68 ORGANIC AGRICULTURAL CHEMISTRY 



the mixed compounds are characterized by possessing properties 

 distinctive of both classes of compounds represented. The 

 hydroxy-acids possess the characteristic properties both of the 

 alcohols and the acids. Because alcohols react toward strong 

 bases as acids it was at first supposed that these hydroxy-acids 

 were dibasic. They are not, however, dibasic unless they at 

 the same time contain two carboxyl groups. 



Lactic Acid 



The simplest acid of this group of importance to us is the 

 hydroxy-propionic acid, CH3 — CH(OH) — COOH. It is the 

 common acid produced by the souring of milk and known as 

 lactic acid. 



By methods of synthesis, which it will not be necessary to 

 enter into, lactic acid has been clearly proven to have the con- 

 stitution of hydroxy-propionic acid as given above. It is a 

 fact, however, that another acid known as hydracrylic acid also 

 has the constitution of hydroxy-propionic acid. According to 

 our ideas of isomerism the existence of these two isomeric acids 

 is readily explained. Two positions are possible in which we 

 may substitute the hydroxyl group in propionic acid. 



Propionic acid is CH3 — CH2 — COOH and we might obtain 

 either 



CH3 - CH(OH) - COOH or CHsCOH) - CH2 - COOH 



Ct-hydroxy-propionic acid /3-hydroxy-propionic acid 



These two compounds are distinguished as cc-hydroxy-propionic 

 acid, in which the hydroxyl group is united to the carbon atom 

 next to the carboxyl group, and ^^-hydroxy-propionic acid, in 

 which the hydroxyl is united to the carbon atom second from 

 the carboxyl group. By reactions which leave no doubt it 

 has been shown that hydracrylic acid is the ^-compound and 

 lactic acid is the ^-compound. 



The ^-hydroxy-propionic acid or hydracrylic acid we need not 

 discuss further. Lactic acid, however, possesses properties 

 which need further explanation and which bring us to the con- 



