BRICK ROADS. 37 
Item 9. The abrasive charge. — The abrasive charge shall consist of cast-iron 
spheres of two sizes. When new, the larger spheres 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 introducing 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 brick 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 3| inches in breadth, and 3f inches to 4J inches in thick- 
ness. 1 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 301 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. 
