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Those who have read the famous story of Alice’s Adventures in Wonderland by Lewis Carroll or seen the movie know about the character known as the Mad Hatter. He is also a character in the Lewis Carroll sequel, Through the Looking Glass.

Alice is a seven-year-old who believes in an orderly and stable world, but has a great curiosity about her surroundings. The story introduces experiences and characters that challenge her perceptions of her world. Some of the characters include the White Rabbit, the Queen of Hearts, the Cheshire Cat, and the March Hare, among many others.

One of the characters is the Mad Hatter. He is a member of the Mad Tea Party. He is a small, impolite character who lives in a perpetual tea-time. He is rude, frequently frustrates Alice and provokes her during the tea party.

The Mad Hatter

Mad Hatter. He is a member of the Mad Tea Party. He is a small, impolite character who lives in a perpetual tea-time. He is rude, frequently frustrates Alice and provokes her during the tea party.

The term “Mad Hatter’s Disease” appeared around 1915 when workers involved in making felt hats exhibited odd and unexplainable behavior. Lewis Carroll published his novel about Alice in 1865. It is most likely that he was not aware of the strange behavior of workers engaged in felt hat manufacturing. However, the later behavior became linked to the behavior of the novel’s character, the Mad Hatter.

Mat Hatter's Party

The Tea Party as depicted in Lewis Carroll published novel about Alice in 1865.

Some History of Mercury and Mercury Poisoning

The mining of mercury dates back to ancient civilizations. It occurred in China during the Kwoll-Chan dynasty. The Romans mined mercury at the Almaden mine in Spain that is still in operation.

Mercury ore, called cinnabar, is a brilliant red. One major mercury mining area in the United States is in southwest Texas. Local Indians discovered the ore and likely used it in war paint and for paintings on rocks and bluffs. Traders told how they obtained some from Indians in the early 1800s.

People knew of the hazards of mercury for a long time. Pliny the Elder (70 A.D.) noted mercury poisoning (sometimes referred to as mercurialism) as a disease of slaves working in the mines. Others noted symptoms among mercury miners in Italy during the 16th century. Ramazzini wrote about it among workers in Venice who coated glass with mercury to create highly reflective mirrors with very clear images. In 1861 the German physician, Adolph Kussmaul described the emotional symptoms of mercury exposure as a first stage preceding other physical effects

Some Uses of Mercury

Mercury, known also as quicksilver, can take various forms. It is a heavy metal found in the earth. In its elemental form, it is liquid and silver in color. It can combine with other elements, such as carbon to form methylmercury (organic mercury compound) or other elements to form salts (inorganic mercury).

Humans have used mercury in various way for much of history. Mercury has been used in many products. It can serve as a preservative. It has been used in cosmetics. It has been a herbal supplement.

Around 1500 mercury in various forms, such as ointments or pills, was a preferred treatment for syphilis.

For many years and in some developing countries today, small-scale gold miners us mercury to extract gold from rock. First, miners crush the rocks containing small amounts of gold. Then they mix mercury with the crushed rock because it has a strong affinity for gold. They heat the mixture, which causes small, pea-shaped nuggets to form. Finally, the nuggets get reheated to vaporize the mercury and leave pure gold.

A similar use of the gold-mercury affinity occurs in “gilding” or “fire gilding.” Artists can enhance trim on high-value items and antiques by mixing mercury and gold, heating it and brushing it onto decorative metal trim. Finally, the artisan removes the mercury through evaporation by heating the finish, leaving the gold as the final decorative surface.

In the felt and felt-hat industry, mercury is used to remove animal hair from the animal skin. This process has the name felting or “carrotting.” During the process when done with mercuric nitrate, the animal skin takes on an orange, carrot color, thus the name carrotting. The carrotting process also aided the removed hair to mat smoothly together. The most preferred furs were beaver, rabbit and camel. Some felts incorporate wool. A mat of hair is processed further using steam and boiling it in hot water so it could be molded to form a hat or other object. At first, a mat is made into a cone and later stretched over a mold and dried to form the desired shape of a hat. The steam and heated processes cause much of the mercury in the felt mat to vaporize and allow workers to inhale the mercury vapor.

Prior to the use of mercuric nitrate for making felt, it was common to use urine, either animal or human urine. An old story suggests that one particular workman was able to produce superior felt. It was determined that this workman was being treated with a mercury compound for syphilis. The conclusion was that the mercury in his urine improved the fibers for felt. That led to using mercury in felt processes.

Mercury is an important part of mercury thermometers, barometers and other instruments. It has use in electrical switches. Mercury vapor is essential in fluorescent lamps. In the 1980s mercury batteries were common.

For centuries, an amalgam of silver and mercury was the main material used in dental fillings. Over time the mixture added tin and copper. Today, dentists use polymer fillings that essentially replace amalgam fillings.

Mercury Poisoning

As noted above, the dangers of mercury exposure were known for a long time. The exact effects on humans became known in the 1800s and early 1900s.

Exposure may occur through ingestion, inhalation and absorption through the skin. The effects of exposure depend on the mercury form, concentration and rate of exposure as well as the duration of exposure.

Working in enclosed spaces often exacerbates the exposures.

There are numerous health effects mainly involving the nervous system. Included are hand tremors, muscle spasms, a lurching walking gait, drooling, slurred speech, insomnia, loss of memory, loss of hair and teeth, and fatigue. Other behavioral effects include personality changes, unfocused thoughts and speech, depression, irritability, excitability, low self-confidence, apathy, shyness, timidity, hallucinations, and unprovoked verbal outbursts.

In addition after long exposures, some people exhibit headaches, general pain, intestinal and kidney problems.

Danbury, Connecticut

Mallory hat factory in Danbury, Connecticut.

Mallory hat factory in Danbury, Connecticut.

As the popularity of hats grew, the need for hat production grew. Tall hats were the fashion in Europe during the 1500s, An early hat worn by both men and women was the “capotain” that the Puritans adopted as a symbol for Puritanism. Hats evolved continually in size, shape and decoration. Some famous hat shapes were the top hat in the 1800s and the stove pipe hat made famous in the United States by President Abraham Lincoln and in England by Prince Albert.

Abraham Lincoln in his stovepipe hat.

Abraham Lincoln in his stovepipe hat.

The hat manufacturing business boomed because everyone wore hats. Popularity of hats as fashion statements for both men and women expanded into the early 1900s. For women felt hats often included an array of felt flowers.

Puritan capotain hat.

Puritan “capotain” hat.

With the popularity of hats, Danbury, Connecticut became the “hat capital of the world.” During the 1800s at least 56 companies there produced as many as 5 million hats a year. Thousands of people worked in the Danbury factories. A sign in the city proclaimed “Danbury Crowns Them All.”

The hat industry slowly waned as the 20th century progressed. For men the prominence of felt hats ended in the 1960s, significantly influenced by President John Kennedy who did not wear a hat.

The last hat factory in Danbury, Stetson, closed in 1965

Although the hat factories of Danbury are gone, some of the mercury remains. For example, there have been efforts to clean up soils at former factory sites, including some sites that fell under the Superfund Cleanup program of the Environmental Protection Agency. Today mercury traces remain in the sediment of the Still and Housatonic rivers that wind through Danbury and surrounding areas.

Mad Hatter’s Disease

A common expression that emerged and applied to milliners involved in hat production was “mad as a hatter.” The expression recognized outbursts and other unusual behaviors found among the hatters. For example, a common story involves people observing a milliner at work. Having someone looking at them while working could be disconcerting and often led to an outburst complaining about being observed: “how can I do my work when someone is standing and watching?” Things could easily upset the workers who perceived that someone was trying to disrupt them or they were simply intimidated to the point of being highly irritated. Their response to a situation was not predictable or did not follow interpersonal norms.

A common name for mercury poisoning among milliners was “Mad Hatter’s Disease.” Many referred to the hand tremors often exhibited as hatter’s shakes or “Danbury Shakes,” named after the hat capital. There are other terms that can apply, such as mercurialis, mercurialism, erethism, and mad hatter syndrome.

Providing Worker Protection

While dangers related to mercury exposure had been known about for a long time, the details about exposure were not.

In 1851 workers in Danbury formed the hatter’s union. A primary focus was on improving working conditions. For example, there were complaints about the steam, not only streaming on the workers and requiring the wearing of rubber aprons, but the concentrate that condensed at the ceiling and fell virtually like rain.

In Connecticut mercury poisoning was added to the state Workmen’s Compensation Act of 1913. Those who saw a doctor and sought compensation claims for the Danbury shakes were often required to sign a waiver against future claims and were blacklisted by the manufacturers. Employers often dismissed claims about mad hatter’s symptoms, responding that the symptoms were the result of excess drinking and tobacco use. Court decisions at the end of the 1900s ruled in favor of employers and weakened the hatter’s union.

Workers in the 19th century faced a great danger from tuberculosis, the leading cause of death at the time. Working closely in the steamy, humid environment aided in transmittal of the disease among workers.

In 1901 the United Hatters of North America went on strike against the D.E. Loewe & Co. The battle damaged the company financially, but the company filed a lawsuit against the union, the American Federation of Labor and individual officers and members. The case went to the U.S. Supreme Court twice. The case move slowly through the courts for 15 years, but a final ruling found the union unlawfully restrained trade and faced a $250,000 fine.

The case also led to study of mercury poisoning by the early industrial hygienist and medical doctor at Harvard, Alice Hamilton. In her study of 100 union hatters, 43 had mercury poisoning. She found some young men in their early 20s with continual hand shakes and others with long experience as hatters who could not feed themselves. She concluded that the symptoms did not come from alcohol and tobacco use.

In France in 1869 the Academy of Medicine demonstrated the health hazards for hatters. Alternate processes were available by 1874. In 1888 the United States Patent Office issued a patent for a hydrochloride-based process. In 1898 France banned the use of mercury in hat making. Shortly thereafter, the use of mercury in felt processing in Britain largely fell out of use.

By 1923 there were only six hat manufacturers left in Danbury. It was not until December 1, 1941 that the state of Connecticut banned the use of mercury in hat making. Hydrochloric acid became the substitute. A primary factor in the ban of mercury in the hat process in the United States was the high demand for mercury in production of detonators for weapons in WWII.



  • https://connecticuthistory.org/ending-the-danbury-shakes-a-story-of-workers-rights-and-corporate-responsibility/
  • http://www.newenglandhistoricalsociety.com/mad-hatters-danbury-conn/
  • https://corrosion-doctors.org/Elements-Toxic/Mercury-mad-hatter.htm
  • https://www.vox.com/science-and-health/2017/4/14/15178528/s-town-podcast-mercury
  • https://www.dartmouth.edu/~toxmetal/mercury/history.html
  • https://www.chemicool.com/elements/mercury.html
  • http://mercurypolicy.scripts.mit.edu/blog/?p=367
  • http://www.environmentalhistory.org/mercury/history
  • https://en.wikipedia.org/wiki/Erethism
  • https://tshaonline.org/handbook/online/articles/dkm02
  • https://www.encyclopedia.com/science-and-technology/chemistry/compounds-and-elements/mercury-metal
  • https://www.history.com/news/where-did-the-phrase-mad-as-a-hatter-come-from
  • https://www.quirkyscience.com/mad-hatters-felt-and-mercury/
  • https://legionofhonor.famsf.org/poisons-part-i-mercurial-world-felt
  • https://corrosion-doctors.org/Elements-Toxic/Mercury-toxicology.htm
  • https://corrosion-doctors.org/Elements-Toxic/Mercury-mad-hatter.htm
  • https://jmvh.org/article/syphilis-its-early-history-and-treatment-until-penicillin-and-the-debate-on-its-origins/
  • https://www.pharmaceutical-journal.com/opinion/blogs/syphilis-and-the-use-of-mercury/20201679.blog
  • From the George W. Harper Collection:
    • A. Link Koven, M.D., “Reporting Makes History,” USPHS Article No. 12 (publication and date unknown)
    • Mercury, Industrial Data Sheet D-Chem. 17 (Revision), National Safety News, January 1947.
    • Stuart Emmrich, “Revlon denies mercury in cream caused injury,” Business Insurance, April 2, 1979.

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