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Summary form only given. Up to now the positive column of high pressure light sources have been investigated mainly as a system in local thermodynamic equilibrium (LTE). Recent measurements in mercury arcs suggest the existence of departures from equilibrium in the axis and in the periphery in such an arc. The deviation from equilibrium leads to complicated distributions such that the plasma cannot be described by a single temperature. In these conditions, the only practical method of investigation is the direct measurement of the neutral atom densities. In the present work we investigate the same range of pressure as Elloumi et al. (1997). We compare the experimental results with those calculated using a two temperature model. The opportunity to compare such densities gave a lot of additional information. Therefore, the results are interpreted in term of nonequilibrium. Results for the lowest pressure (0.2 bar) show that the discrepancy are very pronounced in the arc core and in the periphery of the discharge (the axial density is (0.25/spl times/10/sup 18/ cm/sup -3/), while the departure from equilibrium becomes insignificant for high pressure (the axial density is 6.5/spl times/10/sup 18/ cm/sup -3/).