72 HYDROMETALLURGY. [ill. 



Plating in the cold. — Stein (Polytec. Centralbl. 1847) 

 mixes 1 pt. nitrate of silver and 3 pts. cyanide of potassium, 

 adding sufficient water to make a thick paste, and rubs the 

 mixture with a woollen rag upon a clean surface of copper, 

 bronze, or brass. The process gives a bright silver surface, 

 which, however, will not bear violent friction with chalk or 

 tripoli. 



Roseleur and Lavaux's method (Liebig and Kopp's Rep., 

 and Technologiste, 1847) is the use of a bath of 100 pts. of 

 sulphite of soda, containing 15 pts, of silver-salt. Neither 

 of these processes yields very durable coatings. 



Plating hy dipping. — Levol employed solutions of cyanide 

 of gold and of silver in cyanide of potassium, and articles of 

 copper, bronze, and brass, to be gilt, were dipped into the 

 boiling gold solution ; but silver could not be gilt in this man- 

 ner, and Levol proposed for it a solution of chloride of gold 

 in sulphocyanide (rhodanide) of potassium. It was, however, 

 shown that silver might be gilt in cyanide of gold and po- 

 tassium, by wrapping it with zinc or copper wire, and then 

 dipping it into the boiling-hot solution. Thus, to gild the 

 inner surface of a silver cup, such wire is wound around the 

 interior, and the boiling cyanide solution poured in. The zinc 

 or copper renders the silver more strongly electronegative. A 

 beautiful gilding is obtained by dissolving fine metallic gold in 

 a solution of cyanide of potassium, and the metallic gold is 

 obtained by precipitating its solution by copperas, or by imbu- 

 ing rags with the solution and burning them to ashes. By 

 warming the solution of cyanide of potassium with the latter, 

 the gold is dissolved, and the solution filtered ofi" from charcoal 

 and ashes. Rags imbued with nitrate of silver, and burned, 

 may be similarly used for making a solution of cyanide of 

 silver and potassium. 



Gilding in ElHngton s Liquid. — Experiments in the Ge- 

 werbe-Institut of Berlin lead to the following proportions as 

 the best for this liquid. Fine gold is dissolved in a sufficient 

 quantity of aqua regia, evaporated to dryness at a gentle heat, 

 and dissolved in 13 pts. water; 7 pts. bicarbonate of potassa 



