184 



THEORY OF COLLOIDAL BEHAVIOR 



TABLE XXXV. INFLUENCE OF NaCl ON OSMOTIC PRESSURE OF 1 PER 

 CENT GELATIN CHLORIDE SOLUTION 



4. THE INFLUENCE OF THE CONCENTRATION OF A PROTEIN 

 SOLUTION UPON THE OSMOTIC PRESSURE 



An increase in the concentration of a protein solution at the 

 same pH and in the absence of neutral salts should have a 

 double effect on the osmotic pressure. It should, first, raise the 

 osmotic pressure of the solution on account of the increase in the 

 number of protein particles in the solution; and it should, second, 

 lead to a further increase in osmotic pressure due to an increase 

 in the value of 2y + z 2x or 2y + z 2\/y(y + z), for it is 

 obvious that as long as y is constant, i.e., at constant pH of the 

 gelatin solution, the value of the term 2y -f z 2\/y(y -f z) 

 will increase with increasing z. The two effects can be separated 

 by subtracting the value of the term 2y + z 2x from the 

 observed osmotic pressure. The difference between the two 

 values should (within the limits of the accuracy of the experi- 

 ments) increase with the concentration of the protein. Both 

 expectations are fulfilled. 



Different concentrations of gelatin phosphate from 2 per cent to 

 0.5 per cent were prepared, all having a pH of 3.5. The gelatin 

 phosphate solutions were put into encollodion flasks of 50 c.c. 

 volume, each connected with a glass tube serving as a manometer 

 as described, and these flasks were put into beakers containing 

 350 c.c. of H 2 O, the pH of which was brought at the beginning of 

 the experiment to 3.5 through the addition of H 3 PO4. When the 

 bags containing gelatin phosphate solutions are put into water 



