Page:The American Cyclopædia (1879) Volume VII.djvu/598

 586 GALVANISM were owing to electricity developed in the ani- mals 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 gal- vanism, but it has a wider meaning, and em- braces 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 pres- ent day. The earlier experiments which seemed to support that doctrine were imperfectly per- formed, 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 chemi- cal action as a principal cause of the phenom- ena, 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 inter- esting experiments. Wollaston advocated the chemical theory, and also showed the identity of the electricity of the pile and that of the frictkmal 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 decomposi- tion 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 dis- covered the deflection of the magnetic needle by the galvanic current, and soon afterward Ampere announced a theory which explained its action. (See ELECTEO -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 in- vestigations till near the close of his life, ma- king many remarkable discoveries, among them the law of definite electro- chemical decom- position. From 1836 to the present time many improved modifications of galvanic bat- teries have been Revised 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 galvan- ism may be observed by the following simple experiments : If a plate of commercial zinc is FIG. 1. placed in a glass vessel containing dilute hy- drochloric 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 di- lute 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 con- nected with it, the action upon the respective plates will be reversed. The hydrogen will con- tinue 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 experi- ments, 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 ex- erted upon it, tending to make it take a posi- tion 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 plati- num wire forms a part of the connection, its temperature will be raised ; and if the appa- ratus works energetically, it may become in- candescent, or even fused. If contact is bro- ken in any part of the connecting wire, a mi- nute spark, especially if the room is darken- ed, may be observed at the point of separa- tion, which resembles the spark of the ordi- nary frictional electrical machine, and may be shown to have similar properties. After separation the plates will not present the same appearance as during connection ; but the evo- lution of hydrogen gas on the surface of the