A colorless, odorless, tasteless, non-explosive, and inert gaseous element. It is used in arc welding and gas-discharge lasers, as a component of artificial atmospheres, as a refrigerant, as a lifting gas for balloons. Tank sizes available include 221 cubic feet. Atomic symbol He, atomic number 2, atomic weight 4.0026, boiling point -268.9?C, density at 0?C 0.1785 gram per liter. (pr. hee'lee-m) Also see acetylene, argon, carbon dioxide, hydrogen, nitrogen, and oxygen.