5. _Ammonia, free and albuminoid._--It has already been mentioned that the decomposition of the nitrogenous organic impurities present in polluted water results in the production, first, of ammonia, then of nitrites and nitrates, and, as it is commonly asserted that the deleterious character of water is mainly due to the putrefactive processes taking place, which are probably directly proportionate to the quantity of ammonia produced, it is evident that the determination of this compound is of considerable importance. The proportion of albuminous and allied constituents in a sample can, moreover, be measured by the quantity of ammonia produced when the water is boiled with an alkaline solution of potassium permanganate. Upon the foregoing facts, Messrs. Wanklyn, Chapman, and Smith[124] have based a method for the determination of the sanitary quality of potable waters, which is in very general use. It involves, first, an estimation of the ammonia generated upon distilling the water with sodium carbonate (“free” ammonia); second, the quantity given off by boiling with alkaline potassium permanganate (“albuminoid” ammonia). In case the water tested is contaminated with urea, which is not improbable, this compound will be decomposed into ammonia by the treatment with sodium carbonate. The following solutions are employed in the execution of the test:-- _Ammonium Chloride._--Dissolve 1·5735 grammes of the dry and pure salt in 1 litre of distilled water. When required for use, dilute 100 c.c. of the solution to 1 litre; 1 c.c. of this diluted solution contains ·00005 gramme of NH_{3}. _Pure Sodium Carbonate._--The ordinary pure reagent is freed from any ammonia possibly contained by heating it in a platinum capsule. _Pure distilled Water._--This is obtained as directed on p. 204. _Nessler’s Reagent._--This is a strong alkaline solution of mercury biniodide. It may be prepared by first dissolving 62·5 grammes of potassium iodide in 250 c.c. of hot distilled water (reserving 10 c.c. of the solution), and adding a concentrated solution of mercury bichloride, with constant shaking, to the remainder, until a permanent precipitate remains undissolved; this is then brought in solution by means of the 10 c.c. of iodide solution, set aside, and the addition of mercury bichloride is carefully continued until a slight precipitate reappears. A concentrated solution of potassium hydroxide (200 grammes dissolved in water) is now added, and the volume of the whole made up with distilled water to 1 litre. The solution is then allowed to subside, after which it is decanted and preserved in a well-stoppered bottle. _Permanganate solution._--Dissolve 8 grammes of potassium permanganate and 200 grammes of potassium hydroxide in 1 litre of water, and boil to expel any ammonia present.