1839: Lanthanum - The book of science

Lanthanum
Atomic number 57
Hidden stuff
Commentary

Stockholm—Carl Gustaf Mosander elements

Lanthanum

Carl Gustof Mosander found,
lying hidden in a sample of cerite,
an oxide of a new rare earth, which
he named “that which lies hidden.”
Little did he know that lying hidden
in “that which lies hidden” were five
other rare earths—gadolinium, praseodymium,
neodymium, samarium, and europium.

Atomic number 57

Lanthanum is used
in steel alloys
and molybdenum alloys.
Mischmetal of lanthanum
and other rare earths
are in the anode
of nickel-metal hydride batteries
and in lighter flints.
Lanthanum oxide is in
vacuum-tube emitters
glass that resists alkali,
glass that absorbs infrared,
glass for camera and telescope lenses,
and electrodes for gas tungsten arc welding.

Hidden stuff

A lurking suspicion.
A recessive gene
causing a bias
an unexpected response.
A hidden pattern.
An unexplained secret.
A mystery, an enigma.
The element of surprise.

Lanthanum was the third rare earth that Mosander discovered, after yttrium and cerium. After this, Mosander discovered terbium and erbium. “Earth” is a term for a metallic oxide. They are called “rare” earths not because they are rare, but in the archaic sense of rare meaning “difficult.” They are difficult to separate.