§ 16. _On an improved form of the Voltaic Battery._ § 17. _Some practical
results respecting the construction and use of the Voltaic Battery._
Received June 16,--Read June 18, 1835.
1119. I Have lately had occasion to examine the voltaic trough practically,
with a view to improvements in its construction and use; and though I do
not pretend that the results have anything like the importance which
attaches to the discovery of a new law or principle, I still think they are
valuable, and may therefore, if briefly told, and in connexion with former
papers, be worthy the approbation of the Royal Society.
§ 16. _On an improved form of the Voltaic Battery._
1120. In a simple voltaic circuit (and the same is true of the battery) the
chemical forces which, during their activity, give power to the instrument,
are generally divided into two portions; one of these is exerted locally,
whilst the other is transferred round the circle (947. 996.); the latter
constitutes the electric current of the instrument, whilst the former is
altogether lost or wasted. The ratio of these two portions of power may be
varied to a great extent by the influence of circumstances: thus, in a
battery not closed, _all_ the action is local; in one of the ordinary
construction, _much_ is in circulation when the extremities are in
communication: and in the perfect one, which I have described (1001.),
_all_ the chemical power circulates and becomes electricity. By referring
to the quantity of zinc dissolved from the plates (865. 1120.), and the
quantity of decomposition effected in the volta-electrometer (711. 1126,)
or elsewhere, the proportions of the local and transferred actions under
any particular circumstances can be ascertained, and the efficacy of the
voltaic arrangement, or the waste of chemical power at its zinc plates, be
accurately determined.
1121. If a voltaic battery were constructed of zinc and platina, the latter
metal surrounding the former, as in the double copper arrangement, and the
whole being excited by dilute sulphuric acid, then no insulating divisions
of glass, porcelain or air would be required between the contiguous platina
surfaces; and, provided these did not touch metallically, the same acid
which, being between the zinc and platina, would excite the battery into
powerful action, would, between the two surfaces of platina, produce no
discharge of the electricity, nor cause any diminution of the power of the
trough. This is a necessary consequence of the resistance to the passage of
the current which I have shown occurs at the place of decomposition (1007.
1011.); for that resistance is fully able to stop the current, and
therefore acts as insulation to the electricity of the contiguous plates,
inasmuch as the current which tends to pass between them never has a higher
intensity than that due to the action of a single pair.
1122. If the metal surrounding the zinc be copper (1045.), and if the acid
be nitro-sulphuric acid (1020.), then a slight discharge between the two
contiguous coppers does take place, provided there be no other channel open
by which the forces may circulate; but when such a channel is permitted,
the return or back discharge of which I speak is exceedingly diminished, in
accordance with the principles laid down in the Eighth Series of these
Researches.
1123. Guided by these principles I was led to the construction of a voltaic
trough, in which the coppers, passing round both surfaces of the zincs, as
in Wollaston's construction, should not be separated from each other except
by an intervening thickness of paper, or in some other way, so as to
prevent metallic contact, and should thus constitute an instrument compact,
powerful, economical, and easy of use. On examining, however, what had been
done before, I found that the new trough was in all essential respects the
same as that invented and described by Dr. Hare, Professor in the
University of Pennsylvania, to whom I have great pleasure in referring it.
1124. Dr. Hare has fully described his trough[A]. In it the contiguous
copper plates are separated by thin veneers of wood, and the acid is poured
on to, or off, the plates by a quarter revolution of an axis, to which both
the trough containing the plates, and another trough to collect and hold
the liquid, are fixed. This arrangement I have found the most convenient of
any, and have therefore adopted it. My zinc plates were cut from rolled
metal, and when soldered to the copper plates had the form delineated, fig.
1. These were then bent over a gauge into the form fig. 2, and when packed
in the wooden box constructed to receive them, were arranged as in fig.
3[B], little plugs of cork being used to keep the zinc plates from touching
the copper plates, and a single or double thickness of cartridge paper
being interposed between the contiguous surfaces of copper to prevent them
from coming in contact. Such was the facility afforded by this arrangement,
that a trough of forty pairs of plates could be unpacked in five minutes,
and repacked again in half an hour; and the whole series was not more than
fifteen inches in length.
[Illustration: Fig. 1.]
[Illustration: Fig. 2.]
[Illustration: Fig. 3.]
[A] Philosophical Magazine, 1824, vol. lxiii. p. 241; or Silliman's
Journal, vol. vii. See also a previous paper by Dr. Hare, Annals of
Philosophy, 1821, vol. i. p. 329, in which he speaks of the
non-necessity of insulation between the coppers.
[B] The papers between the coppers are, for the sake of distinctness,
omitted in the figure.
1125. This trough, of forty pairs of plates three inches square, was
compared, as to the ignition of a platina wire, the discharge between
points of charcoal, the shock on the human frame, &c., with forty pairs of
four-inch plates having double coppers, and used in porcelain troughs
divided into insulating cells, the strength of the acid employed to excite
both being the same. In all these effects the former appeared quite equal
to the latter. On comparing a second trough of the new construction,
containing twenty pairs of four-inch plates, with twenty pairs of four-inch
plates in porcelain troughs, excited by acid of the same strength, the new
trough appeared to surpass the old one in producing these effects,
especially in the ignition of wire.
1126. In these experiments the new trough diminished in its energy much
more rapidly than the one on the old construction, and this was a necessary
consequence of the smaller quantity of acid used to excite it, which in the
case of the forty pairs of new construction was only one-seventh part of
that used for the forty pairs in the porcelain troughs. To compare,
therefore, both forms of the voltaic trough in their decomposing powers,
and to obtain accurate data as to their relative values, experiments of the
following kind were made. The troughs were charged with a known quantity of
acid of a known strength; the electric current was passed through a
volta-electrometer (711.) having electrodes 4 inches long and 2.3 inches in
width, so as to oppose as little obstruction as possible to the current;
the gases evolved were collected and measured, and gave the quantity of
water decomposed. Then the whole of the charge used was mixed together, and
a known part of it analyzed, by being precipitated and boiled with excess
of carbonate of soda, and the precipitate well-washed, dried, ignited, and
weighed. In this way the quantity of metal oxidized and dissolved by the
acid was ascertained; and the part removed from each zinc plate, or from
all the plates, could be estimated and compared with the water decomposed
in the volta-electrometer. To bring these to one standard of comparison, I
have reduced the results so as to express the loss at the plates in
equivalents of zinc for the equivalent of water decomposed at the
volta-electrometer: I have taken the equivalent number of water as 9, and
of zinc as 32.5, and have considered 100 cubic inches of the mixed oxygen
and hydrogen, as they were collected over a pneumatic trough, to result
from the decomposition of 12.68 grains of water.
1127. The acids used in these experiments were three,--sulphuric, nitric,
and muriatic. The sulphuric acid was strong oil of vitriol; one cubical
inch of it was equivalent to 486 grains of marble. The nitric acid was very
nearly pure; one cubical inch dissolved 150 grains of marble. The muriatic
acid was also nearly pure, and one cubical inch dissolved 108 grains of
marble. These were always mixed with water by volumes, the standard of
volume being a cubical inch.
1128. An acid was prepared consisting of 200 parts water, 4-1/2 parts
sulphuric acid, and 4 parts nitric acid; and with this both my trough
containing forty pairs of three-inch plates, and four porcelain troughs,
arranged in succession, each containing ten pairs of plates with double
coppers four inches square, were charged. These two batteries were then
used in succession, and the action of each was allowed to continue for
twenty or thirty minutes, until the charge was nearly exhausted, the
connexion with the volta-electrometer being carefully preserved during the
whole time, and the acid in the troughs occasionally mixed together. In
this way the former trough acted so well, that for each equivalent of water
decomposed in the volta-electrometer only from 2 to 2.5 equivalents of zinc
were dissolved from each plate. In four experiments the average was 2.21
equivalents for each plate, or 88.4 for the whole battery. In the
experiments with the porcelain troughs, the equivalents of consumption at
each plate were 3.51, or 141.6 for the whole battery. In a perfect voltaic
battery of forty pairs of plates (991. 1001.) the consumption would have
been one equivalent for each zinc plate, or forty for the whole.
1129. Similar experiments were made with two voltaic batteries, one
containing twenty pairs of four-inch plates, arranged as I have described
(1124.), and the other twenty pairs of four-inch plates in porcelain
troughs. The average of five experiments with the former was a consumption
of 3.7 equivalents of zinc from each plate, or 74 from the whole: the
average of three experiments with the latter was 5.5 equivalents from each
plate, or 110 from the whole: to obtain this conclusion two experiments
were struck out, which were much against the porcelain troughs, and in
which some unknown deteriorating influence was supposed to be accidentally
active. In all the experiments, care was taken not to compare _new_ and
_old_ plates together, as that would have introduced serious errors into
the conclusions (1146.).
1130. When ten pairs of the new arrangement were used, the consumption of
zinc at each plate was 6.76 equivalents, or 67.6 for the whole. With ten
pairs of the common construction, in a porcelain trough, the zinc oxidized
was, upon an average, 15.5 equivalents each plate, or 155 for the entire
trough.
1131. No doubt, therefore, can remain of the equality or even the great
superiority of this form of voltaic battery over the best previously in
use, namely, that with double coppers, in which the cells are insulated.
The insulation of the coppers may therefore be dispensed with; and it is
that circumstance which principally permits of such other alterations in
the construction of the trough as gives it its practical advantages.
1132. The advantages of this form of trough are very numerous and great. i.
It is exceedingly compact, for 100 pairs of plates need not occupy a trough
of more than three feet in length, ii. By Dr. Hare's plan of making the
trough turn upon copper pivots which rest upon copper bearings, the latter
afford _fixed_ terminations; and these I have found it very convenient to
connect with two cups of mercury, fastened in the front of the stand of the
instrument. These fixed terminations give the great advantage of arranging
an apparatus to be used in connexion with the battery _before_ the latter
is put into action, iii. The trough is put into readiness for use in an
instant, a single jug of dilute acid being sufficient for the charge of 100
pairs of four-inch plates, iv. On making the trough pass through a quarter
of a revolution, it becomes active, and the great advantage is obtained of
procuring for the experiment the effect of the _first contact_ of the zinc
and acid, which is twice or sometimes even thrice that which the battery
can produce a minute or two after (1036. 1150.). v. When the experiment is
completed, the acid can be at once poured from between the plates, so that
the battery is never left to waste during an unconnected state of its
extremities; the acid is not unnecessarily exhausted; the zinc is not
uselessly consumed; and, besides avoiding these evils, the charge is mixed
and rendered uniform, which produces a great and good result (1039.); and,
upon proceeding to a second experiment, the important effect of _first
contact_ is again obtained. vi. The saving of zinc is very great. It is not
merely that, whilst in action, the zinc performs more voltaic duty (1128.
1129.), but _all_ the destruction which takes place with the ordinary forms
of battery between the experiments is prevented. This saving is of such
extent, that I estimate the zinc in the new form of battery to be thrice as
effective as that in the ordinary form. vii. The importance of this saving
of metal is not merely that the value of the zinc is saved, but that the
battery is much lighter and more manageable; and also that the surfaces of
the zinc and copper plates may be brought much nearer to each other when
the battery is constructed, and remain so until it is worn out: the latter
is a very important advantage (1148.). viii. Again, as, in consequence of
the saving, thinner plates will perform the duty of thick ones, rolled zinc
may be used; and I have found rolled zinc superior to cast zinc in action;
a superiority which I incline to attribute to its greater purity (1144.).
ix. Another advantage is obtained in the economy of the acid used, which is
proportionate to the diminution of the zinc dissolved. x. The acid also is
more easily exhausted, and is in such small quantity that there is never
any occasion to return an old charge into use. The acid of old charges
whilst out of use, often dissolves portions of copper from the black
flocculi usually mingled with it, which are derived from the zinc; now any
portion of copper in solution in the charge does great harm, because, by
the _local_ action of the acid and zinc, it tends to precipitate upon the
latter, and diminish its voltaic efficacy (1145.). xi. By using a due
mixture of nitric and sulphuric acid for the charge (1139.), no gas is
evolved from the troughs; so that a battery of several hundred pairs of
plates may, without inconvenience, be close to the experimenter. xii. If,
during a series of experiments, the acid becomes exhausted, it can be
withdrawn, and replaced by other acid with the utmost facility; and after
the experiments are concluded, the great advantage of easily washing the
plates is at command. And it appears to me, that in place of making, under
different circumstances, mutual sacrifices of comfort, power, and economy,
to obtain a desired end, all are at once obtained by Dr. Hare's form of
trough.
1133. But there are some disadvantages which I have not yet had time to
overcome, though I trust they will finally be conquered. One is the extreme
difficulty of making a wooden trough constantly water-tight under the
alternations of wet and dry to which the voltaic instrument is subject. To
remedy this evil, Mr. Newman is now engaged in obtaining porcelain troughs.
The other disadvantage is a precipitation of copper on the zinc plates. It
appears to me to depend mainly on the circumstance that the papers between
the coppers retain acid when the trough is emptied; and that this acid
slowly acting on the copper, forms a salt, which gradually mingles with the
next charge, and is reduced on the zinc plate by the local action (1120.):
the power of the whole battery is then reduced. I expect that by using
slips of glass or wood to separate the coppers at their edges, their
contact can be sufficiently prevented, and the space between them be left
so open that the acid of a charge can be poured and washed out, and so be
removed from _every part_ of the trough when the experiments in which the
latter is used are completed.
1134. The actual superiority of the troughs which I have constructed on
this plan, I believe to depend, first and principally, on the closer
approximation of the zinc and copper surfaces;--in my troughs they are only
one-tenth of an inch apart (1148.);--and, next, on the superior quality of
the rolled zinc above the cast zinc used in the construction of the
ordinary pile. It cannot be that insulation between the contiguous coppers
is a disadvantage, but I do not find that it is any advantage; for when,
with both the forty pairs of three-inch plates and the twenty pairs of
four-inch plates, I used papers well-soaked in wax[A], these being so large
that when folded at the edges they wrapped over each other, so as to make
cells as insulating as those of the porcelain troughs, still no sensible
advantage in the chemical action was obtained.
[A] A single paper thus prepared could insulate the electricity of a
trough of forty pairs of plates.
1135. As, upon principle, there must be a discharge of part of the
electricity from the edges of the zinc and copper plates at the sides of
the trough, I should prefer, and intend having, troughs constructed with a
plate or plates of crown glass at the sides of the trough: the bottom will
need none, though to glaze that and the ends would be no disadvantage. The
plates need not be fastened in, but only set in their places; nor need they
be in large single pieces.
§ 17. _Some practical results respecting the construction and use of the
Voltaic Battery_ (1034. &c.).
1136. The electro-chemical philosopher is well acquainted with some
practical results obtained from the voltaic battery by MM.. Gay-Lussac and
Thenard, and given in the first forty-five pages of their 'Recherches
Physico-Chimiques'. Although the following results are generally of the
same nature, yet the advancement made in this branch of science of late
years, the knowledge of the definite action of electricity, and the more
accurate and philosophical mode of estimating the results by the
equivalents of zinc consumed, will be their sufficient justification.
1137. _Nature and strength of the acid._--My battery of forty pairs of
three-inch plates was charged with acid consisting of 200 parts water and 9
oil of vitriol. Each plate lost, in the average of the experiments, 4.66
equivalents of zinc for the equivalent of water decomposed in the
volta-electrometer, or the whole battery 186.4 equivalents of zinc. Being
charged with a mixture of 200 water and 16 of the muriatic acid, each plate
lost 3.8, equivalents of zinc for the water decomposed, or the whole
battery 152 equivalents of zinc. Being charged with a mixture of 200 water
and 8 nitric acid, each plate lost 1.85, equivalents of zinc for one
equivalent of water decomposed, or the whole battery 74.16 equivalents of
zinc. The sulphuric and muriatic acids evolved much hydrogen at the plates
in the trough; the nitric acid no gas whatever. The relative strengths of
the original acids have already been given (1127.); but a difference in
that respect makes no important difference in the results when thus
expressed by equivalents (1140.).
1138. Thus nitric acid proves to be the best for this purpose; its
superiority appears to depend upon its favouring the electrolyzation of the
liquid in the cells of the trough upon the principles already explained
(905. 973, 1022.), and consequently favouring the transmission of the
electricity, and therefore the production of transferable power (1120.).
1139. The addition of nitric acid might, consequently, be expected to
improve sulphuric and muriatic acids. Accordingly, when the same trough was
charged with a mixture of 200 water, 9 oil of vitriol, and 4 nitric acid,
the consumption of zinc was at each plate 2.786, and for the whole battery
111.5, equivalents. When the charge was 200 water, 9 oil of vitriol, and 8
nitric acid, the loss per plate was 2.26, or for the whole battery 90.4,
equivalents. When the trough was charged with a mixture of 200 water, 16
muriatic acid, and 6 nitric acid, the loss per plate was 2.11, or for the
whole battery 84.4, equivalents. Similar results were obtained with my
battery of twenty pairs of four-inch plates (1129.). Hence it is evident
that the nitric acid was of great service when mingled with the sulphuric
acid; and the charge generally used after this time for ordinary
experiments consisted of 200 water, 4-1/2 oil of vitriol, and 4 nitric
acid.
1140. It is not to be supposed that the different strengths of the acids
produced the differences above; for within certain limits I found the
electrolytic effects to be nearly as the strengths of the acids, so as to
leave the expression of force, when given in equivalents, almost constant.
Thus, when the trough was charged with a mixture of 200 water and 8 nitric
acid, each plate lost 1.854 equivalent of zinc. When the charge was 200
water and 16 nitric acid, the loss per plate was 1.82 equivalent. When it
was 200 water and 32 nitric acid, the loss was 2.1 equivalents. The
differences here are not greater than happen from unavoidable
irregularities, depending on other causes than the strength of acid.
1141. Again, when a charge consisting of 200 water, 4-1/2 oil of vitriol,
and 4 nitric acid was used, each zinc plate lost 2.16 equivalents; when the
charge with the same battery was 200 water, 9 oil of vitriol, and 8 nitric
acid, each zinc plate lost 2.26 equivalents.
1142. I need hardly say that no copper is dissolved during the regular
action of the voltaic trough. I have found that much ammonia is formed in
the cells when nitric acid, either pure or mixed with sulphuric acid, is
used. It is produced in part as a secondary result at the cathodes (663.)
of the different portions of fluid constituting the necessary electrolyte,
in the cells.
1143. _Uniformity of the charge._--This is a most important point, as I
have already shown experimentally (1042. &c.). Hence one great advantage of
Dr. Hare's mechanical arrangement of his trough.
1144. _Purity of the zinc._--If pure zinc could be obtained, it would be
very advantageous in the construction of the voltaic apparatus (998.). Most
zincs, when put into dilute sulphuric acid, leave more or less of an
insoluble matter upon the surface in the form of a crust, which contains
various metals, as copper, lead, zinc, iron, cadmium, &c., in the metallic
state. Such particles, by discharging part of the transferable power,
render it, as to the whole battery, local; and so diminish the effect. As
an indication connected with the more or less perfect action of the
battery, I may mention that no gas ought to rise from the zinc plates. The
more gas which is generated upon these surfaces, the greater is the local
action and the less the transferable force. The investing crust is also
inconvenient, by preventing the displacement and renewal of the charge upon
the surface of the zinc. Such zinc as, dissolving in the cleanest manner in
a dilute acid, dissolves also the slowest, is the best; zinc which contains
much copper should especially be avoided. I have generally found rolled
Liege or Mosselman's zinc the purest; and to the circumstance of having
used such zinc in its construction attribute in part the advantage of the
new battery (1134.).
1145. _Foulness of the zinc plates._--After use, the plates of a battery
should be cleaned from the metallic powder upon their surfaces, especially
if they are employed to obtain the laws of action of the battery itself.
This precaution was always attended to with the porcelain trough batteries
in the experiments described (1125, &c.). If a few foul plates are mingled
with many clean ones, they make the action in the different cells
irregular, and the transferable power is accordingly diminished, whilst the
local and wasted power is increased. No old charge containing copper should
be used to excite a battery.
1146. _New and old plates._--I have found voltaic batteries far more
powerful when the plates were new than when they have been used two or
three times; so that a new and an used battery cannot be compared together,
or even a battery with itself on the first and after times of use. My
trough of twenty pairs of four-inch plates, charged with acid consisting of
200 water, 4-1/2 oil of vitriol, and 4 nitric acid, lost, upon the first
time of being used, 2.82 equivalents per plate. When used after the fourth
time with the same charge, the loss was from 3.26 to 4.47 equivalents per
plate; the average being 3.7 equivalents. The first time the forty pair of
plates (1124.) were used, the loss at each plate was only 1.65 equivalent;
but afterwards it became 2.16, 2.17, 2.52. The first time twenty pair of
four-inch plates in porcelain troughs were used, they lost, per plate, only
3.7 equivalents; but after that, the loss was 5.25, 5.36, 5.9 equivalents.
Yet in all these cases the zincs had been well-cleaned from adhering
copper, &c., before each trial of power.
1147. With the rolled zinc the fall in force soon appeared to become
constant, i.e. to proceed no further. But with the cast zinc plates
belonging to the porcelain troughs, it appeared to continue, until at last,
with the same charge, each plate lost above twice as much zinc for a given
amount of action as at first. These troughs were, however, so irregular
that I could not always determine the circumstances affecting the amount of
electrolytic action.
1148. _Vicinity of the copper and zinc._--The importance of this point in
the construction of voltaic arrangements, and the greater power, as to
immediate action, which is obtained when the zinc and copper surfaces are
near to each other than when removed further apart, are well known. I find
that the power is not only greater on the instant, but also that the sum of
transferable power, in relation to the whole sum of chemical action at the
plates, is much increased. The cause of this gain is very evident. Whatever
tends to retard the circulation of the transferable force, (i.e. the
electricity,) diminishes the proportion of such force, and increases the
proportion of that which is local (996. 1120.). Now the liquid in the cells
possesses this retarding power, and therefore acts injuriously, in greater
or less proportion, according to the quantity of it between the zinc and
copper plates, i.e. according to the distances between their surfaces. A
trough, therefore, in which the plates are only half the distance asunder
at which they are placed in another, will produce more transferable, and
less local, force than the latter; and thus, because the electrolyte in the
cells can transmit the current more readily; both the intensity and
quantity of electricity is increased for a given consumption of zinc. To
this circumstance mainly I attribute the superiority of the trough I have
described (1134.).
1149. The superiority of _double coppers_ over single plates also depends
in part upon diminishing the resistance offered by the electrolyte between
the metals. For, in fact, with double coppers the sectional area of the
interposed acid becomes nearly double that with single coppers, and
therefore it more freely transfers the electricity. Double coppers are,
however, effective, mainly because they virtually double the acting surface
of the zinc, or nearly so; for in a trough with single copper plates and
the usual construction of cells, that surface of zinc which is not opposed
to a copper surface is thrown almost entirely out of voltaic action, yet
the acid continues to act upon it and the metal is dissolved, producing
very little more than local effect (947. 996). But when by doubling the
copper, that metal is opposed to the second surface of the zinc plate, then
a great part of the action upon the latter is converted into transferable
force, and thus the power of the trough as to quantity of electricity is
highly exalted.
1150. _First immersion of the plates._--The great effect produced at the
first immersion of the plates, (apart from their being new or used
(1146.),) I have attributed elsewhere to the unchanged condition of the
acid in contact with the zinc plate (1003. 1037.): as the acid becomes
neutralized, its exciting power is proportionally diminished. Hare's form
of trough secures much advantage of this kind, by mingling the liquid, and
bringing what may be considered as a fresh surface of acid against the
plates every time it is used immediately after a rest.
1151. _Number of plates._[A]--The most advantageous number of plates in a
battery used for chemical decomposition, depends almost entirely upon the
resistance to be overcome at the place of action; but whatever that
resistance may be, there is a certain number which is more economical than
either a greater or a less. Ten pairs of four-inch plates in a porcelain
trough of the ordinary construction, acting in the volta-electrometer
(1126.) upon dilute sulphuric acid of spec. grav. 1.314, gave an average
consumption of 15.4 equivalents per plate, or 154 equivalents on the whole.
Twenty pairs of the same plates, with the same acid, gave only a
consumption of 5.5 per plate, or 110 equivalents upon the whole. When forty
pairs of the same plates were used, the consumption was 3.54 equivalents
per plate, or 141.6 upon the whole battery. Thus the consumption of zinc
arranged as _twenty_ plates was more advantageous than if arranged either
as _ten_ or as _forty_.
[A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom. i. p. 29.
1152. Again, ten pairs of my four-inch plates (1129.) lost 6.76 each, or
the whole ten 67.6 equivalents of zinc, in effecting decomposition; whilst
twenty pairs of the same plates, excited by the same acid, lost 3.7
equivalents each, or on the whole 74 equivalents. In other comparative
experiments of numbers, ten pairs of the three inch-plates, (1125.) lost
3.725, or 37.25 equivalents upon the whole; whilst twenty pairs lost 2.53
each, or 50.6 in all; and forty pairs lost on an average 2.21, or 88.4
altogether. In both these cases, therefore, increase of numbers had not
been advantageous as to the effective production of _transferable chemical
power_ from the _whole quantity of chemical force_ active at the surfaces
of excitation (1120.).
1153. But if I had used a weaker acid or a worse conductor in the
volta-electrometer, then the number of plates which would produce the most
advantageous effect would have risen; or if I had used a better conductor
than that really employed in the volta-electrometer, I might have reduced
the number even to one; as, for instance, when a thick wire is used to
complete the circuit (865., &c.). And the cause of these variations is very
evident, when it is considered that each successive plate in the voltaic
apparatus does not add anything to the _quantity_ of transferable power or
electricity which the first plate can put into motion, provided a good
conductor be present, but tends only to exalt the _intensity_ of that
quantity, so as to make it more able to overcome the obstruction of bad
conductors (994. 1158.).
1154. _Large or small plates._[A]--The advantageous use of large or small
plates for electrolyzations will evidently depend upon the facility with
which the transferable power of electricity can pass. If in a particular
case the most effectual number of plates is known (1151.), then the
addition of more zinc would be most advantageously made in increasing the
_size_ of the plates, and not their _number_. At the same time, large
increase in the size of the plates would raise in a small degree the most
favourable number.
[A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom, i. p. 20.
1155. Large and small plates should not be used together in the same
battery: the small ones occasion a loss of the power of the large ones,
unless they be excited by an acid proportionably more powerful; for with a
certain acid they cannot transmit the same portion of electricity in a
given time which the same acid can evolve by action on the larger plates.
1156. _Simultaneous decompositions._--When the number of plates in a
battery much surpasses the most favourable proportion (1151--1153.), two or
more decompositions may be effected simultaneously with advantage. Thus my
forty pairs of plates (1124.) produced in one volta-electrometer 22.8 cubic
inches of gas. Being recharged exactly in the same manner, they produced in
each of two volta-electrometers 21 cubical inches. In the first experiment
the whole consumption of zinc was 88.4 equivalents, and in the second only
48.28 equivalents, for the whole of the water decomposed in both
volta-electrometers.
1157. But when the twenty pairs of four-inch plates (1129.) were tried in
a similar manner, the results were in the opposite direction. With one
volta-electrometer 52 cubic inches of gas were obtained; with two, only
14.6 cubic inches from each. The quantity of charge was not the same in
both cases, though it was of the same strength; but on rendering the
results comparative by reducing them to equivalents (1126.), it was found
that the consumption of metal in the first case was 74, and in the second
case 97, equivalents for the _whole_ of the water decomposed. These
results of course depend upon the same circumstances of retardation, &c.,
which have been referred to in speaking of the proper number of plates
(1151.).
1158. That the _transferring_, or, as it is usually called, _conducting,
power_ of an electrolyte which is to be decomposed, or other interposed
body, should be rendered as good as possible[A], is very evident (1020.
1120.). With a perfectly good conductor and a good battery, nearly all the
electricity is passed, i.e. _nearly all_ the chemical power becomes
transferable, even with a single pair of plates (807.). With an interposed
nonconductor none of the chemical power becomes transferable. With an
imperfect conductor more or less of the chemical power becomes transferable
as the circumstances favouring the transfer of forces across the imperfect
conductor are exalted or diminished: these circumstances are, actual
increase or improvement of the conducting power, enlargement of the
electrodes, approximation of the electrodes, and increased intensity of the
passing current.
[A] Gay-Lussac and Thenard, Recherches Physico-Chimiques, tom. i. pp.
13, 15, 22.
1159. The introduction of common spring water in place of one of the
volta-electrometers used with twenty pairs of four-inch plates (1156.)
caused such obstruction as not to allow one-fifteenth of the transferable
force to pass which would have circulated without it. Thus
fourteen-fifteenths of the available force of the battery were destroyed,
local force, (which was rendered evident by the evolution of gas from the
being converted into zincs,) and yet the platina electrodes in the water
were three inches long, nearly an inch wide, and not a quarter of an inch
apart.
1160. These points, i.e. the increase of conducting power, the enlargement
of the electrodes, and their approximation, should be especially attended
to in _volta-electrometers_. The principles upon which their utility depend
are so evident that there can be no occasion for further development of
them here.
_Royal Institution,
October 11, 1834._