The second installment in the Poisons series looks at cyanide, another notorious murder agent. It has played a role in genocide and suicide pills, and is also found in small amounts in the seeds of many fruits. So why is cyanide so toxic, and why are fewer people dying from cyanide poisoning than arsenic poisoning in modern times?

cyanide formula CN- ion, and as a poison it is usually administered as one of the three compounds shown in the diagram: hydrogen cyanide, a volatile colorless liquid, and potassium and sodium cyanide, All are white powder. Both potassium cyanide and sodium cyanide react with stomach acid to produce hydrogen cyanide formula , which can cause toxic effects.

Although cyanide has been used as a poison for centuries, it was first isolated in Sweden in 1782 by Swedish chemist Carl Scheele. While different sources have varying accounts, some claim exposure to cyanide was a factor in Scherer's untimely death at the age of 43. Scherer's untimely death is not surprising given the number of toxic agents Scherer was exposed to throughout his career. He was also the first to notice the bitter almond smell of hydrogen cyanide – which, it turns out, is only detectable by 40% of people due to genetics.

So, what happens when a person gets cyanide poisoning? It is one of the fastest-acting poisons known, causing rapid death if ingested in large quantities. When ingested, it binds to hemoglobin, the molecule in red blood cells responsible for carrying oxygen to the cells in our body. The hemoglobin then carries it to body tissues, where it can bind to an enzyme called cytochrome oxidase. This enzyme is an important tool cells need to use oxygen, but cells cannot use oxygen because of the cyanide that binds to it.
Symptoms of cyanide exposure can appear quickly and include headaches, nausea, vomiting, rapid breathing and heart rate. At the right dose, these symptoms can rapidly progress to loss of consciousness, respiratory failure and death. The exact dose that causes death depends on the form of cyanide administered, but has been reported to be as low as one milligram per kilogram of body weight.