  We derive the high-temperature expansion of the Helmholtz free energy up to
the order \beta^{17} of the one-dimensional spin-S Ising model, with single-ion
anisotropy term, in the presence of a longitudinal magnetic field. We show that
the values of some thermodynamical functions for the ferromagnetic models, in
the presence of a weak magnetic field, are not small corrections to their
values with h=0. This model with S=3 was applied by Kishine et al. [J.-i.
Kishine et al., Phys. Rev. B, 2006, 74, 224419] to analyze experimental data of
the single-chain magnet [Mn (saltmen)]_2 [Ni(pac)_2 (py)_2] (PF_6)_2 for T<40
K. We show that for T<35 K the thermodynamic functions of the large-spin limit
model are poor approximations to their analogous spin-3 functions.
