10 SOAPS AND PROTEINS 



2. Preparation and Gelation Capacities of Some Pure Soaps 



with Water 



Unless otherwise noted, we prepared all our soaps in exactly 

 the same way, namely, by neutralizing a definite weight (one 

 mol) of the pure fatty acid with a chemically equivalent amount 

 of the hydroxid, oxid or carbonate of the necessary metal in a 

 unit volume (one liter) of water, keeping the whole mixture at 

 the temperature of a boiling water bath until union between the 

 acid and base had been accomplished. Care was taken to prevent 

 or to make good any loss of water from the reaction mixture- 

 while in the bath. Under these circumstances we are dealing in 

 the end, of course, only with a unit weight of some pure soap in 

 the presence of a unit weight of water. This detail regarding 

 the histories of their preparation is of little interest from a 

 " chemical " point of view, but, since the soaps are " colloid," 

 it is of vital importance from a physical one and, therefore, in the 

 elucidation of the final result obtained. After we had prepared 

 our soaps, the reaction mixtures were cooled to 18 C. and the 

 yields of soap weighed. When the entire mixture became gelatin- 

 ous or solid we considered that all the water had been " absorbed " 

 by the soap. 1 When " free " water began to appear above the 

 soap, the weight of the theoretical yield of " dry " soap was sub- 

 tracted from the weight of the soap as produced, the difference 

 being expressed as percent of water "absorbed " by the soap in 

 terms of the weight of the theoretical " dry " yield. 



a. Soaps with Different Basic Radicals. We began our experi- 

 ments by preparing a series of linolates. The exact experimental 

 methods followed and the results obtained may be deduced from 

 Table II. The striking differences in the absolute amounts of 

 water taken up by these different soaps is readily apparent to the 

 naked eye. To illustrate the matter Fig. 1 is introduced. 



The different water-holding capacities of a series of oleates and 

 stearates is shown in Tables III and IV and Figs. 2 and 3. The 

 experimental procedure in their production was the one described 

 above. A comparison of these figures and findings with those 

 obtained in the linolate series is of interest because the three fatty 



1 This is really not the case, for what we actually determined was the 

 gelation point. How this differs from the hydration (or solvation) point will 

 become clear later. See page 74. 



