THE HAMILTON ASSOCIATION. 57 



The function of chlorine is rather to bring the oxygen into the 

 proper condition in which to effect the bleaching. If then the 

 oxygen is the substance which dees the bleaching, how then is it 

 that exposure to the atmosphere does not bleach more rapidly than 

 it does ? I shall refer to this point again in connection with bleach- 

 ing by exposure to the atmosphere. 



Having discussed somewhat fully the process of bleaching by 

 chlorine, I shall deal more briefly with bleaching by the agency of 

 sulphur dioxide. 



The dioxide, as I have already pointed out, is usually obtained 

 by the burning of -sulphur when it is required for the purpose of 

 bleaching, and, as in the case of chlorine, the material which is to 

 be bleached requires to be moistened with water, for if it is not so 

 moistened the material may be left in the dry gas an indefinite 

 period without any perceptible effect on its color, but when it is 

 moistened the color begins to disappear in a very short time. 



The function of the water in this instance is not so easily 

 discovered as in the case of chlorine. A hint as to the kind of 

 chemical action which results in the destruction of the color by the 

 sulphur dioxide, may be obtained if we dip a bright colored rose or 

 other flower in a vessel of the gas for a short time until its color 

 begins to disappear, then if the flower be removed from the sulphur 

 dioxide and exposed to the atmosphere its color will return again. 

 The only element present in the atmosphere so chemically active as 

 to produce such a result is oxygen, and therefore the return of the 

 color to the flower is the result of oxidation. There is then a strong 

 probability that the loss of color in the sulphur dioxide is the result 

 of a deoxidation or reduction. The question then arises^ what is 

 the material produced by the interaction of sulphur dioxide and 

 water upon each other, and does the substance so formed act as a 

 reducing agent ? It is easily shown that the product of the action 

 of sulphur dioxide on water is sulphurous acid. By the addition of 

 some permanganate of potash solution to a solution of the above 

 acid, it is readily oxidized into sulphuric acid. The same fact may 

 be stated as a reduction of the permanganate of potash of the 

 solution. It follows then that while neither water nor sulphur 

 dioxide are reducing agents yet the substance formed by their union 

 has a strong affinity for oxygen. This fact serves, in my opinion, to 

 explain the bleaching action of sulphur dioxide. Before proceeding 



