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3
I
MINERAL TECHNOLOGY AND OUTPUT PER MAN STUDIES  
R O C K D R I I. L I N G  
5E
by  
C. E. Nighman ·  
and §
O. E. Kiessling  
I E
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V .¤
WORK PROJECTS ADMINISTRATION, NATIONAL RESEARCH PROJECT `  
In cooperation with  
DEPARTMENT OF THE INTERIOR, BUREAU OF MINES  
Report No. E—11  
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Phzladelyihw., Penrzsylv<1n1a .  
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February 1Q4O  
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J
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