Christian Friedrich Schoenbein to Faraday   18 January 1845

My dear Faraday,

As you have taken some interest in my researches on Ozone, I flatter myself that the results of my recent investigations which bear upon a similar subject, will engage your attention. After having ascertained that by the slow combustion of phosphorous in atmospheric air a peculiar principle happens to be engendered being in many respects similar to Chlorine I was led to examine those bodies which are capable of exhibiting the same sort of combustion and it is common ether in particular upon which I have lately been making a series of experiments. The results I have already obtained from them are such as will, to my opinion, merit the attention of Chymists. On account of the small space allowed to a letter I cannot state them but in very summary manner. You will however soon have an opportunity to acquaint yourself with the details of the subject.

If a platinum wire being moderately heated at one of its ends be introduced into a mixture of the vapor of common ether and atmospheric air a slow combustion as it is well known takes place and besides aldehydes, aldehydic, formic, and acetic acids, &c. a principle is produced which has hitherto escaped the notice of Chymists and enjoys to a high degree oxidizing and bleaching properties as you will see from the following statements:

1. The principle in question destroys Indigo like Chlorine and Ozone.

2. It decomposes jodide of potassium and hydroiodic acid eliminating at the same time Jodine; it turns therefore blue the paste of starch being mixt up with the jodide like Chlorine and Ozone.

3. It (slowly) decomposes also bromide of potassium like Chlorine and Ozone.

4. Being in contact with water it changes Jodine into Jodic acid like Chl. and Ozone.

5. Being in contact with water it transforms sulphurous acid into sulphuric acid like Chl. and Ozone.

6. It changes the yellow ferro-cyanide of potassium into the red one like Chl. and Ozone.

7. It turns blue the white cyanide of iron, like Chlorine and Ozone.

8. It transforms the salts of protoxide of iron into the salts of the peroxide, like Chl. and Oz.

9. It makes very rapidly disappear the coloration produced by sulphuret of lead, like Chlorine and Ozone. A number of other sulphurets are also destroyed by it.

10. It is readily taken up by water.

11. Water charged with our principle enjoys all the properties before-mentioned.

12. Those properties are destroyed by treating that water with readily oxidable substances such as the solution of [word illegible], sulphurous acid, zinc, iron &c. Even mercury acts in the same way upon the liquid and is taken up by the latter.

13. An aqueous solution of sulphuretted hydrogen being mixt up with a sufficient quantity of water charged with our principle does no more than draw sulphuret of lead from the solutions of that metal.

I have ascertained many other properties but those stated will suffice to give you an idea of the substance produced during the slow combustion of the vapor of ether in atmospheric air. Before passing to other subjects I must not omit to state that the liquid obtained from the action of nascent oxigen upon ether or alkohol does not exhibit the reactions above mentioned. From hence follows and from other observations too that our principle has nothing to do with aldehyd and the other products which the slow combustion of ether and alkohol gives rise to. I am not yet prepared to say how far nitrogen is necessary to obtain the peculiar principle in question, as far as my experiments go it seems as if that body (Nitrogen) acts an important part in the process. I am also not quite sure whether the fragrant smell which is making its appearance during the slow combustion of ether has something to do with the principle in question; some facts seem to speak in favor of their being dependant of each other, others are against such a conclusion[.] After having gone so far and being led by some theoretical views I subjected the rapid combustion of a number of matters to a close examination and did so with the view of ascertaining whether a similar bleaching principle be engendered by the process. The facts which I am going to state will show how far this is the case.

When a jet of hydrogen gas is set on fire in atmospheric air and the following fluids are held (in small glass tubes) above the point of the flame we observe that

1.) a weak indigo solution is bleached.

2.) a solution of jodide of potassium or hydrojodic acid is decomposed or the paste of starch containing the red jodide turned blue.

3.) a solution of the yellow ferro-cyanide is changed into the red one.

4.) The white cyanide of iron being suspended in water is suddenly turned blue.

5.) A solution of sulphurous acid is transformed into sulphuric acid.

6.) The solution of sulphate of protoxide of iron is turned into the salt of the peroxide.

7. The sulphuret of lead being suspended in water or attached to a moistened piece of paper loses its black colour and turns white.

The same results are obtained with the flame of a common candle provided however a current of air be sent through the flame quite in the same way as we do it in making experiments with the blowpipe. But the reactions are not produced in each part of the flame, we obtain them only with the exterior or what they call the oxidising flame. I have been experimenting upon many other flames and invariably found that under certain conditions the bleaching principle in question is engendered in all of them. The flame of phosphorous for instance is in this case, as to that of sulphur, it is obvious, that the bleaching matter cannot be disengaged by it on account of its action upon sulphurous acid, it is however a remarkable fact that water over which that flame had been made playing invariably contains small portions of sulphuric acid the production of which is most likely due to the oxidising principle in question.

From the facts above stated it seems as if our oxidising and bleaching matter is produced in all cases of rapid combustion taking place in atmospheric air and that its generation is independent of the nature of the burned substance; for which matter can be more different from each other than hydrogen is from phosphorous?

The question is now what that principle is and from where it comes? The circumstances under which it happens to be formed lead us to to suspect that the atmospheric air is the source of that principle. Should it be nitric or nitrous acid? Dilute nitric acid does act neither upon jodide nor upon the yellow ferro-cyanide of potassium nor upon the white cyanide of iron, our principle must therefore be different from that acid. Besides nitric acid cannot be formed at a temperature at which it is decomposed. As to nitrous acid all my endeavours to ascertain the presence of that compound failed and I could not find out a trace of it.

In comparing the chemical properties of my ozone with those of the bleaching principle produced during the slow combustion of ether in atmospheric air as well as during the rapid one of many other substances, we easily perceive a striking similarity between them. The most essential reactions effected by these principles are without any exception the same. From that similarity of properties we might be led to believe that there is either identity or at least some close connexion between the substances enjoying the similarity of properties. Admitting the identity of these principles and starting from the hypothesis I have ventured to suggest regarding the nature of nitrogen, we can rather easily account for the production of our bleaching principle. Heat, in many cases acting like common electricity we might suppose that the former agency determines the oxigen of the air to unite with the hydrogen which I think to be contained in Nitrogen. Under these circumstances Ozone, the other constituent part of Azote, would be eliminated in the same way as I suppose that principle to be set at liberty by the action excited by common electricity upon atmospheric air. It is at any rate a most remarkable fact that the chemical effects produced for instance by the point of the hydrogen flame are exactly the same as the chemical effects brought about by the electrical brush and such being the case I at least cannot help thinking that in one respect the same chemical process takes place in both instances. But be that as it may, the facts I have tried to give you the substance of are, to my opinion, far from being unfavorable to the view I have taken of the nature of ozone.

Just now I am about to ascertain whether the bleaching principle can also be obtained by burning a variety of substances in pure oxigen a point which is very important to know. Before I conclude I take the liberty to draw your attention upon some facts which appear to be worthy of notice. Whilst Ozone (like Chlorine) enjoys to a high degree the property of polarizing negatively platinum, I have not yet succeeded in obtaining that effect by the bleaching principle produced during the slow combustion of ether in atmospheric air. This neutral state seems to indicate that the said principle is either loosely united to or mixt up with a matter enjoying opposite voltaic, i.e. electropositive properties and it is perhaps from such a compound that results the pungent smell perceived during the combustion of ether. What that matter is I cannot yet say but it may be that the fact I am going to state has something to do with the subject alluded to.

When an aqueous solution of Jodide of potassium is repeatedly treated with the atmosphere obtained by slowly burning ether in common air, it becomes reddish brown and, if the solution being in that state be heated in a retort only traces of free Jodine are given off but at the same time a crystalline matter distills over, that enjoys all the properties of your Joduret of etherine (I + C<4>H<4>)[.] As perhaps the pungent matter being produced by the slow combustion of ether our bleaching principle united to the olefiant gas and is it the latter that does counteract or mask the negative voltaic properties of the former? Ulterior experiments will answer these questions. If you think the contents of my letter such as to be worthy of being communicated to the Royal Society you have full liberty to do so. I have a mind to read myself at Cambridge¹ the report I am charged to draw up on the Ozone affair² and to make there the more important experiments regarding that delicate subject³. Pray present my humble regards to Mrs. Faraday and believe me

Yours | most truly | C.F. Schoenbein

Bâle, | Jan. 18, 1845.

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