Iodine. Officinal. Iodinum, Dub. Iodine. Syn. lode (F.), Iod (G.), Iodina (I.).

This peculiar substance exists, in a state of nature, in a great number of marine plants; namely, in Fucus vesicidosus, F. serratus, F. nodosus; in Porphyra umbilicalis, Padina pavonia, Ulva linza, Laminaria saccharina and digitata, Chorda filum; Gelidium cartilagineum; Kalysaris polypidiculis; Phyllophera rubens; Rhodominia palmata, and many of the marine Confervae; in some ores; in sea water in combination with sodium; in many mineral waters1; and in the rock salt of the Tyrol: in sponges, and in the envelopes of the eggs of the Cuttle fish. It was discovered in 1812 by M. Courtois, a manufacturer of saltpetre in Paris, and soon occupied the attention of many chymists, and its real nature was determined by Gay Lussac and Sir H. Davy. Dr. Wollaston pointed out the following method of procuring it:-

1 This substance, which was first noticed and its properties investigated by Rose, was named by Dr. Thomson, System of Chymistry, 4th edit. iv. 697.

2 Newman's Chym. by Lewis, 2d edit. ii. 216.

3 Mat, Med. ii. 459.

Digest kelp2 in water, as long as any soluble matter is taken up; then evaporate the solution, to separate by repeated crystallizations all the salts of soda which it contains. To the mother liquor add cautiously sulphuric acid in excess; then boil for some time, and leave the whole at rest. Decant off the clear fluid, introduce it into a glass retort, and add as much of the black oxide of manganese as there has been sulphuric acid employed. On distilling this mixture, the iodine comes over in beautiful violet-coloured vapours3, which condense in the receiver in the form of brilliant blackish, or rather bluish grey scales. The iodine is afterwards purified by mixing it in a retort with a little water and 5/100 parts of potassa; then distilling in a sand bath, condensing the vapours in a very cool, large receiver, and drying the iodine by pressing it between folds of bibulous paper. It ought to be kept in glass-stoppered bottles. The theory of the process is simple. The peroxide of manganese decomposes the hydriodic acid of the hydriodate contained in the mother liquor, forming water, and setting the iodine free, which distils over; whilst the sulphuric acid, which was necessary for decomposing the carbonates, etc, forms sulphates of the salts and the oxide of manganese, and is left in the still.

dualities.-Iodine, as has already been stated, is procured in the form of scales of a metallic lustre, a bluish grey colour, and having an acrid taste and the odour of chlorine. It may also be obtained in crystals, the primitive form of which is a rhombic octahedron. Its sp. gr. is 4.948. It tinges the skin yellow. It melts at 224 1/2° Fahr., and at 847° volatilizes; and when moisture is present this occurs even at low temperatures; the vapour having a rich violet colour and a sp. gr. of 8.716. It is a non-conductor of electricity. It is soluble in 7000 of water, colouring the fluid orange-yellow, is more soluble in alcohol, and still more in sulphuric ether. It unites with many simple bodies, forming compounds that are named iodides. With oxygen it forms iodic acid, with hydrogen hydriodic acid. Dissolved in alcohol it forms a tincture which is employed in medicine, and as a test of the presence of starch, with which it forms Iodide of Amidine, which has a beautiful blue colour. Starch is so delicate a test for iodine, that, according to M. Gaultier de Claubry, it detects it in solutions in which the proportion of the iodine does not exceed 1/450000 of the liquid.1 The atomic weight of iodine is 126.3.

1 Those of Bonnington; Robin's well at Leamington Priors; the old well at Cheltenham; the sulphureous waters of Nuovo d'Asti.

2 French kelp affords less iodine than British kelp : but the Cape of Good Hope kelp still more than the British.

3 Whence its name, from violet-coloured.

Iodinum Iodine 201

Iodine is occasionally adulterated with oxide of manganese and charcoal. To detect this, M. Robiquet directs the mix-ture to be submitted to sublimation; and the residue weighed: it may also be detected by dissolving the suspected iodine in alcohol, and ascertaining the weight of the residue. The iodine of commerce contains generally about 12 parts in 100 of water, which should be separated before the iodine is used for making the tincture. The adulteration with water is detected by pressing the specimen between bibulous paper.

Medical properties and uses.-Iodine operates as a stimulant, acting topically, and also entering the system, and exciting powerfully the capillaries. It has been successfully employed in bronchocele, swelled testicle, scrofula, and other glandular swellings; and has succeeded in reducing enlargements of the liver and spleen when mercury has failed. It has also been administered in paralysis, with variable success; and Dr. Baron, of Gloucester, lory, Lugot, and others, have used it with benefit in ascites. Like foxglove, it does not act while the abdomen is tense, and the absorbents are compressed by the fluids; but after tapping, and. reducing excitement by bleeding, it completely removes the serum. The health is afterwards restored by tonics. On these grounds, I am at present trying it in ovarian dropsy, after tapping: and in two cases it has so far succeeded, that the tumours have not again enlarged. Its influence as an emmenagogue depends on the uterus sharing the excitement it induces. Cases are also recorded in which iodine has cured chorea, after arsenic and carbonate of iron had failed.2

With regard to the modus operandi of iodine, it is evident that it enters the circulation, and affects the whole capillary system, as during its operation in diminishing diseased glands the healthy glands are also affected. I have detected it, by gaseous chlorine, in the urine of patients, where the dose of the tincture has been carried to the extent of fifty drops twice a day; and its presence may be recognised in all the secretions. Endeavouring to clear this point by experiments on dogs, although the iodine was detected in the urine, yet I could not perceive the least trace of it in the chyle.

1 Heat destroys this test; and the presence of the alkalies renders it nugatory. I discovered that the iodine in the iodides, and hydriodates, is instantly set free by pouring over them chlorine gas; and then starch displays its presence. This is a test for it in all mixed fluids.

2 Medical Gazette, vol. i. p. 55.

The use of iodine is sometimes productive of bad effects. When it has been taken daily for a long time, it is apt to excite inflammatory gastric dyspepsia; salivation has occurred during its use. It also may cause reduction of strength, great disturbance of the nervous system, often resembling paralysis agitans, profuse perspirations, pains of stomach and bowels, nausea, purging, vertigo, and headaches; absorption of the mammae, wasting of the testicles, and general emaciation. When these symptoms occur, its use should be either intermitted or relinquished. In large doses it operates as an irritant poison.

Iodine is equally useful, whether exhibited internally or applied externally. As an internal medicine, it is most commonly given in the form of tincture; as an external application the tincture is also useful; or the iodine may be formed into an ointment. It has also lately been employed in the form of vapour, inhaled into the lungs, in tubercular phthisis. It augments the secretion of the bronchial mucus.

Officinal preparations.- Tinctura Iodinii composita, L. Tine-tura Iodinii, D. Unguentum Iodinii L. D. Potassae Iodidum, L. Plumbi Iodidum, L. Hydrargyri Biniodidum, L. Ferri lodidum, L. Potassae Hydriodas, D.