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Washing Test and Grading or Mechanical Analysis of Road Gravel. (Bul- 
letin 555, page 32 (9).—A sample of the material weighing not less than 50 
times the weight of the largest size stone present is used. After thoroughly 
drying at 100° C. (212° F.) in a hot-air bath, the sample is cooled, weighed, 
and placed in a shallow pan, covered with water, and thoroughly agitated by 
means of a trowel for 15 seconds. After 15 seconds sedimentation the water is 
poured off through a 200-mesh sieve, and the operation of agitation, sedimenta- 
tion, and decantation repeated until the wash water is approximately ciear 
after 15 seconds. The washed material, together with any residue retained on 
the 200-mesh sieve, is then dried to constant weight, cooled and weighed and 
passed through such of the following size screens and sieves as are called for 
in the specification, using them in the order named: 
Screens (circular openings ) : 38-inch, 24-inch, 2-inch, 13-inch, 1-inch, #-inch, 
3-inch, and -inch. 
Sieves, A. S. T. M. Standard Method (square mesh): 10, 20, 30, 40, 50, 60, 80, 
100, and 200 meshes per linear inch. 
The percentage by weight retained on each screen or sieve and based on the 
weight of the original sample is calculated, using for the determination of the 
percentage of material passing the 200-mesh sieve the sum of the weights of 
material passing this sieve by analysis and by washing. 
Cementing Value of Gravel, Top Soil, or Sand Clay. (Bulletin 347, page 
15). —A 500-gram sample of that portion of the material which will pass a 
z-inch screen is placed in a ball mill with 18 per cent water, and the machine 
given 5,000 revolutions at the rate of 30 per minute. After grinding the re- 
sulting dough is removed and molded in a hydraulic briquetting machine into 
briquettes 25 mm. in diameter and 25 mm. high, under a pressure of 132 kg. 
per sq. em. Six briquettes should be made from each sample. They are al- 
lowed to dry in the air at ordinary room temperature for 20 hours after mak- 
ing, and are then dried at a temperature of 100° C. for four hours, cooled for 
20 minutes in a desiccator, and immediately tested. In making the test the 
briquette is held in position on the anvil of a Page cementing-value-impact 
testing machine (fig. 3) by means of a drop of thick shellac, extreme care being 
taken to see that there is perfect contact between the upper surface of the 
briquette and the plunger, as well as between its lower surface and the anvil. 
With the briquette in position, the plunger resting on it, and the cam in the 
position shown in figure 3, the end of the pin (F) is brought into contact with 
the surface of the cam and the locknut tightened. This will give an effective 
drop of 1 cm. to the hammer. The brass pencil is so adjusted that on revolving 
the drum a horizontal line will be traced on a piece of sensitized paper which 
has been wrapped around it. On starting the motor, each blow of the hammer 
will then be recorded in a short vertical line above the base line. The number 
of blows required to destroy the resilience of the briquette will equal the num- 
ber of vertical lines showing on the record above the base line. In counting 
the number of vertical lines showing on the record, no attention shouid be paid 
