CHAPTER IX.

EPOCH OF DAVY AND FARADAY.

Sect. 1.-Promulgation of the Electro-chemical Theory by Davy.

THE

THE reader will recollect that the History of Chemistry, though highly important and instructive in itself, has been an interruption of the History of Electro-dynamic Research:-a necessary interruption, however; for till we became acquainted with Chemistry in general, we could not follow the course of Electro-chemistry: we could not estimate its vast yet philosophical theories, nor even express its simplest facts. We have now to endeavour to show what has thus been done, and by what steps;-to give a fitting view of the Epoch of Davy and Faraday.

This is, doubtless, a task of difficulty and delicacy. We cannot execute it at all, except we suppose that the great truths, of which the discovery marks this epoch, have already assumed their definite and permanent form. For we do not learn the just value and right place of imperfect attempts and partial advances in science, except by seeing to what they lead. We judge properly of our trials and guesses only when we have gained our point and guessed rightly. We might personify philosophical theories, and might represent them to ourselves as figures, all pressing eagerly onwards in the same direction, whom we have to pursue and it is only in proportion as we ourselves overtake those figures in the race, and pass beyond them, that we are enabled to look back upon their faces; to discern their real aspects, and to catch the true character of their countenances. Except, therefore, I were of opinion that the great truths which Davy brought into sight have been firmly established and clearly developed by Faraday, I could not pretend

to give the history of this striking portion of science. But I trust, by the view I have to offer of these beautiful trains of research and their result, to justify the assumption on which I thus proceed.

I must, however, state, as a further appeal to the reader's indulgence, that, even if the great principles of electro-chemistry have now been brought out in their due form and extent, the discovery is but a very few years, I might rather say a few months, old; and that this novelty adds materially to the difficulty of estimating previous attempts from the point of view to which we are thus led. It is only slowly and by degrees that the mind becomes sufficiently imbued with those new truths, of which the office is, to change the face of a science. We have to consider familiar appearances under a new aspect; to refer old facts to new principles; and it is not till after some time, that the struggle and hesitation which this employment occasions, subsides into a tranquil equilibrium. In the newly-acquired provinces of man's intellectual empire, the din and confusion of conquest pass only gradually into quiet and security. We have seen, in the history of all capital discoveries, how hardly they have made their way, even among the most intelligent and candid philosophers of the antecedent schools: we must, therefore, not expect that the metamorphosis of the theoretical views of chemistry which is now going on, will be effected without some trouble and delay.

I shall endeavour to diminish the difficulties of my undertaking, by presenting the earlier investigations in the department of which I have now to speak, as much as possible according to the most deliberate view taken of them by the great discoverers themselves, Davy and Faraday; since these philosophers are they who have taught us the true import of such investigations.

There is a further difficulty in my task, to which I might refer; the difficulty of speaking, without errour and without offence, of men now alive, or who were lately members of social circles which exist still around

us.

But the scientific history in which such persons play a part, is so important to my purpose, that I do not hesitate to incur the responsibility which the narration involves; and I have endeavoured, earnestly, and I hope not in vain, to speak as if I were removed by centuries from the personages of my story.

The phenomena observed in the Voltaic apparatus were naturally the subject of many speculations as to their cause, and thus gave rise to Theories of the Pile.' Among these phenomena there was one class which led to most important results: it was discovered by Nicholson and Carlisle, in 1800, that water was decomposed by the pile of Volta; that is, it was found that when the wires of the pile were placed with their ends near each other in the fluid, a stream of bubbles of air arose from each wire, and these airs were found on examination to be oxygen and hydrogen; which, as we have had to narrate, had already been found to be the constituents of water. This was, as Davy says,1 the true origin of all that has been done in electrochemical science. It was found that other substances also suffered a like decomposition under the same circumstances. Certain metallic solutions were decomposed, and an alkali was separated on the negative plates of the apparatus. Cruickshank, in pursuing these experiments, added to them many important new results; such as the decomposition of muriates of magnesia, soda, and ammonia by the pile; and the general observation that the alkaline matter always appeared at the negative, and the acid at the positive, pole.

Such was the state of the subject when one who was destined to do so much for its advance, first contributed his labours to it. Humphry Davy was a young man who had been apprenticed to a surgeon at Penzance, and having shown an ardent love and a strong aptitude for chemical research, was, in 1798, made the superintendent of a 'Pneumatic Institution,' established at Bristol by Dr. Beddoes, for the purpose of discovering medical powers of factitious airs. But his main

1 Phil. Trans. 1826, p. 386.

2 Paris, Life of Davy, i. 58.

attention was soon drawn to galvanism; and when, in consequence of the reputation he had acquired, he was, in 1801, appointed lecturer at the Royal Institution in London, (then recently established,) he was soon put in possession of a galvanic apparatus of great power; and with this he was not long in obtaining the most striking results.

His first paper on the subject3 is sent from Bristol, in September, 1800; and describes experiments, in which he had found that the decompositions observed by Nicholson and Carlisle go on, although the water, or other substance in which the two wires are plunged, be separated into two portions, provided these portions are connected by muscular or other fibres. This use of muscular fibres was, probably, a remnant of the original disposition, or accident, by which galvanism had been connected with physiology, as much as with chemistry. Davy, however, soon went on towards the conclusion, that the phenomena were altogether chemical in their nature. He had already conjectured, in 1802, that all decompositions might be polar; that is, that in all cases of chemical decomposition, the elements might be related to each other as electrically positive and negative; a thought which it was the peculiar glory of his school to confirm and place in a distinct light. At this period such a view was far from obvious; and it was contended by many, on the contrary, that the elements which the voltaic apparatus brought to view, were not liberated from combinations, but generated. In 1806, Davy attempted the solution of this question; he showed that the ingredients which had been supposed to be produced by electricity, were due to impurities in the water, or to the decomposition of the vessels; and thus removed all preliminary difficulties. And then, as he says, 'referring to my experiments of 1800, 1801, and 1802, and to a number of new facts, which showed that inflammable substances and oxygen, alkalies and acids, and oxidable and noble

3 Nicholson's Journal, 4to. iv. 275.

5 Ib. 1826, p. 389.

5

4 Phil. Trans. 1826.

metals, were in electrical relations of positive and negative, I drew the conclusion, that the combinations and decompositions by electricity were referrible to the law of electrical attractions and repulsions,' and advanced the hypothesis, 'that chemical and electrical attractions were produced by the same cause, acting in the one case on particles, in the other on masses;... and that the same property, under different modifications, was the cause of all the phenomena exhibited by different voltaic combinations.'

Although this is the enunciation, in tolerably precise terms, of the great discovery of this epoch, it was, at the period of which we speak, conjectured rather than proved; and we shall find that neither Davy nor his followers, for a considerable period, apprehended it with that distinctness which makes a discovery complete. But in a very short time afterwards, Davy drew great additional notice to his researches by effecting, in pursuance, as it appeared, of his theoretical views, the decomposition of potassa into a metallic base and oxygen. This was, as he truly said, in the memorandum written in his journal at the instant, a capital experiment.' This discovery was soon followed by that of the decomposition of soda; and shortly after, of other bodies of the same kind; and the interest and activity of the whole chemical world were turned to the subject in an intense degree.

At this period, there might be noticed three great branches of speculation on this subject; the theory of the pile, the theory of electrical decomposition, and the theory of the identity of chemical and electrical forces; which last doctrine, however, was found to include the other two, as might have been anticipated from the time of its first suggestion.

It will not be necessary to say much on the theories of the voltaic pile, as separate from other parts of the subject. The contact-theory, which ascribed the action to the contact of different metals, was maintained by Volta himself; but gradually disappeared, as it was