Various other silver coins have been issued. The trade dollar, issued by the Act of 1873, weighed 420 grains, or 7.5 grains more than the standard dollar. Though intended only for circulation in the Orient, the trade dollars circulated freely in our own country because when the price of silver fell it became profitable to take 420 grains of standard silver to the mint and have it minted into a circulating coin. With a view to stopping this circulation, their legal-tender quality was taken from them in 1876, and the Secretary of the Treasury was authorized to limit their coinage, from time to time, to such an amount as he might deem sufficient for the export demand. This he did in 1877, after $30,710,400 had been issued. In 1887 they were retired and discontinued. Special souvenir silver dollars, known as the "Lafayette dollar," were coined to commemorate the Pan-American Exposition at Buffalo in 1899. In 1892 and 1893 a limited number of souvenir Columbian halves and Isabella quarters were coined. By the law of 1918, provision is made for coining 100,000 silver half-dollars of special design, commemorating the centenary of the admission of Illinois into the Union. Similar laws were passed in 1920 for Maine and Alabama; and the coinage of 300,000 half-dollars commemorating the landing of the Pilgrims was also authorized. In addition to these silver coins, the following have also been coined for circulation: the 20-cent piece, 1875-1878; The Half-Dime, 1792-1873; And The 3-Cent Piece, 1851-1873.