The Collaborative International Dictionary of English v.0.48:

Bell metal \Bell" met`al\
   A hard alloy or bronze, consisting usually of about three
   parts of copper to one of tin; -- used for making bells.
   [1913 Webster]

   Bell metal ore, a sulphide of tin, copper, and iron; the
      mineral stannite.
      [1913 Webster]

WordNet (r) 3.0 (2006):

bell metal
    n 1: bronze with 3 or 4 parts copper to 1 part tin; used in
         making bells