Mad as a Hatter?

As Mad as a Hatter

Hatters were, of course, not mad at all, or at least no madder than those in other trades. They were, however, likely to exhibit behaviours which might be interpreted as signs of madness.

Making a felt hat involves the felting (matting together) of wet woollen fibres to make a mouldable material which can be shaped, while wet, on a former into the desired shape to create the required style of hat. Once dried, the material becomes soft, but firm and will hold its shape. Wool can be felted using water only, but very early on, the process was found to be easier and more effective with the addition of urine to the water. The ammonia in the urine opens up the scales on the fibres and encourages them to lock together producing a softer felt.

The story goes that the urine of hatters who were suffering from syphilis, and who were being treated using mercuric chloride, proved more effective in the felting process and so it became the practice to add mercuric nitrate to the water to achieve the same effect. While this undoubtedly improved the process, the consequent effects on the hatters were dire. Mercury fumes were released from the liquid, particularly during the boiling processes. Unfortunately, little was done to remove these fumes from the workplace, where they were inhaled with disastrous results for the hatters, leading to the widespread development of erethism.

Erethism is damage to the central nervous system resulting from the inhalation of mercury vapour. Sufferers show behavioral changes such as irritability, low self-confidence, depression, apathy, shyness, and timidity. In more extreme cases they can exhibit delirium and tremors. Sufferers may even become suicidal.

The use of mercury persisted well into the 19th century. Even after the association with mercury was understood, the symptoms seem to have been regarded as an "occupational hazard" by those in the trade. A short article in the Birmingham Mail of 28 April 1876 sheds an interesting light on the lack of understanding:

In the 1870s it was discovered that the much safer hydrogen peroxide would achieve the desired effects without the same dangers to health. Cases of erethism consequently declined significantly, becoming rare in the early 20th century.

The description could easily have been "Mad as a Gilder", since mercury was also widely used in the "fire gilding" of metalwork and the "silvering" of mirrors, with similar effects on those working in these trades.

The risks of mercury, however, were largely ignored well into the 20th century. At school in the 1960s, it was not seen as unusual for the pupils to handle metallic mercury in science lessons. No gloves or eye protection! Fortunately, I seem to have suffered no ill-effects sixty years on. Such cavalier attitudes are fortunately no longer acceptable.

Incidentally, despite our illustration, Lewis Carroll did not describe his Hatter as "Mad", simply as "The Hatter". His description of the character's behaviour, however, leaves little doubt of the allusion.