A new, well‐defined metal vapor device called the heat‐pipe oven has been developed on the basis of the heat pipe, a heat conductive element designed by Grover and his co‐workers in Los Alamos. It continuously generates homogeneous vapors of well‐defined temperature, pressure, and optical path length. The vapor is confined by inert gas boundaries which remove the window problem and allow a direct pressure measurement without relying on vapor pressure curves. Due to the continuous evaporation and condensation the vapor purifies itself during operation.