Elements of chemistry, including the history of the imponderables and the inorganic chemistry of the late Edward Turner / [Edward Turner].

  • Edward Turner
Date:
1846
Catalogue details

Licence: Public Domain Mark

Credit: Elements of chemistry, including the history of the imponderables and the inorganic chemistry of the late Edward Turner / [Edward Turner]. Source: Wellcome Collection.

    131/880 page 105
    or electro-negative element in each compound, is disengaged at the positive pole. As, from the fact that an equivalent of electricity is required to decompose an equivalent of any compound, we may conclude that the electro-positive and electro-negative elements of that compound, in uniting, would disengage the same amount of electricity, he infers the following laws :— 1. When one equivalent of a body, either simple or compound, unites with one or more equivalents of another, the first playing the part of an electro-nega¬ tive element or acid, one equivalent of electricity is set free. 2. If an equivalent of an electro-negative body, such as oxygen, has already entered into combination with another body, which acts as a base, and if a second equivalent of the former unites with the compound thus produced to form a deuto salt or compound ; at the time of this second action another equivalent of electricity is disengaged. Thus the quantity of electricity set free depends solely on the body which acts the part of acid in the compound. (Comp. Rendus, Mar. 1844.)] THEORIES OF GALVANISM AND ELECTRO-CHEMICAL THEORY. Of the theories proposed to account for the developement of electricity in voltaic combinations, three in particular have excited the notice of philosophers. The first originated with Volta, who conceived that electricity is set in motion, and the supply kept up, solely by contact or communication between the metals (page 82). He regarded the interposed solutions merely as conductors, by means of which the electricity developed by each pair of plates is conveyed from one part of the apparatus to the other. Thus, in the pile or ordinary battery, repre¬ sented by the following series :— 1 zinc copper fluid zinc copper fluid zinc copper — Volta considered that contact between the metals occasions the zinc in each pair to be-f-, and the corresponding copper plate to be —; that the T zinc in each pair except the last, being separated by an intervening stratum of liquid from the — copper of the following pair, yields to it its excess of electricity; and that in this way each zinc plate communicates, not only the electricity developed by its own contact with copper, but also that which it had received from the pair of plates immediately before it. Thus, in the three pairs of plates contained in brackets, the second pair was thought to receive electricity from the first only, and the third pair from the first and second. In batteries constructed on the prin¬ ciple of the crown of cups (fig. 6), the electro-motion, as Volta called it, is ascribed to metallic communication between the zinc of one glass and the copper of the adjoining one. The second is the chemical theory, proposed by Wollaston. Volta attached little importance to the chemical changes which never fail to occur in every voltaic circle, whether simple or compound, considering them as casual or unes¬ sential phenomena, and therefore neglected them in the construction of his theory. The constancy of their occurrence, however, soon attracted notice. In the earlier discussions on the cause of spasmodic movements in the frog (page 82),Fabroni contended, in opposition to Volta, that the effect was not owing to electricity at
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