Why Mercury cell voltage remain constant throughout its life?

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

Why does . Mercury cell provide constant voltage ?

In which sub-phylum Notochord extends from head to tail region and persistent throughout their life?

Notochord occurs all through the length of body and throughout life in

The volume expansion coefficients of glass and mercury are 2.4 times 10^(-5@)C^(-1) " and " 1.8 times 10^(-4@)C^(-1) respectively. What volume of mercury should be kept in the flask so that the volume of the empty space over mercury in the flask remains constant at all temperatures?