THE COLLOID-CHEMISTRY OF SOAP MANUFACTURE 179 



saponification. It may be stated as generally true that alkali 

 may be added in high concentration or in a single charge of the 

 theoretically necessary amount only to such liquid fats as cotton- 

 seed oil, castor oil, linseed oil, cocoanut oil or palm kernel oil. 

 When tallow, stearin or Japan wax soap is to be made, the alkali 

 must be added in several smaller charges and the concentration 

 of alkali in the individual charges must be lower. To give specific 

 examples the following may be cited. Linseed oil may be saponi- 

 fied by adding to it at once the requisite amount of sodium hy 

 dmxid at 24 to 28 Baume* (17.6 to 21.4 percent); cocoanut oil 

 will tolerate a first charge at 16 to 20 Baum6 (10.9 to 14.3 per- 

 cent). Against these figures tallow must, be treated with a first 

 fractional charge at 11 Baum6 (7.3 percent) succeeded by a 

 second at 12 to 15 Baum6 (8.0 to 10.0 percent). Even the 

 final charge may not safely exceed 20 Baum6 (14.3 percent). 

 What is the explanation for these empirically well known facts? 

 It is >wt a matter merely of the readier saponification of the lower 

 melting point fatty acids found in the oils or of the greater tendency 

 of the higher fatty acid soaps to hydrolyze. Were this the case, 

 then the higher concentrations of alkali should act best upon 

 ' he higher melting point fats, while just the opposite is the c;ise. 

 It is the greater sensitiveness of the soaps of the higher fatty acids to 

 salting-out effects (of the sodium hydroxid in this case) 1/7//V// 

 explains these empiric findings. The soaps of castor oil, linseed 

 oil and cocoanut oil can scarcely be salted out by sodium hydroxid 

 at any concentration, while the sodium palmitate, stearate, 

 arachidate, etc., formed from tallow. .Japan wax, etc., come out 

 in very low concentrations of alkali. 1 The use of larger volumes 

 of sodium hydroxid containing lower concent rations of the alkali 

 in the production of the tallow snaps means that the soap as 

 formed has more solvent present in which " to di while 



the concentration of alkali pre>ent in this solvent is not sufficient 

 to salt out the soap. The alkali added in a first char; 

 from the -ysieiii as it combines with the fat to make soap, in 

 consequence of which the second charge may be of higher concen- 

 tration for this is quickly diluted on entering the soap kettle by 

 the volume of water rarried in with the first charge. \Yith the 



of alkali used up in saponificat ion. the third ! 

 i- (jiiickly diluted with the water left from the previous charges to 

 Seepages 116 to 120. 



