Evidence of a Structure in Gelatin Gels. 261 



proteins on the acid side of the isoelectric point. Fig. 3 shows 

 the very marked differences which were obtained. 



In order to be perfectly sure that the shape or thickness of the 

 gelatin plate was not responsible for the differences in swelling, 

 portions of dried plates from 10-gram, 25-gram and 35-gram gels, 

 as well as portions of the "original" Bacto gelatin, were ground 

 and sieved, those particles passing through a 2-mm. sieve and 

 remaining on a i-mm. sieve being retained for experimental work. 

 A weighed quantity of these "granules" were placed in a Gooch 

 crucible and allowed to imbibe water. At frequent intervals the 

 crucibles were removed from the water, centrifuged at low speed 

 for 2 minutes in order to remove excess moisture and weighed. 

 Fig. 4 shows the form of the imbibition curves. 



In order to ascertain whether the lower imbibing capacity of 

 the gels containing the most gelatin might be due to the dehydrat- 

 ing effect of electrolytes in the gelatin "ash," which of course 

 would be present in increasing amount as the concentration of 

 the gelatin increased, a series of experiments was conducted in 

 which the swelling plates were allowed to imbibe in (1) the same 

 portion (100 c.c. of distilled water), and (2) in frequent changes of 

 distilled water. If electrolytes were present they should have 

 been dialyzed out in series (2). No differences in excess of experi- 

 mental error were observed ; in fact, a slightly greater imbibition 

 was noted in series (1). 



The effect of hydrogen-ion concentration upon the physical 

 state of gelatin has been pointed out by many investigators, but 

 it is not clear that we are dealing with any appreciable changes in 

 hydrogen-ion concentration. It is impossible to secure by direct 

 measurement the hydrogen-ion concentration of the dried gelatin 

 plates which are immersed in the distilled water, and we have no 

 means of being sure that it is identical with that of the gel from 

 which the plates were prepared. Electrometric measurements on 

 a 5 per cent, gel gave a P H of 5.19 and the same value was ob- 

 tained for the 10 per cent. gel. The higher concentrations of 

 gelatin were so viscous that electrometric determinations were not 

 attempted. Inasmuch as there was no change between the 5 

 per cent, and 10 per cent, gel we believe that it is safe to assume 

 an initial P H of approximately 5.2 for all gels before drying. This 



