570 Adeney — Dissolved Gases and Fermentative Changes. 



Multiplying each set of differences as before, we get : — 



Table IV. 



We see from the above Table that in solution 1/10 the dissolved oxygen was 

 not in sufficient quantity for the first stage of fermentation; hence putrefactive- 

 fermentation had occurred. 



But in the two following solutions it was ; and in each the volume of carbon 

 dioxide formed and the volume of oxygen absorbed were directly propox'tional to 

 the quantity of fei-mentable matter originally present therein. 



We further note that the time allowed for fermentation, 1/20 and 1/40, was 

 only sufficient for the carbon fermentation, and that in neither had nitrogen 

 fermentation commenced. We may therefore note this result, as in this experi- 

 mentfully aerobic conditions were maintained throughout, and yet no nitrification 

 occurred ; we may consider it as strong evidence in favour of the view that the 

 fermentative changes really occur in two distinct stages — a view which other 

 observers have maintained, and which I have assumed as true in the earlier part 

 of the Paper. 



It is important to note that the oxidation of ammonia to nitric acid is 

 accompanied in solution 1/40 and inferentially in 1/80, by the formation of 

 relatively small quantities of carbon dioxide. 



The gas so formed was probably derived, as I shall show by later experiments, 

 from the small quantities of oxidized organic substance which, as we shall find 

 later, may under certain conditions be formed from the sewage-matters during 

 the first stage of fermentation. The collected results for solution 1/40, and those 

 for 1/80, show that when both stages are complete the quantities of carbon dioxide 

 and nitric acid formed, and the volume of oxygen absorbed, were practically 

 directly proportional to the quantity of fermentable matter originally present. 



Putting the results in a quantitative form as before, we may say that 1000 

 volumes of sewage-water required 306 to 347 volumes of atmospheric oxygen for 

 the complete fermentation, 125 to 132 volumes being required for the first stage, 

 and 181 to 215 for the second stage. 



The filtered sample of sewage from the Richmond Works, when similarly 

 examined, gave the following results: — 



