On the other hand, if allowed to remain in contact with a second 
molecule of benz aldehyde, it oxidizes the second molecule of the 
aldehyde with the production of two molecules of benzoic acid, 
C 6 H 5 CO.O.OH + C 6 H 5 CHO = 2C 6 H 5 COOH ; 
or finally, if an oxidizable substance, such as indigo, be present, it 
oxidizes the indigo, with the production of benzoic acid and isatin, 
thus — 
C 16 H 10 X 2 O 2 + C 6 H 5 CO.O.OH = 2C 8 H 5 X0 2 + 2C 6 H 5 COOH. 
Hence when a solution of indigo is shaken with benzaldehyde both 
are oxidized, whereas the indigo alone is unchanged by molecular 
oxygen. 
