In 1967 an electrostatic precipitator followed by a 200-ft stack was placed in operation. This is highly effective and requires a min. of attention. The stack consists of 3 concentric layers of various reinforced plastics and is supported on a galvanized steel framework, with provision to extend the height to 240-ft if necessary. Stack effluent with 2 furnaces operating showed a maximum of 3.1 grain/ft3 SO3 equivalent