Indian Science and Technology in the Eighteenth Century: Some Contemporary European Accounts c24: XVI. Manufacture of Bar Iron in Southern India

Indian Science and Technology in the Eighteenth Century: Some Contemporary European Accounts c24

Language: English

XVI. Manufacture of Bar Iron in Southern India

c24.2

(*By Captain J. Campbell, Assistant Surveyor General, Madras Establishment. (A.D. 1842).)

1. In the commerce between India and England, a source of deep injury to the former country arises from England having deprived her of the trade in cotton cloth, the manufacture of which was, but a few years ago, one of the most valuable and extensive of Indian products; while from no other having been as yet introduced as an export to balance the imports from England, it has become necessary to drain India of her specie to pay the expenses of the Government, and for the articles she requires from the mother country. The Government both in England and in India have therefore been unremitting in their endeavours to promote and foster the export trade from India; and in the mean time have endeavoured to economise by means of the internal productive resources of the country, and thus in some measure reduce the export of specie, and at the same time disseminate a knowledge of practical manufacturing processes.

c24.4

2. Among the most extensive of the exports of England to India, is the trade of bar iron, which to Madras alone amounts to 1,000 tons per annum; and while India is known to produce malleable iron of a superior quality, it has been frequently proposed as a question whether she could not supply her own wants in this article at a cheaper rate than if procured from England, if improved processes were introduced in the reduction of the native ores. I am not aware that any satisfactory experimental investigation of this point has ever been instituted, or given to the public; but from the remarks in the reports of the Committee for investigating the coal and mineral resources of India, it would seem that little or nothing is as yet known upon the subject.

c24.5

3. English iron is not used inland in Southern India, in consequence of the great expense of land carriage, and from the same cause, it is probable, that in Northern India also, the only iron used is that made upon the spot; and as the manufacture must be very limited in quantity (‘quality’ in original; appears to be a misprint.—Editor.), it becomes of much importance, both to individuals and to the Government, to be acquainted with the mode of supplying any extraordinary demand. Indeed, we are informed by Captain Drummond, in the Journal of the Asiatic Society of Bengal, that the carriage of a suspension bridge erected in Kernnon, alone cost about 80 rupees per ton, or as much as the iron might have been made for upon the spot.

c24.6

4. In projecting the establishment of a new manufacture, persons are but too prone to copy an old established process, without studying sufficiently the principles by which the result is produced, so as to be able to modify the mode of operation to suit the resources of the locality, and the capabilities of the workmen; and because the English mode of manufacturing iron has been found to be the most profitable in England, it has been supposed that a similar process could alone answer in India. This process has also been styled ‘scientific’, but the fact is, that the principles of the mode of operation are still totally unknown, and the manufactures are not only unable to produce at pleasure a certain result, but even the quantities of the results produced depend upon the weather, and other causes as yet not explained, or beyond the control of the workmen. We do not as yet even know what cast iron is; nor with any certainty what its component parts are; nor in what it differs from steel, or the varieties of what are generally called carburets of iron. On this point Barlow remarks: (Encyclopedia Metropolitana) ‘There is certainly much to be learned in the iron trade, before we can boast of any thing like a complete knowledge of its different processes. We observe many facts in this, as well as in other branches of the manufacture, of which, the most we can say is, that they are connected with, or caused by certain other accompanying facts, though we are ignorant how this connection exists; often, indeed, our knowledge does not extend so far.’ Again, ‘it is, however, so difficult to follow up chemical analysis, and to obtain results with minute accuracy, in a process requiring intense heat, that hitherto the phenomena attendant upon the refining of pig iron, and its conversion into bars, may be said rather to be guessed at, than perfectly explained.’ Upon the same point also Dr Ure remarks: (Dictionary of Manufacture) ‘but philosophers have been, and still are, too much estranged from the study of the useful arts, and content themselves too much with the minutiae of the laboratory and theoretic abstractions.’ Such being the state of our present knowledge of this subject, it may be doubted if a careful examination of the principles of the long established, cheap, and simple mode of manufacture of the native of India, might not lead to improvements and modifications, which would be found to answer better, than the operose methods of the English manufacture, which require much capital, costly building, and a considerable trade to make them profitable.

c24.7

5. In England the fuel now most generally used in smelting the impure iron ores of the coal fields is coke; and the ore after being first roasted to separate the volatile impurities, as much as possible, is exposed to its action in blast furnaces, generally about forty-five feet in height, but varying sometimes from thirty-six feet to even sixty feet. In the middle, these furnaces are about twelve feet in diameter, but at top are contracted to about four feet, and at bottom, where the blast of air is introduced by pipes from powerful blowing machines, the diameter is only about two feet. The pressure upon the air forced into the furnace is about three pounds upon the square inch, and the quantity of air amounts generally to as much as 4,000 cubic feet per minute. The cast iron as it forms, falls down into the bottom of the furnace; which is always hot enough to maintain it in a state of fusion; where it is protected from the action of the blast by a covering of fused slag which floats upon it. These furnaces are kept in action unremittingly, night and day, for several years together; the metal being allowed to flow out every twelve hours in quantities of about six tons at a time. The material used in building the blast furnace is principally fire brick, and a pair of furnaces cost upwards of £1,800 sterling. The proportion of coal used in making a ton of cast iron, varies very much, from three tons in Wales, to sometimes eight tons in Derbyshire; but the use of heated air in blowing the furnaces has very much increased the quantity of the products of the blast furnace, and has also diminished the expenditure of fuel, but the quality of the cast iron is said to be deteriorated. The estimated expense of making a ton of cast iron is about £3 sterling.

c24.8

6. For converting cast iron into bar iron, the first process generally employed in England is called ‘refining’, and consists in fusing about a ton of cast iron at once in flat open furnaces about three feet square, where it is exposed to two hours or more to the action of a strong blast, by which it is supposed a portion of the carbon it contains is burnt off. Much gas escapes from the surface of the metal during the operation, and a large quantity of black bubbly slag separates, after which the metal when run out and allowed to cool, has a white silvery appearance, is full of bubbles, is very brittle, and has acquired the property of hardening by being suddenly cooled. In ‘refining’, about four or five hundredweight of coals is used to the ton of cast iron, and the metal loses from twelve to seventeen per cent of its weight.

c24.9

7. The ‘refined’ cast iron, now termed ‘fine metal’, is then exposed in a reverberatory furnace, called the ‘puddling furnace’, to the action of the flame of a large coal fire, by which it is first partially melted, then falls into a coarse powder; and on being stirred up and presented to the flame, becomes at last adhesive and tenacious. It is then formed into large balls, and after receiving a few blows from a large hammer to consolidate it, is passed between rollers which squeeze out much of the impurities, and form it into ‘mill bar iron’. This is however too impure for use, and it is necessary to cut the rough bars into pieces and to weld them together afresh, in a ‘reheating furnace’, and expose them to another rolling, and even to repeat the operation a third time, before good tough bar iron is produced. In the ‘puddling furnace’ about a ton of coals is expended to each ton of ‘fine metal’, and in the ‘reheating furnace’, about 150 pounds more are expended; and in each operation a loss of about ten per cent takes place in the weight of metal operated upon.

c24.10

8. Upon an average about nine tons of coal are expended in England in forming one ton of finished bar iron, and it is probable, that if the above processes were attempted upon any smaller scale than that of the English works, a still greater quantity would be used. Some of these works cost £27,000, and turn out 120 tons of bar iron per week.

c24.11

9. In France, Sweden, Norway, and parts of Germany, the fuel principally used is charcoal, and the ores are pure oxides of iron; the furnaces are about thirty feet in height, and in shape resemble in great measure the blast furnaces of England. Leathern forge bellows are frequently used to blow them, and the results vary from five hundredweight of cast iron per day, to sometimes five tons. The quantity of charcoal used also varies very much, from one and quarter ton, to two and half tons for each ton of cast iron, according to the nature of the mineral oxide smelted.

c24.12

10. The cast iron thus made is treated with charcoal in a refining furnace, not differing much from the English ones, but the metal is not allowed to run out, the operation being continued for nearly five hours, until the metal has become tenacious and adhesive, when it is removed in lumps of about two hundred weight each, which are forged under a large tilt hammer, then cut into smaller pieces, and is drawn out into bars at once. In this process the metal loses about twenty-six per cent of its weight, and 149 pounds of charcoal are consumed for every 100 pounds of iron produced.

c24.13

11. Formerly a kind of furnace called in Germany a ‘steuck often’ was sometimes used, which was from ten to fifteen feet high, and three feet in diameter, resembling very much an iron founder’s cupola furnace, but with a larger door, which was broken open after the operation was finished, which required about twelve hours, and the lump of cast iron weighing about a ton, was removed with powerful tongs to the refining furnace. The quantity of charcoal used was from two and a quarter to three and a half cwt. for every cwt. of cast iron, and about one and half cwt. more was required in the refining and forging, making the whole expenditure from four to five cwt. for every cwt. of bar iron.

c24.14

12. In some parts of France, malleable iron is made at once from the mineral oxides of iron, in what are termed ‘catalan forges’, which are cavities about 16 inches square, and two feet in depth, sunk in the floor of the workshop, the blast being thrown in by a pipe sloping towards the bottom of the furnace. The cavity being filled with charcoal, the ore is added in small quantities, alternately with fresh charges of charcoal, and in about five or six hours a lump of iron is procured, weighing from two to four cwt. which is removed, and forged at once into bars. The expenditure of charcoal is very great, amounting sometimes to eight times the weight of the iron procured. But when wood is cheap and abundant, there can be little doubt this process would be a convenient one for smelting any of the mineral peroxides of iron.

c24.15

13. The mode of smelting iron used by the natives of India, appear to be very much the same from the Himalayas down to Cape Comorin, and in some degree resembles that alluded to in paragraph 11.

c24.16

The ore principally used is either the common magnetic iron sand found in the nullahs, or else pounded magnetic iron ore, separated from the ferruginous granite, but I have seen specular iron ore used by the Konds of Goomsoor.

c24.17

14. The material used for the native furnaces, is the common red potter's clay of India, which unless carefully selected, is not generally very refractory, and will hardly stand a heat sufficient to fuse cast iron, but by mixing it with sand, and by concentrating the heat in the centre of the furnace as much as possible by a projecting blast pipe, the reduction of the ore is effected before the furnace has become much more than red hot; the operation being completed in about a couple of hours.

c24.18

15. In constructing these furnaces, a platform about two feet square and five inches thick is first made, with a hole in the centre nine inches in diameter. A half-cylinder or curved piece is then formed also of the red clay, eighteen inches high, four inches thick, and thirteen inches diameter inside, and the same depth, and also a cone about two inches thick of the same height, and the same diameter at bottom, and seven inches at top. When these are quite dry, a little wet clay being put round the hole in the platform, the half-cylinder is placed upon it, and the open front is built up with clods of clay, and the inside part is plastered for two inches thick until a hollow cylinder is produced, about twenty-three inches deep, nine inches in diameter inside, and about six inches thick. When nearly dry, an arch is cut out in front at bottom about nineteen inches high, to form the door of the furnace. The cone is then placed on the top, and the inside plastered with clay to correspond with the bottom part, and the neck or throat reduced in the same way to about five inches diameter. The upper part of a chatty with the neck is then placed inverted on the apex of the cone, to form a funnel to conduct the charge into the throat, and the chatty and the whole of the outside of the furnace is then plastered over with clay about two inches thick, so as to give the appearance of a large sugar loaf enlarged a little at the point. When finished, the height inside from the bottom to the neck is about three feet ten inches, and the whole takes about a week to finish before it is quite dry.

c24.19

16. The blast pipe is a cylinder of dried clay fourteen inches long, and about four inches thick, pierced with a hole of an inch in diameter. It is introduced into the furnace at the bottom of the door, with the point about the centre of the furnace, and about five inches above the bottom. The door is then closed with a tile of dried clay, and the outside is built up and secured with wet clay plastered over, a layer of charcoal dust, about two inches thick, having been first placed at the bottom of the furnace to prevent the reduced oxide adhering to it.

c24.20

17. The bellows are two goat skins taken off the animal, by opening the hinder part only. The orifices at the legs are sewn up, and a piece of bamboo is inserted, and tied tightly into the neck of each skin, and these bamboos being inserted into the outer part of the blast pipe, which is made conical for that purpose, the vacant openings are then stopped with wet clay. The open end of the skin is finished by folding the edge of one side, as a flap, about four inches over the other edge, and sewing up the upper and lower corners, so as to leave a part of both flaps open for about nine inches. When the skin is filled with wind, and pressed, the inner flap closes therefore against the outer, and stops the passage. Each skin is managed by one man, who places it in his lap, and squeezes it down with the elbow and lower part of the right arm, grasping at the same time a projecting sort of handle of leather, formed at about the part where the tail of the animal might have been. To enable the blower to fill the skin again with wind, a piece of string is attached to the lower corner of the posterior part, which is tied to a peg driven into the ground about a foot behind the man's elbow, and keeps the skin distended to its full extent as it lays in his lap; and a loop of leather is also fastened to the outer flap, through which the arm is passed, by which the opening into the skin is distended upon raising the elbow; and the skin being pulled out horizontally by the neck in one direction, and the string and the peg in the other; upon pulling up the middle part vertically by the leather grasped in the hand, the skin is opened out into a triangular shape, and fills with wind through the open flap. While squeezing one skin in blowing also, by pressing the hand forward, so as to pull against the string attached to the posterior part, the valve flaps are made to close fairly and properly, so as to allow hardly any wind to escape. The left hand is employed in assisting the right, or in squeezing the distended parts of the skin upon the side. It will be observed, that as both the necks of the skins open into the blast pipe, a portion of the wind expelled from one skin passes back again into the other; as they are worked alternately, a defect which might have been remedied in a most simple manner, by attaching little hanging door valves to the ends of the pipes.

c24.21

18. A small quantity of charcoal being thrown into the furnace, the fire is introduced, and the blast commenced, and the furnace is filled to the neck with about twenty-six pounds of charcoal. In about half an hour flame issues from the throat, and the fuel begins to sink, at which time the charge is commenced, which consists of ten pounds of charcoal and five pounds of ore, wetted to prevent it running down too fast. The charge is repeated seven times, and the furnace is allowed to burn down, and in about two and a half hours as soon as welding heat sparks are seen to issue with the flame, the bellows are removed; the door broken open; and the lump of reduced iron is removed, and cut open while hot with a hatchet, to show the quality. Four men are required to work one of these furnaces, one being a maistry superintendent, and the other three labourers, and they are able to make about three lumps in a day of twelve hours, but after four days’ work, the lining of the furnace is destroyed, and requires renewal.

c24.22

19. The lumps which result from the native furnaces weigh about eleven pounds, and are sold sometimes at the rate of two annas each. They are not, however, all iron, and on bringing them to a welding heat in a forge, a large portion consisting of fused oxide, melts away, and the best lumps I have examined yield only about six pounds of iron, (generally they do not contain more than three pounds). Taking forty rupees a ton as the expense of forging the iron into rought bars by hand hammers, we shall have eighty rupees a ton as the expense of bar iron, made with these diminutive furnaces, which is less than the present market price at Madras of the cheapest English bar iron. In my experimental investigation of the best methods of managing small blast furnaces, not larger than the native ones, I have found that two men can procure in a day’s work of twelve hours forty pounds of crude iron, with an expenditure of half the quantity of charcoal and ore used by the natives. Furnaces of this size offer therefore a cheap, convenient, and ready mode of smelting iron wherever charcoal is abundant.

c24.23

20. Although the aggregate manufacture of iron in India is no doubt very considerable, yet from the difficulty of inland transport in Southern India, it is probable that no extensive iron works will ever be established by European capitalists; and the only improvements which are capable of being introduced with advantage, or may be within the comprehension of natives, are those by which the expenditure of fuel may be economised by increasing the size of the furnace, and by which a sufficiently powerful blast may be produced. From my own experiments, I am led to believe, that the catalan forge will not answer except when the ores of the peroxide are procurable, in consequence of a peculiar property possessed by the magnetic oxide. But I am of opinion that the German, ‘steuck often’ might be used with great advantage, and the complete reduction of the ore at one operation to malleable iron, is easily effected. One of these furnaces may be easily built for ten rupees. The bellows for it may cost about ten rupees. A small tilt hammer about fifty rupees, and the whole stock in trade capable of turning out a ton of bar iron per week, need hardly cost one hundred rupees. I believe that nearly all the jungly tracts of Southern India are granitic, and in them of course fire clay and magnetic iron sand abound. Charcoal can be made at about fifty pounds for an anna, and the iron sand is sold at thirty pounds for an anna, which prices are as cheap as the iron stone and coal are now sold for in South Wales.

c24.24

21. With regard to the quality of the iron produced by the native methods, we have the most contradictory remarks from various authors; and indeed I am not aware of any good researches upon this point having been published. From what I have seen of Indian iron, I consider the worst I have ever seen to be as good as the best English iron, and that its supposed defects arise from its almost always containing a considerable portion of steel.

c24.25

22. If it is attempted to bend a bar of English iron of inferior quality when cold, it will be found to snap short off, almost without bending at all, and the fractured end will exhibit a series of minute glistening planes inclined at irregular angles, and which by the lens, will be seen to resemble exactly the spangles of ‘kisk’, or graphite, which appear upon the surface of highly carburetted cast iron. A bar of the best English bar iron, when bent cold, will exhibit on the sides of the bent angle a series of longitudinal fissures, evidently produced by impurities between the fibrous portions, and before it is bent as far as an angle of 120°, it will break, and the fracture will be half glistening, and the rest very much resembling lead when forcibly pulled asunder. This last portion is the pure iron, and when viewed endways, will generally appear nearly black. The glistening portions are portions of carburet imperfectly reduced. It is a common remark of authors, that pure iron is either granular or fibrous in texture, the former being produced by sudden cooling, and the latter by elongation under the hammer. This remark I consider, however, to be erroneous, and I have never found pure fibrous iron to become granular, if properly worked, although granular iron will become fibrous; not, however, by the mechanical effect of the hammering, but by the action of the fire and blast reducting the carburet. In working the best kinds of English iron, they let fall upon the anvil a quantity of red powder, which very much resembles in appearance the residue left by burning the carbon separated by muriatic acid from cast iron. Even the charcoal-made English iron will hardly bear drawing out under the hammer without splitting, and a small rod will generally snap after bending it two or three times. English hoop iron, although it will stand curling up into a roll of about ¼ inch in diameter, yet on the slightest attempt to bend it longitudinally into a hollow trough, it will crack in three or four places immediately. The following remarks by Dr Ure (Dictionary of Manufacture) are evidently from a person practically acquainted with the subject. The quality of iron is tried in various ways; 1. As first by raising a bar by one end, with the hands over one’s head, bringing it forcibly down to strike across a narrow anvil at its centre of percussion on one-third from the other extremity of the bar, after which it may be bent backwards and forwards at the place of percussion several times. 2. A heavy bar may be laid obliquely over props near its end, and struck strongly with a hammer with a narrow pane, so as to curve it in opposite directions, or while heated to redness, they may be kneed backwards and forwards at the same spot on the edge of the anvil. This is a severe trial which the hoop (Swedish iron) bears surprisingly, emitting as it is hammered, a phosphoric odour peculiar to it, and to the bar iron of Ulverstone, which also resembles it in furnishing a good steel. The forging of a horseshoe is reckoned a good criterion of the quality of iron.’

c24.26

23. There is hardly one of the above tests, which good native iron of Southern India will not bear, and some iron which was produced in my own furnaces, has stood drawing out under the hammer into a fine nail rod not th inch thick, without splitting, and when kneed backwards and forwards, only broke after six or seven times. When twisted like a hank of whipcord until some of the plies began to draw out, no fracture occurred in any part, and a half inch bar ¼ inch in thickness bore doubling together *cold*, and the angle hammered down close with very little signs of separation between the fibres. As I have shown that native Indian iron contains steel, the quality can be easily tested by a very simple method, which is merely to bring the middle part of the bar to a red heat, and then immersing it in water, by which all the steely portions will be rendered brittle, without the fibrous portions being affected. An inch bar of good iron thus treated will bear a dozen blows of a heavy sledge hammer before it will break.

c24.27

24. The fractured end of a bar of Indian iron presents a very different appearance to that of English, none of the glistering portions being visible, but if not fibrous, it shows the granular fracture of an aggregation of crystalline grains, either large or small, according to the hardness of steel which it contains. The iron thus examined may be separated for different purposes into four different kinds.

c24.28

1st. Completely fibrous. Fit for nails, horseshoes, bolts, straps, crowbars, tongs, & c., in which softness is of no consequence, and great tenacity and ductility are requisite.

c24.29

2nd. Half fibrous and half granular. Fit for axle trees, wheel tyres, & c., where tenacity and strength are both requisite.

c24.30

3rd. Nearly all granular and steely, resisting the file in some parts, and brittle, breaking with one or two blows of the sledge. Fit for lathe bars and iron work in mathematical instruments, where hardness is requisite to prevent bruising.

c24.31

4th. All granular, with the fine snow-white fracture of cast steel in parts. Only touched by the file in some parts. Very brittle unless annealed. Hard, and resists the hammer in forging, drawing out with difficulty, and cracking slightly at the edges unless carefully forged. Fit for plough shares, spades, and pickaxes, bricklayers’ trowels, & c. which require to be hard.

c24.32

25. Some native made iron which I have met with was difficult to forge, from its cracking very much under the hammer at the edges of the bar, though not otherwise deficient in tenacity; but as such iron is not common, I have not had opportunities of examining it properly. The native workmen say, that iron of this kind is quite as ductile as any other if it is forged with bamboo charcoal. Should this be a fact, it seems to be well worth the attention of chemists, considering that the coat of the bamboo contains much finely divided silica, and remembering that the English smiths, when welding together steel and iron, use freely large quantities of a white quartzose sand. It is probable that it is this last kind of Indian iron, which has by some been called ‘red short’, which is however a mistake. The English red short iron snapping off like a carrot when bent.