Philosophical transactions of the Royal Society of London v. 186:pt. 1 (1895)
Part of: Philosophical transactions of the Royal Society of London
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50. The Inert Gases
vol. 186, pp. 187-241 "Argon, a New Constituent of the Atmosphere"
Rayleigh's discovery of argon came about when he noticed that the density of nitrogen depended on how it was obtained. Thinking that the difference was caused by the appearance of an undetected component on the atmosphere, he finally succeeded in isolating the inert gas argon, which he named from the Greek word for "inactive."