62 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
immersed in water for 24 hours, removed, and the surface water wiped off 
with a slightly dampened cloth. The specimen is then quickly weighed and 
the percentage of absorption computed. 
( b ) Brittleness. — A sample 2 by 6 inches is cut from the joint material parallel 
to the lay of the fiber and maintained at a temperature of from 4° to 6° C. in 
water for at least two hours prior to testing. It is then clamped between 
two boards so that expansion joint cantilevers SV2 inches and is held in any 
suitable support. A cast-iron ball, weighing 0.95' pound and having a diameter 
of 1.875 inches, is suspended by a cord which is tied to an eyelet soldered to 
the ball. For samples having a thickness of nine-sixteenths inch or less, the 
ball is suspended 1 foot above the center of the projected portion of the speci- 
men. For samples over nine-sixteenths inch in thickness the ball is suspended 
2 feet above the specimen. The ball is relased by burning the string above 
the eyelet. 
(c) Distortion. — A sample 2 by 6 inches, absolutely flat and straight, which 
has been cut parallel to the lay of the fiber, is clamped between two blocks so 
that the expansion joint cantilevers 3% inches. The clamp with the expansion 
joint is then placed in an oven maintained at 125° F. for two hours. The 
deflection from the horizontal is then measured. 
43. METHODS OF TEST FOR SPECIFIC GRAVITY OF 
BITUMINOUS MATERIALS 
1. The specific gravity of bituminous materials shall be expressed preferably 
as the ratio of the weight of a given volume of the material at 25° C. (77° F.) 
to that of an equal volume of water at the same temperature, and shall be 
expressed thus: 
Specific gravity 25°/25° C. (77°/77° F.) 
HYDROMETER METHOD 
(Used for thin fluid bitumens) 
2. The specific gravity of thin fluid bituminous road materials may be deter- 
mined with the above-mentioned apparatus by first pouring a sufficient quantity 
of the material into a tin cup which is then placed in a large dish containing 
cold or warm water, as occasion may require. The material in the cup should 
be stirred with the thermometer until it is brought to a temperature of 25° C, 
after which it should be immediately poured into the hydrometer jar and its 
gravity determined by means of the proper hydrometer. In case the hydrometer 
sinks slowly, owing to the viscosity of the material it should be given sufficient 
time to come to a definite resting point, and this point should be checked by 
raising the hydrometer and allowing it to sink a second time. The hydrometer 
should never be pushed below the point at which it naturally comes to rest 
until the last reading has been made. It may then be pushed below the reading 
for a distance of three or four of the small divisions on the scale, whereupon 
it should immediately begin to rise. If it fails to do so, the material is too 
viscous for the hydrometer method, and the pycnometer method should be 
employed. 
3. The direct specific gravity reading obtained by the foregoing method is 
based upon water at 15.5° C. taken as unity. For all practical purposes this 
reading may be corrected to water at 25° C. considered as unity, by multiplying 
it by 1.002. Thus: 
Specific gravity 25°/25° C.=specific gravity 25°/15.5° C.X 1.002 
PYCNOMETER METHOD 
(Used for viscous fluid and semisolid bitumens and emulsions) 
4. The determination of specific gravity shall be made with a pycnometer 
(Hubbard-Carmick type recommended) or weighing bottle, which shall consist 
(if a conical or Erlenmeyer-shaped flask approximately 45 millimeters high, 40 
millimeters in diameter at the bottom, and 25 millimeters in diameter at the 
