PROPERTIES OF WATER AND SOURCES OF SUPPLY. 9 



provide all the information required by a steam 

 user. They indicate and measure any changes in 

 hardness, and the corresponding alterations are 

 easily made in the softening process or in the anti- 

 fouling composition used in the boilers. 



The measure of hardness in grains per gallon 

 may be deduced from the conductivity by means of 

 the curve given by the makers which shows the re- 

 lation between quantity of chalk in solution and 

 conductivity. 



POLLUTION OF RIVERS. 



The Dionic Tester can be usefully applied in cases 

 of suspected sewage pollution in rivers. If two 

 tests of the water are made, "one above the outfall 

 and the other below, the presence of sewage effluent 

 will be immediately detected by the increased con- 

 ductivity of the water below the outfall. The method 

 has the advantage that an inspector can easily carry 

 the apparatus with him and make his tests on the 

 spot. 



It will be concluded then that spring water is 

 superior to river water for potable l purposes. In 

 the geological strata through which it naturally has 

 to pass it undergoes a high degree of filtration, 

 usually unattainable by artificial means. It is bright 

 and sparkling and contains certain natural gases 

 which render it very palatable ; these as desirable 

 properties, however, are no indication of purity in 

 themselves ; surface flow often has the means of re- 

 ducing impurities (organic and inorganic) in water 



1 The term potable in this book is used to denote water which will be 

 used for drinking and cooking purposes and making up liquids for internal 



