<unk>  is an organic<unk> , also known as 3,4,5-trihydroxybenzoic<unk> , found in<unk> llnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H2(OH)3CO2H.<unk>  is found both free and as part of tannins. It is commonly used in the pharmaceutical industry.<unk>  can also be used to synthesize the hallucinogenic alkaloid mescaline, also known as 3,4,5-trimethoxyphenethylamine.
Salts and esters of<unk>  are termed<unk> llates.<unk>  was one of the substances used by Angelo Mai among other early investigators of palimpsests to clear the top layer of text off and reveal hidden manuscripts underneath.  Mai was the first to employ it, but did so "with a heavy hand," often damaging manuscripts for future study.
Gallic acid
Cholic acid
Beta-carotene
Glycolic acid
Thiamin
Thiol
Biotin
Lipoic acid