110 SOAPS AND PROTEINS 



plete separation of the anhydrous soap from the dispersion medium. 

 Since the nature of the changes seen under these circumstances 

 covers the question of the theory of the " salting-out " process 

 in soap manufacture (as well as that of the salting-out process 

 in many other lines of chemical industry), and since many attempts 

 have been made to explain these changes, it is well to interrupt 

 our general argument here to review such theories, as far as they 

 are known to us, before proceeding further with suggestions of 

 our own. 



b. Historical Remarks on the " Salting-out " of Soaps. F. HOF- 

 MEISTER l recorded in 1888 what seem to be the first quantitative 

 studies in this field when, in studying the " water-attracting " 

 powers of various salts, he determined the minimal concentrations 

 in which they would bring about the separation of a soap from 

 its aqueous dispersion medium. Finding that the ordinary mixed 

 soaps gave inconstant results, he set out to discover the lowest 

 concentrations of various sodium salts necessary to bring about 

 a beginning turbidity in solutions of sodium oleate. In determin- 

 ing this point he noted that his soap solutions frequently jellied. 

 F. BOTAZZI and C. VICTOROW 2 detailed, some twenty years later, 

 the effects on viscosity of adding sodium hydroxid to a Marseilles 

 soap solution. Their soap (in essence sodium oleate) had been 

 dialyzed and contained in consequence free fatty acid and what 

 is commonly designated, since the work of F. KRAFFT and H. 

 WiGLOw, 3 " acid soap." 4 Addition of sodium hydroxid to such 

 dialyzed soap was found to be followed by an increase in viscosity 

 which at higher concentrations of the alkali gave way to a decrease. 



1 FRANZ HOFMEISTER: Arch. f. exp. Path. u. Pharm., 25, 6 (1888). 

 2 F. BOTAZZI and C VICTOROW: Accad. Lincei, 19 (1910), accessible only 

 as review in Kolloid-Zeitschr., 8, 220 (1911). 



3 F. KRAFFT and H. WIGLOW: Ber. d. deut. chem. Gesell., 28, 2566 (1895). 



4 If it is true, as generally supposed, that the fatty acids are monobasic it 

 becomes a difficult mental maneuver to figure out how a partial saturation 

 of the replaceable hydrogen is going to yield an "acid" soap. While the 

 concept is widely accepted, no one has ever isolated such an acid soap and 

 the only reason for believing in it seems to depend upon the fact that a clear 

 solution or jelly may be obtained when a fatty acid is only partially neutralized 

 with alkali in the presence of small amounts of water. But these are the ideal 

 conditions for the production of emulsions, the emulsions in this case consisting 

 of fatty acid in hydrated soap. When the indices of refraction of fatty acid 

 and of hydrated soap lie close together the mixture looks homogeneous. See 

 MARTIN H. FISCHER and MARIAN O. HOOKER: Science, 43, 468 (1916); 

 Fats and Fatty Degeneration, 29 and 100, New York (1917). 



