134 CHEMISTRY OF PLANT LIFE 



atoms in their molecules, indicates a very great biological sig- 

 nificance of the chain of six carbon atoms. This has been alluded 

 to in connection with the discussion of the biological significance 

 of molecular configuration (see page 57) and will be mentioned 

 again in other connections. 



THE ALCOHOLS WHICH OCCUR IN NATURAL FATS 



Glycerol, as has been pointed out, is by far the most common 

 alcoholic constituent of natural fats and oils. This substance, 

 which is familiar to everyone under its common name " glycerine," 

 is a colorless, viscid liquid having a sweetish taste. It is a very 

 heavy liquid (specific gravity 1.27) which mixes with water in all 

 proportions and when in concentrated form is very hygroscopic. 



Glycerine is made from fats and oils by commercial processes 

 which clearly prove that the constitution of fats is as described 

 above. The fat is boiled with a solution of caustic soda and is 

 decomposed, the sodium of the alkali taking the place of the 

 glyceryl (CsHs) group, the latter combining with three (OH) 

 groups from the three molecules of alkali necessary to decompose 

 the fat. A sodium salt of the organic acid, or soap, and glycerol 

 are thus produced, and are separated by saturating the hot solu- 

 tion with common salt, which causes the soap to separate out as a 

 layer on the surface of the liquid, which, on cooling, solidifies 

 into a solid cake, which is then cut and pressed into the familiar 

 bars of commercial soap. From the remaining solution, the 

 glycerine is recovered by evaporation and distillation under reduced 

 pressure. Taking stearin, a common fat, as the example, the 

 reaction which takes place in the above process may be expressed 

 by the following equation: 



COO) 3 +3NaOH = 3Ci 



Stearin Sodium stearate a soap Glycerol 



This process, since it yields soap as one of its products, is 

 called " saponification." All fats, when saponified, yield soaps 

 and either glycerol or (more rarely) some of the other alcohols 

 which are described below. 



Glycerine is also prepared from fats by hydrolysis with super- 

 heated steam. Using olein, a glyceride which is present in olive 



