Columbia subject headings:
Iron and steel workers--Germany--Duisburg--History.
Phoenix AG für Bergbau und Hüttenbetrieb--History.
Harvard subject headings:
Iron and steel workers--Germany--Duisburg--History.
Phoenix AG für Bergbau und Hüttenbetrieb--History.
Princeton subject headings:
Foundry workers--Germany--North Rhine-Westphalia--History.
North Rhine-Westphalia (Germany)--Economic conditions.
North Rhine-Westphalia (Germany)--Social conditions.