The ratio between the density in a liquid of two minerals that are to be separated (M_hand M₁being the heavy and light one, respectively); C = M_h- 1/M_l, 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.