276 



COLLOIDS AND ELECTROLYTES 



gelatinate which had 6.4 cc. of m/4 NaOH in 100 cc. was clipped into 

 a beaker with water which had 6.4 cc. of m/4 NaOH per 100 cc. of 

 H2O. Since a small part of the NaOH inside the collodion bag had 

 combined with the gelatin, the concentration of NaOH in the outside 

 solution was at first slightly greater than that inside, and as a conse- 

 quence some NaOH diffused from the outside into the bags. Part 

 of the NaOH in the outside solution was gradually neutralized by 



240 



Cone of NaOH ° -Il-llilil-n.-l:lliliil 



^^uiiu.u| iMQwii 4000 2000 1000 500 250 125 62 31 15 

 pM 4.7 5.1 5.3 7.9 104 11.6 12.0 122 124 



Fig. 1. Curve of osmotic pressure of 1 per cent Na gelatinate solutions con- 

 tained in collodion bags and surrounded by solutions of NaOH of the same con- 

 centration as that in which the isoelectric gelatin was dissolved. Abscissa are 

 the logarithms of concentration of NaOH in which the isoelectric gelatin was 

 dissolved; below is given the pH of the gelatin solution at the conclusion of the 

 experiment (4i hours after beginning). The osmotic pressure rises steeply at 

 first until the pH is about 8.4, and then when more NaOH is contained in 

 solution the osmotic pressure falls again equally steeply with a further increase 

 in concentration of NaOH added. 



