Gold chloride (AUCl3), dihydrate, also called gold trichloride or auric chlorise, is a compound comprised of gold and chloride. It exists as a chloride-bridged dimer, both as a solid and as a vapor. AUCl3 is very hygroscopic and highly soluble in water and ethanol. It is used in organic chemistry as a mild acid catalyst and as a alternative to mercury salts. It is known to cause allergic reactions in subjects with known gold allergy.