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The absorption of ultrasound in CO2‐H2O mixtures at 150° and 200°C was measured at frequencies of 1.25, 3.3, 4.8, 9.9, and 14.0 MHz for H2O vapor concentrations from 0.5% to 50%. The measured absorptions are compared with calculated results and agree reasonably well. The effect of H2O vapor on the relaxation frequency is linear at least up to 20% H2O vapor and a decrease in relaxation frequency is observed with increasing temperature.

Spectral emissivities in the 2.7-μ band were obtained for hot gas mixtures of CO2 and H2O between 1000°K and 2200°K for various (CO2/H2O) sample ratios. The emission measurements were made at the exit of a small tripropellant rocket burner which produced the variable (CO2/H2O) mixtures by burning hydrogen, oxygen, and carbon monoxide. The spectral emissivities were determined from a calibrated emission spectrum and a spectroscopic determination of the temperature of the hot gas. The composition was evaluated from a semiempirical fit to a thermochemical flow calculation. The hot CO2–H2O mixtures were observed at a total pressure of 1 atm in the optically thin absorption region with a constant geometric pathlength. The variations of the spectral emissivities as a function of temperature are given for constant density of CO2 and H2O in the optical path. The experimental results agree with semitheoretically derived predictions. The characteristic area ratios of the integrated emissivities or integrated radiances within portions of the 2.7-μ band were derived and given as a function of temperature and (CO2/H2O) sample ratio. These area ratios can be used to determine the (CO2/H2O) concentration in hot gas samples.

Sound‐absorption and ‐dispersion measurements have been made using the tube method on CO2‐H2O mixtures over the temperature range of 23°–195°C. A single relaxation time was found to describe adequately both the absorption and dispersion curves. The reciprocal of the relaxation time at each temperature was found to be linearly dependent on the concentration of H2O. The relaxation time τAB was calculated at each temperature, and τAB was found to increase as the temperature increased. A significant result is that log τAB exhibited no minimum value when plotted versus T−13, as has been previously reported by Eucken and Numann, but rather log τAB shows a linear decrease versus T−13. The number of collisions Z10(AB) necessary to deexcite the lowest vibrational mode of CO2 has been calculated from the measured relaxation time and is essentially temperature‐independent. [This work was supported by the U. S. Office of Naval Research.]