Carl Gustaf Mosander discovers the element lanthanum as the oxide (lanthana) in 1839, distinguishing it from cerium oxide, or ceria, after partially decomposing a sample of cerium nitrate by heating and treating the resulting salt with dilute nitric acid.

He names the element for Greek lanthanein, to be concealed, indicating that it is difficult to isolate.

Mosander, who had worked as a teacher of chemistry at the Karolinska Institute and as an assistant in the mineralogical collection of the Swedish Museum of Natural History, had been a chemistry student of Berzelius during his medical studies, and in 1836 had succeeded him as professor of chemistry and pharmacy in the Institute.