50 FOREST CULTURE AND 
during the burning process. Caution is needed to 
prevent the expansive vapors and gases causing ex- 
plosions during the glowing of the wood. To pro- 
mote combustion on places where it may have been 
suppressed, holes are forced through the covering on 
the second or third day, particularly on the lee side. 
A bursting forth of gases of a blueish hue indicates 
active burning, and under such circumstances the 
access given to the air must be closed, while new per- 
forations are made in any yet inactive portion of the 
meiler. 
Over-great activity of fire is suppressed by water 
applied to the covering, or by adding to the thickness 
of the latter. Strong sinking of the cover during the 
earlier burning proves more or less complete combus- 
tion of the coal, and it may then become necessary to 
refill hurriedly the holes with wood or coal, under- 
closure of all openings, and careful restoration of the 
cover thus temporarily removed on one spot. This 
refilling in large meilers may be required for five days 
in succession ; but the more carefully the mound has 
been built, and the more watchfully the early glow- 
ing process has been conducted, the less necessity will 
arise for the troublesome and wasteful process of re- 
filling. A final additional covering becomes frequent- 
ly needful. The operation closes by the sinking of 
the cover, or by its being partially foreed downward, 
and the ready coals are removable one day afterward. 
Partial withdrawals of coal can be effected from the 
lee side while the meiler is still active. 
The specific gravity of charcoal stands generally in 
a precise proportion to the specific weight of the wood 
employed. Dryer wood realizes a heavier, moister 
