Helium: Uraninite Heated with Dilute Sulphuric Acid, Purified through Hot Quartz (Thorpe 1912)

Uranium minerals hold helium trapped inside them. Heating the powder with dilute sulphuric acid lets all of it out. Fused quartz at 1000–1200 °C lets helium through and nothing else, so the helium comes out pure. Result: helium free from nitrogen and the other inert gases. For comparison, 1 g of cleveite (a kind of uraninite) gives over 3.2 cc. Source: Thorpe, Dictionary of Applied Chemistry vol. 3 (1912), p. 34, after Travers and after Jacquerod and Perrot. Not given: acid strength, amounts, yield from plain uraninite. Uraninite is radioactive. Picture drawn by Youblob.