456 



Mr. J. Napier on Cupper Smelting. 



Silica combined .... 30'0 



Silica mixed 30"5 



Oxide of iron 28" 5 



Alumina 29 



Magnesia • '6 



Different oxides .... 1'4 



Lime 2*0 



. . 21 



"5 



. . -9 



. . -6 



Fluoride of calcium 

 Copper . . . . 



Iron 



Sulphui' . . . . 



1000 



By comparing this with the above analysis of ore, we find that 

 lime' and fluor-spar have been added to assist fusion, which should, 

 when it is possible, be avoided ; it will also be observed that the 

 oxide of iron is the principal flux for the silica. The following 

 table exhibits the general character and composition of diff'erent 

 qualities of slag :■ — 



ch] 



Slag very difficult to fuse, liaving niu 

 silica»n>e^,requinng one-fourth Ion; 

 time than usual to fuse each charge 



Slag a little stiff in working, homo- 

 geneous 



Good thin slag, homogeneous 



Good slag, easily fused 



Slag good, and easily fused 



Black glassy slag, easily fused 



Silica. Oddeof Lime. ^^ides of 

 iron. other metals. 



707 



631 



48-2 

 57-6 

 55-2 

 05 



28-4 



35-9 



37-0 

 41-5 



38-5 

 20-8 



1-2 



•5 



40 



Trace. 



•5 



9-9 



6 



3 soda. 



The first in the above table had pieces of quartz mixed with 

 it, which is of very frequent occurrence in the slags, and may to 

 a certain extent be calculated upon without prejudice to the 

 fusion of the ores. Indeed, taking the average of analyses we 

 have made of slags which the smelters tei-ni good working slags, 

 and grinding the whole, mixed and combined quartz together, 

 the weight of the protoxide of iron averages about one-half that 

 of the silica. If w^e take the homogeneous slags, where the silica 

 and iron are chemically combined, it will be observed how close 

 the ingredients are to the table of proportions. 



To follow the operation of calcination, let it be supposed that 

 the mixture of ore has the following composition : — 



Copper .... 13 



Iron 29 



Sulphur ... 24 



Silica .... 34 



100 



