26 
CHEMISTRY: BAXTER AND HARTMANN 
A REVISION OF THE ATOMIC WEIGHT OF CADMIUM 
By Gregory Paul Baxter and Miner Louis Hartmann 
COOUDGE MEMORIAL LABORATORY. HARVARD UNIVERSITY 
Presented to the Academy, October 31,1914 
In several recent investigations by Hulett and his collaborators^ 
concordant values have been obtained for the atomic weight of cadmium 
by the electrolytic deposition, in a mercury cathode, of the metal in 
hydrated and anhydrous cadmium sulphate and in anhydrous cadmium 
chloride and bromide, and by the comparison of simultaneous electro- 
lytic deposits of cadmium and silver. The average value so obtained 
for the constant in question is 112.3. On the other hand, Baxter, Hines, 
and Frevert^ had previously found a considerably higher value, 112.42, 
by the estimation of the halogen-content of cadmium chloride and bro- 
mide. So wide a discrepancy is disturbing and obviously needs attention. 
We therefore decided to repeat a portion of the work of Quinn and 
Hulett by analyzing anhydrous cadmium chloride through the electro- 
lytic deposition of the cadmium in a mercury cathode. 
Cadmium material was purified (1) by electrolytic deposition with 
a dissolving anode (yielding samples A and B), (2) by fractional pre- 
cipitation with hydrogen sulphide (yielding samples C and D), and 
(3) by crystallization of cadmium bromide (yielding samples E and F) ; 
these operations being followed by crystallization of cadmium chloride 
(except in the case of sample E where the bromide was converted 
into chloride by fusion in a current of dry chlorine). Another sam- 
ple (G) was obtained by combining the mother-liquors of the other 
specimens of cadmium chloride and, after crystallizing the salt, fus- 
ing the mixture in dry chlorine. In order to follow the purity of the 
different samples, the metal was deposited electrolytically from the 
mother-Kquor of the last chloride crystallization in each case; and, after 
conversion into electrodes by fusion, it was used for the production of 
spark-spectra which were photographed in a Fery quartz spectograph. 
Careful examination of the spectrograms in the visible and ultraviolet 
regions showed that some of the samples were wholly free from im- 
purities, and that, although some of them contained traces of copper and 
lead, the proportions of these impurities were too small to have any 
perceptible effect upon the outcome. Furthermore, the analyses of the 
chloride showed no apparent differences between the different samples. 
On the whole, crystalKzation of cadmium bromide seemed to be the most 
rapid and efficient method of purifying cadmium material. 
