.ties. 



EXPERIMENTS ON ASTRINGENT VEGETABLES. 35 



tn every aftringent bark, the interior white bark (that is, the The Interior coat 



, ,, • 1 1 n ■ r °^ oarK. contains 



part next to the alburnum) contains the largeit quantity of tan- moft tannin • 

 nin. The proportion of extractive matter is generally greateft ^'^^ middle moll 

 in the middle or coloured part : but the epidermis feldom fur- ^i^^ epidermis 

 nifties either tannin or extraflive matter. little of either. 



The white cortical layers are comparatively mofl abundant in Young trees 

 young trees ; and hence their barks contain, in the fame weight, ^^°''^ ™°'^* 

 a larger proportion of tannin than the barks of old trees. In 

 barks of the fame kind, but of different ages, which have been 

 cut at the fame feafon, the fimilar parts contain always very 

 nearly the fame quantities of aftringent principles; and the in- 

 terior layers afford about equal portions of tannin. 



An ounce of the white cortical layers of old oak bark, fur- Relative qnanti- 

 nifhed, by lixiviation and fubfequent evaporation, 108 grains of' 

 folid matter; and, of this, 72 grains were tannin. An equal 

 quantity of the white cortical layersof young oak produced 111 

 Ijrains of folid matter, of which 77 were precipitated by gela- 

 tine. 



An ounce of the interior part of the bark of the Spanlfli 

 chefnut, gave 89 grains of folid matter, containing 63 grains 

 of tannin. 



The fame quantify of the fame part of the bark of the Lei- 

 cefter willow, produced 1 J7 grains, of which 79 were tannin. 



An ounce of the coloured or external cortical layers from the 

 oak, produced 43 grains of folid matter, of which 19 were 

 tannin. 



From the Spanifli chefnut, 41 grains, of which 14 were 

 tannin. 



And, from the Leicefler willow, 34 grains, of which 16 were 

 tannin. 



In attempting to afcertain the relative quantities of tannin in 

 the different entire barks, I felecfed thofe fpecimens which ap- 

 peared fimilar with regard to the proportions of the external 

 and internal layers, and which were about the average thick- 

 nefs of the barks commonly ufed in tanning, namely, half an 

 inch. 



Of thefe barks, the oak produced, in the quantity of am 

 ounce, 61 grains of matter diffolved by water, of which 29 

 grains were tannin. 



The Spanilh chefnut 53 grains, of which 21 were tannin. 



And the Leicelier willow 71 grains, of which 33 were tan- 

 nin. 



D2 The, 



