BLAST FURNACE. Many costly experiments have been tried of late years in order to determine, along with other related questions, the hest form of the blast furnace in which iron is smelted. Which is the most serviceable form is as yet a very much disputed point; but, according to the pub lished accounts, furnaces of the unusual height of 80 to 100 ft. give, as a rule, the best results. There are two types of blast furnaces, irrespective of differences in their forms, as regards the way in which they are con structed. Some are built with thick walls, either entirely of brick or of brick and stone, hooped with iron, forming massive towers. Others, again, are formed of comparatively thin brick walls, and depend for their strength on an outer malleable iron casing, in which case they are called cupola furnaces. The fur nace A., in fig. 1, article 'cox, is an example of the former. and the annexed figure represents one of the latter kind.
The various parts of the furnace are distinguished as follow: A. is the shaft or body, generally either in the form of a cone or cylinder, or somewhat barrel shaped, in which case, the portion marked B is not distinguishable from the shaft. B. is called the bodies, and is the part of the furnace which, from the high heat to•which it is exposed, usually gives way first. fr
is the hearth, and 0 is the tunnel-head, which, how ever, is usually wanting when the mouth is closed by a bell and cone to save the gases generated in the fur nace. P is the charging platform, and Q, Q, the openings through which the ore, fuel, ete., are fed. These materials are brought to the platform by hoists, inclines. or level gangways, according to the situation of the furnace. Just below the Noshes there are four or five openings in the circumference of the tuyeres t, and another for the arrange ments required for tapping, the furnace. As respects the latter, a is called the tyrup arch, immediately below which is placed the lynzp its:lf, consisting of a rectangular iron box containing water in a coiled pipe. The hearth is prolonged in the direction of the damp-plate d, and the space between it and the tymp is filled up witli sand or clay, in which there is a channel for the escape of slag. In the damp-plate is pla.xt: Pie tapping hole, i, through which the molten iron is run off. The pipe at p conveys the blast, pro duced by a powerful blowing-engine, and heated to between 600° and 1400° F. In 1875, there were in Great Britain 093 blast-furnaces. See IRON.