To extend knowledge concerning the positive and negative point-to-plane corona, studies were made of the discharge in very pure ${\mathrm{H}}_2$, ${\mathrm{N}}_2$, and A. Neither pre-onset streamers nor burst pulses were observed in pure ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$, in accordance with present theories of these effects. At high fields weak streamers developed which ultimately led to breakdown. Adding traces of ${\mathrm{O}}_2$ to either ${\mathrm{H}}_2$ or ${\mathrm{N}}_2$ at once produced weak pre-onset streamers, and at higher concentrations produced burst pulses. Trichel pulses, which occur in properly triggered corona discharges in gases which form negative ions, are not observed in pure ${\mathrm{H}}_2$ and ${\mathrm{N}}_2$ but are immediately produced upon the addition of traces of ${\mathrm{O}}_2$. For these gases the potentials for negative corona were observed to be lower than for the positive corona. In the case of argon, it was found that with positive point potential the first streamer formed was intense enough to cause spark breakdown, while with the point at a negative potential a heavy arc replaced the corona. Contamination of the argon with ${\mathrm{H}}_2$ or ${\mathrm{N}}_2$ introduced streamers for the positive corona which showed all the characteristics of those formed in air. This effect is attributed to the suppression of metastable atoms in the argon due to the presence of the impurity. For the negative corona small amounts of these gases (0.1 to 0.5 percent) prevented arcing and yielded a strong corona with glow discharge characteristics but no Trichel pulses. Addition of sufficient ${\mathrm{O}}_2$ causes argon to act in all respects like air except that the onset potentials were much lower than in air. A clean-up of impurities in the negative corona in ${\mathrm{H}}_2$ is shown to be due to formation and absorption of water vapor. The etching of negative points in the discharges in pure gases appears to be related to the sputtering process.

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