Lectionary Calendar
Friday, March 29th, 2024
Good Friday
There are 2 days til Easter!
Attention!
Tired of seeing ads while studying? Now you can enjoy an "Ads Free" version of the site for as little as 10¢ a day and support a great cause!
Click here to learn more!

Bible Encyclopedias
Gallic Acid

1911 Encyclopedia Britannica

Search for…
or
A B C D E F G H I J K L M N O P Q R S T U V W Y Z
Prev Entry
Gallia Cisalpina
Next Entry
Gallicanism
Resource Toolbox

Trioxybenzoic acid (HO)3(3.4.5.) C6H2C02H

H20, the acidum gallicum of pharmacy, a substance discovered by K. W. Scheele; it occurs in the leaves of the bearberry, in pomegranate root-bark, in tea, in gall-nuts to the extent of about 3%, and in other vegetable productions. It may be prepared by keeping moist and exposed to the air for from four to six weeks, at a temperature of 20° to 25° C., a paste of powdered gall-nuts and water, and removing from time to time the mould which forms on its surface; the paste is then boiled with water, the hot 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 ice-cold water. The production of the acid appears to be due to the presence in the galls of a ferment. Gallic acid is most readily obtained by boiling the tannin procured from oak-galls by means of alcohol and ether with weak solution of acids. It may also be produced by heating an aqueous solution of di-iodosalicylic acid with excess of alkaline carbonate, by acting on dibromosalicylic acid with moist silver oxide, and by other methods. It crystallizes in white or pale fawn-coloured acicular prisms or silky needles, and is soluble in alcohol and ether, and in loo parts of cold and 3 of boiling water; it is without odour and has an astringent and an acid taste and reaction. It melts at about 200° C., and at 210° to 255° it is resolved into carbon dioxide and pyrogallol, C 6 H 3 (OH) 3. With ferric salts its solution gives a deep blue colour, and with ferrous salts, after exposure to the air, an insoluble, blue-black, ferroso-ferric gallate. Bases of the alkali metals give with it four series of salts; these are stable except in alkaline solutions, in which they absorb oxygen and turn brown. Solution of 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 gum, gelatin. Salts of gold and silver are reduced by it, slowly in cold, instantaneously in warm solutions, hence its employment in photography. With phosphorus oxychloride at 520° C. gallic acid yields tannic acid, and with concentrated sulphuric acid at 100°, rufigallic acid, C14H808, an anthracene derivative. Oxidizing agents, such as arsenic acid, convert it into ellagic acid, C 14 H 8 0 9 +H 2 0, probably a fluorene derivative, a substance which occurs in gall-nuts, in the external membrane of the episperm of the walnut, and prob ably in many plants, and composes the "bezoar stones" found in the intestines of Persian 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 local astringent action. So far is it from being an haemostatic that, if perfused through living blood-vessels, it actually dilates them. Its rapid neutralization in the intestine renders it equally devoid of any remote actions.

Bibliography Information
Chisholm, Hugh, General Editor. Entry for 'Gallic Acid'. 1911 Encyclopedia Britanica. https://www.studylight.org/​encyclopedias/​eng/​bri/​g/gallic-acid.html. 1910.
adsFree icon
Ads FreeProfile