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The electro-motive force produced by the contact of alkaline
liquids with the metals, is generally directed from the metal to
the liquid, and its energy is greater the higher is the place held
by the metal in the series of electromoters (1847). Thus, tin,
antimony, and zinc, in contact with caustic potash, caustic
soda, or ammonia, have a more energetic action than platinum,
bismuth, or silver.

The electro-motive force of nitric acid in contact with a
metal, is invariably directed from the acid to the metal. In
this acid, iron and platinum are the most powerful, and zinc the
most feeble electromoters.

Sulphuric and hydrochloric acid, in contact with those
metals which stand at the head of the series (1847), develop a
force directed from the acid to the metal, and in contact with
those at the lowest part of the series, produce a force directed
from the metal to the acid. Thus, these acids in contact with
the less oxydable metals, as gold, platinum, copper, give an
electro-motive force directed from the acid to the metal ; but in
contact with the more oxydable, as antimony, tin, or zinc, give
a force directed from the metal to the acid.

When the metals are placed in contact with weak acid, or
saline solutions generally, the electro-motive force is directed
from the metal to the liquid, the energy of the force being in



SIMPLE VOLTAIC COMBINATION. 2/3

general greater the higher is the place of the metal in the series
of electrometers (1847). In the case of the metals holding the
lowest places in the series, the electro-motive force is in some
instances directed with feeble intensity from the liquid to the
metal.

1851. Differences of opinion as to the origin of electro-motive
action. Since the date of the discoveries of Volta to the
present day, opinion has been divided in the scientific world as
to the actual origin of that electrical excitation which is here
expressed by the term electro-motive force, and which, as has
been explained, Volta ascribed to the mere mechanical contact
of heterogeneous conductors. Some have contended and
among them many of the most eminent recent discoverers in
this branch of physics that the real origin of the electro-
motive force is the chemical action which takes place between
the solid and liquid conductors ; and that, in the cases where
there is an apparent development of electricity by the contact
of heterogeneous solid conductors, its real source has been the
unperceived chemical action of moisture on the more oxydable
electromoter. Others, without disputing the efficacy of chemical
action, maintain that it is a secondary agent, merely exciting
the electro-motive energy of the solid conductors. Thus,
Martens holds that liquids are not properly electrometers at all,
but rather modify ^the electro-motive force of the metals in
contact with them ; so that they may be considered as some-
times augmenting and sometimes diminishing the effect of the
two metals. It is admitted by the partisans of the theory of
contact, that the liquids which most powerfully influence the
electro -motive force of the solids are those which act chemically
on them with greatest energy. But it is contended, that liquids
which produce no chemical change on the metal with which
they are in contact, do nevertheless affect its electro-motive
action.

It fortunately happens, that this polemic can produce no
obstacle to the progress of discovery, nor can it affect the
certitude of the general conclusions which have been based
upon observed facts ; while, on the other hand, the spirit of
the opposition arising from the conflicting theories, has led to
experimental results of the highest importance.

Whatever, therefore, be the origin of the electricity developed
under the circumstances which have been described, we shall

N 5



274



VOLTAIC ELECTRICITY.



continue to designate it by the term electro-motive force, by
which it was first denominated by its illustrious discoverer ;
and we shall invariably designate as the direction of this force
that which the positive fluid takes in passing from one element
to another in the voltaic combination.

1852. Polar arrangement of the fluids in all electro-motive
combinations. In every voltaic combination, therefore, the
effect of the electro-motive force is a polar arrangement of the
decomposed fluids ; the positive fluid being driven towards that
extremity of the system to which the electro-motive force is
directed, and the negative fluid retiring towards the other
extremity.

1853. Positive and negative poles. These extremities are
therefore denominated the POLES of the system ; that towards
which the electro-motive force is directed, and where the positive
fluid is collected, being the POSITIVE, and the other the NEGATIVE
pole.

1854. Electro-motive effect of a liquid interposed between two
solid conductors. When a liquid conductor is placed in contact
with and between two solid conductors, an electrical condition
is induced, the nature of which will be determined by the
quantities and direction of the electro-motive forces developed
at the two surfaces of contact. The several varieties of con-
dition presented by such a voltaic arrangement are represented
\njig. 531. to fig. 536.




Fig. 535. Fig. 536.

Let z and c represent the solid, and L the liquid conductors ;
and let the arrows directed from the two surfaces of contact
represent in each case the direction of the electro-motive forces.



SIMPLE VOLTAIC COMBINATION. 275

If the electro-motive forces be both directed to the same pole,
as in figs. 531, 532., that pole receiving all the positive fluid
transmitted by the conductors will be the positive pole, and the
other, receiving all the negative fluid transmitted, will be the
negative pole.

The quantity of electricity with which each pole will be
charged, will be the sum of the quantities developed by the
electro-motive forces at the two surfaces, diminished by the sum
of the quantities intercepted by reason of the imperfect con-
ducting power of the liquid and solids, and by reason of the
quantity intercepted in passing from the liquid to the solid
conductors at their common surface.

If the electro-motive forces be directed to opposite poles, that
pole to which the more energetic is directed will be the positive
pole. The varieties of conditions presented by this case are
represented in figs. 533, 534, 535, and 536. Each pole in
these cases receives positive fluid from one surface, and negative
from the other. That to which the more energetic electro-
motive force is directed receives more positive than negative
fluid, and is therefore charged with positive fluid equal to their
difference, and is, consequently, the positive pole. The other
receives more negative than positive fluid, and is, consequently,
the negative pole.

In the case represented in fig. 533., the electro-motive force
between z and L is the more energetic. A greater quantity of
positive fluid is received by c from the surface ZL than of
negative fluid from the surface CL, and the surplus of the former
above the latter constitutes the free electricity of the positive
pole c. In like manner, the quantity of negative fluid received
by the pole z from the surface ZL predominates over the quantity
of positive fluid received from the surface CL, and the surplus
of the former over the latter constitutes the free electricity of
the negative pole z.

The like reasoning, mutatis mutandis, will be applicable to
figs. 534., 536., in which the electro-motive force between z and
L is the more energetic, and to fig. 535., in which the electro-
motive force between c and L is the more energetic.

In all these cases, the quantity of electricity with which the
poles are charged is the difference between the actual quantities
developed by the two electro-motive forces, diminished by the

N 6



276 VOLTAIC ELECTRICITY.

difference between the quantities intercepted by the imperfection
of the conduction of the liquid and solid, and in passing through
the surface which separates the liquid and solid conductors.

1855. Electro-motive action of two liquids between two solids.
The quantity of electricity developed may be augmented by
placing different liquid conductors in contact with the two solid
conductors. In this case, however, it is necessary to provide
some expedient by which the two liquids, without being allowed
to intermingle, may nevertheless be in contact, so that the
electricities transmitted from the electro-motive surfaces may
pass freely from the one liquid to the other. This may be
accomplished by separating the liquids by a diaphragm or
partition composed of some porous material, which is capable
of imbibing the liquids without being

z I. P I. C sufficiently open in its texture to allow
I the liquids to pass in any considerable
i^Ji quantity through it. A partition of un-



Fig. 537. glazed porcelain is found to answer this

purpose perfectly. Such an arrange-
ment is represented in fig. 537., where z and c are the solid
electrometers, L and i/ the two liquids, and P the porous par-
tition separating them.

1856. Practical examples of such combinations. As a
practical example of the application of these principles, let the
liquid \^,fig. 531., be concentrated sulphuric acid placed between
a plate of zinc z, and a plate of copper c. In this case the
electro-motive force is directed from z to L, and from L to C ;
and, consequently, the tension of the negative electricity on z,
and the positive electricity on c, will be the sum of the tensions
transmitted from the two surfaces, and z will be the negative,
and c the positive pole (1854).

If the liquid be a dilute solution of acid or salt, or a strong
alkaline liquid, the electro-motive forces are both directed from
the metal to the liquid, but that of the zinc is more energetic
than that of the copper ; consequently z, fig. 533., will in this
case be the negative, and c the positive pole, the energy of the
combination being proportional to the difference of the two
electro-motive forces.

If the liquid be concentrated nitric acid, the electro-motive
forces will be both directed from the liquid to the metals. In
this case the zinc z, _/?<?. 535., being the more feeble electrometer,



SIMPLE VOLTAIC COMBINATION. 277

the copper element c will be the positive, and the zinc z the
negative pole.

If two different liquids be interposed between plates of the
same metal, the conditions which affect the development of
electricity may be determined by similar reasoning.

If z and c, fig. 537., be two plates of the same metal, and L
and i/ be two liquids, between which and the metal there are
unequal electro-motive forces, the effect of such an arrange-
ment will be a polar development, the positive pole being that
to which the electro-motive forces are directed if they have a
common direction, and that of the more energetic if they act in
opposite directions. The intensity of the charge at the poles
will be in the one case the sum, and in the other the difference
of the quantities of fluid transmitted.

As a practical example of the application of this principle,
let the metals z and c be both platinum, and let L be an
alkaline solution, and i/ concentrated nitric acid. In this case
the electro-motive forces will be directed from z to L, and from
L' to c, and the effect of the arrangement will be similar to that
represented vbfig. 531.

1857. Most powerful combinations determined. The most
powerful voltaic arrangements are produced by taking two
metals from the extremes of the electro-motive series (1847), and
interposing between them two liquids, the electro-motive force
of one being directed from the metal to the liquid, and of the
other from the liquid to the metal, and so selecting the liquids,
subject to this latter condition, as to have the greatest possible
electro-motive action on the respective metals.

Observing these principles, voltaic combinations of extra-
ordinary power have been produced by interposing dilute
sulphuric ^,fig. 537., and concentrated nitric acid i/, between
zinc z, and carbon or platinum c. In such a combination,
strong electro-motive forces are developed, directed from the
zinc to the acids, and from the acids to the carbon or platinum.
The zinc is therefore the negative, and the carbon or platinum
the positive pole of the system.

1858. Form of electro-motive combination. We have se-
lected the form of parallel plates or columns, which has been
supposed in the arrangements here described, merely because of
the clearness and simplicity which it gives to the exposition of
the principles upon which all voltaic combinations act. This



278 VOLTAIC ELECTRICITY.

form, although it was that of the earliest voltaic systems, and
is still in some cases adhered to, is neither essential to the
principle of such arrangements, nor convenient where the
development of great force is required. In order to obtain as
great an extent of electro-motive surface in as small a volume
as is practicable, the form of hollow cylinders of varying
diameters, placed concentrically in cylindrical vessels a little
larger, and containing the exciting liquid, is now generally
preferred.

1859. Yalta's first combination. The simple arrangements
first adopted by Volta consisted of two equal discs of metal, one
of zinc, and the other of copper or silver, with a disc of cloth
or bibulous card, soaked in an acid or saline solution, between
them. These were usually laid, with their surfaces horizontal,
one upon the other.

1860. Wollastorfs combination The late Dr. Wollaston
proposed an arrangement, in which the copper plate was bent
into two parallel plates, a space between them being left for the
insertion of the zinc plate, the contact of the plates being pre-
vented by the interposition of bits of cork or other non-con-
ductor. The system thus combined was immersed in dilute
acid contained in a porcelain vessel.

1861. Hare's spiral arrangement. This consists of two
metallic plates, one of zinc and the other of copper, of equal
length, rolled together into the form of a spiral, a space
of a quarter of an inch being left between them. They are
maintained parallel without touching, by means of a wooden
cross at top and bottom, in which notches are provided at
proper distances, into which the plates are inserted, the two
crosses having a common axis. This combination is let into
a glass or porcelain cylindrical vessel of corresponding mag-
nitude, containing the exciting liquid.

This ai'rangement has the great advantage of providing a
very considerable electro-motive surface with a very small
volume.

The exciting liquid recommended for these batteries when
great power is desired, is a solution in water of 2 per cent of
sulphuric, and 2 per cent of nitric acid. A less intense but
more durable action may be obtained by a solution of common
salt, or of 3 to 5 per cent of sulphuric acid only.

1862. Amalgamation of the zinc. Whatever be the form



SIMPLE VOLTAIC COMBINATION.



279



of the arrangement, its force and uniformity of action will be
promoted by amalgamating the zinc element, which may be best
accomplished in the following manner.

Immerse the rough plate or cylinder of zinc in a solution of
sulphuric acid containing from 12 to 16 per cent, of acid, until
the thin film of oxyde which usually collects on the surface of the
metal be dissolved. Then wash it well in water, and immerse
it in a dilute solution of the nitrate of mercury. After a short
time a perfectly uniform amalgam will be formed on the surface
of the zinc. Let the zinc be then washed in water and rubbed
dry with saw-dust.

1863. Cylindrical combination with one fluid. Voltaic
systems of the cylindrical form usually consist of two hollow
cylinders of different metals, one of which, however, is always
zinc. The exciting liquid being placed in a cylindrical vessel
a little longer than the greater of the two hollow metallic
cylinders, these are immersed in it concentrically with it and
with each other. A part of each projecting from the top of the
vessel becomes the pole of the system.

Such a combination is represented in vertical section in fig.
538., where vv is a vessel of glazed porcelain, containing the
acid or saline solution, zz is a hollow cylinder of zinc, and cc
a similar hollow cylinder of copper, each being open at both
ends, and separated from each other by a space of a quarter to
half an inch. Strips of metal CP and ZN represent the poles,
that connected with the zinc being the negative, and that con-
nected with the copper being the positive pole.

In some cases the porcelain vessel vv is dispensed with, and
the acid solution is placed in a cylindrical copper vessel, in





Fig. 538.



Fig. 539.



280



VOLTAIC ELECTRICITY.




Fig. 540.



which the hollow cylinder of zinc is immersed, resting upon
some non-conducting support. Such an arrangement is re-
presented \nfig. 539. in vertical section, cc being the copper
vessel, zz the zinc cylinder, and p and N the poles.

1864. Cylindrical combinations with two fluids. Cylin-
drical arrangements with two exciting liquids are made in the

following manner. The hollow
cylinder of zinc z z, open at both
ends as already described, is
placed in a vessel of glazed
porcelain *vv,fig. 540. Within
this is placed a cylindrical ves-
sel vv, of unglazed porcelain,
a little less in diameter than
the zinc z z, so that a space of
about a quarter of an inch
may separate their surfaces.
In this vessel vv, is inserted
a cylinder cc of platinum, open
at the ends, and a little less than vv, so that their surfaces may
be about a quarter of an inch asunder. Dilute sulphuric acid
is then poured into the vessel vv, and concentrated nitric
acid into vv. According to what has been already explained
(1857), P proceeding from the platinum will then be the positive,
and N proceeding from the zinc the negative pole.

1865. Grove's battery. This arrangement is known as
GROVE'S BATTERY. Various modifications have been suggested
with the view to increase the electro-motive surface of the
platinum and economize expense. Gruel suggests the use of
thin platinum, attached by platinum wires to a central axis,
from which from 4 to 6 leaves or flaps diverge. Poggendorf
proposes a single leaf of platinum, greater in breadth than the
diameter of the vessel vv in the ratio of about 3 to 2, and bent
into the form of an S, so as to pass freely into it. Pfaff
proposes to coat the inner surface of the vessel vv with leaf
platinum. Peschel affirms, after having tried this expedient,
that it is less effective than the former.

In these systems it is recommended to use a solution of sul-
phuric acid containing from 10 to 25 per cent, of acid, and
nitric acid of the specific gravity of 1-33.

1866. Bunsen's battery. The voltaic system known as



SIMPLE VOLTAIC COMBINATION.



281



BUNSEN'S, is similar to the preceding, substituting charcoal for
platinum. The charcoal cylinder used for this purpose, is made
from the residuum taken from the retorts of gas-works. A
strong porous mass is produced by repeatedly baking the pul-
verized coke, to which the required form is easily imparted.
Messrs. Deleuil and Son, of Paris, have fabricated batteries on
this principle with great success. I have one at present in use
consisting of fifty pairs of zinc and carbon cylinders, the zinc
being 2^ inches diameter, and 8 inches high, which performs
very satisfactorily.

The electro-motive forces of Grove's and Bunsen's batteries
are considered to be, ceteris paribus, equal.

1867. Daniel's constant battery. The voltaic arrangement
known as Daniel's constant battery consists of a copper cylin-
drical vessel C C, fig. 541., widening near the top ad. In this
is placed a cylindrical vessel of unglazed
d porcelain p. In this latter is placed the
hollow cylinder of zinc z, already described.
The space between the copper and porce-
lain vessels is filled with a saturated solu-
tion of the sulphate of copper, which is
maintained in a state of saturation by crys-
tals of the salt placed in the wide cup abed,
in the bottom of which is a grating com-
posed of wire carried in a zigzag direction between two con-
centric rings, as represented in plan at G. The vessel p, con-
taining the zinc, is filled with a solution of sulphuric acid, con-
4. taining from 10 to 25 per cent, of acid
when greater electro-motive power is re-
quired, and from 1 to 4 per cent, when
more moderate action is sufficient.

1868. PouilleCs modification of Da-
niel's battery. The following modi-
fication of Daniel's system was adopted
by M. Pouillet in his experimental re-
searches. A hollow cylinder a, fig. 542.,
of thin copper, is ballasted with sand b,
having a flat bottom c, and a conical
top d. Above this cone the sides of
the copper cylinders are continued, and
terminate in a flange e. Between this




Fig. 541.



c,

h




j


i a i


- -., : -(, -;.,-_;.. -
./ . . ..._,. -

\:... - ">. \ ,



Fig. 542.



282 VOLTAIC ELECTRICITY.

flange and the base of the cone, and near the base, is a ring of
holes. This copper vessel is placed in a bladder which fits
it loosely like a glove, and is tied round the neck under the
flange e. The saturated solution of the sulphate of copper is
poured into the cup above the cone, and, flowing through the
ring of holes, fills the space between the bladder and the copper
vessel. It is maintained in its state of saturation by crystals
of the salt deposited in the cup.

This copper vessel is then immersed in a vessel of glazed
porcelain i, containing a solution of the sulphate of zinc or the
chloride of sodium (common salt). A hollow cylinder of zinc
//, split down the side so as to be capable of being enlarged or
contracted at pleasure, is immersed in this solution surrounding
the bladder. The poles are indicated by the conductors p and
n, the positive proceeding from the copper, and the negative
from the zinc.

M. Pouillet states that the action of this apparatus is sus-
tained without sensible variation for entire days, provided the
cup above the cone d is kept supplied with the salt, so as to
maintain the solution in the saturated state.

1 869. Advantages and disadvantages of these several systems.
The chief advantage of Daniel's system is that from which it
takes its name, its constancy. Its power, however, in its most
efficient state, is greatly inferior to that of the carbon or pla-
tinum systems of Bunsen and Grove. A serious practical in-
convenience, however, attends all batteries in which concen-
trated nitric acid is used, owing to the diffusion of nitrous
vapour, and the injury to which the parties working them are
exposed by respiring it. In my own experiments with Bunsen's
batteries the assistants have been often severely affected.

In the use of the platinum battery of Grove, the nuisance
produced by the evolution of nitrous vapour is sometimes miti-
gated by enclosing the cells in a box, from the lid of which a
tube proceeds which conducts these vapours out of the room.

In combinations of this kind, Dr. O'Shaugnessy substituted
gold for platinum, and a mixture of two parts by weight of
sulphuric acid to one of saltpetre for nitric acid.

1870. Smee's battery. The voltaic combination called SJIEE'S
BATTEUY, consists of a porcelain vessel A, Jig. 543., containing
an acid solution, which may be about 15 per cent, of sulphuric
acid in water. A plate of iron or silver s, whose surfaces are



SIMPLE VOLTAIC COMBINATION.



283




Fig. 543.
in Jig. 544.



platinized by a certain chemical process, is sus-
pended from a bar of wood a, between two
plates of zinc z, suspended from the same bar
without contact with the plate s. The electro-
motive action is explained on the same prin-
ciple as the combinations already described.
Mr. Smee claims, as an advantage for this sys-
tem, its great simplicity and power, the quantity
of electricity evolved being, ceteris paribus, very
great, and the manipulation easy.

1871. Wheatstone's system Professor Wheat-
stone has proposed the combination represented
A cylindrical vessel v v, of unglazed and half-baked



Fig. 544.



red earthenware, is placed in another w larger one of glazed
porcelain or glass. The vessel vv is filled
with a pasty amalgam of zinc, and the space
between the two vessels is filled with a satu-
rated solution of sulphate of copper. In the
latter solution is immersed a thin cylinder
of copper cc. A rod or wire of copper N is
plunged in the amalgam. The electro-motive



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