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BELL SYSTEM TECHNICAL JOURNAL 



Table III — Rockwell Hardness Tests on Alloy G Brass Sheet Showing 

 Effect of Using Unpolished and Polished Anvil 



sized the need for keeping these blocks clean and free from oxide, 

 grease or other accumulated matter. This applies with equal force 

 to the test specimens. Various methods of cleaning the test blocks 

 have been tried. A successful and convenient method is to rub the 

 surfaces of the test block by hand with chiffon velvet or other lap 

 material dipped in tripoli and water. Test blocks cleaned in this way 

 do not show a greater variation in readings than that of the original 

 test for uniformity. 



A variation in hardness must be permitted in these five readings 

 and on the basis of experience with a large number of blocks it is 

 considered that test blocks should have no greater variation than as 

 follows: When tested using the "B" scale, i^-in. ball, 100-kg. load 

 (red figures) ; for blocks under 40, 3 points variation is allowed ; for 



