_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°,
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 fluoride when heated to low redness, and at a
slightly higher temperature the fluoride is dissociated into metallic
gold and fluorine gas.
The action of fluorine on _platinum_ has been studied with special
care. It is evident, in view of the corrosion of the positive platinum
terminal of the electrolysis apparatus, that nascent fluorine rapidly
attacks platinum at a temperature of -23°. At 100°, however, fluorine
gas appears to be without action on platinum. At 500°-600° it is
attacked strongly, with formation of the tetrafluoride. PtF_{4}, and a
small quantity of the protofluoride, PtF_{2}. If the fluorine is
admixed with vapor of hydrofluoric acid, the reaction is much more
vigorous, as if a fluorhydrate of the tetrafluoride, perhaps
2HF.PtF_{4}, were formed. The tetrafluoride is generally found in the
form of deep-red fused masses, or small yellow crystals resembling
those of anhydrous platinum chloride. The salt is volatile and very
hygroscopic. Its behavior with water is peculiar. With a small
quantity of water a brownish yellow solution is formed, which,
however, in a very short time becomes warm and the fluoride
decomposes; platinic hydrate is precipitated, and free hydrofluoric
acid remains in solution. If the quantity of water is greater, the
solution may be preserved for some minutes without decomposition. If
the liquid is boiled, it decomposes instantly. At a red heat platinic
fluoride decomposes into metallic platinum and fluorine, which is
evolved in the free state. This reaction can therefore be employed as
a ready means of preparing fluorine, the fluoride only requiring to be
heated rapidly to redness in a platinum tube closed at one end, when
crystallized silicon held at the open end will be found to immediately
take fire in the escaping fluorine. The best mode of obtaining the
fluoride of platinum for this purpose is to heat a bundle of platinum
wires to low redness in the fluorspar reaction tube in a rapid stream
of fluorine. As soon as sufficient fluoride is formed on the wires,
they are transferred to a well stoppered dry glass tube, until
required for the preparation of fluorine.