force, but diminishes the resistance. In fact, the battery is
equivalent to a single cell having plates equal in area to the
total area of all the plates. Although unable to overcome a high
resistance, it can produce a large volume or quantity of
electricity.

Numerous voltaic combinations and varieties of cell have been
found out. In general, where-ever two metals in contact are placed
in a liquid which acts with more chemical energy on one than on
the other, as sulphuric acid does on zinc in preference to copper,
there is a development of electricity. Readers may have seen how
an iron fence post corrodes at its junction with the lead that
fixes it in the stone. This decay is owing to the wet forming a
voltaic couple with the two dissimilar metals and rusting the
iron. In the following list of materials, when any two in contact
are plunged in dilute acid, that which is higher in the order
becomes the positive plate or negative pole to that which is
lower:--

POSITIVE Iron Silver
Zinc Nickel Gold
Cadmium Bismuth Platinum
Tin Antimony Graphite
Lead Copper NEGATIVE

There being no chemical union between the hydrogen and copper in
the zinc and copper couple, that gas accumulates on the surface of
the copper plate, or is liberated in bubbles. Now, hydrogen is
positive compared with copper, hence they tend to oppose each
other in the combination. The hydrogen diminishes the value of the