SWELLING 

 TABLE XXXVIII 1 



191 



1 Observed values are taken from PROCTER, H. R., J. Chem. Soc., vol. 105, p. 313, 1914. 

 The observed value for V given in this table is the increase in volume in cubic centimeters 

 of 0.768 gm. of gelatin. Values for x, y, and z are given in moles per liter. 



Procter and Wilson then explain on the basis of theDonnan 

 equation why the value of e, and therefore also V, should follow 

 a curve of the particular type it does. By proper substitution 

 from the thermodynamic and osmotic equations it follows that: 



e = -2x + \/4x 2 + z 2 



"As the concentration of acid is increased from zero to some small, but 

 finite, value, z must necessarily increase at a very much greater rate than 

 x. This is shown very markedly in the most dilute solutions, where 

 almost all the acid added combines with the gelatin : but z has a limiting 

 value, which is determined by the total concentration of gelatin with 

 which we started. Now z must either approach this limiting value or 

 diminish, which it would do if the ionization of the gelatin chloride were 

 sufficiently repressed. In either case: 

 limit 



