Note 512 — PHARMACOLOGIA. (continued 4)
Reading edition
Seguin first proved that gallic acid, and tannin or the astringent principle, are different substances; it is to the former that the property of giving a black colour to the solutions of iron is owing.
Mr. Hatchett has shewn that tan or tannin may be artificially produced by the action of nitric acid upon various vegetable substances.