METEOROLOGICAL TABLE.

The London Observations by Mr. CARY, of the Strand. The Boston Observations by Mr. SAMUEL VEALL.

The quantity of Rain in London since the 26th Oct. amounts to 3 In.

PHILOSOPHICAL MAGAZINE

AND JOURNAL.

31st DECEMBER 1822.

LXXXII. On the Origin of the Blast Furnace.
DAVID MUSHET, Esq.*

By

Ir is a matter of considerable regret, to those interested in the rise and progress of our national metallurgy, that the comparative recent invention of the blast furnace should already be involved in so much doubt and obscurity; and that we should be unable to assign to it "a local habitation and a name.”

In the writings of the Saxon Agricola, published in the year 1556, there is no mention made of the blast furnace as known to us in after ages, as the means of making and procuring that strong but fusible state of iron now so universally used in every mechanical art and contrivance. Agricola describes the blast bloomery and the usual processes for obtaining malleable iron, but no where does he describe a process by which cast iron was obtained and applied to foundry purposes. He gives the detail, however, of a curious process for making steel, which renders it probable that the more fusible species of cast iron was not unknown in that day, though not used for the purpose of castings.

Pieces of the most fusible iron were introduced into a large crucible, in the hearth of the iron furnace, along with a mixture of flux and charcoal; the action of the bellows was directed so as to produce fusion; when this was ascertained, four pieces of bar iron, about 30lbs. each, were inserted in the fluid, where they remained for five or six hours, till they had nearly absorbed the melted iron. The masses of malleable iron, being thus penetrated, enlarged in size and became soft and pasty. The furnace-man then made a trial of one of the bars, placing it under a large or forge hammer. The cake while yet hot was plunged into cold water, and the fracture examined, to ascertain whether it had been all converted into steel: if this was not the case, a fresh fusion became necessary; and the imperfect steel was again inserted for a length of time sufficient for its perfect conversion.

Whether this fusible mixture was in the first instance gray * Communicated by the Author.

Vol. 60. No. 296. Dec. 1822.

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cast

cast iron, or iron containing less carbon, it will hardly be contended that it did not become so when fused in contact with flux, in a crucible containing pounded charcoal. Besides, it is not altogether improbable, that some particular qualities of ore, finely reduced and added in sparing quantities compared with the mass of the fuel (at that time the charcoal of wood), were found to yield, even in the low ancient bloomery, what is now so generally known to us under the name of gray cast iron. The cost of its production, as to fuel, time and labour, would confine its use to some rare and valuable purposes: and as we know of none more useful or more generally valuable in metallurgy than the manufacture of steel, it is probable that the making of the more fusible qualities of cast iron was for the exclusive purpose of fabricating steel; and it is also probable, that gray cast iron was discovered by endeavours to form a metal as fusible as the rude and limited nature of the operation would permit: the fusibility of iron being always in proportion to the quantity of carbon with which it is united.

No circumstance with which I am acquainted, conveys so lively a picture of the state of the arts, as far as regards the manufacture of iron,-than that the most enlightened nation in Europe, as to mining and metallurgy, should in the middle of the sixteenth century possess no other process for making steel, than the one described above; a process which, when performed in a manner much more perfect than that described by Agricola, is yet productive of an inferior and uncertain quality of steel; and in point of expense, compared with the present manner of making steel, utterly impracticable but for the purpose of mere experiment.

The perfection of such a process (however incomplete we may now consider it) may probably have led to a discovery of the manifold combinations of iron with carbon in the furnace : for as dark or gray fractured cast iron contained double the quantity of carbon that united itself to white iron, and four times the quantity contained in the crude steel (the natural product of iron ores when smelted in furnaces not more than three or four feet in height, as must have been the case in the blast bloomery)-so in the same proportion would it be prized, and found more valuable for the manufacture of steel.

For a great length of time, a fusion of this species of cast iron might have been considered as a sacred menstruum into which iron was plunged for its purification, to pass into the more noble, useful, and exalted state of steel. But as the arts advanced, and the genius of war revealed to her ambitious sons the direful effects produced by the inflammation of gunpowder in strong metallic tubes, the attention of the founder would

naturally

naturally be directed to every known state of iron, to prove its capacity for resisting the violence of the necessary explosion: and as œconomy seldom enters into the views of the warrior, quantity, more than the cost of production, would be the first object of consideration when experiment had determined the superior strength of carbonated cast iron, and its capability of being run or cast into form. The malleable iron artillery with its numerous hoops and cases would be abandoned, and the strongest sorts of cast iron sought after. Demand would sti-mulate the exertions of the iron-maker, who in time might be led to reason that a larger furnace might produce a larger quantity of iron. The old bloomery furnace would be enlarged: and as every addition to the size, by increasing the period of cementation and contact of the ores with the fuel, would not only increase the fusibility and strength of the iron by additional carbonation, but also materially reduce the cost of production,-a permanently enlarged furnace would be the consequence, though still possessing the form and proportions of the bloomery furnace. A decided advantage having been obtained by the enlargement of the furnace, in producing gray or fusible cast iron, it is probable this improvement would be pushed to the extreme; and long before any adequate improvement took place in the blowing machine, the soft and very limited quantity of blast that was found sufficient to penetrate a column of iron-making materials in the blast bloomery, three or four feet high, would be found of difficult ascent through a furnace of three or four times that height. The combustion would in consequence proceed languidly, the increased height and greater pressure of the ores would repress the blast as it entered the twyre, and a period of difficulty and distress be likely to ensue. In such an emergency as this, a suspending medium was probably first thought of, and introduced into the blast furnace; to which, at the time or since, has been given the name of boshes: these, by creating immediately above the twyre a lateral suspension of the entire column of smelting materials, removed the pressure from the central parts of the furnace, and allowed the blast to ascend with more freedom and effect. Whatever benefit was derived from the introduction of boshes into the earliest blast furnaces, it would soon be found, that although by their means quality of iron and regularity of process were obtained; yet quantity, which alone can yield profit, still depended upon some other cause. This evil would be partially remedied by the increase of the size or number of the bellows in those times, chiefly urged by the labour of man or the strength of cattle: but this would increase the number of labourers, the value of the operative

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operative stock, and create a great competition among all classes.

Independent of this, the effects of the intermitting and uncertain action of such a power on a large furnace, would entail difficulties of the most ruinous nature; and the iron-maker, at last forced to look out for a cheaper and more permanent blowing power, the rude machinery of the hand and foot blasts would be enlarged, strengthened, and transferred to the motion of the water-wheel. The advantages of local situations would be abandoned, and the iron trade pass from the township in the neighbourhood of the mines, to the banks of the adjacent streams.

In examining the sites of the oldest blast furnaces situated on the upper level of the brooks, the smallness of the stream and the uncertainty of the supply sufficiently indicate the limited operations of the early pig-iron maker; the small scale on which the machinery was erected; and the slow step by which improvement in some ages advances. So long as there was water in the brook sufficient to move the bellows with a certain effect, the operation of blowing continued; when this supply ceased, smelting was at an end for the season; and the labourers dispersed, some to the mines, and some to the woods to prepare materials for another blast.

The first furnaces seem seldom to have exceeded the height of fifteen feet, and six feet at the widest diameter; and the whole capacity not more than four hundred cubical feet. In after times, as machinery became enlarged and improved, and the operations of the furnace better understood, the blast furnace seems by common consent to have been removed to lower levels, where the confluence of several streams gave a more powerful and durable supply of water to the machinery. A good stream of water near to wood, in almost every instance determined the situation of the second and improved class of blast furnaces; locality to the mines was in many instances abandoned, and the ores were carried a distance of eight or ten miles to the furnace.

In the neighbourhood of the ancient forest of Sherwood, this fact seems particularly illustrated; the alluvial soil of that district furnishing only a few specimens of blood-stone, could not have supplied any quantity of ore for the smelting operations of the furnace: the supply of ore seems to have come from the basset edges of the argillaceous veins of ironstone which accompany the coal formation in Derbyshire. The same circumstance occurred in Monmouthshire; the ores of the Forest of Dean were in many instances carried to the furnaces, a distance of eight or ten miles.

The