25 



parts of the country. Without this cooperation 011 the part of the 

 factory proprietors this exhibit would have been impossible. 



EXHIBIT OF ROAD-MATERIAL LABORATORY. 



By LOGAN WALLER PAGE. 



The Road-Material Laboratory was established in October last for 

 testing road materials free of charge for any citizen of the United 

 States. As most of the machinery necessary for this work had to be 

 especially designed, the actual testing of road materials was not begun 

 until December. 



The short time which has intervened since then, together with the 

 lack of available funds, has made it impossible to do more than install 

 a part of the equipment necessary for the testing of rock and gravel. 

 The present exhibit is consequently far from complete. In order to 

 make an understanding of the exhibit as clear as possible, a brief 

 description will be given of the entire process of testing rock and 

 gravel at the present time. 



When a request is received at the laboratory for making a test, a 

 blank form containing a number of questions as to the exact location 

 from which the material comes, by whom owned, and the amount 

 available is sent, together with a tag envelope and instructions for 

 selecting and shipping. In the case of rock, as soon as a sample is 

 received at the laboratory, a hand specimen about 4 by G by 1 inches 

 in dimensions is properly dressed and put aside for reference. Exam- 

 ples of such hand specimens can be seen in exhibit case No. 8. (See 

 PL I, frontispiece). 



ABRASION TEST. 



The first test made on rock is the abrasion test, for determining the 

 relative resistance to wear. This test is made by placing 5 kilograms 

 (11 pounds) of rock of the usual size employed in road making (3 to 

 6 cm) in one of the C3'linders of the abrasion machine. (See PI. II, 

 fig. 1.) These cylinders are 34 cm in depth and 20 cm in diameter, 

 and are arranged on a shaft at an angle of 30 to the axis or rotation 

 of the shaft. The cover of the cylinder is bolted on, and the cylinder 

 is allowed to rotate for five hours, making 10,000 revolutions. Each 

 revolution of the cylinder throws the fragments of rock from one end 

 to the other twice, which causes them to grind and pound against one 

 another and against the walls of the cylinder. The contents of the 

 cylinder, after 10,000 re volutions/(is) brushed into a basin and the 

 resulting fine detritus is sifted into several sizes (shown in the exhibit 

 under the head of abrasion-test results) with an automatic sifter, a 

 photograph of which is shown in the exhibit case. From the dust 

 .worn off two coefficients of wear and the percentage of wear are 

 computed. 



