This folder contains correspondence and other documents concerning the technical and commercial development of Edison's technologies for ore concentration. The documents relate primarily to Edison's collaboration with Henry B. Clifford, a mine and mill operator and former associate of humanist Robert G. Ingersoll, who applied Edison's technologies at sites in Colorado.

Approximately 40 percent of the documents have been selected. The unselected material consists primarily of unsolicited inquiries without a substantive reply from Edison. A few of these inquiries have been selected as a sample.

Courtesy of Thomas Edison National Historical Park.