XI, A, 1 



Heise: Water Supply of Manila 



11 



that even the higher concentrations of chlorine failed to operate 

 successfully. It is known that waters have the power of chem- 

 ically combining with free chlorine, and as pointed out by 

 Hairi/'* this power varies widely for different waters. This 

 chlorine-consuming capacity is not equal or necessarily pro- 

 portional to the oxygen-consuming capacity, although a high 

 organic content is generally associated with a high chlorine- 

 consuming capacity. A few rough experiments on the un- 

 chlorinated water from the city reservoir showed that the 

 chlorine consumption in one hour varied from 0.5 to 1.0 part per 

 million of chlorine consumption in samples taken on different 

 days. 



The chlorine consumption was determined by digesting reser- 

 voir water in the dark with a measured amount of clear, filtered 

 chloride of lime solution of known strength, and determining 

 the available chlorine from time to time by adding potassium 

 iodide and phosphoric acid," and titrating the liberated iodine 

 with 0.02 N sodium thiosulphate solution, using starch indicator. 



Adding a quantity of chloride of lime corresponding to 1 

 milligram of available chlorine per liter of water, approximately 

 60 per cent was generally used up in one hour. A typical series 

 of determinations follows : 



Table X. — Decomposition of chloride of lime in waters 



Diges- 

 tion. 



Chloride of lime. 



Left. 



Con- 

 sumed. 



Hrs. min. 

 3 



35 



1 45 

 3 45 



20 



0.8 



0.45 



0.35 



0.20 



0.14 



0.2 



0.55 



0.65 



0.80 



0.86 



» One milligram available chlorine added per liter of water. 



The results obtained show how rapidly the chlorine loses its 

 effect. It is possible that the chlorine has such highly selective 

 action that dangerous organisms are generally eliminated; how- 

 ever, the bacteriological data (Tables V to IX) indicate that the 

 chlorine loses its effect before the bacteria count is sufficiently 

 reduced to render the water absolutely safe. 



'Zeitschr. f. Hyg. (1913), 75, 46. 

 Winkler, Zeitschr. f. angew. Chem. (1915), 28, 1. 



