Arsenic

Category: metalloid Atomic number: 33 Colour: grey Melting point: n/a Sublimation point: 616°C (1,141°F) First identified: ancient civilizations

Its compounds have been used to kill insects; as colouring agents; to preserve wood; for animal feed; as a medical treatment for syphilis, cancer and psoriasis; in fireworks; and (compounded with gallium) as a semiconductor. However, the name of arsenic will always be synonymous with its historic use as a poison.

For centuries before it became possible to identify its presence through analysis of hair samples in 1836, it was more or less impossible to detect arsenic poisoning from analysis of a victim’s body, whether they had been given one large dose or slowly poisoned over time. It was known as ‘inheritance powder’ because of how often it was used to eliminate rich relatives. The Borgias are notorious for having used arsenic to amass their wealth – Pope Alexander VI and his two children Cesare and Lucrezia were responsible for the murder of numerous wealthy bishops and cardinals (whose property the pope would inherit after their death).

Alchemical Magic

The alchemists are often depicted as mad magicians who harboured weird beliefs about gold. In fact, they were merely the chemists of their time, struggling to understand what the world around them was made of – it can be easier to understand where their beliefs came from when you realize how many metals or metallic substances can be produced by truly astonishing processes. The writings of the thirteenth-century polymath Albertus Magnus include a description of how white arsenic (which looks like a white rock or sandy powder) could be mixed with olive oil and heated, producing the grey, metallic form of arsenic – as if by magic!

Arsenic was known to the ancient Egyptians, in the form of the yellow crystal sulphide compound called ‘orpiment’. The Chinese used it as a pesticide at least 500 years ago, and Paracelsus (the alchemist also known as the father of modern toxicology) wrote of the preparation of metallic arsenic. Orpiment was used as a pigment in a historic type of paint known as Paris Green or Scheele’s Green – it is known that Napoleon Bonaparte’s apartment on St Helena during his final exile was decorated with wallpaper of this shade, which would give off arsenic gas when it became damp or mouldy, and it is speculated that this might have contributed to his death (although the evidence is not conclusive).

Mostly produced as a by-product of copper or lead refining, arsenic can come in various forms. Grey (or metallic) arsenic is a brittle semi-metallic solid, which is sometimes found in pure form, but it generally oxidizes to form arsenous oxide (giving off a pretty unpleasant garlicky smell in the process – that same smell could have been a tell-tale sign that someone had died of arsenic poisoning before better tests were available).