THE EFFECT OF FIRING TEMPERATURE ON THE DIELECTRIC STRENGTH OF PORCELAIN1

An electrical porcelain body (H and G A1 English china clay, 30%; Tennessee ball clay No. 7, 20%; Buckingham feldspar, 30%; Ottawa flint, 20%) was fired to various cone temperatures and the puncture voltages were determined. The mean values in kilovolts per quarter-inch thickness were cone 7, 37; cone 8, 51; cone 9, 60; cone 10, 63; cone 11, 61; cone 12, 64. The probable error of the mean in each case is approximately ± 1 kilovolt per quarter inch. The differences of the means between cones 9 and 12 were shown statistically to be without significance. Other conditions remaining identical, it was shown that the most uniform body resulted when fired to cone 9.