5i0 Adeney — Dissolved Gases and Fermentative Changes. 



This explanation rests chiefly on the results of bacteriological research, and 

 especially upon the fact that the germs of these micro-organisms are present, 

 practically, everywhere — in the air, in water, and in ordinary soil ; and that 

 they require but the necessary pabulum, such as refuse animal or vegetable 

 matters, in a neutral or slightly alkaline medium, for rapid growth and 

 multiplication. 



The importance, fi-om the chemists' point of view, of the recognition of the 

 true agencies at work in setting up processes of oxidation in natural and polluted 

 waters does not appear to have been sufficiently realized. 



It suggests at once the possibility of classifying the organic matters to be met 

 with in natural and polluted waters into two classes, viz. fermentable and non-fer- 

 mentable, and of differentiating the one from the other when present in the same 

 water.* 



We know that some of the organic matters found in natural waters either do 

 not ferment at all, or do so with difficulty, such as peaty colouring matters and 

 the organic matters found in good well and spring waters. Of a like character, 

 also, are those which are found in sewage-water after they have undergone 

 complete fermentation under aerobic conditions, such as obtain during slow 

 filtration through sand or soil. 



Amongst the fermentable matters may probably be included most, if not all, 

 known organic substances, with the exception of antiseptics. Dr. Munro has 

 shown, in his interesting and suggestive Paper on " The Formation and Destruc- 

 tion of Nitrates and Nitiites in Artificial Solutions and in River and Well 

 Waters,"! that not only are such simple bodies as acetates and oxalates attacked 

 by the organisms usually present in soil and water, but also such unlikely sub- 

 stances as ethylamine, cyanides, and thiocyanates, and he concludes that it would 

 be difficult to make out a list of known organic comjiounds which are not 

 fermentable under these conditions. 



One of the most obvious results of the fermentation of small quantities of an 

 organic substance in fully aerated water would, no doubt, be an absorption of the 

 dissolved atmospheric oxygen therein, and an evolution of carbon dioxide ; and 

 if the water were preserved during fermentation imder conditions, such that gases 

 could neither escape from, nor gain access to it, these results would also be the 

 most easily detected by chemical means. 



A few tentative exjieriments carried out on the lines here suggested showed 

 very distinctly that the above view was correct, and that even relatively minute 



* It is due to Dr. Dupre to make reference in connection with this point to a short Paper by him, 

 entitled — " On Changes in Aeration of "Water, as indicating the Nature of the Impurities present in it," 

 and published in the Ileport of the Medical Officer to the Local Government Board, 1884. 



t " Chem. Soc. Joum.," vol. 49, p. 677. See also p. 651. 



