178 SOAPS AND PROTEINS 



!<>\\er fatty acids of the acetic series and the oleates, linolates, 

 etc., act best as emulsifying agents, for these yield liquid hydrated 

 colloids at the low temperatures prevailing in the reaction mixture. 

 When, however, soap manufacture is carried out at a higher 

 temperature it is obvious that soaps of the higher fatty acids 

 will act better, for at these higher temperatures the soaps of the 

 lower fatty acids will have " gone into true solution," thus losing 

 their hydrophilic character. While the soaps of the higher fatty 

 acids are solid in the cold process and of little use for emulsi- 

 fication purposes, they become liquid hydrated colloids at the 

 higher temperatures and stabilize any emulsion that may be 

 formed. 



It is of interest to examine microscopically the changes inci- 

 dent to this emulsification process. Fig. 95 shows the successive 

 changes observable when soap is made by the cold process from 

 cottonseed oil and caustic soda. After the two materials have 

 been stirred into each other as previously described for the middle 

 beaker of Fig. 93, a soap is rapidly formed (since cottonseed oil 

 usually contains some free fatty acid) in which the unused portions 

 of oil then become dispersed as shown in photomicrograph A 

 of Fig. 95. If a drop of this mixture is watched under the micro- 

 scope for a little time, the oil droplets are found to diminish in 

 size while becoming surrounded with an increasingly thicker halo 

 of hydrated soap. This is shown in B. The halo grows in thick- 

 ness until the whole alkali-fat mixture sets into a firm jelly, the 

 appearance at this stage being represented by C. In the course 

 of a number of hours or several days the whole reaction mixture 

 comes to chemical equilibrium, when it presents the more or 

 less uniform appearance of D. This final picture represents a 

 hydrated mixed soap in which the soaps of the higher fatty acids 

 tend to crystallize within the soaps possessed of lower melting 

 points. 



6. Concentration of Alkali and Method of Adding it for 

 Saponification 



We need now to go back over the course of soap making a 

 third time in order to analyze for a moment some of the practical 

 facts utilized in determining the method and the concentration 

 at which an alkali is added to different fats and oils for their 



