JACQUES LOEB 



583 



level of liquid in the glass tube after 20 minutes. The reader will 

 notice that the curve for m/256 CaCl2 is low and flat as long as the pH 

 > 4.0 and that a sharp rise in the curve begins at a pH of about 4.0 

 or a little less. The curve rises steeply with diminishing pH {i.e. in- 

 creasing hydrogen ion concentration) until it reaches a maximum at 



-+— • 



I 



c 

 o 



to 



•1—1 



CD 



t 



c 



Collodion membrane treated with gelatin 



isoelectric 

 point 4.7 



Fig. 1. Collodion membranes previously treated with 1 per cent gelatin solution. 

 Abscissae, pH (logarithms of hydrogen ion concentration with minus sign omitted). 

 Ordinates, initial rate of diffusion of water from pure water through collodion 

 membranes into solutions of salt indicated. Reversal of sign of charge of mem- 

 brane at pH = 4.0; i^., on the acid side of the isoelectric point of gelatin. 



