66 SILVER AND COPPER. 



hydrogen, or if the solution be concentrated by evapo- 

 ration, by sulphuric acid in the presence of alcohol. 



IV. Another method consists in precipitating the 

 solution of the two rnetals by a slight excess of car- 

 bonate of soda, and digesting the precipitate with 

 cyanide of potassium, which dissolves the silver in the 

 form of a double cyanide, leaving the carbonate of 

 lead untouched. Since, however, itcontains some alkali, 

 it must be dissolved in nitric acid, and precipitated by 

 sulphuretted hydrogen or sulphuric acid. From the 

 solution containing the silver, the latter may be preci- 

 pitated as cyanide by nitric acid. 



V. The solution of the lead and silver in nitric acid 

 is neutralized with an akali, mixed with an akaline 

 formate, and heated to boiling, when all the silver is 

 precipitated in the metallic state. 



41. SILVER AND COPPER. 



(Silver-coin.) 



The alloy is dissolved in moderately strong nitric 

 acid, the silver precipitated from the hot solution by 

 dilute hydrochloric acid with violent agitation, and the 

 chloride of silver treated as in No. 1. 



The oxide of copper is precipitated from the filtrate 

 by caustic potassa at a boiling heat, washed, dried, 

 ignited and weighed, the filter being completely incin- 

 erated apart from the precipitate. 



If the alloy contain gold also, it is left behind by the 

 nitric acid as a brown powder. If it be present in 

 very small quantities as, for example, in all old silver 

 coins the small insoluble residue is filtered off; thor- 

 oughly washed, the filter incinerated, and the ash fused 

 before the blowpipe with carbonate of soda, when the 

 gold appears in small globules. 



