Christian Friedrich Schoenbein to Faraday   20 October 1838

Bale Oct. 20, 1838.

My dear Sir

I take the liberty to make you acquainted with some results which I have lately obtained from my researches and which I think are such, as to merit some attention on the part of philosophers.

Plausible and ingenious as the views of Mr. Becquerel on the cause of the currents of Ritter's secondary piles and of the electro-motive power acquired by polar wires are¹, some facts led me the other day to doubt of the correctness of the theory of the celebrated french philosopher and induced me to investigate once more the circumstances, under which, what they call secondary currents are excited. I found that platina-wires acting as electrodes within aqueous solutions of chemically pure acids or alcalies acquire the property of exciting secondary currents just as well as they do within solutions of salts. As in those circumstances the decomposition and recom‑position of a salt is quite out of the question, I think we must infer from such a fact, that the hypothesis of Mr. B. is erroneous. But is it not possible, that some portions of the constituent parts of the body electrolysed stick to the polar wires and produce by their reunion the secondary current. By the result of the following experiment, we are, to my opinion entitled to answer that question in the negative. Platina-wires plunging into chemically pure muriatic acid and being connected with the poles of a pile the current of which was so feeble as not to he capable of decomposing even jodide of potassium, I say wires, thus circumstanced, acquired in a few seconds an electro-motive power, which produced a deviation of the needle of my delicate galvanometer of 160°. As under these circumstances, neither muriatic acid nor water could have been electro‑lysed, the secondary current obtained is consequently not due to the reunion of Chlorine and Hydrogen, or Oxigen and Hydrogen.

But there is another fact, to which I take the liberty of drawing your attention, a fact which on account of its novelty and peculiarity cannot fail exciting a good deal of scientific curiosity.

When the branches of a tube bent in the shape of a U are filled with chemically pure muriatic acid and by the means of two platina-wires connected with the poles of a pile, whose current is not able of causing the electrolysation of the fluid mentioned, the two columns of acid (contained in the branches), after the current having for a few seconds passed through them appear to be voltaically polarised. For if the electrodes are removed from the branches and replaced by another pair of platina-wires a delicate galvanometer (of about 2000 coils) on being placed between the latter, indicates a current passing from the acid column, which had been connected with the negative polar wire to that column, which had been in commu‑nication with the positive wire; that is to say, one column of acid is to the other, like zinc to platina.

Having drawn up a paper, in which all my observations regarding the voltaic polarisation of fluid and solid bodies are stated and which, I hope will soon be published by the Bibliothèque Universelle² as well as by Poggendorff's Annalen³, I do not enter now into any more details on that subject but I cannot help communicating to you my views on the cause of the strange phenomenon in question.

You have shown, that weak currents can pass through electrolytes, without decomposing them⁴; but are we to infer from such a fact, that a current incapable of electrolysing acts in no way whatever upon the electrolytic body? Is it not probable, that the current in question has so much power as to turn all the hydrogen-sides of the molecules of muriatic acid towards the negative electrode and the Chlorine sides towards the positive one, and is it not allowed to suppose, that the current weakens at the same time the affinity of the constituent parts of the electrolyte for each other? Now if we admit such a state of things and if it be further supposed that the effect does not immediately cease with its cause, we can, I think, rather easily conceive the way in which the secondary current is produced by the polarized muriatic acid. The particles of Chlorine and Hydrogen composing a molecule of acid will, as soon as the current of the pile ceases circulating through the fluid, begin to act upon each other, i.e. enter again into their primitive state of intimate combination. Now such an action being of a chemical nature, a current must be produced by it, as to its direction precisely of the kind as observed. Though I must allow, that my hypothesis is rather bold, yet I cannot conceive another and I am inclined to think, that neither the chemical theory of Galvanism nor that of Volta can easily account for the enigmatical phenomenon. Will you be so kind and let me have your views about the strange fact? Before passing to another subject I must not omit to tell you, that it is not only muriatic acid, which is capable of being voltaically polarized, other electrolytic fluids, for instance the hydrate of sulphuric acid have the same property.

The controversy about the source of current electricity produced by the common voltaic arrangement is still continued in Germany and there is in that country an obvious leaning towards the views of Volta. The arguments, however, brough<<t>> forward in favor of that Theory are, to my opinion at least, by no means such as to be called decisive ones. Mr. Pfaff⁵, for instance, thinks the fact, that a current is excited by muriatic acid acting upon chloride of sodium or by a pile charged with an aqueous solution of sulphate of zinc chemically pure, as quite irreconcilable with the prin‑ciples of the chemical theory⁶. I must confess, that it is beyond my power to conceive, how objections of such a kind can be raised in earnest by such a distinguished philosopher, as Mr. Pfaff is. Will you not come forward and take part in the contest. We must, indeed, stick closely together, if we are not to be over‑powered, and considered as beaten by our antagonists. At the meeting of the german association at Fribourg I had an oppor‑tunity of reconnoitering the field.

I am my very dear Sir | Your's most truly | C.F. Schoenbein

Address: Doctor Faraday | &c &c &c | Royal Institution | London