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GEMS,
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XL.
FLUORINE.
This substance,· known still by the mineralogical name of fluor spar, is very common, and found in many countries.
It
has an unequal and ' chipped cleavage ; transparent and translucent at
the edges; its light is vitreous, and refraction single.
It is found of all the colours of the rainbow, either singly or mixed.
It scratches terra-cotta, but not crystal ; it yields to the knife, and when pounded gives a white powder.
Its
specific weight varies from 3'14 to 3Ί7. It becomes electric by
friction; melts with ebullition under the action of the blow-pipe into
an opaque substance, retaining its globular form; mixed with borax, it
forms a transparent glass ; it becomes phosphoric when thrown on a hot
iron.
It is composed of lime and fluoric acid.
When
fluorine, with its dissolvents, is placed at the fire, it emits a
vapour, which is used for etching on glass. This vapour is fluoric
acid, which is disengaged from the lime, with which it had been
combined ; it has such extraordinary corrosive power that it is
injurious, and sometimes proves fatal, to smell it.
The fluorine, according to its colours when cut, takes the name in commerce of false emerald, false ruby, or
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