PHYSICAL PROPERTIES OF ROAD-BUILDING ROCK. 



9 



around. By means of a small one-fourth-inch steel chisel radial 

 cuts are made in the saw one-eighth of an inch apart and one-eighth 

 of an inch deep. The spaces between the cuts are then slightly 

 opened by bending the projections alternately to the right and left. 

 A mixture of vaseline and fine diamond fragments is inserted in each cut. 

 All of the cuts are then closed with a pair of pincers and hammered 

 down to the original thickness of the saw, thus driving the diamond 

 dust into the metal. The diamonds are not ground to a powder, but 

 are merely broken up into very fine fragments. A very small amount 



Fig. 5. — Details of Dorry hardness machine. 



of the mixture taken on the end of a toothpick is sufficient for each 

 cut. Just enough vaseline is used to enable one to pickup the diamonds. 



The saw is mounted on a spindle (B, fig. 4) driven by the pulley 

 (C) at 600 revolutions per minute from a motor (G). The specimen 

 to be cut is held in the V block (D), which is mounted on a swinging 

 arm pivoted as at (E). The lower end of the saw runs continuously 

 in water contained in the galvanized-iron pan (FF). 



Dorry hardness machine. 



The Dorry machine in use at the present time is a modification of 

 the original French machine, and consists fundamentally of a circular 

 steel disk (A, fig. 5), which is revolved in a horizontal plane by means 

 17025°— Bull. 347—16 2 



