Attached to the inside part of the metal tube are lifter bars. Ore is fed into the trommel through its elevated end. Pressurized water is supplied to the tube and the screen sections. Valuable minerals from the ore are separated by the combination of water and mechanical action. The small pieces of ore bearing the valuable minerals pass through the screen and are concentrated further in sluices. mol-1 Heat of Vaporization: 704 kJ.mol-1 Atomic: Oxidation States: 7, 6, 5, 4, 3, 2, 1, 0, -1 Electronegativity: 1.9 (Pauling scale) Atomic Radius: 137 picometre Covalent Radius: 151 7 picometre Ionization Energies: 760 kJ.mol-1 (first), 1260 kJ.mol-1 (second), 2510 kJ.mol-1 (third) Rhenium is silvery-white in appearance. mol-1 (second), 3177 kJ.mol-1 (third) Palladium is used in the following: 1. Catalytic converters; 2. Jewelry and watch making; 3. Dentistry and surgical instruments; 4. Aircraft spark plugs; 5. Electrical contacts; 6. Connector platings; 7. Manuscript illumination. Since the late 1930s, palladium has been utilized as a precious metal in jewelry. In fact, it is known to be more versatile than any of the other five precious metals in the platinum group. A hard, white metal, ruthenium is known to have four crystal modifications. While it does not tarnish under normal temperature, it does oxidize readily when exposed to air. It can be plated by means of two methods: thermal decomposition and electrodeposition. It is also known to be the most expensive precious metal, with a price estimated to be about USD2,750 per troy ounce (USD88,415 per kilogram) as of January 2010. 3. Palladium - This element is represented by the symbol Pd. Its atomic number is 46. It is also considered one of the rarest precious metals. This composition was meant to make the coins more durable and harder and thus resist dents and scratches, as, again, they were originally intended for circulation. On the obverse of the Krugerrand is the face of Stephanus Jonannes Paulus Kruger, fifth president of the South African Republic (note the surname Kruger and the South African currency Rand were combined to give this precious metal coin its name).