|The discovery of new elements (pre-16)|
William Ramsay – the distillation of liquid air
William Ramsay investigated the observation that nitrogen made by removal of other gases from air had a slightly different density to nitrogen made by chemical decomposition. First he discovered argon and then predicted a complete family of elements between Groups 7 and 1 of the Periodic Table. We now call these the noble gases. By fractional distillation of liquefied air, he and Morris Travers then discovered neon, krypton and xenon. Ramsay won the 1904 Nobel prize for chemistry.
When Ramsay discovered a gas of relative mass approximately 40, chemists were at first reluctant to believe that a whole new group of elements remained to be discovered. At first, Mendeleev was a disbeliever because he felt that the discovery undermined his Periodic Table. Later, however, he came to see that it was actually a confirmation of the basic idea behind the Table.
Some tried to explain the new gas as an allotrope of nitrogen, N3. (Allotropes are forms of the same element which differ in the arrangement of their atoms.) This seemed possible because oxygen has an allotrope O3, usually called ozone. N3 would have a relative molecular mass of 42, close to the measured value for argon of 40. However, N3 has, up to now, never been found or made.