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What Is Prussic Acid?

Prussic acid, despite being a deadly poison, is very widespread. It is produced naturally by plants such as white clover and hydrangea, but it is also used or produced in many industrial processes. These include fumigation, metal processing, chemical synthesis and silver plating. Because prussic acid can be so dangerous, anyone working with this chemical -- or whose animals may be exposed to it -- should be well aware of its properties and hazards.

Chemistry
- Prussic acid is an alternative name for the chemical compound hydrogen cyanide. This substance is also often called hydrocyanic acid or sometimes simply cyanide. It has the chemical formula HCN, meaning that each molecule is made of one hydrogen atom, one carbon and one nitrogen. It is a weak acid made from the combination of two charged chemical species, or ions. The two ions which make up prussic acid are the positive hydrogen ion (H+) and the negative cyanide ion (CN-).
Physical Properties
- Prussic acid has a melting point of 7 degrees F and is a liquid at room temperature. It boils and becomes a gas at 79 degrees F, just above room temperature. It is colorless as a gas and bluish-white as a liquid. Its odor can be detected when it is present in air at very low parts per million (ppm) level concentrations and it is reported to have a bitter smell, somewhat like almonds.
Toxicity
- Prussic acid is highly toxic through inhalation, ingestion and skin and eye contact. Exposure to low levels in air can cause a variety of symptoms ranging from irritation of eyes, skin and throat to thyroid changes through long-term exposure. HCN interferes with the body's ability to use oxygen, and Inhalation or ingestion or even skin contact of high concentrations rapidly produces very serious symptoms up to and including death. This chemical is also highly flammable.
Forage Concerns
- Ranchers are particularly concerned about prussic acid poisoning of their livestock. Certain common plants that livestock graze on, such as sorghum species, have the potential to form HCN internally. This happens when plants are damaged, allowing chemicals which have the potential to produce HCN to mix with enzymes. The damage which produces HCN in these plants can occur through trampling, cutting and even due to frost. Cattle that eat these plants can become severely ill due to HCN poisoning.

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