WATEE 13 



The Removal of Hardness from water on a large scale is 

 brought about by what is known as Clark's process. The 

 principle involved is the precipitation of the lime by con- 

 verting it into an insoluble carbonate. This is accom- 

 plished by adding lime-water to the hard water and well 

 mixing. The lime-water combines with the carbonic acid 

 holding the chalk in solution, and the latter is precipitated. 



By this process several degrees of temporary hardness 

 may be removed from water. Thames water may be 

 reduced from 16 degrees to 4 degrees of hardness.* At 

 the same time a certain amount of organic matter is also 

 removed by this method. 



Clark's process does not reduce the permanent hardness 

 of water, which is due to calcium sulphate or chloride, or 

 to salts of magnesium. 



EXAMINATION OF WATEE FOE HYGIENIC PUEPOSES. 



The object of a water analysis is to determine whether 

 any organic pollution has occurred, or whether the inorganic 

 substances are in excess. 



It is by no means easy for the untrained mind to grasp 

 the significance of chlorine, ammonia, etc., as revealed in the 

 results of a chemical analysis, nor is it even always possible 

 for the chemist to make an accurate judgment of any given 

 water as based on his analysis. 



If the organic substances which pollute water were on 

 analysis met with in the form in which they entered it, an 

 examination would be comparatively easy, but this is not 

 so; ffeces, urine, and filth are not met with in water 

 as such. They have all undergone decomposition, and 

 yielded simpler chemical compounds or elements, and it is 

 only by the isolation of the elements or compounds that a 

 guess is made as to their probable origin. 



Ammonia in the form of free and organic ammonia is one 

 of the most important determinations in water analysis, not 



* One degree of hardness is equal to 1 grain of calciuna carbonate 

 per gallon. 



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