This sheet is clamped to another sheet of the metal standing in another vessel that contains water feebly acidulated—say, with hydrochloric acid. The two vessels are then connected by a bent glass tube full of gelatine in a firm but gelatinous condition, when a lively evolution of gas proceeds from the platina in the hydrochloric acid, while the tannin solution acquires a deep-brown tint in the immediate vicinity of the metal. The gas is hydrogen. If the acid solution is changed for a solution of auric chloride or cupric sulphate, metal is rapidly deposited upon the platina there. Evidently water^* has been decomposed, its oxygen combining with tannin, and its hydrogen depositing the metal in the other vessel: we have, in fact, a galvanic cell formed in this way and brought into action.

In this experiment I take it that the metals do not contribute to the results by any so-named catalytic action^† or condensation of oxygen, but only by affording the means by which the chemical combinations in the liquids may produce, not heat, but electricity, and electricity in the current or dynamic form—that is, speaking more in accord with the electrical theories of the day, a series of electrical polarizations. Of course, it is only the tannin that is in absolute contact with the metal that acts on the water—that is, in fact, oxidized.

In accordance with the custom of designating new forms of voltaic cells after some distinguishing or novel feature in them, I propose to name the apparatus here described the “tannin cell”; a group of these, the “tannin battery.”