Manual of Forestry, Vol. V. (rev.
ed.), p. 75.]

Under ordinary conditions wood contains more or less moisture,
so that the application of heat has a drying effect which is
accompanied by shrinkage. This shrinkage completely obscures the
expansion due to the heating.

Experiments made at the Yale Forest School revealed the effect
of temperature on the crushing strength of wet wood. In the case
of wet chestnut wood the strength decreases 0.42 per cent for
each degree the water is heated above 60 deg. F.; in the case of
spruce the decrease is 0.32 per cent.

The effects of high temperature on wet wood are very marked.
Boiling produces a condition of great pliability, especially in
the case of hardwoods. If wood in this condition is bent and
allowed to dry, it rigidly retains the shape of the bend, though
its strength may be somewhat reduced. Except in the case of very
dry wood the effect of cold is to increase the strength and
stiffness of wood. The freezing of any free water in the pores
of the wood will augment these conditions.

The effect of steaming upon the strength of cross-ties was
investigated by the U.S. Forest Service in 1904. The conclusions
were summarized as follows:

"(1) The steam at pressure up to 40 pounds applied for 4 hours,
or at a pressure of 20 pounds up to 20 hours, increases the
weight of ties. At 40 pounds' pressure applied for 4 hours and
at 20 pounds for 5 hours the wood began to be scorched.

"(2) The steamed and saturated wood, when tested immediately
after treatment, exhibited weaknesses in proportion to the
pressure and duration of steaming. (See Table XVI.) If allowed
to air-dry subsequently the specimens regained the greater part
of their strength, provided the pressure and duration had not
exceeded those cited under (1). Subsequent immersion in water of
the steamed wood and dried specimens showed that they were
weaker than natural wood similarly dried and resoaked."[51]

[Footnote 51: Cir. 39. Experiments on the strength of treated
timber, p. 18.]

|------------------------------------------------------------------------------------------|
| TABLE XVI |
|------------------------------------------------------------------------------------------|
| EFFECT OF STEAMING ON THE STRENGTH OF GREEN LOBLOLLY PINE |
| (Forest Service, Cir. 39)