Argon is the third-most abundant gas in the Earth's atmosphere, used in inert gas welding.
Core Principles & Analysis
Lord Rayleigh and William Ramsay discovered argon in 1894 after noticing atmospheric nitrogen was slightly denser than nitrogen from compounds, work that won both men Nobel Prizes.
It makes up 0.93% of the atmosphere, the third most abundant gas, and is so unreactive its name comes from the Greek for 'lazy'.
Argon shields molten metal during arc welding, fills incandescent bulbs and insulating double-glazed windows, and blankets the US Declaration of Independence in its display case.