  Specific heat, dc- and ac-magnetic susceptibility are reported for a large
single crystal of PrOs$_4$Sb$_{12}$ and, after grinding, its powder. The room
temperature effective paramagnetic moment of the crystal was consistent with
the Pr$^{3+}$ ionic configuration and full occupancy of the Pr-sublattice. The
crystal showed two distinct anomalies in the specific heat and an overall
discontinuity in $C/T$ of more than 1000 mJ/K$^2$mol. The upper transition (at
$T_{c1}$) was rounded, in an agreement with previous reports. The anomaly at
$T_{c2}$ was very sharp, consistent with a good quality of the crystal. We
observed a shoulder in $\chi$' and two peaks in $\chi$'' below $T_{c1}$.
However, there were no signatures in $\chi$' of the lower temperature
transition. PrOs$_4$Sb$_{12}$ is extremely sensitive to grinding, which
suppresses the upper superconducting transition in both the specific heat and
magnetic susceptibility. $\Delta C/T_{c}$ was reduced to 140 mJ/K$^2$ mol in
the powdered sample. Existing data on ground, polished, and sliced crystals
suggests the existence of a length scale of order 100 $\mu$, characterizing the
higher temperature superconducting phase.
