BROMELIACEAE

bromeliaceae, in botany, a natural order of monocotyledons, confined to tropical and sub-tropical america. it includes the pine-apple (fig. 1) and the so-called spanish moss (fig. 2), a rootless plant, which hangs in long grey lichen-like festoons from the branches of trees, a native of mexico and the southern united states; the water required for food is absorbed from the moisture in the air by peculiar hairs which cover the surface of the shoots. the plants are generally herbs with a much shortened stem bearing a rosette of leaves and a spike or panicle of flowers. they are eminently dry-country plants (xerophytes); the narrow leaves are protected from loss of water by a thick cuticle, and have a well-developed sheath which embraces the stem and forms, with the sheaths of the other leaves of the rosette, a basin in which water collects, with fragments of rotting leaves and the like. peculiar hairs are developed on the inner surface of the sheath by which the water and dissolved substances are absorbed, thus helping to feed the plant. the leaf-margins are often spiny, and the leaf-spines of _puya chilensis_ are used by the natives as fish-hooks. several species are grown as hot-house plants for the bright colour of their flowers or flower-bracts, e.g. species of _tillandsia_, _billbergia_, _aechmea_ and others. bromine (symbol br, atomic weight 79.96), a chemical element of the halogen group, which takes its name from its pungent unpleasant smell ([greek: bromos], a stench). it was first isolated by a.j. balard in 1826 from the salts in the waters of the mediterranean. he established its elementary character, and his researches were amplified by k.j. lowig (1803-1890) in _das brom und seine chemischen verhaltnisse_ (1829). bromine does not occur in nature in the uncombined condition, but in combination with various metals is very widely but sparingly distributed. potassium, sodium and magnesium bromides are found in mineral waters, in river and sea-water, and occasionally in marine plants and animals. its chief commercial sources are the salt deposits at stassfurt in prussian saxony, in which magnesium bromide is found associated with various chlorides, and the brines of michigan, ohio, pennsylvania and west virginia, u.s.a.; small quantities are obtained from the mother liquors of chile saltpetre and kelp. in combination with silver it is found as the mineral bromargyrite (bromite). _manufacture._--the chief centres of the bromine industry are stassfurt and the central district of michigan. it is manufactured from the magnesium bromide contained in "bittern" (the mother liquor of the salt industry), by two processes, the continuous and the periodic. the continuous process depends upon the decomposition of the bromide by chlorine, which is generated in special stills. a regular current of chlorine mixed with steam is led in at the bottom of a tall tower filled with broken bricks, and there meets a descending stream of hot bittern: bromine is liberated and is swept out of the tower together with some chlorine, by the current of steam, and then condensed in a worm. any uncondensed bromine vapour is absorbed by moist iron borings, and the resulting iron bromide is used for the manufacture of potassium bromide. the periodic process depends on the interaction between manganese dioxide (pyrolusite), sulphuric acid, and a bromide, and the operation is carried out in sandstone stills heated to 60°