The electric strength of air at high pressure

OVER thirty years ago work was done by Ryan^1,2,4 and his student, Ekern,³ to determine the electrical strength of air at pressures of many atmospheres. It was discovered that the voltage required for sparking between points bears a roughly linear relation to the air pressure until the voltage has risen to approximately ten times that required for sparking between the same points, at the same spacing, at normal atmospheric pressure. A maximum voltage is reached at an air pressure of between 100 and 200 pounds per square inch. As the pressure is further raised, the sparking voltage does not rise correspondingly — in fact it drops somewhat if sharp points are used, and then at still higher pressure (above 400 pounds per square inch) the voltage rises slowly with pressure.