476 DR GEORGE WILSON ON THE ACTION OF THE DRY GASES 



taining chlorine. The chlorine in some cases replaces hydrogen ; in others, it 

 combines directly with the colouring matter ; in others, again, water is decom- 

 posed, and the product, besides containing chlorine, is also more highly oxi- 

 dised."* 



Beautiful, however, and satisfactory as the investigations of Kane, Erdman, 

 Dumas, Laurent, and others are, they leave unconsidered the question, why has 

 chlorine, which so rapidly and permanently destroys the colour of organic com- 

 pounds when moist, no action on them when dry ? 



The object of the researches I am about to detail, is to supply, in part at least, 

 this defect in the theory of bleaching, by endeavouring to shew how the removal 

 of water from chlorine arrests or suspends its decolorising power. Before enter- 

 ing at length into this question, however, I would observe, that Davy's conclu- 

 sion, that oxygen is the efficacious bleaching constituent of moist chlorine, cannot 

 be regarded as marked by the felicity which generally characterised that gi-eat 

 chemist's interpretations of obscure or complicated phenomena. 



1. His view assumed, against all probability, that the acknowledged great 

 affinity of chlorine for hydrogen would be exerted solely towards the hydrogen 

 of water, but not towards that present in a colouring matter ; or at all events, 

 that the affinity in question Avould be efficacious only in relation to the elements 

 of water. We certainly must set aside, as entirely arbitrary, the notion, if that 

 were implied in Davy's statement, that chlorine in the presence of two bodies — 

 water and a colouring matter — each containing hydrogen, would be indifferent to 

 that element, as a constituent of the one, but eager to unite with it as present in 

 the other. Although free chlorine, however, must be regarded as equally ready 

 to unite with the hydrogen of every compound which comes within the sphere of 

 its affinity, it does not follow that it will obtain that element with equal ease 

 from every substance containing it. On the other hand, we may be certain, that 

 those more unstable compounds which part most readily with their elements, 

 will be the first to have the hydrogen removed from them by chlorine, whilst 

 less easily decomposed substances may resist its action altogether. Davy's view, 

 however, gains nothing from this acknowledgment ; for it represents water, an 

 enduring compound of but single equivalents of two elements, as compelled to 

 abandon its hydrogen to chlorine, whilst the proverbially fading colom-ing prin- 

 ciple of a flower or an insect — a frail combination of many equivalents of three 

 or more elements — is assumed to be able to retain its hydrogen unaffected by 

 chlorine. In the justice of such a conclusion, no chemist could concur. 



2. Again, Davy's argument proved too much, and was in truth, self-destruc- 

 tive ; for if chlorine be denied the character of a positive bleaching agent, be- 

 cause it does not bleach when dry, then oxygen, judged by the same rule, must 



* Elements of Chemistry, p. 1054. 



