Sherman Silver Purchase Act
The Sherman Silver Purchase Act was a United States federal law enacted on July 14, 1890, which increased the amount of silver the government was required to purchase on a recurrent monthly basis to 4.5 million ounces, roughly the entirety of the American output. The act did not authorize the free and unlimited coinage of silver that the Free Silver supporters wanted.
Source: Wikipedia — Sherman Silver Purchase Act (CC BY-SA 4.0)