pieces, unroasted, but mixed with unslaked quick-lime, was laid on alternately with the charcoal. As soon as it had descended low enough to be within the immediate influence of the blast (which in a furnace of this construction would be in a few minutes) the lime and earthy part of the ore become fused into a slag, and enveloping the iron, now in a metallic state, , sunk down into the crucible, displacing the charcoal with which it had been at first charged. The matter remaining at rest in the crucible gave an opportunity to the particles of iron to sink to the bottom, which they did in greater or less proportion according to the fluidity of the slag and the completely metallic state of the iron. After this process had been going on for the space of from eight to twelve hours, the crucible became filled with melted matter at this time the hole which had been at first stopped up with clay was opened by means of an iron bar introduced through the channel in the brickwork, and the scoriæ immediately flowed out, leaving the iron behind covered with hot charcoal. The blast being stopped, the furnace soon got sufficiently cool to allow the workmen to take out the iron, which was found imperfectly concreted together into a mass nearly of the shape of a wooden bowl: this being transferred to an anvil was first carefully hammered with wooden mallets to break off the encrusting scoriæ and render it sufficiently compact to bear the tilt hammer, to which it was next subjected; being then divided into five or six pieces, each was separately forged into a bar, and thus the operation was finished. The iron thus obtained was extremely tough and hard, but difficult to work, and was in great request for helmets and ather articles of defensive armour, and in general for all purposes where toughness and hardness united were particularly required. The rich quality of the ore, and the circumstances under which it was reduced, were probably the chief causes of the excellence of this kind of iron; a peculiarity however in the method of forging it may also have somewhat contributed to this; for, while it was under the tilt hammer, an assistant stood by with a ladle of water, with which he sprinkled the bar as often as it was struck by the hammer.

The poorer ores, which were incapable of being smelted in the above method, were first picked, washed, and roasted, then reduced to pieces no larger than hazle-nuts, and reduced (no doubt with the addition of lime) in blast furnaces from seven to eight feet high and shaped like a chimney. In these a considerably greater heat could be produced than in the former, but it does not appear that the metal when taken out of the furnace was in the state of cast iron; certain it is that it was always allowed to cool there, and was never run into pigs as is the modern practice.

However simple this process may at first view appear, it is attended with some very serious practical difficulties, and we may now describe another method by which the richer veins of iron ore may be worked. The ore being broken into small pieces is heaped upon a bed of charcoal in a very simple reverberatory furnace.

When the whole has been glowing hot for some time, the pieces, being now soft and at a welding heat, are by the dextrous management of the workmen brought in close contact with each other by means of an iron bar; they are then lightly hammered while still in the furnace, and thus the whole mass acquires sufficient compactness to be removed to the anvil without falling to pieces; it is now hammered with a gradually increasing force, the earthy impurities are thrown off, together with the scales of black oxide; the lump is divided into pieces of a convenient size, which by repeated heating and hammering are drawn into bars. The rich red hæmatite, as appears from an experiment of Mr. Mushet, is capable of being manufactured in the same way.

These ancient methods have fallen into disuse, not because the quality of the iron thus produced was objected to, but because the time and fuel consumed were enormous, and the iron that remained in the scoriæ àmounted at least to one-half of the original metallic contents of the

ore.

When iron-stones are said to contain good or bad iron, the expression ought to be understood as a comparative assertion, confined to local rules, and judged by certain fixed local standards; into the account of which many things must be taken, which are frequently overlooked. At every iron-work, a certain portion of fuel, coke or charcoal, by weight, is understood to be sufficient to smelt and manufacture a determinate weight and quality of iron-stones combined together, in order that a certain quality of crude iron may be produced. In this case, should a new iron-stone be substituted for one whose quality and effects are already known, and should its application be productive of iron less carbonated than formerly, it would instantly be denominated a bad iron-stone, or an iron-stone containing bad iron; an assertion only true comparatively so far as it would affect the interest of the manufacturer, unless corrected by an addition of fuel, a change of the mixture of ores, or a varied application of the lime-stone used as a solvent or flux. But this is no proof that the quality of iron, as it exists in the ore, is bad, since a larger proportion of coke, or a change of mixture, which incurs no additional expense, can correct the evil. It rather furnishes a demonstration that the iron in all ores is the same; but that, in calling it into a metallic form, the quality is affected chiefly by the reduction of those mixtures originally united with it.

Taking as a general principle that the crude iron contained in all iron-stones is the same, and that it can be called into existence as a metal of all the various degrees of carbonation, by regulating the proportion of fuel and of the solvent, we shall proceed to mention those mixtures which determine the future quality of the crude iron.

1. Argillaceous iron-stone having fine clay as its chief component earth, lime in the next proportion, and both these nearly destitute of sand; which, when properly torrefied, exhibits fibres on its internal surface, of a brown, dark brown, or claret color, running either in streaks or ra

diated, and adhering tenaciously to the tongue, will afford, with a moderate proportion of cokes and lime-stone, iron of the finest quality, possessing strength conjoined with an intimate degree of fusibility.

2. Calcareous iron-stone, that which contains lime as its principal earthy mixture; holding clay in the next proportion, and both these comparatively unalloyed (totally they never are) with sand; which, when regularly torrefied, assumes a variety of shades generally lighter in the color than the former class, which sometimes, and sometimes not, presents internal fibres, and which adheres less tenaciously to the tongue; always contains iron which can be revived, richly carbonated with a comparatively small quantity of cokes, and with a trifling addition of lime. Under this class of iron-stones are found those which produce iron of a fusible nature, seldom connected with strength, but valuable for its utility in fine castings, which require ornament more than durability.

3. Those iron-stones whose component parts are nearly an equalised mixture of clay, lime, and sand, which torrefy with a slight degree of adhesion to the tongue, assuming a darkened or brownish color, void of every internal fibre, always afford, with the local proportion of fuel, iron of an intermediate quality for fusibility and softness, but generally possessing strength in an eminent degree. Such iron is excellently adapted for the manufacture of great guns, mortars, and the large species of machinery. Its application to the purpose of bar-iron making would also be attended with the most beneficial effects, possessing neither the extreme of fusibility nor of infusibility: it would greatly prevent, in the manufacturing, a tendency, which iron possessed of these extremes has, to become red or cold

short.

4. Iron-stones which unite a large proportion of sand with sparing portions of clay and lime, which, upon being slightly exposed to heat, exhibit masses of semivitrification, neither obedient to the magnet, nor adhesive to the tongue, having a refractory disposition to part, and possessing a dark blue or blue color, always afford, with the usual proportion of fuel, crude iron of the worst quality, either as to strength or fusibility. Such metal is commonly highly oxygenated and brittle; incapable of being used alone for any melting purpose; and, when applied to the use of the forge, affords malleable iron, which possesses the cold short quality.

These are the four principal classes under which Mr. Mushet has arranged his iron-stones, with regard to their tendency to afford their iron carbonated, possessing strength, or otherwise, when smelted in the brass furnace with a determinate quantity of fuel. As this classification is exactly analogous to the results obtained in the large way, it may serve as a groundwork to those who may wish to attain a practical knowledge of these ores, so far as it relates to their manufacture.

It is, however, easy to counteract the natural tendency which every iron-stone has in this case, to afford its iron of a certain quality, and to make each of them yield crude iron of all the

different degrees of fusibility and strength. Is it not obvious, since the qualities of crude iron depend upon the mixtures and their kinds composing the stones, that, if nature be assisted by adding or subtracting from them in the blastfurnace, every quality of crude iron may be produced from the same iron-stone?

The usual criterions by which iron-stone is judged, whether it be sufficiently rich in iron for the purpose of smelting, are the following

1. The degree of tenacity with which it adheres to the tongue after torrefaction. 2. Its color. 3. The obedience to the magnet when pulverised. 4. By depriving of its iron a given weight of the ore, in contact with charcoal and fusible earths in the assay furnace.

The first and third of these methods are liable to great error. The adhesion to the tongue will be more in proportion to the quantity of clay and its kind contained in the stone, than to its real contents in iron. Iron-stone may also be torrefied in such a manner as to deprive its internal surface of this property; as it is only peculiar to the stone at a certain stage of torrefaction.

The influence which the magnet possesses over some ores of iron is no direct proof of the quantity of iron contained, as some ores which contain fifteen parts in 100 are completely magnetic, while others again that contain sixty to seventy parts of iron in 100 are not in the smallest degree affected with this property. The magnetic test is more used to ascertain the existent state of the metal, whether mineralised with an acid, combined with sulphur or with oxygen, or existing in a disengaged state more or less metallic. No iron-stones, which in their native state contain their iron mineralised with oxygen, or in the state of an oxide, completely dispersed through an intimate combination of clay, lime, and silex, containing water, carbonic acid, and sometimes concrete sulphur, are obedient to the magnet till such time as torrefaction has passed upon them, either exposed to open air, or in contact with charcoal in close vessels. If this process is continued for a short time, the whole mass will become obedient; but this affection will still depend upon the relative quantity of concrete oxygen fixed with the iron. Individually, however, iron-stones are affected by the proportion of heat conveyed to them while torrefying. If the quantity communicated has been sparing, so as not to have carried off all the water, carbonic acid, &c., the magnetic virtue will also be proportionally absent; if the dissipation of these substances has been complete, the magnet will possess an influence in the exact ratio of the quantity of oxygen which remains combined with the metal. Should it happen that a degree of heat, capable of exciting fusion, is applied, the mass will then rapidly lose its magnetic obedience by an extra-fixation of oxygen; if driven so far as to make it exhibit a semi-vitrified appearance, this principle would be found to be entirely annihilated.

Although the color which iron-stones assume in torrefying intimately depends upon the degree of heat presented to them in the operation of burning, yet, by regulating this agent in a