SAMPLING AND TESTING HIGHWAY MATERIALS. 31 



1.75 inches in diameter, drilled in an iron plate one-fourth inch in thickness, or weigh 

 less than 0.75 pound (0.34 kg.). Further, the small spheres shall be tested, by pass- 

 ing them over the above plate or by weighing, after every 10 tests, and any which 

 pass through or fall below the specified weight, shall be replaced by new spheres; 

 provided, further, that all of the* small spheres shall not be rejected and replaced 

 by new ones at any one time, and that so far as possible the small spheres shall com- 

 pose a graduated series in various stages of wear. At any time that any sphere is 

 found to be broken or defective, it shall at once be replaced. 



The iron composing these spheres shall have a chemical composition within the 

 following limits: 



Combined carbon Not under 2.50 per cent. 



Graphitic carbon Not over 0.25 per cent. 



Silicon Not over 1.00 per cent. 



Manganese Not over 0.50 per cent. 



Phosphorus Not over 0.25 per cent. 



Sulphur Not over 0.08 per cent. 



For each new batch of spheres used, the chemical analysis shall be furnished by 

 the maker or be obtained by the user, before introducing into the charge, and unless 

 the analysis meets the above specifications, the batch of spheres shall be rejected. 



THE OPERATION OF THE TEST. 



(10) The brick charge. — The number of bricks per test shall be 10 for all bricks of 

 so-called "block-size," whose dimensions fall between 8 and 9 inches in length, 

 3 and 3| inches in breadth, and 3| and 4{ inches in thickness. 6 No brick should 

 be selected as part of a regular test that would be rejected by any other requirements 

 of the specifications under which the purchase is made. 



(11) Speed and duration of revolution.- — The rattler shall be rotated at a unifom rate 

 of not less than 29.5 nor more than 30.5 revolutions per minute, and 1,800 revolu- 

 tions shall constitute the test. A counting machine shall be attached to the rattler 

 for counting the revolutions. A margin not to exceed 10 revolutions will be allowed 

 for stopping. Only one start and stop per test is generally acceptable. If, from 

 accidental causes, the rattler is stopped and started more than once during a test, 

 and the loss exceeds the maximum permissible under the specifications, the test 

 shall be disqualified and another made. 



(12) The scales. — The scales must have a capacity of not less than 300 pounds, and 

 must be sensitive to 0.5 ounce, and must be tested by a standard test weight at 

 intervals of not less than every 10 tests. 



(13) The results. — The loss shall be calculated in percentage of the initial weight 

 of the brick composing the charge. In weighing the rattled brick, any piece weighing 

 less than 1 pound shall be rejected. 



(14) The records. — -A complete and continuous record shall be kept of the operation 

 of all rattlers working under these specifications. This record shall contain the 

 following data concerning each test made: 



1. The name of the person, firm, or corporation furnishing each sample tested. 



2. The name of the maker of the brick represented in each sample tested. 



3. The name of the street, or contract, which the sample represented. 



4. The brands or marks upon the bricks by which they were identified. 



5. The number of bricks furnished . 



6. The date on which they were tested. 



s Where "brick of larger or smaller sizes than the dimensions given above for blocks are to be tested, the 

 same number of bricks per charge should be used, but allowance for the difference in size should be made 

 in setting the limits for average and maximum rattler loss. 



