Silver certificates are a type of representative money issued between 1878 and 1964 in the United States as part of its circulation of paper currency. They were produced in response to silver agitation by citizens who were angered by the Fourth Coinage Act, which had effectively placed the United States on a gold standard. The certificates were initially redeemable for their face value of silver dollar coins and later (for one year – 24 June 1967 to 24 June 1968) in raw silver bullion. Since 1968 they have been redeemable only in Federal Reserve Notes and are thus obsolete, but still valid legal tender and thus are still an accepted form of currency.