Origin

Muriatic acid was described by Basil Valentine in the fifteenth century. To the older chemists it was known by the name of spirit of sea salt; when better understood, but before its composition had been discovered, it was called muriatic acid; at present, chemists usually denominate it hydrochloric or chlorohydric acid. In the U. S. Pharmacopoeia the name of muriatic acid has been retained as sufficiently expressive, and best adapted for a medical and pharmaceutical title, until chemists shall adopt one upon which all can unite. The term is applied to the liquid acid obtained by acting upon chloride of sodium with sulphuric acid and a little water, and receiving the hydrochloric acid gas given off in distilled water, which condenses it. The U. S. Pharmacopoeia directs that it should have the sp. gr. 1.16.

Properties

Muriatic acid when pure is a colourless liquid, but is often somewhat yellowish as in the shops. It emits a vapour which forms a white cloud in contact with the air. Its smell is strong, pungent, and peculiar; its taste, when diluted, extremely sour. It yields with nitrate of silver a white precipitate, insoluble in nitric acid, but readily dissolved by solution of ammonia. Undiluted, it is corrosive or escharotic.

Effects on the System

So far as regards its action upon the digestive function, it closely resembles sulphuric and nitric acids. Like them, too, when given largely, it produces heat and pain in the stomach, and occasionally disturbs the bowels. In very large quantity, or in a concentrated state, it operates as a corrosive poison, with symptoms similar to those produced by the acids just named; but distinguishable, it is said, by the emission of its peculiar odour from the mouth. At least this effect has been observed, when it has been given in poisonous quantities to the lower animals. The treatment of its poisonous effects is the same as that indicated for the other mineral acids. (See page 358).

Therapeutic Application

Muriatic acid may be used as a tonic to the digestive organs, and indirectly to the system, under the same circumstances as the sulphuric and nitric. From the fact that, mixed with gastric mucus, it will dissolve food, and from the supposition, at one time entertained, that it was an essential agent in the solution of the food in the stomach, the inference seemed reasonable, that it would prove peculiarly useful in facilitating digestion when impaired. It certainly has this effect occasionally; but experience has not proved it to possess any superiority over the other mineral acids. Dr. Paris considers it, when taken in connection with strong infusion of quassia, as one of the best preventives of the reproduction of worms, after they have been expelled from the bowels. The acid has been much used in typhus, malignant scarlatina, and other fevers of a malignant character, partly under an impression of its antiseptic qualities; and much has been said of its efficiency in these affections. It has also been considered specially useful in scrofulous and syphilitic complaints and cutaneous eruptions. But there may be some doubt whether it acts in all these cases by any other than its tonic powers. It has been used, like the other mineral acids, to correct the phosphatic urinary deposits, and probably acts in a similar manner.

Administration

The dose of the undiluted acid is from five to twenty drops, which may be given in half a tumblerful of sweetened water, and repeated more or less frequently according to the nature of the case; every two or three hours, for example, in acute cases, and two or three times a day in chronic. The same caution should be observed as with the other acids, to prevent injury to the teeth. (See page 364).

To the incompalibles, mentioned under nitric acid, may be added, for the muriatic, the soluble salts of silver and lead.

The acid is sometimes used locally. Applied carefully, without dilution, to diphtheritic or pseudomembranous surfaces, it will effectually change the morbid action; but, though strongly recommended for this purpose by Bretonneau, it is probably in no respect superior to the nitrate of silver, while it is less convenient In ulceration of the mouth and fauces, it has been used, largely diluted, as a mouth-wash or gargle. For this purpose, from one to two fiuidrachms may be added to eight fluidounces of water.

There is an officinal Diluted Muriatic Acid (Acidum Muriaticum Dilutum, U. S.), containing, according to the directions of the present U. S. Pharmacopoeia, four troyounces in a pint of the diluted acid, the remainder being distilled water. The dose is from fifteen to sixty drops.