Chlorine
Oxidation and reduction applied to water treatment - Oxygen, chlorine and derived products

Diatomic chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, by reacting a few drops of hydrochloric acid (then called "muriatic") with pyrolusite (MnO₂): he obtained a dense, greenish gas, which was later named chloric gas by Sir Humphrey Davy in 1810 (from the Greek khlôros meaning "pale green").

Chlorine is the 20th most abundant element in the earth's crust (see the main properties of chlorine in Box 2); it is a metalloid (or non-metal) that belongs to the halogen family and appears in the periodic table with the following...