JACQUES LOEB 



373 



this causes the drop in the curves for the osmotic pressure of the 

 gelatin, since the free HBr, being able to diffuse through the collodion 

 membrane, cannot cause any increase in osmotic pressure. The drop 

 begins usually when pH becomes <3.3 and the drop is the more con- 

 siderable the more pH falls below this level. 



The correctness of this view is proved by the fact that if we wash 

 away the traces of free acid left in the capillary spaces between the 

 particles of gelatin after the process of draining, by perfusing the 



Isoelectric 

 Rejjion ol Gelatin -Br point Region ot Gelatin 



X M 128 ,M| 51! 1024 ffl« fflW 

 pM U 14 l& iO 15*' 4.4*^.9 54 6X 6.6 63 70 7.1 



Figs. 5 and 6. Same curves as in Figs. 3 and 4 except that the gelatin after 

 the acid had been allowed to drain off was washed once with 25 cc. of H2O. 

 Parallelism between curves for Br number, conductivity, osmotic pressure (Fig. 

 6), viscosity, and swelling from pH = 4.7 to pH = 3.0. No Br found for 

 pH ^ 4.7. 



gelatin on the filter with 25 cc. of HoO, and if we allow the water to 

 drain off also before we make up the gelatin into a 1 per cent solution 

 in distilled water, the drop will disappear, as is obvious from Figs. 5 

 and 6. In Fig. 6 the drop has disappeared, the pH going only to 

 3.3, and in these curves there is as complete a paralleHsm between 

 the bromine number and the osmotic pressure of the gelatin solution 

 as the strict validity of the theory of van't Hoff demands. We still 

 observe the drop for the curves for viscosity and swelling, but the pH 

 in these cases falls below 3.3; namely, to 2.2 (Fig. 5). 



