diff options
Diffstat (limited to '33941.txt')
| -rw-r--r-- | 33941.txt | 3534 |
1 files changed, 3534 insertions, 0 deletions
diff --git a/33941.txt b/33941.txt new file mode 100644 index 0000000..dddfdbd --- /dev/null +++ b/33941.txt @@ -0,0 +1,3534 @@ +The Project Gutenberg EBook of The Methods of Glass Blowing and of Working +Silica in the Oxy-Gas Flame, by W. A. Shenstone + +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: The Methods of Glass Blowing and of Working Silica in the Oxy-Gas Flame + For the use of chemical and physical students + +Author: W. A. Shenstone + +Release Date: October 6, 2010 [EBook #33941] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE METHODS OF GLASS BLOWING *** + + + + +Produced by Harry Lame and the Online Distributed +Proofreading Team at http://www.pgdp.net (This file was +produced from images generously made available by The +Internet Archive/American Libraries.) + + + + + + +-------------------------------------------------------------------+ + | Transcriber's Notes: | + | | + | Italics are indicated by the underscore character, as in _word_. | + | Bold face is indicated by the equal character, as in =word=. | + | Subscript is indicated by _{subscript}. | + | Footnotes have been moved to below the paragraph they refer to. | + | Table of contents: 84-05 changed to 84-95. | + | Paragraph starting Uniting Pieces of Glass to Each Other, known as| + | Welding, or Soldering: footnote anchor [1] and number 1. before | + | next paragraph deleted. | + | Caption FIG. 18 added to illustration. | + | Paragraph directly below FIG. 18: comma added (or better,...). | + | 2nd paragraph under FIG. 19: _DE through E_ changed to _DE_ | + | through _E_. | + | 2nd paragraph under FIG. 34: _whence it might gradually lead into_| + | changed to _whence it might gradually leak into_. | + | ToC: several sections added, so that all named sections are | + | included. | + | endiometer changed to eudiometer. | + | Some minor typographical errors and inconsistencies corrected. | + +-------------------------------------------------------------------+ + + + + + THE METHODS OF GLASS BLOWING + AND OF + WORKING SILICA + + + + + BY THE SAME AUTHOR _With 25 Illustrations. Crown 8vo, 2s._ + + =A Practical Introduction to Chemistry.= Intended to + give a _practical_ acquaintance with the Elementary Facts + and Principles of Chemistry. + + LONGMANS, GREEN, AND CO. + LONDON, NEW YORK, BOMBAY, CALCUTTA, AND MADRAS. + + + + + The Methods of Glass Blowing + AND OF + Working Silica in the Oxy-Gas Flame + + _FOR THE USE OF CHEMICAL AND + PHYSICAL STUDENTS_ + + BY + + W. A. SHENSTONE, F.R.S. + + FORMERLY LECTURER ON CHEMISTRY IN CLIFTON COLLEGE + + _NINTH IMPRESSION_ + + LONGMANS, GREEN, AND CO. + 39 PATERNOSTER ROW, LONDON + FOURTH AVENUE & 30TH STREET, NEW YORK + BOMBAY, CALCUTTA, AND MADRAS + + 1916 + + + + +PREFACE + + +This book consists of a reprint of the third edition of my Methods of +Glass-blowing, together with a new chapter in which I have described the +comparatively new art of working vitreous silica. + +The individual operations of glass-blowing are much less difficult than +is usually supposed, and considerable success in the performance of most +of them may be attained by any one who is endowed with average powers of +manipulation and who is moderately persistent. Constructing finished +apparatus is often more difficult, as it may involve the performance of +several operations under disadvantageous conditions, and may demand a +little ingenuity on the part of the operator. But I think the +suggestions in Chapter IV. will make this comparatively easy also to +those who have mastered the operations described in Chapter III. + +The working of vitreous silica, though more tedious and expensive than +glass-blowing, is not really more difficult, and as it seems certain +that this new material will soon play a useful part in chemical and +physical research, I believe the addition now made to the earlier book +will add considerably to its value. + +As glass is much less expensive to work with than silica, the beginner +will find it best to spend a few days working with the common gas +blow-pipe and glass before he attempts to manipulate the new and more +refractory material. Therefore, in writing the new chapter, I have +assumed that the reader is already more or less familiar with the rest +of the book, and have given only such instructions and advice as will be +required by one who is already able to carry out simple work at the +blow-pipe. + + W. A. SHENSTONE. + + CLIFTON COLLEGE, + _Dec. 1901_. + + + + +CONTENTS + + + CHAPTER I. + + GLASS-BLOWER'S APPARATUS. + PAGE + + Introductory--The Working-place--The Blow-pipe--The + Bellows--Automatic Blower--Blow-pipe Flames, 1-11 + + + CHAPTER II. + + VARIETIES OF GLASS AND THEIR MANAGEMENT. + + Characters of good Glass--Cleaning and Preparing a + Tube--Presenting Glass to the Flame--Methods of working with + Lead and Soft Soda Glass respectively--Management of Soda + Glass--Annealing--The Use of Combustion Tube, 12-25 + + + CHAPTER III. + + CUTTING AND BENDING GLASS--FORMING GLASS APPARATUS BEFORE + THE BLOW-PIPE--MAKING AND GRINDING STOPPERS TO APPARATUS, + ETC. + + Cutting Glass Tubes--Bending Glass Tubes--Rounding and + Bordering the Ends of Tubes--Sealing--Choking, or + Contracting the Bore of a Glass Tube--Widening + Tubes--Piercing Tubes--Uniting Pieces of Glass to Each + Other, Known as Welding, or Soldering--Blowing a Bulb or + Globe of Glass--Making and Grinding Stoppers, 26-54 + + + CHAPTER IV. + + MAKING THISTLE FUNNELS, U-TUBES, ETC.--COMBINING THE PARTS + OF COMPLICATED APPARATUS--MERCURY, AND OTHER AIR-TIGHT + JOINTS--VACUUM TAPS--SAFETY TAPS--AIR-TRAPS. + + Electrodes--U-Tubes--Spiral Tubes--Thistle Funnels--Closing + Tubes containing Chemicals--Construction of Apparatus + Consisting of Several Parts--Modes of Combining the Parts of + Heavy Apparatus--Mercury Joints--Vacuum Taps--Lubricating + Taps--Air-Traps, 55-69 + + + CHAPTER V. + + GRADUATING AND CALIBRATING GLASS APPARATUS. + + To Graduate Tubes, etc.--To Divide a Given Line into Equal + Parts--To Calibrate Apparatus--To Calibrate Tubes for + Measuring Gases--To Calibrate the Tube of a Thermometer, 70-81 + + + CHAPTER VI. + + GLASS TUBING. + + Diagrams of Glass Tubes, showing the chief sizes in which + they are made, 82-83 + + + CHAPTER VII. + + VITREOUS SILICA + + Introductory--Properties of Vitreous Silica--Preparing + non-splintering Silica from Brazil Pebble--Apparatus--The + Method of Making Silica Tubes--Precautions--Making Larger + Tubes and other Apparatus of Silica--Quartz Fibres, 84-95 + + + INDEX, 97 + + + + +CHAPTER I. + +_GLASS-BLOWER'S APPARATUS._ + + +=Introductory.=--I shall endeavour to give such an account of the +operations required in constructing glass apparatus as will be useful to +chemical and other students; and as this book probably will come into +the hands of beginners who are not in a position to secure any further +assistance, I shall include descriptions even of the simple operations +which are usually learned during the first few hours of practical work +in a chemical or physical laboratory. I shall not give any particular +account of the manufacture of such apparatus as thermometers, taps, +etc., because, being in large demand, they can be bought so cheaply that +time is not profitably spent in making them. But it will be found that +what is included will enable any one, who will devote sufficient time to +acquiring the necessary manipulative dexterity, to prepare such +apparatus as test-tubes, distillation flasks, apparatus for washing +gases, ozone generating tubes, etc., when they are required, as they +often are, without delay or for special purposes. The amateur probably +will not succeed in turning out apparatus so finished in appearance as +that of the professional glass-blower until after long practice, but +after a little daily practice for the space of a few weeks, any one who +is fairly skilful in ordinary manipulation, and who perseveres in the +face of failure at first, will find himself able to make almost all the +apparatus he needs for lecture or other experiments, with a considerable +saving in laboratory expenses, and, which very often is more important, +without the delay that occurs when one depends upon the professional +glass-worker. In the case of those who, like myself, work in the +provinces, this latter advantage is a very weighty one. + +After the description of the instruments used in glass-blowing, which +immediately follows, the following arrangement of the subject has been +adopted. In the first place, an account of the two chief kinds of glass +is given, and of the peculiarities in the behaviour of each of them +before the blow-pipe, which is followed by a tolerably minute +description of the method of performing each of the fundamental +operations employed in fashioning glass apparatus. These are not very +numerous, and they should be thoroughly mastered in succession, +preferably upon tubes of both soda and lead glass. Then follows, in +Chapter IV., an account of the application of these operations to +setting up complete apparatus, full explanations of the construction of +two or three typical pieces of apparatus being given as examples, and +also descriptions of the modes of making various pieces of apparatus +which in each case present one or more special difficulties in their +construction; together with an account, which, I think, will be found +valuable, of some apparatus that has been introduced, chiefly during +recent years, for experimenting upon gases under reduced pressure, +_e.g._ vacuum taps and joints. Finally, in Chapter V., there is a short +account of the methods of graduating and calibrating glass apparatus for +use in quantitative experiments. + + +=The Working-place.=--The blow-pipe must be placed in a position +perfectly free from draughts. It should not face a window, nor be in +too strong a light, if that can be avoided, for a strong light will +render the non-luminous flames, which are used in glass-blowing, almost +invisible, and seriously inconvenience the operator, who cannot apply +the various parts of the flames to his glass with the degree of +certainty that is necessary; neither can he perceive the condition of +the glass so correctly in a strong light, for though in many operations +the glass-worker is guided by feeling rather than by seeing, yet sight +plays a very important part in his proceedings. + +My own blow-pipe is placed near a window glazed with opaque glass, which +looks southwards, but is faced by buildings at a short distance. In dull +weather the light obtained is good; but on most days I find it +advantageous to shade the lower half of the window with a green baize +screen. Some glass-blowers prefer gaslight to daylight. + +The form of the table used is unimportant, provided that it is of a +convenient height, and allows free play to the foot which works the +blower underneath it. The blower should be _fixed_ in a convenient +position, or it will get out of control at critical moments. The table, +or that part of it which surrounds the blow-pipe, should be covered with +sheet-iron to protect it from the action of the fragments of hot glass +that will fall upon it. The tubes that supply air and gas to the +blow-pipe should come from beneath the table, and may pass through holes +cut for the purpose. + +Many glass-blowers prefer to work at a rather high table, and sit on a +rather high stool, so that they are well above their work. No doubt this +gives extra command over the work in hand, which is often valuable. On +the other hand, it is somewhat fatiguing. For a long spell of labour at +work which is not of a novel character nor specially difficult, I am +disposed to recommend sitting on a chair or low stool, at a table of +such height as will enable the elbows to rest easily upon it whilst the +glass is held in the flame. The precise heights that are desirable for +the table and stool, and the exact position of the blow-pipe, will +depend upon the height and length of arm of the individual workman, and +it must therefore be left to each person to select that which suits him +best. A moveable rest made of wood, for supporting the remote end of a +long piece of glass tube a few inches above the table, whilst the other +end is being heated in the flame, will be found convenient. + + +=The Blow-pipe.=--Formerly a lamp, in which sweet oil or tallow was +burnt, was employed for glass-working, and such lamps are still +occasionally used. Thus, lamps burning oil or tallow were used on board +the _Challenger_ for hermetically sealing up flasks of water collected +at various depths to preserve them for subsequent examination. I shall +not, however, give an account of such a lamp, for the gas apparatus is +so much more convenient for most purposes that it has now practically +superseded the oil lamps. Fig. 1 shows a gas blow-pipe of exceedingly +simple construction, which can be easily made, and with which good work +can be done. + +[Illustration: FIG. 1.] + +The tube _A_ is of brass, and has a side tube _B_ brazed to it, ten to +twelve centimetres from the end _E_, according to the dimensions of the +tube. A tube of glass, _EC_, is fitted into _A_ by a cork at _D_. _B_ +is connected to a supply of gas by a flexible tube, _C_ is similarly +connected to the blower. By means of _CE_ a stream of air can be forced +into gas burning at the mouth of the blow-pipe _G_, and various flames, +with the characters described in a later section, can be produced with +this instrument. For producing the pointed flame (Fig. 3, p. 9) the +opening _E_ of the air-tube should be contracted to the size of a large +knitting needle. For producing a flame of large size, rich in air (Fig. +4, p. 9), the internal diameter of _E_ may be nearly half as great as +that of _A_ without disadvantage. + +This blow-pipe may be fixed in position by the spike _F_, which will fit +into holes in a block of wood or a large cork. Several of these holes in +various positions should be made in the block, so that the position of +the blow-pipe may be varied easily. Two taps must be provided in +convenient positions near the edge of the table to enable the workman to +regulate the supplies of air and gas. These taps should be fixed to the +table and be connected with the gas and air supplies respectively on one +side, and with the blow-pipe on the other, by flexible tubes. If +blow-pipes of this kind be used, at least two of them should be +provided; one of small dimensions for working on small tubes and joints, +the other of larger size for operations on larger tubes. It will be +convenient to have both of them ready for use at all times, as it is +sometimes necessary to employ large and small flames on the same piece +of work in rapid succession. By having several air-tubes of different +sizes fitted to each blow-pipe, a greater variety of work may be done. + +For the larger blow-pipe, the internal diameter of _A_ may be fifteen to +seventeen millimetres. + +For the smaller instrument, eleven millimetres for the diameter of _A_ +would be a useful size. + +When a slightly greater outlay can be afforded it will be most +convenient to purchase the blow-pipe. They can be obtained of compact +form, supported on stands with universal joints giving great freedom of +movement, and with taps for regulating the supplies of gas and air, at +comparatively small cost. + +As figures of various blow-pipes can be seen in the price-lists of most +dealers in apparatus, they are not given here. Their introduction would +be of but little service, for the construction of that which is adopted +can be readily ascertained by taking it to pieces. The simplest +blow-pipe usually used for glass-working is that of Herapath. This has +two taps to regulate the air and gas supplies respectively, and will +give a considerable variety of flames, which will be discussed +subsequently. + +An excellent blow-pipe, made on the same principle as that shown in Fig. +1, but more substantially and with interchangeable jets, can be obtained +from Messrs. Muller of Holborn for a moderate outlay. + +Another very good blow-pipe is the Automaton blow-pipe of Mr. Fletcher +of Warrington. In this, one tap regulates the supply both of air and +gas, which is a great gain when difficult work is in hand. Automaton +blow-pipes are made of two sizes. I have found that the larger size, +with a powerful bellows, heats large pieces of lead glass very +satisfactorily. On the other hand, the fine-pointed oxidising flame of +the Herapath blow-pipe is, perhaps, the most suitable for working joints +of lead glass. Therefore a good equipment would be a small Herapath +blow-pipe and a large-sized Automaton. If only one blow-pipe is +purchased it should be either a medium-sized Herapath, or the smaller +Automaton, as those are most useful for general work. + +Mr. Fletcher also makes an ingenious combination of two blow-pipes in +which the gas and air supplies are regulated by a single lever-handle. +This is very convenient, and gives flames that answer well with tubes +made of soft soda glass, and it is very useful for general work. For use +with lead glass the supply of air is rather too small, and does not +enable one to get such good results. This can be easily amended, +however. By slightly increasing the size of the air-tube of the smaller +blow-pipe, and having increased the supply of air to the larger +blow-pipe also, by reducing the external diameter of the end of the +innermost tube, I now get medium-sized brush flames and pointed flames +with this blow-pipe, that are equal to any I have used for heating lead +glass. + +For small laboratories the inexpensive No. 5 Bunsen burner of Mr. +Fletcher, which is convertible into a blow-pipe, will be very useful. + +Jets of several sizes to fit the air-tubes of blow-pipes may be obtained +with them, and will serve for regulating the supply of air to the flame. + + +=The Bellows.=--The usual blowing apparatus is some form of foot-blower. +These may be obtained fitted to small tables with sheet-iron tops. But a +much less expensive apparatus is the large foot-blower made by Mr. +Fletcher of Warrington, which can be used at an ordinary table or +laboratory bench. Good foot-blowers can also be obtained from makers of +furnace bellows. + +No part of the glass-blower's equipment exceeds the bellows in +importance. The best blower procurable should therefore be adopted. A +bellows which, when used with a large blow-pipe, will not enable you to +heat large pieces of lead glass tube to redness without blackening the +glass when the directions for heating lead glass on pages 17-21 are +followed, should on no account be received. I am told that at some +places, where the water-supply is at very high pressure, it is utilised +for working blow-pipes by means of the apparatus described below, and +that some glass-workers find it advantageous to use such automatic +blowers. But after a little practice, the effort of working the blower +with the foot whilst manipulating the glass is not a source of serious +inconvenience. Indeed, as it gives a certain degree of control over the +flame without the use of the hands, the foot-blower is preferable. It is +worth while to describe an automatic blower, however. + + +=Automatic Blower= (Fig. 2).--A strong glass tube _A_ is welded into a +somewhat larger tube _B_ so that its end is about 2 mm. from the +contraction at _G_. _B_ has a side tube _C_ joined to it. The narrow end +of _B_ is fixed by an india-rubber cork to a strong bottle _D_ of two or +three litres capacity. The india-rubber cork also carries an exit tube +_E_, and _D_ is pierced near its bottom by a small hole at _F_. + +[Illustration: FIG. 2] + +In using the apparatus _A_ is connected with the water-supply, and water +passing through _G_, carries air with it into _D_. The water escapes +from _D_ by the opening at _F_, and the air is allowed to pass out by +the tube _E_, its passage being regulated by a tap. Fresh supplies of +air enter _B_ by _C_. + + +=Blow-pipe Flames=--_The Pointed Flame._--If the gas tap of a Herapath +blow-pipe be adjusted so that comparatively little gas can pass, and if +the foot-blower be then worked cautiously, a long tongue of flame ending +in a fine point will be produced (Fig. 3). This flame will subsequently +be described as the _pointed flame_. It should be quite free from +luminosity, and as the amount of air necessary for securing a pointed +flame is large, in proportion to the gas, there is excess of oxygen +towards the end _C_. By adjusting the proportions of air and gas, +pointed flames of various dimensions can be obtained with the same +blow-pipe. The part of a pointed flame to be used in glass-working is +the tip, or in some cases the space slightly beyond the tip. + +[Illustration: FIG. 3.] + +[Illustration: FIG. 4.] + +_The Brush Flame._--If a large supply of gas be turned on and a +considerable blast of air sent into the flame, a non-luminous flame of +great size will be obtained (Fig. 4). In form it somewhat resembles a +large camel's hair pencil, and may conveniently be described as a +_brush flame_. The chief advantage of a large-sized blow-pipe is, that +with it a large brush flame may be produced, which is often invaluable. +By gradually diminishing the supply of gas and air smaller brush flames +may be produced. + +The jet used to supply air to the Herapath blow-pipe is usually too +fine, and consequently does not permit the passage of sufficient air to +produce a brush flame that contains excess of oxygen, even with the aid +of a very powerful blower. My own Herapath blow-pipe only gives a +satisfactory oxidising brush flame when the jet is removed altogether +from the end of the air-tube. For producing pointed flames the finer jet +of the air-tube must be used, but when a highly oxidising flame of large +size is required it must be removed. The internal diameter of the +central air-tube should be nearly half as great as that of the outer or +gas-supply tube. Fletcher's Automaton with the large air jet gives a +very liberal supply of air, and produces an excellent oxidising brush +flame. In the case of the larger-sized Automaton a consequence of this +is, however, that when fitted with the large jet it will not give so +good a pointed flame as the Herapath, which, in its turn, gives an +inferior oxidising brush. By fitting finer jets to the air-tube of +Fletcher's apparatus pointed flames can be secured when necessary. + +_The Smoky Flame._--By turning on a very free supply of gas, and only +enough air to give an outward direction to the burning gas, a smoky +flame, chiefly useful for annealing and for some simple operations on +lead glass, is produced. + +The Gimmingham blow-pipe and Fletcher's combination blow-pipe, in +addition to the above flames, are also adapted to produce a non-luminous +flame, resembling that of the Bunsen gas-burner, which is very +convenient for the preliminary heating of the glass, and also for +gradually cooling finished apparatus. It is not necessary to describe +the method of using these last-mentioned blow-pipes. With the more +complicated of them directions for its use are supplied. + +Mr. Madan has suggested the use of oxygen in place of air for producing +the oxidising flame required for working lead glass, and to produce a +flame of high temperature for softening tubes of hard, or combustion, +glass. For the latter purpose the employment of oxygen may be adopted +with great advantage. For working lead glass, however, it is quite +unnecessary if the directions already given are followed. + +The student's subsequent success will so largely depend upon his +acquaintance with the resources of his blow-pipe, and on the facility +with which he can take advantage of them, that no pains should be spared +in the effort to become expert in its management as soon as possible. A +few experiments should now be made, therefore, upon the adjustment of +the flame, until the student is able to produce and modify any form of +flame with promptness and certainty. + +[Illustration: FIG. 5.] + +The remaining apparatus used in glass-working consists of triangular and +other files, charcoal pastils for cutting glass, pieces of sound +charcoal of various diameters with conical ends; it is convenient to +have one end somewhat less pointed than the other (Fig. 5). Corks of +various sizes; the smallest, which are most frequently needed, should be +carefully cut with sharpened cork borers from larger corks. Besides +these there should be provided some freshly distilled turpentine in +which camphor has been dissolved,[1] fine and coarse emery powder, and +some sheets of cotton-wadding, an india-rubber blowing-bottle, glass +tubes, a little white enamel, and a pair of iron tongs. + +[1] Half an ounce of camphor to about six ounces of turpentine will do +very well. + + + + +CHAPTER II. + +_VARIETIES OF GLASS AND THEIR MANAGEMENT._ + + +All the varieties of glass that are ordinarily met with contain silica +(SiO_{2}) associated with metallic oxides. In a true glass there are at +least two metallic oxides. The unmixed silicates are not suitable for +the purposes of glass. They are not so capable of developing the viscous +condition when heated as mixtures--some of them are easily attacked by +water, and many of those which are insoluble are comparatively +infusible. There is generally excess of silica in glass, that is, more +than is necessary to form normal silicates of the metals present. The +best proportions of the various constituents have been ascertained by +glass-makers, after long experience; but the relation of these +proportions to each other, from a chemical point of view, is not easy to +make out. + +The varieties of glass from which tubes for chemical glass-blowing are +made may be placed under three heads, and are known as[2]-- + + Soft soda glass. Also known as French glass. + Lead glass. Also known as English glass. + Hard glass. + +[2] For details of the composition of the various glasses, some work on +glass-making may be consulted. + +In purchasing glass tubes, it is well to lay in a considerable stock of +tubes made of each of the two first varieties, and, if possible, to +obtain them from the manufacturer, for it frequently happens that pieces +of glass from the same batch may be much more readily welded together +than pieces of slightly different composition. Yet it is not well to lay +in too large a stock, as sometimes it is found that glass deteriorates +by prolonged keeping. + +As it is frequently necessary to make additions, alterations, or repairs +to purchased apparatus, it is best to provide supplies both of soft soda +glass and lead glass, for though purchased glass apparatus is frequently +made of lead glass, yet sometimes it is formed from the soda glass, and +as it is a matter of some difficulty to effect a permanent union between +soda glass and lead glass, it is desirable to be provided with tubes of +both kinds. + +Many amateurs find that soda glass is in some respects easier to work +with than lead glass. But, on the other hand, it is somewhat more apt to +crack during cooling, which causes much loss of time and disappointment. +Also, perhaps in consequence of its lower conductivity for heat, it very +often breaks under sudden changes of temperature during work. If, +however, a supply of good soda glass is obtained, and the directions +given in this book in regard to annealing it are thoroughly carried out, +these objections to the use of soda glass will, to a great extent, be +removed. I find, however, that when every precaution has been taken, +apparatus made of soda glass will bear variations of temperature less +well than that made of lead glass. Therefore, although the comparatively +inexpensive soda glass may be employed for most purposes without +distrust, yet I should advise those who propose to confine themselves to +one kind of glass, to take the small extra trouble required in learning +to work lead glass. + +In order to secure glass of good quality, a few pieces should be +obtained as a sample, and examined by the directions given below. When +the larger supply arrives, a number of pieces, taken at random, should +be examined before the blow-pipe, to compare their behaviour with that +of the sample pieces, and each piece should be separately examined in +all other respects as described subsequently. + +Hard glass is used for apparatus that is required to withstand great +heat. It is difficult to soften, especially in large pieces. It should +only be employed, therefore, when the low melting points of soda or lead +glass would render them unsuitable for the purpose to which the finished +apparatus is to be put. What is sold as Jena combustion tube should be +preferred when this is the case. + + +=Characters of good Glass.=--Glass tubes for glass-blowing should be as +free as possible from knots, air-bubbles, and stripes. They should be in +straight pieces of uniform thickness, and cylindrical bore. It is not +possible to obtain glass tubes of absolutely the same diameter from one +end to the other in large quantities, but the variations should not be +considerable. + +When a sharp transverse scratch is made with a good file on a piece of +tube, and the scratch is touched with a rather fine point of red-hot +glass (this should be lead glass for a lead glass tube, and soda glass +for a tube of soda glass), the crack which is started should pass round +the glass, so that it may be broken into two pieces with regular ends. +If the crack proceeds very irregularly, and especially if it tends to +extend along the tube, the glass has been badly annealed, and should not +be employed for glass-blowing purposes. It is important that the point +of hot glass used shall be very small, however. Even good glass will +frequently give an irregular fracture if touched with a large mass of +molten glass. + +Finally, glass tube which is thin and of small diameter should not +crack when suddenly brought into a flame. But larger and thicker tubes +will not often withstand this treatment. They should not crack, however, +when they are brought into a flame gradually, after having been held in +the warm air in front of it for a minute or so. + +Good glass does not readily devitrify when held in the blow-pipe flame. +As devitrified glass very often may be restored to its vitreous +condition by fusion, devitrification most frequently shows itself round +the edges of the heated parts, and may be recognised by the production +of a certain degree of roughness there. It is believed to be due to the +separation of certain silicates in the crystallised form. Hard glass, +which contains much calcium, is more apt to devitrify than the more +fusible varieties.[3] + +[3] The presence of silicates of calcium and aluminum are considered to +promote a tendency to devitrification in glass; and glasses of complex +composition are more apt to devitrify than the simpler varieties. See +_Glass-making_, by Powell, Chance, and Harris, Chap. IV. + +Glass tubes are made of various sizes. When purchasing a supply, it is +necessary to be somewhat precise in indicating to the vendor the sizes +required. I have therefore placed at the end of the book, in an +appendix, a table of numbered diagrams. In ordering tubes it will +usually only be necessary to give the numbers of the sizes wished for, +and to specify the quantity of each size required. In ordering glass +tubes by weight, it must be remembered that a great many lengths of the +smaller sizes, but very few lengths of the larger sizes, go to the +pound. Larger-sized tubes than those on the diagram are also made. In +ordering them the external diameter and thickness of glass preferred +should be stated. + + +=Cleaning and Preparing a Tube.=--It is frequently much easier to clean +the tube from which a piece of apparatus is to be made than to clean +the finished apparatus. A simple method of cleaning a tube is to draw a +piece of wet rag which has been tied to a string through the tube once +or twice, or, with small tubes, to push a bit of wet paper or cotton +wool through them. If the dirt cannot be removed in this way, the +interior of the tube should be moistened with a little sulphuric acid in +which some bichromate of potassium has been dissolved. In any case, it +must finally be repeatedly rinsed with distilled water, and dried by +cautiously warming it, and sucking or blowing air through it. In order +to avoid heating delicate apparatus which has become damp and needs +drying, the water may be washed out with a few drops of spirit, which is +readily removed at a low temperature. + +Before using a glass tube for an operation in which it will be necessary +to blow into it, one end of it must be contracted, unless it is already +of such a size that it can be held between the lips with perfect ease; +in any case, its edges must be rounded. For descriptions of these +operations, see page 35. The other end must be closed. This may be done +by means of a cork. + + +=Presenting Glass to the Flame.=--Glass tubes must never be brought +suddenly into the flame in which they are to be heated. All glass is +very likely to crack if so treated. It should in all cases be held for a +little while in front of the flame, rotated constantly in the hot air +and moved about, in order that it may be warmed over a considerable +area. When it has become pretty hot by this treatment, it may be +gradually brought nearer to the flame, and, finally, into contact with +it, still with constant rotation and movement, so as to warm a +considerable part of the tube. When the glass has been brought fairly +into contact with the flame, it will be safe to apply the heat at the +required part only. Care must be taken in these preliminary operations +to avoid heating the more fusible glasses sufficiently to soften them. + + +=Methods of working with Lead and soft Soda Glass respectively.=--When +lead glass is heated in the brush flame of the ordinary Herapath +blow-pipe, or within the point of the pointed flame, it becomes +blackened on its surface, in consequence of a portion of the lead +becoming reduced to the metallic state by the reducing gases in the +flame. The same thing will happen in bending a lead glass tube if it is +made too hot in a luminous flame. A practical acquaintance with this +phenomenon may be acquired by the following experiment:-- + +Take a piece of lead glass tube, bring it gradually from the point of a +pointed flame to a position well within the flame, and observe what +happens. When the glass reaches the point _A_ (Fig. 3), or thereabouts, +a dark red spot will develop on the glass, the area of the spot will +increase as the glass is brought further in the direction _A_ to _B_. If +the glass be then removed from the flame and examined, it will be found +that a dark metallic stain covers the area of the dark red spot +previously observed. Repeat the experiment, but at the first appearance +of the dark spot slowly move the glass in the direction _A_ to _C_. The +spot will disappear, and, if the operation be properly performed, in its +place there will be a characteristically greenish-yellow luminous spot +of highly heated glass. In this proceeding the reduced lead of the dark +spot has been re-oxidised on passing into the hot gases, rich in oxygen, +which abound at the point of the flame. If one end of the tube has been +previously closed by a piece of cork, and if air be forced into the tube +with the mouth from the open end before the luminous spot has become +cool, the glass will expand. If the experiment be repeated several +times, with pointed flames of various sizes, the operator will quickly +learn how to apply the pointed flame to lead glass so that it may be +heated without becoming stained with reduced lead. + +If the spot of reduced metal produced in the first experiment be next +brought into the oxidising flame, it also may gradually be removed. On +occasion, therefore, apparatus which has become stained with lead during +its production, may be rendered presentable by suitable treatment in the +oxidising flame. The process of re-oxidising a considerable surface in +this way after it has cooled down is apt to be very tedious, however, +and, especially in the case of thin tubes or bulbs, often is not +practicable. In working with lead glass, therefore, any reduction that +occurs should be removed by transferring the glass to the oxidising +flame at once. + +Small tubes, and small areas on larger tubes of English glass, may be +softened without reduction by means of the pointed oxidising flame; but +it is not easy to heat any considerable area of glass sufficiently with +a pointed flame. And though it is possible, with care, to employ the hot +space immediately in front of the visible end of an ordinary brush +flame, which is rich in air, yet, in practice, it will not be found +convenient to heat large masses of lead glass nor tubes of large size, +to a sufficiently high temperature to get the glass into good condition +for blowing, by presenting them to the common brush flame. + +It may seem that as glass which has become stained with reduced lead can +be subsequently re-oxidised by heating it with the tip of the pointed +flame, the difficulty might be overcome by heating it for working in the +brush flame, and subsequently oxidising the reduced lead. It is, +however, difficult, as previously stated, to re-oxidise a large surface +of glass which has been seriously reduced by the action of the reducing +gases of the flame, after it has cooled. Moreover, there is this very +serious objection, that if, as may be necessary, the action of the +reducing flame be prolonged, the extensive reduction that takes place +diminishes the tendency of the glass to acquire the proper degree of +viscosity for working it, the glass becomes difficult to expand by +blowing, seriously roughened on its surface, and often assumes a very +brittle or rotten condition. + +When it is only required to bend or draw out tubes of lead glass, they +may be softened sufficiently by a smoky flame, which, probably owing to +its having a comparatively low temperature, does not so readily reduce +the lead as flames of higher temperature. But for making joints, +collecting masses of glass for making bulbs, and in all cases where it +is required that the glass shall be thoroughly softened, the smoky flame +does not give good results. + +In the glass-works, where large quantities of ornamental and other glass +goods are made of lead or flint glass, the pots in which the glass is +melted are so constructed that the gases of the furnace do not come into +contact with the glass;[4] and as the intensely-heated sides of the +melting-pot maintain a very high temperature within it by radiation, the +workman has a very convenient source of heat to his hand,--he has, in +fact, only to introduce the object, or that part of it which is to be +softened, into the mouth of the melting-pot, and it is quickly heated +sufficiently for his purpose, not only without contact of reducing +gases, but in air. He can therefore easily work upon very large masses +of glass. In a special case, such a source of heat might be devised by +the amateur. Usually, however, the difficulty may be overcome without +special apparatus. It is, in fact, only necessary to carry out the +instructions given below to obtain a considerable brush flame rich in +air, in which the lead glass can be worked, not only without +discoloration, but with the greatest facility. + +[4] See _Principles of Glass-making_, p. 31. + +_To Produce an Oxidising Brush Flame._--The blower used must be +powerful, the air-tube of the blow-pipe must be about half as great in +diameter as the outer tube which supplies the gas. The operator must +work his bellows so as to supply a strong and _steady_ blast of air, and +the supply of gas must be regulated so that the brush flame produced is +free from every sign of incomplete combustion,[5] which may be known by +its outer zone being only faintly visible in daylight, and quite free +from luminous streaks (see Fig. 4, p. 9). When a suitable flame has been +produced, try it by rotating a piece of lead glass at or near the end of +the inner blue part of the flame (_A_ Fig. 4); the appearance of the +glass will quickly indicate reduction. When this occurs move the glass +forward to the end of the outer zone _B_, but keep it sufficiently +within the flame to maintain it at a high temperature. If all is right +the metallic reduction will quickly disappear, the glass will become +perfectly transparent once more, and will present the appearance +previously observed in the experiments with the pointed flame, or, if +very hot, assume a brownish-red appearance. If this does not occur, the +supply of air must be increased or the supply of gas diminished until +the proper effects are secured. + +[5] Nevertheless the supply of air must not be so excessive as to reduce +the temperature of the flame sufficiently to prevent the thorough +softening of the glass, which will occur if the bellows is worked with +too much zeal. + +In working upon lead glass with the highly oxidising brush flame, it is +a good plan to heat it in the reducing part of the flame _A_ for +thoroughly softening the glass, and to remove it to the oxidising flame +_B_ to burn away the reduced metal. In prolonged operations, in order +that reduction may never go too far, hold the glass alternately in the +hot reducing flame and in the oxidising flame. The inferiority of the +outer oxidising flame to those portions nearer the inner blue zone for +softening the glass, may perhaps be accounted for by the presence of a +larger proportion of unconsumed air in the former, which being heated at +the expense of the hot gases produced by combustion, thereby lowers the +temperature of the flame. At or near _A_ (Fig. 4) where the combustion +is nearly complete, but no excess of air exists, the temperature will +naturally be highest. + +If a very large tube be rotated in the oxidising flame at _B_ (Fig. 4) +it may happen that the flame is not large enough to surround the tube, +and that as it is rotated those parts of it which are most remote from +the flame will cool down too considerably to allow all parts of the tube +to be simultaneously brought into the desired condition. This difficulty +may be overcome by placing two blow-pipes exactly opposite to each +other, at such a distance that there is an interval of about an inch +between the extremities of their flames, and rotating the tube between +the two flames. It may be necessary to provide two blowers for the +blow-pipes if they are large. + +Again, if a very narrow zone of a tube of moderate size is to be heated, +two pointed flames may be similarly arranged with advantage. +Occasionally more than two flames are made to converge upon one tube in +this manner. + +Another method of preventing one side of a tube from cooling down whilst +the other is presented to the flame, is to place a brick at a short +distance from the extremity of the flame. The brick checks the loss of +heat considerably. A block of beech wood may be used for the same +purpose, the wood ignites and thereby itself becomes a source of heat, +and is even more effective than a brick. + +Fuller details of the management of lead glass under various +circumstances will be found in the subsequent descriptions of operations +before the blow-pipe. + +Before proceeding to work with soda glass, the student should not only +verify by experiments what has been already said, but he should +familiarise himself with the action of the blow-pipe flame on lead glass +by trying the glass in every part of the flame, varying the proportions +of gas and air in every way, repeating, and repeating, his experiments +until he can obtain any desired effect with certainty and promptitude. +He should practice some of the simpler operations given in Chapter III. +in order to impress what he has learned well on his mind. + + +=Management of Soda Glass.=--In working with soda glass the following +points must be constantly kept in mind. That as it is much more apt than +lead glass to crack when suddenly heated, great caution must be +exercised in bringing it into the flame; and that in making large joints +or in making two joints near each other, all parts of the tube adjacent +to that which, for the moment, is being heated, must be kept hot, as it +is very apt to crack when adjacent parts are unequally heated. This may +be effected by stopping work at short intervals and warming the cooler +parts of the tube, or by the use of the brick or block of wood to check +radiation, or even by placing a supplementary blow-pipe or Bunsen burner +in such a position that its flame plays upon the more distant parts of +the work, not coming sufficiently into contact to soften the glass, +however, but near enough to keep it well heated. Lastly, to prevent the +finished work from falling to pieces after or during cooling, the +directions given under the head of annealing must be carefully carried +out. + +In very much of his work the glass-blower is guided more by the _feel_ +of the glass than by what he sees. The power of feeling glass can only +be acquired by practice, and after a certain amount of preliminary +failure. As a rule I have observed that beginners are apt to raise their +glass to a higher temperature than is necessary, and that they employ +larger flames than are wanted. If glass be made too soft it may fall so +completely out of shape as to become unworkable except in very skilful +hands. The following rules, therefore, should be strictly adhered to. +Always employ in the first instance the smallest flame that is likely to +do the work required. In operations involving _blowing out_ viscous +glass, attempt to blow the glass at low temperatures before higher ones +are tried. After a little experience the adoption of the right-sized +flame for a given purpose, and the perception of the best condition of +glass for blowing it, become almost automatic. + +I may add that glass which is to be bent needs to be much less heated +than glass which is to be blown. + + +=Annealing.=--If apparatus, the glass of which is very thin and of +uniform substance, be heated, on removal from the source of heat it will +cool equally throughout, and therefore may often be heated and cooled +without any special precautions. If the glass be thick, and especially +if it be of unequal thickness in various parts, the thinner portions +will cool more quickly than those which are more massive; this will +result in the production of tension between the thicker and thinner +parts in consequence of inequality in the rates of contraction, and +fractures will occur either spontaneously or upon any sudden shock. +Thus, if a hot tube be touched with cold or wet iron, or slightly +scratched with a cold file, the inequality of the rate of cooling is +great, and it breaks at once. It is therefore necessary to secure that +hot glass shall cool as regularly as possible. And this is particularly +important in the case of articles made of soda glass. Some glass-blowers +content themselves with permitting the glass to cool gradually in a +smoky flame till it is covered with carbon, and then leave it to cool +upon the table. But under this treatment many joints made of soda glass +which are not quite uniform in substance, but otherwise serviceable, +will break down. In glass-works the annealing is done in ovens so +arranged that the glass enters at the hottest end of the oven where it +is uniformly heated to a temperature not much below that at which it +becomes viscous, and slowly passed through the cooler parts of the +chamber so that it emerges cold at the other end. This method of +annealing is not practicable in a small laboratory. But fortunately very +good results can be obtained by the following simple device, viz.:-- + +By wrapping the hot apparatus that is to be annealed closely in cotton +wool, and leaving it there till quite cold. The glass should be wrapped +up immediately after it is blown into its final shape, as soon as it is +no longer soft enough to give way under slight pressure. And it should +be heated as uniformly as possible, not only at the joint, but also +about the parts adjacent to the joint, at the moment of surrounding it +with the cotton. Lead glass appears to cool more regularly than soda +glass, and these precautions may be more safely neglected with apparatus +made of lead glass; but not always. At the date of writing I have had +several well-blown joints of thick-walled capillary tube to No. 16 (see +diagram, p. 82), break during cooling, in consequence of circumstances +making it dangerous to heat the neighbourhood of the joint so much as +was necessary. + +The black carbonaceous coat formed on hot glass when it is placed in +cotton wool may be removed by wiping with methylated spirit, or, if it +be very closely adherent, by gently rubbing with fine emery, moistened +with the spirit. + +Cotton wool is rather dangerously inflammable; it should therefore be +kept out of reach of the blow-pipe flame, and care should be taken that +the glass is not placed in contact with it at a sufficiently high +temperature to cause its ignition. + +Another method of annealing is to cover the hot glass with hot sand, and +allow it to cool therein. + +As in the case of lead glass, so with soda glass. A thorough +acquaintance with the effect of the various parts of the flame upon it +should be gained before further work is entered upon, for which purpose +an hour or more spent in observing its behaviour in the flame will be +fully repaid by increased success subsequently. + + +=The Use of Combustion Tube.=--It is often necessary to construct +apparatus of what is known as hard glass or combustion tube. It is +almost as easy to work combustion tube as to deal with lead and soda +glass if the oxy-hydrogen flame be employed. + +It is not necessary to set up a special apparatus for this purpose; many +of the ordinary blow-pipes can be used with oxygen instead of with air. +It is only necessary to connect the air-tube of the blow-pipe with a +bottle of compressed oxygen instead of with the bellows. The connecting +tube should not be too wide nor too long, in order to avoid the +accumulation in it, by accident, of large quantities of explosive +mixtures. + +Two precautions are necessary in manipulating hard glass in the +oxy-hydrogen flame. The glass must _not_ be overheated. At first one is +very apt to go wrong in this direction. The supply of oxygen must _not_ +be too great; a small hissing flame is not what is wanted. If either of +these precautions are neglected most glass will devitrify badly. With a +little care and experience, devitrification can be absolutely avoided. +Ordinary combustion tube can be used, but I find that the glass tube +(Verbrennungsroehr) made by Schott & Co. of Jena, which can be obtained +through any firm of dealers in apparatus, is far better than the +ordinary tube. + +By following these instructions, any one who has learned how to work +with lead or soda glass will find it easy to manipulate hard glass. + + + + +CHAPTER III. + +_CUTTING AND BENDING GLASS--FORMING GLASS APPARATUS BEFORE THE +BLOW-PIPE--MAKING AND GRINDING STOPPERS TO APPARATUS, ETC._ + + +In the later pages of this Chapter it will be assumed that the +operations first described have been mastered. The beginner should +therefore practise each operation until he finds himself able to perform +it with some degree of certainty. Generally speaking, however, after the +failure of two or three attempts to perform any operation, it is best to +give up for a few hours, and proceed to the work next described, +returning to that upon which you have failed subsequently. If, +unfortunately, it should happen that the work next in order involves the +performance of the operation in which the failure has occurred, it is +best to pass on to some later work which does not demand this particular +accomplishment, or to rest a while, and re-attack the difficulty when +refreshed. + + +=Cutting Glass Tubes.=--The simplest method of cutting a glass tube is +to make a sharp scratch with a file across the glass at the point where +it is desired to cut it, and on pulling apart the two ends, it will +break clean off. It is important that the file be sharp. In pulling +apart the ends the scratch should be held upwards, and the pull should +have a downward direction, which will tend to open out the scratch. In +the case of a large tube, a scratch will not ensure its breaking clean +across. The tube must be filed to some depth, half-way, or even all +round it. A good way of breaking a tube is to place the file in the +table after scratching the glass, to hold the glass tube above its edge +with one hand on each side of the scratch, and to strike the under side +of the tube a sharp blow upon the edge of the file, directly beneath the +scratch. In this way very even fractures of large and moderately thin +tubes may be made. It answers particularly well for removing short ends +of tube, not long enough to hold; the tube is held firmly upon the file, +and a sharp blow given to the short end with a piece of large tube or a +key. + +A file whose faces have been ground till they are nearly smooth, so as +to leave very finely-serrated edges, will be found useful for cutting +glass tubes. Such a file should be used almost as a knife is used for +cutting a pencil in halves. + +The simple methods just described are too violent to be applied to +delicate apparatus, too tedious when employed upon the largest tubes, +and very difficult to apply when the tube to be cut is very thin, or too +short to permit the operator to get a good grip of it on either side of +the file mark. In such cases, one or other of the following methods will +be useful:-- + +1. Make a scratch with a file, and touch it with the end of a _very +small_ piece of glass drawn out and heated at the tip to its melting +point. It is important that the heated point of glass be very small, +or the fracture is likely to be uneven, or to spread in several +directions. Also, it is best to use hot soda glass for starting cracks +in tubes of soda glass, and lead glass for doing so in lead glass +tubes. If the crack does not pass quite round the tube, you may pull +it asunder, as previously described, or you may bring the heated piece +of glass with which the crack was started to one end of the crack, and +slowly move it (nearly touching the glass) in the required direction; +the crack will extend, following the movements of the hot glass. +Instead of hot glass, pastils of charcoal are sometimes employed for +this purpose. They continue to burn when once lighted, and there is +no need to re-heat them from time to time. They should be brought as +close to the glass as is possible without touching it, and, when no +longer needed, should be extinguished by placing the lighted end under +sand, or some other incombustible powder, for they must not be wetted. + +2. A method much practised by the makers of sheet glass, and suitable +for large objects, is to wrap a thread of hot glass round the tube, at +once removing it, and touching any point of the glass which the thread +covered with water or a cold iron, when a crack will be started and will +pass round the glass where it was heated by the thread. + +3. Tubes which are large and slightly conical may have a ring of red-hot +iron passed over them till it comes into contact with the glass, then, +the iron being removed, and a point on the heated glass being at once +touched with cold iron as before, it will break as desired. Or a string, +moistened with turpentine, may be loosely twisted round the tube, and +the turpentine ignited, afterwards the application of sudden cold to any +point on the zone of hot glass will usually start a crack, which, if +necessary, may be continued in the usual manner. The last three methods +are chiefly useful in dealing with the largest and thickest tubes, and +with bottles. + +A fairly stout copper wire, bent into the form of a bow so that it can +be applied when hot to a considerable surface of a glass tube, will be +found superior to the point of hot glass or metal usually employed, for +leading cracks in glass tubes. With such a wire a tube can be cut so +that the cross section of the end is at any desired angle to the axis of +the tube, with considerable precision. I am indebted for this suggestion +to Mr. Vernon Boys and Dr. Ebert. + + +=Bending Glass Tubes.=--The blow-pipe flame is not a suitable source of +heat for bending tubes, except in certain cases which will be mentioned +in a subsequent paragraph. For small tubes, and those of moderate size, +a fish-tail burner, such as is used for purposes of illumination, will +answer best. Use a flame from one to two inches in breadth--from _A_ to +_A_ (Fig. 6), according to the size of the tube which is to be bent. If +the length of tube that is heated be less than this, the bend will +probably buckle on its concave side. + +[Illustration: FIG. 6.] + +The tube to be heated should be held in the position shown in Fig. 6, +supported by the hands on each side. It should be constantly rotated in +the flame, that it may be equally heated on all sides. In the figure the +hands are represented above the tube, with their backs upwards. A tube +can be held equally well from below, the backs of the hands being then +directed downwards, and this, I think, is the more frequent habit. It is +difficult to say which position of the hands is to be preferred. I +lately observed how a tube was held by three skilful amateurs and by a +professional glass-blower. All the former held the tube with the hands +below it. The latter, however, held it from above, as in Fig. 6. He, +however, was working with a rather heavy piece of tube, and I am +inclined myself to recommend that position in such cases. During a long +spell of work, the wrist may be rested from time to time by changing the +position of the hands. + +When the tube has softened, remove it from the flame, and gently bend +it to the desired angle. The side of the tube last exposed to the flame +will be slightly hotter, and therefore softer, than that which is +opposite to it. This hotter side should form the concave side of the +bent tube. + +[Illustration: FIG. 7.] + +The exact condition in which the glass is most suitable for bending can +only be learned by making a few trials. If it is too soft in consequence +of being overheated, the sides will collapse. If, in the endeavour to +heat the side _A_ of Fig. 7 a little more than _B_, _B_ is +insufficiently heated, the tube will be likely to break on the convex +side _B_. If the bent tube be likely to become flattened, and this +cannot always be prevented in bending very thin tubes, the fault may be +avoided by blowing gently into one end of the tube whilst bending it, +for which purpose the other end should be closed beforehand. A tube +already flattened may, to some extent, be blown into shape after +closing one end and re-heating the bent portion, but it is not easy to +give it a really good shape. + +When making a bend like that in Fig. 7, to secure that the arms of the +tube _C_ and _D_, and the curve at _B_, shall be in one plane, the tube +should be held in a position perpendicular to the body, and brought into +the position shown in the figure during bending, by which means it will +be found easy to secure a good result. Lead glass tubes must be removed +from the flame before they become hot enough to undergo reduction. If +they should become blackened, however, the stain may be removed by +re-heating in the oxidising flame (see p. 18). + +When a very sharp bend is to be made, it is sometimes best to heat a +narrow zone of the glass rather highly in the blow-pipe flame, and to +blow the bend into shape at the moment of bending it, as previously +described, one end having been closed for that purpose beforehand. Lead +glass should be heated for this purpose in the oxidising flame (pp. 17 +to 22). + +The processes of bending large tubes, making U-tubes and spiral tubes, +are more difficult operations, and will be explained in Chap. IV. + + +=Rounding and Bordering the Ends of Tubes.=--After cutting a piece of +glass tube in two pieces, the sharp edges left at its ends should be +rounded by holding them in a flame for a few moments till the glass +begins to melt. The oxidising point of a pointed flame may be used for +both kinds of glass. The flame will be coloured yellow by soda glass at +the moment of melting. This indication of the condition of soda glass +should be noted, for it serves as a criterion of the condition of the +glass. The ends of soda glass tubes may also be rounded in the flame of +a common Bunsen's burner. + +When the end of a tube is to be closed with a cork or stopper, its +mouth should be expanded a little, or =bordered=. To do this, heat the +end of the tube by rotating it in the flame till it softens, then remove +it from the flame, at once introduce the charcoal cone (Fig. 5, p. 11), +and rotate it with gentle pressure against the softened glass till the +desired effect is produced. In doing this it is very important that the +end of the tube shall be uniformly heated, in order that the enlargement +shall be of regular form. If the tube cannot be sufficiently expanded at +one operation, it should be re-heated and the process repeated. + +Borders, such as are seen on test-tubes, are made by pressing the +softened edge of the tube against a small iron rod. The end of the rod +should project over the softened edge of the tube at a slight angle, and +be pressed against it, passing the rod round the tube, or rotating the +tube under the rod. + +=Sealing=, that is closing the ends of tubes, or other openings, in +glass apparatus. + +In performing this and all the other operations of glass blowing, the +following points must be constantly kept in mind:-- + +(_a._) That it is rarely safe to blow glass whilst it is still in the +flame, except in certain special cases that will be mentioned +subsequently. Therefore always remove apparatus from the flame before +blowing. + +(_b._) That when heating glass tubes, unless it is specially desired to +heat one portion only, the tube must be constantly rotated in the flame +to ensure that it shall be uniformly heated, and to prevent the tube or +mass of glass from assuming an irregular form. + +(_c._) Always blow gently at first, and slowly increase the force +applied till you feel or see the glass giving way. It is a good plan to +force the air forward in successive short blasts rather than in one +continued stream. + +(_d._) When it is necessary to force air into tubes of fine bore, such +as thermometer tubes, the mouth must not be used, for moisture is +thereby introduced into the tube, which it is very difficult to remove +again in many cases. All tubes of very small bore should be blown with +the aid of an india-rubber blowing-bottle, such as are used for +spray-producers, Galton's whistles, etc. The tube to be blown must be +securely fixed to the neck of the bottle, which is then held in one +hand, and air is forced from it into the tube as it is required. These +bottles are frequently of service to the glass-blower--_e.g._, when +tubes of very fine bore have to be united, it is necessary to maintain +an internal pressure slightly exceeding that of the air throughout the +operation, in order to prevent the viscous glass from running together +and closing the tube. An india-rubber blowing-ball is very convenient +for this purpose. + +To seal the end of a glass tube (Fig. 8), adjust the flame so that it +will heat a zone of glass about as broad as the diameter of the tube to +be sealed (see _A_, Fig. 8). Hold the tube on each side of the point +where it is to be sealed in the manner described in the description of +bending glass tubes (p. 28). Bring the tube gradually into the flame, +and heat it with constant rotation, till the glass softens (for lead +glass the oxidising flame must be used, as has been already +explained).[6] When the glass begins to thicken, gently pull asunder the +two ends, taking care not to pull out the softened glass too much, but +to allow the sides to fall together, as shown at _A_. When this has +occurred, heat the glass at the narrow part till it melts, and pull +asunder the two ends. The closed end should present the appearance +shown at _D_. If the glass be drawn out too quickly its thickness will +be unduly reduced, and it will present the appearance shown at _B_. In +that case apply a pointed flame at _b_, and repeat the previous +operation so as to contract the tube as at _c_, taking care not to allow +the glass to become much increased nor decreased in thickness. + +[6] Remember that when the lead glass is heated to the proper +temperature it will present an appearance which may be described as a +greenish phosphorescence. At higher temperatures it assumes an +orange-red appearance. If it loses its transparency and assumes a dull +appearance, it must be moved further into the oxidising parts of the +flame. + +If a considerable mass of glass be left at _d_, it may be removed by +heating it to redness, touching it with the pointed end of a cold glass +tube, to which it will adhere, and by which it may be pulled away. + +[Illustration: FIG. 8.] + +When the end of the tube presents the appearance shown in the diagram +_D_, and the mass of glass at _d_ is small, the small lump that remains +must be removed by heating it till it softens, and _gently_ blowing with +the mouth, so as to round the end and distribute the glass more +regularly, as shown in _E_. The whole end, from the dotted line _e_, +must then be heated with constant rotation in the flame. If this final +heating of the end _e_ be done skilfully, the glass will probably +collapse and flatten, as at _F_. The end must then be gently blown into +the form shown at _G_. + +If a flat end to the tube be desired, the tube may be left in the +condition shown by _F_, or a thin rounded end may be flattened by +pressure on a plate of iron. + +If a concave end be wished for, it is only necessary to gently suck air +from the tube before the flattened end has become solid. + +In each case, _immediately_ after the tube is completed, it must be +closely wrapped in cotton wool and left to cool. With good lead glass +this last process, though advantageous, is not absolutely necessary; and +as glass cools slowly when enveloped in cotton wool, this precaution may +frequently be neglected in the case of apparatus made from lead glass. + +[Illustration: FIG. 9.] + +In order to draw out tubes for sealing, close to one end, and thus to +avoid waste of material, it is a good plan to heat simultaneously the +end of the glass tube _A_ which is to be sealed, and one end of a piece +of waste tube _E_ of about the same diameter, and when they are fused to +bring them together as at _DD_ (Fig. 9). _E_ will then serve as a handle +in the subsequent operations on _A_. Such a rough joint as that at _D_ +must not be allowed to cool too much during the work in hand, or _E_ and +_A_ may separate at an inconvenient moment. Or the glass at the end of +the tube may be pressed together to close the tube, and the mass of +glass may be seized with a pair of tongs and drawn away. + + +=Choking, or Contracting the Bore of a Glass Tube.=--If it be not +desired to maintain the uniformity of external dimensions of the tube +whilst decreasing the diameter of the bore, the tube may be heated and +drawn out as described in the description of sealing tubes on pp. 32-35. +This may be done as shown at _A_ or _B_ in Fig. 8, according to the use +to which the contracted tube is to be put. + +[Illustration: FIG. 10.] + +Greater strength and elegance will be secured by preserving the external +diameter of the tube unchanged throughout, as shown in Fig. 10. For this +purpose heat the tube with the pointed flame, if it be small, or in the +brush flame if it be of large size, constantly rotating it till the +glass softens and the sides show an inclination to fall together, when +this occurs, push the two ends gently towards _A_. If the tube should +become too much thickened at _A_, the fault may be corrected by removing +it from the flame and gently pulling the two ends apart till it is of +the proper size. If the bore at the contracted part of the tube should +become too much reduced, it may be enlarged by closing one end of the +tube with a small cork, and blowing gently into the open end after +sufficiently heating the contracted part. The tube should be rotated +during blowing or the enlargement produced may be irregular. + +When the external diameter of the tube is to be increased as well as its +bore diminished, press together the ends of a tube heated at the part to +be contracted, as already described, and regulate the size of the bore +by blowing into the tube if at any time it threatens to become too much +contracted. + + +=Widening Tubes.=--Tubes may be moderately expanded at their extremities +by means of the charcoal cone (see Bordering, p. 31). They may be +slightly expanded at any other part by closing one end and gently +blowing into the open end of the tube, after softening the glass at the +part to be widened before the blow-pipe. But the best method of +obtaining a wide tube with narrow extremities (Fig. 11) is to join +pieces of narrow tube _AA_ to the ends of a piece of wider tube _B_ of +the desired dimensions. The method of performing this operation is +described under welding, on pp. 39-47. + +[Illustration: FIG. 11.] + +[Illustration: FIG. 12.] + + +=Piercing Tubes.=--The glass-blower very frequently requires to make a +large or small opening in some part of a tube or other piece of +apparatus. This is known as piercing. Suppose it is desired to make a +small hole at the point _a_ in _A_ (Fig. 12). When the tube has been +brought to the flame with the usual precautions, allow the end of the +pointed flame to touch it at _a_ till an area corresponding to the +desired size of the opening is thoroughly softened. Then expand the +softened glass by blowing to the form shown at _B_. Re-heat _a_, blow a +small globe as at _C_, and carefully break the thin glass, then smooth +the rough edges by rotating them in the flame till they form a mouth +like that of _D_. Instead of leaving the bulb to be broken at the third +stage _C_, it is a good plan to blow more strongly, so that the bulb +becomes very thin and bursts, the removal of the thin glass is then +accompanied by less risk of producing a crack in the thicker parts of +the glass. Openings may be made in a similar manner in the sides of +tubes or in globes, in fact, in almost any position on glass apparatus. +If another tube is to be attached at the opening, it is a good plan to +proceed to this operation before the tube has cooled down. + +[Illustration: FIG. 13.] + +The openings obtained by the method above described are too large when +platinum wires are to be sealed into them. Suppose that it is necessary +to pierce the tube _A_ of Fig. 13 in order to insert a platinum wire at +_a_; direct the smallest pointed flame that will heat a spot of glass to +redness on the point _a_. When the glass is viscous, touch it with the +end of a platinum wire _w_, to which the glass will adhere; withdraw the +wire and the viscous glass will be drawn out into a small tube, as shown +at _B_; by breaking the end of this tube a small opening will be made. +Introduce a platinum wire into the opening, and again allow the flame to +play on the glass at that point; it will melt and close round the wire. +Before the hot glass has time to cool, blow gently into the mouth of the +tube to produce a slightly curved surface, then heat the neighbouring +parts of the tube till the glass is about to soften, and let it cool in +cotton wool. Unless this is done, I find that glass tubes into which +platinum wires have been sealed are very apt to break during or after +cooling. + +To ensure that the tube shall be perfectly air-tight, a small piece of +white enamel should be attached to the glass at _a_ before sealing in +the wire. + + +=Uniting Pieces of Glass to Each Other, known as Welding, or +Soldering.=--The larger and more complicated pieces of glass apparatus +are usually made in separate sections, and completed by joining together +the several parts. This is therefore a very important operation, and +should be thoroughly mastered before proceeding to further work. + +In order to produce secure joints, the use of tubes made of different +kinds of glass must be avoided. Soda glass may be joined securely to +soda glass, especially if the tubes belong to the same batch, and lead +glass to lead glass. But, though by special care a joint between lead +glass and soda glass, if well made, will often hold together, yet it is +never certain that it will do so. + +_To join two Tubes of Equal Diameters._--Close one end of one of the +tubes with a small cork. Heat the open end of the closed tube, and +either end of the other tube in a small flame until they are almost +melted, taking care that only the ends of the tubes are heated, and not +to let the glass be thickened; bring the two ends together with +sufficient pressure to make them adhere, but not sufficient to compress +the glass to a thickened ring. Before the joint has time to cool too +much, adjust your blow-pipe for a pointed flame, if you are not already +working with that kind of flame, and allow the point of the flame to +play on any spot on the joint till it is heated to redness; rotate the +tube a little so as to heat the glass adjacent to that which is already +red-hot, and repeat this till the whole circumference of the rough joint +has been heated.[7] Repeat the operation last described, but, when each +spot is red-hot, blow gently into the open end of the tube so as to +slightly expand the viscous glass. Finally, rotate the whole joint in +the flame till the glass is softened, and blow gently as before into the +open end of the tube, still rotating it, in order that the joint may be +as symmetrical as possible. If in the last operation the diameter of the +joint becomes greater than that of the rest of the tube, it may be +cautiously re-heated and reduced by pulling it out, or this may be +secured by gently pulling apart the two ends, whilst the operator blows +it into its final shape. + +[7] Some glass-blowers at once work on the glass as next described, +without this preliminary treatment. I find that some glass, usually soda +glass, will not always bear the necessary movements without breaking +unless first heated all round. + +[Illustration: FIG. 14.] + +When small tubes, or tubes of fine bore, are to be joined, in order to +prevent the fused glass from running together and closing the tube, it +is a good plan to border and enlarge the ends that are to be united, as +at _A_ (Fig. 14). Some glass-blowers prefer to border all tubes before +uniting them. + +When a narrow tube is to be joined to one that is only slightly wider, +expand the end of the narrow tube till it corresponds in size to the +larger tube. If the tube be too narrow to be enlarged by inserting a +charcoal cone, seal one end and pierce it as directed (on p. 37). + +For joining small thin-walled tubes Mr. Crookes recommends the use of a +small Bunsen flame. + +In welding pieces of lead glass tube, take care that the heated glass is +perfectly free from reduced lead at the moment when the two ends of +viscous glass are brought into contact. + +[Illustration: FIG. 15.] + +_To join Tubes of Unequal Sizes End to End_ (Fig. 15).--Draw out the +larger tube and cut off the drawn-out end at the part where its diameter +is equal to that of the smaller tube, then seal the smaller tube to the +contracted end of the larger according to the directions given for +joining tubes of equal size. When a good joint has been made, the tube +presents the appearance of _A_, Fig. 15, the union being at about _bb_. +Next heat the whole tube between the dotted lines _aa_, and blow it into +the shape of _B_ in which the dotted line _dd_ should correspond to the +actual line of junction of the two tubes. + +In making all joints it is important to leave no thick masses of glass +about them. If the glass be fairly thin and uniformly distributed, it is +less likely to break during or after annealing under any circumstances, +and especially if it has to bear alternations of temperature. + +_Joining a Tube to the Side of another Tube_ (Fig. 16).--One of the +tubes must be pierced as at _A_ in Fig. 16 (for the method, see p. 37), +and its two ends closed with small pieces of cork. The edges of the +opening, and one end of the other tube, must then be heated till they +melt, and united by pressing them together. The joint may then be +finished as before. + +[Illustration: FIG. 16.] + +A properly blown joint will not present the appearance of _B_ (Fig. 16), +but rather that of _C_. This is secured by directing the pointed flame +upon the glass at _aa_ (_B_) spot by spot, and blowing out each spot +when it is sufficiently softened. If the tubes are large, the whole +joint should subsequently be heated and blown, but in the case of small +tubes this is of less importance. Finally it is to be wrapped whilst hot +in cotton wool for the annealing process. + +If a second tube has to be joined near to the first one, say at _b_, it +is well to proceed with it before the joint first made cools down, and +the joint first made, especially if soda glass be used, must be held in +the flame from time to time during the process of making the second +joint to keep it hot; if this be not done the first joint is very likely +to break. A joint previously made may, however, be re-heated, if well +made and well annealed. + +A three-way tube, like that in Fig. 17, is made by bending _A_ (Fig. 16) +to an angle, and joining _B_ to an opening blown on the convex side of +the angle; or, _A_ of Fig. 16 may be bent as desired after attaching _B_ +in the ordinary way. + +[Illustration: FIG. 17.] + +Tubes may also be joined to openings made in the sides of globes or +flasks; great care must be taken, however, especially if the walls of +the globe be thin, to secure that the tube is well attached to the mouth +of the opening when the melted ends are first brought into contact, for, +with thin glass, any hole that may be left will probably increase whilst +the joint is being blown into shape, owing to cohesion causing the glass +to gather in a thickened ring round an enlargement of the original +opening.[8] + +[8] If such an opening be observed, it may usually be closed by touching +its edges with a fused point of glass at the end of a drawn out tube. + +In order to unite a tube of soda glass to a tube of lead glass, the end +of the soda glass tube must be carefully covered with a layer of soft +arsenic glass.[9] This must be done so perfectly that when the ends to +be united are brought together the lead and soda glass are separated by +the enamel at every point. + +[9] This can be obtained from Messrs. Powells, Whitefriars Glassworks. + +_To Seal a Tube inside a Larger Tube or Bulb._--Suppose that an air-trap +(3 of Fig. 18) is to be constructed from a small bulb (_A_) blown on a +glass tube (1). + +[Illustration: FIG. 18] + +Either cut off the tube close to the bulb at _B_, or better, remove the +end by melting the glass and pulling it away from _B_, and then pierce +_A_ at _B_, No. 2, by heating the glass there and blowing out a small +bulb as described under Piercing. + +Prepare a tube (4) drawn out at _E_ with a bulb blown at _D_. Insert _E_ +into the opening _B_, press _D_ well against the mouth _B_ and slowly +rotate before the blow-pipe till _D_ adheres to _B_. Then heat and blow +the joint spot by spot as in other cases, taking care that the glass is +blown out on each side of the joint; lastly, heat the whole joint +between _aa_, and blow it into its final shape. + +These joints are very apt to break after a few minutes or hours if the +glass of _D_ be much thicker than that of the bulb _A_. They should be +wrapped in cotton wool for annealing as soon as possible, as the rate at +which the tube _E_ cools is likely to be less rapid than that of the +parts of the apparatus which are more freely exposed to the air; +therefore all such internal joints require very careful annealing, and +they should always be made as thin as is consistent with the use to +which they are to be put. + +Tubes may also be sealed into the ends or sides of larger tubes by +piercing them at the point at which the inserted tube is to be +introduced, and proceeding as in the case of the air-trap just +described. + +Ozone generators of the form shown on next page (Fig. 19), afford an +interesting example of the insertion of smaller tubes into larger. + +On account of the small space that may be left between the inner and +outer tubes of an ozone generator, and of the length of the inner tube, +its construction needs great care. I find the following mode of +procedure gives good results. Select the pieces of tube for this +instrument as free from curvature as possible. For the inner tube, a +tube 12 mm., or rather more, in external diameter, and of rather thin +glass, is drawn out, as for closing, until only a very narrow tube +remains at _C_, the end of _C_ is closed the area round _C_ is +carefully blown into shape, so that by melting off _C_ the tube _A_ will +be left with a well-rounded end. A small bulb of glass is next blown on +_A_ at _B_. This bulb must be of slightly greater diameter than the +contracted end _E_ of the larger tube (II.), so that _B_ will just fail +to pass through _E_. The length from _B_ to _C_ must not be made greater +than from _E_ to _G_ on the outside tube. The end at _C_ is then to be +cut off so as to leave a pin-hole in the end of _A_. + +[Illustration: FIG. 19.] + +The outer tube (II.), whose diameter may be 5 or 6 mm. greater than that +of _A_, is prepared by sealing a side tube on it at _F_, after +previously contracting the end _E_. For this purpose the end _E_ should +be closed and rounded, and then re-heated and blown out till the bulb +bursts. To ensure that the diameter of the opening is less than that of +the tube, care must be taken not to re-heat too large an area of the end +before blowing it out. It is very important that the cross section at +_E_ shall be in a plane at right angles to the axis of the tube. + +Wrap a strip of writing paper, one inch in breadth, closely round the +end of _A_ at _C_ till the tube and paper will only just pass easily +into the mouth _D_ of the outer tube, push the inner tube _A_, with the +paper upon it, into _D_, and when the paper is entirely within _D_, +withdraw _A_, and cautiously push the paper a little further into the +outer tube. Insert _A_ into _DE_ through _E_, so that the bulb _B_ is +embraced by _E_. Close _D_ with a cork. Ascertain that the paper does +not fit sufficiently tightly between the two tubes to prevent the free +passage of air, by blowing into the mouth _K_ of _A_. Air should escape +freely from _E_ when this is done. Gradually bring the line of contact +of _B_ and _E_ and the surrounding parts of the tube before a pointed +flame, after previously warming them by holding near a larger flame, and +rotate them before the flame so that the glass may soften and adhere. +Then heat the joint spot by spot as usual. In blowing this joint, take +care that the glass on each side of the actual joint is slightly +expanded. It should present the form shown by the dotted lines in III. +(these are purposely exaggerated, however). Finally, heat the whole +joint between the lines _JI_ till it softens, and simultaneously blow +and draw it into its final shape as seen at III. + +The side tube _F_ should not be too near the end _E_. If, however, it is +necessary to have them close together, the joint _F_ must be very +carefully annealed when it is made; it must also be very cautiously +warmed up before the construction of the joint at _H_ is begun, and must +be kept warm by letting the flame play over it from time to time during +the process of making the latter joint. + +A good joint may be recognised by its freedom from lumps of glass, its +regularity of curve, and by a sensibly circular line at _H_, where the +two tubes are united. + +When the joint after annealing has become quite cold, the pin-hole at +_C_ on the inner tube may be closed, after removing the paper support, +by warming the outer tube, and then directing a fine pointed flame +through _D_ on to _C_. And the end _D_ of the outer tube may be closed +in the ordinary manner, or a narrow tube may be sealed to it. As the end +of glass at _D_ will be too short to be held by the fingers when hot, +another piece of tube of similar diameter must be attached to it to +serve as a handle (see p. 35, Fig. 9). + + +=Blowing a Bulb or Globe of Glass.=--For this purpose it is very +important that the glass tube employed shall be of uniform substance. +The size and thickness of the tube to be employed depends partly on the +dimensions of the bulb desired, and partly on the size of neck that is +required for the bulb. It is easier to blow large bulbs on large-sized +tubes than on those of smaller size. When it is necessary to make a +large globe on a small tube, it can be done, however, if great care be +taken to avoid overheating that part of the small tube which is nearest +to the mass of viscous glass from which the bulb is to be formed. For +the purpose of blowing a very large bulb on a small tube, it is best to +unite a wide tube to that which is to serve as the neck, as it will save +some time in collecting the necessary mass of glass from which to form +the globe. + +[Illustration: FIG. 20.] + +_To blow a Bulb at the End of a Tube._--Select a good piece of tube, say +1.5 cm. in diameter, and about 30 cm. long; draw out one end to a light +tail (_a_, Fig. 20) about 3 inches in length. Then heat up a _short_ +length of the tube at _b_, with a small brush flame, by rotating the +glass in the flame, and gently press it together when soft to thicken +it; blow into it if necessary to preserve the regularity of its figure. +Repeat this process on the portion of tube nearest to that which has +been first thickened, and so on, till as much glass has been heated and +thickened as you judge will serve to make a bulb of the size desired. +You should have a mass of glass somewhat resembling that shown at _B_ +(Fig. 20), but probably consisting of the results of more successive +operations than are suggested in that diagram. Apply the flame as before +to the narrower parts _cc_ of _B_, gently compress and blow until all +the small bulbs first made are brought together into a mass still +somewhat resembling the enlarged end of _B_, but more nearly +cylindrical, with the glass as regularly distributed as possible, and of +such length from _d_ to the contracted part that the whole of it may +easily be heated simultaneously with the large brush flame of your +blow-pipe. Take great care in the foregoing operations not to allow the +sides of the mass of glass to fall in and run together, and, on the +other hand, do not reduce the thickness of the glass needlessly by +blowing it more than is necessary to give the glass as regular a form as +possible. When you are satisfied with the mass of glass you have +collected, melt off the tail _a_, and remove the pointed end of glass +that remains, as directed on page 33. Turn on as large a brush flame as +is necessary to envelop the whole mass of glass that you have collected, +and heat it with constant rotation, so that it may gradually run +together to the form seen at _C_ (Fig. 20), taking care that it does not +get overheated near _d_, or the tube which is to form the neck will +soften and give way. + +The position in which the mass of heated glass is to be held will depend +upon circumstances; if the mass of glass be not too great, it is best to +keep it in a nearly horizontal position. If the mass of glass be very +large, it may be necessary to incline the end _B_ downwards; but as that +is apt to result in an excess of glass accumulating towards _d_, avoid +doing so if possible by rotating the glass steadily and rapidly. If at +any time the glass shows indications of collapsing, it must be removed +from the flame and gently blown into shape, during which operation it +may be rotated in the perpendicular position; indeed, to promote a +regular distribution of the glass by allowing it plenty of time to +collect, it is well from time to time to remove the heated mass of glass +from the flame, and slightly expand it by blowing. Finally, when a +regular mass of glass, such as is shown at _C_ (Fig. 20) has been +obtained, remove it from the flame, and blow it to its final dimensions. +A succession of gentle puffs _quickly_ succeeding each other should be +employed, in order that the progress of the bulb may be more easily +watched and arrested at the right moment. During the process of blowing, +the hot glass must be steadily rotated. + +To collect the glass for blowing a bulb of lead glass, employ the flame +described on pp. 17-22 for heating lead glass. + +If the tube be held horizontally whilst the globe is blown, its form +will most nearly approach that of a true globe. If it be held in the +perpendicular position, with the mass of glass depending from it, the +form of the bulb will usually be somewhat elongated. If it be held +perpendicularly, with the mass of glass upwards, the resulting bulb will +be flattened. + +When a bulb is not of a sufficiently regular form, it may sometimes be +re-made by re-collecting the glass, and re-blowing it. The greatest care +is needed at the earlier stages of re-heating to prevent the glass from +collapsing into a formless and unworkable mass. This is to be prevented +in all such cases by gently blowing it into shape from time to time +whilst gathering the glass. + +[Illustration: FIG. 21.] + +_To blow a Bulb between two Points_ (Fig 21).--Select a piece of +suitable tube, seal or cork one end, gather together a mass of glass at +the desired part, as directed for blowing a bulb at the end of a tube; +when a mass of glass has been collected of sufficient thickness, blow it +into shape from the open end of the tube by a rapid succession of short +blasts of air, till the expanding glass attains the desired dimensions. +The tube must be held horizontally, and must be rotated steadily during +the process. By slightly pressing together the glass while blowing, the +bulb will be flattened; by slightly drawing apart the two ends of the +tube, it will be elongated. + +A pear-shaped bulb may be obtained by gently re-heating an elongated +bulb, say from _a_ to _a_, and drawing it out. It is easiest to perform +this operation on a bulb which is rather thick in the glass. + +If the tubes _bb_ are to be small, and a globe of considerable size is +wanted, contract a tube as shown in Fig. 22, taking care that the narrow +portions of the tube are about the same axis as the wider portions, for +if this be not the case, the mouths of the bulb will not be +symmetrically placed; seal at _C_, cut off the wider tube at _B_, and +make the bulb, as previously described, from the glass between _AA_. +If, as probably will be the case, the contracted portions of the tube be +not very regular, they may be cut off, one at a time, near the bulb, and +replaced by pieces of tube of the size desired. + +[Illustration: FIG. 22.] + +When a bulb has to be blown upon a very fine tube, for example upon +thermometer tubing, the mouth should not be employed, for the moisture +introduced by the breath is extremely difficult to remove afterwards. A +small india-rubber bottle or reservoir, such as those which are used in +spray-producers, Galton's whistles, etc., securely attached to the open +end of the tube, should be used. With the help of these bottles bulbs +can be blown at the closed ends of fine tubes with ease, though some +care is necessary to produce them of good shape, as it is difficult to +rotate the hot glass properly when working in this way. + + +=Making and Grinding Stoppers.=--Apparatus which is to contain chemicals +that are likely to be affected by the free admission of air, needs to +have stoppers fitted to it. Making a good stopper is a much less tedious +process than is commonly supposed. + +Suppose that the tube I. of Fig. 23 is to be stoppered at _A_, it must +be slightly enlarged by softening the end and opening it with a pointed +cone of charcoal; or a conical mouth for the stopper may be made by +slightly contracting the tube near one end, as at _B_, cutting off the +cylindrical end of the tube at the dotted line _C_, and then very +slightly expanding the end at _C_ with a charcoal cone after its edges +have been softened by heat. In either case the conical mouth should be +as long and regular as possible. + +[Illustration: FIG. 23.] + +For the stopper take a piece of rather thick tube, of such size that it +will pass easily, but not too easily, into _A_ or _B_. Expand this tube +at _D_, as shown in II., by softening the glass and gently compressing +it. The configuration of the enlarged tube as shown at _D_ may be +obtained by heating and compressing two or more zones of the tube that +are adjacent, one zone being less expanded than the other, so as to give +the sides of the imperfect stopper as nearly as possible the form shown +at _D_, which, however, is much less regular than may easily be +obtained. Seal off the head of the tube at _H_, and heat the glass till +it runs together into a nearly solid mass; compress this with a pair of +iron tongs to the flattened head _E_. In making _D_, aim at giving it a +form which will as nearly as possible correspond to that of the tube +into which it is to be ground, and make it slightly too large, so that +only the lower part at _D_ can be introduced into the mouth of _A_ or +_B_. Before it is ground, the stopper must be heated nearly to its +softening-point and annealed. + +Moisten _D_ with a solution of camphor in recently distilled +turpentine, and dust the wet surface with finely-ground emery, then +gently grind it into its place till it fits properly. In this operation +the tail _G_, which should fit loosely into the tube _A_, will be of +assistance by preventing _D_ from unduly pressing in any direction on +_A_ in consequence of irregular movements. The stopper should be +completely rotated in grinding it. It must not be worked backwards and +forwards, or a well-fitting stopper will not be produced. Renew the +emery and camphorated turpentine frequently during the earlier part of +the grinding; when the stopper almost fits, avoid using fresh emery, but +continue to remove the stopper frequently at all stages of the +operation. That added at the earlier stages will be reduced to a state +of very fine division, and will therefore leave the stopper and mouth of +_A_ with smoother surfaces than fresh emery.[10] + +[10] Mr. Gimmingham recommends giving stoppers a final polish with +rotten-stone (_Proceedings of the Royal Society_, p. 396, 1876). + +NOTE.--The addition of camphor to the turpentine used for grinding glass +is very important. Notwithstanding its brittle nature, glass will work +under a file moistened with this solution almost as well as the metals. +Small quantities should be made at a time, and the solution should be +kept in a well-closed vessel, for after long exposure to the air it is +not equally valuable. + +If the stopper is to fit a tube contracted like _B_, it must be +constructed from a piece of tube that will pass through the contraction +at _B_. The tail _GF_ will not do such good service as it does in the +case of a tube which has been opened out to receive its stopper, but it +will help to guide the stopper, and should be retained. + +When the stopper has been ground into its place, melt off the tail at +_F_. The flame must be applied very cautiously, as glass which has been +ground is particularly apt to crack on heating. To avoid all risk of +this, the tail may simply be cut off, and its edges filed smooth with a +file moistened freely with camphorated turpentine. + +The stoppers of bottles are not made exactly in the manner described +above, though, on occasion, a new stopper may be made for a bottle by +following those directions. Ill-fitting stoppers, which are very common, +can be very easily re-ground with emery and camphorated turpentine. + + + + +CHAPTER IV. + +_MAKING THISTLE FUNNELS, U-TUBES, ETC.--COMBINING THE PARTS OF +COMPLICATED APPARATUS--MERCURY, AND OTHER AIR-TIGHT JOINTS--VACUUM +TAPS--SAFETY TAPS--AIR-TRAPS._ + + +In Chapter III. the simpler operations used in making the separate parts +of which apparatus is composed have been described. In this Chapter +finished apparatus will be described, and the combination of the +separate parts into the more or less complicated arrangements used in +experiments will be so far explained as to enable the student to set up +such apparatus as he is likely to require. I have thought it would be +useful that I should add a short account of various contrivances that +have come much into use of late years for experimenting under reduced +pressure, such as safety taps, air-traps, vacuum joints, etc. + +[Illustration: FIG. 24.] + +=Electrodes.=--On page 38 (Fig. 13) is shown a simple form of electrode +sealed into a glass tube, which for many purposes answers very well. But +frequently, in order that there may be less risk of leakage between the +glass and the metal, the latter is covered for a considerable part of +its length with solid glass, which at one extremity is united to the +apparatus. In Fig. 24 _W_ is the metal core of the electrode, and _G_ +the glass covering around it. The wire is fused into the glass, and the +glass is then united to the apparatus; a little white enamel should be +applied at one end and combined with the glass by fusion. + + +=U-Tubes.=--A U-tube is but a particular case of a bent glass tube. It +is scarcely possible when bending very large tubes in the manner +described on p. 29 to produce regular curves of sufficient strength. + +To make a U-tube, or to bend a large tube, close one end of the tube +selected with a cork, soften and compress the glass in the flame at the +part where it is to be bent till a sufficient mass of glass for the bend +is collected, then remove the mass of glass from the flame, let it cool +a little, and simultaneously draw out the thickened glass, bend it to +the proper form, and blow the bend into shape from the open end of the +tube. Small irregularities may be partly corrected afterwards. + +To make a good U-tube of large size, and of uniform diameter from end to +end, requires much practice, but to make a tolerably presentable piece +of apparatus in which the two limbs are bent round till they are +parallel, without any considerable constriction at the bend, can be +accomplished without much difficulty.[11] + +[11] Large tubes may also be bent by rotating a sufficient length of the +tube in a large flame till it softens, and bending in the same manner as +in the case of smaller tubes, and after filling them with sand, closing +one end completely, and the other so that the sand cannot escape, though +heated air can do so. + + +=Spiral Tubes.=--These may be made by twisting a tube gradually softened +by heat round a metal cylinder. Spiral tubes made of small thin tubes +possess considerable elasticity, and have been used by Mr. Crookes for +making air-tight connections between separate pieces of apparatus when a +rigid connection would have been unnecessary and inconvenient. By the +use of such spiral tubes it is possible to combine comparatively free +movement with all the advantages attached to hermetically-sealed joints. + +To make a flexible spiral tube, mount a copper cylinder on a screw, so +that the cylinder will travel in the direction of its axis when it is +rotated. Fix a fine glass tube to the cylinder, and direct a flame +towards the cylinder so as to heat and soften the glass, which will then +bend to the form of the cylinder. Gradually rotate the cylinder before +the source of heat, so that fresh portions of tube are successively +brought into position, softened, and bent. Useful spirals may also be +made by hand without a cylinder. As each length of tube is bent, a fresh +length may be united to it until the spiral is completed. The fine tubes +employed are prepared by heating and drawing out larger tubes. + +[Illustration: FIG. 25.] + + +=Thistle Funnels= (Fig. 25).--Seal a moderately thick piece of small +glass tube at _A_, then heat a wide zone of it a little below _A_ by +rotating it horizontally in the blow-pipe flame till the glass softens, +and expand the glass to a bulb, as shown at _B_ of 1; during the +operation of blowing this bulb, the end _A_ must be directed to the +ground. + +Soften the end _A_ and a small portion of _B_ as before, and, holding +the tube horizontally from the mouth, blow out the end _C_ as at 2. Heat +the end of _C_ gradually, till the glass softens and collapses to the +dotted line _dd_, and at once blow a steady stream of air into the open +end of the tube, rotating it steadily, till it is about to burst; +finally clean off the thin glass from round the edges of the funnel, +which should have the form shown at 3, and round them. An inspection of +a purchased thistle funnel will generally show that the head _B_ has +been formed from a larger tube sealed to _E_ at _f_. + +[Illustration: FIG. 26.] + + +=Closing Tubes containing Chemicals= for experiments at high +temperatures.--Tubes of the hard glass used for organic analyses answer +best for this purpose; the operation of drawing out the end of such a +tube is practically identical with what has been described under the +head of choking, p. 35. A well-sealed tube presents the appearance of +that shown by Fig. 26. + +In order to secure a thick end to the point of the tube _a_, about an +inch or so of the tube near the contracted part should be warmed a +little, if it is not already warm, at the moment of finally sealing it; +the contraction of the air in the tube, in consequence of the cooling of +the warm tube, will then ensure the glass at _a_ running together to a +solid end when it is melted in the flame. + +If it will be necessary to collect a gas produced during a chemical +action from such a tube, make the contracted end several inches long, +and bend it into the form of a delivery tube. It will then be possible +to break the tip of this under a cylinder in a trough of liquid. + + +=In order to explain the construction of apparatus consisting of several +parts=, it will be sufficient to take as examples, two very well-known +instruments, and to describe their construction in detail. From what is +learned in studying these, the student will gather the information that +is wanted. + +[Illustration: FIG. 27.] + +1. _To make Hofman's Apparatus for the electrolysis of water_ (Fig. 27). + +Take two tubes about 35 cm. in length, and 14 mm. in diameter for _AA_, +join taps _TT_ to the end _B_ of each of them, draw out the other end, +as shown at _D_, after sheets of platinum foil with wires attached to +them[12] have been introduced into the tubes, and moved by shaking to +_BB_. Then allow the platinum wires to pass through the opening _D_ left +for the purpose, and seal the glass at _D_ round the platinum as at _E_. +Pierce the tubes at _JJ_, and join them by a short piece of tube _K_, +about 14 mm. in diameter, to which the tube _T_, carrying the reservoir +_R_, has been previously united. _R_ may be made by blowing a bulb from +a larger piece of tube attached to the end of _T_. The mouth _M_ of the +reservoir being formed from the other end of the wide tube afterwards. +One of the taps can be used for blowing through at the later stages. +Each joint, especially those at _JJ_, must be annealed after it is +blown. Some operators might prefer to join _AA_ by the tube _K_ in the +first instance, then to introduce the electrodes at _E_ and _D_. In some +respects this plan would be rather easier than the other, but, on the +whole, it is better to make the joints at _JJ_ last in order, as they +are more apt to be broken than the others during the subsequent +manipulations. + +[12] Red-hot platinum welds very well. The wire may be joined to the +sheet of foil by placing the latter on a small piece of fire-brick, +holding the wire in contact with it at the place where they are to be +united, directing a blow-pipe flame upon them till they are at an +intense heat, and smartly striking the wire with a hammer. The blow +should be several times repeated after re-heating the metal. + +2. I have before me the vacuum tube shown by Fig. 28, in which the +dotted lines relate to details of manipulation only. + +[Illustration: FIG. 28.] + +It is usually possible to detect the parts of which a piece of apparatus +has been built up, for even the best-made joints exhibit evidence of +their existence. Thus, although I did not make the tube that is before +me, and cannot therefore pretend to say precisely in what order its +parts were made and put together, the evidence which it exhibits of +joints at the dotted lines _A_, _B_, _C_, _D_, _E_, _F_, enables me to +give a general idea of the processes employed in its construction, and +to explain how a similar tube might be constructed. I should advise +proceeding as follows:-- + +Join a piece of tube somewhat larger than _M_ to its end _A_, draw out +the other end of the larger tube, and blow a bulb _L_ as directed on p. +47. Then seal the electrode _R_ into the bulb _L_ (p. 55). + +Blow a similar but larger bulb _N_ from a large piece of tube sealed +between two tubes of similar size to _M_, as described at p. 50. Cut off +one of the tubes at _B_, and join the bulb _N_ to _M_ at _B_. Form the +bulb _Q_ in the same manner as in the case of _L_, seal into it the +electrode _R_, and add the tube marked by the dotted lines at _F_. + +Seal a narrow tube _P_ to the end of a larger tube, and blow out the +tube at the joint till the glass is thin and regular. Take a tube _O_, +of similar size to _M_, slightly longer than _P_, contract its mouth +slightly to meet the wide end of _P_ at _D_, and after loosely +supporting _P_ inside _O_ with a cork, or otherwise, close the end _N_ +of _O_ by sealing or corking it, and join _P_ to _O_ at _D_. Cut off _O_ +just above _D_ at _E_, and join it to the bulb _Q_, closing either _O_ +or _F_ for the purpose. Cut off the end of _O_ at _C_ parallel to the +end of _P_, and connect _O_ to _N_, using _F_ for blowing the joint at +_C_. _F_ may be used subsequently for introducing any gas into the tube, +and, when a vacuum has been established, may be sealed before the +blow-pipe. + + +[Illustration: FIG. 29.] + +=Modes of combining the Parts of Heavy Apparatus.=--It is often +necessary to connect pieces of apparatus which are too heavy to be +freely handled before the blow-pipe, and which, therefore, cannot be +welded together as described on p. 39, by some more effective method +than the ordinary one of connecting by india-rubber tubing. For example, +apparatus which is to be exhausted by a Sprengel air-pump must be +attached to the pump by a joint as perfectly air-tight as can be +obtained. This, indeed, often may be done by welding the apparatus to be +exhausted to the air-pump before the blow-pipe. But such a method is +open to the obvious objection that it is very troublesome to connect and +disconnect the parts as often as may be necessary, and that there is +some risk of accidental breakages. Nevertheless it may be done on +occasion, especially if there be no objection to the use of the +flexible spiral tubes already alluded to. When the use of a spiral +connecting-tube is not admissible the difficulty is considerably +increased. For example, the author has lately required to attach an +ozone generator, of the form shown by Fig. 19, which previously had been +cemented into a heavy copper jacket, to a pressure-gauge rigidly fixed +to a support, and of considerable size. The employment of a flexible +spiral connection was prohibited by the fact that it was necessary that +the volume of the connecting-tube should be but a small fraction of that +of the ozone generator, a condition which compelled the use of a tube of +almost capillary bore, and of inconsiderable length. At the same time +the frailness of such a connection made it necessary to fix the +generator and pressure-gauge rigidly to their supports, in order to +avoid the possibility of breakage by slight accidental movements of +either of them, and it was obviously necessary to fix the pieces of +apparatus in their final positions before joining them, lest the fine +tube which connected them should be fractured during adjustment. The +possibility of a strain being caused by the contraction that would occur +during the cooling down of the joint last made had to be provided for +also. The desired object was effected as follows. In Fig. 29 _A_ +represents a section of the ozone generator at the point where the tube +to connect it to the gauge was fixed. _B_ represents the top of the +gauge, with the side tube _C_, which was to be connected with that from +_A_, viz. _D_. The ends of _C_ and _D_ were expanded as shown at _D_ (by +melting them and blowing them out), so that one of them, made rather +smaller than the other, could be overlapped by the larger one. _A_ and +_B_ being rigidly fixed in their final positions, with _C_ and _D_ in +contact, as shown in the figure, all openings in the apparatus were +closed, except one, to which was attached an india-rubber blowing-bottle +by means of a tube of india-rubber long enough to be held in the hand of +the operator, and to allow him to observe the operation of joining the +tubes at _D_. When everything was in readiness, a very small-pointed +flame from a moveable blow-pipe held in the hand was directed upon the +glass at _D_ till it melted and the two tubes united. To prevent the +fine tube when melted from running into a solid mass of glass, and so +becoming closed, a slight excess of pressure was maintained inside the +apparatus during the operation by forcing air into it with the +india-rubber blower from the moment at which _C_ and _D_ united. A point +of charcoal was kept in readiness to support the softened glass at _D_ +in case it showed any tendency to fall out of shape. + +The V-tube at _C_ served to prevent the subsequent fracture of the joint +in consequence of any strain caused by the contraction of the glass in +cooling.[13] + +[13] For a method of joining soda glass to lead glass, see p. 81. + +It is not difficult to connect several pieces of apparatus successively +in this manner, nor is this method only useful in such cases as that +just described. Pieces of apparatus of great length and weight may be +joined in a similar manner, irrespective of the size of the tubes to be +united. + +The ends to be joined, prepared as before, so that one slightly overlaps +the other, must be held firmly in contact by clamps, and heated in +successive portions by a blow-pipe held in the hand of the operator, +each patch of glass being re-heated and gently blown, after a rough +joint has been made. Finally, a larger flame may be used to heat up the +whole joint for its final blowing. It is important to place the +apparatus so that the operator has free access to it on all sides. A +revolving table might be employed. An assistant to work the bellows is +necessary. Or, better still, air may be admitted to the blow-pipe from a +large gas-bag placed in some convenient position. + +But in most cases one or other of the following air-tight joints can be +employed, and will be found to be very convenient:-- + +=Mercury Joints.=--The simplest form of mercury joint is shown at Fig. +30. _A_ and _B_ are the two tubes which are to be connected. A larger +tube or cup _F_ is attached to _A_ by the india-rubber tube _E_, and +placed on _A_ so that the end of _B_ may be brought into contact with +_A_ at _C_, and connected to it by a well-fitting piece of india-rubber +tube _C_. The cup _E_ is then brought into the position shown in Fig. +30, and mercury is introduced till the india-rubber tube at _C_ is +covered. As mercury and glass do not come into true contact, however, +such a joint, though said to give good results in practice, is not +theoretically air-tight, for air _might_ gradually find its way between +the liquid and the glass. By covering the mercury with a little +sulphuric acid or glycerine the risk of this occurring may be removed. +The same result may be attained by the use of glycerine in place of the +mercury in the cup _F_; but glycerine is less pleasant to work with than +mercury.[14] + +[14] If the india-rubber tube _C_ be secured by wires, iron wire, not +copper wire, should be employed. + +[Illustration: FIG. 30.] + +When sulphuric acid is to be employed in such a joint, or when for any +other reason the use of an india-rubber tube is undesirable, the joint +may consist of a hollow stopper _B_ (Fig. 31), made of glass tube, and +ground to fit the neck of a thistle funnel _A_. _A_ and _B_ are joined +respectively to the pieces of apparatus to be connected, and connection +is made by placing _B_ in position in the neck of _A_; the joint is made +air-tight by introducing mercury with strong sulphuric acid above it +into the cup _A_. The joint may be rendered air-tight by introducing +sulphuric acid only into the cup. But this plan must not be adopted if +the interior of the apparatus is to be exhausted, as sulphuric acid is +easily forced between the ground glass surfaces by external pressure. +Mercury, however, will not pass between well-ground glass surfaces, and +is therefore to be employed for connecting apparatus which is to be +exhausted, and, if necessary, protected by a layer of strong sulphuric +acid to completely exclude air. + +[Illustration: FIG. 31.] + +Tubes placed horizontally may be joined by a glycerine or mercury joint +such as is shown in Fig. 32. The two tubes _A_ and _B_ are joined as +before by an india-rubber connection _C_, or one may be ground to fit +the other, and the joint is then enclosed within a larger jacketing-tube +_D_, with a mouth at _F_, which is filled with glycerine or mercury. _D_ +is easily made by drawing out both ends of a piece of tube, leaving them +large enough to pass over the connection at _C_, however, and piercing +one side at _F_. + +[Illustration: FIG. 32.] + +=Vacuum Taps.=--It is not necessary to enter into a description of the +construction of ordinary glass taps, which can be purchased at very +reasonable prices. It may be remarked here, however, as a great many of +them are very imperfectly ground by the makers, that they may easily be +made air-tight by hand-grinding with camphorated turpentine and fine +emery, finishing with rotten-stone. A well-ground tap, which is well +lubricated, should be practically air-tight under greatly reduced +pressure for a short period; but when it is necessary to have a tap +which absolutely forbids the entrance of air into apparatus, one of the +following may be employed:-- + +[Illustration: FIG. 33.] + +[Illustration: FIG. 34.] + +(1.) _Mr. Cetti's Vacuum Tap_ (Fig. 34): This tap is cupped at _A_ and +sealed at _B_, and the cup _A_ is filled with mercury when the tap is in +use, so that if, for example, the end _C_ be attached to a flask, and +_D_ to an apparatus for exhausting the flask, it will be possible to +close the flask by turning off the tap _E_, and if no air be allowed +access through _D_, the vacuum produced in the flask at _C_ cannot be +affected by air leaking through the tap at _A_ or _B_. + +A passage _F_ must be drilled from the bottom of the plug _E_ to meet +_G_, in order that when the plug is in position no residue of air shall +be confined within _B_, whence it might gradually leak into any +apparatus connected to it. + +It is obvious, however, that this tap does not protect a flask sealed +to _C_ from the entrance of air through _D_, which, in fact, is the +direction in which air is most likely to effect an entrance. When using +one of these taps as part of an apparatus for supplying pure oxygen, I +have guarded against this by attaching a trap (Fig. 33) to the end _D_, +_C_ being joined to the delivery tube from the gas-holder. The structure +and mode of action of the trap are as follows:-- + +A narrow tube _G_ is joined to _D_ of Fig. 34, and terminates in the +wide tube _I_, which is connected above to _H_, and below to the +air-trap _J_. _J_ is connected at _K_, by a piece of flexible tube, to a +reservoir of mercury, from which mercury enters the air-trap, and +passing thence to _I_, can be employed for filling the V-trap _HLG_. The +air-trap _J_ is in the first instance filled with mercury, and then +serves to intercept any stray bubbles of air that the mercury may carry +with it. The particular form of the trap shown at _HLG_ was adopted +because with it the arm _LG_ is more readily emptied of mercury than +with any other form of trap made of small tube that I have tried. It has +been used in my apparatus in the following manner:--_H_ was connected +with a vessel to be filled with pure oxygen, the tap _E_ closed, and the +rise of mercury above _L_ prevented by a clamp on the flexible tube; the +vessel to be filled and the trap were then exhausted by a Sprengel pump, +and oxygen allowed to flow into the exhausted space by opening _E_, the +operation of exhausting the tubes and admitting oxygen being repeated as +often as necessary. + +To prevent access of air to _E_ on disconnecting the vessel at _H_, the +mercury was allowed to flow into the trap till it reached to _MM_. _E_ +was then closed, and _H_ exposed without danger of air reaching _E_, the +length of the arms of the trap being sufficient to provide against the +effects of any changes of temperature and pressure that could occur. + +A delivery tube may be connected to _H_ and filled with mercury, by +closing _E_ and raising the mercury reservoir. All air being in that +way expelled from the delivery tube, and the supply of mercury cut off +by clamping the tube from the reservoir, oxygen can be delivered from +the tube by opening _E_, when it will send forward the mercury, and pass +into a tube placed to receive it without any risk of air being derived +from the delivery tube. + +[Illustration: FIG. 35.] + +(2.) _Gimmingham's Vacuum Tap_,[15] shown in Fig. 35, consists of three +parts. A tube _A_ is ground to fit the neck of _B_. _B_ is closed at its +lower end, and has a hole _d_ drilled through it; when _B_ is fitted to +_C_, _d_ can be made to coincide with the slit _e_. When _A_, _B_, _C_ +are fitted together, if _d_ meet _e_, there is communication between any +vessels attached to _A_ and any other vessel attached to _C_, entrance +of external air being prevented by mercury being placed in the cups of +_C_ and _B_. The tap may be opened and closed at pleasure by rotating +_B_. + +[15] From _Proceedings of Royal Society_, vol. XXV. p. 396. + +If _A_ has to be removed, _C_ may be converted into a mercury joint _pro +tem._ by letting a little mercury from the upper cup fall into the tube +and cover _d_, the tap being closed. This mercury must be removed by a +fine pipette in order to use the tap again. It should be noted, however, +that though external air cannot enter by way of the ground glass joints, +there is no absolute protection against the passage of air between _A_ +and _C_, or vessels joined to _A_ and _C_, even when the tap is closed. +The passage of air from _A_ to _C_ depends upon the grinding and +lubrication of the joint at _C_. + + +=Lubricating Taps.=--For general purposes resin cerate answers very +well. In special cases burnt india-rubber, or a mixture of burnt +india-rubber and vaseline will answer well, or vaseline may be used +alone. Sulphuric acid and glycerine are too fluid. When a lubricant is +wanted that will withstand the action of ether, the tap may be +lubricated by sprinkling phosphorus pentoxide upon it, and exposing it +to air till the oxide becomes gummy. The joint must then be protected +from the further action of the air if possible. For example, if a safety +tap be used the cup may be filled with mercury. + +=Air-Traps.=--In Fig. 33, p. 66, an air-trap (_J_) is shown. An air-trap +is a device for preventing the mercury supplied to Sprengel pumps, etc., +from carrying air into spaces that are exhausted, or are for any reason +to be kept free from air. Figs. 36 and 37 give examples of air-traps. In +the simpler of the two (Fig. 36) mercury flowing upwards from _C_ that +may carry bubbles of air with it passes through the bulb _A_, which is +_filled_ with mercury before use.[16] Any air which accompanies the +mercury will collect at _a_, the mercury will flow on through _b_. So +long as the level of the mercury in A is above _b_, the trap remains +effective. + +[16] This may be done by clamping the tube which supplies mercury below +_C_, exhausting _A_, and then opening the clamped tube and allowing the +mercury to rise. + +[Illustration: FIG. 36.] + +[Illustration: FIG. 37.] + +In the trap shown by Fig. 37, the tube _d_, which corresponds to _b_ in +Fig. 36, is protected at its end by the cup _E_. _E_ prevents the direct +passage of minute bubbles of air through _d_. This trap, like the other, +must be filled with mercury before it is used, and it will then remain +effective for some time. + + + + +CHAPTER V. + +_GRADUATING AND CALIBRATING GLASS APPARATUS._ + + +Although the subjects to which this concluding chapter is devoted do +not, properly speaking, consist of operations in glass-blowing, they are +so allied to the subject, and of such great importance, that I think a +brief account of them may advantageously be included. + +=Graduating Tubes, etc.=--It was formerly the custom to graduate the +apparatus intended for use in quantitative work into parts of equal +capacity; for example, into cubic centimetres and fractions of cubic +centimetres. For the operations of volumetric analysis by liquids this +is still done. But for most purposes it is better to employ a scale of +equal divisions by length, usually of millimetres, and to determine the +relative values of the divisions afterwards, as described under +calibration. It rarely happens that the tube of which a burette or +eudiometer is made has equal divisions of its length of exactly equal +capacities throughout its entire length, and indeed, even for ordinary +volumetric work, no burette should be employed before its accuracy has +been verified. An excellent method for graduating glass tubes by +hand[17] has been described in Watts's _Dictionary of Chemistry_, and +elsewhere. Another excellent plan, which I have permission to describe, +has been employed by Professor W. Ramsay. It will be sufficient if I +explain its application to the operation of graduating a tube or strip +of glass in millimetre divisions. + +[17] Originally suggested by Bunsen. + +The apparatus required consists of a standard metre measure,[18] divided +into millimetres along each of its edges, with centimetre divisions +between them, a ruler adapted to the standard metre, as subsequently +explained, and a style with a fine point for marking waxed surfaces. + +[18] Such measures can be obtained of steel for about _fifteen +shillings_ each. They are made by Mr. Chesterman of Sheffield. They can +be obtained also from other makers of philosophical instruments, at +prices depending upon their delicacy. Those of the greatest accuracy are +somewhat costly. + +[Illustration: FIG. 38.] + +Fig. 38 represents the standard measure, and the ruler. + +At _AA_ are the millimetre divisions on the edges of the measure, the +longer transverse lines at _BB_ are placed at intervals of five +millimetres and of centimetres. The ruler is in the form of a +right-angled triangle; it is shown, by the dotted lines, in position on +the standard metre measure at _I_; and again, with its under surface +upwards, in the smaller figure at 2. It consists of a perfectly flat +sheet of metal, about ten centimetres in length from _C_ to _C_, +sufficiently thick to be rigid, and has a ledge, _DD_ in each figure, +which is pressed against the side of the measure when using it, to +ensure that the successive positions of the edge (_LL_) shall be +parallel to each other. At _GG_ are two small holes, into which fit +small screws with fine points. These must be in a line parallel to the +edge (_LL_), so that when the ruler is in position on the scale, the +points of the two screws, which project slightly, shall fall into +corresponding cuts on the divided scales (_AA_). + +To graduate a strip of glass, or a glass tube (_HH_), the surface to be +marked must first be coated with wax, which should be mixed with a +little turpentine, and be applied to the surface of the glass, +previously made _warm_ and _dry_, by means of a fine brush, so as to +completely cover it with a thin, closely-adherent, and +evenly-distributed coat of wax, which must be allowed to cool. + +Fix _HH_ firmly on a table, and fix the standard measure by the side of +_HH_. If the thickness of _HH_ be about equal to, but not greater than +that of the standard measure, this may be done by large drawing-pins. +If, however, a large tube or thick sheet of glass is to be graduated, +fix it in position by two strips of wood screwed to the table on each +side of it. One of these wooden strips, on which the measure may be +placed, may be about as broad as the standard measure, and of such +thickness that when the measure lies upon it beside the tube to be +graduated, the ruler, when moved along the measure, will move freely +above the tube, but will not be elevated more than is necessary to +secure free movement. The second strip of wood may be narrower, and of +the same thickness as the broader piece on which the standard measure +rests. In any case, let the standard measure and the object to be +graduated be very firmly secured in their places. Bring the ruler into +position at any desired part of the tube by placing the points of the +screws (_GG_) in corresponding divisions of the scales (_AA_). With the +style, which may be a needle mounted in a handle, make a scratch in the +wax along the edge of the ruler at _F_, move the ruler so that the +screws rest in the next divisions, and repeat the operation till the +required number of lines has been ruled. Longer marks may be made at +intervals of five and ten millimetres. Great care must be taken to hold +the needle perpendicularly, and to press it steadily against the edge +(_LL_) of the ruler in scratching the divisions.[19] The length of the +lines marking the millimetre divisions should not be too long; about 1 +mm. is a good length. If they are longer than this, the _apparent_ +distance between them is diminished, and it is less easy to read +fractions of millimetres. Before removing the scale to etch the glass, +carefully examine it to see that no mistakes have been made. If it is +found that any lines have been omitted, or that long lines have been +scratched in the place of short ones, remelt the wax by means of a +heated wire, and make new marks. Finally, mark the numbers on the scale +with a needle-point, or better, with a fine steel pen. + +[19] To avoid variations of the position in which the needle is held +when marking the divisions, the edge (_LL_) should not be bevelled; and +an upright support may be placed upon the ruler, with a ring through +which the handle of the needle passes, thereby securing that the angle +formed by the needle and surface of the ruler is constant, and that +equal divisions are marked. + +The marks on the wax should cut through it. When they are satisfactory, +they may be etched by one of the following processes:-- + +(1.) By moistening some cotton wool, tied to a stick, with solution of +hydrofluoric acid, and gently rubbing this over the scratched surface +for a minute or so; then washing away the acid with water, and cleaning +off the wax. This is the simplest method, but the marks made are +generally transparent, and therefore not very easy to read. The +simplicity of this method is a great recommendation, however. + +(2.) Expose the tube to the fumes of hydrofluoric acid generated from a +mixture of powdered fluor-spar and strong sulphuric acid, in a leaden +trough. The marks produced in this way are usually opaque, and are +therefore very visible, and easily read. + +After the above detailed account it will only be necessary to give an +outline of the other process of graduating tubes. + +[Illustration: FIG. 39.] + +The standard scale to be copied, _A_, which may in this case be another +graduated tube, or even a paper scale, and the object to be ruled, _B_, +are securely fixed, end to end, a little distance apart, in a groove +made in a board or in the top of a table. A stiff bar of wood, _C_, has +a point fixed at _D_, and a knife edge at _E_, _D_ is placed in any +division of _A_, _C_ is held firmly at _E_ and _D_, and a cut is made by +the knife through the wax on _B_, the point _D_ is then moved into the +next division, and the operation is repeated. To regulate the length and +position of the cuts, _B_ is usually held in position by two sheets of +brass projecting over the edges of the groove in which it lies; the +metal sheets have notches cut into them at the intervals at which longer +marks are to be made. + +When the scale is completed, the equality of the divisions in various +parts of it may be, to some extent, verified as follows:--Adjust a +compass so that its points fall into two divisions 5, 10, or 20 mm. +apart. Then apply the points of the compass to various parts of the +scale. In every part the length of a given number of divisions should be +exactly the same. The individual divisions should also be carefully +inspected by the eye; they should be sensibly equal. If badly ruled, +long and short divisions will be found on the scale. Very often a long +and a short division will be adjacent, and will be the more easily +observed in consequence. + +=To Divide a Given Line into Equal Parts.=--Occasionally it is necessary +to divide a line of given length into _x_ equal parts. For instance, to +divide the stem of a thermometer from the freezing-point to the +boiling-point into one hundred degrees. + +The following outline will explain how a line may be so divided. Suppose +the line _AB_ (Fig. 40) is to be divided into nine equal parts. Adjust a +hinged rule so that the points _A_ and _B_ coincide with the inside +edges of the limbs, one of them, _A_, being at the ninth division +(_e.g._ the ninth inch) of _CE_. Then if lines parallel to _ED_ be drawn +from each division of the scale to meet _AB_, _AB_ will be divided into +nine equal parts. + +[Illustration: FIG. 40.] + +A very convenient and simple arrangement on this principle for dividing +a line into any number of equal parts with considerable accuracy, is +described by Miss S. Marks in the _Proceedings of the Physical Society_, +July 1885.[20] One limb of a hinged rule _D_ is made to slide upon a +plain rule fixed to it; the plain rule carries needles on its under +surface which hold the paper in position. The position of the divided +rule and line to be divided being adjusted, the hinged rule is gently +pushed forwards, as indicated by the arrow in Fig. 40, till division +eight coincides with the line _AB_. A mark is made at the point of +coincidence, and division seven on the scale is similarly brought to the +line _AB_, and so on. The inner edge of _EC_ should have the divisions +marked upon it, that their coincidence with _AB_ maybe more accurately +noted. The joint _E_ must be a very stiff one. + +[20] Since this was printed I have observed that the above method is not +identical with that described by Miss Marks, but for ordinary purposes I +do not think it will be found to be inferior. + +A line drawn of given length or a piece of paper may be divided into any +given number of equal parts, and will then serve as the scale _A_ of +Fig. 39, p. 74, the thermometer or other object to be graduated taking +the place of _B_. + +Scales carefully divided according to any of the methods described will +be fairly accurate _if trustworthy instruments have been employed as +standards_. + +It will be found possible when observing the volume of a gas over +mercury, or the height of a column of mercury in a tube, to measure +differences of one-sixth to one-eighth of a millimetre with a +considerable degree of accuracy. To obtain more delicate measurements a +vernier[21] must be employed. + +[21] For the nature and use of the vernier, a treatise on Physics or +Physical Measurements may be consulted. + +=To Calibrate Apparatus.=--The glass tubes of which graduated apparatus +is made are, as already stated, very rarely truly cylindrical +throughout their entire lengths. It follows that the capacities of equal +lengths of a tube will usually be unequal, and therefore it is necessary +to ascertain by experiment the true values of equal linear divisions of +a tube at various parts of it. + +A burette may be calibrated by filling it with distilled water, drawing +off portions, say of 5 c.c. in succession, into a weighing bottle of +known weight, and weighing them. + +Great care must be taken in reading the level of the liquid at each +observation. The best plan is to hold a piece of white paper behind the +burette, and to read from the lower edge of the black line that will be +seen. Each operation should be repeated two or three times, and the mean +of the results, which should differ but slightly, may be taken as the +value of the portion of the tube under examination. + +If the weights of water delivered from equal divisions of the tube are +found to be equal, the burette is an accurate one, but if, as is more +likely, different values are obtained, a table of results should be +drawn up in the laboratory book showing the volume of liquid delivered +from each portion of the tube examined. And subsequently when the +burette is used, the volumes read from the scale on the burette must be +corrected. Suppose, for example, that a burette delivered the following +weights of water from each division of 5 c.c. respectively:-- + + C.C. Grams. + + 0 to 5 gave 4.90 + 5 " 10 " 4.91 + 10 " 15 " 4.92 + 15 " 20 " 4.93 + 20 " 25 " 4.94 + 25 " 30 " 4.95 + 30 " 35 " 4.96 + 35 " 40 " 4.97 + 40 " 45 " 4.98 + 45 " 50 " 4.99 + +and that in two experiments 20 c.c. and 45 c.c. respectively of a liquid +re-agent were employed. The true volumes calculated from the table would +be as 19.66 to 44.46. + +If the temperature remained constant throughout the above series of +experiments, and if the temperature selected were 4 deg. C., the weights of +water found, taken in grams, give the volumes in cubic centimetres, for +one gram of water at 4 deg. C. has a volume of one cubic centimetre. If the +temperature at which the experiments were made was other than 4 deg. C., and +if great accuracy be desired, a table of densities must be consulted, +with the help of which the volume of any weight of water at a known +temperature can be readily calculated. + +Pipettes which are to be used as measuring instruments should also have +the relation one to another of the volumes of liquid which they deliver +determined, and also the proportions these bear to the values found for +the divisions of the burettes in conjunction with which they will be +employed. + + +=To Calibrate Tubes for Measuring Gases.=--Prepare a small glass tube +sealed at one end and ground at the other to a plate of glass. The tube +should hold about as much mercury as will fill 10 mm. divisions of the +graduated tube. Fill this tube with mercury, removing all bubbles of air +that adhere to the sides by closing the open end of the tube with the +thumb, and washing them away with a large air-bubble left for the +purpose. If any persistently remain, remove them by means of a fine +piece of bone or wood. Then completely fill the tube with mercury, +removing any bubbles that may be introduced in the operation, and remove +the excess of mercury by placing the ground-glass plate on the mouth of +the tube, and pressing it so as to force out all excess of mercury +between the two surfaces. Clean the outside of the tube, and place it on +a small stand (this may be a small wide-mouthed glass bottle), with +which it has been previously weighed when empty, and re-weigh. Repeat +this operation several times. From the mean of the results, which should +differ one from another but very slightly, the capacity of the tube can +be calculated. + +The purest mercury obtainable should be used. Since the density of pure +mercury at 0 deg. C. is 13.596, the weight of mercury required to fill the +tube at 0 deg. C., taken in grams, when divided by 13.596, will give the +capacity of the tube at 0 deg. C. in cubic centimetres. If the experiment be +not made at 0 deg. C., and if a very exact determination of the capacity of +the tube be required, the density of mercury must be corrected for +expansion or contraction. + +Having now a vessel of known capacity, it can be employed for +ascertaining the capacities of the divisions of a graduated tube in the +following manner:--The graduated tube is fixed perpendicularly, mouth +upwards, in a secure position. The small tube of known capacity is +filled with mercury as previously described, and its contents are +transferred to the divided tube. The number of divisions which the known +volume of mercury occupies is noted after all air-bubbles have been +removed. This process is repeated until the divided tube is filled. A +table of results is prepared, showing the number of divisions occupied +by each known volume of mercury introduced. + +In subsequently using the tube the volumes of the gases measured in it +must be ascertained from the table of values thus prepared. + +In observing the level of the mercury, unless a cathetometer is +available, a slip of mirror should be held behind the mercury close to +the tube, in such a position that the pupil which is visible on the +looking-glass is divided into two parts by the surface of the mercury. + +A correction must be introduced for the error caused by the meniscus of +the mercury. As the closed end of the tube was downwards when each +measured volume of mercury was introduced, and as the surface of mercury +is convex, the volume of mercury in the tube when it is filled to any +division _l_ (Fig. 41) is represented by _A_ of 1. But in subsequently +measuring a gas over mercury in the same tube, when the mercury stands +at the same division _l_, the volume of the gas will be as represented +by _B_ of 2, which is evidently somewhat greater than _A_. This will be +seen still more clearly in 3, where _a_ represents the boundary of the +mercury, and _b_ the boundary of the air, when the tube is filled to the +mark _l_ with mercury or a gas over mercury respectively. + +[Illustration: FIG. 41.] + +It is plain that when the level of the mercury in measuring a gas is +read at _l_, the volume of the gas is greater than the volume of the +mercury recorded, by twice the difference between the volume _A_ of +mercury measured, and that which would fill the tube to the level _l_, +if its surface were plane. + +The usual mode of finding the true volume of a gas collected over +mercury is as follows:-- + +Place the graduated tube mouth upwards, introduce some mercury, and, +after removing all bubbles, note the division at which it stands. Then +add a few drops of solution of mercuric chloride; the surface of the +mercury will become level, read and record its new position. Then, in +any measurement, having observed that the mercury stands at _n_ +divisions of the tube, add twice the difference between the two +positions of the mercury to _n_, and ascertain the volume which +corresponds to this reading from the table of capacities. + + +=To Calibrate the Tube of a Thermometer.=--Detach a thread of mercury +from half an inch to one inch in length from the body of the mercury. +Move it from point to point throughout the length of the tube, and note +its length in each position. If in one part it occupies a length of tube +corresponding to eight degrees, and at another only seven degrees, then +at the former point the value of each division is only seven-eighths of +those at the latter position. + +From the results obtained, a table of corrections for the thermometer +should be prepared. + +It is sometimes necessary to join soda glass to lead glass. In this case +the edge of the lead glass tube may be bordered with white enamel before +making the joint. Enough enamel must be used to prevent the lead and +soda glasses from mingling at any point. The enamel is easily reduced, +and must be heated in the oxidising flame. Dr. Ebert recommends _Verre +d'urane_ for this purpose. It is supplied by Herr Goetze of Leipzig +(Liebigstrasse). + + + + +CHAPTER VI. + +_GLASS TUBING._ + + +The diagrams given below show the sizes and thickness of the glass tubes +most frequently required. In ordering, the numbers of these diagrams may +be quoted, or the exact dimensions desired may be stated. + +Glass tubes are usually sold by weight, and therefore the weight of tube +of each size that is wished for should be indicated, and also whether it +is to be of lead or soda glass. + +[Illustration] + +[Illustration] + + + + +CHAPTER VII. + +_VITREOUS SILICA._ + + +=Introductory.=--Vitreous Silica was made in fine threads by M. Gaudin +in 1839,[22] and small tubes of it were made in 1869 by M. A. Gautier, +but its remarkable qualities were not really recognised till 1889, when +Professor C. V. Boys rediscovered the process of making small pieces of +apparatus of this substance, and used the torsion of "quartz fibres" for +measuring small forces. More recently the author of this book has +devised a process for preventing the "splintering" of quartz which gave +so much trouble to the earlier workers, and jointly with Mr. H. G. +Lacell, has produced a variety of apparatus of much larger dimensions +than had been attempted =previously=. At the time of writing we can +produce by the processes described in the following pages tubes 1 to 1.5 +cm. in diameter and about 750 cm. in length, globes or flasks capable of +containing about 50 cc., masses of vitreous silica weighing 100 grams or +more, and a variety of other apparatus. + +[22] A brief summary of the history of this subject will be found in +_Nature_, Vol. 62, and in the Proceedings of the Royal Institution, +1901. + + +=Properties of Vitreous Silica.=--For the convenience of those who are +not familiar with the literature of this subject, I may commence this +chapter with a brief account of the properties and applications of +vitreous silica, as far as they are at present ascertained. Vitreous +silica is less hard than chalcedony, but harder than felspar. Tubes and +rods of it can be cut with a file or with a piece of sharpened and +hardened steel, and can afterwards be broken like similar articles of +glass. Its conducting power is low, and Mr. Boys has shown that fine +fibres of silica insulate remarkably well, even in an atmosphere +saturated with moisture. The insulating qualities of tubes or rods of +large cross sections have not yet been fully tested; one would expect +them to give good results provided that they are kept scrupulously +clean. A silica rod which had been much handled would probably insulate +no better than one of glass in a similar condition. The density of +vitreous silica is very near to that of ordinary amorphous silica. In +the case of a small rod not absolutely free from minute bubbles it was +found to be 2.21. + +Vitreous silica is optically inactive, when homogeneous, and is highly +transparent to ultraviolet radiations. + +The melting point of vitreous silica cannot be definitely stated. It is +plastic over a considerable range of temperature. Professor Callendar +has succeeded in measuring the rate of contraction of fine rods in +cooling from 1200 deg. to 1500 deg. C., so that its plasticity must be very +slight below the latter temperature. If a platinum wire embedded in a +thick silica tube be heated from without by an oxy-hydrogen flame the +metal may be melted at temperatures at which the silica tube will retain +its form for a moderate length of time, but silica softens to a marked +extent at temperatures a little above the melting point of platinum. + +It has been observed by Boys, Callendar, and others that fine rods of +silica, and also the so-called "quartz fibres," are apt to become +brittle after they have been heated to redness. But I have not observed +this defect in the case of more massive objects, such as thick rods or +tubes; and as I have repeatedly observed that mere traces of basic +matter, such as may be conveyed by contact with the hand, seriously +injure the surface of silica, and have found that silica quickly becomes +rotten when it is heated to about 1000 deg. in contact with an infusible +base such as lime, I am disposed to ascribe the above-mentioned +phenomenon to chemical rather than to purely physical causes.[23] It is +certain, however, that silica apparatus must never be too strongly +heated in contact with basic substances. Silica is easily attacked by +alkalis and by lime, less readily by copper oxide, and still less by +iron oxide. + +[23] In a recent communication Professor Callendar tells me that the +devitrification commences at the outside and is hastened by particles of +foreign matter. + +The rate of expansion of vitreous silica has been studied by H. le +Chatelier, and more recently by Callendar. The former found its mean +coefficient of expansion to be 0.0000007 between 0 deg. and 10000 deg.,[24] and +that it contracted when heated above 700 deg.. + +[24] The silica blocks used were prepared by fusion in an electric +furnace; it is therefore probable that they were not quite pure. + +Professor Callendar used rods of silica prepared by the author from +"Brazil crystal"; these were drawn in the oxy-gas flame and had never +been heated in contact with solid foreign matter, so that they +consisted, presumably, of very pure silica. His results differ in some +respects from those obtained by Le Chatelier, for he finds the mean +coefficient of expansion to be only 0.00000059, _i.e._ about one +seventeenth as great as that of platinum. Callendar found the rods of +silica expanded very regularly up to 1000 deg. but less regularly above that +temperature. Above 1200 deg. they contracted when heated. + +The behaviour of vitreous silica under sudden changes of temperature is +most remarkable. Large masses of it may be plunged suddenly when cold +into the oxy-gas flame, and tubes or rods at a white heat may be thrust +into cold water, or even into liquid air, with impunity. As a +consequence of this, it is in one respect much more easily worked in the +flame than any form of glass. Difficult joints can be thrust suddenly +into the flame, or removed from it, at any stage, and they may be heated +unequally in different parts with impunity. It is safe to say that +joints, etc., in silica never crack whilst one is making them nor during +the subsequent cooling. They may be set aside in an unfinished state and +taken up again without any precautions. Therefore it is possible for an +amateur to construct apparatus in silica which he would be quite unable +to produce from glass. + +The behaviour of vitreous silica with solvents has not yet been fully +investigated, but Mr. H. G. Lacell has this subject in hand. If it +behaves like the other forms of anhydrous silica it will withstand the +action of all acids except hydrofluoric acid. It is, of course, very +readily acted upon by solutions of alkalis and alkaline salts. + +As regards the use of silica in experiments with gases, it must be +remarked that vitreous silica, like platinum, is slightly permeable to +hydrogen when strongly heated. One consequence of this is that traces of +moisture are almost always to be found inside recently-made silica tubes +and bulbs, however carefully we may have dried the air forced into them +during the process of construction. Owing to the very low coefficient of +expansion of silica, it is not possible to seal platinum wires into +silica tubes. Nor can platinum be cemented into the silica by means of +arsenic enamel, nor by any of the softer glasses used for such purposes. +I have come near to success by using kaolin, but the results with this +material do not afford a real solution of the problem, though they may +perhaps point to a hopeful line of attack. Possibly platinum wires might +be soldered into the tubes (see _Laboratory Arts_, R. Threlfall), but +this also is uncertain. + +The process of preparing silica tubes, etc., from Lumps of Brazil +Crystal may be described conveniently under the following headings. I +describe the various processes fully in these pages, as those who are +interested in the matter will probably wish to try every part of the +process in the first instance. But I may say that in practice I think +almost every one will find it advantageous to start with purchased +silica tubes, just as a glass-worker starts with a supply of purchased +glass tubes. The manufacturer can obtain his oxygen at a lower price +than the retail purchaser, and a workman who gives much time to such +work can turn out silica tube so much more quickly than an amateur, that +I think it will be found that both time and money can be saved by +purchasing the tube. At the same time the beginner will find it worth +while to learn and practise each stage of the process at first, as every +part of the work described may be useful in the production of finished +apparatus from silica tubes. + +This being so, I am glad to be able to add that a leading firm of +dealers in apparatus[25] has commenced making silica goods on a +commercial scale, so that the new material is now available for all +those who need it or wish to examine its properties. + +[25] Messrs. Baird and Tatlock. + + +=Preparing non-splintering Silica from Brazil Pebble.=--The best variety +of native Silica is Brazil Pebble, which may be obtained in chips or +larger masses. These should be thoroughly cleaned, heated in boiling +water, and dropped into cold water, the treatment being repeated till +the masses have cracked to such an extent that they may be broken easily +by blows from a clean steel pestle or hammer. + +The fragments thus produced must be hand-picked, and those which are not +perfectly free from foreign matter should be rejected. The pure and +transparent pieces must then be heated to a yellow-red heat in a covered +platinum dish in a muffle or reverberatory furnace and quickly plunged +into a deep clean vessel containing clean distilled water; this process +being repeated, if necessary, till the product consists of semi-opaque +friable masses, very much like a white enamel in appearance. After these +have been washed with distilled water, well drained and dried, they may +be brought into the hottest part of an oxy-gas flame safely, or pressed +suddenly against masses of white hot silica without any preliminary +heating, such as is necessary in the case of natural quartz. Quartz +which has not been submitted to the above preparatory process, splinters +on contact with the flame to such an extent that very few would care to +face the trouble and expense of working with so refractory a material. +But after the above treatment, which really gives little trouble, all +the difficulties which hampered the pioneer workers in silica disappear +as if by magic. + + +=Apparatus.=--Very little special apparatus need be provided for working +with silica, but it is absolutely essential to protect the eyes with +very dark glasses. These should be so dark as to render it a little +difficult to work with them at first. If long spells of work are +undertaken, two pairs of spectacles should be provided, for the glasses +quickly become hot enough to cause great inconvenience and even injury +to the eyes. + +Almost any of the available oxy-gas burners may be used, but they vary +considerably in efficiency, and it is economical to obtain a very +efficient burner. The 'blow-through' burners are least satisfactory, and +I have long since abandoned the use of them. Some of the safety +'mixed-gas jets' have an inconvenient trick of burning-back, with sharp +explosions, which are highly disconcerting, if the work be brought too +near the nozzle of the burner. I have found the patent burner of Mr. +Jackson (Brin's Oxygen Company, Manchester) most satisfactory, and it +offers the advantage that several jets can be combined in a group easily +and inexpensively for work on large apparatus. The large roaring flames +such as are used, I understand, for welding steel are very expensive, +and not very efficient for the work here described. + + +=The method of making Silica Tubes.=--Before commencing to make a tube a +supply of vitreous silica in rods about one or two millimetres in +diameter must be prepared. To make one of these, hold a fragment of the +non-splintering silica described above in the oxy-gas flame by means of +forceps tipped with platinum so as to melt one of its corners, press a +small fragment of the same material against the melted part till the two +adhere and heat it from below upwards,[26] till it becomes clear and +vitreous, add a third fragment in a similar manner, then a fourth, and +so on till an irregular rod has been formed. Finally re-heat this rod in +sections and draw it out whilst plastic into rods or coarse threads of +the desired dimensions. If one works carefully the forceps do not suffer +much. I have had one pair in almost constant use for several years; they +have been used in the training of five beginners and are still +practically uninjured. + +[26] This is to avoid bubbles in the finished glass. + +The beginner should work with a gauge and regulator on the bottle of +oxygen, and should watch the consumption of oxygen closely. A large +expenditure of oxygen does not by any means necessarily imply a +corresponding output of silica, even by one who has mastered the initial +difficulties. + +When a supply of the small rods of vitreous silica has been provided, +bind a few of them round a rod of platinum (diameter say, 1 mm.) by +means of platinum wires at the two ends and heat the silica gradually, +beginning at one end after slightly withdrawing the platinum core from +that end, till a rough tube about four or five centimetres in length has +been formed. Close one end of this, expand it, by blowing, into a small +bulb, attach a silica rod to the remote end of the bulb, re-heat the +bulb and draw it out into a fine tube. Blow a fresh bulb on one end of +this and again draw it out, proceeding in this way till you have a tube +about six or eight centimetres in length. All larger tubes and vessels +are produced by developing this fine tube suitably. + + +=Precautions.=--The following points must be carefully kept in mind, +both during the making of the first tube and afterwards:-- + +(1) The hottest spot in the oxy-gas flame is at a point very near the +tip of the inner cone of the flame, and silica can be softened best at +this hot spot. The excellence of a burner does not depend on the size of +its flame, so much as on the temperature of its "hot spot," and the +success of the worker depends on his skill in bringing his work exactly +to this part of the flame. Comparatively large masses of silica may be +softened in a comparatively small jet if the hot spot is properly +utilised. + +(2) Silica is very apt to exhibit a phenomenon resembling +devitrification during working. It becomes covered with a white +incrustation, which seems to be comparatively rich in alkali.[27] This +incrustation is very easily removed by re-heating the whitened surface, +provided that the material has been kept scrupulously clean. If the +silica has been brought into the flame when dusty, or even after much +contact with the hands of the operator, its surface is very apt to be +permanently injured. _Too much attention cannot be given to cleanliness +by the workman._ + +[27] The rock crystal exhibits a yellow flame when first heated in the +oxy-gas flame, and most samples contain spectroscopic quantities of +lithium. + +(3) When a heated tube or bulb of silica is to be expanded by blowing, +it is best not to remove it from the flame, for if that is done it will +lose its plasticity quickly unless it be large. The better plan is to +move it slightly from the "hot spot" into the surrounding parts of the +flame at the moment of blowing. + +It is best to blow the bulb through an india-rubber tube attached to the +open end of the silica tube. At first one frequently bursts the bulbs +when doing this, but holes are easily repaired by stopping them with +plastic silica applied by the softened end of a fine rod of silica and +expanding the lump, after re-heating it, by blowing. After a few hours' +practice these mishaps gradually become rare. + +I find it a good plan to interpose a glass tube packed with granulated +potash between the mouth and the silica tube. This prevents the interior +of the tube from being soiled. The purifying material must not be packed +so closely in the tube as to prevent air from passing freely through it +under a very low pressure. + +It may be mentioned here that a finished tube usually contains a little +moisture, and a recognisable quantity of nitric peroxide. These may be +removed by heating the tube and drawing filtered air through it, but not +by washing, as it is difficult to obtain water which leaves no residue +on the silica. + + +=Making larger tubes and other apparatus of Silica.=--In order to +convert a small bulb of silica into a larger one or into a large tube, +proceed as follows:--Heat one end of a fine rod of silica and apply it +to the bulb so as to form a ring as shown in the figure. Then heat the +ring and the end of the bulb till it softens, and expand the end by +blowing. If this process is repeated, the bulb first becomes ovate and +then forms a short tube which can be lengthened at will, but the most +convenient way to obtain a very long tube is to make several shorter +tubes of the required diameter, and say 200 to 250 mm. in length, and to +join these end to end. It does not answer to add lumps of silica to the +end of the bulb, for the sides of the tube made in this way become too +thin, and blow-holes are constantly formed during the making of them. +These can be mended, it is true, but they spoil the appearance of the +work. + +[Illustration] + +Tubes made in the manner described above are thickened by adding rings +of silica and blowing them when hot to spread the silica. If a +combination of several jets is employed, very large tubes can be +constructed in this way. One of Messrs. Baird and Tatlock's workmen +lately blew a bulb about 5 cm. in diameter, and it was clear that he +could have converted it into a long cylindrical tube of equal diameter +had it been necessary to do so. + +Very thin tubes of 1.5 cm. diameter, and tubes of considerable thickness +and of equal size, are easily made after some practice, and fine +capilliaries and millimetre tube can be made with about equal readiness. + +If a very fine tube of even bore is required, it may be drawn from a +small thick cylinder after a little practice. + +When a tube becomes so large that it cannot be heated uniformly on all +sides by rotating it in the flame, it is convenient to place a sheet of +silica in front of the flame a little beyond the object to be heated, in +order that the former may throw back the flame on those parts of the +tube which are most remote from the jet. A suitable plate may be made by +sticking together small lumps of silica rendered plastic by heat. + +The silica tubes thus made can be cut and broken like glass, they can be +joined together before the flame, and they can also be drawn into +smaller tubes when softened by heat. + +In order to make a side connection as in a T piece, a ring of silica +should be applied to the tube in the position fixed upon for the joint. +This ring must then be slightly expanded, a new ring added, and so on, +till a short side tube is formed. To this it is easy to seal a longer +tube of the required dimensions. It is thus possible to produce Geissler +tubes, small distilling flasks, etc. Solid rods of silica are easily +made by pressing together the softened ends of the fine rods or threads +previously mentioned. Such rods and small masses can be ground and +polished without annealing them. + + +=Quartz Fibres.=--These were introduced into physical work by Mr. Boys +in 1889. They may be made by attaching a fine rod of vitrified quartz to +the tail of a small straw arrow provided with a needle-point; placing +the arrow in position on a cross-bow, heating the rod of silica till it +is thoroughly softened and then letting the arrow fly from the bow, when +it will carry with it an extremely fine thread of silica. A little +practice is necessary to ensure success, but a good operator can +produce threads of great tenacity and great uniformity. Fuller accounts +of the process and of the various properties and uses of quartz fibres +will be found in Mr. Boys' lectures (Roy. Inst. Proc. 1889, and Proc. +Brit. Assn. 1890), and in Mr. Threlfall's Laboratory Arts. + + + + + INDEX. + + + Air-traps, 69. + Annealing, 23. + Apparatus needed for Glass-working, 11. + Appendix, 82. + + Beginners, Failures of, 22. + Bellows, Position of, 3. + ---- Various forms of, 7. + _See also_ Blower. + Bending Glass Tubes, 28. + Blower, Automatic, 8. + Blow-pipe, Cheap form of, 4. + ---- Dimensions of, 4-5. + ---- Fletcher's Automaton, 6. + ---- Fletcher's Compound, 6. + ---- Gimmingham's, 6. + ---- Herapath's, 6. + ---- Jets for the, 7. + ---- Use of the, 8. + _See also_ Flames. + Blow-pipes, Use of several in combination, 21. + Brush Flame, 9. + ---- Oxidising, 20. + Bulbs, Methods of blowing, 47. + + Calibrating Apparatus, 76-81. + Camphorated Turpentine, 11. + Cetti's Vacuum Tap, 66. + Charcoal Pastils, 11. + Choking or Contracting the Bores of Tubes, 35. + Combining the Parts of Complicated Apparatus, 61. + Combustion Tube, how to work it, 25. + Contracting the Bore of a Tube, 35. + Cotton Wool for Annealing, 24. + Cutting Glass Tubes, 26, 27, 28. + + Dividing a Line into Equal Parts, 75. + + Electrodes, 38, 55. + Electrolysis, Making Apparatus for, 59. + + Files for Cutting Glass, 27. + Flame, the Pointed, 8. + ---- the Brush, 9. + ---- the Oxidising Brush, 20. + ---- the Smoky, 10. + Fletcher's Automaton Blow-pipe, 6. + Fletcher's Compound Blow-pipe, 6. + Funnels, Thistle-headed, 57. + + Gimmingham's Blow-pipe, 6. + Gimmingham's Vacuum Tap, 68. + Glass, Annealing, 23. + ---- Devitrification of, 15. + ---- Method of Working with Lead, 17. + ---- Method of Working with Soda, 22. + ---- Nature of, 12. + ---- Presenting to the Flame, 16. + Glass Tubes, Bending, 28. + ---- Bordering, 31. + ---- Characters of good, 14. + ---- Choking, 35. + ---- Cleaning, 15. + Glass Tubes, Cutting, 26, 27, 28. + ---- Piercing, 37. + ---- Purchase of, 12. + ---- Sealing, 32. + ---- Sealing Hermetically, 58. + ---- Sizes of, 82. + ---- Welding or Soldering, 39, 62. + ---- Widening the Ends of, 36. + Graduating Apparatus, 70. + Grinding Stoppers, 51. + + Herapath's Blow-pipe, 6. + Hofman's Apparatus for Electrolysis, 59. + + Inside Joints, 43. + + Jets for Blow-pipes, 7. + Joints, Air-tight, 64. + + Lead Glass, Method of Working with, 17. + Lead Glass, Blackening of, 17. + Light, Effect of, in Working, 3. + Line, to Divide into Equal Parts, 75. + + Mercury Joints, Various, 64. + + Non-splintering Silica, Preparation of, from Quartz, 88. + + Ozone Generator, To Make an, 44. + + Pastils of Charcoal, 11. + Piercing Tubes, etc., 37. + Platinum Electrodes, Sealing in, 38, 55. + Pointed Flame, the, 9. + + Quartz Fibres, 94. + + Rounding Ends of Tubes, 31. + + Sealing or Closing Openings in Tubes, 32. + Side-tubes, Fixing, 41. + Smoky Flame, 10. + Soda Glass, Method of Working, 22. + Soldering or Welding, 39, 62. + Spiral Tubes, 56. + Stoppers, Making and Grinding, 51. + + Table for Glass-blower, 3. + Taps, Vacuum, 65. + Thistle-headed Funnels, 57. + Traps, Air, 69. + Tube, Combustion, how to work it, 25. + Tubes. _See_ Glass Tubes. + ---- T-, 41. + ---- U-, 56. + Turpentine, Camphorated, for Grinding, 11. + + U-Tubes, 56. + + Vacuum Taps, 65-68. + ---- Tube, To Make a, 60. + Vitreous Silica, Apparatus required for Making, 89. + ---- Behaviour under sudden changes of Temperature, 87. + ---- Bulbs, etc., Making Joints on, 93. + ---- Expansion of, 86. + ---- Hardness of, 85. + ---- Insulating Power of, 85. + ---- Melting Point of, 85. + ---- Permeability to Gases, 87. + ---- Properties of, 84. + ---- Rods, Making Joints on, 94. + ---- Tubes, Method of Making, 90. + ---- Tubes, Making Joints on, 94. + + Welding or Soldering Tubes together, 39, 62. + White Enamel, Uses of, 39, 56. + Widening the Ends of Tubes, 36. + Working-place, 2. + + + + + Printed by T. and A. CONSTABLE, Printers to His Majesty + at the Edinburgh University Press, Scotland + + + + + +End of the Project Gutenberg EBook of The Methods of Glass Blowing and of +Working Silica in the Oxy-Gas Flame, by W. A. Shenstone + +*** END OF THIS PROJECT GUTENBERG EBOOK THE METHODS OF GLASS BLOWING *** + +***** This file should be named 33941.txt or 33941.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/3/9/4/33941/ + +Produced by Harry Lame and the Online Distributed +Proofreading Team at http://www.pgdp.net (This file was +produced from images generously made available by The +Internet Archive/American Libraries.) + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. Special rules, +set forth in the General Terms of Use part of this license, apply to +copying and distributing Project Gutenberg-tm electronic works to +protect the PROJECT GUTENBERG-tm concept and trademark. Project +Gutenberg is a registered trademark, and may not be used if you +charge for the eBooks, unless you receive specific permission. If you +do not charge anything for copies of this eBook, complying with the +rules is very easy. You may use this eBook for nearly any purpose +such as creation of derivative works, reports, performances and +research. They may be modified and printed and given away--you may do +practically ANYTHING with public domain eBooks. Redistribution is +subject to the trademark license, especially commercial +redistribution. + + + +*** START: FULL LICENSE *** + +THE FULL PROJECT GUTENBERG LICENSE +PLEASE READ THIS BEFORE YOU DISTRIBUTE OR USE THIS WORK + +To protect the Project Gutenberg-tm mission of promoting the free +distribution of electronic works, by using or distributing this work +(or any other work associated in any way with the phrase "Project +Gutenberg"), you agree to comply with all the terms of the Full Project +Gutenberg-tm License (available with this file or online at +http://gutenberg.org/license). + + +Section 1. General Terms of Use and Redistributing Project Gutenberg-tm +electronic works + +1.A. By reading or using any part of this Project Gutenberg-tm +electronic work, you indicate that you have read, understand, agree to +and accept all the terms of this license and intellectual property +(trademark/copyright) agreement. If you do not agree to abide by all +the terms of this agreement, you must cease using and return or destroy +all copies of Project Gutenberg-tm electronic works in your possession. +If you paid a fee for obtaining a copy of or access to a Project +Gutenberg-tm electronic work and you do not agree to be bound by the +terms of this agreement, you may obtain a refund from the person or +entity to whom you paid the fee as set forth in paragraph 1.E.8. + +1.B. "Project Gutenberg" is a registered trademark. It may only be +used on or associated in any way with an electronic work by people who +agree to be bound by the terms of this agreement. There are a few +things that you can do with most Project Gutenberg-tm electronic works +even without complying with the full terms of this agreement. See +paragraph 1.C below. There are a lot of things you can do with Project +Gutenberg-tm electronic works if you follow the terms of this agreement +and help preserve free future access to Project Gutenberg-tm electronic +works. See paragraph 1.E below. + +1.C. The Project Gutenberg Literary Archive Foundation ("the Foundation" +or PGLAF), owns a compilation copyright in the collection of Project +Gutenberg-tm electronic works. Nearly all the individual works in the +collection are in the public domain in the United States. If an +individual work is in the public domain in the United States and you are +located in the United States, we do not claim a right to prevent you from +copying, distributing, performing, displaying or creating derivative +works based on the work as long as all references to Project Gutenberg +are removed. Of course, we hope that you will support the Project +Gutenberg-tm mission of promoting free access to electronic works by +freely sharing Project Gutenberg-tm works in compliance with the terms of +this agreement for keeping the Project Gutenberg-tm name associated with +the work. You can easily comply with the terms of this agreement by +keeping this work in the same format with its attached full Project +Gutenberg-tm License when you share it without charge with others. + +1.D. The copyright laws of the place where you are located also govern +what you can do with this work. Copyright laws in most countries are in +a constant state of change. If you are outside the United States, check +the laws of your country in addition to the terms of this agreement +before downloading, copying, displaying, performing, distributing or +creating derivative works based on this work or any other Project +Gutenberg-tm work. The Foundation makes no representations concerning +the copyright status of any work in any country outside the United +States. + +1.E. Unless you have removed all references to Project Gutenberg: + +1.E.1. The following sentence, with active links to, or other immediate +access to, the full Project Gutenberg-tm License must appear prominently +whenever any copy of a Project Gutenberg-tm work (any work on which the +phrase "Project Gutenberg" appears, or with which the phrase "Project +Gutenberg" is associated) is accessed, displayed, performed, viewed, +copied or distributed: + +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 + +1.E.2. If an individual Project Gutenberg-tm electronic work is derived +from the public domain (does not contain a notice indicating that it is +posted with permission of the copyright holder), the work can be copied +and distributed to anyone in the United States without paying any fees +or charges. If you are redistributing or providing access to a work +with the phrase "Project Gutenberg" associated with or appearing on the +work, you must comply either with the requirements of paragraphs 1.E.1 +through 1.E.7 or obtain permission for the use of the work and the +Project Gutenberg-tm trademark as set forth in paragraphs 1.E.8 or +1.E.9. + +1.E.3. If an individual Project Gutenberg-tm electronic work is posted +with the permission of the copyright holder, your use and distribution +must comply with both paragraphs 1.E.1 through 1.E.7 and any additional +terms imposed by the copyright holder. Additional terms will be linked +to the Project Gutenberg-tm License for all works posted with the +permission of the copyright holder found at the beginning of this work. + +1.E.4. Do not unlink or detach or remove the full Project Gutenberg-tm +License terms from this work, or any files containing a part of this +work or any other work associated with Project Gutenberg-tm. + +1.E.5. Do not copy, display, perform, distribute or redistribute this +electronic work, or any part of this electronic work, without +prominently displaying the sentence set forth in paragraph 1.E.1 with +active links or immediate access to the full terms of the Project +Gutenberg-tm License. + +1.E.6. You may convert to and distribute this work in any binary, +compressed, marked up, nonproprietary or proprietary form, including any +word processing or hypertext form. However, if you provide access to or +distribute copies of a Project Gutenberg-tm work in a format other than +"Plain Vanilla ASCII" or other format used in the official version +posted on the official Project Gutenberg-tm web site (www.gutenberg.org), +you must, at no additional cost, fee or expense to the user, provide a +copy, a means of exporting a copy, or a means of obtaining a copy upon +request, of the work in its original "Plain Vanilla ASCII" or other +form. Any alternate format must include the full Project Gutenberg-tm +License as specified in paragraph 1.E.1. + +1.E.7. Do not charge a fee for access to, viewing, displaying, +performing, copying or distributing any Project Gutenberg-tm works +unless you comply with paragraph 1.E.8 or 1.E.9. + +1.E.8. You may charge a reasonable fee for copies of or providing +access to or distributing Project Gutenberg-tm electronic works provided +that + +- You pay a royalty fee of 20% of the gross profits you derive from + the use of Project Gutenberg-tm works calculated using the method + you already use to calculate your applicable taxes. The fee is + owed to the owner of the Project Gutenberg-tm trademark, but he + has agreed to donate royalties under this paragraph to the + Project Gutenberg Literary Archive Foundation. Royalty payments + must be paid within 60 days following each date on which you + prepare (or are legally required to prepare) your periodic tax + returns. Royalty payments should be clearly marked as such and + sent to the Project Gutenberg Literary Archive Foundation at the + address specified in Section 4, "Information about donations to + the Project Gutenberg Literary Archive Foundation." + +- You provide a full refund of any money paid by a user who notifies + you in writing (or by e-mail) within 30 days of receipt that s/he + does not agree to the terms of the full Project Gutenberg-tm + License. You must require such a user to return or + destroy all copies of the works possessed in a physical medium + and discontinue all use of and all access to other copies of + Project Gutenberg-tm works. + +- You provide, in accordance with paragraph 1.F.3, a full refund of any + money paid for a work or a replacement copy, if a defect in the + electronic work is discovered and reported to you within 90 days + of receipt of the work. + +- You comply with all other terms of this agreement for free + distribution of Project Gutenberg-tm works. + +1.E.9. If you wish to charge a fee or distribute a Project Gutenberg-tm +electronic work or group of works on different terms than are set +forth in this agreement, you must obtain permission in writing from +both the Project Gutenberg Literary Archive Foundation and Michael +Hart, the owner of the Project Gutenberg-tm trademark. Contact the +Foundation as set forth in Section 3 below. + +1.F. + +1.F.1. Project Gutenberg volunteers and employees expend considerable +effort to identify, do copyright research on, transcribe and proofread +public domain works in creating the Project Gutenberg-tm +collection. Despite these efforts, Project Gutenberg-tm electronic +works, and the medium on which they may be stored, may contain +"Defects," such as, but not limited to, incomplete, inaccurate or +corrupt data, transcription errors, a copyright or other intellectual +property infringement, a defective or damaged disk or other medium, a +computer virus, or computer codes that damage or cannot be read by +your equipment. + +1.F.2. LIMITED WARRANTY, DISCLAIMER OF DAMAGES - Except for the "Right +of Replacement or Refund" described in paragraph 1.F.3, the Project +Gutenberg Literary Archive Foundation, the owner of the Project +Gutenberg-tm trademark, and any other party distributing a Project +Gutenberg-tm electronic work under this agreement, disclaim all +liability to you for damages, costs and expenses, including legal +fees. YOU AGREE THAT YOU HAVE NO REMEDIES FOR NEGLIGENCE, STRICT +LIABILITY, BREACH OF WARRANTY OR BREACH OF CONTRACT EXCEPT THOSE +PROVIDED IN PARAGRAPH 1.F.3. YOU AGREE THAT THE FOUNDATION, THE +TRADEMARK OWNER, AND ANY DISTRIBUTOR UNDER THIS AGREEMENT WILL NOT BE +LIABLE TO YOU FOR ACTUAL, DIRECT, INDIRECT, CONSEQUENTIAL, PUNITIVE OR +INCIDENTAL DAMAGES EVEN IF YOU GIVE NOTICE OF THE POSSIBILITY OF SUCH +DAMAGE. + +1.F.3. LIMITED RIGHT OF REPLACEMENT OR REFUND - If you discover a +defect in this electronic work within 90 days of receiving it, you can +receive a refund of the money (if any) you paid for it by sending a +written explanation to the person you received the work from. If you +received the work on a physical medium, you must return the medium with +your written explanation. The person or entity that provided you with +the defective work may elect to provide a replacement copy in lieu of a +refund. If you received the work electronically, the person or entity +providing it to you may choose to give you a second opportunity to +receive the work electronically in lieu of a refund. If the second copy +is also defective, you may demand a refund in writing without further +opportunities to fix the problem. + +1.F.4. Except for the limited right of replacement or refund set forth +in paragraph 1.F.3, this work is provided to you 'AS-IS' WITH NO OTHER +WARRANTIES OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO +WARRANTIES OF MERCHANTIBILITY OR FITNESS FOR ANY PURPOSE. + +1.F.5. Some states do not allow disclaimers of certain implied +warranties or the exclusion or limitation of certain types of damages. +If any disclaimer or limitation set forth in this agreement violates the +law of the state applicable to this agreement, the agreement shall be +interpreted to make the maximum disclaimer or limitation permitted by +the applicable state law. The invalidity or unenforceability of any +provision of this agreement shall not void the remaining provisions. + +1.F.6. INDEMNITY - You agree to indemnify and hold the Foundation, the +trademark owner, any agent or employee of the Foundation, anyone +providing copies of Project Gutenberg-tm electronic works in accordance +with this agreement, and any volunteers associated with the production, +promotion and distribution of Project Gutenberg-tm electronic works, +harmless from all liability, costs and expenses, including legal fees, +that arise directly or indirectly from any of the following which you do +or cause to occur: (a) distribution of this or any Project Gutenberg-tm +work, (b) alteration, modification, or additions or deletions to any +Project Gutenberg-tm work, and (c) any Defect you cause. + + +Section 2. Information about the Mission of Project Gutenberg-tm + +Project Gutenberg-tm is synonymous with the free distribution of +electronic works in formats readable by the widest variety of computers +including obsolete, old, middle-aged and new computers. It exists +because of the efforts of hundreds of volunteers and donations from +people in all walks of life. + +Volunteers and financial support to provide volunteers with the +assistance they need, are critical to reaching Project Gutenberg-tm's +goals and ensuring that the Project Gutenberg-tm collection will +remain freely available for generations to come. In 2001, the Project +Gutenberg Literary Archive Foundation was created to provide a secure +and permanent future for Project Gutenberg-tm and future generations. +To learn more about the Project Gutenberg Literary Archive Foundation +and how your efforts and donations can help, see Sections 3 and 4 +and the Foundation web page at http://www.pglaf.org. + + +Section 3. Information about the Project Gutenberg Literary Archive +Foundation + +The Project Gutenberg Literary Archive Foundation is a non profit +501(c)(3) educational corporation organized under the laws of the +state of Mississippi and granted tax exempt status by the Internal +Revenue Service. The Foundation's EIN or federal tax identification +number is 64-6221541. Its 501(c)(3) letter is posted at +http://pglaf.org/fundraising. Contributions to the Project Gutenberg +Literary Archive Foundation are tax deductible to the full extent +permitted by U.S. federal laws and your state's laws. + +The Foundation's principal office is located at 4557 Melan Dr. S. +Fairbanks, AK, 99712., but its volunteers and employees are scattered +throughout numerous locations. Its business office is located at +809 North 1500 West, Salt Lake City, UT 84116, (801) 596-1887, email +business@pglaf.org. Email contact links and up to date contact +information can be found at the Foundation's web site and official +page at http://pglaf.org + +For additional contact information: + Dr. Gregory B. Newby + Chief Executive and Director + gbnewby@pglaf.org + + +Section 4. Information about Donations to the Project Gutenberg +Literary Archive Foundation + +Project Gutenberg-tm depends upon and cannot survive without wide +spread public support and donations to carry out its mission of +increasing the number of public domain and licensed works that can be +freely distributed in machine readable form accessible by the widest +array of equipment including outdated equipment. Many small donations +($1 to $5,000) are particularly important to maintaining tax exempt +status with the IRS. + +The Foundation is committed to complying with the laws regulating +charities and charitable donations in all 50 states of the United +States. Compliance requirements are not uniform and it takes a +considerable effort, much paperwork and many fees to meet and keep up +with these requirements. We do not solicit donations in locations +where we have not received written confirmation of compliance. To +SEND DONATIONS or determine the status of compliance for any +particular state visit http://pglaf.org + +While we cannot and do not solicit contributions from states where we +have not met the solicitation requirements, we know of no prohibition +against accepting unsolicited donations from donors in such states who +approach us with offers to donate. + +International donations are gratefully accepted, but we cannot make +any statements concerning tax treatment of donations received from +outside the United States. U.S. laws alone swamp our small staff. + +Please check the Project Gutenberg Web pages for current donation +methods and addresses. Donations are accepted in a number of other +ways including checks, online payments and credit card donations. +To donate, please visit: http://pglaf.org/donate + + +Section 5. General Information About Project Gutenberg-tm electronic +works. + +Professor Michael S. Hart is the originator of the Project Gutenberg-tm +concept of a library of electronic works that could be freely shared +with anyone. For thirty years, he produced and distributed Project +Gutenberg-tm eBooks with only a loose network of volunteer support. + + +Project Gutenberg-tm eBooks are often created from several printed +editions, all of which are confirmed as Public Domain in the U.S. +unless a copyright notice is included. Thus, we do not necessarily +keep eBooks in compliance with any particular paper edition. + + +Most people start at our Web site which has the main PG search facility: + + http://www.gutenberg.org + +This Web site includes information about Project Gutenberg-tm, +including how to make donations to the Project Gutenberg Literary +Archive Foundation, how to help produce our new eBooks, and how to +subscribe to our email newsletter to hear about new eBooks. |