A brilliant rich blue rock, prized in antiquity as a gemstone and a prominent pigment, lazurite is the basis of lapis lazuli, the original ultramarine paint and – as Brian Clegg finds – it even adorns Tutankhamun's death mask.

Cases of sleeping sickness – human African trypanosomiasis – are in decline, dropping 86% in Africa between 2000 and 2014. Gege Li explores the role that this toxic, arsenic-based medication has to play.

Many consume cod liver oil due to 'a vague sense we should be taking them for something' – but what to the omega-3 fatty acids actually do?

It made Robert Bunsen seriously ill, Michael Faraday thought it 'barbaric' to use in battle and even Fritz Haber – the 'father of chemical warfare' – abandoned it after a fatal accident in his lab. This week, Mike Freemantle tells the story of tetramethyldiarsine, otherwise known as cacodyl.

Kit Chapman takes us back to the 1904 Olympics in St Louis, via the bronze age and ancient Greece

Louise Crane introduces the antioxidant that led to exaggerated claims that 'whisky helps fight cancer'

The spice that gives your Christmas eggnog its distinctive taste and aroma is also a toxic narcotic that played an important role in international history. Florence Schechter shares the history of myristicin – the active ingredient in nutmeg

Post-nuclear steel is a little bit radioactive, so for some specialist jobs we need to find a source of steel from before the bomb

The compounds that put the 'tin' in tin cans and help you to reflect on your appearance

Kat Arney's investigation of the pungent chemical in onions is enough to bring tears to your eyes