Some time ago, Mr. Laurent Naudin, it will be remembered,[1] devised a method of converting the aldehydes that give a bad taste and odor to impure spirits, into alcohol, through electrolytic hydrogen, the apparatus first employed being a zinc-copper couple, and afterward electrolyzers with platinum plates.
[Footnote 1: See SCIENTIFIC AMERICAN SUPPLEMENT of July 29, 1882, p. 5472.]
His apparatus had been in operation for several months, in the distillery of Mr. Boulet, at Bapeaume-les-Rouen, when a fire in December, 1881, completely destroyed that establishment. In reconstructing his apparatus, Mr. Naudin has availed himself of the experience already acquired, and has necessarily had to introduce important modifications and simplifications into the process. In the zinc-copper couple, he had in the very first place proposed to employ zinc in the form of clippings; but the metal in this state presents grave inconveniences, since the subsidence of the lower part, under the influence of the zinc's weight, soon proves an obstacle to the free circulation of the liquids, and, besides this, the cleaning presents insurmountable difficulties. This is why he substituted for the clippings zinc in straight and corrugated plates such as may be easily found in commerce. The management and cleaning of the pile thus became very simple.
FIG. 1.--APPARATUS FOR HYDROGENIZING IMPURE SPIRITS.
The apparatus that contains the zinc-copper couple now has the form shown in Fig. 1. It may be cylindrical, as here represented, or, what is better, rectangular, because of the square form under which the sheets of zinc are found in commerce.
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: