Mill-cinder
The slag produced at the reheating and puddling furnaces. This slag, after several days' roasting, becomes highly refractory, and is known as bulldog, making an excellent substance for the bottoms of puddling-furnaces. These rich slags are sometimes mixed with the ores in the blast-furnace, and the iron thus produced is then denominated cinder-pig; but, owing to the large percentage of phosphorus usually present in pig iron made by this method, it is very inferior in quality. These slags are frequently called tap and forge cinder. See SLAG.