"Take of dried chloride of sodium, two pounds; sulphuric acid (by weight), twenty ounces; distilled water, twenty-four ounces. First mix the acid with twelve ounces of .the water, in a glass retort; and when the mixture is cold, add to it the chloride of sodium. Pour the remainder of the water into the receiver; and having fitted it to the retort placed in a sand bath, distil over the acid into this water, with a heat gradually raised."

Edinburgh.

"Take of muriate of soda, which had been previously exposed to a red heat, sulphuric acid, water, of each two pounds. Pour the acid, mixed with eight ounces of the water, and cooled, upon the muriate of soda, in a glass retort; to which adapt a receiver, containing the remainder of the water, and distil from a sand bath with a moderate fire. In a short time the vessels may be luted together, and the distillation continued to dryness.

"The specific gravity of this acid is, to that of distilled water, as 1.170 to 1.000."

Dublin.

"Take of muriate of soda dried, one hundred parts; sulphuric acid of the market, eighty-seven parts; water, one hundred and twenty-four parts. Dilute the acid with half of the water, and after it is cold add it gradually to the muriate of soda put into a glass retort. Put the remainder of the water in the receiver, that it may absorb the elastic gas as it comes over: then distil the liquor until the residuum become dry.

"The specific gravity of this acid is, to that of distilled water, as 1.160 to 1.000."

Syn. Acide Muriatique (F.), Kochsalzaure (G.), Zoutzuur (Dutch), Acido Muriatico (I.), Ooppoo travagum (Tam.).

The principal difference in these formulae is in the quantity of sulphuric acid ordered for decomposing the chloride. The sulphuric acid is properly ordered to be diluted, to moderate the strong action, and to prevent the too rapid disengagement of the hydrochloric acid gas, which would both endanger the bursting of the apparatus, and render the process otherwise very unmanageable. The directions of the London and Edinburgh Colleges, to put part of the water into the receiver, is preferable to mixing the whole with the acid, and pouring it on the chloride, as it facilitates very much the condensation. In the manufacturing laboratories, although the process is in principle the same as the above, yet the retort is generally of earthenware or of iron, which communicates the yellow colour that characterises the common hydrochloric acid, and which depends on a small portion of iron being raised and brought over with the acid. Even when iron vessels are not employed, the acid often assumes a yellowish colour, which depends either on a small portion of iron in the salt, or on the presence of some chlorine.

The acid is rendered pure by redistillation.

1 Spiritus Salis, P. L. 1720. Spiritus Salis Marini Glauberi, P. L .1745.

These processes are easily explained. Common salt is a compound of 35.42 parts of chlorine and 23.3 of sodium, and consequently contains neither hydrochloric acid nor soda; but, when the sulphuric acid is added to the salt, 1 equivalent of water is decomposed, its oxygen unites to the sodium, and forms soda, which combining with the sulphuric acid produces a sulphate of soda, while its hydrogen combines with the chlorine, and forms anhydrous hydrochloric acid, a gaseous fluid consisting of equal volumes of hydrogen and of chlorine, or 1 equivalent of hydrogen = 1, + 1 of chlorine = 35.42 parts, which dissolving in the water contained in the receiver constitutes the liquid acid. The residue of the process is sulphate of soda with an excess of acid, or a bisulphate; to separate which, without breaking the retort, boiling water may be poured into the retort, after its contents have cooled down to 212°.

Qualities. - Liquid hydrochloric acid, thus obtained, is a colourless or a very pale straw-coloured fluid : it has a strong pungent odour, and an intensely sour taste; it reddens strongly the vegetable blues, emits white suffocating fumes when exposed to the air, and erodes animal and vegetable substances. It is wholly vaporized by heat. It unites with the alkalies, forming hydrochlorates; but when it acts upon metals or metallic oxides chlorides are formed : in the first instance, the hydrogen of the acid is given off in a gaseous form, and the chlorine unites with the metal; in the second, the hydrogen unites with the oxygen of the oxide, and forms water. The acid obtained by the process of the London College of the sp. gr. 1.160, consists of nearly 32.4 of real acid gas, and 67.6 of water: 100 grains of it should saturate 132 grains of crystallized carbonate of soda. The following part of a table, constructed by Mr. E. Davy, shows the quantity of real hydrochloric acid gas contained in 100 parts of fluid acid of different densities, at the temperature of 60°: -

The fluid hydrochloric acid found in the shops often contains sulphuric acid, sometimes nitric, with small portions of oxide of iron; the first is detected by diluting the acid with 5 or 6 parts of distilled water, and adding a few drops of chloride of barium 1, which is precipitated white if sulphuric acid be present; nitric acid is detected by the property of dissolving gold leaf; iron is discovered by ferrocyanate of potassa producing Prussian blue. If much chlorine be present it will decolour solution of indigo.

Medical properties and uses. - This acid is tonic and antiseptic. It has been efficaciously used in typhus fevers, and in some cutaneous eruptions. It is a common and useful adjunct to gargles, in the proportion of from f 3ss. to f 3ij. in f vj. of any fluid, in ulcerated sore throats, and scarlatina maligna; and, in a very highly diluted state, viz. viij. in f iv. of water, it has been recommended as an injection in gonorrhoea.

This acid has even been regarded as an antidote in general syphilitic affections; but the observations of Mr. Pearson have showed this opinion to be erroneous; yet, by its salutary effects on the stomach and general health, "it is a medicine capable of ameliorating the appearance of venereal ulcers, and of restraining for a time the progress of the disease," where it is desirable "to gain a little time, previously to the entering on a mercurial course."2 The dose is from x. to xx. in a sufficient quantity of water, or in any bland fluid. It is incompatible in prescriptions with alkalies and their carbonates, most of the earths, and the oxides, sulphuret of potassium, and tartrate of potassa, potassio-tartrate of antimony and of iron, nitrate of silver, and acetate of lead. In typhus, and fevers of a typhoid type, I have generally given it in the infusion of cinchona or cusparia bark. Dr. Paris states that he has found it a preventive of the generation of worms, when given after copious evacuations of the bowels.1 Largely diluted in any mucilaginous fluid, and sweetened, it is a useful remedy in calculous cases depending on an excess of the phosphates.

1 Strong hydrochloric acid precipitates chloride of barium when no sulphuric acid is present; but this does not happen when the acid is much diluted. 2 Pearson on Remedies for Lues Venerea, 194.

When hydrochloric acid is taken as a poison, it may be detected by its sensible qualities : but if mixed with wine or other fluids, let a portion of it be distilled from a small retort over a candle, into a phial containing a solution of nitrate of silver: the precipitation of chloride of silver, which is soluble in ammonia, but not in nitric acid, will take place if the poison contain hydrochloric acid. The best antidotes, if exhibited in time, are soap and calcined magnesia, suspended in water.

A very important property of this acid, in the state of gas, is the power it possesses of neutralizing putrid miasmata, discovered by Morveau in 1773. It is therefore used as an agent for destroying infection in sick rooms and hospitals, disengaged by pouring sulphuric acid on common salt.

Officinal preparations.-Acidum Benzoicum, D. Aciclum Hydro-chloricum Dilutum, L. Acidum Nitro-muriaticum. D. Acidum Hydrocyanicum, L. D. Murias Barytae, E. Solutio Muriatis Calcis, E. D. Tinctura Ferri Sesquichloridi, L. Tinctura Ferri Muriatis, E. D. Solutio Muriatis Calcis, E. Antimonii Oxydum nitro-muriaticum, D. Hydro-sulphuretum Ammoniae, E. Antimonii Potassio-tartras, L. Ferri Ammonio-chloridum, L.

Acidum Hydrochloricum Dilutum. Lond. Acidum Muriaticum dilutum, Dub. Diluted Hydrochloric Acid.

"Take of hydrochloric acid, four fluid ounces, distilled water, twelve fluid ounces. Mix them."

This formula is intended to render the dose of the acid more easily apportioned : one fluid drachm contains about 32 grains of real acid. The dose is xx. to 1 x.