360 4 GALLIC ACID. 



position even at this temperature ; its solution reduces 

 an alkaline solution of copper and an ammoniacal solu- 

 tion of silver ; and gives a green reaction with iron 

 chloride. It is decomposed in alkaline solution in con- 

 tact with the air. 



4. Hydrocaffeic acid, C 9 H 10 O. Is produced by 

 the action of sodium-amalgam on a hot solution of caf- 

 feic acid. Colorless, rhombic crystals ; easily soluble 

 in water; the aqueous solution is colored an intense 

 green by iron chloride, this turning to a cherry-color 

 on the subsequent addition of sodium carbonate. Its 

 salts are amorphous, decompose readily in a moist con- 

 dition in contact with the air, and reduce solutions of 

 copper and silver. 



d. Monobasic, Tetratomic Acids. 

 Gallic Acid. 



P 7 TI 6 O 5 = P 6 TT 2 



L ( CO.OH. 



Occurrence. In gallnuts, in mango kernels, in divi- 

 divi (fruit of Ccesalpina coriaria), in tea, in the bark of 

 the root of the pomegranate tree, and in several other 

 plants. 



Formation and preparation. From gallotannic acid 

 by boiling with dilute acids or alkalies, and by keep- 

 ing the solution in contact with the air ; by heating 

 diiodosalicylic acid with an excess of an alkaline car- 

 bonate at 140-150 ; and also probably by evaporating 

 a solution of bromprotocatechuic acid (p. 356) in an 

 excess of potassa-ley. 



Properties. Crystallizes from water in fine prisms of 

 a silky lustre with one molecule of water of crystalli- 

 zation ; soluble in 100 parts cold, in 3 parts of boiling 

 water, easily in alcohol ; fuses by about 200, and is 

 resolved into carbonic anhydride and pyrogallol (p. 310) 

 at 210-220. The aqueous solution reduces solutions of 

 gold and silver, throwing down the metals, and yields 

 a blue-black precipitate with iron chloride. Its salts 



