Six years later, the United Kingdom decided to temporarily stop the gold bullion standard because of the large amount of gold that flowed out across the Atlantic Ocean. The gold standard eventually ended that same year. One of the advantages of the gold standard is that it sort of restricts the government's power in inflating prices, which is possible through excessive issuance of paper currency. In fact, this is shown even in temperatures of as high as 2000 C (3632 F or 2273.15 K). Iridium was discovered in 1803 by the English chemist Smithson Tennant. It was identified from the residue of platinum ore which was dissolved in nitro-hydrochloric acid (also known as aqua regia). Platinum ores are still the main sources today of iridium. Placer mining may be done through a number of tunneling procedures into riverbeds. There also are the open-cast mining and hydraulic mining. 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. Significant amounts of mineable palladium are also found in two other places: the Lac des les igneous complex in northwestern Ontario, Canada and the Stillwater igneous complex in the state of Montana in the United States. Such is the rarity and preciousness of palladium that many metric tons of ore have to be processed to obtain just a troy ounce of the precious metal. Osmium: Osmium, like iridium, can ignite spontaneously in air when in finely divided form. The compound osmium tetroxide, in particular, is highly volatile and is extremely toxic if accidentally inhaled, ingested, or comes into contact with the skin. Gold: Gold, in its elemental form, does not cause irritation and is not toxic even when ingested. Precious Metals Discoverers And Name Etymologies The group of precious metals consists of two coinage metals, six platinum group metals, and one metal considered the last naturally occurring stable element to be discovered. Except for gold and silver (the two coinage metals), the rest of the precious metals have recorded discoveries.