36 BULLETIN 1704, U. S. DEPARTMENT OF AGRICULTURE. 
be omitted in cases where material from a well-known source of supply has 
been tested within one year previous to the date of acceptance or rejection. In 
such case the report of the last previous test may be used as the basis of ac- 
ceptance or rejection. Mixed samples may be taken when deemed necessary. 
Each sample should weigh at least 25 pounds and be composed only of sound 
interior rock strictly representative of that which it proposed to use. The 
fragments should be 2 inches in size or larger. In addition, one piece which 
should measure at least 3 by 4 by 6 inches will be required if a toughness test 
is to be made. This piece should be free from seams and cracks, and should 
have the bedding plane marked if Dracaeane Samples should be shipped in 
tight boxes or heavy burlap bags. 
Sampling for Size or Grading.—Broken stone may be sampled for size at 
the crusher, from bins, cars, or storage piles on’ the job. A composite sample 
composed of samples from different parts of the supply is advisable. Samples 
should weigh not less than 10 pounds for material containing fragments # 
inch in diameter. Samples of larger aggregates should increase in size up to 
about 60 pounds, depending upon the diameter and weight of the largest frag- 
ments present. When laboratory tests for size are required, samples should be 
shipped in tight boxes or heavy close canvas bags. 
BROKEN SLAG. 
Sampling for Quality.—Slag should be sampled from the crusher or that por- 
tion of the dump which it is proposed to use, at least two weeks and not more 
than one month before final acceptance. Additicnal samples should be taken 
during progress of the work, whenever the quality or appearance of the slag 
changes, and at such other times as may be directed. For the French co- 
efficient of wear determination, each sample should weigh at least 25 pounds 
and be composed of fragments 2 inches in size or larger. Samples of approxi- 
mately 100 pounds of each size will be needed for determinations of weight per 
cubie foot, but such test should ordinarily be made at the crusher or on the job. 
Tight boxes or heavy burlap bags should be used as containers when shipping 
samples of slag. 
Sampling for Size or Grading.—The same directions given under broken 
stone apply to broken slag. 
GRAVEL. 
Samples of pit run gravel proposed for use in water-bound gravel road con- 
struction should be taken at least 10 days and not more than 6 months prior 
to the date of acceptance or rejection, and, if from an accepted source of supply, 
whenever, during the progress of the work, the gravel appears to change 
markedly in either quality or grading. Great care should always be exercised 
in sampling a gravel -pit to insure obtaining material for test which is strictly 
representative of that which it is proposed to use. A number of samples may 
be taken from a Single pit if necessary to cover the probable range in grading 
of the available material. Samples of pit run gravel should weigh from 50 to 
75 pounds. 
Samples of screened gravel may be taken at the plant, from bins, storage 
piles, barges, or cars. A composite sample composed of samples from different 
parts of the supply is advisable in order to determine the average composi- 
tion of the material. Every shipment of gravel for bituminous concrete or 
Portland cement concrete should be sampled, in which case no single sample 
should represent over 100 cubic yards. Samples should weigh from not less 
oe? es a ee ee 
———EEOoo eer 
