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58 ‘ THE BOY ELECTRICIAN

are liberated by the chemical action collect on the copper
plate and cause the strength of the battery to fall 03
rapidly.

There are a great number of elements, as the zinc and
copper are called, and an even greater number of different
solutions or excitants which can be employed in place of
sulphuric acid to make a cell, forming an ahnost endless
number of possible combinations.

Leclanche Cell. One of the most common forms of cell
employed for bell-ringing, telephones, etc., is called the
Leclanche cell, after its inventor, and consists of two ele-
ments, one of zinc and the other of carbon, immersed in a
solution of sal ammoniac or ammonium chloride. This cell
has an E. M. F. of 1.4 volts, which is about half as much
again as the voltaic cell.

The most common form of Leclanche cell is illustrated
in Figure 5 5. This type is usually known as a “- carbon cylin-

" - - - I _ der ” cell because the positive
7 V element is a hollow carbon
' cylinder. The zinc is in the
form of a rod passing through
a porcelain bushing set in the
center of the carbon cylinder.
CARBON A battery of such cells can

FIG. 55.—Carbon—Cylinder Cell, and only be used successfully for
Cylinder.

   

“ open circuit ” work. The
“ open circuit ” is used for bells, burglar alarms, telephone
circuits, etc., or wherever the circuit is such that it

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