262 OILS AND [CH. XI 



siderable. The oils and fats will always be mixtures of 

 glycerides of fatty acids or of free fatty acids or of both. 



It is not necessary to attempt the separation of the 

 acids, which is a difficult and complicated operation ; it will 

 suffice to determine the amount of substances which can 

 be saponified by potash, and the glycerin produced in 

 saponification. 



Oils and Fats. 



Qualitative examination (of benzene extract). 



Distil off the greater portion of the solvent, transfer 

 the residue to a dish and completely evaporate the 

 remainder of the solvent on a water bath or in a steam 

 oven. 



Note the character of the residue, whether liquid, solid, 

 or semi-solid, etc. 



Warm the residue on a water-bafch with strong potash 

 solution for about one hour, dilute with water and filter if 

 necessary (the portion of the residue which remains 

 undissolved is probably resins and terpenes). To the hot 

 solution add hydrochloric acid until litmus shows acidity, 

 and allow to cool. 



The free fatty acids will generally solidify in a cake on 

 cooling but may remain liquid, in either case they can 

 easily be separated by filtering through a wet filter-paper. 



The acid filtrate is examined for glycerin (it will 

 contain considerable quantities of potassium chloride) by 

 evaporating to the smallest possible volume on a water- 

 bath and applying the following tests for glycerin to 

 portions of the residue. 



