red, when tests on
such forms are not available.

A comparison of the results of tests on seasoned material with
those from tests on green material shows that, without
exception, the strength of the 2" X 2" specimens is increased by
lowering the moisture content, but that increase in strength of
other sizes is much more erratic. Some specimens, in fact, show
an apparent loss in strength due to seasoning. If structural
timbers are seasoned slowly, in order to avoid excessive
checking, there should be an increase in their strength. In the
light of these facts it is not safe to base working stresses on
results secured from any but green material. For a discussion of
factors of safety and safe working stresses for structural
timbers see the Manual of the American Railway Engineering
Association, Chicago, 1911. A table from that publication,
giving working unit stresses for structural timber, is
reproduced in this book, see Table XXII.

|-----------------------------------------------------------------------------------------------------------------------------------|
| TABLE XVIII TABLE XVIII |
|-----------------------------------------------------------------------------------------------------------------------------------|
| BENDING TESTS ON GREEN MATERIAL |
|-----------------------------------------------------------------------------------------------------------------------------------|
| | Sizes | | | | F.S. at E.L. | M. of R. | M. of E. | Calculated |
| |-----------------| Num- | Per | Rings | | | | shear |
| Species | | | ber | cent | per |-----------------+-----------------+-----------------+-----------------|
| | Cross | Span | of | mois- | inch | Average | Ratio | Average | Ratio | Average | Ratio | Average | Ratio |
| | Section | | tests | ture | | per sq. | to 2" | per sq. | to 2" | per sq. | to 2" | per sq. | to 2" |
| | | | | | | inch | by 2" | inch | by 2" | inch | by 2" | inch | by 2" |
|-----------------+----------+------+-------+-----