Introduction

While studying chemistry, we decided to explore the lime cycle by building a lime kiln.  Limestone was historically quarried in Rockland County where I live and was used as a building material and was also burned to be used as a fertilizer. Slaked lime is used in mortar.

Below is a diagram of the lime cycle and its chemical reactions and what is needed to produce them, as well as the element’s names and basic components.

Limestone = CaCO3 (calcium carbonate)

Quicklime = CaO (calcium oxide)

Slaked Lime = Ca(OH)2 (calcium hydroxide)

Building a Lime Kiln

In order to create the first chemical reaction of the lime cycle, we needed to heat limestone to a very high temperature (900  degrees  Celsius or 1652 Fahrenheit), so we built a kiln. Using bricks laid down in a 2' by 2' shallow pit with a flue tunnel to blow air into with a fan, we piled up 14 tiers of bricks. Then we dumped in 20 lbs of charcoal, put in our limestone, and piled in another 20 lbs of charcoal and lit it up.

 

Firing the Lime

Every hour or so, we went out to check the kiln. If the kiln needed more charcoal, we put more in. Close to night time we ran out of charcoal, so we let it burn out and cool down overnight.

Quicklime

Next morning there was hardly anything left in the kiln, except for some ashes from the charcoal and our pieces of fired lime, now quicklime. It looked very different.

                 Quicklime                                                               Limestone

An unexpected surprise was this hard, black stuff which was stuck to most of our quicklime. We figured it was varnish that had coated the limestone and had melted off.

Slaked Lime

We brought our quicklime inside and slowly poured water on some of our pieces of it. The stone heated up very quickly and started sizzling and steaming. After a while (and lots more water) the quicklime crumbled into a powder, which was slaked lime.The name is slaked lime because the quicklime has “slaked” its thirst with the water.

Making Mortar

We took some of our powdery slaked lime and mixed it with some sand and created a paste by adding more water. Now we had mortar, which we used to cement some bricks together.

Tests with Litmus

We created lime water by dissolving some of our slaked lime in water and then running it through a coffee filter to remove the big clumps. We used cabbage-water litmus to test the alkalinity of the lime water. When litmus was added, it changed to green, showing that lime water is a base.

Test tubes from left: limewater, cabbage-water, and limewater + cabbage-water.

Breath Test

When we put a straw into our lime water and breathed through it, the liquid turned from clear to a milky white color. After letting it sit for a while, the white particles, small lime deposits created by a reaction with the carbon dioxide in our breath, had settled to the bottom and our liquid was clear again.

Bibliography

Bedell, Cornelia F., Now and Then and Long Ago in Rockland County. New City, NY, The Historical Society of Rockland County, 1992.

Mitchell, David S., The Wonders of Waldorf Chemistry. Fair Oaks, CA, The Association of Waldorf Schools of North America, 2004.

Hoffman, John, “Building a Portable Lime Kiln,” reproduced in Mitchell, The Wonders of Waldorf Chemistry,

Limebase Products, Ltd., http://www.limebase.co.uk/guide_chemistry.htm.

Additional resources:

www.lime.org/aboutlime.html

www.mainecoastguide.com/sidebars/lime.htm

http://en.wikipedia.org/wiki/Limestone

http://www.mcasv.org/Points/JAN_2K6.pdf