34 BULLETIN 246, U. S. DEPARTMENT OF AGRICULTURE. 



Tlie 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 6J 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. 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 </oini>ose 

 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 0.0S per cent. 



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

 by Hie 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. 



