Hydrogen chloride is a diatomic molecule, consisting of a hydrogen atom H and a chlorine atom Cl. It was discovered in 1648. When hydrogen chloride gas is dissolved in water, hydrochloric acid is formed. The covalent compound ionises in water because of its polar nature, and it can conduct electricity: hydrochloric acid and one part of concentrate Nitric acid gives nascent chlorine. Hydrogen Chloride occurs in a free state in volcanic gases and gastric juices of mammals. It is a compound of the elements hydrogen and chlorine. The molecular formula is HCl, and Molecular mass is 36.5. It condenses at -85° C (-121° F) and freezes at -114° C (-173° F). The gas is highly soluble in water. Because of its high solubility, the gas fumes in moist air. Hydrogen chloride is mostly used in the production of hydrochloric acid. It is useful in the preparation of aqua regia, manufacture of chlorine, and some other chlorides and as a solvent for noble metals and as a reagent in laboratories.