the wood. To
successfully accomplish this, adjustments must be available to
regulate the temperature, circulation, and humidity according to the
variations of the atmospheric conditions, the kind and condition of
the material to be dried.

This ideal effect is only attained by the use of a type of dry kiln in
which the surface of the lumber is kept soft, the pores being left
open until all the moisture within has been volatilized by the heat
and carried off by a free circulation of air. When the moisture has
been removed from the pores, the surface is dried without closing the
pores, resulting in timber that is clean, soft, bright, straight, and
absolutely free from stains, checks, or other imperfections.

Now, no matter how the method of drying may be applied, it must be
remembered that vapor exists in the atmosphere at all times, its
volume being regulated by the capacity of the temperature absorbed. To
kiln-dry properly, a free current of air must be maintained, of
sufficient volume to carry off this moisture. Now, the capacity of
this air for drying depends entirely upon the ability of its
temperature to absorb or carry off a larger proportion of moisture
than that apportioned by natural means. Thus, it will be seen, a cubic
foot of air at 32 degrees Fahrenheit is capable of absorbing only two
grains of water, while at 160 degrees, it will dispose of ninety
grains. The air, therefore, should be made as dry as possible and
caused to move freely, so as to remove all moisture from the surface
of the wood as soon as it appears. Thus the heat effects a double
purpose, not only increasing the rate of evaporation, but also the
capacity of the air for absorption. Where these means are applied,
which rely on the heat alone to accomplish this purpose, only that of
the moisture which is volatile succumbs, while the albumen and resin
becoming hardened under the treatment close up the pores of the wood.
This latter result is oft-times accomplished while moisture yet
remains and which in an enforced effort to escape bursts open the
cells in which it has been confined and creates what is known as
"checks."

Therefore, taking the above facts into consideration, the essentials
for the successful kiln-drying of wood may be enumerated as follows:

1. The evaporation from the surface of a stick should not
exceed the rate at which the moisture transfuses from the
interior to the surface.

2. Drying should proc