"The experimental technique was checked out and the equipment put in working order for the study of the capacity and efficiency of the hydraulic cleaning of coal by water fluidization. The method to determine operating capacity consists of determining the segregation rate by dynamic tracing of radioactive mineral impurities of various size and density ranges, that are injected into the fluidized bed of coal. The equilibrium position of the injected tracer in the fluidized bed of solids is also determined. Obtaining capacity and efficiency data, as needed for design of commercial units, is very much less expensive and much more rapid than operation of a continuous flow pilot plant to get the same data. The required tracer solids were prepared by neutron irradiation of selected fractions of mineral impurities and the experimental work with these tracers is now in progress."