Chloroplatinic Acid: Platinum Dissolved in Aqua Regia, Nitric Acid Driven Off with Hydrochloric Acid (Thorpe 1912)

Platinum dissolves in aqua regia. Evaporate the solution with hydrochloric acid until no nitric acid is left, and you have chloroplatinic acid, the soluble form of platinum used to put it on catalysts. Result: chloroplatinic acid, H2PtCl6, crystallising with 6 molecules of water as reddish-brown prisms that take up water from the air. Source: Thorpe, Dictionary of Applied Chemistry, vol. 4 (1912), Platinum. Not given: amounts, how it is heated, how many evaporations. Danger: aqua regia burns and gives off chlorine. Picture drawn by Youblob.