An arc‐image stagnation‐flow reactor has been developed to study the rates of gas‐solid reactions between 2000 and 3000°K. Most refractory solids can be heated in this reactor to their melting points in a partial atmosphere of almost any gas except strong oxidizers such as fluorine. The standard deviation of a datum point, in the case of oxidation of tungsten by CO2at 100 Torr, is 6% at 2500°K, corresponding to a temperature uncertainty of ±9°K.