Use of a series of heavy liquids diminishing (or increasing) in density by accurately controlled stages for the purpose of dividing a sample of crushed coal into gravimetric fractions either equal-settling or equal-floating at each stage. The floats at a given specific gravity are defined as the percentage floating at that density and the sinks have a 1231 defined higher density. Each product (minus one density and plus another) is analyzed after weighing and the ash sulfur and Btu content is found. From this testing, a washability curve is drawn that relates density with ash sulfur and Btu content, in the form of cumulative float, sink, and specific gravity curves. The ash curve plots ash against density for successive fractions. The densimetric curve plots specific gravity against cumulative weight. The Mayer curve (M-curve) plots cumulative weight against that of a constituent (e.g., ash).