GELATION OF THE NATURAL EMULSOIDS 69 



If one regards the precipitated particles as consisting of 

 aggregates of amicroscopic crystals or filaments, the specific 

 surface would be so great that the volume of the compressed 

 surface layer of adsorbed liquid would be considerable and 

 would explain the contraction of the total volume of liquid 

 and gel and the evolution of heat during imbibition. The 

 amicrons may also be regarded as surrounded by a liquid 

 envelope due to the molecular cohesion between the liquid and 

 solid phases. From this point of view the phenomena exhibited 

 by gels should be influenced by the lyotrope series of dissolved 

 salts which affect the surface tension and the affinity of the 

 liquid and solid phases. The connection between adsorption 

 of solvent and imbibition, and the similar effect of the 

 Hofmann series on both, was pointed out by Lillie [1907]. 



If osmotic pressure is due, as Lillie suggests, to adsorption 

 of solvent by the dissolved particles, the osmotic pressure of 

 emulsoid sols should be decreased by salts in the order 

 CNS<I . . . <S0 4 as was found to be the case. The dimin- 

 ished pressure should hardly be caused by aggregation of the 

 sol particles, since the precipitating effect of the cations has not 

 commenced at the concentrations employed, although anions 

 hinder the precipitation in the opposite order [Pauli, 191 3]. 

 Hatschek found the same series for the clearing of oil emulsions. 

 The temperature of gelation should, however, be diminished in 

 the order CNS>I . . . >S0 4 as was found by Levites [1908]. 

 The change in viscosity with time [Schroder, 1903] follows in 

 the same way as due to a diminution in the precipitating 

 forces. If the velocity of crystallisation is reduced, aggregation 

 will be hindered and precipitation will not take place until 

 a lower temperature. Dialysis will leave a sol containing 

 smaller particles, the effect being similar to that of prolonged 

 heating. Similarly the elasticity of gels is increased by salts 

 which favour imbibition and vice versa. And the double 

 refraction of deformed sols shows the same lyotrope effect 

 [Lieck, 1904]. 



From these considerations the application of v. Weimarn's 

 theory to the gelation of the natural emulsoids appears to 

 account for most of the properties of gels, including their re- 

 markable hysteresis so suggestive of their connection with vital 

 phenomena, nor is the theory necessarily inconsistent with their 

 elasticity and the thermal anomaly of stretched gels, though, 



