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). Also here are the Afrikaans and English versions of the name "South Africa", both inscribed in capital letters. Nuggets that have very rich deep orange/yellow color are sure to have higher gold content than pale ones. Also, there is a system called "millesimal fineness" which is used to denote the purity of gold alloy (also of silver and platinum alloys) by parts per thousand of pure metal by mass in the alloy. Various industrial and commercial uses (silver is ideal for use as a catalyst in chemical reactions). 8. Clothing (silver ions are mixed with the polymer to make yarns). 9. Medicine (silver compounds and silver ions have toxic effect on some viruses, fungi and bacteria, but not on humans). 10. Currency or coinage (as in silver bullion). Bullion is commonly made of either gold or silver. Its value is determined by the worth of the metal rather than by its face value as money. To put it another way, bullion is valued based on the mass and purity of the metal used, instead of its artificial currency value. New sources of ore have been discovered and there also have been improvements in the mining and refining processes. cm-3 Melting Point: 1554.9 C, 2830.82 F, 1828.05 K Boiling Point: 2963 C, 5365 F, 3236 K Heat of Fusion: 16.74 kJ.mol-1 Heat of Vaporization: 362 kJ.mol-1 Atomic: Oxidation States: 0, +1, +2, +4, +6 Electronegativity: 2.2 (Pauling scale) Atomic Radius: 137 picometre Covalent Radius: 139 6 picometre Van der Waals Radius: 163 picometre Ionization Energies: 804.4 kJ. Thus, metals that are labeled "precious" are also considered noble metals (note, however, that noble metals are not necessarily precious metals). There are nine known precious metals - gold, platinum, iridium, palladium, osmium, silver, rhodium, ruthenium, and rhenium. With the exception of the latter, all are considered noble metals.