Chlorine

Webster's Dictionary

(n.) One of the elementary substances, commonly isolated as a greenish yellow gas, two and one half times as heavy as air, of an intensely disagreeable suffocating odor, and exceedingly poisonous. It is abundant in nature, the most important compound being common salt. It is powerful oxidizing, bleaching, and disinfecting agent. Symbol Cl. Atomic weight, 35.4.

The Nuttall Encyclopedia

Elementary, greenish-yellow gas obtained from common salt; powerful as a disinfectant, and a bleaching agent.