142 TRANSACTIONS iSqQ-'OO 



chlorides will be found in the water, and so on. In a neighbor- 

 ing area, separated, say, by a ridge of granite from the first, and 

 having a soil resulting chiefly from the weathering and disinteg- 

 ration of granite, we shall find a ground- water much softer than 

 the first, and having small quantities of silicates, and other pro- 

 ducts of the disintegration of granite in solution. Now all the 

 wells, and there may be hundreds of them, which are dug into 

 this ground- water, will fall into a class by themselves, and ex- 

 hibit common characters, provided that local soakage is prevented 

 and the water they contain be the uncontaminated ground- water 

 of that region. How then will an individual well be affected, in 

 whose case sewage finds entrance ? Organic matter will increase, 

 and especially will this be true of nitrogenous organic matter ; 

 phosphates and chlorides will be increased, nitrates and nitrites 

 may be found in it, and a bacteriological examination may reveal 

 the presence of new forms of microbial life. To determine all 

 this, a full analysis is of course needed. What I propose to do, 

 is to confine attention to some one characteristic, and to select 

 that one which is most surely altered by the entrance of sewage, 

 and is at the same time most easily and certainly determined. 

 This I find to be the Chlorine in Chlorides. 



-■ The determination of chlorine, in chlorides, is one of the 

 simplest and most definite estimations that a chemist can be called 

 upon to make. Owing to the presence of common salt (chloride 

 of sodium) in human food, and its use by domestic animals, it is 

 always found in sewage, so that any notable admixture of sewage 

 with a well water, at once raises the chlorine precentage. 



Chlorine is, however, invariably present in normal ground- 

 water, and the question arises for each region ; "How much 

 chlorine is normally present in the ground-water of this locality?' ' 

 Of course the answer can only be given after analysis of normal 

 samples, but once it is known, any marked variation from that 

 standard, stamps a well of that region as suspicious, and justifies 

 discontinuance of its use until fuller examination can be made. 

 It must not, however, be forgotten that contiguous wells, like 

 W^ and W5 in Fig. 3, may obtain their water from entirely dif- 

 ferent sources, so that it becomes necessary to take depth, and 

 other factors into consideration. For the lower or second water 

 bearing stratum may have a very different nor;Hlal content of 

 chlorine from the first or ground-water proper ; but its number 



