A two-liquid battery, of the type invented in 1836 by the English physicist John Frederic Daniell (1790 – 1845), consisting of a cylindrical copper vessel with a funnel-shaped mouth, to which a clamp is attached. Inside the vessel is placed a hollow cylinder made of a porous material, into which a zinc rod is inserted, connected to a second clamp. Copper sulphate crystals may be placed in the flared part of the vessel in order to keep the concentration of the electrolyte constant. The permeable barrier keeps the two liquids separate, sulphuric acid inside and copper sulphate outside, but allows the passage of ions between them. This avoids the inconvenient loss of efficiency that occurs in single-liquid batteries due to the accumulation of hydrogen at the battery’s positive terminal.

Device on display.