JACQUES LOEB 



585 



can be expected at this point. When the hydrogen ion concentration 

 of the solution becomes higher than this, an increasing amount of 

 gelatin is transformed into gelatin-acid salt. With an increase in the 

 concentration of the gelatin-acid salt an increasing proportion of the 

 surface of the membrane assumes a positive charge. Hence the steep 



Collodion membrane treated with gelatin 





g 



•T-l 



-a 



220 



200 



180 



160 



140 



120 



100 



80 



60 



40 



20 



isoelectric 

 point 4.7 



Fig. 2. Collodion membranes treated with gelatin. Reversal of sign of charge of 

 membrane on acid side of the isoelectric point of gelatin. 



rise of the curves in which CaClg or MgCU are used as test solutions 

 must lie near the isoelectric point but on the acid side from the 

 latter. 



It may be pointed out that the influence of acids on the reversal of 

 the sign of charge is not an additive effect of the oppositely charged 



