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.
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.