Lead

Category: post-transition metal Atomic number: 82 Colour: dull grey Melting point: 327°C (621°F) Boiling point: 1,749°C (3,180°F) First identified: ancient civilizations

The alchemists regarded heavy, malleable lead as a lowly metal, but knew that it could be turned from its natural grey to a variety of other colours. Soaked in vinegar and left in a shed of animal dung, it would turn white. Heated, it would form a surface layer of yellow lead monoxide, which they called ‘litharge’, and then a bright red (which was used as a red paint in the Middle Ages – although this fades over time to a dull brown). Some wrongly believed that if they kept working on the metal, it might eventually turn to gold.

It was obtained from the mineral galena at least as long ago as the Ancient Greeks. The Romans used it for piping, pewter, paint, pottery glazes and even cosmetics (in the form of lead carbonate or ‘lead white’, which was also used as a paint pigment), although the doctor Cornelius Celsus warned against the bad effects of this.

Trust Me, I’m a Scientist

In the US, in 1924, a press conference was held after an outbreak of lead poisoning at the Standard Oil plant in New Jersey – one worker had become psychotic and died, and thirty-five more were hospitalized. Thomas Midgley, the inventor of lead petrol, had himself only just recovered from lead poisoning in Florida, though he tried to convince sceptical reporters of the fuel’s safety by washing his hands in a container of the additive tetraethyl lead, as well as claiming that the petrol would be safe because ‘the average street will probably be so free from lead that it will be impossible to detect it or its absorption’. He did, however, concede that ‘no actual experimental data has been taken’.

Today, in spite of its toxicity, it is still used in car batteries, some pigments, weights and in solders. As the heaviest stable element that is not radioactive, it can be used for radiation protection; for instance, in containers that contain mildly radioactive material. Lead is not especially reactive, so can be used to hold corrosive acids. Until recently it was used to prevent knocking (ignition problems) in car engines, but this has been banned due to the pollution it caused. It is no longer used in water pipes and containers, but still causes some nasty cases of lead poisoning in antiquated buildings that contain lead piping.

Incidentally, the alchemists weren’t completely wrong. Many radioactive elements with a higher atomic number than 82 turn into lead at the end of their decay chains, so, in theory, it is easier to turn gold into lead than vice versa. Nuclear experiments have shown that it is feasible to make the opposite transmutation, but the expense would far outweigh the possible gain.