GALL-NUTS. Excrescences produced by the cz/nips, a small insect which depo sits its eggs in the tender shoots of the Quercus infectoria, a species of oak abun dant in Asia Minor. When the maggot is hatched it produces a morbid excres cence of the surrounding parts, and ulti mately eats its way out of the nidus thus formed. The best galls are imported from Aleppo and Smyrna ; their princi pal ingredients are tan and ga]lic acid. The infusion of galls affords a dense white precipitate in solution of jelly, and a black precipitate with the persalts of iron. The latter property leads to the use of galls in the manufacture of ink and black dye ; they are also used as an as tringent in medicine.
Galls consist principally of three sub stances ; tannin or tannic acid; yellow extractive ; and gallie acid. Their decoc tion has a very astringent and unpleasant bitter taste. 'The following are their ha bitudes with various re-agents : Litmus paper is powerfully reddened. Proto-chloride of tin produces an Isa bel-yellow precipitate.
Alum ; a yellowish precipitate. • Acetate of lead ; a thick yellowish white precipitate.
Acetate of copper ; a chocolate brown precipitate.
Ferric sulphate (red sulphate of iron); a blue precipitate.
Sulphuric acid ; a dirty yellowish pre cipitate.
Acetic acid brightens the muddy de coction.
The galls of the Quercus Cerris and common oak are of a brown color, prickly on the surface, and irregular in shape and size. They are used chiefly for tan ning in Hungary, Dalmatia, and the southern provinces of the Austrian states, where they abound.
Tannin or tannic acid is prepared as follows :—Into a long narrow glass adopt er tube, shut at its lower orifice with a cotton wick, a quantity of pounded galls are put, and slightly pressed down. The tapering end of the tube being inserted into a matrass or bottle, the vacant upper half of the tube is filled with sulphuric ether, and then closed with a ground glass stopper. Next day there will be found in the bottle in two distinct strata, of which the more limpid occupies the upper part, and the other, of a sirupy consistence and amber color, the lower. More ether must be filtered through the galls, till the thicker liquid ceases to aug ment. Both are now poured into a fun nel, closed with the finger, and after the dense liquor is settled at the bottom, it is steadily run off into a capsule. This, af ter being washed repeatedly with ether, is to be transferred into a stove chamber, or placed under the receiver of an air• pump, to be evaporated. The residuary
matter swells up in a spongy crystalline form of considerable brilliancy, some times colorless, but more frequently of a faintly yellowish hue.
This is pure tannin, which exists in galls to the amount of from 40 to 45 per cent. It is indispensable that the ether employed in thepreceding process be previously agitated with water, or that it contain some water, because by using anhydrous ether, not a particle of tannin will be obtained.
Tannic acid is a white or yellowish so lid, inodorons, extremely astringent, very soluble in water and alcohol, much less so in sulphuric ether, and uncrystalliza ble. Its watery solution, out of contact of air, undergoes no change ; but if, in a very dilute state, it be left exposed to the atmosphere, it loses gradually its trans parency, and lets fall a slightly grayish crystalline matter, consisting almost en tirely of gallic acid. For procuring this acid in a perfectly pure state, it is merely necessary to treat that solution thus changed with animal charcoal, and to fil ter it, in a boiling state, through paper previously washed with dilute muristic acid. The gallic acid will fall down in crystals as the liquid cools.
Gallic acid is always produced when any substance containing tannic acid is exposed to the air.
Tannin or tannic acid consists of car bon 51.56 ; hydrogen 4-90; oxygen 44-24.
Gallic acid does notexist ready formed in gallnuts, but that is produced by the reaction of atmospheric oxygen upon the tannin of these concretions.
Gallic acid is a solid, feebly acidulous and styptic to the taste, inodorons, crys tallizing in silky needles of the greatest whiteness ; soluble in about 100 times its weight of cold, and in n much smaller quantity of boiling water ; more soluble in alcohol than in water, but little so in sulphuric ether.
Gallic acid does not decompose the salts of protoxyde of iron, but it forms, with the sulphate of the peroxyde, a dark blue precipitate, much less insoluble than the tannate of iron. Gallic acid takes the oxyde from the acetate and nitrate of lead, and throws down a white gallate unchangeable in the air, when it is mixed with that acetate and nitrate. It occa sions no precipitate in solutions of gela tine (isinglass or glue), by which its freedom from tannin is verified.