'230

Materia Medico,

Part II",

h

nuts come at the shoots of the young boughs, and are produ-ced by the puncture of diplolepi&gallcetinctorue to depositcanegg. They acquire from four to twelve lines in diameter,and are generally round and covered with tuberosities. Theyare in perfection when they have acquired their full size andweight, but before the insect has pierced them, after whichthey get a brighter colour, and lose some of their weight. Theharvest takes place about the middle of Messidor. The gallsfirst picked are, laid apart, and are known under the name ofYorli, and in commerce are called Black and Green galls.Those gathered later arc called White galls, and are very in-ferior in value. In commerce they occur of different sizes,smooth or knotty on the surface, of a whitish, reddish, orblackish colour, and generally penetrated with a small hole.Internally they consist of a spongy, but hard, more of lessbrown substance, and the)'have a Very rough astringent ta>te.Good galls are of a blackish-grey, or yellow colour, heavy,and fuberculated on the surface. They are the most power-ful astringents we possess ; and since the discovery of the tan-ning principle by Mr Seguin, have very much engaged the at-tention of chemists. Neumann got from 960 grains of coarse-ly powdered galls 840 watery extract, and afterwards only 4>alcoholic ; and inversely, 760 alcoholic, and 80 watery. Butthe most minute analysis is that of Sir H. Davy, who found that500 grains of good Aleppo galls gave, by lixiviating them un-til their soluble matters were taken up, and evaporating thesolution slowly, 185 grains of solid matter, which, when exa-mined by analysis, appeared to consist of,

Tannin, - - - - 130

Mucilage, and matter rendered insoluble by

evaporation, 12

Gallic acid, and a little extractive matter, 31

Remainder, calcareous earth and saline matter, 12

From my experiments, I am disposed to think that Sir H.Davy has under-rated the tannin of nut-galls; for by simplerepeated infusions in hot water, the residuum of 500 grains inone experiment amounted only to 158, and in another only to136 grains. The quantity of tannin, estimated in Sir H. Davy'sway, amounted, in the first to 220 grains, and in the second to256. The great difference in these results from Sir H- Davy'smust be entirely ascribed to some differences in the galls them-selves, or in the mode of operation. A saturated decoction ofgalls, on cooling, deposites a copious pale yellow precipitate,which seems to be purer tannin than what can be got by any