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The Hurstville Lime Kilns are located just off highway 61. At the site you will find signs explaining the history of the kilns as well as information about their restoration. This historic site is owned by the Jackson County Historical Society and is managed by the Jackson County Conservation Board. It is open for viewing from 6:30 am to 10:30 pm.
Brief history of the kilns
Built in the 1870's, the Hurstville Lime Kilns heated limestone (Calcium Carbonate) rock mined from nearby quarries to form lime mortar used primarily for building construction as a stabilizer in mud renders and floors. The production of lime became one of Iowa's most important early industries. The last time the kiln was fired was in 1930.
The firing process
Simplified, a lime kiln is an oven used to produce quicklime by the “calcination” of limestone. Limestone is made up mainly of three components: calcium, carbon and oxygen. When limestone is heated the carbon escapes as carbon dioxide, leaving lime. This reaction takes place at 750°F, but a temperature up to 1300°F is usually used to make the reaction proceed more quickly. The process of lime burning was carried out by a kilnsman who was experienced in the reduction of limestone. An experienced kilnsman was required to monitor many variables in order to reduce the amount of "dead burnt" lime which was not useful as an end product. The heating and cooling process took several days.
These kilns were "draw" kilns. Draw kilns operate under the principal of gravity. Limestone is fed into the top of the kiln and the cooked stone is removed from the bed of the kiln. Fireplaces were located at the sides of the kiln where fuel was burnt to cook the limestone. One advantage of the draw kiln was that it could be operated on a continual basis. Even though this type of lime kiln was more effective than past versions, it was still extremely inefficient and the lumber needed to fire it could easily necessitate the clearing of large tracts of woodland.
After the lime was fired it was cooled in cooling sheds and slaked. Slaking involves adding moisture to the lime; this occurred in a number of possible ways from sprinkling water on the lime to letting it sit and absorb water from the atmosphere. The correct mix is approximately one part lime to one part water. Other additives were combined with the lime to create various products.
The end days
In the early settlement days the lack of a good road system necessitated the production of lime wherever the raw materials were easily mined. The development of the rail network made the local small-scale kilns unprofitable, and they gradually died out through the 19th century, replaced by larger industrial plants. At the same time as transportation methods improved, so to did the use of Portland cement. Both of these factors combined with a growing shortage of available hardwoods for fuel made operations such as this become unprofitable and eventually cease production.
Limestone (Calcium carbonate)
Uses of Calcium carbonate-
The limestone mined here dates back to the Silurian Period of the Paleozoic Era (410-438 million years ago). A common sedimentary rock, limestone was formed when a shallow sea existed over the area. In this sea accumulations (reefs) were created by shell and shell fragments consisting of corals, brachiopods, crinoids and other types of early life. Many marine organisms extract calcium carbonate from the seawater to make shells or bones and when these organisms die their shells and bones accumulate on the seafloor. Over millions of years these sediments harden into what we see today as limestone. Calcium carbonate is found naturally as a component of aragonite, calcite, vaterite, chalk, marble, and travertine.
· As a filler in plastics.
· As an extender in paints.
· As an ingredient of cement.
· In swimming pools as a pH corrector.
· In agriculture to improve acidic soils.
· In forensic science to reveal fingerprints.
· As a major component of blackboard chalk.
· In adhesives, sealants, and decorating fillers.
· In water and sewage treatment to reduce acidity.
· As a building material in the form of marble or limestone aggregate.
· Medically as a calcium supplement, an antacid or as a base material for pill tablets.
· When cured, to create firebrick which was used to line furnaces and build fire-resistant structures.
(Your log may be deleted if you do not follow these logging requirements)
E-MAIL ME (Do NOT post in your log)
#1 ESTIMATE: How high are the kilns?
#2 What is stamped on the bricks to the right of the kilns? - optional if snow covered
#3 According to the signage at the site why did the Lime Kilns cease production?
POST WITH YOUR FOUND IT LOG
#4 Upload a photo (with your "found it" log) taken at a recognizable part of the site and include your GPS in the picture NOTE: Pictures are now OPTIONAL. But still appreciated .
Permission for this EarthCache has been granted by Daryl Parker, Director Jackson Co. Conservation.