280 ApENEY—Dissolved Gases and Fermentative Changes. 
This brief summary of the fermentative changes which nitrifiable organic 
substances may undergo in the presence and absence of ammonia shows how 
definitely and easily this class of inorganic substances may be differentiated from 
unfermented or “‘ carbon oxidizable” substances when both classes occur together 
in a water; and it emphasizes the point I put forward in Part III. of my first 
communication, viz. that the analysis of suspicious and polluted waters should 
always include an examination of the fermentative changes which may occur in 
the composition of the dissolved gases and of the inorganic nitrogen compounds 
contained in such waters—an examination which is easily made, when the waters 
are preserved in the manner and under the conditions I have described. 
If, for example, a water be regarded as suspicious for potable purposes, on 
account either of its containing too much organic matter, or an abnormally large 
amount of ammonia, an examination of it by the methods I have employed in 
these studies will yield exact information, whether, in the first case, any portion 
of the organic matters are in an unfermented condition or not, and, in the second, 
whether the ammonia will suffer rapid nitrification or not. 
Information as to both these points are essential before a definite opinion can 
be expressed as to the suitability or otherwise of the water for potable purposes. 
Since a positive result in either case would definitely condemn the water for such 
use, for, in the first case, very recent pollution would be indicated, while in 
the second case an abnormal bacterial activity would be revealed, which, in the 
light of recent bacteriological teachings as to the true functions of a filter, ought 
to be regarded as indicating insufficient filtration. As an example of this latter 
case, I may quote the examination of a water which recently came under my 
notice. An ordinary analysis showed that the water contained ammonia in some- 
what excessive quantity, viz. ‘016 parts (nitrogen as ammonia) per 100,000 of the 
water. It also yielded 009 nitrogen as albuminoid ammonia per 100,000. The 
water was classed as suspicious, and I examined it for fermentative changes with 
the following results :— 
CO2 O2 Ne NasNH; NasN203 WN as N2O5 
Before keeping, . 5 - 1138°69 4:03 15°69 “00016 0 “0025. 
After keeping for 7 days, . 1138°59 3°76 15°76 0 0 0025. 
Fermentative changes, a — 0°33 — —°00016 — — 
The constituents are expressed as in the previous Tables, viz. gases as ¢.c. 
at N. T. P., and nitrogen compounds as parts by weight, per 1000 c.es. of 
water. It should be noted the water was slightly turbid, but contained no 
suspended matter. The results show the ammonia was completely taken up, and 
that a corresponding volume of oxygen was consumed during the seven days the 
water was kept, but that no carbon dioxide was formed. This comparatively 
rapid nitrification of the ammonia must have been due to a decided bacterial 
