Elements of chemistry : including the most recent discoveries and applications of the science to medicine and pharmacy, and to the arts / by Robert Kane.

  • Kane, Robert, 1809-1890.
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry : including the most recent discoveries and applications of the science to medicine and pharmacy, and to the arts / by Robert Kane. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

    141/716
    bells, tVc ; for there being a continual source of electricity in the action of the moisture of the paper on the zinc, these phenomena may continue manifested for years without diminution. Such a dry pile, when insulated, shows opposite electrical excitation at the two extremities, these being, however, of equal force, and hence producing neutrality When combined. If, therefore, the two ends of a dry pile be connected by a wire, the electricities which had accumulated recombine, and the pile becomes inert, and requires a certain time before it can recover a charge equal to that which it had lost. When the pile is examined at a distance from its ends, the excitation is found to be less powerful, until at the centre it is exactly neutral. This arises from the action at each point being the resultant of the opposing actions of the two extrem- ities, and vanishing at the centre where these last are equal, precisely as there ex- ist-, a neutral place upon the surface of any body inductively excited by ordinary electricity. If the pile be held in the hand by one extremity, the electricity of that end is dissipated, and the other end becomes capable of acting more powerfully upon the electroscope, from the opposing influence being removed. No principle has ever been discovered in science more rich in consequences than this of the increase of tension given to electricity in motion by the connexion of a number of simple galvanic circles. Hence, deservedly, the instrument so formed has obtained the name of the Voltaic pile. It has enriched chemistry with a crowd of important substances discovered by its means, and has led, by its results, to the suggestion of the most plausible theory of chemical combination that has been as yet proposed Ik physical science it became the origin of all subsequent improvement in the domain of electricity, for without its agency it is hard to see how the steps which followed could have been made. The form in which the Voltaic pile was first constructed was sim- ilar to that of the dry pile noticed above. The disks were of zinc and silver or copper. The fluid conductor, which was rendered more capable of acting- on the zinc by the addition to it of some acid or of common salt, was imbibed in disks of common cloth, which were interposed between every pair of metallic disks. There were thus, copper-zinc, acid, copper-zinc, acid, copper-zinc, and so on to an indefinite extent. It is a peculiarity of this instrument, which, as it extends to many forms of it even now in use, and affects our chemical nomenclature remarkably, it is necessary to notice, that the current in the connecting wires appears to be in a direction opposite to that described in the battery of cells of page 131; for the outer copper plate at the one end, and the outer zinc plate at the other, having no communication with the exciting acid, trans- mit the current merely as portions of the attached wires, and hence the direction of the current is in appearance from the zinc to the copper end, while it is properly the copper from which the positive fluid emanates, and it is the negative which arises from the zinc. This diversity had its origin in the circumstance that the theory of the pile maintained by Volta, and even at the present moment sup- ported by some illustrious men, ascribed the orio-in of the electri- cily not to the action of the acid upon the zinc, but to the contact of the zinc with the copper ; the point where the metals touched being supposed to be a continual source of positive electricity to the copper. It was even attempted to prove this by solderino- to- gether plates of zinc and copper, and testing their electrical condi- tion by the gold-leaf condenser, which was supposed to indicate a permanent state of excitation, independent of all fluid or chemically acting media. It has been fully proved, however, that, according as such contact experiments are made with increased care, the re- suits become less evident in favour of that theory. Such trials tend to show the evolution of minute traces 01 statical electricity, where-