MUXICIPAL WATER SUPPLIES. I07 



ilar to the natural process, is rapidly produced by boiling the 

 sample with a strongly alkaline solution of potassium per- 

 manganate, the product being ammonia. This ammonia is 

 then distilled off and its amount determined by Nessler's test. 

 Albuminoid ammonia is a measure of the undecomposed 

 nitrogenous matter of the water. 



The free ammonia in the water is determined by simple 

 distillation of the sample and subsequent determination by 

 Nessler's reagent. From what has been said it will be seen 

 that free ammonia indicates the presence in the water of 

 nitrogenous organic matter in the active process of decompo- 

 sition. 



Nitrogen as nitrites is indicated by the depth of the pink 

 color produced when the water is treated with sulphanilic 

 acid and naphthylamine hydrochloride. Nitrites indicate the 

 first step toward oxidation and show that the water is begin- 

 ning to purify itself. 



Nitrogen as nitrates is determined b}' the depth of the 

 3'ellow color produced when a sample of the water is evapo- 

 rated to dryness with a little sodium carbonate and then 

 treated with phenol-sulphonic acid and ammonium hydroxide. 

 Nitrates indicate that the nitrogenous organic matter in the 

 water is now fully oxidized and inert. 



Chlorine as chlorides in the water is tested for in the usual 

 way with silver nitrate, using potassium chromate as an indi- 

 cator. By reason of the large amount of sodium chloride in 

 sewage this determination is very important as indicative of 

 this kind of pollution. As, however, all soils, and, therefore, 

 all waters contain this salt, allowance must be made for the 

 normal chloride content of the water of the given district. 



Required oxygen, or oxygen consuming capacity, is deter- 

 mined by measuring the amount of potassium permanganate 

 required to oxidize the organic matter in the sample. From 

 this determination is found the amount of oxygen required to 

 oxidize all the animal and vegetable impurity in the water. 

 It differs from the determination of the free and albuminoid 



