Ar

Argon

In 1894, Lord Rayleigh and William Ramsay were studying nitrogen and noticed a persistent discrepancy: nitrogen extracted from air was slightly heavier than nitrogen produced from chemical compounds. This small but consistent difference led them to discover argon, a noble gas that makes up about 1% of earth’s atmosphere. The discovery resolved a mystery first noted by Henry Cavendish in 1785, when he observed that a small portion of air wouldn’t react with anything. The name “argon” comes from the Greek word for “lazy” or “inactive,” referring to its chemical inertness.

The discovery was significant enough that both scientists received Nobel Prizes in 1904 – Rayleigh in Physics and Ramsay in Chemistry.