468 LEON S. MEDALIA 



If highly colored fluids are to be titrated they may be diluted 

 with equal parts or more of distilled water, since the addition of 

 distilled water does not change the H. I. C. materially, if at all. 

 A little experience will greatly facilitate the practical application 

 of this method, with respect to choosing the proper indicator to 

 use, and in estimating readily which pair of color standard tubes 

 to use. 



SUMMARY AND CONCLUSIONS 



The colorimetric measurement of the H. I. C. by means of the 

 " color standards" described is the simplest method yet published. 



These color standards are easily prepared, lasting, and their 

 use is readily applicable in the average bacteriological laboratory. 



The practical application of the ''color standards" for the ti- 

 tration of culture media, by the H-ion concentration method; 

 also for the pH measurement of the acid or alkali production by 

 bacteria, and for the pH measurement of other fluids as described 

 in this paper, is simple and easily handled, and because of its 

 simplicity, it promises to take a foremost place in the colorimetric 

 measurement of the H. I. C. of any fluid as well as in bacteriology. 



In concluding I wish to express my appreciation to Professor 

 W. T. Sedgwick through whose kindness this work was made 

 possible, and to Professor S. C. Prescott, and the other members of 

 the Department of Biology and Public Health of the Institute, 

 for their helpful assistance rendered me in this work. 



REFERENCES 



Babnett, G. D., and Chapman, H. S. 1918 Colorimetric determination of 

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 Assn., 70, 1062-1063. 



Clark, W. M., and Lubs, H. A. 1917 The colorimetric determination of hydro- 

 gen-ion concentration and its applications in bacteriology. Jour. 

 Bact., 2, 109-136; 191-236. 



Committee of American Bacteriologists Report 1919 Jour. Bact., 1919, 4, 107- 

 132. 



Hurwitz, Meyer, and Ostenberg 1916 Bull. Johns Hopkins Hospital, 1916, 

 27, 16. 



Salm, E. 1904 Ztschr. Electrochem., 10, 341. 



Sorensen, S. P. L. 1909 Ztschr. Biochem., 21, 131, 201. 



Sorensen, S. P. L. 1912 Ergebn. Physiol., 12, 393. 



Talbot, H. P. 1908 Quantitative Chemical Analysis. Macmillan Co., New 

 York. Pp. 157. 



