JACQUES LOEB 



559 



same as outside. The osmotic pressure of the 1 per cent gelatin 

 chloride solution, which was after 18 hours 435 mm. when no salt 

 was present, was only 63 mm. when the inside and outside solutions 

 were made up in m/32 NaNOs. 



Table I gives the influence of the concentration of NaNOs on the 

 osmotic pressure. It is obvious that the osmotic pressure diminishes 

 with the concentration of the salt. This phenomenon had already 

 been described by Lillie^ and by the writer.^ Donnan has shown 

 that this depressing effect of a salt on the osmotic pressure of a 

 colloidal solution is a necessary consequence of his theory of mem- 

 brane equilibrium, and this conclusion is supported by the following 

 experiments. 



TABLE I. 



Original inside solution, 1 per cent gelatin chloride of pH 3.5 made up in 

 various concentrations of NaNOs of the same pH. 



Outside solution, HCl of pH 3.0 made up in the same concentrations of NaNOs 

 of pH 3.0 as the inside solution. 



The writer undertook measurements of the potential difference 

 between the gelatin chloride solutions inside the collodion bag and 

 the aqueous solutions outside the collodion bag with the aid of a 

 Compton electrometer. It was found that the gelatin chloride solu- 

 tion was always positively charged while the outside aqueous solution 

 was negatively charged, as was to be expected. The second important 

 fact is that the p.d. diminishes with the increase in concentration of 

 the neutral salt added and (if the necessary corrections are made) in 

 approximately the same ratio as the osmotic pressure diminishes (lower 

 row in Table I). 



« LiUie, R. S., Am. J. Physiol., 1907-08, xx, 127. 

 ^ Loeb, J., /. Gen. Physiol., 1920-21, iii, 391. 



