Om Materialprøvningens Udvikling i Norden
Og om Statsprøveanstaltens Virksomhed

182 there is room for the screws by which the aluminium plates are fastened to the wooden block. As the aluminium plates can be screwed on and off the wooden block, while the test-pieces are pasted to them, it is obtained that before and after the experiment the aluminium plates alone with the test-pieces can be weighed without weighing the whole block, consequently a finer balance can be employed. The block, when using rough sand-paper, wan- dering much more unsteady than when the linoleum was tested, owing to the elasticity of the test-pieces, so that the block wandered in small jumps, and the wear on fine sand-paper wood become slight, Carborundum-paper from the Carborundum Co., Niagara Falls, N. Y., Nr. 70 grain is employed. Further, the Carborundum-paper is changed only for every thousandth stroke, and the wooden block is turned for every two- hundredth stroke. The latter is done because a sheet of Carbo- rundum-paper is employed round each half-part of the plate- glass. Another deviation from the experiments with linoleum has finally been necessary namely to reduce the distance which the block has to wander, the velocity of rotation of the machine being continually the same, by which a slower and more steady movement of the block has been obtained. Thus it is possible now to get the rubber soles worn plane, while the unsteady move- ment wears off the surfaces to be extremely convex. The size of the test pieces is 7,5 X 5,0 cm. The block and the load is the same as that employed during the experiments with linoleum and explained in the treatise mentioned above. The size of the aluminium plates is 7,5 X 9,5 X 0,4 cm. The weight of the block together with the aluminium plates and the load is 3,61 kg. In the Table XII below are seen results from the experiments of the Laboratory up to 1st of August 1909; r and 1 designate that a test-piece is derived respectively from a right or left sole, i'j and r2 that the two test-pieces are derived from the same right sole. Instead of testing in the named way a test-piece of each sole in a pair of rubbers, each of the test-pieces can, of course, be made to derive from a sole in two different sorts of rubbers. From the loss of weight, the weight of the test-piece and the specific gravity of the stuff the volume worn off is, of course, to be calculated.