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III. On the joint Influence exerted by Light and the Oxidability 

 of certain substances upon common Oxygen. By C. F. Schosn- 



BEIN*. 



My dear Faraday, 



SINCE I wrote to you last, I have been engaged in making 

 researches on the different ways of exalting the chemical 

 affinities of oxygen at the common temperature, and trust that 

 the labour bestowed upon the subject will have been not entirely 

 lost. 



You know that I was inclined to consider phosphorus as the 

 type of all the substances that are capable of undergoing oxida- 

 tion in atmospheric air or oxygen at the common temperature, 

 f. e. that I thought common oxygen unfit to unite chemically to 

 any body ; or to speak still more distinctly, I was disposed to 

 conjecture that the slow oxidation of any substance is always 

 preceded by a change of condition, or, if you like, an allotropic 

 modification of the oxygen causing that oxidation. To be able 

 to test the correctness of that conjecture, I wanted a substance 

 which was not affected by common oxygen, but readily oxidized by 

 ozonized or excited oxygen, and at the same time such as to 

 allow perceiving easily and surely its oxidation. Such a matter 

 I think is indigo dissolved in sulphuric acid, i. e. common indigo 

 solution, whose colour cannot be discharged by common oxygen, 

 but very easily by means of oxygen in the ozonic condition. 



Now I reasoned thus : if any mJitter (undergoing oxidation in 

 atmospheric air at the common temperature) should have the 

 power of effecting, previously to its oxidation, an allotropic mo- 

 dification of the common oxygen, indigo solution being mixed 

 with that matter and bi'ought in contact with atmospheric air 

 ought to be oxidized conjointly with the oxidable substance, just 

 in the same way as the colour of indigo solution placed in con- 

 tact with phosphorus and atmospheric air, is discharged whilst 

 phosphorus is undergoing oxidation. 



My anticipations have, I think, been confirmed by the results 

 of numerous experiments ; for I have ascertained that a series of 

 organic and inorganic matters, capable of oxidation at the common 

 temperature, have indeed the power of discharging the colour of 

 indigo solution, and exhibit in this respect a befiaviour exactly 

 like that of phosphorus. But, before I proceed further, I must 

 not omit to mention tliat that power is vei-y small in the dark, 

 and, comparatively speaking, strong in direct solar light. 



The organic matters as yet tested are-^spirit of wine, spirit of 

 wood, linseed oil, tartaric acid, nitric acid, formic acid, acetic 



* Communicated by Prof. Faraday. 



