368 



W. E. TOTTINGHAM AND A. J. BECK 



L:.riiiOiiy with the results of the former series, however, it antago- 

 nized the combined effects of sodium bi-carbonate and mangan- 

 ous chloride to a great extent. 



REACTION OF THE NUTRIENT SOLUTIONS 



In view of the apparent importance of the acidity or alka- 

 linity of the nutrient solution in the regulation of injury, as 

 observed in the preceding experiments, determinations of the 

 hydrogen-ion concentration^ were made upon some of the solu- 

 tions there employed. The measurements were made by the 

 colorimetric method of Sorensen,^" after exposing the solutions 

 for three or four days to a rather uniform temperature of about 

 20°C. The data, which are presented in table 3, should be con- 

 sidered as approximate only, on account of comparative lack 

 of refinement ij^ the technique appUed.^^ 



TABLE 3 

 Approximate hydrogen ion concentration of selected nutrient solutions 



9 It may be desirable to explain here that hydrogen ion concentration and 

 acidity, in the sense in which the latter term is commonly employed, are not 

 always synonymous. They are synonymous only at very low concentrations of 

 some acids, where electrolytic dissociation is complete. In other cases the hy- 

 drogen ion concentration is a measure only of the dissociated, acid hydrogen 

 atoms. The ordinary method of titration with a standard solution of alkali 

 gives the total concentration of acid hydrogen atoms. 



^^ Sorensen, S. P. L. tjber die Messung und Bedeutung der Wasserstoffionen- 

 Konzentration bei biologischen Prozessen. Ergebnisse der Physiologic 12: 393- 

 532, 1912. 



*i The unit of measurement is 1 gram of hydrogen ion per 10 million liters 



N 



of solution or ..„ „„^ „^„ Water, which is taken as the basis of neutrality, has 



this concentration of hydrogen ion at 21°C. Sodium alizarin sulfonate was 

 employed as the indicator in Series 1 and 2 A. Neutral red, more sensitive near 

 the neutral point, was employed in Series 2 B. 



