On the Influence exerted by Light upon common Oxygen. 23 



acid, wine and beer; the inorganic ones are — sulphuretted, 

 arseniuretted, antimoniuretted hydrogen, sulphurous acid. 



The most distinguished of the first series is tartaric acid, of 

 the second series, sulphurous acid. 



I put into a spacious bottle (charged with atmospheric air) 

 100 grammes of water, 10 grammes of tartaric acid, and one 

 gramme of my standard indigo solution, continually shaking the 

 whole exposed to strong sunlight, and within forty minutes the 

 colour of the liquid appeared to be discharged. In this way I 

 have already destroyed 50 grammes of indigo solution by the 10 

 grammes of the acid, without having as yet exhausted its dis- 

 charging power. 



A strip of linen cloth rather strongly dyed by indigo solution, 

 drenched with a solution of tartaric acid, continually kept moist 

 by water and exposed to the joint action of a strong sun and 

 atmospheric air, was completely bleached within five hours. In 

 the dark, under the same circumstances, the bleaching of the 

 dyed cloth, or the discharge of the colour of the indigoferous 

 tartaric acid solution, takes place very slowly. I have kept these 

 last four weeks a bit of moist blue linen impregnated with a solu* 

 tion of tartaric acid in a dark room, and now it appears certainly 

 to be a shade lighter than it was in the beginning ; but it is still 

 very blue. 



To test the discharging power of the other otganic matters 

 named, I put 10 grammes of the one or the other of them into 

 a spacious white bottle filled with air, add to it 100 grammes of 

 water, and 1 gramme of the standard indigo solution, expose 

 the mixture to the action of light, and shake the whole as often 

 as I can, taking care to renew now and then the air of the bottle. 

 Experimenting in this way, the discharging power of the sub- 

 stances mentioned and that of others is easily ascertained. 



As to the hydrogenated compounds of sulphur, selenium, 

 arsenic and antimony, I mix them with atmospheric air, putting 

 some water on the bottom of the vessel holding the mixture, 

 suspend within it a moist strip of linen dyed with dilute indigo 

 solution, and expose the whole to the action of solar light. The 

 bleaching of the cloth does not take place very rapidly in those 

 gaseous mixtures ; for instance, in that of sulphuretted hydrogen 

 the strip had to remain for a week before its colour was entirely 

 discharged. In the mixture of arseniuretted or antimoniuretted 

 hydrogen and atmospheric air, the cloth becomes brown in con- 

 sequence of metallic arsenic or antimony being deposited upon 

 the strip. 



By far the most interesting oxidable inorganic substance, as 

 to its indirect bleaching power, is sulphurous acid. This acid, 

 as well as the other oxidable matters mentioned, when deprived 



