Lexington-Concord Sesquicentennial half dollar Monroe Doctrine Centennial, this coin does no credit to Beach's stature as a first-class artist. What the coin exudes in patriotism, it lacks in art." A total of 162,099 Lexington-Concord Sesquicentennial half dollars were struck at the Philadelphia Mint in April and May, 1925, with 99 pieces set aside for inspection and testing by the 1926 Assay Commission. The coins were made from blanks, or planchets, that had been intended for mintage into 1924 Stone Mountain Memorial half dollars, but had not been used. The first coin struck was presented to President Coolidge. The half dollars were sold at the
Glass-to-metal seal dark. Oxygen-free copper has to be used if the metal comes in contact with hydrogen (e.g. in a hydrogen-filled tube or during handling in the flame). Normally, copper contains small inclusions of copper(I) oxide. Hydrogen diffuses through the metal and reacts with the oxide, reducing it to copper and yielding water. The water molecules however can not diffuse through the metal, are trapped in the location of the inclusion, and cause embrittlement. As copper bonds well to the glass, it is often used for combined glass-metal devices. The ductility of copper can be used for compensation of the thermal expansion