Neon: Atmospheric Argon Fractionated in Liquid Air, then Parted from Helium in Liquid Hydrogen (Ramsay and Travers, 1901)

Liquefy atmospheric argon (Travers used 15 litres) in a bulb of about 25 cc set in liquid air, boiled under a few centimetres of mercury by a pump. Open the tap to the first of a row of mercury gasholders and lower the reservoir to draw off the lowest-boiling part, keeping the pressure on the boiling air as low as possible. This gas is rich in neon and holds helium. Let the rest of the argon boil back into its gasholder. Repeat three times.

Use the apparatus of Fig. 109: a mercury gasholder joined through a stopcock to a small bulb, which also opens to a Topler pump. Pump the bulb empty, cool it in liquid air boiled under reduced pressure inside a second vessel of liquid air (-205 °C), and raise the mercury to drive the gas in. Let it boil off in five roughly equal fractions. Liquefy them again one by one, letting the lighter part go and pumping off the denser rest, until the lightest fraction no longer shows argon in the spectroscope.

The lightest gas will not condense in liquid air on its own, even at two atmospheres. Mix it with a good volume of oxygen, liquefy and let it boil off in three fractions; repeat with excess oxygen. Remove the oxygen from each fraction (Travers does not say how here) and check each in the spectroscope. Most of the argon is removed this way, but not the helium.

Condense the gas in a bulb cooled by liquid hydrogen. Neon condenses (vapour pressure no more than 50 mm), helium stays a gas and argon does not evaporate. Pump off the first fraction (much helium). Collect the second, which evaporates slowly. Take away the liquid hydrogen and collect the third (argon) separately.

Condense the second fraction again in liquid hydrogen. Let a little evaporate into the pump and throw it away, collect the main bulk as pure neon, and discard the last traces, which may hold argon. Travers found its density 10 (oxygen = 16).