Currently, no country operates under a silver standard. During the 1870s, most European countries adopted the gold standard and, in the early 20th century, only China and Mexico and a few small countries were still using the silver standard. For about five years, gold was the only metallic standard in the United States until the Bland-Allison Act was passed on February 28, 1878, which required the United States Treasury to purchase domestic silver ingots to be minted in legal tender coins that coexisted with gold coins. Finally, on August 15, 1971, President Richard Nixon announced that the United States would no longer exchange currency for gold or any other precious metal, which was the last step in abandoning gold and silver standards.
As a result, silver left the country and gold came in, leading Britain to effectively follow a gold standard. Through acts of Congress in 1933, including the Gold Reserve Act and the Silver Purchase Act of 1934, the national economy was moved off the gold standard and placed on the silver standard for the first time. The law of March 13, 1932 stipulated that, until the normal economic situation was restored and the possibility of paying with gold or with gold-based foreign currency, suspended due to the economic crisis, was stabilized, the National Bank (Bank Melli Iran) could not receive silver coins or banknotes in circulation that could be offered with a purchase of gold (currency, ingots or foreign currency). However, the fixed gold-silver rate overvalued silver relative to the demand for gold to trade or borrow in England.