Abstract: The apparatus and the method are provided for the generation of a reference gas consisting of a gaseous medium carrying a known concentration of vapors of a volatile liquid substance. The gaseous medium is introduced into a container enclosing an absorbing material filled with the volatile liquid substance for obtaining a mixed gas. The mixed gas is cooled with thermoelectric Peltier cells in a condenser to a given temperature lower than the temperature of the mixed gas in the container for condensing a part of the vapors. Condensates of the vapors fall back by gravity towards the container. A temperature probe at the outlet and a cooling control device are used for maintaining the mixed gas at the outlet at the given temperature. The apparatus is particularly useful for suprathreshold odor intensity olfactometers, gas calibrators and in medicine.