Christian Friedrich Schoenbein to Faraday   25 November 1844

Bâle November 25th 1844.

My dear Faraday

I think it is full time to acknowledge the last two letters you have been kind enough to address to me¹.

The official invitation to prepare a report about my researches on ozon for the british association I received the other day and certainly I shall not fail complying with the wishes expressed to me. If possible I shall read that report myself at Cambridge² and perform the necessary experiments. You know perhaps that I attended the meeting of the italian association at Milan to make there a communication on my recent investigations³; unfortunately however the chemical section was not such as I could have wished it to be only a few chymists being there who really deserved that denomination. Amongst them was Piria⁴ who suggested the idea that all the effects I ascribe to a peculiar principle, "to my ozon" might be due to nitrous acid⁵. Though the smell of the two substances be as different as possible and other properties of ozon stated in my last memoir be not those of nitrous acid the italian Chymist stuck rather tenaciously to his opinion. Immediately after my return from Milan I took up the subject again and made a series of experiments with the view of getting the most decisive matter of fact evidence for proving the peculiarity of my principle and I think I have perfectly succeeded in putting even beyond the shade of a doubt that Ozon and nitrous acid have nothing to do with one another.

My principal proofs are as follows⁶:

1. Two stripes of platinum after having been plunged equally long one into atmospheric air mixt up with vapour of nitrous acid the other into air containing ozon produce a current the direction of which is such as to indicate the ozonized stripe to be the negative part of the circuit. Ozon is therefore a body more electro-negative than nitrous acid.

2. A stripe of platinum having been negatively polarized by Ozon looses its voltaic condition and becomes neutral when plunged for a short time into an atmosphere containing nitrous acid.

3. Air being ever so much charged with Ozon looses its peculiar smell, its electro-motive power, its property of destroying vegetable colours &c when mixt up with the proper quantity of the vapour of nitrous acid. The smell of the latter acid also disappears under the circumstances mentioned.

4. An ozonized atmosphere may be shaken for a great length of time with peroxide of lead being suspended in some water without loosing its characteristic properties, whilst air charged with vapours of nitrous acid and treated in the same manner becomes inodorous and looses its properties which are due to nitrous acid.

5. A solution of sulfate of protoxide of iron turns brownish when shaken with an atmosphere containing only traces of nitrous acid whilst the same solution being treated with air which happens to be ever so much charged with Ozon remains as to its colour unchanged and yields a whitish precipitate.

6. Blue and humid litmus paper placed within a strongly ozonized atmosphere is completely bleached within about 10-15 minutes without assuming the slightest reddish tint, whilst paper of the same description <being> suspended in vapours of nitrous acid first turns red and requires hours or even days to become entirely bleached. And in that case the paper is very strongly acid i.e. impregnated with nitric acid, whilst the paper bleached by Ozon is always quite free from any trace of acid.

7. Phosphorus being (in darkness) introduced into atmospheric air which is only slightly charged with vapours of nitrous acid, ceases to give out any light and becomes and continues to be completely dark whilst phosphorus put into strongly ozonized air happens to shine even more lively than it does in common air.

The facts above mentioned clearly show that Ozon is no acid principle and not to be confounded with nitrous acid.

I must not omit to mention that the voltaic bearings of Chlorine and Bromine to nitrous acid are strikingly similar to those in which Ozon and the last-named acid are standing to each other. A stripe of platinum ever so powerfully polarized either by Chlorine or Bromine looses its negative polarity when plunged into an atmosphere containing vapours of nitrous acid.

The electro-motive power enjoyed by a chlorine or Bromine atmosphere is also destroyed if mixt up with a proper quantity of the vapour of nitrous acid. Such a close analogy as does exist between Chlorine, Bromine and Ozone appears to me to be an important fact and to speak in favour of the view I have taken of the nature of Ozon. Indeed the more I compare experimentally the properties of Chlorine and Bromine with those of Ozon the more I get struck with the similarity of the three prin<ciples.> But whatever Ozon may be, it is at any rate a very interesting substance and just the thing made to excite the curiousity both of Chymists and natural philosophers. As to me, I shall do what I can to clear up the subject. You may easily imagine that I feel very anxious to hear soon about the results of your present philosophical doings and I am quite sure that they will be highly interesting to science, for, allow me to tell you so, you cannot take any subject into your hands without getting something excellent out of it, be it sooner or later.

Mrs. Schoenbein and the Children are quite well and all of them charge me with their best salutations both to you and your lady. Pray remember me also very kindly to Mrs. Faraday and believe me

Yours | most truly | C.F. Schoenbein

I ardently wish and earnestly hope that your brother⁷ will by this time have entirely recovered from his serious accident.

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