348 Mr. J. Napier on Copper Smelting, 



added. The produce of tliis fusion is about three-fourths mat 

 and one-fourth slag, consisting of — 



Copper .... 7 ^ 



Oxide of iron . . 64 

 Silica .... 24 



The mat or metal will be described further on. This calcina- 

 tion and fusing replaces a roasting of 24 hours ; and where the 

 process of selecting is required, it is considered preferable. 



When oxides and carbonates, such as the Australian ores, are 

 on hand, they are generally fused with the calcined coarse metal, 

 by which means a double advantage is obtained ; the excess of 

 oxide of iron in the calcined metal fluxes the silica of the ore 

 which has little iron, and the copper in the ore is converted into 

 subsulphuret, a condition necessary for reduction by the presenf 

 method of smelting. The produce of this fusion is a mat termed 

 pimpled metal, from its having small rough pimples on the sur- 

 face of the ingots. The average composition of this metal is — 



Copper 78 



Sulphur 18 



Iron 2 



- »> U» ■ OlllCa «W llWUiVI VrtUW f 



>^<f n. iL "Too ^-lamaDfisaimoo 



■• • v'-M 

 When this metal is produced by the admixture of Australian 



ores, it has generally a redder colour than when obtained by 

 fusing calcined fine metal, or roasting blue metal ; it also con- 

 tains a little more iron, but the reddish tint is caused by reduced 

 copper diffused through it. 



The slags from this process are stiff, and generally contain 

 copper ; the following is their average composition : — 



Copper 3*5 



Silica 60-4 



Oxide of iron . . . 36-1 



1000 



These slags are fused with sulphuret ores, to obtain the copper 

 from them. 



It will be remarked, that the mixing of the Australian ores 

 advances the mat obtained from the Cornish ores twenty-four 

 hours ; but it must also be borne in mind that the copper in the 

 Australian ores is put back at least thirty-six hours by converting 

 it into sulphuret. 



Roasting. 



The next operation to be described is that termed roasting ; a 

 process which, in chemical books, is generally identified with 



