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.

[Illustration: 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