The electrical state of the electromotive apparatus will thus be exactly similar to a heated tourmalin ; or, to take a more obvious example, it will be similar to that of an electrical pile formed by a mass of seve ral plates of glass, coated with metal, and of which the opposite faces, parallel to each other, communi cate by metallic conductors. Fig. 12. An apparatus, indeed, constructed in this manner, being charged with ordinary electricity, presents, both in theory and in fact, an exact representation of the electrical phenomena which the electromotive apparatus pro duces, whether one of its poles communicates with the ground, or is in a state of insulation; and if it does not exert the same power of decomposition on chemical combinations, it is very probable that this arises from the impossibility of recharging its elec trical poles instantaneously and continually, in pro portion as they discharge themselves along the sub stances through which the electrical currents pass ; a faculty which the electromotive apparatus possesses of itself; when the humid conductors, which sepa rate its metallic elements, present a sufficiently open passage for the transmission of the electricity. This view of the electromotive apparatus will enable us to conceive how it can excite such violent commo Cons, and, above all, those chemical phenomena which we can only produce, by accumulating con siderable quantities of electricity, either with batte ries, or by means of extremely fine points, as has been done by Dr Wollaston. This great energy will not be at all surprising, since a very great quantity of electricity would thus appear to be also operating in the chemical action of the electromotive apparatus. Lastly, it will be understood, why piles, even the most powerful, when they are insulated at their base, scarcely communicate any sensible electricity to the condenser, while they give charges of considerable power, and which even emit sparks, if we make one of their poles communicate instantaneously with the ground. For the charges of the condenser, as they are indicated by calculation for these two circum stances, would bear to each other an extreme dispro portion, which is not the case according to the first view of the subject.
Having thus examined the electrical phenomena, which the Voltaic apparatus produces in consequence of the electromotive action alone of the metals which compose it, let us now inquire into the modifications that the more or less perfect conductibility of the humid bodies which separate them must occasion in these effects.
In the first place, if these bodies,in their contact with the metals, exert a sensible electromotive ac tion, they will modify the electric state of every pair of metal plates, as well by the very existence of the new portion of electricity which they develope, as by the changes which hence result in the conditions of the electrical equilibrium of each pair ; but whenever the electromotive action of these bodies shall become known or determined, their influence will then only form an additional element to join to the considera tions which we have already employed ; and the new state of electrical equilibrium which must now be es tablished in the column will be determined precisely in the same manner, and by the application of the same process of reasoning.
But, besides the conditional modifications which may thus be determined by the nature of the con ducting liquids themselves, there are others in some measure inevitable, and which arise from the changes that the various constitution, or the pro gressive alteration of the humid conductors intro duce, either in their electromotive faculty, or in the rapidity of the transmission of the electricity. As
the current of electricity, excited by the Voltaic apparatus, acts on the bodies through which it passes, and often attacks and decomposes them (as is shown in the article GALVANISM); it must also, by the same power, act upon all the decompoaible bodies which enter into the construction of its own system ; so that it becomes indispensable to examine, by experiment, the nature, the extent, and the consequences of this action.
Among the phenomena which it produces, the first to be examined, because it is the most gene ral, is a rapid absorption of the oxygen of the air around the apparatus. This may be rendered ap parent in a very simple manner, by placing a ver tical pile upon a support surrounded with water, and covering it with a cylindrical jar of glass, which also dips into the water at its base. See fig. 13. In a few instants, the water will be seen to rise in the interior of the jar, especially if we form the com munication between the two poles of the pile by metal wires, so as to direct through them the circulation of the electricity : when no communi cation is formed, the absorption still goes on, but with much greater slowness. In every case, in more or less time, according to the volume of the pile, and the quantity of air which surrounds it, the absorption ceases, and the air remaining under the jar presents no more traces of oxygen. This phe nomenon was discovered by MM. Biot and Frederic Cuvier, when the electromotive apparatus became first known in France.
But, by a fine observation of Dr Wollaston, we are now enabled to proceed farther, and to penetrate into its cause. It consists, without doubt, in the af finity of oxygen, for the surfaces electrified vitre onsly, as the zinc elements of the pile are ; and it is, in fact, these elements which are found to be oxydized. The effect is peculiarly strong and last lug when the pile is placed under a jar filled with pure oxygen. In that case, the effect on the or gans, if tried, is found to be prolonged far beyond the time it would have lasted in common air ; and, in this last case, when the pile, having absorbed all the oxygen, is surrounded by an atmosphere of azote, and its energy now appears completely extinguish ed, the letting in of a small quantity of oxygen is sufficient to revive it.
When we separate the elements of the piles which have been thus kept in action during several hours, or even days, under a cover which prevents the re newal of the atmospheric air, and having a constant communication kept up between their poles, we find that the metallic plates which compose them adhere to each other, and to the intermediate moistened cloths, with so great a force, that it is difficult to separate them. When this is done, we observe that the chemical action of the pile appears to have reacted on it, and produced remarkable alterations on its own elements. If the pile has been rais ed, according to the order, zinc, moisture, copper, zinc, &c. fig. 14, and placed on its zinc base, we observe invariably that particles detached from the inferior zinc plate have been carried to, and have fixed themselves on the plate of copper above it, while particles of copper have been transported to the superior zinc, and so on from the bottom to the top of the column. If the situation of the pile is the reverse, namely, copper, moisture, zinc, cop. per, &c. fig. 15, the copper descends upon the zinc, which is below it, and the zinc on the copper, from the bottom to the top of the column. The direction of the transport along the pile is reversed, but it remains the same relatively to the order of the elements of which the apparatus is composed.