Text: The original theory of Volta was incomplete in an essential point because he was not aquatinted with the fact of electrolytic decomposition. His original conception of the force of contact is, therefore, in contradiction to the law of conservation of energy; and even before this law was established enunciated with scientific precision, there were many chemists and physicists, among them Faraday, who had the right instinct that this could not be the true explanation. The opponents of Volta's opinions tried to give chemical explanations also of those experiments of his which were carried out exclusively with metallic conductors. They might be oxidized be the oxygen of the air, and the amount of oxidation required for a very slight electric charge was so infinitesimal that no chemical analysis could ever discover it- so small that even to the highest vacuum, and in the purest specimens of hydrogen or nitrogen with which we might surround the plates, there was oxygen enough to continue the effect for years. From this point of view the chemical theory cannot be refuted. On the other hand, the so-called chemical theory of Volta's Fundamental experiments was rather indefinite. It scarcely did more than tell us: here is the possibility of a chemical process, here electricity can be produced. But which kind, how much, to which potential, remained indefinite. I have not found in all the papers which have been written for the defense of the chemical theory a clear explanation of why zinc opposed to copper in liquids, where zinc really is oxidized and dissolved, become negative and why in air and other gases it becomes positive, if the same cause- namely, oxidation- is at work. The hypothesis, on the contrary, of a different degree of affinity between the metals and the two electricities gives a perfectly definite answer. I do not see why an actual chemical process should be wanted to charge the zinc and copper on contact. But you see that the forces, which according to their hypothesis produce the electric effect, are the same as those which must be considered the cause of a main part of all chemical reactions. Again, the electric charges produced by contact of zinc and copper are very feeble. They have become measurable only with the help of the latest improvements introduced into the construction of electrometers by Sir W. Thomson; but the cause of their feeble intensity is evident. If you bring into narrow contact two plain and well-polished plates of zinc and copper, the quantity of electricity collected at both sides of their common surface is probably very great; but you cannot observe it before having separated the plates. Now, it is impossible to separated them at the same instant over the whole extent of their surface. The charge which they retain will correspond with the inclined position which they have at the moment when the last point of contact broken; then all the other parts of the surfaces are already at a distance from one another infinitely greater than molecular distance, and conduction in metals always establishes nearly instantaneously the electric equilibrium corresponding to the actual situation. If you wish to avoid this discharge during the separation of the plates, one of them must be insulated; then indeed we get a far more striking series of phenomena, those belonging to electricity of friction. Friction, probably, is only the means of producing a very close contact between the two bodies. If the surfaces are very clean and free from air, as for instance in a Geissler tube, the slightest rolling contact is sufficient to develop the electric charge. I can show you two such tubes exhausted so far that very high electric tension is necessary to make the vacuum luminous, on containing a small quantity of mercury, the other the fluid compound of potassium and sodium. In the first the negative metal is intensively negative relatively to glass, in the second the metal is on the positive extremity of Volta's series; the glass proves to be more positive also in this case, but the difference is much smaller than with mercury, and the charge is feeble. Faraday very often recurs to this express his conviction that the forces termed chemical affinity and electricity are one and the same. I have endeavored to give you a survey of the facts connected with the question and to avoid as far as possible the introduction of hypotheses, except the atomic theory of modern chemistry. I think the facts leave no doubt that the very mightiest among the chemical forces are excluded, working directly from atom to atom. Several of our leading chemists have lately begun to distinguish two classes of compounds, viz.,molecular aggregates and typical compounds, the latter being united by atomic affinities, the former not. Electrolytes belong to the latter class. If we conclude form the facts that every unit of affinity is charged with one equivalent either positive or of negative electricity, they can form compounds, being electrically neutral only if every unit charged positively unites under the influence of a mighty electric attraction with another unit charged negatively. You see that this ought to produce compounds in which every unit of affinity of every atoms connected with one and only one other unit of another atom. This, as you will see immediately, is the modern chemical theory of quantivalence, comprising all the saturated compounds, The fact, that even elementary, with, few exceptions, have molecules composed of two atoms, makes it probable that even in these cases electric neutralization is produced by the combination of two atoms, each charged with its full electric equivalent, not by neutralization of every single unit of affinity. Unsaturated compounds with an even number of unconnected units of affinity offer no objection to such a hypothesis; they may be charged with equal equivalents of opposite electricity. Unsaturated compounds with one unconnected unit, existing only at high temperature, may be explained as dissociated by intense molecular motion of heat in spite of their electric attractions. But there remains on single instance of a compounds which, according to the law of Avogadro, must be considered unsaturated even at the lowest temperature, namely, nitric oxide (NO), a substance offering several very uncommon peculiarities, the behavior of which will be perhaps explained by future researches. But I abstain from entering into further particulars; perhaps I have already gone too far. I would not have dared to do it, had I not felt myself sheltered by the authority of that great man who was guided by a never erring instinct of truth. I thought that the best I could do for his memory was to recall to the minds of the men by whose energy and intelligence chemistry has undergone has undergone its modern astonishing development, what important treasures of knowledge lie still hidden in the works of that wonderful genius. I am not sufficiently acquainted with chemistry to be confident that I have given the right interpretation, the interpretation which Faraday himself would have given, if he had been acquainted with the law of chemical quantivalence. Without the knowledge of this law I do not see how a consistent and comprehensive electrochemical theory could be established. Faraday did not try to develop a complete theory of this kind. It is as characteristic of a man of high intellect to see where to avoid going further in his theoretical speculations for want of facts, as to see how to proceed when he finds the way open. We ought therefore to admire Faraday also in his cautious reticence, although now, standing on his shoulders, and assisted by the wonderful development of organic chemistry, we are able, perhaps, to see further than he did. I shall consider my work of today well rewarded if I have succeeded in kindling anew the interest of chemists in the electrochemical part of their science.

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