WORLD'S SUPPLY OF COPPER 259 



bonato, sulphate and sulphide. The cheap solvents us\ially 

 employed arc water, hydrochloric acid, sulphuric acid, or 

 solutions of metallic chlorides. 



The electro-metallurgical method of extracting copper 

 is used principally in extracting copper from alloys of the 

 same metal and the precious metals. Briefly the process is as 

 follows : 



The ingot of alloy is attached to a conductor from one 

 pole of a dynamo and a sheet of copper is attached to the 

 other pole and both are immersed in an acid solution of sul- 

 phate of copper. A current of electricity then is passed 

 through the solution betw^een the poles and dissolves from 

 the ingot the copper and deposits it on the copper plate, the 

 other metal falling to the bottom of the tank. This method 

 is properly a refining process applied to alloys, rather than 

 an extracting method, but it has been applied to the extrac- 

 tion of copper from the ore and matte, although such use is 

 not extensive at the present time. This same process can 

 be used in refining coarse copper, but not with profit unless 

 the copper is alloyed with gold, silver or nickel. The method 

 usually emplojxd in refining coarse copper is to fuse it in a 

 reverberatory furnace, subjecting it to the oxidizing influence 

 of the air, and then to reduce the cuprus oxide formed by 

 stirring the molten mass with a green wood pole. 



