WATER 23 



the chlorine be derived from calcium chloride, there would 

 be a large precipitate with ammonium oxalate after boiling. 

 If from sea-water, the chlorine would be found in very large 

 quantities ; there would also be much magnesia, and very 

 little evidence of oxidized products of organic matter. If 

 it be from sewage the chlorine is marked, the nitric, nitrous, 

 phosphoric acids and ammonia largely present, and if the 

 contamination be recent, the organic oxidizable matter 

 would be large. A stream fouled by excreta may thus 

 show at different times of the day different amounts of 

 chlorine, and this in the absence of rain will certainly 

 indicate contamination. 



Ammonia is nearly always present, but in minute quan- 

 tities in good water. If it can be detected without distilla- 

 tion it is exceedingly suspicious. If nitrates and nitrites 

 are present they are likely to be from excreta. Nitrates 

 found in water indicate previously existing organic matter, 

 probably animal ; nitrites indicate recent contamination. 

 The coincidence of readily oxidizable matter, ammonia, and 

 chlorine indicate the contamination as being of animal 

 origin. 



If a water gives the test for nitric and not nitrous acid, 

 and there is almost an absence of ammonia, the origin of 

 the nitric acid is not from organic matter, but probably 

 from potassium, sodium, and calcium nitrate, derived 

 from a soil impregnated with organic matter at some 

 previous date. Large evidence of nitric acid, with little 

 evidence of organic matter, indicates old contamination. 

 If nitrous as well as nitric acid and organic matter be 

 present, the pollution is recent. Phosphoric acid indicates 

 an origin from phosphatic strata, or from sewage impreg- 

 nation. 



Lime in large quantities indicates a very hard water ; if 

 boiling removes it, it is calcium carbonate ; if it has but 

 little effect upon it, it is calcium sulphate or chloride. If 

 sulphuric acid is large, it is in combination with lime ; if 

 the latter is small, it is combined with soda. If the water 

 is acid and the acidity disappears on boiling, it is due to 



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