Mercury

Mercury was known to the earliest civilizations in China, India, and Egypt. The oldest known sample of mercury metal was found by the German archaeologist Heinrich Schliemann (1822-90) in an ancient Egyptian tomb at Kurna which dated from around 1600 bc. The name mercury, by which we know this element, comes from the name of the planet and its first recorded use was by the Greek philosopher Theophrastus around 300 bc. The Romans called it hydrargyrum and it is from this word that today's chemical symbol for mercury, Hg, is derived. The early English name of quicksilver derived from the old English word cwic, meaning living, as in the phrase: 'the quick and the dead'. The Romans knew that heating cinnabar reduced it to globules of metallic liquid mercury. At the other side of the world, the Chinese were also observing the same phenomenon and the alchemist Ko Hung (281-361) wrote of the wonder of turning bright red cinnabar into silver mercury simply by heating.*

Mercury has a strong affinity for sulphur atoms, and the two combine to form insoluble mercury sulphide, HgS, which is how it occurs as the main mercury ore, bright red cinnabar. When used as a pigment, cinnabar is known as vermilion and it was even used by cave painters 20000 years ago in Spain and France. Vermilion was especially popular with the Romans, who decorated whole rooms in their villas with it. The Roman writers Vitruvius and Pliny refer to mercury metal but were of the opinion that the mercury which was found naturally in the mines of Spain was somehow superior to that which was obtained by roasting cinnabar; the former they referred to as argentum vivum (living silver) and the latter as hydrargyrum

* The sulphur is oxidized by the oxygen of the air, forming sulphur dioxide gas, and mercury metal is left behind.

(silver water). Pliny was clearly familiar with mercury and wrote of it as follows:

It acts as a poison upon everything, and pierces vessels, even making its way though them by the agency of its malignant properties. All substances float upon the surface of quicksilver, with the exception of gold, this being the only substance it attracts to itself. Hence it is an excellent refiner of gold, for on being briskly shaken in an earthen vessel with gold it rejects all the impurities that are mixed with it. When once it has expelled these superfluities, there is nothing to do but to separate it from the gold.

Pliny reported that more than four tonnes of mercury metal were imported into Rome every year. He also said that men who worked with the ore protected themselves against the dust by covering their heads with bladders.

Down the centuries mercury continued to fascinate all those who were attracted to alchemy. There was nothing quite like it and it seemed to have almost magical properties. Mercury chloride still has its uses in magic even today, witness the 'psychic' Uri Geller who used it to demonstrate his supposed mind-over-matter mental powers in night clubs in Israel in the 1970s. According to Joe Schwarcz in his book The Genie in the Bottle, Geller would demonstrate his remarkable ability to heat metal by thought alone. A member of the audience would be invited on stage to hold a piece of aluminium foil which would mysteriously get hotter and hotter until it was too hot to hold, during which time Geller closed his eyes and supposedly focused his mind on the metal, supposedly willing it to heat up. The trick was to put a tiny amount of mercury chloride* powder on the aluminium and fold it over. A chemical reaction between the aluminium and the powder slowly begins to take place and eventually it gives off a lot of heat.

Mercury was important to the Scientific Revolution for barometers and thermometers, and while these uses could coexist with alchemy there was a discovery about mercury which fatally undermined belief that this metal was somehow forever different from all other metals. For alchemical theory it was the element, a component of all metals, and so held the key to the transmutation of base metals into gold. It uniquely represented the quintessential property of fluidity. Reports from Siberia, that mercury could freeze solid and become like any other metal were dismissed as little more than travellers' tales.

* This is the higher chloride, mercury(II) chloride, formula HgCl

What could not be discounted was a report from two Russian scientists, A. Braun and M. V. Lomonosov, of St Petersburg. In December 1759 they had experimented with snow to see how low a temperature they could achieve. Mixing snow with salt causes its temperature to fall by several degrees and they thought that mixing acids with snow might produce even lower temperatures - and so it did. Suddenly the mercury in their thermometer stopped moving, and indeed it appeared to be solid. When they broke away the glass they found it had become a solid metal ball with a protruding piece of wire, which they could bend, just like other metals. Mercury was just a metal with a low freezing point of -39°C.

What was still not truly appreciated was the toxicity of mercury vapour and it is this which could have insidious effects on alchemists, and even on amateur dabblers including a famous king and his most intelligent subject.

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