SAMPLING AXD TESTIXG HIGHWAY MATERIALS. 
13 
5. The method is as follows : 
(1) Dry at not more than 110° C. (230° F. ) to constant weight 
a sample weighing about 55 grams; (2) weigh 50 grams of the 
dry sample to 0.1 gram and pour it into the unstoppered Erlen- 
meyer flask, which shall be cleaned and dried before each deter- 
mination : (3) fill the bulb and burette with kerosene, leaving 
just space enough to take the temperature by introducing a ther- 
mometer through the neck: (4) remove the thermometer and add 
sufficient kerosene to fill exactly to the mark on the neck, drawing 
off any excess with the burette; (5) run into the flask about one- 
half of the kerosene in the bulb to remove air bubbles and then 
run in more kerosene, removing any material adhering to the 
neck of the flask, until the kerosene is just below the ground glass : 
(6) place the hollow ground-glass stopper in position and turn 
it to fit tightly, and then run in kerosene exactly to the 200 
cubic centimeter (6.76 ounces) graduation on ihe neck, care being 
taken to remove all air bubbles in the flask: (7) read the speci- 
fic gravity from the graduation on the burette, and the tempera- 
ture of the oil in the flask, noting the difference between the 
temperature of the oil in the bulb before the determination and 
that of the oil in the flask after the determination; (S) make a 
temperature correction to the reading of the specific gravity in 
accordance with the table furnished by the manufacturer of the 
apparatus, adding the correction if the temperature of the kero- 
sene has increased and subtracting it if the temperature of the 
kerosene has decreased. 
TEST FOR UNIT WEIGHT OF AGGREGATE FOR CONCRETE 
AND PERCENTAGE OF VOIDS. 
(A. B. T. M. standard method, serial designation C 29-21, slightly 
modified.) 
1. The unit weight of fine, coarse, or mixed aggregates for con- 
crete shall be determined by the following method ; 
2. {a) The apparatus required consists of a cylindrical metal Apparatus. 
measure, a tamping rod, and a scale or balance, sensitive to 0.5 
per cent of the weight of the sample to be weighed. 
(b) Measure*. — The measure shall be of metal, preferably ma- 
chined to accurate dimensions on the inside, cylindrical in form, 
water-tight, and of sufficient rigidity to retain its form under 
rough usage, with top and bottom true and even, and preferably 
provided with handles. 
The measure shall be one-tenth, one-half, or 1 cubic foot 
capacity, depending on the maximum diameter of the coarsest par- 
ticles in the aggregate, and shall be of the following dimensions: 
Capaci,,. d I-^ r 
Inside 
height. 
Diameter 
of largest 
particles of 
aggregate. 
Inches. 
^ cubic foot 6. 06 
i cubic foot 10.00 
1 cubic foot 14.00 
Inehes. 
6.10 
11.00 
11.23 
Inches. 
Under i 
Under 1 J 
Over 1 1 
(c) Tamping rod. — The tamping rod shall be a straight metal 
rod three-fourths inch in diameter and IS inches long, with one 
end tapered for a distance of 1 inch to a blunt, bullet-shaped point. 
3. The measure shall be calibrated by accurately determining 
the weight of water at 16.7° C. n;2 D P.) required to fill it. The 
factor for any unit shall be obtained by dividing the unit weight 
of water at 16.7° C. (62° F.) 5 by the weight of water at 16.7 C. 
(62° F.) required to fill the measure. 
5 The unit weight of water at 16.7' C. (62° F.) is 62.355 pounds por 
cubic foot. 
