place in the process of gel formation from the 

 sols of lyophilic colloids. On the contrary, the 

 work of Bachmann and Zsigmondy and of Mc- 

 Bain has shown that in gelatin and in soaps, 

 and therefore probably in many other if not all 

 lyophilic colloids, there is no reversal of phases 

 in the formation of a gel, but merely an aggre- 

 gation of the colloidal particles— the disper- 

 sion medium in the sol is still the dispersion 

 medium in the gel. The conception of a rever- 

 sal of phases in the process of gelation owes its 

 origin to the earlier supposition that the lyo- 

 philic colloids are liquid-liquid, "emulsoid" sys- 

 tems, an idea which is not now held by such 

 chemists as Donnan, Freundlich, McBain and 

 Zsigmondy. One wonders, therefore, how far 

 we dare go in our phase reversal speculations 

 on the mechanism of permeability changes and 

 similar vital phenomena. 



The full account of the experimental data 

 here briefly reported will include a discussion 

 of the remarkable behavior of the emulsion 

 with a gelatose emulsifier. This is an emulsion 

 of the oil-in-water type and is reversible, in the 

 same direction with the hydroxide of either the 

 bivalent cation Ba or the monovalent cation Na, 

 but not with the salt of either cation. There 

 will also be published data on the possible in- 

 fluence of acidity on phase reversal. That pH 

 value is a factor in phase reversal is apparently 

 true in certain cases, but that it is the deter- 

 mining factor in other cases is certainly not 

 true. H-ion concentration must affect the 

 ability of an emulsion to reverse through acting 

 on the emulsifier — possibly the hydration power 

 of the emulsifier— consequently, the effect of pH 

 will differ in emulsions with different emulsi- 

 fiers, and this the experiments show to be true. 



William Seifriz 

 Osborn Botanical Laboratory, 

 Yale University 



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