THE COLLOID-CHEMISTRY OF SOAPS 



79 



gel or a liquid mixture) turns the liquid portion of the system a 

 bright red while the masses of soap floating in this liquid remain 

 pure white. 



The common explanation of what happens in these instances 

 is, of course, that of the physical chemists, who assume that in 

 the concentrated soap " solution " there is little hydrolysis of the 

 soap, while in the more dilute one such 

 hydrolysis is increased and, sodium hydroxid 

 being a stronger alkali than oleic acid is an 

 acid, an indicator at once betrays the excess 

 of hydroxyl ions. 



Without listing the objections which may 

 be raised against such an explanation 

 (which at best accounts for but a small por- 

 tion of what happens), it seems necessary, 

 in order to get a more satisfactory interpre- 

 tation of the whole picture, to call to mind 

 the physical constitution of the lyophilic 

 colloids as previously discussed in these 

 pages and, in the case of the soaps, to dis- 

 tinguish between the behavior of those por- 

 tions of such systems which have the com- 

 position water-dissolved-in-soap and those 

 which have the composition soap-dissolved- 

 in- water. The two are totally different, 

 and, while indicator methods may be used 

 in an attempt to analyze the latter, they 

 need not be (and are not) so applicable to 

 the former. The so-called concentrated soap 

 " solutions " are essentially solutions of the 

 solvent in the soap, while the more dilute FIGURE 60 



ones are systems of the opposite type, and 

 physico-chemical methods and the laws governing dilute solutions 

 may therefore be applied only to the latter. 



The correctness of these various dedu< -tions may 1>< tested by 

 the use of such an indicator as phenolphthalein upon solid soap 

 gels which, as previously emphasized, represent mixed systems of 

 soap-water in (solid) solvated-soap. If phenolphthalein is applied 

 directly to a fresh section of sodium stcarate, for example, the 

 framework of the gel (in other words, the watcr-in-soap portion 



