This operation was repeated several times. Before, however, the operation had been in progress for very long it was found that if the last fraction was taken to the pump without removing the liquid air after allowing the bulb to warm up, a further small quan tity of gas could be pumped off and collected, and this gas showed a spectrum quite different from that of the gas to which the in creased density of the inactive residue in liquid air was evidently partly due. The least volatile part of liquid air therefore con sisted of three gases to which the names argon, krypton and xenon were given. By this process of fractionation the argon was removed from the mixture as the most volatile of its constituents, the xenon as a constituent almost non-volatile at liquid air tem perature, till finally four fractions were obtained, the middle two of which were apparently practically pure krypton. Then finally by repeated condensation of the least volatile fractions the slightly volatile krypton was freed from the practically non-volatile xenon. In a similar manner a mixture of inactive gases, lighter than pure argon, first obtained by liquefying and evaporating a large quan tity of the inactive residue from air, was subjected to liquefaction and fractional evaporation. It was clear from spectroscopic ex
amination that the gas consisted mainly of argon, with some he lium, and also a third gas, previously unknown, and probably inter mediate in density between helium and argon, to which the name neon was given. The mixture was first treated in the manner already described, but after some of the argon had been separated from the mixture the more volatile fraction could no longer be liquefied at liquid air temperature, even under pressure. How ever, by replacing the liquid air by liquid hydrogen, at the tem perature so obtained helium did not condense at all ; the neon condensed but was volatile, having a vapour pressure of 1 o mm. of mercury; while the argon was quite non-volatile. The neon and argon therefore condensed together, and the neon was allowed to evaporate slowly from the mixture, and was collected, while the argon remained in the apparatus.
The melting point of ice on the absolute or Kelvin scale (°A or °K) = 273.1 (International Chemical Tables, vol. 1, 1926). Low est temperature reached o•8 °A = —272.3° C.