CUPOLA, in metallurgy, a tall tubular structure built of steel plates and lined with firebrick. It is employed in iron foundries to melt pig and scrap for the castings, or pig-iron in steel works for the Bessemer converter. Dwarf cupolas for small requirements are about aft. 6in. in diameter and 'oft. high, melting from i o to i 5cwt. per hour, while on a large scale the dimensions may reach 9ft. and over 4oft. respectively, having capacity of 3o tons per hour. A bed charge of coke is first laid at the bottom and then alternate layers of iron and coke, which are thrown through the charging door, the furnacemen standing on the charging-platform. Supplies are brought up by a crane or a cupola-hoist. Blast to furnish means for increasing the com bustion is sent in from a fan or blower, through tuyeres commu nicating with the interior of the furnace, these being made with flaring mouths to soften the force. An air-belt generally surrounds the tuyere zone, so as to conduct the air to the tuyeres in an ade quate amount at uniform pressure. The molten metal is either tapped directly from the cupola, or flows into a receiver, which keeps it hot, and ready for drawing off supplies as required. This is the type shown in the diagram. Some cupolas are solidly built at the bottom, but a better style is with drop-bottom, which has hinged doors kept up by a catch. At the end of the melting process the catch is released, from a safe distance, and the doors fall and with them the slag, residue of iron and unburnt coke, the two lat ter items being put •in again at the next blow. A spark-arrester is fitted on the top of a cupola when there is risk of fire to adjacent buildings, or the flying grit is objectionable. A large cupola is more economical to work than a small one, hence the consump tion of coke varies in different cases, from i 4cwt. to 4cwt. per ton of iron melted ; this relation is termed the melting-ratio. (See