Submurias Hydrargyri PraeCipitatus. Edin. Precipitated Submuriate of Mercury

"Take of diluted nitrous acid, purified mercury, of each eight ounces; muriate of soda, four ounces and a half; boiling water, eight pounds. Mix the mercury with the diluted nitrous acid, and towards the termination of the effervescence digest with a gentle heat, frequently shaking the vessel. It is requisite, however, that more mercury be mixed with the acid than it can dissolve, so that a completely saturated solution be obtained.

"Dissolve at the same time the muriate of soda in the boiling water; then to this add the other solution while it is yet warm, and mix them very quickly together. After the precipitate has subsided, pour off the saline fluid, and wash the submuriate of mercury by frequent affusions of warm water, which are to be poured off each time after the precipitate subsides, until the water comes off tasteless."

Calomelas praecipitatum, Dub. Precipitated Submuriate of Mercury

"Take of purified mercury, seventeen parts; diluted nitrous acid, fifteen parts. Pour the acid upon the mercury in a glass vessel, and when the effervescence has ceased, digest with a gentle heat for six hours, with frequent agitation. Then raise the heat, that the solution may boil a little, which is to be poured off from the residual mercury, and quickly mixed with forty parts of boiling water, in which seven parts of muriate of soda have been previously dissolved: wash the powder that subsides with warm distilled water, as long as the fluid poured off from it yields a precipitate on the addition of a few drops of the solution of (sub) carbonate of potassa; lastly, let it be dried."

1 Doses of calomel were formerly given which appear almost incredible to the modern physician. Thus Michaelis Alberti informs us, that Helwichiusgave Э v. for a dose to two patients, and to a third 72 grains, which affected the mouth for a fortnight. Neuterus gave at first gr. xv.; second dose, Эj.; third, 3ss.; fourth, 3j, which he continued till ptyalism was excited. Halleri Dissert, vol. vii.

These processes are framed on the process originally suggested by Scheele, and the error into which he was led by reasoning from a false analogy has not been corrected by the colleges; the product of the above process being a mild chloride of mercury, mixed with subnitrate of mercury, which modifies its powers; a smaller proportion also of chloride being obtained than should follow from the quantity of mercury employed. The cause of this effect is, that by dissolving mercury in nitric acid, with the assistance of heat, the metal contained in the acid solution is oxidised to a maximum, and when water is added to it, a subnitrate is precipitated, while a supernitrate remains in solution. Hence, on the addition of the watery solution of chloride of sodium, the water occasions the subnitrate to be precipitated before the decomposition which takes place is effected; at the same time part of the oxide combines with the chlorine of the chloride of sodium, and forms a portion of chloride, which is held in solution with the newly-formed nitrate of soda, while the bichloride is precipitated in combination with insoluble subnitrate of mercury.

To obtain, therefore, the greatest proportion of pure chloride of mercury by precipitation, the nitrate must be prepared slowly and without the aid of heat, which should not be employed in any part of the process. Dr. Murray ascertained, that "the quantity of mild muriate obtained from a solution ofSubmurias Hydrargyri PraeCipitatus Edin Precipitat 547 j. of mercury in diluted nitric acid in the cold, is a little more thanSubmurias Hydrargyri PraeCipitatus Edin Precipitat 548 j.; whereas, from the same quantity dissolved with the application of heat, the precipitate did not exceed

Submurias Hydrargyri PraeCipitatus Edin Precipitat 549 ss., and the liquor held much more corrosive muriate in solution than the other."1

Qualities. - Precipitated chloride of mercury, when properly prepared, is inodorous and insipid. It is whiter, smoother, and lighter than the sublimed preparation, but otherwise agrees with it, both in its chymical qualities and medicinal effects. As prepared, however, according to the directions of the pharmacopoeias, subnitrate of mercury, which it contains, may have some effect in altering its powers in a small degree.

Medical properties and uses.-It is said to be more liable to run off by the bowels than common calomel; but as its properties are essentially the same, it may be regarded as a superfluous preparation.