1911 Encyclopædia Britannica/Pyrogallol
PYROGALLOL, or Pyrogallic Acid, a trioxybenzene, C6H3(OH)3 (1: 2: 3), prepared by Scheele in 1786 by heating gallic acid, C6H3(OH)3CO2H. It is also obtained by heating para-chlorphenoldisulphonic acid with potassium hydroxide. It forms white plates, melting at 132°, readily soluble in water, and subliming without decomposition. It is an energetic reducing agent, a property utilized in its application in gas analysis to absorb oxygen, and in photography (q.v.) as a developer. The aqueous solution is turned bluish black by ferrous sulphate containing a ferric salt. It does not combine with hydroxylamine, as does the isomeric phloroglucin which yields a trioxide (see Polymethylenes). Pyrogallol dimethyl ether is found in beechwood tar. Pyrogallol has antiseptic properties and is employed medicinally in the treatment of psoriasis. Eugallol, or monacetyl pyrogallol and lenigallel, or triacetyl pyrogallol, are also used.