ts original size by soaking in
water, boiling, or steaming. Soaked pieces on drying shrink again as
before; boiled and steamed pieces do the same, but to a slightly less
degree. Neither hygroscopicity, _i.e._, the capacity of taking up
water, nor shrinkage of wood can be overcome by drying at temperatures
below 200 degrees Fahrenheit. Higher temperatures, however, reduce
these qualities, but nothing short of a coaling heat robs wood of the
capacity to shrink and swell.

Rapidly dried in a kiln, the wood of oak and other hardwoods
"case-harden," that is, the outer part dries and shrinks before the
interior has a chance to do the same, and thus forms a firm shell or
case of shrunken, commonly checked wood around the interior. This
shell does not prevent the interior from drying, but when this drying
occurs the interior is commonly checked along the medullary rays,
commonly called "honeycombing" or "hollow-horning." In practice this
occurrence can be prevented by steaming or sweating the wood in the
kiln, and still better by drying the wood in the open air or in a shed
before placing in the kiln. Since only the first shrinkage is apt to
check the wood, any kind of lumber which has once been air-dried
(three to six months for one-inch stuff) may be subjected to kiln heat
without any danger from this source.

Kept in a bent or warped condition during the first shrinkage, the
wood retains the shape to which it has been bent and firmly opposes
any attempt at subsequent straightening.

Sapwood, as a rule, shrinks more than heartwood of the same weight,
but very heavy heartwood may shrink more than lighter sapwood. The
amount of water in wood is no criterion of its shrinkage, since in wet
wood most of the water is held in the cavities, where it has no effect
on the volume.

The wood of pine, spruce, cypress, etc., with its very regular
structure, dries and shrinks evenly, and suffers much less in
seasoning than the wood of broad-leaved (hardwood) trees. Among the
latter, oak is the most difficult to dry without injury.

Desiccating the air with certain chemicals will cause the wood to dry,
but wood thus dried at 80 degrees Fahrenheit will still lose water in
the kiln. Wood dried at 120 degrees Fahrenheit loses water still if
dried at 200 degrees Fahrenheit, and this again will lose more water
if the temperature be raised, so that _absolutely dry wood_ cannot be
obtained, and chemical destruction sets in before all the wate