42.) Upon the revolving horizontal disk is glued a commercial sandpaper, known as garnet paper, which is commonly employed in factories in finishing wood.
[Illustration: FIG.

42 .-- Abrasion machine for testing the wearing qualities of woods.] A small block of the wood to be tested is fixed in one clamp and a similar block of some wood chosen as a standard, as sugar maple, at 10 per cent moisture, in the opposite, and held against the same zone of sandpaper by a weight of 26 pounds each.

The size of the section under abrasion for each specimen is 2" X 2".

The conditions for wear are the same for both specimens.

The speed of rotation is 68 revolutions a minute.
The test is continued until the standard specimen is worn a specified amount, which varies with the kind of wood under test.
A comparison of the wear of the two blocks affords a fair idea of their relative resistance to abrasion.
Another method makes use of a sand blast to abrade the woods and is the one employed in New South Wales.[60] The apparatus consists essentially of a nozzle through which sand can be propelled at a high velocity against the test specimen by means of a steam jet.
[Footnote 60: See Warren, W.H.: The strength, elasticity, and other properties of New South Wales hardwood timbers.