1930

ARBOllETUM AND FRUTICETUM.

PART III.

being slightly exposed. After impregnation, the eggs are deposited by meansof this boring instrument, which is exsertile, within the leaves or twigs ofvarious plants; shortly after which the galls are formed on the outside of theattacked part, the eggs being forced from the place where they were originallydeposited, and occupying the centre of the newly formed gall, which is gene-rally of a fleshy nature, and serves as food to the young grub (Jig. 1822. b),when hatched; the pupa state (Jig. 1822. c) succeeds, and is passed eitherwithin the gall, as in the insect now under consideration, or in the earth;the larva having previously to its change eaten its way out; soon after which,the insect assumes its imago state. Hence, it will be at once obvious, that agall, from which the insect has escaped, must necessarily contain less astringentprinciple than one which has its interior less consumed by the insect, whichstill remains enclosed therein; and hence it is that there are two kinds of gallnuts known in commerce : those which still contain the insect, and which areknown in the trade under the names of black or blue galls and green galls, andtermed yerli by the natives of the countries where they are collected; andthose from which the insect has escaped, and which are called white galls.The latter contain not more than two thirds of the astringent qualities of theformer, and are of a pale brown or whitish colour, less compact, and not soheavy. (Oliv. Voy. dans VEmpire Ottoman; and Travels in Egypt , vol. ii. p. 61.)Mr. M'Culloch states that these galls “ are principally exported from Aleppo ,Tripoli, Smyrna, and Said : those brought from the first come chiefly fromMosul, on the western bank of the Tigris, about 10 days’journey from Aleppo .The real Mosul galls are unquestionably the best of any: but all that aregathered in the surrounding country are sold under this name. Those fromCaramania are of very inferior quality. The gall nuts met with in India arecarried thither from Persia by Arabian merchants.” (Com. Diet. , p. 595.)General Hardwicke, however, states that he discovered the tree upon whichthey are found in the neighbourhood of Adwuanie. (Asiat. Rep., vol. vi.p. 376.) “ The price of galls, in the London markets, varies from 65s. to85s. per cwt. The duty is 5s. per cwt.” (M‘Cull. Com. Diet., art . Gall.) Thewhite and blue galls are generally sold mixed together in about equal propor-tions, and are then called galls in sorts; and occasionally fraud is attemptedby dyeing the white galls with a blue dye, but then 1 lighter weight will renderit easy to detect them at once.

The chief use made of these galls is in the manufacture of common writingink, which is made by adding an infusion of the gall nut to sulphate of iron dis-solved in water. A very fine precipitate is thrown down, the speedy subsidenceof which is prevented by the addition of a proper quantity of gum arabic. Thisis usually accounted for by the superior affinity of the gallic acid; which, com-bining with the iron, takes it from the sulphuric acid, and occasions it to falldown. Logwood is also a useful ingredient in ink, its e<}louring matter unitingwith the oxide of iron, and rendering it not only of a very dark colour, but lessliable to change from the action of acids, or the external air. The applicationof heat is also necessary; because by its action the galls are almost entirelysoluble in water, which is not the case when they are simply macerated.Gallic acid may be obtained from the infusion, merely by sublimation. Thesolution also contains a large quantity of tannin, as it gives a very copiousprecipitate with solution of gelatine. The proportion of these ingredients in815 grains of solid matter are, according to Sir Humphry Davy , as follows :130 of tannin, 31 gallic acid, 12 saline and earthy matter, and 12 supposed tobemucilage and extractive matter. Gall nuts are also very extensively usedin dyeing; and, being the most powerful of vegetable astringents, “ they are fre-quently used with great effect in medicine, both externally and internally, inthe form of powders, infusions, tinctures, or ointments; as in long protractedand obstinate diarrhoeas, intestinal haemorrhages, and intermittents; and,when judiciously combined with tonics and aromatics, have been found usetu .Much caution is, however, required in administering so powerful a medicine,and the dose should not exceed 10 grains or a scruple three times a day. An