SAMPLING AND TESTING HIGHWAY MATERIALS. 
47 
(e) Weighings shall be made quickly after filling the pycnometer 
and shall be accurate to 1 milligram. A number of trial fillings 
and catchweights may be necessary to obtain the desired degree 
of accuracy. 
(/") To prevent breakage of the pycnometer when cleaning it out 
after a determination has been made upon a very viscous or semi- 
solid material, it will be found advisable to warm it in an oven 
at not over 100° C. until most of the material may be poured out 
and then to swab it with a piece of soft cloth or cotton waste. 
When cool, it may be finally rinsed with carbon disulpbide, benzol, 
or other solvent and wiped clean. 
9. The limit of accuracy of the test is ±0.005 specific gravity. 
C. Displacement Method (Used fob Hard, Solid Bitumens). 
10. For materials which are hard enough to be broken and 
handled in fragments at room temperature the following method 
will prove convenient: A small fragment of the bitumen (about 
1 cubic centimeter) is suspended by means of a silk thread from 
the hook on one of the pan supports, about li inches above the 
pan. and weighed. This weight is called a. It is then weighed 
immersed in water at 25° C, and this weight is called b. The 
specific gravity may then be calculated by means of the following 
formula : 
Displacement 
method for 
solids. 
Specific gravity= ^^ 
D. Displacement Method (Used ion Semisolids). 
11. The specific gravity of semisolid bituminous materials may Displacement 
be determined by the displacement method. Weigh a silica cru- method tor 
cible suspended from the beam of the balance in air and call the semisolids. 
weight <i, and in water and call the weight b. Fill the crucible 
approximately two-thirds full with the material under examina- 
tion. Free from bubbles by heating on a hot plate, cool and 
weigh, calling this weight c. Immerse the filled crucible in water 
at 25° C. for one-half hour, then suspend by a wire from the beam 
of the balance and weigh it immersed in water at 25° ('.: call 
this weight d. The specific gravity is then calculated by means of 
the following formula : 
Specific gravity 
d-b 
DETERMINATION OF BITUMEN SOLUBLE IN CARBON 
BISULPHIDE. 
1. This test consists in dissolving the bitumen in carbon disul- 
pbide and recovering any insoluble matter by filtering the solution 
through an asbestos felt. The form of Gooch crucible best 
adapted for the determination is 4.4 centimeters wide at the top, 
tapering to 3.6 centimeters at the bottom, and is 2.5 centimeters 
deep. 
2. For preparing the felt, the asbestos is cut with scissors into Method of test. 
pieces not exceeding 1 centimeter in length, after which it is 
shaken up with just sufficient water to pour easily. The Gooch 
crucible is filled with the suspended asbestos, which is allowed to 
settle for a low moments. A light suction is then applied to draw 
off all the water and leave a firm mat of asbestos in the crucible. 
More of the suspended material is added, and the operation is 
repeated until the felt is so dense that it scarcely transmit-: 
light when held so that the bottom of the crucible is between the 
eye and the source of light. The felt should then be washed 
several times with water and drawn firmly againsl the bottom 
of the crucible by an increased suction. The crucible is removed 
to a drying oven for a few 'minutes, alter which it is ignited at 
red heat over a Bunsen burner, cooled in a desiccator, and 
weighed. 
