228 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 Grilbert 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 tlie Chemical Society, April, 1866. 



