COPPER, SILVER, AND GOLD 451 



T>y the potassium cyanide into aurous oxide, which dissolves in potas- 

 sium cyanide and forms KAu(CN) 2 . This substance is soluble in 

 water, and gives a colourless solution, which can be kept for a long 

 time, and is employed in electro-gilding that is, for coating other 

 metallic objects with a layer of gold, which is deposited if the object 

 be connected with the negative pole of a battery and the positive pole 

 consist of a gold plate. When an electric current is passed between 

 them, the gold from the latter will dissolve, whilst a coating of gold 

 from the solution will be deposited on the object. 



