ACTION OF FLUORINE UPON THE NON-METALLIC ELEMENTS.

Hydrogen.—­As just described, hydrogen combines with fluorine, even at -23 deg. and in the dark, with explosive force.  This is the only case in which two elementary gases unite directly without the intervention of extraneous energy.  If the end of the tube delivering fluorine is placed in an atmosphere of hydrogen, a very hot blue flame, bordered with red, at once appears at the mouth of the tube, and vapor of hydrofluoric acid is produced.

Oxygen.—­Fluorine has not been found capable of uniting with oxygen up to a temperature of 500 deg..  On ozone, however, it appears to exert some action, as will be evident from the following experiment.  It was shown in 1887 that fluorine decomposes water, forming hydrofluoric acid, and liberating oxygen in the form of ozone.  When a few drops of water are placed in the apparatus shown in Fig. 3, and fluorine allowed to enter, the water is instantly decomposed, and on looking through the fluorspar ends a thick dark cloud is seen over the spot where each drop of water had previously been.  This cloud soon diminishes in intensity, and is eventually replaced by a beautiful blue gas—­ozone in a state of considerable density.  If the product is chased out by a stream of nitrogen as soon as the dense cloud is formed, a very strong odor is perceived, different from that of either fluorine or ozone, but which soon gives place to the unmistakable odor of ozone.  It appears as if there is at first produced an unstable oxide of fluorine, which rapidly decomposes into fluorine and ozone.

Nitrogen and chlorine appear not to react with fluorine.

Sulphur.—­In contact with fluorine gas, sulphur rapidly melts and inflames.  A gaseous fluoride of sulphur is formed, which possesses a most penetrating odor, somewhat resembling that of chloride of sulphur.  The gas is incombustible, even in oxygen.  When warmed in a glass vessel, the latter becomes etched, owing to the formation of silicon tetrafluoride, SiF_{4}.  Selenium and tellurium behave similarly, but form crystalline solid fluorides.

Bromine vapor combines with fluorine in the cold with production of a very bright but low temperature dame.  If the fluorine is evolved in the midst of pure dry liquid bromine, the combination is immediate, and occurs without flame.

Iodine.—­When fluorine is passed over a fragment of iodine contained in the horizontal tube, combination occurs, with production of a pale flame.  A very heavy liquid, colorless when free from dissolved iodine, and fuming strongly in the air, condenses in the cooled receiver.  This liquid fluoride of iodine attacks glass with great energy and decomposes water when dropped into that liquid with a noise like that produced by red-hot iron.  Its properties agree with those of the fluoride of iodine prepared by Gore by the action of iodine on silver fluoride.