Page:Dictionary of National Biography volume 18.djvu/202

Faraday Electric 'Conduction' was read before Royal Society on 23 May 1833. On 20 June he communicated a paper on electro-chemical decomposition, in which be combated the notion of an attractive force exerted by the poles immersed in the decomposing cell. He wishes obviously to get rid of the idea of a current, substituting for it that of 'an axis of power, having contrary forces exactly equal in amount in opposite directions.' This definition could have yielded him but little help; it however left him free from the trammels of a definite symbol. He now glances at a subject of collateral interest. The power of spongy platinum to provoke the combination of oxygen and hydrogen was discovered by Dobereiner in 1823, and applied in the construction of his philosophic lamp. Dulong and Thénard proved afterwards that a well-cleansed platinum wire could be raised to incandescence by its action on a jet of cold hydrogen. Faraday found this power of provoking combination to be possessed in a striking degree by the positive platinum plate of his decomposing cell. The purification of the platinum by the oxygen discharged against it was the cause of its activity.

'In our conceptions and reasonings regarding the forces of nature we perpetually make use of symbols which, when they possess a high representative value, we dignify with the name of theories. Thus, prompted by certain analogies, we ascribe electrical phenomena to the action of a peculiar fluid, sometimes flowing, sometimes at rest. Such conceptions have their advantages and their disadvantages; they afford peaceful lodging to the intellect for a time, but they also circumscribe it, and by-and-by, when the mind has grown too large for its lodging, it often finds difficulty in breaking down the walls of what has become its prison instead of its home,' These words are quoted because they so chime in with Faraday's views, that when he heard them he could not repress a warm expression of assent. In regard to what may be called the philosophy of the voltaic pile, he was anxious to abolish all terms which tended to pledge him to theory. Aided by Dr. Whewell, he sought to invent a neutral terminology. For the word 'poles,' previously applied to the plates plunged in a decomposition cell, he substituted the word 'electrodes.' The decomposing liquid he called an 'electrolyte.' and the act of decomposition 'electrolysis.' These terms are now of everyday use in science. The term 'anode 'for the positive electrode and 'cathode 'for the negative one, are less frequently used, while the terms 'anion' and 'cation,' names given to the respective constituents of the decomposed electrolyte, and the term 'ion,' including both anions and cations, are hardly used at all. Having thus cleared his way, he fixed, as a measure of voltaic electricity, on the quantity of water decomposed by the voltaic current. The correctness of this measure was first established. He sent the same current through a series of cells with electrodes of different sizes—some of them plates of platinum, others strips, others mere wires — and found the quantity of gas collected to be the same for all the cells. The electro-chemical action was therefore independent of the site of the electrodes. It was also independent of the intensity of the current. Whether the battery was charged with strong acid or weak, whether it consisted of five pairs or of fifty, in short, whatever its force might be, the same current, sent through the series of cells, decomposed the same amount of water in all. Hence the conclusion that electro-chemical decomposition depends solely upon the quantity of electricity which passes through the decomposing cell. On this law Faraday based the construction of his celebrated 'voltameter.' And now he swoops down upon one of his most considerable discoveries. In the same circuit he introduced his voltameter and a cell containing chloride of tin, and measured the decomposition in both cases. The water and the chloride were found to be broken up in proportions expressed by their respective chemical equivalents. The electric force which severed the constituents of the water molecule proved competent, and neither more nor less than competent, to sever the constituents of the molecule of the chloride of tin. The fact was typical. With the electrolysis of water, as measured by his voltameter, he compared the electrolysis of other substances, both singly and in series, and proved beyond doubt that the decompositions of the voltaic battery are as definite in their character as those chemical combinations which gave birth to the atomic theory.

In 1800 Volta discovered the pile and sent an account of his discovery to Sir Joseph Banks, who lodged it, as a pearl of great price, in the 'Philosophical Transactions.' The source of power in the pile, the force which generated the current and urged it forward, was long a subject of fierce contention. Volta himself supported it to be excited by the contact of different metals. He established beyond all doubt that electricity is developed by such contact, and he assumed that at the place of contact an electro-motive force came into play which severed the two electricities, pouring the positive over one