Boron: Boric Oxide Reduced with Sodium under Salt (Wöhler and Deville, Thorpe 1912)

Sodium takes the oxygen from boric oxide in a violent reaction under a blanket of salt. Hydrochloric acid dissolves the rest and leaves the boron. Result: boron powder, but not pure: it holds compounds of boron with sodium, iron and hydrogen, and boron nitride (Moissan's magnesium route gives a purer product). Source: Thorpe, Dictionary of Applied Chemistry vol. 1 (1912), pp. 497-498, after Wöhler and Deville (Ann. Chim. Phys. [3] 52, 63). Not given: the furnace and acid strength. Picture drawn by Youblob.