OSMOTIC PRESSURE AND VISCOSITY 



237 



20C. and then kept at that temperature throughout the entire 

 experiment. The pH is that of the gelatin solution at the end of 

 the experiment. 



The middle curve represents an experiment in which 0.5 gm. 

 of the isoelectric gelatin in solution was replaced by 0.5 gm. of 



500 

 475 

 450 

 425 

 400 

 375 

 350 

 g 325 



| soo 



275 



P- 



250 



225 



200 

 o 

 175 



150 

 125 



Osr ioti 



2 



/ 



> 



sf, 



Y 



pH 1.6 16 2.0 2.2 24 26 25 3.0 3.2 3.4 3.6 3.8 40 42 4.4 4.6 



FIG. 70. A suspension of 1 gm. of a fine powder of gelatin in 100 c.c. of 

 water has practically no osmotic pressure (lowest curve), while a solution of 

 1 gm. of the same gelatin has a maximal osmotic pressure of over 500 mm. 

 (uppermost curve). A mixture of 0.5 gm. of powdered and 0.5 gm. of liquid 

 gelatin in 100 c.c. water has practically the osmotic pressure of the 0.5 per cent 

 liquid gelatin in 100 c.c. of water (middle curve). 



isoelectric powdered gelatin. The latter did not contribute to 

 the osmotic pressure, the observed osmotic pressure being due to 

 the isolated ions of the 0.5 per cent gelatin in solution which 

 determined the Donnan effect, and in addition to the gas pres- 



