THE COLLOID-CHEMISTRY^OF SOAPS 151 



In order not to lengthen this discussion unduly, the experi- 

 mental facts in the case may be summed up as follows: those soaps 

 nn the best emulsifying agents which at the temperature of their use 

 ami in the presence of water yield essentially liquid systejns of the 

 type water-dissolved-Jn-soap. For this reason the oleates, lino- 

 lates, etc., are, of all the soaps studied, the best emulsifiers at 

 ordinary (room) temperatures because, besides having high hydra- 

 tion values, they are liquid. 



The sodium soaps of the acetic acid series when used in equi- 

 molar concentration show the following characteristics. The soaps 

 of the lowermost members through the caproate yield no perma- 

 nent emulsions. If a sodium caprylate or sodium caprate/water 

 system is kept just above its liquefaction point, a permanent 

 emulsion may be obtained. A slight rise in temperature, how- 

 ever, makes for separation of the oil from the water phase. The 

 same is true for the sodium soaps of the higher fatty acids. At 

 low temperatures sodium myristate, sodium palmitate, sodium 

 stearate, etc., in water do not emulsify, but if the temperature 

 of these mixtures is raised so that the soaps " go into solution " 

 (in reality yield liquid colloid systems of the type water-dissolved- 

 in-soap) permanent emulsions can be obtained at once. With 

 too great increase in temperature, however, the emulsions again 

 crack, and the oil separates off. 



In interpretation of these general findings it may be said that 

 the lowermost soaps do not emulsify because they yield only true 

 solutions of the soaps in the water. The systems, in other words, 

 have no hydrophilic properties or, put another way, the water 

 in them is essentially "free" and permanent emulsifieation of 

 oil in such " free " water cannot be obtained. \Yith the develop- 

 ment of distinctly hydrophOk properties by the soapfl in the middle 



of the series emuUifiralinn lnTonies possible, luit only while 4 the 

 systems are liquid and of the type water-dissolved-in-soap. Only 

 slight further increase in teni|MTatmv. however, i^ necessary in 

 ;ise of soaps like the caprylate and raprate to carry them 

 through this region into the realm of the true solutions of soap 

 in water, and as this happens pennanent cmuLsification again 

 becomes impossible. 



Similar facts hold for the soaps of the higher fatly acids. 

 An nil earmot be emulsified in any <>f these higher soaps 



possessed of a high hyd ration capacity as long as they arc 



