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 2| inches in size and is 
sensitized on one side to take the impression of a brass point. 
METHOD. 
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- 
J//ustrating Method of removing Pos/f/on of mo/of he fore compress/on. 
brigueffe 
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 
