532 GALL-NUTS 



infectoria, which grows in the Levant. They are produced in consequence of tho 

 puncture of the female of tho gall-wasp (Cynips folli gucrciis), made in order to 

 deposit her eggs ; round which the juice of the tree exudes, and dries in concentric 

 portions. When tho insect gets fully formed, it eats through the nut and flies off. 



The Levant galls are of two different appearances and qualities ; the first are heavy, 

 compact, imperforated, tho insect not having been sufficiently advanced to eat ite way 

 through tho shell ; prickly on the surface ; of a blackish or bluish green hue ; about 

 the size of a musket-ball. These are called black, blue, or Aleppo galls. Tho second 

 are light, spongy, pierced with one or more holes ; smooth upon the surface, of a pale 

 greyish or reddish yellow colour, generally larger than the first, and are called white 

 galls ; but they are inferior to the former, and great care should be taken in tho pur- 

 chase of the best quality, for these are often dyed by dishonest traders to imitate the 

 best blue Aleppo galls, but the fraud may be detected by the small hole made by the 

 insect in the white galls, so that if tho blue galls have holes, we may bo sure they are 

 not genuine. 



Besides the galls of the Levant, others como from Dalmatia, Illyria, Calabria, &c. ; 

 but they are of inferior quality, being found upon the Quercus cerris; they are smaller, 

 of a brownish colour, and of inferior value. The farther south the galls are grown, 

 the better they are reckoned. 



The galls of the Quercus cerris and common oak ( Galles a Vepine, Fr. ; Knoppern, 

 Ger.) are of a dark-brown colour, prickly on the surface, and irregular in shape and 

 size. They are used chiefly for tanning in Hungary, Dalmatia, and the southern 

 provinces of the Austrian States, where they abound. 



Galls consist principally of three substances : tannin, or tannic acid ; yellow extrac- 

 tive ; and gallic acid. Their decoction has a very astringent and unpleasant bitter 

 taste. The following are their habitudes with various reagents : 



Litmus paper is powerfully reddened. Stannous chloride (protomuriate of tin) 

 produces an Isabel-yellow precipitate. Alum : a yellowish grey 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 precipitate. Acetic acid brightens the muddy decoction. 



Tannin or tannic acid is prepared as follows : Into a long narrow glass adopter tube, 

 shut at its lower orifice with a cotton wick, a quantity of pounded galls is 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 a liquid in 

 two distinct strata ; of which the more limpid occupies tho upper part, and the other, 

 of a syrupy consistence and amber colour, the lower. More ether must be filtered 

 through the galls, till the thicker liquor ceases to augment. Both are now poured 

 into a funnel, closed with the finger, and after the dense liquor is settled at the bottom, 

 it is steadily run off into a capsule. This, after 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, sometimes colourless, but more frequently of a faintly-yel- 

 lowish 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 the preceding process bo previously 

 agitated with water, or that it contain some water, because by using anhydrous other, 

 not a particle of tannin will be obtained. 



Tannic acid is a white or yellowish solid, inodorous, extremely astringent, very 

 soluble in water and alcohol, much less so in sulphuric ether, and uncrystallisable. 

 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 transparency, and lets 

 fall a slightly -greyish crystalline matter, consisting almost entirely 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 filter it in a boiling state, through 

 paper previously washed with dilute muriatic acid. Tho gallic acid will fall down in 

 crystals as the liquid cools. 



If the preceding experiment bo made in a graduated glass tubo containing oxygen 

 over mercury, this gas will be absorbed, and a corresponding volume of carbonic acid 

 gas will be disengaged. In this case the liquor will appear in tho course of a few 

 weeks as if traversed with numerous crystalline, colourless needles of gallic acid. 



Tannin or tannic acid consists of carbon, 51*56 ; hydrogen, 4 - 20 ; oxygen, 44*24. 



From the above facts it is obvious thai gallic acid does not exist ready formed in 

 gall-nuts, but that it is produced by tho reaction of atmospheric oxygen upon the 

 tannin of these concretions. 



Gallic acid is a solid, feebly acidulous and styptic to the taste, inodorous, crystal- 



