The year following the issuance of the first greenbacks Congress passed the National Bank Act (1863), which provided for the establishment of banks with federal charters. These banks were required to invest in government bonds, which they could use as security for national bank notes. Two years later the government gave to the national banks a monopoly of bank-note issue by imposing a prohibitive tax on state bank notes. In reality the government's credit served as the basis of national bank notes as well as of greenbacks, for neither were redeemable at the time in specie. During the war and for a dozen years after its close, gold was kept out of circulation by the operation of Gresham's law. The only money the people in general saw during this period was greenbacks and bank notes. Gold was bought and sold just as was wheat or corn. Any one desiring gold for export could always find it for sale at the New York Stock Exchange in what was known as the "gold room." There, also, the importers of gold could find buyers. The heavy issues of greenbacks and bank notes caused prices to rise, since, as we have seen in the discussion of the quantity theory of money, the value of the dollar declined. Another objection to both greenbacks and bank notes was that they were inelastic. The government could not regulate the amounts of either or both to meet the seasonal demands for money. In this respect they were little better, if any, than gold or silver coins.