HYDRARGYRI SUBCHLORIDUM - CALOMELAS - MERCURIUS DULCIS - SUBCHLORIDE OF MERCURY, OR MERGUROUS CHLORIDE - CALOMEL, Hg2Cl2, = 471.

Preparation

(1) Ten parts of sulphate of mercury are triturated with seven of metallic mercury and a little water, so that a subsulphate is formed - thus

HgSO4 + Hg = Hg2SO4. (2) Chloride of sodium is then added with trituration, the mixture is heated, and the subchloride of mercury sublimes as vapor, while sulphate of sodium is left - thus

Hg2SO4 + 2NaCl = Na2SO4 + Hg2Cl2. A large condensing chamber is required in order to obtain a fine powder, and this is washed with hot water in order to remove any perchloride that may be formed.

Characters And Tests

Calomel usually occurs as a heavy, dull, white powder, which is rendered yellow by trituration or by gentle heat: if sublimed in a small chamber, fibrous crystalline lumps are produced. The sp. gr. is 7.2. It has no taste, and hence its name of mercurius dul-cis. It is not acted upon by hot water, ether, alcohol, or dilute acids, but potash or soda decomposes it with precipitation of the black oxide of mercury. Prussic acid also turns calomel black by causing the separation of metallic mercury. Pure calomel is entirely volatilized by heat, and warm ether shaken with it should leave no residue on evaporation (showing the absence of corrosive sublimate).

HYDRARGYRI PERCHLORIDUM - PERCHLORIDE OF MERCURY - CORROSIVE SUBLIMATE, HgCl2,=271.

Preparation

By subliming dry mercuric sulphate with four-fifths of its weight of dried sodium chloride, 2 or 3 per cent. of oxide of manganese being previously added to the mixture. The reaction is as follows:HgSO4 + 2NaCl = HgCl2 + Na2SO4.

Sulphate of soda being left, and corrosive sublimate condensing in the cooler part of the subliming apparatus. It will be noticed that the manganese has no share in the decomposition; it is introduced in order that it may set free from the excess of sodic chloride some free chlorine to combine with any calomel that may be formed, and convert it into corrosive sublimate: calomel would be formed if the mercuric sulphate contained any mercurous salt, as it is apt to do. "The fumes are extremely acrid and poisonous" (Miller).

Characters And Tests

Corrosive sublimate occurs in white crystalline heavy masses - sp. gr. 5.2 - it is entirely volatilized by heat, is soluble in 16 parts of cold and 3 of boiling water, soluble also in alcohol, and still more so in ether. The strong mineral acids dissolve it without decomposition. Alkaline chlorides render it more soluble in water, and hence ammonium chloride is introduced into the officinal solution of the sublimate, and it forms with it a double salt (sal-alembroth). A simple solution in water readily decomposes, calomel being precipitated, and if exposed to light and to contact with organic substances, metallic mercury separates. Ammonia gives a white precipitate of ammonio-chloride, potassic iodide produces the red iodide, potash a precipitate of the yellow oxide, and nitrate of silver a curdy white silver chloride. Albumen also combines directly with corrosive sublimate, and precipitates its solutions. Liquor Hydrargyri Perchloridi - Solution of Perchloride of Mercury (v. p. 224).

HYDRARGYRUM AMMONIATUM - AMMONIATED MERCURY - WHITE PRECIPITATE, NH1HgCl, = 251.5.

Preparation

By adding solution of corrosive sublimate to ammonia, chloride of ammonium is formed, and an ammonio-chloride of mercury precipitatedHgCl2 + 2NH3 = NH1HgCl + NH1C1.

The ammonium salt is removed by washing, after filtration.

Characters And Tests

This compound occurs as a heavy white powder, or in small cones marked by the linen filters: it has a metallic taste; no odor; is insoluble in cold water, alcohol, and ether; soluble in warm acids; decomposed by caustic potash, evolving ammonia, while yellow oxide of mercury is precipitated. Boiled with chloride of tin it gives a precipitate first gray and then black, from the presence first of subchlor-ide and metallic mercury, and next of the metal wholly; this has been called the magpie test. "Chlorine and bromine both act violently on white precipitate, forming mercuric chloride or bromide, the action in many cases being attended with explosion. With iodine, an explosion almost invariably takes place after a few minutes: it would appear that iodide of nitrogen is formed" ("Miller's Elements of Chemistry," 1878).

HYDRARGYRI IODIDUM V1RIDE - GREEN IODIDE OF MERCURY, Hg2I2, = 654.

Preparation

By triturating together mercury and iodine in proper atomic proportions: some rectified spirit is added in order to dissolve the iodine, and to lessen, by evaporation, the heat evolved in the process.

Characters And Tests

The pure mercurous iodide is a yellow powder, but according to the mode of preparation, or degree of exposure to light, becomes greenish, and olive-colored or even black; it is insoluble in water or ether; entirely volatilized when rapidly heated, but if warmed slowly in a test tube, it yields a yellow sublimate (pure mercurous iodide), metallic mercury being left: the yellow sublimate turns red on friction.

HYDRARGYRI IODIDUM RUBRUM - RED IODIDE OF MERCURY, HgI2, = 454.

Preparation

By mixing together boiling solutions of iodide of potassium and corrosive sublimate: double decomposition ensues, and the red iodide is precipitated.

HgCl2 + 2KI = 2KCl + HgI2.

Characters And Tests

A crystalline red powder, which becomes yellow when gently heated, and again red upon friction or after cooling: this change in color is due to a change in crystalline form, the yellow crystals being rhomboidal, the red, octahedral prisms. The salt is insoluble in water, soluble in ether and solutions of iodide of potassium. The presence of iodine may be verified by starch producing a blue color in a solution which has been digested with soda and acidified with nitric acid.

HYDRARGYRI OXIDUM FLAVUM - YELLOW OXIDE OF MERCURY, HgO, = 216.

Preparation

By adding solution of perchloride of mercury to excess of solution of soda: chloride of sodium and water are formed, and the yellow mercuric oxide precipitates.

HgCl2 + 2NaHO = 2NaCl + HgO + H10.

Characters And Tests

A smooth yellow heavy powder, becoming gray on exposure to light; it is insoluble in water, readily soluble in acid, entirely volatilized by heat, being resolved into oxygen and mercurial vapor. This oxide is an allotropic form of the red oxide; it is smoother, and combines more readily with certain acids; it is better adapted for ointment used on delicate surfaces, as the eyelids, and is preferred for the preparation of oleates.

HYDRARGYRI OXIDUM RUBRUM - RED OXIDE OF MERCURY - RED PRECIPITATE, HgO,=216.

Preparation

By triturating and heating nitrate of mercury with an equivalent of metallic mercury: nitrous oxide gas is given off.

Hg2NO3 + Hg = 2HgO + 2NO2.

Characters And Tests

An orange-red crystalline powder, almost insoluble in water, soluble in acids, the solution giving a yellow precipitate with caustic potash in excess, and a white one with ammonia; it is wholly volatilized by a heat below redness, and was the salt from which Priestley first disengaged oxygen (by means of a lens and sun-light).

LIQUOR HYDRARGYRI NITRATIS ACIDUS - ACID SOLUTION OF NITRATE OF MERCURY, Hg2NO3, = 324.

Preparation

By dissolving mercury in cold, slightly diluted nitric acid, when mercurous nitrate is formed.

3Hg + 4HNO3 = 3HgNO3 + 2H1O + NO. By subsequent boiling, this is changed into the mercuric nitrate. 3HgNO3 + 4HNO3=3(Hg2NO3) + 2H1O + NO.

Free nitric acid is also contained in the solution.

Characters And Tests

A colorless, strongly acid solution, from which excess of caustic potash precipitates the yellow oxide; water also decomposes the solution, precipitating oxynitrates. The presence of nitric acid is shown by the darkening of crystals of ferrous sulphate when introduced.

HYDRARGYRI SULPHURETUM - SULPHURET OF MERCURY - CINNABAR, HgS, = 232 (NOT OFFICINAL).

Preparation - (L. P). - By melting together, with proper precautions, equivalents of mercury and sulphur, triturating the mixture, and then subliming.

Characters And Tests

In dark-scarlet crystalline masses, which, when powdered, become vermilion; volatilizes on heating; on reduction with potash, the metallic mercury separates.

HYDRARGYRI SULPHAS - SULPHATE OF MERCURY, HgSO4, =296.

Preparation

By heating mercury with sulphuric acid, sulphurous acid gas escapes, and mercuric sulphate and water are formed, as represented in this formula:Hg + 2H1SO4 = HgSO4 + SO2 + 2H1O. The mixture is then evaporated to dryness.

Characters

A heavy white crystalline powder, which is decomposed by water into a soluble acid sulphate and a yellow oxysulphate, known as turpeth mineral.

HYDRARGYRI CYANIDUM - CYANIDE OF MERCURY, HgCy2 (NOT OFFICINAL).

Preparation

By dissolving 1 part of ferro-cyanide of potassium in 15 of boiling water, adding 2 parts of mercuric sulphate, heating for ten minutes, filtering, and cooling to crystallization: besides the cyanide, mercury, ferric sulphate, and sulphate of potassium are formed in this process.

Characters And Tests

Rectangular prisms, sometimes transparent, generally opaque and white, taste metallic. Is stable in air, soluble in water, sparingly so in alcohol.

Absorption And Elimination