190 \rs AM) l'i;oi KINS 



When half molar" solutions " of sodium and potassium oleale 

 are studied under similar circumstances the values differ as 

 follow-: 



Na K 

 Oleate 86 81 



11. The Conversion of One Soap into Another 



The fact previously stated that one metal will never com- 

 pletely displace the metal from another soap but that the system 

 will merely tend to the production of a state of equilibrium 

 between the two has long been taken advantage of in various 

 ways in practical soap manufacture, both in the direction of the 

 production of a less " soluble " soap from a more soluble one 

 and vice versa. 



Under the first heading may be cited the production of sodium 

 soaps from potassium soaps. While the process has been largely 

 discarded, it remains an interesting illustration of how, empiri- 

 cally, good methods are followed even when the reasons for the 

 practices are imperfectly understood. Especially in the manu- 

 facture of sodium " tallow " soap was it long considered best 

 to start its production through the addition of caustic potash 

 to the " tallow." After the fat was converted into potassium 

 soap, this was changed into sodium soap and subsequently salted 

 out through addition of sodium chlorid. It is self-evident that 

 the procedure in reality represents the production of a potassium 

 soap followed by its (partial) decomposition to sodium soap 

 through addition of the sodium salt, and the subsequent salting- 

 out of this mixed potassium-sodium soap by the excess of sodium 

 chlorid mixed with the potassium chlorid formed through double 

 decomposition. The process has been largely discarded in this 

 country because of the high cost of potassium hydroxid and 

 the lower cost of sodium hydroxid, but it is a question whether 

 in so doing something of advantage in the quality of the soap 

 produced has not also been sacrificed. The " tallow " soaps 

 (and still more those now produced from hydrogcnated cotton- 

 seed and other oils) are soaps rich in the higher fatty acids (espe- 

 cially palmitic and stearic) and to produce in the soap kettle 

 the potassium soaps of these compounds is to produce such as 

 are decidedly more soluble (and hence more quickly obtained) 



