Unit coal and the composition of coal ash

“Unit coal and the composition of coal ash,” by S. W. Parr and W. F. Wheeler, is issued by the Engineering Experiment Station of the University of Illinois as Bulletin No. 37. By unit coal is meant the organic material which is involved in combustion, as apart from the mineral constituents which, in their natural state, enter into the composition of all coals. From the experiments described in the bulletin, it appears that when similar cases are compared, the variations in composition are chiefly in the extraneous matter; that for a given district, and more especially for a given mine, the value of the unit coal is practically constant. The heating value of the actual coal may vary considerably, but when the portion of the whole which is not coal is eliminated, the resulting material is of constant value.