This folder contains correspondence and other documents relating to the technical and commercial development of Edison's technologies for ore concentration. The selected documents pertain primarily to Edison's collaboration with Henry B. Clifford, a mine and mill operator who employed longtime Edison associate James B. Ballantine as his engineer and experimenter.

Approximately 25 percent of the documents have been selected. The unselected documents consist primarily of letters of transmittal and unsolicited inquiries that received no substantive reply from Edison.