18 VETEEINAEY HYGIENE 



ness. If the ammonium oxalate test be applied to two 

 specimens of the water, the one in the ordinary way, the 

 other after boiling and filtration through paper, the 

 difference, if any, in the turbidity produced will enable an 

 opinion to be formed as to whether the hardness is largely 

 temporary or permanent. 



A solution of soap of definite strength may also be 

 employed in the same way. For qualitative purposes the 

 ordinary soap liniment of the Pharmacopceia may be 

 used, one minim of which in half an ounce of water is 

 equal to about one and a half grains of lime to the gallon. 

 If the number of minims employed with half an ounce of 

 water, to produce a permanent lather on shaking, be 

 multiplied by 1'5, the number of grains per gallon of lime 

 is approximately known. This test can be repeated on 

 the boiled and filtered water, as iir the ammonium oxalate 

 observation. 



Magnesia. — To obtain this the lime must first be 

 precipitated by ammonia oxalate and the fluid filtered ; 

 to the filtrate is now added a mixture of sodium phosphate, 

 ammonium chloride, and liquor ammonia. A crystalline 

 precipitate of triple phosphate forms in the course of some 

 hours. 



Chlorine. — If a solution of silver nitrate be added to a 

 soluble chloride, a white precipitate insoluble in dilute 

 nitric acid is produced. The precipitate may be a mere 

 haze or a considerable opacity, depending entirely on the 

 amount of chloride present. One grain of chlorine per 

 gallon in water gives a haze, four grains a marked 

 turbidity, and ten grains a considerable precipitate. 



Sulphuric Acid is commonly found in association with 

 lime, calcium sulphate being one of the causes of per- 

 manent hardness. The amount of sulphate can be roughly 

 determined by adding barium chloride to the water, which 

 produces a white precipitate insoluble in nitric acid. One 

 and a half grains of sulphate per gallon gives a- faint haze 

 after standing some time, three grains gives an immediate 

 haze and after a time a slight precipitate. 



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