This method involves two essential features: (1) the circulation in the jig of a middling of approx. 3/16 in (4.8 mm) or smaller in size, with sp gr, 1.7 to 2.0--which fills the interstices of the jig bed and in effect converts the jig into a float-and-sink machine; and (2) the use of a suction stroke to hold the medium in the bed and prevent its washing over with the coal.