xii. a. i Heise : Chloride of Lime 33 



this laboratory were treated with chloride of lime solution and 

 immediately titrated with sodium thiosulphate in the usual man- 

 ner. Acidified, 100 cubic centimeter samples showed 6.5 milli- 

 grams of available chlorine, whereas unacidified samples showed 

 only 2.4 and 4.0 milligrams, respectively. Since the amount of 

 chlorine taken up by water or sewage depends upon the amount 

 and concentration of chlorine added, on the temperature and 

 time of digestion, on light, and on the quality of the liquid 

 studied, it is obvious that, at best, only relative data, available 

 for laboratory control of disinfection problems, are obtained by 

 the methods ordinarily employed. Such determinations do not 

 necessarily give any indication of the presence of germicidal 

 products formed by the interaction of hypochlorites and the in- 

 gredients of waters and sewage ; hence they lose much of their 

 significance for disinfection problems unless they are studied in 

 conjunction with bacteriological data. In all cases, the chlorine 

 consumption should be determined as nearly as possible under 

 the same conditions of temperature, illumination, and concen- 

 tration that obtain in actual practice. 



SUMMARY 



The decomposition rate of chloride of lime in water, sewage, 

 and solutions of organic substances was studied. In the dark, 

 at 28° C, the reactions proceeded with almost constant velocity 

 for periods of thirty minutes to one hour, after which they pro- 

 ceeded very slowly. In the light the decomposition rate was 

 greatly accelerated. 



In general, the amount of available chlorine consumed is pro- 

 portional to the concentration in which it is added, as shown by 

 the interaction of chloride of lime and urea solution. However, 

 for certain definite concentrations of sewage this regularity 

 fails. 



A study of the reaction between chloride of lime with varying 

 quantities of urea showed that the chlorine consumption, as meas- 

 ured by the starch-potassium-iodide reaction, is not necessarily 

 proportional to the concentration of organic matter. 



The determination of the chlorine consumption of a water or 

 sewage, though of importance in the control of hypochlorite 

 disinfection, is not sufficient in itself and should be supplemented 

 by bacteriological tests. 



