10 



Scientific Proceedings (93). 



The extreme delicacy of this reaction naturally suggested the 

 possible use of anthocyanin as an indicator. Anthocyanin, pre- 

 pared according to Willstatter's method and dissolved in abso- 

 lute alcohol, was compared with phenolthalein, by the Henderson 

 and Palmer indicator-method for the determination of the con- 

 centration of hydrogen ions, with the results tabulated below: 



Tubes 



fin 



Phenolthalein 



Anthocyanin 



I 



9.27 ' 



Red + + 



Yellowish 



■ + + 









green 



2 



8.70 • 



Red + 



Yellowish ' 







8.00 J 





green ; 





3 



Colorless 



Colorless 





4 



7-48 1 





Pink + 





5 



7-38 • 





Pink + + 





6 



6.90 





Pink + + + 



7 



6.70 







Intensity of pink 



8 



6.30 







coloration increases 



9 



6.00 ■ 



11 



■ 



in the direction of 



10 



5-70 







11, with increase in 



11 



5-30 , 







acidity 





From these data it is obvious that, in point of delicacy, under 

 the conditions specified, anthrocyanin is, in general, the equal of 

 phenolthalein. Furthermore, anthocyanin is superior to the latter 

 in the fact that a change from alkali to acid is indicated by a 

 sharp change from green to red, and not, as for phenolthalein, 

 from red to no color at all. 



The relationship of these observations to those by Gies, 1 on 

 "alkaverdin," will be indicated in a later communication. 



7 (1382) 



The probable cause for the failure of some sodium tungstate to 

 give a suitable reagent for the determination of 

 uric acid. 



By Grete Egerer and Frances Ford (by invitation). 



{From the Chemical Laboratory, Department of Medicine, Medical 

 School, University of Minnesota, Minneapolis, Minn.] 



In one of his articles, Folin mentions that some preparations 

 of sodium tungstate on the market do not yield a satisfactory 



1 Gies, Chemical studies of the pitcher plant, Sarracenia purpurea; Journal of 

 the New York Botanical Garden, 1903, iv, p. 37. 



