JACQUES LOEB 



91 



free in the solution. The more acid we add, the greater the amount 

 of isoelectric gelatin transformed into gelatin-acid salt. We assume 

 that there is a definite equilibrium between the hydrogen ion concen- 

 tration of the solution, the amount of gelatin-acid salt formed, and 

 isoelectric gelatin. If this view is correct, it follows that at the same 



340 

 320 

 300 

 280 

 260 

 240 



^ 220 

 i 200 

 g 160 



.y ^^° 

 o 140 



B 



J5 120 

 o 



100 

 80 

 60 

 40 

 20 

 



pH2 



T 5 

 47 



Fig. 2. The ordinates indicate the osmotic pressure (in mm. of the height of 

 a column of the gelatin solution) of 1 per cent solutions of originally isoelectric 

 gelatin which have been brought to different pH by the addition of the acids used 

 in Fig. 1. The abscissae are the pH. The curves are practically identical, the 

 sHght differences at the summit being inside the range of the variation found for 

 the same acids. 



