This is prepared by precipitating a solution of corrosive sublimate, by means of another of iodide of potassium. The reaction, which takes place between one equivalent of the bichloride and two eqs. of the iodide, results, through an interchange of principles, in the formation of chloride of potassium which remains in solution, and deutiodide of mercury which is thrown down. The precipitate is to be well washed, dried, and kept in a closely stopped bottle.

Properties

This preparation is usually in the form of a heavy, scarlet powder, inodorous, of a very slight metallic taste, insoluble in water, but soluble in heated alcohol, and in solutions of the chloride of sodium, iodide of potassium, and other soluble iodides, with which it is disposed to combine chemically, forming double iodides. When heated it melts, and on solidifying assumes a yellow colour, which it again changes for red on further cooling, or on being mechanically disturbed. At a higher heat it is vaporized, and condenses in yellow scales, which also become red on cooling. These are sufficiently characteristic properties.

Effects on the System

These are both locally and generally like those of corrosive sublimate, though perhaps somewhat less violent. it probably acts through the agency of the chloride of sodium in the liquids of the body, which enables them to dissolve it. The dose is the sixteenth or twelfth, gradually increased to the sixth or fourth of a grain.

Therapeutic Application

As this iodide is capable of bringing the system under the mercurial influence, it is applicable to the same purposes as most of the preparations of mercury, and especially to the treatment of scrofulous syphilis; but its harshness, and the danger that might arise from an over-dose, have prevented its use to any extent as an internal remedy.

Externally it is employed as a powerful alterative stimulant and es-charotic, in obstinate ulcerous diseases, and has been found by Cazenave especially useful in lupus. Forming it into an ointment with equal parts of olive oil and lard, he applies it in a thin layer over a portion of the diseased surface, which becomes violently inflamed, and, on the subsidence of the inflammation, is left in a state disposed to heal. in the of a grain each, of which from one to three are taken daily, also into an ointment by mixing one part with eighty parts of lard, which is to be applied daily by friction. Considerable inflammation is produced, and serum or pus is discharged, which, on the suspension of the application after two or three days, dries into crusts. These fall after a time, leaving the part less red and hardened. The process is to be repeated till recovery is effected. (B. and F. Medico-chir. Rev., July, 1856, p. 185.) - Note to the second edition.

An Ointment (Unguentum Hydrargyri Iodidi Rubri, Dub.) was directed in the late Dublin Pharmacopoeia to be made by rubbing a drachm of the iodide with seven drachms of simple ointment. This may be applied to indolent and insusceptible scrofulous ulcers, and, much diluted, to other chronic ulcerations of a less obstinate character. For application to the eye, as above mentioned, it should be diluted with at least four times its weight of lard or simple ointment. in about the same strength, it has been used, in India, with great asserted advantage in goitre, in connection with the solar influence; the patient, after a thorough application of the ointment, being directed to sit with the tumour exposed to the direct rays of the sun as long as he can bear them. Blistering is generally induced, after which the ointment is again applied, but on this occasion delicately. No other treatment is required in ordinary cases. {Ed. Med. Journ., III. 525.) Prof. Maclean, of the Royal Victoria Hospital, Netley, states that this local application of the biniodide of mercury is scarcely less useful in the treatment of enlarged spleen than that of goitre. A piece of the ointment of the size of a nutmeg is rubbed over the affected gland, and the patient is then directed to sit before the fire until much smarting is produced, after which about half the quantity is applied to the tender surface. The process is repeated in two or three weeks, and the local treatment is aided by the internal use of quinia and iron, and by a good diet. (N. Y. Med. Journ., June, 1866, p. 232.)