A colorless, odorless, noble gas element found in minute quantities in the atmosphere, extracted commercially from liquefied air and used in stroboscopic, bactericidal, and laser-pumping lamps. Atomic number 54; atomic weight 131.29; melting point -111.74°C; boiling point -108.09°C; density (gas) 5.89 grams per liter; specific gravity (liquid, at -109°C) 2.95; valence 0, 2, 4, 6. See Periodic Table.