WATER SUPPLY FOR TROOPS 465 



chemical remaining after treatment must be removed by some 

 other chemical such as sodium thiosulphate. Bromine waa 

 strongly advocated in Germany aJbout 1897 but has fallen into 

 disrepute on account of the difficulties of administration. The 

 French recommend the use of iodine only when chlorine or the 

 permanganates are not at hand. 



The most important process at the present time, however, is 

 the chlorine treatment and I shall therefore describe it much 

 more fully than i have described the uses of the other chemicals. 



Chlorine is used in American municipal water purification in. 

 one of two forms, calcium hypochlorite or liquid chlorine. For 

 treatment of water in the field the alkaline hypoclilorites and 

 lately aromatic oftloramines also are employed. The action with 

 all of these is probably much the same, namely, an oxidation and 

 a substitution of chlorine for the hydrogen of amido groups in 

 the bacterial protoplasm. 



The germicidal power of calcium hypochlorite — also called 

 chloride of lime or bleaching powder — was known in the early fif- 

 ties. Koch's work in 1881 showed the great germicidal power of 

 the subvstance in a more practical way for he tried out its germi- 

 cidal action on anthrax bacteria and their spores, using the 

 thread method. From these results and those of Nissen (113), 

 Traube (131) took his cue for the application of calcium hypo- 

 chlorite to the purification of drinking water. Traube used a 

 little less than four parts per million of the chemical, correspond- 

 ing to a little more than one part per million of "free chlorine." 

 He added about two parts per million of sodium thiosulphate to 

 remove the excess of free chlorine. Later experimenters fol- 

 lowed Traube and tried both the calcium and the alkaline hypo- 

 chlorites in water purification. The success of the hypochlorite 

 treatment at the Bubbly Creek filter plant in Chicago in 1908 

 (106) showed the utility of the chemical for municipal water 

 works and almost immediately this method of treatment was 

 adopted as a standard procedure all over the country. About 

 1911 liquid chlorine began to supplant the hypochlorite on ac- 

 count of the greater mechanical advantages of the former in its 

 administration. Chlorination of drinking water is now depended 

 upon by hundreds of cities as a final safeguard for their water 

 supplies. In the treatment of the stored surface water or lake 

 supplies of some great cities like New York (using five hundred 

 fifty million gallons of water a day) and Chicago (pumping 

 30 



