TERBIUM [[[symbol]] Tb, atomic weight 159.2 (0=16)], a metallic chemical element belonging to the rare earth group; it was originally called erbia by its discoverer Mosander (see Rare Earth).
In 1841 Mosander, having in 1839 discovered a new element lanthanum in the mineral cerite, isolated this element and also a hitherto unrecognized substance, didymia, from crude yttria, and two years later he announced the determination of two fresh constituents of the same earth, naming them erbia and terbia.
Mosander from cerite (1839-1841).
Mosander from the "cerium" of J.
The metal was obtained by Mosander on heating its chloride with potassium, and by W.
Mosander, by fusing its chloride with sodium.