G. P. (George Payn) Quackenbos.

A natural philosphy: embracing the most recent discoveries in the various branches of physics .. online

. (page 31 of 42)
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ing? What is the greatest distance at which lightning rods have been found effica-



316 ELECTRICITY.

they project above the building ; for example, a rod projecting five feet will
protect every point of the surrounding surface within ten feet of itself.

819. ELECTRICAL FISH. The torpedo, the Surinam eel,
the si-lu'-rus electricus, and several other species of fish, have
a peculiar organ with which they can give electric shocks,
more or less powerful according to their size. They use
this organ for defending themselves against enemies, and
for stunning and thus securing their prey. The power of
giving shocks ceases with life ; its too frequent exercise
exhausts the fish and ultimately kills it. The shock of a
torpedo fourteen inches long is borne with difficulty ; and
the Surinam eel has been found of such size that its shock
proved immediately fatal.

The Surinam eel gives as many as twenty shocks a minute, yields the
electric spark in the air, and charges a Leyden jar. Faraday computed that
the average shock of one of these eels on which he experimented was equal
to the discharge of a battery of fifteen jars, containing 3,500 square inches of
glass, charged as heavily as possible. The South American Indians catch
these eels by driving a number of wild horses into a pond containing them.
The eels, roused from their muddy retreats, vigorously defend themselves
by pressing against the stomachs of the horses and repeatedly discharging
their electrical battery. The poor beasts, panting from their struggles, with
mane erect and haggard eyes expressing fright and aguish, seek to escape
from their invisible foes, but are driven back by the Indians who surround
the pond, armed with long reeds, and making terrible outcries. After sev-
eral of the horses are stunned and drowned the eels become exhausted by
their continued discharges, and are no longer objects of dread to the Indians.
Slowly approaching the shore, they are captured with harpoons fastened to
long cords ; and to such a degree is their electrical power weakened that
hardly any shock at all is received in drawing them ashore.

The silurus is a fish twenty feet long, found in the Nile and the Niger ;
its electrical apparatus lies immediately below the skin and extends round
the whole body.

Voltaic Electricity ;

OE, ELECTRICITY PRODUCED BY CHEMICAL ACTION.

820. Having considered electricity produced by fric-
tion, we proceed to treat of that developed by chemical

cious? Within this limit, how great a space do they protect? 819. What species of
fish have the power of giving an electric shock ? For what purposes do they use this
power ? What is the effect of its too frequent exercise ? What is said of the shock
of a torpedo fourteen inches long ? Of the Surinam eel ? What was the power of one
Dxperimentcd on by Faraday ? How do the South American Indians capture these



VOLTAIC ELECTRICITY. 317

action. This branch of the subject is known as Gal<
vanism.

821. GALVANI'S DISCOVERY AND THEORY. The first
discoverer in this department of science was he from whom
it received its name, Galvani \gal-vaH -ne\, Professor of
Anatomy in the University of Bologna, Italy. The effects
of atmospheric electricity on the animal frame had long
engaged his attention. In the year 1790, having prepared
the hind legs of some frogs suitably for experiment, and
hung them on copper hooks till they should be needed, he
observed to his surprise, on accidentally pressing the lower
extremities against the iron railing of a balcony, that they
were drawn up with a singular convulsive action. He
found upon experiment that similar contortions were pro-
duced whenever copper and iron, connected with each
other, were brought in contact, the one with the nerves of
the thigh, the other with the muscles of the leg.

Galvani's experiment is often repeated at the present day. To perform
it, separate the lower extremities of a frog from the rest of the body, skin
them, and pushing back the muscles on either side of the back-bone, lay bare
the lumbar nerves. Stretching out the
legs in the position shown in Fig. 292,
lay a thin curved rod of zinc under the
nerves, and touch the muscles of the
leg with a similar rod of copper. As
long as the rods are kept apart, there is
no movement in the legs ; but the in-
stant they are brought in contact, a vi-
olent convulsive motion takes place, the
legs are drawn into the position shown
by the dotted lines, and these contor-
tions are repeated as often as the rods
are separated and again brought to-
gether.

Galvani attributed this convulsive

movement to a certain vital fluid which he supposed to reside in the nerves,
and to pass to the muscles over the metallic conductors, in a manner similar
to the passage of electricity between the inner and the outer coating of a

eels ? What is said of the silurus ? 820. What is Galvanism ? 821. From whom did
it receive its name ? Give an account of Gal vani's discovery. How may Galvani's
experiment be repeated at the present day ? When do the contortions take place ?
To what did Galvani attribute this convulsive movement ? What did ho call this




318 VOLTAIC ELECTKICITY.

Leyden jar when it is discharged. He therefore called this supposed fluid
Animal Electricity ; but in compliment to its discoverer it soon became known
as Galvanic Electricity, or the Galvanic Fluid.

822. VOLTA'S THEORY AND THE VOLTAIC PILE. Prof.
Volta, of Pavia, experimenting further on the subject, soon
laid aside Galvani's theory of a " vital fluid ", and held that
the effects in question were caused by the contact of the
two dissimilar metals ; that the legs of the frog had no
agency in producing the galvanic excitement, but merely
gave indications of its presence, like the pith ball electro-
scope in the case of ordinary electricity. To prove this, he
combined the metals apart from all animal organizations ;
and advancing step by step, about the year 1800, he gave
to the world his celebrated PILE, the appearance of which
marked a new era in the history of electrical science.

Volta's "contact theory'"' was at one time generally received; but it is
now known that the galvanic excitement is not produced by the mere con-
tact of the metals, but by chemical action. A third element, such as the
moisture of the hand, animal fluids, an acid, or some saline solution, must
act chemically on one of the metals. It is believed that no chemical action
ever takes place without the development of free electricity, though the quan-
tity may be so small as to escape our senses.

823. Volta's Pile consisted of a number of circular plates
of copper and zinc, and pieces of cloth moistened with a
weak acid or saline solution, alternating as follows, the same
order being observed throughout. At the base of the pile
was a plate of copper, and on this a zinc plate, the two
constituting a pair. On this pair was a piece of cloth moist-
ened as above, then a second similar pair (the copper al-
ways below), then a piece of cloth, a third pair, and so on
to the top of the pile. The whole was insulated on glass,
and a wire was attached to each end. The wire connected
with the zinc plate at the top of the pile yielded positive
electricity ; that connected with the copper plate at the
base, negative. When the ends of these wires were brought

supposed yital fluid? What other names were soon given to it ? 822. Who experi-
mented further on the subject ? State Volta's theory. To what invention did Volta's
investigations lead ? TV hat is now thought of Volta's " contact theory " ? With what
fc chemical action always accompanied ? 823. Of what did Volta's Pile consist ? De-



VOLTA'S PILE. 319

together or separated, a bright spark was produced. A
very fine platinum wire, half an inch long, stretched between
the ends of the wires, was made red hot. A person taking
one of these wires in each hand, received a succession of
shocks, like those from a Leyden jar, but slighter, their
intensity depending on the number of plates. These effects
were produced as long as the arrangement and condition
of the plates remained unchanged.

Volta's pile, immediately connected as it was with the Galvanic Battery
(which has since superseded it), was one of those inventions to which science
is most largely indebted. It has immortalized its author, in honor of whom
this species of excitement produced by chemical action is now generally
called Voltaic Electricity.

824. FAMILIAR EXPERIMENTS. The effects of voltaic
electricity may be illustrated with familiar experiments.

Experiment 1. Place a piece of zinc under the tongue, and on the tongue
a silver coin. As long as the metals do not touch, nothing is perceived ;
but as soon as they are brought in contact, the voltaic circuit is formed, a
thrilling sensation is felt in the tongue, a taste somewhat like copperas is
perceived, and, if the eyes are closed, a faint flash of light is seen. Here
electricity is developed by the chemical action of the saliva upon the zinc.

Exp. 2. Lay a silver dollar on a sheet of zinc, and on the coin place a
living snail or leech. No sooner does the creature in moving about get
partly off the dollar and on the zinc, than it receives a shock and re.
coils. In this case it is the slime of the snail or leech that acts chemically on
the zinc.

825. GALVANIC BATTERIES. Soon after inventing the
pile, Yolta proposed another arrangement for the metallic
plates, identical in principle, but more convenient for use.
He discovered that electrical excitement was exhibited
whenever slips of copper and zinc were immersed in a ves-
sel containing some diluted acid, if the circuit was com-
pleted by bringing the metals themselves, or wires con-
nected with them, in contact above the vessel. Such an
arrangement is called a Simple Galvanic Circle ; it is

scribe some of its effects. How long were these effects produced ? What is said of
the invention of Volta's Pile ? What is electricity produced by chemical action now
generally called ? 824. What is the first experiment with which the effects of voltaic
electricity are familiarly illustrated? The second experiment ? 825. Soon after in-
venting the pile, what discovery did Volta make ? What is such an arrangement



320



VOLTAIC ELECTRICITY.





SIMPLE GALVANIC
CIRCLE.



rig. 293. shown in Fig. 293. Combining a num-

ber of vessels similarly prepared, Yolta
made the first galvanic battery, known
as the Couronne des Tasses \Jcoo-rone' da
tahs\.

826. The Couronne des Tasses, or " crown of cups ",
represented Fig. 294.

in Fig. 294,
consisted of
any number
of vessels,
each con-
taining a slip
of copper
and zinc, the
copperofone

vessel being COITRONNE DES TASSES.

connected by a conductor with the zinc of the next.
To complete the circuit, wires attached to the extreme
metallic slips of the series were brought together,
when a spark and other electrical phenomena were produced.

827. Trough Battery. Instead of the separate cups used by Yolta, one
long vessel divided into cells was subsequently employed. The zinc and
copper plates, connected in pairs by a slip of metal, and arranged at such
Fig. 295. distances as to enclose a partition between the zinc

and copper of each pair, were fastened to a common
frame, so that they could all be immersed in acid and
thus subjected to chemical action at the same time.
This improved arrangement was known as the Trough
Battery.

828. Smee's Battery Smee's Battery (see Fig. 295)
has three metallic plates suspended, without touching
each other, from a wooden frame. The middle plate is
of silver coated with platinum. The outside ones are
of amalgamated zinc, that is, zinc coated with mer-
cuiy. The whole are immersed in dilute sulphuric
acid contained in an earthenware vessel. JS T o action
takes place till communication is established between
the metals, when a bubbling immediately commences
in the liquid, and voltaic electricity is produced. This
SMEE'S BATTERY. battery, though not so powerful as those hereafter de-




called? What name was given to the first galvanic battery, made by Volta?
20. Describe the Couronne des Tasses. 827. Describe the Trough Battery. 828. De-
scribe Smec's Battery. What are tho advantages of this battery ? For what is it



DANLELL'S CONSTANT BATTERY. 321

scribed, is economical, may be kept in operation for several days, and is much
used in plating the inferior metals with gold atfd silver. "With certain mod-
ifications it is also employed in working the magnetic telegraph.

829. In the batteries thus far described but one fluid
was used, and two metals of such a nature that one was
more readily acted on by the fluid than the other. Dilute
sulphuric acid being used as the fluid, zinc (which it readily
acts upon) was generally taken for one of the metals.
Great improvements have been made on these single fluid
batteries. With the exception of Smee's, they have been
entirely superseded by instruments in which two fluids are
employed, and which are not only more powerful, but also
more regular and permanent in their action. The most
important of these we proceed to describe.

830. DanielVs Constant JBatteryThQ two-fluid batteries are Fig. 296.
all modifications of Daniell's, which was invented in 1836. It con-
sists of an outer cylinder of copper, within which is a cup of un-
glazed porcelain, of the shape represented in Fig. 296. Within
this cup is a solid cylinder of amalgamated zinc. From both the
zinc and the copper cylinder project brass cups (see Fig. 297) pro-
vided with screws for the insertion of wires ; the extremities of jrjg. 297.
which, if there be but one cell, are called the Poles of the bat-
tery. If there be several cells, strips of metals inserted in these
cups connect the zinc of one with the copper of the next, and
wires for conducting the fluid are attached to the zinc of one of
the extreme cells and the copper of the other. The porous cup
is filled with dilute sulphuric acid. The copper cylinder is filled
with the came fluid saturated with sulphate of copper; and on a
perforated shelf near its top (represented by the circular dotted
lines in the figure) is placed some of the solid sulphate, that as
fast as this substance is used up by the chemical action a fresh
supply may be obtained, and the operation of the battery thus
made constant.

As soon as the poles are joined, a powerful action commences, which,
instead of constantly diminishing as in the single fluid batteries, is main-
tained for hours without losing any of its efficiency. For ordinary use
two dozen such cells are combined in a battery. One of the chief im-
provements in this apparatus is the introduction of the porous cup, which

used ? 829. In the batteries thus far described, what are employed for the purpose
of producing chemical action ? Which is the most efficient of the single fluid batte-
ries? How do the single fluid batteries compare with those in which two fluids arc
used ? 30. By whom and when was the first two-fluid battery invented ? Describe
Daniell'a Constant Battery, and its mode of operation. What is ono of the chief im-

14*




322



VOLTAIC ELECTRICITY.



Fig. 293.




keeps the liquids apart, yet does not prevent the passage of voltaic cur-
rents.

831. Grove's Battery. Grove's Battery is the most powerful one yet con-
structed. It operates on the same principle as Daniell's, but employs differ-
ent metals and fluids, which render it more active. The porous cup contains
a strip of platinum immersed in strong nitric acid, and is itself contained in

a zinc cylinder filled with dilute
sulphuric acid. The whole is
set in a vessel of glass or earth-
enware. Fig. 298 shows one of
Grove's batteries consisting of
six cells, as arranged by Benja-
min Pike, jr., of New York.
The platinum of each cup is con-
nected with the zinc of the next.
At the extremities of the cir-
cuit, wires are attached respec-
GROVE'S BATTEEY. fa&j to the platinum of one

cell and the zinc of the other, the former of which exhibits positive electricity
and the latter negative.

Grove's battery is the best for performing the more striking experiments
of galvanism, being nearly twenty times as powerful as a zinc and copper
battery containing the same amount of metallic surface. Its superiority is
owing to the absorption of the hydrogen evolved, the high conducting power
of the fluids employed, and the ease with which nitric acid is decomposed.

832. Jjuysen's Battery. The cost of platinum renders Grove's apparatus
expensive. Bunsen therefore devised a battery, in which plates of carbon
acted on by nitric acid are substituted for platinum. In other respects it is
like Grove's, but it is less efficient.

833. DEY PILES. Feeble galvanic currents may be pro-
duced by compressing a great number of circular pieces of
copper and zinc paper (sometimes called gold and silver
paper), placed back to back, in a varnished glass tube,
which they exactly fit. As in Volta's pile, the same order
must be observed throughout. The electrical excitement
produced by a Dry Pile (as such an apparatus is called)
lasts a long time. Bells have been kept constantly ringing
for eight years by the alternate attraction and repulsion of
a clapper suspended between two such piles.



provements in this apparatus ? 831. Describe Grove's Battery. How does it com-
pare in power with a zinc and copper battery? To what is its superiority owing?
832. What is the objection to Grove's battery ? To remove this, what modification
did Bunsen propose ? 833. How are Dry Piles formed ? What evidence is adduced



THEORY OF THE GALVANIC BATTERY. 323

834. QUANTITY AND INTENSITY. The quantity of vol-
taic electricity produced by a battery, depends on the size
of the metallic plates employed ; its intensity, on their
number.

The difference between the quantity and the intensity of the electric fluid
is analogous to the difference between the quantity of a solid dissolved in a
given liquid and the strength of the solution. Into a hogshead of water
throw a wine-glass full of salt, and into a tea-spoon full of water put as much
salt as it will dissolve. The former solution will contain a greater quantity
of salt than the latter, but it will be less strong.

835. THEORY OP THE GALVANIC BATTERY. Let us now
inquire how electricity is developed with the galvanic bat-
tery. Take, as an example, Volta's single fluid apparatus.
When the zinc and copper plates are immersed in acidu-
lated water, and connection is established between them,
the water is decomposed into its elements, oxygen and hy-
drogen. The oxygen combines with the zinc, for which it
has a strong affinity, and forms oxide of zinc ; while the
hydrogen appears about the copper in the form of minute
bubbles. The zinc, in consequence of the chemical change
produced in its surface, parts with its positive electricity to
the liquid, and remains negatively electrified. The copper,
not acted on by the liquid as the zinc is, attracts from it
this same electricity, and becomes positively electrified.
The acid mixed with the water tends to dissolve the oxide
of zinc as fast as it is formed, and thus to keep a fresh sur-
face of the metal exposed to the liquid.

836. The terminal wires of a battery, or, when no wires
are attached, the plates from which they would proceed,
are called its Poles. The pole connected with the metal
most easily acted on by the fluid, always exhibits negative
electricity ; the other, positive. For pole some substitute
the term electrode, meaning the path by which a voltaic
current enters or leaves a body. The positive pole they

of the permanency of their action ? 834. On what does the quantity of voltaic elec-
tricity produced by a battery depend ? On what, its intensity ? Illustrate the differ-
ence between the quantity and the intensity of th electric fluid. 885. Give the the-
ory of the operation of the galvanic battery. 836. What is meant by the Poles of a
battery ? Which pole exhibits negative electricity ? Which, positive ? What term



324 VOLTAIC ELECTBICITY.

call the Anode (ascending or entering path) ; the negative,
the Cathode (descending or departing path). When the
electrodes are brought in contact, the galvanic circuit is
said to be closed. The two currents then meet and neu-
tralize each other; but, as fresh currents are all the time
being produced, the action continues without interruption.

837. DIFFERENCE BETWEEN FKICTIONAL AND VOLTAIC
ELECTEICITY. Voltaic electricity and that developed by
friction are the same in kind, but are characterized by cer-
tain points of difference.

1. The electricity developed by friction is far more in-
tense ; that produced by chemical action is far greater in
quantity.

A simple galvanic circle ( 825) develops as much electricity in three sec-
onds as would be accumulated in a battery of Ley den jars by thirty turns of
a powerful plate machine. Yet so weak is this voltaic electricity that a per-
son receiving it through his system would hardly be aware of its passage,
while the same quantity from the Ley den jars might prove fatal to life. It
takes a galvanic battery of about fifty pair of plates (no matter what their
size) to affect a delicate electroscope, and one of nearly a thousand pair to
make pith balls diverge.

2. The voltaic fluid will not pass through an insulating
medium/as the electric spark does. If the circuit is broken,
all action at once ceases. It will pass thousands of miles
over a conducting wire, but will not leap a break the fiftieth
part of an inch.

3. The chemical effects of the voltaic fluid are incom-
parably greater than those of frictional electricity.

The galvanic battery produces the most intense heat, and readily deconv
poses compound substances ; no such effects belong to the electrical machine.
An ordinary galvanic battery will decompose a grain of water into oxygen
and hydrogen. To do this with frictional electricity would require the power
of an electrical plate having a surface of 32 acres, which would be equiva-
lent to a flash of lightning.

838. EFFECTS OF VOLTAIC ELECTRICITY. Among the

is by some substituted for pole? What is the Anode ? What is the Cathode ? AYhen
is the galvanic circuit said to bo closed ? What then takes place ? 837. What is the
first point of difference between frictional and voltaic electricity ? State some facts
illustrating this difference. What is the second point of difference between frictional
and voltaic electricity ? The third point of difference ? What facts are stated in tho



DECOMPOSING EFFECTS. 325

effects of voltaic electricity on substances brought within
the circuit, may be mentioned the following :

839. Decomposition. Compound substances may be
decomposed into their elements with the galvanic battery ;
and it is a singular fact, that of the elements so obtained
some always arrange themselves about the positive pole, and
others about the negative. Thus, oxygen, chlorine, iodine,
and the acids, invariably fly to the positive pole, when set
free from any compound substance ; hydrogen, the oxides,
and the alkalies, to the negative. As the elements must be
in an opposite electrical state to the poles that attract them,
we conclude that oxygen, chlorine, &c., are naturally neg-
ative, and hydrogen, the oxides, and alkalies, positive.
Every chemical compound seems to consist of a positive
and a negative element, held together by electrical at-
traction.

The great discovery that water could be decomposed by voltaic electricity
was made in 1800, immediately after the announcement of Volta's pile, by
an experimenter, who observed that gas bubbles rose when the terminal
wires were immersed in water. Several years later, Davy, after a long course
of experiments, decomposed the earths and alkalies, which had before been
universally regarded as simple substances, and thus brought to light a num-
ber of new metals, the existence of which had not even been suspected.

840. The decomposition of water is effected with Fig. 299.

the apparatus represented in Fig. 299. A large glass
goblet has a frame fitted to its rim, from which are
suspended two small receivers for the purpose of col-
lecting the two gases evolved. As water consists of
two parts of hydrogen to one of oxygen, one of the
receivers should be twice as large as the other. Two
holes in the bottom of the vessel, to which screw
cups are attached, admit the electrodes from a bat-
tery, and terminate on the inside in strips of plat-
inum, which enter the receiver. The vessel being
filled with water and the battery set in operation, de-



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 31 of 42)