UTILIZATION OF CALIFORNIA EUCALYPTS. ~ 
sapwood, and it must be borne in mind that the results of the tests 
were only such as could be obtained with wood from immature 
trees. The tests were made at the testing laboratory of the Forest 
Service, at the University of California, Berkeley, Cal. 
Clear, straight-grained specimens are needed in determining the 
strength of the wood itself apart from the influence of defects. 
The results of tests made on this class of material can also be 
used for comparison with similar tests on other kinds of woods. 
Pieces 2 by 2 inches in section have been found well suited to tests 
of this kind. For bending % they are cut about 30 inches long, and 
for compression parallel to the grain and compression perpendicular 
to the grain, from 6 to 10 inches long. The blocks for shear parallel 
to the grain are cut with a projecting lip, which is sheared off under 
test. In making a bending test the beam is supported at the ends 
and loaded at the middle. The supports for the beam are on the 
weighing platform of the testing machine, so that the load on the 
beam can be determined at any time during the test. This load is 
applied by a crosshead which can be forced down on the test specimen 
by means of heavy screws turned by a train of gears. The deflection 
or bending of the beam is measured by an apparatus consisting of a 
light steel frame on which is mounted a movable pointer. In making 
a test the frame is rested on two nails driven into the beam near the 
ends and the pointer attached to the center of the beam in such a 
way that it moves over a graduated arc when the beam bends, and 
thus shows the deflection. 
The test is conducted by loading the beam with about one-twentieth 
of the probable breaking load and noting the deflection. The load 
is then increased by a certain increment which is recorded with the 
corresponding deflection and the process continued until the beam 
breaks. The results of tests on beams of various sizes are reduced 
to a unit basis, so that direct comparisons as to strength and stiffness 
can be made between pieces of different sizes of the same or different 
species of wood. 
In computing the results, the breaking strength is represented by 
‘“‘modulus of rupture,” the stiffness by ‘‘modulus of elasticity,’ the 
load the material will carry without taking a set by ‘‘fiber stress at 
the elastic limit,’ and the ability to withstand shock without taking 
a set by ‘‘elastic resilience.” 
Tests in compression parallel with the grain are made by crushing 
the specimens endwise as they stand upright on the platform of the 
@ Fora detailed description of methods used in the tests, see Forest Service Circular 
38 (revised), “‘Instructions to Engineers of Timber Tests.”’ 
51755°—Cir. 179—10——2 
