Compounds between carbon and nitrogen are called cyanides. The carbon atom is triple-bonded to the nitrogen atom. It therefore has one valence left to become hydrocyanic acid with hydrogen, for example, or potassium cyanide ("cyanide") with potassium. These are usually highly toxic. however, there are more complex molecules in which the cyanide is so tightly bound that it is no longer toxic. For example, the additive E536 (potassium hexacyanidoferrate(II)) is approved as a food additive. Cyanides could also have prepared the way for the emergence of life in the early days of the Earth, four billion years ago. This…