The tendency which different substances possess to at tach themselves to their appropriate wires, causes them to be transferred across a medium which may be interposed. Thus, if muriate of lime be at the positive wire, the lime will pass, for a considerable space, to gain the negative wire, (Plate CCLXIII. Figs. 10, 11.) and may be convey ed from one vessel to another along the conducting fibres of the asbestos. In the same manner, when nitrate of sil ver was on the positive side, and distilled water on the ne gative, the silver passed along the transmitting amianthus, so as to cover it with a thin metallic film. When a neu tral salt was placed in a vessel, between two other vessels of water connected by asbestos, the alkali passed to the ne gative, and the acid to the positive side : the decomposi tion in this case is complete, and the substances produced quite pure. A small vessel of the infusion of litmus was interposed between pure water and the solution of sulphate of potash, and the latter was negatively electrified. The acid passed across to the positive wire, and reddened the litmus, but the change of colour did not extend beyond the centre; so that the negative side, although it was transmit ting the acid, was not affected by it, An experiment of precisely an opposite kind was performed with the infu sion of turmeric, with a similar result ; and afterwards the two operations were combined in the same experiment, so that soda passed through turmeric, and muriatie acid through litmus, each without changing their colour.
As it appeared that acids and alkalies could be convey ed through water, without affecting colouring substances dissolved in it, Sir H. Davy next tried whether this power might not extend to other bodies. He accordingly found, that acids could be transmitted through alkalies, and alka lies through acids, to their respective wires, without neu tralizing each other ; and, in short, that the electrical state which was induced upon a substance, by the contact of the galvanic apparatus, had the power of counteracting, or even changing, the effects of chemical affinity. The general principle was thus completely established, that hydrogen, alkalies, and metals, are attracted by the negative and re pelled by the positive end of the pile, while acids and oxy gen are attracted by the positive, and repelled by the nega tive. For the production of this effect, it is necessary teat there be a conducting chain of particles through the trans mitting fluids ; the transfer cannot take place where inso luble compounds are formed, because in this case the new compound is carried out of the sphere of action.
The establishment of the general principle mentioned above, suggested some views of the nature of the change produced by electricity, which led to a new train of expe riments. , Sir H. Davy observes, that many bodies, after being brought into contact, exhibit opposite states when they are separated. When a galvanic combination is form
ed from an acid, an alkali, and a metal, the alkali appears to acquire, and the acid to part with, a quantity of electri city ; the alkali is therefore rendered positive, and the acid negative, and they will of course have an attraction for each other. lie found, that when such acids as were capable of being en ployed in the dry state were touched by metals, and then separated, the acids were rendered negative, and the metals pisitive; but when the metals were touched by the alkaline earths, the metals became negative. Hence it may be concluded, that acids and alkalies not only exhibit opposite electricities, when they have been in contact with metals, but also when they have been in contact with each other. The attraction of oxygen and acid for the positive, and of hydrogen and alkalies for the negative electricity, is so powerful, as to counteract their usual chemical affi nities.
These considerations induced the author to enter into some farther speculations respecting the relation between the electricity of bodies and their chemical affinities. We have seen that chemical affinity is destroyed by giving a body an electricity different from its natural one, and is, on the contrary, increased by giving it a greater share of its natural electricity. It would farther appear, that all those bodies which possess a chemical affinity for each other are naturally in opposite states of electricity ; and hence we conclude, that by inducing a state of electricity upon any body, contrary to its natural one, its chemical relations may be changed, and that thus we have in our possession an agent of indefinite power for affecting the decomposi tion of substances which had hitherto withstood all our at tempts.
With respect to the action of the voltaic pile, Sir H. Davy conceives, that the first step in the process is the de struction of the electrical equilibrium, and that the chemi cal changes tend to restore it to its original state. The saline solution, which is interposed between each pair of plates, is decomposed, the acid is transferred to the zinc, and the alkali to the copper surface. This tends to restore the equilibrium, which is destroyed by the contact of the metallic elements of the pile ; but the solution of the zinc, which then takes place, again alters the electrical condition of the bodies, and maintains the energy of the apparatus. Upon the whole, although it may be supposed that the che mical changes are an essential part of the process, they are considered by the author as only of secondary importance ; the first step in the process, and that which immediately gives Ilse to all the rest, being an electrical effect arising from the action of bodies placed in contact.