As well as mercury, gallium and francium can all be liquids at room temperature. Gallium was discovered by French chemist in 1875. It was the first new element to confirm Dmitri Mendeleev’s prediction of the periodic table. Gallium is used chiefly in microchips because of its strange electronic properties. Compact disc players also make use of it because when mixed with arsenic it transforms an electric current directly into laser light.

Francium is one of the rarest elements. It has been calculated there are only ever thirty grams of it present on Earth. This is because it is so radioactive it quickly decays into other, more stable elements. So it is a liquid metal, but not for very long  — a few seconds at most. It was the last element to be found in nature. These elements are liquid at unusually low temperatures for metals because the arrangement of electrons in their atoms makes it hard for them to get close enough to each other.