Poggendorff cell

This device is a chromic acid cell (old name: bichromate cell) or Poggendorff cell. It is an improved version of a previous Bunsen design, in which toxic gases were produced from oxides of nitrogen. This non-rechargeable battery can supply about two volts. It was used as a power source for telegraphy by telegraph wire from the mid-nineteenth century to the 1920s.
The bottle is filled with an aqueous solution of chromic acid and some sulphuric acid. A chemical reaction then takes place in which a zinc plate slowly dissolves. The zinc plate is the negative pole of the battery and hangs between two carbon plates. When a conductive wire is placed between the terminals, current begins to flow.
A drawback of the construction is that the chemical reaction continues even when no power is being drawn. Therefore these devices have a mechanism that lifts the zinc plate out of the liquid, stopping the chemical reaction.