Mrs. (Jane Haldimand) Marcet.

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metals, which is excited by the moisture of the animal, the organs
of the fng being only a delicate test of the presence of electric in-
fluencej

CaroHne, I suppose, then, the saliTa of the mouth answers the
same purpose as the moisture 9f a frog, in exciting the electricity
of the pieces of silver and zinc, with which Emily tried the exper-
iment on ber.tongue ?

Jirs. B. Precisely. It does appear, however, necessary that
the fluid used for this purpose shoula be of animal nature. W ater»
and acids very much diluted by water, are found to be the most ef-
fectual in promoting the developement of electricity m metals ; and
accordingly the original apparatus which Volta first constructed
for thi^urpese consisted of a pile or succession of plates ofmnc and
copi)eivieach pair of which was connected by pieces of cloth or pa-
per iipffregnated with water; and this instrument, from its orig[inal
inconvenient structure and limited strength, has graduallv arrived
at its present state of power and improvement, such as exhibited in
the Voltaic battery. In this apparatu?) a specimen of which you



fig. n)

Vottaie BattMT.



'before you
the plates of zinc
and copper are
soldered together]
in pairs,each pair'
b^mg placed at
regular distan-
ces in wooden
troughs and the
interstices being
filled with fluid.

Caroline. Though you will not allow us to Inquire into the pre-
cise* cause of electricity, may we not ask in what manner the fluid
acts on the metals so as to produce it ? |

Jtfri. B, The action of the fluid on the metals, whether water or
acid be used, is entirely of a chemical nature. But whether elec-
tricity is excited by this chemical action, or whether it is produced
by the contact of the two metals, is a point upon which philoso-
phers do not yet perfectly agree.

Emily. But can the mere contact of two metals, without any in-
tervening fl^id. produce electricity P

Mn, B. /x e8,\f they are afterwards separated. It is an establish-




352. How did Galvnni account for the moving of the hmb on a
communicT^lion being made between the two metals.^

363. What was the true cause of it ?

364. ^^ hat metals are used in the production of ntlvanic action ?'
3^5. Which figure represents a Voltaic battery?

356. Can galvanism be produced without water?



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BIACTRO-CHEXISTBV. 67

ed fact4hat when tiro metals are pat in contact, and aftenrardi lep-
arated} that which has the strongest attraction for oxygen exhibits
signs of positive, the other of negative electricity^

Caroline. It seems, then, hot reasonable to iniiT that the power
of the Voltaic battery should arise from the contact of the plates of
z^nc and copper. ^

Mr*. B, it is upon this principle that/Volta and Sir H. DaTnsx-
plain the phenomena of the pile ; but notwithstanding these^wo
g^reat authorities, many philosophers entertain doubts on the truth
of this theory. The cnief difficulty which occurs in explaming the
phenomena of the Voltaic battery on this principle, is thai two
such plates show no signs of different states of electricity whilst in
contact, but only oo t^mg separated after contact Now, io the
Voltaic battery, those plates that are io contact always continue so,
beiug soldered together ; and they cannot, therefore, receive a suc-
cession of charges. . Besides, if we consider the mere liisturbance
of the balance of electricity ^v the contact of the plates, as the sole
cause of the production of Voltaic electricity, it remains to be
explained how this disturbed balance becomes an inexhaustible
source of electrical energy, capable of pouring forth a constant and
copious supply of electrical fluid, though without any means of re-
plenishing itself from other sources This subject it must be own-
ed, is involved in too much obscurity to enable us to s)>eak very de-
cidedly in favor of any theory But. in order to avoid perplexine
you with different explanations, I shall confine myself to one whidb
appears to me to be least encumbered with difficulties, and most
likely to accord with truth.*

This theory supposes the electricity to be excited by the chemic-
al action of the acid oo the zinc ; but you are jei such novices in
chemistry, that 1 think it will be necessary to g^ve you some previ*
ous explanation of the nature of this action.

All metals have a strong attraction^r oxygen^ and this element
is found in great abundance, both in water and/n acids. T>.e ac-
tion of the diluted acid on the zinc consists, therefore, in its oxygen
combining with it, and dissolving its surfpice.

Caroline. In the same manner, I suppose, as we saw an acid dis-
solve copper ?

Mrt, B, Yes ; but in the Voltaic battery the diluted acid is not
strong enough to produce so complete an effect ; it acts only on the

* This mode of explaining the phenomena of the Volt >ic pile is
called the chemical Aeory of electricity, bee -use it asrriKes the
cause of these phenomeua to ascertain chemical changes which taike
place during their appearance. The mode ivhich is here sketched
was long since suggested by Dr. Bostock, who has lately (thl8)
publish^ ^^ An account of the History and Present State of Galvan-
ism ;" which contains a fuller and more complete statement of his
opinions and those of other writers on the subject, than any of his
former papers.



357. 'What established fact in galvanic experiments is mentioned ?

358. What two chemists have explained the phenomena of the
Voltaic battery, as proceeding solely from the contact of the two
metals ?

359. For what have all metals strong attraction f

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88 ElECTRO-CHEXISTBT.

surface of theziqc, to which it yields its oxygen, forming upon it a
film or crust, which is a compound of the oxygen and the melal.

Emily, Since there is so strong a chemical attraction between ox-
ygen and metals, I suppose they are naturally in different states of
electricity.

Mrs. B. Yes^ it appears that all metals are united with the pos-
itive, and that^ygeniis the grand source of the negative electri-
city. ^

Caroline, Does not, then, the acid act on the plates of copper, as
well as on those of zinc ?*

Mrs, B, Tso ;«br though copper has an affinity for oxygen, it is
less strong than that of zin^ and therefore the energy of the acid
As only exerted upon the zinci

It will be best I believe, iiforder to render the action of the Vol-
taic baitery more intelligible, to confine our'attention at first to the
efijWJt produced on two plates only. (Fig. 12.)

pi" a plate of zinc be placed opposite to one of copper, or Fig. 12.
any other metal less attractive of oxygen, and the space Voiuic Bat-
between them (suppose of half an inch in thickness,) be fil- ^'^'
led with an acid or any fluid capable of oxydating the zinc, -^
the oxydated surface will have its capacity for electricity
diminished, so that a quantity of electricity will be evolv-
ed from that surface. This electricity will be received
by the contiguous fluid, by which it will be transmitted to
the opposite metallic surface, the copper, which is not ox-
ydated, and is therefore disposed to receive it ; so that the
copper plate will thus become positive, whilst the zinc
plate will be in the negative state.

This evolution of electrical fluid, however, will be very
limited ; for as these two plates admit of but very little ac-.
cumulation of electricity, and are supposed to have no communica-
tion with other bodies, the action of tfce acid, and further develop-
ment of electricity, will be immediately stopped^

Emily, This action, I suppose, can no more continue than that
of a common electrical machine, which is not allowed to communi-
cate with other bodies .^

Mrs, B. Precisely ; mie common electrical machine when excit-
ed by the friction of the^ubber, gives out both the positive and neg-
ative electricities. —(Fig. 13.) The positive, by the rotation of the
glass cylinder, is conveyed into the conductor, whilst the negative
goes into the rubber .| But,ninless there is a communication made
between the rubber alid the ground, a very inconsiderable quantity

♦ The acid acts upon the copper, but not so strongly as on the
zinc. Any two metals, one of which has a stronger attraction for
oxygen than the other, will form the galvanic series.— C.



360. What is the grand source of negative electricity ?

361. Why in the Voltaic battery is the energy of the action ex-
erted only upon the zinc ?

362. How would you explain the principle of the Voltaic battery
by Fig. 12 ?

363. How would you describe the mode of collecting electricity
in the common electrical machine.^

364. Why must the rubber be connected with the ground?




EUICTEO-CHEMISTRT. 89

of electricity can be excited ; for the mbber like the plates of the
battery, has too small a capacity to admit of aD accumalation of
electHcity^ Unless, therefore, the electricity can pass out of the
rubber, it^ill not continue to gfo into it, and consequently, no ad-
ditional accumalation will take place. Now, as one kind of elec-
tricity cannot be ^iven out without the other, the developement of
the positive electricity is stopped as well as that of the negative, and
the conductor, therefore, cannot receive a succession of chargpes.
Fig. 13. Electrical Machine.




Fiff. 13. A. the CjUnder. B, the Condaetor. R, the Rubb«r. C, the Chain.

Caroline, But does not the conductor, as well as the rubber, re-
quire a communication with the earth, in order to get rid of its
electricity f ^

Mr$, B, No ; nor it is susceptible of receiving atid containing a
considerable quantity of electricity, as it is much largv^r than the
robber, and therefore has a greater capacity; and this continued
accumulation of electricity in the conductor is what is caUed a
charge's

EtnUfi, But when an electrical machine is furnished with two
conductors to receive the two electricities, I suppose no communi-
cation with the earth is required ?

Jtfr<. B, Certainly not, until the two are fully cbar|^ed ; for the
tiro conductors will receive equal quantities of electricity.

Caroline, I thought the use of the chain had been to convey the
elect^ity^rom the ground into the machine.

Mrs. B. That was the idea of Dr. Franklin, who supposed Chat
tkire was but one kind of electricity, and who by the terms posi-
tive and negative (which he first introduced,) meant only differenlt
quanfities of the same kind of electricity.* The chain was in that

*The idea of Dr. Franklin wa8,|6iat the positire state consisted

• "' ' ' I ■ I I III • ■■ I > I .^ ii I ■)

365. What ii called a charge in the use of the common electrical
machiDe ?
36e. What was Dr. Franklin^ opinioD GoncemiDg electricity ?



90 ELECTBO-CHEMISTRY.

case supposed to convey electricity /rowi the ground through the
rubber into the conductor. But as we have adopt^ the hypothesis
of two electricities, we must consider the chain as^ vehicle to con-
duct the negative electricity into the earthA >,..,.
Emily, And^re both kinds produced whenever electricity is ex-

^^%rs. B, (tes, invariably) If you rub a tube of glass with a wool-
len cloth Che glass becomes positive, and the cloth negative * If,
on the contrary, you excite a stick of sealing-wax by the same means,
it is the robber which becomes positive, and the wax negative.

But with rec'ard to the Voltaic battery, in order that the acid may
act freely on the zinc, and the two electricities be given out without
interruption, fsome method must be devised, by which the plates
may part witft their electricities as fast as they receive themx Can
vou think of any means by which this might be effected ? «

Emily. Would not two chains or wires, suspended from either
plate to the ground, conduct the electricities into the earth, and thus

answer the purpose ? - • «• *u i * •

Mrs, B. It would answer the purpose of carrying off the electri-
city, I admit; but recollect, that though it is necessary to find a
vent for the electricity, yet we must not lose it, since it is the pow-
er we are endeavoring to obtain. Instead, therefore, of conduct-
ino" it into the ground, let us/fnake the wires, from either plate,
meet ; the two electricities wHl thus be brought together, and will
combine and neutralize each other; and as long as this communi-
cation continues, the two plates having a vent for their respective
electricities, the action of the acid will go on freely and uninler-

^uptedly"^^ ^ , * i

EmilyJ That is very clear, so far as two plates only are concern-
ed ; buf^I cannot say 1 understand how the energy of the succes-
sion of plates, or rather pairs of plates, of which the Galvanic trough
is composed, is propagated and accumulated throughout a battery ?

in the presence, or accumulation of the electric fluid, and that the
negative was merely its absence or diminution.! Hence the terms
used by him to indicate these states were posilife and negative. In
this chapter Mrs. B. has used these terms of the American Philoso-
pher improperly, for plus and minus were never meant to signify
two sorts of electricity, but only its presence or absence. Where
authors have adopted Dufay's theory of two electricities, they have
used the terms, vitreous and resinous, — C.

* Most probably, because the glass takes the electric fluid from
the cloth. Indeed, we conceive there is about the same reason for
believing that the negative state is the absence of the electric fluid
as there is for believing that cold is the absence of heat.— C.



367. What is the use of the chain in the common electrical ma-

368. Are negative and positive electricity always produced when
electricity is excited ?

369. What is necessary in the Voltaic battei^r, that the two elec-
tricities be given out without interruption ?

370. In what manner do two pieces of wire produce this effect ?



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ELECTBO-CHEMISTRY. 9l

Mrs. B: In order to show you how the intensity of the electrici-
ty is increased by increasing^ the number of plates, we" will exam-
ine the action of four plates ; if you understand these, you will
readily comprehend that of any number whatever.
(T ^. ^ Fig. 14. Voltaic Battery.

yn this Dgure you will observe that the
two central plates are united ; they are
soldered together, (as we observed in
describing the Voltaic trough,) so as to
form but one plate, which offers two
different surfac^ ; the one of copper,
the other of zincA

^ow you recollect, that, in explaining
to^ action of two plates, we supposed
that a quantity of electricity was evolved
from the surface of the first zinc plate, in
consequence of the action of the acid, and-

was conveyed by the interposed fluid to the copper plate No. 2,
which thus became positive. This copper plate communicates its
electricity to the contiguous zinc plate. No 3, in i;vhich, conse-
quently, some accumulation of electricity takes place. When,
therefore, the fluid in the next cell acts upon the zinc plate, elec-
tricity is extricated from it in larger quantity, and in a more con-
centrated form, than before. This concentrated electricity is again
conveyed by the fluid to the next pair of the plates, No. 4 and 5,
when it is further increased by the action of the fluid in the third
cell, and so on, to any number of plates,.Af which the battery may
coDsist , so that the electrical energy will continue to accumulate
in proportion io the number of double plates, the first zinc plate of
the series being the most negative, and the last copper plate the
most positiveTj

Caroline. Bdt does the battery become more and more strongly
charged, merely by being allowed to stand undisturbed ?

Mrs. B. No : for the action will soon stop, as was explained be-
fore, unless a vent be given to the accumulated electricities. This
is easily done, however, by establishing acoramunicationiby means
of the wires (See Fig. 11,) between the two ends of the battery ;
these being brought into contact, the two electricities meet and
neutralize each other, producing the shock and other effects of
electricity : and the action goes on with renewed energy, being no
longer obstructed by the accumulation of the two electricities "
whiqh impeded its progress.

Emily. Is it the union of the two electricities which produces the
electric spdrk ?

Mrs. B. Yes ; and it is, I believe, this circumstance which gave
rise to Sir H. Davy's opinion, that caloric may be^ compound of
the two electricities.N \

Caroline. Yet, sui^ly, caloric is very different from the electoral
spark .^ . .

Mrs. B. The difference may consist, probably, only in intensity ;



371. How would you explain fijure 14 ?

372. How would you explain figure 14, which represents the
Voltaic battery, so as to produce the electric spark ? .

373. What does Sir H. Davy sujppose caloric to be ? >Ogle



92 ELECTBO^BEinSTRY.

for the heat omhe electrip spark is coosiderably more intense
though confinecKo a yerj minute spot,. than any heat'^^e can pro*
ducefby other means'^

Emtiy, Is it quitencertain that the electricity of the Voltaic
batter> is precisely of the same nature as that of the common elec-
trical machine? ^

Mrs, B, Uudoubtedly ;Qhe shock gfiren to the human body, the
, spark, the circumstaoce o^the same substances which are conduct-
ors of the one, bein^ also conductors of the other, and of those bodies,
such as glass and sealing- irax, which are non conductors of the one,
being ako non conductors of the other, are striking proofs of it\~
Besides, Sir H. Davy has shown, in his Lectures that a Leyden ^r,
and a common electric battery, can be charged with electricity
obtained from a Voltaic baitery, the effect produced being perfect-
ly similar to that obta ned by a common machine.

Dr. Wollaston has likewise proved, that similar chemical decom-
positions are effected by the electric machine and by the Voltaic
battery ; and has made other experiments whieh render it highly
probable, that the origin of both electricities is essentially the same,
as they show that the rubber of the common electrical machine,
Jike the zinc in the Voltaic battery, produces the two electricities,
fty combining with oxygen^

Caroline. But 1 do not see whence the rubber obtains oxygen, for
there is neither acid nor water used in the common machine ; and I
always understood that the electricity was excited by the friction.'

Jlfr#. B It appears that/by friction the rubber obtains ^ygen
from the atmosphere, which K par- ly composed of that element The
oxygen combines with the amalgam of the rubber, which Is of a
metallic nature, much in the same way as the oxygen of the acid
combines wiih the zinc in the Voltaic battery, and it is thus that
the two electricities are disengaged.

Caroline But if the electricities of both niachines are similar,
why not useuthe common machine for chemical decompositions ?

Mrs. B. ^ough its effects are sinnlar to those of the Voltaic
battery, they are incomparably weakerN Indeed Dr. Wollaston, in
using It for chemical decompositions, ^s obliged to act upon the
most minute quantities of matter, tind though the result was satis-
factory in proving the similarity of its effects to those of the Voltaic
battery, these effects were too small in extent to be in any consid-
erable degree applicable to chemical decompositions.

Caroline. How terrible, then, a shock must be from a Voltaic
battery, since it is so much more powerful than an electrical ma-
chine.
Mrt, B, It is not nearly so formidable as you think ; at least it is



374. How does the degree of heat in the electric spark compare
with that produced by other means ?

375. What proves that the electricity in the Voltaic battery ii of
the same nature as that of the common electrical machine ?

376. How do the rubber of the common electrical machine and
the zinc in the Voltaic battery produce the two electricities f

377. How does the rubber obtain oxygfen, in the ose of the com-
mon electrical machine f

S78. Why is not the oommon etoctrioal machine used for chemi-
cal decompositions f ^ i

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£LECTK0.CH£HI8TSY. 93

bj no means proportional t(f the chemical effect. The ^reat supe-
riority of the Voltaic battery consists^ the large quantity of elec-
tricity that passes'^ but ih regard to AkBrapidUy or intensity of the
charge, it is greatly suiTt^sed by the common electrical machine^
It would seem that the shock or sensation depends chiefly upon the
intensity ; whilst, on the contrary, for chemical purposes, it is .
quantity which is required. In the Voltaic battery, the electricity,
though copious, is so weak as not to be able to force its way through
the fluid which separates the plates, whilst that of a common ma-
chine will pass through any space of water.

Caroline. Would it not be possible to increase the intensity of
the Voltaic battery till it should equal that of the common machine;?

Mrs, B. It can actually be increased till it imitates a weak elec-
trical machine, so as to produce a visible spark when accumulated
in a Leyden jar. But it can never be raised sufficiently to pass
through any considerable extent of air, because of the ready com
mjutication through the fluids employed.

^y increasing the number of plates of a battery, you increase its
inmuityy whilst, by enlarging the dimensions of the plates, you aug-
ment its 9tean/i/jX-and as the superiority of the battery over the
common machioe/Consists entirely in the quantity of electricity pro-
duced, it was at first supposed that it was the size, rather than the
number of plates that was Essential to the augmentation of power.
It was, however, found upon trial, that the quantity of electricity
produced by the Voltaic battery, even when of a very moderate
size, was sufficiently^ copious, and that the chief advantage in this
apparatus was obtained by increasing the intensity, which, howev-
er, still falls very far short of that of the common machine.

I should not omit to mention, that a very splendid, and, at the
same time, most powerful battery, was alfew years ago, constructed
under the direction of Sir H. Davy, which hg repeatedly exhibited
in his course of electro-chemical lectures. /Tt consists of two thou-
sand double plates of zinc and copper, of \ix square inches in di-
meosiona, arranged in troughs M Wedgwood-ware, each of which
contains twenty of these platesil The troughs are furnished with a
contrivance for lifting the plater out of them in a very convenient
and expeditious manner.*



* A model of this mode of construction is exhibited in (Fig. 15.)
.Note. In consequence of the discoveries ofiProf. Hare, of Phil -
adelphia,\he present theory of galvanism must^robably undergo a
radical cmange. This gentleman has inrented a new method of ex-
tricating the vollaic influence, by so connecting the plates, that in
effect only two great surfaces of the metuls are presented to each
other. By this arrangement, the galvanic action on different sub-



379. In what does the superiority of the Voltaic battery consist ?

380. In what respect does the common electrical machine surpass
the Voltaic battery .? »

381. What is^he difference in the action of the Voltaic battery,
whether the number of plates is increaBcd or their size is enlarged ?

382. How extensive was the large battery constructed by Sir H.
Davy?

383. What American chemist has dUtin%uislied himself by discover
ies in galvanism ? Digitized by L^OOg I



94



EIiBCTRO-CHSmSTBT.



Canline. Well, now that we aoderstand the natare of the action
of the Voltaic battery, I long to hear an account of the chemical
discoveries to which it has g^ven rise.

Mrs, B, Tou mast restrain your impatience, my dear, for I cannot
with any propriety introduce the subject of these discoveries till we
come to them in the regular course of our studies. 1 here is, how-
ever, a recent discovery respecting the Voltaic pile, which, though
not immediately connected with chemistry, is too curious to be pass-
ed over vin silence. It relates /o the influence of electricity on mag-
netismMately discovered by vJ)aDish philosopher. Mr. Oersted.

Caroline. What ! anima! magnetism ? i have often beard of mag-
netic tractors ; but I thought there was no truth in them.

Mrs. B. Nor is there ; it is only the magnetic needle to which I
allude. You already know something of the wonderful property of
the magnetic needle to direct one of its extremities towards the
north ; and you may easily conceive how interestmg any new fact
relating to this trniy mysterious agent, must be to science. The
principal fact is this ; gf a Voltaic battery be so placed as to have its



Online LibraryMrs. (Jane Haldimand) MarcetConversations on chemistry .. → online text (page 11 of 43)