Document ypydN902EDMRM9gqqM8neK6jn

R. I. 3^5 TABLE 2. - Summary of data for mines in United States using rock dust Number Percent Production mines of all from mines Year using underground using rock mines using rock dust, dust rock dust short tons 1926 177 - -- Percent of Percent of total produc total under tion from ground em underground ployees in mines using mines using rock dust rock dust --- Percent of total man hours worked in mines using rock dust - Rock dust used, pounds -- Rock dust used per ton of coal mined in rock-dusted mines, pounds -- 1927 463 6.5 137,280,000 24.0 21.3 -- 1930 474 8.4 l4g,634,912 33.2 27.5 3c.1 137,738,000 0.93 1931 449 8.3 115.904,819 31.9 26.8 29.1 119,621,000 1.03 1932 393 7.5 88,632,327 30.6 25.7 27.1 74,938,000 .85 1933 382 7.2 96,691,753 30.7 25.4 27.4 73,150,000 .76 193^ 4i4 7.0 112,300,000 33*2 28.4 29.8 104,234,000 93 1935 413 6.9 116,600,000 33 .'4 r\ n ClO*"T 29.9 99,188,000 .85 1936 462 7.5 161,000,000 39.3 32.5 35.7 153,686,000 95 7239 - 6- -'j O K a Hj H- P* O H- o' H- o' Cl- CT5 slca40fafa<pi+ ! I--111--1 M M t--'1