72 SOAPS AND PROTEINS 



saturation point is attained, the soap particles assume not only 

 molecular size but more than molecular size. By definition, 

 therefore, we approach with falling temperature the realm of the 

 colloids, or that of dispersions of one material in a second with the 

 degree of dispersion showing dimensions greater than molecular. 

 The gradual increase in the size of the soap particles (or increase 

 in their number) with lowering of the temperature is represented 

 by the regions B, C, D, E and F in the two diagrams. 



Thus far we have explained merely the production of a colloid 

 system by the ordinary process of bringing about supersaturation 

 and an agglomeration of particles previously more highly dis- 

 persed. It is obvious that such agglomeration may yield either 

 a lyophobic (or so-called suspension colloid) or a lyophilic (or 

 so-called emulsion colloid). The lyophobic colloid results when the 

 solvent is not soluble in the precipitating phase; the lyophilic colloid 

 when the solvent is soluble in the precipitating phase. When soap 

 falls out of solution from such a solvent as allyl alcohol the former 

 of these possibilities is realized; when it falls out in water, alcohol, 

 toluene, benzene, etc., the latter is realized. The black circles in 

 the diagram of Fig. 48 or the black crystal masses in Fig. 49 

 represent more therefore in the latter instance than a mere pre- 

 cipitate of pure soap; they are this, plus a certain amount of the 

 water, alcohol or other " solvent " dissolved in them. 1 



At a sufficiently low temperature the soap aggregates will have 

 become so large or so numerous as to touch and coalesce. If this 

 process continues to a sufficient extent the system will ultimately 

 represent, in essence, nothing but soap in which the previous 

 " solvent " has been dissolved. This situation is represented 

 diagram matically by the zone Z of Figs. 48 and 49. 



A study of Figs. 48 and 49 shows, however, that between the 

 upper extreme (A) of a solution of the soap in the solvent and the 



1 We do not here distinguish between such "dissolved" water and water 

 of crystallization. Obviously both values are included. While we have no 

 desire to trespass upon the fields of theoretical chemistry we feel strongly 

 compelled to the view that "solution" always means (chemical) union between 

 solvent and dissolved substance. In the "dilute" solutions this effect is 

 largely lost sight of, however, because of the large overplus of the pure 

 "solvent," the properties of which then continue to dominate the whole 

 system. The union between solvent and any substance X need not, more- 

 over, be of one kind only. When phenol dissolves in water one type of union 

 between the two is accomplished; when water dissolves in phenol the combi- 

 nation is a totally different one. 



