on the constituent Parts of astringent Vegetables. 265 
part next to the alburnum) contains the largest quantity of 
tannin. The proportion of extractive matter is generally greatest 
in the middle or coloured part : but the epidermis seldom fur- 
nishes either tannin or extractive matter. 
The white cortical layers are comparatively most abundant in 
young trees ; and hence their barks contain, in the same weight, 
a larger proportion of tannin than the barks of old trees. In 
barks of the same kind, but of different ages, which have been 
cut at the same season, the similar parts contain always very 
nearly the same quantities of astringent principles; and the 
interior layers afford about equal portions of tannin. 
An ounce of the white cortical layers of old oak bark, fur- 
nished, by lixiviation and subsequent evaporation, 108 grains of 
solid matter; and, of this, 72 grains were tannin. An equal 
quantity of the white cortical layers of young oak produced in- 
grains of solid matter, of which 77 were precipitated by gelatine. 
An ounce of the interior part of the bark of the Spanish 
chesnut, gave 89 grains of solid matter, containing 6 g grains of 
tannin. 
The same quantity of the same part of the bark of the Lei- 
cester willow, produced 117 grains, of which 79 were tannin. 
An ounce of the coloured or external cortical layers from the 
oak, produced 43 grains of solid matter, of which 19 were tannin. 
From the Spanish chesnut, 41 grains, of which 14 were 
tannin. 
And, from the Leicester willow, 34 grains, of which 16 were 
tannin. 
In attempting to ascertain the relative quantities of tannin in 
the different entire barks, I selected those specimens which 
appeared similar with regard to the proportions of the external 
mdccciii. M m 
