this slag contains some copper it is not thrown away, but 
worked over again with the next charge of calcined ore* 
The number of fusions and granulations entirely depend 
on the quantity of impurities, and the obstinacy with 
which they combine with the copper ; but when these pro- 
cesses have been repeated the requisite number of times,, 
the granulated mass is melted and cast into pigs. These 
again are broken to pieces, and roasted for one or two 
days in a low red heat, and again melted and roasted se- 
veral times, till the metal approaches to the state of mal- 
leable copper. It is now cast into oblong masses, about 
14 inches in length, and is fit for the refining furnace. In 
this it is again melted, with the addition of a little char- 
coal, till it acquires the necessary degree of malleability, 
and thus becomes saleable copper. 
Sometimes lead is employed with good effect in the re- 
fining of copper, as it combines with, and scorifies iron, 
and the other easily oxydable metals in preference to cop- 
per. For this purpose the rough copper is spread on the 
floor of a furnace, and when it is in complete fusion, about 
6 or 8 per cent . of lead is thrown in, and well mixed with 
the rest. In a short time the surface of the melted me- 
tal becomes covered with a semi-vitreous blackish-brown 
scoria, consisting of the mixed oxyds of lead, iron, and 
other impurities, together with a little copper. The first 
scoria being removed, a second is formed, which is in like 
manner scummed off, and so on successively, till, after 
ten or twelve hours the copper is sufficiently purified % 
this is ascertained by the thinness of the film with which 
the melted copper is covered, and by its being of a brick- 
red colour, also by the circumstance that if a rod of po- 
lished iron is dipped into the fused mass the portion of 
copper that adheres to it immediately falls off when the 
rod is dipped in cold water. 
So far the editors of Rees’s Encyclopaedia : but the pro- 
cess is not so -easy, and deserves to be treated more at 
D J 
