103
OF ENGINEERING F0RMULÆ.
Notes on Timber.
GENERAL CHARACTER.
In the same class of timber the slower the
growth or the narrower the annular rings the
better. In the same class the heavier the better.
The cellular tissue (when visible) in the medullary
rays should be hard and compact. The fibrous
tissues should adhere firmly together, and should
show no woolliness at a freshly-cut surface; loose
fibres should not clog the teeth of the saw. If
the wood has colour, deepness of colour indicates
strength and durability. The freshly-cut surface
of wood should be firm, shining, and somewhat
translucent. A dull, chalky appearance is a sign
of bad timber. In resinous timber, those with
least resin in their pores are strongest and most
durable. In non-resiuous timber, those with least
sap or gum are best.
SEASONING TIMBER.
Timber should be felled in winter when the sap
is down. Timber should be seasoned from three
to five years before it is fit for use. It should be
removed from the forest as soon as possible, and
stacked where it will not be exposed to the sun,
the butt end downwards; the pores of the butt
exposed to the action of the air. Squared timber
is less apt to split than round timber; split
timber less than sawn timber. Seasoning may
be effected more rapidly by soaking in water, or
boiling. These processes, however, weaken the
timber. Soaking in water should continue for
about a fortnight; the timber should be freshly