G. P. (George Payn) Quackenbos.

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

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composition at once commences. Oxygen passes to the positive electrode

text to illustrate this difference? 839. What is the first effect of voltaic electricity ?
What singular fact is stated respecting the elements tlras obtained ? What elements
go to the positive pole ? What, to the negative ? What is inferred from this fact?
"When and under what circumstances was it discovered that water could be decom-
posed by voltaic electricity ? What great discovery was made by Davy ? 840. De-
scribe the mode of decomposing water with the galvanic battery. How is the process





320 VOLTAIC ELECTRICITY.

(which should be inserted in the smaller receiver) and hydrogen to the nega-
tive. The identity of the gases may be proved by subsequently experiment-
ing on them. As water is not a very good conductor of voltaic electricitv,
the process is facilitated by the addition of a little sulphuric acid.

Fig. 800. 841. The decomposition of a neutral salt may be performed

with the apparatus represented in Fig. 300. A glass tube
shaped like a V is fitted at each end with a cork and screw.
Through these screws pass the wires from a battery, termi-
nating inside in platinum strips. The tube having been filled
with a solution of sulphate of soda or any other neutral salt,
colored blue with tincture of violets, the battery is set in ac-
tion. No sooner is a current passed from pole to pole through
the liquid, than the latter is decomposed. The acid passes to the positive
pole, and the alkali to the negative. This is shown by the change of color
produced, the liquid becoming red around the positive wire and green around
the negative. If the poles be transposed, the effects will be reversed.

842. The decomposing power of the galvanic battery is
turned to practical account in the various processes of
ELECTRO-METALLURGY. This is the art of depositing on
any substance a coating of metal from a metallic solution
decomposed by voltaic electricity. One of the branches
of this art is Plating, which consists in covering the inferior
metals with a thin coat of gold or silver. When the metal
coating is not to adhere permanently to the surface on
which it is deposited, but to form a copy of it and be re-
moved, the process is called Electrotyping.

The different processes of Electro-metallurgy differ
somewhat in their details and in the apparatus employed,
but the principle involved is the same in all ; viz., that any
compound metallic solution is decomposed by the passage
through it of a voltaic current ; whereupon the pure metal
is attracted to the negative pole, while the substance be-
fore combined with it goes to the positive. A medal, an
engraving, or any conducting substance, has therefore only
to be attached to the negative pole, and the metal in ques-
tion will be deposited on it, the thickness of the coat de-

facilitated ? 841. With what apparatus, and hoTv, may a neutral salt be decomposed?
842. How is the decomposing power of the galvanic battery turned to practical ac-
count? What is Electro-metallurgy? In what does Plating consist? In what,
Electrotyping? What is the principle involved in all the processes of electro-metal-
lurgy? When any conducting substance is attached to the negative pole, what takes



ELECTROTYPING. 327

pending on the length of time it is left to the action of the
battery.

Reversed copies are thus obtained ; the minutest indentations on the sur-
face of the original being represented by elevations on the copy, and projec-
tions on the original by corresponding indentations in the copy. If an exact
and not a reversed copy is wanted, a mould, taken from the original in wax
or plaster, must be submitted to the above process.

This metallic deposit will take place only on a good conductor ; if, there-
fore, the object to be copied is not such, it must be endowed with conducting
power by dusting over it some fine plumbago. On the contrary, if there is
any part of which a copy is not wanted, it may be covered with varnish
which is a non-conductor. That the copy may be readily removed from the
original, the surface of the latter should be rubbed with oil or powdered
plumbago.

843. The most convenient mode of electrotyping is as follows : Fill a
trough with a solution of sulphate of copper, and over its top extend two par-
allel rods of wood a short distance apart. Kun the positive wire from a bat-
tery along one of these rods, and the negative along the other. From the
negative wire suspend in the fluid the object to be copied, and from the posi-
tive one apiece of copper plate. Sulphate of copper is composed of sulphu-
ric acid and copper. When the battery begins to operate, this fluid is de-
composed ; the copper is drawn to the negative pole and deposited on the
object attached to it. The sulphuric acid goes to the copper plate, and
combining with it forms sulphate of copper, thus providing fresh metallic
solution as fast as the original supply is used up.

844. Much use is made of the electrotype process. It has to a certain ex-
tent taken the place of stereotyping in the preparation of plates from which
books, charts, maps, &c., are printed. Copperplates being harder than those
of type-metal, a far greater number of copies can be printed from them, and
they are therefore preferable for works that are likely to have an extensive
circulation. "When the types are set, a mould of each page is taken in wax,
brushed over with plumbago, and subjected to the above process till a thin
deposit is formed, which is made of sufficient thickness to print from by back-
ing it with type-metal. This book is printed from electrotype plates.

Engravings both on wood and copper are reproduced in the same way,
their fine lines being brought out with exquisite perfection. The originals
are put away, and the duplicates alone used in printing. By multiplying
copies, which is done with little or no injury to the face of the original, any
number of impressions can be obtained. Fac-similes of delicate leaves, the
wings of insects, and even daguerreotypes, may be made in a similar way.

place ? What sort of copies are thus obtained ? "What must be done, to obtain fac-
similes? On what alone will this metallic deposit take place ? How may it be made
to take place on a bad conductor ? "What precaution is necessary, to enable us to re-
move the copy from the original ? 843. Describe the most convenient mode of elec-
trotyping. 844. For what is the electrotype process used? In what case are copper
plates preferable to those of type-metal ? State the process gone through in prc-



328 VOLTAIC ELECTRICITY.

845. Protection of Metals. Voltaic electricity has been
applied to the protection of metallic surfaces from corro-
sion. If a given metal is acted on by an acid or saline so-
lution, we have only to immerse in the liquid some other
metal more readily acted on by it, and close the circuit by
connecting the two, when the chemical action on the for-
mer metal at once ceases and is transferred to the latter.

Davy proposed on this principle to protect the copper sheathing on the
bottom of vessels from the action of sea-water. Strips of zinc were fastened
at certain distances on the copper, and it was found that the latter metal was
thus perfectly preserved from corrosion. No practical use, however, could
be made of this proposed improvement ; for shell -fish, sea- weed, &c., which
had before been kept off by the poisonous properties of the corroded copper,
now adhered to the bottom in such quantities as to make the vessel sail more
slowly.

846. Luminous and Heating Effects. When the gal-
vanic circle is closed or broken, that is, when the two
terminal wires are brought in contact or separated, a
bright spark passes between them. With the proper ap-
paratus, this spark may be intensified into the most bril-
liant light yet produced by art, known as the Electric
Light, or the Voltaic Arch.

To produce the electric light, connect the poles of a
powerful battery with the rods of a universal discharger
( 780), and to the extremities of these rods fix charcoal
points, or pieces of graphite pointed like a pencil. The
battery being set in operation, the charcoal points are
brought in contact, and then gradually withdrawn from
each other a short distance, when the space between them
is spanned by an arch of intensely bright light.

The voltaic arch is widest in the centre ; its length varies with the power
of the battery, ranging between three-fourths of an inch and four inches.
No luminous appearance is produced unless the points first touch, no matter
how close together they are brought, the air between being an insulator and

paring the plates. What else are reproduced by the electrotype process ? 845. To
what has voltaic electricity been applied ? How may a metal acted on by a liquid in
which it is immersed be protected from corrosion ? What application of this princi-
ple was proposed by Davy ? What was the result of the experiment ? S4G. What
takes place when the galvanic circuit is closed or broken ? Into what may this spark
be intensified 2 How is the electric light produced ? What is the shapo of the arch,



THE ELECTRIC LIGHT. 329

breaking the circuit. In a vacuum, however, the arch may be formed with-
out previous contact ; and even in the air, if when the points are brought
near each other a charge from a Ley den jar is passed from one to the other.

The electric light, like the electric spark, is entirely independent of com-
bustion. None of the carbon is consumed, though a portion of it is mechan-
ically carried over with a sort of hissing sound from the positive to the
negative electrode, as is shown by the change of shape in the points when
the experiment is over. The electric light may be produced in a vacuum
and even under water, which shows that it is not the result of combustion.

The intensity of the electric light depends rather on the size of the me-
tallic plates employed than on their number ; that is, on the quantity of
electricity developed more than its intensity. The arch produced with a
powerful battery is about one-third as intense as that of the sun ; while the
Drummond light, which stands next to it among artificial lights in point of
brilliancy, has only about l /i 50 of the sun's intensity. It has been proposed
to use the electric light for illuminating the streets of cities ; but the great
expense of maintaining a sufficient voltaic current has thus far prevented its
introduction for that purpose.

847. Heat, as well as light, is produced in the greatest
intensity yet known to man by the galvanic battery. The
hardest substances introduced within the voltaic arch, or
brought between the electrodes of a powerful battery to
close the circuit, are instantly ignited or fused. Platinum,
which withstands the fiercest heat of the furnace, melts like
wax in the flame of a candle. Quartz, the precious stones,
the earths, the firmest and most refractory compounds, are
fused in like manner. Thin leaves of metal subjected to
the action of a battery burn with great brilliancy and beau-
ty, yielding flames of different colors. Gold and zinc burn
with a vivid white light, silver with an emerald green, cop-
per and tin with a pale blue, lead with a brilliant purple,
and steel watch-spring with the brightest scintillations.
The heat produced by a battery, like its light, depends on
the size of the plates rather than their number.

The heating power of a galvanic battery may be shown by experiments
with wires of different metals stretched between the electrodes. A wire so

and its length ? What is essential to its production in the air ? Is this necessary in.
a vacuum ? How is it proved that tho electric light is not the result of combustion ?
On what does the intensity of the electric light depend ? Ho\v does its intensity
compare with that of the sun and the Drummond light? For what has it been pro-
posed to use the electric light ? 847. What is said of the heat produced by the galvan-
ic battery ? State some of its effects. On what docs the heat produced by a battery



330 VOLTAIC ELECTRICITY.

placed instantly becomes hot ; if not too long, red hot. By reducing its length,
we may raise it to a white heat, and by shortening it still further we may
fuse or ignite it. Experiments with different metallic wires of the same size
and length, show that they are not all heated to the same degree by a given
battery. The best conductors allow the current to pass with the least ob-
struction, and are therefore heated the least.

Platinum wire (which is one of the poorest metallic conductors and there-
fore most readily heated), immersed in a small quantity of water between the
electrodes of a battery, causes the water to boil. Passed through phospho-
rus, ether, and alcohol, it ignites them. Gunpowder is exploded by contact
with such a wire, a fact which is turned to account in the firing of blasts nnd
submarine batteries. The platinum wire being carried through the powder
and connected with the positive and negative electrodes, no matter how far
off the battery may be, the moment the circuit is completed the platinum be-
comes red hot, and the explosion takes place. By thus simultaneously firing
a number of charges of powder placed in deep holes at certain distances,
600,000 tons of rock have been instantly blown off from the face of a cliff,
with an immense saving of labor, and with perfect safety on the part of the
operator, who with his instrument was a fifth of a mile from the scene of
the blast.

848. Physiological Effects. The singular effects of the
galvanic fluid on the nerves and muscles of animals, origi-
nally led, as we have seen, to the development of the sci-
ence of Galvanism, and were carefully investigated in the
earlier stages of its history. The more powerful instru-
ments since invented have enabled experimenters to push
their researches still further.

When we grasp the electrodes of a battery of fifty cups,
one in each hand, we feel a peculiar twinge in the elbow
and sometimes in the shoulder, as if the joints were being
wrenched apart. This sensation continues as long as the
electrodes are held in the hands, and when we first grasp
them or let them go is sufficiently sudden and vivid to be
called a shock. A number of persons may take the shock
at once by joining their hands, which should be previously



depend? What is the effect of the galvanic battery on metallic wires ? When wires
of different metals are used, what is found ? How is this explained ? What experi-
ments may be performed with a platinum wire fixed between the electrodes of a bat-
tery ? Describe the process of firing a blast with such a wire. What instance is
mentioned of the practical application of this process ? 848. What originally led to
the development of galvanism as a science ? What sensation is experienced on grasp-
ing the electrodes of a battery ? How may a number of persons take the shock ?



PHYSIOLOGICAL EFFECTS. 331

moistened. A weak current passed through the eyes pro-
duces a faint flash ; passed through the ears, a roaring
sound ; and through the tongue, a metallic taste.

The effects of the galvanic battery on the animal system, unlike its lumi-
nous and heating effects, are found to depend on the number of plates em-
ployed rather than their size, that is, on the intensity of the electricity pro-
duced, and not its quantity. A battery of several hundred pair of plates
proves fatal to life. One of a hundred pair gives a shock that few would
like to bear a second time, though, if the plates are small, it has no effect on
wires stretched between the electrodes. Put the same amount of metallic
surface in a few pair of very large plates, and such a battery will instantly
fuse wires subjected to its action, while its shock will hardly be felt.

849. There seems to be a remarkable analogy between
a voltaic current and the nervous energy. Experiment has
shown that, if a nerve be divided, a galvanic current di-
rected through the region in which it runs will in a meas-
ure supply its place. The part, which would otherwise be
palsied from a want of nervous energy, may thus bo re-
stored to its usual action. If, for example, the nerves of
the stomach are divided, digestion ceases ; but it is resumed
if the stomach is subjected to galvanic influence. Galvan-
ism is therefore medically applied in asthma, paralysis, and
other diseases arising from a prostration of the nervous
system.

850. Among the most remarkable effects of voltaic elec-
tricity are the violent contortions it produces in bodies just
deprived of life.

A few years ago, the body of a murderer hanged in Glasgow was sub-
jected, about an hour and a quarter after his execution, to the action of a
battery consisting of 270 pair of four-inch plates. One pole was applied to
the spinal marrow at the nape of the neck, and the other to the sciatic nerve
in the left hip, when the whole body was thrown into a violent tremor as if
shivering with cold. On removing the wire from the sciatic nerve to a nerve
in the heel, the leg was thrown out so violently as nearly to overturn one of



What is the effect of passing a weak current through the eyes ? Through the ears ?
Through the tongue ? On what do the effects of the galvanic battery on the animal
system depend ? Compare the different effects of a given amount of metallic surface,
when thrown into many small plates, and a few large ones. 849. To what does the
Voltaic current bear a remarkable analogy ? What has been shown by experiment ?
Give an example. In what diseases is galvanism medically applied ? 850. What is
one of the most remarkable effects of voltaic electricity ? Describe the experiments



332 THERMO-ELECTRICITY.

the assistants, who tried in vain to prevent its extension. On directing a
current to the principal muscle of respiration, the chest heaved and fell, and
labored breathing commenced. When one of the poles was applied to a
nerve under the eyebrow and the other to the heel, the most extraordinary
grimaces were produced : " every muscle of the countenance was simulta-
neously thrown into fearful action ; rage, horror, despair, anguish, and
ghastly smiles, united their hideous expression in the murderer's face." Sev-
eral spectators were so overcome by the sight that they had to leave the
room, and one gentleman fainted. In the last experiment, the fore finger,
which had previously been bent, was instantly extended, and shaking vio-
lently, with a convulsive movement of the whole arm, seemed to point to the
persons present, some of whom thought that the body had really returned
to life.



OR, ELECTRICITY DEYELOPED BY HEAT.

851. How PRODUCED. If two strips of metals which
differ in their conducting power, are soldered together at
one end so as to form an acute angle with each other, and
heat is applied at the place of junction, a current of elec-
tricity is produced, which may be carried off by any good
conductor. Antimony and bismuth exhibit this phenome-
non in its greatest perfection, and are generally used in
performing the experiment. Electricity thus developed by
heat is known as Thermo-electricity. Its properties are the
same as those of frictional electricity.

rig. sol. 852. THERMO-ELECTRIC BATTERIES.

3 b TJ b Thermo-electricity may be developed

XAAAA/ abundantly by combining a number of

\U V \/ \J v thin bars of antimony and bismuth, or

01 a a a l platinum and iron. They may be ar-

t> T> ranged in either of the forms represent-

1 JTl [TJ ri I! ed in Fig. 301, or may be laid flat one

1=0 I=U t=y *=!1 upon another, with pasteboard between

to prevent them from touching except

THERMO-ELECTRIC BAT- . . _ , .

at their extremities. By heating the



points of junction at one end, , a, a, a, and cooling those

performed on the body of a murderer shortly after his execution. 851. What is
Thermo-electricity ? How is it produced ? What metals are generally used in pro-
ducing it ? 852. How may thermo-electricity be developed abundantly ? How is a



THERMO-ELECTRIC BATTERIES. 333

at the other, #, #, #, #, an electric current is produced, the
intensity of which is equal to the sum of the intensities of
the separate pairs. With a wire attached to the first bar
of bismuth and another attached to the last bar of anti-
mony, the thermo-electric current may be conducted wher-
ever it is desired.

When thirty or forty such combinations are needed, thin metallic bars
are used, connected alternately at their extremities, and arranged for conve-
nience' sake in parallel piles of five or six each. Such a battery indicates
changes of temperature at its junctions so minute that they can be detected
in no other way, even to the hundredth part of a degree of the thermometer.
The heat radiated from the hand is sufficient to produce a slight electric
current.

853. Electricity, besides being produced by friction,
chemical action, and heat, is also developed under certain
conditions by magnetism. When so produced, it is called
Magneto-electricity. This branch of the subject can not
be understood till we have treated of Magnetism, and will
therefore be considered in the next chapter, which is de-
voted to that subject.



CHAPTER XVII.
MAG-NETISM.

854. A MAGNET is a body which has the property of
attracting iron and being attracted by it.

855. Magnetism is the science that treats of the laws,
properties, and phenomena of magnets.

Kinds of Magnets.

856. There are two kinds of *nagnets, Natural and Ar-
tificial.

thermo-electric battery formed ? What is the usual arrangement when a large num-
ber of such combinations are needed ? How minute changes of temperature are indi-
cated with such a battery ? S53. By what oilier agency is electricity also developed ?
What is it then called?



834 MAGNETISM.

857. NATURAL MAGNETS. The natural magnet, or load-
stone, is an ore of iron, found in great quantities in differ-
ent parts of the earth, which has the property of drawing
to itself steel filings, needles, or small pieces of unmagnetic
iron. Its texture is hard, and its color varies from reddish-
brown to grey. Besides the loadstone, nickel, cobalt, and
brass when hammered are found to have magnetic proper-
ties, though in an inferior degree.

858. The attraction of the loadstone for particles of iron appears to have
been known to the Greeks, Chinese, and other nations in remote antiquity.
It is distinctly alluded to by Homer and Aristotle. Piiny speaks of a chain
of iron rings suspended one from another, the first of which was upheld by
a loadstone. He tells us, also, that Ptolemy Philaclelphus proposed to build
a temple at Alexandria, the ceiling of which was to be of loadstone, that its
attraction might hold an iron statue of his queen Ar-sin'-o-e suspended in the
air. Death prevented Ptolemy from carrying out his design ; but St. Au-
gustine, at a later day, mentions a statue thus actually held in suspension in
the temple of Ser'-a-pis, at Alexandria. The magnet (magnes in Greek) is
supposed to have received its name from Magnesia, a city of Asia Minor, near
which it was first found.

859. Poles. The attractive power of a natural magnet
does not reside equally in all its parts, but is strongest at
its extremities and diminishes towards the middle, where
it is entirely wanting. This is shown by rolling a piece of
loadstone in iron filings. They will be found to cluster
about the ends, those that first adhere being endowed with
the power of attracting others, till large tufts are formed,
while the middle is left entirely bare.

The points at which the greatest attractive power is
exhibited, are called the Poles of the magnet. The central
part, where it is wanting, is called the Neutral Line.

If a piece of loadstone is broken, each portion becomes
a perfect magnet, and has poles of its own.

854. What is a Magnet ? 855. What is Magnetism ? 856. How many kinds of
magnets are there ? Name them. 857. What is the natural magnet ? What other
metals have magnetic properties ? 853. To whom and when was the attraction of
loadstone for iron known ? What ancient authors allude to it ? Of what does Pliny
speak ? What use did Ptolemy Philadelphia propose to make of the loadstone ?
What is mentioned by St. Augustine ? From what did the magnet receive its name ?
859. What is shown by rolling a piece of loadstone in iron filings ? What is meant
by the Poles of the magnet ? What is the Neutral Line ? If a piece of loadstone is



NATURAL MAGNETS.



335



Fig. 302.




860. Power of Natural Magnets. When quite small, a
natural magnet will sustain many times its own weight of



Online LibraryG. P. (George Payn) QuackenbosA natural philosphy: embracing the most recent discoveries in the various branches of physics .. → online text (page 32 of 42)