Abstract: An apparatus for metallurgically heat treating workpieces, the apparatus comprises a rotatable retort having an elongated treating chamber. A workpiece conveyor is within the treating chamber whereby the workpieces can be moved from the entrance end to the exit end of the treating chamber. A plurality of partitions within the treating chamber cooperate with the conveyor and treating chamber to divide the treating chamber into a plurality of distinct atmospherically isolated chambers and to allow for the movement of the workpieces into and out of the chambers. A gas distributor is within the treating chamber. The gas distributor is operatively connected to a reactive gas source and has gas outlets in selected ones of the chambers.