When heated in dry oxygen it becomes incandescent, forming magnesia.
Wehnelt discovered that the same effect could be produced by using instead of a carbon filament a platinum wire covered with the oxides of calcium or barium, which when incandescent have the property of copiously emitting negative ions.
Staite in 1848 had made incandescent electric lamps of an elementary form, and T.
Practically the first of these furnaces was that of Despretz, in which the mixture to be heated was placed in a carbon tube rendered incandescent by the passage of a current through its substance from end to end.
It belongs to the group of metals whose oxides are generally denominated "rare earths," and its history is bound up in the history of the group, which is especially interesting from the fact that it supplies the material for the manufacture of the mantles used in incandescent gaslighting, and also that the radio-active substances are almost invariably associated with these oxides.