60 CADMIUM AND ZINC. 



35. CADMIUM AND ZINC. 



The alloy of the two metals is dissolved in hydro- 

 chloric acid, the solution, which must be decidedly 

 acid, is largely diluted, and saturated with a slow 

 stream of sulphuretted hydrogen, which precipitates 

 all the cadmium in the form of a yellow sulphide. 

 The latter is thrown upon a weighed filter, and dried 

 at 100 till of constant weight. 



It is more accurate to dissolve the sulphide of cad- 

 mium in hydrochloric or nitric acid, and to precipitate 

 the oxide of cadmium from the solution, as white car- 

 bonate, by means of carbonate of soda. The precipi- 

 tate is washed, dried and ignited, when it is converted 

 into the brown oxide. Previously to the incineration 

 of the filter, the precipitate should be detached, as far 

 as possible. 



The filtrate is boiled to expel the sulphuretted hy- 

 drogen, and the zinc precipitated from the hot liquid 

 by carbonate of soda. 



Another method of separation consists in decom- 

 posing the solution of the two metals by considerable 

 tartaric acid, and then adding caustic soda to distinctly 

 alkaline reaction, dilute with considerable water, and 

 boil for some hours. The cadmium is alone precipi- 

 tated. The zinc may be precipitated from the filtered 

 solution by sulphide of ammonium. 



36. CADMIUM AND COPPER. 



'Both metals may be precipitated from a weak acid 

 solution by sulphuretted hydrogen, the washed pre- 

 cipitate washed off from the filter, boiled with dilute 

 sulphuric acid, when all the cadmium will be dissolved. 



Or the washed precipitate of both metals, with the 



