In Fischer Ringe's method, air free from moisture and $\mathrm{CO}_2$ is passed over a heated mixture $\left(800^{\circ} \mathrm{C}\right)$ of $90 \%$ $\mathrm{CaC}_2+10 \% \mathrm{CaCl}_2$ in an iron tube, when following reactions take place
$\begin{aligned}
& \mathrm{CaC}_2+\mathrm{N}_2 \stackrel{800^{\circ} \mathrm{C}}{\longrightarrow} \mathrm{CaCN}_2+\mathrm{C} \\
& 2 \mathrm{C}+\mathrm{O} \longrightarrow 2 \mathrm{CO} \\
& \mathrm{C}+\mathrm{O}_2 \longrightarrow \mathrm{CO}_2 \\
& 2 \mathrm{CaC}_2+3 \mathrm{CO}_2 \longrightarrow 2 \mathrm{CaCO}_3+5 \mathrm{C} \\
& \mathrm{CuO}+\mathrm{CO} \longrightarrow \mathrm{Cu}+\mathrm{CO}_2
\end{aligned}$
$\mathrm{CO}_2$ gas is now absorbed by $\mathrm{KOH}$ solution.
Thus a mixture of inert gases is obtained.