Structure of Simpler Organic Compounds. 91 



The general formula of all these acids is C n H 2n 2 . The 

 higher ones, which are all " long-chained " derivatives (that 

 is, CH 3 -CH 2 -CH 2 . . . CH 2 -COOH),* are derived by the 

 " saponification " of fats and oils (see p. 181). In the higher 

 members of the series a large number of isomerides can be 

 obtained, and, as in the case of other homologous series, the 

 larger the number of carbon atoms, the greater the number 

 capable of existence. There is, however, a general syn- 

 thetical method for preparing these higher acids which will 

 be discussed later. There are, however, apart from the 

 acids derived from fats and oils, few of them which are of 

 any direct interest in connection with this subject. 



Formic acid, H C0 2 H, occurs in nature in ants, 

 stinging nettles, and other organisms, and is usually pre- 

 pared by heating glycerol (glycerine) with anhydrous 

 oxalic acid (see p. 106). The reaction is a somewhat com- 

 plex one, but the ultimate result may be expressed by the 

 equation 



The formic acid is separated from the crude product thus 

 obtained in the form of its lead salt by warming the 

 aqueous distillate produced in the reaction with litharge. 

 The salt (H-COO) 2 Pb is then produced, from which pure 



* For the meaning of " long-chained," see p. 50. 



