Cyanides

Continuing with the poison 'all-star' series started by arsenic, in terms of homicidal popularity cyanide has to be a close contender.

Name: Cyanide (Hydrogen, Potassium and Sodium Cyanide are the most common forms)

Formula: HCn, KCn, NaCn

Effect on Victim: Cyanide is one of the most popular poisons seeing use not just in 'standard' homicides but also in even more horrendous circumstances such as in the Nazi gas chambers and even as far back as ancient Egyptian death sentences (where it was referred to as death by peach due to the fact it could be extracted from peach kernels). Cyanide kills by inhibiting the enzyme aa3, which is found in the mitochondria of eukaryotic cells. The blocking of this enzyme inhibits the cells ability to respire aerobically, which is especially deadly for the CNS (central nervous system) and heart. The effect of stopping cells from effectively respiring is known as histotoxic hypoxia. Histotoxic hypoxia rapidly leads to mass cell death and then complete death, usually within minutes. The gaseous cyanide, hydrogen cyanide, is especially deadly as inhaling only a very small amount will kill extremely rapidly. Cyanide deaths are quick but also extremely unpleasant. A victim of acute cyanide poison will quickly collapse, convulse and then gasp for air through a bloody, frothy vomit before succumbing to the poison and falling into a coma before dying. Not the way I'd want to go, its relatively widespread use in suicides really puzzles me.

Lethal Dose: Cyanide is very deadly, the gaseous form requiring a lethal dose of just 270 ppm in air (that's parts per million!) and the solid or aqueous forms only 200 mg of the stuff.

Diagnosis: Luckily, like arsenic, cyanide is relatively easy to detect. In fact most cyanide corpses are a text book study in violent death by poison. Straight off, before any post mortems are carried out, the corpse will be bruised and a discoloured bluish, hideously twisted by the convulsions involved in the death and if you're on the crime scene quickly enough the poison's trademark 'almond' scent will still be hanging in the air. Autopsying the corpse can prove suspicions of cyanide poisons beyond a doubt. First of all cyanide poisoning causes the blood to become a much darker red, in some cases even purple. There are many tests for cyanide in the body. One of the most popular is a test called the prussian blue test, pioneered by a toxicologist named Alexander Gettler. Take 200g of lung tissue and mince it into a paste and then break this paste down with a small amount of acid. Distill the resultant liquid in a steam bath and then condense it into a chilled flask. Now you are ready to perform the test:

1. Add 2ml of the solution to a test tube in the fume cupboard.
2. Add 2 drops of 10% ferrous sulphate and 3 drops of 10% sodium hydroxide solution.
3. Warm the mixture to 50ºC for 5 minutes.
4. Add one drop of 1% ferric chloride solution and then acidify the solution with a couple of drops of concentrated HCl.
5. A blue precipitate or colouration will display the presence of Cyanide in the tissue.

this is the blue you're looking for

And that's that, armed with these techniques identifying and proving a cyanide poisoning should be no problem for the adept chemist. On a side note beware of peach kernels (as I mentioned earlier), there have been more than a couple accidental deaths due to the arsenic levels in these. Over and out, thanks for reading.