Arsenic vs Antimony

Few elements carry as much reputation as arsenic. It was the classic murder weapon of Renaissance courts and Victorian novels, tasteless and once impossible to detect. Yet it has also been a medicine for over two thousand years, a pigment that coloured wallpapers and paintings, and today a licensed drug for a form of leukaemia. Its compound with gallium is a high-performance semiconductor inside almost every mobile phone.

• At normal air pressure arsenic never becomes a liquid: it goes straight from solid to vapour at about 615 °C.
• Copper alloyed with arsenic was in use before tin bronze, so arsenic metallurgy is older than the Bronze Age name suggests.

Antimony sits on the staircase of metalloids that separates metals from non-metals. It looks like a metal, silvery and shiny, but it is brittle, conducts electricity poorly and behaves chemically like a cross between a metal and a non-metal. That in-between character has made it useful in surprising ways for thousands of years.

• Stibnite, antimony's main ore, was ground up and used as kohl eye make-up in ancient Egypt.
• Antimony is one of the few substances that expands when it freezes, a property shared with water, bismuth and gallium.