Liquid Rheostats are variable resistors which use a liquid electrolyte. The electrolyte, usually common salt, is used as the resistor whose resistance value is varied by changing the level.
The construction consists of two electrolyte placed in a container. The container is filled with a solution of common salt. There is a provision to vary the level of the electrolyte in the container.
This changes the conductivity and thus the resistance is varied. At high levels of the electrolyte, the resistanc is very low and increases as the level decreases.
Liquid rheostats are silent and are supposed to have long life. They are usually only used in AC circuits as DC may cause electrodeposition between the electrodes.
Liquid rheostats can also be used as load banks to test generator output at testing facilities. The output of the generator is connected to electrodes which are placed in a container filled with a salt solution.
Liquid rheostats are also used as resistances for starting induction motors. Some large liquid rheostats have a heat exchanger to control the temperature of the electrolyte.