98 N1CCOLITE. 



water. Dilute hydrochloric acid is then poured upon 

 the sulphides of the metals, which dissolves only the 

 sulphide of zinc. 



The most accurate method for the separation of the 

 three metals consists in dissolving the German silver 

 in hydrochloric acid, adding nitric acid, drop by drop, 

 and saturating the solution, which must not be too 

 acid, with sulphurous acid, and precipitating the cop- 

 per as*subsulpho-cyanide. (See No. 33.) The filtered 

 solution is then evaporated to a small volume, mixed 

 with an excess of caustic potassa, and gradually with 

 hydrocyanic acid, until the precipitate is completely 

 dissolved, and is of a yellow color. From this solu- 

 tion of double 'cyanides the zinc may be precipitated 

 as a sulphide, by sulphide of potassium, and not sul- 

 phide of ammonium. After digestion by itself for 

 some hours, at a gentle heat, it is filtered. The- solu- 

 tion is then boiled with fuming nitric and hydrochloric 

 acids, or in place of the latter, chlorate of potassa, and 

 the protoxide of nickel precipitated while hot, by 

 caustic potassa. It is then dried and ignited. 



65. NICCOLITE.* 



NiAs. 



I. PREPARATION OF PURE NICKEL. The finely 

 powdered arsenide of nickel is heated in a crucible 

 placed obliquely in the fire where the draught is 

 strong to carry off the fumes, and roasted at a gentle 

 heat with continual stirring, until the vapors of arsenic 

 cease to be given off, and it is changed into greenish 

 basic arsenate of nickel. 



* Arsenide of nickel, with a varying amount of cobalt and iron. 

 The smelting-products, known by the name of cobalt- and nit-kel- 

 speiss, have a similar composition, and contain besides frequently 

 accidental admixtures of copper and bismuth. 



