Unlike dry cell, the mercury cell has a constant cell has a constant cell potential throughout its useful life, why?

Explanation

In the mercury cell, ions are not involed in the overall cell reaction. Therefore, it generates a constant cell potential of 1.35" V" throughout. On the other hand, in a dry cell, ions participate in the overall cell reaction. As the concentration of the ions changes, the cell potential which is initially 1.25" V " is also likely to change. It does not remain constant.