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A numerical equation of state for heavy rare gases in the neighborhood of the critical point has been computed, using a cell model distribution function containing a parameter which correlates the probability of a distribution with the number of pairs of particles in adjacent cells for the distribution, as well as a variable mean number of particles per cell (range zero to one), a variable cell size, and a variable distribution of particles with respect to the cell centers. The energy was approximated by the sum of the interactions of pairs of particles in adjacent cells only, and the parameters of the distribution function were then chosen so as to minimize the Helmholtz free energy per particle at constant density and temperature. The critical constants were determined, and the vapor pressure and the molecular volumes of the liquid and gas phases in equilibrium with each other were determined as functions of the temperature near the critical temperature. An estimate was made of the improvement in the Helmholtz free energy to be expected from the inclusion of the interactions of nonadjacent particles in the calculation of the energy.

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A method is described for making estimates of the total emissivity of hydrogen in the temperature and pressure ranges where hydrogen atoms predominate under equilibrium conditions. For a typical geometrical depth of 50 cm, and temperatures of the order of 12 500 0 K and higher, with pressures of the order of 100 atmos and higher, the emissivity approaches unity «:;0.95), while for temperatures of the order of 9500 0 K and lower, with pressures of the order of 10 atmos and lower, the emissivity approaches zero «<0.05). The variations of the emissivity between these approximate limits are shown graphically as functions of temperature and pressure with the geometrical depth set at 50 cm. The variation of the emissivity with geometrical depth is also shown graphically at 12 600 0 K and 20 at mos.

The physical principles involved in conventional absolute intensity measurements are reviewed. Experimental difficulties rule out the use of extrapolation techniques for some spectral transitions. For this reason it is of interest to re-examine the possibility of using total absorption measurements, in conjunction with the curves of growth, for making intensity estimates. Extrapolation methods yield results which are independent of spectral line shape. Use of the curves of growth, on the other hand, implies the assumption that the line contour can be described by combined Doppler and Lorentz broadening.The curves of growth permit a unique correlation between total absorption andj-value either for spectral lines with pure Doppler broadening or for pure collision broadening. Furthermore, a simple experimental procedure can be devised for estimating both the absolute intensity and the spectral line profile on the basis of single-path and multiple-path absorption measurements. The suggested procedure involves absorption' measurements for optical densities (path lengths) under conditions in which the integrated fractional absorption is a relatively sensitive function of spectral line shape. Representative calculations referring to utilization of the proposed method have been carried out for spectral lines belonging to the 2~--c>2II transitions, (O,O)-banc!, of OH, and also for lines belonging to the fundamental vibration-rotation spectrum of CO.