Damp magnesium chloride. Magnesium chloride (MgCl2) is an inorganic compound consisting of one magnesium and two chloride ions. It is an eye and skin irritant and should be kept away from moisture. Magnesium chloride is used in medicine as a source of magnesium ions, which are essential for many cellular activities. It has also been used as a laxative and in alloys. The compound is damp and it therefore being held on a watchglass. See A710/036 for dry magnesium chloride.