Stratified Sampling of 2-Manifolds

An elongated furnace for heat treatment of metallic workpieces which are pushed through the heated furnace chamber along guide means extending from an inlet at one end of the furnace chamber to an outlet at the other end thereof. The elongated guide means comprise metallic elements supported on and in direct contact with water-cooled pipes extending upwardly spaced from the bottom wall of the furnace from the inlet towards the outlet, and a ceramic hearth portion in the region of the outlet and having an upper guide face flush with upper faces of said metallic elements.