58 JOURNAL AND PROCEEDINGS. 



with what seems to me the best explanation of this process, I shall 

 state another view held Dy some good authorities, and which has 

 the endorsation of such eminent chemists as Professors Roscoe and 

 Schorlemmer, who, in their excellent treatise on chemistry give, on 

 page 310, vol. I, this statement of the explanation referred to "The 

 decolorizing action of sulphur dioxide depends upon its oxidation 

 in presence of water with formation of sulphuric acid, the hydrogen 

 which is liberated uniting with the coloring matter to form a color- 

 less body thus :— S0.2 + 2H20 = H2SO4+ Ha." 



As I have already stated this view is that held by some 

 chemists well qualified to speak on the subject, and 1 only quote 

 from the above mentioned authors, as their treatise contains a 

 concise statement of the explanation referred to. 



I may be permitted to poinf out that in the absence of 

 experimental evidence, it is difficult to believe that two substances 

 as stable as water and sulphur dioxide are, can effect the liberation 

 of hydrogen when they act upon each other ; and further if the 

 reaction takes place, which is represented by the above equation, 

 what becomes of the hydrogen which is liberated if there is no 

 coloring matter present? An experiment similar to that of the 

 chlorine water in the sunlight ought to give us free hydrogen, but so 

 far as I am aware such a result has never been obtained. This, I 

 believe, is a serious, if not fatal, objection to the explanation 

 given above. 



I have, to some extent, already indicated what seems to me the 

 correct explanation of the bleaching action of sulphur dioxide. It 

 has been stated that water unites with sulphur dioxide to form 

 sulphurous acid, and this acid was shown to act as a reducing agent, 

 in that it readily deprives such a substance as permanganate of 

 potash of its oxygen and becomes sulphuric acid. It is also well 

 known that it is difficult to preserve sulphurous acid when exposed 

 to the action of the atmosphere, as it is eventually oxidized into 

 sulphuric acid when it is so exposed. This serves to still further 

 demonstrate the fact that sulphurous acid is oxidizable into 

 sulphuric acid and thus will act as a reducing ageut. 



It is conceded by all authorities that bleaching by means of 

 sulphur dioxide is a reducing process, and as the explanation I have 

 ventured seems to be fully in accord with the results of the reactions 

 between the materials present, and at the same time gives due 



