074

The Iron Bridge, Ironbridge, England

52° 37′ 38.08″ N, 2° 29′ 7.92″ W

Birthplace of the Industrial Revolution

The Iron Bridge crossing the river Severn is the first bridge ever made from cast iron (see Figure 74-1). Its 30-meter span, created from 379 tons of cast iron, has been standing since 1779. Today, as in the 18th century, the bridge is a major tourist attraction. Though closed to cars, it is open to foot traffic.

Figure 74-1. The Iron Bridge

Prior to its construction, the only way to cross the river was by ferry, and the surrounding area had rich coal deposits supplying industries in local towns. The businesses needed a more reliable crossing, and shares were issued to raise the money necessary to build a bridge.

The bridge was constructed by Abraham Darby III, whose grandfather, Abraham Darby, had perfected coke smelting to produce iron goods. Coke smelting greatly reduced the cost of making cast iron, and led the surrounding area to be called “the Birthplace of the Industrial Revolution.”

Once the bridge was open, the town of Ironbridge grew beside it, and with advent of steam power, cheap cast iron, and spinning wheels, the Industrial Revolution was underway. Today the entire Ironbridge area is a UNESCO World Heritage site, and features the Blists Hill Victorian Town (with costumed staff portraying daily 19th-century life and a weekly demonstration of ironwork at The Foundry), a number of museums covering the area and local industry, and the bridge itself.

The Coalbrookdale Museum of Iron contains the excavated remains of Abraham Darby’s first coke-burning blast furnace and an explanation of the cast iron production process. For children, the interactive design and technology center Enginuity has hands-on exhibits and demonstrations for all ages.

Since the entire village of Ironbridge is an open-air museum, visitors should plan to spend the entire day in the area. If you’re staying overnight, try to get a room at the Tontine Hotel. The hotel was built in 1784 to profit from the popularity of the bridge—it sits at the end of the Iron Bridge, and some rooms have a view directly over the bridge itself.

The hotel gets its unusual name from a form of financing called a tontine. Investors buy shares in a business, such as the hotel, and receive dividends. When a shareholder dies, their shares are divided among the remaining living shareholders, providing an enormous motivation for shareholders to benefit from each other’s deaths (accidental or otherwise). For that reason, tontines are illegal in many countries.

Practical Information

Extensive information about the Iron Bridge can be found at its website: http://www.ironbridge.org.uk/.

Iron Smelting

Prior to Abraham Darby’s invention of the coke blast furnace, charcoal was used to extract iron from iron ore. In a blast furnace, a mixture of fuel (charcoal or coke) and iron ore is continuously added to the top of the furnace. Air is pumped into the bottom of the furnace, the fuel burns, and the ore reacts with carbon in the fuel to extract iron. The molten iron and the residue (called slag) are extracted from the bottom of the furnace.

Charcoal-based blast furnaces required an enormous amount of wood to operate. The wood was first burned to create charcoal, and the charcoal then used to extract iron. Darby’s use of coke was more efficient because coke is made from coal instead of wood (which was in critically short supply as the demand for iron rose), and coke is physically stronger than charcoal, which meant that much larger blast furnaces were possible. Coke blast furnaces were capable of producing 5 to 10 tons of iron per week.

Coke is produced by burning coal at up to 2000ºC in an airless oven. This high-temperature baking leaves just the carbon (and a little ash), extracting water, gases, and tar from the coal.

In the blast furnace, the carbon from the burning coal reacts with the oxygen in the air, creating carbon dioxide and additional heat. Further up the furnace, the carbon dioxide reacts with more carbon in the coke and turns into carbon monoxide (see Equation 74-1).

Equation 74-1. Coke turns into carbon dioxide, then carbon monoxide

Near the top of the furnace, the carbon monoxide reacts with the iron ore (such as naturally occurring haematite, Fe2O3) to separate the iron and produce carbon dioxide gas (Equation 74-2).

Equation 74-2. Carbon monoxide extracts the iron