Mercuric and Potassium Iodo-cy′anide. Syn. Hydrargyri et potassii iodo-cyanidum, L. Prep. To a concentrated solution of mercuric cyanide add a rather strong solution of potassium iodide, and dry the precipitate by a gentle heat.
Prop., &c. Small, white, pearly, crystalline plates or scales. It is chiefly used as a test of the purity of hydrocyanic acid. When put into this liquid it is instantly turned red if any mineral acid is present.
Mercuric Nitrate. Hg(NO3)2. Syn. Protonitrate of mercury, Pernitrate of mercury. Prep. 1. (Neutral.) This is obtained by solution of mercuric oxide, in excess of nitric acid. The solution, evaporated in a bell-jar over sulphuric acid, yields crystals which are neutral. The same compound is obtained as a crystalline powder when the syrupy liquid is dropped into strong nitric acid.
(Basic.) 1st. 2Hg(NO3)HO.H2O. Prep. a. By saturating hot dilute nitric acid with mercuric oxide. The salt, which is bibasic, crystallises on cooling.
b. By dissolving mercury in excess of nitric acid, with heat, until the solution, when diluted with distilled water, ceases to give a precipitate with common salt. It is now a mixed solution of the neutral and bibasic pernitrates; but by evaporation crystals of the latter salt only are deposited. The acid solution (before evaporation) is used as a caustic in cancerous, syphilitic, and other ulcerations; but it frequently produces intense pain, and occasionally the usual constitutional effects of mercury. It was formerly given in similar cases to those in which the bichloride is now employed.—Dose (of the dry salt), 1⁄20 to 1⁄12 gr. This is the preparation ordinarily referred to under the name ‘pernitrate of mercury.’
2nd. 2Hg(NO3)HO.HgO. c. By saturating strong nitric acid with mercury, by heat, throwing the solution into cold water, and collecting and drying the precipitate. This salt, which is tribasic, is also formed when
the preceding crystallised salts are put into hot water.
Obs. This last preparation is a heavy, yellow powder, but the shade varies according to its basicity, which increases with the temperature of the water employed to effect the precipitation, until, at the boiling temperature, the colour is a dull red. It is extensively employed for the extemporaneous preparation of the ointment of nitrate of mercury, according to the formula on the following label which accompanies each bottle:—“Hydrarg. subnitras.” “Two scruples, mixed with one ounce of simple cerate, make the ung. hydrarg. nit. of the London Pharmacopœia.” We need scarcely add that this statement, so unblushingly uttered, is a dangerous falsehood. An ointment so made possesses neither the quantity of mercury nor of nitric acid employed in the Pharmacopœia preparation, besides wanting many of its most sensible and valuable properties.
Mercuric Oxide. HgO. Syn. Protoxide of mercury, Red oxide of mercury, Oxide of m., Binoxide of m., Deutoxide of m., Peroxide of m.; Hydrargyri oxydum, H. o. rubrum, B. & L. There are several methods by which this substance may be prepared. The following are those which have been ordered at different times in the Pharmacopœias:—
1. By precipitation (Hydrargyri binoxydum—Ph. L. 1836.). Mercuric chloride (corrosive sublimate), 4 oz.; distilled water, 6 pints; dissolve and add of liquor of potass, 28 fl. oz.; drain the precipitate, wash it in distilled water, and dry it by a gentle heat.