34 BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 
The staves when bolted to the heads shall form a barrel 20 inches long, inside 
measurement, between head liners. The liners of the staves must be so placed 
as to drop between the head liners. The staves shall be bolted tightly to the 
heads by four f-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 shall be kept tight. A record shall be made after each inspection showing 
in what condition the bolts were found. 
Item 8. 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 
one to four. The countershaft upon which the driving pinion is mounted shall 
not be less than lit inches in diameter, with bearings not less than 6 inches in 
length. If a belt drive is used, the pulley shall not be less than 18 inches in 
diameter and 6| inches in face. A belt at least 6 inches in width, properly 
adjusted to avoid unnecessary slipping, should be used. 
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 diam- 
eter 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 pos- 
sible 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. Xo 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. 
