THE COLLOID-CHEMISTRY OF SOAPS 115 



It does not matter for our purposes whether such union with 

 the " solvent " is brought about by the molecules or the ions or 

 any other derivatives of the salt. The solvates (hydrates) after being 

 formed then separate out in dispersed form in the potassium oleate. 



Diagrammatically the successive changes are illustrated in 

 Fig. 74. If, to simplify matters, we represent the original pure 

 potassium oleate solution as a homogeneous system * as indicated 

 in tube A of Fig. 74, the effect of adding some molecules of fixed 

 alkali or salt may be represented by the diagram marked B. 

 Hydration of the salt molecules has two effects: (1) It with- 

 draws water from the original potassium system and thus through 

 increase in the concentration of the potassium oleate tends to 

 stiffen the system. But this effect is probably not large as com- 

 pared with (2) the effects upon viscosity of the dispersion of one 

 material in a second. The increase in viscosity due to such sub- 

 division of one material in a second is observed under widely 

 varying circumstances. A good example for our purposes is that 

 represented by the increase in viscosity when one liquid (like 

 cottonseed oil) is emulsified in a second (like a soap solution). 

 The " mayonnaise " which results may become so stiff that it 

 will stand alone. But the same type of change is observed when 

 a dry sand (which " flows " readily) is mixed with a little water 

 and a mass results that can be molded. Even a gas subdivided 

 into a liquid will yield such " solid " structures as when air is 

 beaten into a liquid white of egg to yield a " foam." 



The viscosity of such diphasic systems and it is well to bear 

 in mind, in the case of the soaps, more particularly diphasic 

 systems consisting of one liquid dispersed in a second or of a 

 solid dispersed in a liquid increases with every increase in the 

 concentration of the internal dispersed phase and with every 

 decrease in the size of the individual dispersed particles. The 

 viscosity of an emulsion of liquid oil in liquid soap, for instance, 

 increases as more and more oil is beaten into the soap; on the 

 other hand, with a given amount of oil subdivide! into a given 

 volume of snip tli<> viscosity of the mixture is increased if the 

 previously coarse emul.-inn is made finer by " homogenizing." 



1 It is at least a diphaaic system as emphasised on page 09, but for our 

 purposes we will call it a monophasic one. 



r.-fi-renceii to the literature and specific studies of the emulsions see 

 MAUN II I isrHERand MAUINN <> HOOKER: Science, 41, 468. (1916); Fate 

 and Fatty Degeneration, New York (1917). 



