e. In other
forms the carbon electrode has moulded with it the manganese
depolarizer.

In order to prevent the salts within the cell from creeping over the
edge of the containing glass jar and also over the upper portion of
the carbon electrode, it is common practice to immerse the upper end
of the carbon element and also the upper edge of the glass jar in hot
paraffin.

In setting up the LeClanche cell, place not more than four ounces of
white sal ammoniac in the jar, fill the jar one-third full of water,
and stir until the sal ammoniac is all dissolved. Then put the carbon
and zinc elements in place. A little water poured in the vent hole of
the porous jar or carbon cylinder will tend to hasten the action.

An excess of sal ammoniac should not be used, as a saturated solution
tends to deposit crystals on the zinc; on the other hand, the solution
should not be allowed to become too weak, as in that case the chloride
of zinc will form on the zinc. Both of these causes materially
increase the resistance of the cell.

A great advantage of the LeClanche cell is that when not in use there
is but little material waste. It contains no highly corrosive
chemicals. Such cells require little attention, and the addition of
water now and then to replace the loss due to evaporation is about all
that is required until the elements become exhausted. They give a
relatively high electromotive force and have a moderately low internal
resistance, so that they are capable of giving rather large currents
for short intervals of time. If properly made, they recuperate quickly
after polarization due to heavy use.

_Dry Cell_. All the forms of cells so far considered may be quite
properly termed _wet cells_ because of the fact that a free liquid
electrolyte is used. This term is employed in contradistinction to the
later developed cell, commonly termed the _dry cell_. This term "dry
cell" is in some respects a misnomer, since it is not dry and if it
were dry it would not work. It is essential to the operation of these
cells that they shall be moist within, and when such moisture is
dissipated the cell is no longer usable, as there is no further useful
chemical action.

The dry cells are all of the LeClanche type, the liquid electrolyte
of that type being replaced by a semi-solid substance that is capable
of retaining moisture for a considerable period.

As in the ordinary wet LeClanche cell, the electrodes are of carbon
and zinc, the