1866.] with the supply of water to Calcutta. 220 



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 



