Today's question for Mailbag Friday comes to us from Valerie P. of Ottawa, Ontario. Valerie writes: "I was visiting a heritage village in Nova Scotia when a guide in a traditional tailor's house told me the origin of the expression, mad hatter. He said that the beaver fur the popular top hats were made of was preserved with mercury. The workers gradually absorbed this mercury while making the hats and eventually became mad. The explanation seems a bit sketchy; can you fill in the details, or correct the explanation?"

One of my basic rules of thumb is that when it comes to etymology, never trust tour guides. The job of a tour guide, after all, is to entertain people with fanciful stories about a particular place, not to be a serious word historian. If you're visiting New York City, for instance, you might hear a tour guide tell you an apocryphal story about how 23 skidoo comes from police slang used to disperse crowds of ogling men in front of the Flatiron Building on 23rd Street, where high winds would blow up women's skirts. (See here for more on skidoo. We're not sure where the "23" comes from, but Barry Popik, master word sleuth and bane of the tour guides, points out that the number appeared in slang expressions well before the construction of the Flatiron Building.)

In her trip to Nova Scotia, Valerie has come across that special case of a tour guide who actually seems to care about etymological veracity. The explanation that the guide gave is pretty much on the money. We're all familiar with the famous tea party in Lewis Carroll's Alice's Adventures in Wonderland, presided over by the Mad Hatter. Carroll, who published the children's classic in 1865, came up with the character based on the expression as mad as a hatter, which the Oxford English Dictionary dates back to 1829. As the OED explains, "the allusion is to the effects of mercury poisoning sometimes formerly suffered by hat-makers as a result of the use of mercurous nitrate in the manufacture of felt hats."

Those felt hats were very often made of beaver pelts or other animal fur, as the tour guide suggested. In the heyday of hatmaking, one center of industry was Danbury, Connecticut, nicknamed "The Hat City." Peg Van Patten of the Connecticut Sea Grant writes about how mercury poisoning afflicted the hatmakers of Danbury:

At the peak of the industry, five million hats a year were produced in 56 different factories in Danbury. A process called "carroting" was used in the production, but it had nothing to do with vegetables. Carroting involved washing animal furs with an orange-colored solution containing a mercury compound, mercury nitrate.
The colorful solution facilitated the separation of the fur from the pelt and made it mat together smoothly. The fur was then shaped into large cones, then shrunk in boiling water and dried many times before final shaping, smoothing, and finishing. Workers would often be exposed to mercury vapors in the steamy air. Many hatters with long-term exposure, particularly those involved in carroting, got mercury poisoning.
Mercury poisoning attacks the nervous system, causing drooling, hair loss, uncontrollable muscle twitching, a lurching gait, and difficulties in talking and thinking clearly. Stumbling about in a confused state with slurred speech and trembling hands, affected hatters were sometimes mistaken for drunks. The ailment became known as "The Danbury Shakes." In very severe cases, they experienced hallucinations.

Outside of Danbury, the physical effects of mercury poisoning on hatmakers was simply called "hatter's shakes." Fortunately for the hatters, mercury nitrate stopped being used in the production of hats in the 1930s, when new processes involving hydrogen peroxide and acids were developed.

Clearly, being a hatmaker back in olden times was a tough job. But even those suffering "hatter's shakes" would rarely exhibit psychological disorders that we associate with "madness." That, as it turns out, was more of a popular perception than a medical reality. Despite the fact that there weren't many hatmakers actually going mad from exposure to mercury, common stereotypes about the occupation were enough to give rise to the phrase as mad as a hatter and ultimately inspire Lewis Carroll. Now, where Carroll got the idea for another mad creation, the March Hare, is a story for another day.

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