32 
Copper . 
The plates of fine red copper, called Rosette Copper, 
are made in the following way.* When the refined cop- 
per is found by the way just mentioned to be sufficiently 
pure, the surface of the melted metal is well scummed 
and suffered to cool till it is ready to fix, at which time a 
workman brushes it over with a wet broom, which imme- 
diately fixes the surface and causes a thin plate to sepa- 
rate from the still fluid metal below. This plate is taken 
off and thrown into water, where it takes a high red co- 
lour, and the same process of wetting the surface is re- 
peated with the remaining fluid metal successively, till 
the whole is reduced to these thin irregular plates. 
A considerable quantity of copper is obtained from the 
springs of native sulphat of copper or blue vitriol, which 
are found in most copper mines or flow from hills contain- 
ing this metal. To obtain it, the vitriol water is pump- 
ed up into large square open pits, two or three feet deep, 
made with rammed clay, into which is thrown a quantity 
of refuse iron of any kind, and suffered to remain for a 
considerable time, during which the iron is dissolved, 
displacing by superior affinity the copper which is pre- 
cipitated in the form of a brown mud. When the water 
is thus exhausted of its copper, the pits are raked out, and 
the oxyd collected from them is simply dried in the sun* 
It is then fit for reduction in the reverberatory furnaces in 
the usual manner. This is by far the richest material 
employed, for, though containing some clay and iron mix- 
ed with the copper, it yields on an average full 50 per 
cent, of pure metal, and therefore it is seldom smelted by 
itself, but mixed with the poorer ores, some of which con- 
tain no more than five per cent, of metal. 
Many of the finest copper ores contain so much silver 
as to make it worth while to extract this last metal by a 
separate operation, which will be described under the ar* 
# Macquer Chem. Diet. 
