JOURNAL OF BACTERIOLOGY 



THE COLORIMETRIC DETERMINATION 

 OF H-ION CONCENTRATIONS 



The convenience and relative precision with which the Hydrogen-ion concentration of solutions 

 can be colorimetrically determined with the use of certain indicators and standard buffer solutions has 

 led to wide use in laboratorj' work in the study of many physiological processes, of the activation of 

 enzymes and of the growth of bacteria. In this latter field, the method has already become standard 

 for the control of the true reaction of culture media. See Clark and Tubs, Journal of Bacteriology, 2: 

 1,2,3(1917). 



A comprehensive discussion of the whole subject from both the theoretical and practical stand- 

 point is to be found in "The Determination cf Hydro(,en-hns," Tr. W. LI. Claik, Ealtimoie, 1920. 



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Set of Clark and Lubs Indicators, standardized dry powders 



*CLARK AND LUBS INDICATORS, Standardized Dry Powders 



.\ set of indicators covering the important zones of pH, carefully selected for their brilliancy, and 

 which are relatively unaffected by conditions other than Hydrogen-ion concentration, such as sjilt and 

 protein errors. 



The Thymol Blue of this series is a three-color indicator, recommended for differential titrations; 

 see Clark and Lubs, Journal of the American Chemical Society, Vol. 50 [1918). The Brom Cresol 

 Purple covers practically the same range as litmus, and is more brilliant and reliable. 



• Prepared for us in the laboratories of Hynson, Westcott & Dunning. 



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