218 



Chemical Analysis of Potable Waters. 



running water, and secondly water companies drawing their supplies 

 from below the sewer outfalls of towns." {Journal Chemical Society, 

 May and July, 1880.) Such improvement as does take place in run- 

 ning streams probably depends more upon the part played by fresh- 

 water plants and micro-organisms than upon direct chemical oxida- 

 tion, and of course no accurate conclusions can be reached as to the 

 effect of these varying and little understood agencies. Mere dilution 

 also doubtless accounts for the apparent disappearance of much noxious 

 matter. Professor Wm. Eipley Nichols, in his Water Supply, itali- 

 cises the following statement: "The apparent self-purification of 

 running streams is largely due to dilution, and the fact that a river 

 seems to have purified itself at a certain distance below a point where 

 it was certainly polluted, is no guaranty that the water is fit for do- 

 mestic use." 



To what extent, therefore, must a polluted water be diluted before 

 it is safe to use, is a question of the greatest interest, but one to 

 which no answer can as yet be given. Nor can we prove that the spe- 

 cific poisons of certain diseases — admitting their existence — may 

 not contain living organisms capable of rapid multiplication, nor can 

 we tell for how long a period or under what conditions these organ- 

 isms may retain their vitality. In this absence of positive knowledge, 

 but in the light of countless facts which all but prove our suppositions 

 true, we had best err, if err we must, on the safe side, avoiding the 

 use of polluted waters and recognizing the fact that although chemi- 

 cal analysis may detect no impurities in a water, it is not, therefore, 

 necessarily safe to drink. 



The views here presented, may seem extreme to those who have 

 long believed on insufficient grounds that from a chemical analysis 

 alone the character of a drinking water may be decided. My endeavor 

 has been to deal with facts, and make no claims for the chemist's 

 ability in this direction which may not be substantiated, and until 

 we have more knowledge than we now possess of the real causes of 

 disease, and until other methods of analytical research shall have 

 been discovered, it is futile to ask the chemist to recognize and meas- 

 ure forms of matter of which he is ignorant, and to state what will 

 be the effect upon the human system of substances the very nature 

 of which is as yet to him unknown. 



