SURFACES 37 



and its stabilization. The making of an emulsion is essentially a 

 mechanical process concerned with the mere obtaining of the sub- 

 division of one liquid in a second, as oil in water. The problem of 

 the stabilization, after such a subdivision has been brought about, 

 is a totally different matter. In a certain sense the main feature in 

 this stabilization consists of the getting rid of the water as such in the 

 emulsion and substituting for it a hydrated colloid. 



An emulsion is stabilized through any so-called emulsifying agent 

 only because this emulsifying agent is a hydrophilic (lyophilic) col- 

 loid. Oil, for example, cannot be permanently emulsified in water 

 in amounts exceeding a fraction of one per cent, but in a medium in 

 which the water is bound to an emulsifying agent as a hydrate (or 

 solvate) the oil content can be carried to a very high figure (50 or 60 

 per cent) . When, for example, acacia is used as an emulsifying agent, 

 it means that the permanent emulsion is made permanent because 

 the acacia unites with the water to form an acacia-hydrate. 



After the stabilization of an emulsion has been accomplished 

 through the production of a colloid hydrate, secondary concentration 

 effects may be brought about which lead to a concentration of the 

 colloid material upon or in the surface of the oil droplets but these 

 secondary effects are not to be confused with the primary ones neces- 

 sary for the stabilization of the emulsion. 



W. D. BANCROFT asserts in a review of FISCHER'S book that there 

 are no criteria which these alleged compounds (the solvates) could 

 satisfy. J. of Ind. & Eng. Ch., vol. 9, No. 12, Dec., 1917. 



BANCROFT observed that while soaps of mono-valent cations used 

 as emulsifying agents for oil and water, promote the formation of 

 emulsions like cream, in which oil is dispersed in a continuous water 

 phase, soaps of di- and tri-valent cations form emulsions of the 

 opposite type like butter, in which water is dispersed in oil. BAN- 

 CROFT considers that soaps of sodium or potassium, being readily dis- 

 persed in water but not in oil, form an interfacial film or membrane, 

 the surface tension on the water side of which is much lower than on 

 the oil, and that consequently an emulsion of oil in water is formed, 



soap. Free water, in consequence, appears in the mixture, and the oil separates 

 out in gross form, as described above, for only very little oil can be permanently 

 subdivided in "pure" or "free" water. We describe the consequences of such 

 changes from highly hydratable to less'hydratable soaps upon the stability of an 

 emulsion on p. 49. 



Neither do we wish our statement that an agreement is possible between 

 CLOWES' and our views on simple emulsions to be expanded to include his beliefs 

 regarding the biological behavior of the fat in living cells. We long ago gave up 

 the notion of lipoid membranes about cells and the complex notions of their 

 changing permeability to which CLOWES and many authors still hold." 



