18 



THE TESTING OF ROAD MATERIALS. 





in depth, was closed at one end and 

 had a tightly fitting iron' cover for 

 the other. A cut of a similar ma- 

 chine slightly modified and in use in 

 the Road Material Laboratory is shown 

 in fig. 1. 



In adopting the Deval machine, the 

 onl} T change made by the School of 

 Roads and Bridges was to increase the 

 number of cylinders to eight in order 

 to increase the output. The eight cylin- 

 ders are mounted four by four on two 

 parallel shafts geared to rotate with 

 the same rapidity. This arrangement 

 renders it possible to make eight tests 

 simultaneously. The method of oper- 

 ation is as follows: 



The rock to be tested is broken in 

 sizes as nearly uniform as possible, 

 each fragment being made to pass in 

 all positions through a 6-cm ring. 

 Five kilograms of rock thus prepared 

 and previously cleansed by washing 

 and subsequent drying are placed in 

 one of the cylinders. The cover is 

 then bolted on and the cylinders re- 

 volved at the rate of 2,000 revolu- 

 tions per hour. The fragments of 

 stone are thrown from one end of 

 the cylinder to the other twice in each 

 revolution, and thus grind and pound 

 against one another and the ends of 

 the cylinder. At the end of five hours, 

 or 10,000 revolutions, the machine is 

 stopped, the cylinder- opened, and tin 4 

 contents emptied into a basin. The 

 cylinder and the cover arc carefully 

 washed and the water u>ed i> poured 

 into the suue receptacle. Kach stone 

 i> then washed and brushed under 

 the water until all adhering dust is 

 removed. After drying, the detritus 

 IS -eparated into the following three 

 -i/e-: Above 1 cm. between 1 cm and 

 0.16 cm. and below o. !' cm. Only 



y the 



