230 Chemistry. [Lecture 32. 



will mix with a metal in its metallic state, we 

 may separate those which are difficult from those 

 which ere more easy to be oxidized. The mixed 

 metal is exposed to a heat sufficient for the oxid- 

 izement of the more oxidizable metal : the 

 oxide is kept melted as fast as formed, by addi- 

 tions of saline substances, or other metallic 

 oxides, which promote its fusibility. If the 

 process is long enough continued, the whole of 

 the more oxidizable metal is separated in the 

 form of an oxide, which, being incapable of 

 mixing with the more entire metals, remains 

 separate. 



Thus gold, silver, and copper, are separated 

 from other metals which are accidentally mixed 

 with them, or contained in their ores ; for though 

 all the other metals do not of themselves oxidize, 

 yet by the addition of an oxide of lead they are 

 brought into fusion, and produce scoria?, which 

 float round the metal. It is true, a part of the 

 metal is sometimes brought into the state of an 

 oxide, particularly copper. But gold and silver 

 suffer no loss in this way, and if the operation is 

 properly conducted, only a small part of the 

 copper is oxidized during the calcination of the 

 more oxidizable metals ; and its oxide is mixed 

 with the scoriae, and may be afterwards re- 

 covered. 



Oxides weigh more than the metals from which 

 they are obtained. If we oxidize an hundred 

 weight of metal, its oxide will be heavier. Red 



