Rutherford had shown that thorium gave what he called an "emanation". We hope to include photos of these at some later stage. We have many of Ramsay's original gas tubes and a direct vision spectrometer which he used to observe the discharge which they gave, and these tubes will still show their discharge with a Tesla coil. In 1898, they cooled the crude neon with liquid hydrogen and isolated the forth and fifth members of the series, Krypton (the hidden one), and Xenon (the stranger) which was present in air to the extent of 1 in 10 8. Under an electrical discharge it gave blaze of crimson light, and they called it Neon, the newcomer. Ramsay and his student, Maurice Travers, cooled bulbs of argon in liquid air, and separated off the uncondensed portion. At the Royal Institution in Piccadilly, Dewar had liquefied air in 1872. After 2 years, he decided that it might be hiding in the atmosphere. They were now faced with an almost insuperable problem: they have found the first and the third member of the Group, and now need to find the intermediate member, and Ramsay says: "Here is a supposed gas, endowed no doubt with inert properties, and the whole world to find it in". With an atomic weight of 4, it fits between hydrogen and lithium, in the same group as argon.
He sent out his technician to a minerals dealer for a specimen of cléveite and, in two days, he showed that it was a new inert gas, helium, the spectrum of which Sir William Crookes had observed from the light of the sun in 1868. Ramsay thought that it might be a compound of argon. In 1895, Henry Meirs, at the British Museum, told Ramsay that, on heating, a mineral cléveite gave off a gas that Meirs though might be nitrogen. Ramsay's Apparatus of the Isolation of Neon
History -Chemical History of UCL The Discovery of Neon and Other Gases
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