An induction furnace for rapidly heating substances by induction to volatilize them includes a split cylindrical carbon susceptor spaced inwardly of a cylindrical outer wall and surrounding a carbon cup holding the substance for bringing the temperature of the hot zone up to as high as 2000*C. very rapidly. A metal-tometal seal is provided for sealing a tantalum rod holding the cup while permitting adjustment of the position of the cup axially of the cylindrical outer wall.