The image is of a traditional alchemical symbol for mercury. This is also an astrological symbol for the planet Mercury. The dragon or serpent in the background comes from early alchemical drawings and is often associated with the element.

Fact Box

Uses

Mercury has fascinated people for millennia, as a heavy liquid metal. However, because of its toxicity, many uses of mercury are being phased out or are under review.

It is now mainly used in the chemical industry as catalysts. It is also used in some electrical switches and rectifiers.

Previously its major use was in the manufacture of sodium hydroxide and chlorine by electrolysis of brine. These plants will all be phased out by 2020. It was also commonly used in batteries, fluorescent lights, felt production, thermometers and barometers. Again, these uses have been phased out.

Mercury easily forms alloys, called amalgams, with other metals such as gold, silver and tin. The ease with which it amalgamates with gold made it useful in recovering gold from its ores. Mercury amalgams were also used in dental fillings.

Mercuric sulfide (vermilion) is a high-grade, bright-red paint pigment, but is very toxic so is now only used with great care.

History

Cinnabar (aka vermilion, mercury sulfide, HgS), was used as a bright red pigment by the Palaeolithic painters of 30,000 years ago to decorate caves in Spain and France. Cinnabar would yield up its mercury simply on heating in a crucible, and the metal fascinated people because it was a liquid that would dissolve gold. The ancients used in on a large scale to extract alluvial gold from the sediment of rivers. The mercury dissolved the gold which could be reclaimed by distilling off the mercury.

The Almadén deposit in Spain provided Europe with its mercury. In the Americas, it was the Spanish conquerors who exploited the large deposits of cinnabar at Huancavelica in order to extract gold. In 1848 the miners of the Californian Gold Rush used mercury from the New Almaden Mines of California.

Although highly toxic, mercury had many uses, as in thermometers, but these are now strictly curtained.