It is a depolarizing pile: the potassium dichromate dissolved in the liquid hinders the polarization of the zinc electrode; indeed the dichromate, since it is a strong oxidant, frees oxygen in continuestion which, on combining with the hydrogen freed in the reaction between the zinc and the sulphuric acid, forms water and keeps the hydrogen from depositing on the zinc electrode. Consequently the current delivered gains in intensity and constancy.
Preferred to others in that it emits no harmful gases, the Grenet voltaic pile was widely used in the 19th century and the first decades of the 20th.