Origin

Gallic acid is procured from galls, either through the gallic acid fermentation which these undergo when exposed, in the state of powder, to water and atmospheric air, or through the reagency of sulphuric acid.

Sensible and Chemical Properties. The acid is in delicate, silky, acicular crystals, colourless when quite pure, somewhat brownish as commonly kept in the shops, inodorous, of an acidulous slightly astringent taste, sparingly soluble in cold, but freely in hot water, very soluble in alcohol, and slightly soluble in ether. It produces a deep bluish-black colour with solutions of the salts of sesquioxidc of iron, but has no effect on that of sulphate of the protoxide, and differs from tannic acid in not causing precipitates with gelatin, albumen, or salts of the organic alkalies.

Effects on the System

In small doses, gallic acid produces no sensible effect when swallowed, and, in the largest ever given for medical purposes, is said to occasion only a feeling of internal heat. Externally applied, it produces little of the corrugating effects characteristic of the sstringent.

Therapeutic Application

This substance has but recently been em-ployed as a medicine. Formerly supposed to be the active principle of the vegetable astringents, though not used in the isolated state, it lost this reputation almost entirely upon the discovery of the much greater astringency of tannic acid; and it is only within a few years, that it has partially recovered its original credit.

There can be no doubt of its great inferiority to tannic acid in affections of the skin, alimentary canal, and all those parts with which the medicine can be brought into direct contact. But, not having those chemical relations which render the absorption of tannic acid as such impossible, it may enter the circulation, and thus reach all parts of the system; and, as tannic acid may possibly be converted into gallic acid before being absorbed, and through this agent produce all its general effects upon the system at large, the inference is not unreasonable, that the latter medicine might, perhaps, be substituted for the former, without disadvantage, in all cases in which the effects are to be produced through admixture with the blood. We might go further, and calculate upon results even more favourable from the gallic than the tannic acid; as, independently of its more ready entrance into the circulation, it is less apt to disturb the stomach and constipate the bowels, and thus to interfere with digestion. Experience, however, upon these points is not yet settled; and, though gallic acid has been of late much employed, very different opinions have been given of its powers. These remarks on the relative efficiency of gallic and tannic acids, have reference only to the latter acid as it is procured from galls.

The complaints in which gallic acid may be most advantageously given are the hemorrhages, and especially those proceeding from parts which are conveniently accessible only through the circulation, as haemoptysis, haematuria, and Menorrhagia or uterine hemorrhage. In the last-mentioned affection it is thought to have proved peculiarly efficacious; and in haematuria it might reasonably be expected to be so, as it passes out of the system through the kidneys. In all these complaints, it has the great advantage of being quite destitute of irritant or general stimulant properties, at least in medicinal doses, and it is not improbable that it is somewhat sedative to the circulation, or refrigerant, like many other vegetable acids. The power has been claimed for it of arresting, in some degree, the escape of albumen from the blood in cases of albuminous urine; and it has been employed with supposed benefit in simple diuresis, and in chronic mucous discharges from the urinary organs. It has been found, moreover, one of the most effective remedies in cases of chylo-serous or spontaneously coagulable urine.

The dose is from five to twenty grains three times a day. It may be given in the form of pill, made with conserve of roses, or with syrup and powdered gum arabic; in the form of powder; or in liquid mixture.