REFINING METALS. 



go out, and the rqetal is permitted to cool, that it 

 may be separated from the cement, and boiled re- 

 peatedly in large quantities of pure water. This 

 gold is afterwards to be tried on a touch-stone ; 

 and if it is not sufficiently purified, the process 

 must be performed a second time. By the above 

 method, we see how powerfully silver is dissolved 

 by muriatic acid, when it is in a state of subtile va- 

 pour which is disengaged from the common salt 

 of the cement. Instead of common salt, nitre may 

 be used, as the nitrous acid readily dissolves silver ; 

 but the mixture of common salt and nitre together 

 is highly injudicious, because the joint acids are 

 able to dissolve some of the gold with the silver. 

 Whatever silver has been separated, will now re- 

 main in the cement ; but it may be freed from this 

 by lead, in the method described in cupellation. 



Parting gold from silver in the dry way.- This is 

 also called parting by fusion, and is performed by 

 means of sulphur, which has the property of uniting 

 easily with silver, while it does not attack gold. 

 This dry parting is troublesome, and even expen- 

 sive, and ought not to be undertaken but when the 

 silver far exceeds the gold, because sulphur will 

 not separate it so easily as aqua fortis, and will 

 therefore require a further application to cupell- 

 ation and solution. 



Refining Silver by Nitre. 



The principle upon which this operation is 

 founded, consists in the property of nitre to oxy- 

 date very powerfully all base metals ; whereas, on 

 the contrary, the noble metals are not at all affected 

 by it. For as the metallic oxides and glasses dp 



