Keywords: Charcoal, Pennsylvania forests, chemical reaction, ground forest kiln, smelt; Grade Level: 7 - 10; Total time required by lesson: 2 class periods each 45 minutes; Setting: Classroom

Goals for the lesson

  • Student will identify the historical purpose of forests in Pennsylvania.
  • Student will explain the iron manufacturing process.
  • Student will write and explain the chemical formula of making charcoal.

Materials needed

  • Piece of natural made charcoal
  • piece of wrought iron
  • Computer with digital projector

State Standards Addressed: Science and Technology (3.4.10) - Physical Science, Chemistry and Physics ; Environment and Ecology (4.8); Humans and the Environment (4.2) - Renewable and Nonrenewable Resources

Teaching Model: Goal-based Instruction

Subject Covered: Chemistry, Social Studies, Ecology

Topic Covered: Chemistry process behind charcoal, how to make charcoal, use of charcoal in iron furnaces


Show the class the piece of charcoal and have them write down three things about it on a piece of paper to be handed in. It can be questions or comments about how it was formed, what it is, and where it came from. It should not be descriptors about it i.e. black, brittle.

Collect the responses. Flip through the papers and read off about 6-10 different responses, concentrating on answers that relate to the lessons topics and goals. Do not answer any of the questions at this time. Next display the picture of an iron furnace. (See fig 1) Begin a classroom discussion about what the picture is and what it was used for. Use the following background information as a guide.

Samuel Miles and John Patton led in the creation of the Centre Furnace in the early 1790's. Its purpose was to utilize the natural resources that were so very abundant in the region to manufacture iron. What natural resources are we talking about here? (Iron ore, hardwood trees, limestone and water)

Iron ore is a rock that contains a certain amount of iron but mixed with various silicates and oxygen atoms.

In 1792 Centre Furnace began manufacturing iron by filling the 35 foot furnace stack with charcoal and sending a blast of air through the furnace with use of bellows powered by a water wheel. What is a bellow and why was it needed to ignite the furnace?

Display picture of a bellow - Courtesy of Pearson Scott Foresman - Donated to the Wikimedia Foundation for use in the public domain. This image illustrates what a bellow can do. It obviously is much small than the one used for the furnace.

The bellows are used to send large amounts of air into the furnace resulting in increased combustion and higher heat output which was needed for the iron smelting process. If you have ever seen anyone blowing into a low campfire to get it to burn better that is essentially what the bellows are doing, except on a larger scale. (Show figure 2 from the Centre County Historical Society -

Smelting is the process of refining the iron ore into useable purer iron. Here is where some chemistry gets involved. Starting with the iron ore, you want to remove the impurities and deoxygenate the ore so you are left with only iron atoms. In order to take the oxygen atoms away you need something for the oxygen atoms to bond with, and of course you need heat. That is where the charcoal comes into play. The charcoal is primarily carbon which likes to bond with oxygen to form CO and CO2. This gets rid of the oxygen atoms nicely, but we are still left with the silicates because they will not bond with carbon.

At this point you have wrought iron. (Show the piece of wrought iron) This is a useful piece of iron and was used throughout history by blacksmiths. We see it today in fences and decorative hooks. It is strong and can be shaped easily and pounded thin. What chemical property is that called? (Malleable)

To get rid of the silicates and make even purer iron you need the last resource we mentioned is so prevalent to this area - limestone. Limestone contains calcium which will bond with the silicates and float to the top of the blast furnace. Then the iron workers would essentially drain the liquid iron out of the bottom furnace on one side and drain the liquid calcium silicate mixture, called slag, on the other side.

That entire operation was very successful and resulted in additional furnaces to go into operation throughout the region. It led to the development of Centre Furnace Village which became basically a self sufficient community and included saw mills, a post office, stores, housing, a church, and a school.

Class Discussion

What it means to be a self-sufficient community.

Utilizing and managing the land that surrounds you is very important. In order to be successful they needed an abundance of trees to make the charcoal that powered the furnace. The Centre Furnace used 16,000 acres of forested land which would include modern day Ferguson, College, Harris, Patton, Halfmoon, and Benner townships as well as the Borough of State College. These trees were essentially clear cut over many years and still managed to regenerate themselves into the present day forests.

The process of making the charcoal also involves chemistry. Some of you said that this looks like a piece of burnt wood. Essentially it is wood that heat has been applied to in order to remove impurities and leave the carbon. The hardwoods that were present in this area were perfect for making charcoal because hardwoods have higher carbon contents than softwoods. (Possible side discussion on Hardwoods vs. Softwoods)

When you burn wood in a campfire what result? (ash) How come you can take a huge pile of firewood and only end up with a small amount of ash? (goes into the air) Does the wood contain water? (Yes) What happen to it? (turns into water vapor) It also turns into carbon dioxide. Since we are trying to use the carbon part of the wood it is not good if it turns into a gaseous CO2. We need to remove the impurities and be left with the carbon. To do this we need a small amount of oxygen to limit the combustion.

Workers built large 30 - 40 foot diameter forest kilns out the timber that was harvested in the area. The wood was layered around a center post and small chimney opening in such a fashion that all possible gaps were filled with wood. The chimney was filled with small kindling while the rest of the pit was covered with dirt and leaves. (Show Figure 4 from Figure 4 - Hopewell Furnace National Historic Site ) It was ignited by either dropping hot coals or lit touches down the chimney. The result was a very slow burn with little oxygen for the wood. If more oxygen was needed on a particular side of the pit a small vent could be made, but they needed to be very careful with how much combustion was occurring inside the pit. The wood was aloud to burn for about 10-14 days until it all became charcoal. The pits were then carefully uncovered and the cooled charcoal was removed to be sent to the furnace.

Now lets put this process into a basic chemical equation: Start with the basic combustion of wood. What is on the reactants side (chemicals that will react go on the left side)? (Wood, air), What does it need to combust? (Heat) What are the products (chemicals produced through a reaction go on the right side)? (Ash, smoke)

To make this more specific we say wood is mostly cellulose (CH2O) and the part of the air that affects the reaction is mostly oxygen O2. So the reaction can be written: CH2O + O2 -----> CO2 + H2O What happened to the ash and smoke? Remember we talked about the impurities in the wood - that non-flammable material is what causes the ash. The smoke is caused by tiny pieces of charcoal that formed because there was not enough oxygen present being allowed to be lifted away.

Now in the forest kilns we have a different situation. We have the wood with little to no oxygen present being heated. We end up with the following equation:

CH2O -----> C + H2O

The cellulose is heated and the product is carbon as a solid and water vapor. Charcoal!


On a piece of paper to be handed in I want you to answer the following questions:

  1. Explain the role of the forested land in this area in the late 18th and much of the 19th century.
  2. Explain the iron making process that occurred at Centre Furnace and how the village surrounding it became self sufficient.
  3. Compare and contrast the chemical equation for the ordinary combustion of wood with the chemical equation for the production of charcoal. Include both written equations.

Literature/Sources Cited

Figure 2 - Courtesy of Pearson Scott Foresman

Figure 3 - Centre County Historical Society -

Figure 4 - Hopewell Furnace National Historic Site


Bryan R. Fatzinger, 8th Grade teacher - Mount Nittany Middle School, State College Area School District