Galvanism, Or Voltaic Electricity (So Named From Its Discoverers, Galvani of Bologna and Volta of Pavia), that form of dynamical electricity which is developed by chemical action. An account of the discovery of Galvani is given under Animal Electricity, and also a notice of the controversy which was carried on between these philosophers, Galvani maintaining that the peculiar phenomena which he produced were owing to electricity developed in the animals on which he experimented, and Volta contending that they were due to the contact of dissimilar metals. Galvani may therefore be regarded as more particularly the discoverer of animal electricity, while Volta, who did not invent the celebrated pile which bears his name till 1799, the year after the death of Galvani, is entitled to most of the credit of the discovery of chemical or galvanic electricity. The term dynamical electricity is often applied to galvanism, but it has a wider meaning, and embraces the phenomena of all electrical currents, irrespective of their origin. Volta's theory that the galvanic current was produced by the contact of two dissimilar metals is not held by the majority of the scientific world at the present day.
The earlier experiments which seemed to support that doctrine were imperfectly performed, and when chemical action or other external force is strictly excluded, no electrical effects can be produced. Fabroni of Florence is said to have been the first to suggest chemical action as a principal cause of the phenomena, an opinion formed from observing the rapid oxidation which took place in the zinc plates of the voltaic pile. This opinion was supported by Sir Humphry Davy in England, who soon after the publication of a letter of Volta to Sir Joseph Banks in 1800, giving an account of his battery, made numerous interesting experiments. Wollaston advocated the chemical theory, and also showed the identity of the electricity of the pile and that of the trictional machine by reducing the electrodes of the latter to small points, and causing the current which passed through them from a large machine to produce chemical decomposition and other similar effects. In 1807 Davy obtained the metals potassium and sodium by electrolysis, and in 1809 Deluc made dry piles of gold and silver paper, which were afterward improved by Zamboni. In 1819 Oersted discovered the deflection of the magnetic needle by the galvanic current, and soon afterward Ampere announced a theory which explained its action. (See Electho-Magnetism.) In 1827 Ohm of Munich enunciated the celebrated law which bears his name, and developed a strictly mathematical theory.
Faraday in 1831 discovered the induction of galvanic currents by means of magnetism, and continued his investigations till near the close of his life, making many remarkable discoveries, among them the law of definite electro-chemical decomposition. From 1836 to the present time many improved modifications of galvanic batteries have been devised by Daniell, Grove, Bunsen, and others, which, although of minor importance when compared with discoveries and developments of great principles, have been of much advantage in the prosecution of various branches of scientific research and in the arts.-The ordinary phenomena of galvanism may be observed by the following simple experiments: If a plate of commercial zinc is placed in a glass vessel containing dilute hydrochloric acid, chemical action will take place, accompanied with the evolution of bubbles of hydrogen gas upon the surface of the plate, which successively form and rise to the surface of the liquid, and upon examination chloride of zinc will be found in solution.
If a plate of copper is placed in the liquid near the zinc and brought into contact or connected by a wire with it, as shown in fig. 1, the evolution of hydrogen upon the surface of the zinc plate will mostly cease and be transferred to the surface of the copper; but chlorine will continue to unite with the zinc, which metal, if weighed, will be found to have lost weight, while the copper will neither have lost nor gained. If, in the first place, when the zinc plate alone was immersed in the acid, pure metal had been used, there would not have been so much chemical action; but upon the introduction and connection of the plate of copper there would have been more, and the evolution of hydrogen gas would have been entirely confined to the surface of the copper. If a plate of iron is placed in dilute hydrochloric acid, it will dissolve with evolution of hydrogen and the formation of chloride of iron, the action being the same as with the employment of zinc; and if a copper plate is connected with it, the action will still be similar to that which is obtained between the zinc and copper; but if a zinc instead of a copper plate is placed near the iron and connected with it, the action upon the respective plates will be reversed.
The hydrogen will continue to be evolved at the surface of the iron, but this metal will cease to combine with chlorine, the chemical action being transferred to the zinc plate. In either of these experiments, when chemical action takes place wholly or principally upon one metal, if a magnetic needle is brought near the connecting wire it will be observed that a peculiar force is exerted upon it, tending to make it take a position at right angles to the wire, turning one way or the other, according to the position of the latter, and the relative connections of the copper and zinc plates. If a very fine platinum wire forms a part of the connection, its temperature will be raised; and if the apparatus works energetically, it may become incandescent, or even fused. If contact is broken in any part of the connecting wire, a minute spark, especially if the room is darkened, may be observed at the point of separation, which resembles the spark of the ordinary frictional electrical machine, and may be shown to have similar properties.