Moritz Hermann Jacobi to Faraday   19 January 1847

St. Petersburg 7th / 19th Jan. 1847.

Dear Sir,

I have the honour to communicate to you, a very interesting phenomenon which I have observed in consequence of having made some months ago, experiences with the Voltameter. Since about 4 or 5 years I employ frequently and particularly for practical purposes the Voltameter of the form, described in your Researches art 710 fig 65¹, which form I found to be of great utility because of the easiness of its manipulation. I use different specimens of these Voltameters, with Platinum plates of different size or provided with Platinum wires, if only feeble currents are employed. For the moment I am not in the possession of a Voltameter of this latter espece. Now the fact which has escaped till now, not only myself, but many other Electricians which used the Voltameter in their researches, is the following. The mixed gazes resting for some time over the fluid in the state where they are developed, diminishes by degree in volume and disappears entirely in a greater or lesser space of time. A resorbition of the gazes by the fluid and under the action of the platinum plates takes place, and your Voltameter acts indeed as a very eudiometrical Voltameter. I have repeated very often this experience, with the same success, but other researches, wherein I am engaged, and particularly many business of a more practical nature, prevented me from varying the experiences, so much as it would be necessary. Some series of observations which I made, will be soon published in our Bulletin scientifique²; in the meanwhile I take the liberty to give you the series which presents the greatest intensity of resorbition

At this experience the current was produced by a magneto-electrical Machine, with platinum Electrodes of about 3/4 square inches. The electrolyte was water acidulated with sulphuric acid. In the other experiences partly made with the magneto-electrical Machine, partly with a Grove's nitric acid battery, the intensity of resorbition was much less. Although I have not yet determined all the conditions upon which depends this phenomenon and particularly its intensity, nevertheless I believe, that the intensity of the current, the cleanliness of the platinum electrodes & the degree of acidulation of the fluid, are thereby of much influence. In this latter respect I remark, that in using dilute sulphuric acid of 1,25 to 1,30 sp.gr. a very slow resorbition takes place. The most probable explanation of the disappearance of the mixed gazes may be, that a part of them, diffused throughout the whole liquid, is brought in contact with the platinum plates and after being recombined on their surface are replaced by another part and so forth.

In the above mentioned experience where twenty seven parts of gaz had been absorbed, I permitted the remaining gaz to escape, and I introduced in the Voltameter 39 parts of atmospheric air. Here a resorbition likewise took place, the progress of which is assigned in the following table.

After the disappearance of 14,5 parts, the absorbition ceased entirely. As 39 parts of atm. air contain only about 8 parts of oxygen, a part of the nitrogen must likewise have been absorbed. In another experience only 9 parts of 41 parts atm. air have been absorbed. This is nearly the exact measure of the oxygen contained in 41p. atmospheric air.

Strong muriatic acid having served as electrolyte, instead of dilute sulphuric acid, chlorine and hydrogen was developed in the Voltameter. The recombination of the gazes was very rapid, but only during the day; during the night the resorbition stopped entirely, but recommenced the following day. As in this case, the recombination must be attributed to the chemical action of light on a mixture of chlorine and hydrogen, the stopping of the action, seems to be a proof, that an absorbition and recombination of these gazes, by the action of platinum plates does not take place.

As it could be, that the fact which I took the liberty to communicate to you, might interest some other electricians, I beg of you, dear Sir, to present this note to the Royal Society³ or cause it to be published in the Philosophical Magazine (after having translated it in english!⁴[)]

If you should have any occasion of seeing Mr. Grove and Mr. Gassiot, you would be so kind, to present my best compliments to them. At the same time I beg of you, to remember me to the kind regards of Mrs. Faraday and to receive the respects of

Yours | M.H. Jacobi

P.S. It seems to me, that the above mentioned resorbition is entirely or almost stopped, when, after having developed the mixed gazes, the ends of the platinum electrodes are united by a short and thick wire. If this experience, which I only made yesterday, be right this may be as a consequence of the theory of the Grove's Gaz-battery⁵.

Endorsed by Faraday: Letter to Faraday