CORRECTNESS OF THE CHEMICAL VIEWPOINT 



59 



It was found in these experiments that all strong monobasic 

 acids, like HBr or HNO 3 , gave the same titration curve as HC1. 

 This, however, was, of course, no longer the case for weak acids. 

 The weaker the acid the more is required to bring the protein 

 solution to the same pH. This is illustrated in Fig. 10, which 

 gives the titration curves for 0.1 N acetic, mono-, di-, and tri- 



3 



22 



6 28 3.0 32 3.4 3.6 3.8 40 42 44 46 48 



FIG. 10. The ordinates represent the number of c.c. of 0.1 N acetic, mono-, 

 di-, and trichloracetic acids required to bring about 0.8 gm. of isoelectric gelatin 

 to the pH indicated by the abscissae. Enough HoO was added to bring the 

 gelatin-acid solution to a volume of 100 c.c. 



chloracetic acids with the same mass of isoelectric gelatin (about 

 0.8 gm.) in 100 c.c. solution. It is obvious that the weaker the 

 acid the more is required to bring the same mass of isoelectric 

 gelatin to the same pH. 



On account of the enormous quantities required in the case of 

 weak acids, it is not well possible to plot the quantity of acid in 

 combination with a given mass of protein in the same way as done 

 in the case of HC1 ; but it will be shown in the next chapter by an 

 indirect method that the amount of anion combined with a given 



