C £95 ] 



LIIT. An Account of some Experiments and Olsprvadons 

 on the constituent Parts of certain astringent Fegctalles ; 

 and on their Operation in Tanning. By Humphrey 

 Daw, Esq., Professor of Chcmistiy in the Royal In- 

 stitution, 



[Concluded from p. 217.] 



IV. Expe/nnents and Observations on the astringent Infw^ 

 sions of Barks, and other FegetaUe Productions. 



X HE barks that I examined were furnished me by my 

 friend Samuel Purkis, cgq., of Brentford : they had been 

 collected in the proper season, and preserved with care. 



In making the infusions, I employed the barks in coarse 

 powder; and, to expedite the solution, a heat of from 100 

 to 120° Fahrenheit was applied. 



The strongest infusions of the barks of the oak, of the 

 Leicester willow, and of the Spanish chestnut, were nearly 

 of the same specific gravity, 1-05. Their tastes were alike, 

 and strongly astringent ; they all reddened litmus paper ; 

 the infusion of the Spanish cliestnut bark producing the 

 highest tint, and that of the Leicester willow bark the 

 feeblest tint. 



Two hundred grains of each of the inflisions were sub- 

 mitted to evaporation ; and in this process the infusion of 

 the oak hark furnished 17 grains of solid matter, that of 

 the Leicester willow about 16^ grains, and that of the Spa- 

 nish-chestnut nearly an equal quantity. 



The tannin given by these solid matters was, in that from 

 the oak bark infusion, 14 grains, in that from the willow 

 bark infusion 14-^ grains, and in that from the SpanisJ) 

 chestnut bark infusion 13 grains. 



The residual substances of the infusions of the Spanish 

 chestnut bark, and of the oak bark, slightly reddened litmus 

 paper, and precipitated the solutions of tin of a fawn colour 

 $nd those of iron black. The residual matter of the mfu- 

 sion of the willow bark, did not perceptibly change the co- 

 lour of litmus ; but it precipitated the salts of iron of an 

 olive colour, and rendered turbid the solution of ijitrate pf 

 aluminc. 



The solid matters produced by the evaporation of the inr 



fusions, gave, by incineration, only a vciy small quantity^ 



of aiihes, which couW not have been more than jj-^th ot 



their original weights, Thtse ashes chiefly consisted of 



T 4 jialcareous 



