The ratio between the density in a liquid of two minerals that are to be
separated (Mh and M1 being the heavy and light one,
respectively); C = Mh - 1/Ml , where water (sp gr, 1) is the
liquid. This ratio indicates the grain size above which separation by
gravity methods should be commercially practicable. Above 2.5 fine sands
(down to below 200 mesh) can be tabled. At 1.75 the lower limit is 100
mesh; at 1.5 about 10 mesh, and at 1.25 only gravel sizes can be treated.
Dictionary of Mining, Mineral, and Related Terms