62 



THEORY OF COLLOIDAL BEHAVIOR 



gelatin (Fig. 13). In this latter case the solution contained only 

 about 0.8 gm. of originally isoelectric gelatin in 100 cc. solution. 1 



q 



e 



<&- 



1 



8 

 ^ 



8 



0.1N 



0.1N 



o.iNBaio: 



Nate 



KOH 



and 



01N 



:a(ort) 



/ 



67 72 7.7 82 87 92 97 10.2 107 112 11.7 



3 DH47 5.2 5.7 62 



8 



FIG. 13. Curves for the number of c.c. of 0.1 N NaOH, KOH, Ba(OH) 2 , 

 and Ca(OH) 2 required to bring the same mass of about 0.8 gm. of isoelectric 

 gelatin in 100 c.c. solution to different pH. All four curves are identical. 



The question may be finally raised, How many molecules of 

 acid or alkali can combine with one molecule of protein? The 

 smoothness of the titration curves of isoelectric proteins with 

 acids indicates that either only one or many molecules of a 

 monobasic acid, e.g., HC1, combine with one molecule of protein, 

 since otherwise, the curves could not be smooth. It is not 

 probable that only one molecule of acid combines with one mole- 

 cule of protein. 



Procter and Wilson, have reached the conclusion that the 

 equivalent weight of gelatin is 768 (see Chap. XI), and Wintgen 

 and Kruger 2 give the value as 839. According to the recent 



, J., J. Gen. PhysioL, vol. 3, p. 85, 1920-21. 

 2 WINTGEN, R., and KRUGER, K., Kolloid-Z., vol. 28, p. 81, 1921. 



