I. On some varieties of tannin

In two communications “On some Astringent Substances as sources of Pyrogallic Acid,” read before the London Chemical Society in the years 1842, 1843, I showed that the usual division of the varieties of tannin into two genera—to wit, those which give black, and those which give green precipitates with salts of iron,—though called in question by Berzelius, is still well-founded : and likewise, that these two genera consist of a great variety of species, which, though closely resembling each other in properties, are still dissimilar in nature ; the only instances in which the same species of tannin had been procured from two different plants, being those of nut-galls and sumach. Professor Strecker’s important observation made some seven years ago, that grape-sugar is produced when the tannin of gall-nuts is boiled with dilute sulphuric acid, seemed to render a further examination of the varieties of tannin desirable.