Our general conclusion on the subject that part of the effects, usually proceeding from the pile, ate purely elec trical, and do not, in any degree, depend upon a chemical change in the state of the metals. \Ve conceive it to be a doubtful point in what way this electrical action is induced, because, for the reasons which we have already given, we do not think that the experiments of Volta, and the others that lime been supposed to coincide with them, are appli cable to the state of things as they exist in the pile ; nor do we think that if we were to admit them, they would account for the continued evolution of fresh portions of electricity ; or that they would explain, why the disturbance of the elec tric fluid, or the eleetro-motion, as it is stiled, is not coun teracted by the conductors that are connected with the me tals. As to the proper galvanic effects of the pile, we con sider them to be always immediately caused by the chemi cal action of the fluid upon the metals; and that, in propor tion to the extent of this action, as depending upon the quantity of surface exposed, or the nature of the fluid em ployed, we obtain the evolution of electricity in greater or less quantity, and in a more or less intense state. Our readers will perceive, from these observations, that we are, upon the whole,. advocates for the chemical hypothesis ; but at the same time that we attach ourselves to this doc trine, we do it with the restriction already referred to. If we conceive that the proper galvanic phenomena depend upon the chemical changes, we also admit, that there are electrical effects produced by the pile, independent of the others, and unconnected NI ith them.
The great discoveries that have been made by Sir II. Davy, in his application of galvanism to chemical decom position, and the importance which must attach to all his opinions upon the subject, induce us to inquire, what view he takes of the question that we have now been discussing. \Ve have already related the experiments which he performed on the chemical action of the pile ; and it appears that hd formerly considered it as the primary cause of the pheno mena. This opinion, however, he afterwards retracted, and adopted an hypothesis which lie conceived might re concile the doctrine of Volta with the experiments of the English chemists. Ile supposes, that both electrical and chemical actions are necessarily concerned in the produc tion of the effect ; that the former are the first in order of time, and that their tendency is to disturb the electric equi librium of the different parts of the apparatus, while the chemical changes operate in restoring this equilibrium. In the farther detail of the hypothesis we shall employ the author's own words. ca In the voltaic pile of zinc, copper, and solution of muriate of soda, in what has been called its condition of electrical tension, the communicating plates of copper and zinc are in opposite electrical states. And with regard to electricities of such very low intensity, water is an insulating body ; every copper plate, consequently, produces by induction an increace of positive electricity upon the opposite zinc plate, and every zinc plate an in crease of negative electricity on the opposite copper plate; and the intensity increases with the number, and the quan tity with the extent of the series."
When a communication is made between the two ex treme points, the opposite electricities tend to annihilate each other ; and if the fluid medium could be a substance incapable of decomposition, the equilibrium, there is eve ry reason to believe, would be restored, and the motion of the electricity cease. But solution of muriate of soda be ing composed of two series of elements, possessing oppo site electrical energies, the oxygen and acid are attracted by the zinc, and the hydrogen and alkali by the copper. The balance of power is momentary only ; for solution of zinc is formed, and the hydrogen is disengaged. The ne gative energy of the copper, and the positive energy of the zinc, are consequently again exerted, enfeebled only by the opimsing energy of the soda in contact with the copper ; and the process of elcctro-motion continues, as long as the chemical changes are capable of being carried on." See Phil. Trans. for 1807, vol. xlv.
This hypothesis agrees with that of Volta, in ascribing the train of actions to the electric condition of the metals, yet it differs from it in many essential points. It supposes the chemical decomposition of the interposed fluid to be a necessary although not the first step in the process. The conducting power of the fluid is, in both cases, taken into account, yet it is regarded in an opposite point of view. According to Volta, the better is the conducting fluid, the more energetic is the action of the pile ; while the hypo thesis of Sir II. Davy seems to require the fluid to possess almost a non-conducting property.
Some of the late speculations of this illustrious chemist have led him to deviate still farther from ordinary hypothe sis, not only as it respects galvanism, but electricity in general. Those effects, which were formerly attributed to a material agent, capable of being added to, or subtract ed from a body, at pleasure, are now conceived, like gra vitation, to be inherent qualities of matter. To these, which are called electric energies, all chemical decompositions are to be ultimately referred ; for it is supposed, that che mical attraction, in all cases, results from the circum stance of two bodies, possessing opposite electric energies, and consequently having a strong tendency to unite. By means of the galvanie combinations, we have it in our pow er to excite the electric state of a body to an indefinite de gree, and to induce an electricity contrary to that which is natural to it. But the farther consideration of the merits of this theory, belong rather to electricity than to galvanism strictly so called. To whatever cause we ascribe the elec tric state of bodies, whether to a material agent distributed through them in different quantities, or to some affec tion of their primary qualities, the states of positive and negative electricity actually exist, and our present busi -ness is merely to inquire, what relation they bear to the phenomena of the galvanic pile.