Manganese dioxide 45 per cent
Carbon or graphite, or both 45 per cent
Sal ammoniac 7 per cent
Zinc chloride 3 per cent

Water is added to the above and a sufficient amount of mixture is
taken for each cell to fill the zinc cup about seven-eighths full when
the carbon is in place. The most suitable quantity of water depends
upon the original dryness and fineness of material and upon the
quality of the paper lining.

In some forms of dry batteries, starch or other paste is added to
improve the contact of the electrolyte with the zinc and promote a
more even distribution of action throughout the electrolyte. Mercury,
too, is often added to effect amalgamation of the zinc.

As in the ordinary wet type of LeClanché cell, the purpose of the
manganese is to act as a depolarizer; the carbon or graphite being
added to give conductivity to the manganese and to form a large
electrode surface. It is important that the sal ammoniac, which is the
active agent of the cell, should be free from lumps in order to mix
properly with the manganese and carbon.

A small local action takes place in the dry cell, caused by the
dissimilar metals necessarily employed in soldering up the zinc cup
and in soldering the terminal rod of zinc to the zinc cup proper. This
action, however, is slight in the better grades of cells. As a result
of this, and also of the gradual drying out of the moisture within the
cell, these cells gradually deteriorate even when not in use--this is