SAMPLING AND TESTING HIGHWAY MATERIALS. 37 
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 condition 
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 long, inside measurement, between head liners. The liners 
of the staves shall be so placed as to drop between the head 
liners. The staves shall be bolted tightly to the heads by four 
three-quarter-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 bolts 
were found. 
3. The frame and driving mechanism. — 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 
foundation with or without the interposition of wooden plates, 
and shall be fastened thereto by bolts at not less than four points. 
It shall be driven by gearing whose ratio of driver to driven 
is not less than 1 to 4. The countershaft upon which the driving 
pinion is mounted shall be not less than 111 inches in diameter, 
with bearing not less than 6 inches in length. If a belt is used, 
the pulley shall not be less than 18 inches in diameter and 6i 
inches in face. A belt at least 6 inches in width, properly ad- 
justed to avoid unnecessary slipping, should be used. 
4. The abrasive charge. — The abrasive charge shall consist of Abrasive 
cast-iron spheres of two sizes. When new, the larger spheres charge. 
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; pro- 
vided, however, that all of the large spheres shall not be dis- 
carded and new ones substituted 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 spheres shall be 1.875 inches in diameter 
and shall weigh approximately 0.95 pounds (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 near 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 diameter, drilled in an 
iron plate one-quarter 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 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 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 compo- 
sition within the following limits: 
• 
Per cent. 
Combined carbon Not under 2. 50 
Graphitic carbon Not over 0. 25 
Silicon Not over 1. 00 
Manganese Not over 0.50 
Phosphorus Not over 0. 25 
Sulphur Not over 0. 08 
