- This plant consists of eight blast-furnaces, seven of which are 55 feet high, with a hearth diameter of 10 feet. One furnace is 75 feet high, with hearth diameter of 12 feet 6 inches. A 7-ton crane is arranged over the pig-beds to load the combs of pig-iron, by means of magnet, on to bogies for transport to the pig-breakers. Melting Shop