Chlorine (Gr. green), a gaseous chemical element of yellowish green color, discovered by Scheele in 1774, called dephlogisti-cated marine acid air, also oxidized muriatic acid, and first pronounced a simple body by Gay-Lussac and Thenard in 1809; a conclusion afterward confirmed by Sir Humphry Davy, who gave it the name it now bears. It occurs very abundantly disseminated over the earth, in salt brines in combination with sodium, with copper as atacamite, with potassium as sylvine, with silver as horn silver, with mercury as native calomel, and in smaller quantities with other minerals and volcanic gases. In the animal kingdom it is found in the gastric juice, in perspiration, etc, and among vegetables in marine plants. It is therefore one of the most abundant constituents of the earth. For laboratory use it can be conveniently prepared by heating in a retort a mixture composed of 10 parts by weight of common salt, 8 parts of manganese dioxide, and 24 parts of sulphuric acid, diluted with 12 parts of water. On a large scale it is usually prepared from hydrochloric acid, which in England is an incidental product.
According to Weldon's process, the crude muriatic acid of the soda ash manufactory is decomposed by manganese dioxide, and the resulting manganese chloride is regenerated to be employed again. Deacon has modified the operation by conducting the muriatic acid directly from the condensing towers into a rever-beratory furnace along with some oxygen of the air, over bricks saturated with salts of copper. Chlorine is liberated, and the reaction is said to be continuous, as the same copper salt will decompose an indefinite amount of the acid. Enormous quantities of chlorine are thus made in England, to be chiefly used in the manufacture of bleaching powders. Chlorine is a yellowish green, pungent, suffocating gas; specific gravity compared to air, 2.44, 30 times heavier than hydrogen. Under four atmospheres of pressure it can be condensed to a yellow limpid liquid of specific gravity 1.33. Copper, previously heated, burns readily in chlorine; arsenic, antimony, and phosphorus ignite spontaneously. A lighted candle gives off copious volumes of smoke and is soon extinguished; and ignited charcoal also ceases to burn on account of the weak affinity of carbon for chlorine: but hydrogen gas burns readily in chlorine, producing effects similar to those attained by the oxyhydrogen blowpipe.
A piece of paper previously saturated with turpentine bursts into flame when plunged into a jar of chlorine gas. The affinity of chlorine for hydrogen is so powerful that if the two gases be mixed in the dark and subsequently exposed to the solar rays, they unite with a loud explosion. The electric light, or burning magnesium, can be substituted for the sunlight in this experiment. Water at 60° F. absorbs twice its volume of chlorine gas; and if the mixture be exposed to cold, crystals of a hydrate of chlorine will form, which resemble ice excepting in crystalline form, and contain variable quantities of chlorine according to the circumstances of their formation. This hydrate was employed by Faraday in his celebrated experiment of liquefying chlorine gas. Chlorine water is gradually decomposed in the light, oxygen gas being liberated, and hydrochloric acid formed. Schonbein has shown that spongy ruthenium will also liberate oxygen from chlorine water, the same as the sunlight. Chlorine decomposes steam; hence the hydrochloric acid fumes which issue from the crater of Mt. Vesuvius. It will also expel oxygen from many metallic bases at high temperatures.
The bleaching properties of chlorine were early investigated by Berthollet, Mackintosh, and Tennant, and through their recommendation many thousand acres of land were restored to agricultural uses which had previously been devoted to bleach-eries. (See Bleaching Powders.) Chlorine is a most efficient agent in decomposing putrid and noxious vapors and gases, and it is largely employed as a disinfectant. In combination it is employed in medicine as a stimulant and antiseptic, also as a gargle in scarlatina, putrid sore throat, and in smallpox. When inhaled, it instantly produces great irritation in the trachea, which may prove fatal. The vapor of ether and alcohol affords some relief. The compound of chlorine with nitrogen is a thin yellow oil, somewhat resembling nitroglycerine, excessively explosive, especially in contact with grease or oil. - Chlorine unites with oxygen in various proportions to form anhydrides and acids. The acids are hypochlorous, chlorous, chloric, and perchloric. The salts of hypochlorous acid, called hypochlorites, possess bleaching properties. The salts of chloric acid are called chlorates, and are used in medicine and the arts. The most important is the potassium chlorate.
The compound of chlorine with hydrogen, called hydrochloric acid, hydrogen chloride, and muriatic acid, is one of the most important chemical products known in the arts. (See Hydrochloric Acid.)