Tannic acid

an acid occurring in oak bark and nut-galls, and in the bark of other trees, and which constitutes the astringent principle of these. It is obtained in a solid form by the action of ether on coarsely-powdered nut-galls, and in this form is white, not at all crystalline, is very soluble in water, and has a bitter, astringent taste. This acid has many important uses, as in tanning leather in oak bark and sumach, and in medicine, where it is used in its pure form as an astringent. Gregory.