This folder contains correspondence and other documents concerning the development of Edison's technologies for ore concentration. Many of the letters relate to experiments undertaken in collaboration with Henry B. Clifford, a mine and mill operator who would apply Edison's ore milling technologies at sites in Colorado. The documents for 1911 reflect Edison's involvement in the technical aspects of Clifford's proposition. Included are letters offering advice on the erection of an experimental mill, along with others regarding tests undertaken at Edison's laboratory in West Orange.

Approximately 40 percent of the documents have been selected. The unselected material consists of additional material pertaining to Clifford, along with letters requesting information about ore milling or soliciting Edison's assistance in developing mine properties.