Mercury Hg

Discovery

Mercury has been known since antiquity. Heating the red mineral cinnabar (mercury sulfide) releases the metal, and mercury has been found in Egyptian tombs dating to around 1500 BCE. The historian Sima Qian wrote that the tomb of China's first emperor contained rivers and seas of mercury, and surveys have reported elevated mercury levels in the soil around the mound.

Alchemists regarded mercury as a basic principle of all metals. In 1643 Evangelista Torricelli used a column of mercury to build the first barometer, and around 1714 Daniel Gabriel Fahrenheit made mercury thermometers. In 1911 Heike Kamerlingh Onnes cooled mercury with liquid helium and saw its electrical resistance vanish at about 4.2 K, the first observation of superconductivity.

Origin of the name

The English name honours Mercury, the swift messenger of the Roman gods, also the name of the fastest planet. The symbol Hg comes from the Latin hydrargyrum, from the Greek for "water-silver", a description echoed in the old English term quicksilver.

Main uses

• Lighting: fluorescent tubes and some high-intensity discharge lamps use mercury vapour, whose ultraviolet emission a phosphor converts to visible light. LEDs are rapidly replacing them.
• Instruments: thermometers, barometers and blood-pressure gauges once relied on mercury; most have been replaced by digital devices.
• Dental amalgam: an alloy of mercury with silver, tin and other metals was a standard filling material and is being phased down.
• Industry: mercury-cell chlor-alkali plants have mostly closed. Artisanal and small-scale gold mining, which uses mercury to capture gold, is now among the largest sources of mercury pollution worldwide.

Isotopes

Natural mercury has seven stable isotopes, of which mercury-202 is the most abundant at about 30%. Mercury-199 and mercury-201 are used in nuclear magnetic resonance studies. Radioactive mercury-197 and mercury-203 were once used in medical diagnostics.

In everyday life

In the 1950s, methylmercury in industrial wastewater accumulated in fish and shellfish at Minamata, Japan, causing severe neurological disease among local people. The disaster gave its name to the Minamata Convention on Mercury, adopted in 2013 and in force since 2017. Large predatory fish such as tuna and swordfish accumulate more methylmercury, so pregnant women and young children should follow official advice on how much to eat. If a mercury thermometer breaks, ventilate the room, do not use a vacuum cleaner, gather the droplets with stiff paper, seal them and follow local disposal guidance.