Argon

Argon was discovered in 1894 by Lord Rayleigh and William Ramsay, who traced a small persistent discrepancy in the density of nitrogen from air to an unknown, unreactive gas mixed with it. Its name comes from the Greek argos, idle or lazy, chosen for its complete chemical inertness; it was the first of the noble gases to be found. Argon makes up nearly one per cent of the atmosphere, more than every other trace gas combined, yet had gone unnoticed precisely because it does nothing. Obtained in bulk from the distillation of liquid air, argon supplies the inert atmosphere that shields arc welding, protects growing crystals of silicon, and once filled ordinary light bulbs, and it is sealed between the panes of insulating double glazing.

Argon has an unexpected role in paleoanthropology and geology: because a small, known fraction of radioactive potassium-40 decays into argon-40 at a fixed rate, measuring the argon trapped in volcanic rock allows geologists to date it with potassium-argon and the more refined argon-argon methods, techniques that have fixed the ages of some of the most important hominin fossil sites in East Africa. The gas is also chemically almost entirely inert even by noble-gas standards, forming no confirmed stable compounds under ordinary conditions, which is why, alongside welding and lighting, it is the standard shielding atmosphere for handling reactive metals like titanium and for preserving opened bottles of wine.

Argon's discovery was a triumph of careful measurement over the assumption that air held no surprises: the gap between the weight of atmospheric nitrogen and chemically pure nitrogen was tiny, and pursuing it opened an entire new column of the periodic table. The name argos, the lazy one, captured the property that had hidden it, and set the pattern for naming its inert relatives. Argon has no mythology or alchemical role, being a discovery of the 1890s, but its story carries a quiet moral often drawn from it: that a small anomaly, taken seriously, can reveal a whole family of elements no one had thought to look for.

Rayleigh received the 1904 Nobel Prize in Physics for the density anomaly that led to argon's discovery, awarded the same year as Ramsay's Chemistry prize for the noble gases as a family, a rare instance of one discovery earning both prizes at once. The German chemist Hugo Erdmann coined the collective term noble gas, Edelgas, in 1898, drawing an explicit analogy to the noble metals such as gold and platinum, which likewise resist reacting with other substances; argon, as the first and most abundant of the family, effectively defined what nobility meant on the periodic table.