WATER 31 



y>. enter id it is sporogencs is present, the evidence may be regarded 

 a> conclusive. 



The search for specific pathogenic organisms in water is un- 

 >.Mi>i'acmry. Though it is not impossible to isolate and detect 

 them when special methods are adopted, the process is difficult 

 and the result uncertain. A negative result of such an examination 

 can never be regarded as conclusive. 



Chemical Examination. The chemical examination of water 

 is carried out to detect pollution. It may be either qualitative or 

 quantitative. A qualitative examination of water serves only to 

 give an indication of the presence or absence of any particular sub- 

 >tance, and if it is present in large or small a quantity. It does 

 not tell the actual amount that is present, and is, therefore, of limited 

 utility. While the veterinary practitioner or inspector will not be 

 called upon to make analyses of suspected waters, it is necessary 

 that a knowledge of the processes should be acquired in order to 

 fully understand an analyst's report and to appreciate the signific- 

 ance of the findings. Such knowledge can only be obtained 

 through systematic and practical study in a laboratory. Hereunder 

 are given some of the qualitative tests with some remarks on the 

 interpretation of the results of a chemical analysis. For further 

 information the reader should consult appropriate works on the 

 subject. 



Reaction. It is necessary to test the reaction of water owing 

 to the action of acid waters on lead. 



Lime (calcium). The addition of ammonia and the powdered 

 crystals of ammonium oxalate gives a white haze, turbidity, or 

 precipitate according to the amount of calcium present. The 

 presence of 8 parts of calcium per 100,000 or 5 6 grains per gallon 

 gives a distinct turbidity. 



Magnesium. Add ammonium chloride, solution of sodium 

 phosphate and an excess of ammonia. The crystals of ammonium- 

 magnesium-phosphate are precipitated, and the precipitation is 

 hastened if the solution is freely stirred. 



Chlorides. The addition of dilute nitric acid and a solution 

 of silver nitrate gives a white haze, turbidity or precipitate of silver 

 chloride according to the amount of chlorides present. One grain 

 per gallon or 1 5 parts per 100,000 gives a decided haze, while 

 4 grains per gallon or 5 7 parts per 100,000 gives a marked 

 turbidity. 



Sulphates. Dilute hydrochloric acid and a solution of barium 

 chloride gives a white haze, turbidity or precipitate of barium 

 sulphate according to the amount of sulphates present (the sulphates 



