At one time the hat-making industry involved the use of baths of orange nitrate of mercury to soak animal skins. This process, called carroting after the typical colour of the fur being treated, helped make the stiff hairs more pliant, thereby producing a superior felt product. Unfortunately the vapour from the process filled the factory with toxic levels of mercury. With trembling hands and blackened teeth, mercury-poisoned hatters had slurred speech and other nervous disorders, odd behaviours, and symptoms of dementia. It is therefore little surpise that we ended up with the phrase ‘Mad as a Hatter’.
(Engraving by Andy English - available for purchase)
In Spring, hares can be seen boxing in the fields as part of their courtship ritual. Females weren’t always interested in the males' advances early in the season. The females actually “boxed” the amorous male hares using their forelegs to put a stop to it. For a long time it was thought to be bouts between males competing for females. Their strange behaviour led to the equally common phrase ‘Mad a March Hare’.
Lewis Carroll incorporated both the Hatter and the March Hare in Alice’s tea party.
Less easily explained are some of the other expressions used to designate strange behaviour like ‘Mad as Cheese’, 'Mad as a Brush',, ‘Mad as a Bag of Hammers’ or ‘Mad as a Wet Hen’.
Of the many variants one of my favourites is ‘Mad as a Box of Frogs’. I imagine that one at least is self-explanatory.
