48 
BULLETIN 691, U. S. DEPARTMENT OF AGBICTILrtTEE. 
W 
•warmed, to fill it about half full, without allowing the material to touch the 
sides of the tube above the desired level. The tube and contents are then 
allowed to cool to room temperature, after which the tube 
is carefully weighed with the stopper. This weight is 
called " c ". Distilled water, at 25° C, is then poured in 
until the pycnometer is full. After this the stopper is 
inserted, and the whole cooled to 25° C. by a 30-minute 
immersion in a beaker of distilled water maintained at 
this temperature. All surplus moisture is then removed 
with a soft cloth, and the pycnometer and contents are 
weighed. This weight is called " d ". From the weights 
obtained the specific gravity of the bitumen may be readily 
calculated by the following formula : 
Specific gravity 25° C,/25° C.- ^,^,^ 
The specific gravity of fluid bitumen may be determined 
in the ordinary manner with this pycnometer by completely 
filling it with the material and dividing the weight of the 
bitumen thus obtained by that of the same volume of water. 
Fig. 1. — Pycnometer 
(Hubbard type). 
FLASH POINT. 
[Bulletin 314, p. IT.] 
r 
* 
OPEN-CUP METHOD. 
The open-cup oil tester, shown in figure 2, consists of a brass oil cup a of 
about 100 cubic centimeters capacity, and an outer vessel & which serves as an 
air jacket ; a suitable thermometer c is suspended from 
the wire support d directly over the center of the cup so 
that its bulb is entirely covered with oil but does not 
touch the bottom of the cup. The testing flame is obtained 
from a jet of gas passed through a piece of glass tubing, 
and should be about 5 millimeters in length. 
The test is made by first filling the oil cup with the 
material under examination to within about 5 millimeters 
of the top. The Bunsen flame is then applied in such a 
manner that the temperature of the material in the cup 
is raised at the rate of 5° C. per minute. From time to 
time the testing flame is brought almost in contact with 
the surface of the oil. A distinct flicker or flash over the 
entire surface of the oil shows that the flash point is 
reached and the temperature at this point is taken. 
SPECIFIC VISCOSITY. 
[Bulletin 314, p. 7.] 
KEJ 
ENGLER VISCOSIMETER METHOD. 
The specific viscosity of fluid bituminous road materials 
is determined at the specified temperature by means of 
the Engler viscosimeter. This apparatus shown in figure 
3 may be described as follows: a is a brass vessel for 
holding the material to be tested, and may be closed by 
the cover b. To the conical bottom of a is fitted a conical outflow tube c, 
exactly 20 millimeters long, with a diameter at the top of 2.9 millimeters and 
at the bottom of 2.8 millimeters. This tube may be closed and opened by the 
Fig. 2. — Open-cup oil 
tester. 
