These two are different
Gallic acid = 3,4,5-tri-hydroxybenzoic acid
Pyrogallol = 1,2,3-trihydroxybenzene (AKA pyro and pyrogallic acid)
Both readily available from chemical suppliers. Pyrogallol is normally in
fine feathery white crystals. In a chunkier crystal from it used to be
called pyraxe - there is no chemical difference.
Gallic acid is soluble around 1% in cold water and 33% in boiling.
Pyrogallol is pretty soluble. It also oxidises very rapidly, especially in
solution, and sodium sulphite is often dissolved in water before adding the
pyro to prevent this.
While we are on the pyros, should also mention:
pyrocatechin (1,2-dihydroxybenzene) also used as a developer,
pyroligneous acid (crude ethanoic acid - acetic acid to the non-chemist),
pyroxyline - gun cotton or collodion cotton (fun stuff to make and work
with but please don't try this at home.)
Peter
petermarshall@cix.compulink.co.uk