lion is obtained from the ore by an operation called smelt ing, and in this state it is called cue-iron, or pig iron, hut it is very impure. The art of smelting iron was practised in this conntry during the time of the Homan uteen patiou and in many ancient beds of eitulers—the refuse of irun-works—Roman eying have been found. ']'he principal ancient seats of the iron manutheture in this country appear to have been the Sussex and the Forest of Dean. or Arden, as it was then called. It is known that iron storks existed in that part of Gloucestershbe in 1 ;2:_tS, because there occurs, among the patent-rolls of I I enry III. of that date, it led " De Fnrgeis let andis Ill Forestal de Dean." Remains of ancient iron-titrnaves have been noticed in Lancashire, Star fordshire, and Yorkshire. The art of working in iron and steel was nmelt praetised in this island bethre the Norman conquest; and we are nth). that not only was the army of Harold well supplied with weapons asteel and with defensive armour, bat that the hurses were riveted %%ith steel and iron armour ; and that every officer of rank maintained a smith, who constantly attendA his master to the wa•:, and to4tk charge of his arms and armour, to keep them in proper repair.
The iron of commerce is usually divided into two distinct qualities, viz., pig-iron, and malleable or bar-iron—the being the result of an extension of the processes necessary for the production of the first, The first process is that of reducing the iron stone or ore into a metallic state by means 1 If fusion. This operation is conducted in a biaSt-ItIVIIIICV, •hi•i is charged with certain proportions of iron-ore, of coke, and of limestone. The ore must previously have been roasted or calcined in a kiln, in order to drive out the water, sulphur, and arsenic. with N% hich it is more or loss combined in its native state ; by the process, it loses one-sixth part of its weight. A furnace the size commonly used in Wales will produce from 5 to i; tons of pig.iron in twelve hours. For the largest oplantity, the furnace must be charged progressively with IS tuns. of roasted t2:2-.1 tons of coke, and about of tons of line• stone. These ingredients are supplied at 50 eharges, and must be intimately mixed together in the furnace. The limestone must be broken into small pieces ; its Is to act as a flux, to the ore, and promote its fusion. The heat that would he produced in any furnace by merelv setting fire to the fuel which is contained io it, would he altogether insuffi cient for the fusion or the ore, Jr its intenseness were not promoted by the forcing in of a current or blast of air. Fur this purpose it is necessary to use a strong mechanical force, and, of late Years, the agency of steam has been commonly entph)yed for this purpose. This power is applied to the workiffir of a blowing cylinder, which may be timr times the area of the cylinder of the strain-engine. the blast thus produeed were passed ilinnediAel) from the blowing eylinder through the tnyi•es or tubes to the frnace, the effect WI mid be intermitting and irregular, ceasing at the end of each stroke of the steam-piston. To remedy this inconvenience,
the blast is carried into an intermediate chamber, of a spheri cal or cylindrical shape, called a legislator; aod as the air is in a state of el indensatiott when admitted, its effort to expand itself again to its natural volume causes the continuous mid regular supply to the furnace which is necessary. The air thus Mrced into the furnace keeps the heat at the degree of intenseness which is indispensable for the smelting of' the ore.
• t til the last few years, the air thus supplied was uniformly at the temperature of the atmosphere from which it was immediately taken ; and the effect was, not only to produce a lower degree of heat. but also to supply a quantity of moisture which is prejudicial to the smelting process.
The blowing of healed air has, however, recently been at several tiamderies, and likewise at the Clyde iron-works. This improvement is the invention or A. B. Nielson, of Glasgott, whose pateut was enrolled in 11arch, Is•9, and is designated an improved application of air to produre heat in fires, forges, and furnaces, where bellows or other !doming apparto ns is equired." Ile proposes, that the air s gybed by any kind of in whine shall, before it enters the or cupola. be made to pass through un air-vessel heated to very high temperatnre—a red heat, if pussi hle—by Which means a current of hot air will be thrown on the tire, instead of the cold current usually employed. It is recom mended that the air-vessel be surrounded with some non conducting substance, and imbedded in masonry. The capa city of this vessel for a smith's forge he recommends to be about 1.200 cubic inches ; and for a cupola or blast-thrnace, about 10.000 cubic inches. It was much doubted whether the increased temperature of the fire thus blown would pro duce advantages equivalent to the expense of constructing the air-vessel and keeping it at the requisite heat ; and, as respects the smelting of iron in particular, the theory seems opposed to the well-known tact, that a much larger quantity Jf iron is yielded by the blast-furnaces in the winter season, or when the air is cold, than during the summer season, w hen the air is warm. The experiment at the Clyde ironworks have, however, been reported most favonrably of; and the sat ing of coal attending it is so great, that it wits stated in the Wavyou, Chronicle to be calculated to accomplish a caving in the consumption of this island to the amount of £200,000 annually. At the Clyde iron-works, the air was heated to 220° Fahrenheit before it was discharged into the furnace— an etryct which was produced by the expenditure of only one-eleventh part of the cost of fuel it takes to heat it to the same temperature in the blast-furnace, which nay be accounted finr by the circumstance, that Mr. Nielson's air vessel is heated coals, while the blast-ffirnace is heated by coke. Further expel ience in this invention has fully eon finned the views of the patentee, and it must now be regardol 'as one, ut' the most valuable improvements in modern metal 'lurgic operations.