Adeney — Dissolved Gases and Fermentative Changes. 585 



When the first stage of fermentation is carried on under conditions such as 

 obtained in the experiments with solution A, viz. the presence of a considerable 

 excess of fermentable organic matters, relatively to the oxygen present, during 

 the earlier steps of the fermentation, we find that the organic carbon present in 

 the solution may be almost completely oxidized to carbon dioxide during the said 

 first stage fermentation, and that little or none of this gas is formed during the 

 after-fermentation of the ammonia in the same solution. 



When, on the other hand, the conditions at the commencement are reversed, 

 viz. the oxygen is large relatively to the fermentable matters present, we see 

 from the experiments with the dilutions of solution A, and from those with the 

 filtered sewage-water used in Series III., that the oxidation of the organic carbon 

 to carbon dioxide during the first stage may be far from complete before the 

 commencement of the second stage of fermentation, but that the organic matters 

 undergo, partially at least, an intermediate stage of oxidation, and that the 

 oxidized matters which result suffer further change during nitrification, and give 

 rise to the formation of decided volumes of carbon dioxide. 



2. We also learn that, under the same conditions, not clearly defined by the 

 experiments in question (solution 1/4, Series III., and exp. 6, Series IV.), 

 carbon dioxide and ammonia, and possibly also nitrous acid, may become fixed, 

 even in the presence of organic matters (fermented) presumably to form organic 

 matter. 



At the same time we are warranted in believing, from the results hitherto 

 considered, that when a number of dilutions of a water under examination are 

 experimented with, as was done with the samples of sewage-waters above 

 examined, a series of results are obtained which reveal at once an exceptional 

 course of fermentation, such as that shown by solution 1/4 in Series III., and 

 from which definite and valuable conclusions may be drawn as to the character of 

 the organic matters present. 



The experiments I have next to quote were made with a view more particularly 

 of gaining further evidence in addition to that already given, as to the re- 

 lationship between the quantity of inorganic nitrogen formed by the fermen- 

 tation of sewage- waters under continued aerobic conditions, and that of the total 

 organic nitrogen originally present. These experiments were made with three 

 samples of partially purified sewage, from the same sewage-works. Each sample 

 was filtered to separate matters in suspension, and diluted with tap-water in the 

 proportion of 1 to 49, respectively. The dilutions were marked for reference, 

 Si, Sj, and S3. 



The total organic and ammoniacal nitrogen in each dilution was determined 

 at the time of bottling, by Kjeldahl's method, and the ammoniacal nitrogen by 

 direct nesslerization. 



