Lead
Lead is a chemical element – a substance that contains only one type of atom. Its official chemical symbol is Pb, and its atomic number is 82, which means that a lead atom has 82 protons in its nucleus. Lead has the highest atomic number of any stable (non-radioactive) element. It is a dense, heavy metal – yet it is soft and can be shaped and stretched without breaking.
Elemental lead
On the periodic table of elements, lead is represented by the symbol Pb. It has an atomic number of 82 because it has 82 protons in its nucleus.
Image of lead pieces adapted from Hi-Res Images of Chemical Elements and licensed under CC BY 3.0
Lead’s chemical symbol – Pb – comes from the Latin word plumbum. The Roman Empire used lead to make waterpipes, so the word plumbum was associated with systems that carried water into buildings. Today, we call this plumbing and those who work with it plumbers.
A similar word, plumbago, also has an association with lead and it has caused misconceptions for centuries. Plumbago (also known as black lead) is actually graphite. The soft black substance in your wooden pencil has never been made of lead.
Metals of antiquity
Lead is one of the seven metals of antiquity – metals that humans identified and used in ancient times. The other metals of antiquity are gold, silver, copper, tin, iron and mercury. Each metal was associated with one of the seven known celestial bodies. Gold, for example, was associated with the Sun due to its colour and value. Lead was the least desirable of the ancient metals due to its dull grey colour and heaviness, so it was associated with Saturn – the furthest of the known planets.
Metals of antiquity
In ancient times, each of the seven known metals were paired with the seven known celestial bodies. The symbols of the planets also represented the metals. The symbols are a mix of circles – denoting perfection or an association with the Sun – and crosses – signifying the connection between alchemy and religion.
Fast forward to the Middle Ages, and lead became an object of great interest to alchemists. Alchemy was a mix of chemistry and philosophy that sought to turn lead into gold. Alchemists thought that all metals were made of the same substance, but metals like lead were spiritually and physically immature forms of the higher metals. With refinement, lead could become spiritually perfect just like gold. Even famous scientists like Sir Isaac Newton dabbled in alchemy.
Nature of science
It this of modern science, the historical mix of science, philosophy and religion may appear unusual. All scientific knowledge is produced within a larger society and . The tentative scientific knowledge of ancient and classical civilisations was influenced by cultural aspects of the time. As new information was discovered, the old ways of thinking were discarded.
Uses of lead
Lead is usually found as an ore – in combination with other elements such as silver. This type of ore has a low melting point so it was relatively easy to smelt, and lead became a byproduct of the more valuable silver. Humans have been making items from lead for around 9,000 years. The ancient Egyptians and Greeks used lead in cosmetics, glass and enamels. Other early civilisations used lead to make coins, as a writing material and for medicinal purposes.
Roman lead waterpipes
Lead is easy to mould and is non-corrosive so the ancient Romans used it to make waterpipes. The Latin word for lead is plumbum and is the origin of the English word plumbing.
During the Middle Ages, lead was commonly used in roofing and piping due to its malleability and durability. In 1160, builders used 182 tonnes of thin lead panels to cover the roof of Notre Dame Cathedral, and later 680 tonnes went into its spire. Lead was also a key component in the construction of firearms and printing presses. Lead production increased during the Industrial Revolution due to a growing demand for lead paints and plumbing.
Some ancient uses of lead continue today – weights, roofing materials, organ pipes and sculptures. Other uses are more modern – radiation shields in medical X-ray rooms and nuclear science labs and in lead-acid batteries.
Lead rubber bearings
A cross-section of a lead rubber bearing used in base isolation. They consist of three basic components – a lead plug, and rubber and steel, which are generally placed in layers.
Lead plays a part in protecting important New Zealand buildings like the Museum of New Zealand Te Papa Tongarewa. The buildings use base isolators to protect them during an earthquake. The lead core deforms during an earthquake, absorbing some of the energy, and then reverts to its original shape.
Lead cosmetics, 500 BC
Lead was used in cosmetics from ancient periods through to the Renaissance. People used it to whiten their faces and later to whiten wigs. Historians think that the use of lead whiteners contributed to the death of Queen Elizabeth I.
(artefact from Kerameikos Archaeological Museum)
Concerns about lead poisoning
It was during the Industrial Revolution that doctors noticed diseases like gout were more commonly found in painters and plumbers than in the rest of the population . Other health issues – including blindness, anaemia and kidney and brain damage – convinced officials to create laws that decreased the public’s exposure to lead. In New Zealand, lead was removed from all but clearly labelled special-purpose paints in 1965 and banned from petrol in 1996.
The useful links section at the end of this article has information regarding lead poisoning, treatment and prevention.
Nature of science
Science and society can have differing views on an issue. When it was proposed to add lead to petrol in the 1920s, scientists advised that it would be dangerous to people and the environment. The desire for cheaper fuel and safer cars prevailed, and lead was added. As scientific evidence on the dangers of lead grew, public intolerance of lead also grew, and leaded petrol was banned.
Useful links
The New Zealand Ministry of Health has information regarding:
lead poisoning – symptoms, treatment and prevention
