PHENOLIC CONSTITUENTS 281 



C6H3(OCH3)2COOH, occurs together with the alkaloid vera- 

 trine in the seeds of Veratrum sahadilla. 



Protocatechuic acid is soluble in water and melts at 199°. 



Reactions. 



1 . Aqueous solutions of protocatechuic acid are precipitated 

 by lead acetate. 



2. It gives a green colour with ferric chloride ; on addition 

 of very dilute sodium carbonate the green colour changes first 

 to blue and then to red. 



3. Ferrous salts produce with protocatechuic acid a violet 

 colour. 



PYROGALLOL OR PYROGALLIC ACID. CgH3(OH)3. 



OH 



jOH 



^OH 



Pyrogallol 



This substance is so called because it is formed by heating 

 gallic acid according to the reaction — 



CeHoJOHJaCOOH = C6H3(OH)3 + COj 

 Gallic acid Pyrogallol 



It is also formed by fusing haematoxylin with caustic potash. 



Pyrogallol crystallizes in colourless needles or plates melt- 

 ing at 132° and is soluble in water; its solution, in excess 

 of caustic alkali, absorbs oxygen with great avidity, turning 

 brown and forming carbon dioxide, acetic acid and other 

 substances. 



Pyrogallol reduces salts of silver, mercury, or gold to their 

 respective metals. 



Reactions. 



1. Pyrogallol is precipitated from solution by lead acetate 

 but not by lead nitrate. 



2. It gives a blue colour with ferrous sulphate and a red 

 colour with ferric chloride. 



3. Aqueous or alcoholic solutions of pyrogallol, in common 

 with those of gallic acid or tannic acid, are coloured purple 

 by iodine. 



