Chlorine is an element, having the symbol CI with an atomic weight of 35.45. Gaseous chlorine is greenish yellow in colour and is approximately 2.5 times heavier than air. Under pressure, it is a liquid with an amber colour and oily nature approximately 15 times as heavy as water. Liquefaction of chlorine gas is accomplished by drying, cleaning and compressing the gas to 35 kg/c$m^2$.

When chlorine is dissolved in water at temperature between 49°F and 212°F, it reacts with water to form hypochlorus acid (HOCI) and hydrochloric acid (HCI) within few seconds according to the equation

C$l_2$ + $H_2$O HOCl + HCI (Hydrolysis)

This hydrolysis reaction is reversible. The HOCI ionizes or dissociates into hydrogen ion ($H^+$) and hypochlorite ions (OC$l^-$) according to the equation,

HOCI $H^+$ + OC$l^-$(Ionization)

This reaction is also reversible. It is the hypochlorus acid and hypochlorite ions which accomplish disinfection.