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GALLIC ACID

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Originally appearing in Volume V11, Page 418 of the 1911 Encyclopedia Britannica.
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GALLIC See also:

ACID , trioxybenzoic acid(HO) (HO)3(3 .) C 6H2CO2H•H2O, the acidum gallicum of See also:pharmacy, a substance discovered by K. W. See also:Scheele; it occurs in the Leaves of the bearberry, in See also:pomegranate See also:root-bark, in See also:tea, in See also:gall-nuts to the extent of about 3 %, and in other See also:vegetable productions. It may be prepared by keeping moist and exposed to the See also:air for from four to six See also:weeks, at a temperature of 20° to 25° C., a See also:paste of powdered gall-nuts and See also:water, and removing from See also:time to time the See also:mould which forms on its See also:surface; the paste is then boiled with water, the hot See also:solution filtered, allowed to cool, the separated gallic acid drained, and purified by dissolving in boiling water, recrystallization at about 27° C., and washing of the crystals with See also:ice-See also:cold water. The See also:production of the acid appears to be due to the presence in the See also:galls of a ferment. Gallic acid is most readily obtained by boiling the See also:tannin procured from See also:oak-galls by means of See also:alcohol and See also:ether with weak solution of acids. It may also be produced by See also:heating an aqueous solution of di-iodosalicylic acid with excess of alkaline carbonate, by acting on dibromosalicylic acid with moist See also:silver See also:oxide, and by other methods. It crystallizes in See also:white or See also:pale fawn-coloured acicular prisms or silky needles, and is soluble in alcohol and ether, and in too parts of cold and 3 of boiling water; it is without odour and has an astringent and an acid See also:taste and reaction. It melts at about 200° C., and at 2100 to 215° it is resolved into See also:carbon dioxide and See also:pyrogallol, C6H3(OH)3. With ferric salts its solution gives a deep See also:blue See also:colour, and with ferrous salts, after exposure to the air, an in-soluble, blue-See also:black, ferroso-ferric gallate. Bases of the See also:alkali metals give with it four See also:series of salts; these are See also:stable except in alkaline solutions, in which they absorb See also:oxygen and turn See also:brown. Solution of See also:calcium bicarbonate becomes with gallic acid, on exposure to the air, of a dark blue colour.

Unlike tannic acid, gallic acid does not precipitate albumen or salts of the alkaloids, or, except when mixed with See also:

gum, See also:gelatin. Salts of See also:gold and silver are reduced by it, slowly in cold, instantaneously in warns solutions, hence its employment in See also:photography. With See also:phosphorus oxychloride at 12o° C. gallic acid yields tannic acid, and with concentrated sulphuric acid at See also:roe, rufigallic acid, C14H808, an See also:anthracene derivative. Oxidizing agents, such as See also:arsenic acid, convert it into ellagic acid, C14H809+H20, probably a See also:fluorene derivative, a substance which occurs in gall-nuts, in the See also:external membrane of the episperm of the See also:walnut, and ;probably in many See also:plants, and composes the " bezoar stones " found in the intestines of See also:Persian See also:wild goats. Medicinally, gallic acid has been, and is still, largely used as an astringent, styptic and haemostatic. Gallic acid, however, does not coagulate albumen and therefore possesses no See also:local astringent See also:action. So far is it from being an haemostatic that, if perfused through living See also:blood-vessels, it actually dilates them. Its rapid neutralization in the See also:intestine renders it equally devoid of any remote actions.

End of Article: GALLIC ACID

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