Shrouded in mystery and myth, mercury has dazzled and bemused for centuries - seen at different times as the key to alchemy, a cure for syphilis and a cause of madness. A heavy metallic element known historically as 'quicksilver', mercury is 13.5 times denser than water and has a host of extraordinary qualities. The metal is so dense you could play a game of billiards on its surface. One theory about Mozart's death is that the composer suffered from mercury poisoning after being treated for syphilis. The wobbly handwriting in his final compositions is a symptom of the effects of the poisoning. Further back in history, mercury was widely believed by alchemists to be the key ingredient to turn base metals into gold, possibly because gold itself dissolves in mercury. Disappointingly there is no documented case of anyone managing to unlock the secret formula and perform the process in reverse. In the 19th century, animal skins were dipped in mercuric nitrate to produce a matted felt used to make hats. Fumes from the process left workers with damage to their brains and nervous systems, possibly leading to the expression 'mad as a hatter' and providing inspiration for Lewis Carroll's eccentric Mad Hatter character from the 1865 classic Alice's Adventures in Wonderland. In another bizarre story about its potency, allied spies are said to have spread mercury paste on the wings and bodies of German planes in the second world war, causing the aluminium to dissolve and fighter planes to disintegrate in mid-air. Mercury is rarely found in its native state, usually coming from minerals such as cinnabar (pictured). The mainland is the biggest producer of the metal, accounting for two thirds of worldwide production. Kyrgyzstan is the only other country to mine for virgin mercury but China is unique in that virtually all the mercury it unearths is for domestic use. Mercury is used in plastics manufacturing, acting as a catalyst for the production of PVC from coal and is essential for the country's legions of furniture factories. Demand remains so high that the mainland imports tonnes of mercury every year to meet the need within its own borders. About 700 tonnes were brought in during 2004, 600 tonnes of which was used in PVC production. As well as its more widely known use in barometers and thermometers, mercury is used in the production of modern low-energy light bulbs, many of which are made in factories in southern China. With the European Union banning the production of many old-style light bulbs, demand for the so-called eco-friendly bulbs is booming - and thus mercury is once again sought after.