THE COLLOID-CHEMISTRY OF SOAPS 5 



Another variable is represented by (3) the water. It must 

 be constantly borne in mind that soap manufacture is carried out 

 in the presence of relatively little water. As ordinarily expressed, 

 soap making proceeds in a highly concentrated reaction mixture. 

 Not without its important influence is the presence of (4) the alco- 

 hol (glycerin) split off in the process of manufacture. A final 

 variable that must be considered in the ordinary process of soap 

 manufacture is (5) the temperature. Many soaps can be made, 

 and are made, at ordinary temperatures or by the " cold " proc- 

 ess; more commonly, however, they are " boiled." 



The so-called TWITCHELL process of soap manufacture differs 

 from the above only in the fact that instead of the neutral fats 

 (in other words, glycerids or esters) the free fatty acids are used. 

 In this process the original fat is first broken into fatty acids and 

 glycerin, and the separated fatty acids are brought by themselves 

 into the soap kettle. To them is then added an appropriate 

 hydroxid, and the soap is made. Fundamentally, however, the 

 variables in the reaction mixture are, from both a chemical and a 

 physical standpoint, essentially those already listed, except that 

 glycerin is missing. 



The conversion of a neutral fat (or of a fatty acid) into soap 

 requires time. However, if the reaction has been carried to com- 

 pletion, and if no excess of any of the ingredients has been 

 employed, it is obvious that the final mixture in the soap kettle 

 must consist of (1) water, (2) alcohol (glycerin) and (3) soap. 

 The soap must be examined (a) from the point of view of the fatty 

 acids which it contains, and (6) from that of the basic radical or 

 radicals which it may hold. This fundamental process of soap 

 manufacture is complicated, however, by a procedure which 

 introduces a new variable into the general problem and which, 

 in consequence, requires special analysis. This is (4) the " salting- 

 out " process. In the manufacture of the ordinary washing 

 soaps, for example, the fat with its added alkali or the fatty acid 

 with its requisite alkali is boiled until soap formation is assumed 

 to be complete. There is then added either (a) a great surplus of 

 the alkali (like -odium hydroxid) or more commonly (b) a neutral 

 salt. Usually sodium chlorid is shoveled int.<> the soap kettle. 

 As generally expressed, the excess of alkali or the presence of the 

 sodium chlorid makes the snap " insoluble " in the " lye," where- 

 fore it " grains " and floats to the top of the boiling soap mixture. 



