Hydrargyri Bichloridum. Lond. Bichloride of Mercury

1 System of Materia Medicn, etc. ii. 319.

"Take of mercury, two pounds; sulphuric acid, three pounds (by weight); chloride of sodium, one pound and a half. Boil the mercury with the sulphuric acid in a proper vessel, until the bipersulphate of mercury become dry: rub this, when it is cold, with the chloride of sodium in an earthenware mortar; then gradually raise the heat, and sublime."

Murias Hydrargyri corrosivus, Edin, Corrosive Muriate of Mercury.

"Take of purified mercury, two pounds; sulphuric acid, two pounds and a half; dried muriate of soda, four pounds. Boil the mercury with the sulphuric acid in a glass vessel placed in a sand bath, until the matter become dry. Mix this, when it is cold, in a glass vessel, with the muriate of soda; then sublime in a glass cucurbit with a gradually raised heat. Separate the sublimed matter from the scoriae."

Hydrargyri Murias corrosivum, Dub. Corrosive Muriate of Mercury.

"Take of persulphate of mercury, five parts; dried muriate of soda, two parts; rub the salts together to a fine powder in an earthenware mortar: then sublime the corrosive sublimate in a proper vessel, with a gradually-raised heat, into a receiver."

Syn. Muriate de Mercure corrosif (F.), Azzendes alssaures Quecksilber (G), Mercurio sublimato corrosivo (I.).

Sulphuric acid does not act upon mercury at a low temperature : but when three parts of this acid are boiled upon two of mercury the metal decomposes the acid and is oxidised, sulphurous gas being emitted with effervescence; and there remains a dry mass of a fine white colour, which is a bipersulphate of the oxide of mercury. By triturating this salt with dried chloride of sodium, and exposing the mixture to heat, a double decomposition is effected. According to the old doctrines, the muriatic acid leaves the soda, and combines with the oxide of mercury of the bipersulphate, while the sulphuric acid unites with the soda, thus forming muriate of mercury and sulphate of soda, the former of which, being easily volatilised, is separated from the latter by sublimation. But, according to the present generally received doctrines, the chlorine of the common salt leaves the sodium, and uniting with the mercury of the bipersulphate, forms a bichloride of mercury, which sublimes; while the oxygen of the oxide of mercury combining with the sodium converts it into soda, which, uniting with the sulphuric acid and forming sulphate of soda, remains in the bottom of the cucurbit.

This process was first proposed by Kunkel, but no salt has been prepared by a greater variety of methods; and as it is now generally manufactured on the large scale, the proportions of the ingredients ordered by the colleges are perhaps but seldom adopted. Of the three formulae of the British colleges, however, that of the London College is to be preferred, as by employing the larger proportion of sulphuric acid, and the smaller of chloride of sodium, a more complete decomposition of the chloride of sodium is effected; and, consequently, a greater quantity of chlorine being evolved, a larger proportion of the mercury must necessarily be converted into the bichloride. Sixteen ounces of mercury should yield about xx. of corrosive sublimate. The most simple process, and perhaps the best, is the direct solution of the red oxide of mercury in hydrochloric acid, by which the salt is obtained by spontaneous crystallisation l; but it is too expensive for general purposes.

Qualities. - Bichloride, corrosive muriate, of mercury 2, is obtained by the above process in the form of a white, shining, semitransparent, easily-pulverised mass, made up of small, acicular crystals. When the process is very carefully and slowly conducted, the crystals when separately obtained, are regular tetrahedrons, compressed and pointed. On exposure to the air the mass effloresces on the surface. Its specific gravity is 5.206. It is inodorous, and has a very acrid, disagreeable, metallic taste, and gives an alkaline reaction; water at 60° dissolves one twentieth of its weight, at 212° one third; alcohol at 60° four parts. It is soluble also in the sulphuric, nitric, and hydrochloric acids, and may be again obtained unaltered by evaporating the solutions. The fixed alkalies and alkaline earths decompose it, precipitating it from its solution of an orange-yellow colour, which becomes brick-red. It is also partially decomposed by exposure to light, and by some metals; and changed into calomel.3 The carbonates of the fixed alkalies precipitate it of a fixed yellow hue, and ammonia forms with it a white, triple, insoluble, com-pound, the ammonio-chloride of mercury.

When triturated with olive oil, the oil is whitened; and when boiled with it, a small portion of calomel is thrown down; and the same is the case when it is boiled with sugar. The volatile oils reduce it. It is also decomposed by solutions of tartrate of potassa and antimony, nitrate of silver and acetate of lead; and forms precipitates in infusions and decoctions of the following vegetable substances : - camomile flowers, horse-radish root,

1 Annales de Chimie, xxviii. 12.

2 The old names were Hydrargyrus Muriatus, Mercurius sublimatus corrosivus, Hydrargyri oxymurias, P. L. 1824.

3 Mr. Chenevix found, "that if a bit of copper be put into a solution of corrosive sublimate, a white powder shortly falls to the bottom; and that powder is calomel. When washed, it does not contain an atom of copper, nor of corrosive sublimate." columbaroot, catechu,cinchona bark,rhubarbroot, senna leaves, simaruba bark, oak bark, tea; consequently it is incompatible in extemporaneous formulae with these substances. The components of this salt are 25.46 parts of chlorine, and 74.54 of mercury in 100 parts; taking the analysis of Zaboada, and correcting it so as to make it correspond with the real composition of the bichloride.l According to Mr. Phillips, the proportions are of chlorine 26.27, of mercury 73.73 parts in 100; or of 2 eq. chlorine (35.42 x 2) =70.84, and 1 of mercury = 202; making the equivalent 272/.84 (Hg Cl 2.).

Medical properties and uses.- This salt has been long known to chymists.2 It is a powerful stimulant and alterative; and in large doses is one of the most violent of the metallic poisons. As an antisyphilitic it was early much extolled, and is the active ingredient of many a celebrated empirical nostrum; but modern practice has fixed its real merits much lower than they were formerly placed. When taken in over doses, either by mistake, or designedly as a poison, the best antidote is white of egg diluted with water, and given in large, frequently repeated doses. The albumen decomposes the bichloride, reducing it to the state of the chloride, while the compound which it forms with it exerts no deleterious effect on the stomach.3 M. Taddei has found that gluten and rye-meal are equally serviceable as antidotes to this poison. He ascertained that gr. j. of the bichloride is neutralised by 13 grains of dried gluten, and by 500 to 600 grains of rye-meal.3 The presence of bichloride of mercury in any solution suspected to contain it may be detected by putting into the fluid a sovereign, with a piece of clean polished copper wire wound around it: if the poison be present, the gold will be covered with a white coating, which acquires a metallic lustre when rubbed.

Another very ingenious galvanic mode of detecting it is a modification of one proposed by Mr. Sylvester. He recommended to bend a piece of iron wire, three inches long, into this shape and tie the two ends to a common gold wedding ring: on a plate of glass, placed horizontally, drop some sulphuric acid, diluted with six parts by weight of water, till it spread the size of a halfpenny; and then, at a little distance, some of the solution supposed to contain the sublimate, till the two edges of the liquids join, and place the wire and the ring in such a manner that the wire may touch the acid and the ring the solution. If any sublimate be present, the ring will in a few minutes be coated with mercury, where it touches the solution. The modified test is simply to drop a little of the suspected solution on a gold watch held in one hand, and to touch it with a key or the point of a penknife, held in the other; a galvanic circle is thus formed; the solution is decomposed, and forms an amalgam of mercury and gold on the spot if bichloride of mercury be present.

1 Thomson's Chemistry, 5th edit. vol. i. p. 465.

2 The preparation is said to have been long known to the Chinese, and it is mentioned by Rhazis and Avicenna. Bergman, iv. 281. 3 Giornale di Fisica et Isis, 4. 1. 1823, p. 419.

Bichloride of mercury sometimes succeeds in curing the primary symptoms of syphilis; but it as often fails : it checks the progress of the secondary symptoms, relieving venereal pains, and healing ulcers of the throat; "yet even in these cases," says Mr. Pearson, "it never confers permanent benefit; for new symptoms will appear during the use of it; and on many occasions it will fail of affording the least advantage to the patient from first to last."l I have found it most useful when dissolved in nitric acid. It is given with more advantage in some other affections, as old ulcers, chronic rheumatism, and some cutaneous diseases, particularly lepra; in which Willan justly affirms, that it is the only useful preparation of mercury, "its operation being promoted by giving at the same time an antimonial2;" and the decoction of dulcamara. Its sensible operation is by urine; but sometimes it occasions the most violent nausea, griping and purging; in which cases it should be combined with opium: and it is always necessary to take, during its use, some mucilaginous fluid, to moderate the irritation it is apt to induce. It is also used as an external application; in which case the best vehicle is the bitter almond emulsion: and it has the property of preventing this emulsion from fermenting.

The dose is from gr. one eighth to gr. one fourth, twice a day, made into a pill with crumb of bread or extract of poppies. The dose is best divided by adding an equal weight of hydrochlorate of ammonia.

Officinal preparations.-Liquor Hydrargyri Bichloridi L. Hy-drargyri Chloridum, L. E. D. Hydrargyri Ammonio-chloridum, L. Hydrargyri Binoxydum, L. Hydrargyri Submurias mitis, E. Calomelas Sublimatum, D.