791
COMBUSTIBLES.
with a slope towards its centre, or at least formed of a
thick bed of well-rammed clay. From near the centre a
trough, or covered gutter is formed, which is frequently
only a tree split, hollowed, and then joined together with
clay, with which it is also coated to defend it from the fire.
This trough ends in a cistern sunk in the ground to receive
the tar as it flows from the trough.
A pole 15 or 18 feet long being stuck upright in the
centre of the hearth, the billets, or faggots of resinous
wood is piled round it in a bed of about 20 feet in diame
ter. Upon this a bed of less diameter is made, and so on
decreasing gradually to form a conical pile; which is covered ¬
with fresh cut turfs, leaving a few openings round the
pile on a level with the ground. The whole being left for
a day or two to settle, the pole in the middle is withdrawn
and the pile lighted at the bottom holes. When the pile is
well lighted the holes are stopped, and should the fire appear ¬
by any cracks in the covering, fresh turfs are laid to the
place. The third day the end of the gutter next the cistern ¬
is opened, which had hitherto been stopped, and the
tar already made permitted to run out. This opening is
then closed again, and only opened two or three times a
day during the remainder of the process.
The tar thus obtained generally requires to be heated in
large iron pots, to drive away the water and pyroligneous
acid that runs out along with it, and cannot be separated
by ladling, and also to allow the sand and other impurities
which the tar contracts in this rude process to settle, and
be thus separated.
In Sweden and Norway where the Scotch fir, or pinus
sylvestris, is a regular crop, tar furnaces are built of brick
work, perfectly similar to these piles, and hence their tar
being clean, is of superior value in the market.
In North Carolina, from whence the greater part of American ¬
tar is brought, the piteh pine, pinus palustris, is used;
and those trees which have fallen down in the woods, and
the sap wood rotted off, are preferred, under the name of
light wood, so called because it takes fire very readily. A
pile of this pitch pine, 20 feet in diameter and 14 feet high,
is computed to produce 200 barrels of tar.
Green Tar.
This is made in the same manner as common tar, from the wood of those
trees which have done yielding turpentine by incision.
All the French, or Bordeaux, tar is made in this manner from the seapine, ¬
pinus maritima, and much of the American.
