The Dielectric Constant of Mica

Dielectric Constant of Mica.—The constant was determined for 18 samples of mica, varying in thickness from 0.005 to 0.073 inch and including 12 different grades. Each sheet was placed between two mercury electrodes and the capacity of the condenser thus formed was determined with a shielded capacity and conductance bridge using alternating current at 1,000 cycles per second. It was found that while thick sheets with plainly visible air films had low dielectric constants, those without such films gave fairly consistent results, running from 6.4 to 9.3 with an average of 8.1. When a thick sheet was split, the thinner sheets had higher constants except in the case of a sample of Canadian amber.

Power Loss in Mica Condensers was too small to determine accurately with the apparatus used, but was higher for stained than for clear micas.