METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 23 
14. METHOD OF TEST FOR APPARENT SPECIFIC GRAVITY 
AND ABSORPTION OF STONE AND OTHER COARSE 
MATERIALS 
1. The apparent specific gravity shall be obtained by weighing the water dis- 
placed by a sample of tbe material weighing approximately 1,000 grams, broken 
into pieces about 1^4 inches in diameter. The vessel r* > be nsed consists of a 
galvanized-iron cylinder closed at one end and measuring 5 inches in diameter 
by 8 inches high. A brass spoilt one-half inch in diameter is soldered into the 
side of the cylinder 6 inches from the bottom. The spout is inclined at an 
angle of 2° with the horizontal and is 2% inches long. A notch is filed across its 
lower end to stop the drip from the displaced water. To determine the specific 
gravity and absorption, the dried and cooled sample shall be weighed to the 
nearest 0.5 gram and immersed in water for 24 hours. The pieces shall then be 
surface dried individually with a towel, the sample reweighed and immediately 
placed in the cylinder, which has been previously filled to overflowing with 
water at room temperature. 
2. The weight of water displaced by the sample shall be used to calculate its 
apparent specific gravity. The difference between the original weight of the 
sample and its weight after 24 hours shall be used to determine the absorption. 
15. METHOD OF TEST FOR APPARENT SPECIFIC GRAVITY 
AND ABSORPTION OR FREE MOISTURE CONTENT OF 
SAND, GRAVEL, STONE, OR OTHER NONBITUMINOUS 
HIGHWAY MATERIALS 
PYCXOMETER METHOD 
1. This method is designed primarily for the purpose of determining the 
apparent specific gravity of saturated surface-dry materials and the absorption 
or the free moisture content of materials as used in the field. While this 
method has been adapted for field use. it is suggested as a convenient method 
for making these determinations in the laboratory. 
2. The special apparatus used consists of a pycnometer which shall conform to 
the following conditions. 
(a) The opening at the top shall be approximately three-eighths inch in 
diameter. 
(6) The shape of the apparatus shall be such as will facilitate the escape 
of air bubbles. 
(c) It shall have an opening for the introduction of samples which will 
admit particles as large as 2 inches. 
(d) It shall be capable of being cleaned quickly and easily. 
APPARENT SPECIFIC GRAVITY 
3. (a) Coarse material. — The apparent specific gravity of coarse material shall 
be determined upon material that has been immersed in water at 70° F. for 24 
hours. Tlie pieces shall be individually surface dried with a towel. Two thou- 
sand grams of this surface-dried material shall be weighed out to the nearest 
0.5 gram. This sample shall be placed in the pycnometer and the pycnometer 
partly filled with water at 70° F. The pycnometer shall be gently shaken and 
rolled to remove entrained air. The pycnometer shall then be exactly filled 
with water and its outside surface dried. The pycnometer and its contents 
shall then be weighed to the nearest 0.5 gram. The apparent specific gravity 
shall be computed from the formula 
S 
Specific gravity= p+ ^__ w 
where 
S=the weight of the sample in grams. 
P=the weight in grams of the pycnometer full of water. 
TT=the weight in grams of the pycnometer plus the sample plus sufficient 
water to fill the pycnometer. 
