conslituent Paris of astringent VegeiaUes, sgs 



ihe oak, produced 43 grains of solid matter, ofwlilch 19 

 were tannin. 



P>om the Spanish chestnut, 41 grains, of Avhich 14 -ftere 

 tannin. 



And, from the Leicester willow, 34 grains, of which 16 

 were tannin. 



In attempting to ascertain the relative quantities of tannia 

 in the different entire barks, I selected those specimens 

 ivhich appeared similar with regard to the proportions of 

 the external and internal layers, and which were about the 

 average thickness of the barks commonly used in tanning, 

 namely, Ixalf an inch. 



Of these barks, tiie oak produced, in the quantity of an 

 ounce, 61 grains of matter dissolved by water, of which, 

 S9 grains were tannin. 



The Spanish chestnut 53 grains, of which 21 were tan- 

 nin. 



And the Leicester willow 71 grains, of which 33 were 

 tannin. 



The proportions of these quantities, in respect to the tan- 

 ning prmciple, are not very different from those estimated 

 in Mr. Eiggin's table *. 



The residual substances obtained in the different experi- 

 ments differed considerably in their properties ; but certain 

 portions of them were, in all instances, rendered insoluble 

 during the process of evaporation. The residuum of the 

 chestnut bark, as in the instance of the strongest infusions 

 possessed slightly acid properties; but more than 3-4ths of 

 its weight consisted of extractive matter. All the residuums 

 in solution, as in the other cases, were precipitated by mu- 

 riate of tin ; and, after this precipitation, the clear fluids 

 acted much more feebly than before on the salts of iron; 

 so that there is great reason for believing that the power of 

 astringent infusions to precipitate the salts of Iron black, or 

 dark coloured, depends partly upon the agency of the ex- 

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

 tanning principle and gallic acid. 



In pursuing the experiments upon the different astringent 

 infusions, 1 examined the infusions of the bark of the elm 

 and of the common willow. These Ini'uslous were acted on 

 by re-agents in a manner exactly similar to the infusions of 

 the other barks : they were precipitated by the acids, by so- 

 Jutions of the alkaline earths and of the carbonated alkalis : 



• Philosophical Transactions for 1799, p. 263. 



5 and 



