GALVANIC BATTERY. The names of Gal vani and Volta have both become inseparably associated with the earliest device to produce a continuous current of electricity—a device now commonly known as a voltaic cell. In its simplest form it consisted of a strip of zinc and one of copper immersed in a solution of salt, or of an alkali.
Galvani, in 1786, made the capital discovery that freshly prepared frogs' legs, hung by a copper wire on an iron balcony, twitched con vulsively whenever the flesh touched the iron. He rightly ascribed this effect to electricity, but erroneously supposed that it proved the existence of animal electricity generated by nerves and muscles. Volta showed by experiment that Gal vani was wrong, but he made the equally erro neous assumption that the electricity was due to the contact of the two dissimilar- metals. His experiments led, however, to the invention of the celebrated 'crown of cups' about 1800, consisting of a number of simple elements or cells joined in series, the copper strip of one being connected with the zinc of the next. Such cells and their
less simple successors are therefore properly called voltaic cells, though the word 'galvanism' is still retained in medical literature to denote the current obtained from them.
When Davy, in 1801, substituted dilute acid for Volta's salt or alkaline solution, it was found that there was local action which caused the zinc to waste away. Kemp and Sturgeon, in 1830, drew attention to the fact that a diminu tion of this local action was brought about by the amalgamation of the zinc plate. The amal gamation consists in forming a mercury-zinc al loy on the surface of the zinc. This is best done by first cleaning the zinc by rubbing it with dilute sulphuric acid, and then applying a small quantity of mercury. The amalgamated zinc plate acts like pure zinc, and wasteful local action is largely prevented. See VOLTAIC CELL OR BATTERY for a full discussion of primary cells and batteries.