Prussic acid, also known as hydrogen cyanide or HCN, is a chemical compound both useful and dangerous. Although it is naturally present in some plants, this substance can also be synthesized through a variety of chemical processes. While the substance is useful in many industries, it is also deadly poisonous to humans and has been used as a chemical weapon.
The acid was first discovered by scientist Carl Scheele in the 1780s, who would also discover and describe several elements. It was later examined by Joseph Gay-Lussac in the early 19th century and began being used in mining. Early processes for obtaining quantities of prussic acid included holding ammonia over heated coal and combining coal, ammonia and sodium and mixing it with an acid solution, which produces HCN gas.
The uses of prussic acid in industry are varied. Engraving, explosives and dye processes all make use of HCN. Historically, it has also been used in vermin or insect poisons, but has recently been replaced with materials less toxic to humans. The United States is one of the leading producers of prussic acid for industrial purposes.
Hydrogen cyanide is extremely poisonous to mammals, and high concentrations can kill a human being within a few minutes. It forms a major component of Zyklon B, a brand-name gas used by the Nazis during World War II to kill prisoners in the concentration camps of Auschwitz and Majdanek. Originally developed as a pesticide by a German Jew named Fritz Haber, Zyklon B was used in the gas chambers of the concentration camps, resulting in the deaths of untold numbers of prisoners.
Under the restrictions of the worldwide Chemical Weapons Convention, prussic acid is considered a Schedule 3 substance, meaning it has large-scale use for industrial purposes. Any country producing more than a specified amount of the material must declare it and are subject to inspection. There are also regulations guiding export of the material to other nations.
Occasionally, high concentrations of prussic acid will occur naturally in some plants, particularly in plants related to Sorghums. Small amounts of the compound are found in fruits with pits, such as cherries and plums, although this amount is generally not enough to harm a human. Foraging or grazing animals are susceptible to prussic acid poisoning if they consume plants with a high concentration. Poisoning restricts oxygen intake and causes suffocation, so treatment is difficult and must be immediately carried out by a veterinarian. If you have an animal you think is ill or has died from this variety of poisoning, obtain samples of any material the animal has eaten and have it analyzed by a chemical lab.