Columbia subject headings:
Harvard subject headings:
Gutehoffnungshütte--History.
Industries--Germany--Ruhr (Region)--History.
Metal trade--Germany--Ruhr (Region)
Ruhr (Germany : Region)
Ruhr (Germany : Region)--Economic conditions
Princeton subject headings:
Coal mines and mining--Germany (West)--Ruhr (Region)--History.
Iron industry and trade--Germany (West)--Ruhr (Region)--History.