  (Abridged) We present in this paper a sample of 14 nearby clusters of
galaxies observed with the ROSAT/PSPC. We only select clusters with low
galactic nH in order to trace the X-ray emitting intra-cluster medium (ICM) out
to large radii. We convert the X-ray surface brightness profiles of the
clusters into emission measure profiles scaled to the classical scaling
relations based on the spherical collapse model. We sort the clusters into
different temperature bins and stack the scaled emission measure (ScEM)
profiles of clusters together. The stacked profiles allow us to observe out to
radii r>r_200. In the center we find that the ScEM profiles deviate from
predicted scaling laws. This result is in very good agreement with current
studies on the L_X-T relation and the entropy - temperature relation (S \propto
T^0.65) found recently. At radii r>0.4r_200 we find that the ScEM profiles
agree well within the error bars, suggesting self-similarity. Fitting
beta-models to the overall ScEM profiles we find for the different sub samples
r_c=0.15-0.18 r_200 and beta=0.8, which is higher than beta=2/3 often found.
The beta-model is generally a better representation for hotter than for cooler
clusters. We see indications for continuous steepening of the profiles with
increasing radius: at radii r>0.8r_200 the profiles are systematically below
the beta-model curve with beta=0.8. We discuss our results with respect to the
observed X-ray luminosity L_X-T relation, the gas mass M_gas-T relation and the
total mass M-T relation. We also address implications on the origin of the
observed S-T relation. Furthermore we discuss the observed steepness of the
X-ray profiles, which falls off more rapidly than predicted from the
NFW-profile for cold dark matter halos.
