‘EXAMINATION OF BITUMINOUS ROAD MATERIALS, 7 
' DISPLACEMENT METHOD (USED FOR HARD SOLID BITUMENS). 
EQUIPMENT. 
1 chemical thermometer reading from —10° C. to 110° C. 
1 analytical balance, capacity 100 grams, sensitive to 0.1 milligram. 
1 wood or metal platform. 
1 150 cubic centimeter low-form glass beaker. 
1 piece of fine silk thread. 
METHOD. 
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 cc.) is sus- 
pended by means of a silk thread from the hook on one of the pan 
supports, about 14 inches above the pan, and weighed. This weight 
is called “a.” It is then weighed immersed in water at 25° C, 
as shown in figure 3, 
and this weight is call- 
ed ‘“‘b.” The specific 
oravity may then be 
calculated by means 
of the following for- 
mula: 
Specificgravity = a 
7 
USE OF SPECIFIC GRAVITY 
DETERMINATION. 
The specific gravity 
determination is made 
on all bitumens con- 
taining less than 50 
per cent mineral matter, and also on bitumens recovered from 
bituminous aggregates. The specific. gravity is usually reported 
to the third decimal place. 
Fie. 3.—Displacement method of determining specific gravity. 
SPECIFIC VISCOSITY DETERMINATION. 
EQUIPMENT. 
1 Engler viscosimeter complete with thermometers, burner, and rubber tubing. 
1 100 cubic centimeter cylindrical glass graduate. 
1 stop watch. 
METHOD. 
The viscosity of fluid bituminous road materials may be determined 
at any suitable temperature by means of the Engler viscosimeter. 
This apparatus is shown in figure 4, and may be described as follows: 
a is a brass vessel for holding the material to be tested, and may be 
