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.)

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    the excited surfaces, the zinc and acid, are placed in communication, the negative electricity of the zinc unites with the positive of the copper, whether by direct translation or by inductive action, and the positive electricity of the liquid unites with the negative of the cop- per to produce neutralization ; at the same time the + of the zinc and the —of the acid combine. As, on the theory of Franklin, 1 he single electric fluid is supposed to pass from the body which is positively to the body which is neg ativ'ely excited, it is usual to imagine this exchange of electricities to take place by a current, which in this case, as shown by the arrows in the figure, is from the copper to the zinc at the superior junction, but from the zinc to the copper in the acid under- neath. At every moment, according as the neutral ization of the electricities is effected, the system is competent to generate new quantities, and hence the analogy of the weakly-charged Leyden jar, noticed above, docs not completely hold ; for, to be accurate, it would require the jar to pos- sess a power of charging itself as rapidly as it could be discharged The passage of the current is accompanied by the solution of the zinc and the liberation of the hydrogen. This hydrogen accompa nies the positively electrified molecules of the acid across the fluid, and is discharged under the form of gas upon the surface of the copper plate. The essential elements of an arrangement by which a current of electricity may be produced are, therefore, first, two bodies, one simple and one compound, which act chemically upon one another in such a way as that the simple element shall be substituted for a constituent of the other, which shall be expelled ; and, second, a conducting substance, which is indifferent in a chemical point of view, and only furnishes a route for the fluids of the actual elements to recombine continually with each other. In the example given just now, this conduct- or was a slip of copper ; but it may be of any form, or almost any substance; thus, as in the figure, a wire may be soldered to the end of each slip, and on bring- ing these wires into contact at X, the current passes precisely as if the contact of Z with C had been direct. Such an arrangement is termed a simple circle. It is not even necessary that the conductor should be solid or me- tallic ; it is, indeed, only for convenience that the ordinary conduct- ing plates and wires are metallic. Thus, in the figure, A Z W, a plate of zinc is in contact on the one side with muriatic acid, A, and on the other with water, W, to which a better conducting power has been given by dis- solving in it a little common salt. The current is then es- tablished, being from the conductor to the zinc, and from the zinc to the acid, precisely as in the former instances. The passage of the current under these various circumstances may be shown, and also that, for its origin and transfer, metallic communication between the plates Z and C is not necessary, by a very simple experiment. If the slip of zinc be bent, as in B, and f n ^ A. VT