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diff --git a/old/67396-0.txt b/old/67396-0.txt deleted file mode 100644 index dc2f085..0000000 --- a/old/67396-0.txt +++ /dev/null @@ -1,2059 +0,0 @@ -The Project Gutenberg eBook of Determination of The Atomic Weight Of -Cadmium and The Preperation of Certain Of Its Sub-Compounds, by Harry C. -Jones - -This eBook is for the use of anyone anywhere in the United States and -most other parts of the world 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. If you are not located in the United States, you -will have to check the laws of the country where you are located before -using this eBook. - -Title: Determination of The Atomic Weight Of Cadmium and The Preperation - of Certain Of Its Sub-Compounds - -Author: Harry C. Jones - -Release Date: February 13, 2022 [eBook #67396] - -Language: English - -Produced by: The Online Distributed Proofreading Team at - https://www.pgdp.net (This file was produced from images - generously made available by The Internet Archive) - -*** START OF THE PROJECT GUTENBERG EBOOK DETERMINATION OF THE ATOMIC -WEIGHT OF CADMIUM AND THE PREPERATION OF CERTAIN OF ITS -SUB-COMPOUNDS *** - - - - - -Transcriber’s Notes: - - Underscores “_” before and after a word or phrase indicate _italics_ - in the original text. - Small capitals have been converted to SOLID capitals. - Typographical and punctuation errors have been silently corrected. - The symbol “ī” (small i with macron)was used in place of the numeral - 1 (one) with macron. - The symbol “̅2” (overline + 2) was used in place of numeral 2 with - macron. - - - - - Determination of The Atomic Weight - of Cadmium and The Preparation of - Certain Of Its Sub-Compounds. - - Dissertation, - - Presented to The Board of University Studies - of The - Johns Hopkins University, - - For The Degree of - Doctor of Philosophy, - - By - Harry C. Jones - - 1892. - - - - -_Contents._ - - - Page - Determination of the Atomic Weight of Cadmium 1 - Introduction and Historical Statement 2 - Preparation of Pure Cadmium 22 - The Preparation of Pure Nitric Acid 28 - The Arrangement of Crucibles 30 - The Mode of Procedure 32 - The Weighing 37 - Taring the Crucibles 40 - The Results 42 - Objections to the Method 45 - Advantages of the Method 48 - The Oxalate Method 50 - Preparation of Pure Oxalic Acid 51 - Preparation of Cadmium Oxalate 52 - Mode of Procedure 53 - The Drying and Weighing of the Oxalate 55 - The Results 58 - Advantages of the Method 60 - Disadvantages of the Method 61 - Preparation of Certain Sub-compounds of Cadmium 63 - Historical 64 - The Preparation of Cd₄Cl₇ 66 - The Preparation of Cd₄Br₇ 78 - The Preparation of Cd₁₂I₂₃ 82 - The Preparation of Cadmium Hydroxide and Oxide 82 - Notes on Crystals of Metallic Cadmium 97 - The Cohesion Phenomena of Cadmium 103 - Biographical Sketch 106 - - - - -Acknowledgment. - - -It affords me great pleasure to express my sincere thanks to Professor -Remsen for his instruction and personal supervision during my entire -connection with the University; to Dr. Morse, under whose immediate -guidance the work described in this dissertation was completed; to -Dr. Renouf for valuable assistance in qualitative chemistry and to -Dr. Williams, with whom the branches of mineralogy and geology were -followed as subordinate subjects. - - - - -Determination of the Atomic Weight of Cadmium. - -Introduction and Historical statement. - -A careful examination of the literature on the atomic weight of cadmium -will convince any one that considerable uncertainty yet remains in -reference to this constant. Six experimenters have worked on this -problem but the results of no one of them can be accepted as being more -accurate than those of all others. The value assigned to cadmium varies -from 111.48 to 112.32 on the basis of oxygen = 16. The best work has -apparently been done by von Hauer, Lenssen and Huntington. The results -of these three seem entitled to about equal confidence, yet the figure -obtained by von Hauer differs from that of Huntington by three tenths -of a unit. - -The more prominent difficulties which have been encountered were: - - First. The preparation of cadmium compounds free from all - impurities, and which at the same time were well adapted - to weighing. - - Second. The lack of a thoroughly simple and exact method - for the analysis of cadmium compounds. - - Third. Insufficient care in weighing in many cases whereby - small errors were introduced into the results. - -The methods which have been employed are: - - 1 Conversion of the metal into the oxide. (Stromeyer). - - 2 Conversion of the sulphate into the sulphide. (von Hauer - and Partridge). - - 3 Decomposition of the oxalate to the oxide. (Lenssen and - Partridge). - - 4 Determination of the chlorine in cadmium chloride, by - which the relation between the chloride and metallic silver - was established. (Dumas.) - - 5 Precipitation of the bromine in cadmium bromide as silver - bromide. (Huntington.) - - 6 The conversion of the oxalate into the sulphide. - (Partridge.) - -The different pieces of work will be taken up in chronological order -and briefly considered. - -Stromeyer, Schurigg Journ. 22, 366. 1818, determined the atomic weight -of cadmium a short time after the discovery of the element. He does -not describe his method in detail but established the relation between -cadmium and oxygen to be: - - Cd : O = 100 : 14.352. - - If the atomic weight of oxygen = 16, - ” ” ” ” cadmium = 111.483. - -The very low result as compared with all subsequent work was probably -due to the presence of a small amount of zinc, since the cadmium used -was obtained from zinc ores and no adequate means of separation from -the zinc is described. - -von Hauer, Journ. f. prakt. Chem. 72, 338. 1857. His method consisted -in reducing a weighed amount of cadmium sulphate to the sulphide -in a stream of hydrogen sulphide, under pressure, at an elevated -temperature, and weighing the sulphide. The reduction was shown to be -complete by proving the absence of sulphate in the sulphide. - - 64.2051 grams of cadmium sulphate - gave 44.4491 ” ” ” sulphide. - - If the atomic weight of oxygen = 16, - ” ” ” ” ” sulphur = 32.059, - ” ” ” ” cadmium = 111.935. - -The atomic weight of cadmium calculated as an average of the nine -determinations made using the above values for oxygen and sulphur = -111.94. - - Maximum, 112.121. - Minimum, 111.796. - Mean, 111.940. - -The work of von Hauer is greatly to be preferred to that of Stromeyer. -The large amount of material used in each determination tended to -lessen any experimental error. A very considerable degree of care -seems to have been exercised in purifying the cadmium sulphate. In -determinations 1-5 a different specimen of sulphate was employed from -that in determinations 6-9. The average value found in the first -five determinations = 111.910, in the last four = 111.977. The close -agreement between the results obtained from the different preparations -of the sulphate argues in favor of a fair degree of purity for all the -material. - -The method of weighing the more or less hygroscopic cadmium sulphate is -open to criticism when employed in accurate work. The cadmium sulphate -was placed in an open boat, dried, cooled over sulphuric acid, and -weighed. It was again dried, cooled as before, and weighed. The second -weighing could be quickly accomplished since the approximate weight -was known. The two weighings agreed to within less than a milligram -or a third drying and weighing were made. An error of a milligram -in the weight of the sulphate produced an average error in the atomic -weight of cadmium of about .06. That a discrepancy of greater or less -magnitude was introduced from this source will be readily seen. - -Dumas Ann. Chim. Phys. 55, 158. 1859, determined the relation between -cadmium chloride and the metallic silver required to precipitate the -chlorine. Metallic cadmium was dissolved in boiling hydrochloric acid -and the solution evaporated. The cadmium chloride was fused for five or -six hours in a stream of hydrochloric acid gas. Six determinations were -made. 23.0645 grams of cadmium chloride were equivalent to 27.173 grams -of metallic silver. - - If the atomic weight of silver = 107.93. - ” ” ” ” ” chlorine = 35.45. - ” ” ” ” cadmium = 112.322. - -The atomic weight of cadmium calculated as the average of the six -determinations made, using the above values for silver and chlorine = -112.241. - - Maximum, 112.759. - Minimum, 111.756. - Mean, 112.241. - -The large difference between the results would indicate some -considerable source of error in part or all of the determinations. -The first three determinations were made from a different specimen of -cadmium from the last three. - -In the first three the cadmium used does not seem to have been -purified and the cadmium chloride prepared from it was more or less -tinted brown. In the last three a new specimen of metal was used -which in Dumas’ words could reasonably be considered to be absolutely -pure. The chloride prepared from it was colorless, well crystallized -and perfectly soluble in water. In order to show clearly the wide -discrepancy between the results obtained from the two specimens of -cadmium which were used, the separate determinations are given in -detail. - - At. Wt. - CdCl₂ Ag. Cadmium. - 1 2.369 2.791 112.322 - 2 4.540 5.348 112.347 - 3 6.177 7.260 112.759 - 4 2.404 2.841 111.756 - 5 3.5325 4.166 112.135 - 6 4.042 4.767 112.130 - -The average result of the first three determinations = 112.476. The -average result of the last three determinations = 112.007. From Dumas’ -own statement concerning the purity of the cadmium chloride analyzed, -determinations 4-6 are much to be preferred to determinations 1-3 and -the most probable value from Dumas’ work would be very nearly 112. - -Lenssen Journ. f. prakt. Chem. 79, 281. 1860, regarded the oxalate of -cadmium as well adapted to the determination of the atomic weight of -cadmium. A solution of cadmium chloride which had been purified by -repeated crystallization was treated with an excess of a solution of -pure oxalic acid. The cadmium oxalate formed was filtered off, washed, -and carefully dried in the air at 150° C. until the last trace of -water was removed. 1.5697 grams cadmium oxalate gave 1.0047 grams -cadmium oxide. - - If the atomic weight of oxygen = 16, - ” ” ” ” carbon = 12.003, - ” ” ” cadmium = 112.043. - -The average of the three determinations using the above values for -oxygen and carbon is 112.067. - - Maximum, 112.304. - Minimum, 111.911. - Mean, 112.067. - -The small amount of material used in each determination, the small -number of determinations made, and the rather large difference between -the highest and lowest result are objectionable. There are certain weak -points in the method but to these reference will be made later. - -Huntington, Proc. Amer. Acad. 17, 28. 1882, working with Cooke, made -two series of determinations of the atomic weight of cadmium. In the -first series the relation between cadmium bromide and the silver -bromide formed from it was determined. In the second, the relation -between cadmium bromide and the silver required to precipitate the -bromine. - -The cadmium bromide was prepared by dissolving the carbonate in -hydrobromic acid and subliming the product in a stream of carbon -dioxide. - -In the first series of eight determinations 23.3275 grams of cadmium -bromide were equivalent to 32.2098 grams of silver bromide. - - If the atomic weight of silver = 107.93. - ” ” ” ” ” bromine = 79.95. - ” ” ” ” cadmium = 122.239. - - Maximum, 112.290. - Minimum, 112.169. - -Where the difference between the maximum and minimum value is slight, -the average of the separate determinations agrees closely with the -number found by comparing the total substance used with the total -product obtained. The latter method of calculation seems however to be -preferable. - -In the second series of eight determinations 28.6668 grams of cadmium -bromide were equivalent to 22.7379 grams of silver. - -Using the same values for silver and bromine, the atomic weight of -cadmium = 112.245. - - Maximum, 112.320. - Minimum, 112.180. - -The agreement of the separate determinations with each other is -fairly close and the average of the two series of determinations is -nearly the same. Huntington took great care in the purification of -his material and in the carrying out of his method, which are strong -arguments in favor of his work, yet his method is not as simple as -could be desired where the nature of the work demands the greatest -possible accuracy in all details and it also appears to be subject to -some of the errors common to ordinary analytical operations. - -Partridge. Amer. Journ. Science XL, 377. 1890. Methods: 1ˢᵗ. -Decomposition of the oxalate to the oxide. 2ⁿᵈ. Reduction of the -sulphate to the sulphide. 3ʳᵈ. Conversion of the oxalate into the -sulphide. As an average of the determinations made by each method -Partridge gives: - - 1ˢᵗ series, atomic weight of cadmium = 111.8027. - 2ⁿᵈ ” ” ” ” ” = 111.7969. - 3ʳᵈ ” ” ” ” ” = 111.8050. - -An excellent agreement between results obtained by different methods[1]. - -That this very close agreement is only apparent has been shown by -Clarke. He has found that the above calculations are based on the -assumption that the atomic weight of carbon = 12, and that of sulphur -= 32 when oxygen = 16. There seems to be little justification for -this rather arbitrary selection by Partridge since the most refined -work shows that whole numbers do not express the most probable atomic -weights of carbon and sulphur in a system where oxygen = 16. - -[1] Amer. Chem. Journ. 13, 34. 1891. - -The atomic weight of cadmium calculated from the total material used -and the total product found in each of the three series is: - - O = 16. C = 12. S = 32. At.Wt.Cd. - 1ˢᵗ series, CdC₂O₄ : CdO = 12.66368g. : 8.10031g. 111.805. - 2ⁿᵈ ” CdSO₄ : CdS = 15.93505g. : 11.02691g. 111.786. - 3ʳᵈ ” CdC₂O₄ : CdS = 16.85228g. : 12.12906g. 111.806. - difference, 0.020. - - O = 16. C = 12.003 S = 32.059 At.Wt.Cd. - 1ˢᵗ series, CdC₂O₄ : CdO = 12.66368g. : 8.10031g. 111.816. - 2ⁿᵈ ” CdSO₄ : CdS = 15.93505g. : 11.02691g. 111.727. - 3ʳᵈ ” CdC₂O₄ : CdS = 16.85228g. : 12.12906g. 111.610. - difference, 0.206. - -As Clarke has pointed out when those values are chosen for carbon -and sulphur which are founded on the best experimental evidence the -agreement between the different series of results as calculated by -Partridge is somewhat modified. - -I have repeated the work on which series I is based and would call -attention to the following points in which it appears to have been -experimentally defective. - - 1 The metal was only distilled twice in a vacuum. It has - been found in this laboratory that perfectly pure - cadmium or zinc can be prepared only by repeated - distillations, each one being carried on slowly to allow - the impurities to separate by means of their difference - in volatility. - - 2 The supposed mixture of metal and oxide resulting from - the decomposition of the oxalate was only moistened with - a few drops of nitric acid in order to reoxidize any - reduced metal. Unless the entire mass of metal and oxide - was dissolved there would be danger of the presence of - free undissolved metal which would possess an appreciable - vapor-tension below the temperature of decomposition of - cadmium nitrate. An appreciable loss in weight resulting - from a distillation of the metal out of the crucible might - easily result. - - 3 It seems very probable that the cadmium nitrate was - not heated sufficiently to remove all traces of the - oxides of nitrogen. I have found that this could only be - accomplished by long continued heating. Constant weight - was not sufficient to have decided this point since it was - also found that this could be reached short of complete - decomposition, if the temperature was too low to remove - the last traces of these oxides. Some very delicate test - for such oxides should have been applied at the end of - each experiment. - -The following table contains a summary of the results thus far obtained. - -When two values are given for one series of determinations, the first -is calculated from the total material used and the total product found, -the second is an average of the results of the separate experiments. -Oxygen is taken as 16 throughout. - - Date. Investigators. At.Wt.Cd. - 1818, Stromeyer, 111.483 - - 1857, von Hauer, 111.935 } - 111.940 } - - 1859, Dumas, 112.322 } - 112.241 } - - 1860, Lenssen, 112.043 } - 112.067 } - - 1882, Huntington, 1ˢᵗ series 112.239 - ” 2ⁿᵈ ” 112.245 - - 1890, Partridge, 1ˢᵗ series 111.805 - ” 2ⁿᵈ ” 111.786 - ” 3ʳᵈ ” 111.806 - -In the above calculation of Partridge’s results C = 12. S = 32. In the -following carbon is taken as 12.003 and sulphur is 32.059. - - 1890, Partridge, 1ˢᵗ series 111.816 - ” 2ⁿᵈ ” 111.727 - ” 3ʳᵈ ” 111.610 - -After a careful examination of the methods available it becomes evident -that no one of them was _per se_ as accurate as the method employed -by Morse and Burton,[2] for the determination of the atomic weight of -zinc, and more recently by Burton and Morse,[3] for the determination -of the atomic weight of magnesium. The method of work was to prepare -pure metallic cadmium, to convert a weighed portion of the metal -into nitrate by means of pure nitric acid, to decompose the nitrate -completely to oxide and to weigh the oxide. - -[2] Amer. Chem. Journ. X, 311. - -[3] ib. XII, 219. - - - - -Preparation of Pure Cadmium. - - -The work of preparing pure cadmium was begun more than two years ago -by Mr. W. V. Metcalf with Dr. H. N. Morse. I wish to express here -my sincere thanks to him for the material with which the following -determinations were made. The cadmium used by him was obtained from -Schuchart and marked “Met. prss. (galv.) redus.” - -The method of purification by fractional distillation in a vacuum, was -essentially that employed by Morse and Burton for the purification of -metallic zinc. - -The distillation was carried out in hard glass tubes of the size of -ordinary combustion tubing. - -[Illustration: FIG. 1.] - -Fig. 1. represents such a tube. A hard glass tube, 600-700 mm. -in length, was closed at one end and about 130 grams of cadmium -introduced. The walls of the tube were heated and indented at the two -points a, and b, with a red-hot file, dividing the tube into three -sections marked A, B and C. The open end of the tube was drawn out, -bent, and attached to a Sprengel air-pump by means of a rubber tube. - -The joint was tied tightly with waxed cord and surrounded by mercury. -When the manometer indicated that the tube was exhausted, it was -gradually heated by the combustion furnace in which it rested. The -metal in A melted and distilled slowly into the front portion of the -tube. Most of it condensed in B, while a small part, together with -any more volatile impurity, collected in C which was kept cooler than -the remainder of the tube. When about four-fifths of the metal placed -in A had distilled over, the tube was very slowly cooled. When cold, -the tube was broken open, the portions in A and C being rejected in -every case, while the metal was recovered from B in the form of a -bar resting on the bottom of the tube, together with some crystal -aggregates, suspended from the top and sides. A few crystal individuals -were secured but the measurement of these will be considered later. The -metal separated from the glass with a highly lustrous surface and did -not attack the glass in the least. - -The first distillation was effected in a tube bridged as represented -in Fig. 1, but drawn out at each end. The original cadmium powder was -heated in the tube in a stream of pure hydrogen gas, for the purpose -of obtaining the metal in the form of bars, and to reduce any cadmium -oxide contained in the powder. - -Six distillations were made in a vacuum. In the first, 630 grams of -metal were used being distilled in quantities of about 130 grams -each. At the end of the sixth distillation, there were about -100 grams of pure cadmium at disposal. In the fifth and sixth -distillations, the metal was heated just above the melting point for -from twenty to twenty-four hours, before being forced over into the -middle portion of the tube. By this means all the remaining traces of -the more volatile arsenic were driven into the front part of the tube -and separated from the cadmium. - - -The distillations. - -The residue represents the undistilled portion remaining in A. The -distillate, the material obtained from B after the distillation was -completed. The coating, the substance which condensed in C. - - Residue, Cd, Pt, Zn,? As?. - Distillation I Distillate, Cd, Zn,? As? - Coating, Cd, Zn,? As?. - - Residue, Cd, Zn?, As?. - Distillation II Distillate, Cd, Zn?, As?. - Coating, Cd, Zn?, As?. - - Residue, Cd, Zn?, As?. - Distillation III Distillate, Cd, Zn?, As?. - Coating, Cd, Zn?, As?. - - Residue, Cd, Zn?, As?. - Distillation IV Distillate, Cd, Zn?, As?. - Coating, Cd, Zn?, As?. - - Residue, Cd. - Distillation V Distillate, Cd. - Coating, Cd, As?. - - Residue, Cd. - Distillation VI Distillate, Cd. - Coating, Cd. - -The distillate from the last distillation was examined -spectroscopically by Professor Rowland and found to be free from all -traces of impurity which would be detected by that method. The chemical -test for arsenic was more delicate than the spectroscopic and this -failed to reveal a trace. - - -The preparation of pure nitric acid. - -The method of preparing the pure acid and of preserving and -transferring it was the same as adopted by Morse and Burton in their -work on the atomic weight of zinc. - -[Illustration: FIG. 2.] - -The simple form of apparatus is represented in fig. 2. A large platinum -vessel containing fragments of ice was supported on a smaller platinum -dish, from which it was separated by hooks of large platinum wire. The -acid was distilled from a small flask as represented in the drawing. - -The purest nitric acid which could be obtained was diluted with about -an equal volume of water. The vessel containing the acid was heated -very gently that the distillation might take place without boiling. -The dilute acid condensed on the cold surface of the larger dish and -collected in the smaller, in which it was preserved until used. This -acid gave no residue on evaporation. - - -The arrangement of crucibles. - -[Illustration: FIG. 3.] - -The arrangement of the crucibles in which the determinations were -made is represented in fig. 3. 1 is a small porcelain crucible, (00) -from the exterior and lid of which the glaze had been removed by -hydrofluoric acid. The lid was separated from the crucible by hooks -made from thick platinum wire, to allow free communication between the -contents of the crucible and the external air. This would facilitate -the outward diffusion of the oxides of nitrogen when liberated from -the nitrate. 2 is an uncovered porcelain crucible (no. II) in which 1 -was placed. From the exterior the glaze had been removed to prevent -the crucible from adhering to the unglazed porcelain scorifier on -which it rested. The exterior was carefully brushed after treatment -with hydrofluoric acid to remove all loose particles adhering to its -surface. Crucibles 1 and 2 were not separated during a determination. - -3 is a nickel crucible about two and a half inches in diameter. The -porcelain crucibles were not allowed to touch the nickel at any point. -The nickel crucible was covered by a lid of nickel. - - -The mode of procedure. - -A piece of cadmium weighing from two to three grams was cut from the -bar of the metal by means of a steel chisel. This was seized with steel -forceps and filed with a hard steel file to about one half the original -weight. Care was taken to remove the entire exterior portion of the -metal which had come in contact with the chisel or had stood exposed to -the air. The plug of metal was then carefully brushed and examined with -a lens to insure the removal of all loose particles from the surface. - -Crucibles 1 and 2 having been brought to constant weight against -their tare, were ready for use. The piece of cadmium was weighed and -placed in 1. An excess of pure nitric acid was added and a gentle heat -applied until all the metal had dissolved. This required from twenty -to forty hours. - -A sand-bath was constructed by placing a large porcelain crucible in -an iron crucible and filling the intervening space with sand. The pair -of crucibles (1 and 2) was placed in the porcelain crucible and the -contents evaporated to dryness by warming very carefully at first and -gradually increasing the temperature. The pair of crucibles was then -transferred to a bath constructed as the above where iron filings took -the place of sand. This was heated by a single burner until the nitrate -was all decomposed when a triple burner was added and finally two -for six or eight hours. This was not sufficient to effect complete -decomposition. When cold, the pair of crucibles was placed in the -nickel crucible as represented in fig. 3 and sharply heated over a -blast-lamp for several hours. This completed the decomposition of the -nitrate and the removal of the last traces of oxides of nitrogen. - -During the blasting the lid on crucible 3 was raised a little to one -side to allow free access of air. The nickel crucible was forced -tightly into a hole cut in the center of an asbestos board about -ten inches in diameter, to prevent any reducing gases from the lamp -entering the crucibles while hot. This was the same arrangement as was -used by Partridge[4]. - -[4] Amer. Journ. Science XL, 379. - -It was found that the final decomposition of the nitrate could not -be effected in a muffle furnace as with zinc, since at very high -temperatures cadmium oxide attacked the porcelain with great energy and -injured the crucibles. - -The decomposition of the nitrate was shown to be complete not by -constant weight alone, but by testing for oxides of nitrogen with -starch paste rendered extremely sensitive with potassium iodide. That -the test should be reliable, Morse and Burton have pointed out that all -the reagents used must be free from oxidizing agents. The presence of -iodate in the iodide is especially to be avoided. This was removed by -boiling the solution with zinc amalgam. Air was removed from all the -solutions by boiling. - -When the starch-potassium-iodide solution had been prepared as -sensitive as possible, a portion of it was treated with a little -hydrochloric acid, to determine if any iodine was liberated. If no -coloration was observed the cadmium oxide was added. It dissolved in -the hydrochloric acid and if any oxides of nitrogen were present they -would have revealed themselves by the liberation of iodine and a blue -coloration of the starch paste. - -In no one of the ten determinations was the slightest coloration -detected. - -An equal volume of nitric acid was added to the pair of crucibles used -as a tare as to those containing the determination, and they were -heated in exactly the same manner and for the same length of time. - -The crucibles containing the cadmium oxide were heated over the -blast-lamp for an hour, weighed against their tare, reheated, again -weighed, and this continued until there was no further change in -weight. Usually from two to four hours heating over the blast-lamp was -sufficient to completely decompose the nitrate. The test for oxides of -nitrogen was then applied. - -I found that practically constant weight could be reached short of -compete decomposition, at a temperature below that necessary to -transform all the nitrate into the oxide. This necessitated the final -test for oxides of nitrogen. - - -The Weighing. - -The balance used was a No. 8 long-armed one, made by Becker and Sons. -It was supported by iron brackets fastened to one of the foundation -walls of the laboratory. - -Here it would be subjected to the least jar and was also well protected -from air currents. All weighings were made between the hours of one and -five in the morning when the surroundings were as quiet as could be -desired. A very slight disturbance was detected by the vibrations on -the surface of a cup of mercury placed conveniently between the pans. - -That the presence of the operator might not produce any change in the -balance during the weighing, he closed the room, placed the light above -and behind his head and took his position in front of the balance at -least an hour before making a weighing. When his presence no longer -affected the balance (which was shown by the zero point remaining -constant in a series of determinations) the weighing was begun. The -method of weighing by vibrations and upon both pans was employed -throughout. - -Each zero point was taken as the mean of three closely agreeing zero -determinations; each one of the three being the mean of seven readings. -The zero of the balance empty was determined just before and after -each weighing to detect any change in its position. Usually none was -observed. The sensibility of the balance was taken at each weighing -with the weights used at that weighing. A displacement of the zero -point about six divisions of the ivory scale was effected by the -addition of one milligram. - -The weights had been especially adjusted and were carefully compared -with each other before using. - -Weighing by tares was adopted as preferable to any other method. By -this means all errors resulting from changes in the moisture of the air -were avoided and any errors which might have been introduced by heating -or manipulating the crucibles would be counteracted by treating the -tare in exactly the same manner. - - -Taring The Crucibles. - -A pair of crucibles (1 and 2 in the figure) was selected and treated as -described. Another pair about the same size but a little lighter was -prepared in exactly the same way. Each pair was placed in the nickel -crucible and heated by means of the blast-lamp for half an hour. - -After cooling in desiccators, both pairs of crucibles where placed in -the closed balance until no longer affected by the moisture of the -air, which was also dried by calcium chloride. The tare was brought to -within one tenth of a milligram of the weight of the crucibles against -which it was being tared, by adding fragments of porcelain obtained -from another crucible of the same composition. The difference in weight -between the tare and its mate was then accurately ascertained. - -Each pair of crucibles was again placed in the nickel crucible and -blasted for half an hour. They were then reweighed, to determine if the -difference in weight previously found had remained constant. In no case -was any change detected, yet this precaution was always taken. - - -The Results. - -The following table contains the results of ten successive -determinations. - - At. Wt. Cd. At. Wt. Cd. - Wt. of Cd. Wt. of CdO. (O = 16) (O = 15.96) - I 1.77891 2.03288 112.070 111.790 - II 1.82492 2.08544 112.078 111.798 - III 1.74688 1.99626 112.078 111.798 - IV 1.57000 1.79418 112.053 111.773 - V 1.98481 2.26820 112.061 111.781 - VI 2.27297 2.59751 112.059 111.779 - VII 1.75695 2.00775 112.086 111.806 - VIII 1.70028 1.94305 112.059 111.779 - IX 1.92237 2.19679 112.083 111.803 - X 1.92081 2.19502 112.078 111.798 - ------- ------- ------- ------- - Mean, 112.0705. 111.7905. - Maximum, 112.086. 111.806. - Minimum, 112.053. 111.773. - Difference, .033. .033. - -Calculating the atomic weight of cadmium from the total amount of metal -used and oxide found, we have: - - At. Wt. of Cd. At. Wt. of Cd. - (O = 16) (O = 15.96) - 112.0706. 111.7904. - -These results agree more closely with those of von Hauer and Lenssen -than with those of any other experimenter. The following table gives -a comparison of the work of these investigators with that herein -described: - - von Hauer. Lenssen. Work here described. - 9 determinations. 3 determinations. 10 determinations. - (O = 16) (O = 16) (O = 16) - Mean 111.940 112.067 112.0705 - Max. 112.121 112.304 112.086 - Min. 111.796 111.911 112.053 - Diff. .325 .393 .033 - -A difference of three or four tenths of a unit between the different -results of a series leaves considerable doubt as to the accuracy of the -method employed and to the value obtained. - -The figure selected by Ostwald,[5] as most probable for the atomic -weight of cadmium is 112.08. This is the mean of the results on von -Hauer and Huntington. My own work leads me to believe that this number -is very close to the true value when oxygen is taken as 16. - -[5] Lehrb. d. Allg. Chem. I, 60. - - -Objections to the method. - -Marignac[6] offered the objection to this method for determining the -atomic weight of zinc that the zinc oxide dissociated when heated in -platinum over the blast-lamp. The same objection might be urged against -this method for determining the atomic weight of cadmium, had it not -been shown that the objection does not hold for zinc[7]. What took -place was a reduction of the zinc oxide by the highly heated hydrogen -which passed through the hot platinum. - -[6] Archives des Sciences Phys. et Nat. (3) 10, 193. - -[7] Amer. Chem. Journ. X, 148. - -It was shown that zinc oxide can be heated in a platinum vessel in a -muffle furnace, to the melting point of steel, without undergoing any -dissociation, or in any wise losing in weight. This source of error was -avoided by using porcelain vessels, which were not brought into contact -with the free flame. - -The statement of Marignac that the oxide of zinc derived from the -nitrate retains oxides of nitrogen even when heated to the temperature -at which it begins to undergo dissociation, was shown by the same -authors to be without foundation. The basis of this objection is -doubtless to be found in the imperfect method of testing for such -oxides. - -It might be urged as an objection to this method that the difference -in weight between the metal and oxide is not very great, therefore any -error in weighing would be multiplied in the result. At first sight -this objection may appear valid, but since the substances weighed were -so well adapted to that purpose and the weighings could be made with -such a high degree of accuracy no appreciable error could have resulted -from this source. - -A crucible with its contents was repeatedly weighed against its tare -and weights to ascertain the difference between successive weighings -under the conditions employed. A number of weighings agreed to .00002 -gr. and in some instances to half this amount. - - -Advantages of the Method. - - 1 The great advantage of the method is its extreme - simplicity. From the beginning of an experiment until - the end the contents of the crucible are not brought - into contact with any foreign substance. By this means - small errors resulting from incomplete precipitation, - and filtration and all other errors incident to ordinary - processes of analysis were avoided. - - 2 The nature of the metal and its oxide rendered them well - adapted to weighing. The specific gravity of the metal and - oxide approached so closely to that of the weights, that - it was unnecessary to reduce the weighings to a vacuum - standard. - - 3 The advantages derived from weighing by tares have been - pointed out. - - 4 The closely agreeing results speak strongly in favor of - the accuracy of the method. - - - - -The Oxalate Method. - - -The method consists in taking a weighed amount of cadmium oxalate, -decomposing it by heat, when a mixture of oxide and metal are said -to be formed, dissolving this mixture in nitric acid, converting the -nitrate into oxide and weighing the oxide. - -Lenssen[8] obtained results by this method which agree very closely -with those recorded in the earlier part of this dissertation. - -Working with the same method, Partridge[9] arrived at a value about one -fourth of a unit lower than that of Lenssen. - -[8] Journ. f. prakt. Chem. 79, 281. - -[9] Amer. Journ. Science XL, 377. - -It appeared desirable that this method should be repeated with the -greatest care to ascertain what result it would give under the most -favorable conditions. - -Having a supply of pure cadmium it was necessary to prepare pure oxalic -acid. - - -Preparation of Pure Oxalic Acid. - -The commercial acid was crystallized three times from cold water to -separate it from acid oxalates. It was then boiled for two days with -a 15 per cent solution of hydrochloric acid, to remove any mineral -matter present. The acid which crystallized from the hydrochloric acid -solution was recrystallized twice from hot, redistilled alcohol and -twice from pure ether. It was finally boiled with water to decompose -any ethyl oxalate and twice crystallized from pure water. The acid was -dried in the air at ordinary temperatures. This acid left no residue on -ignition. - - -Preparation of Cadmium Oxalate. - -A piece of cadmium was dissolved in pure nitric acid. On carefully -evaporating the solution cadmium nitrate was obtained. Twenty-five -grams of the nitrate were dissolved in 750 c.c. of redistilled water. -Somewhat less than an equivalent of the oxalic acid was dissolved in -an equal volume of water, and slowly added to the solution of the -nitrate with constant shaking. A little less than an equivalent of -oxalic acid was used to avoid any tendency to form acid oxalates. -Cadmium oxalate was precipitated on standing a few minutes as a white -crystalline compound, well adapted to washing. The oxalate was filtered -off and washed until the wash water was free from all traces of nitric -acid. It was then washed ten times with water which had been twice -redistilled and dried in an air-bath for twenty hours at 150°C. - -The arrangement of the crucibles which were weighed was in all respects -like that in the preceding method. - - -Mode of Procedure. - -The crucibles were heated, tared, and weighed exactly as in the -preceding method. The oxalate was weighed in ground-stoppered weighing -tubes from which it was transferred to the inner of the two porcelain -crucibles. The pair of crucibles, (1 and 2 fig. 3) was placed in a -third porcelain crucible and the whole system introduced into an -upright air-bath. The outer crucible was supported on a porcelain -triangle about an inch from the bottom of the bath and was not allowed -to touch its walls at any point. The top of the bath was covered with a -sheet of iron over which was placed an asbestos board. The exterior was -also covered with a lining of asbestos. A thermometer was introduced -well into the bath. The temperature was allowed to rise slowly until -the oxalate began to show a brown color around the edge. From this -stage the temperature was kept as low as possible in order to effect -the decomposition. When the oxalate was decomposed the bath was allowed -to cool and the contents of the crucible completely dissolved in nitric -acid. The nitrate was evaporated to dryness and decomposed as in the -method first described. The end of the decomposition was determined in -the same manner and the oxide, free from all impurities, weighed. - - -The Drying and Weighing of the Oxalate. - -It was necessary to dry the oxalate before weighing from fifteen to -twenty hours at 150°C. in addition to the twenty hours drying of the -whole preparation. At this temperature the last traces of moisture were -removed by prolonged heating. - -The weighing of the oxalate was made in the weighing glasses in which -it was dried. Two of these glasses had been previously tared against -each other, using the lighter as the tare and adding fragments of -glass to it until the difference in weight was a small fraction of -a milligram. The oxalate having been dried to constant weight, was -weighed. It was then poured as carefully and completely as possible -from the weighing glass into the crucible and the glass again weighed -against its tare. The difference in the two weights gave the amount of -oxalate. The glass and its tare were dried and reweighed to determine -if the few milligrams of oxalate adhering to the walls of the glass -had absorbed any moisture during the transfer of the oxalate. In one -experiment a slight difference was detected when a second drying and -weighing were made. - -The weight of the cadmium oxalate as obtained from the balance was -corrected for the difference in specific gravity between the cadmium -oxalate and the weights. - - -The Results. - - At. Wt. At. Wt. At. Wt. At. Wt. - Cd. Cd. Cd. Cd. - (O=16) (O=16) (O=15.96) (O=15.96) - (C=12.001) (C=12.003) (C=11.971) (C=11.973) - CdC₂O₄ CdO - I 1.53937 .98526 112.026 112.033 111.746 111.753 - II 1.77483 1.13582 111.981 111.988 111.701 111.708 - III 1.70211 1.08949 112.049 112.056 111.769 111.776 - IV 1.70238 1.08967 112.051 112.058 111.771 111.778 - V 1.74447 1.11651 112.019 112.026 111.739 111.746 - ------- ------- ------- ------- - Mean, 112.025 112.032 111.745 111.752 - Maximum, 112.051 112.058 111.771 111.778 - Minimum, 111.981 111.988 111.701 111.708 - Difference, .070 .070 .070 .070 - -The values assigned to carbon in the last two columns were found thus-- - - When O = 16, C = 12.001, when O = 15.96, C = 11.971. - ” O = 16, C = 12.003, ” O = 15.96, C = 11.973. - -Calculating the atomic weight directly from all the oxalate used and -oxide found it would give: - - At. Wt. Cd. At. Wt. Cd. At. Wt. Cd. At. Wt. Cd. - (O = 16) (O = 16) (O = 15.96) (O = 15.96) - (C = 12.001) (C = 12.003) (C = 11.971) (C = 11.973) - - 112.025. 112.032. 111.745. 111.752. - -There seems about equal evidence for the two values assigned to carbon -when oxygen = 16. The value of cadmium as given by this method is -therefore 112.025 or 112.032. - -As will be seen at a glance this figure agrees much more closely with -that of Lenssen than with that of Partridge. - - Lenssen Partridge My work - 112.043. 111.816. 112.025 or - 112.032. - -It also agrees fairly well with the figure 112.0706 which I obtained by -the first method described. - - -Advantages of the Method. - -The method possesses no advantage whatever over the one which involves -starting with the element itself. The oxalate can however be obtained -pure having pure metal. The salt is of definite composition when -perfectly dry. - -The method as carried out avoided the contact of any foreign material -with the salt after it was weighed. - - -Disadvantages of the Method. - - 1 The avidity with which the dried oxalate takes up - moisture from the air is an objection to its use for the - determination of atomic weights. Even with the greatest - care there is a slight element of uncertainty introduced - from this source. - - 2 The oxalate is stated to decompose into a mixture of - the oxide and metal. The temperature required for this - decomposition is somewhat higher than the melting point - of cadmium. The metal heated above its melting point - possesses a vapor-tension and loss in weight must result, - whatever precaution is taken in heating. This is the - probable explanation why the results obtained by this - method are lower than those of the preceding. - -A comparison of the two methods leads me to attach much more importance -to the results of that one which establishes the relation between -cadmium and cadmium oxide directly and I therefore regard the atomic -weight of cadmium as very closely expressed by the figure 112.07 when -oxygen = 16. - - - - -Preparation of Certain Sub-compounds of Cadmium. - -Historical. - -Cadmium acts so generally as a bivalent element that it is usually -regarded as entering into combination only where it can play this rôle. -The only compound described, in which it has apparently a lower valence -than two, was prepared by Marchand[10]. It was obtained by heating -cadmium oxalate to the melting point of lead when a green powder -remained behind which resembled chromium oxide. When heated on the air -it appeared to be decomposed into metal and oxide. When treated with -mercury the compound was not altered. An analysis showed it to have the -composition represented by the formula Cd₂O. - -[10] Pogg. Ann. XXXVIII, 143. - -A. Vogel[11] has shown that the green powder described by Marchand -consists of a mixture of the metal and oxide. When this mixture is -treated with dilute acetic acid the metal remains behind as microscopic -glistening globules. The lower the temperature at which the oxalate is -decomposed the more oxide and the less metal were found in the product. - -There was then no compound known in which cadmium acted as if its -valence was less than two when this work was undertaken. - -That it may act with a greater valence was shown by R. Haafs[12]. He -found that when zinc hydroxide was treated with hydrogen dioxide -certain compounds of zinc and oxygen were formed containing more oxygen -than the normal oxide ZnO. The close resemblance between zinc and -cadmium led him to try the same reaction with cadmium. Hydrogen dioxide -was accordingly allowed to act on cadmium hydroxide and the resulting -product analyzed. There were formed Cd₅O₈, Cd₃O₅ and Cd₄O₇. In no case -was the compound CdO₂ obtained. These compounds are described as fairly -stable even at a hundred degrees. - -[11] Jahrb. 1855, 390. - -[12] Ber. 1884, 2249. - - -The Preparation of Cd₄Cl₇. - -When anhydrous cadmium chloride is heated with metallic cadmium in a -vacuum, or in an atmosphere of nitrogen, to the fusing point of the -chloride, the molten chloride quickly assumes a garnet red color. -In order to investigate this phenomenon a quantity of the chloride -was prepared by dissolving the redistilled metal in an excess of -hydrochloric acid, evaporating the chloride to dryness on a water -bath, and finally removing the water of crystallization by heating in -a current of dry hydrochloric acid gas. The heating was effected by -placing the chloride in a long platinum boat, which was shoved into a -large glass tube, through which was passed a current of the acid gas. -The tube was heated by means of a combustion furnace and the chloride -kept in the molten condition for two or three hours. By this means -a perfectly white crystalline chloride of the composition CdCl₂ was -obtained, free from water or oxychloride. - -The chloride and an excess of metal were placed in a long-necked flask -of hard glass and after the displacement of the air by nitrogen, heated -to the melting point of the chloride. The liquid chloride attained its -maximum depth of color in a few minutes, nevertheless the heating was -continued for five hours. When the temperature was allowed to rise much -above the melting point of the chloride the red substance underwent -decomposition and globules of metal collected upon the walls of the -flask. For this reason no more heat was applied than was just necessary -to keep the contents of the flask in a liquid condition. During the -very gradual cooling of the flask it was shaken gently in order to -facilitate the sinking of any metal, which might be mechanically -retained by the chloride. - -On cooling, the solidified mass possesses a slightly greenish tint -which disappeared when cold, the substance having then a grayish white -color and a cleavage resembling that of talc or brucite. When examined -under the microscope it was found to be perfectly homogeneous and -free from metal. It gave no metallic streak when rubbed between agate -surfaces. - -An analysis of the first preparation showed the following composition; - - Amount of chloride used .33541 gr. - ” ” cadmium found .21559 ” - ” ” chlorine ” .11943 ” - - Cadmium. Chlorine. - 64.27 per cent. 35.61 per cent. - -These proportions are nearly those of a compound having the composition -Cd₄Cl₇, in which the calculated percentages are: - - Cadmium. Chlorine. - 64.34 35.66 - - (Foot note). In the paper in the American Chemical Journal - XII, 488, which records this work the analyses and - percentages were calculated on the basis of the atomic - weight of cadmium = 111.7. Although my work since this date - has shown that 112.07 is the true value, yet I think it - preferable to use the old number here since the changes to - be introduced would be very slight and the same results are - thereby kept uniform in the two publications. - -In order to determine whether the close approximation to definite -atomic proportions might not be accidental, the material was reheated -with an excess of the metal for twenty hours. The product was analyzed. - - Amount of chloride used 1.45970 gr. - ” ” cadmium found .93904 ” - ” ” chlorine ” .52329 ” - - Cadmium. Chlorine. - 64.33 per cent. 35.85 per cent. - -A second preparation of the substance was made in all respects like the -first. Two analyses were made. - -First Analysis: - - Amount of chloride used .61010 gr. - ” ” cadmium found .39235 ” - ” ” chlorine ” .21725 ” - - Cadmium. Chlorine. - 64.31 per cent. 35.61 per cent. - -Second Analysis: - - Amount of chloride used .20616 gr. - ” ” cadmium found .13266 ” - ” ” chlorine ” .07352 ” - - Cadmium. Chlorine. - 64.35 per cent. 35.66 per cent. - -A third preparation was made like the first and second and analyzed. - -Analysis: - - Amount of chloride used .2832 gr. - ” ” cadmium found .18244 ” - ” ” chlorine ” .10123 ” - - Cadmium. Chlorine. - 64.42 per cent. 35.74 per cent. - -When the new substance is heated it fuses to a red liquid and then -breaks up into metal and the chloride of cadmium. Its reactions are in -general those of a strong reducing agent. Treated with nitric acid, -oxides of nitrogen are liberated. With dilute hydrochloric, sulphuric -and acetic acids it gives free hydrogen. In the presence of dilute -acids it reduces mercuric to mercurous chloride, or to metallic mercury. - -Three determinations of the reducing power of the substance were made -with a freshly prepared specimen, by dissolving weighed portions in -hydrochloric acid and measuring the hydrogen liberated. - -The following results were obtained: - - Hydrogen found. Hydrogen calculated - for Cd₄Cl₇. - 1ˢᵗ determination 15.67 c.c. 15.65 c.c. - 2ⁿᵈ ” 11.80 c.c. 11.82 c.c. - 3ʳᵈ ” 23.00 c.c. 23.03 c.c. - -An examination of the analyses shows beyond question that the -substance formed by the action of metallic cadmium on the molten -anhydrous chloride is of definite composition. The proportion of -cadmium to chlorine could not be changed even when the substance was -heated with the metal for twenty hours, while a very short time was -sufficient for its formation when the metal and chloride were melted -together. - -It may be possible that a substance possessing these properties is -not a definite chemical compound but a mixture of cadmous and cadmic -chlorides or a solution of one in the other. - -If it were a solution it is difficult to see why the composition of the -solution should be so constant, since the solubility of a substance -is generally altered by a change in temperature. The different -preparations were not made at exactly the same temperature yet the -composition of the different preparations was the same. - -If the substance was a mixture of the two chlorides, when treated with -water the cadmic chloride would most probably dissolve directly leaving -the cadmous chloride to be acted upon by the water. The decomposition -by water will however be seen not to be as simple as would be expected -under these conditions. - -From the above considerations it appears highly probable that the -substance is a definite chemical compound of cadmic and cadmous -chlorides. If cadmic chloride can form a chemical compound with the -chloride of another element there appears to be no reason why it -should not form a compound with another chloride of cadmium, as with -cadmous chloride. - - -The preparation of Cd₄Br₇. - -The anhydrous bromide of cadmium was prepared by dissolving the -carbonate in an aqueous solution of hydrobromic acid, evaporating -the bromide to dryness on the water bath and heating the residue in -a current of dry hydrobromic acid gas. When the bromide was heated -with an excess of the metal in an atmosphere of nitrogen it conducted -itself in general like the chloride. When the molten bromide and the -metal came in contact the salt quickly became deep red in color. -After heating for some time considerable dissociation was produced by -raising the temperature. This was more apparent in the preparation of -the bromide than with the chloride. On cooling, the mass possessed -a greenish tint which disappeared when cold, the bromide then being -very nearly the same color as the corresponding chloride. Also like -the chloride it appeared to be homogeneous and free from metal. Two -determinations of cadmium and two of bromine were made, using the -product as soon as prepared. - -First determination of cadmium: - - Amount of substance used .3736 gr. - ” ” cadmium found .16658 ” - - Cadmium. - 44.59 per cent. - -Second determination of cadmium: - - Amount of substance used .35930 gr. - ” ” cadmium found .16013 ” - - Cadmium. - 44.57 per cent. - -First determination of bromine: - - Amount of substance used .66640 gr. - ” ” bromine found .36953 ” - - Bromine. - 55.45 per cent. - -Second determination of bromine: - - Amount of substance used .56035 gr. - ” ” bromine found .31085 ” - - Bromine. - 55.47 per cent. - -The percentage of cadmium and bromine found agrees very closely with -that of a compound of the formula Cd₄Br₇. The relation of cadmium to -bromine in this would be: - - Cadmium. Bromine. - 44.44 per cent. 55.56 per cent. - -When this compound was heated for a long time with an excess of the -metal its composition was not appreciably changed. - -The compound Cd₄Br₇ is a strong reducing agent: giving with nitric -acid oxides of nitrogen, with dilute hydrochloric, sulphuric or acetic -acid, free hydrogen, and with mercuric chloride, mercurous chloride or -metallic mercury. The action of water on the bromide by means of which -cadmous hydroxide was formed, was not studied as carefully as with the -chloride but appeared to be essentially the same. - - -The Preparation of Cd₁₂I₂₃. - -Cadmic iodide was prepared in the same manner as the bromide. It was -dried in a stream of hydriodic acid gas at as low temperature as -possible to lessen the decomposition of the hydriodic acid. When the -anhydrous iodide was heated with an excess of metal in an atmosphere of -nitrogen the red color of the iodide became intensified. Heating was -continued until there was evidence of dissociation, which, under the -same conditions, was less marked than with the chloride and much less -than with the bromide. Owing to the high specific gravity of the iodine -compound some difficulty was experienced in obtaining a preparation -free from metal. This difficulty was finally overcome by keeping -the material just above its melting temperature for a long time and -constantly jarring the flask. During the process of cooling a decidedly -greenish tint was observed which disappeared as the process was -continued. When cold the substance resembled the chloride and bromide. -Two determinations of cadmium were made in the first preparation. - -First determination: - - Amount of substance used .55540 gr. - ” ” cadmium found .17456 ” - - Cadmium. - 31.43 per cent. - -Second determination: - - Amount of substance used .47535 gr. - ” ” cadmium found .14980 ” - - Cadmium. - 31.51 per cent. - -As these results did not correspond to the composition represented by -the formula Cd₄I₇, which our experience with the chloride and bromide -had led us to expect, we reheated the material for several hours with -an excess of the metal. Two analyses of the product gave: - - Cadmium. Iodine. - 31.44 per cent. 68.65 per cent. - 31.39 68.68 - -showing that the iodide had taken up during the first heating all the -metal which it could retain. The analytical results suggest the formula -Cd₁₂I₂₃, in which the calculated percentages are: - - Cadmium. Iodine. - 31.53 per cent. 68.47 per cent. - -In its conduct towards dilute hydrochloric and acetic acids and water -the substance behaves like the corresponding chloride and bromide. - - -The Preparation of Cadmous Hydroxide and Oxide. - -When the substance Cd₄I₇ is treated with water a complicated reaction -takes place. The general character of the reaction appears to be the -same with the chloride, bromide and iodide. The decomposition of the -chloride was studied more thoroughly than that of the other compounds. - -When the finely powdered chloride is treated with water it yields -cadmic chloride which passes into solution, a small quantity of a white -flocculent material which may be cadmic hydroxide but which in no case -could be entirely freed from traces of chlorine, and a highly lustrous -crystalline substance which rapidly lost its crystalline appearance -and passed over into a grayish white amorphous compound, which when -freed from chlorine was found to be cadmous hydroxide, of the formula -Cd(OH). The separate products resulting from the treatment with water -were analyzed. - -First Analysis: - - Amount of Cd₄Cl₇ treated with water 1.45970 gr. - Cadmium found in flocculent precipitate .02318 ” - ” ” ” crystalline substance .09614 ” - ” ” ” solution in water .81970 ” - Total cadmium found .93902 ” - - Chlorine found in crystalline compound .00371 gr. - ” ” ” solution in water .51671 ” - Total chlorine found .52042 ” - -Approximately seven-eighths of the total cadmium dissolved as -cadmic chloride while the remainder was contained in the flocculent -precipitate and in the gray crystalline compound. - -Second Analysis: - - Amount of Cd₄Cl₇ treated with water 1.0794 gr. - Cadmium found in flocculent precipitate .01469 ” - ” ” ” solution in water .60795 ” - - Chlorine found in solution in water .38491 ” - -The percentage of cadmium in the white precipitate is less in this -analysis than in the former. The cadmium in solution is again about -seven-eighths of the total and the chlorine present in the same -solution shows that the cadmium was all combined as cadmic chloride. - -All attempts to determine the composition of the gray crystalline -compound failed, owing to the rapidity with which it decomposed with -water. Even with the most rapid work it could not be isolated in the -undecomposed condition. - -Analyses of the partially decomposed crystals gave variable proportions -of metal and halogen but never less than eight equivalents of the -former to one of the latter. - -While the decomposition of Cd₄Cl₇ with water cannot at present be fully -explained, yet it is clear from the analyses that one eighth of the -total cadmium is thrown down as a white precipitate and a crystalline -compound which as will be seen passes over into cadmous hydroxide. One -half of the cadmous chloride is oxidized to cadmic chloride taking the -chlorine from the other half. - -The compound Cd₄Cl₇ was treated directly with absolute alcohol with -the hope of obtaining the crystalline substance in an undecomposed -condition. Although a substance of the same general appearance as that -formed in the presence of water was obtained yet it decomposed so -readily that a satisfactory analysis could not be made. - -Notwithstanding the rapidity with which the decomposition of the -crystalline compound begins, long continued washing was necessary in -order to completely remove the chlorine. The extraction of the last -traces of the halogen is hastened by the use of warm instead of cold -water. The temperature of the water must not exceed 50°C. In water -whose temperature approaches the boiling point the hydroxide is slowly -decomposed with liberation of metal. - -The new hydroxide is a strong reducing agent. It dissolves in dilute -acids; yielding with nitric acid oxides of nitrogen, with hydrochloric -or sulphuric acid free hydrogen. After washing with warm water until -all the chlorine had disappeared, it was dried over phosphorus -pentoxide and analyzed. - -First determination of cadmium. - - Amount of substance used .0968 gr. - ” ” cadmium found .08415 ” - - Cadmium. - 86.93 per cent. - -Second determination of cadmium. - - Amount of substance used .09806 gr. - ” ” cadmium found .08522 ” - - Cadmium. - 86.91 per cent. - -The calculated percentage of cadmium in Cd(OH) is: - - Cadmium. - 86.79 per cent. - -The determination of water in cadmous hydroxide was made by placing a -small specimen tube containing the hydroxide in a Kjeldahl flask which -was heated in a bath of concentrated sulphuric acid. During the heating -a slow current of dry nitrogen was passed over the substance. - -First determination of water. - - Amount of substance used .08434 gr. - ” ” water found .00609 ” - - Water. 7.22 per cent. - -Second determination of water. - - Amount of substance used .08895 gr. - ” ” water found .00600 ” - - Water. 6.74 per cent. - -Third determination of water. - - Amount of substance used .11766 gr. - ” ” water found .00856 ” - - Water. 7.25 per cent. - - Average amount of water = 7.07 per cent. - -The calculated percentage of water in Cd(OH) is, 6.99. - -At the temperature at which concentrated sulphuric acid gives off -dense white fumes cadmous hydroxide gives off all its water and passes -over into a heavy yellow powder. At 150°C not a trace of water was -liberated. Under the microscope the yellow powder was found to consist -of minute translucent crystals. - -First determination of cadmium. - - Amount of substance used .08064 gr. - ” ” cadmium found .07511 ” - - Cadmium. 93.14 per cent. - -Second determination of cadmium. - - Amount of substance used .10846 gr. - ” ” cadmium found .10106 ” - - Cadmium. 93.17 per cent. - -The calculated percentage of metal in Cd₂O is 93.32 per cent. - -If water of too high temperature is employed in washing the -subhydroxide, the presence of free metal in it can be detected under -the microscope and by rubbing between agate surfaces. If the yellow -suboxide is strongly heated it breaks up into a mixture of oxide and -metal which possesses a distinctly green color. Towards acids the -suboxide conducts itself like the subhydroxide. - -It is a fact of some interest in connection with the periodic -arrangement of the elements, that the tendency toward the formation -of a lower series of compounds which becomes so strongly developed in -mercury begins to exhibit itself in some slight degree in cadmium. - - - - -Notes on Crystals of Metallic Cadmium. - - -The measurements of the cadmium crystals were made by Dr. Williams who -has very kindly furnished me with his results. - -No reliable crystallographic description of the element cadmium seems -thus far to have appeared--a fact due to the difficulty in obtaining -suitable material. The crystals examined, although not capable of -yielding entirely satisfactory results are nevertheless such as to make -them of interest. - -In 1852 G. Rose noted the fact that distilled cadmium collected at the -neck of the retort in drops which solidified as complex polyhedral -aggregates[13] similar to those formed by zinc[14]. In 1874 Kammerer -encountered the same aggregates which he explained as complicated -isometric combinations[15]. This opinion was cited in 1881 by -Rammelsberg[16]. In 1884 Brögger and Flink stated that in their opinion -zinc, magnesium and probably cadmium were from analogy with beryllium -which they had studied, hexagonal and holohedral.[17] - -[13] Pogg. Ann. 85, 293. - -[14] Amer. Chem. Journ. 11, 219. - -[15] Ber. d. deutch. Chem. Gesell. 1874, 1724. - -[16] Handb. d. krystallographisch physicalischen Chemie. I, 184. - -[17] Zeits & Kryst. 9, 236. - -This supposition has already been substantiated in the case of the two -former elements[18] while the present material leads to the same result -for the last named. - -The cadmium crystals were produced in the same manner as were those of -zinc and magnesium measured before, viz; by distillation in a vacuum. -The appearance of the tubes thus obtained was closely like that in the -other cases. - -[18] Amer. Chem. Journ. 11, 225 and Ibid. 12, 225. - -The polyhedral aggregates were abundant and reached considerable -dimensions. The crystallizing power of the cadmium however, seems to be -less, so that the only crystals suitable for measurement were extremely -minute. The largest individuals were barrel-shaped, like those of zinc -and resembled little piles of basal plates. Their side planes are not -infrequently uneven and bent, probably as the result of the softness -and great ductility of the metal. - -Only the most minute crystals show pyramidal planes of comparative -perfection. These are well suited for a microscopic examination, but -their small size renders their measurement on a reflecting goniometer -a matter of difficulty. After a careful search two crystals were -secured which, although they had a diameter of only one third of a -millimeter, from their microscopic appearances promised good results. -Their planes however were found to give compound reflections and a -somewhat disappointing variation in corresponding angles. On the best -crystal three zones were measured as follows: (normal angles) - - Zone I Zone II Zone III - 0001 : 01ī1 = 62° 35′ |0001 : 10ī1 = 62° 4′ |0001 : 1ī01 = 62° 29′ - 0001 : 01ī0 = 89° 50½′| | - 0001 : 01īī = 118° 57′ |0001 : 10īī = 118° 28′| - -The second crystal was much less satisfactory, since values for the -angle between the base and pyramid (0001): (01ī1) were obtained which -varied all the way from 61° 2′ to 63° 43′. These measurements must -therefore be regarded as of little or no value. If we average the -readings for this angle on the first crystal we obtain 62° 23′, from -which - - ̲a : ̲c = 1 : 1.6554. - -A comparison of the axial ratios of the four rhombohedral and four -holohedral hexagonal elements gives the following: - - - { Bismuth ̲a : ̲c = 1 : 1.3035 (G. Rose, 1849). - Rhombo- { Antimony ̲a : ̲c = 1 : 1.3235 (Laspeyres, 1875). - hedral. { Tellurium ̲a : ̲c = 1 : 1.3298 (G. Rose, 1849). - { Arsenic ̲a : ̲c = 1 : 1.4025 (Zepharovich, 1875). - - { Zinc ̲a : ̲c = 1 : 1.356425 (Williams and - { Burton, 1889). - Holohedral. { Beryllium ̲a : ̲c = 1 : 1.5802 (Brögger, 1884). - { Magnesium ̲a : ̲c = 1 : 1.6202 (Williams, 1890). - { Cadmium ̲a : ̲c = 1 : 1.6554 (Williams, 1891). - -Zinc appears from its axial ratio to belong rather to the rhombohedral -group and this is the only one of the last four elements upon which the -faintest indication of any divergence from a holohedral development -of all of its forms has been observed. On crystals of this substance -there is an occasional rhombohedral alternative of the faces of -certain of the pyramids, although the crystals otherwise appear to be -holohedral.[19] - -The crystals of cadmium like those of magnesium show only the three -forms OP (0001), P (10ī1)₂, and ∞P (10ī0). Brögger and Flink observed -on beryllium the additional forms ∞P₂ (2īī0) and ½P (20{̅2}1); while -upon zinc a large number of forms in the zone of the unit pyramid occur. - -[19] Amer. Chem. Journ. 11, 224. pl. 2 fig. 8. - -Not infrequently the cadmium crystals show a tendency toward a -hemimorphic development. This is plainly seen when a large number -of them are examined together under the microscope. The little -barrel-shaped crystals are mostly attached by their sides and yet one -of their ends is often broader than the other. Sometimes they taper -nearly to a point, quite like greenockite crystals. - - - - -The Cohesion Phenomena of Cadmium. - - -The cohesion phenomena of cadmium are similar to those of zinc but -are still more striking. When a crystal is sharply focused under the -microscope and then gently pressed on the side with the point of a -needle an unbroken pyramidal face is seen to suddenly become striated -parallel to the basal plane, as though a gliding in the basal section -took place. Some of these crystals were kindly examined by Prof. Otto -Mügge of Münster, Germany, who has added so much to our knowledge -of the cohesion phenomena in crystals. He has written in regard to -his observations as follows; “The cadmium crystals as far as their -gliding phenomena are concerned behave quite like zinc. If a crystal -is carefully loosened and then squeezed with a pair of pincers it is -easy to see that the smooth surface where it was attached to the glass -became striated parallel to OP (0001) and that at the same time two -other sets of striations are produced which meet at an angle of about -85° and intersect the trace of the basal plane at about 47½°. The plane -of attachment was selected for observation because it was smoother than -the pyramidal faces. In the above case this plane has the position of -a steep pyramid inclined to the base at an angle of about 100°. The -oblique sets of striations appear to represent gliding planes parallel -to the unit pyramid faces (2P (10ī2) of Rose) as in the case with zinc. -Whether the horizontal striations were due to gliding parallel to the -base I could not certainly decide. Many of the crystals appear when -pinched to be completely overturned, in which cases ordinary bending -accompanies gliding as in the case of gold set. This is shown by the -fact that both faces and striations become rounded.” - - - - -Biographical Sketch. - - -Harry Clary Jones was born near New London, Frederick County, Maryland, -Nov. 11ᵗʰ 1865. - -After attending several schools in that state he entered the Johns -Hopkins University in the autumn of 1885 as a special student of -chemistry and physics. He matriculated in 1887 and received the degree -of Bachelor of Arts in 1889, having held an ordinary and an honorary -scholarship. For the last three years he has continued his studies -in the University following chemistry as a principal subject and -mineralogy and geology as subordinates. During this time he has been -appointed twice to a university scholarship, was lecture assistant to -professor Remsen,90-91, and Fellow in chemistry,91-92. - -*** END OF THE PROJECT GUTENBERG EBOOK DETERMINATION OF THE ATOMIC -WEIGHT OF CADMIUM AND THE PREPERATION OF CERTAIN OF ITS -SUB-COMPOUNDS *** - -Updated editions will replace the previous one--the old editions will -be renamed. - -Creating the works from print editions not protected by U.S. copyright -law 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. 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