XI, A, 1 Ueise and Aguilar: Oxygen Consumption of Waters 45 



action between hypochlorite and potassium permanganate in 

 acid solution. 



The presence of hypochlorites introduces an error in addition 

 to, and opposite in sign from, the one caused by an increased 

 chloride content. In hot digestion the hypochlorite changes to 

 chlorate," probably in accordance with the equation 



3CaCl2 • Ca(0Cl)2 -= SCaCb + Ca(C103)2 

 and reacts with the organic matter present or with the oxalic 

 acid generally used for titration purposes. The amount of per- 

 manganate required is, therefore, reduced, and a low oxygen 

 consumption is recorded. 



When chloride of lime is added to a water of known organic 

 content, the oxygen consumption as determined by the standard 

 method is invariably low, even when digestion is performed at 

 room temperature (the sample being brought to boiling at the 

 end of the digestion period and titrated in the regular way). 

 This is clearly shown by the results of the following experiments : 



Table IX. — Effect of hypochlorites on oxygen consumption. 



SERIES 1. 

 [Distilled water, 200 cubic centimeter samples, digested thirty minutes at 100° C. with a 

 standard permanganate solution, decolorized with standard oxalic acid solution, and titrated 

 with permanganate at boiling temperature.] 





Available 

 chlorine 



(parts per 

 million) . 



Perman- 

 ganate re- 

 quired. 



Error in- 

 volved in 

 terms of ox- 

 ygen con- 

 sumed (parts 

 per million). 



Sample A 



Sample B — 



f 



1-75 

 4.3 



^ 17.5 



{ ' 



I 10 



cc. 

 10.45 

 10.15 

 9.45 

 8.8 

 10.8 

 10.1 

 9.7 







0.15 



0.5 



0.8 







0.3 



0.5 



SERIES 2. 

 [River water treated as in series 1.] 



Available 



chlorine 



added (parts 



per million). 



Perman- 

 ganate re- 

 quired. 



Errors in- 

 volved in 

 terms of ox- 

 ygen con- 

 sumed (parts 

 per million). 







0.5 



1.0 



ec. 

 12.0 

 11.6 

 11.6 







0.2 



0.2 



Bhaduri, Zeitschr. f. anorg. Chem. (1897), 13, 385. 



