Chlorine

Chlorine (CI., atomic weight 35.37), a gaseous element which does not occur free in nature, but, combined with other elements, occurs largely in sea water, and beds of mineral salts. It is chiefly prepared by the action of hydrochloric acid on manganese dioxide,

Mn0₂ + 4HCl = MnCl₂ + 20H₂ + Cl₂.

It is also largely prepared by passing hydrochloric acid gas and air over heated bricks impregnated with copper sulphate,

4HCl + 0₂ = 20H₂ + 2Cl₂,

the copper sulphate undergoing no change (Deacon's process). It is a greenish gas (hence its name chloros = green) with a very disagreeable suffocating smell. When strong it is a violent irritant, causing inflammation of the mucous membrane of the throat. By pressure and cold it can be condensed to a yellow liquid. It is soluable in water, but is evolved on warming the solution. Many metals burn in chlorine, and it acts energetically on many organic substances containing hydrogen. When moist, it possesses the power of bleaching vegetable colours, but the dry gas has not this property. It has also antiseptic properties, which, like the bleaching, appear to depend on its oxidising power. It is largely used for the preparation of bleaching powder and other manufacturing purposes, and its solution is much employed in the chemical laboratory. Together with bromine, iodine, and fluorine, it constitutes the group of elements known as the Halogens (q.v.).