run in
again and is kept in the cylinders under 100 pounds pressure for from
ten to twelve hours, until the required amount of absorption has been
reached (about 12 pounds per cubic foot).

Out-of-door Seasoning

The most effective seasoning is without doubt that obtained by the
uniform, slow drying which takes place in properly constructed piles
outdoors, under exposure to the winds and the sun. Lumber has always
been seasoned in this way, which is still the best for ordinary
purposes.

It is probable for the sake of economy, air-drying will be eliminated
in the drying process of the future without loss to the quality of the
product, but as yet no effective method has been discovered whereby
this may be accomplished, because nature performs certain functions in
air-drying that cannot be duplicated by artificial means. Because of
this, hardwoods, as a rule, cannot be successfully kiln-dried green or
direct from the saw, and must receive a certain amount of preliminary
air-drying before being placed in a dry kiln.

The present methods of air-seasoning in use have been determined by
long experience, and are probably as good as they could be made for
present conditions. But the same care has not up to this time been
given to the seasoning of such timber as ties, bridge material, posts,
telegraph and telephone poles, etc. These have sometimes been piled
more or less intelligently, but in the majority of cases their value
has been too low to make it seem worth while to pile with reference to
anything beyond convenience in handling.

In piling material for air-seasoning, one should utilize high, dry
ground when possible, and see that the foundations are high enough off
the ground, so that there is proper air circulation through the bottom
of the piles, and also that the piles are far enough apart so that the
air may circulate freely through and around them.

It is air circulation that is desired in all cases of drying, both in
dry kilns and out-of-doors, and not sunshine; that is, not the sun
shining directly upon the material. The ends also should be protected
from the sun, and everything possible done to induce a free
circulation of air, and to keep the foundations free from all plant
growth.

Naturally, the heavier the material to be dried, the more difficulty
is experienced from checking, which has its most active time in the
spring when the sap is rising. In fact the main period of da