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theory of chlorine-bleaching, by endeavouring to explain why the 

 remoral of water from that gas arrests its bleaching action. In the 

 preliminary discussion, he refers at some length to Davy's theory, 

 that moist chlorine does not bleach directly, but only in a secondary 

 way, by combining with the hydrogen of the associated water, and 

 liberating the oxygen, which is the true bleacher. After pointing 

 out the untenable assumptions and self-destructive arguments on 

 which this theory is built, the author proceeds in the second section, 

 which discusses the influence of sunlight on the bleaching action 

 of dry chlorine, to shew, that Davy's proposition that dry chlorine 

 does not bleach dry organic colours is true, provided direct sunlight 

 be excluded, but does not apply to the gas when exposed to the 

 actinic influence of the sunbeam. In a cumparative trial, one speci- 

 men of dry litmus paper was found to resist the decolorizing action 

 of dry chlorine for more than eight months when kept in dai-kness ; 

 whilst the colour of another portion of the same paper totally disap- 

 peared after six weeks' exposure to sunshine. Another comparative 

 experiment was not so successful as regarded rapidity of actinic 

 bleaching ; but both sets of trials led the author to infer, that 

 darkness as well as dryne>s is essential to the negative action of 

 chlorine on colours. 



The third section is occupied with the record of experiments, 

 instituted with a view to determine whether the presence of water is 

 as essential to the bleaching action of oxygen, sulphurous acid, and 

 sulphuretted hydrogen, as it is to that of chlorine. The general re- 

 sult of the trials made was, that the gases mentioned may be retained, 

 when dry, for months over dry litmus, without decolorizing it ; and 

 that they are, therefore, at least as much dependent as chlorine on 

 water for their power of bleaching. 



The fourth section investigates, in like manner, the extent to 

 which the acid gases and ammonia have their power to change or- 

 ganic colouring matters, influenced by the absence of water from the 

 gas and the colour. The author finds that the modifying action of 

 carbonic, sulphurous, and hydrosulphuric acids on colours, is totally 

 arrested by the abstraction of water ; and that that of hydrochloric 

 acid and ammonia is long delayed. He infers, from the results 

 detailed in sections third and fourth, that there is nothing exceptional 

 or anomalous in the non-bleaching action of dry chlorine, and that 

 it is only a particular case of a general law, applying to all gases 



