264 METALS. 



The mass of metal grows smaller as the process pro- 

 ceeds, till finally pure silver remains. The moment 

 of its production is indicated by a beautiful play of 

 colors and a sudden brightening of the metal. The 

 above process is carried on upon a hollowed and com- 

 pacted mass of bone-ash, called a cupel. The object of 

 the cupel is not alone to support the metal, but to ab- 

 sorb the hot and fused oxide of lead as fast as it is 

 formed. If a. little copper is present, it is also absorbed 

 with the lead. The process is called cupellation. 



661. It may be illustrated on a small 



How mcf/ the 



process be u~ scale, by making an excavation in a piece 

 lustrated? Q f c [ iarcoa ] ) an( j pressing into it a lining 



of well burned and moistened bone 

 ash. A globule of lead, to which a little 

 silver has been added, is to be heated, 

 on the support, in the oxidizing flame. 

 For separating a small quantity of lead from silver, 

 the bone ash is not essential. The process may be 

 conducted before the blowpipe, upon the naked char- 

 coal. A small portion of silver may often be obtained 

 from the lead of commerce by this means. 

 What is said 662. SILVER COIN. The standard sil- 

 of silver coins? ver o f t h e United States is an alloy con- 

 taining ten per cent, of copper. Silver plate should 

 have the same composition. The object of alloying 

 with copper, is to impart greater hardness to the metal, 

 and secure against the gradual loss from attrition, which 

 would otherwise occur. Spanish silver often contains 

 a small proportion of gold. The gold is left as a black 



