_Arsenic_ combines with fluorine at the ordinary temperature with
incandescence. If the current of fluorine is fairly rapid, a colorless
fuming liquid condenses in the receiver, which is mainly arsenic
trifluoride, AsF_{3}, but which appears also to contain a new
fluoride, the pentafluoride, AsF_{5}, inasmuch as the solution in
water yields the reactions of both arsenious and arsenic acids.
_Carbon._--Chlorine does not unite with carbon even at the high
temperature of the electric arc, but fluorine reacts even at the
ordinary temperature with finely divided carbon. Purified lampblack
inflames instantly with great brilliancy, as do also the lighter
varieties of wood charcoal. A curious phenomenon is noticed with wood
charcoal; it appears at first to absorb and condense the fluorine,
then quite suddenly it bursts into flame with bright scintillations.
The denser varieties of charcoal require warming to 50 deg. or 60 deg. before
they inflame, but it once the combustion is started at any point it
rapidly propagates itself throughout the entire piece.
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