_Symptoms._--Iodide of potassium acts as an irritant in large doses, producing also many of the symptoms which attend a violent catarrh, with profuse discharge from the nose, lachrymation, and swelling of the eyelids, also pustular eruptions like acne on the face and body generally. Small doses--three to five grains--have produced in some persons most unpleasant and even alarming symptoms. In chronic poisoning, certain glands, the mammary and testicles, are said to waste away. Salivation is not infrequently present. I have seen the administration of the salt produce a severe bullous and hæmorrhagic eruption, simulating hæmorrhagic smallpox, with sloughing. (See also the account in _British Medical Journal_, 1878, of a case of purpura in a child five months old, after a dose of two and a half grains of the salt.) _Treatment._--The use of emetics and the stomach pump, starch, &c. _Chemical Analysis._--In solution, iodide of potash gives the following characteristic reactions: 1. With a salt of lead Bright yellow precipitate. 2. With corrosive sublimate Bright scarlet precipitate. 3. With strong nitric acid and starch A blue colour. In organic mixtures the mode of detecting it is more complicated. Sulphuretted hydrogen should be first passed through the mixture in order to convert any free iodine into hydriodic acid. The excess of the gas is then driven off by the application of heat, and potash added, the resulting liquor filtered, and the filtrate evaporated to dryness. To get rid of any organic matter, the residue left after evaporation is charred at a low red heat, reduced to powder, and dissolved in water. This solution is then concentrated, and strong nitric acid and solution of starch added, when, if iodine be present, the blue colour will be developed. CHAPTER IV METALLIC IRRITANTS ARSENIC Arsenic is found as metallic arsenic, as arsenious acid, in the form of two sulphides--realgar and orpiment, and as a constituent of several ores--iron, copper, &c. Metallic arsenic is of a steel-grey colour, brittle, and sublimes at a temperature a little below 400° F., without, however, previously fusing. The vapour of the metal has a peculiar garlic-like odour, which is not possessed by any of its compounds. Arsenious Acid