BRICK ROADS. 37 



Item 9. The abrasive charge. — The abrasive charge shall consist of cast-iron 

 spheres of two sizes. When new, the larger splieres shall be 3.75 inches in 

 diameter and shall weigh approximately 7.5 pounds (3.40 kilos) each. Ten 

 spheres of this size shall be used. 



These shall be weighed separately after each 10 tests, and if the weight of 

 any large sphere falls to 7 pounds (3.175 kilos), it shall be discarded and a new 

 one substituted, provided, however, that all of the large spheres shall not be 

 discarded and substituted by new ones at any single time, and that so far as 

 possible the large spheres shall compose a graduated series in various stages 

 of wear. 



When new, the smaller sized spheres shall be 1.875 inches in diameter and 

 shall weigh approximately 0.95 pound (0.43 kilo) each. In general the number 

 of small spheres in a charge shall not fall below 245 nor exceed 260. The col- 

 lective weight of the large and small spheres shall be as nearly as possible 300 

 pounds. No small sphere shall be retained in use after it has been worn down 

 so that it will pass a circular hole 1.75 inches in diameter, drilled in an iron 

 plate i inch in thickness, or weigh less than 0.75 pound (0.34 kilo). Further, 

 the small spheres shall be tested by passing them over the above plate, or shall 

 be weighed after every 10 tests, and any which pass through the plate or fall 

 below the specified weight shall be replaced by new spheres ; and 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 compose 

 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 less than 2.50 per cent. 



Graphitic carbon, not more than 0.25 per cent. 



Silicon, not more than 1 per cent. 



Manganese, not more than 0.50 per cent. 



Phosphorus, not more than 0.25 per cent. 



Sulphur, not more than 0.08 per cent. 



For each new batch of spheres used the chemical analysis must be furnished 

 by the maker or be obtained by the user before inti'oducing into the charge, and 

 unless the analysis meets the above specifications the batch of spheres shall be 

 rejected. 



THE OPERATION OF THE TEST. 



Item 10. The drick charge. — The number of brick per test shall be 10 for all 

 bricks of so-called "block size," whose dimensions fall between from 8 to 9 

 inches in length, 3 to 3i inches in breadth, and 3f inches to 4i inches in thick- 

 ness.i ' No brick should be selected as a part of a regular test that would be 

 rejected by any other requirements of the specifications under which the pur- 

 chase is made. 



Item 11. Speed and duration of revolution. — The rattler shall be rotated at a 

 uniform rate of not less than 29^' nor more than 30i revolutions per minute, 

 and 1,800 revolutions shall constitute the test. A counting machine shall be 

 attached to the rattler for counting the revolutions. A margin of 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 per- 



1 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. 



