Fly ashes from the coal combustion were analyzed for chem. compn. and grain size distribution by std. methods. The ashes differed significantly. The chem. compn. of ashes depended on the grain size. The conventional fly ash contained unburnt C. The fly ash from fluidized-bed combustion did not contain any microspheres but contained 10 times more of CaSO4 than that from the conventional combustion.