This double lime kiln is an example of the kilns once found throughout the Musconetcong River Valley. Early settlers farmed an area until its fertility was depleted. By the early 1800s German immigrants introduced the practice of sweetening and enriching their fields with lime burned in kilns to restore the land. During the 19th century kilns of different sizes but similar design could be found on nearly every farmstead, located near outcroppings of limestone which is abundant in the region. Kilns faced with flat fieldstone would be built into a bank of a hill like this one, with a wagon path to the top. From Rock to Fertilizer
Little is known of the history of this kiln, but its good condition and absence from the 1874 Warren County Atlas indicate its relatively late construction. As a double kiln it likely served several farms, but the evolution of industrial production techniques using gas for fuel caused the rapid abandonment of such kilns during the early 20th century. Most are now gone, dismantled for reuse of their stones or simply collapsed. But others have survived.
Heating limestone (calcium carbonate) converts it to quicklime. The quicklime would be slaked with water resulting in hydrated lime. This powdered lime was easily absorbed by the soil. Farmers didn't know the chemistry,
but they knew what worked.
Kilns were filled from above with alternating layers of fuel (cut wood, scrap wood, timbers and/or coal) and limestone in softball sized chunks at an approximate rate of a cord of wood to the bushel of limestone, the yield being about ½ bushel of finished lime for each bushel of stone. The amount of hardwood fuel required for a single burn is two to three times the volume of lime produced. Local forest wood, which also used for nearby iron furnaces, was exhausted by the 1850s.
The fire would be set from below and work its way up through the kiln. Temperatures range from 1600 to 2100 degrees, breaking the stone into smaller chunks. The temperature of the fire would be controlled by adjusting the air flow in the draft hole. Depending on the kiln and conditions, they would burn for several days or longer. Loading and firing the kiln took an enormous amount of time and work, and "lime frolics" gave farmers and their families a chance to gather together.
The finished lime would filter through the grate and be raked out, set in mounds and wet down with water. Bushels of cooled, slaked lime were loaded onto wagons to be spread onto the fields at rates of 40-50 up to 90 bushels/acre.
Produced by Musconetcong River Management Council and Musconetcong Watershed Association
Funded by Hawk Pointe Foundation, Village Supermarkets
ShopRite, Washington Township Historical Commission and US National Park Service