To many persons the only methods of obtaining electricity are by the use
of the battery or dynamo, or by pulling the beaded chain beneath the
electric light socket. Several little known methods of producing
electricity are set forth here. While not commercially applicable, they
illustrate some forces of everyday life not generally known.
Our Figure 1 shows two metals - brass and iron riveted together. If the
couple is set vibrating, one end being clamped while the free end is
struck a blow, a current is set up which actuates the indicating
instrument, which can be a galvanometer or a millivoltmeter. The current
ceases when the couple stops vibrating.
The mere bending of a metal can generate a current of electricity as the
illustration, Figure 2, shows. Even lead, which is very inelastic, will
produce an emf. Copper generates a greater current than any other metal.
If the metal under test is stretched or pulled, the current is also
generated. Volpicelli noticed this phenomena in 1872.
When an electrolyte - a liquid which conducts electricity - is driven
with pressure through a tube with a small aperture a current of
electricity is produced between the nozzle of the tube and a metal plate
upon which the exuding stream of electrolyte falls. The conducting liquid
must be of the same chemical characteristics as the nozzle. If a copper
nozzle is used the solution or electrolyte passing through the tube must
be a solution of a copper salt, such as copper sulphate. The pressure
within the tube must be above 15 atmospheres. Emfs. of 0.063 volt have
been recorded. The experiment is shown in Figure 3.
Mercury dropping into sulphuric acid (dilute) will also produce an emf.
In this case the galvanometer or indicating instrument should be
connected with the mercury which is dropping, and also with mercury at
the bottom of the vessel which contains the dilute acid.
In 1840 W. Paterson observed that when a metal rod was held in the hand
and the rod exposed to a jet of live steam, the free hand coming into
contact with the boiler, an electric shock was felt. Sparks could be
formed between the free hand and the boiler. In Figure 4 is shown how
this measurement can be carried out.
The jet of steam, which must have about 10 or 15 atmospheres of pressure,
is allowed to strike a metal plate, the metal plate being connected to a
galvanometer, along with the boiler. The plate is always positive, and
the boiler negative in respect to polarity when pure water is used.
If two plates of metal, one at a higher temperature than the other, are
immersed in a conducting liquid, a current will be produced, which is
easily detected by a sensitive indicating instrument. Using a solution of
sodium sulphate, the warmer plate is the positive one. The plates must
not be attacked by the liquid, for in this case the emf. would not be the
true emf. produced by hot and cold plates, but would be due to chemical
reaction. (Fig. 5.)
When bar magnets, opposite ends down, are immersed in a solution of
oxalic or other acid solution, the millivoltmeter connected across their
ends will show that a current is being produced. This effect was first
noticed by Balsame in 1867.
Discussion would probably be raised here, that the two metals were of
different chemical composition, thereby generating the current according
to facts well known in elementary electricity. (See Fig. 6.)
Observations made indicate that the roots as well as all interior
portions of plants containing sap are constantly acquiring a negative
charge of electricity, while the green branches, leaves, flowers and
fruits are all electrified positively.
By making a “Plant Pile” as shown in Figure 7, the presence of plant
electricity can readily be shown.
This plant pile is simply a stack of discs freshly cut from beet roots.
Between each pair of discs is interposed several moistened leaves of the
cochlearia. This plant electropile was first made In 1807 by Baconic and
the current produced was sufficient to produce the familiar muscular
contraction of a frog’s leg.
Rusting is but a process of atmospheric oxidation. If a copper and an
iron plate are heated in a crucible containing powdered glass and sodium
hydroxide a very strong current is obtained between the two metallic
electrodes (Figure 8).