Poisoning People for Fun and Profit—Part 7: Cyanide

Cyanide, also known as Prussic Acid, is one of the most notorious and deadly poisons. As hydrogen cyanide gas, it can be an instrument of mass murder and when swallowed in solid form, it causes a quick, nasty death. It's the legendary "poison pill" that spies are supposed to swallow if captured.

It's also the poison that gives off a tell-tale "scent of bitter almonds" that has signaled many a fictional sleuth that a death is not from natural causes. But not everyone can detect the scent.

It does not leave a pretty corpse. The victim often froths at the mouth.

Cyanide occurs in nature in many benign plants like apple and orange seeds, almonds, apricot kernels, bamboo shoots and cassava. Some insects also release cyanide as a protective mechanism.

Tobacco smoke contains cyanide

Hydrogen cyanide is present in tobacco and wood smoke, and burning plastic can send off enough of the toxic gas to make people sick or even kill.  A hydrogen cyanide concentration of 300 mg/m3 in the air will kill in as little as 10 minutes.

A hundred grams (about a quarter of a pound) of dried, crushed apple seeds yields about 50-70 mg of cyanide, which is enough to kill. But that's a lot of apples! Maybe your murderer could be a pie baker or a cider-maker....hmmm.

Cyanide kills by preventing the body from absorbing oxygen. The victim will first feel a headache, dizziness, vertigo and confusion. They will then have difficulty breathing and lose consciousness before suffering cardiac arrest. The face may turn a cherry red. A fatal dose for humans can be as low as 1.5 mg/kg body weight.

Apple seeds contain cyanide

The most common antidote, which must be administered immediately, is amyl nitrate, followed by intravenous sodium nitrate and sodium thiosulfate. 

It was first isolated as a component of the blue pigment, "Prussian blue" and sodium cyanide and potassium cyanide have been used for centuries in gold and silver mining and for electroplating. Cyanide has been long used as a pesticide, and has many industrial applications, including photography processes, like sepia toning. (So maybe the wedding photographer is the murderer?)

Bitter almonds contain 42 X the cyanide of sweet almonds 

Probably because it acts so fast, it's one of the most popular poisons with mystery writers. Agatha Christie used it in numerous novels, including Sparkling Cyanide and And Then There Were None. Raymond Chandler used it in The Little Sister and Ngaio Marsh used it in Death at the Bar.

In the Doctor Who episode about Agatha Christie, The Unicorn and the Wasp, the Doctor himself is poisoned with cyanide, but with his Gallifreyan metabolism, he was able to detoxify himself. 

Some people think the fictional poison "the Strangler" in Game of Thrones is based on cyanide, although others think it's more like strychnine. 

Do you have a favorite poisoning mystery? What poison was used? 

Other Posts in this Series

Part 1: Digitalis

Part 2: Wolfsbane

Part 3: Hemlock

Part 4: Poison Dart Frogs
Part 5: Arsenic
Part 6: Oleander

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