ich is being rotated. Only
superheated steam strikes the block, thus leaving the wood dry.
The test is continued for two minutes, after which the specimen
is removed and immediately weighed.

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.)