264 



Scientific Proceedings (121). 



might be explained by a crystal structure where the crystals melt 

 or soften at the gelation temperature. The micelles would then 

 be formed by the solidification of crystals and later when micelle 

 touched micelle the hardened surface of the crystal would prevent 

 cohesion. We have recently shown 1 that a crystal gel may be 

 very dilute and yet possess considerable rigidity so that a crystal 

 structure is not incompatible with the properties of gelatin gels. 



These experiments likewise show the marked influence that 

 hysteresis may have on experiments where gelatin is involved. 

 This is particularly noticeable in Fig. 4 where uniform-sized par- 

 ticles prepared from gels of different concentration were used. 

 Inasmuch as a dried sheet of gelatin apparently reflects the struc- 

 ture of the original gel from which it was prepared, the production 

 of different samples of dry gelatin possessing uniform physico- 

 chemical properties would appear to be extremely difficult. It is 

 possible that these experiments may account for the differences 

 between the experimental data of various workers. 



It would be interesting to know whether alcohol precipitation 

 from sols of differing concentration produces gelatin particles of 

 uniform physico-chemical properties. It is our intention to in- 

 vestigate this problem in the near future. 



Addendum, March i, 1922. 



Since the above MS. was prepared, Sheppard and Elliott 2 

 have published on the same question. They do not find it neces- 

 sary to assume a gel structure and believe that the different swell- 

 ing rates are due to "casehardening" or surface drying effects. 

 We believe that our experiment where uniform sized gelatin 

 particles were employed excludes such an explanation and con- 

 sequently prefer to adhere to the structure theory outlined above. 



1 Gortner, R. A., and Hoffman, W. F., /. Amer. Chem. Soc, 1921, xliii, 2199. 

 1 Sheppard, S. E., and Elliott, F. A., J. Amer. Chem. Soc, 1921, xliv, 373. 



