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.

    520/562 (page 496)
    a long thin wire, so that the quantity of the current. is diminished, the rise of temperature in the liquid likewise becomes less [partly because the chemical action is slackened, partly because the combination of the electric fluids within the wire develops a quantity of heat which would otherwise have been evolved in the troughs]. In Daniell’s apparatus, on the other hand (zinc, dilute sulphuric acid, sulphate of copper, and metallic copper, p. 421), a cousiderable reduction of temperature takes place. (Joule, Phil. Mag. J. 19, 260.) [This de- serves attention, inasmuch as heat is evolved during the precipitation of a solution of sulphate of copper by zinc. | Development of Heat in the Troughs of a Trough Battery. When a battery consisting of four porcelain troughs filled with dilute nitric acid—each trough containing 10 cells, having a pair of zinc and copper plates immersed in each, and therefore making 40 pairs in all— is left for some time with its poles connected, a rise of temperature takes place in the liquid contained in the cells. In one experiment of this kind, the temperature of the liquid was at first 16°6° C.; in the middle of the trough, containing the positive pole, it rose to 55:5°; in the next to 54°7°; in the third to 53°6°; and in the trough which contained the negative pole, only to 43:2°. (Murray, V. Hd. Phil. J. 12, 57.) Development of Heat in the Decomposing Cell. [Watery liquids are the only substances, the decomposition of which has hitherto been observed to be accompanied by elevation of tempera- ture. If we suppose (according to p. 494) that of the heat produced in the combination of oxygen and hydrogen, a great part remains united with the water (2,290 parts out of 5,290), then this quantity of heat must be liberated during the electrolysis of the water. For, at the positive poles, the full quantity of heat combines with one atom of oxygen, and at the negative pole, one atom of hydrogen takes up the full quantity of negative electricity,—the heat, which was held in a state of combina- tion by the atom of water decomposed, remains in the liquid in the free state. tre gold cups containing water are connected by asbestus, and into one of the’cups, in which the positive wire of a battery of 100 pairs is immersed, a drop of a solution of sulphate of potash is let fall: the potash then passes rapidly into the negative cup, and the water is raised in two minutes to the boiling point. When the current acts on a solution of nitrate of ammonia, all the water evaporates in three or four minutes, producing a hissing noise and a white cloud, and the remaining nitrate of ammonia takes fire—When one of the cups contains strong solution of potash, and the other oil of vitriol, only a slight elevation of temperature is produced. (H. Davy.) When dilute sulphuric acid is decomposed by Grove’s battery, it is converted into oil of vitriol, and becomes so hot, that wood placed under the vessel which contains it is charred. (Grove.) In the electrolysis of a watery liquid, a greater rise of temperature takes place at the positive than at the negative pole,—because less gas is evolved at the former, and therefore less heat is rendered latent. The evolution of heat is greater when the liquid is divided into a number of separate parts by porous bodies, such as membranes, bundles of thread,