IRON MANUFACTURE. The art of smelting iron was practised in this country during the time of the Roman occupation, and in many ancient beds of cinders, the refuse of iron-works, Roman coins have been found. The principal ancient seats of the iron manu facture in this country appear to have been Sussex and the Forest of Dean, or Arden, as it was then called. Remains of ancient iron furnaces have been noticed in Lancashire, Staffordshire, and Yorkshire. The art of work ing in iron and steel was much practised in this island before the Norman Conquest. At the present day the chief iron manufacturing districts in this country are the Lanark district of Scotland, South Wales, and South Stafford shire; the works distributed in other parts of the kingdom are much less extensive, though many even of these are of great import ance.
There are two distinct qualities into which this metal is commonly divided, viz. pig-iron. and malleable or bar iron, tiro socopti being the result of an extension of the processes nem sary for the production of the first kind.
The first process is that of reducing the iron-stone or ore, or, as it is technically called, the mine, into a metallic state by means of fusion. This operation is conducted in a blast smelting-furnace. [FURNACE.] The furnace is charged from the top with certain proportions of iron ore, coke, and lime stone. The ore is previously roasted in a kiln, in order to drive off the water, sulphur, and arsenic, with which it is more or less combined in its native state : by this process it loses one sixth part of its weight. A furnace of the size commonly used in Wales will produce from 5 to 0 tons of pig-iron in twelve hours. For the largest quantity the furnace is charged progressively with 15 tons of roasted iron ore 221 tons of coke, and about 6 tons of lime: stone. These ingredients are supplied at charges, and are intimately mixed together in the furnace. The limestone is broken into small pieces, and is used to act as a flux to the ore and promote its fusion. The heat that would be produced in any furnace by merely setting fire to the fuel which is con tained in it would be altogether insufficient for the fusion of the ore, if its intensity were not promoted by the forcing in of a current or blast of air. For this purpose it is necessary
to use a strong mechanical force, and of late years the agency of steam has been most com monly employed for this purpose. The blast is carried into an intermediate chamber of a spherical or cylindrical shape, called a regu lator; and, as the air is in a state of conden sation when admitted, its effort to expand itself again to its natural volume causes the continuous and regular supply to the furnace which is necessary. The air thus forced into the furnace keeps the heat at a degree of in tenseness which is indispensable for the smelt ing of the ore. A most important improve ment was made by Neilson, some years ago, in using the hot blast instead of the cold, that is, drying and highly heating the air be fore it is forced into the furnace. This has proved to be the most valuable and economical of all modern inventions in the iron manufac ture.
The iron is run from the furnace every twelve hours, by tapping the front of the fur nace on a level with the bottom of the hearth. When the furnace is tapped, the metal is allowed to run into channels formed in the sand of the smelting-house floor. The names of sew-metal and pig-metal, which were origi nally given by the workmen, signify in one case the blocks of iron which arc formed in the large main channels, and in the other case the smaller blocks which are formed in smaller side channels communicating with the larger ones.
The quality of pig-iron varies according to the purposes for which it is intended, and depends not only upon the quality of the ore, but also upon that of the fuel. The principal division is into foundry-iron and forge-iron, the former being used for castings, the latter for conversion into malleable iron. Foundry-iron is further divided into three qualities, distin guished by the numbers 1, 2, and 3, and dif fering in the amount of carbon combined, the fluidity when melted, and the hardness when cooled. Forge iron is divided also into three qualities, and is distinguished as bright iron, mottled iron, and white iron, which names are indicative of the appearance which each quality presents to the eye ; they have less carbon, less fluidity, and more hardness, than foundry iron.