856 Mr. J. Napier on Copper Smelting. 



quantity of iron and other metals; and until all the iron is 

 removed, there is no proper roasting reaction. When this chatige 

 is eflfected before the twenty-four hours allowed for the operation 

 expires, the mat will be in the condition termed sponge regulus, 

 and a quantity of copper reduced to the metallic state. Which 

 will be found at the bottom of the ingots or pigs, which are 

 termed copper bottoms. This sponge regulus is composed as 



follows: — 



LePlay. 

 Copper . . 80-5 79*5 80-0 81-1 

 Sulphur . . 18-8 19-5 18-5 18-5 

 Iron ... -4 -5 '7 '2 (« 



99-7 99-5 99-2 998 



This composition is still very close to the formula Cu2S. It 

 will be seen that the results obtained by roasting the blue 

 metal are similar to those described when fusing calcined fine 

 metal, and also by mixing calcined coarse metal with carbonates ; 

 so that whatever modification be adopted, they all meet at the 

 stage of sponge regulus. 



The next process is what is termed roasting proper, where the 

 chemical reactions are different from those that take place in 

 calcining, and where the copper is reduced to the metallic state. 



About three tons of the regulus described is put into a roasting- 

 fumace and fused as stated above. When the air-holes are all 

 opened, so that a free current is allowed to pass over the surface, 

 a brisk effervescence ensues over the surface of the fluid mass, 

 much sulphurous acid is evolved, and a small quantity of scoria 

 is formed, which is carefully removed before it accumulates. 

 This scoria generally contains pieces of metallic copper. The 

 average composition of these slags is — 



Oxide of copper . . 45 



Oxide of iron ... 25 



Silica 28 



Sulphur 2 



100 



The chemical reactions which take place during this effer- 

 vescence may be explained thus : if we take 1 equivalent of sub- 

 sulphuret of copper^ which is composed of 16 sulphur and 64 

 copper, and 2 equivalents of oxide of copper, which is com- 

 posed of 16 oxygen and 64 copper — incidentally equal weights, — 

 mix them together in a crucible and expose them to a heat suffi- 

 cient to melt copper, the whole of the copper will be reduced, 

 and the sulphur evolved as sulphurous acid, 



Cu 2S -h 2CuO = S0« -f 4Cu. 



