The original Bill of Rights did not contain any expiration dates with them in case the states changed their minds and wanted them later, I assume. Recent amendments proposed to the Constitution usually have an expiration date written into the text so they don't sit around forever. The ERA expired in the early 1980s, if memory serves me correctly. There are a few other amendments "floating around" the United States at the moment, though. One of the original proposed Bill of Rights (there were twelve proposed and ten ratified) is still out there, which would strictly regulate the size of Congressional districts.