18th January: Day of Mercury

In the French Revolutionary calendar, today was dedicated to the element Mercury.

1. An old name for mercury was hydrargyrum, deriving from the Greek words for water and silver, because it is liquid like water and shines like silver. This is where its chemical symbol, Hg, comes from.
2. The atomic number of mercury is 80.
3. Mercury has a freezing point of −38.83 °C and a boiling point of 356.73 °C, and is the only metallic element which is liquid at room temperature.
4. Mercury reacts readily with other metals, corroding them and forming amalgams. Iron is an exception, so iron containers were used to transport and store it. Mercury is particularly damaging to aluminium, and for this reason, mercury is not allowed on aircraft. It is said to have been used by Allied spies in the second world war - they would apply mercury paste to German aircraft to cause structural failure.
5. In ancient China and Tibet, mercury was believed to be very good for you - prolonging life and maintaining good health. The first emperor of China, Qín Sh Huáng Dì drank a mixture of mercury and powdered jade which his alchemists told him would grant him eternal life. Now we know that mercury has rather the opposite effect, which Qín Sh Huáng Dì discovered the hard way - he died of mercury poisoning. His tomb allegedly contained rivers of flowing mercury representing the rivers of China.
6. Mercury has been found in Mayan tombs and in caches on various sites. It has been suggested the Mayans used it as a mirror for divination.
7. In Spain, decorative pools were filled with mercury, and in 1937, American artist Alexander Calder built a mercury fountain for the Spanish Pavilion at the 1937 World Exhibition in Paris.
8. Mercury is mainly used for the manufacture of chemicals and electronics. It has had a number of uses in recent times, although many of them have been, or are being, phased out for health and safety reasons: thermometers for measuring high temperatures; fluorescent lights; dental amalgams (fillings); mirror telescopes; in the manufacture of mascara.
9. As recently as the early 20th century, children would be given a dose of mercury each year to get rid of worms and keep them "regular". It was also used in teething powders and ointments for nappy rash.
10. Fish and shellfish have a higher concentration of mercury in their bodies - a natural result of their body chemistry. The higher up the food chain they are, the higher the concentration.