Three Regions of Dielectric Breakdown

In a previous paper, the writers published results on the dielectric strength of various glasses and concluded that for ordinary thicknesses there were three distinct types of breakdown. The present paper emphasizes the fact that this is true not only for glass but also for fused quartz and for celluloid. By the elimination of edge-effect the following breakdown gradients were obtained: For celluloid, 2,500,000 volts/cm.; for glass, 3,100,000 to 5,000,000 volts/cm.; and for mica, 10,600,000 volts/cm. The various methods of eliminating edge-effect are discussed and compared and an attempt is made to correlate the electrical properties of the glasses with their chemical composition.