CHEMICAL COMPOSITION OF PLANTS 47 



Fats are complex esters of glycerin and fatty acids either of 

 the saturated or unsaturated series having the general formulas 

 CnH2n02, CnH2n-202, CnH2n-402. Saturatcd aclds, such as 

 stearic and palmitic, give solid fats, while unsaturated acids, 

 such as oleic, linoleic, and linolenic, form mostly liquid fats. 

 Natural oils, found in seeds, are composed mostly of a mixture 

 of different fats. In this connection, it is of interest to note 

 that in plants of warm climates fats with a higher melting point 

 predominate, e.g., the oil of cacao, coconut, and other tropical 

 products; but in plants of a temperate zone, such as hemp, flax, 

 poppy, and others, liquid unsaturated fats predominate. Unsat- 

 urated fats are easily oxidized in the air, usually forming a hard 

 film on the surface; hence, they are called ''drying oils'' and 

 are used in the manufacture of oil paints. 



Through the action of alkalies and acids, fats are easily 

 hydrolyzed, even at low temperatures, through the addition of 

 3 molecules of water and breaking up into glycerin and a fatty 

 acid. 



The hydrolysis of palmitin, the fat of palm oil, for instance, 

 proceeds according to the following formula: 



C3H5(Ci6H3i02)3 + 3H2O — ^ C3H5(OH)3 + 3C16H32O2. 

 Palmitin Glycerin Palmitic acid 



This process is known as ''saponification." It is applied in 

 industry in the manufacture of soap (sodium palmitate, etc.) 

 and glycerin. 



As reserve substances, fats have a number of important 

 advantages over carbohydrates. Being insoluble in water, they 

 readily become inert reserve substances, thus entirely disappear- 

 ing from the sphere of other reactions and processes going on in 

 the cell. Being liquids, they can completely fill the tissues of 

 reserve organs. Moreover, they do not contain hygroscopic 

 water, of which 15 to 20 per cent is present in reserve carbo- 

 hydrates as a useless weight in dry seeds. Finally, they contain 

 very little oxygen and consequently upon oxidation develop a 

 large amount of heat per unit weight. When 1 g. of fat is 

 oxidized in the organism, or outside of it, there is obtained on 

 the average 9.3 cal. of heat, while 1 g. of protein will give 5.7 cal. 

 and 1 g. of starch only 4.1 cal. These properties make oils 

 extremely valuable reserve substances, and hence it is but 



