22 VETEEINAEY HYGIENE 



water containing vegetable, and particularly animal matter 

 such as urine and feces, contains a decided quantity. The 

 test is really a valuable one when carefully considered with 

 the others. The presence of this substance is detected by 

 adding to the water a little dilute nitric acid, and then 

 molybdate of ammonia. If phosphoric acid be present in 

 quantity, an immediate yellowish-green colour appears ; if 

 it be small in amount, the colour is produced on boiling the 

 liquid. 



Lead, Copper, or Iron may be present in water. The 

 former is dangerous, the copper very rare, the iron harm- 

 less. Lead or copper are precipitated by ammonium sul- 

 phide, a dark or black precipitate resulting which is 

 insoluble in hydrochloric acid. Lead may further be 

 distinguished by the addition of crystals of potassium 

 bichromate, which give a turbidity at once if the amount 

 of lead present is equal to one-tenth of a grain per gallon. 

 One-twentieth of a grain will cause a turbidity in one 

 minute, and one-iiftieth of a grain will produce it in half 

 an hour. 



Iron, which is quite unobjectionable, is detected by the 

 red or yellow jjrussiate of potash and dilute hydrochloric 

 acid, which produce a blue colour. The yellow prussiate is 

 used for ferric the red for ferrous salts. 



Hydrogen Sidphide may be found in an exceedingly bad 

 water. It is determined by its smell on boiling, or by its 

 blackening a salt of lead. 



The Inferences from the Qualitative Tests are thus sum- 

 marised by Parkes : 



If chlorine be present in considerable quantity it either 

 comes from a strata containing salt, from impregnations of 

 sea-water, or from the admixture of liquid excreta of animals 

 or man. If from the first cause, viz. salt strata, the water 

 would be alkaline from carbonate of soda ; there would be 

 an absence, or nearly so, of oxidizable organic matter as 

 determined by the tests for nitric and nitrous acids 

 ammonia, and the chloride of gold tests ; and there would 

 probably be a large amount of sulphuric acid present. If 



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