Answer by
LeheckaG (1826)
Epsom-salt (MgSO4ยท7H2O), pH 5.5 to 6.5, is hepta-hydrated Magnesium-sulfate/sulphate (MgSO4).
Epsom-salt can be hygroscopic (absorbing-water) resulting in a "drying"-effect as a bronchodilator, and for various muscle & skin conditions.