Sir Henry Bessemer is renowned for inventing the Bessemer process, the world's first mass production system for producing high-quality carbon steel. Charles Murray ranks the Bessemer process in the all-time top 10 human achievements. Greater production efficiency led to lower steel prices. Affordable high-quality steel facilitated the construction of countless railways, bridges, buildings and ships that would otherwise have been unviable. It transformed the design, performance and durability of vehicles, munitions and consumer appliances. Understandably then, Bessemer is widely regarded as one of Britain's greatest inventors. We investigate whether his reputation is deserved, then go on a tour of the places he lived and worked.
The Bessemer process
Bessemer's process, in case anyone does not know, was to blow cold air through molten pig iron to separate and remove appropriate amounts of silicon and carbon impurities, thereby leaving carbon steel. It has no external heat source. Somewhat counter-intuitively, the cold air heats rather than cools the pig iron, because it creates exothermic chemical reactions.
The carbon floats away as carbon monoxide. The silicon is converted into silicon dioxide which floats on liquid steel allowing its easy removal. The chemical reaction generates enough heat to be self-sustaining. It can get pretty violent. William Kelly referred to it as 'air-boiling', because the reaction makes the metal roil, as if boiling. Bessemer said it was like a volcano, shooting molten slag up the ceiling in a sheet of white flame.
The process is embodied in a contraption known as a Bessemer Converter, which is an egg-shaped container mounted on a trunnion. It is tipped over to take a charge of molten pig iron, righted for 20 minutes while air is blown in at the bottom, tipped over again to remove the newly separated impurities which float, then tipped over further to empty the steel. The process takes less than 30 minutes to produce 7 tons of steel in a standard 10m device.
The easy part of our investigation is that, notwithstanding some initial difficulty controlling the amount of residual carbon, Bessemer's process worked well. And cheap high-quality steel did have the transformational impact claimed. Bessemer patented his process in October 1855. The first Bessemer Converter went live in 1858. The price of high-quality steel fell from £60/ton in 1855 to less than £10/ton in 1870.
Lower steel prices did indeed make steel viable for a plethora of new purposes. Steel production in Britain grew from 51,000 tons in 1855 to 830,000 tons in 1880 and to 2 million tons by the eve of WWI. Half of the new steel was consumed by railway companies who were thrilled to find that steel rails might last 20 years, whereas their cast-iron and wrought-iron predecessors had to be replaced every 3 to 6 months.
Or should it be the Martien/Kelly process?
An American engineer named William Kelly disputed Bessemer's U.S. patent on the grounds that he had invented the process a year earlier. Kelly reckoned that Bessemer stole his idea, having heard about it from some itinerant foundrymen that he had employed before they went to England. On that basis, Kelly received the patent for the Bessemer process in the United States. It is generally thought, at least in Britain, to be the other way around: that Kelly learned the technique from foundrymen that had previously worked for Bessemer. Neither of them were the original inventors. The Chinese, albeit on a small scale mainly for weapons, had already been blowing cold air through molten pig iron to remove impurities for more than a thousand years.
Another American engineer named Joseph Martien, working at the Ebbw Vale ironworks in Wales, filed a patent application for something like the Bessemer process just days before Bessemer. The timing is more than a little suspicious.
No permutation can be discounted. Bessemer and/or Kelly and/or Martien might have independently devised the idea themselves. Any or all of them might have learned the technique from itinerant Chinese foundrymen. Or foundrymen working for whoever was the first in the western world to experiment with the technique could have spilled the beans to either or both of the others.
Bessemer tells his story in his autobiography. It starts with his invention of an elongated artillery shell that would spiral in flight without barrel rifling. He demonstrated it to Napoleon III. The steel used for artillery barrels proved to be too weak for his shell. He resolved to improve the quality of bulk steel, then made using the Huntsman process.
Wrought iron is similar to steel, only with some of the slag left in. In the mid-19th century it was made in a reverbatory furnace, depicted above, by puddling (i.e. stirring) moulten pig iron in the hearth. This oxidised away most of the carbon and sulphur impurities. Silicon and manganese impurities converted to slag which was stirred into the moulten iron, leaving a characteristic grain in the metal when it had cooled.
In 1850, Lohage, Bremme and Lehrkind in Westphalia discovered that the same process could produce mild-steel, if the furnace was prepared in a particular way and charged with a particular type of ore. It was lower quality than Huntsman steel but less expensive. Their process was licensed to Low Moor Ironworks in 1851. It became the major source of mild steel for the next decade.
Bessemer says that his discovery of the Bessemer process started with an experiment in a reverbatory furnace in the early 1850s. It sounds like he was trying to improve the Westphalia process. He says that he noticed that some pig-iron ingots beside the cooler walls did not melt but had instead turned to pure iron on the outside.
"Thus a new direction was given to my thoughts, and after due deliberation I became convinced that if air could be brought into contact with a sufficiently extensive surface of molten crude iron, it would rapidly convert into malleable iron."
Bessemer's account relies on a mini-Bessemer chemical process in the reverberatory furnace. It is credible. The device heats pig-iron ingots by the flow of hot air (red line on diagram above) from a firebox and by the reflection of radiated heat off the parabolic roof. The sides would be cooler. If the oxidisation starts at less than the melting temperature of iron, the chemical reaction will oxidise impurities and create enough extra heat to melt the surface of the ingot. The slag will drop off into the hearth. When most of the surface carbon and silicon has oxidised away, the chemical reaction will stop and the ingot will cool back to the ambient temperature of that part of the furnace. It is still in a part of the furnace that is below the melting temperature of iron, so the surface will solidify, thereby creating a pure iron shell that prevents oxygen getting to the impurities inside. It seems plausible to us.
We checked Bessemer's account against other serendipitous discoveries, by Goodyear, Roentgen, Becquerel, Fleming, Spencer, de Mestral and others. They all take the form "I was investigating X when I noticed Y" or "I was expecting X but found Y". Bessemer's seems to fit. Moreover, if he knew the likely result in advance - because he had stolen the fully formed technique from Martiens, Kelly or the Chinese - we think he would have come up with a more heroic story and that he would have prepared more thoroughly for his first experiments in the blast furnace.
Bessemer's jump to a tilting blast furnace is more suspicious. Bessemer says that his plan was to get as much air as possible in contact with molten crude iron. The obvious way to achieve this would be to make a wider shallower hearth in a bigger reverbatory furnace. Instead, he started experimenting with tilting blast furnaces, and at roughly the same time as Kelly and Martiens.
Frankly, we don't trust any of them. The Chinese did not participate in international law, so their inventions were freely available in the developed world. We suspect that Bessemer, Kelly and Martiens had all heard vague descriptions of the Chinese air boiling process from itinerant Chinese foundrymen, and that they were all trying to recreate it. They may well have spied on each other too. Martien and Kelly both worked on the U.S. East coast for a time. Martien and Bessemer were working 150 miles apart. All of them would claim that they invented the technique because admitting that they had cribbed it from someone else would invalidate a subsequent patent application.
Regardless how Bessemer came to experiment with tilting blast furnaces for the mass production of steel, he stole a march on Kelly and Martien in its commercialisation, mostly because he had more money. We think he was indeed the first person to successfully scale up the air boiling process into something commercially viable.
Bessemer's greatness and momentousness
Making a great discovery is not necessarily a sign of greatness and it is particularly not a sign of momentousness. As we always say about discoveries, someone else would have devised the exact same discovery eventually. The benefits of any discovery are just the advances that are brought forward by the time it would have taken for someone else to make the same discovery. In the case of the Bessemer process, assuming for the time being that he did discover it, this is unlikely to have more than a year or two, and might have been no more than a few months if Martien and/or Kelly independently made the same discovery. The brought forward benefits would have been modest.
Bessemer's greatness and momentousness therefore derive from the business he built around his Bessemer process patents. His rivals were hard-nosed businessmen. Intellectual Property theft was rife. Hardly any inventors benefited from the fruits of their inventions. Bessemer was one of four notable exceptions in Britain, along with Richard Arkwright, James Watt and William Armstrong.
Bessemer played his hand well but it has to be said that he was incredibly lucky. Very few inventors are good businessmen and hardly any build successful businesses on their own. He did have partners at Henry Bessemer & Co, most of whom were trustworthy relations through marriage, but they were not businessmen either. Bessemer was effectively forced to take the steps that made him rich. It happened like this.
Bessemer wanted to monetise the Bessemer process by licensing it to established foundries, so that he could move on to new inventions. They were reluctant to cannibalise their profits by paying for the license. They hoped to wait out the patent expiry. But Bessemer was making enough money from his bronze dust business to construct his own foundry. The threat of getting undercut by a superior product forced the incumbants to take a Bessemer license.
None of the licensees could make the Bessemer process work consistently. One problem was that leaving the right amount of carbon proved horribly hit and miss. The most malleable steel has roughly 0.03% carbon. The hardest steel has roughly 1.7%. Not much room for error. A small miscalculation of the original carbon content, a small timing error, or bad luck with impurities, caused the process to create the wrong type of steel. Bessemer knew this to be a problem, for which he had never found a solution.
Even when Bessemer's licensees got the residual carbon content right, their steel was not as high quality as he had promised. Bessemer worked out that this problem was caused by sulphur and phosporus impurities in their iron ore. Bessemer supplied them with purer ore, but this made the process unviably expensive.
Robert Forester Mushet devised a solution to two of the three problems. His idea was to oxidise away all carbon impurities, shut off the compressed air tuyeres, then add back exactly the amount of carbon needed for the type of steel being produced. He improved on this by using a mineral named spiegeleisen as the source of the added carbon because its manganese content also removed sulphur impurities. Mushet patented his process. Bessemer claimed that Mushet's patent was invalid because the properties of manganese in steel making were well known. Josiah Heath had indeed patented the use of manganese for the puddling process in 1839, although Bessemer was presumably ignorant of it beforehand.
Bessemer spiked Mushet's patent by refusing to give Mushet a Bessemer process license, with the veiled threat that he might revoke the Bessemer process licence from anyone that took out a Mushet license. It was enough to prevent Mushet finding customers, which left him unable to afford the patent renewal. Bessemer acquired it cheaply. William Kelly, meanwhile, still held the U.S. patent for the Bessemer process. Bessemer acquired that cheaply when Kelly got into financial difficulty. Now holding all the aces, virtually every bulk steel manufacturer in the world had to take a Bessemer license. This was the source of his success.
Away from steel, Bessemer successfully filed 119 other patents. Most were duds, although there were a few exceptions. His first successful invention was a way of compressing plumbago into pencil lead. Another was a new way of producing oil paint. Both were sold cheaply and made their purchasers rich. The latter was re-purposed in the production of linoleum, which became a huge global business. Bessemer designed the first modern solar furnace, although it was not much use in the days before electricity generation. He invented the system of contra-rotating rollers now used for producing continuous metal strip. He claimed to have invented the centrifugal pump. None of these inventions were adopted during their patent protection. None of them had anything like the commercial impact of the Bessemer converter.
Bessemer's only other commercially successful innovation was for high-volume production of bronze dust. His rather ignominious contribution was to reverse engineer and upscale the secret production process that had been used for generations by the only other manufacturer in the western world, a family firm in Germany. He felt no guilt because they had snitched the technique from the Chinese. It gives a clue to Bessemer's approach.
Bessemer's paint oil process was also snitched from the Chinese. James Gwynne said that Bessemer's centrifugal pump was only a minor variation of an invention he had patented the previous year. Bessemer's experiments with pig-iron in reverbatory furnaces started soon after Low Moor Ironworks had licensed the Westphalian mild-steel production process. We suspect that his plan was to recreate, and then try to improve, the Westphalian process. It would be an obvious stepping stone to the Chinese air boiling process, thereby redirecting him onto the path for which he is famous.
In his autobiography, Bessemer says that his most valuable skills were inventiveness and tenacious perseverance. Misdirection we fear. Rather, we think he devised a business process based on the deconstruction, reverse engineering, refinement and/or upscaling of existing processes or recent inventions. His most valuable skill was understanding how best to use, abuse, avoid and enforce patent laws. He was a bully, who not only enforced his patents but who used the threat of legal action to subdue competition. This might be morally dubious, but it is a valid business model. Others followed. By and large, it is how Edison worked. More recently, it is how Apple have grown into one of the world's most successful businesses. It is good business, just not based on invention or innovation.
In our opinion, Bessemer is no where near the top rank of Britain's inventors. The Bessemer process transformed Victorian business, transportation, armaments, bridged to modern society, and made Sheffield into the world's biggest steel manufacturing city. But Bessemer's contribution to the process, as far as we can see, was modest. His other inventions were trivial. He lived at a time when virtually every device and every manufacturing process could be improved out of all recognition by someone with a bit of spark. Given his wealth, skills and contacts, Bessemer process aside, four minor commercially successful products is a disappointing return.
Our main interest here is in momentousness, by which we mean lasting benefit. Bessemer was more momentousness than typical inventors because he developed the Bessemer process into a successful business that made him rich. Unfortunately, he did nothing useful with his wealth. He wrote little, did not involve himself in politics or philanthropy, and he had no proteges. His intangible legacies are almost invisible. Despite his shortcomings, the Bessemer process was an important milestone in human history. It reinforced Britain's world leading position during Victorian times. We think he was one of Britain's most momentous inventors and mechanical engineers, just about justifying our five medal rating.
Some of our tours take months. Bessemer's took two days. He was born in the tiny village of Charlton on the outskirts of Hitchin, then moved to London as a teenager and seldom left.
In a rather embarrassing inditement of his product, the 1/4 inch sheet steel sign that marks the northern end of Charlton village has cracked in two. There are no obvious signs of vandalism. Perhaps the manufacturer is making the point that steel is no longer made in Bessemer converters. As the sign says, Henry Bessemer was born here in 1813.
Charlton House, where he was born, is still there. We used to say that it was opposite 'The Windmill' pub, but the pub has closed. Don't rely on satnavs or phone maps either. They all lead to another Charlton House. The best way to find Bessemer's home now is to park in what used to be the pub car park beside the footpath to the Hicca Way. Here is the MB2 doing just that, with the former pub back left and Charlton House back right. If the car park is developed, look for the footpath sign pointing to Hitchin Hill.
The Bessemers must have been pretty wealthy. Henry explains that the house was on a small country estate. Assuming it was within the 1870 field boundaries, it stretched back some 200m east and 300m south. The house is large and sprawling, looking as if it has been extended many times. It is privately owned now. We peeked in through the window, only to find the owners sitting in their parlour peeking out. Oops. Still, they didn't seem to mind us taking a picture of the blue plaque beside their window.
Bessemer talks in his autobiography about his childhood delights and inspirations. Daguerreotype photographs feature prominently. We forget how magical it must have been to see a photograph for the first time. He says how he was spellbound by the scenes in 'Arabian Nights'. He mentions his school, and picking up yellow clay beside the road with which he made models, and two sources of inspiration. One was his father's type foundry. The other a nearby watermill. He says that the type foundry was on his father's estate. No outbuildings are visible now. It must have gone. As far as we know, no one has ever found his school or the watermill. We went in search.
Bessemer talks at length about the watermill: "I was very fond of machinery, and of watching it in motion ; and if ever I was absent from meals, I could probably have been found at the flour mill at the other end of the village, where I passed many hours, gazing with pleasure upon the broad sheet of water falling into the ever-receding buckets of the great overshot water-wheel." The River Hiz passes through the village. We walked up and down looking for the remains of a water mill. Nothing obvious. He says that the watermill was at the other end of the village. Charlton House is just about in the middle today. The 1880 Ordnance Survey map below only shows a handful of houses. We gather that the mill was probably at least 200m from Charlton House.
Charlton House is labelled B on the map above. Bessemer says that the wheel has an overshoot of water. It must be at a waterfall. There could not have been a waterfall at the southern end of the village because The Hiz only rises a few hundred metres south of the village. The only waterfall labelled on the map is at W. We went to look. There is an old looking brick dam - picture below - exactly where we would expect to find the mill. There are bricks in the ground, as if there had once been a building. We think it must have been the mill's location. Admittedly, there is no waterfall now, or indeed any significant water drop. It was obviously there in 1880. We guess that it must have silted up, which probably put paid to the mill.
Bessemer gives no clues about his school. Some have assumed that he must have attended William Wilshere's school in Hitchin, now the site of the British Schools Museum. It opened in 1810, so it is possible. But Wilshere opened the school specifically for children of the poor and specifically to help them to read and write. Henry Bessemer came from a wealthy family. We know he was literate from a young age because he read Arabian Nights. There is only one other school on the 1880 Ordnance Survey map (S) that is within walking distance. It is on the A602, 1500m from Bessemer's house (B). We went to check it out.
There is an old looking, but heavily modernised, building on the corner and two cottages at the spot labelled 'School' on the map. We think the one on the corner (below) looks more like an erstwhile school.
When Henry Bessemer left school, presumably at 14, his father gave him a workshop and machine tools on the estate, so that he could teach himself to become an engineer. There are no outbuildings now, so we guess it has gone.
Bessemer's father decided to move his family to London for business reasons. They arrived on 4th March, 1830, when Henry Bessemer was 17. We could find no evidence for where they lived.
In 1833 Bessemer moved into 15 Northampton Gardens, Islington, as a bachelor. He was married in 1834. This was their family home. His house has been replaced by the University of London's Talt Building. The foundations of Bessemer's house were found during the construction. A blue plaque to Bessemer was unveiled in 2017.
At some point before September 1841, the Bessemers moved into Baxter House at 171 Old St Pancras Road. In the grounds he established the St Pancras Ironworks. They made a wide range of iron products, some of which are listed in the 1868 advert above. It was here that Bessemer devised the Bessemer process and where he conducted his experiments. It was here that he nearly set fire to the roof when his first Bessemer Converter spewed molten slag like a volcano.
There is no trace of Baxter House now. One advert says that it was opposite St Pancras Old Church. The church is now on Pancras Road, so we guess it dropped the 'Old St' prefix during the intervening 150 years. The building opposite is a block of flats named 'The Chenies'. We guess this was the location of Baxter House, although we could find no sign that Bessemer was ever there.
We went looking for surviving St Pancras Ironworks products. Actually, we went looking specifically for St Pancras Ironworks drain covers, manhole covers and pavement lights, due to a slightly weird obsession we have about Wood & Stannard, a foundry that operated from land adjacent to our back garden. We came across these St Pancras Ironworks pavement lights over a cellar in Broad Street, Hereford. They do not hold a candle to those made by rival Hayward Brothers, but they are far rarer.
In 1858, Bessemer moved to Sheffield where, the following year, he opened the Bessemer Steel Works in Carlisle Street. The factory was opposite Bessemer House (below), now at 59 East Carlisle Street. The current Bessemer House dates to 1901, long after Bessemer sold his shares and moved back to London. Never the less, it carries a blue plaque explaining that Bessemer's factory was opposite. When we were last there, it had become dilapidated, with the blue plaque hidden behind a 'For Sale' sign, as if they were ashamed of it. Pests. The factory over the road continued making steel until the 1970s. It has been replaced by a modern industrial park (that does not seem to manufacture anything).
By 1863, Bessemer was a very wealthy man. He bought a 40 acre estate in Denmark Hill from Dulwich College. Architect Charles Barry, who had previously designed the Palace of Westminster, was commissioned to refurbish and extend the main house, which was renamed Bessemer House. A few years later Bessemer Grange was built in the grounds for his daughter's family. Both buildings were demolished after WWII. The land was used for council housing. Bessemer House stood at the exact location of the Basingdon Way roundabout. We could find no indication of its famous history.
While we were in Sheffield, we went to Kelham Island to look at Britain's last surviving complete tilting Bessemer Converter. Very impressive it is too.
Bessemer left his possessions to the London Science Museum. When we were children, we (think we) can remember seeing a complete display hall of Bessemer's possessions, as well as the prototype Bessemer Converter from the Barrow Haematite Steel Company (above). Only the prototype is left on display. It seems that Bessemer's standing has fallen in the last 50 years. Not in our eyes. We think he was at least Watt's equal.
Bessemer died in 1898 at his home in Denmark Hill. He is buried in West Norwood Cemetery in a relatively modest plot; well, modest compared to his contemporaries and resting place neighbours Sir Henry Tate and Sir Henry Doulton.