Structure of Simpler Organic Compounds. 159 



Hydroxy Acids. 



Salicylic Acid, C 6 H 4 (OH)(COOH), 1 : 2. This sub- 

 stance is important as a therapeutic agent and disinfectant, 

 and occurs in the form of its methyl ester in oil of winter 

 green. It is prepared synthetically on a large scale by 

 treating sodium phenate with carbon dioxide under 

 pressure. The substance, C 6 H 4 -0-COONa, forms first, and 

 then undergoes intramolecular change. Salicylic acid 

 dissolves in hot water, from which it separates on cooling 

 in colourless crystals, melting point 156. 



Gallic acid, C 6 H 2 (OH) 3 (COOH), has been already 

 mentioned (p. 157). 



