Two papers on "Experiments with Airs," printed in 1784 and 1785, contain the great discoveries of the compound nature of water and the composition of nitric acid of English chemist Henry Cavendish (1731-1810). The presence of unknown material (actually the Noble Gases) was noted by Cavendish. He carried an experiment whether the whole of a given portion of nitrogen could be reduced to nitric acid (by combination with magnesium) and oxygen. Starting with a chamber containing air from which he was able to remove nitrogen he found that a small fraction, resisted the change - the residual content of the chamber - and in fact, mostly argon together with other trace elements in air.
In his book The Gases of the Atmosphere (1896), William Ramsay (1852-1916) repeated a suspicion he had stated in 1892 that there was an eighth group of new elements at the end of the periodic table. Noting that the element had a valence of zero, he postulated that a new group existed in the periodic table, and began the search for its new members. Using spectroscopy, he was able to determine that lines of a gas corresponded to lines found in the Sun and attributed to a new element called helium. Further experimentation in 1898 yielded three as yet unknown fractions in air: neon, krypton , and xenon. Ramsay was awarded the Nobel Prize for Chemistry in 1904 for his discovery of inert gases in air and their locations in the periodic table. He was made a KCB in 1902.
|Element||Atomic number||Atomic weight||Boiling point||Density||Heat fusion||Heat vapour||Melting point||Specific heat capacity||Thermal conductivity|
|Argon||18||39.95||87.36° K||1400 kg/m³||1.18 kJ/mol||6.53 kJ/mol||83.76° K|
|Helium||2||4||4.26° K||126 kg/m³||0.02 kJ/mol||0.08 kJ/mol||3.46° K|
|Krypton||36||83.8||121.16° K||2600 kg/m³||1.63 kJ/mol||9.05 kJ/mol||115.86° K|
|Neon||10||20.18||27.16° K||1200 kg/m³||0.34 kJ/mol||1.77 kJ/mol||24.56° K|
|Xenon||54||131.3||165.16° K||3060 kg/m³||2.3 kJ/mol||12.65 kJ/mol||161.26° K|