124 



LACTIC ACIDS. 



dinarily great emulsifying power of a mixture of bile, free fatty 

 acids and soluble soaps. The same decomposition takes place 

 when fats, more especially butter, turn rancid. 



III. ACIDS OF THE GLYCOLIC AND OXALIC SERIES. 



When one atom of hydrogen in ,a paraffin is replaced by 

 hydroxyl a primary monatomic alcohol is obtained ; if a second 

 atom is replaced a parallel series of diatomic alcohols may be pre- 

 pared, which are known as glycols. The replacement of a third 

 atom of hydrogen by hydroxyl yields the triatomic alcohols (e. g. 

 glycerin). Further, just as the monatomic alcohols yield acids 

 by oxidation, so also do the glycols ; but from the latter two series 

 of acids can be obtained, known respectively as the glycolic and 

 oxalic (succinic) series. Thus at first : 



Ethvl-glycol. Glvcolic acid. 



C 2 H 4 (OH) 2 -f- 2 = CH 2 (OH) . COOH.+ H 2 O. 



By further oxidation a member of the glycolic series can be 

 converted into a member of the oxalic series, thus : 



Glycolic acid. Oxalic acid. 



CH 2 (OH) . COOH + 2 = (COOH) 2 + H 2 O. 



The acids of the glycolic series are monobasic, those of the 

 oxalic dibasic. 



The following table exhibits the above relationships in a con- 

 venient form. 



GLYCOLIC ACID SERIES. 

 Lactic (hydroxy-propionic) acid. C 3 H 6 8 . 



This, after carbonic acid, is to the physiologist the most important 

 acid of the series. 



If lactic acid is regarded as derived from propionic acid 

 CH 8 . CH 2 . COOH, it may be noticed at once that two isomeric 



1 This acid is frequently classed in the preceding group of acids as the first of 

 the glycolic series. 



