Mercury is the only metal that is liquid at room temperature. It does not become solid until it is cooled to -38.72 degrees Celsius and it becomes a gas at 375 degrees Celsius. When heated with an electrical charge, mercury can be used for lighting. Mercury is number 80 on the periodic table and its symbol is Hg. Mercury is a very dangerous neuro-toxin, especially in its gaseous state. It was used extensively in the felting process prior to the 1940s and its exposure by hat makers is the origin of the term “mad as a hatter”.
The ancients found mercury seeping out of rocks and collecting in pools in grottoes. It could also be obtained by heating cinnabar. It was impressive to see the silver liquid oozing out of the rock. When nitric acid and mercury are heated together, a red vapor hovers over the material and bright red crystals form below. This impressive reaction earned mercury a special place in the hearts of alchemists. Mercury was said to transcend both liquid and solid states and to exist above and below. It symbolized heaven and earth, life and death, etc. It was used to make deadly poisons as well as medicines that were used by the ancients.
Mercury symbolizes the Roman messenger God Mercury and the Greek messenger God Hermes, the guides between worlds. The symbol for the metal mercury is sometimes identical to the symbol for the planet mercury.