An examination of some methods employed in determining the atomic weight of Cadmium

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A Thesis
Presented to the Board of University Studies of the Johns Hopkins University for the Degree of Doctor of Philosophy.
John E. Bucher.
1894
The author wishes to acknowledge his indebtedness for advice and instruction to Professor Morse at whose suggestion and under whose guidance this work has been carried on. He also wishes to express his thanks for instruction to Professor Remsen in Chemistry, Professor Williams in Mineralogy, Dr. Ames in Physics and Mr. Hulburt in Mathematics.
The atomic weight of cadmium has been investigated by a number of chemists but the results obtained vary between wide limits. The work described in this paper was undertaken with the object of finding the cause of the discrepancy in some of the methods employed. A complete historical statement has been given by Morse and Jones, (Amer. Chem. Jour., 14. 261.) and it is only necessary, here, to give a summary for the purpose of reference:
In this summary as well as in the rest of this paper the following atomic weights are used:
“Cadmium met. puriss. galv. reduc”, obtained from Schuchardt, was used for preparing pure cadmium. It was heated to redness in a current of hydrogen which had been purified by washing with both acid and alkaline solutions of potassium permanganate. This treatment converted the metallic powder into a bar which could be distilled in a vacuum. The metal was then distilled nine times in the same manner that Morse and Burton, Amer. Chem. Jour. 12, 219, had distilled zinc. All distillations were made slowly except the last one, which was made quite rapidly.
Whenever pure nitric acid was required, it was purified by distilling against a platinum dish and collecting the distillate in a smaller one of the same metal. The nitric acid used was dilute and free from chlorine.
The water used in this work was purified by distilling twice from an alkaline solution of potassium permanganate, always rejecting the first part of the distillate. Whenever water was needed in the preparation of a pure compound e.g. cadmium oxalate, oxalic acid, cadmium nitrate, etc., it was subjected to the additional process of being distilled against a large platinum dish which was kept cool by placing ice inside it.