THE ISO HLORS OF NOVA SCOTIA. — VICKERY. 357 



ocean; that is to say, due to pollution. The correctness of 

 his judgment, therefore, wouhl tU^ppnd upon an accurate 

 knowledge of this amount. For example: a potable water 

 showing a chlorine content of 10 parts per million, coming 

 from a region where the normal chlorine content was three 

 parts per million, would be subject to suspicion; while coming 

 from a region where the normal chlorine content was 12, 

 it would probably be perfectly wholesome, as far as the 

 analyst could judge from this determination alone. 



Method of Procedure in Analysis. The estimation of 

 chlorine in drinking water depends upon the titration of 

 the chlorine with standardized silver nitrate solution, using 

 pota.ssium chromate as an indicator; the theory being that 

 the chloride ion will be removed from the solution by the 

 silver ion before the chromate ion is attacked. When all 

 the chloride ion has been removed, the reddish color of the 

 insoluble silver chromate appears, this forming a most 

 delicate end point. 



The silver nitrate solution is so made that one cubic 

 centimeter contains sufficient silver to combine with one 

 milligram of chlorine. Silver nitrate is carefully dried at 

 100 degrees in the oven, and an amount slightly exceeding 

 4.7937 grams is weighed out; this is dissolved in water, and 

 the solution is made up to one liter in a flask which has 

 previously been standardized and its error corrected. This 

 solution was carefully mixed. In order to standardize this 

 solution, potassium chloride was re-crystalized from a 

 sample of known purity (Merck's guaranteed). The fine 

 crystals thus obtained were carefully dried to a constant 

 weight in the oven, and exactly 2.1065 grams were weighed 

 out, dissolved in distilled water and made up to one liter 

 in the standardized flask. This solution thus contained 

 one milligram of chlorine per cubic centimeter. The silver 

 •solution was standardized by titrating from two to three 

 cubic centimeters of potassium chloride solution, using 



