Of lesser importance is the Degussa process (BMA process) in which no oxygen is added and the energy must be transferred indirectly through the reactor wall:
In the laboratory, small amounts of HCN are produced by the addition of acids to cyanide salts of alkali metals:
The first source for hydrogen cyanide was the reaction of acid on ferrocyanides. The rising demand due to the use of cyanides for mining operations in the 1890s was met by the Bleiby process. George Thomas Beilby patented a method to produce hydrogen cyanide by passing ammonia over glowing coal in 1892. This method was used until Hamilton Castner in 1894 developed a synthesis starting from coal, ammonia and sodium yielding sodium cyanide, which reacts with acid to form gaseous HCN.
Fruits that have a pit, such as cherries, apricots, apples, and bitter almonds from which almond oil and flavoring are made, contain small amounts of cyanohydrins such as mandelonitrile (CAS#532-28-5). Such molecules slowly release hydrogen cyanide. Some millipedes release hydrogen cyanide as a defense mechanism, as do certain insects such as some burnet moths. Hydrogen cyanide is contained in the exhaust of vehicles, in tobacco and wood smoke, and in smoke from burning nitrogen-containing plastics.
100 g of crushed apple seeds can yield 219 mg of Amygdalin which can generate ~10 mg of HCN.
Hydrogen cyanide can also be used to purify water. This is so because it affects the respiration of the bacteria and other germs in the water.
An HCN concentration of 300 mg/m3 in air will kill a human within a few minutes. The toxicity is caused by the cyanide ion, which prevents cellular respiration. Hydrogen cyanide (under the brand name Zyklon B) was most infamously employed by the Nazi regime in the mid-20th century.
Hydrogen cyanide is commonly listed amongst chemical warfare agents that cause general poisoning. As a substance listed under Schedule 3 of the Chemical Weapons Convention as a potential weapon which has large-scale industrial uses, manufacturing plants in signatory countries which produce more than 30 tonnes per year must be declared to, and can be inspected by, the OPCW.
Hydrogen cyanide gas in air is explosive at concentrations over 5.6%, equivalent to 56,000 ppm.
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