82 Mr. J. Napier on Copper Smelting. 



adopted and practised by any of the smelters, up to the stage of 

 coai'se metal they are all the same; all modifications generally 

 begin at the coarse metal. Before referring to any of these 

 modifications, we will first inquire into the. changes which have 

 taken place in the operation described ; and that these changes 

 may be the better understood, we will take a small charge of the 

 average quality and follow out the actual results of practice. 

 25 cwt. of calcined ore, containing in 100 parts, — 



Copper 12-5 



Iron 28-5 



Sulphur .... 16-0 



Silica 39-0 



Oxygen, &c. . . . 6 



1000 



y cwt. of sharp slag from more advanced operations, com- 

 posed of — 



Oxide of iron ... 53 

 Oxide of copper ... 2 

 SiUca 45 



lOO" 



2 cwt. of cobbing, composed mostly of old bottoms, contain- 

 ing— 



Silica 75 



Oxide of iron ... 15 

 Oxide of copper ... 10 



loo 



These on being fused together yielded about 9^ cwt. of coarse 

 metal and 18 cwt. of slag, there being always a loss upon the 

 weight put in, owing to the volatilization of sulphur, water, &c. 

 The composition of the coarse metal was — 



Copper 31*4 



Sulphur .... 27-3 

 Iron 41-3 



100-0 



That of the slag, including the silica in pieces that were mixed, 

 was-— 



Silica ...... 71 



Protoxide of iron . . 27 

 Lime, &c 2 



loo 



These results correspond closely to the principles laid down in 



