MURIATIC acid, in chemistry, may be procured in various ways: if a retort with a curved tube be halffilled with well dried common salt, and some strong sulphuric acid be poured upon it, a copious efferves cence takes place, and the elastic fluid extricated appears in the form of a white vapour as soon as it comes in contact with the atmosphere. When all the common air has been driven out of the retort, the subsequent portions of gas may be col lected in the usual manner in glass jars, filled with mercury, and inverted in a bath of the same fluid. This is muriatic acid gas : it is transparent, colourless, and possessed of the same mechanical pro perties as common air. It is almost twice as heavy as common air : 100 cubic inches of it weighs nearly 60 grains. Its smell' is pungent, and its taste highly acid. it is instantaneously fatal to animal life, and is incapable of supporting combus tion : but if a burning taper be plunged into it, the flame, just before it goes out, may be observed to assume a green colour. 11 a little water be let into a jar filled with this gas, the whole gas disap pears, and the liquid, which consists of a solution of muriatic gas in water, is usually denominated simply muriatic acid. Being obtained from salt, it was original ly called "spirit of salt," then " marine acid," and now it is almost universally de nominated "muriatic acid." A cubical inch of water, at the temperature of absorbs 515 inches of muriatic acid gas, which are equivalent to 308 grains : hence water thus impregnated contains more than half its weight of muriatic acid, in the same state of purity as when gaseous. During the absorption of the gas, the wa ter becomes hot. Ice also absorbs this gas, and is at the same time liquified. The quantity of this gas absorbed by wa ter diminishes as the heat of the water increases, and at a boiling heat water will not absorb any of it : of course the gas is easily expelled from the liquid acid by heat, and may readily be procured by heating the common muriatic acid of commerce. By this process Dr. Priestley
i first obtained it. The muriatic acid of the shops is always yellow, owing to a small quantity of iron which it holds in solution.
Muriatic acid is capable of combining with oxygen, and forms with it com pounds, which have a considerable analo gy to the compounds of azote with the same principle. When this acid is pour ed upon black oxide of manganese, a gas comes over, that is sometimes called " de phlogisticated muriatic acid," but more generally "oxy-muriatic acid." It is green, has a very bad odour, and is readily absorbed by water. The consti tuent parts of oxy-muriatic acid are, Muriatic acid . . 89 Oxygen • 11 100 When a current of oxy-muriatic acid is passed through water holding potash in solution, a number of flat shining crystals are deposited : these are denominated hyper-oxy-muriate of potash. They con tain Muriatic acid . . 34 Oxygen 66 100 It does not appear that either hydrogen or carbon combines with muriatic acid, but charcoal absorbs it abundantly. Phos phorus absorbs a little, and sulphur im bibes it slowly. When mixed with nitric acid, it forms what was formerly denomi nated "aqua regia," but is now called "ni tro-muriatic acid." Muriatic acid in a state of gas neutralizes putrid miasmata, and destroys their bad effects. By this the most contagious diseases are prevented from spreading : two parts of sulphuric acid, and six of common salt, heated over a spirit lamp, or in a hot sand bath, will give out the as very plentifully. The use of muriatic acid in the laboratory is very considerable ; but in medicine and the arts it is employed only in the form of a muriate, or combined with some safi fiable base. Nothing, says Mr. Aikin, takes off the crust of oxide of iron, which is sometimes found adhering to glass vessels, so safely and quickly, as a little warm dilute muriatic acid.