​The Metals Of Antiquity – Mercury

When Charles Lutwidge Dodgson penned his now famous children's book, he couldn't have known that the Hatter, one of the best-known characters in the story, would become synonymous with a type of mercury poisoning that affects the brain and nervous system1. That story is of course "Alice In Wonderland", and the author's pen name was Lewis Carroll.

We're All Mad Here

Lewis himself didn't name his eccentric hatter character 'Mad'. He simply called him 'the Hatter', and left it up to other characters in the story to conclude that his somewhat strange behaviour meant he was a bit mad. However, as the Cheshire Cat politely points out 'we're all mad here' and overall, the Hatter's behaviour was really no stranger than that of many other characters in the story. He didn't appear to suffer from obvious mercury poisoning symptoms at any rate.

It's far more likely Lewis's Hatter acquired his 'mad' prefix because hatters in real life were associated with a type of mental illness that had led to the popular phrase 'mad as a hatter' and later 'the hatter's shakes'2. Granted, some of the Hatter's behaviour may be reminiscent of that of real hatters but Lewis later claimed he hadn't meant anything in particular, or singled out any specific group/s in society, with his characters. It was all, he said, written purely to amuse his young companions and any similarities between the behaviour of his Hatter and that of professional hatters was unintentional.

Hats And Hatting

Traditionally, hats are made from a type of felt comprised of compressed animal hairs, primarily rabbit and badger. The hair was originally separated from the hides with urine (felting or carroting) then treated with heat, moisture and pressure to compress it into felt. In the 17th century, French hatters noticed that hatters who took mercury chloride for syphilis treatment produced a much softer and more pliable felt. The reason was tracked down to their mercury-laden urine. Eventually, the mercury-laden urine was replaced with mercury salts, notably mercuric nitrate, and the 'new' felting or carroting process spread to other countries.

The problem was that workers in these establishments weren't only physically handling mercury salts in the carroting process without any type of PPE but also inhaled mercury vapours when the felts were heated. Further, some of them believed that additional 'saliva treatment' improved the softness and flexibility of the felts and had taken to giving the mercury-laden hairs a good 'chewing' over, thus ingesting the toxic substance as well.

Needless to say, once mercury had been introduced into the felt making process it didn't take long for many of those who worked in the industry to develop a range of mental, nervous, and gastrointestinal disorders. They included:

  • Mental and emotional problems – depression, anxiety, excitability, irritability, psychosis, increased sensitivity to sensory stimulation etc,
  • Memory loss
  • Dental problems, notably loose teeth
  • Semi paralysis and/or weakness in the lower limbs
  • Trembling and deterioration of motor skills
  • Slurred speech
  • Gastrointestinal disorders
  • Sleep disorders

In 1941, the medical reason behind these disorders was identified as mercury poisoning from the mercuric nitrate and it was subsequently banned in hat manufacturing in the US. Other countries followed suit and today modern hat makers use hydrogen peroxide instead. It's slower but also a lot safer!

The 3 States Of Mercury

Whilst elemental mercury is the most common type of mercury, mercury also occurs naturally in the environment (soil, air, and water) as organic and inorganic compounds. All types are toxic but each has its own set of detrimental health effects3.

Organic mercury compounds are amongst the most toxic of the mercury 'family'. They form when microorganisms (naturally or artificially) mix carbon with elemental and/or inorganic mercury. Examples of organic mercury compounds include methylmercury, thimerosal and its thiosalicylate salt ethylmercury, phenylmercuric acetate etc. Methylmercury is commonly accepted as the most toxic of all mercury compounds, and the one most closely associated with mercury exposure in the broader population. Other organic mercury compounds like thimerosal and phenylmercuric acetate have a long history of use as preservatives, biocides, herbicides, pesticides and the like.

Inorganic mercury compounds are mostly mercurous and mercuric salts, created when elemental mercury is mixed with elements like oxygen, chlorine, and sulphur. These salts are created naturally in the environment (cinnabar ore is a case in point) or can be produced artificially in a lab – the mercuric nitrate used in hatting is one such example, vermilion (mercuric sulphide) is another. Inorganic mercury compounds are the least toxic form of mercury but on a scale of 1 to 10, are still highly toxic!

Elemental mercury can be considered a type of inorganic mercury, although it's most commonly listed as a 'type' on its own.

Mercury Throughout History

Mercury has a long history of significant use by humans, which is why it is considered one of the metals of antiquity. The elemental form of the metal, with its almost mystical liquid silver properties, has always fascinated ancient, and not so ancient, cultures.

Although the first formal records of elemental mercury use date to around 1,500 BC, there is evidence that some forms of mercury have been used for much longer. Powdered mercury sulphide for instance was commonly used to produce red paints, dyes, lacquers, and cosmetics well before any recorded uses of elemental mercury. Notably, ancient cave paintings in Turkey that date to around 7,100 BC have red paint that contains mercuric sulphide. These paintings are currently the oldest known examples of mercury use.

Up until the 8th century AD, the bright and popular red powder was commonly made from crushed cinnabar, a naturally occurring volcanic mercuric sulphide ore. A synthetic version of the powder, made by combining mercury and sulphur, came into widespread use in the late 700s / early 800s after it was described in a recipe book of colours. It's possible the process had actually been developed much earlier in China (perhaps as early as the 4th century BC) but if so, it wasn't widely known about outside that culture until the recipe book. In the 17th century, the sulphur was swapped out for melted sulphur AKA the Dutch method. The powder had also had a name change from cinnabar to vermilion, and is still known as that today.

Mercury, particularly inorganic and organic forms, were also part of Indian and Chinese traditional medicine well before 2,000 BC where they were included in many of the restorative and health compounds of the day. Over the ensuing centuries, these compounds continued to find their way into a LOT more health and wellbeing products!

Mercurial Medical Matters

The long list of mercury containing health and medical products includes laxatives, diuretics, antiseptics, disinfectants, syphilis treatment products, antidepressants, wormers, tuberculosis treatments, infant teething powders and various pain relief products. Some of these uses linger today – merbromin, a compound of mercury and bromine, is used in a range of healing products. Mercurochrome for instance is the trade name of a widely used merbromin-based antiseptic cream.

Other modern medical uses for mercury (all forms) include:

  • In blood pressure meters (sphygmomanometers) and other pressure measuring laboratory instruments (elemental),
  • In amalgam dental fillings (elemental),
  • As a preservative in vaccines and pharmaceuticals (thimerosal) (organic) 
  • In medical laboratory reagents (ie CPK / Millon's / Takata's, etc) (inorganic) 
  • In skin lightening products (creams and soaps) (inorganic)  
  • In skin lightening products (creams and soaps) (inorganic)

Many of these uses are being phased out as safer alternatives for the mercury are found.

Modern Mercury Materials

Elsewhere, we can still, or could until recently, find elemental mercury and various inorganic and organic mercury compounds being used in processes and products such as:

  • Sodium hydroxide and chlorine electrolysis plants,
  • Mercury relays and switches, and tilt switches,
  • Float valves,
  • Electrochemical batteries, notably button batteries,
  • Fluorescent lighting and mercury-vapour lamps,
  • Various chemical catalysts, buffers and reagents (Nessler's etc),
  • Non-medical pressure measuring devices (thermometers, manometers, barometers etc),
  • Hydraulic mineral extraction amalgams (particularly gold and silver),
  • Calomel electrodes,
  • Biocides for seed grains, paper, paints etc,
  • Insecticides,
  • Detergents,
  • Pigments and dyes ie vermilion,
  • Fixatives,
  • Explosives (mercury fulminate),
  • Liquid mirror telescopes,
  • Lighthouses; the supporting bed for their Fresnel lenses was often made of mercury; the lenses floated and rotated on the bed, which acted as a bearing,
  • Wobbler fishing lures,
  • Coolant in nuclear reactors,
  • Handheld games,
  • Precursor to xenon gas as the preferred propellant in ion thrusters and engines used in early electric space propulsion systems (ie NASA's SERT-1 and 2 spacecrafts),

And many more…. 4

The God, The Metal, And The Planet

The metal acquired its name from the mercurial Roman god of the same name, noted for his 'quicksilver' speed as he scurried about his messenger duties. Its chemical symbol Hg comes from 'hydrargyrum', the Latin word for 'liquid silver'. It's clear that in naming the metal, the ancients had elemental mercury in mind.

Mercury the planet was likewise named after the speedy god because ancient astronomers observed it speeding around the sun more than 4 times faster than Earth does. The fleet little planet is closest to the sun and only takes 87.97 Earth days to circumnavigate it.

The 3 Mercuries were so closely connected in ancient cultures that the planet's astrological symbol is also one of the metal's alchemy symbols. Mercury is also the only metal whose alchemical planetary name remained its common name.

Speaking of alchemy….

Ancient alchemists believed the Earth has three primary substances – mercury, sulphur, and salt. Mercury was thought to be the First Matter, the base from which all other metals derive by virtue of varying amounts of sulphur mixed with the mercury. Therefore, by using the correct ratios of mercury and sulphur, chemical mass production of minerals like gold should be possible. Alchemists spent a huge amount of time and energy trying to find these golden 'mother' formulas until a Roman emperor called Diocletian put an end to it in the late 3rd century AD by burning their writings on the subject. He thought mass production of artificial gold would undermine the Roman currency, and provide alchemists with the means to build themselves huge fortunes they could then use to bribe their way into positions of power.

Why Mercury?

Mercury, elemental or otherwise, has a number of properties that make it ideal for the uses to which it has historically been put. It is very stable, conducts electricity well, heats evenly across its mass, has good acoustic properties, a long shelf life, very high surface tension, readily forms an amalgam with precious metals like gold and silver etc.

On the other hand ….

  • It doesn't take much heat for elemental mercury to start producing its highly toxic vapour. For this reason, it needs to be stored in airtight containers kept at cool temperatures. It is also often handled in cool water to reduce vapourisation plus the water acts as an absorbing buffer for any vapour that does escape.
  • Mercury contamination is a serious environmental and health issue in many parts of the world where careless handling and inadequate disposal of mercury containing items has allowed it to leach into the water and soil.

Cinnabar – Ore Of Mercury

Elemental mercury is extracted from cinnabar, a highly toxic mercuric sulphide ore that is around 86% mercury and 14% sulphur. Some sources say it is in fact the most toxic ore we currently know about, whilst others suggest it's more than rivalled by crocidolite, which is better known as blue asbestosis!

Cinnabar is found in areas of active volcanic activity and hot springs, which places it in many geologic regions across the world. The ore's bright red crystals likely brought it to the attention of humans very early on, and its widespread distribution contributed to it being one of the few ores discovered and utilised autonomously across many diverse civilisations, well before they were linked by trade and 'information exchange' routes. Crushed cinnabar powder for instance was widely used to colour red paints, dyes, lacquers and cosmetics from around 7,100 BC up until the 8th century AD when it was replaced by a chemically produced mercury / sulphur mix.

It's Elementary – Elementary Mercury That Is

Historically mining has been the major user of elemental mercury. It is a perfect medium for extracting other minerals, significantly gold and silver. The metals form a solid amalgam with mercury when they're mixed together. This amalgam is then heated to vaporise the mercury, leaving behind pure gold (or silver). The mercury vapour is usually captured, cooled to return it to its liquid state, and reused. The process is efficient, simple, and relatively cost effective so long as the mercury vapour doesn't escape, even in miniscule amounts. Unfortunately, keeping it contained has not always been given priority, resulting in severe environmental contamination and major mercury-related health issues.

Mercury's toxicity was actually recognised very early in the metal's mining history. It's one reason prisoners and other persons considered 'disposable' were used in mercury mines. It's also the reason most gold processing plants progressively started switching over to cyanide from the 1960's, and the reason mercury was gradually phased out. These days, the only sector of the industry that still uses mercury consistently is artisanal mining where it remains the cheapest and easiest option.

Today's Mercury Users

Overall, the biggest 'official' consumers of all the various forms of mercury today are industrial chemicals, and electrical and electronic goods.

On a global scale, China is by far the biggest miner, producer, user, supplier and emitter of mercury in all its forms, and mercury containing products. Notably, its huge PVC manufacturing industry – China produces 240 million tonnes of PVC annually – uses the catalyst mercuric chloride which accounts for half the country's total mercury use. Under the terms of the Minamata Convention on Mercury, to which China is a signatory, the industrial behemoth is reducing reliance on mercury in this and many other industries but compliance has been slow and expensive with multiple extensions sought, and granted. Further, China is committed to ending all domestic mercury mining by 2032. When she does, it should remove around 3.5 thousand metric tonnes of the toxic metal from the global market annually.

A Brief Word About Mercury Pollution

Elemental mercury and its noxious vapours aren't the only 'mercury problems' facing the world. Its inorganic and organic forms are also hugely problematic. Inorganic mercury for instance is found in minute quantities in coal (and other fossil fuels). When these fuels are burned, it releases the mercury into the atmosphere as a by-product. Coal-fired power stations are particularly big producers of inorganic atmospheric emissions. The issue though is not so much the mercury itself but what happens when that mercury falls back to earth and gets into water systems. Microorganisms in water convert the inorganic mercury into highly toxic organic methylmercury, which then enters the aquatic food chain and subsequently ends up in humans.

In fact, coal-fired power stations and other fossil-fuel burning industries are now considered the primary source of anthropogenic mercury contamination for most of the world's population. It's not because these fuels are loaded with mercury but rather the sheer volume being burnt on a global scale in areas of dense populations. That and the fact that so much of their inorganic mercury emissions end up being converted to methylmercury because of where it lands.

However, serious though the problem of fossil fuel burning is, the highest anthropogenic mercury pollution emitter of all is now artisanal gold mining but more on that in our next article.


  1. Mad hatter's disease: Definition, causes, and symptoms
  2. According to the Oxford Dictionary, the term 'mad as a hatter' first appeared around 1829, whilst 'hatter's shakes' appeared in 1883.
  3. Mercury Compounds
  4. Test Procedure, Use or Product Name Mercury Containing Component or Reagent
​Cinnabar Mining - A Complex Situation
​Spotlight On Mine Managers

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