THE ■VOLATILE PABT OF PLANTS. 77 



The other acids of this series are mostly found in veg- 

 etable and animal fats or fatty oils. (See p. 85.) 



OxTPATTY Acids. — The acids of this class differ from 

 the corresponding fatty acids by having an additional 

 atom of oxygen, or by the substitution of OH for H in 

 the latter. There are two acids of this class that may be 

 briefly noticed, viz. : oxyacetic, or glycoUic acid; and oxy-, 

 propionic or lactic acid. ' 



Glycollic Acid, CaHiO, or HOCH^OOOH, exists in 

 the juices of plants (grape-vine), and like acetic acid may 

 be formed by oxidizing alcohol. 



Lactic, GsHsOs, or CHgCH (OH) COOH, is the acid 

 that is formed in the souring of milk, where it is produced 

 from the milk-sugar by a special organized ferment. It 

 is also formed in the "lactic fermentation" of cane- 

 sugar, starch and gum, and exists accordingly in sour- 

 k^aut and ensilage. 



The fatty and oxyfatty acids are monobasic, i.e., they 

 contain one carboxyl, COOH, and each acid forms one 

 salt only, with potassium, for instance, in which the hy- 

 drogen of the carboxyl is replaced by the metal. Thus, 

 potassium acetate is CHsCOOK. 



The oxyfatty acids are especially prone to form anhy- 

 drides by loss of the elements of water. Lactic acid 

 cannot be obtained free from admixed water when its 

 aqueous soluti(^s are evaporated, without being partially 

 converted into an. anhydride. Gentle heat up to 270° 

 changes it, with, loss of water, into so-called lactolactic 

 . acid,* CjHioOj, a solid, scarcely soluble in water, but that 

 slowly reproduces lactic acid by contact with water, and 

 dissolves in alkalies to form ordinary lactates. Lacto- 

 lactic acid, heated to 290°, loses water with formation 

 of lactide,] C6H8O4, a solid nearly insoluble in water, but 

 also convertible into lactic acid by waterj and into lactates 

 by alkalies. 



« 3 (CaHeOs) - CsH^Os + H^O t C,H„05 = C,H,0, + H,0 



