Lesson Plan

Chemistry of the Blacksmith's Forge

A blacksmith working at a traditional forge.
A ranger works the traditional forge of the blacksmith shop at Herbert Hoover NHS.
NPS Photo by John Eicher

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Subject:
Chemistry, Engineering, History, Science and Technology, Social Studies
Duration:
2 to 3 classes for research and presentations
Group Size:
Up to 24 (4-8 breakout groups)
Setting:
classroom
National/State Standards:
Next Generation Science Standards: HS-PS3 Energy; Iowa Core: 21st Century Skills (Grades 9-12); National Science Standards: Physical Science (Levels 9-12)

Overview

Students research four questions and present their findings to each other. One class is needed for the research and one to two classes are needed for the presentations. Students can do additional research as homework, so allow a couple days between the initial research and presentations.

Objective(s)

Students will be able to:

  1. Compare and contrast the use of coal and coke as fuels.
  2. Describe the process of destructive distillation and apply it to the process of converting coal to coke in the blacksmith's forge.
  3. Explain how blacksmiths shape iron in the forge and the science behind it.


Background

Coke is produced from coal by the destructive distillation of low-ash, low-sulfur bituminous coal. Destructive distillation is when coal is decomposed by heat in the absence of air. Volatiles in the coal like water, coal-gas (composed of mainly hydrogen, carbon dioxide and methane), and coal-tar, burn off as gases at greater than 1000 degrees Celsius in a forge. The remaining carbon and residual ash is fused into coke. 1000 kg of coal can produce 700 kg of coke. In the Blacksmith's forge, air is fed upward by the bellows through the inner pile of coke which is the hottest part and the part used to shape the iron. The coke (which almost pure carbon) is undergoing combustion as it combines with oxygen to form carbon dioxide.Coke is a better fuel than coal because it has a higher carbon content and so emits less pollution like smoke when burned. It also reaches a much higher temperature when burned, due to the greater carbon content and it's large internal surface area that traps air when air is fed into it by the bellows. The air provides the oxygen allowing the coke to undergo combustion. Coal instead absorbs heat, lowering the temperature.

A blacksmith's fire has an outer cone of coal which is turning into coke as it is heated. The impurities like sulfur are vaporized and the methane and hydrogen and other flammables in it burn off leaving only the carbon. This pits the surface of the coal leaving air pockets in the resulting coke to trap oxygen and allow combustion to occur all through the coke. This inner cone of coke burns at a high enough temperature to soften iron so the blacksmith can shape it. The temperature of a white-hot fire at the inner cone is between 1400-1600 degrees Celsius, and iron placed here can be shaped by hammering to flatten and lengthen the iron as well as taper it. It can also be bent over the anvil. This temperature is even hot enough to weld iron together

Sometimes iron needs to be annealed. This is because the more a blacksmith hammers iron, the harder it becomes. It is said to be "work-hardened" and it may crack or break if it continues to be hammered. So, the blacksmith heats it so hot, it loses its magnetic properties, then lets it cool slowly by burying overnight in the coal of the forge or sand. Now the blacksmith can continue to shape the iron without breaking or cracking it.



Materials

  1. Access to research materials (library books, World Wide Web)
  2. Access to a working traditional blacksmith shop.




Procedure

Students research four questions in groups of 4 to 5:

  1. How are coal and coke different?
  2. How does coal become coke?
  3. Why is coke used by a blacksmith to shape iron and coal is not?
  4. How does a blacksmith shape iron (Include the importance of the bellows as a tool)? 

Allow 1 class period for them to get started and the rest of the report can be assembled as homework.

Students present their findings to the class, answering questions as they occur. It will take at least one class period for this and possibly 2.

(Optional) Students visit a working, traditional blacksmith shop to answer the following questions:

  1. How does a blacksmith create fuel for the forge?
  2. How is the combustion of that fuel more useful than the original material?
  3. What steps does the blacksmith take to shape the metal?
  4. What is the role of the bellows? 

The tour of the blacksmith shop should take 30 to 45 minutes and should answer the above questions. If not, have the students find the answers later.

Assessment

Was the presentation coherent and informative? Was the group presenting able to answer all of the questions they were asked? Did all of the group members participate in the research and presentation?

Above proficient: Students completely answered the question they were given and were able to answer all of the audience's questions unless the questions were off-topic.

Proficient: Students answered the assigned question thoroughly and most of the questions asked by the class.

Below proficient: Students answered their assigned question in very basic terms with no elaboration or extra information. Students answered less than half of the questions they were asked.



Park Connections

Herbert Hoover's father was a blacksmith who went on to become a successful businessman through hard work and economy. Herbert would have observed these qualities in his father even at his young age. His father had a skill that provided the people of his community with valuable resources necessary in their daily lives. Additionally, the blacksmith shop represents a technology built on the foundations of scientific knowledge common during Herbert's boyhood.The technology used today, while further advanced, still owes it's birth to scientific knowledge common to the era.

Extensions

Research and discuss:

  1. How is a welder the modern-day equivalent of the blacksmith? 
  2. What fuel do welders use in their torches? How do the torches work? 
  3. How does a welder differ from a blacksmith?


Vocabulary

destructive distillation, coal, coke, bellows, anvil, volatiles, weld, anneal