Epsom salts

Named after Epsom in Surrey, England; the town had a spring which gave forth bitter saline water containing the compound.

Epsom salts (countable and uncountable, plural Epsom salts)

1. magnesium sulfate, used as a laxative and in the preparation of tofu as a coagulator, and formerly as a medicated soaking solution.
   • 2010, Andrea Levy, The Long Song, Tinder Press (2017), pages 71–72:

     And who but July would know […] that her back needed to be rubbed after she had drank her Epsom salts so as to release, into a belch or fart, the wind that so plagued her.

• mesoplasts