Boil′ing-furnace.
（Metallurgy.) A reverberatory furnace employed in the decarbonization of cast-iron to reduce it to the condition or mechanical treatment by hammer, squeezer, and rolls, by which it is brought into bar or plate iron. The term boiling refers to the bubbling which takes place during the process of conversion, and the word is somewhat local. This modification of the puddling-furnace was invented by Hall, and consists mainly in some differences in the proportion of the parts, the use of cinder, and of a greater heat.
The furnace is heated to an intense heat by a fire urged with a blast. The cast-iron sides are double, and a constant circulation of water is kept passing through the chamber thus made, in order to preserve the structure from fusion by the heat. The inside is lined with fire-brick covered with metallic ore and slag over the bottom and sides, and then, the oven being charged with the pigs of iron, the heat is let on. The pigs melt, and the oven is filled with molten iron. The puddler constantly stirs this mass with a bar let through a hole in the door, until the iron boils up or “ferments,” as it is called. This ebullition is caused by the combustion of a portion of the carbon in the iron, and as soon as the excess of this is consumed, the cinders and slag separate from the semifluid mass, which the puddler stirs and forms into balls of such a size as he can conveniently handle, which are taken out and carried on ball-trolleys to the squeezer.
