SPECIFICATIONS FOE, NONBITUMINOUS KOAD MATERIALS. 31 



Per cent. 



Total passing J-inch screen 



Total passing lO-mesh sieve 



Total passing 20-mesh sieve 



Total passing 30-mesli sieve 



Total passing 40-mesh sieve 



Total passing 50-mesh sieve 



Total passing 80-mesh sieve 



Total passing lOO-mesh sieve 



Total passing 200-mesh sieve 



Passing 200-inesli sieve elutriation 



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° O. (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 clear 

 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) : 3-inch, 2i-inch, 2-inch, IJ-inch, 1-inch, |-inch, 

 i-inch, and i-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 tlie 

 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 

 i-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. cm. 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 should be paid 



