EXPERIMENT STATION REPORTS. 199 



A STUDY OF THE RELATIONSHIP BETWEEN THE OXYGEN CON- 

 SIMING POWER OF WATER i^ND ITS HYDROGEN-ION 



CONCENTRATION 



F. W. Fabian and W. L. Mallmann. 



Introduction. — In making a sanitary chemical analysis of water or of 

 sewage, it is of value to know the oxygen consuming power of the sample, 

 not that the oxygen consuming power is all important in itself but it is simply 

 the evidence in determining certain sanitar};- conditions concerning 

 the sample in question. The ox3^gen consuming power is defined as "the 

 oxygen that the oxidizable compounds of sewage and water consume when 

 treated in an acid solution with potassium permanganate." (1) 



The significance of oxj^gen consumed from the chemical viewpoint is that 

 it is a rough ind^x of the amount of carbonaceous matter present. Its sig- 

 nificance from the bacteriological viewpoint is that if organic matter is 

 present it affords a better medium for the growth of bacteria. This may be 

 desirable as in the case of sewage or undesirable as in the case of drinking 

 water. 



Plan of Work. — Our work had in mind a study of the relationship between 

 hydrogen-ion concentration and oxygen consuming power together with a 

 bacteriological study of the samples of water. The water was collected from 

 wells in the vicinity of the College and East Lansing, analyzed when fresh 

 and allowed to stand for several days or a week and analyzed daily. The 

 analysis consisted of making a hydrogen-ion determination, testing for the 

 oxygen consuming power, plating on plain agar and seeding in lactose fer- 

 mentation tubes. 



Methods. — The method used in determining the hydrogen-ion concentration 

 is the colorometric method of Clark and Lubs (2). The method used for 

 determining the oxygen consumed was the standard (recommended) method 

 (pp. 26-27, Std. Methods, 1920). Suitable dilutions were made on standard 

 plain agar (1) the plates incubated at 37°C. and counted at the end of 48 

 hours. Two 10 cc, one 1 cc. and one 0.1 cc. portions of water were placed 

 in lactose fermentation tubes and incubated for 48 hours at 37°C. The 

 above determinations were made on each sample when fresh and every day 

 for four days and some cases (at the end of) the seventh day, in order to study 

 the changes that took place. 



Results. — A study of tables 1 to 12 indicates that the hydrogen-ion con- 

 centration of these samples of water decreases upon standing, the reaction of 

 all samples being slightly alkaline. The oxygen consuming power increased 

 then decreased as the water stood. The bacterial count, like the oxygen con- 

 suming power, first increased then decreased as the water stood, while in the 

 case of gas production there was no constant relationship. The gas producing 

 bacteria survived the period of experiment very well in most cases showing 

 up well at the end of 4 or 7 days. 



