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. |