|Eastburn-Jeanes Lime Kilns along Upper Pike Creek Rd|
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|
|One of the Eastburn Lime Kilns|
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.