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The adsorption of CO, on alumina, alumina-magnesia mixed oxides and magnesia has been studied by means of i.r. transmission absorption spectroscopy. CO, was found to be weakly adsorbed on accessible cations. With high densities of surface hydroxyl groups lateral interactions of these cationicly bound CO, molecules with hydroxyl groups have also been observed. Several surface carbonates were formed and were identified as bicarbonates and monodentate, bidentate and ionic carbonates. The wavenumbers of the symmetric stretching vibration of the surface bicarbonates and the wavenumber difference of the symmetric and antisymmetric stretching vibration of the monodentate carbonates decreased with increasing content of MgO in the mixed oxides.

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The exact calculation of the density of a steady-state gas flow by means of the Boltzmann function generally leads to great mathematical difficulties, in the case of an expanding gas passing from the viscous flow region into the molecular flow region. An approximate solution can be found by replacing the actually continuous transition from viscous to molecular flow with a suitably defined discontinuity surface. Molecules that leave the viscous region through this surface continue to fly in straight lines with their respective velocities. By adopting this conception, the density at each point of the molecular-flow region can be found by integration. The general procedure is specialized for the case of the two-dimensional flow and can be applied to the supersonic flow around a corner in vacuum.