THE COLLOID-CHEMISTRY OF SOAPS 155 



persion medium into another possessed of those characteristic 

 of a liquid hydrated colloid. 



From a gas and a liquid, as from two immiscible liquids, it 

 is possible, of course, to produce two types of systems represented 

 in the first instance by the dispersion of a gas in a liquid (a foam) 

 or of a liquid in a gas (a fog) and represented in the second instance 

 by the dispersion of the liquid a in b (as oil in water) or the dis- 

 persion of the liquid 6 in a (as water in oil). When one regards 

 as a whole the field of the dispersoids consisting of gas plus liquid 

 and similarly that of the dispersoids consisting of liquid in liquid, 

 one is quickly struck by the fact that lasting dispersions of gas 

 in liquid (foams) can be more readily produced than the opposite 

 type of system; while certain liquids a can be more readily 

 emulsified in a second b than vice versa. 



In trying to discover what is the first general relationship 

 which determines this behavior, it has seemed to us that a pre- 

 viously expressed opinion 1 covers the case satisfactorily. Other 

 conditions remaining the same, that material is dispersed within 

 any second which in response to mechanical deformation shows 

 the shorter breaking length. Our meaning may be illustrated 

 by reference to Figs. 91 and 92. When air and some liquid 

 like liquid hydrated soap are subjected to a deforming move- 

 ment (like the beat of a flail) it is obvious that the gas 



PPP PPP PPP PPP PPP P PPP Gna 



m ! Hydratod Sodium Oleate 



FI..I U ( .H. 



HydratrdSfxIium 

 FlGUKE 92. 



will " l>re,'ik" sooner than the liquid columns of hydrated soap. 

 The -oap will, in oilier words. le drawn into longer threads in- 

 coherent -in faces than will the air. in consequence of which 

 .is will liecnme eiiine-hed \\ithiii the hydrated colloid, and 

 a foam will result. 



What happen- in the case of two liquids i^ represented diairram- 

 dlv in I If the middle line of the diagram i< taken 



\1\i:ir. M M.I M\UI\N<> HI.., ;ml i':itty Dcgcn- 



N.w Yori l'.H7). 



