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MIT. An ylccoiivt of some Experiments and Ol'servnf/ons 

 on the constituent Parts (>/' certain astringent lucretables ; 

 and on their Operation in Tanning. By Hlmphuv Davy, 

 jL.sq., Professor of Ckemistrij in the Roi/al Jnslitntion.* 



J- HE discovery made by M. Seguin, of a peculiar vegetable 

 matter which is essential to the tannino; of skin, and which 

 is possessed of the property of precipiFating aelaiine from 

 its solutions, has added considerably to ourkno'.vlcdiic of tlie 

 constiUient parts of astrinivent vegetables. 



IVJr. Proust has investigated manv of the properties of 

 tliis substance; but though his labours, and those of other 

 chenjists, have led to various interesting observations, yet 

 they are far from having exhausted the subject. The aM- 

 nities of tannin have been hitherto very little examined; 

 and the manner in which its action upon animal matters is 

 modilied by combination with other substances, has been 

 scarcely at all studied. 



At the desire of the managers of the Royal Institution, I 

 began, in September 1801, a series of experiments on the 

 substances employed in the process of tanning, and on the 

 chemical agencies concerned in it. These experiments have 

 occupied, ever since, a considerable portion of my leisure 

 hours; and I now presume to lay before the Royal Society 

 an account of their general results. My chief design was, to 

 attempt to elucidate the practical part of tlic art: Ixit in pur- 

 suing it, I w as necessarily led to genera! chemical inquiries, 

 concerning the analysis of the ditferent vegetable substances 

 containing tannin, and their peculiar properties. 



I. Observations on the Analysis of astrimient Vcm-talls 

 Jnjusions. 



The substances that iiave been supposed to exist most o:e- 

 ncrally in astringent infusions are, tannin, galUe acid, and 

 extractive matter. 



The presence of tannin in an infusion, is denoted by the 

 ]>recipilate it forms with th(; solution of glue or of isintiiass. 

 And, when this principle is wholly separated, if the renuiin- 

 ing liquor gives a dark colour with the oxygenated salts of 

 iron, and an immediate precipitate with the solutions of 

 ahun and of nuiriate of tin, it is Ix'lieved to contain gallic 

 acid and extractive matter. 



'i'he experiments of MM. Fourcroy, Vauquelin, and Se- 



* From Philosophical Tia:;»actions for locj.J 



