Capacity‐vs.‐temperature plots have been determined for two series of barium titanate ceramics prepared from (1) reagent‐grade and (2) spectrographic‐grade chemicals fired at various temperatures from 1100° to 1500°C. Dielectric constants in the spectrographic‐grade series were found to be as high as 12,000 and were, in general, 2 to 3 times as great as those in the reagent‐grade series. Also, the change of capacity (and dielectric constant) with temperature was larger for the purer titanates, amounting in some cases to 125% per °C. near the Curie point. Variations in firing temperature were observed to impart different properties to titanates of both series. The optimum firing temperature appears to be about 1400°C. A Curie point minimum was noted for materials fired near 1230°C. and a maximum for those fired near 1430°C. Shifts in Curie temperatures amounted to as much as 25°C. (111° to 136°C.). The rate of cooling from the firing temperature affects this shift in Curie point. In general, Curie points for the reagent‐grade titanates were about 10°C. lower than those for the purer material. Repeated cycling through the Curie point resulted in a progressive lowering of the dielectric constant. When subjected to temperatures above 150°C. these aged specimens were restored to their initial activity. Exposure to sunlight and ultraviolet radiations reduced