and Enlarged. With Numerous Diagrams.</p>
+
+<p>Cloth, 7s. 6d.</p>
+
+<h3>A TREATISE ON MINE-SURVEYING:</h3>
+
+<h5>For the use of Managers of Mines and Collieries, Students at the Royal
+School of Mines, &amp;c.</h5>
+
+<h4>By BENNETT H. BROUGH, F.G.S., <span class="smcap">Assoc.</span>R.S.M.,</h4>
+
+<h6>Formerly Instructor of Mine-Surveying, Royal School of Mines.</h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;General Explanations.&mdash;Measurement of
+Distances.&mdash;Miner's Dial.&mdash;Variation of the
+Magnetic-Needle.&mdash;Surveying.&mdash;German Dial.&mdash;Theodolite.&mdash;Traversing
+Underground.&mdash;Surface-Surveys.&mdash;Plotting the Survey.&mdash;Calculation of
+Areas.&mdash;Levelling.&mdash;Measuring Distances by
+Telescope.&mdash;Setting-out.&mdash;Problems.&mdash;Photographic
+Surveying.&mdash;<i>Appendices.</i></p>
+
+<p>"Its <span class="smcap">clearness</span> of <span class="smcap">style, lucidity</span> of
+<span class="smcap">description</span>, and <span class="smcap">fulness</span> of <span class="smcap">detail</span> have long
+ago won for it a place unique in the literature of this branch of mining
+engineering, and the present edition fully maintains the high standard
+of its predecessors. To the student, and to the mining engineer alike,
+<span class="smcap">its value</span> is inestimable. The illustrations are
+excellent."&mdash;<i>The Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 8vo.</i> <span class="smcap">Second Edition</span>. <i>Price 10s. 6d.</i></p>
+
+<h3><b>Mine Accounts and Mining Book-keeping.</b></h3>
+
+<h5>For Students, Managers, Secretaries, and others.</h5>
+
+<h5><i>With Examples taken from Actual Practice of Leading Companies.</i></h5>
+
+<h6>BY</h6>
+
+<h4>JAMES GUNSON LAWN, Assoc.R.S.M., Assoc. Mem. Inst. C.E., F.G.S.,</h4>
+
+<h6>Professor of Mining at the South African School of Mines.</h6>
+
+<h4><span class="smcap">Edited by</span> C. LE NEVE FOSTER, D.Sc., F.R.S.</h4>
+
+<p><span class="smcap">General Contents</span>.&mdash;Introduction.&mdash;Part I. Engagement and
+Payment of Workmen.&mdash;Part II. Purchases and Sales.&mdash;Part III. Working
+Summaries and Analyses.&mdash;Part IV. Ledger, Balance Sheet, and Company
+Books.&mdash;Part V. Reports and Statistics.</p>
+
+<p>"It seems <span class="smcap">impossible</span> to suggest how Mr. <span class="smcap">Lawn's</span> book
+could be made more <span class="smcap">complete</span> or more <span class="smcap">valuable</span>, careful,
+and exhaustive."&mdash;<i>Accountants' Magazine</i>.</p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 8vo, with Illustrations and Folding-Plates. 10s. 6d.</i></p>
+
+<h3><b>BLASTING</b>:</h3>
+
+<h5>AND THE USE OF EXPLOSIVES.</h5>
+
+<h5>A Handbook for Engineers and others Engaged in Mining, Tunnelling,
+Quarrying, &amp;c.</h5>
+
+<h4><span class="smcap">By OSCAR GUTTMANN, Assoc. M. Inst. C.E.</span></h4>
+
+<h6><i>Member of the Societies of Civil Engineers and Architects of Vienna and
+Budapest, Corresponding Member of the Imp. Roy. Geological Institution
+of Austria, &amp;c.</i></h6>
+
+<p>"This <span class="smcap">admirable</span> work."&mdash;<i>Colliery Guardian.</i></p>
+
+<p>"Should prove a <i>vade-mecum</i> to Mining Engineers and all engaged in
+practical work."&mdash;<i>Iron and Coal Trades Review.</i><span class='pagenum'><a name="Page_lviii" id="Page_lviii">[Pg lviii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Crown 8vo. Handsome cloth. With Numerous Illustrations. 6s. net.</i></p>
+
+<h3><b>ELECTRICAL PRACTICE IN COLLIERIES.</b></h3>
+
+<h4><span class="smcap">By D. BURNS, M.E., M.Inst.M.E.,</span></h4>
+
+<h6>Certificated Colliery Manager, and Lecturer on Mining and Geology to the
+Glasgow and West of Scotland Technical College.</h6>
+
+<p>Units of Measurement, Conductors, &amp;c.&mdash;The Theory of the Dynamo.&mdash;The
+Dynamo, Details of Construction and Working.&mdash;Motors.&mdash;Lighting
+Installations in Collieries.&mdash;Pumping by Electricity.&mdash;Electrical
+Haulage.&mdash;Coal Cutting.&mdash;Miscellaneous Applications of Electricity in
+Mines.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"A clear and concise introduction to electrical practice in
+collieries."&mdash;<i>Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition.</span> Large Crown 8vo. Handsome Cloth. With over 520
+Illustrations in the Text. 12s. 6d.</p>
+
+<h3><b>PRACTICAL COAL-MINING:</b> </h3><h5>A MANUAL FOR MANAGERS, UNDER-MANAGERS, COLLIERY
+ENGINEERS, AND OTHERS.</h5>
+
+<h5><i>With Worked-out Problems on Haulage, Pumping, Ventilation, &amp;c.</i></h5>
+
+<h4><span class="smcap">By</span> GEORGE L. KERR, M.E., M.<span class="smcap">Inst.</span>M.E.</h4>
+
+<p>"An <span class="smcap">essentially practical work</span>, and can be confidently
+recommended. No department of Coal-Mining has been
+overlooked."&mdash;<i>Engineers' Gazette.</i></p>
+
+<p>"This book <span class="smcap">just meets</span> the wants of Students preparing for the
+Colliery Managers' Examinations. I have decided to use it for our
+classes here.... We have, I believe the largest atining class in Great
+Britain."&mdash;<i>The Principal of a Training College.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3>ELEMENTARY COAL-MINING: </h3><h5>For the Use of Students, Miners, and others
+preparing for Examinations. By <span class="smcap">George L. Kerr, M.E.,
+M.Inst.M.E.</span>, Author of "Practical Coal-Mining." In Crown 8vo.
+Handsome Cloth. With 200 Illustrations. 3s. 6d.</h5>
+
+<p>"An abundance of information conveyed in a popular and attractive
+form.... Will be of great use to all who are in any way interested in
+coal mining."&mdash;<i>Scottish Critic.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition.</span> <i>With Illustrations. Cloth, 3s. 6d.</i></p>
+
+<h3><b>GETTING GOLD:</b></h3>
+
+<h5>A GOLD-MINING HANDBOOK FOR PRACTICAL MEN.</h5>
+
+<h4><span class="smcap">By</span> J.C.F. JOHNSON, F.G.S., A.I.M.E.,</h4>
+
+<h6>Life Member Australasian Mine-Managers' Association.</h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;Introductory: Prospecting (Alluvial and
+General)&mdash;Lode or Reef Prospecting&mdash;Genesiology of Gold&mdash;Auriferous
+Lodes&mdash;Drifts&mdash;Gold Extraction&mdash;Lixiviation&mdash;Calcination&mdash;Motor Power
+and its Transmission&mdash;Company Formation&mdash;Mining Appliances and
+Methods&mdash;Australasian Mining Regulations.</p>
+
+<p>"<span class="smcap">Practical</span> from beginning to end ... deals thoroughly with the
+Prospecting, Sinking, Crushing, and Extraction of gold."&mdash;<i>Brit.
+Australasian.</i><span class='pagenum'><a name="Page_lix" id="Page_lix">[Pg lix]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><i>With Plates and Illustrations. Handsome Cloth. At Press.</i></p>
+
+<h3><b>THE CYANIDE PROCESS OF GOLD EXTRACTION.</b></h3>
+
+<h5><i>A Text-Book for the Use of Metallurgists and Students at Schools of
+Mines, &amp;c.</i></h5>
+
+<h4><span class="smcap">By JAMES PARK, F.G.S., M.Inst.M.M.</span>,</h4>
+
+<p>Professor of Mining and Director of the Otago University School of
+Mines; late Director Thames School of Mines, and Geological Surveyor and
+Mining Geologist to the Government of New Zealand.</p>
+
+<p><span class="smcap">Third English Edition.</span> Thoroughly Revised and Greatly Enlarged.
+With additional details concerning the Siemens-Halske and other recent
+processes.</p>
+
+<p><span class="smcap">Contents.</span>&mdash;The MacArthur Process.&mdash;Chemistry of the
+Process.&mdash;Laboratory Experiments.&mdash;Control Testing and Analysis of
+Solutions.&mdash;Appliances for Cyanide Extraction.&mdash;The Actual Extraction by
+Cyanide.&mdash;Application of the Process.&mdash;Leaching by Agitation.&mdash;Zinc
+Precipitation of Gold.&mdash;The Siemens-Halske Process.&mdash;Other Cyanide
+Processes.&mdash;Antidotes for Cyanide Poisoning.&mdash;Cyaniding in New Zealand.</p>
+
+<p>"Mr. Park's book deserves to be ranked as amongst the <span class="smcap">best of
+existing treatises on this subject</span>."&mdash;<i>Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">At Press</span>. <i>With Numerous Plates, Maps, and Illustrations.</i></p>
+
+<h3><b>CYANIDING GOLD &amp; SILVER ORES.</b></h3>
+
+<h5>A Practical Treatise on the Cyanide Process; its Application, Methods of
+Working, Design and Construction of Plant, and Costs.</h5>
+
+<h4><span class="smcap">By</span> H. FORBES JULIAN,</h4>
+
+<h6>Mining and Metallurgical Engineer; Specialist in Gold: Late Technical
+Adviser of the Deutsche Gold und Silber Scheide Anstalt,
+Frankfort-on-Maine.</h6>
+
+<h4><span class="smcap">And</span> EDGAR SMART, A.M.I.C.E.,</h4>
+
+<h6>Civil and Metallurgical Engineer.</h6>
+
+<p>*** This book deals with the Cyanide Process from Technical, Commercial,
+and Scientific points of view. It is adapted for the Use of Directors,
+Managers, and Superintendents of Mines and Metallurgical Works, Mining
+Engineers, Metallurgists, Chemists, Assayers, Working Cyaniders, and
+Students.</p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Crown. 8vo. Illustrated. Fancy Cloth Boards.</i> 4<i>s</i>. 6<i>d</i>.</p>
+
+<h3><b>GOLD SEEKING IN SOUTH AFRICA:</b></h3>
+
+<h5>A Handbook of Hints for intending Explorers, Prospectors, and Settlers.</h5>
+
+<h4><span class="smcap">By</span> THEO KASSNER,</h4>
+
+<h6>Mine Manager, Author of the Geological Sketch Map of the De Kaap Gold
+Fields.</h6>
+
+<p><i>With a Chapter on the Agricultural Prospects of South Africa.</i></p>
+
+<p><span class="smcap">Abstract of Contents</span>&mdash;History.&mdash;Geology.&mdash;Prospecting.&mdash;The De
+Kaap Goldfields.&mdash;Komati and Swaziland.&mdash;Cost of Mining, Native Labour,
+&amp;c.&mdash;Lydenberg Goldfields&mdash;Zoutspanberg.&mdash;Witwatersrand.&mdash;Other
+Goldfields.&mdash;General Considerations&mdash;Conclusions.&mdash;Agricultural
+Prospects, Tables, Index, &amp;c.</p>
+
+<p>"As fascinating in its way as anything ever penned by Jules Verne. Mr.
+Kassner manages to impart his information in a way that enables him to
+be understanded even of the dullest."&mdash;<i>African Commerce.</i><span class='pagenum'><a name="Page_lx" id="Page_lx">[Pg lx]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">At Press.</span> Large 8vo. Handsome Cloth. With Illustrations.</p>
+
+<h3>METALLURGICAL ANALYSIS &amp; ASSAYING:</h3>
+
+<h5>A THREE YEARS' COURSE FOR STUDENTS OF SCHOOLS OF MINES.</h5>
+
+<h4>By W.A. MACLEOD, B.A., B.Sc., A.O.S.M. (N.Z.),</h4>
+
+<h6>Formerly Assist.-Director, Thames School of Mines (N.Z.), and Lecturer
+in Chemistry, University of Tasmania; Director of Queensland Government
+School of Mines, Charters Towers;</h6>
+
+<h4><span class="smcap">And</span> CHAS. WALKER, F.C.S.,</h4>
+
+<h6>Formerly Assist.-Demonstrator in Chemistry, Sydney University; Lecturer
+in Chemistry and Metallurgy, Charters Towers School of Mines</h6>
+
+<p><span class="smcap">Part</span> I.&mdash;<span class="smcap">Qualitative Analysis and Preparation and
+Properties of Gases.</span></p>
+
+<p><span class="smcap">Part</span> II.&mdash;<span class="smcap">Qualitative and Quantitative Analysis.</span></p>
+
+<p><span class="smcap">Part</span> III.&mdash;<span class="smcap">Assaying, Technical Analysis (Gas, Water, Fuels,
+Oils, &amp;c.).</span></p>
+
+<p>*** "The aim of this work is to provide the student with a graded course
+of work leading from Simple Quantitative Analysis up to the Technical
+Quantitative Methods. It has been specially prepared to meet the
+requirements of Schools of Mines, and more especially, of those in the
+Colonies, the subject matter having been selected to cover a three
+years' laboratory course."&mdash;<i>Extract from Author's Preface.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition.</span> With Folding Plates and Many Illustrations. 36s.</p>
+
+<h3>ELEMENTS OF METALLURGY.</h3>
+
+<h5>A PRACTICAL TREATISE ON THE ART OF EXTRACTING METALS FROM THEIR ORES.</h5>
+
+<h4><span class="smcap">By</span> J. ARTHUR PHILLIPS, M. <span class="smcap">Inst.</span> C.E., F.C.S., F.G.S.,
+&amp;c., <span class="smcap">And</span> H. BAUERMAN, V.P.G.S.</h4>
+
+<p><span class="smcap">General Contents.</span>&mdash;Refractory Materials.&mdash;Fire-Clays.&mdash;Fuels,
+&amp;c.&mdash;Aluminium.&mdash;Copper.&mdash;Tin.&mdash;Antimony.&mdash;Arsenic.&mdash;Zinc.&mdash;Mercury.&mdash;Bismuth.&mdash;Lead.&mdash;Iron.&mdash;Cobalt.&mdash;Nickel.&mdash;Silver.&mdash;Gold.&mdash;Platinum.</p>
+
+<p>"Of the <span class="smcap">Third Edition</span>, we are still able to say that, as a
+Text-book of Metallurgy, it is <span class="smcap">the best</span> with which we are
+acquainted."&mdash;<i>Engineer.</i></p>
+
+<p>"A work which is equally valuable to the Student as a Text-book, and to
+the practical Smelter as a Standard Work of Reference.... The
+Illustrations are admirable examples of Wood Engraving."&mdash;<i>Chemical
+News.</i></p>
+
+<hr style='width: 45%;' />
+
+<p class="center"><b>THE MINING ENGINEERS' REPORT BOOK AND DIRECTORS'</b> AND SHAREHOLDERS'
+GUIDE TO MINING REPORTS. By <span class="smcap">Edwin R. Field</span>,
+<span class="smcap">M.Inst.M.M.</span> With Notes on the Valuation of Mining Property and
+Tabulating Reports, Useful Tables, &amp;c., and provided with detachable
+blank pages for MS. Notes.</p>
+
+<p>"An <span class="smcap">admirably</span> compiled book which Mining Engineers and Managers
+will find <span class="smcap">extremely useful</span>."&mdash;<i>Mining Journal.</i><span class='pagenum'><a name="Page_lxi" id="Page_lxi">[Pg lxi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition.</span> <i>In Preparation. In Two Volumes, Large 8vo.
+With Numerous Maps, Plates, and Illustrations in the Text. Price 45s.</i></p>
+
+<h3><b>PETROLEUM <i>AND ITS PRODUCTS:</i> A PRACTICAL TREATISE.</b></h3>
+
+<h4>By Dr. BOVERTON REDWOOD, <span class="smcap">F.R.S.E., F.I.C., Assoc.R.C.S.</span>,</h4>
+
+<h6>Hon. Corr. Mem. of the Imperial Russian Technical Society; Mem. of the
+American Chemical Society; Adviser to the Home Office and to the
+Corporation of London under the Petroleum Acts, &amp;c., &amp;c.</h6>
+
+<h5><span class="smcap">Assisted by GEO. T. HOLLOWAY, F.I.C., Assoc. R.C.S.</span>, And
+Numerous Contributors.</h5>
+
+<p><span class="smcap">General Contents.</span>&mdash;I. Historical.&mdash;II. Geological and
+Geographical Distribution of Petroleum and Natural Gas.&mdash;III. Chemical
+and Physical Properties.&mdash;IV. Origin&mdash;V. Production.&mdash;VI.
+Refining.&mdash;VII. The Shale Oil and Allied Industries.&mdash;VIII. Transport,
+Storage, and Distribution.&mdash;IX. Testing.&mdash;X. Application and Uses.&mdash;XI.
+Legislation at Home and Abroad.&mdash;XII. Statistics.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"The <span class="smcap">MOST COMPREHENSIVE AND CONVENIENT ACCOUNT</span> that has yet
+appeared of a gigantic Industry which has made incalculable additions to
+the comfort of civilised man."&mdash;<i>The Times.</i></p>
+
+<p>"A <span class="smcap">splendid contribution</span> to our technical
+literature."&mdash;<i>Chemical News.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>With Plates (One Coloured) and Illustrations. Price 8s. 6d. net.</i></p>
+
+<h3>A HANDBOOK ON PETROLEUM.</h3>
+<h5><i>FOR INSPECTORS UNDER THE PETROLEUM ACTS,</i></h5>
+
+<h5>And for those engaged in the Storage, Transport, Distribution, and
+Industrial Use of Petroleum and its Products, and of Calcium Carbide.
+With suggestions on the Construction and Use of Mineral Oil Lamps.</h5>
+
+<h4><span class="smcap">By CAPTAIN J.H. THOMSON</span>, H.M. Chief Inspector of Explosives,</h4>
+
+<h6>AND</h6>
+
+<h4><span class="smcap">Dr. BOVERTON REDWOOD</span>,</h4> <h6>Author of "Petroleum and its Products."</h6>
+
+<p><span class="smcap">Contents.</span>&mdash;I. Introductory.&mdash;II. Sources of Supply.&mdash;III.
+Production.&mdash;IV. Chemical Products, Shale Oil, and Coal Tar.&mdash;V. Flash
+Point and Fire Test.&mdash;VI. Testings.&mdash;VII. Existing Legislation relating
+to Petroleum.&mdash;VIII.&mdash;IX.&mdash;Precautions Necessary.&mdash;X. Petroleum Oil
+Lamps.&mdash;XI. Carbide of Calcium and
+Acetylene.&mdash;Appendices.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"A volume that will enrich the world's petroleum literature, and render
+a service to the British branch of the industry.... Reliable,
+indispensable, a brilliant contribution."&mdash;<i>Petroleum.</i></p>
+
+<hr style='width: 45%;' />
+
+<p class="center"><b>THE PETROLEUM LAMP: Its Choice and Use.</b> A Guide to the Safe Employment
+of Mineral Oil in what is commonly termed the Paraffin Lamp. By
+<span class="smcap">Capt. J.H. Thomson</span> and Dr. <span class="smcap">Boverton Redwood</span>. Popular
+Edition, Illustrated. 1s. net.</p>
+
+<p>"The book contains a great deal of interesting reading, much of which is
+thoroughly practical and useful. It is a work which will meet every
+purpose for which it has been written."&mdash;<i>Petroleum.</i><span class='pagenum'><a name="Page_lxii" id="Page_lxii">[Pg lxii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h2>Griffin's Metallurgical Series.</h2>
+
+<hr style='width: 45%;' />
+
+<h3><i>STANDARD WORKS OF REFERENCE</i></h3>
+
+<h6>FOR</h6>
+
+<h5>Metallurgists, Mine-Owners, Assayers, Manufacturers, and all interested
+in the development of the Metallurgical Industries.</h5>
+
+<h4>EDITED BY Sir W. ROBERTS-AUSTEN, K.C.B., D.C.L, F.R.S.</h4>
+
+<p><i>In Large 8vo, Handsome Cloth. With Illustrations.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><b>INTRODUCTION to the STUDY of METALLURGY.</b> By the <span class="smcap">Editor</span>.
+<span class="smcap">Fifth Edition.</span> 18s. (See p. 63.)</p>
+
+<p><b>GOLD (The Metallurgy of).</b> By <span class="smcap">Thos. Kirke Rose</span>, D.Sc.,
+Assoc.R.S.M., F.I.C., Chemist and Assayer of the Royal Mint. <span class="smcap">Fourth
+Edition.</span> 21s. (See p. 63.)</p>
+
+<p><b>LEAD AND SILVER (The Metallurgy of).</b> By <span class="smcap">H.F. Collins</span>,
+Assoc.R.S.M., M.Inst.M.M. Part I., Lead, 16s; Part II., Silver, 16s.
+(See p. 64.)</p>
+
+<p><b>IRON (The Metallurgy of).</b> By <span class="smcap">T. Turner</span>, A.R.S.M., F.I.C.,
+F.C.S. <span class="smcap">Second Edition</span>, Revised. 16s. (See p. 65.)</p>
+
+<p><b>STEEL (The Metallurgy of).</b> By <span class="smcap">F.W. Harbord</span>, Assoc.R.S.M.,
+F.I.C., with a Section on Mechanical Treatment by <span class="smcap">J.W. Hall</span>,
+A.M.Inst, C.E. (See p. 65.) [<i>Ready shortly.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Will be Published at Short Intervals.</i></p>
+
+<p><b>METALLURGICAL MACHINERY:</b> the Application of Engineering to
+Metallurgical Problems. By <span class="smcap">Henry Charles Jenkins</span>, Wh.Sc.,
+Assoc.R.S.M., Assoc.M.Inst.C.E., of the Royal College of Science. (See
+p. 64).</p>
+
+<p><b>ALLOYS.</b> By the <span class="smcap">Editor</span>.</p>
+
+<p>*** Other Volumes in Preparation.<span class='pagenum'><a name="Page_lxiii" id="Page_lxiii">[Pg lxiii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Fifth Edition</span>, thoroughly Revised and considerably Enlarged.
+Large 8vo, with numerous Illustrations and Micro-Photographic Plates of
+different varieties of Steel. 18s.</p>
+
+<h3><b>An Introduction to the Study of METALLURGY.</b></h3>
+
+<h6>BY</h6>
+
+<h4>Sir W. ROBERTS-AUSTEN, K.C.B., D.C.L., F.R.S., A.R.S.M., </h4><h6>Late Chemist
+and Assayer of the Royal Mint, and Professor of Metallurgy in the Royal
+College of Science.</h6>
+
+<p><span class="smcap">General Contents.</span>&mdash;The Relation of Metallurgy to
+Chemistry.&mdash;Physical Properties of Metals.&mdash;Alloys.&mdash;The Thermal
+Treatment of Metals.&mdash;Fuel and Thermal Measurements.&mdash;Materials and
+Products of Metallurgical Processes.&mdash;Furnaces.&mdash;Means of Supplying Air
+to Furnaces.&mdash;Thermo-Chemistry.&mdash;Typical Metallurgical Processes.&mdash;The
+Micro-Structure of Metals and Alloys.&mdash;Economic Considerations.</p>
+
+<p>"No English text-book at all approaches this in the
+<span class="smcap">completeness</span> with which the most modern views on the subject
+are dealt with. Professor Austen's volume will be <span class="smcap">invaluable</span>,
+not only to the student, but also to those whose knowledge of the art is
+far advanced."&mdash;<i>Chemical News.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Fourth Edition</span>, Revised, Considerably Enlarged, and in part
+Re-written. Including the most recent Improvements in the Cyanide
+Process. With Frontispiece and numerous Illustrations. 21s.</p>
+
+<h3><b>THE METALLURGY OF GOLD.</b></h3>
+
+<h6>BY</h6>
+
+<h4>T. KIRKE ROSE, D.Sc.Lond., Assoc.R.S.M.,</h4><h6> <i>Chemist and Assayer of the
+Royal Mint</i>.</h6>
+
+<p><span class="smcap">General Contents.</span>&mdash;The Properties of Gold and its
+Alloys.&mdash;Chemistry of Gold.&mdash;Mode of Occurrence and
+Distribution.&mdash;Placer Mining.&mdash;Shallow Deposits.&mdash;Deep Placer
+Mining.&mdash;Quartz Crushing in the Stamp Battery.&mdash;Amalgamation.&mdash;Other
+Forms of Crushing and Amalgamating.&mdash;Concentration.&mdash;Stamp Battery
+Practice.&mdash;Chlorination: The Preparation of Ore.&mdash;The Vat Process.&mdash;The
+Barrel Process.&mdash;Chlorination Practice in Particular Mills.&mdash;The Cyanide
+Process.&mdash;Chemistry of the Process.&mdash;Pyritic Smelting.&mdash;The Refining and
+Parting of Gold Bullion&mdash;The Assay of Gold Ores.&mdash;The Assay of
+Bullion&mdash;Economic Considerations.&mdash;Bibliography.</p>
+
+<p>"A <span class="smcap">comprehensive practical treatise</span> on this important
+subject."&mdash;<i>The Times.</i></p>
+
+<p>"The <span class="smcap">most complete</span> description of the <span class="smcap">chlorination
+process</span> which has yet been published."&mdash;<i>Mining Journal.</i></p>
+
+<p>"Adapted for all who are interested in the Gold Mining Industry, being
+free from technicalities as far as possible, but is more particularly of
+value to those engaged in the industry."&mdash;<i>Cape Times.</i><span class='pagenum'><a name="Page_lxiv" id="Page_lxiv">[Pg lxiv]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h4><span class="smcap">Edited by SIR W. ROBERTS-AUSTEN, K.C.B., F.R.S., D.C.L.</span></h4>
+
+<p><i>In Large 8vo. Handsome Cloth. With Illustrations.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>In Two Volumes, Each Complete in Itself and Sold Separately.</p>
+
+<h3><b>THE METALLURGY OF LEAD AND SILVER.</b></h3>
+
+<h4><span class="smcap">By H.F. COLLINS, Assoc.R.S.M., M.Inst.M.M.</span></h4>
+
+<p><b>Part I.&mdash;LEAD:</b></p>
+
+<p>A Complete and Exhaustive Treatise on the Manufacture of Lead, with
+Sections on Smelting and Desilverisation, and Chapters on the Assay and
+Analysis of the Materials involved. Price 16s.</p>
+
+<p><span class="smcap">Summary of Contents.</span>&mdash;Sampling and Assaying Lead and
+Silver.&mdash;Properties and Compounds of Lead.&mdash;Lead Ores.&mdash;Lead
+Smelting.&mdash;Reverberatories.&mdash;Lead Smelting in Hearths.&mdash;The Roasting of
+Lead Ores.&mdash;Blast Furnace Smelting; Principles, Practice, and Examples;
+Products.&mdash;Flue Dust, its Composition, Collection and Treatment.&mdash;Costs
+and Losses, Purchase of Ores.&mdash;Treatment of Zinc, Lead Sulphides,
+Desilverisation, Softening and Refining.&mdash;The Pattinson Process.&mdash;The
+Parkes Process.&mdash;Cupellation and Refining, &amp;c., &amp;c.</p>
+
+<p>"A <span class="smcap">thoroughly sound</span> and useful digest. May with <span class="smcap">every
+confidence</span> be recommended."&mdash;<i>Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><b>Part II. SILVER.</b></p>
+
+<p>Comprising Details regarding the Sources and Treatment of Silver Ores,
+together with Descriptions of Plant, Machinery, and Processes of
+Manufacture, Refining of Bullion, Cost of Working, &amp;c. Price 16s.</p>
+
+<p><span class="smcap">Summary of Contents.</span>&mdash;Properties of Silver and its Principal
+Compounds.&mdash;Silver Ores.&mdash;The Patio Process.&mdash;The Kazo, Fondon, Kr&ouml;hnke,
+and Tina Processes.&mdash;The Pan Process.&mdash;Roast Amalgamation.&mdash;Treatment of
+Tailings and Concentration.&mdash;Retorting, Melting, and
+Assaying.&mdash;Chloridising-Roasting.&mdash;The Augustin, Claudet, and Ziervogel
+Processes.&mdash;The Hypo-Sulphite Leaching Process.&mdash;Refining.&mdash;Matte
+Smelting.&mdash;Pyritic Smelting.&mdash;Matte Smelting in
+Reverberatories.&mdash;Silver-Copper Smelting and Refining.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"The author has focussed <span class="smcap">a large amount of valuable information</span>
+into a convenient form.... The author has evidently considerable
+practical experience, and describes the various processes clearly and
+well."&mdash;<i>Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b><i>IN PREPARATION.</i></b></h3>
+
+<h3>METALLURGICAL MACHINERY: </h3><h5>The Application of Engineering to
+Metallurgical Problems.</h5>
+
+<h4><span class="smcap">By HENRY CHARLES JENKINS</span>,</h4>
+
+<h6><i>Wh.Sc., Assoc.R.S.M., Assoc.M.Inst.C.E.</i></h6>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_lxv" id="Page_lxv">[Pg lxv]</a></span></p>
+<p><span class="smcap">Ready Shortly.</span> With Numerous Illustrations. Large 8vo. Handsome
+Cloth.</p>
+
+<h3><b>THE METALLURGY OF STEEL.</b></h3>
+
+<h4><span class="smcap">By F.W. HARBORD, Assoc.R.S.M., F.I.C.</span>, </h4><h6><i>Consulting Metallurgist
+and Analytical Chemist to the Indian Government, Royal Indian
+Engineering College, Coopers Hill.</i></h6>
+
+<p>With over 40 Plates, 500 Illustrations (comprising nearly 100
+Micro-Sections of Steel), Diagrams of Plant and Machinery, reduced from
+Working Drawings, and a Section on Mill Practice.</p>
+
+<p><span class="smcap">By J.W. HALL, A.M.Inst.C.E.</span></p>
+
+<p><span class="smcap">Abridged Contents.</span>&mdash;The Plant, Machinery, Methods and Chemistry
+of the Bessemer and of the Open Hearth Processes (Acid and Basic).&mdash;The
+Mechanical Treatment of Steel comprising Mill Practice, Plant and
+Machinery.&mdash;The Influence of Metalloids, Heat Treatment, Special Steels,
+Microstructure, Testing, and Specifications.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition</span>, Revised. Price 16s.</p>
+
+<h3><b>THE METALLURGY OF IRON.</b></h3>
+
+<h4><span class="smcap">By THOMAS TURNER, Assoc.R.S.M., F.I.C.</span>, </h4><h6><i>Professor of
+Metallurgy in the University of Birmingham.</i></h6>
+
+<p>In Large 8vo, Handsome Cloth, With Numerous Illustrations (many from
+Photographs).</p>
+
+<p><i>General Contents.</i>&mdash;Early History of Iron.&mdash;Modern History of
+Iron.&mdash;The Age of Steel.&mdash;Chief Iron Ores.&mdash;Preparation of Iron
+Ores.&mdash;The Blast Furnace.&mdash;The Air used in the Blast Furnace.&mdash;Reactions
+of the Blast Furnace.&mdash;The Fuel used in the Blast Furnace.&mdash;Slags and
+Fluxes of Iron Smelting.&mdash;Properties of Cast Iron.&mdash;Foundry
+Practice.&mdash;Wrought Iron.&mdash;Indirect Production of Wrought Iron.&mdash;The
+Puddling Process.&mdash;Further Treatment of Wrought Iron.&mdash;Corrosion of Iron
+and Steel.</p>
+
+<p>"A <span class="smcap">most valuable summary</span> of knowledge relating to every method
+and stage in the manufacture of cast and wrought iron ... rich in
+chemical details.... <span class="smcap">Exhaustive</span> and <span class="smcap">thoroughly
+up-to-date.</span>"&mdash;<i>Bulletin of the American Iron and Steel
+Association.</i></p>
+
+<p>"This is <span class="smcap">a delightful book</span>, giving, as it does, reliable
+information on a subject becoming every day more elaborate."&mdash;<i>Colliery
+Guardian.</i></p>
+
+<p>"A <span class="smcap">thoroughly useful book</span>, which brings the subject <span class="smcap">up to
+date</span>. <span class="smcap">Of great value</span> to those engaged in the iron
+industry."&mdash;<i>Mining Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>*** For Details of <span class="smcap">Works on Mining</span>, see pages 55-59.<span class='pagenum'><a name="Page_lxvi" id="Page_lxvi">[Pg lxvi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>A TEXT-BOOK OF ASSAYING:</b></h3>
+
+<h5><i>For the use of Students, Mine Managers, Assayers, &amp;c.</i></h5>
+
+<h4><span class="smcap">By J.J. BERINGER, F.I.C., F.C.S.</span>,</h4><h6> Public Analyst for, and
+Lecturer to the Mining Association of, Cornwall.</h6>
+
+<h4><span class="smcap">And C. BERINGER, F.C.S.</span>,</h4><h6> Late Chief Assayer to the Rio Tinto
+Copper Company, London.</h6>
+
+<p>With numerous Tables and Illustrations. Crown 8vo. Cloth, 10s. 6d.
+<span class="smcap">Eighth Edition.</span></p>
+
+<p><span class="smcap">General Contents.</span>&mdash;<span class="smcap">Part I.&mdash;Introductory</span>;
+<span class="smcap">Manipulation</span>: Sampling; Drying; Calculation of
+Results&mdash;Laboratory-books and Reports. <span class="smcap">Methods</span>: Dry
+Gravimetric; Wet Gravimetric&mdash;Volumetric Assays: Titrometric,
+Colorimetric, Gasometric&mdash;Weighing and Measuring&mdash;Reagents&mdash;Formul&aelig;,
+Equations, &amp;c.&mdash;Specific Gravity.</p>
+
+<p><span class="smcap">Part II.&mdash;Metals</span>: Detection and Assay of Silver, Gold,
+Platinum, Mercury, Copper, Lead, Thallium, Bismuth, Antimony, Iron,
+Nickel, Cobalt, Zinc, Cadmium, Tin, Tungsten, Titanium, Manganese,
+Chromium, &amp;c.&mdash;Earths, Alkalies.</p>
+
+<p><span class="smcap">Part III.&mdash;Non-Metals</span>: Oxygen and Oxides; The Halogens&mdash;Sulphur
+and Sulphates&mdash;Arsenic, Phosphorus, Nitrogen&mdash;Silicon, Carbon,
+Boron&mdash;Useful Tables.</p>
+
+<p>"A <span class="smcap">really meritorious work</span>, that may be safely depended upon
+either for systematic instruction or for reference."&mdash;<i>Nature.</i></p>
+
+<p>"This work is one of the best of its kind."&mdash;<i>Engineer.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition</span>, <i>Revised. Handsome Cloth. With Numerous
+Illustrations. 6s.</i></p>
+
+<h3>A TEXT-BOOK OF <b>ELEMENTARY METALLURGY.</b></h3>
+
+<h5>Including the Author's Practical Laboratory Course.</h5>
+
+<h4><span class="smcap">By A. HUMBOLDT SEXTON, F.I.C., F.C.S.</span>,</h4> <h6>Professor of Metallurgy
+in the Glasgow and West of Scotland Technical College.</h6>
+
+<p>GENERAL CONTENTS.&mdash;Introduction.&mdash;Properties of the
+Metals.&mdash;Combustion.&mdash;Fuels.&mdash;Refractory
+Materials.&mdash;Furnaces.&mdash;Occurrence of the Metals in Nature.&mdash;Preparation
+of the Ore for the Smelter.&mdash;Metallurgical
+Processes.&mdash;Iron.&mdash;Steel.&mdash;-Copper.&mdash;Lead.&mdash;Zinc and
+Tin.&mdash;Silver.&mdash;Gold.&mdash;Mercury.&mdash;Alloys.&mdash;Applications of
+<span class="smcap">Electricity</span> to Metallurgy.&mdash;<span class="smcap">Laboratory Course.</span></p>
+
+<p>"Just the kind of work for Students commencing the study of Metallurgy,
+or for <span class="smcap">Engineering</span> Students."&mdash;<i>Practical Engineer.</i></p>
+
+<p>"<span class="smcap">Excellently</span> got-up and <span class="smcap">well-arranged</span>."&mdash;<i>Chemical
+Trade Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>In Large 8vo. Handsome Cloth. Price 4s.</p>
+
+<h3><b>TABLES FOR QUANTITATIVE METALLURGICAL ANALYSIS.</b> FOR LABORATORY USE.</h3>
+
+<h5><i>ON THE PRINCIPLE OF "GROUP" SEPARATIONS.</i></h5>
+
+<h4><span class="smcap">By J. JAMES MORGAN, F.C.S., M.S.C.I.</span></h4>
+
+<p>"The Author may be <span class="smcap">CONGRATULATED</span> on the way his work has been
+carried out."&mdash;<i>The Engineer.</i></p>
+
+<p>"Will <span class="smcap">commend itself</span> highly in Laboratory Practice. Its
+<span class="smcap">clearness</span> and <span class="smcap">precision</span> mark the book out as a highly
+useful one."&mdash;<i>Mining Journal.</i><span class='pagenum'><a name="Page_lxvii" id="Page_lxvii">[Pg lxvii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition</span>, Revised, Enlarged, and in part Re-written. With
+Additional Sections on <span class="smcap">Modern Theories of Electrolysis Costs</span>,
+&amp;c. Price 10s. 6d.</p>
+
+<h3>A TREATISE ON <b>ELECTRO-METALLURGY:</b></h3>
+
+<h5>Embracing the Application of Electrolysis to the Plating, Depositing,
+Smelting, and Refining of various Metals, and to the Reproduction of
+Printing Surfaces and Art-Work, &amp;c.</h5>
+
+<h6>BY</h6>
+
+<h4>WALTER G. M<sup>c</sup>MILLAN, F.I.C., F.C.S.,</h4><h6><i>Secretary to the Institution of
+Electrical Engineers; late Lecturer in Metallurgy at Mason College,
+Birmingham.</i></h6>
+
+<h4>With numerous Illustrations. Large Crown 8vo. Cloth.</h4>
+
+<p>"This excellent treatise, ... one of the <span class="smcap">BEST</span> and <span class="smcap">MOST
+COMPLETE</span> manuals hitherto published on
+Electro-Metallurgy."&mdash;<i>Electrical Review.</i></p>
+
+<p>"This work will be a <span class="smcap">standard</span>."&mdash;<i>Jeweller.</i></p>
+
+<p>"Any metallurgical process which <span class="smcap">reduces</span> the cost of production
+must of necessity prove of great commercial importance.... We recommend
+this manual to <span class="smcap">ALL</span> who are interested in the <span class="smcap">practical
+application</span> of electrolytic processes."&mdash;<i>Nature.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>In large 8vo. With Numerous Illustrations and Three Folding-Plates.
+Price 21s.</p>
+
+<h3><b>ELECTRIC SMELTING &amp; REFINING:</b></h3><h5> A Practical Manual of the Extraction and
+Treatment of Metals by Electrical Methods.</h5>
+
+<h4>Being the "<span class="smcap">Elektro-Metallurgie</span>" of <span class="smcap">Dr. W. BORCHERS</span>.</h4>
+
+<h4>Translated from the Second Edition by WALTER G. M<sup>c</sup>MILLAN, F.I.C.,
+F.C.S</h4>
+
+<hr style='width: 45%;' />
+
+<h4>CONTENTS.</h4>
+
+<p><span class="smcap">Part I.&mdash;Alkalies and Alkaline Earth Metals</span>: Magnesium,
+Lithium, Beryllium, Sodium, Potassium, Calcium, Strontium, Barium, the
+Carbides of the Alkaline Earth Metals.</p>
+
+<p><span class="smcap">Part II.&mdash;The Earth Metals</span>: Aluminium, Cerium, Lanthanum,
+Didymium.</p>
+
+<p><span class="smcap">Part III.&mdash;The Heavy Metals</span>: Copper, Silver, Gold, Zinc and
+Cadmium, Mercury, Tin, Lead, Bismuth, Antimony, Chromium, Molybdenum,
+Tungsten, Uranium, Manganese, Iron, Nickel, and Cobalt, the Platinum
+Group.</p>
+
+<p>"<span class="smcap">Comprehensive</span> and <span class="smcap">authoritative</span> ... not only
+<span class="smcap">full</span> of <span class="smcap">valuable information</span>, but gives evidence of
+a<span class="smcap">thorough insight</span> into the technical <span class="smcap">value</span> and
+<span class="smcap">possibilities</span> of all the methods discussed."&mdash;<i>The
+Electrician.</i></p>
+
+<p>"Dr. <span class="smcap">Borchers' well-known work</span> ... must of <span class="smcap">necessity be
+acquired</span> by every one interested in the subject.
+<span class="smcap">Excellently</span> put into English with additional matter by Mr.
+<span class="smcap">M<sup>c</sup>Millan</span>."&mdash;<i>Nature.</i></p>
+
+<p>"Will be of <span class="smcap">GREAT SERVICE</span> to the practical man and the
+Student."&mdash;<i>Electric Smelting.</i><span class='pagenum'><a name="Page_lxviii" id="Page_lxviii">[Pg lxviii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 4to, Library Style. Beautifully Illustrated with 20 Plates,
+many in Colours, and 94 Figures in the Text.</i></p>
+
+<h3><b>PRECIOUS STONES: Their Properties, Occurrences, and Uses.</b></h3>
+
+<h5><i>A Treatise for Dealers, Manufacturers, Jewellers, and for all
+Collectors and others interested in Gems.</i></h5>
+
+<h4><span class="smcap">By Dr. MAX BAUER</span>, Professor in the University of Marburg,</h4>
+
+<h4><span class="smcap">Translated by L.J. SPENCER, M.A. (Cantab.), F.G.S.</span></h4>
+
+<p><span class="smcap">General Contents.</span>&mdash;General Properties of Gems: Their Natural
+Characters, Occurrence, Application, and Uses.&mdash;Detailed Description of
+Particular Gems: The Diamond, Rubies, Sapphires; Emeralds, Tourmalines,
+and Opals; Felspars, Amphiboles, Malachite.&mdash;Non-mineral Gems: Amber,
+&amp;c.&mdash;Optical Features, Transparency, Translucency, Opacity, Refraction
+and Dispersion, &amp;c.&mdash;<span class="smcap">Appendix</span>: Pearls; Coral.</p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large Crown 8vo. With Numerous Illustrations. 8s. 6d.</i></p>
+
+<h3>The Art of the Goldsmith and Jeweller</h3><h5> A Manual on the Manipulation of
+Gold and the Manufacture of Personal Ornaments.</h5>
+
+<h4><span class="smcap">By THOS. B. WIGLEY</span>, </h4><h6>Headmaster of the Jewellers and
+Silversmiths' Association Technical School, Birmingham.</h6>
+
+<h4><span class="smcap">ASSISTED BY J.H. STANSBIE, B.Sc. (Lond.), F.I.C.</span>,</h4> <h6>Lecturer at
+the Birmingham Municipal Technical School.</h6>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">General Contents.</span>&mdash;Introduction.&mdash;The Ancient Goldsmith's
+Art.&mdash;Metallurgy of Gold.&mdash;Prices, &amp;c.&mdash;Alloys.&mdash;Melting, Rolling, and
+Slitting Gold.&mdash;The workshop and Tools.&mdash;Wire Drawing.&mdash;Rings.&mdash;Chains
+and Insignia.&mdash;Antique Jewellery and its Revival.&mdash;Etruscan
+Work.&mdash;<span class="smcap">Precious Stones.</span>&mdash;Cutting.&mdash;Polishing and
+Finishing.&mdash;Chasing, Embossing, and Repouss&eacute; Work.&mdash;Colouring and
+Finishing.&mdash;Enamelling.&mdash;Engraving.&mdash;Moulding and Casting Ornaments,
+&amp;c.&mdash;Fluxes. &amp;c.&mdash;Recovery of the Precious Metals.&mdash;Refining and
+Assaying.&mdash;Gilding and Electro
+Deposition.&mdash;Hall-Marking.&mdash;Miscellaneous.&mdash;Appendix.<span class='pagenum'><a name="Page_lxix" id="Page_lxix">[Pg lxix]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h2><b>Griffin's Chemical and Technological Publications.</b></h2>
+
+<hr style='width: 45%;' />
+
+<p><i>For Metallurgy and Electro-Metallurgy, see previous Section.</i></p>
+
+
+<div class='center'>
+<table border="0" cellpadding="4" cellspacing="0" summary="">
+<tr><td align='left'></td><td align='left'></td><td align='left'>PAGE</td></tr>
+<tr><td align='left'><b>Inorganic Chemistry</b>,</td><td align='left'>Profs. Dupr&eacute; and Hake,</td><td align='left'>70</td></tr>
+<tr><td align='left'><b>Quantitative Analysis</b>,</td><td align='left'>Prof. Humboldt Sexton,</td><td align='left'>70</td></tr>
+<tr><td align='left'><b>Qualitative&nbsp;&nbsp;&nbsp;"</b></td><td align='left'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>70</td></tr>
+<tr><td align='left'><b>Chemistry for Engineers</b>,</td><td align='left'>Blount and Bloxam,</td><td align='left'>71</td></tr>
+<tr><td align='left'><b>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Manufacturers</b>,</td><td align='left'>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>71</td></tr>
+<tr><td align='left'><b>Foods, Analysis of</b>,</td><td align='left'>A. Wynter Blyth,</td><td align='left'>72</td></tr>
+<tr><td align='left'><b>Poisons, Detection of</b>,</td><td align='left'>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>72</td></tr>
+<tr><td align='left'><b>Tables for Chemists and Manufacturers</b>,</td><td align='left'>Prof. Castell-Evans,</td><td align='left'>79</td></tr>
+<tr><td align='left'><b>Agricultural Chemistry</b>,</td><td align='left'>Prof. J.M.H. Munro,</td><td align='left'>75</td></tr>
+<tr><td align='left'><b>Dairy Chemistry</b>,</td><td align='left'>H. D. Richmond,</td><td align='left'>73</td></tr>
+<tr><td align='left'><b>Milk</b>,</td><td align='left'>E.F. Willoughby,</td><td align='left'>73</td></tr>
+<tr><td align='left'><b>Flesh Foods</b>,</td><td align='left'>C.A. Mitchell,</td><td align='left'>73</td></tr>
+<tr><td align='left'><b>Practical Sanitation</b>,</td><td align='left'>Dr. G. Reid,</td><td align='left'>78</td></tr>
+<tr><td align='left'><b>Sanitary Engineering</b>,</td><td align='left'>F. Wood,</td><td align='left'>78</td></tr>
+<tr><td align='left'><b>Technical Mycology</b>,</td><td align='left'>Lafar and Salter,</td><td align='left'>74</td></tr>
+<tr><td align='left'><b>Ferments</b>,</td><td align='left'>C. Oppenheimer,</td><td align='left'>74</td></tr>
+<tr><td align='left'><b>Brewing</b>,</td><td align='left'>Dr. W.J. Sykes,</td><td align='left'>75</td></tr>
+<tr><td align='left'><b>Sewage Disposal</b>,</td><td align='left'>Santo Crimp,</td><td align='left'>76</td></tr>
+<tr><td align='left'><b>Trades' Waste</b>,</td><td align='left'>W. Naylor,</td><td align='left'>76</td></tr>
+<tr><td align='left'><b>Cements</b>,</td><td align='left'>G.R. Redgrave,</td><td align='left'>76</td></tr>
+<tr><td align='left'><b>Water Supply</b>,</td><td align='left'>R.E. Middleton,</td><td align='left'>77</td></tr>
+<tr><td align='left'><b>Road Making</b>,</td><td align='left'>Thos. Aitken,</td><td align='left'>79</td></tr>
+<tr><td align='left'><b>Gas Manufacture</b>,</td><td align='left'>W. Atkinson Butterfield,</td><td align='left'>77</td></tr>
+<tr><td align='left'><b>Acetylene</b>,</td><td align='left'>Leeds and Butterfield,</td><td align='left'>77</td></tr>
+<tr><td align='left'><b>Fire Risks</b>,</td><td align='left'>Dr. Schwartz,</td><td align='left'>77</td></tr>
+<tr><td align='left'><b>Petroleum</b>,</td><td align='left'>Redwood and Holloway,</td><td align='left'>61</td></tr>
+<tr><td align='left'><b>&mdash;&mdash; (Handbook)</b>,</td><td align='left'>Thomson and Redwood,</td><td align='left'>61</td></tr>
+<tr><td align='left'><b>Oils, Soaps, Candles</b>,</td><td align='left'>Dr. Alder Wright,</td><td align='left'>81</td></tr>
+<tr><td align='left'><b>Lubrication and Lubricants</b>,</td><td align='left'>Archbutt and Deeley,</td><td align='left'>32</td></tr>
+<tr><td align='left'><b>India Rubber</b>,</td><td align='left'>Dr. Carl O. Weber,</td><td align='left'>81</td></tr>
+<tr><td align='left'><b>Painters' Colours, Oils, and Varnishes</b>,</td><td align='left'>G.H. Hurst,</td><td align='left'>80</td></tr>
+<tr><td align='left'><b>Painters' Laboratory Guide</b>,</td><td align='left'>&nbsp;&nbsp;&nbsp;"&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;"</td><td align='left'>80</td></tr>
+<tr><td align='left'><b>Painting and Decorating</b>,</td><td align='left'>W.J. Pearce,</td><td align='left'>80</td></tr>
+<tr><td align='left'><b>Photography</b>,</td><td align='left'>A. Brothers,</td><td align='left'>21</td></tr>
+<tr><td align='left'><b>Dyeing</b>,</td><td align='left'>Knecht and Rawson,</td><td align='left'>82</td></tr>
+<tr><td align='left'><b>Dictionary of Dyes</b>,</td><td align='left'>Rawson, Gardner, and Laycock,</td><td align='left'>82</td></tr>
+<tr><td align='left'><b>Textile Printing</b>,</td><td align='left'>Seymour Rothwell,</td><td align='left'>83</td></tr>
+<tr><td align='left'><b>Textile Fibres of Commerce</b>,</td><td align='left'>W.I. Hannan,</td><td align='left'>83</td></tr>
+<tr><td align='left'><b>Dyeing and Cleaning</b>,</td><td align='left'>G.H. Hurst,</td><td align='left'>84</td></tr>
+<tr><td align='left'><b>Bleaching and Calico-Printing</b>,</td><td align='left'>Geo. Duerr,</td><td align='left'>84</td></tr>
+</table></div>
+
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_lxx" id="Page_lxx">[Pg lxx]</a></span></p>
+<h3><b>A SHORT MANUAL OF INORGANIC CHEMISTRY.</b></h3>
+
+<h4>BY A. DUPR&Eacute;, Ph.D., F.R.S.,</h4>
+
+<h6>AND</h6>
+
+<h4>WILSON HAKE, Ph.D., F.I.C., F.C.S., </h4><h6>Of the Westminster Hospital Medical
+School</h6>
+
+<p><span class="smcap">Third Edition</span>, Revised, Enlarged, and Re-issued. Price 6s. net.</p>
+
+<p>"A well-written, clear and accurate Elementary Manual of Inorganic
+Chemistry.... We agree heartily with the system adopted by Drs. Dupr&eacute;
+and Hake. <span class="smcap">Will Make Experimental Work trebly interesting because
+intelligible</span>."&mdash;<i>Saturday Review.</i></p>
+
+<p>"There is no question that, given the <span class="smcap">perfect grounding</span> of the
+Student in his Science, the remainder comes afterwards to him in a
+manner much more simple and easily acquired. The work is <span class="smcap">an example
+of the advantages of the Systematic Treatment</span> of a Science over the
+fragmentary style so generally followed. <span class="smcap">By a long way the best</span>
+of the small Manuals for Students."&mdash;<i>Analyst.</i></p>
+
+<hr style='width: 45%;' />
+
+<h4><b>LABORATORY HANDBOOKS BY A. HUMBOLDT SEXTON,</b></h4>
+
+<h6>Professor of Metallurgy in the Glasgow and West of Scotland Technical
+College.</h6>
+
+<hr style='width: 45%;' />
+
+<h3><b>OUTLINES OF QUANTITATIVE ANALYSIS.</b></h3>
+
+<h5><i>FOR THE USE OF STUDENTS.</i></h5>
+
+<p>With Illustrations. <span class="smcap">Fourth Edition</span>. Crown 8vo, Cloth, 3s.</p>
+
+<p>"A <span class="smcap">compact laboratory guide</span> for beginners was wanted, and the
+want has been <span class="smcap">well supplied</span>.... A good and useful
+book."&mdash;<i>Lancet</i>.</p>
+
+<hr style='width: 45%;' />
+
+<h3><b>OUTLINES OF QUALITATIVE ANALYSIS.</b></h3>
+
+<h5><i>FOR THE USE OF STUDENTS.</i></h5>
+
+<p>With Illustrations. <span class="smcap">Fourth Edition</span>, Revised. Crown 8vo, Cloth,
+3s. 6d.</p>
+
+<p>"The work of a thoroughly practical chemist."&mdash;<i>British Medical
+Journal.</i></p>
+
+<p>"Compiled with great care, and will supply a want."&mdash;<i>Journal of
+Education.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>ELEMENTARY METALLURGY:</b> </h3><h5>Including the Author's Practical Laboratory
+Course. With many Illustrations. [See p. 66.</h5>
+
+<p><span class="smcap">Third Edition</span>, Revised. Crown 8vo. Cloth, 6s.</p>
+
+<p>"Just the kind of work for students commencing the study of
+metallurgy."&mdash;<i>Practical Engineer.</i><span class='pagenum'><a name="Page_lxxi" id="Page_lxxi">[Pg lxxi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>CHEMISTRY FOR ENGINEERS AND MANUFACTURERS.</b></h3>
+
+<h5>A PRACTICAL TEXT-BOOK.</h5>
+
+<h6>BY</h6>
+
+<h4>BERTRAM BLOUNT, F.I.C., F.C.S.,</h4> <h6>Assoc.Inst.C.E., Consulting Chemist to
+the Crown Agents for the Colonies.</h6>
+
+<h6>AND</h6>
+
+<h4>A.G. BLOXAM, F.I.C., F.C.S.,</h4> <h6>Consulting Chemist, Head of the Chemistry
+Department, Goldsmiths' Inst., New Cross.</h6>
+
+<p>In Two Vols., Large 8vo. With Illustrations. Sold Separately.</p>
+
+<hr style='width: 45%;' />
+
+<p>"The authors have <span class="smcap">succeeded</span> beyond all expectations, and have
+produced a work which should give <span class="smcap">fresh power</span> to the Engineer
+and Manufacturer."&mdash;<i>The Times</i>.</p>
+
+<hr style='width: 45%;' />
+
+<p><b>VOLUME I. Price 10s. 6d.</b></p>
+
+<h3>CHEMISTRY OF ENGINEERING, BUILDING, AND METALLURGY.</h3>
+
+<p><i>General Content.</i>&mdash;INTRODUCTION&mdash;Chemistry of the Chief Materials of
+Construction&mdash;Sources of Energy&mdash;Chemistry of Steam-raising&mdash;Chemistry
+of Lubrication and Lubricants&mdash;Metallurgical Processes used in the
+Winning and Manufacture of Metals.</p>
+
+<p>"<span class="smcap">Practical throughout</span> ... an <span class="smcap">admirable text-book</span>,
+useful not only to Students, but to <span class="smcap">Engineers</span> and <span class="smcap">Managers
+of works</span> in <span class="smcap">preventing waste</span> and <span class="smcap">improving
+processes</span>."&mdash;<i>Scotsman.</i></p>
+
+<p>"<span class="smcap">Eminently practical.</span>"&mdash;<i>Glasgow Herald.</i></p>
+
+<p>"A book worthy of <span class="smcap">high rank</span> ... its merit is great ...
+treatment of the subject of <span class="smcap">gaseous fuel</span> particularly good....
+<span class="smcap">Water gas</span> and the production clearly worked out.... Altogether
+a most creditable production. <span class="smcap">We warmly recommend it</span>, and look
+forward with keen interest to the appearance of Vol. II."&mdash;<i>Journal of
+Gas Lighting.</i></p>
+
+<p><b>VOLUME II. Price 16s.</b></p>
+
+<h3>THE CHEMISTRY OF MANUFACTURING PROCESSES.</h3>
+
+<p><i>General Contents.</i>&mdash;Sulphuric Acid Manufacture&mdash;Manufacture of Alkali,
+&amp;c.&mdash;Destructive Distillation&mdash;Artificial Manure
+Manufacture&mdash;Petroleum&mdash;Lime and Cement&mdash;Clay Industries and
+Glass&mdash;Sugar and Starch&mdash;Brewing and Distilling&mdash;Oils, Resins, and
+Varnishes&mdash;Soap and Candles&mdash;Textiles and Bleaching&mdash;Colouring Matters,
+Dyeing, and Printing&mdash;Paper and Pasteboard&mdash;Pigments and
+Paints&mdash;Leather, Glue, and Size&mdash;Explosives and Matches&mdash;Minor Chemical
+Manufactures.</p>
+
+<p>"Certainly a <span class="smcap">good</span> and <span class="smcap">useful book</span>, constituting a
+<span class="smcap">practical guide</span> for students by affording a clear conception of
+the numerous processes as a whole."&mdash;<i>Chemical Trade Journal.</i></p>
+
+<p>"We <span class="smcap">confidently recommend</span> this volume as a <span class="smcap">practical</span>,
+and not overloaded, <span class="smcap">text-book</span>, of <span class="smcap">great value</span> to
+students."&mdash;<i>The Builder.</i><span class='pagenum'><a name="Page_lxxii" id="Page_lxxii">[Pg lxxii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p class="center"><span class="smcap">Just Out.</span> <span class="smcap">Fifth Edition</span>, Thoroughly Revised, Greatly
+Enlarged and Re-written. With additional Tables, Plates, and
+Illustrations. 21s.</p> <h3><b>FOODS: THEIR COMPOSITION AND ANALYSIS.</b></h3>
+
+<h4><span class="smcap">By A. WYNTER BLYTH, M.R.C.S., F.I.C., F.C.S.</span>,</h4>
+
+<h6>Barrister-at-Law, Public Analyst for the County of Devon, and Medical
+Officer of Health for St. Marylebone.</h6>
+
+<h4><span class="smcap">And M. WYNTER BLYTH, B.A., B.Sc., F.C.S.</span></h4>
+
+<p><span class="smcap">General Contents.</span>&mdash;History of
+Adulteration.&mdash;Legislation.&mdash;Apparatus.&mdash;"Ash."&mdash;Sugar.&mdash;Confectionery.&mdash;Honey.&mdash;Treacle.&mdash;Jams
+and Preserved
+Fruits.&mdash;Starches.&mdash;Wheaten-Flour.&mdash;Bread.&mdash;Oats.&mdash;Barley.&mdash;Rye.&mdash;Rice.&mdash;Maize.&mdash;Millet.&mdash;Potato.&mdash;Peas.&mdash;Lentils.&mdash;Beans.&mdash;Milk.&mdash;Cream.&mdash;Butter.&mdash;Oleo-Margarine.&mdash;Cheese.&mdash;Lard.&mdash;Tea.&mdash;Coffee.&mdash;Cocoa
+and
+Chocolate.&mdash;Alcohol.&mdash;Brandy.&mdash;Rum.&mdash;Whisky.&mdash;Gin.&mdash;Arrack.&mdash;Liqueurs.&mdash;Absinthe.&mdash;Yeast.&mdash;-Beer.&mdash;Wine.&mdash;Vinegar.&mdash;Lemon
+and Lime Juice.&mdash;Mustard.&mdash;Pepper.&mdash;Sweet and Bitter
+Almonds.&mdash;Annatto.&mdash;Olive Oil.&mdash;Water Analysis.&mdash;Appendix: Adulteration
+Acts, &amp;c.</p>
+
+<p>"Simply <span class="smcap">indispensable</span> in the Analyst's laboratory."&mdash;<i>The
+Lancet.</i></p>
+
+<p>"A new edition of Mr. Wynter Blyth's Standard work, <span class="smcap">enriched with
+all the recent discoveries and improvements</span>, will be accepted as a
+boon."&mdash;<i>Chemical News.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition.</span> In Large 8vo, Cloth, with Tables and
+Illustrations. Price 21s.</p>
+
+<h3><b>POISONS: THEIR EFFECTS AND DETECTION.</b></h3>
+
+<h4><span class="smcap">By A. WYNTER BLYTH, M.R.C.S., F.I.C., F.C.S.</span>,</h4>
+
+<h6>Barrister-at-Law, Public Analyst for the County of Devon, and Medical
+Officer of Health for St. Marylebone.</h6>
+
+<h4>GENERAL CONTENTS.</h4>
+
+<p>I.&mdash;Historical Introduction. II.&mdash;Classification&mdash;Statistics&mdash;Connection
+between Toxic Action and Chemical Composition&mdash;Life Tests&mdash;General
+Method of Procedure&mdash;The Spectroscope&mdash;Examination of Blood and Blood
+Stains. III.&mdash;Poisonous Gases. IV.&mdash;Acids and Alkalies. V.&mdash;More or less
+Volatile Poisonous Substances. VI.&mdash;Alkaloids and Poisonous Vegetable
+Principles. VII.&mdash;Poisons derived from Living or Dead Animal Substances.
+VIII.&mdash;The Oxalic Acid Group. IX.&mdash;Inorganic Poisons. Appendix:
+Treatment, by Antidotes or otherwise, of Cases of Poisoning.</p>
+
+<p>"Undoubtedly <span class="smcap">the most complete work</span> on Toxicology in our
+language."&mdash;<i>The Analyst (on the Third Edition).</i></p>
+
+<p>"As a <span class="smcap">practical guide</span>, we know <span class="smcap">no better</span> work."&mdash;<i>The
+Lancet (on the Third Edition).</i></p>
+
+<p>*** In the <span class="smcap">Third Edition</span>, Enlarged and partly Re-written,
+<span class="smcap">New Analytical Methods</span> have been introduced, and the
+<span class="smcap">Cadaveric Alkaloids</span>, or <span class="smcap">Ptomaines</span>, bodies playing so
+great a part in Food-poisoning and in the Manifestations of Disease,
+have received special attention.<span class='pagenum'><a name="Page_lxxiii" id="Page_lxxiii">[Pg lxxiii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p>With Numerous Tables, and 22 Illustrations. 16s.</p>
+
+<h3><b>DAIRY CHEMISTRY FOR DAIRY MANAGERS, CHEMISTS, AND ANALYSTS</b></h3>
+
+<h5>A Practical Handbook for Dairy Chemists and others having Control of
+Dairies.</h5>
+
+<h4><span class="smcap">By H. DROOP RICHMOND, F.C.S.</span>,</h4> <h6>CHEMIST TO THE AYLESBURY DAIRY
+COMPANY.</h6>
+
+<p><i>Contents.</i>&mdash;I. Introductory.&mdash;The Constituents of Milk. II. The
+Analysis of Milk. III. Normal Milk: its Adulterations and Alterations,
+and their Detection. IV. The Chemical Control of the Dairy. V.
+Biological and Sanitary Matters. VI. Butter. VII. Other Milk Products.
+VIII. The Milk of Mammals other than the
+Cow.&mdash;Appendices.&mdash;Tables.&mdash;Index.</p>
+
+<p>" ... In our opinion the book is the <span class="smcap">best contribution on the
+subject that has yet appeared</span> in the English language."&mdash;<i>Lancet.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">At Press</span>, Fully Illustrated.</p>
+
+<h3><b>MILK: ITS PRODUCTION &amp; USES.</b></h3>
+
+<h5><i>With Chapters on Dairy Farming, The Diseases of Cattle, and on the
+Hygiene and Control of Supplies.</i></h5>
+
+<h4><span class="smcap">By EDWARD F. WILLOUGHBY</span>, M.D. (Lond.), D.P.H. (Lond. and
+Camb.),</h4> <h6>Inspector of Farms and General Scientific Adviser to Welford and
+Sons, Ltd.</h6>
+
+<hr style='width: 45%;' />
+
+<p>Crown 8vo, Handsome Cloth. Fully Illustrated. 10s. 6d.</p>
+
+<h3>FLESH FOODS: </h3><h5>With Methods for their Chemical, Microscopical, and
+Bacteriological Examination.</h5>
+
+<h5><i>A Practical Handbook for Medical Men, Analysts, Inspectors and others.</i></h5>
+
+<h4><span class="smcap">By C. AINSWORTH MITCHELL, B.A.(Oxon)</span>,</h4><h6>Fellow of the Institute
+of Chemistry; Member of Council, Society of Public Analysts.</h6>
+
+<p><i>With Numerous Tables, Illustrations, and a Coloured Plate.</i></p>
+
+<p><span class="smcap">Contents.</span>&mdash;Structure and Chemical Composition of Muscular
+Fibre.&mdash;of Connective Tissue, and Blood.&mdash;The Flesh of Different
+Animals.&mdash;The Examination of Flesh.&mdash;Methods of Examining Animal
+Fat.&mdash;The Preservation of Flesh.&mdash;Composition and Analysis of
+Sausages.&mdash;Proteids of Flesh.&mdash;Meat Extracts and Flesh Peptones.&mdash;The
+Cooking of Flesh.&mdash;Poisonous Flesh.&mdash;The Animal Parasites of Flesh.&mdash;The
+Bacteriological Examination of Flesh.&mdash;The Extraction and Separation of
+Ptomaines.&mdash;<span class="smcap">Index.</span></p>
+
+<p>*** This work is a complete compendium of the <span class="smcap">chemistry of animal
+tissues</span>. It contains directions for the detection of morbid
+conditions, putrefactive changes, and poisonous or injurious
+constituents, together with an account of their causes and
+effects.&mdash;<i>Publishers' Note.</i></p>
+
+<p>"A compilation which will be most useful for the class for whom it is
+intended."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"A book which <span class="smcap">no one</span> whose duties involve considerations of
+food supply <span class="smcap">can afford to be without</span>."&mdash;<i>Municipal Journal.</i></p>
+
+<hr style='width: 45%;' />
+<p><span class='pagenum'><a name="Page_lxxiv" id="Page_lxxiv">[Pg lxxiv]</a></span></p>
+<p>In Large 8vo. Handsome Cloth. With numerous Illustrations.</p>
+
+<p><i>Each Volume Complete in Itself, and Sold Separately.</i></p>
+
+<h3><b>TECHNICAL MYCOLOGY:</b> THE UTILISATION OF MICRO-ORGANISMS IN THE ARTS AND
+MANUFACTURES.</h3>
+
+<h5><i>A Practical Handbook on Fermentation and Fermentative Processes for the
+Use of Brewers and Distillers, Analysts, Technical and Agricultural
+Chemists, and all interested in the Industries dependent on
+Fermentation.</i></h5>
+
+<h4><span class="smcap">By Dr.</span> FRANZ LAFAR,</h4>
+
+<h6>Professor of Fermentation-Physiology and Bacteriology in the Technical
+High School, Vienna.</h6>
+
+<p>With an Introduction by <span class="smcap">Dr.</span> EMIL CHR. HANSEN, Principal of the
+Carlsberg Laboratory, Copenhagen.</p>
+
+<p><span class="smcap">Translated by</span> CHARLES T.C. SALTER.</p>
+
+<p><b>Vol. I.&mdash;SCHIZOMYCETIC FERMENTATION.</b> 15s.</p>
+
+<p><i>Including the Theory of Fermentation, the Principles of Sterilization,
+and Pure Culture Processes.</i></p>
+
+<p><b>Vol. II., Part I. EUMYCETIC FERMENTATION.</b> 7s. 6d.</p>
+
+<p><i>The Morphology, Chemistry, Physiology, and Fermentative Processes of
+the Eumycetes, Zygomycetes, and Saccharomycetes.</i></p>
+
+<p>"The first work of the kind which can lay claim to completeness in the
+treatment of a fascinating subject. The plan is admirable, the
+classification simple, the style is good, and the tendency of the whole
+volume is to convey sure information to the reader."&mdash;<i>Lancet</i>.</p>
+
+<p>*** The publishers trust that before long they will be able to present
+English readers with the whole of the second volume, arrangements having
+been concluded whereby, upon its appearance in Germany, the English
+translation will be at once put in hand. This is now being done with
+Part I., which will be issued shortly, and which will be followed by the
+two final parts.</p>
+
+<hr style='width: 45%;' />
+
+<p>In Crown 8vo, Handsome Cloth. Price 7s. 6d. net.</p>
+
+<h3><b><i>FERMENTS</i> AND THEIR ACTIONS.</b></h3>
+
+<h5><i>A Text-book on the Chemistry and Physics of Fermentative Changes.</i></h5>
+
+<h4><span class="smcap">By</span> CARL OPPENHEIMER, <span class="smcap">Ph.D.,</span> M.D.,</h4><h6>Of the Physiological
+Institute at Eilangen.</h6>
+
+<h4><span class="smcap">Translated from the German by</span> C. AINSWORTH MITCHELL, B.A.,
+F.I.C., F.C.S.</h4>
+
+<p><span class="smcap">Abridged Contents</span>.&mdash;Introduction.&mdash;Definition.&mdash;Chemical Nature
+of Ferments.&mdash;Influence of External Factors.&mdash;Mode of
+Action.&mdash;Physiological Action.&mdash;Secretion.&mdash;Importance of Ferments to
+Vital Action.&mdash;Proteolytic Ferments.&mdash;Trypsin.&mdash;Bacteriolytic and
+H&aelig;molytic Ferments.&mdash;Vegetable Ferments.&mdash;Coagulating
+Ferments.&mdash;Saccharifying
+Ferments.&mdash;Diastases.&mdash;Polysaccharides.&mdash;Enzymes.&mdash;Ferments which
+decompose Glucosides.&mdash;Hydrolytic Ferments.&mdash;Lactic Acid
+Fermentation.&mdash;Alcoholic Fermentation.&mdash;Biology of Alcoholic
+Fermentation.&mdash;Oxydases.&mdash;Oxidising
+Fermentation.&mdash;Bibliography.&mdash;<span class="smcap">Index</span>.</p>
+
+<p><b>The present Translation embodies Notes and Additions to the Work made
+by the Author subsequent to its Publication in Germany.</b></p>
+
+<p>"Such a veritable <i>multum in parvo</i> has never yet appeared. The author
+has set himself the task of writing a work on Ferments that should
+embrace human erudition on the subject"&mdash;<i>Brewers' Journal</i>.<span class='pagenum'><a name="Page_lxxv" id="Page_lxxv">[Pg lxxv]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition</span>, Revised. In Large 8vo. Handsome Cloth. With
+Plate and Illustrations. Price 21s.</p>
+
+<h3><b>THE PRINCIPLES AND PRACTICE OF BREWING.</b></h3>
+
+<h5>FOR THE USE OF STUDENTS AND PRACTICAL MEN.</h5>
+
+<h6>BY</h6>
+
+<h4>WALTER J. SYKES, M.D., D.P.H., F.I.C.,</h4>
+
+<h6>EDITOR OF "THE ANALYST."</h6>
+
+<h4>ABSTRACT OF CONTENTS.</h4>
+
+<p>
+I. Physical Principles involved in Brewing Operations.<br />
+Chemistry with special reference to the materials used in Brewing.<br />
+<br />
+II. The Microscope.<br />
+Vegetable Biology.<br />
+Fermentation.<br />
+<br />
+III. Water.<br />
+Barley and Malting.<br />
+Brewery Plant.<br />
+Brewing.<br />
+Beer and its Diseases.<br />
+<br />
+Appendices.<br />
+<br />
+Index.<br />
+</p>
+
+<p>"A volume of Brewing Science, which has long been awaited.... We
+consider it one of <span class="smcap">the most complete</span> in <span class="smcap">contents</span> and
+<span class="smcap">novel in arrangement</span> that has yet been published.... Will
+command a large sale."&mdash;<i>The Brewers' Journal.</i></p>
+
+<p>"The appearance of a work such as this serves to remind us of the
+<span class="smcap">enormously rapid advances</span> made in our knowledge of the
+Scientific Principles underlying the Brewing Processes.... Dr. Sykes'
+work will undoubtedly be of the <span class="smcap">greatest assistance</span>, not merely
+to Brewers, but to all Chemists and Biologists interested in the
+problems which the Fermentation Industries present."&mdash;<i>The Analyst.</i></p>
+
+<p>"The publication of <span class="smcap">Dr. Sykes' masterly treatise</span> on the art of
+Brewing is quite an event in the Brewing World.... Deserves our warmest
+praise.... A better guide than Dr. Sykes could hardly be
+found."&mdash;<i>County Brewers' Gazette.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>In Large 8vo. Handsome Cloth.</p>
+
+<h3><b>AGRICULTURAL CHEMISTRY AND ANALYSIS:</b></h3>
+
+<h5><i>A PRACTICAL HANDBOOK FOR THE USE OF AGRICULTURAL STUDENTS.</i></h5>
+
+<h6>BY</h6>
+
+<h4>J.M.H. MUNRO, D.Sc., F.I.C., F.C.S.,</h4>
+
+<h6>Professor of Chemistry, Downton College of Agriculture.</h6>
+
+<p>[<i>In Preparation.</i><span class='pagenum'><a name="Page_lxxvi" id="Page_lxxvi">[Pg lxxvi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition, Revised and Enlarged.</span></p>
+
+<p>With Tables, Illustrations in the Text, and 37 Lithographic Plates.
+Medium 8vo. Handsome Cloth. 30s.</p>
+
+<h3><b>SEWAGE DISPOSAL WORKS:</b></h3>
+
+<h5>A Guide to the Construction of Works for the Prevention of the Pollution
+by Sewage of Rivers and Estuaries.</h5>
+
+<h4><span class="smcap">By W. SANTO CRIMP, M.Inst.C.E., F.G.S.</span>,</h4><h6> Late
+Assistant-Engineer, London County Council.</h6>
+
+<p><span class="smcap">PART I.&mdash;Introductory. PART II.&mdash;Sewage Disposal Works In
+Operation&mdash;Their Construction, Maintenance, and Cost.</span></p>
+
+<p>*** From the fact of the Author's having, for some years, had charge of
+the Main Drainage Works of the Northern Section of the Metropolis, the
+chapter on <span class="smcap">London</span> will be found to contain many important
+details which would not otherwise have been available.</p>
+
+<p>"All persons interested in Sanitary Science owe a debt of gratitude to
+Mr. Crimp.... His work will be especially useful to <span class="smcap">Sanitary
+Authorities</span> and their advisers ... <span class="smcap">eminently practical and
+useful</span>."&mdash;<i>Lancet.</i></p>
+
+<p>"Probably the <span class="smcap">most complete and best treatise</span> on the subject
+which has appeared in our language.... Will prove of the greatest use to
+all who have the problem of Sewage Disposal to face."&mdash;<i>Edinburgh
+Medical Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Beautifully Illustrated, with Numerous Plates, Diagrams, and Figures in
+the Text. 21s. net.</i></p>
+
+<h3><b>TRADES' WASTE: ITS TREATMENT AND UTILISATION.</b></h3>
+
+<h5>A Handbook for Borough Engineers, Surveyors, Architects, and Analysts.</h5>
+
+<h4><span class="smcap">By W. NAYLOR, F.C.S., A.M.Inst.C.E.</span>, </h4><h6>Chief Inspector of Rivers,
+Ribble Joint Committee.</h6>
+
+<p><span class="smcap">Contents.</span>&mdash;I. Introduction.&mdash;II. Chemical
+Engineering.&mdash;III.&mdash;Wool De-greasing and Grease Recovery.&mdash;IV. Textile
+Industries; Calico Bleaching and Dyeing.&mdash;V. Dyeing and
+Calico-Printing,&mdash;VI. Tanning and Fellmongery.&mdash;VII. Brewery and
+Distillery Waste.&mdash;VIII. Paper Mill Refuse.&mdash;IX. General Trades'
+Waste.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"There is probably no person in England to-day better fitted to deal
+rationally with such a subject."&mdash;<i>British Sanitarian.</i></p>
+
+<p>"The work is thoroughly practical, and will serve as a handbook in the
+future for those who have to encounter the problems
+discussed."&mdash;<i>Chemical Trade Journal.</i></p>
+
+<hr style='width: 45%;' />
+
+<p>In Crown 8vo, Extra. With Illustrations. 8s. 6d.</p>
+
+<h3><b>CALCAREOUS CEMENTS: <i>THEIR NATURE, PREPARATION, AND USES</i>.</b></h3>
+
+<h5><b>With some Remarks upon Cement Testing.</b></h5>
+
+<h4><span class="smcap">By GILBERT R. REDGRAVE, Assoc. Inst. C.E.</span>,</h4> <h6>Assistant Secretary
+for Technology, Board of Education, South Kensington.</h6>
+
+<p>"<span class="smcap">Invaluable</span> to the Student, Architect, and
+Engineer."&mdash;<i>Building News.</i></p>
+
+<p>"Will be useful to all interested in the <span class="smcap">manufacture, use</span>, and
+<span class="smcap">testing</span> of Cements."&mdash;<i>Engineer.</i><span class='pagenum'><a name="Page_lxxvii" id="Page_lxxvii">[Pg lxxvii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p>Just Out. With Four Folding Plates and Numerous Illustrations. Large
+8vo.</p>
+
+<h3><b>WATER SUPPLY:</b></h3>
+
+<h5><i>A Practical Treatise on the Selection of Sources and the Distribution
+of Water.</i></h5>
+
+<h4><span class="smcap">By</span> REGINALD E. MIDDLETON, <span class="smcap">M.Inst.C.E.</span>,
+<span class="smcap">M.Inst.Mech.E.</span>, F.S.I.</h4>
+
+<p><span class="smcap">Abridged Contents</span>.&mdash;Introductory.&mdash;Requirements as to
+Quality.&mdash;Requirements as to Quantity.&mdash;Storage
+Reservoirs.&mdash;Purification.&mdash;Service Reservoirs.&mdash;The Flow of Water
+through Pipes.&mdash;Distributing Systems.&mdash;Pumping Machines.&mdash;Special
+Requirements.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition</span>, Revised. Fully Illustrated. <i>At Press.</i></p>
+
+<h3>THE CHEMISTRY OF <b>GAS MANUFACTURE:</b></h3>
+
+<h5><i>A Hand-Book on the Production, Purification, and Testing of
+Illuminating Gas, and the Assay of the Bye-Products of Gas Manufacture.</i></h5>
+
+<h4><span class="smcap">By</span> W.J. ATKINSON BUTTERFIELD, M.A., F.I.C., F.C.S., </h4><h6>Formerly
+Head Chemist, Gas Works, Beckton, London, E.</h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;I. Raw Materials for Gas Manufacture.&mdash;II.
+Coal Gas.&mdash;III. Carburetted Water Gas.&mdash;IV. Oil Gas.&mdash;V. Enriching by
+Light Oils.&mdash;VI. Final Details of Manufacture.&mdash;VII. Gas
+Analysis.&mdash;VIII. Photometry.&mdash;IX. Applications of Gas.&mdash;X.
+Bye-Products.&mdash;XI. Acetylene.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"The <span class="smcap">best work</span> of its kind which we have ever had the pleasure
+of reviewing."&mdash;<i>Journal of Gas Lighting</i>.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Just Out</span>. With Diagrams and Illustrations. 5s. net.</p>
+
+<h3><b>ACETYLENE:</b></h3>
+
+<h5>THE PRINCIPLES OF ITS GENERATION AND USE.</h5>
+
+<h4>BY F.H. LEEDS, F.I.C., F.C.S.,</h4><h6>Member of the Society of Public Analysts
+and of the Acetylene Association;</h6>
+
+<h4><span class="smcap">And</span> W.J. ATKINSON BUTTERFIELD, M.A., F.I.C., F.C.S.,</h4><h6>Consulting
+Chemist, Author of "The Chemistry of Gas Manufacture."</h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;Introductory.&mdash;Advantages of Acetylene and
+other Illuminants.&mdash;Chemistry and Physics.&mdash;General Principles of
+Acetylene Generation.&mdash;Choice of a Generator.&mdash;Statutory
+Regulations.&mdash;Treatment of Acetylene after Generation.&mdash;General
+Properties.&mdash;Mains and Service Pipes.&mdash;Subsidiary
+Apparatus.&mdash;Burners.&mdash;Incandescent Burners.&mdash;Heating Apparatus and
+Motors.&mdash;Carburetted, Compressed, and Dissolved Acetylene.&mdash;Mixtures
+with other Gases.&mdash;Sundry Uses.&mdash;Acetylene Lamps.&mdash;Valuation and
+Analysis of Carbide.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Ready Immediately</span>. Large 8vo. Handsome Cloth. Price 16s. net.</p>
+
+<h3><b>FIRE AND EXPLOSION RISKS.</b></h3>
+
+<h5><i>A Handbook of the Detection, Investigation, and Prevention of Fires and
+Explosion.</i></h5>
+
+<h4><span class="smcap">By Dr</span>. VON SCHWARTZ.</h4>
+
+<h5>Translated from the Revised German Edition <span class="smcap">By</span> C.T.C. SALTER.</h5>
+
+<p><span class="smcap">Abridged General Contents</span>.&mdash;Fires and Explosions of a General
+Character.&mdash;Dangers arising from Sources of Light and Heat.&mdash;Dangerous
+Gases.&mdash;Risks Attending Special Industries.&mdash;Materials
+Employed.&mdash;Agricultural Products.&mdash;Fats, Oils, and Resins.&mdash;Mineral Oils
+and Tar.&mdash;Alcohol, &amp;c.&mdash;Metals, Oxides, Acids, &amp;c.&mdash;Lightning, Ignition
+Appliances, Fireworks.<span class='pagenum'><a name="Page_lxxviii" id="Page_lxxviii">[Pg lxxviii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Tenth Edition</span>, Revised. Price 6s.</p>
+
+<h3><b>PRACTICAL SANITATION: <i>A HAND-BOOK FOR SANITARY INSPECTORS AND OTHERS
+INTERESTED IN SANITATION.</i></b></h3>
+
+<h4><span class="smcap">By</span> GEORGE REID, M.D., D.P.H.,</h4> <h6><i>Fellow, Mem. Council, and
+Examiner, Sanitary Institute of Great Britain, and Medical Officer to
+the Staffordshire County Council.</i></h6>
+
+<h5><b>With an Appendix on Sanitary Law.</b></h5>
+
+<h4><span class="smcap">By</span> HERBERT MANLEY, M.A., M.B., D.P.H.,</h4> <h6><i>Medical Officer of
+Health for the County Borough of West Bromwich.</i></h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;Introduction&mdash;Water Supply: Drinking Water,
+Pollution of Water&mdash;Ventilation and Warming&mdash;Principles of Sewage
+Removal&mdash;Details of Drainage; Refuse Removal and Disposal&mdash;Sanitary and
+Insanitary Work and Appliances&mdash;Details of Plumbers' Work&mdash;House
+Construction&mdash;Infection and Disinfection&mdash;Food, Inspection of;
+Characteristics of Good Meat; Meat, Milk, Fish, &amp;c., unfit for Human
+Food&mdash;Appendix: Sanitary Law; Model Bye-Laws, &amp;c.</p>
+
+<p>"Dr. Reid's very useful Manual ... <span class="smcap">abounds in practical
+detail</span>."&mdash;<i>British Medical Journal</i>.</p>
+
+<p>"A <span class="smcap">very useful Handbook</span>, with a very useful Appendix. We
+recommend it not only to <span class="smcap">Sanitary Inspectors</span>, but to
+<span class="smcap">Householders</span> and <span class="smcap">all</span> interested in Sanitary
+matters."&mdash;<i>Sanitary Record</i>.</p>
+
+<hr style='width: 45%;' />
+
+<h3>COMPANION VOLUME TO REID'S SANITATION.</h3>
+
+<p>In Crown 8vo. Handsome Cloth. Profusely Illustrated. 8s. 6d. net.</p>
+
+<h3><b>Sanitary Engineering:</b> <i>A Practical Manual of Town Drainage and Sewage
+and Refuse Disposal.</i></h3>
+
+<h5>For Sanitary Authorities, Engineers, Inspectors, Architects,
+Contractors, and Students.</h5>
+
+<h6>BY</h6>
+
+<h4>FRANCIS WOOD, <span class="smcap">A.M.Inst.C.E.</span>, F.G.S., </h4><h6>Borough Engineer and
+Surveyor, Fulham; late Borough Engineer, Bacup, Lancs.</h6>
+
+<h4>GENERAL CONTENTS.</h4>
+
+<p>Introduction.&mdash;Hydraulics.&mdash;Velocity of Water in Pipes.&mdash;Earth Pressures
+and Retaining Walls.&mdash;Powers.&mdash;House Drainage.&mdash;Land
+Drainage.&mdash;Sewers.&mdash;Separate System.&mdash;Sewage Pumping.&mdash;Sewer
+Ventilation.&mdash;Drainage Areas.&mdash;Sewers, Manholes, &amp;c.&mdash;Trade
+Refuse.&mdash;Sewage Disposal Works.&mdash;<span class="smcap">Bacteriolysis</span>.&mdash;Sludge
+Disposal.&mdash;Construction and Cleansing of Sewers.&mdash;Refuse
+Disposal.&mdash;Chimneys and Foundations.</p>
+
+<p>"The volume bristles with information which will be greedily read by
+those in need of assistance. The book is one that ought to be on the
+bookshelves of <span class="smcap">every practical engineer</span>."&mdash;<i>Sanitary Journal</i>.</p>
+
+<p>"<span class="smcap">A veritable pocket compendium</span> of Sanitary Engineering.... A
+work which may, in many respects, be considered as <span class="smcap">complete</span> ...
+<span class="smcap">commendably cautious</span> ... <span class="smcap">interesting</span> ...
+<span class="smcap">suggestive</span>."&mdash;<i>Public Health Engineer</i>.<span class='pagenum'><a name="Page_lxxix" id="Page_lxxix">[Pg lxxix]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Vol. I. Now Ready. in Half Morocco, 24s.</span></p>
+
+<p><i>In Two Volumes, each complete in itself.</i></p>
+
+<h3><b>PHYSICO-CHEMICAL TABLES</b></h3>
+
+<h5>FOR THE USE OF ANALYSTS, PHYSICISTS, CHEMICAL MANUFACTURERS, AND
+SCIENTIFIC CHEMISTS.</h5>
+
+<p>Volume I.&mdash;Chemical Engineering, Physical Chemistry. [<i>Just Out.</i></p>
+
+<p>Volume II.&mdash;Chemical Physics, Pure and Analytical Chemistry.</p>
+
+<p><span class="smcap">By</span> JOHN CASTELL-EVANS, F.I.C., F.C.S., Superintendent of the
+Chemical Laboratories, and Lecturer on Inorganic Chemistry and
+Metallurgy at the Finsbury Technical College.</p>
+
+<p>The Tables may almost claim to be exhaustive, and embody and collate all
+the most recent data established by experimentalists at home and abroad.
+The volumes will be found invaluable to all engaged in research and
+experimental investigation in Chemistry and Physics.</p>
+
+<p>The Work comprehends as far as possible <span class="smcap">all rulles and tables</span>
+required by the Analyst, Brewer, Distiller, Acid- and
+Alkali-Manufacturer, &amp;c., &amp;c.; and also the principal data in
+<span class="smcap">Thermo-chemistry</span>, <span class="smcap">Electro-chemistry</span>, and the various
+branches of <span class="smcap">Chemical Physics</span>. Every possible care has been
+taken to ensure perfect accuracy, and to include the results of the most
+recent investigations.</p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 8vo. Handsome Cloth. Beautifully Illustrated. With Plates and
+Figures in the Text.</i> 21s.</p>
+
+<h3><b>Road Making and Maintenance:</b></h3>
+
+<h5>A PRACTICAL TREATISE FOR ENGINEERS, SURVEYORS, AND OTHERS.</h5>
+
+<h5><span class="smcap">With an Historical Sketch of Ancient and Modern Practice</span>.</h5>
+
+<h4><span class="smcap">By</span> THOS. AITKEN, <span class="smcap">Assoc.M.Inst.C.E.</span>,</h4> <h6>Member of the
+Association of Municipal and County Engineers; Member of the Sanitary
+Inst.; Surveyor to the County Council of Fife, Cupar Division.</h6>
+
+<p><i>WITH NUMEROUS PLATES, DIAGRAMS, AND ILLUSTRATIONS.</i></p>
+
+<p><span class="smcap">Contents</span>.&mdash;Historical Sketch.&mdash;Resistance of Traction.&mdash;Laying
+out New Roads.&mdash;Earthworks, Drainage, and Retaining Walls.&mdash;Road
+Materials, or Metal.&mdash;Quarrying.&mdash;Stone Breaking and
+Haulage.&mdash;Road-Rolling and Scarifying.&mdash;The Construction of New, and the
+Maintenance of existing Roads.&mdash;Carriage Ways and Foot Ways.</p>
+
+<p>"The Literary style is <span class="smcap">excellent</span> ... <span class="smcap">A comprehensive</span>
+and <span class="smcap">excellent</span> Modern Book, an <span class="smcap">up-to-date</span> work ...
+Should be on the reference shelf of every Municipal and County Engineer
+or Surveyor in the United Kingdom, and of every Colonial
+Engineer."&mdash;<i>The Surveyor</i>.<span class='pagenum'><a name="Page_lxxx" id="Page_lxxx">[Pg lxxx]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Third Edition</span>, Revised and Enlarged. With Illustrations, 12s.
+6d.</p>
+
+<h3><b>Painters' Colours, Oils, &amp; Varnishes:</b></h3>
+
+<h5><b>A PRACTICAL MANUAL.</b></h5>
+
+<h4><span class="smcap">By</span> GEORGE H. HURST, F.C.S.,</h4><h6>Member of the Society of Chemical
+Industry; Lecturer on the Technology of Painters' Colours, Oils, and
+Varnishes, the Municipal Technical School, Manchester.</h6>
+
+<p><span class="smcap">General Contents</span>.&mdash;Introductory&mdash;<span class="smcap">The Composition,
+Manufacture, Assay</span>, and <span class="smcap">Analysis</span> of <span class="smcap">Pigments</span>,
+White, Red, Yellow and Orange, Green, Blue, Brown, and
+Black&mdash;<span class="smcap">Lakes</span>&mdash;Colour and Paint Machinery&mdash;Paint Vehicles (Oils,
+Turpentine, &amp;c., &amp;c.)&mdash;Driers&mdash;<span class="smcap">Varnishes</span>.</p>
+
+<p>"<span class="smcap">A thoroughly practical</span> book, ... the <span class="smcap">only</span> English
+work that satisfactorily treats of the manufacture of oils, colours, and
+pigments."&mdash;<i>Chemical Trades' Journal</i>.</p>
+
+<p>*** <span class="smcap">For Mr. Hurst's Garment Dyeing and Cleaning</span>, see p. 84.</p>
+
+<hr style='width: 45%;' />
+
+<p>In Crown 8vo. Handsome Cloth. With Illustrations. 5s.</p>
+
+<h3><b>THE PAINTER'S LABORATORY GUIDE.</b></h3>
+
+<h5>A Student's Handbook of Paints, Colours, and Varnishes.</h5>
+
+<h4><span class="smcap">By</span> GEORGE H. HURST, F.C.S., M.S.C.I.</h4>
+
+<p><span class="smcap">Abstract of Contents</span>.&mdash;Preparation of Pigment
+Colours.&mdash;Chemical Principles Involved.&mdash;Oils and Varnishes.&mdash;Properties
+of Oils and Varnishes.&mdash;Tests and Experiments.&mdash;Plants, Methods, and
+Machinery of the Paint and Varnish Manufactures.</p>
+
+<p><i>This Work has been designed by the Author for the Laboratory of the
+Technical School, and of the Paint and Colour Works, and for all
+interested or engaged in these industries.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition</span>, Revised. In Crown 8vo. extra. With Numerous
+Illustrations and Plates (some in Colours), including Original Designs.
+12s. 6d.</p>
+
+<h3><b>Painting and Decorating:</b></h3>
+
+<h5><i>A Complete Practical Manual for House Painters and Decorators.</i></h5>
+
+<h4><span class="smcap">By</span> WALTER JOHN PEARCE,</h4>
+
+<h6>LECTURER AT THE MANCHESTER TECHNICAL SCHOOL FOR HOUSE-PAINTING AND
+DECORATING.</h6>
+
+<h4>GENERAL CONTENTS.</h4>
+
+<p>Introduction&mdash;Workshop and Stores&mdash;Plant and Appliances&mdash;Brushes and
+Tools&mdash;Materials: Pigments, Driers, Painters' Oils&mdash;Wall Hangings&mdash;Paper
+Hanging&mdash;Colour Mixing&mdash;Distempering&mdash;Plain Painting&mdash;Staining&mdash;Varnish
+and Varnishing&mdash;Imitative
+Painting&mdash;Graining&mdash;Marbling&mdash;Gilding&mdash;Sign-Writing and
+Lettering&mdash;Decoration: General Principles&mdash;Decoration in
+Distemper&mdash;Painted Decoration&mdash;Relievo Decoration&mdash;Colour&mdash;Measuring and
+Estimating&mdash;Coach-Painting&mdash;Ship-Painting.</p>
+
+<p>"<span class="smcap">A thoroughly useful book</span> ... <span class="smcap">good, sound, practical
+information</span> in a <span class="smcap">clear</span> and <span class="smcap">concise
+form</span>."&mdash;<i>Plumber and Decorator</i>.</p>
+
+<p>"<span class="smcap">A thoroughly good and reliable text-book</span>.... So <span class="smcap">full</span>
+and <span class="smcap">complete</span> that it would be difficult to imagine how anything
+further could be added about the Painter's craft."&mdash;<i>Builders'
+Journal</i>.<span class='pagenum'><a name="Page_lxxxi" id="Page_lxxxi">[Pg lxxxi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p>In Large 8vo. Handsome Cloth. With 4 Plates and Several Illustrations.
+16s. net.</p>
+
+<h3><b>THE CHEMISTRY OF INDIA RUBBER.</b></h3>
+
+<h5>A Treatise on the Nature of India Rubber, its Chemical and Physical
+Examination, and the Determination and Valuation of India Rubber
+Substitutes.</h5>
+
+<h5><i>Including the Outlines of a Theory on Vulcanisation.</i></h5>
+
+<h6>BY</h6>
+
+<h4>CARL OTTO WEBER, <span class="smcap">Ph.D.</span></h4>
+
+<p><span class="smcap">Abstract of Contents</span>.&mdash;Introduction.&mdash;The Chemistry of India
+Rubber.&mdash;The Examination and Valuation of India Rubber.&mdash;Examination of
+India Rubber Substitutes.&mdash;Inorganic Filling Materials.&mdash;Vulcanisers and
+Sulphur Carriers.&mdash;India Rubber Solvents.&mdash;Colouring Matters and Pigment
+Colours.&mdash;Constructive Components of India Rubber Articles.&mdash;Analysis of
+Manufactured India Rubber.&mdash;Sanitary Conditions in India Rubber
+Works.&mdash;<span class="smcap">Index</span>.</p>
+
+<p>"Replete with scientific and also with technical interest.... The
+sub-section on the physical properties is a complete <i>r&eacute;sum&eacute;</i> of every
+thing known to-day on the subject."&mdash;<i>India-rubber Journal</i>.</p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">New Edition</span>. In Large 8vo. Handsome Cloth. With 144
+Illustrations.</p>
+
+<h3>OILS, FATS, BUTTERS &amp; WAXES:</h3><h5><i>THEIR PREPARATION AND PROPERTIES, AND
+MANUFACTURE THEREFROM OF CANDLES, SOAPS, AND OTHER PRODUCTS.</i></h5>
+
+<h6>BY</h6>
+
+<h4>C.R. ALDER WRIGHT, D.Sc., F.R.S.,</h4> <h6>Late Lecturer on Chemistry, St. Mary's
+Hospital Medical School; Examiner in "Soap" to the City and Guilds of
+London Institute.</h6>
+
+<h5>Thoroughly Revised, Enlarged, and in Part Rewritten</h5>
+
+<h4><span class="smcap">By</span> C. AINSWORTH MITCHELL, B.A., F.I.C.</h4>
+
+<p>"Dr. <span class="smcap">Wright's</span> work will be found <span class="smcap">absolutely
+indispensable</span> by every Chemist. <span class="smcap">Teems</span> with information
+valuable alike to the Analyst and the Technical Chemist."&mdash;<i>The
+Analyst</i>.</p>
+
+<p>"Will rank as the <span class="smcap">Standard English Authority</span> on <span class="smcap">Oils</span>
+and <span class="smcap">Fats</span> for many years to come."&mdash;<i>Industries and Iron</i>.<span class='pagenum'><a name="Page_lxxxii" id="Page_lxxxii">[Pg lxxxii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>THE TEXTILE INDUSTRIES.</b></h3>
+
+<hr style='width: 45%;' />
+
+<p><i>In Two Large Volumes, 920 pp., with a Supplementary Volume, containing
+Specimens of Dyed Fabrics. 45s.</i></p>
+
+<h3>A MANUAL OF DYEING:</h3><h5><i>FOR THE USE OF PRACTICAL DYERS, MANUFACTURERS,
+STUDENTS, AND ALL INTERESTED IN THE ART OF DYEING.</i></h5>
+
+<h6>BY</h6>
+
+<h4>E. KNECHT, Ph.D., F.I.C.,</h4> <h6>Head of the Chemistry and Dyeing Department of
+the Technical College, Manchester; Editor of "The Journal of the Society
+of Dyers and Colourists;"</h6>
+
+<h4>CHR. RAWSON, F.I.C., F.C.S.,</h4> <h6>Late Head of the Chemistry and Dyeing
+Department of the Technical College, Bradford; Member of Council of the
+Society of Dyers and Colourists;</h6>
+
+<h4>And RICHARD LOEWENTHAL, Ph.D.</h4>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">General Contents.</span>&mdash;Chemical Technology of the Textile
+Fabrics&mdash;Water&mdash;Washing and Bleaching&mdash;Acids, Alkalies,
+Mordants&mdash;Natural Colouring Matters&mdash;Artificial Organic Colouring
+Matters&mdash;Mineral Colours&mdash;Machinery used in Dyeing&mdash;Tinctorial
+Properties of Colouring Matters&mdash;Analysis and Valuation of Materials
+used in Dyeing, &amp;c., &amp;c.</p>
+
+<p>"The <span class="smcap">most valuable</span> and <span class="smcap">useful work</span> on Dyeing that has
+yet appeared in the English language ... likely to be the <span class="smcap">Standard
+Work of Reference</span> for years to come."&mdash;<i>Textile Mercury</i>.</p>
+
+<p>"This authoritative and exhaustive work ... the <span class="smcap">most complete</span>
+we have yet seen on the subject."&mdash;<i>Textile Manufacturer.</i></p>
+
+<p>"The <span class="smcap">most exhaustive and complete work</span> on the subject
+extant."&mdash;<i>Textile Recorder.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Companion Volume to Knecht &amp; Rawson's "Dyeing." In Large 8vo. Handsome
+Cloth, Library Style. 16s. net.</i></p>
+
+<h3><b>A DICTIONARY OF DYES, MORDANTS, &amp; OTHER COMPOUNDS USED IN DYEING AND
+CALICO PRINTING.</b></h3>
+
+<h5><i>With Formul&aelig;, Properties, and Applications of the various substances
+described, and concise directions for their Commercial Valuation. and
+for the Detection of Adulterants.</i></h5>
+
+<h4><span class="smcap">By CHRISTOPHER RAWSON, F.I.C., F.C.S.</span>,</h4><h6>Consulting Chemist to
+the Behar Indigo Planters' Association: Co-Author of "A Manual of
+Dyeing;"</h6>
+
+<h4>WALTER M. GARDNER, F.C.S.,</h4>
+
+<h6>Head of the Department of Chemistry and Dyeing, Bradford Municipal
+Technical College; Editor of the "Journ. Soc. Dyers and Colourists;"</h6>
+
+<h4><span class="smcap">And W.F. LAYCOCK, Ph.D., F.C.S.</span>,</h4><h6>Analytical and Consulting
+Chemist.</h6>
+
+<p>"Turn to the book as one may on any subject, or any substance in
+connection with the trade, and a reference is sure to be found. The
+authors have apparently left nothing out. Considering the immense amount
+of information, the book is a cheap one, and we trust it will be widely
+appreciated,"&mdash;<i>Textile Mercury.</i><span class='pagenum'><a name="Page_lxxxiii" id="Page_lxxxiii">[Pg lxxxiii]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><i>In Large 8vo, Handsome Cloth, with Numerous Illustrations. 9s. net.</i></p>
+
+<h3><b>TEXTILE FIBRES OF COMMERCE.</b></h3>
+
+<h5>A HANDBOOK OF The Occurrence, Distribution, Preparation, and Industrial
+Uses of the Animal, Vegetable, and Mineral Products used in Spinning and
+Weaving.</h5>
+
+<h4><span class="smcap">By WILLIAM I. HANNAN</span>,</h4> <h6>Lecturer on Botany at the Ashton
+Municipal Technical School, Lecturer on Cotton Spinning at the Chorley
+Science and Art School, &amp;c.</h6>
+
+<h4>With Numerous Photo Engravings from Nature.</h4>
+
+<p>*** The subjects discussed in this volume are, in order to facilitate
+reference, arranged in alphabetical order under their respective heads.
+The work may thus be regarded as a Dictionary of Textile Fibres. A
+feature of the work is the wealth of botanical description which
+accompanies the Section dealing with Vegetable Fibres.&mdash;<i>Publishers'
+Note.</i></p>
+
+<p>"<span class="smcap">Useful Information</span>.... <span class="smcap">Admirable Illustrations</span>....
+The information is not easily attainable, and in its present convenient
+form will be valuable."&mdash;<i>Textile Recorder.</i></p>
+
+<hr style='width: 45%;' />
+
+<h3><b>TEXTILE PRINTING: A PRACTICAL MANUAL.</b></h3>
+
+<h5>Including the Processes Used in the Printing of COTTON, WOOLLEN, SILK,
+and HALF-SILK FABRICS.</h5>
+
+<h4>By C.F. SEYMOUR ROTHWELL, F.C.S.,</h4><h6><i>Mem. Soc. of Chemical Industries;
+late Lecturer at the Municipal Technical School, Manchester</i>.</h6>
+
+<p>In Large 8vo, with Illustrations and Printed Patterns. Price 21s.</p>
+
+<p><span class="smcap">General Contents.</span>&mdash;Introduction.&mdash;The Machinery Used in Textile
+Printing.&mdash;Thickeners and Mordants.&mdash;The Printing of Cotton Goods.&mdash;The
+Steam Style.&mdash;Colours Produced Directly on the Fibre.&mdash;Dyed
+Styles.&mdash;Padding Style.&mdash;Resist and Discharge Styles.&mdash;The Printing of
+Compound Colourings, &amp;c.&mdash;The Printing of Woollen Goods.&mdash;The Printing
+of Silk Goods.&mdash;Practical Recipes for Printing.&mdash;Appendix.&mdash;Useful
+Tables.&mdash;Patterns.</p>
+
+<p>"<span class="smcap">By far the best</span> and <span class="smcap">most practical book</span> on
+<span class="smcap">textile printing</span> which has yet been brought out, and will long
+remain the standard work on the subject. It is essentially practical in
+character."&mdash;<i>Textile Mercury.</i></p>
+
+<p>"<span class="smcap">The most practical manual</span> of <span class="smcap">textile printing</span> which
+has yet appeared. We have no hesitation in recommending it."&mdash;<i>The
+Textile Manufacturer.</i><span class='pagenum'><a name="Page_lxxxiv" id="Page_lxxxiv">[Pg lxxxiv]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p>Large 8vo. Handsome Cloth. 12s. 6d.</p>
+
+<h3><b>BLEACHING &amp; CALICO-PRINTING.</b></h3>
+
+<h5>A Short Manual for Students and Practical Men.</h5>
+
+<h4><span class="smcap">By GEORGE DUERR</span>,</h4> <h6>Director of the Bleaching, Dyeing, and
+Printing Department at the Accrington and Bacup Technical Schools;
+Chemist and Colourist at the Irwell Print Works.</h6>
+
+<h4><span class="smcap">Assisted by WILLIAM TURNBULL</span> (of Turnbull &amp; Stockdale,
+Limited).</h4>
+
+<p>With Illustrations and upwards of One Hundred Dyed and Printed Patterns
+designed specially to show various Stages of the Processes described.</p>
+
+<p>GENERAL CONTENTS.&mdash;<span class="smcap">Cotton</span>, Composition of; <span class="smcap">Bleaching</span>,
+New Processes; <span class="smcap">Printing</span>, Hand-Block; Flat-Press Work; Machine
+Printing&mdash;<span class="smcap">Mordants</span>&mdash;<span class="smcap">Styles of Calico-Printing</span>: The
+Dyed or Madder Style, Resist Padded Style, Discharge and Extract Style,
+Chromed or Raised Colours, Insoluble Colours, &amp;c.&mdash;Thickeners&mdash;Natural
+Organic Colouring Matters&mdash;Tannin Matters&mdash;Oils, Soaps,
+Solvents&mdash;Organic Acids&mdash;Salts&mdash;Mineral Colours&mdash;Coal Tar
+Colours&mdash;Dyeing&mdash;Water, Softening of&mdash;Theory of Colours&mdash;Weights and
+Measures, &amp;c.</p>
+
+<p>"When a <span class="smcap">ready way</span> out of a difficulty is wanted, it is <span class="smcap">in
+books like this</span> that it is found."&mdash;<i>Textile Recorder.</i></p>
+
+<p>"Mr. <span class="smcap">Duerr's work</span> will be found <span class="smcap">most useful</span>.... The
+information given is of <span class="smcap">great value</span>.... The Recipes are
+<span class="smcap">thoroughly practical</span>."&mdash;<i>Textile Manufacturer.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><span class="smcap">Second Edition.</span> Revised and Enlarged. With Numerous
+Illustrations. 4s. 6d.</p>
+
+<h3><b>GARMENT DYEING AND CLEANING.</b></h3>
+
+<h5>A Practical Book for Practical Men.</h5>
+
+<h4><span class="smcap">By GEORGE H. HURST, F.C.S.</span>,</h4> <h6>Member of the Society of Chemical
+Industry.</h6>
+
+<p><span class="smcap">General Contents.</span>&mdash;Technology of the Textile Fibres&mdash;Garment
+Cleaning&mdash;Dyeing of Textile Fabrics&mdash;Bleaching&mdash;Finishing of Dyed and
+Cleaned Fabrics&mdash;Scouring and Dyeing of Skin Rugs and Mats&mdash;Cleaning and
+Dyeing of Feathers&mdash;Glove Cleaning and Dyeing&mdash;Straw Bleaching and
+Dyeing&mdash;Glossary of Drugs and Chemicals&mdash;Useful Tables.</p>
+
+<p>"An <span class="smcap">up-to-date</span> hand book has long been wanted, and Mr. Hurst
+has done nothing more complete than this. An important work, the more so
+that several of the branches of the craft here treated upon are almost
+entirely without English Manuals for the guidance of workers. The price
+brings it within the reach of all."&mdash;<i>Dyer and Calico-Printer.</i></p>
+
+<p>"Mr. Hurst's work <span class="smcap">decidedly fills a want</span> ... ought to be in the
+hands of every <span class="smcap">GARMENT DYER</span> and cleaner in the
+Kingdom"&mdash;<i>Textile Mercury.</i><span class='pagenum'><a name="Page_lxxxv" id="Page_lxxxv">[Pg lxxxv]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p>"Boys <span class="smcap">could not have a more alluring introduction</span> to scientific
+pursuits than these charming-looking volumes."&mdash;Letter to the Publishers
+from the Headmaster of one of our great Public Schools.</p>
+
+<p>Handsome Cloth, 7s. 6d. Gilt, for Presentation, 8s. 6d.</p>
+
+<h3><b>OPEN-AIR STUDIES IN BOTANY: SKETCHES OF BRITISH WILD FLOWERS IN THEIR
+HOMES.</b></h3>
+
+<h4><span class="smcap">By R. LLOYD PRAEGER, B.A., M.R.I.A.</span></h4>
+
+<h5>Illustrated by Drawings from Nature by S. Rosamond Praeger, and
+Photographs by R. Welch.</h5>
+
+<p><span class="smcap">General Contents.</span>&mdash;A Daisy-Starred Pasture&mdash;Under the
+Hawthorns&mdash;By the River&mdash;Along the Shingle&mdash;A Fragrant Hedgerow&mdash;A
+Connemara Bog&mdash;Where the Samphire grows&mdash;A Flowery Meadow&mdash;Among the
+Corn (a Study in Weeds)&mdash;In the Home of the Alpines&mdash;A City
+Rubbish-Heap&mdash;Glossary.</p>
+
+<p>"A <span class="smcap">fresh and stimulating</span> book ... should take a high place....
+The Illustrations are drawn with much skill."&mdash;<i>The Times.</i></p>
+
+<p>"<span class="smcap">Beautifully illustrated</span>.... One of the <span class="smcap">most accurate</span>
+as well as <span class="smcap">interesting</span> books of the kind we have
+seen."&mdash;<i>Athen&aelig;um.</i></p>
+
+<p>"Redolent with the scent of woodland and meadow."&mdash;<i>The Standard.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>With 12 Full-Page Illustrations from Photographs. Cloth. Second
+Edition, Revised. 8s. 6d.</i></p>
+
+<h3><b>OPEN-AIR STUDIES IN GEOLOGY: An Introduction to Geology Out-of-doors.</b></h3>
+
+<h4><span class="smcap">By GRENVILLE A.J. COLE, F.G.S., M.R.I.A.</span>,</h4> <h6>Professor of Geology
+in the Royal College of Science for Ireland, and Examiner in the
+University of London.</h6>
+
+<p><span class="smcap">General Contents.</span>&mdash;The Materials of the Earth&mdash;A Mountain
+Hollow&mdash;Down the Valley&mdash;Along the Shore&mdash;Across the Plains&mdash;Dead
+Volcanoes&mdash;A Granite Highland&mdash;The Annals of the Earth&mdash;The Surrey
+Hills&mdash;The Folds of the Mountains.</p>
+
+<p>"The <span class="smcap">fascinating 'Open-Air Studies'</span> of <span class="smcap">Prof. Cole</span> give
+the Subject a <span class="smcap">glow animation</span> ... cannot fail to arouse keen
+interest in geology."&mdash;<i>Geological Magazine.</i></p>
+
+<p>"A <span class="smcap">charming book</span>, beautifully illustrated."&mdash;<i>Athen&aelig;um.</i></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Beautifully Illustrated. With a Frontispiece in Colours, and Numerous
+Specially Drawn Plates by Charles Whymper. 7s. 6d.</i></p>
+
+<h3><b>OPEN-AIR STUDIES IN BIRD-LIFE: SKETCHES OF BRITISH BIRDS IN THEIR
+HAUNTS.</b></h3>
+
+<h4><span class="smcap">By CHARLES DIXON.</span></h4>
+
+<p>The Spacious Air.&mdash;The Open Fields and Downs.&mdash;In the Hedgerows.&mdash;On
+Open Heath and Moor.&mdash;On the Mountains.&mdash;Amongst the Evergreens.&mdash;Copse
+and Woodland.&mdash;By Stream and Pool.&mdash;The Sandy Wastes and
+Mud-flats.&mdash;Sea-laved Rocks.&mdash;Birds of the Cities.&mdash;<span class="smcap">Index.</span></p>
+
+<p>"Enriched with excellent illustrations. A welcome addition to all
+libraries."&mdash;<i>Westminster Review.</i><span class='pagenum'><a name="Page_lxxxvi" id="Page_lxxxvi">[Pg lxxxvi]</a></span></p>
+
+<hr style='width: 45%;' />
+
+<p><i>Twentieth Annual Issue. Handsome cloth, 7s. 6d. (To Subscribers, 6s.).</i></p>
+
+<h3>THE OFFICIAL YEAR-BOOK OF THE SCIENTIFIC AND LEARNED SOCIETIES OF GREAT
+BRITAIN AND IRELAND.</h3>
+
+<h5>COMPILED FROM OFFICIAL SOURCES.</h5>
+
+<p><i>Comprising (together with other Official Information) LISTS of the
+PAPERS read during the Session 1902-1903 before all the LEADING
+SOCIETIES throughout the Kingdom engaged in the following Departments of
+Research</i>:&mdash;</p>
+
+<p>&sect; 1. Science Generally: <i>i.e.</i>, Societies occupying themselves with
+several Branches of Science, or with Science and Literature jointly.</p>
+
+<p>&sect; 2. Mathematics and Physics.</p>
+
+<p>&sect; 3. Chemistry and Photography.</p>
+
+<p>&sect; 4. Geology, Geography, and Mineralogy.</p>
+
+<p>&sect; 5. Biology, including Microscopy and Anthropology.</p>
+
+<p>&sect; 6. Economic Science and Statistics.</p>
+
+<p>&sect; 7. Mechanical Science, Engineering, and Architecture.</p>
+
+<p>&sect; 8. Naval and Military Science.</p>
+
+<p>&sect; 9. Agriculture and Horticulture.</p>
+
+<p>&sect; 10. Law.</p>
+
+<p>&sect; 11. Literature.</p>
+
+<p>&sect; 12. Psychology.</p>
+
+<p>&sect; 13. Arch&aelig;ology.</p>
+
+<p>&sect; 14. Medicine.</p>
+
+<p>"<span class="smcap">Fills a very real want.</span>"&mdash;<i>Engineering.</i></p>
+
+<p>"<span class="smcap">Indispensable</span> to any one who may wish to keep himself abreast
+of the scientific work of the day."&mdash;<i>Edinburgh Medical Journal.</i></p>
+
+<p>"The <span class="smcap">Year-book of Societies</span> is a Record which ought to be of
+the <i>greatest use for the progress of Science</i>."&mdash;<i>Lord Playfair,
+F.R.S., K.C.B., M.P., Past-President of the British Association.</i></p>
+
+<p>"It goes almost without saying that a Handbook of this subject will be
+in time <i>one of the most generally useful works for the library or the
+desk</i>."&mdash;<i>The Times.</i></p>
+
+<p>"British Societies are now <i>well represented</i> in the 'Year-Book of the
+Scientific and Learned Societies of Great Britain and Ireland'"&mdash;(Art.
+"Societies" in New Edition of "Encyclop&aelig;dia Britannica," vol. xxii.)</p>
+
+<hr style='width: 45%;' />
+
+<p>Copies of the <span class="smcap">First Issue</span>, giving an Account of the History,
+Organization, and Conditions of Membership of the various Societies, and
+forming the groundwork of the Series, may still be had, price 7/6. <i>Also
+Copies of the Issues following.</i></p>
+
+<p>The <i><span class="smcap">year-book of societies</span></i> forms a complete <i><span class="smcap">index to the
+scientific work</span></i> of the sessional year in the various Departments.
+It is used as a <span class="smcap">Handbook</span> in all our great <span class="smcap">Scientific
+Centres, Museums</span>, and <span class="smcap">Libraries</span> throughout the Kingdom,
+and has become an <i><span class="smcap">indispensable book of reference</span></i> to every
+one engaged in Scientific Work.</p>
+
+<h4><i>READY IN OCTOBER EACH YEAR.</i></h4>
+
+
+<h3><b>Griffin's Metallurgical Series.</b></h3>
+
+<h4>Edited by <span class="smcap">Sir</span> W. ROBERTS-AUSTEN, K.C.B., F.R.S., D.C.L.</h4>
+
+<hr style='width: 45%;' />
+
+<p><i>Fifth Edition, Thoroughly Revised and Considerably Enlarged.</i> 18s.</p>
+
+<p><b>INTRODUCTION TO THE STUDY OF METALLURGY.</b> By Sir <span class="smcap">W.C.
+Roberts-Austen</span>. With additional Illustrations and
+Micro-Photographic Plates of Different Varieties of Steel.</p>
+
+<p><i>Fourth Edition, Thoroughly Revised and Enlarged.</i> 21s. <b>THE METALLURGY
+OF GOLD.</b> By <span class="smcap">T. Kirke Rose</span>, D.Sc., Assayer of the Royal Mint.
+Including the most recent Improvements in the Cyanide Process. With new
+Frontispiece and additional Illustrations.</p>
+
+<p><i>In Two Volumes, each complete in itself.</i></p>
+
+<p><b>THE METALLURGY OF LEAD AND SILVER.</b> By <span class="smcap">H.F. Collins</span>, Assoc.
+R.S.M., M.Inst.M.M. <b>Part I.&mdash;LEAD.</b> With Sections on Smelting and
+Desilverisation, and the Assay and Analysis of the Materials Involved.
+16s. <b>Part II.&mdash;SILVER.</b> Sources and Treatment of Ores, with
+Descriptions of Plant, Machinery, &amp;c. 16s.</p>
+
+<p><i>Second Edition, Revised. With numerous Illustrations.</i> 16s. <b>THE
+METALLURGY OF IRON.</b> By <span class="smcap">Thomas Turner</span>, F.I.C., Assoc. R.S.M.
+Professor of Metallurgy at the University of Birmingham.</p>
+
+<p><i>Large 8vo. Profusely Illustrated with Plates and Diagrams.</i> <b>THE
+METALLURGY OF STEEL.</b> By <span class="smcap">F.W. Harbord</span>. With a Section on the
+Mechanical Treatment of Steel. By <span class="smcap">J.W. Hall</span>. 25s. net.</p>
+
+<hr style='width: 45%;' />
+
+<p><b>ASSAYING.</b> By <span class="smcap">J.J. Beringer</span>, F.I.C., F.C.S., and <span class="smcap">C.
+Beringer</span>, F.C.S. <span class="smcap">Ninth Edition</span>, Revised. With Diagrams,
+10s. 6d.</p>
+
+<p><b>GETTING GOLD.</b> A Practical Treatise for Prospectors and
+<span class="smcap">Miners</span>. By <span class="smcap">J.C.F. Johnson</span>, A.I.M.E.. F.G.S., Life
+Member Australian Mine Managers' Association. Numerous Illustrations.
+<span class="smcap">Second Edition.</span> 3s. 6d.</p>
+
+<p><b>GOLD SEEKING IN SOUTH AFRICA.</b> A Handbook of Hints for Intending
+Explorers, Prospectors, and Settlers. By <span class="smcap">Theo. Kassner</span>. With a
+Chapter on Agriculture. Crown 8vo, Fancy Cloth Boards. Illustrated. 4s.
+6d. net.</p>
+
+<p><b>THE CYANIDE PROCESS OF GOLD EXTRACTION.</b> By <span class="smcap">James Park</span>,
+F.G.S., M.Inst.M.M., late Geological Surveyor and Mining Geologist to
+the New Zealand Government. <span class="smcap">New Edition</span>, Revised and Enlarged
+from the last New Zealand Edition. With Frontispiece, Plates and
+Illustrations. 6s. net.</p>
+
+<p><b>PROSPECTING FOR MINERALS.</b> A Practical Handbook. By <span class="smcap">S. Herbert
+Cox</span>, Assoc. R.S.M., M.Inst.M.M., F.G.S., &amp;c. With Illustrations.
+<span class="smcap">Second Edition</span>, Revised. Cloth, 5s.; Leather, 6s. 6d.</p>
+
+<p><b>TABLES FOR QUANTITATIVE METALLURGICAL ANALYSIS FOR LABORATORY USE.</b> By
+<span class="smcap">J. James Morgan</span>, F.C.S. Large 8vo, strongly bound, cloth, 4s.</p>
+
+<p><b>ELECTRIC SMELTING AND REFINING.</b> By Dr. <span class="smcap">W. Borchers</span>.
+Translated by <span class="smcap">Walter G. M<sup>c</sup>Millan</span>, F.I.C., F.C.S., from the
+Second German Edition. With numerous Illustrations and Three Folding
+Plates. 21s.</p>
+
+<p><b>MINE ACCOUNTS AND MINING BOOKKEEPING.</b> From the <span class="smcap">Actual
+Practice</span> of leading Mining Companies. By <span class="smcap">James G. Lawn</span>,
+Assoc. R.S.M., A.M.Inst.C.E.F.G.S. Edited by Sir <span class="smcap">Le Neve
+Foster</span>, D.Sc., F.R.S. Large 8vo. <span class="smcap">Third Edition.</span> 10s. 6d.</p>
+
+<hr style='width: 45%;' />
+
+<p><i>Large 8vo. Handsome Cloth. Illustrated, 12s. 6d. net.</i> <b>METALLURGICAL
+ANALYSIS AND ASSAYING:</b> A Three Years' Course for Students. By <span class="smcap">W.A.
+Macleod</span>, B.A., B.Sc., A.O.S.M. (N.Z.), and <span class="smcap">Chas. Walker</span>,
+F.C.S.</p>
+
+<p><b>Part I.&mdash;Qualitative Analysis, and Preparation and Properties of
+Cases.</b> <b>Part II.&mdash;Qualitative and Quantitative Analysis.</b> <b>Part
+III.&mdash;Assaying, Technical Analysis (Gas, Water, Fuels, Oils, &amp;c.).</b></p>
+
+<hr style='width: 45%;' />
+
+<p>LONDON: CHARLES GRIFFIN &amp; CO., <span class="smcap">Ltd.</span>, <span class="smcap">Exeter Street,
+Strand</span>.</p>
+
+
+<p>&nbsp;</p>
+<p>&nbsp;</p>
+<hr class="full" />
+<p>***END OF THE PROJECT GUTENBERG EBOOK A TEXTBOOK OF ASSAYING: FOR THE USE OF THOSE CONNECTED WITH MINES.***</p>
+<p>******* This file should be named 18751-h.txt or 18751-h.zip *******</p>
+<p>This and all associated files of various formats will be found in:<br />
+<a href="http://www.gutenberg.org/dirs/1/8/7/5/18751">http://www.gutenberg.org/1/8/7/5/18751</a></p>
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@@ -0,0 +1,11 @@
+This eBook, including all associated images, markup, improvements,
+metadata, and any other content or labor, has been confirmed to be
+in the PUBLIC DOMAIN IN THE UNITED STATES.
+
+Procedures for determining public domain status are described in
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+
+No investigation has been made concerning possible copyrights in
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+status under the laws that apply to them.
diff --git a/README.md b/README.md
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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #18751 (https://www.gutenberg.org/ebooks/18751)