  Magnetization and x-ray diffraction have been measured on polycrystalline
samples of LaCo$_{0.8-y}$Rh$_{0.2}$Ga$_{y}$O$_{3}$ for $0 \leq y \leq 0.15$ in
order to understand the spin state of Co$^{3+}$ through the Ga$^{3+}$
substitution effect. The ferromagnetic order in LaCo$_{0.8}$Rh$_{0.2}$O$_{3}$
below 15 K is dramatically suppressed by the Ga$^{3+}$ substitution, where the
ferromagnetic volume fraction is linearly decreased. The normal state
susceptibility also systematically decreases with the Ga content, from which we
find that one Ga$^{3+}$ ion reduces 4.6 $\mu_{\rm B}$ per formula unit. We have
evaluated how the concentration of the high-spin state Co$^{3+}$ changes with
temperature by using an extended Curie-Weiss law, and have found that the
substituted Rh$^{3+}$ ion stabilizes the high-spin state Co$^{3+}$ ion down to
low temperatures. We find that Ga$^{3+}$ preferentially replaces the high-spin
state Co$^{3+}$, which makes a remarkable contrast to our previous finding that
Rh$^{3+}$ preferentially replaces the low-spin state Co$^{3+}$. These results
strongly suggest that the magnetically excited state of LaCoO$_{3}$ at room
temperature is a mixed state of high-spin state Co$^{3+}$ and low-spin state
Co$^{3+}$.
