In order to obtain, at the first distillation, from coal, shale, and bituminous substances an oil sufficiently pure for illuminating and other purposes, the material broken into very small pieces and placed on the bottom of the retort, is evenly covered with common sand, about four times greater in weight than the weight of the coal. The coal and sand are then gradually raised to a temperature of 212/sup 0/F. Steam containing carbonaceous impurities first passes to the condenser, and subsequently oil, which rises to the surface of the water in the receiving-vessel. When some bituminous substances are employed, the temperature, after oil ceases to come over, may be gradually raised until the oil produced ceases to be pure. Most kinds of clay and earth, chalk, gypsum, black oxide of manganese, plumbago, or charcoal may be used separately, in combination, or with added chemicals, instead of sand as the medium for filtering the gas or vapor from which the oil is formed. Either the oil obtained by the first distillation or oils obtained by other means may be rectified by distilling with sand.