Radon: Radium Emanation Boiled Off a Radium Solution under Reduced Pressure and Frozen Out in Liquid Air (Roscoe 1913)

Radium never stops making radon, a heavy inert gas then called radium emanation. Dissolve a radium salt in water, boil the solution under reduced pressure, and the gas comes off with the air; a U-tube in liquid air freezes it out. Result: radon gas, at most about 0.6 cubic millimetre from one gram of radium (one curie); half of it decays in 3.85 days. Source: Roscoe and Schorlemmer, A Treatise on Chemistry vol. 2 (1913), pp. 1434-1435. Not given: amounts of water, pressure, how long to wait between collections. Radium and radon are radioactive: shield, ventilate, never breathe the gas. Picture drawn by Youblob.