SAMPLING AND TESTING HIGHWAY MATERIALS. 



11 



through the neck; (4) remove the thermometer and add sufficient kerosene to fill 

 exactly to the mark on the neck, drawing off any excess with the burette; (5) run into 

 the flask about one-half of the kerosene in the bulb to remove air bubbles and then 

 run in more kerosene, removing any material adhering to the neck of the flask, until 

 the kerosene is just below the ground glass; (6) place the hollow ground-glass stopper 

 in position and turn it to fit tightly and then 

 run in kerosene exactly to the 200 c. c. (6.76 

 ounces) graduation on the neck, care being- 

 taken to remove all air bubbles in the flask; 

 (7) read the specific gravity from the gradua- 

 tion on the burette, and the temperature of 

 the oil in the flask, noting the difference be- 

 tween the temperature of the oil in the bulb 

 before the determination and that of the oil in 

 the flask after the determination; (8) make a 

 temperature correction to the reading of the 

 specific gravity in accordance with the table 

 furnished by the manufacturer of the apparatus, 

 adding the correction if the temperature of the 

 kerosene has increased and subtracting it if the 

 temperature of the kerosene has decreased. 



7. WEIGHT PER CUBIC FOOT AND VOID 

 TESTS ON COARSE AGGREGATE. 



(1) The weight per cubic foot of coarse aggre- 

 gate shall be determined as follows: A cylin- 

 drical measure of at least one-fourth cubic foot 

 capacity, with inside diameter approximately 

 equal to inside height, or a box approximately 

 cubical in shape and of not less than one-half 

 cubic foot capacity shall be used. Ordinarily, 

 the determination should be made on aggregate 

 in air-dry condition. When the aggregate con- 

 tains an appreciable amount of moisture, the 

 percentage of water by weight shall be deter- 

 mined and recorded. 



(2) About one-fourth of the total amount of 

 aggregate necessary to fill the measure shall 

 first be introduced in such manner as to avoid 

 separation of sizes. This material shall then be 

 shaken down by rocking the measure from side 

 to side until no further settlement takes place. 

 The process shall be repeated until the measure 

 has been filled to overflowing, after which it shall be struck off level with the top 

 with a straightedge and weighed. 



The percentage of voids in the aggregate may be determined from the weight per 

 cubic foot and specific gravity in the usual manner. 



Fig. 9. — Jackson specific-gravity apparatus. 



8. WEIGHT PER CUBIC FOOT TEST FOR FINE AGGREGATE. 



(1) For determining weight per cubic foot of fine aggregate use a cylindrical metal 

 measure having an inside diameter equal to the inside depth. A measure of capacity 

 of one-fifth to one-half cubic foot is suggested, but a measure as small as one-twentieth 

 cubic foot capacity may be used. Ordinarily the weight per cubic foot should be 



