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Hydrogen cyanide (HCN) was discovered by the Swedish chemist Carl Wilhelm
Scheele in 1782, who prepared it from the pigment Prussian blue (hence its
other name of prussic acid).

There are many naturally occurring substances yielding cyanide in certain
seeds, such as the pit of the wild cherry. It usually occurs in combination
with plant sugars. The tuberous edible plant of the spurge family called
cassava (also known as manioc, mandioc, or yuca) was used by primitive peoples
to produce HCN for poison darts and arrows. HCN is produced by other plants,
bacteria and fungi. Emissions from CN radicals are occasionally observed from
lightning disturbed air. Hydrogen cyanide is produced by biomass burning since
nitrogen in plant material is mostly present as amino acids and upon combustion
this nitrogen is emitted as a variety of compounds including NH3, NO, NO2, N2O,
organic nitriles and nitrates. It is interesting to note that the atmospheric
measurements of HCN reported by Zander et al. (1988) gave a mixing ratio for
HCN in the Southern Hemisphere which was approximately 5% higher than that for
the Northern Hemisphere. This may be due to biomass burning.
There are many anthropogenic sources of compounds containing CN which can be
released into the atmosphere. Cyanides are used in a variety of chemical
processes including fumigation, case hardening of iron and steel,
electroplating and in the concentration of ores. Hydrogen cyanide is used to
prepare polyacrylonitrile fibres (known by the generic name of acrylic)
synthetic rubber, plastics, and in gas masers to produce a wavelength of 3.34
mm. Hydrogen cyanide is a combustion product which is a human hazard during
domestic and industrial fires and from tobacco smoking. Some catalytic
converters in bad repair can produce large amounts of Hydrogen cyanide.
Hydrogen cyanide is produced in large quantities for laboratory and commercial
use by three principle methods: Treatment of sodium cyanide with sulphuric
acid, catalytic oxidation of a methane-ammonia mixture, and decomposition of
formamide (HCONH2).

From the Cambridge Atmospheric Chemistry Modeling Support Unit.