592 



REVERSAL OF SIGN OF CHARGE 



ions Na and H of the solution on the negative charge of the mem- 

 brane. The drop of the curve at the alkaline end (pH = 10 to 12) 

 is due to the high concentration of the cations Na and K, the latter 

 introduced with the KOH added. 



Collodion membrane not treated with protein 



rTenbranes char^ ^ed 



ne gatii/ely 



10 11 12 



Fig. 7. Collodion membranes not treated with protein. No reversal of sign of 

 charge of membrane. 



VI. Theoretical Remarks. 



Collodion membranes treated with oxyhemoglobin in the way men- 

 tioned remain red after they are washed, showing that the treatment of 

 the membrane with a protein solution results in the formation of a dur- 

 able protein film at the surface of the collodion membrane and probably 

 also in the interstices of the membrane, since traces of oxyhemoglobin 

 or at least of red pigment diffuse out of the membrane. Applying 

 Werner's idea concerning the combination between acid and NH3 to 

 proteins we should expect that acids are added to an amino-acid 

 group of a protein in a way similar to that in which they are added to 

 NH3; namely (if the acid added is HNO3), by forming a salt of the 

 /HNO3 



type R - N / - 



which dissociates into a positive R — NH3 ion 



