283,717. Farnham, R. V. Dec. 18, 1926. Retorts. - Coking apparatus comprises a chamber built up of superposed sections containing rotary trays of channel or H-section for cascading the material as it falls from an air-tight feed hopper b to an air-tight discharge hopper b'. The trays are disposed so that as the material falls from one the next below is in position to receive it. Heating gases may be passed into the uppermost section of the chamber and exhausted from the lowermost. The chamber may be water-jacketed or formed of refractory material, and it may be heated externally. The trays may be formed with corrugated bases.