10 The Philippine Journal of Science i9i6 



Table IX. — Effect of 0.75 part of free chlorine per million of water." 



Date. 



Reservoir. 



San Juan. 



Reduc- 

 tion. 



Colony 

 count. 



Test for B. 

 coli group, b 



Colony 

 count. 



Test for B. 

 coli group, b 



1914. 

 June 22-. 



275 

 450 

 120 

 190 

 IRO 



Positive 



do 



do 



do 



Negative 



180 

 70 

 48 

 38 

 44 



Negative— - 



do 



Positive 



Negative ... 

 do 



Per cent. 

 35 

 84 

 60 

 80 

 71 



65 



June 23 



June 24 



June 25 



June 26 



Average reduction in bact 



eria count . 









» Examination by O. SchobL, bacteriologist, Bureau of Science. 



" In 2 cubic centimeter samples. Bacillus coli remained in one instance. 



It will be noted that in no case has the sterilization efficiency 

 reached a figure comparable with those generally reported. Ac- 

 cording to a committee report to the American Public Health 

 Association * the bacterial reduction which may be reasonably 

 expected of typical installations in American cities is about 

 98 per cent, with which the 50 to 70 per cent reductions here 

 obtained compare rather poorly. However, since the Manila 

 water comes from a watershed well guarded against trespass, 

 pathogenic organisms are probably absent or at any rate very 

 few in number; and since the pathogenes succumb more readily 

 than other forms to the attack of chloride of lime, it is reason- 

 able to suppose that the water is safer, so far as potability is 

 concerned, than would appear from the actual reduction in 

 bacteria count. It is interesting to note the greatly increased 

 efficiency of 0.625 part of available chlorine per million as 

 compared with 0.5 part and the relatively slight increase in 

 efficiency of 0.75 part over 0.625. 



The results of these tests show that hypochlorite treatment is 

 not adapted to a turbid water high in organic matter. The 

 high temperature of the Manila water is an added complicating 

 factor which probably accounts in a large measure for the dis- 

 agreeable odor chlorination imparts to the water. 



The low efficiency of the chlorination treatment finds a ready 

 explanation in the high chlorine-consuming power of the Mon- 

 talban water. The results of the chlorination tests indicate 

 both that a large amount is taken up immediately, which ac- 

 counts for the low efficiency of small additions of chloride of 

 lime, and that the reaction proceeds more slowly with time, 

 though a definite end point is not reached for many hours, so 



'Am. Journ. Pub. Health (1915), 5, 918. 



