184 SOAPS AND PROTEINS 



1 



The grained or curd soap is obtained whenever enough sodium 

 chlorid is added for complete salting-out of the soap. Under such 

 circumstances the vat contents separate into two distinct phases; 

 an upper consisting in essence of pure soap containing very little 

 water and very little sodium chlorid, and a lower, in essence only a 

 strong sodium chlorid solution containing practically no soap. 



For the production of a settled soap a lower concentration of 

 sodium chlorid is used. Under such circumstances separation 

 into two phases also occurs. The upper is again essentially a 

 curd soap but it is less dry this time. Because of the larger 

 proportion of water the soap is smoother and of a more homogene- 

 ous structure. It also contains a larger fraction of salt. The 

 lower phase is still in essence a " salt solution " but because of 

 the less perfect salting-out of the soap (especially of those soaps 

 least sensitive to salt action) this phase still contains so high a 

 fraction of " dissolved " soap that on cooling it jellies. The soap 

 system as a whole represents what the Germans call " Kernseife 

 auf Leimniederschlag " and it is this system which FRANCOIS 

 MERKLEN l has studied in detail and to which he has applied the 

 phase rule. We question whether the true nature of the two phases 

 has been correctly understood by this author, scarcely a matter 

 of surprise when it is remembered that he worked throughout 

 with mixed soaps. In our judgment, the series of changes ob- 

 served and the nature of the two phases finally obtained seems 

 to be as follows. The concentration of sodium chlorid added to 

 the original soap solution is such as will salt out the various soaps 

 unequally well and only partially. The soaps most sensitive to 

 the presence of salt will obviously tend to come out first, whence 

 the upper phase or " curd " (rich in soaps of the higher members 

 of the acetic series, the oleates, linolates, etc., and relatively poor 

 in water) caught in the meshes of which is a certain amount of 

 salt water. The latter is responsible for the higher fraction of 

 salt found in settled soaps when compared with pure curd soaps. 

 Some soaps, especially those produced from the lower members of 

 the acetic series, remain in solution in the lower or salt water 

 phase but with time these, too, fall out of solution and become 



1 FRANCOIS MERKLEN: Etude surla constitution des savons du commerce, 

 Marseilles (1906). 



