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of whitish matter. Solution of pure fixt alcalinc salt dis-solved very little of it: the liquor received a reddish browncolour, and the powder became blackish brown. Thisresiduum was attracted by the magnet after being madered hot, though not before: the alcaline tincture, passedthrough a filter, and mixed with solution of green vitriol,struck a deep brownish-black colour, nearly the same withthat which results from mixing with the vitriolic solutionan alcaline tincture of galls.

From these experiments it seems to follow, that thecolouring matter in the black mixtures is iron,- extricatedfrom its acid solvent in a highly attenuated or dividedstate, and combined with a peculiar species of matter, con-tained in astringent vegetables; which matter, after thewatery fluid that the compound floats in has been separated,,is in part extracted from the iron by alcaline liquors, andmay thence be again transferred into fresh dissolved iron.

The blackness is generally attributed to the iron beingbarely revived from the vitriol in its metallic state; theblack matter being supposed to be of the fame nature withthe impalpable black powder, into which fine iron filingsare changed by lying for many months under water. Butthis black matter differs from that of our mixtures in twovery material properties. It is attracted in its black state,by the magnet ■, and when moistened and exposed to theair, it changes speedily into rust. The resistance of oursto the magnet and to the air proceeds doubtless from thecombination of the other matter with the iron; and thereappears some analogy, in regard to the manner of production,between this black substance and Prussian blue,- one beinga precipitation and coalition of dissolved iron with onespecies of matter, and the other with another: the prin-cipal difference is, that the substance combined with theiron in the Prussian blue defends the metal from the action

of