Christian Friedrich Schoenbein to Faraday   5 November 1837

Bâle 5 Novemb. 1837.

My dear Sir

I am exceedingly obliged to you for your very kind letter of last month¹. It made me deeply regret not to have been present at the late meeting of the british association, but as I told you before my absence from Liverpool was rather a forced than a voluntary one². If possible I shall cross the channel next year to remain in dear Old England as long as circumstances will allow it; for I will not conceal it from you, that I am strongly attached to your native country, so much so that I should consider one of the most ardent wishes I am entertaining as fulfilled, if I could for ever live in that happy and interesting Island. Your language, history, literature and science have been favorite objects of my study and Leisure‑ occupation these last fifteen years and up to this present moment every thing regarding Great Britain has a peculiar interest with me.

I do not know, whether I mentioned it to you in one of my former letters, that about a dozen of years ago, when I was in London a gentleman from there introduced me into the Royal Institution at the same day you delivered a lecture on the then new discovery of Arago's respecting the action of rotating metallic plates on suspended magnets &c³. I still recollect the great pleasure with which I witnessed your experiments on that subject, but being then rather a shy and bashful young man I did not venture to enter into a conversation with you in spite of my inclination to do so and though I had, after the lecture was over, a favorable opportunity to speak to you. I mention these trifling occurrences to show you that my acquaintance with you has already been of rather a long standing. You can easily imagine, how sorry I must be for having lost the favorable opportunity of seeing you at Bâle during your stay there; it is only the hope of meeting you soon on your side of the water, that mitigates a little my vexation. Mr. de la Rive on his return from England⁴ to Geneva passed through Bâle about a fortnight ago and paying me a visit, I learned from him some particulars regarding the state of your health, after which I was very anxious to enquire, having been told by yourself, you were rather suffering. I wish from all my heart and as ardently as any of your friends can do, the speedy and complete reestablishment of your health. Mr. de la Rive seemed to be quite satisfied with the meeting at Liverpool.

The short notice contained in the last number of the Biblioth. univers. respecting Dr. Andrews'⁵ researches on the action of nitric acid upon Bismuth⁶, has induced me to make some experiments on the same subject and I now take the liberty to give you a short account of the results obtained from them. It certainly cannot be denied, that there exists some analogy between the peculiar condition of Iron and that of Bismuth but my impression at present is, that there is only a similarity and not an identity of cases. This opinion is founded upon the following facts. The chemical action of Iron upon nitric acid can, as it is now well known, be entirely stopped by a variety of ways, whilst according to my experiments it is impossible to obtain such a result with Bismuth. I voltaically associated this metal with all the substances known to be capable of rendering Iron completely inactive but by so doing I could never succeed so far as to prevent Bismuth from being chemically acted upon by nitric acid. It is true, by putting in contact the metallic body in question with Platinum the chemical action of nitric acid spec. gr. 1.4 may be reduced to such a low degree of intensity, that no visible disengagement of binoxide of nitrogen takes place and the piece of Bismuth (immersed in nitric acid) assumes a bright appearance. But the oxidable metal being in this state is nevertheless uninterruptedly attacked by the acid fluid, as it can be easily shown by having recourse to the galvanometer. There are besides some other facts, which put the continuance of chemical action in the circumstances mentioned beyond any doubts[.] I think I have first ascertained the remarkable fact, that Iron can be rendered thoroughly inactive not only towards the oxigen of nitric acid (of any degree of dilution) but also to the oxigen disengaged (by the action of a voltaic current) out of aqueous solutions of any oxidized body or any oxyelectrolyte. You know, that such a state of Iron is called forth by making this metal act the part of the positive electrode of a pile and closing the circuit in a certain manner. Now if Bismuth be placed in these very same circumstances, it does not seem to undergo any change whatever, for it is violently acted upon by nitric acid (of spec. gr. 1.4) and unites with the oxigen resulting from the electro-chemical decomposition of water or any other oxyelectrolyte. It is particularly the last mentioned difference of bearing between the two metals, which makes me suspect, that the peculiar condition of Iron is not produced by the same cause which occasions the inactivity of Bismuth, that is to say that the latter effect is not brought about by a current passing in a certain direction through Bismuth. There is another fact which seems to speak in favor of this opinion. According to my experiments peroxide of Lead proves to be the most powerful of all substances, which are capable of turning common Iron into its peculiar state. Peroxide of lead in whatever manner I tried to combine it with Bismuth did not appear to have any action upon the metal, for this substance was dissolved by nitric acid just in the same way, as it was, when put into the said fluid without any voltaic association. Now it is to be asked in what manner does Platinum weaken the chemical action of nitric acid upon Bismuth? Are we to believe that in the case in question the former acts in a quite peculiar way, that it puts into play an agency of a nature as yet unknown and entirely different from current electricity? I am certainly not much inclined to draw any such inference from the fact alluded to but at the same time I must confess, that for the present at least, I am not able at all of accounting for the anomaly spoken of. Before passing from the subject of the peculiar condition of Bismuth to another one, allow me to mention to you some more phenomena, which bear upon the same matter and which have, perhaps, not yet been observed by Mr. Andrews. After (by the agency of Platinum) the violent action of nitric acid (spec. gr. 1.4) upon Bismuth has been changed into a slow one and both metals brought out of contact, Bismuth loses its metallic lustre and assumes a blackish appearance; after a short time, however, the metal turns bright again by itself and remains so, until it is touched a second time by platinum. As long as the contact between both metals is maintained, certainly there is no change of the surface of Bismuth to be observed, but no sooner have they ceased to touch each other, than the Bis‑muth begins to blacken again, it reassumes however after some lapse of time its former lustre. This change of surface can be effected as often, as you like. I have ascertained, that Bis‑muth covered with the said blackish coating is more energeti‑cally acted upon by nitric acid, than it is, when its surface appears to be bright. Now as Platinum by means of its contact with Bismuth causes a very considerable diminution of the energy of chemical action of the acid upon the latter metal and makes always and instantaneously disappear the black film from it, the reproduction of this coating under the circumstances before-mentioned is a fact very strange, indeed, and altogether anomalous. Another fact also worthy of being stated is that the black film can be produced either by moving the bright Bismuth about within the acid or by causing the acid to be moved about the metal. I do not yet know what the black substance consists of, but whatever it may be its production in the last-mentioned way is no doubt due to the removal of some stratum surrounding the bright metal and protecting the Bismuth against the violent action of nitric acid. This supposed stratum consists perhaps of a solution of nitrate of Bismuth mixt with some nitrous acid.

If Bismuth being in its peculiar state or covered with the blackish film be s[l]ightly touched with a platinum wire within nitric acid of spec. gr. 1.4 a gazeous substance will be disengaged at the wire all the while contact is maintained between the metals. Having not yet made the experiment on a scale large enough as to allow the collection of the gas, I do not know its nature. I have stated however the fact to you, because the development of a gazeous body under the circumstances alluded to must appear very odd, if we consider, that no gas whatsoever is disengaged at the negative electrode when nitric acid of some strength for instance one of spec. gr. 1.4, will be subject to the action of the current of a pile. Now in the case spoken of the platinum wire does certainly act the part of the negative electrode. As every circumstance connected with the peculiar condition of readily oxidable metals appears to me to be of some importance I will not omit to mention the fact, that inactive Iron cannot be brought into contact with inactive Bis‑muth, without being thrown into chemical action. Iron, however, voltaically associated with Platinum is proof to the exciting influence of the passive Bismuth and capable of destroying the often mentioned black substance just in the same manner, as Platinum. Some few words more on the peculiar state of Bis‑muth and I have done with this subject of which I am afraid I have already entertained you too long. By immersing that metal for a few seconds into nitrous acid it is turned inactive so, that it can he put into nitric acid of spec. gr. 1.4 without being sensibly attacked by the latter.

The Biblioth. univers. also alludes to a paper read at Liver‑pool by Mr. Hartley⁷ on the preservation of Iron against the action of Seawater⁸. The fact stated by that gentleman is on account of its anomaly highly interesting and seems to enter into that class of electro-chemical phenomena, which have been the subject of my researches these last two years. If you recollect a statement of mine made in a paper "on a peculiar action of Iron"⁹ &c. you will be aware that the result obtained from Mr. Hartley's experiments does not quite agree with what I have found and to be a general fact. The statement alluded to runs as follows: In solutions, containing, besides oxyelectrolytes, others of a different nature, for instance hydracids, haloid salts &c, no evolution of oxigen takes place (at the Iron being the positive electrode of the pile) in whatever manner the circuit may be closed¹⁰. Now if in Mr. Hartley's voltaic arrangement Brass is to Iron (in an electrical point of view) what Platinum is to the latter or any other readily oxidable metal according to my experiments we should suppose that Iron, being voltaic‑ally associated with Brass, would be chemically, acted upon by Seawater, that is to say be oxidized and chloridized. You may easily ascertain the correctness of my statement by plunging an Iron wire which is connected with the positive pole of a pile into an aqueous solution of chloride of sodium closing thereby the circuit. You will observe that Iron is not turned inactive, but corroded and effects are produced quite consonant to the well known electro-chemical laws. I made a couple of days ago some experiments with sea water itself and I found that Iron was attacked when a current passed from the metal into the fluid. As you can easily imagine the disagreement of Mr. Hartley's observations with mine makes me exceedingly desirous of getting as soon as possible acquainted with the particulars of that gentleman's researches. I hope the next number of the Philosophical Magazine will satisfy my curiosity on this point¹¹.

Last Summer during a short stay at Stuttgart I made in the laboratory of Professor Degen¹² there and in company with this able Chemist some experiments upon Cobalt and Nickel to ascertain, whether these metallic bodies are capable of being rendered inactive. Having but a very small quantity of those metals at our disposal, we were obliged to limit the number of our experiments to very few ones and to execute them on a very small scale. The results obtained from them were, how‑ever, such as to convince us, that the peculiar condition cannot be excited either in Cobalt or in Nickel, at least not in the same way as it is done in Iron. This fact seems to indicate, that the peculiar voltaic state of the latter metal has nothing to do with its magnetic properties¹³.

The french papers have been talking for some time about a discovery (said to have been made by a certain Mr. Sorel¹⁴ a Frenchman) which if it should turn out to be something more than a mere news-papers' invention, would be indeed a most wonderful thing. By dint of god knows what sort of substance, the news- papers call it voltaic powder, Mr. Sorel is said to be able of changing Iron and any other readily oxidable metal such, as to give them (with regard to their chemical bearings to oxigen) the properties of the precious ones. Such a discovery, of course, cannot be made in our days without being turned to practical advantage and so, indeed, the papers tell us, that Mr. Sorel is going to enter into partnership with the well known Mr. Cockerill¹⁵ in order to make use of his discovery in the large establishments of the latter gentleman. By the manner in which some German papers took notice of the results of my late researches on the peculiar condition of Iron, I too have already gained the reputation of being a little bit of an Alchymist. Nay offers of money even have been made to me, in order to get the secret of changing Iron into Platinum or some such thing out of me.

You will oblige me very much by forwarding in a way most convenient to you the inclosed parcel to its place of destination.

Believe me ever to be | Yours very truly | C.F. Schoenbein

Dr. Faraday | &c &c &c

Address: Dr. Faraday | &c &c &c | Royal Institution | London