THE COLLOID-CHEMISTRY OF SOAP MANUFACTURE 191 



than the corresponding sodium soaps. But even after their 

 conversion into the sodium soaps, those made by the indirect 

 process have advantages not possessed by the sodium soaps 

 produced directly, the sodium soaps produced by the indirect 

 process being not only softer and smoother but being generally 

 more satisfactory in the matter of lathering and for washing 

 purposes than the straight sodium soaps. These advantages 

 are dependent upon the fact that through indirect manufacture 

 the potassium soap is not completely converted to sodium soap; 

 it continues to carry admixed a certain remnant of potassium 

 soap, the technologic advantage of which over the sodium soap 

 is particularly marked when the higher fatty acids are concerned. 



Advantage of these general truths continues to be taken in the 

 present day manufacture of the " shaving " soaps, which are 

 essentially only carefully neutralized soaps, which in addition to 

 sodium carry a certain amount of potassium as the base combined 

 with the fatty acids. Because of their content of potassium 

 soaps, especially of the higher fatty acids, the shaving soaps 

 lather more easily than the pure sodium soaps and are subse- 

 quently less likely to " dry on the face." 



Various patents and processes are known to the soap manu- 

 facturer in which fats and oils are first saponified with ammo- 

 nium hydroxid and the ammonium soap is then converted into 

 sodium soap through addition of sodium chlorid or sodium car- 

 bonate. The underlying principles are again the same; the advan- 

 tages of the resulting soap are again those of having admixed in 

 the sodium soap a certain amount of " more soluble " ammo- 

 nium soap. 



The reverse situation, namely, that of making a " more sol- 

 uble " soap from a less soluble one is illustrated in the P. KREBITZ 

 process of glycerin and soap manufacture. In this the fat or oil 

 is first converted into calcium soap by boiling it with caustic lime. 

 Tin* granular calcium soap thus produced is then changed i<> 

 sodium soap through tin- addition of ><>dium carbonate. As in 

 the previously described prOOQflf, in which a certain amount of 

 potassium is carried over, the re>uhant soap in this instance 

 carries over certain of the attributes of the original calcium soap. 

 Soaps made by this process are therefore dryer, more brittle, 

 and incline to be whiter than the corresponding pure sodium 

 soaps made directly from the same fatty acids. 



