Harry C. Jones

“ 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. ”

“ Analysis: 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ Second Analysis: 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. ”

“ 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. ”

“ Owing to the high specific gravity of the iodine compound some difficulty was experienced in obtaining a preparation [Pg 83] 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. ”

“ 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. ”

“ 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. [Pg 46]
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. ”

“ 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. ”

“ 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. [Pg 92]
First determination of cadmium. Second determination of cadmium. ”

“ Oxygen is taken as 16 throughout.
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.
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 [Pg 22] determination of the atomic weight of magnesium. ”

“ 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. ”

“ 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. [Pg 3]
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. ”

“ 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 [Pg 7] that in determinations 6-9. ”

“ 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 [Pg 62] 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. ”

“ 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 [Pg 33] until all the metal had dissolved. ”

“ 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. ”