The American Quarterly Review, No. 18, June 1831 (Vol 9)

by Various

Coke being more dense than charcoal, will, in its combustion, furnish a more intense heat;—hence it is hardly possible to obtain by a charcoal fire, iron of as deep a colour as may be procured by the use of the former fuel. It will also resist the pressure of far greater weights than charcoal, and hence the proportion of ore may be much greater when it is used; containing more and less fusible earthy matters than charcoal, it requires a greater quantity of flux.

In the manufacture of cast iron then, coke gives iron better suited for small castings, for those which require turning or filing, and yields a far greater quantity from a furnace. Hence arises the very great superiority which Great Britain has, until recently, possessed over most other countries, in those fabrics in which these qualities are valuable; and hence it has been found until lately, in this country, hardly possible to manufacture fine machinery that requires workmanship after it is cast, without the aid of the higher qualities of Scotch iron, which, in these qualities, exceeds even the English. Recently, however, iron fully equal to the best Scotch, but like it wanting in tenacity, has been manufactured at the Bennington furnace in Vermont:—so also at the Greenwood furnace in Orange county, N. Y., and at West Point, iron approaching to the Scotch in softness, but very superior in strength, has been produced. In these cases, the height of the furnace has been carried up to the limits we have before laid down, and powerful blowing cylinders substituted for the ancient bellows.

When the pig iron is to be used for re-casting, every effort ought to be used to obtain it of the deepest possible colour. This, as may be seen from what has been already stated, will be effected by keeping the furnace at the highest possible temperature, and exposing the metal to it a sufficient length of time. In effecting this, however, certain defects may arise:—thus a longer exposure to a high heat, will cause the reduction of other oxides that may be present, as of manganese and the metallic bases of the earths; and the iron in becoming more soft, and approaching in fact more nearly to the form of the pure metal, will combine and form alloys with these bases. In this way, it will, as has been stated, become cold short; and to this may be attributed the want of strength in the greater part, if not all, of the British iron. The use of coke as a fuel, tends to increase this defect, in consequence of the great quantity of earthy matter it contains.

When the ores are pure, cast iron manufactured by charcoal, is not liable to such a fault. Hence the cast iron of Sweden and the United States, manufactured from the magnetic iron, or, in some cases in this country, from rich hæmatites, has very superior tenacity, insomuch that these two nations have alone been able to use this material in the construction of field pieces. When white iron is obtained from a furnace, it may have two different qualities. The first arises from a mere defect of heat, where all other circumstances are favourable, and the ore is completely reduced. The second arises when the reduction is not complete, and the separation of the earths and other oxides has not been fully effected. Of all the varieties of cast iron, this latter is by far the worst. It is indeed more easily converted into wrought iron than the other species, but the product is always of very inferior quality; it is rarely or never produced by furnaces fed with charcoal, but may be obtained by accident or design in those where coke is used, by a surcharge of ore, or by too great a proportion of flux, and sometimes cannot be avoided in warm and moist weather, where the air is rarefied and charged with vapour.

The grey iron obtained by the use of each of the different kinds of fuel, has its own peculiar advantages; that made with coke possessing, as a general rule, when melted, a higher degree of fluidity which adapts it for more delicate castings; being softer and better suited for fitting; while that manufactured with charcoal, possesses a greater degree of strength. One solitary instance has been quoted, in which a manufacturer of great intelligence has obtained by the use of charcoal, from a very pure ore, a union of both these valuable properties, and another, in which iron as soft as that made with coke, has been produced by means of charcoal.

In spite of this apparent balance in the properties of the two fuels, the introduction of coke into the art of reducing iron has been attended with the most important advantages. These lie in the superior economy of the process, and in the enormous quantity of the product. The manufacture of iron by charcoal is limited, by the growth of the forests, which replace themselves only at distant periods, by the large space they occupy, and the consequent labour of transportation; by the cost of cutting the wood and preparing the coal; and finally, even when the fuel can be obtained in abundance, and at small cost, the burden of the furnace, and the heat obtained in a given space are less than when coke is used, and the quantity of metal yielded is in consequence comparatively small. The coke furnaces of Great Britain, have therefore supplied cast iron in such abundance and at such diminished prices as to have brought it into use for a great variety of purposes, to which, until recently, it was hardly considered applicable.

In England, as in other countries, charcoal was the only fuel at first used; and after bloomeries had been in vogue for centuries, the blast furnace was introduced from the shores of the Rhine. For many years the growth of the forests proved sufficient to supply the demand, but at length the increase of population caused them to be encroached upon by cultivation; the growth of the manufacture was first prevented, and finally, almost extinguished.

The method by charcoal appears to have reached its acme of prosperity, at the close of the reign of the First James, when the furnaces of the kingdom yielded 180,000 tons of pig iron. About this period, Dudley first proposed the use of pit coal; but the time had not yet arrived in which it was absolutely necessary to seek for a new process, in consequence of the failure of the old one.

In 1745, or in the course of one hundred and thirty years, the forests had been so far encroached upon, that the product of the furnaces had fallen to 17,000 tons per annum, and in 1788, the quantity made with charcoal had dwindled as low as 13,000 tons. At this epoch, coke was introduced into blast furnaces, and in eight years the whole quantity produced by both methods had mounted up to 150,000 tons, or increased more than tenfold.

At nearly the lowest ebb of the British manufacture, the art of preparing iron was introduced into her then provinces, the present United States; and in 1737 it was attempted to obtain permission to introduce the product into England. The attempt failed, and in 1750 an act was passed to protect the exportation of English iron to America, and to prevent the establishment of forges. Had the other policy prevailed, England would probably have seen her manufacture of iron transferred to the United States, and with great immediate advantage both to herself and her then most valuable colony; but she would probably have seen herself at the present day degraded from her high stand in the scale of nations, to the secondary place in which the extent of her territory would keep her, were it not for the superiority of her manufacturing industry, of which iron is the basis. The quantity of iron now produced in England, exceeds that furnished by the rest of the world united, and does not fall short of 800,000 tons. It has a value even in its raw state of near four millions sterling, and is of far greater intrinsic worth, in consequence of the spur which its abundance gives to every other branch of industry.