Tanning Principle and Gallic Acid in Barks. 424 
one day find, in thefe ravaged countries, objects worthy of 
their refearches. Fragments of the minerals and earths of 
Tunguragua are about to be tranfported to Spain: but it is 
notin fuch fragments that we ought to fearch for the caufé 
of thefe furprifing phenomena; we miuft vifit the country it- 
felf, where this conflict of the elements took place, and where 
the ruins it occafioned are {till to be feen *. 
HI. Experiments to determine the Quantity of Tanning Prin- 
ciple and Gallic Acid contained in the Bark of various 
Trees. By GeorGe Biccin, Efg.t 
Tur bark of trees contains the aftringent principle called 
gallic acid, and alfo that principle which has a peculiar afhi- 
nity to the matter of fkin, and which, from the ufe to which 
it is applied, is called the tanning principle: But, in the 
prefent mode of tanning, bark is applied in ma/s to the 
fkins ; confequently, doth principles are applied. It remains 
for examination, whether both principles are ufeful in the 
procefs of tanning; for, if they are not both ufeful, probably 
6ne is detrimental. 
To a nobleman, whofe zeal on every occafion by which | 
the fciences or arts may receive illuftration or improvement, 
is eminently confpicuous, and to whofe public energy, as 
well as private friendfhip, I feel myfelf much indebted, to 
his Grace the Duke of Bedford, I owe the means of profé- 
cuting fome experiments on this fubje&t. His Grace, by 
collecting a variety of barks, at Woburn, gavé me an op- 
portunity of making fome experiments to afcertain thé quan- 
tity of tanning principle and gallic acid each bark contained, 
For that purpofe I made ufe of the following methods, ac- 
eording to the principles laid down by M. Seguin :— 
By diffolving an ounce of common glue in two pounds of 
‘boiling water, I procured a mucilaginous liquor, which, as 
‘H, contains the matter of fkin in folution, is a teft for the 
* The volcano of Tunguragua oceafioned an earthquake in 1557 
# From the Philoophical Tranfattions of the Royal Society of Londop. 
Vor. V. Tf tanning 
