J. H. NORTHROP 611 



It was found that 20 cc. of this solution added to 100 cc. of the 

 protein solution caused the hydrolysis to be about one-third complete 

 in 4 hours and two-thirds complete in 24 hours. This concentration 

 was therefore used. 



Edestin Solution A. — 25 gm. of crystalline edestin were dissolved 

 in 300 cc. of dilute NaOH and precipitated by the addition of dilute 

 HCL. The reaction was adjusted to the isoelectric point of edestin 

 and the solution then dialyzed for a week against tap water and 2 

 days against distilled water. It was then diluted to 500 cc. A fine 

 suspension was obtained which could be accurately pipetted. The 

 conductivity was about that of an m/1,500 KCL solution, showing that 

 only traces of electrolytes were present. The other protein solu- 

 tions were purified in the same way by dialysis at the isoelectric 

 point (Loeb).^ 



Adjustment and Measurement of the Reaction. 



The required amount of protein solution was pipetted into a 100 

 cc. volumetric flask and a drop of indicator added (methyl orange or 

 thymol blue, depending on the reaction desired). Hydrochloric acid 

 was then added until the approximate reaction desired was reached. 

 The solutions containing the other acids were prepared in the same 

 way by adding the acid to the protein solution until the color matched 

 exactly that of the flask containing the hydrochloric acid solution. 

 In this way solutions of the same pH could be easily prepared. 



Control experiments showed that the indicator had no effect on 

 either the rate of digestion or the analysis. The absolute reaction 

 of the mixtures could not be measured colorimetrically owing to the 

 "protein error." A sample of the solution was removed shortly 

 after adding the pepsin therefore and the pH determined by the 

 E.M.F. method. It was found as stated by Sorensen that the change 

 in reaction during the digestion was insignificant. 



