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.

    507/562 (page 483)
    If two decomposing cells with platinum partitions contain two liquids of unequal decomposibility—e. g., water and dilute sulphuric acid—the current passes through them more easily when the positive electricity of the latter is conducted into the liquid of least conducting power, 7. e., the water, and the negative electricity into the dilute acid, than in the con- trary case. (Matteucci.) The current of a single pair of zinc and copper in water or dilute sulphuric acid, is completely stopped by three or four decomposing cells with copper partitions, when the decomposing cells are likewise filled with water or dilute sulphuric acid. But if a quantity of nitrie acid be added to the latter, sufficient to produce a slight action upon the copper, the current will not be greatly weakened, even by a considerable number of decomposing cells: the copper will be most attacked at that part from which the positive electricity passes from it to the liquid. (Buff.) The current of one pair of zinc and platinum in dilute sulphuric acid is not perceptibly weakened by three decomposing cells containing dilute sulphuric acid, when the partitions consist of ordinary zine plates; but when these plates are amalgamated, a considerable diminution of power ensues. Partitions of copper give free passage to the current at first, but stop it completely after a few minutes, probably because they become polarized. On turning one of these copper plates round, the current is reproduced for a short time. (Faraday.) If the decomposing cells contain dilute sulphuric acid, the current is most impeded when the electrodes and interposed plates consist of pla- tinum; then follows lead, then copper, then tin, then cadmium. If a zinc plate enclosed between two moist conductors, be placed between a pair of plates of a voltaic battery, the current is much less weakened than it would be by a copper plate introduced in a similar manner. (De la Rive.)—Decomposing cells containing dilute sulphuric acid offer the greatest resistance to the current when the electrodes consist of platinum ; then follows copper, then zinc. If, on the contrary, the cells contain ammonia, copper and zinc produce the same amount of resistance. Volume and Surface of the Liquid. If the current of a battery of 100 pairs be passed through decom- posing cells by means of platinum plates, each of which presents a square: inch of surface to the liquid on either side, the strength of the current is’ the same, whether the partitions are placed at the distance of a foot or of only four lines from each other; but when the thickness of the inter- posed liquid exceeds a foot, while its section is only one square inch, the current diminishes. Consequently, the loss of the current in its passage through the liquid is almost as nothing [or in other words, the length of the portion of liquid throughout which atomic transposition must be effected, is almost without influence], and the principal loss is sustained in the passage of the electric fluids between the plates and the liquid [or in the decomposition of the liquid, which must take place if the cur- rent is to pass]. (De la Rive. )—-Faraday likewise found no difference. The current passes more easily when the partition is nearer to the anode than when it is nearer to the cathode. (Matteucci.) | Even when the interposed platinum plate is nearly a foot long and the polar wires are only three inches distant from it, gas is evolved over the whole surface of the platinum plate. When the decomposing cells 212