For this reason, gold or silver must be alloyed with other metals (example, manganese) so that the resulting coins will come out harder, more wear-resistant, and not easily damaged or deformed. As numismatic items, gold and silver coins are made almost entirely of the precious metals, respectively. Current collectible gold coins (the 22-carat gold coins), for example, are made of 92% gold, with silver and copper comprising the rest. In this gold 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 gold and its value at contract time. In case the difference is negative, the seller receives payment instead from the buyer. 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. Also by providing a fixed pattern of exchange rates, the gold standard may effectively lessen uncertainty in international trade. He discovered this precious metal from crude platinum samples obtained from South America. The name rhodium was derived from the Greek word "rhodon", which means "rose". 6. Ruthenium - Karl Karlovich Klaus, a Russian chemist and naturalist, is usually credited with the discovery of ruthenium (in 1844). As treatment for liver cancer, because of its radioactive isotopes. Rhenium resources are identified in several countries, which include Chile, Peru, Armenia, Mexico, Russia, Canada, Kazakhstan, and Uzbekistan. The estimated total resource from these eight countries is 6,000 tonnes (6 million kilograms). Direct-ignition engine (as a catalyst); 4. Radiotherapy (as a source of radiation); 5. X-ray telescopes. In 2007, worldwide demand for iridium reached 3,701 kilograms (119,000 troy ounces). Distribution of these were as follows: electrochemical uses (1,100 kilograms); electrical uses (780 kilograms); for catalysis (750 kilograms); and other applications (1,100 kilograms).