Ramsay's Apparatus for Isolating Argon
Ramsay repeatedly passed nitrogen from the air over red hot magnesium, which reacted to form magnesium nitride, and as the volume decreased, the density rose. 22 Litres of the gas with a density of 14 were reduced to 1.5 l with a density of 16.1, and then finally to a residual 290 cm 3 with a density of 16.1 and then to 290 cm 3 with a density of 19.95, and which would no longer react with magnesium. Measurement of the specific heat showed it to be monatomic, and therefore the atomic weight was 39.9, and it fitted into the Periodic Table between chlorine and potassium as the first member of a new Group. With the advice of a colleague from the Classics Department, he called this gas argon, after the name argon given in the Greek Old Testament to describe 'the workers who stand idle in the market place'.
On August 4th he wrote to Rayleigh: 'I have isolated the gas; Its density is 19.4, and it is not absorbed by magnesium...'. These experiments were later described by Lord Rayleigh in an informal but fascinating evening lecture . Ramsay's paper on the discovery is also available online .
(We are grateful to Prof Carmen Giunta for putting the above papers online).