After working for sometime, in electrochemical cell, at the side of anode +ve potential is developed and at the side of anode -ve potential is developed. In order to neutralize +ve and -ve potentials, a U tube containing a paste of electrolyte(SALT BRIDGE) is suspended into electrolytic solutions so that the electrochemical cell remains working till the Zn rod is fully depleted.

In salt bridge KCl is mainly used becoz the transfer of number of K+ and Cl- is nearly the same.( use of any other salt for eg- NaCl, causes the imbalance of ions in the electrochemical cell as the transport number of Na+ ions in the infinitely diluted solution is abt 0.40 whereas for K+ ion it is 0.49)