The solution is then set aside to cool, when a quantity of crystals will be deposited. By a further evaporation, more crystals may be obtained, until finally the mother-liquor ceases to yield any more. The dark-colored liquid contains the iodides, which may be precipitated by a mixture of five parts of sulphate of iron and two parts of sulphate of copper. The precipitate is subiodide of copper, which, by treatment with sulphuric acid, the deutoxide of manganese and heat, yields iodine in violet vapors, which by condensation form the metallic-looking crystals of iodine. There are other methods of separating the iodides.
Water dissolves about one part in seven thousand parts, and receives a brown color.
Iodine in solution, as tincture, or in iodide of potassium preferably, has very valuable medicinal properties. It is regarded as a specific in the reduction of glandular swellings, and in scrofulous diseases. It is said to cause the pustules of small-pox to abort. The impurities in iodine are plumbago, sulphide of antimony, and iodide of cyanogen. The iodine in an iodide has first to be set free before it can be thus tested.