STRUCTURE OF WOOD, &C. 
101 
occasionally raise the cover for a moment, on one side, even Preparation 
when surmounted by a considerable weight ; but as it is only fromvroo^ 
raised a very little, and falls again immediately, the vase is &c. 
never open more than an instant at a tiqne, and then not so as 
to admit the obtrusion of any extraneous matter. 
When one of these vases is put into the stove, it is placed 
upon a square tile, or half brick, of burnt earth, and another 
of the same kind is also laid upon the cover to keep it steady. 
During the carbonisation of the wood, the interior of the vase 
is always clouded, assuming a very deep blackish yellow colour j 
and during the operation, a strong smell of soot, or of pyrolig- 
neous acid, issues from the stove ; which is even insupportable 
at the commencement, if it be too nearly approached, as well 
as on withdrawing t ie vases from the stove, if the covers be 
removed without due precaution. 
There is, therefore, a decomposition during the carbonisation 
of wood, and a formati n of pyroligneous acid. This fact has 
been long known ; but in some of my experiments, and parti- 
cularly in those made upon fir, with a very moderate fire, I ob- 
tained a product, which, upon a very exact scrutiny, appeared to 
me to be bitumen. 
This product had been condensed upon the glass cover, 
whence it had afterwards run in large drops upon the vertical 
surface of the side of the vase. It was hard and brittle, of a 
dark yellow colour ; it was not affected by boiling water, nor 
by boiling alcohol \ but was gradually dissolved by sulphuric 
ether. 
It would be superflous here to enter upon the detail of all 
my experiments relative to the carbonisation of wood. As the 
process I have employed cannot now but be well known, after 
what I have said in this memoir, and in the one that I had the 
honour to present to the class on the 30th of December, in last 
year*, I shall here only give the results of those experiments. 
The six following, made with different species of wood, were 
so uniformly alike in their results, that I was much surprised. 
One hundred parts (10 grammes) of the six following kinds 
of wood, in thin shavings, and thoroughly dried, were carbonis- 
ed at one time in the stove, in glass vases, well closed with flat 
* Inserted in this Journal, Voh XXXII. p. 100. 
glass 
