Indium: From Freiberg Zinc, Thrown Down on Undissolved Zinc, Purified as Sulphite and Reduced in Hydrogen (Roscoe 1913)

Freiberg zinc carries a trace of indium. Dissolve most of the zinc in acid and the indium plates out on the zinc that is left. Acids and ammonia then strip away the other metals, sodium bisulfite throws the indium down as a sulphite, heat turns it to oxide, and hydrogen takes the oxygen away. Result: white, soft indium metal, softer than lead, melting at 155 °C. Source: Roscoe and Schorlemmer, A Treatise on Chemistry vol. 2 (1913), p. 754. Unknown: the indium-bearing zinc; no blueprint smelts it yet. Not given: amounts. Sulphur dioxide is a poison gas. Picture drawn by Youblob.