THE HAMILTON ASSOCIATION. 59 



prominence to reduction by means of sulphurous acid, I am 

 forced to the conclusion that the last explanation is the correct one, 

 namely, that the water which is necessary to the bleaching process 

 unites with the sulphur dioxide to form sulphurous acid, and this 

 acting as a reducing agent deprives the coloring matter of its oxygen 

 and thus destroys its color. 



It may be well in closing the subject of bleaching by these two 

 agencies to contrast their action in this respect. In the first place 

 it was pointed out that in the case of chlorine the bleaching was the 

 result of the oxidation of the coloring matter, while in the second 

 case the same result is effected by reduction. It will thus be seen 

 that the one process is exactly the reverse of the other, although the 

 same end is attained in both cases. 



In dealing with the subject I have made no reference to the 

 cases in which the chlorine and sulphur dioxide unite with -the col- 

 oring matter and thus destroy it, although such is frequently the 

 case. 



Having shown how these two agents operate in the process of 

 bleaching, I shall refer very briefly to the action of the atmosphere 

 as a bleaching agent. Although the bleaching effect of the 

 atmosphere was known and taken advantage of long before either 

 chlorine or sulphur dioxide was discovered, yet there is much less 

 known as to how it brings about these results than in the case of 

 either of the other two. We have shown that in the bleaching by 

 chlorine the action of oxygen brought about the final result. If in 

 that case the oxygen actually does the bleaching^ why might not the 

 atmospheric oxygen do the same thing ? It must be remembered 

 that in chlorine bleaching the oxygen which effects the change is 

 that which is Hberated from the water by the chlorine. Now if we 

 remember that every element is liberated from its compounds in the 

 form of atoms, we shall perhaps see why oxygen, just as it is 

 liberated from water, acts differently from atmospheric oxygen. 

 The atoms of an element, if kept free to do so, will at once unite 

 with each other to produce molecules of the element in which form 

 the elements for the most part exist. These molecules must 

 necessarily be decomposed again before the element, can take part 

 in a chemical reaction such as is necessary to effect bleaching. We 

 thus see why it is that while nascent oxygen is capable of bleaching, 

 it may be quite impossible for oxygen, in its ordinary form, to do so. 



