lish this, "sticking" is employed, i. e.,
strips of wood are placed crosswise close to the ends and at intervals
between the boards. In this way the weight of the superposed boards
tends to keep those under them from warping. The pile is skidded a
foot or two off the ground and is protected above by a roof made of
boards so laid that the rain will drain off.

Fire-wood is best dried rapidly so that it will check, making air
spaces which facilitate ignition, but lumber needs to be slowly dried
in cool air so that the fibers may accommodate themselves to the
change of form and the wood check as little as possible. Good
air-drying consumes from two to six years, the longer the better.

(2) Kiln-drying or hot-air-seasoning is a much more rapid process than
air-seasoning and is now in common use, Fig. 57. The drying is also
more complete, for while air-dried wood retains from 10% to 20% of
moisture, kiln-dried wood may have no more than 5% as it comes from
the kiln. It will, however, reabsorb some moisture from the air, when
exposed to it.

The wood of conifers, with its very regular structure, dries
and shrinks more evenly and much more rapidly than the wood of
broad-leaved trees, and hence is often put into the kiln without
previous air-drying, and dried in a week or even less time.

Oak is the most difficult wood to dry properly. When it and other
hardwoods are rapidly dried without sufficient surrounding moisture,
the wood "case-hardens," that is, the outer part dries and shrinks
before the interior has had a chance to do the same, and this forms a
shell or case of shrunken, and often checked wood around the
interior which also checks later. This interior checking is called
honeycombing. Hardwood lumber is commonly air-dried from two to six
months, before being kiln-dried. For the sake of economy in time,
the tendency is to eliminate yard-drying, and substitute kiln-drying.
Kiln-drying of one inch oak, takes one or two weeks, quarter-sawn
boards taking one and a half times as long as plain-sawn.

The best method of drying is that which gradually raises the
temperature of both the wood and of the water which it contains to the
point at which the drying is to take place. Care is therefore taken
not to let the surface become entirely dry before the internal
moisture is heated. This is done by retaining the moisture first
vaporized about the wood, by means of wet steam. When the surface is
made permeable to moisture, d