Mercury is the only metal that is liquid at room temperature and atmospheric pressure, says Allan Blackman in ep 49 of Elemental.

Mercury is an unusual metal that is liquid at standard room temperature and atmospheric pressure.

Mercury is named after the planet, and its chemical symbol Hg comes from the Latin hydrargyrum or liquid silver.

Its silver-grey colour was a familiar sight in old-fashioned thermometers and in amalgam fillings in our teeth.

Mercury alloys easily with other metals, in a process called amalgamation.

It was widely used to extract gold during mining, and to plate metals with gold in a process known as gilding.

Mercury is highly toxic, and there are many examples of widespread mercury poisoning incidents.

The term Mad Hatter refers to the health consequences of the use of mercury by milliners and hatters in the felting process that was part of making hats, says Professor Allan Blackman from AUT.

Go to this episode on rnz.co.nz for more details