APPENDIX 423 



The carboxyl group to the right of the dotted line is characteristic 

 of the acids. 



The oxidation may be carried on at each end of the line and the 

 divalent acids are thus produced 



O 



II II 

 H C C H Oxalic acid. 



If in the radical of one of these acids a hydrogen is replaced by 

 hydroxyl OH an oxi-acid is formed, thus : 



H H 



I I II 

 H C C C H Propionic acid 



may be converted to the two Lactic acids called (a) and (b) oxy- 

 propionic acid, according to the carbon which is oxidised 



H OH O 



I I I 

 H C C C O H 



I I 

 H H 



and 



OH H 



I II 



H C C C H 



H H 



Similar oxy-acids are formed from the divalent acids. 



BENZENE COMPOUNDS. 



An important series of carbon compounds contain a ring of six 

 carbons, each with an unsatisfied affinity, thus : 



_/ V 

 J L 



V 



When each hand holds a hydrogen, benzene is formed l 



