GERMAN SILVER. 97 



free access, until all the iron is converted into sesqui- 

 oxide, and its weight remains constant. 



64. GERMAN SILVER (ARGENTAN). 

 (Cu, Ni, Zn). 



The alloy is dissolved in nitric acid, the greater 

 excess of acid evaporated, the solution diluted with 

 water, and the copper precipitated by means of sul- 

 phuretted hydrogen. (See No. 30.) 



The filtered liquor is concentrated by evaporation, 

 precipitated by an excess of solution of potassa, and 

 heated with it, when the protoxide of nickel is sepa- 

 rated and the oxide of zinc dissolved. From this solu- 

 tion the latter is precipitated by sulphide of potassium, 

 or, after being saturated with hydrochloric acid, by 

 carbonate of soda at a boiling heat. 



In this manner, however, the oxides of nickel and 

 zinc cannot be separated with precision; some oxide 

 of zinc remains with the protoxide of nickel. 



The separation is also effected incompletely by fusing 

 the mixture of the oxides with hydrated potassa, or by 

 precipitating both oxides with carbonate of soda at a 

 boiling heat, converting the protoxide of nickel into 

 black sesquioxide by digestion with hypochlorite of 

 soda, and then extracting the oxide of zinc by means 

 of caustic potash, or the solution is mixed with acetate 

 of soda and sulphuretted hydrogen passed into it. At 

 first white sulphide of zinc is precipitated, and by de- 

 grees the black sulphide of nickel. A more accurate 

 result is obtained if the mixture of both oxides is 

 mixed with 3 times its weight of carbonate of potassa 

 and the same quantity of sulphur, carefully fused to- 

 gether in a porcelain crucible, until it flows quietly, 

 and when cool the alkaline sulphide extracted with 

 9 



