which possesses the characteristic Properties of Tannin. 127 
had the goodness to send me a piece of the oak, which was 
perfect in all of its vegetable characters, and did not appear to 
have suffered any change excepting, that it was harder, and 
of a darker colour than recent oak wood. From some expe- 
riments 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 vegetable 
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 precipitate ; with acetite 
of lead, a precipitate of a deeper brown ; with sulphate of iron, 
a copious brownish-black precipitate ; but with solution of isin- 
glass 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 dissolved by 
water, was the extractive matter. This last, in the present 
case, was 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 contained in the Iceland 
schistus,-f ) I am much inclined to believe, that an extractive 
substance of secondary formation, if I may be permitted to 
employ such a term, is produced during the process of car- 
bonization. If a substance, therefore, so compact and solid as 
oak timber can by long submersion be deprived of its tannin, 
it naturally follows that the same effect must be more speedily 
produced by the action of water on the smaller vegetable 
* Phil. Trans, for 1804, p. 399. f Ibid. p. 391. 
