262 



Scientific Proceedings (121). 



is slightly on the alkaline side of the isoelectric point of gelatin. 1 

 The hydrogen-ion concentration of the water in which the 

 plates were immersed was probably between Ph 5.0 and 6.0. 

 The water as it came from the still was a fair grade of conduc- 

 tivity water and was free from carbon dioxide and ammonia. 

 Naturally it afterward absorbed some carbon dioxide from the air. 

 Kendall 2 has recently presented data showing the rapidity with 

 which this takes place. According to his work distilled water is 

 about P H 57 when in equilibrium within the carbon dioxide of 

 laboratory air. We have tried a number of times to determine 

 the P H of distilled water, as used in these experiments, but have 

 failed to secure sharp readings on the potentiometer because of 

 the slight conductance of the water, our values ranging between 

 P H 5.0 and 6.o. 3 Colorimetric measurements of hydrogen-ion 

 concentration could not give accurate readings due to the fact 

 that the indicators are all acids or bases which have greater 

 ionizing power than has the water which is being measured. 



If we assume, therefore, that the hydrogen-ion concentration 

 of the dried gelatin plate is identical with that of the original gel 

 from which it was prepared, i.e., P H 5.2, and that the distilled 

 water was in equilibrium with the carbon dioxide of laboratory 

 air, i.e., P H 5.7, we should still have no appreciable effect of hy- 

 drogen-ion concentration on our experimental results for the same 

 water and gelatin were used in all experiments. We doubt whether 

 the above assumptions as to P H values are justified, but we do 

 feel that the differences in the swelling of dried gelatin plates which 

 we have described are not due primarily to differences in hydrogen- 

 ion concentration. 



Conclusions. — The above data appear to indicate that gelatin 

 gels have a structure and that this structure is more or less fixed 

 at the time that gelation takes place. It would appear that the 

 gelatin aggregates or micelles are more and more interlaced at 

 increasing concentrations of gelatin. This structure is apparently 

 not appreciably altered by drying at a temperature below the 



1 Loeb, J., J. Gen. Physiol., 1918, i, 39. 



2 Kendall, J., /. Amer. Chem. Soc, 1916, xxxviii, 2460. 



1 As a matter of fact the Ph of the distilled water is probably not an important 

 factor since the water is so feebly buffered that a mere trace of acid or alkali will 

 change the hydrogen-ion concentration through a wide range. 



