EXPERIMENTS ON ASTRINGENT VEGETABLES. 259 



150°. This method I have found much better than that of 

 drying at the temperatures of the atmofphere, as the different 

 flate: of the air, with regard to moifiure, materially influence 

 the remits. ' 



Mr. Hatchett has noticed, in his excellent Paper on Zoo- Ifinglafs Is gela- 

 phytes, &c* that ifinglafs is almoft wholly compofed of ge- tmw neai y pure ' 

 latine, I have found, that 100 grains of good and dry ifin- 

 glafs contain rather more than 98 grains of matter foluble in 

 water. So that, when the quantity of ifinglafs, in any folu- 

 tion employed for acting upon aftringent infufion, is compared 

 with the quantity of the precipitate obtained, the difference 

 between them will indicate the proportion of tannin, as it exifts 

 in the combination. 



After the tannin has been feparated from an aftringent in- After precipf- 



fufion, for the purpofe of afcertaining its other component taring the tan- 



l ti in i i r i i ii- inn, the fluid is 



parts, 1 nave been accuftomed to evaporate the retidual liquor p art iyevapo- 



very flowly, at a temperature below 200°. f In this procefs, rated, and the 



if it contains extractive matter, that fubflance is in part ren- Jy,,^ extraft 



dered infoluble, fo as to fall to the bottom of the veffel. When taken up by 



the fluid is reduced to a thick confidence, I pour alcohol upon pmt * 



it. If any gallic acid or foluble extractive matter be prefent, 



they will be diflblved, after a little agitation, in the alcohol ; 



whilft the mucilage, if any exift, will remain unaltered, and 



may be feparated from the infoluble extract, by lixiviation with 



water. 



I have made many experiments, with the hope of difcover-it Is difficult to 



ing a method by which the respective quantities of gallic acid afcertam tne 



i n- ,i •« • r i • ■ i i proportions of 



and extractive matter, when they exift in lolution in the alco- gallic acid and 



hoi, may be afcertained; but without obtaining fuccefs in the extra<ft in the 



refults. It is impoflible to render the whole of any quantity 3 



of extractive matter infoluble by expofure to heat and air, 



without at the fame time decompofing a portion of the gallic 



* Phil. Tranf. for 1800, page 327. 



f M. Deyeux has fhewn, (Annates de Chimie. Tome XVII. page 

 36,) that in the procefs of evaporating folutions of galls, no gallic 

 acid is carried over by the water, at a temperature below that of 

 ebullition. Many aftringent infufions, however, lofe a portion of 

 their aromatic principle, even in cafes when they are not made to 

 boil $ but this fubftance, though evident to the fmell, in the water 

 that comes over, cannot be detected by chemical reagents. 



S 2 acid* 



