Columbia subject headings:
M.A. Hanna Company--History.
Mineral industries--Ohio--History.
Mineral industries--United States--History.
Plastics industry and trade--United States--History.
Harvard subject headings:
M.A. Hanna Company--History.
Mineral industries--Ohio--History.
Mineral industries--United States--History.
Plastics industry and trade--United States--History.
Princeton subject headings:
M.A. Hanna Company--History.
Mineral industries--Ohio--History.
Mineral industries--United States--History.
Plastics industry and trade--United States--History.