NEW MODE OF PREPARING CHARCOAL. 
681 
The 6rst of these is best suited to the hard 
woods which, contain but l ittle resinous matter. 
This opeiation is performed in a kiln of the 
shape of a cylinder, or ratiiera truncated cone 
whose larger base is uppermost. It may be 
built of sods or tenacious earth above the 
natural surface of the soil, but may be more 
conveniently excavated to suci) a depth tliat 
the earth thrown out may serve to form the 
upper part of the enclosure. In the only in- 
stance in which we have seen it employed in 
this country, namely, at tire West Point Foun- 
dry, tire excavation is lined with brick. 
In order to admit air to the kiln, when 
made by excavation, for the purpose of 
maintaining the combustion, tnbes of earthen- 
ware or cast iron are carried down fVom the 
surface of the ground to the bottom of the 
excavation : the-e lie behind the lining, and 
are either passed through it near the bottom, 
or enter small brick vaults, which communi- 
cate wiih the interior of the kiln. 'I'he kiln 
may be closed at top by a cover made of sheet 
iron, tosupport which, when the lining is not 
of orick, a ring of bribks must be placed 
around the top of the excavation. The cover 
must extend on all sides three or four inches 
beyond the opening^of the kiln, in order to 
have a sufficient support, lu this cover there 
are seveial openings, one at the centre, the 
others near the circurafeience. Through 
each of these a short tube or flue of sheet iron 
passes, and the several tubes are furnished 
with stoppers of iron. 
The size described by Dumas is ten feet. 
(French) in diameter, and nine feet deep. 
The central tube is nine inches in diameter. 
The number of these at the circumference is 
four, each four inches in diameter. 
That used at the West Point Foundry is 
twelve feet in diameter and nine feet deep. 
In order to condense the volatile matter, 
one opening is made in the lining near the lop 
of the kiln, to which a tube of cast iron or 
earthenware is applied. This tube communi- 
cates with a small chamber built of biick, 
about eighteen inches long, a foot in width, 
and fifteen inche.s high, entering about the 
middle of its height. Fiora the top of this 
chamber proceeds a pipe of sheet iron, which, 
after rising vertically four or five leet, assumes 
a horizontal diiection for about fifteen feet 
more ; at this distance there is no fear of 
fire, and the rest of the pipe may be of wood. 
The extension of the pipe communicates 
with a condensing apparatus, on the principle 
of Woolf, but which may be formed of com- 
mon barrels. 
In charging the kiln with wood, a post 
whose height is equal to the depth of the 
excavation is setup in the middle, and sup- 
ported in its place by a heap of fragments of 
charcoal. A number of the larger lous are 
chosen and laid on the bottom of the kiln in 
such a manner as to form rudiating flues, ter- 
minating at the places when the air tubes pass 
through the lining- Across these a horizontal 
layer of logs is laid. The radiating logs must 
neither touch the post or the lining of the 
kiln 5 the secondary layers extend from the 
one to the other. Layers are then placed in 
succession in such a manner as to leave as 
little empty space as possible, particu- 
larly^ near the circumference until the kiln 
is filled. The kiln having been charged, 
the post is drawn out of the middle, the cover 
set in its place, and coated to the depth of 
not le.'^s than two inches with dry earth. 
The stoppers being withdrawn from the 
flues in the cover, lighted charcoal is poured 
down through the middle tube ; this falls 
through the space left by the post, to the 
heap of charcoal by which it was steadied, 
and sets it on fire. The central flue is then 
tightly closed, in order that the draught 
may be directed towards the outside of the 
mass of wood. In order to make the joint of 
the stopper tight, it is luted with plastic clay. 
The other flues begin to discharge smoke, 
which is surounded by flame. As soon as the 
flame|ceases to have a blue colour and becomes 
white and clouded, the flues have their stoppers 
loosely applied to them, and the openings of 
the descending air tubes are diminished. The 
draught will thus be directed to the condens- 
ing apparatus. But if the collection of the 
acid be not intended, the tubes in the cover 
are but partially closed. The combustion may 
be regulated within the kiln by the air tubes 
and those in the cover. Thus, too rapid an 
action in any one part may be checked by com- 
pletely closing the several air tubes and the 
opposite flue ; and if it be too slow, these 
must be opened as far as possible until the 
action be restored. 
^ For a kiln ten by nine, the operation occu- 
pies from sixty to eighty hours, and is known to 
be complete when the upper layer of wood ap- 
pears to be incandescent ; when this has taken 
place, the stoppers of all the openings except 
that of the central flue are removed for a 
short time, and a quantity of hydrogen will 
be expelled, whch, if it does not injure the quan- 
tity of charcoal, would rei>der it less saleable. 
As soon as the peculiar flame of hydrogen 
ceases, all the opening, both of the air tubes 
and flues, must be closed by shutting their 
stofjpers with clay, and covering them with 
caps of sheet iron containing clay, d he di\y 
earth is removed from the cover, and it is plas- 
tered with earth mixed with water. The 
charcoal thus shut up will take sixty to eighty 
hours to cool. ® ^ 
A plan and section of this description of 
kiln is represented in plate viii, figs. 1, 2 3 
4, and 5. » » s 
Fig. 1 , and 2, being plan and section of one 
formed in an excavation, and 
Fig. 3, and 4, of one built above ground. 
Fig. 5, cover of sheet iron applicable to 
either. ^ 
A. Interior of kiln. 
B. Wail, or lining of earth. 
C. Chamber in which the tar may be con- 
densed. 
d. Pipe leading to the condenser for pyro- 
lignous acids. 
e, e, e. Air-vaults. 
. />/» /• Openings by which the external air 
IS admitted. 
