40 



reagent can be easily shown with Donnan's pipette. ') (see § 7). 



It may seem arbitrary that where it appears that already traces 

 of TwiTCHKLL reagent considerably decrease the surface tension 

 between fat and water, it has been assumed in § 2, that those traces 

 cannot practically influence the solubility of the fat in water. Yet 

 this is by no means the case. In order to increase the solubility of 

 fat in water sufficiently a solvent for triglyceride would have to be 

 added to the waterphase, which mixes with water. Further the 

 waterphase would have to exhibit a certain (pretty considerable) 

 concentration of this solvent throughout its volume. For a substance, 

 however, which lowers the surface tension between fat and water 

 this need not be the case. For the action of a substance to lower 

 the surface tension is accoinpanied with adsorption at the surface 

 common to the two phases, in consequence of which such a sub- 

 stance, though if calculated over the whole mass, it is present only 

 in traces, can occur in pretty considerable concentration at the 

 common surface. It is exactly this surface layer that counteracts 

 the tendency of two colliding drops to join to one whole. '^) 



The same considerations are also valid for the saponification in 

 alcalic surroundings. Here the soap formed in the saponitication acts 

 so as to lower the surface tension between fat and water. 



We arrive therefore at the conclusion that in the saponification 

 in emulsion the reaction practically takes entirely place on the boun- 

 dary of the fat and the water phase. We may then apply the 

 equations of velocity holding in solution, when we take the fact 

 into account that the constant of velocity depends on the fineness 

 of the emulsion. 



§ 5. Measurements of velocity have been carried out by M. Nicloux '), 



who studied the saponification of cottonseecl oil by the aid of the 



ferment found in ricinus seed. He found for : 



1 a 



k = — log 



t a - a; 



a good constant especially at low temperature (15°). From this it 

 appears that in this case the fineness of the emulsion does not appre- 

 ciably change during the saponification and that the ratio of the 

 saponification velocities of the three glycerides is as 3 : 2 : 1 or as 

 1 : 00 : 00.") 



1) Z. f. phys. Chem. 31, 42 (1899). 



^) DONNAN loC. Cit. 



3) Saponification des corps gras (1906). 

 ^) See § 12. 



