_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.

Amorphous silicon likewise burns with great energy in fluorine.

ACTION OF FLUORINE UPON METALS.

_Sodium_ and _potassium_ combine with fluorine with great vigor at
ordinary temperatures, becoming incandescent, and forming their
respective fluorides, which may be obtained crystallized from water in
cubes. Metallic _calcium_ also burns in fluorine gas, forming the
fused fluoride, and occasionally minute crystals of fluorspar.
_Thallium_ is rapidly converted to fluoride at ordinary temperatures,
the temperature rising until the metal melts and finally becomes red
hot. Powdered _magnesium_ burns with great brilliancy. _Iron_, reduced
by hydrogen, combines in the cold with immediate incandescence, and
formation of an anhydrous, readily soluble, white fluoride.
_Aluminum_, on heating to low redness, gives a very beautiful
luminosity, as do also _chromium_ and _manganese_. The combustion of
slightly warmed zinc in fluorine is particularly pretty as an
experiment, the flame being of a most dazzling whiteness. _Antimony_
takes fire at the ordinary temperature, and forms a solid white
fluoride. _Lead_ and _mercury_ are attacked in the cold, as previously
described, the latter with great rapidity. _Copper_ reacts at low
redness, but in a strangely feeble manner, and the white fumes formed
appear to combine with a further quantity of fluorine to form a
perfluoride. The main product is a volatile white fluoride. _Silver_
is only slowly attacked in the cold. When heated, however, to 100 deg.,
the metal commences to be covered with a yellow coat of anhydrous
fluoride, and on heating to low redness combination occurs, with
incandescence, and the resulting fluoride becomes fused, and afterward
presents a satin-like aspect. _Gold_ becomes converted into a yellow
deliquescent volatile flu