pn ce l  AI cl 
a a ee let 
- ApEnry— Studies in Chemical Analysis of Fresh & Salt Waters. 351 
The composition of the dissolved gases, however, before and 
after fermentation, show a marked difference, and indicate, when 
taken into consideration with the inorganic nitrogen compounds, 
the presence of very decided quantities of fresh organic matter in 
sample 1, and show also that the quality of sample 2, is much 
better than that of sample 1. 
The difference in composition of the dissolved gases also affords 
the means of estimating exactly the quantity and character of 
the polluting matters in each sample. No. 1, for instance, is 
shown to have undergone a very decided fermentation on keeping, 
- during which nearly the whole of the dissolved oxygen had 
been consumed; and the fermentative process is shown also to 
have consisted of both a carbon fermentation and a nitrogen 
fermentation. 
We may also conclude from the relative proportions of carbon 
and nitrogen fermented that the unfermented organic matters, 
originally present in the water, were of vegetable origin. 
The analysis of sample 2 shows that the fermentative process 
which went on in the sample, when kept, was almost entirely 
confined to a nitrogen fermentation, and that consequently but 
little, if any, unfermented organic matter was originally present in 
the sample. 
The carbon fermentation in this sample had, no doubt, taken 
place during the time of storage in the distributing tank. 
I ought, perhaps, to explain the particular meaning I attach 
to the terms ‘carbon fermentation’ and ‘nitrogen fermentation ’ 
before proceeding further. 
I have used these two terms to indicate the two progressive 
steps in which the bacterial fermentation under complete aérobic 
conditions of organic substance and of ammonia takes place. 
The organic substances are first completely broken down, and 
oxidized almost entirely into carbon dioxide, water, and ammonia. 
Traces of oxidized organic matters are also formed, and these 
undergo a more or less complete further oxidation into carbon 
dioxide and nitric acid during the subsequent fermentative process 
of the oxidation of the ammonia into nitric acid. Thus during 
the first step of the fermentative process, the oxidation of the 
unfermented organic carbon is the main factor of the process; 
while the oxidation of the ammoniacal nitrogen into nitric acid is 
the main factor of the second step of the fermentative process; 
SCIENT. PROC. R.D.S., VOL. IX., PART III. 2C 
