1866.] with the supply of water to Calcutta. 931 
be satisfactory, and that was to determine the amount of nitrogen 
existing in other forms than those of ammonia and nitric acid, this 
being the only way in which the amount of undecomposed or 
imperfectly decomposed animal matter can be estimated. The way in 
which this is usually done is by what is well known to chemists as the 
soda lime process, and depends on the circumstance that all such 
animal substances containing nitrogen (this not including nitric acid 
however), when heated to redness in contact with a hydrated alkali, 
yield up all their nitrogen combined with hydrogen as ammonia, and 
this ammonia can by suitable arrangement be collected and its amount 
ascertained. Iam not aware that this plan has been much applied 
to the examination of animal matter in waters, no doubt on account of 
the minute quantity of nitrogen present ; nevertheless it appeared to me 
that it might be modified so as to estimate it even in drinking water. 
I intended to have postponed the trial of this process altogether, as I 
had not time to make proper arrangements and test the accuracy of the 
plan. However I made three experiments in a rather hasty and 
crude manner with such means as [ had at hand. They are not at all 
to be depended on, but I may give the results as obtained. 
River water of 2nd June, Ebb, from Chandernagore, containing very 
little tidal water. 100,000 grains gave .028 grains ammonia. 
River water of 91st August, Ebb, from Barnagore. 100,000 grains 
gave .030 grains ammonia. 
River water of May and June, Flood tide, from Barnagore. 100,000 
grains gave .010 grains ammonia. 
The results, as I have already said, are not to be depended on. Yet 
it cannot be denied that they are in accordance with the results 
obtained in other ways, respecting the organic matter. The ready 
formed ammonia existing in the water had of course been previously 
removed, 
In a practical point of view this portion of the subject is of the 
principal importance, as more than any other it bears on the question 
as to how far the river water is contaminated by the sewage of 
Calcutta. Judging from the results obtained and just mentioned 
respecting ammonia and fixed nitrogenous organic matter, the amount 
is not great: even at the highest tide at flood on the 14th June of 
this year, after twelve months of an unusually small amount of rain- 
29 
