The Jeffersonian. [volume] (Stroudsburg, Pa.) 1853-1911, 1873-05-08
THE STRENGTH OF TIMBER.

which it is taken. Up to a certain age
the heart of the tree is the best after
that period it begius to fail gradually
The worst part Of "a tree is the sap wood
which is next the bark. 1t is softer than
the other parts of the wood, and is liable
to premature decay The deletcrious
component of the sap wood is absorbed if
the tree is allowed to grow for longer
period and in time the old sap wood be-
comes proper timber fibre similar to heart
wood Hence, the goodness of tree, for
/ timber purposes, depends upon the age
al which the tree was cut down When
young, the heart wooG is best at ma
turity, with the exception of the sap
wood, the tree is equally good through
cut; and when the tree is allowed to grow
too long the heart wood is the first to
show symptoms Of weakness, and dete
riorates gradually.
j he best timber is secured by telling
the tree at the age Of maturity, which de
pends on its nature as we'll as on the soil
aud climate. The ash, beech, elm and
fir are generally considered at their best
when of seventy or eighty years growth,
and the oak is seldom at its best in less
time than one hundred years but much
depends on the surrounding circum-
stances. As Il rule trees should not be
cut down before arriving at maturity be-
cause there is then too much sap wood
and the durability of the timber is much
Inferior to that Of trees felled after they
have arrived at their full development
The strength Of many woods is doubled
by the process of seasoning, hence it is
very thrilt!css to use timber in a green
state, as it is not only weak, but it is ex
posed to continual change of bulk, form
aud stability. After timber is cut, and
before it is properly seasoned, the out
side is found to crack and to split more
than the inside of the mass, because it is
more exposed to the desiccating effect of
the surrounding atmosphere but, as the
outside drys the air gradually finds its
way to the interior. If timber is cut by
the saw when green, and allowed to sea
son in gradual manner, it is found to
be the most durable La the arts, how
ever, artificial drying is often resorted to,
as in the case Of gun stocks. These are
put iuto desic -atiug chamber, where
current of air at 90 or 100 degrees is
passed over them, at such rate as to
change the whole volume of air in the
chamber every three minutes, and it is
found that year Of seasoning may thus
be saved The walnut wood is as good,
after this pracess, as if the seasoning had
been accomplished by time and exposure,
and works more smoothly under the cut
ting instruments of the stock machinery.
Wood will always warp after fresh
surface has been exposed, and will like
wise change its form by the presence of
any moisture, either from that contained
in the atmosphere, or from wetting the
suface The effect of moisture on dry
wood is to cause the fibres to swell hence
it is that if board or plank is wetted up
on one side, the fbres there will be dis
tended, and the plank iu consequence,
must bend.
The amount of shrinkage Of timber 10
length, when seasoning. is so inconsider
able that it may in practice be disregard
ed. But the shrinkage in transverse di
rections is much greater, and presents
some reculiarities which can ouly be ex
planned by examining the structure of the
wood as resulting from its mode of growth.
Mahogany is beautiful close grained
wood, but is used not so much on account
of its strength, but more frequently be-
cause OF its non liability to shrink, warp
or twist, and from the peculiar property
Of taking firm hold of glue. In the
last respect it is superior to any other
wood Mahogany differs greatly in re
gard to its closeness, hardness, strength
and beauty. That from Honduras, call
ed Ibay wood is much inferior to that
called Spanish" mahogany, which comes
from the West Indies the former is much
used in the construction of light textile
machinery, bat chiefly on account of Its
cheapness the latter is used for furniture
OK for Other ornamental purposes. AS re
CARDS strength this wood is inferior TO
oak in ali respects, and its great charac
tcristic defect is unsuitability for exposure
to the weather, or indeed, for any pur
pose where it is made alternately wet and
dry. When SO subjected, it rapidly de-
Gays and loses all its good qualities.
Oak, taken as whole, is one of the
strongest and most durable of woods, and
is especially adapted for exposure to the
weather of damp climate, aud is indeed
suitable for almost every purpose where
the properties of strength, stiffness, and
toughness, combined with endurance are
required. Its value for ship building is
proverbial, and in its employment for the
slaves of casks, for treenails, for carriage
wheels, aud for all such purposes requir
ing lightness and strength in combination
tits equally useful. From time immemorial
it was esteemed the best timber for heavy
roofs and the condition in which some of
these grand old roofs have reached our
era fully attests the wisdom of the selec-
ton"