and should
always be culled. If the grain is diagonal or the stress is
unevenly applied a diagonal shear may occur from top to bottom
of the test specimen. Such tests are also invalid and should be
culled. When the plane (or several planes) of failure occurs
through the body of the specimen the test is valid. It may
sometimes be advantageous to allow the extreme ends to dry
slightly before testing in order to bring the planes of failure
within the body. This is a perfectly legitimate procedure
provided no drying is allowed from the sides of the specimen,
and the moisture disk is cut from the region of failure.

_Calculating the results:_ The formulae used in calculating the
results of tests on endwise compression are as follows:

P
(1) C = -----
A

P_{1}
(2) c = -------
A

P_{1} l
(3) E = ---------
A D

P D
(4) S = -----
2 V

C = crushing strength, pounds per square inch.
c = fibre strength at elastic limit, pounds per square inch.
A = area of cross section, square inches.
l = distance between centres of collars, inches.
D = total shortening at elastic limit, inches.
V = volume of specimen, cubic inches.

Remainder of legend as in BENDING LARGE BEAMS, above.

COMPRESSION ACROSS THE GRAIN

_Apparatus_: An ordinary static testing machine, a bearing
plate, and a deflectometer are required. (See Fig. 35.)

[Illustration: FIG. 35.--Compression across the grain. Note
method of measuring the deformation by means of a
deflectomoter.]

_Preparing the material_: Two classes of specimens are used,
namely, (1) sections of commercial sizes of ties, beams, and
other timbers, and (2) small, clear specimens with the length
several times the width. Sometimes small cubes are tested, but
the results are hardly applicable to conditions in practice. In
(2) the sides are surfaced and the ends squared. The specimens
are then carefully measured and weighed, defects noted, rate of
growth and proportion of late wood determined, as in bending
tests. (See BENDING LARGE BEAMS, above.) After the test a
moisture section is cut and weighed.

_Sketching_: Sketches are made as in endwise compression tests.
(See ENDWISE COMPRESSION, above.)

_Adjusting specimen in machine_: The specimen is laid
horizontally upon the platform of the machine and a steel
bearing plate placed on