use, is commonly recrystallized, or electrolysed
with insoluble anodes to recover the copper.

The yield of copper per ampere (in round numbers, 1 oz. of copper per
ampere per diem) by Faraday's law is never attained in practice; and
although 98% may with care be obtained, from 94 to 96% represents the
more usual current-efficiency. With 100% current-efficiency and a
potential difference of 0.3 volt between the electrodes, 1 lb. of
copper should require about 0.154 electrical horse-power hours as the
amount of energy to be expended in the tank for its production. In
practice the expenditure is somewhat greater than this; in large works
the gross horse-power required for the refining itself and for power
and lighting in the factory may not exceed 0.19 to 0.2 (or in smaller
works 0.25) horse-power hours per pound of copper refined.

Many attempts have been made to use crude sulphide of copper or matte
as an anode, and recover the copper at the cathode, the sulphur and
other insoluble constituents being left at the anode. The best known
of these is the Marchese process, which was tested on a working scale
at Genoa and Stolberg in Rhenish Prussia. As the operation proceeded,
it was found that the voltage had to be raised until it became
prohibitive, while the anodes rapidly became honeycombed through and,
crumbling away, filled up the space at the bottom of the vat. The
process was abandoned, but in a modified form appears to be now in use
in Nijni-Novgorod in Russia. Siemens and Halske introduced a combined
process in which the ore, after being part-roasted, is leached by
solutions from a previous electrolytic operation, and the resulting
copper solution electrolysed. In this process the anode solution had
to be kept separate from the cathode solution, and the membrane which
had in consequence to be used, was liable to become torn, and so to
cause trouble by permitting the two solutions to mix. Modifications of
the process have therefore been tried.

Modern methods in copper smelting and refining have effected enormous
economy in time, space, and labour, and have consequently increased the
world's output. With pyritic smelting a sulphuretted copper ore, fed
into a cupola in the morning, can be passed directly to the converter,
blown up to metal, and shipped as 99% bars by evening--an operation
which formerly, with heap roasting of the ore and repeated roasting of