Galva'ni, Aloysio

(or LUIGI), an Italian physiologist, celebrated as the discoverer of galvanism, was B. at Bologna, 1737. He studied medicine under Galeazzi, whose daughter he married. In 1762 he became lecturer on anatomy at Bologna, and obtained a considerable reputation. By experiments on frogs he discovered that all animals are endued with a peculiar kind of electricity; and he followed up this discovery with so much perseverance and succe , as to give his name to a new system of philosophy, which excited universal attention. His first publication on this subject was in 1791, and entitled: Aloysii Galvanii de Viribus Electric it at is in Motu Muscular i i Com men tar i us. Upon this system the famous Volta made vast improvements. G., on the death of his wife in 1790, fell into a state of melancholy, and D. in 1798. Besides the above work, he wrote several memoirs upon profe ional subjects. Galvan'ic, a. [Fr. galvanique.] Pertaining to galvanism; containing or exhibiting galvanism. B Galvan'ic Battery, n . ( Phys .) The combination of a number of elements or cells each of which generates a certain quantity of voltaic or dynamic electricity. The first electro-motive apparatus or battery was constructed by Volta in 1800, and consisted of a series of discs of silver or copper, zinc and flannel, or pasteboard soaked in salt water or dilute acid. These discs were alternately laid on each other until a pile of them had been built up. (A B, Fig. 1110.) To the metallic ends of this pile, wires, ww , were connected. With a pile of 40 or more of these alternations, a shock was felt on joining the wires, or the gold leaves of an electrometer could be diverged. Dry piles are constructed that will remain active for years. One of the best of these consists of discs of paper rubbed over on one side with peroxide of manganese, and coated on the other with thin tin or silver leaf, generally sold attached to the paper. The best of these piles are but feeble, and the inconvenience of using them, soon led Volta to the improved A modification represented in Fig. 1111. The Fig . 1110. flannel or paper in the pile is rejected, and in its place a cup of dilute acid is substituted. In each of these cups is a plate of zinc, and one of silver or copper, so connected that each silver and zinc plate is in me Fig . 1111. Z IMG:content-0318.png:[ocr errors] tallic communication though in separate ve els; the arrangement being zinc, acid, silver, in a continuous circuit. We will not follow the various modifications and improvements made on the simple "crown of cups," as Volta styled it, but describe some of the more important kinds of G. B. now in use. If the strips of zinc in the cups of Fig. 1111 be first amalgamated (i. e. dipped in mercury), no action takes place so long as the zinc and copper are not connected. On joining them the acid begins to di olve the zinc plate, and bubbles of hydro-. gen gas appear at the copper plate. One such cup forms a voltaic pair or cell. The zinc is called the active plate or negative pole, and the copper the pa ive plate or positive pole of the cell. Whatever connects these is called the circuit . The pa ive plate is often made of other substances. The current flows from the positive pole through the wire to the negative pole. A cell arranged as above described is not constant in its action; its power is constantly diminishing. Particles of zinc are precipitated on the copper plate, and the hydrogen liberated at the zinc plate adheres as a film on the surface of the copper. These actions tend to destroy the negative character of the copper. Smee's 88 + battery obviates the latter difficulty, and from its simplicity and power is in frequent use. In this battery (Fig. 1112) the negative plate, P, is of silver, coated with a deposit of finely divided platinum; on each side of this plate are fixed two plates of amalgamated zinc, Z7, and the whole are united to a clamp and plunged in dilute sulphuric acid, about 1 of acid to 7 of water. The hydrogen cannot adhere to the platinum surface and is given off with a hi ing sound. Daniell's battery Fig . 1112. (Fig. 1113) consists of a cylindrical ve el of copper, C, closed at the lower end; E, a similar smaller cylinder of porous earthenware; Z is a rod of amalgamated zinc connected by the wire w with the next copper cylinder, and so on in succe ion. The porous tube is filled with dilute sulphuric acid, and the copper cylinders with a strong solution of sulphate of copper, which is kept saturated by crystals of the salt lying on a perforated shelf. The porous partition keeps the finids from mingling, but does not hinder the pa age of the current; and the sulphate of copper in contact C W W C Fig . 1113. with the copper serves to take up the hydrogen. This is an excellent battery, and its freedom from fumes, its constancy and its power, render it invaluable in many cases for manufacturing use and scientific research. Grove's battery is constructed on the same principle. One form of it is shown in Fig. 1114. A rectangular plate of amalgamated zinc, Z Z, is bent in the form shown in the figure, and immersed in a porcelain or gla ve el, A B, filled with dilute sulphuric acid. Within the bend Fig. 1114. of the zinc is a porous cell filled with strong nitrie acid, in which is a plate of platinum, P. The hydrogen is taken up by the nitric acid, which it decomposes with the liber a- A tion of red fumes of nitrous acid. These irritating fumes are the greatest objection to this form of battery, which is more powerful than Daniell's, and of compact arrangement. Bunsen's battery is a modification of Grove's, in which the platinum is replaced by a cylinder of the hard coke obtained from gas-retorts. The relative value of different batteries has been estimated in various ways. The following statement shows the amount of copper deposited from a solution of the sulphate in one hour by each of the batteries mentioned; in each case one pair of plates, exposing the same surface of zinc, was used: Grove's battery deposited 104 grains; Daniell's 33 grains, Smee's 22 grains. Daniel's was found to have the advantage in respect to constancy. Many other forms of G. B. have been brought into use, and the adaptability to this purpose of a great variety of chemical substances have ben tried. The G.B. is now generally called VOLTAIC BATTERY. Galvanism, n. [From Galvani .] That branch of the science of electricity which treats of the electricity de veloped by chemical action. In 1789, Galvani, a profe or of anatomy at Bologna, made the discovery that the limb of a frog is convulsed when the nerves and muscles are touched with two different metals and the metals brought in contact. Upon this and similar phenomena, Galvani based his theory of "animal electricity," according to which every animal is endowed with an inherent electricity, generated in the brain, and distributed through the nervous system, the principal reservoirs being the muscles. Volta, a profe or of natural philosophy at Pavia, repeated the experiment, and proved that the contractions depended not on any electrical condition of the animal frame, but on a feeble action derived from the metals with which the nerves and muscles were brought in contact. His researches led to the discovery of the pile , an apparatus which must be regarded as the source of all the great discoveries in this department of science in modern times. It, with its important modifications, is fully described under the head of GALVANIC BATTERY. The contact theory of Volta a umes that different metals have different electrical capacities, and that electrical disturbance results from simple contact, The chemical theory, now generally adopted, a umes that the chemical action between the solids and liquids of the battery is the source of its power. Many facts support this theory that are inexplicable when viewed by the light of the contact theory. Faraday and others have proved that chemical action does give rise to electrical force; that, when the chemical action of a battery diminishes or ceases, the current diminishes or ceases; and that powerful currents may be generated without bringing di imilar metals into contact. There are, indeed, many reasons for supposing that chemical affinity and electricity are only modifications of the same force. The current force of the galvanic battery has been practically applied to many useful purposes. It is employed in telegraphy (see TELEGRAPH), and its power of converting iron bars into temporary magnets of great power is used in the construction of electro-motive engines and clocks. (See ELECTRO-MAGNETISM; ELECTRO-MOTIVE POWER; HOROLOGY.) Its power of causing chemical decomposition is used by the metal worker, the engraver, the stereotyper, the calico printer, and in many other arts. (See ELECTROLYSIS, ELECTRO-PLATING AND GILDING, ELECTROTYPING, ELECTRO-CALICO PRINTING, .) The current is used as a remedial agent in the treatment of many forms of disease, in some of which it has afforded decided relief. For its luminous effects, see ILLUMINATION. When a strong current traverses a bad conductor, the resisting medium becomes hot. It has been proved that for currents of equal strength, the heat developed in a wire is directly proportioned to its resistance, or inversely as its conducting power. When an imperfect conductor or platinum is used, a fine wire may be raised to incandescence and even fused. If the two wires of a battery are connected by a fine iron or platinum wire, it can be heated at any distance from the battery, and a charge of gunpowder fired, as in blasting or mining, while the operator is removed at a safe distance from the explosion. Galvanist, n. [Fr. galvaniste . See above.] One skilled in the phenomena of galvanism.