In the former, placer mining is done by open-pit; in the latter, water pressure is used for excavation. There are three placer mining methods used to mine placer gold: Gold Panning: This method, which involves the use of a pan, is the oldest and simplest way to extract gold from a placer deposit. In this method, mined ore is placed in a large pan (made either of plastic or metal) and poured with a liberal amount of water; it is then agitated. The first known major area in the world to be on a gold specie standard in modern times is the British West Indies. That standard, however, was more of a commonly applied system rather than an officially established one. It was based on the Spanish gold coin called the doubloon. The United States adopted the gold specie standard "de jure" (by law) in 1873, using the American Gold Eagle as unit. And of all these precious metal coins, the South African gold bullion coin Krugerrand is perhaps the most popular. In 1967, the South African Mint Company introduced the Krugerrand, with the intention of circulating it as currency. Its status as a legal tender was seen as the best way for marketing South African gold around the world. The extreme toxicity and volatility of osmium's oxide makes it nearly impossible for this element to be used in its pure state. For this reason, it is often necessary to alloy osmium with other elements for use in high-wear applications. For example, osmiridium (a natural alloy of osmium and iridium) is alloyed with the other metals in the platinum group and used in instrument pivots and phonograph needles (apart from electrical contacts and fountain pen tips as mentioned earlier). 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. Trading in ETFs means doing away with the inconveniences associated with the handling of physical silver bars. Entering in a Contract For Difference (CFD): Some of the noted financial services firms, especially those in the United Kingdom, provide Contract for Difference (CFD). In this silver investment vehicle, two parties (a "buyer" and a "seller") enter into a contract, in which the seller agrees to pay the buyer the difference between the current value of silver and its value at contract time.