Most other metals like copper, lead, palladium, and rhodium were precipitated with zinc. He then precipitated the platinum as ammonium chloroplatinate by adding ammonium chloride ( NHĤCl). His procedure dissolved the ore in aqua regia and neutralized the acid with sodium hydroxide (NaOH). He used crude platinum ore presumably obtained from South America. Rhodium ( Greek rhodon (ῥόδον) meaning "rose") was discovered in 1803 by William Hyde Wollaston, soon after he discovered palladium. Other uses of rhodium include asymmetric hydrogenation used to form drug precursors and the processes for the production of acetic acid. Rhodium detectors are used in nuclear reactors to measure the neutron flux level. Rhodium is sometimes used to cure silicones: a two-part silicone in which one part containing a silicon hydride and the other containing a vinyl-terminated silicone are mixed one of these liquids contains a rhodium complex. White gold is often plated with a thin rhodium layer to improve its appearance, while sterling silver is often rhodium-plated to resist tarnishing. Because rhodium metal is inert against corrosion and most aggressive chemicals, and because of its rarity, rhodium is usually alloyed with platinum or palladium and applied in high-temperature and corrosion-resistive coatings. The element's major use (consuming about 80% of world rhodium production) is as one of the catalysts in the three-way catalytic converters in automobiles. It was discovered in 1803 by William Hyde Wollaston in one such ore, and named for the rose color of one of its chlorine compounds. Rhodium is found in platinum or nickel ores with the other members of the platinum group metals. It is one of the rarest and most valuable precious metals. Naturally occurring rhodium is usually found as a free metal or as an alloy with similar metals and rarely as a chemical compound in minerals such as bowieite and rhodplumsite. It has only one naturally occurring isotope: 103Rh. It is a noble metal and a member of the platinum group. It is a very rare, silvery-white, hard, corrosion-resistant transition metal. Rhodium is a chemical element with the symbol Rh and atomic number 45.
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