The Titration Curve of Gelatine. 



77 



which is sub-divided, gives values for Pn calculated from E, and read from 

 the smoothed curve N : Ph (marked D in fig. 3). The sixth column gives 

 [OH] the concentration of hydroxyl ions on the normality scale, and the 

 final column gives n' , which is equated to N— [OH]/a, and is the first 

 calculation for the amount of base " fixed " by the gelatine. 



In taking the " acid-fixed " values, the calculations in Table I were made 

 directly from the experimental readings of E. These lie so very closely to a 

 smooth curve that it is safe to assume that the experimental error is slight. 

 In the case of the values of E in alkaline solution, the error is obviously 

 very much greater. Chemical destruction of the gelatine by hydroxyl in the 

 presence of spongy platinum is probably the cause, aud hydrolysis has also 

 been shown to have a slight effect on the reading. For this reason, an 

 arbitrary smooth curve (Ph : N or D in fig. 3) was drawn through the 



Curve of base fixed, n'. 



