76 LIPIDES (fats and RELATED SUBSTANCES) 



Glycerol, C3H5(OH)3 



During and after World War I, considerable quantities of glycerol, 

 or glycerine as it is commonly called, were produced by a yeast fermenta- 

 tion process. Today, however, it is obtained mainly as a by-product of 

 the soap industry. The liquors that remain after the soap has been 

 removed are distilled in a vacuum, and by a series of fractionations 

 glycerol is obtained free from impurities. In many cases the glycerol 

 is not removed from the soap. If left in, it tends to make the soap 

 transparent and of better quality. A process for the manufacture of 

 glycerol from certain petroleum fractions has also been developed. 



Glycerol is a viscous, colorless liquid that has a sweet taste and no 

 odor. It is extensively used in the manufacture of nitroglycerine, an 

 ester of glycerol and nitric acid, C3H5(N03)3, which is the basis for a 

 large number of explosives such as dynamite, blasting gelatin, etc. Nitro- 

 glycerine also finds use as a drug for alleviation of the severe pain asso- 

 ciated with some types of heart disease. Glycerol is also widely used 

 as a solvent in many technical operations. It is extensively used in 

 the manufacture of cosmetics and toilet and pharmaceutical prepara- 

 tions. It can be used both internally and externally with perfect safety 

 and, in fact, can be utilized as a food by human beings. 



The saturated fatty acids 



Saturated fatty acids contain all the hydrogen with which they are 

 capable of uniting, whereas unsaturated fatty acids contain carbon atoms 

 joined together by double bonds and hence can unite with more hydrogen. 



Thus it may be seen from the following graphic formulas that butyric 

 acid is saturated and crotonic acid is unsaturated: 



H H H O 

 I I I II 

 H— C— C— C— C-O-H 



I I I 

 H H H 



Butyric acid 



H H H O 



I I I II 

 H— C— C=C— C— 0-H 



I 

 H 



Crotonic acid 



Saturated acids have a higher melting point than unsaturated fatty 

 acids with the same number of carbon atoms. Hard fats, such as tallow, 

 give a high percentage of saturated acids, and soft fats, a low percentage. 



