79 
rte) 
AprneY—Dissolved Gases and Fermentative Changes. 
surface waters), or from those to be met with in waters in which a complete 
carbon oxidation of the organic matters from past pollution by sewage, or other 
surface drainage waters, has taken place (most, if not all, good river-waters). 
We have, in fact, from these experiments, and those I have already published, 
fairly complete information as to the possible fermentative changes which the 
nitrifiable substances to be met with in natural waters, whethe they be upland 
surface, well or spring, or river waters, may undergo. 
These changes may be briefly summarized as follows :— 
1. When the nitrifiable substances are freshly formed, and are present in 
comparatively large quantity in a water, the formation of a decided volume of 
carbon dioxide, in proportion to the volume of dissolved oxygen consumed, and 
the formation also of a quantity of nitrous or of nitric acid, or both, but in 
small quantities, may attend the earliest stuge of fermentative change they may 
undergo.* 
2. At subsequent stages the volume of carbon dioxide formed is not so large, 
and the inorganic nitrogen products, nitrous or nitric acid, become the more 
marked in quantity in proportion to the oxygen consumed.f 
3. Ata still later stage, at the completion of which all the ammonia becomes 
fermented, little or no carbon dioxide may be found, but, on the contrary, a little 
may become “ fixed”; the inorganic nitrogen products consists then of nitric 
acid solely.t 
4. When little or no ammonia is present, freshly formed nitrifiable organic 
matters may undergo at first a slow change, during the first steps of which dis- 
tinct volumes of carbon dioxide and of dissolved oxygen may be formed and 
consumed, respectively ; small quantities of nitric acid are formed at the same 
time. § 
5. But after these earlier steps of change the fermentation becomes slower, 
and finally becomes so slow as to be scarcely appreciable; still the results are 
the formation of carbon dioxide and nitric acid, and the consumption of a pro- 
portionately small volume of dissolved oxygen.|| 
* Loc. cit., Table V., exp. 1.; Table XIV., exp. 2; Table XV., exps. la and 18. 
¢ Loc. cit., Table V., exp. 3; Table VIII.; Table XIII., exp. 7; Table XV., exps. 3, 4, 5, 2a and 3a; 
also Table XVIII. (above) exps. 4 and 4a. 
t Loc. cit., Table V., exp. 4; Table VII., exp. 6; Table X., exp. 3; Table XV., exp. 20; also Table 
on p. 588 ; also Table XVIII. (above), exps. 5 and 5a. 
§ Loc. cit., Table XIV., exp. 5. 
|| Zoe. ctt., p. 561; Table IX., exp. 4; Table XIII., exps. 5 and 6; Table XIV., exp. 6; also Table 
XVIII. (above), exps. 1 and la, and 3 and 3a. 
