46 FATS, OILS, AND WAXES 



Being free from glycerides the waxes, when heated, give 

 110 sfnell of acrolein ; they do not become rancid like the fats, 

 and are less easily hydrolysed, but they can be decomposed 

 by prolonged heating with alcoholic potash. 



Owing to the high molecular weight of their constituent 

 acids, the saponification value of waxes is low. 



Saponification Value. 

 Carnauba wax ...... 79-95 



Waxes are further characterized by giving abnormally 

 high values for the unsaponifiable residue. 



WAXES. 



As already stated (p. 22) all fats and waxes on saponifica- 

 tion with caustic alkalis yield a certain amount of substance, 

 known as the unsaponifiable residue, which is insoluble in the 

 alkaline solution remaining after hydrolysis and may be ex- 

 tracted therefrom by means of ether. This material in the 

 case of fats is composed chiefly * of a group of alcohols known 

 as sterols, while in the case of waxes it will include in addition 

 the higher saturated alcohols. 



The sterols may occur in the uncombined state in fats, 

 or combined with fatty acids as esters. The sterols form a 

 group of highly complex hydro-aromatic monohydric secondary 

 alcohols whose constitution has not as yet been completely 

 determined. They fall into two main groups, the cholesterols 

 and the phytosterols which are characteristic of the animal 

 and vegetable world respectively. 



REACTIONS AND PROPERTIES OF CHOLESTEROL AND 



PHYTOSTEROL. 



Cholesterol. 



Cholesterol is a monohydric alcohol of the formula 

 C27H45OH ; its constitution is still unknown, although a 

 great deal of work has been expended on this question ; 



* It may be mentioned that the unsaponifiable residue of fats contain 

 also the fat soluble vitamin A when this substance is present. 



