. An analytical compendium of the various branches of medical science, for the use and examination of students. Anatomy; Physiology; Surgery; Obstetrics; Medicine; Materia Medica. »b CHEMISTRY. and the copper end positive. When the two extremities are joined, the current continues to pass from the copper to the zinc; so that in fact, we may consider that there are two currents: one, in the battery, passing from the zinc to the copper; the other, out of the battery, going from the copper to the zinc, as shown by the arrows in the preceding figure. Cruikshank''s trough, is a modification of Volt
. An analytical compendium of the various branches of medical science, for the use and examination of students. Anatomy; Physiology; Surgery; Obstetrics; Medicine; Materia Medica. »b CHEMISTRY. and the copper end positive. When the two extremities are joined, the current continues to pass from the copper to the zinc; so that in fact, we may consider that there are two currents: one, in the battery, passing from the zinc to the copper; the other, out of the battery, going from the copper to the zinc, as shown by the arrows in the preceding figure. Cruikshank''s trough, is a modification of Volta's pile; it consists of numerous pairs of zinc Fig- 13. and copper plates soldered together,and cemented water- tight into a mahogany trough, which thus becomes divided into a series of cells or com- partments, capable of receiv- ing the exciting liquid. This apparatus is well adapted to exhibit effects of tension, and to give shocks. The quantity of electricity set free, is to be distinguished from its tension ; the first is measured by its chemical effects—particularly the power of decomposition ; the last, by its power of overcoming obstacles, and passing through imperfect conductors. Different theories as to the nature a?id cause of galvanism.— Galvani supposed it to be developed in the animal upon which he was experimenting, and that the metals served merely as conductors; Volta, on the other hand, supposed it to be developed by the contact of dissimilar metals. Subsequently, Faraday brought forward the theory oi chemical action, which is now most generally adopted. The most important effect produced by galvanism, is that of the decomposition of compound bodies. It was by means of this agent that Sir H. Davy made the discovery of the metals of the alkalies. When compound bodies in the fluid slate are traversed by a galvanic circuit, a decomposition usually takes place according to a uniform and constant rule; certain elements, as oxygen, chlorine, iodine, acids, &
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