1. A. G. Ayal and J. W. Leonard ,Mineral and Metallurgical Processing. Feb. ( 1987 ) 43 – 45 .
2. JW Leonard , III. JW Leonard , IV. Method for monitoring the efficiency of raw material beneficiation apparatus . U.S. Patent 4 345994. Aug. 24 1982 ( priority date Dec. 5 1980 ).