a gas mixer and reactor is provided which includes an elongated gas flow chamber with a nozzle arrangement at its inlet end for passing a first gaseous reactant into the interior of the chamber , toward the outlet of the chamber from points uniformly about the inner periphery of the chamber , and an annular nozzle arrangement near the outlet of the gas flow chamber for directing another gaseous reactant , or reactants , through the outlet of the gas flow chamber and into a thermal reaction chamber which communicates with the outlet of the gas flow chamber . in this manner controlled amounts of gaseous reactants may be thoroughly admixed and reacted to produce an atmosphere of desired composition . atmospheres for kilns having controlled amounts of free hydrogen , carbon monoxide , oxygen , or carbon for example , are produced by burning controlled ratios of fuel , air and in some cases an inert gas , mixed by the reactor .