150 SOAPS AND PROTKINS 



2. The Emulsifying Properties of Soaps 



We wish now to discuss the ivJationsliip which exists between 

 the emulsifying properties of the different soaps and their hydra- 

 t ion capacity. Excepting as the concentration necessary for emulsi- 

 jicdtion /x different (usually higher) the same general truths hold for 

 (inulxijicntion, previously expressed for foaming. 



An emulsion is, by definition, a mixture of two immiscible 

 liquids in each other. But from any two liquids such as oil and 

 water, two types of emulsion may be prepared, the one consist \\\^ 

 of a subdivision of oil in water, the other of water in oil. Milk, 

 which readily mixes with water and wets a paper dipped into it, 

 may be cited as an example of the former. Butter, which will 

 mix with oil but not with water, which greases paper and imparts 

 an oily feel to the touch, may be cited as an example of the latter. 

 The type of emulsion important for an analysis of the emulsifying 

 properties of the ordinary soaps is that represented by the sub- 

 division of oil in water. 



In the discussion of emulsification we must also distinguish 

 between (a) the mere production of an emulsion and (b) its 

 stabilization after production. Just as in the case of foams, the 

 former represents essentially a mechanical process the one 

 liquid must by some means or other be divided into the second. 

 When we talk about emulsification or emulsifying agencies with- 

 out modifying clauses we usually mean methods or substances 

 through which an emulsion produced by mechanical means may 

 be stabilized. 



It has been shown previously 1 that an oil cannot be sub- 

 divided permanently into pure water, and that the so-called 

 emulsifying agents which make possible the permanent sub- 

 division of oil in water are hydrophilic (lyophilic) colloids. Among 

 the best representatives of this group are the soaps. As ordi- 

 narily employed for emulsification purposes the soaps are, of course, 

 mixed. The quantitative studies on the hydration capacities of 

 the different pure soaps outlined in the preceding pages, now 

 allow us to test out this whole concept of emulsification more 

 accurately. What is the relationship between the hydrophilic 

 properties of any soap and its emulsifying power? 



1 MARTIN H. FISCHKK ;md MARIAN O. HOOKER: Science, 43, 468 (1916); 

 Kolloid-Zeitschr., 18, 129 (1916); Fats and Fatty Degeneration, New York 

 (1917). 



