Hyposulphite of soda occurs in the form of large translucent groups of crystals, which include five atoms of water. These crystals are soluble in water almost to any extent, the solution being attended with the production of cold; they have a nauseous and bitter taste.
Hyposulphite of Gold. (See [Gold, Hyposulphite of.])
Hyposulphite of Silver. (See [Silver, Hyposulphite of.])
Iceland Moss.
Cetraria Islandica.—A species of lichen found in Iceland and the mountainous parts of Europe; when boiled in water, it first swells up, and then yields a substance which gelatinizes on cooling.
It contains lichen starch; a bitter principle soluble in alcohol, termed "cetrarine;" and common starch; traces of gallic acid and bitartrate of potash are also present.
Iodine.
Symbol, I. Atomic weight, 126.
Iodine is chiefly prepared at Glasgow, from kelp, which is the fused ash obtained by burning seaweeds. The waters of the ocean contain minute quantities of the iodides of sodium and magnesium, which are separated and stored up by the growing tissues of the marine plant.
In the preparation, the mother-liquor of kelp is evaporated to dryness and distilled with sulphuric acid; the hydriodic acid first liberated is decomposed by the high temperature, and fumes of iodine condense in the form of opaque crystals.