Characters. - Greyish-black, crystalline lumps. It smells like iodine and stains the skin. When boiled with water it is decomposed, iodine passing off and sulphur remaining.

Preparation. - By fusing iodine and sublimed sulphur together.

Officinal Preparation, b.p. Unguentum Sulphuris Iodidi. - Ointment of iodide of sulphur (30 grains to an ounce of prepared lard).

Iodine is rendered much more soluble either in water or spirit by the addition of iodide of potassium, hence this substance is used in the liniment, liquor, tincture, and ointment of the B.P., and in the compound solution and ointment of the U.S.P. It is not contained in the tincture of the U.S.P., which is a simple solution of iodine in alcohol.

Dose. - The only preparations of iodine used for internal administration are the tincture B.P. and U.S.P., the liquor B.P. and compound solution U.S.P., of all of which the dose is 5 to 20 minims.

Physiological Action. - Like chlorine and bromine, iodine is a powerful antiseptic and oxidising agent. When applied to the unbroken skin, iodine stains it of a dark yellowish-brown colour, causes slight warmth, and afterwards a little itching. In stronger solutions it will cause a painful burning sensation, and desquamation of the epidermis. In still stronger solution it may produce vesication. When taken internally, in small doses, it acts as an irritant to the intestinal canal, causing catarrh of the mucous membrane. When absorbed into the blood it somewhat increases the rapidity of the pulse. It has little action upon blood-pressure. Its influence upon the temperature is very slight, but it seems rather to raise it. Iodine appears to have a tendency to cause absorption of enlarged glands and thickenings caused by chronic inflammation. It seems to combine with such metals as lead and mercury, which have become deposited in the tissues in cases of chronic poisoning, forming with these soluble iodides, which are eliminated in the same way as iodine itself. It is eliminated by the urine, nasal mucous membrane, saliva, intestinal mucus and milk, in all of which it may be readily detected. It appears to be eliminated even more readily by the saliva than by the urine (p. 358), and on this account it may remain a considerable time in the body. During the process of elimination it may irritate those parts where it is set free from its compounds, as the nose or skin. Even in small doses it may cause symptoms of iodism. These consist in irritation, either of the nose or intestinal tract; the most prominent are great running at the nose, lacrimation, and sometimes frontal headache. Similar symptoms are produced by exposure to the fumes of iodine for a length of time. The nasal symptoms may be accompanied or replaced by symptoms of gastric irritation, loss of appetite, slight nausea, and tendency to looseness of the bowels. The symptoms of poisoning, such as have occurred from the injection of large quantities of iodine solution into an ovarian cyst, were, first, collapse, followed after a little while by an appearance of fever, with rapid pulse and flushed face, but without any rise of temperature. This condition passed off in several days, but during apparent convalescence the patient suddenly died. Small doses of iodine, by improving the health of patients, may increase the menstrual flow, and may act as aphrodisiacs. Larger doses generally have a very marked anaphrodisiac action, and it has been stated that long-continued use has produced atrophy of the mammae, ovaries, and testes. It has been stated that very large doses affect the nervous system, causing delirium, and twitching or paralysis of the muscles (p. 549).

uses. - Iodine applied to the epidermis acts as a parasiticide, and may be used in cases of tinea to destroy the fungus, either alone or combined with tar in the proportion of two drachms of iodine to one ounce of light oil of wood tar. Its solution, painted on the surface, is useful in removing muscular pains, and in causing absorption of thickening around joints, or of enlarged strumous glands. When painted on the surface it sometimes causes absorption of the enlarged thyroid gland in goitre, and, when outward application is insufficient, success is sometimes obtained by injecting from ten to thirty minims of tincture of iodine into the substance of the tumour by means of a hypodermic syringe, care being taken to avoid injection into a vein. Its solution, painted on the surface, is also useful in causing absorption of fluid from serous cavities, as in pleurisy. Sometimes, after the fluid has been evacuated from a serous sac, such as the pleura, or the tunica vaginalis in hydrocele, or from ovarian cysts, a dilute tincture of iodine is injected into the sac to prevent the fluid from again accumulating.

In removing slight consolidation of the lung, remaining after pneumonia or pleurisy, or in cases of commencing phthisis, the external application of liniment of iodine is very useful. It should be painted on the surface, every second or third day, so as always to keep one part a little tender. By mixing the liniment with the tincture in varying proportions any degree of strength can be obtained. Cases of ozaena are sometimes much benefited by washing out the nose with a solution of common salt to which a few drops of tincture of iodine have been added. The vapour of iodine is employed in chronic bronchitis and phthisis.

On account of its irritating action on the intestinal mucous membrane, iodine is rarely given internally, its place being supplied by iodide of potassium, but some consider that iodine is sometimes more effectual, and it has been given in scrofula, skin diseases, and glanders. The liquor iodi B.P., or compound solution of iodine U.S.P., is useful in arresting vomiting when administered internally in doses of 3 to 5 minims.