Copy 1, Volume 1

Hand-book of chemistry / Translated by Henry Watts.

  • Gmelin, Leopold, 1788-1853
Date:
1848-1872
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of chemistry / Translated by Henry Watts. Source: Wellcome Collection.

    442/562 (page 418)
    If the union of the electricities collected in the poles has been effected by connecting the poles by a perfect conductor, and the connection is after- — wards broken, the two electricities again accumulate in the poles with their former tension. In piles with moist semi-conductors, this effect takes place almost instantaneously; in those with dry semi-conductors, often very slowly. So long as the poles remain connected by a good conductors the positive and negative electricities rapidly generated in the battery continually recombine within the conductor. ‘The quantity of electricity thus neutralized in a given time depends on the circumstances above noticed. E The difference between the effects of the voltaic pile and those of the electrical machine consists in the two following points: 1. By means of the latter, a large quantity of electricity may easily be accumulated in a body of small dimensions; in consequence of which, the electricity acquires a high tension or a strong tendency to combine with electricity of the opposite kind, and makes its way through non-conductors, such as the air, in the form of a spark. On the other hand, the tension of the electricity developed by the contact of two metals is so extremely small, that, accord- ing to Children, it requires no fewer than 1250 zinc and copper plates to - give such a tension to the electricity accumulated at the poles, as will enable it to pass in the form of a spark between two platinum wires ter- minating in points, placed at an interval not exceeding <> inch, and con- nected-with the poles of the battery.—(2.) But a small voltaic battery generates in a given time a much greater quantity of electricity than a large electrical machine,—provided the electricities are conducted away as fast as they are generated. The electrical machine, therefore, is best adapted to the production of those effects which depend on great electrical tension, such as the penetration of air, glass, and other insulators; the voltaic battery, especially when large plates are used, is most efficacious | in producing those effects which depend on the combination of large quan- tities of electricity in a given time,—e. g., an elevated temperature in the | conductors in which the combination takes place, and the decomposition of chemical compounds. : Since an increased number of plates augments, not the quantity, but only the intensity of the current, it follows that the number of pairs united in the battery ought to be different, according to the conducting power of the body through which the current has to pass. A greater number of pairs than that required for completely overcoming the resist- ance, is of no ayail—and may even diminish the quantity of the current, if any among them act less powerfully than the rest. Hence a single pair is proper when the current has to pass through a thick wire only (as for magnetic action or for fusing), a small number of pairs when it has to traverse a long thin wire, a larger number when watery liquids are placed in the circuit, and a still larger number when the liquids are divided into separate portions by interposed plates. (De la Rive.) : The greater the number of pairs, the sooner does the action diminish; so that a battery of a small number of pairs is stronger after a time than one containing a large number. (De la Rive.) : Strongly acting pairs must not be united with such as act weakly, é. g., zinc and copper with copper and platinum; or pairs acted upon by fresh acid with pairs subjected to the action of acid which has been used and is therefore saturated; neither should large pairs be united with small ones. The addition of pairs which act less powerfully [though it increases the tension] diminishes the quantity of the current considerably. If 40