In this vessel of wood or iron plate, P, the corrugated zinc plates, b, b', b", are placed one above the other, each alternating with a flat one, a, a', a". These plates have previously been scoured, first with a weak solution of caustic soda in order to remove every trace of fatty matter derived from rolling, and then with very dilute hydrochloric acid, and finally are washed with common water. In order to facilitate the disengagement of hydrogen during the reaction, care must be taken to form apertures in the zinc plates, and to incline the first lower row with respect to the bottom of the vessel. A cubical pile of 150 hectoliters contains 105 rows of No. 16 flat and corrugated zinc plates, whose total weight is 6,200 kilogrammes. We obtain thus a hydrogenizing surface of 1,800 square meters, or 12 square meters per hectoliter of impure spirits of 50° to 60° Gay-Lussac. The raw impure spirits enter the apparatus through the upper pipe, E, and, after a sufficient stay therein, are drawn off through the lower pipe, H, into a reservoir, R, from whence, by means of a pump, they are forced to the rectifier. 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°, 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° 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 ½ 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° 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.