METHODS OF SAMPLING AND TESTING HIGHWAY MATERIALS 43 
liner shall consist of medium-carbon steel plate, and shall be riveted to the chan- 
nel by three one-half-inch rivets, one of which shall be on the center line both 
ways and the other two on the longitudinal center line and spaced 7 incbes 
from the center each way. The rivet holes shall be countersunk on the face 
of the liner and the rivets shall be driven hot and chipped off flush with the 
surface of the liners. These lines shall be inspected from time to time, and if 
found loose shall be at once reriveted. 
15. When a new rattler, in which a complete set of new staves is furnished, 
is first put into operation, it shall be charged with 400 pounds of shot of the 
same sizes and in the same proportion as provided in section 19, and shall 
then be run for 18,000 revolutions at the rate of speed specified in section 22 ( a | . 
The shot shall then be removed and a standard shot charge inserted, after which 
the rattler may be charged with brick for a test. 
16. No stave shall be used for more than 70 consecutive tests without renewing 
its lining. Two of the 14 staves shall be removed and relined at a time in such 
a way that of each pair one falls upon one side of the barrel and the other 
upon the opposite side, and also so that the staves changed shall be consecutive 
but not contiguous. For example, 1 and 8, 3 and 10, 5 and 12, 7 and 14, 2 and 9, 
4 and 11,6 and 13, etc., to the end that the interior of the barrel at all times 
shall present the same relative conditions of repair. The changes in the staves 
should be made at the time when the shot charges are being corrected, and the 
record must show the number of charges run since the last pair of new lined 
staves was placed in position. 
The staves when bolted to the heads shall form a barrel 20 inches in length, 
inside measurement, between headliners. The liners of the staves shall be so 
placed as to drop between the headliners. The staves shall be bolted tightly 
to the heads by four %-inch bolts, and each bolt shall be provided with a lock nut 
and shall be inspected at not less frequent intervals than every fifth test and all 
nuts kept tight. A record shall be made after each inspection, showing in what 
condition the l*>lts were found. 
17. The barrel shall be mounted on a cast-iron frame of sufficient strength and 
rigidity to support it without undue vibration. It shall rest on a rigid founda- 
tion with or without the interposition of wooden plates, and shall be fastened 
thereto by hots at not less than four points. 
18. The barrel shall be driven by gearing whose ratio of driver to driven is 
not less than one to four. The countershaft upon which the driving pinion is 
mounted shall not be less than It! inches in diameter, with bearing not less than 
6 inches in length. If a belt drive is used, the pulley shall be not less than 18 
inches in diameter and 6^ inches in face. A belt at least 6 inches in width, 
pro} icily adjusted to avoid unnecessary slipping, should be used. 
19. The abrasive charge shall consist of cast-iron spheres of two sizes. 
(a) Large spheres. — When new, the larger spheres shall be 3.75 inches in 
diameter and shall weigh approximately 7.5 pounds (3.40 kilograms) 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 kilo- 
grams) 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 in so far as possible the large spheres shall compose ;i 
graduated series in various stage of wear. 
(Z>) Small spheres. — When new. the smaller spheres shall be 1.875 inches in 
diameter and shall weigh approximately 0.95 pound (0.43 kilogram) each. In 
general, the number of small spheres in a charge shall not fall below 245 nor 
exceed 260. The collective weight of the large and small spheres shall be 
as nearly 300 pounds as possible. 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 diam- 
eter, drilled in an iron plate one-fourth inch in thickness, or weigh less than 
0.75 pound (0.34 kilogram). 
Further, the small spheres shall be tested by passing them over the plate 
mentioned or by weighing, after every 10 tests, and any which pass through 
or fall below the specified w T eight shall be replaced by new spheres, provided, fur- 
ther, 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. 
20. The cast-iron abrasive spheres shall conform to the following require- 
ments as to chemical composition : 
