ELECTRO-PLATING. 



THE next applications of the electro-deposition we have to notice 

 are those relating to silver and gold, embracing the arts of electro- 

 plating and gilding arts which are gradually revolutionizing some 

 extensive branches of manufacture, having the same object, but 

 acting by a different means. 



To Make Silver Solution. The solution of silver used for plating 

 consists of cyanide of silver dissolved in cyanide of potassium 

 which may be prepared in various ways. We shall first describe 

 some of the preparations most in use, and also point out practical 

 objections which, in special cases, have occurred under our own 

 observation, not omitting to specify and recommend those methods 

 which have approved themselves to us as being most simple and 

 effective. 



The method generally adopted is as follows : Metallic silver is 

 dissolved in four parts of nitric acid, diluted with one part of water : 

 the diluted acid is heated in a vessel, and the silver is added by 

 degrees. The operator must avoid breathing the fumes which ascend, 

 as they are highly deleterious. The metal being dissolved, the solu- 

 tion is transferred to a large vessel, and diluted with water. To this 

 is added a solution of cyanide of potassium so long as a white preci- 

 pitate is formed. This precipitate is cyanide of silver, and the action 

 which ensues may be thus represented : 



Substances used : Substances produced : 



Nitrate of silver AgO, NO 5 

 Cyanide of potassium = KCy 



Nitrate of potash = KO, NO 5 

 Cyanide of silver = AgCy 



AgO, NO 5 + KCy = KO, NO 5 + AgCy 



The propriety of diluting the nitrate of silver before precipitating 

 by the cyanide of potassium arises from the fact, that the salts of 

 potash and soda (such as the nitrates, chlorides, and sulphates), when 

 in strong solution, dissolve small quantities of the silver salt, and 

 thus cause a loss, which is prevented by previous dilution with water. 



