There is given a complete review of the literature concerning the supposedly “allotropic modification” of fused alumina known as “Beta”. The results of experiments with Bayer and “Dry Ore Process” alumina are quoted to show the definite relation which exists between the alkali content of the fusion and the amount of “Beta” produced. Evidence is adduced to indicate that “Beta” is not an allotropic modification of alumina, but is an alkali aluminate tentatively assumed to be composed of 1 mole of alkali oxide to 12 moles of aluminum oxide. Both a sodium and a potassium aluminate of compositions Na2O.12Al2O3 and K2O.12Al2O3 respectively have been prepared and described.