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
$\mathrm{CaC}_2+\mathrm{N}_2 \xrightarrow{800^{\circ} \mathrm{C}} \mathrm{CaCN}_2+\mathrm{C}$
$\begin{aligned} & 2 \mathrm{C}+\mathrm{O} \longrightarrow 2 \mathrm{CO} \\ & \mathrm{C}+\mathrm{O}_2 \longrightarrow \mathrm{CO}_2\end{aligned}$
$\begin{array}{r}2 \mathrm{CaC}_2+3 \mathrm{CO}_2 \longrightarrow 2 \mathrm{CaCO}_3+5 \mathrm{C} \\ \mathrm{CuO}+\mathrm{CO} \longrightarrow \mathrm{Cu}+\mathrm{CO}_2\end{array}$
$\mathrm{CO}_2$ gas is now absorbed by KOH solution. Thus a mixture of inert gases is obtained.