Mr. J. Napier on Copper Smelting. 



459 



and fuse this in the same way, it woxild yield a coarse metal con- 

 taining 30 per cent, of copper ; so that here the poorest ore gives 

 the richest mat. In order, then, to show the principle of mixing, 

 and to obtain a fusible slag without flux, we will take two parts 

 of the above rich ore and one of the poor ore, giving a mixture 

 having the composition — 



Copper . . . 18-4 



Iron .... 26-8 



Sulphui- . . . 25-5 



Silica .... 29-3 



If this be calcined to volatilize half the sulphur, the remaining 

 half, viz. 12' 7, when the ore is fused, will combine thus : — 



4-6 will combine with . . 18-4 copper, 

 8-1 will take 14-0 iron, 



producing a mat or coarse metal with 40 per cent, of copper. 

 The oxide of iron being equal to 16-5 will combine with the 29'3 

 silica, forming the slag. We will enter more fully into these 

 combinations fui'ther on. 



With respect to the time any mixture of ore has to be calcined, 

 the rate at which calcination proceeds has also to be considered, 

 and forms a most important inquiry. Thus suppose the above 

 mixture of ores lost half of its sulphur in nine hours, nine hours 

 more would not suffice to di'ive off the remaining half. 



^Ve took a charge of Cuba ore and calcined twelve hours ; 

 samples taken out and tried every hour gave the following 

 results : — 



The iron in all these is calculated as being in the metallic state, 

 although in many of them it was much oxidized : a small part 

 of the sulphur in some of the trials was present as sulphuric 

 acid. When wc take into consideration the several amounts of 

 sulphur, wc observe what appears very anomalous, that there is 

 less sulphur at the end of six hours than after twelve. It may 

 be asked, where the sulphur is gone, whence comes it again ? 

 In all our experiments this intermitting action of the sulphur 

 is exhibited. It is probably connected with the increase of volume 

 of the sublimed sulphur and sulphurous acid. A sudden evolu- 



