Correspondence, 1899-1913, consisting of exchanges between James Cooper, the superintendent of the Calumet and Hecla Mining Company's smelter in Lake Linden, Michigan and H.Y. Bassett, a Calumet and Hecla Mining Company executive from the East Coast offices. The letters, including reports, address metallurgical issues as well as the results of comparative testing of Michigan copper versus copper from other regions as used by consumers of copper.