THE ANALYSIS OF CADMIUM CHLORIDE. 5 



long Standing for the precipitate to settle after each washing, although the flasks 

 which contained the precipitates were kept warm by being placed upon a steam 

 radiator. During the washing the original fine yellow precipitate was gradu- 

 ally converted into an orange-red crystalline modification. When, as was usu- 

 ally the case, both forms were present in the same flask, the red form quickly 

 settled to the bottom with a sharp line of division from the yellow form. Nearly 

 all the yellow form was changed into the red modification upon standing about 

 three weeks. 



In order to free the sulphide from included and occluded impurities each frac- 

 tion was dissolved and reprecipitated. The red form of the sulphide was ap- 

 parently nearly insoluble in dilute sulphuric acid, for in one case the washed 

 sulphide was boiled with the acid for 12 hours without any appreciable amount 

 of solution. Finally, hydrochloric acid was used to dissolve the cadmium 

 sulphide. The solution of each fraction was diluted to 8 liters and was sat- 

 urated with hydrogen sulphide. Since only a portion of the cadmium was 

 precipitated in this way, owing to the large excess of acid, the acid was par- 

 tially neutralized with ammonia. This resulted in the precipitation of more 

 cadmium sulphide, although the solution still contained considerable cadmium, 

 for cadmium sulphide is soluble to a marked extent in an acid solution of 

 ammonium chloride. 



The sulphide obtained from each of the original three fractions, both before 

 and after the addition of ammonia, was combined and washed until free from 

 chlorides. Each fraction was dissolved in redistilled nitric acid, then enough 

 redistilled sulphuric acid to convert the nitrate into sulphate was added, and 

 the solutions were evaporated and the residues heated until all volatile acids 

 were expelled. Finally the sulphate was recrystallized three times from 

 aqueous solution. 



The cadmium sulphate was converted into cadmium chloride by first obtain- 

 ing metallic cadmium electrolytically. A saturated solution of cadmium sul- 

 phate was electrolyzed with about one ampere current per square decimeter 

 in a platinum dish, which served as the cathode, until deposition ceased. After 

 the deposit of metal had been thoroughly washed with hot water until free from 

 sulphate, it was dissolved in hydrochloric acid which had been distilled with the 

 use of a platinum condenser. 



In order to prepare the double chloride of cadmium and ammonium of the 

 formula CdCl2NH4Cl, the calculated amount of ammonium chloride was added 

 to the cadmium chloride and the solution evaporated to crystaUization. This 

 ammonium chloride was synthesized from hydrochloric acid and ammonia. 

 The hydrochloric acid had been distilled in platinum, and the ammonia had 

 been freed from amines and purified as follows : Ammonium chloride was boiled 

 with concentrated nitric acid for about 20 hours, and then after crystallization 

 was converted into ammonia by distillation with sodium hydroxide. The solu- 

 tion of pure ammonia was distilled into the pure hydrochloric acid in a 



