Iridium: Osmiridium Opened with Zinc and Barium Nitrate, Thrown Down as Ammonium Iridichloride (Deville and Debray, Roscoe 1913)

Osmiridium resists aqua regia. Alloying it with zinc and burning the zinc away leaves it porous; barium nitrate then oxidises it, the osmium boils off as tetroxide, and the iridium is cleaned through its ammonium double chloride, a nitre fusion and a lead bath. Result: pure iridium, as made for the standard metre bars. Source: Roscoe and Schorlemmer, A Treatise on Chemistry vol. 2 (1913), pp. 1361-1362, after Deville and Debray. Not given: amounts and temperatures. Osmium tetroxide vapour is highly poisonous: it attacks the eyes. Picture drawn by Youblob.