36 
POPULAR SCIENCE REVIEW. 
adopted in determining the constituents of organic origin con- 
tained in water, and the two Commissions are not at one as to 
the inferences to he drawn from analyses, even when correctly 
obtained. 
The older analyses of water refer only to “ organic matter,” 
without reference to its character ; but this really gives us little 
information of value. One water containing organic matter 
may be comparatively harmless ; whilst another, containing a 
far smaller quantity, may be highly dangerous. It depends 
altogether upon the source and nature of the organic matter. 
This is a very complicated question and cannot be briefly dis- 
cussed with advantage ; but we will note the chief points relied 
upon by chemists, especially Dr. Frankland. It is necessary to 
know the precise amount of nitrogen and of carbon (other than 
that existing as carbonic acid or carbonates) ; the relative pro- 
portion of organic carbon and organic nitrogen gives a clue to 
the character of the organic matter — whether of vegetable or 
animal origin ; the smaller the absolute amount of nitrogen, 
and the higher the proportion of carbon to nitrogen, the less 
the danger of animal matter. 
But here a difficulty occurs ; during the oxidation of vege- 
table organic matter the proportion of carbon to nitrogen lessens , 
whilst during the oxidation of animal organic matter the pro- 
portion of carbon to nitrogen increases . We are thus often 
thrown back on a knowledge of the source of the water to 
enable us rightly to interpret the chemical analyses. But, apart 
from this knowledge, if the absolute amount of organic nitrogen 
be high, we may reasonably regard the water with suspicion. 
Nitrogenous organic matter or “albuminoid ammonia” 
undergoes putrefaction, and is converted into “ free ammonia.” 
The presence of much free ammonia in the water of shallow 
wells denotes very recent contamination with animal matter. 
A large proportion of nitrates or nitrites shows that the pollution 
is more remote, the ammonia having become oxidized into 
nitrates. But in the case of deep wells the presence of a little 
ammonia need not denote recent pollution, it may have been 
formed by the deoxidation of nitrates. But of this at least we 
may be certain — if the amount of nitrates, nitrites, or ammonia 
be large, the animal pollution of the water, recent or remote, 
must have been considerable. 
Water from deep wells in the chalk often contains variable 
proportions (though rarely large) of ammonia and nitrates. 
One curious result of the careful tabulation of the analyses in 
the Biver Pollution Beport is this : — The wells sunk through 
London clay into the chalk yield water of less hardness and with 
more ammonia than those sunk into the chalk when that rock 
forms the surface of the ground ; nitrates are frequently absent. 
