An empty 19th-century hatter's workshop with steaming copper pots and rows of unfinished top hats — A Victorian hat workshop — where the mercury did its damage. AI-generated dramatization art — not a historical depiction.

Mercury and Madness

The Hatter's madness has a real-world twin — and it was written in mercury.

The phrase came first

“Mad as a hatter” was in print decades before Carroll’s Hatter existed. The earliest known appearance is in Blackwood’s Edinburgh Magazine (January–June 1829), in the Noctes Ambrosianae series:

NORTH: Many years — I was Sultan of Bello…

TICKLER (aside to SHEPHERD.): He’s raving.

SHEPHERD (to TICKLER.): Dementit.

ODOHERTY (to both.): Mad as a hatter. Hand me a segar.

It appears again in Thomas Haliburton’s The Clockmaker (1835). Carroll, writing in the 1860s, was borrowing a phrase his readers already knew — he never uses it in the books himself.

The mercury

Eighteenth- and nineteenth-century hat-makers turned animal fur — rabbit, beaver — into felt using mercuric nitrate in a process called carroting, which roughened the fibers so they would mat. The workshops filled with mercury vapor, and the hatters breathed it for years. Chronic mercury poisoning — erethism — produced exactly the symptoms the phrase describes: tremors, slurred speech, shyness and irritability, mood swings, confusion, and in severe cases hallucinations.

In the United States the industry centered on Danbury, Connecticut, where the condition was so common it had a local name: the “Danbury shakes.” Mercury was eventually driven out of the trade — banned from American hat factories by the early 1940s — but the phrase outlived the poison.

The competing theories

Honesty requires the rivals, and they are worth knowing:

The verb “hatter.” Samuel Johnson’s Dictionary (1755) lists hatter as a verb meaning “to harass, to weary” — “He’s hatter’d out with pennance” (Dryden). A “hatter” might be one who harries.
“Atter,” the adder. Old English atter meant poison; the Morris dictionary of word origins argues “mad as a hatter” descends from “mad as an atter” — as venomous as a viper.
The evidence problem. Phrase-origin researchers (notably at phrases.org.uk) note that beyond the hatters’ trembling fits, there is little direct evidence linking the trade to the coining of the phrase. The mercury theory is plausible and popular; it is not proven.

The Hatter himself

Here is the twist the books insist on: Carroll’s Hatter shows none of mercury poisoning’s symptoms. He is neither timid nor trembling — he is loud, logical, and socially relentless. His madness is theatrical and verbal, not medical. Whatever the phrase’s origins, the character is not a case study; he is a comedian.

The human cost

The comedy has a shadow. Real hatters — including, by wide report, Boston Corbett, the former hatter who shot John Wilkes Booth — suffered and died of the trade’s poison. The “Danbury shakes” were not a joke to the men who had them. This page treats the phrase as history, not just wordplay.

Source notes

The 1829 Blackwood’s citation is the earliest known printed use (Noctes Ambrosianae No. XLIV). The mercury/erethism account and the Danbury history are the standard medical-historical narrative; the verb and “atter” theories are reported with attribution, and the evidence gap is stated plainly. “Mad Hatter’s disease” remains a colloquial name for mercury poisoning.