180 SOAPS AND PROTEINS 



a concentration which will not in its turn salt out the soap, for 

 it is at all times the concentration and not the amount of alkali 

 (or other salt) in the entire soap/water system which determines 

 its salting-out effects. 



Given the qualitative composition of a fat, the upper limit of the 

 concentration of any hydroxid which may be used for its saponi- 

 fication is determined by the concentration at which the soap of the 

 highest fatty acid found in that fat is salted out at the temperature 

 prevailing in the soap vat. 



7. The Changes in Soap Systems Consequent upon Cooling 



The first change to be discussed as the temperature of a boiling 

 soap/water system is lowered (whether it contains glycerin or 

 not) is that of its tendency to change from what at the higher 

 temperature was a solution of soap-in-water to that which at the 

 lower is one of water-in-soap. The apparently contradictory 

 findings and views which different authors have recited covering 

 the nature of the changes observed may all be harmonized when 

 these changes from one system to the other (including the pos- 

 sible intermediates of an " emulsion " of hydrated soap in soap 

 water followed by one of soap water in hydrated soap) are kept 

 in mind. 



Beginning with the days of CHEVREUL, the soaps were held to 

 be salts of the fatty acids containing a definite amount of water 

 of crystallization which on solution in water yielded " solutions " 

 like all other salts. Many physical chemists held to this view 

 into the nineties of the last century, for pure and mixed soaps in 

 dilute solution showed an osmotic pressure, an electrical conduc- 

 tivity, a depression of the freezing point or elevation of the boiling 

 point quite like " normal " electrolytes. (JAMES W. McBAiN, M. 

 TAYLOR, C. C. V. CORNISH and R. C. BOWDEN, J McBAiN and 

 TAYLOR 2 ). Following the studies of F. KRAFFT and H. WiGLow, 3 



1 JAMES W. McBxiN, M. TAYLOR, C. C. V. CORNISH and R. C. BOWDEN: 

 Berich. d. deut. chem. Gesellsch., 43, 321 (1910); Jour. Chem. Soc., 101, 

 2041 (1913). 



2 McBAiN and TAYLOR: Zeitschr. f. physik. Chem., 76, 179 (1911); 

 since this time, however, these authors have modified their views; see 

 Jour. Am. Chem. Soc., 42, 426 (1920). 



3 F. KRAFFT and H. WIGLOW: Berich. d. deut. chem. Gesellsch., 28, 2573 

 (1895). 



