XI, A, 3 Heise and Aguilar: Purification of Swimming Pools 119 



position rate of hypochlorite is below that in the others. This 

 furnishes explanation for the fact that the treatment with 0.5 

 part of chlorine, found necessary in tank III, was greater than 

 the requirement for tank I, while the same treatment in tank II 

 caused numerous complaints of excessive and disagreeable odor. 



Table XIII. — Effect of daily additions of 0.25 part of chlorine per million 



parts of water. 



[Results expressed as parts per million.] 

 TANK I. 



Age of water in 

 days. 



Turbid- 

 ity. 



Qualitative test for 

 free chlorine. 



Chlorine present. 



Chlorine con- 

 siuned.a 



Dark. 



Light. 



1 



bll 



13 

 10 



8 

 11 



9 



Positive 



Trace 



0.6 



1.4 

 cO.7 

 2.5 

 3.3 

 3.5 

 2.5 



2 



do 



do - -- 



c 0.7 



3 



Negative 



Nil 



1.2 

 1.2 

 1.2 

 1.2 



4 



do 



Negative 



do 



5 



do 



6. 



do 



do 









TANK in. 



1 



15 



Negative 



Nil 



1.25 

 c2.3 

 2.3 

 2.2 

 2.1 

 1.5 



2.3 

 e2.3 

 3.3 

 4.4 

 4.2 

 3.2 



2 



do - 



do 



3 





do. 



do 



4 



20 

 20 

 15 







— do. 



do 



5. 



do . 



do 



6 



do 



do 







» Two hundred cubic centimeter samples digested two hours at room temperature with 2.8 

 milligrams available chlorine. 



*> Immediately after chlorination. 

 = Dull day. 



In disinfecting municipal water supplies or sewage there is 

 a certain quantity of contaminating material present; once this 

 is destroyed or removed, there is usually no further influx of 

 noxious matter. Glaser,^" in contradiction of the findings of 

 Grether," concluded that a single addition of disinfectant is 

 as efficaceous as the same amount added at intervals in smaller 

 quantities. His results may be correct for ordinary water or 

 for sewage, but it is obvious that different conditions obtain for 

 swimming pools, where the contaminating substances are being 

 continually added. In the latter case the periodic addition of 

 chlorine in small quantities, but sufficiently great to effect puri- 



^'Arch. f. Hyg. (1912), 77, 279. 

 "Ibid. (1896), 27, 189. 



