the Arseniates of Copper , and of Iron. 239 
copper and of black oxide of copper, or, when metallic copper 
with a corresponding proportion of hydrate or of carbonate of 
copper, were intimately mixed, and heated at a low red heat, 
the oxygen seemed to be equally distributed through all the 
mass ; and every particle seemed perfectly homogeneous. 
In the ore here spoken of, it is by no means rare to find 
large pieces of real native copper ; and, whether we consider it 
mineralogically or chymically, it certainly is an interesting 
substance. But, how much more will it be esteemed, if it is 
regarded with a view to public utility. 
The Baron de Born has mentioned a grey cupreous pyrites, 
which, he says, contains 90 per cent, of copper. I have ana- 
lyzed a similar one from Cornwall, (grey vitreous copper ore, 
page 203.) which I found to contain 86 of the same metal. 
But, if we reflect, not so much on the quantity as upon the 
extreme purity of this copper, and the wonderful facility with 
which this useful metal may be extracted, it will be found much 
superior to every copper ore hitherto discovered. It would be 
well worth the attention of miners, to keep a constant look out 
for this substance, which, 1 am informed, is not rare in Corn- 
wall. It contains no iron, and no sulphur ; the absence of which 
latter is a peculiar advantage. It is a fact not generally known, 
I believe, that there is hardly such a thing in commerce, as cop- 
per which does not contain a little sulphur ; at least I have rarely 
met with any such ; and it requires but a very minute portion 
of sulphur, to increase the fusibility of copper. The advantage 
of obtaining copper free from sulphur, is too obvious to require 
to be pointed out ; and that advantage does this ore possess. 
To work it separately, if ever it should be found in sufficient 
quantity, would well repay the labour it would cost ; and a very 
