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- a compound of hydrogen and fluorine dissolved in water to produce an
extremely corrosive acid traditionally used to etch glass.
Fluorine is the most reactive of the
halogens and extremely dangerous to handle. Paradoxically, many fluorine compounds are
extremely stable, and used to inhibit corrosion, adhesion and oxidation, eg sodium
monofluorophosphate in toothpaste, bromochlorodimethylfluoride in fire extinguishers and
chlorinated fluorocarbons as nearly inert working fluids in heat pumps. Unfortunately these
compounds become unstable when exposed to intense UV radiation and ozone, hence the
problems in the upper atmosphere. All of which makes it seem particularly extraordinary that
hydrofluoric acid is used in stone cleaning.