194 Mr. J. Napier on Copper Smelting. 



wtich case the crucible must be instantly removed from the fire 

 and the heat lowered. After a great quantity of the sulphur is 

 volatilized, there is less tendency to cake ; the heat may then be 

 increased gradually to a bright red, and continued until all the 

 sulphur is expelled, which is ascertained by taking out the cru- 

 cible and holding the head cautiously over it. The success of 

 the operation depends upon the perfect calcination of the regulus ; 

 should any sulphur be left in the powder, there is great risk of 

 the copper not being all got in the fusion. When calcination is 

 complete, the crucible is allowed to cool, and the contents mixed 

 with from one to two times its weight of black flux (according 

 to its richness in copper), and its weight of ground crown-glass 

 and borax mixed in about equal parts. The whole is put into 

 the same crucible as used for calcining, and a layer of borax 

 spread over the surface ; the crucible is placed in a furnace, and 

 the heat raised until the whole fuses : the more intense the heat 

 in this operation the better. It is kept in fusion for about ten 

 minutes. The mass should not only be fluid, but there should 

 be no effervescence or ebullition. WTien removed from the fire, 

 the contents are either rapidly transfeiTed to an iron ladle, or 

 allowed to cool in the crucible, which is then broken ; in either 

 case a button of metallic copper is found at the bottom. The 

 scoi-ia from this operation is ground fine, and carefully examined 

 for metal ; and if any particles are seen, it has to be re-fused 

 with a little more flux, and the small button or prill obtained 

 added to the first. 



The copper obtained is often brittle and hard, and has conse- 

 quently to be refined; this is an operation requiring some little 

 experience to perform properly. The metal is put into a clean 

 crucible with a very small portion of black flux, or borax, and 

 brought to fusion ; the fused bixtton should not be covered with 

 the flux ; there is then thrown upon the fused metal from time 

 to time small portions of refining flux, made by mixing together 



3 parts nitre, 

 2 parts argal, 

 1 part common salt, 



and igniting them in the same way as in preparing black flux. 

 'V\Tien the metal is very impure, a little more common salt is 

 added. The addition of this flux is made until the button 

 appears to clear easily from a red skin over it : this operation 

 requires time ; a little borax is added just previous to taking 

 from the fire. The metal thus refined shoidd be ductile, 

 capable of being hammered thin without cracking on the edge, 

 and when broken, the fracture should be fine-grained, and have 

 a silky lustre. The scoria from this refining operation generally 



