  We calculate the specific heat of the antiferromagnetic spin-1 chain compound
Y_2BaNi_{1-x}Zn_xO_5 in the presence of a magnetic field. The low-energy
spectrum of a Heisenberg Hamiltonian, which includes realistic anisotropies,
has been solved using the density matrix renormalization group. The observed
Schottky anomaly is very well described by this theory. For large chains
($N>50$), contrary to previous interpretations of the specific heat data, we
find S=1/2 states. These results are thus also consistent with electron-
spin-resonance data for NENP.
