104
molesworth’s pocket-book
Notes on Timber—continued,
cut when soaked. Boiling iu steam or water
should last from four to six hours. The wood
should be gradually dried afterwards.
DESICCATING PROCESS.
The timber Is placed iu a chamber through
which a current of hot air is passed.
Temperature of air 100° Fahr, for hard, wood
in logs , 120° for pine ; up to 180° or 200° Fahr,
for thin planks. Mahogany 280° to 300°.
Velocity of current of air 100 feet per second.
Sufficient air should be forced into the chamber
to displace all the air in three minutes; or for
every 3 cubic feet of air in the chamber, 1 cubic
foot of air per minute should be supplied.
Duration of process, one week for each iaeh of
thickness of the timber.
IMPREGNATION OF TIMBER.
Relative absorbing power of timber, Memel
being assumed = 1'00 ; elm=l,35; yellow pine
= 115; beech = ‘ 4 ; English oak = ’ 34.
CHEOSOTiNG. (Bethell’s.)
The sleepers are either dried in the open air for
1J year, or oven-dried at temperature varying
from 212,J to 250° Fahr., either until they cease to
emit steam or for twenty-four hours. They are
then placed in the impregnating chamber, and
subjected, to a vacuum of 3 to 5 lbs. per square
inch, from | to f of an hour. The creosote is
then forced in at a pressure varying from 100 to
150 lbs. per square inch, according to the length