Palladium: historical information
William Hyde Wollaston discovered palladium in 1803-4 in crude platinum ore from South America. He dissolved the ore in aqua regia (a mixture of hydrochloric and nitric acids), neutralised the acid with sodium hydroxide (NaOH), and precipitated the platinum by treatment with ammonium chloride, NH4Cl, as ammonium chloroplatinate. Palladium was then removed as palladium cyanide by treatment with mercuric cyanide. The metal was produced from this cyanide by heating.