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.

    444/562 (page 420)
    on account of its tenacity. (Bunsen, Ann. Pharm. 88, 211.) (Comp. p. 392. aoe oa the following may be used: spring-water, aqueous solu- tions of common salt, sal-ammoniac, nitre, alum, sulphate of copper, bisulphate of potash, and other salts, aqueous ammonia or potash, and — dilute sulphuric, hydrochloric, or nitric acid, or a mixture of dilute sul+ — -phuric and nitric acids. . | Water gives a continuous current of small quantity and attacks the zinc but very little. With saline solutions, the current is at first abund- ant, but soon diminishes (p. 377). Sulphate of copper is the only salt - that gives a more permanent current; it also acts without evolution of gas. A mixture of water, sulphuric acid, and nitric acid (e. g., 100 mea- sures of water to 4:5 oil of vitriol and 4 nitric acid) possesses this advan- tage,—that it not only excites an intense and abundant current, but that neither hydrogen nor nitric oxide gas is evolved from it, because the hydrogen evolyed from the water combines with the nitrogen set free from the nitric acid, and forms ammonia. (For Fyfe’s experiments on the power of different circuits, vid. Pogg. 43, 228.) When dilute sulphuric and nitric acid are used together, instead of dilute sulphuric acid alone, in a battery of ten pairs of amalgamated zinc and platinum, the quantity of the current (measured by the Voltameter) is nearly trebled, and the quantity of hydrogen gas evolved in the differ- ent cells is small and unequal; but in five minutes the current ceases almost entirely, and is but imperfectly restored by opening the circuit. When more nitric acid is added, the evolution of hydrogen ceases entirely in some cells, and almost wholly in others: the current is strengthened, but diminishes rapidly. If when the circuit has been closed for thirty hours, and the current has almost wholly ceased, the platinum plates be removed and replaced by new ones, the battery will again act as strongly as at first, but only for a short time. The platinum plates, which have ~ become inactive, are not completely restored by ignition, polishing, or boiling with strong solution of potash; but they recover their activity entirely by boiling in nitric acid. For they are covered with zine partly — crystalline, partly of a warty texture,—the coating even extending, though in smaller quantity, to the side which is turned away from the | zinc. The rapidity with which this coating is formed, increases with the quantity of zinc dissolved in the liquid; it is therefore greatest when un- amalgamated zinc is used.—Every time the circuit is broken, the zine deposited upon the platinum dissolves again, provided a sufficient quan- tity of free acid be present. When the acid liquid holds a quantity of copper in solution, that metal is first deposited on the platinum, and afterwards the zinc, but with less facility. But when a larger quan- tity of copper is contained in the liquid, the copper is precipitated on the | amalgamated zinc, and causes an evolution of hydrogen upon it. The addition of nitric acid to the dilute sulphuric acid assists the action by diminishing the evolution of hydrogen gas on the platinum, inasmuch as. it gives rise to the production of ammonia [by which however the acid is so much the more quickly saturated]. (Daniell.) : Remarkably powerful currents are produced by the proper combination of two metals with two liquids (p. 889). . With plates of given surface, the quantity of the current varies accord- ing to their nature and that of the liquid, as follows: Amalgamated zine, dilute sulphuric acid, copper : 0°19;—amalgamated zine, dilute sulphuric acid, platinized silyer (according to Smee) : 0°29;—amalgamated zine,