 Silver sulfate reference electrode

A silver electrode in contact with silver sulfate and a solution of controlled sulfate activity. The reduction is $\mathrm{A}{\mathrm{g}}_2\mathrm{S}{\mathrm{O}}_4+2{\mathrm{e}}^{-}\rightleftharpoons 2Ag+\mathrm{S}{\mathrm{O}}_4^{2-}$.