XI, A, 3 Heise and Aguilar: Purification of Swimming Pools 117 



the two weeks' run. The odor of chlorine was usually marked 

 (even in some cases where it could not be detected chemically), 

 but was not strong enough to be objectionable. 



A second run of one week's duration in tank III, using the 

 same daily addition of 0.5 part of chlorine per million parts of 

 water, substantiated our conclusions throughout. In this run 

 conditions were markedly improved, probably because of the par- 

 tial cessation of building operations. There was generally a 

 sufficient excess of chlorine in the pool to give a reaction with 

 potassium iodide and starch in the presence of phosphoric acid. 

 The bacterial count was low throughout the week. The chemical 

 data secured are shown in Table XI. 



Table XI. — Effect of daily additions of 0.5 part of chlorine per million 

 parts of water. Tank III." 



[Results expressed as parts per million.] 



Age of water in days. 



Turbid- 

 ity. 



Qualitative test for free chlorine. 



Avail- 

 able 

 chlorine 

 present. 



Chlorine 

 consump- 

 tion, b 



1 .. 



9.9 

 9 







2.5 



2 



do 





3 



do 



trace 

 0.2 

 0.30 

 0.35 



0.35 

 1.2 

 2.4 

 1.75 



4 



8.7 

 7.8 

 <7 



do 



5 



do 



6 



do . 







» Chlorination occurred daily at 4 o'clock in the afternoon ; the sample was taken at 6 o'clock 

 in the afternoon and analyzed during the following morning. 



" Two hundred cubic centimeter samples digested two hours at 30° C. with 3.5 milligrams 

 available chlorine. 



Although the results of turbidity measurements are somewhat 

 conflicting, it is evident that there was a slight clearing of the 

 water due to the addition of chloride of lime. In spite of the 

 amount of disinfectant added, no bad effect on the swimmers was 

 noted and no complaint was made. 



A series (on tank I) was performed, substituting sodium 

 hypochlorite (as antiformin) for calcium hypochlorite. Unfor- 

 tunately a weak solution was used, so that bacteriologically the 

 results left much to be desired ; however, there can be no question 

 that in proper concentration it would have given efficient purify- 

 ing action. Sodium hypochlorite has the advantage that it in- 

 troduces no calcium salts or irritating substances into water, and 

 the results of this work indicate that, for Manila water at any 

 rate, a large amount of clearing of water occurs. The chemical 

 data secured are shown in Table XII. 



