The Daniell cell is constructed in various ways.  In the earlier models the two plates with their solutions were separated by a porous jar or partition, which allowed the solutions to meet without mixing, and the current to pass.  Sawdust moistened with the solutions is sometimes used for this porous separator, for instance, on board ships for laying submarine cables, where the rolling of the waves would blend the liquids.

In the “gravity” Daniell the solutions are kept apart by their specific gravities, yet mingle by slow diffusion.  Figure 15 illustrates this common type of cell, where Z is the zinc plate in a solution of sulphate of zinc, and C is the copper plate in a solution of sulphate of copper, fed by crystals of the “blue vitriol.”  The wires to connect the plates are shown at WW.  It should be noticed that the zinc is cast like a wheel to expose a larger surface to oxidation, and to reduce the resistance of the cell, thus increasing the yield of current.  The extent of surface is not so important in the case of the copper plate, which is not acted on, and in this case is merely a spiral of wire, helping to keep the solutions apart and the crystals down.  The Daniell cell is much employed in telegraphy.  The Bunsen cell consists of a zinc plate in sulphuric acid, and at carbon plate in nitric acid, with a porous separator between the liquids.  During the action of the cell, hydrogen, which is liberated at the carbon plate, is removed by combining with the nitric acid.  The Grove cell is a modification of the Bunsen, with platinum instead of carbon.  The Smee cell is a zinc plate side by side with a “platinised” silver plate in dilute sulphuric acid.  The silver is coated with rough platinum to increase the surface and help to dislodge the hydrogen as bubbles and keep it from polarising the cell.  The Bunsen, Grove, and Smee batteries are, however, more used in the laboratory than elsewhere.

The Leclanche is a fairly constant cell, which requires little attention.  It “polarises” in action but soon regains its normal strength when allowed to rest, and hence it is useful for working electric bells and telephones.  As shown in figure 16, it consists of a zinc rod with its connecting wire Z, and a carbon plate C with its binding screw, between two cakes M M of a mixture of black oxide of manganese, sulphur, and carbon, plunged in a solution of sal-ammoniac.  The oxide of manganese relieves the carbon plate of its hydrogen.  The strength of the solution is maintained by spare crystals of sal-ammoniac lying on the bottom of the cell, which is closed to prevent evaporation, but has a venthole for the escape of gas.