Rayleigh and Ramsay

Rayleigh and Ramsay decided that overall the balance of evidence seemed to... 

If argon be a single element then there is reason to doubt whether the periodic classification of elements is complete whether in fact elements may not exist that cannot be fitted among those of which it is composed. (Rayleigh and Ramsay, 1895, p. 58)... 

It seems clear that Armstrong s motivation for taking the polyatomic structure hypothesis seriously was indeed to defend the periodic table. Even on this score, however, there is nothing of the feeling of a Kuhnian commitment to a paradigm. For example, Rucker, the President of the Royal Society, while ready to consider non-rotating polyatomic molecules, was, like Rayleigh and Ramsay themselves, also ready to see the periodic table rejected if necessary ... 

Unsurprisingly, Mendeleev (1895, p. 543) himself was more committed Rayleigh and Ramsay s gas had to fit in the table somehow, and an atomic weight of 40 meant it did not fit—his favoured hypothesis was that the gas consists of tri-atomic nitrogen, N3, with the hypothesis of an hexatomic element the runner-up. 

Mendeleeff had found himself forced to leave a number of places in his system unoccupied. He believed correctly that elements as yet unknown would find their places in these gaps. His accurate prediction of the properties of these missing elements, which he named eka-boron, eka-aluminium and eka-silicon, was brilliantly confirmed a short time later by the discovery of scandium (21), gallium (31) and germanium (32). The Inert (or Rare) Gases discovered later by Rayleigh and Ramsay could also be readily included in the system. Again, the latest, non-radioactive elements discovered, hafnium (72) [Von Hevesy and Coster, (1923)] and rhenium (75) [Nod-... 

Nitrogen obtained from air was found to have density 1.2572 g/1 at 0 C and I atm, whereas nitrogen made by chemical methods had a density 1.2505 g/1. Rayleigh and Ramsay then repeated Cavendish s experiments, and showed by spectroscopic analysis that the residual gas was indeed not nitrogen but a new element. They then searched for the other stable noble gases and discovered them. 

Rayleigh and Ramsay discovered argon by the fractional distillation of liquid air. Fractional distillation is the process of letting liquid air slowly warm up. As the air warms, different elements change from a liquid back to a gas. The portion of air that changes back to a gas at -302.55°F (-185.86°C) is argon. 

Lord Rayleigh and Ramsay both won Nobel Prizes in 1904 for the discovery of argon. Lord Rayleigh received the prize in physics and Ramsay s award was in chemistry. 

DOS, Argon. Ar at. wt 39,948 at- no. 18. Three stable isotopes 36 (0.337%) 38 (0.063%) 40 (99.600%) artificial, radioactive isotopesr 33 35. 37 39 4] 42. Abundance in earth s crust 4 X 10 % concentration in the atmosphere 0.93% by vol cosmic abundance 1.5 X 10 atom M0 atoms of Si. Elemental, monoatomic, gaseous constituent Of air, discovered by Rayleigh and Ramsay in 1894. Although molecular ions, hydrates and cl at h rates of argon have been observed, it should be considered a noble , chemically inert gas, due to its electronic structure. The outer p subshell is entirely filled ls22s42p63s23p6. Obtained commercially... 

Rayleigh and Ramsay characterized the new gas by observing its light spectrum The spectrum seen in this tube has nothing in common with that of... 

And in an eloquent salute to Henry Cavendish, who first reported in 1785 the isolation of an unreactive gas comprising Vuo of the phlogisticated air, Rayleigh and Ramsay writek... 

There is another amazing aspect in the discovery of argon beyond its total chemical inertness. Rayleigh and Ramsay reported measurements of the speed of sound in argon that indicated that the ratio of its heat capacity at constant pressure to that at constant volume (Cp/Cy) was too high for a diatomic molecule. The only other similar observation was for monatomic mercury (vapor) whose atomic weight was known since it forms compounds. At constant volume, heat added to a diatomic molecule such as N2 goes into both movement of the molecule (translation) as well as vibration of the bond. In a monatomic substance there is no bond vibration and, thus, less capacity to absorb heat. 

Other scientists were initially skeptical. It would not have been the first time a report of the discovery of a new element turned out to be false, and it would not be the last. Berthelot was sent a sample to subject to an electrical discharge, but he reported null results. He also reported that his assistant hurt himself undoing the iron wire used to clamp down the rubber tubing sealing the sample tube. Years later it was realized that Rayleigh and Ramsay had used copper wire to tie off the tube, so the sample had been opened, presumably by customs officials, and Berthelot s experiment had been on air. 

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