Mercury: Dr Jekyll or Mr Hyde?

Mercury has captured human imagination – both as fearsome and beautiful. Dr Andrea Sella, lecturer in inorganic chemistry at University College London (UCL), gave a fascinating account of its history, and what he described as 'its deep ties to human development'.

In Renaissance art, mercury ore, consisting of mercuric sulphide (HgS), was mined to make vermilion; a dense, rich, red pigment. Initially, the common ore called cinnabar, was pounded using a copper pestle and mortar to extract it. Sella explained that due to light refraction, painters believed the more it was ground, the richer its colour became. Art historian Daniel Thompson notably felt no other colour invented, had as lasting an effect on painting as vermilion. Mercury was captured in other artistic ways too. Sella played a clip of Jean Cocteau’s film Orphée showing the famous scene where actor Marais passes into another world through a mirror that turns to water. Sella quipped that the silvery liquidity of mercury was captured in film long before Arnold Schwarzennegar appeared in The Terminator. Cocteau’s magical ‘looking glass’ was created by turning the camera to one side and shooting the actor as he touched a pail of mercury with a gloved hand.

When placed on a spinning disk, mercury assumes a parabolic surface – the ideal shape for a telescope, providing us with our own ‘magic mirror’ to look into space. Canada’s Zenith Telescope is the largest of this type. Its name reflects the fact that it can only ever look straight up ahead; tilting the disk would cause the mercury to spill.

The fascination with mercury extends to its high density. In 1972, National Geographic pictured a man sitting on the surface of an open vat of mercury. Sella reinforced this by dropping lumps of steel and copper into a jar of mercury, showing the audience that both metals float. Mercury was used widely in lighthouses thanks to Augustin Fresnel. In 1828, he used it to create near frictionless bearings to support over three tonnes of surface structure in a lighthouse. The bearings didn’t jam because no rusting occurred. Sella revealed how Aristotle’s false assumption about the impossibility of vacuums was disproved. Torricelli’s experiment was simple: he filled a glass tube with mercury, used his finger to close off the open end, turned the tube upside down, and lowered it into a container holding more mercury. He noted that the mercury in the tube only ran down into the container to a certain point. He concluded that the space created within the tube was empty and that it was air pressure, pushing down onto the mercury in the container, that held the mercury in the tube at this specific level. The discovery of the barometer, a greater understanding of our weather systems, and the creation of the Sprengel and diffusion pumps all followed from this.

Scientists soon discovered that moving a barometer in the dark created a flashing light. Dr Sella demonstrated this to the audience by waving around some mercury in a tube in the darkened lecture theatre. He then explained how this lead to the discovery of the mercury light and the electric mercury vapour light. Sella jokingly encouraged students in the audience to use diffraction gratings to see the emission spectrum of mercury street lights. Following explanations of mercury’s role in the creation of the seismometer, Faraday’s motor and MRI machines, Sella examined its darker side. He told his enthralled audience that Roman criminals sentenced to work in the Almadén mercury mines of Spain, saw this punishment as a fate worse than death.

The 'insidious' poison of mercury was described by Alfred Stock, a scientist who developed methods of handling reactive gasses. Stock went near deaf when working with mercury. After he discovered what his ailments were connected to, he cleaned up his workplace and a large part of his hearing returned. Karen Wetterhan, internationally renowned chemistry professor and researcher, died of heavy metal poison after mistakenly dropping a little dimethuite mercury on her glove. Within a year she was dead, having experienced serious neurological problems and finally falling into a coma.

Dr Sella cited the case of Japan's Minamata city where mercury salt was dumped into Minamata Bay. The fish in the bay accumulated the mercury and for the population that consumed them, the result was extreme brain damage and many other horrific ailments, claiming 3000 victims. Sella left the audience to contemplate modern sources of mercury exposure. For example, the omega-3-rich fish we are encouraged to eat are the worst for accumulating mercury from sea pollution; so, if we eat more 'healthy' cod and tuna, what will the trade-off be?

Organised jointly by SCI's London Regional Group and UCL, 'Mercury – our troubled twin', was held in a packed lecture theatre at UCL on Tuesday 7 October 2008.

Communications Team on behalf of SCI London Regional Group

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