Hydrogen Ions. 



285 



144 (1726) 



Hydrogen ions, titration and the buffer 

 index of bacteriological media. 



By J. HOWARD BROWN. 



[From the Department of Animal Pathology of The Rockefeller In- 

 stitute for Medical Research, Princeton, N. J.] 



The titration of bacteriological media should not be regarded 

 as a crude method of determining the reaction of media, but a 

 process which reveals facts not disclosed by a simple hydrogen ion 

 determination. For many puposes a knowledge of the buffer 

 content of media is quite as important as the hydrogen ion con- 

 centration. The importance of the buffer content of media has 

 been indicated by Kligler, 1 Bermann and Rettger, 2 Bronfenbrenner 

 and Schlesinger, 3 H. Jones, 4 L. F. Foster 5 and C. G. L. Wolf. 6 



The buffer content of media between stated limits of hydrogen 

 on concentration is easily determined by titration against a 

 standard acid or alkali solution. The amount of alkali required 

 to reduce the hydrogen ion concentration of a medium from its 

 initial reaction to a stated lower hydrogen ion concentration, say 

 Ph 8.0, maybe called the "reserve acidity" 7 of the medium in- 

 dicated by the symbols Rn(Pun — 8) in which n = the initial Ph. 

 The amount of acid required to raise the hydrogen ion concentra- 

 tion from Pun to, say, Ph 5.0 maybe called the "reserve al- 

 kalinity" 7 indicated by the symbols R 0 w(Pnn — 5). The "buffer 

 index" indicated by the symbols BI(PhS — 5) is the sum of the 

 reserve acidity plus the reserve alkalinity. Each of these values 

 is to be expressed in terms of per cent, normal acid or alkali, i.e., 

 the number of cubic centimeters of N/i acid or alkali required to 



1 I. J. Kligler, J. Bad., 1916, i, 663. 



s N. Bermann and L. F. Rettger, Bad., 1918, iii, 389. 



8 J. Bronfenbrenner and M. J. Schlesinger, Proc. Soc. Exp. Biol, and Med., 

 1918, xvi, 44. 



* H. M. Jones, J. Inf. Dis., 1920, xxvii, 169. 



6 L. F. Foster, J. Bad., 1921, vi, 161. 



« C. G. L. Wolf, Brit. J. Exp. Path., 1920, i, 288. 



7 E. W. Washburn, Proc. 2nd Meeting III. Water Supply Assn., 1910, p. 93. 



