SOAP 199 



ing with alkali, the fat disappears into solution ; it is changed 

 into the sodium salt (soap) and glycerine. Both of these 

 are soluble; but when salt is added to the solution the soap 

 is "salted out/ 7 and floats on top of the solution. It is then 

 skimmed off, pressed, and cut into cakes. 



FIG. 196. 



Modern Way of Making Soap. The kettle is three stories high, and holds perhaps 275,000 

 Ibs. : enough to make, say, 700,000 bars of soap. Courtesy of Swift and Company. 



In many modern soap factories (Fig. 196) the fat is 

 first heated with steam. The products are then glycerine 

 and the fatty acids. The soap is made from the fatty acids 

 and sodium carbonate (instead of the hydroxide). Gly- 

 cerine is a very valuable " by-product " of the soap fac- 

 tory. 



Until a few decades ago soap was made in the home. In the spring 

 the winter's accumulation of wood ashes was pounded down into a 

 barrel, and set on a platform to be " leached," or extracted by water. 

 A hole was made in the ashes, water was poured into it, and the solu- 



