  The isoscaling behavior is investigated using the isotopic/isobaric yields
from the equilibrated thermal source which is prepared by the lattice gas model
for lighter systems with A = 36. The isoscaling parameters $\alpha$ and
-$\beta$ are observed to drop with temperature. The difference of neutron and
proton chemical potential shows a turning point around 5 MeV where the liquid
gas phase transition occurs in the model. The relative free neutron or proton
density shows a nearly linear relation with the N/Z (neutron to proton ratio)
of system and the isospin fractionation is observed.
