Phosphorus.—­Immediately phosphorus, either the ordinary yellow variety or red phosphorus, comes in contact with fluorine, a most lively action occurs, accompanied by vivid incandescence.  If the fluorine is in excess, a fuming gas is evolved, which gives up its excess of fluorine on collecting over mercury, and is soluble in water.  This gas is phosphorus pentafluoride, PF_{5}, prepared some years ago by Prof.  Thorpe.  If, on the contrary, the phosphorus is in excess, a gaseous mixture of this pentafluoride with a new fluoride, the trifluoride, PF_{3}, a gas insoluble in water, but which may be absorbed by caustic potash, is obtained.  The trifluoride, in turn, combines with more fluorine to form the pentafluoride, the reaction being accompanied by the appearance of a flame of comparatively low temperature.

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.  Graphite must be heated to just below dull redness in order to effect combination; while the diamond has not yet been attacked by fluorine, even at the temperature of the Bunsen flame.  A mixture of gaseous fluorides of carbon are produced whenever carbon of any variety is acted upon by fluorine, the predominating constituent being the tetrafluoride, CF_{4}.

Boron.—­The amorphous variety of boron inflames instantly in fluorine, with projection of brilliant sparks and liberation of dense fumes of boron trifluoride, BF_{3}.  The adamantine modification behaves similarly if powdered.  When the experiment is performed in the fluorspar tube, the gaseous fluoride may be collected over mercury.  The gas fumes strongly in the air, and is instantly decomposed by water.

Silicon.—­The reaction between fluorine and silicon is one of the most beautiful of all these extraordinary manifestations of chemical activity.  The cold crystals become immediately white-hot, and the silicon burns with a very hot flame, scattering showers of star-like, white-hot particles in all directions.  If the action is stopped before all the silicon is consumed, the residue is found to be fused.  As crystalline silicon only melts at a temperature superior to 1,200 deg., the heat evolved must be very great.  If the reaction is performed in the fluorspar tube, the resulting gaseous silicon tetrafluoride, SiF_{4}, may be collected over mercury.