FLUORINE, a gaseous, non-metallic ele ment, possessing properties resembling those of chlorine, and exhibiting powerful chemical ac tivity. It occurs in nature widely but sparingly, and always in combination, notably in the minerals fluorite and cryolite, from the former of which it takes its name. It is found in the topaz, in fluorcerite and yttrocerite, in apatite, wavellite, and wagnerite, in sea water and various mineral springs,' and in the siliceous stems of grasses. In the animal kingdom it appears as a component of bones, blood, the brain, the enamel of the teeth, milk and urine, but always in minute quantities. The ele mentary character of fluorine was first recog nized by Ampere and Davy ,about 1810; but although many attempts were made to isolate it, none was certainly successful until 1887 when Moissan succeeded in preparing it in tile ele mentary state by electrolyzing a solution of hydrogen potassium fluoride, HF.KF, in perfectly anhydrous hydrofluoric acid, the solution being contained in a platinum vessel whose tem perature was maintained at 10° F. below zero, and the electrolysis conducted by means of 20 Bunsen elements connected in series. When thus prepared fluorine is a gas of a light green ish-yellow color. It has a penetrating odor, quite disagreeable, and resembling that of hypo chlormis acid, and it produces irritation in the membranes of the eye and nose. Many of the elements take fire when immersed in it, and burn with the formation of their fluorides. Water is decomposed by it, with the formation of hydrofluoric acid, HF, and the liberation of ozonized oxygen; and in fact fluorine appears to combine with all known elements except oxygen and carbon, and argon, helium, and the other recently discovered inert gases of the at mosphere. Fluorine has the chemical symbol F, is a monad, and has a density of 1.310, a molecular weight of 38.10 and an atomic weight of about 19. Few of the physical properties of the element are yet known, on account of the difficulty of handling it. It corrodes glass rapidly, for example, and for this reason glass vessels cannot be used in experimenting with it. It attacks violently all organic substances, car bonizing and setting fire to cork almost in stantly. Alcohol, ether, benzine and turpentine take fire at once when brought into contact with it.
Fluorine combines with hydrogen directly even in the dark, and with detonation, even at the temperature of liquid hydrogen, the com pound, HF, that is formed being known as hydrofluoric acid. Hydrofluoric acid is more conveniently prepared by means of the action of strong sulphuric acid upon the mineral fluorite (calcium fluoride, CaF,). The reaction is as follows: HiSO. CaF.= 2HF CaSO4.
Hydrofluoric acid is a colorless gas at ordinary temperatures and pressures, fuming strongly in the air. It condenses at 5° F. below zero to a colorless, mobile liquid having a specific grav ity of about 0.988, boiling, at ordinary atmos pheric pressure, at 67° F., and solidifying at — 152° to a transparent white crystalline mass, which melts again at — 134°. As thus prepared, liquid hydrofluoric acid contains traces of water ; but these may be removed by electrolysis, the liberated fluorine combining with the water as noted above, and the oxygen of the water escaping in the free state. When the water has all been eliminated, electrolysis ceases. The compounds of fluorine are antiseptics, useful especially in breweries. Added to cider and sweet wines, sodium fluoride is effective as a i preservative. The commercial importance of hydrofluoric acid depends upon the fact that it attacks glass freely, and hence is much used for etching upon glass, the reaction between the glass and the acid being 4HF SiO3—'211,0 SiF.; the acid attacking the silica of the glass, with the formation of water and a gaseous com pound of silicon, known as silicon tetrafluoride. When silicon tetrafluoride is passed into water, it is decomposed according to the equation 4F120 --;11-12SiF.+H.SiO4; the substance rep resented by the last term in this equation, silicic acid, separates out as an insoluble precipitate, while the compound known as hydro fluo-silicic acid remains in solution. Hydro fluo-silicic acid forms salts which are known as silico-fluorides. Potassium silico-fluoride, KsSi F., is one of the few potassium compounds that are insoluble in water. The fluosilicates are antiseptics still more powerful than the fluor ides. They are not poisonous, have no odor, and a barely perceptible alkaline taste. They are therefore well adapted to use as food pre servatives. They are also of use in the surgical dressing of wounds, as they are not irritating and have greater antiseptic power than any dilution of mercuric chloride which is safely non-poisonous.
Liquid anhydrous hydrofluoric acid does not attack glass, but the action is vigorous when traces of water are present. The diluted acid is therefore used in practical etching, the article that is to be treated being immersed in it, after the parts that are not to be attacked have been protected by a coating of wax, or of a special *etching varnish.' Hydrofluoric acid in aqueous solution acts very similarly to hydrochloric acid, forming salts which are known as fluorides; hydrogen being liberated when the acid acts upon a metal, and water when upon an oxide.