This is the tale of an invention that changed the world.

It's also the tale of the inventor. Had he been less dogged and persistent, he would surely have given up. Had he enjoyed the education of the gentlemen who derided him, then in all probability he wouldn't even have started. On the other hand, had those gentlemen themselves known what we consider to be essential pre-university physical chemistry today, they could have achieved in a few months what took Henry Bessemer half a working life to realise.

They didn't know those things though, and so Bessemer became one of those special men in history who did something that his betters were quite sure was impossible.

Bessemer's great contribution to the fabric of the modern world was perverse in other ways too. He found a way to make a material that most of us nowadays dismiss as a commodity. He wasn't even the first person to find a way to make it: mankind had known how to manufacture high-purity steel (and indeed steel purer than Bessemer ever managed) nearly a hundred years before.

This last point seems so contrary that it needs explanation. Before Bessemer, there was no high-volume process for making steel. Civilisation already knew very well that it needed a better wrought metal than iron with which to realise the burgeoning potential of engineering, but it couldn't make enough of the stuff, at least not with sufficient quality to provide a reliable platform for the pending wonders of a modern age.

Bessemer was an entrepreneur, pure and simple. He wasn't all that interested in steel itself. He was interested in the wealth that would accrue from realising its by then obvious applications. The lure of that wealth made him presumptuous enough to dismiss the metallurgical wisdom of his peers.

Early Life

Henry Bessemer was born on 19 January, 1813 at Charlton in Hertfordshire. He was the third of four children, and the only son. His mother was French and his father was a London-born Francophile. Anthony Bessemer's own parents took him to live in Holland while still in his teens, and by the time he was 21 years old and independent he had moved himself to Paris. Within a few years, he married Elizabeth Minette and made important inventions in both coin minting and microscopy. Anthony was inducted into the French Academy of Sciences before fleeing the country as the Revolution took hold. The wealth he had acquired at a young age would nonetheless secure the Hertfordshire estate and ensure a comfortable living for his family.

Anthony doted on Henry, and soon involved the boy in his new calling in type-founding. By the time Henry Bessemer was in his teens, the seeds of a lifelong interest in the processing of metals had been planted. Though his formal education ended at fourteen, he read avidly throughout his life. He developed a sound grasp of engineering physics, a practical expertise of the law and of finance, and proved himself an accomplished draughtsman.

Much of Henry Bessemer's life story is known through his autobiography, which he cobbled together using his diary notes late in his life. Both the formality and the self-importance of Bessemer's writings are exasperating. He manages not to tell us the names of his sisters or the forename of his wife (her maiden name was the wonderfully improbable Miss Alien). He omits to mention his own children entirely: they are revealed only through his eldest son's¹ postscript to the 1905 edition. Instead, the autobiography describes the inventions in copious detail, and the reader is left in little doubt that Bessemer considered them more important than people.

London Patents

Bessemer had his first money-making idea at the tender age of 17. It concerned the concept of, and a method for, applying an embossed stamp onto title deeds. It put a stop to a form of tax evasion that was rife at the time, the practice of peeling off and re-using the supposedly non-transferable stamps from old documents. A grateful government made Bessemer the Superintendent of Stamps at a handsome salary of £700 a year. Some time later, he had an even better and simpler idea, of dating the stamps. The idea was adopted but he received no money for it, and Bessemer realised too late that he'd rendered his own document embossing process obsolete. This was an important lesson in business practice, and the end of his public sector career.

By the time Henry Bessemer married at the age of 21, he had invented a method of compressing a mixture of plumbago dust and graphite for making pencil leads. This time he was more careful over intellectual property. He took out a patent, but lost his nerve as bigger concerns jostled to exploit it. Bessemer sold his patent to one of these for £200. Its purchaser made a fortune, and another valuable lesson was learned.

The first really lucrative venture was conceived while he was still in his twenties, and exemplified an entrepreneurial model that Bessemer was to repeat throughout his life. This was to identify a basic product that commanded a high price as a result of unsatisfied demand, and then to develop a commodity process by which to manufacture it. The earliest successful example was the making of gold paint. In the 1830s, the sole European manufacturer was in Nuremberg, and their paint sold at five guineas a quart. Bessemer analysed the product, found it consisted of a suspension of milled brass, and proceeded to make fine particulate brass by atomising the alloy in a steam jet. He was soon selling an equivalent product to his competitor's at half its price and with a huge profit margin. Bessemer's production costs were probably less than 10% of the Germans'. This time, Bessemer decided not to patent his idea. Instead he managed to keep the process secret for 35 years, and this single product made him rich even before he turned his attention to steel.

By the late 1840s, Bessemer was operating a foundry at Camden in London, producing a whole range of metallic goods, including paints, powders, wires and foils as well as typeface and medallions in a continuation of his father's business. Bessemer also used these facilities to experiment with different materials, ever on the lookout for new ways to make money. One that never quite caught on was the fashioning of ribbons of glass, but the investigation led to his first exposure to the reverberatory furnace, in which a melting chamber is positioned between a hearth and a flue. This arrangement would soon feature in the early steelmaking trials.

By the end of his life, Bessemer had filed well over 100 patents. Around two-thirds of them concerned iron and steel manufacture (including the anticipation of twin-roll casting of steel sheet, fully a century before the first successful commercial enactment), but others were in fields as diverse as velvet making, sugar refining, mine ventilation, the stabilisation of artillery shells in flight and a luxury cruise ship concept. The last, known as the Bessemer Saloon Steamship, was actually built and incorporated a self-aligning mechanism that supported the entire cabin section on gimbals. This was intended to prevent seasickness, but seems to have achieved the opposite, thus handing Bessemer his only major commercial failure.

Henry Bessemer would thus have been a successful inventor even without his foray into steel. Nonetheless, it would be steel that revealed the one attribute that raised a merely clever man to a position among the truly exceptional. Bessemer would spend the next 15 years proving himself to be the most tenacious industrialist of his age.

The Existing Process and Product

There was very little steel in the world in which Henry Bessemer grew up. In 1850, global production is believed to have been about 70,000 tonnes (more than half of it in the UK). Most of this steel was made in cementation furnaces, with the proportion demanding superior properties being further refined using Huntsman's crucible process.

Wrought iron was used and produced in much higher volumes, at around 1.3 million tonnes in the UK alone in that same year of 1850. Wrought iron is a refined form of 'pig' iron from the blast furnace, with a lower carbon content but no secondary alloying. It was (and is) a useful engineering material, suitable for structural use and capable of being manufactured with consistent and reliable properties. With moderate strength and good corrosion resistance compared with the rarer and more expensive alternative in steel, its main limitation was its much greater susceptibility to wear.

Wrought iron, like Bessemer's glass ribbons, was produced in a reverberatory furnace. The British variant was developed by Henry Cort and was known as the puddling process, with a coal-fired hearth separated from the melting chamber by a bridge wall. Beyond that was a tall chimney, generating a draught which drew air over the iron pool in the chamber. We understand the process better today than Cort and his peers could. 19th-Century metal manufacturers knew that chemical impurities in their iron or steel would embrittle it, and that sulphur and phosphorus were the most detrimental of these contaminants. The separation of hearth and pool ensured that sulphur in the coal was fully oxidised before it could enter the melt, but there was as yet no chemical slag process that could alleviate impurities in the pig iron charge. Only a small percentage of the known iron ore reserves were low enough in sulphur and phosphorus to assure prime product. In Britain these came from the Forest of Dean and Cumbria. The best of all was Swedish iron, from the Dannemora region of that country.

By the late 1850s, the correlation between the degree of decarburisation and the tensile properties of the iron had been recognised, and skilled furnacemen could exploit this to make a product to order. This meant, moreover, that the puddling furnace was now capable of making a crude form of medium-carbon steel, and it was this development that led Henry Bessemer to adapt Cort's methods rather than Huntsman's in his early experiments.

First Experiments

In 1855, Bessemer decided to answer a government call to research steelmaking techniques for large gun barrels. He adapted the glass furnace at his Camden foundry and began puddling iron, designing a series of experiments to determine how the operating conditions affected the properties of the metal product. He found he could accelerate the process and increase the purity of the iron by introducing an air blast above the melt. Reasoning that the process would proceed even more quickly if the air passed through the molten pool, he configured an experiment to investigate the idea.

It was haste rather than insight that induced Bessemer to first try out the principle in a small vessel with no external heat source. He took a crucible of the type used in the Huntsman process and pierced its wall with a ceramic tube. He then attached the tube to a bellows, teemed molten iron from the furnace into the crucible and blew in air. Bessemer did not expect a satisfactory outcome. He had already sketched a modification to the reverberatory furnace incorporating fan-blown vents in the bridge wall. Had he ever implemented this idea, Henry Bessemer might have anticipated the process that would eventually rival his own by more than a decade. He might also have killed himself, however. Bessemer was not expecting the violence of the exothermic reaction that occurs when air passes through molten iron. A tongue of white flame emanated from the mouth of his crucible, and the temperature rose high enough to melt off its base. Once it was cool, he found near-pure iron inside. Bessemer realised that he might be able to refine iron by directing an air blast into a large unfired vessel filled with the molten metal.

The Prototype Converter

Steel was now temporarily forgotten, and Bessemer designed a larger scale experiment. The vessel he built was big enough to contain seven hundredweight of iron (350kg, and the heaviest charge that the primary furnace could produce), and had six tuyeres² arranged in a ring around its girth. The air blowers could be regulated and Bessemer, chastened by the fireworks with the crucible, opted to start at a low pressure of about 10 pounds per square inch.

This time there was no violent reaction, at least at first. If the iron was being decarburised at all, the process was proceeding gently, much as it did in the puddling furnace. The difference was that here there was no hearth and no fuel. Without a sufficiently exothermic reaction, the metal would cool and solidify inside the vessel. Bessemer had been prepared for this eventuality and gradually increased the blast pressure. After about ten minutes, the conditions inside the vessel changed abruptly. The stream of sparks at the vessel's mouth intensified before being replaced by a roaring white flame. A series of sharp explosions occurred within the melt, throwing metal into the air. The vessel and the valve that would reduce the blast pressure were now too dangerous to approach. Bessemer and his hands retreated to a safe distance as the galvanised sheet roof of the shop was consumed by the accidental volcano.

After about ten minutes, and before a serious fire had been set in the foundry, the reaction died back of its own accord. The blast was turned off and the vessel was tapped into an ingot mould. The result was fully decarburised iron with excellent ductility. Bessemer would later call it 'malleable iron', as he wrestled with the problem of controlling the process he had discovered.

Bessemer would soon move on from the near-accident of the first trial, just as he always did, learning from his mistakes. It might all have ended there and then, though. Henry Bessemer, not for the last time, had spectacularly overreached himself. He might have burned down his foundry, he might have died in the inferno and there might have been too little left at the scene for anyone to work out quite what he'd been up to.

Failure and Ridicule

At first, Bessemer assumed that he had lost control of the process because he had exceeded a critical blast volume threshold. He therefore moved the valve, stripped away most of what was left of the workshop roof and opened out the vessel's mouth to reduce the risk of explosion. Then he repeated the experiment, turning down the blast as soon as the white flame appeared. This made no difference whatsoever, and the only significant change from the first attempt was a visit from the police. The shaken entrepreneur now went back to the less dangerous scale of the crucible, and worked out that the reaction is substantially independent of blast volume. The silicon in the molten iron is oxidised first, forming a slag. Once this reaction is complete, the carbon in the melt is oxidised next and it is this reaction that is violently exothermic.

In the small-scale crucible experiment, the reaction was immediate because his reverberatory furnace had already driven out the silicon from the small iron charge. With the larger charge, the primary furnace could not develop sufficient wind to do this, and so the inferno was preceded by ten minutes of quiescence while the silicon was taken up.

After filing patents to protect his invention, Bessemer went public. On 11 August, 1856, he presented a paper to the British Association at Cheltenham. It was entitled The Manufacture of Malleable Iron without Fuel, and was complemented by tensile test results on the metal produced. In addition, Bessemer gave out samples from his ingots. The result was spectacular. Within a month, four steel companies took out stock options to the tune of £27,000. Then things began to go wrong. Bessemer attempted to replicate the process in his backers' works, but in every case the product turned out to be brittle and useless. The British Association excised the paper from the proceedings of their Cheltenham meeting and Bessemer was obliged to pay back all the money.

Unless he could explain and correct the failure to migrate his process, Bessemer was going nowhere. He hired expert metallurgists to help him, and before long they were investigating the bought-in pig iron that Bessemer had used in the Camden trials. It turned out to be from Blaenavon in Wales, and was deemed to have a phosphorus content so low as to render it too scarce for widespread commercial use. There seems at this point to have been an uncritical assumption that Bessemer's process was somehow intolerant of all but impractically low-phosphorus ores (without properly explaining why). Bessemer's metallurgists took their pay and left, some of them uncharitably branding him a charlatan and most of the others dismissing his process as a useless curiosity.

With the benefit of hindsight, we now know that there were other factors in play that neutralised the phosphorus in the Camden melts, to do with the alkaline refractory materials of Bessemer's puddling furnace, originally lined with a view to making glass and not steel. The man who would fully solve this riddle belongs to a later phase of the story. Sidney Gilchrist Thomas was in the meantime living only a few miles away from Bessemer, but was as yet a seven-year-old schoolboy.

Help from Mushet and Goransson

Early 1857 marked the low point of Bessemer's steelmaking endeavours. Some 18 months of effort and a major investment of his own money had left him with a process that seemed to require a rare and expensive ore before it would work. The iron and steel industry at large knew about him now, but most considered him to be a failure and living proof that its arcane practice secrets were impenetrable to outsiders. In return, Henry Bessemer viewed his detractors as self-interested perpetuators of a mystique that had no scientific substance. He was not going to give up until he had seen the proof of impossibility for himself, and he refocused on the central problem of phosphorus.

Bessemer could not understand the failure of the process at one of the original option sites in Cumbria, since this one was using local ores with the lowest phosphorus content in the country. He brought some of the Cumbrian pig iron to London for trials, but found even before he'd melted any that the phosphorus levels were abnormally high, quite the opposite of what its producers claimed. He traced the anomaly to the Workington Iron Company's practice of incorporating tap cinder in their blast furnace charge. The material originated in Black Country puddling furnaces and was shipped as ballast to the export of Cumbrian haematite ore to the Midlands. It was therefore a very cheap way of increasing iron yield – but one that was loaded with phosphorus.

Even though Bessemer was by now far more knowledgeable about metallurgy, getting people to believe him was another matter. The owners of the Workington business remained resolutely sceptical, and declined to carry out the experiment of making some iron without the tap cinder flux. What Bessemer now needed was the effort of practised steelmakers who would use their experience to explore the limitations of the process. Two men were about to rehabilitate Bessemer's fledgling converter, though he would give one scant credit and the other none at all.

Robert Forrester Mushet ran the Darkhill steelworks in the Forest of Dean, and was well known for his experiments in alloying to promote ductility in crucible steels. Late in 1856, an acquaintance named Thomas Brown brought him some specimens of Bessemer iron made at Brown's works at Ebbw Vale, asking if Mushet could propose a way to relieve its brittleness. Mushet realised that the sample had been processed beyond the point of removing the carbon. The iron itself had been partially oxidised too, and Mushet knew how to prevent this over-oxidation by secondary alloying. Manganese did the job, and the commonly-available form of this was a manganese-rich pig iron known as spiegeleisen.

Mushet well understood the commercial prospects of a redeemed process, but Bessemer rejected Mushet's proposal for partnership. Instead he elected to pay Robert Mushet an annual pension of £300, a healthy sum that was probably calculated as sufficient to avoid a lawsuit. Bessemer meanwhile filed more patents, exploiting Mushet's practice and for the first time claiming a steelmaking capability as a result.

Bessemer's other saviour was given even shorter shrift. The first successful demonstration of Bessemer steelmaking was not conducted by Bessemer himself, and didn't even take place in Britain. Goran Goransson owned the Edsken steelworks in Sweden, and took out a licence for the Bessemer process in 1857, at which time Bessemer was offering them cheaply in order to achieve a sufficiently widespread raft of users for them to make operational breakthroughs. In Goransson's case, the strategy worked, because the Edsken engineers soon began to reconfigure the converter. Their main change was to double the area of the tuyere-bores and to increase the air volume while reducing the pressure. The result was markedly increased temperatures and a faster process. Like Mushet, they alloyed with manganese. Goransson took a crucial decision, and relocated his prototype Bessemer converter to a position right alongside his blast furnace so that he could 'blow down' molten pig iron directly. The Edsken plant was soon producing good quality steel above the psychologically-significant level of a tonne per hour, and the reputation of the process began to be restored.

Sheffield

Bessemer's confidence was being restored too. Contrary as ever, he stopped issuing licences for a time, intending to bring them back at much higher fees once the remaining problems were sorted out. He also reasoned that the time was right to move his operation into the iron and steelmaking areas of the country. Sheffield was then the place of origin of three-quarters of Britain's steel, and so he purchased a small foundry in Carlisle Street in the heart of the rapidly-expanding east side of the city. A generation before, the lower valley of the River Don at Attercliffe had been verdant and rural in character. It was rapidly becoming an over-populated and smoke-blackened slum, but Bessemer wanted to be there. Attercliffe was where the expertise as well as the investment in steel was focused.

Bessemer erected a new building on the Carlisle Street frontage of his new site, and incorporated the date '1856' into the facade. Whenever anyone pointed out that the building hadn't even existed until two years after that, Bessemer would declare that the date referred to the genesis of his project. In mind as well as location, Henry Bessemer was making a fresh start.

Convinced that he would sooner or later win over the masters of the low phosphorus ore mines, Bessemer also continued to court the Workington business and also the owners of the Dowlais ironworks at Merthyr, who mined the same deposits that had supplied his Blaenavon pig. Neither afforded him much courtesy in the beginning, but Bessemer was persistent, raising money wherever he could persuade financiers and patiently acquiring stock.

Back in Sheffield, Bessemer now considered himself a steelmaker. He built the biggest converter yet, and began to describe his vessel and process using that term. He bought in Dannemora ore and experimented until he could reliably make steel in a direct process. In June 1859, he began selling the stuff at cost in order to establish a market. It was not yet a business, because importing ore was expensive and Bessemer had no blast furnace at this stage – he was still incurring energy costs to melt his metal in what was by now looking like an unnecessary process step. Nonetheless, Henry Bessemer's dream was starting to get close to reality.

The First Licensees

In his new Attercliffe premises, Bessemer had two neighbours, and they were both business giants in the Golden Age of Steel. On one side was John Brown, master of the biggest plant on earth, the famous Atlas Works. On the other was the Cyclops Works of Charles Cammell, the filemaker who had seized the potential of armour and ordnance and prided himself as the Armourer of Empire.

Both men saw that in spite of all the gainsayers, Bessemer now had a real chance of commercialising his invention, and so they took the decision to acquire a process licence as soon as these became available. Though their initial capital developments were tentative, their investment was to prove a shrewd move. Bessemer's licences would soon become a whole lot more expensive, and though he was too much of a businessman to fix the fees of his first customers, Bessemer did at least show Brown and Cammell some of the gratitude owed to early disciples. Several of their fellow barons had ridiculed Bessemer's requests for funding, and in return they would find themselves faced with eye-watering demands, so extreme that they collectively wondered whether they could afford to remain in a steel business with Bessemer in it.

Their response was their only real alternative. They swallowed their pride and bought in, but immediately embarked on a search for a rival process to cut Bessemer down to size. The one that was found finally assured Sheffield's claim to be the world's first Steel City. In the same place, not one but two volume steelmaking concepts would soon go head to head. The competition meant that for a brief time in the late 1870s, an otherwise unremarkable Yorkshire city was the source of half the world's steel.

Intellectual Property

One of the many twists in the tale of Bessemer Steel is its place in the history of industrial globalisation. It was probably the first large-scale industrial process that was worth more to a part of the world different to the place where it first appeared. The account so far makes it plain, for example, that Sweden was afforded a window of opportunity to become economically dominant in steelmaking. The Scandinavians may or may not regret missing it, but there simply weren't enough people there to run with the ball that Bessemer passed them.

The United States of America was an entirely different matter. By the middle of the 19th Century, the United States had an overriding economic need for steel. The world's largest railway network was opening up a continent, but the poor wear performance of wrought iron rails was holding it back. It was no surprise, therefore, that the uptake of the Bessemer process was aggressive in the United States and neither was it a surprise that a spate of Americans claimed to have thought of it first.

History judges that the most credible of these claims belongs to a Kentucky steelmaker called William Kelly. His family acquired an ironworks at Eddyville in 1846, and not long after this, Kelly discovered the exothermic heating effect in air-blown pig iron. He designed and operated a converter before Bessemer's, but appears to have exploited it as a low-energy melting concept (so that a small amount of pig iron, heated using the air blast, will melt more iron and eventually allows a large melt volume to be built up with no fuel consumption after the first cycle). No patent was applied for until 1857, two years after Bessemer's and a year after its publication. The American authorities somewhat dubiously granted Kelly's patent. Bessemer would surely have embarked on an opposition, but discovered that the Kellys were in financial difficulties and so simply offered to buy the patent instead. William Kelly accepted.

Kelly had plenty to say afterwards, but there is no evidence that he had foreseen the possibility of a controlled decarburisation reaction before Bessemer's patent was published. Nobody could base a patent simply on the exothermic character of the decarburisation reaction, since this had been known 'prior art' since the time of Huntsman. Kelly's claims to have invented the Bessemer process thus have little credence outside America, where they appeal to a patriotic myth of pioneering engineering.

Of far more significance was America's purposeful adoption of the process. Though steel production in the United States would not overtake Britain's volume until the 1920s, Bessemer's invention came at a time when the American industry was investing in capacity. For American steel magnates such as Andrew Carnegie, the Bessemer process was a timely boon, whereas for most of their British peers it was a competitive headache. This may explain why Britain today celebrates one of its greatest inventors through a few landmarks in Sheffield and a streetname in Hitchin, whereas the United States has around a dozen towns called Bessemer.

Upscaling

Bessemer himself was meanwhile pursuing new priorities. His new company, the Bessemer Steel Company, had made losses in its first two years but by 1860 was returning a modest profit. In that year, Bessemer concentrated on engineering aspects of his converter. All of the operating examples so far built had been fixed vessels, charged through an aperture at the top and tapped at the base. In the course of time, a horizontal tuyere line around the waist of the vessel had been replaced with a vertical array through its base, and these tuyeres were also fixed.

At Sheffield, Bessemer built his first tilting converter, with a horizontal axle that passed through its centre of mass. It rotated one way to accept the charge and the other to tap. In the first variant, the rotation was accomplished by a large handwheel, though later there would be gear drives and hydraulic actuators. The blast pipework was progressively refined until the air from the blowing engines was directed first through the hollow axle and then into a tuyere chamber in the vessel base that rotated along with the converter.

The Sheffield equipment was brilliantly engineered and became a showcase for the technology. The largest converter built in this period could process four tonnes of metal in thirty minutes. Through familiarity and regularity of practice in respect of charge weights and blast pressures, the plant could make product on demand to a customer's specified carbon level, yielding anything from heat-treatable steels to fine iron from the same raw material. Over the next 20 years, the shop was progressively re-equipped with bigger and bigger converters, the largest and last being designed for a 12 tonne charge.

Rail Dominance

The annals of the Atlas Works report that in November 1861 a section of wrought iron rail forming part of the Sheffield to Rotherham Railway was secretly replaced by a Bessemer steel replica. When the time came for scheduled replacement, this one section showed no sign of wear. John Brown, who was the city's Mayor at the time, confessed to his company's stunt, and promptly received an order for replacement rails for the entire Midland system. Although this story is probably apocryphal or at least embellished, it is certainly true that by 1865 John Brown's company was supplying half of the nation's rail and dedicating three-quarters of its manufacturing capacity to the product.

Rail was the ideal product for Bessemer steelmakers. Their direct production costs were only slightly higher than those of their wrought iron competitors, but the service life of the steel product in this application was around ten times longer. That left plenty of room for high margins even after the deduction of Bessemer's licence fees.

In addition to Brown's adoption of Bessemer steelmaking in his huge Atlas enterprise, Cammell was investing too. He built a new rail-dedicated Bessemer plant at Dronfield to the south of the city. Nor did it end there: two new businesses were formed to supply the same market, Bailey and Dixon in Attercliffe and the Phoenix Bessemer Company at Ickles. Within a further couple of years, Brown bought a Spanish haematite ore mine and erected a blast furnace next to his Bessemer shop so that he could supply it with his own pig iron.

By 1873, Sheffield had a Bessemer steelmaking capacity in excess of a quarter of a million tonnes per annum deployed in rail-making and a further 100,000 tonnes directed at ship plate. Even so, the city didn't have things all its own way, since the Cumbrian ironmakers had finally bought in. The Workington Haematite Iron Co Ltd, with Henry Bessemer its principal stockholder, was part of the trend but by no means the main player. At Barrow-in-Furness, a new holder of the world's largest steelworks title emerged, with 11 blast furnaces and 18 converters.

The world steel capacity doubled three times in the single decade of the 1870s, and the two towns of Sheffield and Barrow were each making more steel at the end of it than the entire world had done ten years earlier. This explosive expansion could not last, however, and in particular Sheffield's days would be numbered as soon as the growth in demand levelled off. Sheffield had no local ore of its own, and was relying on Cumbrian haematite as its only economic source of raw materials. The competitive compromise is obvious. Brown diversified, while Cammell relocated his entire Dronfield plant to Workington in 1885, where it could receive low-phosphorus molten iron direct from the Derwent Ironworks next door. This transfer of operations marked the effective end of large-scale Bessemer steelmaking in South Yorkshire. The enduring examples of the practice were now at Barrow and Workington in Cumbria and at Dowlais and Ebbw Vale in South Wales, all of them utilising direct charging of blast-furnace iron made from haematite ores.

Rival Processes

The air-blown variant of the puddling furnace, a concept that Bessemer had considered but never adopted, was established and undergoing refinement from the mid-1860s. The first breakthrough was a regenerative type of reverberatory furnace, invented by Sir William Siemens in 1857 and pioneered at Landore near Swansea for copper smelting. In this furnace, flue gases give up their heat to a labyrinth of brickwork, which in turn preheats the gas-air fuel mixture, increasing efficiency. The concept was adapted for iron and steelmaking in 1865 by a Frenchman named Pierre-Emile Martin, who had licensed the technology from Siemens.

Frederick Siemens, nephew of Sir William, began making steel using the Siemens-Martin Process at Landore in about 1867. Also known as the open-hearth process, it was this technology that Mark Firth's scouts discovered in his hunt for a rival to Bessemer's. The two methods coexisted for many years and were in some ways complementary as business alternatives, since the Siemens system had lower investment costs but higher operating costs than the Bessemer converter. Both made good steel, but neither was as yet tolerant of low-grade ore.

Thomas Pulls the Rug

The former Islington schoolboy, Sidney Gilchrist Thomas, entered the picture in 1879. Thomas researched the action of slags in metals refining, and found that the propensity of slags to absorb impurities depended on the relative basicity of the constituents. The nemesis of iron and steelmakers, phosphorus, forms acidic oxides, and thus it follows that it will be absorbed by an alkaline slag. So will other embrittling impurities including sulphur. Thomas proposed that a lime flux would make both the Bessemer and open-hearth processes tolerant of phosphorus-laden ores.

This was all very well, but such a slag would (and did) dissolve the refractory too. The correctness of Thomas's theory was soon proven, but the lifetime of the equipment was compromised. Nonetheless, the abundance and cheapness of low grade ore was incentive enough for a search for non-siliceous refractory materials to ensue. When a suitable formula was found, using a rammed lining of pre-fired dolomite bonded with tar, a new variant of each of the two bulk steelmaking processes emerged. The Basic Bessemer process became established in Europe more than in Britain, and the complete dominance of haematite ores was broken. Though haematite remained useful because it contains more iron per unit weight than lower oxides and carbonates, Thomas' discovery had the ironic consequence of eroding the competitiveness of his home nation's steel industry.

The work of Sidney Gilchrist Thomas marks a new beginning for industrial metallurgy in another way too. From the 1880s on, process development would be scientific and underpinned by a new understanding of chemistry and thermodynamics. Henry Bessemer would therefore be the last example of the 'suck it and see' school of empirical metals manufacture. A contemporary of Darwin, Bessemer can be seen as a kind of missing link in this respect. His predecessors had clever ideas and got lucky. Bessemer got no better than close, time and again, but kept on reconfiguring his concept until he'd reduced it to the core thing that worked.

Hibernation

Thomas's discovery ushered in a new wave of capital development in the industry, because steel production now became possible in regions with low-grade iron ore deposits that were hitherto unsuitable for anything but iron. In Britain, these included the Northamptonshire Weald and its northern outcrop in the Frodingham lias of Lincolnshire.

Bessemer no longer had an exclusive answer to the needs of the volume steelmaker. By the 1880s, his home country began to favour the Siemens-Martin process instead. There was no decisive technical advantage, and so the system that was perceived as less disruptive won adherents in a conservative industry. Bessemer had shaken up the value chain by blurring the distinction between the steelmaker and his equipment supplier. He had also offered a self-contained technology for new market entrants, whereas the open-hearth furnace had a more familiar civil-engineered infrastructural character. Most of all, Bessemer took the control of the industry away from its traditional masters, and they never forgave him for it. Ruthlessness over licence fees was now being repaid by partisan technology choice.

Henry Bessemer's formidable advocacy for his invention waned at the last as well. He was entitled at this time of his life to prefer his Denmark Hill home to his many company offices, while the effort he still gave to engineering was mainly directed at new schemes and intriguing curiosities. The inertia of the steel industry neither earned nor deserved the last of the old man's creativity.

Bessemer died in 1898, with the bulk of Britain's steel now being made using the open-hearth method. The technical breakthroughs that he expected to assure his ascendancy, such as pyrometers that would accurately measure the temperature of the melt, took place as he predicted, but they were exploited as much in the rival process as in his own. Steelmaking did not slow down with the passing of its greatest innovator. At the end of that century, before the ruin of the Great War doused the spirit of the European continent, anything seemed possible as civilisation shone in its fiery glory.

The LD (Linz-Donawitz) Process

Bessemer steelmaking declined in Britain, with the basic process disappearing about 1925 and the acid practice attracting little investment after that time. The assets were robust and they were sweated, but the new capacity and the process refinement were in open-hearth steelmaking right through two world wars and the hunger for the might of steel that they engendered. Then in the early 1950s, with Marshall Plan aid finally reaching the heartlands of the Axis Powers, Bessemer's concept was reinvented in Hitler's hometown itself. The Linz-Donawitz process reintroduced converter steelmaking, except that oxygen instead of air was blown through a topside lance to drive the reaction.

The slag and refractory practice are basic to accommodate the prevalent ores, and the biggest Basic Oxygen Steelmaking (BOS) converters can convert 350 tonnes of iron to a precise steel composition in less than 40 minutes. 60% of the world's steel is now made this way³, and the open-hearth process is obsolete and all but extinct. Henry Bessemer was right in the end.

Kelham

The original acid Bessemer practice lived on at Workington for 40 years longer than anywhere else in Britain. In 1974, the last pair of Bessemer converters to operate in the land of their development cooled for the last time. One of them came back to an industrial museum in Sheffield.

The Bessemer converter at Kelham Island is bigger than any that its inventor ever saw. It was designed for a 30-tonne charge and completely dominates the entrance to the museum. Black and bristling with enormous rivets, it epitomises our notions of a cauldron for a volcanic process. It is still possible to imagine the ground-shaking violence of the steel rising to the boil within, and then the awesome incandescence of the pure white cone of fire that followed, extending several feet from the vessel's mouth with wreathes of fork-shaped flame curling around it. The Bessemer converter in full blow came at all the senses, with terrible energy coursing through the ground and exciting the air itself. Experiencing it was an unforgettable privilege indeed.

A Billion Tonnes a Year

In a single decade, nearly 150 years ago, the world volume of steel increased nearly tenfold. Bessemer's invention was the reason. Although the rise of steel was inevitable and irresistible, it still took the determination of a single man to realise it.

Steel production has kept on mounting. In the ten years that preceded the 2008 crash, almost half a billion tonnes of new capacity were added. The country where the converter process was finally brought to complete dominance, Austria, today uses less electricity and less gas than does ArcelorMittal, the world's largest steel company. We are not talking about the Austrian steel industry here, or even Austrian industry as a whole, but an entire mid-sized European country consuming less energy than does a single steelmaker. Steel is that big.

But just as Bessemer's converter declined in use, so the BOS vessel will wane too. The process that feeds it, blast furnace ironmaking, generates 4% of the world's artificial carbon dioxide according to the steel industry's own figures, and twice that proportion in the reckoning of some serious research assessments. This cannot go on. In any case, as the fresh steel of the new Millennium ages and the scrap volumes rise towards equilibrium, the electric arc route is bound to prevail in the end.

Postscript

Now that we have heard the remarkable story of the Bessemer process, there is one last perversity to note. It should be evident now that Sir Henry Bessemer never completed the development of his invention, and nor did he ever fully prove the broad application base that he claimed for it. He was instead so far ahead of his time that his great idea, after a quarter-century of enthusiastic and world-wide exploitation, went back to sleep for 60 years before the Austrian development made Bessemer's fundamental approach the dominant steelmaking technology of the modern world.

Bessemer himself would never have agreed with this last assertion. He was a vain man, and the toughest target he set himself was living up to his own self-opinion. He never received the respect that he'd properly earned from his peers either, though that was something he hardly cared about. His knighthood, grudgingly conferred, meant little to him. Nor did the fact that most of the people who truly admired him did so with the ameliorating virtue of distance from the man himself. Bessemer made an enormous amount of money in his lifetime, and with it a similarly copious number of enemies.

There will always be a few people who resent genius. There were many more who resented the success of a common man, achieved through a combination of uncommon tenacity and science that they might have foreseen themselves.