Christian Friedrich Schoenbein to Faraday   26 November 1836

Sir

The Philosophical Society of Bale in one of their last meetings¹ elected you their honorary member and I am charged by our President to forward the diploma and ask you the favor to accept of the latter as a weak expression of the high esteem, which our Society entertain for you, on account of the eminent services, you have rendered to natural Science.

I take at the same time the liberty of sending you the paper enclosed and to beg you to lay it before the Royal Society, in case you should think it worthy of being submitted to this distinguished body. If not, there is, perhaps, something or other in it, which deserves to be published in the Philosophical Magazine².

You have, no doubt, taken notice of the hypothesis published in the number of Septbr. of the Bibliothèque universelle, by which Mr. Mousson tries to account for the peculiar condition of iron and all the phenomena connected with this subject³. Though it may be ingenious in some respects it is overthrown by the single fact that by a current the inactive state of iron may be called forth in fluids which do not contain nitric acid and which consequently do not allow of the formation of nitrous acid, the protecting substance of Mr. Mousson. But there are many other reasons besides, which put the fallacy of the theory in question beyond doubt. I have circumstantially stated them in a paper, sent the other day to the Editors of the "Bibliotheque" for being published⁴. I cannot but take a second time the liberty to draw your attention upon the transference of the inactive state of iron from wire to wire, a fact which, to my opinion, is yet very far from being satisfactorily accounted for. Supposing the peculiar condition of iron being due to a film of oxide covering the metal, your hypothesis accounts, indeed, very well for an inactive wire's being thrown into action by another metal, which, itself active, touches the former. In this case, there is a current produced, by which hydrogen is set free at the inactive wire, which hydrogen reduces the film to the metallic state, renders consequently the wire active. Now if an inactive wire is associated with an ordinary one, and one end of the former immersed in common nitric acid previous to the one end of the latter, this wire will also become inactive. The galvanometer shows, that in the moment, where the end of the second wire is plunged into the nitric acid, a current is produced, passing, as in the first case, from the wire last immersed through the acid into the inactive one. Now in one case the current throws the inactive wire into action, and in the other it renders an ordinary wire inactive; that is to say, the same cause pro‑duces two effects exactly opposite to one another. It is obvious, that the current in the latter case should decompose water, evolve hydrogen at the inactive wire and render the latter active in the same way, as in the first case. Now I ask, why does hydrogen in one case decompose the film of oxide covering the inactive wire and not in the other? The two cases present no difference, except in the manner, in which the circuit is closed. It might, perhaps, be said, that in the second case, the current is so soon stopt, that it cannot separate hydrogen enough, as to reduce entirely the film to the metallic state. But this will not do, because the same current, which is supposed to be too weak, to set free that quantity of hydrogen necessary for the complete decomposition of the film of oxide round the inactive wire, is considered to be sufficiently strong to separate so much of oxigen, as is required for forming a protecting film round the ordinary wire. Now from the fact that the quantity of oxigen evolved at the positive electrode is exactly the chemical equivalent to the quantity of hydrogen set free at the negative electrode, we are obliged to draw the conclusion, that the quantity of hydrogen developed during the act of transfering the inactive state from the inactive wire to the ordinary one, is sufficient to decompose the film of the first wire. Insufficiency of the current can, therefore, not be the reason, why the inactive wire remains in its peculiar state under the circumstances mentioned.

I think the preceding observations are such, as to justify my former assertion, that we are still very far from knowing any thing about the way, in which the inactive state of iron is transfered from one wire to another. Before leaving this subject I cannot help recalling to you a circumstance, which bears strongly upon the point in question; it is the fact, that an iron wire performing the function of the positive electrode is rendered inactive in nitric acid, when by its being plunged into this fluid the circuit is closed; whilst the same wire is acted upon by the acid when the circuit is closed by the negative electrode. Now we remark the same difference of effect with a single voltaic pair consisting of ordinary iron and platina or any other negative metal, for when we close the circuit by its positive element ordinary iron, the peculiar condition will be called forth in this metal, when closed by the negative element, the same iron will be active, though, as already stated, there is in both cases a current produced, moving in the same direction. Now why do the different effects depend upon the manner of closing the circuit? This question once satisfactorily answered, we shall be much wiser, than we are now about the subject; but I suspect, it will be a difficult task to get up such an answer. It is not beyond possibility, that our phenomenon is independent of an electric current, though one is always accompanied by the other; and it is, perhaps this very circumstance that renders the tracing of its cause so very difficult. If it should be found to be im‑possible to explain the excitation of the peculiar state of iron and the destruction of it by the action of a current, then I am afraid, we shall be obliged to look out for another hypothesis, which may, perhaps, postulate a new agency different from Electricity for explaining the facts in question. But may heaven preserve us from more agencies, we have still enough of them.

Up to this present moment, I have not yet received the papers, which you were so kind to dispatch for me some time ago. Shall I, perhaps, apply to the british ambassador at Bern, to whom they have most likely been sent?

Before closing this letter, I take the liberty to ask you a favor. Our Establishment wants to get a good magnetic‑-electrical Machine, by means of which the principal experiments on Magneto- electricity may easily be made in classes. Now if it be not too much asked, the Committee of our Museum should feel themselves laid under great obligations to You, would you be so kind as to order such an apparatus to be sent to us by a Londoner instrument-maker⁵.

Excuse my long letter and accept kindly the assurance of my being

Yours | very truly | C.F. Schoenbein

Bale Nov. 26th 1836.

Address: Michael Faraday Esq. | Royal Institution | London.