According to this arrangement, the zinc, in order to reach the copper, must necessarily pass through the small piece of moistened cloth which sepa rates them. In piles where the communication be tween the two poles is not formed, this transmission does not sensibly take place ; the surface of the cop. per remains smooth, and that of the zinc, which is opposite to it, is only covered with minute black lines, which follow the direction of the threads of the cloth. When the communication has been esta blished for a short time, some particles of oxide be gin to pass, and attach themselves to the copper ; and, if the action of the pile is strong, the surface of the copper is at last entirely covered ; then the che mical and physiological action of the pile ceases, ei ther because the oxide of zinc deposited on the cop per exerts on it an electromotive action, which ba lances that of the metallic zinc, touching it on its other side ; or because the interposition of this stra tum of oxide presents too great an obstacle to the transmission of the electricity ; or lastly, what is most probable, because these two effects combine their influence at the same time.
Sometimes the oxide of zinc, after having passed through the piece of cloth, restores itself on the copper to the metallic state. Then the element on which this precipitation falls loses all its electromo tive force, the copper being then in contact between two pieces of zinc.
The motion of transport being directed from the zinc to the copper, through the moistened conchs°. tors ; when the copper attaches itself to the zinc, this always takes place on the sides of their name. diate contact with each other. If the copper then adheres to the zinc, it preserves its metallic polish. Sometimes brass is formed. These revivals of the me tal do not take place when the communication is not established between the extremities of the pile: it is also necessary for their production, that the cloths be not too thick, nor of too compact a texture.
Such, we believe, are the first of the phenomena of transport which have been observed with the electromotive apparatus, and which have been de scribed by Messrs Biot and F. Cuvier ; they are particularly sensible in piles composed of plates of a very small diameter ; the reaction of these piles upon themselves is incomparably stronger and quick er than that of piles of large plates.
All these changes within the pile being well esta blished, we must inquire what influence they can have on the electrical state, and consequently on the chemical permanence of the electromotive apparatus.
Let us begin with the absorption of oxygen, by which the chemical agency of the pile is augmented. It is clear, that this increase would not take place if the conductibility of the pile were perfect ; for each of its elements would, in that case, instantly draw from the ground, by direct transmission, the quantity of electricity necessary for the rank which it occupies.
But the preoeding experiments show that such an ef. feet is quite ideal; and however useful this view of the case may at first be, to illustrate more clearly the increase of electricity which arises from the superposition of pairs of metallic plates, we must modify these ab stractions by introducing the circumstance of an im perfect conductibility, in order to have a complete idea of the pile as it is really in our power to construct it.
According to the notions of Volta, the oxygen can only operate by forming a more intimate communi cation between the mowilic elements of the pile ; binding them, as it were, by oxidation to each other, and to the imperfectly conducting cloths which sepa rate them ; and no doubt this adherence may con tribute to augment the conductibility, especially in the beginning of the action. But when this action becomes so strong that the whole pile only forms, as it were, a solid mass ; when the moistened cloths in terposed between the plates are dried; when all the oxygen which surrounds the pile is absorbed, and its chemical agency seems altogether extinct,—what new degree of adherence can the introduction of a new quantity of oxygen instantaneously produce ? Does it not rather seem that this oxygen revives the pile, by insinuating itself between the pieces of cloth, and carrying to each plate of zinc with which it com bines, the quantity of electricity that this plate re. quires for its recharge, according to the rank which it occupies ? The electrical state of the plates becomes then the same as if they had drawn their electricity from the ground ; they recover their losses with the wane rapidity ; and the chemical action of the pile begins again to exert itself as before the drying of the humid conductors.
But if it be the oxygen which furnishes the elec.
trieity to the zinc, whence does it derive. this elect tricity itself? the latter disengaged in its com bination with the zinc, and do the chemical phe. nomena in general which take place within the pile produce the electricity for which they have occa sion ? Delicate experimenta made on this subject with the electrical balance prove, that the pro, portion of electricity which van arise in this man ner, is incomparably smaller than that which really circulates in the apparatus ; the oxygen, therefore, which surrounds it cannot prolong the action of a pile, but by serving itself as a conductor between the metallic elements which compose it ; and the follow ing is the mode in which we may conceive this com munication to take place.