The hydrogen engendered during the electrolysis is disengaged through an aperture in the cover of the pile.

As a measure of precaution, the hydrogen saturated with alcoholic vapors may be forced to traverse a small, cooled room.  The liquefied alcohol returns to the pile.  At a mean temperature of 15 deg., the quantity of alcohol carried along mechanically is insignificant.  In order to secure a uniformity of action in all parts of the spirits, during the period devoted to the operation, the liquid is made to circulate from top to bottom by means of a pump, O. The tube, N, indicates the level of the liquid in the vessel.  The zinc having been arranged, the first operation consists in forming the couple.  This is done by introducing into the pile, by means of the pump, O, a solution of sulphate of copper so as to completely fill it.

The adherence of the copper to the zinc is essential to a proper working of the couple, and may be obtained by observing the following conditions: 

1.  Impure spirits of 40 deg.  Gay-Lussac, and not water, should be used as a menstruum for the salt of copper.

2.  The sulphatization should be operated by five successive solutions of 1/2 per cent., representing 20 kilogrammes of sulphate of copper per 100 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 deg. 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 deg. the couple no longer works, and above +35 deg. 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 with another one by electrolysis.  The voltameters in which this second operation is performed have likewise been modified.  They consist now (Fig. 2) of cylindrical glass vessels, AH, 125 mm. in diameter by 600 in height, with polished edges.  These are hermetically closed by an ebonite cover through which pass the tubes, B’ C’ and B C, that allow the liquid, E+E-E’+E’, to circulate.