The Burning of Sponge, Burnt Sponge

Cut the sponge in pieces, and bruise it, so as to free it from small stones; burn it in a close iron vessel, until it becomes black and friable; afterwards reduce it to a very fine powder.

This medicine has been in use for a considerable time, and employed against scrofulous disorders and cutaneous foulnesses, in doses of a scruple and upwards. Its virtues probably depend on the presence of a little alkali. It also contains charcoal; and its use may be entirely superseded by these substances, which may be obtained in other manners, at a much cheaper rate.

Source: The Edinburgh New Dispensatory, Andrew Duncan