CHAP. III.
A Description of the Galvanic Trough and Pile.
Professor Volta’s first contrivance for manifesting Galvanism in a more vigorous manner than had hitherto been done, was what he called a couronne de tasses. This consisted of tumblers of glass, half filled with water, or salt and water. These glasses or tumblers, were so placed that a metallic arc, in form of a C, could be fixed with one leg in one glass, and the other in the next glass. On one end of each arc, was fastened a small plate of silver or copper, and on the other end, a similar plate of zinc or tin. These plates were immersed in the fluid contained in the tumblers.—Thus in the water of every glass there was a plate of silver or copper, and another plate of zinc or tin. The metallic arcs were formed of any good conductor. When thirty or forty of these glasses were prepared, the experimenter put one of his hands into the fluid contained in the first glass, and the other hand into that in the last: when this was done a shock, something like the electrical one, was experienced, and would recur as often as the circuit was interrupted and completed.
Mr. Volta remarks, that alkaline solutions are used to the most advantage when one of the metals is tin and the other silver or copper; but that where zinc is substituted for tin, salt water is preferable.
After this discovery, Volta invented a much more convenient instrument, which, besides other advantages over the former, was more powerful and less expensive. The instrument is called the Galvanic pile, and very often the Voltaic pile, from its inventor. It is made in the following manner—Take a number of circular plates of copper, or silver and an equal number of tin or zinc of the same dimensions. Next provide a like number of round pieces of paste-board, leather, or any other substance capable of retaining moisture for a considerable time. This leather, cloth or other substance, must be rather smaller than the metal plates and, when used, well moistened with salt and water. Now form a pile, by laying alternately the zinc over the silver, and, the cloth or other moistened substance, over the zinc; and so on successively.—By thus continuing the series to forty or fifty plates, a Galvanic pile will be constructed. If the pile is intended to be of any considerable height, it ought to be secured by pillars of varnished baked wood; or strong glass tubes.
To get the shock, one hand must touch the bottom, and the other the top plate.—The hands should be wet, as the cuticle or external part of the skin is a bad conductor.
Shocks may be received by applying the hands in this manner, as long as the leather, or other substance interposed between the zinc and silver, continues moist; but as soon as it becomes dry the operation closes.
The drying of the substance was a great inconvenience in the Voltaic pile, and the inventor proposed, as a remedy for this, to station the metallic plates at a greater distance from one another, and to fill up the cells or intervals between them with a saline solution. Mr. Cruickshank, an English chemist at Woolwich, improved this construction.—His trough as it is called, is made thus.—
Get a wooden trough, made of hard baked mahogany, about thirty inches long, and four or five wide and deep.—On the inside let there be cut in the sides and bottom, and at equal distances from one another, as many grooves, as the number of plates required to be put into the trough;—the grooves of a size to admit the plates. The plates are to be cemented[[18]] separately to each of the grooves, so that no fluid can pass from one cell to another. In this instrument the plates are constructed by soldering a plate of zinc to one of copper. The zinc, or which is the same thing, the spelter of the shops, should be melted in a vessel which exposes but a small surface to the action of the air, otherwise it would absorb oxygen so rapidly as to be converted into the flowers of zinc.—The melted metal should be poured as soon as possible into a mould of the proper size, made of stone or brass.—It is not necessary that the plates of copper should be more than one tenth of the thickness of those of zinc.
The two plates are commonly soldered, not through their whole extent, but about one fourth of an inch from the edge; so that at the edge their union may be complete.
Care must be taken that all the plates be cemented to the trough in the same direction; so as to have the copper side of every plate opposite to the zinc side of the next.