HYDROCHLORIC ACID (symbol, II01; equivalent, 36.5) is one of the most important compounds in inorganic chemistry. If the two gases which enter into its composition (hydrogen and chlorine) be mixed in equal volumes, they will remain without action upon each other, if kept in the dark; but as soon as they are brought into direct sun light, they unite with a loud explosion, and hydrochloric acid gas is the result. The principal characters of this gas are that it is colorless, intensely acid, irrespirable, and even, when largely diluted, is very irritating to the lungs and eyes, and very injurious to vegetation; that it is heavier than air (its specific gravity being 1.2474, air being taken at 1.000); that it can be condensed into a colorless liquid; that it is very soluble in water, and that it is neither combustible nor a supporter of combustion. When allowed to escape into the air, it produces white fumes, by condensing the atmospheric moisture. If the air be previously dried, no such fumes are apparent.
The solutions of this gas in water form the acid which was first known as spirit of salt, then as muriatic acid, and which is now termed hydrochloric or chlorhydrk acid. A. saturated watery solution of this gas at 40° has a specific gravity of 1.21, and consists of 1 equivalent of the gas dissolved in G equivalents of water. It forms a colorless, fuming liquid, which acts as a caustic. On heating it, the gas is evolved abundantly until the temperature slightly exceeds 212°, when there distills over a diluted solution, having a specific gravity of 1.1, and consisting of 1 equivalent of the gas, and 16 equivalents of water. It is to these solutions of hydrochloric acid that the term hydrochloric acid is far more commonly applied than to the gas itself. They possess the ordinary characters of an energetic acid, and neutralize the strongest bases. The neutralization is, however, not in consequence of the acid combining with the oxide, but is due to the simultaneous decomposition of the acid and of the oxide, water and a metallic chloride being formed. If M represents the metal, the reaction is expressed by the equation MO ± 1101 = 31C1 + HO. All metals which, at a red heat, decompose water, also decompose this acid, and cause an evolution of hydrogen, the reaction being expressed as follows: 31 + HCl = MCI + H.
Hydrochloric acid gas is a common gaseous volcanic product. Free hydrochloric acid, in a very dilute form, is also a constituent of the gastric juice of man and animals, and plays an essential part in the digestive process.
Commercial muriatic acid—to use the name employed by manufacturing chemists— is made by heating, in iron cylinders, common salt (chloride of sodium) and oil of vitriol (hydrated sulphuric acid), and condensing the evolved gas in water contained in a series of stoneware Wolffian bottles (q.v.), the reaction being explained by the equation: Chloride Oil of Vitriol. Hydrochloric Sulphate of Soda.
of Sodium. Acid.
CINa HO,SO, = HCl NaO,SO, This commercial acid may contain various impurities—as, for example, iron (which gives it a bright deep yellow color), the chlorides of sodium and arsenic—the latter being derived from the oil of vitriol—sulphuric and sulphurous acids, chlorine, etc. ; from which ifrean be pprified to a great extent by dilution and redistillation. " If pure," says prof. Miller, "the acid should leave no residue when evaporated; on satur sting it with ammonia, it should give no precipitate of oxide of iron: sulphureted hydrogen should produce no turbidity in it, which would be the case if arsenic, free chlorine, or sulphurous acid were present; and on dilution with three or four times its bulk of water no white cloud of sulphate of baryta should be produced by the addition of chloride of barium." The presence of hydrochloric acid, or of the soluble chlorides in solution, may be detected by the addition of a few drops of a solution of nitrate of silver, which occasions the formation of a white curdy precipitate of chloride of silvbr, which is insoluble in nitric acid, but dissolves in a solution of-ammonia.
Liquid hydrochloric acid (under the name of spirit of salt) was known to the alchemists. Hydrochloric acid gas was discovered by Priestley in 1772; and Davy, in 1810, ascertained that it was composed of chlorine and hydrogen.
In many of their properties, the analogous acids, hvdrobromic, hydrofluoic, and hydriodic acids resemble hydrochloric acid.
a genus of umbelliferous plants, having simple umbels, entire acute petals, and fruit of two flat orbicular carpels, with five more or less distinct threadlike ribs, and no vittx. The species are numerous, generally more or less aquatic, widely distributed. One only is a native of Britain, II. vulgaris, which grows in marshy places, and is called marsh penny wort from the orbicular leaves, and sometimes white rot, sheeps-bane, flowk-wort, etc., from a notion that it is injurious to sheep which eat it, causing foot-rot or fluke-worm—effects rather to be ascribed to the marshy situa tions in which it grows.