CONSTITUENTS OF PLANTS 351 



figure. The ether vaporized from the flask A is condensed by 

 the cool water running through the condenser B and drops on the 

 substance in C. It dissolves the ether extract and returns to the 

 flask A, carrying the fat with it. It is then ready to be vaporized 

 again and extract a fresh quantity of fat. When the exhaustion is 

 complete, the ether is evaporated off and the fat is dried and 

 weighed. This method is liable to several sources of errors, as 

 follows : 



(1) Loss of volatile fatty acids during the drying of the sub- 

 stance or of the extract. 



(2) Oxidation of fats if the preliminary drying of the material 

 is carried out in the air. 



Fats and Oils. 1 The largest and the most important portion of 

 the ether extract of concentrated feeds is composed of fats and 

 oils. Fats are solid at the ordinary temperature, while oils are 

 liquid. They consist of ethereal salts, termed glycerides, which 

 are compounds of certain fatty acids with the tribasic alcohol, 

 glycerol, C 3 H-,(OH) 3 ; thus, the fat palmitin C 3 H 5 (C 15 H 31 COo) 3 , 

 is the glyceride of palmitic acid C 15 H 31 CO 2 H. When heated with 

 alkalies, fats form glycerol and salts of the fatty acids, which are 

 soaps. The process is called saponification. For example : 

 QH 5 (C ]5 H 31 C0 2 ) 3 + 3NaOH = C 3 H 5 (OH) 3 + 3 C 15 H 31 CO 2 Na. 

 Palmitin -|- Sodium hydroxide = Glycerol + Sodium palmitate. 



All fats are lighter than water and insoluble in it. When pure, 

 they are colorless, odorless, and neutral in reaction; under con- 

 tinued exposure to air, they begin to turn yellow, acquire a dis- 

 agreeable odor and taste, and become acid that is, the fat be- 

 comes rancid. The rancidity is due to partial decomposition of 

 the glycerides, fatty acids being formed which are partly oxidized 

 by the air to volatile substances having a disagreeable odor. 



Oils are divided into the non-drying oils, and the drying oils. 

 The drying oils, of which linseed oil may serve as an example, 

 are oxidized by the air to solid, varnish-like masses. They con- 

 tain linolin and linolenin, which are the glycerides of unsaturated 

 acids. The non-drying oils do not undergo this change. 

 1 See Lewkowitsch, Oils, Fats and Waxes. 



