The energy balance is discussed and a semi‐empirical equation for recovery time is derived; the discussion is based on diffusion alone without consideration of cumulative ionization and metastable states. Corroborating the theoretical considerations, measurements were made of arc drop and recovery time in thyratrons filled with mixtures of Xe with Ar, Ne, and He. The spectral emission lines in these discharges were photographed in the visible range. It was found that the arc drop remained fairly constant down to low concentrations of Xe and then increased steeply. Lines of the gas other than Xe also appeared only at low concentrations of Xe. The recovery time is a monotone declining function of the mixture of the heavy and the light components. The spectral lines are tabulated.