How did Lord Rayleigh and William Ramsay discover argon?

The discovery of argon resulted from a collaborative effort between the British physicist Lord Rayleigh and the Scottish chemist Sir William Ramsay in 1894.12

The investigation began when Lord Rayleigh observed a persistent discrepancy in the density of nitrogen: nitrogen extracted from the atmosphere was consistently about 0.5 percent denser than nitrogen derived from chemical compounds like ammonia. Rayleigh hypothesized that this atmospheric nitrogen contained a small amount of a previously undetected, heavier gas.3421

Building on this, Rayleigh and Ramsay collaborated to isolate this unknown constituent. By employing two different methods to remove all known gases from air, they successfully isolated a monatomic, chemically inert element. They named the new gas argon, derived from the Greek word argos, meaning "lazy," to reflect its lack of chemical reactivity. Their successful isolation of this gas earned both scientists Nobel Prizes in 1904—Rayleigh in physics and Ramsay in chemistry.1432