David Calder, a pupil at Nayland College, asks :-

Where does mercury come from?

Alisa Roddick-Lanzilotta, a chemist at the Wool Research Organisation of New Zealand, responded.

Mercury, which is also known as quicksilver, is the only metal element that is liquid at 25 C. It has been found in an Egyptian tomb dating back to about 1500 BC and its mining from ores was described in the 4th century BC. There are more than 25 known minerals containing mercury, but the most abundant mineral is cinnabar, a soft reddish-brown mercury sulfide, which is found in every continent except Antarctica. Throughout history cinnabar has been used as a pigment or colouring and in the 19th century some American Indians in California complained of illness later diagnosed as mercury poisoning caused by cinnabar in war paint. Mercury is most commonly obtained by extraction from cinnabar by roasting in air, followed by condensation of the mercury vapour. The free metal is found naturally in isolated drops and occasionally in larger fluid masses near volcanos or hot springs.

Despite its toxicity, mercury is still used for many applications. Mercury does not wet glass or cling to it, and this property along with its uniform volume expansion, makes it useful in thermometers. Mercury amalgamates, or mixes, readily with many other metals. Amalgams of mercury, silver, and tin have been successful materials for repairing cavities in teeth. Amalgamation with mercury has been used to extract gold and silver from ores. It is also used in the preparation of pharmaceuticals, agricultural and industrial fungicides, in the electrolytic production of chlorine and caustic soda and in dry-cell batteries. The good electrical conductivity of mercury makes it very useful in sealed electrical switches.