Rapides gazette. (Alexandria, La.) 1869-187?, 1873-07-26
The Strength Of Timber.

The strength of a piece of timber de-
pends upon the part of the tree from
which it is taken. Up to certain age,
the heart of the tree is the best after
that period it begins to fail gradually.
The worst part Of the 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 deleterious
component of the sapwood is absorbed II
the tree Is allowed to grow for longer
period, and In time the old sapwood be-
comes proper timber fiber, similar to
heart wood. Hence, the goodness OF a
tree for timber purposes, depends on the
age ar which the tree was cut down.
When young, the heart wood is the best
at maturity, with the exception of the sap
wood, the trunk Is equally good through
out; and when the tree Is allowed to
grow too long, the heart wood is the first
TO show symptoms of weakness, and de-
teriOrates gradually.
The best timber Is secured by Telling
the tree at the age of maturity, which de-
pends upon its nature as well as on the
soil and climate. The ash, beech, elm,
fir, are generally considered at their hest
when of seventy or eighty years. growth,
and the oak is seldom at its best In less
han one hundred years; but much de-
pends o surrounding circumstances. As
a rule, trees should not be cut before arriv-
ing at maturity, because 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 1t is
very thriftless to use timber In q green
state, as IL Is not only weak, but it Is ex-
posed to continual change Of bulk, form
and stability. After timber Is cut, and
before it is properly seasoned, the outside
is found to crack and to split more than
the inside of the mass, because it Is more
exposed to the surrounding atmosphere
but, as the outside dries, the air gradually
finds its way to the interior.
If timber Is cut by the saw when green,
and allowed to season or dry In a gradual
manner, It is found to be the most dura-
BILE. In the arts. however, artificial dry
ing Is often resOrted to, as in the case Of
gun stocks. These are put into desic-
eating chamber, where a current Of air at
ninety or one hundred 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 process,
as If the seasoning had been accomplished
by time and exposure, and works more
smoothly under the cutting instruments
of The stock machinery.
Wood will always warp after a 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 that wetting
the surface. The effect of moisture on
dry wood is to cause the tubular fibers to
swell /; hence 1t Is that, If plank or
board is wetted upon one side, the fibers
there will be distended, and the plank, In
consequence, must bend.
The amount of the shrinkage Of timber
in length, when seasoning, Is so inconsid-
erable that it may In practice be disre-
garded. But the shrinkage In transverse
directions is much greater, and presents
some peculiarities which can only be ex-
planned by examining the structure Of
the wood, as resulting from its mode Of
growth.-Scientifc american.