As catalysts in making lead-free, high-octane gasoline. 2. As filaments in making ion gauges, mass spectrographs, and photoflash lamps. 3. As electrical contact materials, due to its high resistance to arc corrosion and wear. 4. As catalysts for hydrogenation of fine chemicals, because of its high resistance to chemical poisoning from phosphorus, sulfur, and nitrogen. cm-3 Melting Point: 2334 C, 4233 F, 2607.4 K Boiling Point: 4150 C, 7502 F, 4423 K Heat of Fusion: 38.59 kJ.mol-1 Heat of Vaporization: 591.6 kJ.mol-1 Atomic: Oxidation States: 8, 7, 6, 4, 3, 2, 1, -2 Electronegativity: 2.3 (Pauling scale) Atomic Radius: 134 picometre Covalent Radius: 146 7 picometre Ionization Energies: 710.2 kJ. 2. 1/4 oz. coin - With a face value of USD25, 7.78 g in weight, 1.32 mm thick, and 22 mm in diameter. 3. 1/2 oz. coin - With a face value of USD50, 15.56 g in weight, 1.75 mm thick, and 27 mm in diameter. 4. 1 oz. coin - With a face value of USD100, 31.12 g in weight, 2.39 mm thick, and 32.7 mm in diameter. Another rhenium compound - potassium perrhenate - is known to have a median lethal dose much like that of sodium chloride (commonly known as table salt). Rhodium: Although rhodium is inert (being a noble metal, as almost all the other precious metals are), it can be reactive, especially if used as compounds. Three Methods Of Assay For Raw Precious Metals Items of jewelry or art made of precious metals are hallmarked based on specific requirements either of the country of import or the place of manufacture. Such items, particularly those made of silver, gold, or platinum, are struck with an official mark (or series of marks), which guarantees fineness or purity of the metal used. Iridium is considered the fourth least abundant element in the Earth's crust, after rhenium, ruthenium, and rhodium. Its price is estimated to be about USD408 per troy ounce (USD13,117 per kilogram) as of January 2010. 6. Platinum - This element, after which this group of precious metals is named, is represented by the symbol Pt.