PHYSICAL PROPERTIES OF ROAD-BUILDING ROCK. 



19 



Sensitized paper. 



The paper used for recording the number of blows delivered by the 

 hammer of the impact machine measures 8 by 2f inches in size and is 

 sensitized on one side to take the impression of a brass point. 



A 500-gram sample of the material to be tested is crushed to pea 

 size and placed in the ball mill together with 18 per cent (90 c. c.) of 

 water. After 5,000 revolutions of the mill, at the rate of 30 per min- 



A TopV/ew. 



IJ/ustrating Method of removing Pos/f/on of mo/of before compress/on. 



6r/i£ueffe 



Fig. 10.— Details of briquette mold. 



ute, the resulting dough is removed and molded into briquettes 25 

 mm. in diameter and 25 mm. high. The dough should never be 

 allowed to stand in the open air after grinding and previous to mold- 

 ing, but should be tightly sealed in a fruit jar. Even when sealed, 

 however, the dough should not be allowed to stand more than two or 

 three hours before molding into briquettes. In order to obtain 

 briquettes of the proper height, a trial specimen should be made as 

 follows: 28 grams of the material is weighed and placed in the die, 

 the plunger inserted, and the whole placed upon the platform of the 

 briquetting machine. Water is admitted to the cylinder until the 



