  The role of slight changes of the chemical composition on antiferromagnetic
ordering of Cr in rare-earth orthochoromites was investigated on a series of
ceramic solid-solutions Ce$_{1-x}$Eu${_x}$O$_3$ where x varied from 0 to 1.
Gradual replacement of Ce with Eu reduces the cell volume and acts equivalently
to applying external pressure. Full replacement of Ce by Eu, on the other hand,
reduces the N\'{e}el temperature from 260 K for CeCrO$_3$ to 178 K for
EuCrO$_3$ as established by magnetization, heat capacity and neutron powder
diffraction measurements. High resolution x-ray powder diffraction measurements
on Ce$_{1-x}$Eu${_x}$O$_3$ and neutron powder diffraction studies on CeCrO$_3$
enable to correlate the magnetic properties of the Cr magnetic subsystem with
the size of the lattice and minute changes of the bonding and torsion angles
within and between the CrO$_6$ octahedra. We find that the sizes and the shapes
of the CrO$6$ octahedra remain essentially unchanged as the size of the
rare-earth cations is reduced whereas decreasing Cr - O - Cr bonding angles and
increasing inclination of neighboring octahedra enable to compensate for the
decreasing lattice size.
