In four-jet events from e+e- –> Z0 –> multihadrons one can separate
the three principal contributions from the triple-gluon vertex, double
gluon-bremsstrahlung and the secondary quark-antiquark production, using
the shape of the two-dimensional angular distributions in the
generalized Nachtmann-Reiter angle theta-NR* and the opening angle of
the secondary jets. Thus one can identify directly the contribution from
the triple-gluon vertex without comparison with a specific non-QCD
model. Applying this new method to events taken with the DELPHI-detector
we get for the ratio of the colour factor N(C) to the fermionic Casimir
operator C(F): N(C)/C(F) = 2.55 +/- 0.55(stat.) +/- 0.4(fragm. + models)
+/- 0.2(error in bias) in agreement with the value 2.25 expected in QCD
from N(C) = 3 and C(F) = 4/3
