The object of this research is to find one or more measurable properties of active ceramic powders which can be related to sinterability. Samples of active magnesia were prepared by cal cination of basic carbonate at 400-900 C. and tested for activity in a closed system. The activity measurements, oxygen exchange and 'initial specific adsorption' (of CO2), indicate that the bulk structure as well as the surface of such materials is extremely active. Both of these tests show that magnesia samples calcined at about 500 C. have higher activity than similar samples calcined at either higher or lower tem peratures. There are indications that these measurements can be used to characterize ceramic materials with respect to their sinterability. Data from decomposition experiments and CO2 ad sorption studies are presented and discussed. These results emphasize the difficulties involved in the preparation of uniform, large-scale lots of activated powders, and the care required in their handling to avoid inadvertent contamination by adsorption of atmospheric constituents (H2O and CO2).