ut there is
one element common to all trees, and for that matter to almost all
plant growth, and that is albumen.

Both resin and albumen, as they exist in the sap of woods, are soluble
in water; and both harden with heat, much the same as the white of an
egg, which is almost pure albumen.

These organic substances are the dissolved reserve food, stored during
the winter in the pith rays, etc., of the wood and bark; generally but
a mere trace of them is to be found. From this it appears that the
solids contained in the sap, such as albumen, gum, sugar, etc.,
cannot exercise the influence on the strength of the wood which is so
commonly claimed for them.

Effects of Moisture on Wood

The question of the effect of moisture upon the strength and stiffness
of wood offers a wide scope for study, and authorities consulted
differ in conclusions. Two authorities give the tensile strength in
pounds per square inch for white oak as 10,000 and 19,500,
respectively; for spruce, 8,000 to 19,500, and other species in
similiar startling contrasts.

Wood, we are told, is composed of organic products. The chief material
is cellulose, and this in its natural state in the living plant or
green wood contains from 25 to 35 per cent of its weight in moisture.
The moisture renders the cellulose substance pliable. What the
physical action of the water is upon the molecular structure of
organic material, to render it softer and more pliable, is largely a
matter of conjecture.

The strength of a timber depends not only upon its relative freedom
from imperfections, such as knots, crookedness of grain, decay,
wormholes or ring-shakes, but also upon its density; upon the rate at
which it grew, and upon the arrangement of the various elements which
compose it.

The factors effecting the strength of wood are therefore of two
classes: (1) Those inherent in the wood itself and which may cause
differences to exist between two pieces from the same species of wood
or even between the two ends of a piece, and (2) those which are
foreign to the wood itself, such as moisture, oils, and heat.

Though the effect of moisture is generally temporary, it is far more
important than is generally realized. So great, indeed, is the effect
of moisture that under some conditions it outweighs all the other
causes which effect strength, with the exception, perhaps of decided
imperfections in the wood itself.

The Fi