594 REVERSAL OF SIGN OF CHARGE 



with which it is in contact exceeds a certain limit. It is pointed out 

 in this paper that by treating the collodion membrane with a protein 

 {e.g. oxyhemoglobin) a thin film of protein adheres to the m.embrane 

 and that the positive charge of the membrane must therefore be 

 localized in this protein film. 



2. It is further shown in this paper that the hydrogen ion concen- 

 tration, at which the reversal in the sign of the charge of a collodion 

 membrane treated with a protein occurs, varies in the same sense as 

 the isoelectric point of the protein, with which the membrane has 

 been treated, and is always slightly higher than that of the isoelectric 

 point of the protein used. 



3. The critical hydrogen ion concentration required for the reversal 

 seems to be, therefore, that concentration where enough of the pro- 

 tein lining of the membrane is converted into a protein-acid salt {e.g. 

 gelatin nitrate) capable of ionizing into a positive protein ion (e.g. 

 gelatin) and the anion of the acid used {e.g. NO3). 



