928 Mr. Waldie’s investigations connected [No. 3, 
I have seen few published analyses of water indicating the presence 
or amount of ammonia. Such examinations have been made, but 
they do not seem to be common. In the case of waters examined 
for sanitary purposes it appears to me that the point should be 
attended to. One observation that has come under my notice on 
the subject is in a paper by Messrs. Lawes and Gilbert on town 
sewage,* in which is mentioned the quantity of ammonia found in. 
the River Wandle before and after receiving the drainage water 
from the land irrigated by the sewage of Croydon. In both 
instances, it amounted to .18 grain per gallon or 70,000 grains, being 
therefore more than I have found at the worst in the Hooghly water 
viz. .185 grains per 100,000 grains. 
Nitrates. 
The presence of nitrates has been more noticed than that of 
ammonia, though it appears to me less worthy of attention. It is 
true that they indicate the existence of nitrogenous matter, but it is 
rather as a thing of the past: the animal matter has been there, but 
is no longer now, at least that part of it which now has the form of 
nitric acid ; it is now fully oxydized, its animal essence and corruptibi- 
lity destroyed: it ranks with water and carbonic acid, no longer an 
organic substance. A process has been devised for estimating small 
quantities, known as Pugh’s process, which Dr. Miller in the above 
quoted paper recommends for application to water. I have not made 
use of it, indeed have not had time, but have satisfied myself with 
some other observations and experiments on the presence of nitrates 
in the river water. In many instances indeed very distinct deflagration 
has been observed during ignition of the residue obtained by evapora- 
ting the water. This alone does not give good grounds for forming 
an opinion as to the quantity of the nitrate, as it may be masked or 
altogether obscured by an excessive proportion of other salts, as of 
common salt during the hot season. The presence of nitrites can 
also be observed by the blue colour produced with starch and iodide 
of potassium by the water acidulated. But as nitrites are simply 
imperfectly oxydised nitrates, the same observations apply to the 
former as have been made respecting the latter. 
* Journal of the Chemical Society, April,-1866. 
