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.

    508/562 (page 484)
    are connected by wires instead of plates, the evolution of gas becomes less, in consequence of the diminished surface. (De la Rive.) Particular Cases. When a series of rapidly alternating currents is made to pass, by means of the commutator, from a Daniell’s constant battery through two cells filled with dilute sulphuric acid, the following effects are observed, interposed plate are formed: With platinum, the alternating current is much less weakened than a current which passes constantly in the same direction (and when Clarke's magneto-electric apparatus is used—if 40 alternating currents follow one another rapidly in a second, and the platinum plates present a large surface, a slight diminution takes place just at first ; but when the surfaces, in consequence of the formation of pulverulent platinum, haye become more susceptible of oxidation and reduction, the current suffers no further diminution).—With copper, the alternating current exhibits nearly the same quantity, and with tin and cadmium exactly the same, as in the case of metallic connection without decomposing cells; whereas the con- tinuous current, under the same circumstances, is more or less weakened. Lead, which checks the continuous current almost as much as platinum, and at the same time becomes covered, on the side by which the positive electricity passes into the liquid, with a white crust [sulphate of lead?], which impedes the passage of the current, and does not appear to be re- duced by hydrogen,—offers nearly twice as much resistance to the passage of the alternating current, because, by the action of such a current it becomes coated with this white crust on both sides. A similar white crust [nitrate of lead?] is produced in nitric acid diluted with an equal quantity of water.—In solution of sal-ammoniac, platinum weakens the alternating current less than in dilute sulphuric acid ; chloride of platinum is alternately formed and decomposed by the hydrogen. (De la Rive.) If a cracked glass tube, closed at bottom and filled with solution of nitrate of silver, be immersed in a glass vessel filled with water, and one of the polar wires dipped into each vessel, electric action takes place through the crack, and decomposition ensues, though but slowly—oxygen gas being evolved at the positive wire and on the side of the crack towards the negative wire (peroxide of silver being at the same time deposited on the positive wire), and silver being reduced on the negative wire and on the side of the crack towards the positive wire (no evolution of hydrogen takes place). The crack acts like a solid conductor, through which, on account of its narrowness, the decomposition of the liquid or the transference of the liberated elements cannot take place. (Grotthuss, Schw. 28, 315.) Union of Opposed Batteries. [To the theory of interposed plates likewise belong the cases in which two galvanic batteries are connected together with their plates in inverse order, so that their currents act in opposition to one another. In this arrangement, the exciting cells of each battery act as decomposing cells to the other. The current of the one battery has to overcome not only the resistance which the liquid in the cells of the other battery offers to