ANIMAL LIFE AND ANIMAL PRODUCTS. FOODS 439 



The sodium palmitate or other soap is soluble in the water. When 

 common salt is added, however, the soap coagulates and separates 

 into a floating layer which solidifies on cooling. 



Soft soap is made with potassium hydroxide, and is composed 

 of the potassium salts of the organic acids. 



/ Manufacture of jfeoop. Soap is made in large iron caldrons. 

 These contain closed steam coils for heating, and pipes delivering 

 live steam, when needed, for stirring the mass. The fat is mixeoL 

 with quistic soda solution containing at first, only about one- 

 fourth of the total amount of the base that the above equation 

 requires. When, after heating and stirring, a uniform mixture 

 has been produced, the rest of the alkali is added gradually and 

 foe heating is continued until the reaction appears to be complete. 

 Salt is now dissolved in the mixture and the soap separates as a 

 curd. The curd floats, leaving the " spent lye," containing the 

 salt solution and much of the glycerine, in the lower layer. This 

 process is called salting out. ) 



When the process stops at this point, the upper layer is known 

 as curd soap, and may be dipped out and allowed to cool and 

 solidify. Most " Marseilles " soaps are curd soaps made in this 

 way. A large part of the imported " Castile " soaps are of the 

 same kind. 



Curd soaps contain salt, glycerine, adhering lye, and other 

 impurities. To prepare a purer soap, the spent lye is run off, 

 dilute brine is added to the soap, and the curd and brine are stirred 

 up. When separation has again occurred, the brine is run off 

 and the process repeated. Finally, some water is added, and 

 steam is run in until the curd mixes completely with the water. 

 When the solution stands, it " settles," that is, resolves itself once 

 more into two distinct layers. The upper layer is called settled 

 soap. The washing with brine and temporary dissolving in 

 water remove the impurities, and hence settled soap is the purest 

 variety. The greater part of the soap made in the United States J 



