The Not-So-Mad Hatter: Occupational Hazards of Mercury

The character of the Hatter features prominently in Lewis Carroll's Alice's Adventures in Wonderland, published in 1865 and reprised by Tim Burton's 2010 movie, Alice in Wonderland. The phrase "mad as a hatter" was in use 30 years prior to the publication of Carroll's novel, and is associated with industrial felt hat workers in 19th-century England. Mercurial disease was common among hatters and included such symptoms as tremors, irritability, and mental instability. A document published in 1860 focuses on mercurial disease among hatters and the occupational hazards of mercury.1

To make felt, hatters separated fur from the skin of small animals in a process called carroting. In this process, the secondary nitrous gas released from mercury (II) nitrate (CAS Registry Number® (RN): 10045-94-0) caused the fur to turn orange, lose shape, and shrink. The fur also then became darker, coiled, and more easily removed.2 Prior to the use of mercury to remove fur, hatters used camel urine, which is mostly water but also contains nitrogen waste in the form of urea. When applied to fur, urea disrupts chemical bonds and causes protein denaturation.3 During the expansion of hat-making into 19th-century France and England, hatters frequently replaced camel urine with their own. Subsequently, it was noticed that an individual workman treated with mercury (I) chloride (CAS RN: 10112-91-1) for syphilis consistently produced superior felt.4 As a result, mercury nitrate came into wide use to obtain the same effects as the workman's mercury-contaminated urine.

Elemental mercury occurs naturally and is present in the earth's crust. Commonly referred to as quicksilver, mercury is liquid metal at room temperature. Exposure to mercury affects the skin, kidney, eye, and nervous system, and the respiratory system if inhaled. Telltale signs of mercury poisoning also included those often seen in hatters: emotional instability, cognitive and memory loss, shyness, speech problems, and ataxia. The antidote for mercury poisoning is chelation therapy.5 In this therapy, an organic compound (chelator) binds with mercury to form a heavy-metal chelate, which is subsequently excreted.6 The United States Public Health Service banned use of mercury in the felt industry in 1941, not so much for health risks but because mercury fulminate was needed for World War II detonators.1

Alternatives to mercury use in hat-making were documented as early as 1874.7 U.S. Patent 390,348 addressed the occupational hazards of mercury use and proposed a hydrochloride-based alternative.8 By 1902, various metal nitrate and sulfate derivatives were compiled in a report on the progress of felt hat making.1 This report included a search of the "Patents Records for registered solutions," and provides an early glimpse into the world of patent searchers.

Use SciFinder® and STN® to explore additional information about mercury and chemical poisoning in the CAS databases.

Contributed by
Kathryn J. Kitzmiller, Ph.D.

  1. Wedeen, R. P. Were the hatters of New Jersey "mad"? Am. J. Ind. Med. 1989, 16, 225-233.
  2. Porter, C. Remarks on Felt Hat Making: Its processes and hygiene. Br. Med. J. 1902, 1, 337-381.
  3. Sagle, L. B.; Zhang, Y.; Litosh, V. A.; Chen, X.; Cho, Y.; Cremer, P. S. Investigating the Hydrogen-bonding Model of Urea Denaturation. J. Am. Chem. Soc. 2009, 131, 9304-9310.
  4. Baum, R. M. Mercury. Chem. Eng. News [Online] 2003, 81, (accessed June 22, 2010).
  5. Mercury, 99.999%; MSDS No. 96252 [Online]; Fisher Acros Organics: Fair Lawn, NJ, Mar. 7, 2007. http// (accessed June 15, 2010).
  6. Soffer, A.; Chenoweth, M.; Eichhorn, G.; Rosoff, B.; Rubin, M.; Spender, H. Chelation Therapy, Charles C. Thomas: Springfield, Ill, 1964.
  7. Von Delpech, H. A method of preparing the fur of rabbits and hares for the manufacture of felt without the use of mercury. J. Chem. Soc., Abstr. 1874, 27, 99.
  8. Dargelos, M. J. A. Process of Preparing Animal-Hairs for Felting. U.S. Patent 390,348, Oct 2, 1888.

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