286 Mr David Forbes on Chemical Examination of 



Mineral used for sulphur determination, 

 Free sulphur obtained, 

 Sulphate of barytes do. . 

 Silica, ..... 



Mineral employed for determining the bases, 

 Protoxide of copper obtained, . 

 Sesquioxide of iron do., 



which results give the following per-centage composition — 



Sulphur, .... 33-88 



Copper, .... 32-65 



Iron, .... 32-77 



Manganese, . . . trace, probably = '02 



Silica, .... -32 



Loss, .... '38 



100-00 

 and after deducting the silica and loss, will leave a composi- 

 tion of the pure sulphuret, 



Sulphur, .... 34-11 

 Copper, .... 32-88 

 Iron, .... 3311 



100-00 

 The formula generally assigned is, Cu S + Fe S, or, accord- 

 ing to Rose, Cug S + Fcg Sg, both of which will give the same 

 composition as under. 



Sulphur, .... 35-38 

 Copper, . . . . 34-71 

 Iron, . . . . 29-83 



100-00 

 Most analyses of pure varieties do not differ much from 

 this, yielding from 34 to 37 per cent, sulphur, 30 to 34 per 

 cent, copper, and 30 to 33 per cent, iron, and they can without 

 difficulty be all reconciled to this formula; still we are deficient 

 in analyses of the poorer copper ores of this species, which 

 are so commonly subjected to metallurgical operations, and 

 contain very varying, and often extremely small per-cent- 

 ages of copper, although the ores themselves may at the 

 same time be perfectly free from gangue, and the only dif- 

 ference is that they are sometimes a shade lighter in colour, 

 and somewhat harder when broken by the hammer. In these 



