Weston standard cell
Most electrochemical cells produce around 1.2 V to 1.8 V of electric potential. Different types slightly vary. A mercury cell has a voltage which is a little bit less than that of the zinc-carbon or alkaline cell. The voltage of the cell can be affected by variables in manufacturing process. Most consumer type dry cells can assumed to produce 1.5 Vdc.
There are several types of cells whose voltages are exact. These are called as standard cell,the one example of a standard cell is Weston cell. It produces
1.018 V at the room temperature. This cell uses the solution of cadmium sulfate. The positive electrode is made out of mercury sulfate, and the negative electrode is made by using mercury and cadmium. The whole device is set up in the container as shown in the Figure given to us.
When constructed properly and used at the room temperature, voltage of the Weston standard cell is the same, and this allows it to be used as a direct current voltage standard. There are other types of standard cells, but Weston cell is the very common.