square meters of zinc exposed, or a total of 360 kilogrammes of sulphate
for a pile of 150 hectoliters capacity.

3. A temperature of 25° should not be exceeded during the
sulphatization.

The use of spirits is justified by the fact that the presence of the
alcohol notably retards the precipitation of copper. As each charging
with copper takes twenty-four hours, it requires five days to form the
pile. At the end of this time the deposit should be of a chocolate-brown
and sufficiently adherent; but the adherence becomes much greater after
a fortnight's operation.

Temperature has a marked influence upon the rapidity and continuity of
the reaction. Below +5° the couple no longer works, and above +35° the
reaction becomes vigorous and destroys the adherence of the copper to
such a degree that it becomes necessary to sulphatize the pile anew. The
battery is kept up by adding every eight days a few thousandths of
hydrochloric acid to a vatful of the spirits under treatment, say 5
kilos. of acid to 150 hectoliters of spirits. The object of adding this
acid is to dissolve the hydrate of oxide of zinc formed during the
electrolysis and deposited in a whitish stratum upon the surface of the
copper. The pile required no attention, and it is capable of operating
from 18 months to two years without being renewed or cleaned.

[Illustration: FIG. 2.--ELECTROLYZING APPARATUS.]

Passing them over, the zinc-copper couple does not suffice to deodorize
the impure spirits, so they must be sent directly to a rectifier. But,
in certain cases, it is necessary to follow up the treatment by the pile