E. A. Partridge — Atomic Weight of Cadmium. 379 



The method consists in changing cadmium oxalate to cadmium 

 oxide, and observing the loss of weight from which loss the 

 atomic weight is calculated. 



For working this method cadmium oxalate was made as 

 follows : 



The perfectly pure metallic cadmium obtained by double 

 distillation was dissolved in pure nitric acid, prepared by care- 

 ful distillation, and the solution concentrated so far that on 

 cooling the cadmium nitrate Cd(N0 3 ) 2 + 4:H 2 0, separated in 

 long fibrous crystals. The latter were drained at the filter 

 pump, dissolved in water, and a solution of the theoretical 

 amount of pure oxalic acid added. Cadmium oxalate thus 

 prepared is a heavy crystalline precipitate which can be easily 

 washed. This was done several times by decantation. The 

 precipitate was then placed on a filter and washed at the pump 

 thirty times with distilled water, after which it was dried for 

 10 hours at 150° C. The salt thus obtained was tested for 

 nitric acid by the phenol test and showed not the slightest 

 trace. The pure cadmium oxalate thus obtained was subjected 

 to the following treatment : 



About one grain of cadmium oxalate was placed in a 

 porcelain crucible and was then dried in an air bath at 150° C. 

 for five hours. This length of time was usually sufficient to 

 dry the salt completely. When this had been accomplished, 

 i. e., when a constant weight had been attained, the crucible 

 containing the oxalate was covered with a watch glass and very 

 cautiously heated. This operation required the greatest care, 

 since if the temperature became too high, reduction and con- 

 sequent volatilization of metal occurred. Four of the earlier 

 experiments were lost in this way. That volatilization. of metal 

 had taken place was made evident by a slight sublimate on the 

 watch glass. When the oxalate was completely decomposed 

 (this was shown by the uniform brown color of the resulting 

 cadmium oxide) it was allowed to cool and moistened with a 

 few drops of nitric acid in order to re-oxidize any reduced 

 metal. The nitric acid employed for this purpose was espe- 

 cially purified by very careful distillation. Ten c. c. of it evap- 

 orated in a platinum dish left a visible but imponderable 

 residue. 



The crucible was then very carefully ignited until all the 

 cadmium nitrate was decomposed, then placed inside a nickel 

 crucible 4 cm high by 4 cm wide and strongly ignited for half an 

 hour by means of a Fletcher's improved Bunsen burner. In 

 all cases the ignition was repeated until a constant weight was 

 obtained. There was rarely, however, any loss of weight after 

 the first ignition. To prevent the possibility of any reducing 

 gases reaching the cadmium oxide, the nickel crucible inside 



