82 Mr. Colquhoun on the Life and Writings [Feb. 



the chemist would be deprived of an extremely easy and econo- 

 mical mode of preparing the purest oxygen gas ; and without it, 

 Gay-Lussac and Thenard had not been enabled accurately to 

 disclose the ultimate composition of vegetable and animal prin- 

 ciples. For although the use of chlorate of potash for this latter 

 purpose is now superseded by other still more correct and more 

 manageable instruments, yet it constituted the introduction to 

 this branch of chemical analysis, and indeed suggested the 

 employment of the methods more recently adopted. 



But the researches of our chemist with respect to the nature 

 of chlorine were attended by yet another result, which has 

 redounded, not less to his own honour, than to the prosperity of 

 France and England. It had been previously remarked by 

 Scheele, that among other extraordinary features, chlorine is 

 characterised by the property of destroying every vegetable 

 colour with which it comes in contact ; and this destruction he 

 found to be not merely apparent but complete. The vegetable 

 colour treated with chlorine cannot be restored by any known 

 chemical reagent: its basis has undergone decomposition. 

 When Berthollet, in the course of his researches, came to the 

 consideration of this property, his attention was peculiarly 

 excited by it ; and in the hope of its throwing some light upon 

 the true constitution of chlorine, he was anxious to examine 

 into its mode of operation. It will be remembered that he con- 

 ceived erroneously chlorine to be a compound of muriatic acid 

 and oxygen ; and he soon formed a theory conformable to this 

 idea. He held that, since the pouring of an aqueous solution 

 of chlorine upon a vegetable colouring matter, destroys the 

 colour, and leaves only muriatic acid behind ; it is an oxidation 

 of the colouring matter which produces this effect, and the con- 

 sequence is, that the substance oxidised loses its property of 

 reflecting certain rays of light. 



But it is not that Berthollet formed a theory on the subject, 

 which is now a matter of moment ; it is his immediately con- 

 ceiving that this property of chlorine might in its application be 

 made of the greatest practical utility ; and his persevering with 

 a zeal undamped by difficulties till he really rendered it so, that 

 throws an intense interest over this part of his history. Since 

 chlorine destroys vegetable colours completely, he reasonably 

 inferred that it would produce a similar effect upon those sub- 

 stances which injure and obscure the inherent beauty of thread 

 and cloth, and the separation of which is the object of bleaching. 

 He accordingly immersed a piece of unbleached cloth for some 

 time in a solution of chlorine in water, and was extremely grati- 

 fied to find it come out of a pure white colour. But his mortifi- 

 cation was proportionally great on perceiving that cloth so 

 bleached, after a certain time, gradually assumed a dingy yellow 

 colour ; — an alteration which he found greatly accelerated by 



