CINCHO-TANNIC ACID

This acid is precipitated from a decoction of bark by acetate of lead, after the decoction has been freed from cinchona red by means of magnesia. If the cincho-tannate of lead thus formed be decomposed by sulphuretted hydrogen, and the solution carefully evaporated in vacuo, the acid may be obtained as an amorphous, hygroscopic substance, readily soluble in water. A ferric salt added to a solution of this acid imparts a greenish colour to it. Cincho-tannic acid is very soluble in water, but not in acids. Therefore a concentrated watery infusion (1 to 4) of Indian bark gives a precipitate upon the addition of strong hydrochloric acid. By this means a rough estimation may be formed of the amount of cincho-tannic acid in a sample of bark.