With an average mass fraction of 0.05 parts-per notation in the continental crust, osmium is known to be one of the least abundant elements in the Earth's crust. It is found in nature in natural alloys or as a pure element. Similar to the other precious metals in the platinum group, osmium can be found in alloys with copper or nickel. In this procedure, the price of the precious metal is determined each business day on the London market. The fixing is done twice - once in the morning and another in the afternoon. The latter actually was introduced about 49 years after the procedure itself was introduced, as a means of providing a price when US markets are open. 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. The sluice box method is best suited for excavation in which certain implements, such as shovels, are used to feed ore into the box. Trommel: This method involves the use of a screened cylinder to separate materials by size (trommel is Dutch word for "drum"). A trommel specifically consists of a rotating metal tube that is slightly tilted, with a screen at the discharge end. high-temperature superalloys (used in making the turbine blades in jet engines); 4. fountain pen nibs; 5. removing hydrogen sulfide from various industrial processes; 6. electrolytic cells for various chemical processes (as a component of mixed-metal oxide anodes); 7. optical sensor device; 8. radiotherapy (particularly of eye tumors). These proof Krugerrands are priced above the bullion Krugerrands. The two coin versions can be distinguished from one another by the number of serrations they have - the proof version has 220, while the bullion has 40 less than the former's. Other nations, such as Canada, Australia, the United States, and the United Kingdom, started producing their own precious metal coins one after the other beginning in 1979.