  The paper deals with the properties of thermally excited solitons of the
isotropic spin-$S$ ferromagnetic chain with nearest-neighbor logarithmic
interactions. The exact statistical mechanics of the interacting soliton gas is
developed for the general case (arbitrary $S$, temperature and magnetic field).
At low temperatures the model's thermodynamics coincides with that of the
Heisenberg model. We present analytical approximations of the leading-order
asymptotic behavior of the energy in three limiting cases: (a) zero field, low
temperature, classical limit; (b) zero field, $T\to 0$, $S$ finite (quantum
limit); (c) zero field, high temperature, classical limit. Cases (a) and (c)
are examples of a dense gas of [non-topological] solitons; results are in
agreement with those obtained by the transfer integral method. Case (b)
illustrates the behavior of a dilute, yet strongly interacting soliton gas;
results for the thermodynamics are very close to (but not identical with)
spin-wave and/or Bethe-{\it Ansatz} predictions.

Condensed Matter