  We investigated the yield stress and the apparent viscosity of sand with and
without small amounts of liquid. By pushing the sand through a tube with an
enforced Poiseuille like profile we minimize the effect of avalanches and shear
localization. We find that the system starts to flow when a critical shear of
the order of one particle diameter is exceeded. In contrast to common believe,
we observe that the resistance against the flow of wet sand is much smaller
than that of dry sand. For the dissipative flow we propose a non-equilibrium
state equation for granular fluids.
