JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V NOVEMBER 4, 1915 No. 18 



CHEMISTRY. — On some new indicators for the colorimetric 

 determination of hydrogen-ion concentration.^ Herbert A. 

 LuBS and William Mansfield Clark, Bureau of Animal 

 Industry. 



In the biochemical application of the colorimetric method of 

 determining hydrogen-ion concentrations several difficulties are 

 encountered. The most serious of these are the so-called protein 

 and salt errors and the obscuring effect of the natural coloj s of 

 the solutions to be tested. All of these hindrances to accurate 

 determinations are encountered to a greater or lesser extent in 

 applying the method to bacterial cultures and culture media. 

 Indeed, the method in its particular application to general bac- 

 teriological problems is in a somewhat unsatisfactory condition, 

 and we are, therefore, attempting to simplify and systematize 

 it so that it may be used extensively in general bacteriological 

 work. 



Unsatisfactory color changes alone rule out many indicators 

 which, though useful with perfectly clear solutions, are of httle or 

 no value in bacteriological media; and, as Sorensen- has shown, 

 the great majority of indicators listed in the elaborate tables of 

 Salm, Thiel, and others must be rejected for one reason or 

 another. 



1 From the research laboratory of the Dairy Division, Bureau of Animal In- 

 dustry. Published by permission of the Secretary of Agriculture. 



'-Biochem. Zeitschr. 21: 131. 1909; 22: 352. 1909; Ergebn. d. Physiol., 12: 

 393. 1912. 



609 



