EXAMINATION OF BITUMINOUS ROAD MATEEIALS. 



13 



The penetration test is made as follows : A sample of the material to 

 be tested is first warmed sufficiently to flow, and poured into the tin 

 box. The box and contents, after cooling for one-half hour at room 

 temperature, are immersed in water maintained at the temperature at 

 which the test is to be made, and allowed to remain immersed for one 

 and one-half hours. The sample in the tin box should now be placed 

 in the glass cup and removed in it, covered with as much water as con- 

 venient withont spilling, to the shelf d. The brass rod with the needle 

 is inserted into b and secured by tightening the binding screw. The 

 rod is lowered until the point of the needle almost touches the surface 

 of the sample; then by grasping the frame with both hands it is cau- 

 tiously pulled down until the needle just comes in contact with the 

 surf ace of the sample. 

 This can be seen best 

 by having a light so 

 situated that, upon 

 looking through the 

 sides of the glass cup, 

 the needle will be re- 

 flected from the sur- 

 face of the sample. 

 After thus setting the 

 needle, the counter- 

 weight is slowly raised 

 until the foot "Of the 

 rack rests on the head 

 of the rod and a read- 

 ing of the dial taken. 

 The clamp is then 

 opened wide by press- 

 ing the button and held in this position for exactly five seconds, as 

 determined by the pendulum or metronome. The clamp is then 

 released, the rack lowered until it rests on the rod, and the difference 

 between the first and second readings of the dial in hundredths of a 

 centimeter is taken as the distance penetrated by the needle. 



Owing to the susceptibility of certain bitumens to slight changes 

 in temperature, the water bath should be accurately maintained at 

 the desired temperature, both before and during the test, and, when 

 the room temperature differs greatly from that of the bath, the water 

 in the glass cup should be renewed after each test. An average of 

 from three to five tests, which should not differ more than four points 

 between maximum and minimum, is taken as the penetration of tin; 

 tple. The tests should be made at points on the surface of the 

 pie not less than one centimeter from die side of the container 

 and not less than one centimeter apart. 



Fig. 7.— New York Testing Laboratory penetrometer. 



