HYDROCHLORIC Acm ; H Cl.= 37. This acid is sometimes called " muriatic acid," and " chlorhydric acid." It is formed by combining equal volumes of hydrogen and chlorine, which unite with. out diminution of volume, the result being a strongly acid gas. The simplest mode of effecting this combination is to expose the mixed gases to light. In diffused daylight they combine gradually, but in strong sunshine at once, and with explosion. If a mixture of equal volumes of hydrogen and chlorine be collected over water in a tall graduated glass jar, and exposed to diffused light, the gase.s gradually combine and form hydrochloric acid ; this is absorbed by the water, which has a strong affinity for it, as fast as it is formed, and the water therefore rises in the tube. It is found by this experiment that the quantity of acid produced is proportional to the time of exposure to light.
Hydrochloric acid is readily obtained by adding cliluted sulphuric acid to common salt in a retort, and applying heat to the mixture. The chlorine of the salt combines with the hydrogen of the water to form hydrochloric acid, the sodium is oxidized, and sulphate of soda left in the retort.
Dry hydrochloric acid gas is colourless, and fumes in the air from its absorption of moisture. It is intensely sour, and combines readily with water. The S. G. of the strongest liquid acid is 1.210, and water takes up 600 times its bulk of the gas. It boils at 112°, and freezes at — 60°.
The impurities in commercial liquid hydrochloric acid, and which give it a yellowish colour, are principally organic matter (from bits of cork, lute, lire.), a trace of bromine, chloride of iron, sulphuric acid, and sometimes nitric and sulphurous acids, and also a trace of arsenic. By adding chloride of barium, and redistilling the acid, the principal impurities are removed. ' Hydrochloric acid acts on some of the metals, and produces corresponding chlorides. It precipitates chloride of silver from the soluble salts of the oxide.