1866. ] with the supply of water to Calcutta. 229 
I had intended, and still intend, to estimate the quantity of nitric 
acid for the complete analysis originally contemplated ; but for the 
reasons just stated, I preferred, for the purpose of this communication 
to direct my attention to other points which appeared of greater 
importance. That of ammonia which has been just discussed was 
one of these, and a greater number of determinations of ammonia 
would have been made, but time did not permit: besides I wished 
first carefully to examine the ammonia process in order to ascertain 
the causes of the discrepancies already referred to, with a view to 
discover the precautions necessary to be taken to ensure more 
concordant results. 
Other nitrogenous matter. 
But ammonia and nitric acid are only the ultimate terms of the 
fermentative and oxydised decomposition of nitrogenous organic matter, 
and there may be much more present in all stages of decomposition 
intermediate between these and unchanged animal or vegetable 
constituents. The amount of these could be estimated by ascertaining 
the quantity of nitrogen they contain, but the operation is too trouble- 
some to be generally applied to such minute quantities of matter 
as exists in drinking waters. Animal matters in being ignited or 
burnt, as is well known, omit a peculiar smell, different from that 
produced by burning non-nitrogenous substances such as wood, and 
this has been used as an indication of the presence of, and even as a 
means of forming a judgment respecting the proportion of matter 
of animal origin. But it affords a very uncertain means of judging, 
as even corrupting vegetable matter gives a different smell from fresh, 
and the peculiar animal odour may be more or less obscured by the 
greater or less proportion of vegetable matter mixed with the animal. 
Besides the most characteristic smell given by burning animal matters 
is that produced by albuminous or gelatinous substances such as 
muscular fibre, blood, skin, or in short the undecomposed tissues of 
animal bodies in general. But these substances are probably not to 
be found in sewage except in small quantity, its constituents are 
more nearly of the nature of urine and other excrementitious animal 
matters and the sour products of vegetable decomposition: many of 
them are volatile and evaporate by a moderate heat with a peculiar 
