JACQUES LOEB - 689 



outside solution. 



- H+ concentrated 



- CI" dilute 



membrane 



inside solution. 



H+ dUute + 



Cl~ concentrated + 



The facts of this last chapter prove beyond doubt that the equa- 

 tion x^ — y (y -{- z) is the correct expression for the Donnan mem- 

 brane equilibrium between acid-salts of proteins with monovalent 

 anion and water. The close analogy between the variation of the 

 membrane potentials and the other osmotic properties of solutions 

 of protein-acid salts, such as osmotic pressure, viscosity, and swelling, 

 suggests that an attempt be made to derive the variations of these 

 latter properties directly from the equation for the Donnan equilib- 

 riimi. This has already been done by Procter for the swelling of 

 gelatin chloride. 



SUMMARY. 



1. It is shown that a neutral salt depresses the potential difference 

 which exists at the point of equilibrium between a gelatin chloride 

 solution contained in a collodion bag and an outside aqueous solu- 

 tion (without gelatin). The depressing effect of a neutral salt on 

 the P.D. is similar to the depression of the osmotic pressure of the 

 gelatin chloride solution by the same salt. 



2. It is shown that this depression of the p.d. by the salt can be 

 calculated with a fair degree of accuracy on the basis of Nernst's 

 logarithmic formula on the assumption that the p.d. which exists at 

 the point of equilibrium is due to the difference of the hydrogen ion 

 concentration on the opposite sides of the membrane. 



3. Since this difference of hydrogen ion concentration on both 

 sides of the membrane is due to Donnan's membrane equilibrium 

 this latter equilibrium must be the cause of the p.d, 



4. A definite p.d. exists also between a solid block of gelatin chlo- 

 ride and the surrounding aqueous solution at the point of equiHbrium 

 and this p.d. is depressed in a similar way as the swelling of the gela- 

 tin chloride by the addition of neutral salts. It is shown that the 

 P.D. can be calculated from the difference in the hydrogen ion concen- 

 tration inside and outside the block of gelatin at equilibrium. 



