THE ANALYSIS OF CADMIUM CHLORIDE. IS 



Although in our work with cadmium chloride, the double cadmium ammon- 

 ium chloride was fused in a current of hydrochloric-acid gas which had been 

 finally dried with phosphorus pentoxide, the salt, which contains no crystal 

 water, was essentially free from moisture before coming in contact with the 

 hydrochloric acid. Nevertheless it seemed desirable to repeat the experiments 

 with cadmium chloride in such a way that the danger mentioned above could 

 be completely avoided. This result was easily attained by drying the hydro- 

 chloric-acid gas with concentrated sulphuric acid only. 



In order to ascertain whether concentrated sulphuric acid is appreciably at- 

 tacked by hydrochloric-acid gas, a large quantity of this gas was conducted 

 through the columns and then into water. The aqueous solution was then 

 evaporated and tested for sulphate with barium chloride. Although a slight 

 precipitate of baric sulphate was produced, the quantity was estimated, by 

 comparison in a nephelometer with a standard solution of a sulphate, to be less 

 than 0.05 mg. Evidently nothing is to be feared from this source. 



PREPARATION AND DRYING OF CADMIUM CHLORIDE 

 FOR THE FINAL ANALYSES. 



The material for these experiments was prepared from a portion of fraction 

 II of cadmiimi sulphide, by first depositing the metal electrolytically from the 

 sulphate. At first electrolysis was carried on in a solution of the sulphate in 

 pure water, between two electrodes of platinum foil. A sponge of extremely 

 small crystals was thus produced. These crystals contained occluded sulphate 

 in considerable quantities, and no amount of washing with water was sufficient 

 completely to leach out this occluded material. More satisfactory results were 

 obtained by depositing the metal upon a platinum dish which had been covered 

 with a very thin film of soft paraffine, so that the deposit could be readily sep- 

 arated from the dish.^ The cadmium was first washed with water, then with 

 ether, next with alcohol, and finally with water again. This treatment effect- 

 ually cleansed the metal from paraffine. 



The metal was next dissolved in pure hydrochloric acid in a platinum dish. 

 The chloride does not lend itself readily to crystalhzation from aqueous solu- 

 tion on account of its great solubility even at low temperatures, but by con- 

 ducting hydrochloric-acid gas into the solution the much less soluble double 

 salt with hydrochloric acid, CdCl22HCl7H20, was formed. The salt was thus 

 crystallized 3 times with centrifugal drainage, to free it from the trace of sul- 

 phates occluded by the metal during electrolysis. Finally, it was dried and 

 freed from hydrochloric acid as far as possible in a vacuum desiccator contain- 

 ing solid potassium hydroxide. 



Before fusion the salt was largely freed from water and hydrochloric acid by 

 gentle heating. 



* Richards: Proc. Amer. Acad. ,25, 200 (iSgo). 



