Actually, naturally occurring rhenium is composed of 2 stable isotopes and 26 unstable ones. Following is a list of some of the properties of rhenium: General: Chemical Symbol: Re Atomic Number: 75 Category (as an element): Transition Metal Group/ Period/ Block (in the Periodic Table): 7/ 6/ d Atomic Weight: 186.207 g. In this method, a reagent (titrant) of a known volume and concentration is utilized to react with a solution of the substance being analyzed (titrand), whose concentration is unknown. With the use of an instrument called burette (to add the titrant), the exact consumed amount, on reaching the endpoint, can be determined. 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. These two factors may cause the values of gold, silver, and the other precious metals to diminish. While some accounts point to the year 1848 when gold was discovered in California, history tells us that this precious metal was already being used extensively by the ancient Egyptians, Romans, Greeks, Chinese, and South Americans. Throughout history, gold has served as a measure of value and a symbol of wealth. Gold Exchange Standard: In this gold standard, only the circulation of coins minted from lesser valuable metals (such as silver) may be involved. The authorities, however, will have undertaken a fixed exchange rate with a country that's on the gold standard. Before the turn of the 20th century, countries that were still on silver standard started pegging their monetary units to the gold standard of either the United States or the United Kingdom. Known to be highly resistant to corrosion, this precious metal is used in jewelry, electrical contacts, and laboratory equipment. Its price, as of January 2010, is USD1,555 per troy ounce (USD49,995 per kilogram), making it the second most expensive precious metal, after rhodium. Evident from the description of each of these six precious metals is that all of them have outstanding catalytic properties and high resistance to tarnish and wear.