212 Mr. Hatchett on an artificial tanning Substance. 
The former has derived elucidation from the experiments 
of Mr. Biggin,* and much has been contributed in every 
respect by Mr. Proust, - f but the subject has received the 
greatest extension and some of the most valuable additions- 
from the ingenious labours of Mr. Davy, particularly the 
discovery of the important fact, that catechu or terra japonica 
consists principally of tannin. J 
The united results of the experiments made by these and 
other eminent chemists, appear therefore to have fully esta- 
blished, that tannin is a peculiar substance or principle which 
is naturally formed, and exists in a great number of vegetable 
bodies, such as oak-bark, galls, sumach, catechu, &c. &c. 
commonly accompanied by extract, gallic acid, and mucilage. 
But no one has hitherto supposed that it could be produced 
by art, unless a fact noticed by Mr. Chenevix may be consi- 
dered as some indication of it. 
Mr. Chenevix observed, that a decoction of coffee-berries 
did not precipitate gelatine unless they had been previously 
roasted ; so that tannin had in this case either been formed or 
had been developed from the other vegetable principles by 
the effects of heat. § 
Some recent experiments have however convinced me, that 
a substance possessing the chief characteristic properties of 
tannin may be formed by very simple means, not only from 
vegetable, but even from mineral and animal substances. 
* Phil. Trans. 1799, p. 259. 
+ Annales de Cbimie , Tome XXV. p. 225, Ibid. Tome XLI. p. 331. Ibid. 
XLII. p. 89. % Phil. Trans. 1803, p. 233. 
% Nicholson’s Journal for 5802, Yol. II. p. 114. 
