shall be of a heavy quality.

The treatment will vary according to the dimensions of the timbers and
length of time they have been cut. Timbers of large and small dimensions
shall not be treated in the same charge, neither shall timbers of
differing stages of air seasoning, or the close-grained, be treated in
the same charge with coarse or open-grained timbers.

The timbers shall be subjected first to live steam superheated to from
250 to 275° Fahr., and under a 30 to 40-lb. pressure. The live steam
shall be admitted into the cylinders through perforated steam pipes, and
the temperature shall be obtained by using superheated steam in closed
pipes in the cylinders.

The length of time this steaming shall last will depend on the size of
the timbers and the length of time they have been cut. In piles and
large timbers freshly cut, as long a time as 12 hours may be required.
After the steaming is accomplished, the live steam shall be shut off and
the superheated steam shall be maintained at a temperature of 160° or
more and a vacuum of from 20 to 25 in. shall be held for 4 hours or
longer, if the discharge from the pumps indicates the necessity.

_Oil Treatment._--The temperature being maintained at 160° Fahr., the
cylinders shall be promptly filled with creosote oil at a temperature as
high as practicable (about 100° Fahr.). The oil shall be maintained at a
pressure ranging from 100 to 120 lb., as experience and measurements
must determine the length of time the oil treatment shall continue, so
that the required amount of oil may be injected.

After the required amount of oil is injected, the superheated steam