Columbia subject headings:
Harvard subject headings:
Industries--Pennsylvania--Philadelphia--History.
Industries--Pennsylvania--Philadelphia--Pictorial works.
Philadelphia (Pa.)--Pictorial works.
Working class--Pennsylvania--Philadelphia--Social conditions--Pictorial works.
Working class--Pennsylvania--Philadelphia--Social conditions.
Princeton subject headings:
Industries--Pennsylvania--Philadelphia--History.
Industries--Pennsylvania--Philadelphia--Pictorial works.
Working class--Pennsylvania--Philadelphia--Social conditions--Pictorial works.
Working class--Pennsylvania--Philadelphia--Social conditions.