The Jackson standard. [volume] (Jackson C.H., Ohio) 1847-1888, 1873-04-17
fFrom the Scientific American. i
g The Strength of Timber.
By IoHs. AsDEssoa,. c. Il. D.. F. R. $. :

By JeHS- ANDERSON c. LII. D., F. h >. E.
The strength of a piece of timber de-
pends upon the part of the tree from
which it is taken. Up to a 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 soft
er than the othersparts of the wood, and
is liable to premature decay; The dele
terious component of the sapwood is abb
sorbed if the tree is allowed to grow for
a longer period, and in time the old sap
wood becomes proper timber fiber sirni-
lar to the heart wood. Hence, the good
ness of tree, for timber purposes, de
pends on the age at which the tree was
cut down. When young, the heart wood
is the best at maturity with the excep-
tion of the sapwood, the trunk is equally
good throughout; and when the tree is
allowed to grow too long, the heart wood
is the first to show symptoms of weak
ness, and deteriorates gradually.
The best timber is secured by telling
the tree at the age of maturity, which
depends on its nature as well as on the
soil and climate. The ash, beech, elm
and fir, are generally considered at their
best when of 20 or so years growth, and
the oak is seldom at its best in less time
than one hundred years; but much de
pends on surrounding circumstances.
As a rule, trees should not be cut before
arriving at maturity, because there is
then too much sapwood, and the dura-
bility of the timber is much inferior to
that of trees felled after they have ar
rived at their full development 's
The strength of many woods is doubled
by the process of seasoning, hence it is
very thriftless to use timber in green
state, as it 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 OUT
side is found to crack and to split more
than the inside of the mass, because it is
more exposed to the dessicatIng effect of
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 sea-
son dry. in a gradual manner, it is found
to be the most durable. In the artsg hows
ever, artificial drying is often resorted to-.
as in the case of gun stocks. These are
put into dessicating chamber, where a
current of air at 900 or fo0o is passed
over them, such a. rate as to change
the whole volume of air in the chamber
every three minutes, and it is found that
a year of seasoning may thus be saved.
The walnut wood is as good, after this
process, as if the seasoning had been ae-
complished by time and exposure, and
works more smoothly under the cutting
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
surface. The effect of moisture on dry
wood is to cause the fibers to swell hence
it is that, if a plank or board is Wetted
upon one side the fbers there will be
distended, and the plank in consequence,
must bend. E .s-
!; The amount of the shrinkage of timber
in length, when seasoning; is so inconsid-
cradle 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
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 a firm hold of glue In the last
respect it is superior to any other. wood.
Mahogany differs greatly in regard to its
closeness. hardness, strength, and beau
ty. That from Honduras, called "bay
| 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, but chiefly on account of its
Icheapness and the latter is used for
furniture or for other ornamental pur-
poses. As regards strength, this wood is
| inferior to oak in all respects, and its
great characteristic defect is unsuitabili-
| ty for exposure to the weather or, indeed,
for any purpose where it is made alter
nately wet and dry. When so subjected
it rapidly decays, and Loses all its good
/ qualities. 2@
Oak, taken as a whole, is one of the
strongest and most durable of woods,
and is especially adapted for exposure to
the weather of a damp climate, and is in
deed suitable for almost every purpose
4 where the properties of strength, stiff
| ness, and toughness, combined with en-
duFance, are required. Its value for ship
building is proverbial, and in its employ
ment for the slaves of casks, for tree
nails, for carriage wheels, and for all
such purposes requiring Gghtness and
strength in combination, it is 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-
tion. s5
q as4 Lucky Men.