being peroxide of manganese, which is closely associated with the
carbon element.

The original form of the LeClanché cell, a form in which it was very
largely used up to within a short time ago, is shown in Fig. 61. In
this the carbon element is placed within a cylindrical jar of porous
clay, the walls of this jar being of such consistency as to allow
moisture slowly to permeate through it. Within this porous cup, as it
is called, a plate or disk of carbon is placed, and around this the
depolarizing agent, consisting of black oxide of manganese. This is
usually mixed with, broken carbon, so as to increase the effective
area of the carbon element in contact with the depolarizing agent, and
also to reduce the total internal resistance of the cell. The zinc
electrode usually consisted merely in a rod of zinc, as shown, with a
suitable terminal at its upper end.

[Illustration: Fig. 61. LeClanché Cell]

The chemical action taking place within the LeClanché cell is,
briefly, as follows: Sal ammoniac is chemically known as chloride of
ammonium and is a combination of chlorine and ammonia. In the action
which is assumed to accompany the passage of current in this cell, the
sal ammoniac is decomposed, the chlorine leaving the ammonia to unite
with an atom of the zinc plate, forming chloride of zinc and setting
free ammonia and hydrogen. The ammonia is immediately dissolved in the
water of the cell, and the hydrogen enters the porous cup and would
speedily polarize the cell by adhering to the carbon plate but for the
fact that it encounters the peroxide of manganese. This material is
exceedingly rich in oxygen and it therefore readily gives up a part of
its oxygen, which forms water by combination with the already