Obs. Iodate of potassium is resolved at a red heat into oxygen gas and iodide of potassium. It has been recommended in bronchocele.—Dose, 1 to 5 gr.
Potassium, Iodide of. KI. Syn. Potassii iodidum (B. P., Ph. L., E., and D.).
1. (Ph. L. 1836.) Take of iron filings, 2 oz.; distilled water, 2 quarts; iodine, 6 oz,; mix them, and heat the solution until it turns green, and then add of carbonate of potassium, 4 oz., dissolved in water, 1 quart; filter, wash the residuum on the filter with water, evaporate the mixed filtered liquors and crystallise.—Product, 1 oz. of iodine yields 1 oz. 45 gr. of iodide.
The formulæ of the Ph. D. and Ph. E. are very similar.
2. Add iodine to a hot solution of pure hydrate of potassium until the alkali is perfectly neutralised, carefully avoiding excess; evaporate the liquid to dryness, and expose the dry mass to a gentle red heat in a platinum or iron crucible; afterwards dissolve out the salt, gently evaporate, and crystallise. An excellent process, yielding a large product, but, if the ignition be not carefully managed, it is apt to contain a little undecomposed iodate. To obviate this, Mr Scanlan proposes the addition of a little powdered charcoal to the mass before ignition—a plan adopted in the Ph. U. S.
3. Iodine is treated with a small proportion of phosphorus in water, and is thus converted into ‘hydriodic acid,’ hydrate of calcium is then added, and the ‘iodide of calcium’ formed is first fused, and then decomposed by sulphate of potassium into ‘sulphate of calcium,’ which is precipitated, and ‘iodide of potassium,’ which
remains in solution, and may be crystallised, as in the other processes. This is a modification of a method devised by Liebig.
4. (Ph. B.) Put solution of potash, 1 gall., into a glass or porcelain vessel, and add iodine 29 oz., or q. s., in small quantities at a time, with constant agitation, until the solution acquires a permanent brown tint. Evaporate the whole to dryness in a porcelain dish, pulverise the residue, and mix this intimately with wood charcoal in fine powder, 3 oz. Throw the mixture, in small quantities at a time, into a red-hot crucible, and when the whole has been brought to a state of fusion, remove the crucible from the fire and pour out its contents. When the fused mass has cooled, dissolve it in 2 pints of boiling distilled water, filter through paper, washing the filter with a little distilled boiling water; unite the liquids, and evaporate till a film forms on the surface. Set aside to cool and crystallise. Drain crystals and dry quickly with a gentle heat; more crystals may be obtained by evaporating the mother liquor, and cooling. The salt should be kept in a stoppered bottle.
Prop. It crystallises in cubes, which in the pure salt are extremely white, though frequently opaque; these are anhydrous; fuse when heated, without decomposition; dissolve in less than an equal weight of water, at 60° Fahr., and very freely in alcohol; and do not deliquesce in moderately dry air unless they contain undecomposed hydrate of potassium. Its solution dissolves the iodine freely, and also, less readily, several of the insoluble metallic iodides and oxides.
Pur. It is entirely soluble in both water and alcohol. Its aqueous solution alters the colour of turmeric either not at all or but very slightly, nor does it affect litmus paper, or effervesce with acids. Nitric acid and starch being added together, it becomes blue. It is not coloured by the addition of tartaric acid with starch. No precipitate occurs on adding either a solution of hydrate of calcium or of chloride of barium. 100 gr., dissolved in water, by the addition of nitrate of silver, yield a precipitate of 141 gr. of iodide of silver.