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.

    473/562 (page 449)
    The smaller, therefore, the evolution of gas, and the niore the passage of the current is facilitated by oxidation and deoxidation, the higher is the temperature produced, and the greater, therefore, the quantity of electricity which passes through. The higher the temperature shown by _ the Breguet’s thermometer, the colder does the liquid remain. (De la Rive, Pogg. 54, 497.) [When once a sufficient quantity of finely divided platinum has been formed, the evolution of gas ceases, because the platinum in this state readily takes up the oxygen separated from the water by the action of the current,—and while one wire is oxidized in this manner, the other is deoxidized by the hydrogen: the opposite current which immediately succeeds, reverses the process—and so on. The current has now no further decomposition to effect, which is not immediately compensated by the formation of a new compound, and therefore its whole force is expended in transposing the atoms. Hence, as the evolution of gas diminishes, the current increases in quantity, and heats Breguet’s thermometer more strongly; and as the decomposition of the water ceases, the rise of tem- perature in the liquid which accompanies this decomposition, ceases also. The case is similar with the other metals. | Charcoal used as the anode in the decomposition of water acidulated with sulphuric acid, evolves carbonic acid and carbonic oxide gases. (Faraday. ) Antimony used as an anode in water, becomes covered with suboxide. When mercury is placed under water acidulated with sulphuric acid, and the platinum cathode dipped into the mercury, while the anode is immersed in the water, the negative wire becomes quickly amalgamated; and the mercury, which has thus been made to act for a time as the cathode, has the power, when taken out of the circuit, of quickly amalga- mating wires of platinum, iron, or steel. This effect is due to a trace of an alkali-metal [or hydrogen] which the mercury has taken up by elec- trolytic action. (Grove.) Tellurium acting as cathode in water generates telluretted hydrogen, which dissolves and is again decomposed by the oxygen separated at the anode, the tellurium being precipitated in brown flakes; hence the quantity of oxygen evolved is but small. (Magnus.)—When sulphur or selenium is attached to the platinum cathode, a yellow precipitate of sul- phur or a red precipitate of selenium is obtained, sulphuretted or sele- niuretted hydrogen being first formed and then decomposed by the oxygen, which would otherwise escape at the anode. (Magnus, Pogg. 17, 521.)—Antimony acting in water as cathode, is said by Ruhland to yield a brown-black compound of antimony and hydrogen. Development of an Odorous Substance in the Decomposition of Water. The decomposition of water is attended with the production of a pecu- liar odour, which is confined to the positive electrode, so that when the hydrogen and oxygen gases are collected in separate vessels, the latter only is affected with the odour. The odorous principle is developed only when gold or platinum is used as the anode; not with oxidable metals or charcoal. The odour is perceived when the water holds in solution, phos- phoric acid, sulphuric acid, nitric acid, nitre, phosphate of potash, or sulphate of soda; not when it contains hyponitric acid, hydrochloric acid, hydrobromic acid, metallic iodides, bromides, or chlorides, or protosul- phate of iron; it is only occasionally observed in aqueous solution of VOL, I. 2G