Columbia subject headings:
Businessmen--Germany--North Rhine-Westphalia--History.
Coal trade--Germany--North Rhine-Westphalia--History.
Metal trade--Germany--North Rhine-Westphalia--History.
North Rhine-Westphalia (Germany)--Social conditions.
Harvard subject headings:
Businessmen--Germany--North Rhine-Westphalia--History.
Coal trade--Germany--North Rhine-Westphalia--History.
Metal trade--Germany--North Rhine-Westphalia--History.
North Rhine-Westphalia (Germany)--Social conditions.
Princeton subject headings:
Businessmen--Germany--North Rhine-Westphalia--History.
Coal trade--Germany--North Rhine-Westphalia--History.
Metal trade--Germany--North Rhine-Westphalia--History.
North Rhine-Westphalia (Germany)--Social conditions.