36, EXPERIMENTS ON ASTRINGENT VEGETABIES. 



The proportions of tliefe quantities, in refpecl to the tannin,g 

 principle, are not very different from thofe eflimated in Mr. 

 Biggin's table.* 

 Properties of the The refidual fubRances obtained in the different experiments, 

 •nrifufedTaXs. ^'^"^'"^f^ confiderably in their properties; but certain portions of 

 them were, in all inflances, rendered infoluble during the pro- 

 ceCs of evaporation. The refuluum of the chefnut bark, as in 

 the inflance of the firongeft infufion, pofTefTed flightly acid 

 properties ; but more than | of its weight confifted of extrac- 

 tive matter. All the refiduums in folution, as in the other 

 cafes, were precipitated by muriate of tin ; and, after this pre- 

 cipitation, tlic clear fluids acted much more feebly than before 

 on the falts of iron ; fo that there is great reafon for believing, 

 that tlie power of aftringent infufions to precipitate the falts of 

 iron black, or dark coloured, depends partly upon the agency 

 of the extractive matters they contain, as well as upon that of 

 the tanning principle and gallic acid. 

 Elmandwiilow In purfuing the experiments upon the different aflringent 

 ■"^ ' infufions, I examined the infufions of the bark of the elm and 



of the common willow. Thefe infufions were a6ted on by re- 

 agents, in a manner exa6tly fimilar fo the infufions of the other 

 barks: they were precipitated by the acids, by folutions of the 

 alkaline earths, and of the carbonated alkalis; and they form- 

 ed, with the cauflic alkalis, i^uids not precipitable by gelatine. 

 An ounce of the bark of the elm, furniflied 13 grains of 

 tannin. 



The fame quantity of the bark of the common willow, gave 

 1 1 grains. 



The refidual matter of the bark of the elm, contained a con- 

 fiderable portion of mucilage; and that of the bark of the 

 willow, a fmali quantity of bitter principle. 

 Infufions of The (Irongell infufions of the fumachs from Sicily and Ma- 



fuir.achs from j^^g^j agree with the infufions of barks, in moft of their pro- 

 Sicily and Ma- ^ ! ^, , ,.^ r ,, ,, , n • • r r 



yga^ perties; but they ditier from all the other aftrmgent mtuhons 



that have been mentioned, in one refpecl; they give denfe pre- 

 cipitates with the cauflic alkalis. Mr, Prouft has fliown, that fu- 

 m.ich contains abundance of fulphate of lime; and it is pro- 

 bably to this fubflance that the peculiar effctSl is owing. 



From an ounce of Sicilian fumach, I obtained 165 grains of 

 matter foluble in water, and, of this matter, 78 grains were 

 tannin. 



* Philofophical Tranfaaions for 1799, p. 263. 



An 



