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Richard Green Parker.

A school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of online

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Online LibraryRichard Green ParkerA school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of → online text (page 25 of 38)
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St. Petersburgh, who fell a sacrifice to his zeal for electrical science
by a stroke of lightning from his apparatus.

What are the 1045. Among the most remarkable facts con-
Electrical nected with the science of electricity, may be men-
Animals. tioned the power possessed by certain species of
fishes of giving shocks, similar to those produced by the Leyden
jar. There are three animals possessed of this power,, namely,
the Torpedo, the Gymnotus Electricus (or Surinam Eel), and
the Silurus Electricus. But, although it has been ascertained
that the Torpedo is capable of giving shocks to the animal sys-
tem, similar to those of the Leyden jar, yet he has never been
made to afford a spark, nor to produce the least effect upon the
most delicate electrometer. The Gymnotus gives a small but
perceptible spark. The electrical powers of the Silurus are in-
ferior to those of the Torpedo or the Gymnotus, but still sufficient
to ghe a distinct shock to the human system. This power seems
to have been bestowed upon these animals to enable them to
secure their prey, and to resist the attacks of their enemies.
Small fishes, when put into the water where the Gymnotus is
kept, are generally killed or stunned by the shock, and swallowed
by the animal when he is hungry. The Gymnotus seems to be
possessed of a new kind of sense, by which he perceives whether
the bodies presented to him are conductors or not. The consid-
eration of the electricity developed by the organs of these ani-
mals of the aquatic order, belongs to that department called
Animal Electricity.

1046. It will be recollected that the phenomena which have
now been described with the exception of what has just beer
stated as belonging to animal electricity, belong to the subject
of frictional electricity. But there are other forms in which
this subtle agent presents itself, which are yet to be described,
which show that its operations are not confined to beautiful



GALVANISM.

experiments, such as have already been presented, nor to the
terrific and tremendous effects that we witness in tho storm and
the thunder-gust. Its powerful agency works unseen on ihe
intimate relations of the parts and properties of bodies of every
description, effecting changes in their constitution and character
so wonderfully minute, thorough and universal, that it may
almost be considered as the chief agent of nature, the prime
minister of Omnipotence, the vicegerent of creative power.

What is 1047. GALVANISM, OR VOLTAIC ELECTRIC-

Gilvanism ? ITY . Galvanism, or Voltaic Electricity, is a
branch of electricity which derives its name from Galvani,
who first discovered the principles which form its basis.

1048. Dr. Aloysius Galvani was a Professor of Anatomy in Bolog-
na, and made his discoveries about the year 1790. His wife, being
consumptive, was advised to take, as a nutritive article of diet, some
soup made of the flesh of frogs. Several of these animals, recently
skinned for that purpose, were lying on a table in his laboratory,
near an electrical machine, with which a pupil of the professor was
amusing himself in trying experiments. While the machine was in
action, he chanced to touch the bare nerve of the leg of one of the
frogs with the blade of a knife that he held in his hand, when sud-
denly the whole limb was thrown into violent convulsions. Galvani,
being informed of the fact, repeated the experiment, and examined
minutely all the circumstances connected with it. In this way he
was led to the discovery of the principles' which form the basis of
this science. The science was subsequently extended by the discov
eiies of Professor Volta, of Pavia, who first constructed the galvanic
or voltaic pile, in the beginning of the present century.

To produce electricity mechanically (as has been stated under the
head of frictional electricity), it is necessary to excite an electric or
non-conducting substance by friction. But galvanic action is pro-
duced by the contact of different conducting substances having a
chemical action on one another.

How does gal- 1049. Frictional electricity is produced by the
vanism differ mechanical action of bodies on one another ; but
%lkicityl~ alvanism or galvanic electricity, is produced by
their chemical action.

What is the 1050. The motion of the electric fluid, excited

difference in b y ga l van i c power diff ers f rom tna t explained

(he effects of J _ . ...

frictional and und er the head of frictional electricity in its in-

12*



284 NATURAL PHILOSOPHY.

rJiemtcal elec- tensity and duration ; for, while the xatter exhibits
tricity ? itself in sudden and intermitted shocks and explo-

sions, the former continues in a constant and uninterrupted cui-
rent so long as the chemical action continues, and is interrupted
only by the separation of the substances by which it is produced.*

1051. The nerves and muscles of animals are
What is most
sensitive to mos t easily affected by the galvanic fluid ; and the

the galvanic voltaic or galvanic battery possesses the most sur-
prising powers of chemical decomposition.

How is the 1052 The galenic faid. or influence, is ex-

galvanic jluia

excited ? cited by the contact of pieces of different metal,
and sometimes by different pieces of the same metal.

1053. If a living frog, or a fish, having a slip of tin-foil on its back,
be placed upon a piece of zinc, spasms of the muscles will be ex-
cited whenever a communication is made between the zinc and the
tin-foil.

1054. If a person place a piece of one metal, as a half-dollar,
above his tongue, and a piece of some other metal (as zinc) below
the tongue, he will perceive a peculiar taste ; and, in the dark, will

* The different action of gravity on the particles of water while in the
liquid state, and the same particles in the solid state in the form of ice, has
been explained in the early pages of this volume. In the one case each
particle gravitates independently, while in the form of ice they gravitate
in one mass. The fall of a body of ice would therefore produce more serious
injury than the fall of the same quantity of water in the liquid form. There
is a kind of analogy (which, though not sufficient for a philosophical expla-
nation, may serve to give an insight into the difference between the effects
produced by frictional electricity and that obtained by chemical means.)
between the gravitation of water and ice, respectively, and the motion of
frictional and chemical electricity. If the water be dropped in an infinitely
narrow stream, its effects, although mechanically equal, would be so gradual
as to be imperceptible. So, also, if a given portion of electricity be set in
motion as it were in one mass, and an equal quantity move in an infinitely
narrow current, there will be a corresponding difference in its apparent
results. The difference in intensity may perhaps be partially understood by
this illustration, although a strict analogy may fail to have been made out,
owing in part to the nature of an imponderable agent. A strict analogy
cannot exist between the operations of two agents, one of which is pondera-
ble and the other imponderable. But, that there is something like ar
analogy existing in the cases cited, will appear from statements which have
been made on good authority, namely, that there is a greater quantity of
electricity developed by the action of a single drop of acid on a very niiuuto
portion of zinc, than ib usually brought 'f to action in the darkest cloud thai,
shroud? the hot j SOD.



GALVANISM.

seo a flash of light whenever the outer edges of the metals are in
contact.

1055. A faint flash may be made to appear before the eyes by
putting a slip of tin-foil upon the bulb of one of the eyes, a piece ot
silver in the mouth, and making a communication between then?
In these experiments no effect is produced so long as the metals are
kept apart ; but, on bringing them into contact, the effects above
described are produced.

T;ir7 1056. It is essential in all cases to have three

What is es-

sential lo pro- elements to produce galvanic action. In the ex-
duce galvanic periments which have already been mentioned in
the case of the frogs, the fish, the mouth and the
eye, the moisture of the animal, or of the mouth, supplies the
place of the acid, so that the three constituent parts of the circle
are completed.



What is said of 1057. The conductors of galvanic electric-

conductors of ity, like those of frictional electricity, are of
Galcanism? -., 1 m . . _ ,

all degrees ol excellence. The metals, char-

coal, plumbago, and solutions of acids and salts, are good
conductors ; while gutta-percha, rubber, glass, resin, sul-
phur, dry wood, air, etc., are poor conductors, or, as they
are generally termed, non-conductors. Insulators may be
made of any of the above solid non-conductors.

. 1058. The acid employed in the galvanic cir-
H hat kind of .

acid must be cult must always be one that has a strong am nit y

employed in for one of the metals in tho circuit. When zinc
is employed, sulphuric acid may form one of tbe
three elements, because that acid has a strong affinity for zino.
What is a law 1059 ' ^ certain quantity of electricity is always
of chemical developed whenever chemical action takes plac*.
action? Between a fluid and a solid body. This is a gen-

eral law of chemical action ; and, indeed, it has been ascertained
that there is so intimate a connection between electrical and
chemical changes, that the chemical action can proceed only to
a certain extent, unless the electrical equilibrium, which has
disturbed, be again restored. Hence, we find that in the



280



NATURAL PHILOSOIHY.



simple, as well as in the compound galvanic circle, the oxydatioa

of the zinc proceeds with activity whenever the galvanic circle

is completed ; and that it ceases, or at least takes place very

slowly, whenever the circuit is interrupted.

What is neces- 1060. To produce any galvanic action it it

ITexdte'gaL necessary to form what is called a galvanic

vanic action ? circle , that is, a certain order or succession of

substances capable tf exciting electricity.

Of what 15 the 1061. The simplest galvanic circle is com-

simplest gal- posed of three conductors, one of which must

be solid 5 and ne fluid ; tne third ma y be either

solid or fluid.

What is the 1062. The process usually adopted for obtam-
"fo^ohaininir * n & g alvam ' c electricity is, to place between two
galvanic eke- plates of different kinds of metal a fluid capable
tricity ? O f exerting some chemical action on one of the

plates, while it has no action, or a different action, on the other
A communication is then formed between the two plates.
Explain 1063. Fig. 156 represents a
*&' ' simple galvanic circle. It con-
sists of a vessel containing a portion of
diluted sulphuric acid, with a plate of zinc,
Z, and of copper, C, immersed in it. The
plates are separated at the bottom, and the
circle is completed by connecting the two
plates on the outside of the vessel by means
of wires. The same effect will be pro-
duced, if, instead of using the wires, the
metallic plates come into direct contact.

1064. In the above ar-
What are the
essential parts rangement, there are three

of a galvanic elements or essential parts,
namely, the zinc, the copper,
end the acid The acid, acting chemical 1 ,) upon the zinc, pro-



Fig. 156.




GALVANISM. V&l

duces an alteration in the electrical state of the metal. The
zinc, communicating its natural share of zhc electrical fluid to
the acid, becomes negatively electrified. The copper, attracting
the same fluid from the acid, becomes positively electrified. Any
conducting substance, therefore, placed within the line of com-
munication between the positive and negative points, will re-
ceive the charge thus to be obtained. The arrows in Fig. 156
show the direction of the current of positive electricity, namely,
from the zinc to the fluid, from the fluid to the copper, from
the copper back through the wires to the zinc, passing from
zinc to copper in. the acid, and from copper to zinc out of the
acid. The substance submitted to the action of the electric cur-
Where must a rent must be placed in the line of communication
substance be between the copper and the zinc. The wire con-
affected by *al- necte d w ^ tn tae copper is called the positive pole r
vanic action ? and that connected with the zinc the negative pole,
and in all cases the substance submitted to galvanic action must
be placed between the positive and negative poles.

1065. The electrical effects of a simple galvanic circle, such as
has now been described, are, in general, too feeble to be perceived,
except by very delicate tests. The muscles of animals, especially
those of cold-blooded animals, such as frogs, &c., the tongue, the
eye, and other sensitive parts of the body, being very easily
affected, afford examples of the operation of simple galvanic
circles. In these, although the quantity of electricity set in
motion is exceedingly small, it is yet sufficient to produce verj
considerable effects ; but it produces little or no effect on the
most delicate electrometer.

1066. The galvanic effects of a simple circle

H^w may gat- r , .

vanic action be may be increased to any degree, by a .repetition
increased? of t j ie game s i m pi e combination. Such repe-
titions constitute compound galvanic circles, and are called
galvanic piles, or galvanic batteries, according to the mode
in which they are constructed.




288 NATURAL PHILOSOPHY.

1.0G7. It appears a \ first view to be a singular fact, that, in a simple
galvanic circle, composed of zinc, acid and copper, the zinc enr
will always be negative, anil the copper end positive ; while, in all
compound galvanic circles composed of the same elements, the zinc
will be positive, and the copper negative. This apparent difference
arises from the compound circle being usually terminated by two
superfluous plates.

What is the 1068. The voltaic pile consists of alternate
Voltaic pile ? places of two different kinds of metal, sepa-
rated by woollen cloth, card, or some similar substance.

Explain 1069. Fig. 157 represents a voltaic Fig. 157.

Fig. 157. pile. A voltaic pile may be con-
structed in the following manner : Take a
number of plates of silver, and the same num-
ber of zinc, and also of woollen cloth, the oloth
having been soaked in a solution of sal ammo-
niac in water. With these a pile is to be formed, in the following
order, namely : a piece of silver, a piece of zinc, a piece of cloth,
and thus repeated. These are to be supported by three glass
rods, placed perpendicularly, with pieces of wood at the top and
bottom, and the pile will then be complete, and will afford a
constant current of electric fluid through any conducting sub-
stance. Thus, if one hand be applied to the lower plate, and
the other to the upper one, a shock will be felt, which will be
repeated as often as the contact is renewed.

Instead of silver, copper plates, or plates of other metal, may
be used in the above arrangement. The arrows in the figure
show the course of the current of electricity in the arrangement
of silver, zinc, &c.

1070. Voltaic piles have been constructed of layers of gold
and silver paper. The effect of such piles remains undisturbed
for years. With the assistance of two such piles, an approxi-
mation to perpetual motion, in a self-moving clock, has been in-
vented by an Italian philosopher. The motion is produced by
the attraction and repulsion of the piles exerted on a pith-ball,
on the principle of the electrical bfclls. The ton of one of tht



GALVANISM.

piles was positive, and the bottom negative. T\e other pile was
in an opposite state ; namely, the top negative, and the bottom
positive.

W\aih the 1071. The voltaic, or galvanic battery, is a
galvanic bat- combination of metallic plates, immersed in
tcry pairs in a fluid which exerts a chemical action

on one of each pair of the plates, and no action, or, at least,
a different action, on the other.

What is the 1072. The electricity excited by the battery
diction of the i j th Ud t ^ fl id M h t

current in the r *

galvanic bat- upon it chemically. Thus, in a battery composed

ter y * of zinc, diluted sulphuric acid and copper, the acid

lets upon the zinc, and not on the copper. The galvanic fluid
proceeds, therefore, from the zinc to the acid, from the acid to
the copper, &c. Instead of using two different metals to form
the galvanic circuit, one metal, in different states, may be em-
ployed ; the essential principle being, that one of the elements
shall be more powerfully affected by some chemical agent than
the other. Thus, if a galvanic pair be made of the same metal,
one part must be softer than the other (as is the case with cast
and rolled zinc) ; or a greater amount of surface must be exposed
to corrosion on one side than on the other ; or a more powerful
chemical agent be used on one side, so that a current will be
sent from the part most corroded, through the liquid, to the part
least corroded, whenever the poles are united, and the circuit
thereby completed. "

Explain 1073. Fig. 158 represents Fig. 158.

Fig. 158. a voltaic battery. It con-
sists of a trough made of baked wood,
wedgewood-ware, or some other non-
conducting substance. It is divided
into grooves, or partitions, for the re-
ception of the acid, or a saline solution)
and the plates of zinc or copper (or
other metal) are iniinered by pairs in the grooves. Ti'cse







290 NATURAL PHILOSOPHY.

pairs of plates are united by a slip of metal passing from the
one and soldered to the other ; each pair being placed so aj to
enclose a partition between them, and each cell or groove in tho
trough containing a plate of zinc, connected with the copper
plate or the succeeding cell, and a copper plate joined with the
ainc plate of the preceding cell. These pairs must commence
with copper and terminate with zinc, or commence with zinc and
terminate with copper. The communication between the firsl
and last plates is made by wires, which thus complete the gal-
vanic circuit. The substance to be submitted to galvanic action
is placed between the points of the two wires.

How can a 1074. A compound battery of great power is

compound bat- obtained by uniting a number of these troughs.

tery of great _ . ./

power be ob- ^ a similar manner, a battery may be produced

tained? by uniting several piles, making a metallic com-

munication between the last plate of the one and the first plate
of the next, and so on, taking care that the order of succession
of the plates in the circuit be preserved inviolate.

Describe the 1075 - The ^ouronm Kg . 159>

Couronne des des tosses, represented in
iasses. Fig 159) ig anotacr f orm

of the galvanic battery. It consists of
a number of cups, bowls, or glasses,
with the zinc and copper plates im-
mersed in them, in the order represent-
ed in the figure ; Z indicating the zinc,
and C the copper plates ; the arrows denoting the course 1 , of the
electric fluid.

1076. The electric shock from the voltaic battery may bo
received by any number of persons, by joining hands, having
previously wetted them.

Describe Smee's 1077. SMEE'S GALVANIC B ATI ERY 13 represented
Battery, i n Fig. 160, and affords an instance of a battery

in its simplest form. It consists of a glass vessel (AS a tumbler),
i>n \viiich rest* the frame that supports the apparatus




GALVANISM.




Two screw-v3ups rise from the frame, to which Fig. ieo.

wires may be attached for the conveyance of
the electric current in any direct ice. One of
the screw-cups communicates with a thin strip
of platinum, or platinum-foil, which is sus-
pended within the glass vessel between two
plates of zinc, thus presenting each surface of
the platinum to a surface of zinc ; and the gal-
vanic action is in proportion to the extent of the opposite sur
faces of the two metals, and their nearness to each other. The
other screw-cup is connected with the two zinc plates. The
screw-cup connected with the platinum is insulated from the
metallic frame which supports it, by rosewood, and a thumb-
screw confines the zinc plates, so that they can be renewed when
necessary. The liquid employed for this battery is sulphuric
acid, or oil of vitriol, diluted with ten parts of water by measure.
To prevent the action of the acid upon the zinc plates, their sur-
faces are commonly amalgamated, or combined with mercury
which prevents any chemical action of the acid with the zino
until the galvanic circuit is established, when the zino is imme-
diately attacked by the acid.

Explain 1078. Fig. 161 represents a series of three pairs

Fig. 161. of this battery, in which it will be observed that the

Fig. 161.




platinum of one is connected with the zinc of the next, and that
the terminal wires proceed, consequently, one from a platinum
jjhte, and the other from a zinc plate, as iii a single pair.



2D2



NATURAL PHILOSOPHY.



Describe tht
sulphate of
topper bat-
tery by
Figures 162
and 163



1078. SULPHATE OF COPPER BATTERY. Fig
162 represents a sulphate of copper battery, and
Fig. 163 a vertical section of the same battery.
It consists of a double cylinder of copper, C C,
Fig. 163, with a bottom of the same metal, which

Fig. 162.




Fig. 163.



serves the double purpose of a gal-
panic plate and a vessel to contain
the exciting solution. The solu-
tion is contained in the space be-
tween the two copper cylinders. A
movable cylinder of zinc, Z, is let
down into the solution whenever
the battery is to be used. It rests
on three arms of wood or ivory at
the top, by means of which it is in-
sulated. Thus suspended in the
solution, the surfaces of zinc and
copper, respectively, face each
other. A screw-cup, N, is at-
tached to the zinc, and anoth-
er, P, to the copper cylinder,
to receive the wires. When
a communication is made be-
tween the two cups, electricity
is excited. The liquid em-
ployed in this battery is a
solution of sulphate of copper
(common blue vitriol) in water. A saturated solution is
first made, and to this solution as much more water is added.

1079. A pint of water will dissolve about a quarter of a pound oi
blue vitriol. The solution described above will therefore contain
about two ounces of the salt to the pint. The addition of alcohol
in small quantities increases the permanency of the action of the
oolution The zinc cylinder bhould always betaken out of the solu-
tion when the battery is not in use ; but the solution may remain
in the battery The battery will keep in good action ft r tw?uty or
thirty minutes at a time




GALVANISM. 29.S

1080. The sulphate of copper battery, although not so ener-
getic as Smee's, is found very convenient ir. a large class of
experiments, and is particularly recommended to those who are
inexpert in the use of acids ; because the sulphate of copper, being
entirely neutral, will not injure the color nor the texture of
organic substances.

Describe the 1081. There is another form of the sulphate of
protected sul- copper battery, called the Protected Sulphate of
phate of cop- Copper Battery, which differs from the one described
' in having a porous cell 01 earthenware, or leather,
interposed between the zinc and the copper, thus forming two
cells, in the outer of which sulphate of copper may be used, and
in the inner one a solution of sulphate of soda (Glauber salt),
or chloride of sodium (common salt), or even dilute sulphuric
acid. This battery will continue in use for several days, and it
is therefore of great use in the electrotype process.

1082. GROVE'S BATTERY. This is the most
* energetic battery yet known, and is the one
most generally used for the magnetic telegraph.
The metals employed are platinum and zinc, and the solutions
are strong nitric acid in contact with the pla-
tinum, and sulphuric acid diluted with ten or Fig>
twelve parts of water in contact with the zinc.
This battery must be used with great care, on
account of the strength of the acids used for
the solutions, which send out injurious fumes,
and which are destructive to organic sub-
stances. Fig. 164 represents Grove's bat-
tery. The containing vessel is glass ; within
this is a thick cylinder of amalgamated zinc, standing on short
legs, and divided by a longitudinal opening on one side, in order
to allow the acid to circulate freely. Inside of this is a porous
cell of unglazed porcelain, containing the nitric acid, and strip
uf platinum. The platinum is supported by a strip of bras?



Online LibraryRichard Green ParkerA school compendium of natural and experimental philosophy : embracing the elementary principles of mechanics, hydrostatics, hydraulics, pneumatics, acoustics, pyronomics, optics, electricity, galvanism, magnetism, electro-magnetism, magneto-electricity, astronomy : containing also a description of → online text (page 25 of 38)