THE USE OF WOOD FOR FUEL. 93 
The kiln proper is then constructed in a parabolic form. It con- 
sists of two or more tiers of billets placed more or less vertically with 
the bark turned outward, the big ends downward, the smallest pieces 
near the chimney and near the circumference, the largest pieces 
halfway between. These tiers aré topped by a cap, consisting of 
smaller billets placed sloping. If the chimney is cylindrical it 
extends through the cap; if it is pyramidal it is closed by the cap. 
In the latter case a lighting channel is left on the ground running 
radially on the leeward side from the base of the pyramidal chimney 
to the circumference. This channel, like the chimney, is filled with 
inflammable material. All irregularities, interstices, and cracks 
showing on the outside of the kiln are stuffed with small kindling. 
The kiln is covered by two draft-proof layers so as to exclude the air; 
first the vegetable layer, one-fourth to three-fourths of a foot thick, 
made of green branches, weeds, leaf mold, and moss; second, an 
earth layer, 2 to 6 inches thick, consisting of loam, charcoal dust, etc. 
If the kiln is lighted from below, a belt about 1 foot high running 
around the circumference on the ground is left without the earth 
cover until the fire is well started. The earth layer and the vegetable 
layer are thoroughly joined by beating with a paddle. 
The kiln is lighted early in the morning on a quiet day. The cylin- 
drical chimney is closed on top as soon as the fire is well started in 
the cap. The lighting channel, in Eber case of a pyramidal chimney, is 
similarly closed. 
The regulation of the fire and of the draft are the most important 
functions of the attendant, who guides the fire evenly and gradually 
from the cap down to the bottom. To check the draft the earth 
cover is increased. To increase draft, holes of about 1 inch diameter 
are made through the cover with the paddle reversed. If the wind 
is strong all holes are closed and the earth cover is increased. Cracks 
which form in the cover must be closed at once. The kiln may 
explode if the cover is too heavy and the draft too strong. In dry 
weather the kiln is continuously sprinkled. The color of smoke 
escaping through the punctures indicates, by turning blue and trans- 
parent, the completion of the charring process above the puncture. 
The old punctures are then closed and another row of punctures is 
made about 2 feet below the closed holes. 
Refilling is required where dells are forming irregularly, while 
the kiln gradually shrinks to one-half of its original volume. For 
refilling, the cover over the dell is quickly removed, all holes having 
been closed beforehand, and the dell is rapidly filled with new wood. 
When the bottom holes show the proper color of smoke, the char- 
ring process is completed. All holes are then closed, and the kiln 
is allowed to cool, The duration of the charring process is from 6 to 
