Part 25

Ibid. p. 29.

Ibid. p. 42.

Ibid. p. 42.

484. When in 1826 Sir Humphry Davy wrote again on this subject, he stated that he found nothing to alter in the fundamental theory laid down in the original communication, and uses the terms attraction and repulsion apparently in the same sense as before.

Philosophical Transactions, 1826, p. 383.

Ibid. pp. 389, 407, 115.

485. Messrs. Riffault and Chompré experimented on this subject in 1807. They came to the conclusion that the voltaic current caused decompositions throughout its whole course in the humid conductor, not merely as preliminary to the recompositions spoken of by Grotthuss and Davy, but producing final separation of the elements in the course of the current, and elsewhere than at the poles. They considered the negative current as collecting and carrying the acids, &c. to the positive pole, and the positive current as doing the same duty with the bases, and collecting them at the negative pole. They likewise consider the currents as more powerful the nearer they are to their respective poles, and state that the positive current is superior in power to the negative current.

Annales de Chimie, 1807, tom. lxiii. p. 83, &c.

486. M. Biot is very cautious in expressing an opinion as to the cause of the separation of the elements of a compound body. But as far as the effects can be understood, he refers them to the opposite electrical states of the portions of the decomposing substance in the neighbourhood of the two poles. The fluid is most positive at the positive pole; that state gradually diminishes to the middle distance, where the fluid is neutral or not electrical; but from thence to the negative pole it becomes more and more negative. When a particle of salt is decomposed at the negative pole, the acid particle is considered as acquiring a negative electrical state from the pole, stronger than that of the surrounding undecomposed particles, and is therefore repelled from amongst them, and from out of that portion of the liquid towards the positive pole, towards which also it is drawn by the attraction of the pole itself and the particles of positive undecomposed fluid around it.

Précis Elémentaire de Physique, 3me édition, 1824, tom. i. p. 641.

Ibid. p. 637.

Ibid. pp. 641, 642.

487. M. Biot does not appear to admit the successive decompositions and recompositions spoken of by Grotthuss, Davy, &c. &c.; but seems to consider the substance whilst in transit as combined with, or rather attached to, the electricity for the time, and though it communicates this electricity to the surrounding undecomposed matter with which it is in contact, yet it retains during the transit a little superiority with respect to that kind which it first received from the pole, and is, by virtue of that difference, carried forward through the fluid to the opposite pole.

Précis Elémentaire de Physique, 3me édition, 1824, tom. i. p. 636.

Ibid. p, 642.

488. This theory implies that decomposition takes place at both poles upon distinct portions of fluid, and not at all in the intervening parts. The latter serve merely as imperfect conductors, which, assuming an electric state, urge particles electrified more highly at the poles through them in opposite directions, by virtue of a series of ordinary electrical attractions and repulsions.

Précis Elémentaire de Physique, 3me édition, 1824, tom. i. pp. 638, 642.

489. M.A. de la Rive investigated this subject particularly, and published a paper on it in 1825. He thinks those who have referred the phenomena to the attractive powers of the poles, rather express the general fact than give any explication of it. He considers the results as due to an actual combination of the elements, or rather of half of them, with the electricities passing from the poles in consequence of a kind of play of affinities between the matter and electricity. The current from the positive pole combining with the hydrogen, or the bases it finds there, leaves the oxygen and acids at liberty, but carries the substances it is united with across to the negative pole, where, because of the peculiar character of the metal as a conductor, it is separated from them, entering the metal and leaving the hydrogen or bases upon its surface. In the same manner the electricity from the negative pole sets the hydrogen and bases which it finds there, free, but combines with the oxygen and acids, carries them across to the positive pole, and there deposits them. In this respect M. de la Rive's hypothesis accords in part with that of MM. Riffault and Chompré (485.).

Annales de Chimie, tom, xxviii. p. 190.

Ibid. pp. 200, 202.

Ibid. p. 202.

Ibid. p. 201.

490. M. de la Rive considers the portions of matter which are decomposed to be those contiguous to both poles. He does not admit with others the successive decompositions and recompositions in the whole course of the electricity through the humid conductor, but thinks the middle parts are in themselves unaltered, or at least serve only to conduct the two contrary currents of electricity and matter which set off from the opposite poles. The decomposition, therefore, of a particle of water, or a particle of salt, may take place at either pole, and when once effected, it is final for the time, no recombination taking place, except the momentary union of the transferred particle with the electricity be so considered.

Annales de Chimie, tom, xxviii. pp. 197, 198.

Ibid. pp. 192, 199.

Ibid. p. 200.

491. The latest communication that I am aware of on the subject is by M. Hachette: its date is October 1832. It is incidental to the description of the decomposition of water by the magneto-electric currents (346.). One of the results of the experiment is, that "it is not necessary, as has been supposed, that for the chemical decomposition of water, the action of the two electricities, positive and negative, should be simultaneous."

Annales de Chimie, tom, xxviii. tom. li. p. 73.