Changes in infrared emission and absorption spectra of hot gases brought about by controlled variations of gas temperature profile were measured. Spectral emission-absorption temperatures were determined from the spectral data as a function of wavelength, using the Kirchhoff and Planck laws. These temperatures proved independent of wavelength for an isothermal profile, despite a large variation of absorptance with wavelength. For nonisothermal profiles, the emission-absorption temperature varied with wavelength in a characteristic manner for each profile. These results established more firmly the validity of the infrared emission-absorption technique of gas temperature measurement, and confirmed a previous hypothesis that the wavelength dependence of spectrally determined temperature, observed for most flames, is a temperature profile effect. The spectral emittance equation for a gas was formulated in terms of observable quantities for isothermal and nonisothermal cases, taking the spectrometer slit function into account.

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