ON THE GELATION OF THE NATURAL 



EMULSOIDS 1 



By S. C. BRADFORD, B.Sc, 



The Science Museum, South Kensington , London 



The question of the structure of gels has long been a matter of 

 controversy. Perhaps the theory which has found the most 

 favour is that which considers them as systems of two liquid 

 phases persisting from the sol stage. However, Hatschek 

 [19 1 6] has shown, from the stress-elongation curve, that this 

 theory is untenable. Since it is now recognised that the dis- 

 tinction between the suspensoids and emulsoids is rather a 

 question of the affinity between the two phases than of the 

 solid or liquid state of the disperse phase, there seems to be the 

 less reason for refusing, as he indeed predicted, to extend 

 v. Weimarn's theory to the natural emulsoids and regard their 

 gelation as a crystallisation process. 



As early as 1835 M. L. Frankenheim suggested that these 

 bodies were aggregates of small crystals, and attributed their 

 density and easy solubility to the existence of pores. In 1879 

 it was proposed by K. v. Nageli that gels consisted of 

 molecular complexes, with crystalline properties, separated 

 by skins of water and forming meshes in which the water 

 was contained by molecular attraction. Since that time a 

 number of unsuccessful attempts have been made to devise 

 a geometrical structure which would account for the pro- 

 perties of gels. Any mathematical theory must, however, be 

 consistent with the considerations that (1) the elasticity of 

 gels varies considerably, some being practically inelastic, and 

 (2) that, if the structure is due to the action of the directive 

 forces of crystallisation, it would be likely to vary according to 

 the nature of the gel. The latter principle finds confirmation 

 from the work of Zsigmondy and Bachmann [191 2] on the 

 crystallisation (gelation) of sodium and potassium oleate, pal- 

 metale and stearate solutions. These considerations lead to 



1 Received March 12, 1917. 

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