By comparison with the original weight the loss from abrasion is determined, and by comparison with a certain wood chosen as a standard, a coefficient of wear-resistance can be obtained.  The amount of wear will vary more or less according to the surface exposed, and in these tests quarter-sawed material was used with the edge grain to the blast.

Indentation:  The tool used for this test consists of a punch with a hemispherical end or steel ball having a diameter of 0.444 inch, giving a surface area of one-fourth square inch.  It is fitted with a guard plate, which works loosely until the penetration has progressed to a depth of 0.222 inch, whereupon it tightens. (See Fig. 43.) The effect is that of sinking a ball half its diameter into the specimen.  This apparatus is fitted into the movable head of the static testing machine.

[Illustration:  FIG. 43.—­Design of tool for testing the hardness of woods by indentation.]

The wood to be tested is cut square with the grain into rectangular blocks measuring 2” X 2” X 6”.  A block is placed on the platform and the end of the punch forced into the wood at the rate of 0.25 inch per minute.  The operator keeps moving the small handle of the guard plate back and forth until it tightens.  At this instant the load is read and recorded.

Two penetrations each are made on the tangential and radial surfaces, and one on each end of every specimen tested.

In choosing the places on the block for the indentations, effort should be made to get a fair average of heartwood and sapwood, fine and coarse grain, early and late wood.

Another method of testing by indentation involves the use of a right-angled cone instead of a ball.  For details of this test as used in New South Wales see loc. cit., pp. 86-87.

CLEAVAGE TEST

A static testing machine and a special cleavage testing device are required. (See Fig. 44.) The latter consists essentially of two hooks, one of which is suspended from the centre of the top of the cage, the other extended above the movable head.

[Illustration:  FIG. 44.—­Design of tool for cleavage test.]

The specimens are 2” X 2” X 3.75”.  At one end a one-inch hole is bored, with its centre equidistant from the two sides and 0.25 inch from the end. (See Fig. 45.) This makes the cross section to be tested 2” X 3”.  Some of the blocks are cut radially and some tangentially, as indicated in the figure.

[Illustration:  FIG. 45.—­Design of cleavage test specimen.]

The free ends of the hooks are fitted into the notch in the end of the specimen.  The movable head of the machine is then made to descend at the rate of 0.25 inch per minute, pulling apart the hooks and splitting the block.  The maximum load only is taken and the result expressed in pounds per square inch of width.  A piece one-half inch thick is split off parallel to the failure and used for moisture determination.