EXAMINATION OF BITUMINOUS ROAD MATERIALS. ~ 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 without 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 pulied down until the needle just comes in contact with the 
surface 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 the 
sample. The tests should be made at points on the surface of the 
sample not less than one centimeter from the side of the container 
and not less than one centimeter apart. 
Fig. 7.—New York Testing Laboratory penetrometer. 
