Down's process is used for the preparation of sodium metal, where chlorine is obtained as a by- product. This process involves the electrolysis of a fused mixture of \(\mathrm{NaCl}\) and \(\mathrm{CaCl}_2\) at \(873 \mathrm{~K}\).
Sodium is discharged at the cathode while \(\mathrm{Cl}_2\) is obtained at the anode as a by-product.
\(\mathrm{NaCl}(l) \stackrel{\text { Electrolysis }}{\longrightarrow} \mathrm{Na}^{+}\)(melt) \(+\mathrm{Cl}^{-}\)(melt)
At cathode : \(\mathrm{Na}^{+}+\mathrm{e}^{-} \longrightarrow \mathrm{Na}\)
At anode \(: \mathrm{Cl}^{-} \longrightarrow \frac{1}{2} \mathrm{Cl}_2+\mathrm{e}^{-}\)
If, an aqueous solution of \(\mathrm{NaCl}\) is electrolysed, \(\mathrm{H}_2\) is evolved at the cathode while \(\mathrm{Cl}_2\) is obtained at the anode.