182 SOAPS AND PROTEINS 



While it is ordinarily thought that all the soups present in the mix- 

 ture of soaps in the soap kettle begin to separate out as soon as a 

 sufficient concentration of the salt has been obtained, the quan- 

 titative studies previously detailed show that this is by no means 

 the case. A concentration of salt, which will salt out the soaps 

 of the higher fatty acids of the acetic series will obviously be 

 reached sooner than one which will salt out the lower soaps. 

 While, for instance, a sodium stearate is salted out in the cold 

 ly a f) Bauine sodium chlorid solution, sodium laurate requires 

 a 17 Bum no salt water (C. STIEPEL l ). The general truth of this 

 law finds expression in the fact that after apparent total separation 

 of the mixed soaps as a curd from the spent lye, the latter still 

 contains some soap. But the contained soaps are essentially 

 those of the lower fatty acids. The curd per contra is relatively 

 poor in these. 



During the process of salting-out, a soap mixture frequently 

 " gums," " goes stringy " and tends to boil over, a situation 

 which the practical soap maker has learned to meet by rapidly 

 shoveling in more salt. The explanation of what happens is 

 found in the experiments on the salting-out of soaps. Before 

 complete salting-out is obtained the previously liquid soap mix- 

 tures tend to gel because of the emulsification within them of 

 salt-water. Through the addition of more salt, however, the 

 amount of this salt-water phase is increased and as this happens, 

 change in type of emulsion occurs the hydrated soap now becom- 

 ing dispersed within the salt-water as the external phase, and 

 the viscosity of the kettle contents falls. 



It is the common practice in the salting-out of soaps to add 

 dry salt to the soap kettle. This represents economy, of course, 

 from the point of view of the amount of salt needed, for it is the 

 concentration of the salt in the total volume of water present 

 which det ermines when the mixed soaps will " come out of solu- 

 tion." Solution of the crystals of salt in the soap kettle, how- 

 ever, takes time and even the shoveling in of more salt into the 

 soap kettle does not at once increase the concentration of dis- 

 solved salt. The use of a proper brine under such circumstances 

 would work better and more rapidly in bringing the soap kettle 

 contents to the safe side of the gelation point of the mixture. 



1 C. STIEPEL: Fette, Oele und Wachse, usw., 112, Leipzig (1911). See also 

 page 116. 



