eated in a furnace,
metallic copper resulting from the reduction of the copper oxide by the
hot carbon.

~Metallurgy of sulphide ores.~ Much of the copper of commerce is
made from chalcopyrite and bornite, and these ores are more
difficult to work. They are first roasted in the air, by which
treatment much of the sulphur is burned to sulphur dioxide. The
roasted ore is then melted in a small blast furnace or in an
open one like a puddling furnace. In melting, part of the iron
combines with silica to form a slag of iron silicate. The
product, called crude matte, contains about 50% copper together
with sulphur and iron. Further purification is commonly carried
on by a process very similar to the Bessemer process for steel.
The converter is lined with silica, and a charge of matte from
the melting furnace, together with sand, is introduced, and air
is blown into the mass. By this means the sulphur is
practically all burned out by the air, and the remaining iron
combines with silica and goes off as slag. The copper is poured
out of the converter and molded into anode plates for refining.

~Refining of copper.~ Impure copper is purified by electrolysis. A large
plate of it, serving as an anode, is suspended in a tank facing a thin
plate of pure copper, which is the cathode. The tank is filled with a
solution of copper sulphate and sulphuric acid to serve as the
electrolyte. A current from a dynamo passes from the anode to the
cathode, and the copper, dissolving from the anode, is deposited upon
the cathode in pure form, while the impurities collect on the bottom of
the tank. Electrolytic copper is one of the purest of commercial metals
and is very nearly pure copper.

~Recovery of gold and silver.~ Gold and silver are often present
in small quantities in copper ores, and in electrolytic
refining these metals collect in the muddy deposit on the
bottom of the tank. The mud is carefully worked over from time
to time and the precious metals extracted from it. A surprising
amount of gold and silver is obtained in this way.

~Properties of copper.~ Copper is a rather heavy metal of density 8.9, and
has a characteristic reddish color. It is rather soft and is very
malleable, ductile, and flexible, yet tough and strong; it melts at
1084 deg.. As a conductor of heat and electrical energy it is second only to
silver.

H