47 
Copper . 
1. Great caution is required in washing copper ore. 
It is true the earths and stones adhering to it should be got 
rid of ; but the oxyds and the carbonats of copper inter- 
mixed) are apt to be washed away, 
2. In roasting the sulphurets, the lumps should not 
exceed the size of a hen’s egg : they are usually much 
larger. But the sulphur is not easily dissipated from the 
centre of a large lump, in which the roasting is no more 
than superficial* 
3. In my opinion the roasting can never be perfect 
where the combustion is supplied by the sulphur alone* 
I can see no good reason why the common practice of 
mixing coal dust with the iron ores intended to be roasted, 
should not be applied to the copper ores, 
4. If the sulphur contain arsenic it is not worth saving. 
This may be known by the garlic smell and the white 
fumes that accompany its combustion ; and by its giving 
a white colour to a plate of pure clean copper held over it 
while it burns. If the sulphur be saved, I think it is best 
done by horizontal flues with doors in the side ; the flues 
terminating in a chamber, which however must have an 
opening, to let out gasses and vapour. 
5. I know of no furnace necessary either to the smelt- 
ing, or the refining of the ore, other than the common cu- 
pola or reverberatory furnace. This furnace is so con- 
trived that the ore is melted, not by coming into immedi- 
ate contact with the fuel but by the reverberation of the 
flame upon it. The bottom of the furnace on which the 
ore is placed, is concave, shelving from the sides toward 
the middle, where a cavity (basin) is worked to contain the 
melted metal : it may be laid with free stone, or with fire 
brick set in loam, or made of Brasque (charcoal, burnt clay 
and soft clay, well mixed and beaten). The roof of the fur- 
nace is low and arched, resembling the roof of a baker’s 
oven. The fire is placed at one end of the furnace upon an 
