The behavior of cyanogen flames under a variety of conditions has been observed. Because of the relatively high stability of cyanogen, the behavior is considerably different from that of hydrocarbon flames. Because of the high stability of the combustion products, CO and N2, the flame temperature can reach temperatures above 4800°K. Thus the cyanogen-oxygen flame is the hottest natural flame known.Spectroscopic observations have been made of both the reaction zone and the mantle of completely combusted gases. Rotational and vibrational temperature measurements using the CN violet system have indicated that the reaction zone is not in thermal equilibrium but that the mantle is in thermal equilibrium. Comparison of the calculated flame temperatures based on different heats of dissociation of N2 with the observed mantle temperatures has fixed DN2=9.764±0.005 ev and DCN=8.2±0.2 ev.