@book{BarthelDuvinage1999,
  author    = {Barthel, Helmut and Duvinage, Brigitte},
  title     = {Ozon : Informationsmaterial zur Fortbildung von Chemielehrern},
  publisher = {Gesellschaft Deutscher Chemiker},
  address   = {Frankfurt am Main},
  year      = {1999},
  language  = {de}
}
@book{Barthel1999,
  author    = {Barthel, Helmut},
  title     = {Auch Clor entz{\"u}ndet spontan brennbare leichtfl{\"u}chtige Fl{\"u}ssigkeiten},
  year      = {1999},
  language  = {de}
}
@book{BarthelDuvinage1999,
  author    = {Barthel, Helmut and Duvinage, Brigitte},
  title     = {R{\"u}benzuckergewinnung experimentell behandelt},
  year      = {1999},
  language  = {de}
}
@book{Barthel1997,
  author    = {Barthel, Helmut},
  title     = {Wieviel Kalkstein wird zur Herstellung von einem Liter cola gebraucht},
  year      = {1997},
  language  = {de}
}
@book{Barthel1997,
  author    = {Barthel, Helmut},
  title     = {Kann der Sch{\"u}ler immer schl{\"u}ssige Folgerungen aus Experimentalergebnisse ableiten?},
  year      = {1997},
  language  = {de}
}
@article{Barthel1996,
  author    = {Barthel, Helmut},
  title     = {Ozon - experimentell untersucht},
  year      = {1996},
  language  = {de}
}
@article{BarthelDuvinage1996,
  author    = {Barthel, Helmut and Duvinage, Brigitte},
  title     = {Entz{\"u}nden von Ethanol durch Ozon},
  year      = {1996},
  language  = {de}
}
@article{Barthel1996,
  author    = {Barthel, Helmut},
  title     = {Ein Modellexperiment zur Herstellung von Branntkalk im Schachtofen},
  year      = {1996},
  language  = {de}
}
@book{Barthel1996,
  author    = {Barthel, Helmut},
  title     = {Ozon : sporadische und exemplarische Anmerkungen zu einem Thema und seiner experimentellen Unterlegung},
  publisher = {Univ.},
  address   = {Potsdam},
  pages     = {11 S.},
  year      = {1996},
  language  = {de}
}
@book{BarthelDuvinage1996,
  author    = {Barthel, Helmut and Duvinage, Brigitte},
  title     = {Experimente mit Ozon},
  publisher = {Univ.},
  address   = {Potsdam},
  pages     = {30 S.},
  year      = {1996},
  language  = {de}
}