Gallium melts in your hand: its melting point is 29.76 °C

Gallium melts in your hand because its melting point is just 29.76 °C (85.58 °F), about seven degrees below normal body temperature, so a lump held in a warm palm slowly slumps into a silvery puddle. Along with mercury, caesium and rubidium, it is one of only four metals that are liquid near room temperature.

That melting point is so sharp and repeatable that NIST and other metrology labs use it as a defining fixed point of the International Temperature Scale of 1990, calibrating precision platinum thermometers against cells of pure melting gallium.

Gallium by the numbers	Value
Melting point	29.76 °C (85.58 °F)
Boiling point	roughly 2,400 °C
Liquid range	more than 2,300 degrees
Volume gained on freezing	about 3.1%
Density forecast by Mendeleev	roughly 6 g/cm³
Density measured	5.91 g/cm³

Like water, gallium expands when it freezes, so solid gallium floats on its own melt. Its liquid range is one of the widest of any metal. And it is not mercury: gallium alloys are used in thermometers as a safer, greener substitute for the toxic metal, and gallium’s vapour pressure stays low even when hot. Magicians use gallium spoons that appear to bend as the warmth of their fingers melts them.

It was predicted before it was found. In 1871 Dmitri Mendeleev used a gap below aluminium in his periodic table to forecast an element he called eka-aluminium. In 1875 the French chemist Paul-Émile Lecoq de Boisbaudran spotted its violet spectral lines in zinc ore from the Pyrenees and named it after Gallia, the Latin name for France. The density came out close to the forecast, and Los Alamos calls the discovery a landmark confirmation that the periodic table was a predictive model, not just a filing system.

Today about 98% of gallium goes into semiconductors, mostly as gallium arsenide, used in red LEDs and in the solar panels of NASA’s Mars Exploration Rovers.