3907. To Obtain Gallic Acid from Tannin

3907.     To Obtain Gallic Acid from Tannin. Add a strong aqueous solution of tannic acid (tannin) to sulphuric acid, as long as a precipitate falls; collect the powder, wash, and dissolve it by the aid of heat in diluted sulphuric acid; boil for a few minutes, cool, and collect the crystals of gallic acid which will form in considerable quantity.

3908. To Distinguish Gallic Acid from Tannic Acid

3908.     To Distinguish Gallic Acid from Tannic Acid. Gallic acid does not affect solutions of gelatine, the protosalts of iron, or the salts of the alkaloids; but it produces a black precipitate with the sesquisalts of iron, which disappears when the liquid is heated.

3909. Pyrogallic Acid

3909.    Pyrogallic Acid. This acid, is formed in white, shining scales, inodorous, very bitter; soluble in water, alcohol, and other; fusible at 239° Fahr., and subliming at 410°. When quite pure, it has no action on litmus paper. It is used in photography. A solution of the crude acid mixed with a little alcohol imparts a fine brown color to the hair, but stains the skin also.

3910. To Obtain Pyrogallic Acid

3910.     To Obtain Pyrogallic Acid. It may be prepared by heating gallic acid (previously dried at 212° Fahr.) in a glass retort, by means of a chloride of zinc bath, to 410°, when the pure acid sublimes, and forms in crystals on the neck of the retort, and in the receiver, which should be kept well cooled.

3911. Tannic Acid, also called Tannin

3911.    Tannic Acid, also called Tannin. Pure tannic acid is solid, uncrystallizable, white, or slightly yellow; strongly astringent, but without bitterness; very soluble in water, less so in alcohol and ether, and insoluble in fixed or volatile oils. Its solution reddens litmus. With the bases tannic acid forms

Among the incompatibles of tannin are the alkaloids of opium, and it is altogether unavoidable that if solutions of them are brought together, a precipitate will form of tannates; also, if the preparation of opium contain saffron, as in acetum opii and Sydenham's laudanum, this will cause a further precipitation of the extractive of saffron. (See No. 3908 (To Distinguish Gallic Acid from Tannic Acid).)

3912. To Obtain Tannic Acid

3912.     To Obtain Tannic Acid. Expose nut-gall in fine powder to a damp atmosphere for 24 hours, then mix it with sufficient ether, previously washed with water, to form a soft paste. Set this aside, closely covered, for 6 hours; then envelope it quickly in a close canvas cloth, and obtain the liquid portion by pressing powerfully between tinned plates. Reduce the resulting cake to powder, mix it with sufficient ethe- shaken with 1/16 its bulk of water, to form again a soft paste, and express as before. Mix the liquids, and evaporate spontaneously to a syrupy consistence; then spread it on glass or tinned plates, and dry quickly in a drying closet. Put the dry residue in a well-stopped bottle.