" COLOR STANDARDS" FOR THE COLORIMETRIC 



MEASUREMENT OF H-ION CONCENTRATION 



pH 1.2 TO pH 9.8 



LEON S. MEDALIA 



From the Research Laboratories, Department of Biology and Public Health, Massa- 

 chusetts Institute of Technology 



Received for publication April 7, 1920 



I. H-ION CONCENTRATION METHOD OF ADJUSTING CULTURE MEDIA 



BY THE USE OF " COLOR STANDARDS" 



Introduction 



Sorensen in 1909 demonstrated the value of the "H-ion con- 

 centration" as a basis for measuring the reaction in organic fluids 

 as against the " titration" method then in vogue for adjusting 

 culture media. This method has been adopted by practically all 

 research workers in bacteriology ever since the classic work of 

 Sorensen was published, yet no standard text-book in bacteri- 

 ology however recent, does more than make a passing reference 

 to it, although they all agree upon the value of the proper titra- 

 tion of culture media. It occurred to the writer that the reason 

 why this method of determining reaction was left to the research 

 worker alone, was because of the difficulties encountered in its 

 application. In other words to carry out the standardization of 

 culture media, according to the H-ion concentration properly, as 

 heretofore suggested, one needs to be a fairly well trained chem- 

 ist as well as a mathematician of no mean degree. To overcome 

 these difficulties and make this very valuable method of adjust- 

 ing culture media adaptable to the average laboratory, this 

 research was undertaken. Only the successful results and method 

 will be given in this report, all the attempts and experiments that 

 led up to these results being omitted. Expressions that re- 

 quire a knowledge of higher mathematics and chemistry will be 



441 



