| 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.
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.