|g6 REFINING METALS. 



sels pf silver, plated on copper, is a very consider- 

 able one. On cutting out the rolled plated metal 

 into pieces of the required form and sizes, there 

 are many shreds, or scraps, as they are called, unfit 

 for any purpose, but the recovery of the metals, by 

 separating them from each other. The easiest and 

 most economical method of parting these two me- 

 tals, so as not to lose either of them, is an object 

 of some consequence to the manufacturers. For 

 this purpose, two modes were practised; one, by 

 melting the whole of the mixed metals with lead, 

 and separating them by eliquation and testing ; and 

 the second, by dissolving both metals in sulphuric 

 acid, with the help of heat, and by separating the 

 sulphate of copper^ by dissolving it in water, from 

 the sulphate of silver, which is afterwards to be 

 reduced and purified. 



In the first of these methods, there is a consi- 

 derable waste of lead and copper ; and in the se- 

 cond, the quantity of sulphuric acid employed is 

 very great, as much more is -dissipated in the form 

 of sulphureous acid than remains in the composi- 

 tion of the two sulphates. 



Some years ago, Mr. Keir communicated to an 

 artist the method of effecting the separating of 

 'silver and copper, by means of the above-mentioned 

 compound of sulphuric acid and nitre. It is now 

 commonly practised by the manufacturers at Bir- 

 mingham, and is much more economical, and much 

 easier executed, that any of the above-mentioned 

 methods ; for nothing more is necessary than to 

 put the pieces of plated metal into a glazed earthen 

 pan, to pour upon them some of the acid liquor, to 

 stir them about, that the surfaces may be frequently 

 exposed to fresh liquor, and to assist the action by 

 a gentle heat, from 100 to 200 Fahr. 



