The electric strength of highly compressed gases

An experimental study of spark-breakdown potentials in compressed gases is reported. Direct voltages up to 150kV and electrodes giving a uniform field in the test gap were used. The gap length was in the range 1¿3 mm. The variation of spark-breakdown potentials with gas pressure is given for air and nitrogen in the pressure range 1¿70 atmospheres. The effect of using aluminium instead of steel electrodes is shown. Sulphur hexafluoride, carbon dioxide, and the fluoromethanes CCl2F2, CHClF2, CCIF3 were similarly tested up to their saturation vapour pressures. Comparison is made between the strengths of mixtures containing various proportions of air in nitrogen, with mixtures containing the same proportions of carbon dioxide in nitrogen. Various mixtures of air and sulphur hexafluoride, nitrogen and sulphur hexafluoride, and nitrogen and CCl2F2 were tested. Comparison is made with previous measurements in the limited range where this is possible. Paschen´s Law and the criterion for spark-breakdown at high gas pressure are discussed.