Solved The processing of raw coal involves "washing," in
WEBThe processing of raw coal involves "washing," in which coal ash (non organic, incombustible material) is removed. The article "Quantifying Sampling Precision for Coal Ash Using Gy's Discrete Model of the Fundamental Error" (Journal of Coal Quality, 1989, 3339) provides data relating the percentage of ash to the density of a coal particle.