On the coasts of certain islands belonging to the Duke of Argyll, vast quantities of sea-weed are occasionally torn up from their ocean beds and deposited on the shores. This weed, after being partially dried by exposure to the sun and air, is burnt in a shallow pit; the ashes are then collected, and form the commercial raw material called kelp, from which iodine is procured by a gradual series of processes. Experiments. Iodine has a beautiful metallic luster, with a bluish black color, and should be kept in a well-stoppered bottle. A small quantity placed in a clear flask and heated, affords a magnificent violet vapor, which may be poured from the flask into another glass vessel, when it condenses again into crystalline plates. The color of the vapor originates the name of this element, so called from a Greek word, meaning violet-colored. If a little iodine be placed in contact with a thin slice of phosphorus, the latter takes fire almost immediately. Bromine. From the Greek, signifies a bad odor, and is most intimately allied with chlorine and iodine; like these elements, it belongs to the sea, and is a constituent of sea-water. Bromine is a very heavy fluid, and should be preserved by keeping it covered with water in a stoppered bottle. Experiments with liquid bromine are not recommended, as all the most interesting ones can be performed with the vapor, which is easily procured by letting fall a few drops of bromine into a warm dry bottle. Experiments. Pounded antimony sprinkled into the vapor takes fire immediately. A thin slice of phosphorus placed in a deflagrating ladle and placed into the vapor of bromine ignites very quickly. A solution of sulphate of indigo, or an infusion of red cabbage, are easily bleached by being shaken violently with the vapor of bromine. Fluorine. In many parts of England, especially in Devonshire, Cornwall, and above all in Derbyshire, is found a very beautiful mineral, known by the name of Fluor Spar, Derbyshire Spar, and called by the miners Blue John, to distinguish it from another mineral found in the same locality, called _Black Jack_. It occurs in very regular and frequently large crystals in the form of cubes, and occasionally in octoëdra. It is a compound of calcium with fluorine, and is very abundant in certain fossil bones. This element, in combination with hydrogen and called hydrofluoric acid, acts so energetically upon all substances containing silica, that it cannot be preserved in vessels of glass or porcelain--very few of the metals are capable of resisting its action, lead being nearly the only common metal possessed of this power. Gutta percha may also be employed for vessels to hold it. This property of dissolving silica has caused this acid to be used for engraving on glass. Experiment.