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