Iodine, Bro′mides of. Bromine and iodine unite rapidly by mere mixture. By careful distillation a red vapour is obtained, which, on cooling, condenses into red crystals, of a form resembling fern leaves. This is said to be the protobromide (IBr). By adding more bromine, these crystals are converted into a fluid, said to be a pentabromide (IBr5).
Iodine, Chlo′′rides of. When dry chlorine is passed over dry iodine, at common temperatures, heat is evolved, and a yellow solid terchloride (ICl3) results when the iodine is fully saturated, and an orange-red liquid protochloride (ICl) when the iodine is in excess. They both absorb moisture in the air, are volatile, and very soluble in water.
Iodine and Hydrogen. Hydriodic acid, HI. Syn. Iodhydric acid; Acidum Hydriodicum, L. An acid compound of iodine and hydrogen. Prep. 1. (Gaseous).—a. Into a glass tube, closed at one end, introduce a little iodine, then a small quantity of roughly powdered glass moistened with water, next a few small fragments of phosphorus, and upon this some more glass; this order (iodine, glass, phosphorus, glass) is to be repeated until the tube is one half or two thirds filled; a cork and
delivery tube are then to be fitted, a gentle heat applied, and the gas collected by ‘downward displacement’ or over mercury. If the gas be passed into water a solution of hydriodic acid will be obtained.
Obs. Hydriodic acid gas can only be retained a short time over mercury, owing to its action on that metal.
b. Pour a little water over some pentiodide of phosphorus, previously put into a glass retort, apply a gentle heat, and collect the gas as before.
c. Heat together in a retort water, iodide of potassium, iodine, and phosphorus, and collect the gas as in b.
d. Place pure iodide of barium in a retort, and decompose it with sulphuric acid.
2. (Solution of Hydriodic acid.)—a. The gas prepared by either of the above methods passed into cold distilled water.
b. Iodine, in fine powder, is suspended in water, and a stream of sulphuretted hydrogen passed through the mixture as long as sulphur is deposited, or until it becomes colourless. The liquid is then gently heated, to expel the excess of sulphuretted hydrogen, and either decanted or filtered. A cheap and excellent process.