given. It is shown that the torsion of the Biquard connection vanishes exactly when the trace-
free part of the horizontal Ricci tensor of the Biquard connection is zero and this occurs
precisely on 3-Sasakian manifolds. All conformal transformations sending the standard flat
torsion-free quaternionic contact structure on the quaternionic Heisenberg group to a
quaternionic contact structure with vanishing torsion of the Biquard connection are explicitly …