353] Remarks on Analysis of Drinking Water 211 



Chlorides. The quantity of chlorine in water is of very little 

 importance, but should not exceed 1 grain per gallon. 



Nitrates. Like ammonium salts, the nitrates in drinking 

 water are not harmful in themselves, but their determination is 

 useful in that it gives us an idea of the amount of sewage con- 

 tamination which the water has, at some time or other, undergone. 

 Nitrates are the last oxidation products of sewage, and hence 

 they indicate contamination of less recent date than that indi- 

 cated by free ammonia. The quantity present in water varies 

 from nothing in spring or shallow well waters to 4 grains per 

 gallon in deep wells. 



Hardness. Here all the remarks will apply that have been 

 made concerning total solids, except that the hardness, unless 

 very excessive, cannot be considered injurious in drinking 

 waters. 



P2 



