ELECTRO-GILDING. 



THE operation of gilding, or covering other metals with a coating of 

 gold is performed in the same manner as the operation of plating, 

 with the exception of a few practical modifications, which we shall 

 now notice in detail : 



Preparation of Solution of Gold. The gold solution for gilding is 

 prepared by dissolving gold in three parts of muriatic acid and one 

 of nitric acid, which forms the chloride of gold. This is digested 

 with calcined magnesia, and the gold is precipitated as an oxide ; 

 the oxide is boiled in strong nitric acid, which dissolves any mag- 

 nesia in union with it : the oxide being well washed, is dissolved 

 in cyanide of potassium, which gives cyanide of gold and potas- 

 sium ; thus : 



Substances used: Substances produced : 



Oxide of Gold =AuO 



2. Cyanide of Potassium =2KCy 



Cyanide of Gold } 

 and Potassium. = 



Potash =KO 



Auo + 2 KCy=KO + (KCy + AuCy.) 



By this method a proportion of potash is formed in the solution, 

 as an impurity ; it is not, however, very detrimental to the process. 

 In preparing the oxide of gold there is always a little of the gold 

 lost, to recover which the washings should be kept, evaporated to 

 dryness, and fused. 



Another and very simple method is this : Add a solution of cya- 

 nide of potassium to the chloride of gold, until all the precipitate is 

 redissolved ; but this gives chloride of potassium in the solution, 

 which is not good. In the preparation of the solution by this 

 means there are some interesting reactions. As the chloride of 

 gold has always an excess of acid, the addition of cyanide of potas- 

 sium causes violent effervescence, and no precipitate of gold takes 

 place until all the free acid is neutralized, which causes a con- 



