68 MASON— PURIFICATION OF WATER SUPPLIES. [April 22, 



Numerous similar sowings were made and even lower counts of 

 residual germs were found. 



Upon examining waters charged with pure cultures of Bacillus 

 coli communis, and others contaminated with fresh fecal material of 

 human origin, no gas-forming bacteria of any kind were found alive 

 in any instance after the use of even the smallest dose of " bleach " 

 shown above. 



Other experimenters have reached similar conclusions with still 

 smaller doses of "available chlorine." The most satisfactory test 

 of the process, however, is the practical one of treating the entire 

 municipal supply daily furnished to Jersey City. The dose there 

 used during the month of December, 1908, averaged approximately 

 .03 grain available chlorine per gallon and has since been materially 

 reduced. While using the above amount the daily counts of bac- 

 teria for the month were : 



Raw Water. 



Maximum 1,600 



Minimum 240 



Average 559 



Treated Water. 



Maximum 30 



Minimum o 



Average 2.7 



No part of this minute dose of hypochlorite reaches the con- 

 sumer and protection against pathogenic organisms appears to be 

 assured. 



It is not expected that the process will take the place of filtration 

 because it does not aid in improving the physical appearance of a 

 water, but as an adjunct to a filter plant there can be no question of 

 its usefulness in times of emergency, and it can surely be depended 

 upon to render a reasonably polluted water safe for domestic pur- 

 poses, and do it at a moderate price. 



It goes without saying that the hypochlorite of sodium, obtained 

 by electrolyzing a solution of common salt, can be substituted for 

 the bleaching powder whenever local conditions allow of its cheap 

 manufacture. The effect upon bacterial life is the same. 



Rensselaer Polytechnic Institute, 

 Troy, N. Y., 



April, 1909. . 



