Abstract: A gas mixer and reactor is provided which is especially suitable as a burner 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 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. Also provided are processes utilizing the mixer and in particular a process for converting sulfur containing gas into sulfur.