54 Mr. J. Napier on Copper Smelting. 



Copper Pyrites. — This is by far the most abundant ore of 

 copper bi-ought to the smelting-works. It is easily distinguished 

 by its rich brass tint from iron pyrites, which is generally not 80 

 yellow ; neither is it so hard, copper pyrites yielding easily to the 

 knife. The two pyiites are often mixed together ; and when so 

 in a massive state, a trial of the hardness may give some idea 

 of the quality of the ore. The composition of copper pyrites 

 is a double sulphui-et of copper and iron chemically combined. 

 When pm'e, it is composed of — 



Copper 34 



Sulphur 34 



Iron 32 



loo 



As an ore, it is almost invariably associated with iron pyrites. 

 The quantity may be easily ascertained by an analysis being 

 made for the quantity of copper, sulphur and iron. As an 

 illustration, take what is termed Cobre dust, which is a mixture 

 of iron and copper pyrites. A fair sample gave the following 

 composition : — 



Copper 14 



Iron . 36 



Sulphur 26 



Silica 34 



100 

 The copper, to form copper pyrites, will require — 



Copper 14 



Iron 13 



Sulphur 14, 



leaving -s o i i, 121"^^ ^^^^ pyrites, which is not far from 



being correct ; the composition of that mineral being 38 iron 

 and 32 sulphur; but in analyses of copper and iron pyrites 

 mixed, the iron almost always prevails, probably from a portion 

 being combined with the silica. We thus see, that by observing 

 the chemical character of ores, much may be done, even in com- 

 mercial samples, to distinguish the kind of mineral present ; but 

 we shall have occasion to refer to this subject more fully in future 

 papers. 



To return to the obtaining of the ores from the mines. When 

 the ores are raised from the mines, they are broken up and 

 dressed, separating by mechanical means, as far as possible, the 

 earthy matters from the mineral ; they are then crushed into 

 small pieces, and collected into a heap preparatory for sampling 

 for sale. 



