Transactions of the American Society of Civil Engineers, vol. LXX, Dec. 1910 - Federal Investigations of Mine Accidents, Structural - Materials and Fuels. Paper No. 1171 by Herbert M. Wilson
page 63 of 187 (33%)
page 63 of 187 (33%)
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TABLE 2.--Number of Holes per Square Foot in Zinc Plates with Circular
Perforations. -------------+------------ Diameter, | Number in inches | of holes. -------------+------------ 1/2 | 353 4/10 | 518 1/3 | 782 1/4 | 1,392 1/6 | 1,680 1/8 | 3,456 1/10 | 6,636 1/16 | 12,800 -------------+------------ The finer meshes are obtained by using linen screens with holes of two sizes, namely, 1/20 in. square and 1/28 in. square. Until a few years ago, black blasting powder was manufactured in the sizes given in Table 3. TABLE 3.--Gradation of Black Blasting Powder. ---------+----------- Grade. | Mesh. ---------+----------- CC | 2 - 2½ C | 2½ - 3 |
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