You know how this works
On the evening of May 24th, 1847, a disaster occurred that would help change the trajectory of building material technology.
When a train weighing 60 tons crossed the River Dee bridge in Chester, England, the bridge collapsed. Several passenger cars plunged 40 feet to the river bed, killing five and injuring many more. Outrage ensued, and local media plastered the story on the front page of their papers, embarrassing the designer, Robert Stephenson.
A coroner’s inquest was launched ten days after the accident. Several bystanders reported seeing “the bridge’s iron girders split from the bottom up.”
The Manchester Times and Gazette collected an eyewitness report from a local milkman that provided a blow by blow account:
A crack open in the middle of the girder; the train and tender were about the centre; the crack opened from the bottom; the engine had passed the crack, and the tender was right upon it; the engine and tender went on, and I saw the tender give a rise up; the carriages gave a jump and fell backward; the last carriage went down first according to my judgment; the next I saw was the large stones fall off the wall on the Saltney side; I heard a crash when they fell; I am certain the girder opened up from the bottom.
The inquest uncovered that, presumably, the accident was avoidable. Several of the bridge’s painters reported observing large deflections in the joints of the iron supports. Despite those reports, the jury convicted neither the bridge’s designer nor his staff of professional negligence. Instead, they ruled the deaths as accidental.
However, the juror’s verdict did question the use of “so brittle and treacherous a metal as cast iron,” specifically for infrastructure projects. The jurors capitalized on the highly publicized case and called upon the Queen to investigate the safety worthiness of England’s bridges:
[We] call upon her Majesty’s government to institute such an inquiry into the merits or demerits of these bridges as shall either condemn the principle or establish their safety to such a degree that passengers may rest fully satisfied there is no danger although they deflect from 1 to 5½ inches.
Two years later, a Roral commission began an investigation into the integrity of England’s iron bridges. Through the investigation, the public came to fully recognize the limits of cast and wrought iron.
Ancestors of Steel
Steel has been around for centuries. Archeologists have discovered 2,420-year-old clay crucibles Indian metalworkers used to combine carbon and iron. By sealing wrought iron and charcoal bits inside these crucibles and melting them in a furnace, the molten iron would soak in the carbon, creating an early form of steel.
India exported their "Wootz Steel" around the world. Syrians used it to make high-quality Damascus steel swords, and the Spanish used it to forge weapons for Roman armies.
After the fall of the Roman Empire in 476, Indian exporters had trouble moving their steel through Europe. Without the Romans to keep things in check, merchants were often ambushed, roads were in disrepair, and plague was rampant.
With less Indian steel to go around, Spanish metalworkers supplemented metal production by forging their own inside the Catalan Furnace. The Spanish had advanced techniques and created great steel, but the best steel was found in Japan.
As part of a semi-religious process, the Japanese improved the integrity of their steel by continuously exposing the metal to charcoal while reheating and repeatedly folding it.
Beyond increasing steel quality, they also developed methods to add aesthetic appeal. When making samurai swords known as Katanas, Japanese smiths would brush iron powder along the length of the blade. This created patterns in the metal similar to wood grain. Five of these incredibly artistic blades known as "Five Swords Under Heaven" are still around and considered holy relics in Japan.
Around the 13th century, with no way to mass produce steel and the western world at war, metalworkers made a trade-off between quantity and quality and began pumping out pig iron. The invention of cannons and other firearms created tremendous demand for cheap metal. Low-quality pig iron fit the bill.
Paying the piper
The River Dee Bridge Disaster shows us that trading quality for quantity eventually catches up with you. It’s tragedies like collapsing bridges and countless other cast and wrought iron failures in the 19th century that pushed steel adaptation.
19th-century engineers already knew they needed a more reliable, less brittle material than iron. But what choice did they have? Technology limited their options. As we know from the history of steel, better material existed, but the technology to mass-produce it to the scale needed for the modern world did not.
An economic necessity emerged. How do builders get their hands on affordable quantities of high-quality material?
Questions like these drive innovation.
The innovation that enabled cheap mass-production of steel was the Bessemer process.
Henry Bessemer
British engineer and inventor, Henry Bessemer, is one of the few inventors to successfully monetize his inventions. He held over 117 patents and died a multi-millionaire. He had many lucrative creations such as a paint he managed to infuse with bronze. This paint was used to mimic gold plating and made him his first fortune.
Bessemer also invented a ship with cabins set on gimbals which kept them level no matter how rough the water. The idea came to him after a terrible bout of seasickness in 1868. Bessemer would eventually abandon this invention when a trial version of the ship sunk in port on its maiden voyage. The failure caused investors to lose interest and Bessemer scrapped the idea.
Bessemer was a tinkerer at heart. Between 1850 and 1855, he was constantly trying to find ways to make cheap metal for ordnance production. It’s through his tinkering he stumbled upon what he is most known for; the Bessemer Process.
Material Magic
The process is fairly straightforward, yet incredibly innovative: Heat up iron ore in a furnace until it melts. Then, blow air through the iron from the bottom of the furnace. The air causes the impurities in the iron, such as silicon, to oxidize and burn out, leaving behind steel.
At the time, blowing air through the furnace was counterintuitive. When Bessemer suggested it, his foundry workers thought the idea was foolish. Wouldn't the air just cool and resolidify the molten iron?
When they gave in and followed Bessemer's instructions, the foundry workers, and Bessemer, discovered the process actually raises the furnace temperature. This is the result of an exothermal reaction caused by the oxidation of silicon and carbon, which material science had not yet discovered.
The first test of the Bessemer process was described by Bessemer himself as violent and surprising:
All went on quietly for about ten minutes; sparks such as are commonly seen when tapping a cupola, accompanied by hot gases, ascended through the opening on the top of the converter, just as I supposed would be the case. But soon after, a rapid change took place; in fact, the silicon had been quietly consumed, and the oxygen, next uniting with the carbon, sent up an ever-increasing stream of sparks and a voluminous white flame. Then followed a succession of mild explosions, throwing molten slags and splashes of metal high up into the air, the apparatus becoming a veritable volcano in a state of active eruption.
It cannot be understated how radically the Bessemer process would eventually revolutionize the steel-making industry.
Bessemer had found a way to create incredibly pure iron, but that wasn't enough. He still needed a contraption to safely harness the violent chemical reaction caused by his pioneering process.
He would soon develop a solution.
Steel [Pt. 2] coming next week.