IODINE, IODOFORM, AND OTHER DERIVATIVES.—Iodine, obtained from the ashes of sea-weeds and from crude Chilean saltpeter, occurs in the form of bluish-black scales. It gives off a char acteristic violet vapor and emits an acrid and unpleasant odor when burned. Io dine was discovered by Courtois in 1S12 in sea-salt. It is not found in its pure state in Nature, being combined with potassium or sodium in marine plants, which absorb it from their surround ings. Iodine melts at 107° C., hut vola tilizes completely at 175° C. It gives off fumes at ordinary temperature. It is but slightly soluble in water (1 part in about 7000), but is very soluble in alcohol and glycerin.
imparts a dark-yellow or brown color to all substances over which it is lightly applied, but wherever starch is present the coloring is blue. This prop erty to color starch blue is so marked that it serves as the basis of various tests that make it possible to detect iodine in about four hundred and fifty thousand times its weight of water. Its detection in urine is greatly facilitated by allowing a por tion of the liquid to evaporate; the addi tion of a few drops of nitric acid serves to insure the liberation of any iodine that may be present in combination with other elements.
In estimating the iodides in the urine, the decomposition of these salts by chlo rine may be employed. Two and one half drachms of urine are taken, and an equal quantity of hydrochloric acid and 2 or 3 drops of chlorine-water added. A brown color appears, which is changed to blue by the addition of starch-water. For quantitative estimation the urine is evaporated and charred and the char burned off. The residue is taken up with water acidulated with nitric acid, and nitrate of silver added to excess. The precipitate consists of the chloride and iodide of silver. It is collected, dried, and weighed, and then subjected to chloridization, as above. The differ ence in weight, due to the transforma tion of the iodide into the chloride, is the basis for calculation of the quantity of iodine in the primary precipitate.
Jolles (Zeit. f. anal. Chemie, B. 30, p. 2SS, '91).
Attention called to a source of failure in recognizing the presence of iodine in an ammoniacal urine, which must he of considerable importance. When one adds strong, fuming nitric acid to the urine containing an iodide the iodine is freed, and is usually recognized by solution with a purplish color in chloroform. If, however, the urine contains ammoniacal compounds this reaction may be quite different. The iodine reacts upon the ammonia salts. and is formed into nitric iodide and hydriodie acid 6I= + 3H1). This substance is very un stable, and in decomposing forms iodic acid, hydriodic acid, and nitrogen (-1NI, + 314,0 = 31,0 + 4N). Thus, one may entirely fail to get the character istic chloroform solution. To such a urine caustic potash should be added to replace the ammonia, in order that this mistake be avoided. Gillet (Annales de la Polyclinique, Oct., '9I).
Attention again called to the use of iodine as a test for Idle. The reagent is a dilute tincture of iodine, of a bright mahogany color. The test is made by allowing the iodine to run into an in clined test-tube containing the suspected fluid, and in the presence of bile forms a grass-green ring at the point of con tact. Rosin (Wiener klin. Woch., No. 11, 'OS).
Preparations and Doses.—Iodine is not employed in solid form. The prepara tions generally utilized are the follow ing:— Tincture of iodine is a 7-per-cent. solu tion in alcohol. It is not used internally because the iodine is precipitated by the gastric juices. It should, therefore, only be employed for topical applications. A decolorized tincture has been made and used, but it contains no iodine, and is worthless.
Compound solution of iodine (Lugol's solution). This is, by far, the best prep aration of iodine for internal use. It contains 5 per cent. of iodine and 10 per cent. of iodide of potassium. Dose, 3 to 15 drops, largely diluted.