An experimental examination of the electric and chemical theories of galvanism

After observing that the theory of galvanism originally proposed by Volta, and generally termed the Electric theory, is still the universally received doctrine among continental philosophers, the author adduces several experiments proving the fallacy of the principles on which that theory is founded. He points out the inconclusiveness of the reasoning by which it has been inferred that dissimilar metals, by being simply placed in contact with one another, are instantly thrown into opposite electric states; for in all the experiments which have been made with a view of establishing this fundamental principle of the electric theory, the metals have been exposed to the oxidizing action of the air, which is a constant source of electric disturbance, and the operation of which has been strangely overlooked. The author found, by forming galvanic circles with two different metals and an interposed acid, that when he used different kinds of acid, or varied the degree of their dilution, the electro-magnetic effects, as measured by a delicate galvanometer, bear no sort of relation to the conducting power of the fluid, as is assumed in the Voltaic hypothesis. He deduces the same conclusion from experiments made with an apparatus by which the fluid is confined in a rectangular box, divided by a membranous diaphragm into two compartments, so as to allow of the addition of an acid to the fluid contained in one of the compartments, and thereby limiting its action to one of the metallic surfaces. By means of another contrivance, the author ascertained that of two different metals, the one which, when acted upon by an acid, combines with the greatest quantity of oxygen, as measured by the volume of hydrogen disengaged, is always positive with respect to the other metal. Even two pieces of the same metal, differing in hardness, will be acted upon by the same acid in different degrees, and may thus be brought into different states of electricity. In general it is the harder of the two pieces of metal which becomes positive ; but with steel the reverse obtains. It would appear, however, that with the same pairs of metallic discs, the direction of the electric current is determined by the nature of the acid employed: thus nitrous acid, acting upon zinc, copper, or iron, gives rise to a current in a direction opposite to the current which is produced by the sulphuric, nitric, or muriatic acids. Variations in the temperature of the metals will also occasion diversities in the results, not hitherto satisfactorily explained on any theory. From one experiment the author is led to infer that an acid is capable of combining with a pure metal, without the latter being previously reduced to the state of an oxide.