THE COLLOID-CHEMISTRY OF SOAPS 73 



lower extreme (Z) of a solution of the solvent in the soap, there 

 (MM two main zones of mixed systems, one below the upper (B, 

 C, D and E) consist i MI: of a dispersion of solvated-soap in the 

 soaped-solvent, and a second above the lower (F, X, W and V) 

 consisting of soaped-solvent in the solvated-soap. These two 

 mixed systems are in essence " emulsions " (if both phases are 

 liquid) or "suspensions" (if at least one phase is solid) but of 

 opposite types; and as such (even when of the same quantitative 

 ch finical constitution) are possessed of totally different physical / 

 properties. The former corresponds, for example, to an emulsion / 

 of oil-in-water or a suspension of quartz-in-water; the second toi 

 an emulsion of water-in-oil or a system of water-in-quartz. And V 

 as the former (as illustrated by milk) will mix with water, wet ^ 

 paper and show a certain viscosity value, the latter (as illustrated 

 by butter) will mix only with oil, will grease paper and show an 

 entirely different viscosity. 1 



Returning to the lyophilic soaps and the diagram, it is obvious 

 that as we descend, with lowering of temperature, from the region 

 A, we pass, in the regions B, C and Z), through increasingly viscid 

 liquid colloid " solutions," but all of them emulsions or suspen- 

 sions of the type solvated-soap in soaped-solvent. In the region 

 E, the particles of solvated soap almost touch, and here the highest 

 liiuil i viscosity is obtained. In F they do touch and now form 

 a continuous external phase. At this point we change to the 

 opposite type of emulsion or suspension the previously liquid 

 colloid becomes solid, or, as we say, it gels. As we shall show 

 later 2 the two types of system not only have different physical 

 constants but behave differently toward such added materials as 

 indicators. 



See in this connection MARTIN H. FISCHER and MARIAN O. HOOKER 

 Science, 41, 468 (1916); Ms <-HKK: Fat* and Fatty Degeneration, 



20, New York (1917). 



See page 77; alao MM. UN li II-HKK: Science, 49, 615 (1919); 

 r, 17, 271 (1919). 



