Prep. By rubbing together to a fine powder, fifty grains of iodine, and fifty grains of chlorate of potash, then pouring upon it half an ounce of distilled water with five minims of nitric acid, and digesting in a Florence flask with a gentle heat until the colour of the iodine disappears; then boiling for one minute, transferring the contents of the flask to a capsule, and evaporating to perfect dryness at 212°. The residue should be dissolved in ten ounces of distilled water and the solution kept in a stoppered bottle. In this process, by the powerful oxidizing agency of the nitric and chlorate of potash upon the iodine, the iodate of potash is formed.

Use. Iodate of potash is used for ascertaining the freedom of acetic acid and glacial acetic acid from sulphurous acid. When added to acetic acid previously mixed with mucilage of starch, if no sulphurous acid be present, no change is produced; but if sulphurous acid be present, the iodate is decomposed, iodide of potassium is formed, as represented in the following equation: (KO,

Io5 + 6 (HO, So2) = KI + 6 (HO, So3) and the iodine liberated, which gives rise to a blue colour with the starch.