Monday, January 10, 2011

A Brief Explanation of the Eastburn-Jeanes Lime Kilns

Eastburn-Jeanes Lime Kilns along Upper Pike Creek Rd
 The last two posts have focused on the Eastburn-Jeanes Lime Kiln Historic District, first on its history and then on its structures. Now, in the third installment of what's turning into a series here, I'd like to look closer at the structures at the center of it all -- the lime kilns themselves. In all honesty, this post might get more specific and technical than some prefer, so if you're not interested in exactly how the kilns worked and what they did, feel free to skip this one (you won't hurt my feelings, honest). I'm really only doing this because prior to investigating the subject, I had no idea myself just what a lime kiln was. Some of the resources I found had some fairly in-depth explanations about the industry and processes, so I thought I'd pass along what I found, just on the off chance that someone else might find it interesting.

The process begins with the quarrying of limestone, which, as you might guess, is found near the surface in the area of the Eastburn-Jeanes Lime Kilns. In this area, it was likely done by hand for the most part, although later in the 1800's they may have used some black powder, or later, dynamite. The limestone was broken up into small pieces, no larger than about 10 cubic inches a piece (maybe about baseball-sized?). It was then loaded into the kiln to be heated slowly over several hours. What this did was to cause a heat-induced chemical reaction to take place. Limestone, chemically speaking, is calcium carbonate (CaCO3). When heat is applied to it, the chemical bonds break releasing carbon dioxide (CO2), and leaving behind calcium oxide (CaO), or lime. Also called "quicklime", this was the product that Jeanes and Eastburn sold.

The burning of limestone into lime was by no means a new process. In fact, it was known at least as far back as the Roman Empire, as lime was one of the main ingredients in the concrete that the Romans used to build their monumental structures. When Abel Jeanes and David Eastburn first began producing lime in about 1816, they probably sold it mostly to be used in mortar and as a plaster for homes. For these purposes, water was often added to it to produce "slacked" lime. As luck would have it, though, a new and more widespread use was on the horizon. In the late 1810's and 1820's, the use of lime as an inorganic fertilizer began to catch on in the South. By the 1830's, the practice had made it to the fields of Delaware and Pennsylvania, making possible the rapid flourishing of the local lime industry.

In order for the resulting lime to be of the highest quality, how it was heated was vitally important. In order to drive out all of the CO2, the limestone had to be heated at a slow burn for several hours -- the lower the temperature and longer the burn, the better. Early kilns were not particularly efficient, since they had to cool down completely before the quicklime could be extracted. This method wasted a lot of heat and fuel. In the early 19th century, though, a new kind of kiln, called a "perpetual kiln", was introduced. This was the type that Jeanes and Eastburn erected on their properties. As you might guess, this type could burn continuously instead of having to cool down between loads. Even though it was more efficent than the older types, it still consumed vast amounts of wood. In addition to their own holdings, the Eastburns bought timber rights from surrounding property owners to supplement their lumber supply.
Diagram of a typical perpetual lime kiln
The kilns themselves were anywhere from about 15 to 23 feet high, and usually built into a hillside. This not only helped to insulate the kiln from the wind, but also made loading easier, since loading was done from the top. The interior of the kiln was shaped like an ellipse -- narrower at the top and bottom (about eight feet at the top and five or six at the bottom), and wider in the middle. This shape helped focus the heat and to facilitate settling of the product at the bottom. At the base was the hearth, or "thimble" -- an opening six to ten feet high and about equally wide, with several shafts cut into it to act as flues to regulate the burning of the alternating layers of stone and wood above (this is the space underneath the brick arch seen in the picture). Behind the hearth at the base of the kiln shaft was an iron grate which supported the weight of the charge above. As the burnt lime fell through the grate, it was then raked out by the kiln operator. Interestingly, no two of the Eastburn or Jeanes kilns are identical. Presumably, new kilns were built as they were needed, and the builders constantly tinkered with the design in order to improve efficiency.
One of the Eastburn Lime Kilns
The job of the kiln attendant was a difficult one. First of all, it could take two men a week and a half to fully charge a kiln the size of these. Then the kilns, once lit, burned 24 hours a day for weeks or months at a time. The operator had to monitor the temperature and rate of burn, and then rake out the lime when it was ready. As the Historic American Engineering Record report (third down on the page) states:
A cord or more of wood (128 cubic feet) was required to burn 60 bushels of lime, each weighing approximately 80 pounds. A kiln the size of those in Pike Creek Valley held a limestone charge sufficient to produce a total of 525 bushels of lime. Once started, the burning process could produce 300 bushels every 24 hours.
The lime was raked out every six to eight hours for as long as the kiln burned. After it was loaded into three-bushel capacity casks, it was shipped immediately for use. This was important, because as the quicklime sat, it would absorb carbon dioxide from the air and begin to return to its previous state, making it less useful for fertilizing or other tasks. From beginning to end, the process was difficult, but the operators of the Eastburn-Jeanes lime kilns made it a profitable one for almost one hundred years.


  1. Thank you very much for this interesting explanation of lime kiln activity. I am researching the lime kiln at Kenny's Crossing in the Elverson, PA area and your article is very enlightening. Cal Roth

  2. Great post, much appreciated! Really well done.

  3. Really great article. I printed it out for future reference. Would love to stop out one day to take a look at the old kilns. Are visitors welcomed?

    1. David and Elizabeth (Jeanes) Eastburn are my 2nd great grandparents. Abel Jeanes is my 3rd great uncle. You can see some of the kilns along the side of the road. Just drive south on Upper Pike Creek Rd from Paper Mill Rd. and you will see some.