This double lime kiln is an example of the kilns once found throughout the Musconetcong River Valley. Early settlers farmed the area until its fertility was depleted, and by the early 1800s German immigrants introduced the practice of sweetening and enriching fields with lime burned in kilns to restore the land. During the 19th century, kilns of different sizes but similar design stood on nearly every farmstead near outcroppings of abundant limestone. Faced with flat fieldstone, they were built into a hillside with a wagon path to the top. The good condition of this kiln and its absence from the 1874 Warren County Atlas indicate relatively late construction, and as a double kiln it likely served several farms. Such kilns were rapidly abandoned during the early 20th century as industrial production techniques using gas for fuel developed, and most disappeared through collapse or dismantling for reuse of their stones. Heating limestone converted it to quicklime, which was then slaked with water to produce hydrated lime, a powder easily absorbed by the soil. Kilns were loaded from above with alternating layers of fuel and softball-sized chunks of limestone, at about a cord of wood to a bushel of limestone, yielding about one-half bushel of finished lime for each bushel of stone. A single burn required hardwood fuel amounting to two to three times the volume of lime produced, and local forest wood, also used for nearby iron furnaces, was exhausted by the 1850s. Fires were set from below and worked upward through the kiln at temperatures from 1600 to 2100 degrees, with airflow controlled through the draft hole, and burns could last several days or longer. Loading and firing demanded enormous time and labor, and lime frolics gave farming families a chance to gather together. Finished lime filtered through the grate, was raked out, heaped in mounds, wetted, cooled, and loaded onto wagons to be spread on fields at rates of 40 to 50 up to 90 bushels per acre.