1. (n.) A colorless, tasteless, odorless, gaseous element occurring in the free state in the atmosphere, of which it forms about 23 per cent by weight and about 21 per cent by volume, being slightly heavier than nitrogen. Symbol O. Atomic weight 15.96.

2. (n.) Chlorine used in bleaching.

acetylene ammonia argon asphyxiating gas butane carbon dioxide carbon monoxide chlorine coal gas ethane ether ethylene fluorine formaldehyde helium hydrogen illuminating gas krypton lewisite marsh gas methane mustard gas natural gas neon nitrogen ozone poison gas propane radon sewer gas xenon