28 TANNING MATTER, ScC. 



Experiments, cannot be any doubt (whatever the origin of the tanning 

 &c. on an arti- matter may have been) that it has speedily been extracted 

 havin*»" hech-i- ^^^ drained from the substances which first contained it. 

 racters of tan- TIlis effect is a natural consequence of the great facility 

 nmg matter, -^y^ji which tannin is dissolved by water, and extends even 

 to the most solid vegetable bodies ; I shall here give an 

 example. ♦ , 



In the Philosophical Transactions for 1799, Dr. Coii- 

 REA DE Serra has given an account of a submarine forest 

 at Sutton, on the coast of Lincolnshire, where submerged 

 vegetables are found in great abundance, incli;iding trees 

 of dift'erent descriptions, especially birch, tir, and oak. 

 At the time when I was engaged in those experiments on 

 the Bovey coal, and other substances of a similar nature, 

 which have been printed in the Philosophical Transactions 

 for 1804, Sir Joseph Banks had the goodness to send ipe 

 a piece of the oak, which was perfect in all of its vegeta- 

 ble characters, and did not appear to have suffered any 

 change exceptin*,,that it-was harder, and of a darker co- 

 lour than recent oak wood. From some experiments 

 which I then made, I found, that after incineration it 

 afforded potash, similar to the recent wood, and contrary 

 to substances like the Bovey coal, which retain the vege- 

 table external characters, although imperfectly converted 

 into coal*. 



In the course of my experiments on tannin, I reduced 

 about an ounce of this submerged oak into shavings, and 

 digested them in water. A brown decoction was formed, 

 which with muriate of tin afforded a pale brown precipi- 

 tate ; with acetite of lead, a precipitate of a deeper brown ; 

 with sulphate of iron, a copious brownish-black precipi- 

 tate ; but with solution of isinglass not any effect was 

 produced. 



The tannin of this oak wood, had therefore either been 

 separated by solution, or had been -decomposed ; so that 

 the only substance which remained capable of being dis- 

 solved by water, was the extractive matter. This last, in 

 the present case wag most probably the original extractive 

 matter of the oak, but in some ,other instances, (such, 

 for example, as that which was found in the alder leaves 



• Phil. Trans, for 1804, p. 399. 



contained 



