FLUORINE (from fluor). A non-metallic chemical element, one of the so-called halogens. Its elementary nature was first recognized by Davy, although it was as yet unknown in the free state, and remained unknown until 1857, when Moissan succeeded in isolating it from potassium hydrogen fluoride, by a process of electrolysis. Fluorine is not found native, but occurs combined as fluorite, a calcium fluoride; as cryolite, an aluminum-sodium fluoride; and, in smaller quaw tities, in many other minerals, as apatite, fino cerite, topaz, wagnerite, wavellite, yttrocerite; also in sea-water. mineral springs, and rivers, as well as in the stems of grasses, and in bones and other animal substances.
Fluorine (symbol, F or Fl ; atomic weight, 19.1) is a light, greenish-yellow gas of a pene trating and disagreeable odor that has an ir ritating effect on the eyes and on mucous mem branes. It decomposes water, forming hydrofluoric acid with its hydrogen and setting free ozonized oxygen. Antimony, arsenic, boron, iodine, silicon, and sulphur are capable of burning in an atmos phere of fluorine. and many organic substances, such as alcohol, when brought in contact with iL, take fire. Hydrogen combines with it, even in the dark, forming the well-known hydrofluoric acid.
Hydrofluoric acid is prepared by gently beat ing one part of pure fluorite with about twice its weight of sulphuric acid in a leaden retort, the anhydrous acid thus produced being condensed in a receiver surrounded by a freezing-mixture. It is a colorless, mobile liquid that boils at 19.4° C.
(67° F.), and solidifies to a white crystalline transparent mass at —102.5° C. (-152.5° F.), and has a powerful corrosive action on organic tissues, producing severe burns on the skin. For commercial use, the acid is made by passing the anhydrous vapor directly into a leaden receiver containing water, and is then obtained in dilute form. Owing to its corrosive nature, it must be preserved in lead, gutta-percha, or ceresine bot tles. The aqueous acid has the property of dis solving glass, and is therefore extensively used for etching on glass: e.g. in marking the divisions OH a thermometer tube.
Other compounds of fluorine include hydro fluosilieie acid, wheli is prepared by heating a mixture of sulphuric acid, fluorite, and silica (sand or powdered glass), and passing the gas eous silicon fluoride into water. It does not at tack glass directly, but on heating it decomposes with formation of free hydrofluoric acid, and this attacks the silica of the glass; hence its application for etching. Hydrofluosilicie acid combines with bases to form salts called Iluo silicates or silieolluorides, of which the most im portant are those of potassium and sodium. Cer tain compounds of fluorine have valuable anti septic properties, and a solution containing 0.61 of ammonium fluosilieate has been used as, a wash for wounds. Fluorine compounds may also he employed for preserving food without communi cating any taste to it.