Argon gas, which had been partly ionized by an electric arc with an enthalpy input in the order of 104 BTU/lbm was expanded through a supersonic wind tunnel nozzle. It was found to contain residual positive ions in excess of electrons. These residual ions amounted to 10 to the -4 times the total number of flowing atoms; a slight increase occurred with decreasing enthalpy input. This quantity also represented the only residual ions of the gas jet leaving the expansion nozzle at ambient temperature and a pressure of 0.25 mm Hg. Normalization of these ions was achieved by means of diffusion to the surface of the pipe recapturing the free jet.