HYDRIO′DIC ACID

Syn. Iodhydric acid ; Acidum hydriodicum , L. An acid compound of iodine and hydrogen. See Iodine . Prep. 1. By heating iodine in hydrogen, the volume of the gas becomes doubled, and a colourle acid gas is produced; it is, however, never prepared for use by this means. 2. Place 10 parts of pota ic iodide in a small retort with 5 parts of water, and add 20 of iodide; then drop in cautiously one part of phosphorus, cut into small fragments, and apply a gentle heat. The gas will be given off abundantly and may be collected, by displacement, in dry bottles. A solution of hydriodic acid may be prepared by suspending iodine in water, and pa ing a current of sulphuretted hydrogen through the mixture until the brown colour of the iodine disappears; sulphur is deposited in abundance, and hydriodic acid formed.