[Illustration:  FIG. 34.—­Sample log sheet of an endwise compression test on a short pine column.]

In short specimens the failure usually occurs in one or several planes diagonal to the axis of the specimen.  If the ends are more moist than the middle a crushing may occur on the extreme ends in a horizontal plane.  Such a test is not valid 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 its upper surface immediately beneath the centre of the movable head.  For the larger specimens this plate is six inches wide; for the smaller sizes, two inches wide.  The plate in all cases projects over the edges of the test piece, and in no case should the length of the latter be less than four times the width of the plate.