704 



DONNAN EQUILIBRIUM AND OSMOTIC PRESSURE 



H2O and since 1 liter of a 1 per cent solution of gelatin contains 10 

 gms. of gelatin, the molecular weight of gelatin should be expected to 

 be in the neighborhood of 25,000. The experiment just described 

 for gelatin phosphate was repeated for gelatin chloride, with similar 

 results. 



According to Dakin's^ recent analyses gelatin contains 1.4 per cent 

 phenylalanine. Since 1 molecule of gelatin cannot contain less than 

 1 molecule of phenylalanine and since the molecular weight of this 



TABLE V. 



Influence of Concentration of Albumin Chloride of pH of About 3.4 on the Osmotic 



Pressure. 



amino-acid is 165 the lowest possible molecular weight of gelatin is 

 11,800. If a molecule of gelatin contains two molecules of phenyl- 

 alanine, the molecular weight should be about 23,600. This would 

 be approximately the figure we might expect from the data of Table 

 IV on the assumption that the differences in the last two rows may be 

 considered to be the values of the osmotic pressure of the protein 

 particles. 



« Dakin, H. D., J. Biol. Chem., 1920, xliv, 499. 



