machine, he resolved to prosecute the subject with atmospheric
electricity. With this view he raised a conductor on the roof of his
house, from which he brought an iron wire into his room.—To this he
attached metal conductors, connected with the nerves of the animals,
destined to be the subjects of his experiments: and to their legs he
fastened wires which reached the floor. These experiments were not
confined to frogs alone. Different animals, both of cold and warm blood,
were subjected to them; and in all of them considerable movements were
excited whenever it lightened. These movements preceded thunder, and
corresponded with its intensity and repetition; and even when no
lightning appeared, the movements took place when any strong cloud
passed over the apparatus.—That all these appearances were produced by
the electric fluid was obvious.
Having soon after this suspended some frogs, from the iron palisades
which surrounded his garden, by means of metallic hooks fixed in the
spines of their backs, he observed that their muscles contracted
frequently and involuntarily, as if from a shock of electricity. Not
doubting that the contractions depended on the electric fluid, he at
first suspected that they were connected with changes in the state of
the atmosphere. He soon found, however, that this was not the case; and
having varied, in many different ways, the circumstances in which the
frogs were placed, he at length discovered that he could produce the
movements at pleasure, by touching the animals with two different
metals, which at the same time touched one another, either immediately,
or by the intervention of some other substance capable of conducting
electricity.
CHAP. II.
_Of the Animals best fitted for Galvanic Experiments, of the Metals best
calculated for making these Experiments, and of Conductors._
Almost every animal can be made to produce these muscular contractions
by the Galvanic power, but those called _cold blooded_ are the best.
Thus _frogs_ have been found the most convenient, both on account of
their size and abundance. They also retain their muscular irritability
to the Galvanic influence longer than most other animals, and it is
asserted that strong convulsions can be produced in them many hours
after the brain and spinal marrow have been destroyed; and also that
when pretty far advanced in the process of putrefaction they are capable
of Galvanic excitement.
No contractions have been produced in animals killed by _corrosive
sublimate_, nor in those which have been _starved_ to death: but a very
slight motion can be made to appear in those killed by _opium_, the
_electric shock_, or _azotic gas_.
With regard to the metals used to effect these motions, almost any two
will answer the purpose; but the most powerful are the following, viz.
│ │Gold.
Zinc│ │Silver.
Tin │in conjunction with│Molybdena.
Lead│ │Steel.
│ │Copper.
Those which have the most power are placed first; that is zinc and gold,
will produce greater muscular contractions than tin and silver, or tin
and gold, and so of the rest.
The process by which these wonderful appearances are produced consists
in effecting, by means of the Galvanic apparatus, a communication
between a nerve and a muscle, in any part of an animal body. The part of
the animal upon which the experiment is to be performed is denominated
the _animal arc_: and the Galvanic instruments which form the
communication between the muscle and the nerve, are called the
_excitatory arc_. This latter generally consists of three pieces; one
fixed to the muscle, another to the nerve, and a third forming a
communication between both. This last, called the _communicator_, may be
made of the same metal with either of the others, or be different from
both. The best communicators or conductors, are the following.—The list
begins with the most perfect.
Malleable platina.
Silver.
Gold.
Quicksilver.
Copper.
Brass.
Tin.
Lead.
Iron.
The human body.
Salt water.
Fresh water.
The metallic ores are not so good conductors as the purified metals, and
their conducting power varies, according to the nature of the ores.
The metallic salts are tolerably good conductors.
Dr. Valli observed that human bodies are not all equally good
conductors. Out of four persons in a company, he found that when two of
them formed the circuit of communication between the nerve and muscles
of a frog, the motions took place very readily. When the third person
formed the circuit, the motions were very weak; but that, when the
fourth person formed the communication, no motion took place. This
experiment, he adds, was often repeated with the same success. The
effect however may be owing to the different dryness of the skin.
Vitriolic acid, and even alcohol, appear to conduct the Galvanic
influence rather better than water.
The veins and arteries are not so good conductors as the nerves; for
when a blood-vessel forms part of the circuit of communication, the
contractions will take place only when ramifications of the nerves are
adhering to it, and if these be carefully separated, the motion will not
take place. The same thing may be said of the tendons, the bones, and
the membranes; for when either of those parts is separated from the
body, and is introduced into the circle of communication between the
muscles and nerves of a prepared frog, no motion will ensue; excepting,
indeed, when those parts are full of moisture and in immediate contact
with the nerve.
CHAP. III.
_A Description of the Galvanic Trough and Pile._
Professor Volta’s first contrivance for manifesting Galvanism in a more
vigorous manner than had hitherto been done, was what he called a
_couronne de tasses_. This consisted of tumblers of glass, half filled
with water, or salt and water. These glasses or tumblers, were so placed
that a metallic arc, in form of a C, could be fixed with one leg in one
glass, and the other in the next glass. On one end of each arc, was
fastened a small plate of silver or copper, and on the other end, a
similar plate of zinc or tin. These plates were immersed in the fluid
contained in the tumblers.—Thus in the water of every glass there was a
plate of silver or copper, and another plate of zinc or tin. The
metallic arcs were formed of any good conductor. When thirty or forty of
these glasses were prepared, the experimenter put one of his hands into
the fluid contained in the first glass, and the other hand into that in
the last: when this was done a shock, something like the electrical one,
was experienced, and would recur as often as the circuit was interrupted
and completed.
Mr. Volta remarks, that _alkaline solutions_ are used to the most
advantage when one of the metals is tin and the other silver or copper;
but that where zinc is substituted for tin, salt water is preferable.
After this discovery, Volta invented a much more convenient instrument,
which, besides other advantages over the former, was more powerful and
less expensive. The instrument is called the _Galvanic pile_, and very
often the _Voltaic pile_, from its inventor. It is made in the following
manner—Take a number of circular plates of copper, or silver and an
equal number of tin or zinc of the same dimensions. Next provide a like
number of round pieces of paste-board, leather, or any other substance
capable of retaining moisture for a considerable time. This leather,
cloth or other substance, must be rather smaller than the metal plates
and, when used, well moistened with salt and water. Now form a pile, by
laying alternately the zinc over the silver, and, the cloth or other
moistened substance, over the zinc; and so on successively.—By thus
continuing the series to forty or fifty plates, a Galvanic pile will be
constructed. If the pile is intended to be of any considerable height,
it ought to be secured by pillars of varnished baked wood; or strong
glass tubes.
To get the shock, one hand must touch the bottom, and the other the top
plate.—The hands should be wet, as the cuticle or external part of the
skin is a bad conductor.
Shocks may be received by applying the hands in this manner, as long as
the leather, or other substance interposed between the zinc and silver,
continues moist; but as soon as it becomes dry the operation closes.
The drying of the substance was a great inconvenience in the Voltaic
pile, and the inventor proposed, as a remedy for this, to station the
metallic plates at a greater distance from one another, and to fill up
the cells or intervals between them with a saline solution. Mr.
Cruickshank, an English chemist at Woolwich, improved this
construction.—His _trough_ as it is called, is made thus.—
Get a wooden trough, made of hard baked mahogany, about thirty inches
long, and four or five wide and deep.—On the inside let there be cut in
the sides and bottom, and at equal distances from one another, as many
grooves, as the number of plates required to be put into the trough;—the
grooves of a size to admit the plates. The plates are to be cemented[18]
separately to each of the grooves, so that no fluid can pass from one
cell to another. In this instrument the plates are constructed by
soldering a plate of zinc to one of copper. The zinc, or which is the
same thing, the spelter of the shops, should be melted in a vessel which
exposes but a small surface to the action of the air, otherwise it would
absorb oxygen so rapidly as to be converted into the flowers of
zinc.—The melted metal should be poured as soon as possible into a mould
of the proper size, made of stone or brass.—It is not necessary that the
plates of copper should be more than one tenth of the thickness of those
of zinc.
The two plates are commonly soldered, not through their whole extent,
but about one fourth of an inch from the edge; so that at the edge their
union may be complete.
Care must be taken that all the plates be cemented to the trough in the
same direction; so as to have the copper side of every plate opposite to
the zinc side of the next.
The liquid employed to fill up the cells between the plates, is formed
by diluting muriatic acid with water, in the proportion of one ounce of
the former to a pint of the latter. When the trough is not in use, it
should be emptied of this solution (which may be preserved for
subsequent experiments, unless saturated with the metals) and then
rinsed clean with fresh water.
This construction is preferable to the Voltaic pile, for experiments in
which it is necessary to have the Galvanic action for a length of time.
But for occasional experiments the pile is more convenient; as the
trough, if suffered to remain long without the fluid, is apt to crack
and separate the cement from the plates, which renders it necessary to
cement them again.
When several batteries are required, they should be disposed in the same
order as if they all constituted one trough, (observing through the
whole series to keep the zinc surfaces constantly opposed to the copper
ones,) and connected together by some metallic substance, such as a
piece of sheet lead, or tin-foil, about half the width of the trough.
Batteries combined in this way should all be, as nearly as possible, of
the same power. For if a bad battery be united to five good ones, each
of the same number of plates, the effect of the whole will be equal only
to six times that of the bad one—as in electrical batteries, if three
jars of different sizes be charged together, the whole charge will be
equal to only three times that of the smallest jar.
CHAP. IV.
_The Method of performing Galvanic Experiments with Frogs; with some
conclusions drawn from them._
Every sensible heart must be shocked with the idea of torturing
defenceless animals, merely to gratify an idle curiosity. The chapter
which we shall now lay before the reader is founded entirely on the
assertions of other writers upon this subject; to which, however, we
have not the least doubt that the fullest credit is due. But we have not
chosen to prove the veracity of their statements by our own experiments,
believing that any small additional knowledge we might possibly have
obtained in this way, would have been purchased at too great a price—the
sacrifice of feeling and humanity.
Take a living frog, and after amputating the hind legs, (for they are
the best, on account of the number of joints) let the largest nerve,
called the _crural nerve_, be laid bare, and surrounded with a slip of
tin-foil, or a piece of sheet lead—then lay a piece of zinc, or other
metal different from that on the nerve, in contact with the neighbouring
muscles; form a communication by another piece of zinc, or other good
conductor, between the metal in contact with the muscle and the _armed_
part of the nerve, and violent contractions will be produced in the
limb.
There is another method of producing these convulsions, which has been
preferred on account of its simplicity.—It is by forming a communication
between a nerve, armed as above, and an adjoining muscle, by a piece of
zinc, without the assistance of a communicator.—This was one of the
first methods of Galvanizing frogs, before the invention of the pile and
trough. But since these discoveries, frogs have been made to show more
violent convulsions.
We now proceed to relate some of the conclusions which have been drawn
from the experiments on frogs.
1. The contractions produced in the limb of a frog are stronger the
farther the metal is placed from the origin of the nerve.
2. When the metal has remained for some time on a particular part of the
nerve the motion will cease; but it may be renewed by changing the
position of the metal, and carrying it lower on the nerve.
3. Contractions may be produced in the prepared limb of a frog, by
putting it in water, and then bringing two metals in contact with each
other, at a short distance from the limb.
4. Only those muscles to which the nerves lead suffer contraction from
the Galvanic influence.
5. When a contraction has taken place in any muscle, no other will
follow while the metals remain in contact.—In order to renew the
motions, therefore, the metals must be separated and joined again.
6. Galvanic excitement, instead of destroying the irritability of a
muscle, gives it an additional support. Dr. Valli, an Italian physician,
has fully confirmed this principle by the following experiment. “Having
prepared the wing of a fowl, or the paw of a cat or dog, I subjected it
to the customary trial. At the expiration of half an hour, I armed the
other wing of the fowl, or the other paw of the cat or dog, and had
recourse to my exciting arc.—The latter wing or paw, however, did not
give any sign of electricity, (for he conceived the motion to be
occasioned by electricity,) while the parts which had been subjected in
the first instance to the experiment, still continued in a convulsed and
agitated state.”
7. Galvanic experiments do not succeed so well in a room crowded with
persons, as when only two or three individuals are present.
8. Galvanic contractions are more powerful the instant the animal is
deprived of life, than some time after; and therefore more violent
agitations can be produced in the living animal.
9. Volta concluded that Galvanism was generated by the metal, and not by
the animal upon which he operated.
These are the principal remarks which we think worth noticing. If they
do not content the reader, we must refer him to Wilkinson on Galvanism;
where he will find a detail of almost every thing that happened in the
Galvanic world till the time he wrote.
CHAP. V.
_Various Experiments with the Galvanic Pile._
The first experiments which we shall mention were performed by Mr.
Cruickshank, with the Galvanic pile. He employed plates of zinc and
silver, 1.6 inches square, and the number of plates of both metals
varied from forty to a hundred, according to the power required. The
lower end of the pile we shall denominate the _silver_ end, because the
plate at the bottom is of silver, and the upper end the _zinc_ end,
because the uppermost plate is of zinc. The first experiment of Mr.
Cruickshank with the Galvanic pile, was upon water and silver wires.
These wires were passed through corks, fitted into a glass tube filled
with water, and projected about one third of the way, on both sides,
into the tube; so that the space between the inner ends of the wires was
one third of the length of the tube. One of the corks was made perfectly
tight by cement. The tube was then placed upright in a tumbler of water,
with the uncemented end downwards.
As soon as a communication was made between the extremities of the pile
by the wires, small air bubbles began to ascend from the wire connected
with the silver end, and a white cloud made its appearance at the wire
proceeding from the zinc end.—The cloud gradually increased, assuming a
darker colour, and at last it became purple, and even black. A few air
bubbles were likewise observed upon this wire, which ascended from it;
but when the pile acted well, a considerable stream of air could be
perceived.—When this gas was examined, it was found to be a mixture of
hydrogen and oxygen, in the proportion of three parts of the former to
one of the latter. No great reliance, however, can be placed on the
accuracy of this analysis. The wire proceeding from the zinc end, was
found much corroded, and looked as if a portion of it had been
dissolved.
Mr. Cruickshank supposed the cloud formed round the wire of the zinc end
to be the muriate of silver, proceeding from the silver wire which had
been somehow dissolved, and afterwards precipitated in this state, by
the muriatic salts contained in the common water.
The next experiment was with distilled water, a tincture of litmus, and
silver wires, as before. The apparatus being adjusted in the manner
above described, and one wire connected with one end of the pile, while
the other touched the other end, gas immediately arose from both wires,
but in greater quantity from the one connected with the silver plate. In
a short time the whole fluid below the point of the wire from the zinc
plate, became red, and the fluid below the wire from the silver plate,
looked of a deeper blue. Distilled water tinged with Brazil wood, soon
became of as deep a purple as could be produced by ammonia.—From the two
last experiments, Mr. Cruickshank was led to suppose, that an _acid_,
probably the nitrous, is produced at the wire connected with the zinc
plate, and an _alkali_, probably ammonia, at the one connected with the
silver end of the pile.
As hydrogen gas, whether heated or in its natural state, reduces
metallic oxyds, Mr. Cruickshank resolved to subject solutions of
metallic oxyds to the hydrogen gas which was produced by the pile.—The
result answered his expectation, for in a minute or two after the
communication was formed, fine metallic needles or crystals, something
resembling a feather, were perceived round the wire connected with the
silver plate.—The oxygen too which escaped from the metal, and that
generated from the fluid used in the solution, was commonly pure, when
an excess of acid was added to take up the alkali.—The acetite of lead
and the sulphate of copper, were among the oxyds experimented upon, but
whatever the metal was, the results coincided. These experiments were
made in a tube like the preceding ones.—A number of experiments were
made by the same gentleman upon the _earths_, but we shall not detail
them; we must content ourselves with some conclusions drawn from his
observations.
1. Hydrogen gas, mixed with a small portion of oxygen and ammonia, is
somehow disengaged at the wire communicating with the silver extremity
of the pile; and this effect is equally produced, whatever the nature of
the metallic wire may be, provided the fluid operated upon be _water_.
2. When metallic solutions are used, the same wire which separates the
hydrogen gas, revives the metallic calx, and deposits it at its
extremity, in its pure metallic state; in this case no hydrogen is
disengaged. The wire employed for this purpose may be of any metal.
3. Of the earthy solutions, only those of magnesia and argill are
decomposed by the wire: a circumstance which strongly favours the
production of ammonia.
CHAP. VI.
_Experiments on the deflagration of Metals by the Galvanic Pile._
The pile with which these experiments were made consisted of thirty-six
plates of silver, and an equal number of zinc ones, between which were
interposed disks of flannel, moistened with a solution of the muriate of
ammonia.—Each plate had a diameter of ten inches, or contained 78.58
square inches;—consequently the whole surface of silver in the pile,
reckoning only one side, was 2828.57 square inches, and that of zinc the
same.
With this instrument, in December 1801, gold, silver, copper, tin, lead
and zinc were deflagrated with surprising facility. The gold burned with
a vivid white light, inclining a little to blue, and deposited an oxyd
of a deep purplish-brown colour.—The silver gave a vivid flame of a
greenish hue, and extremely brilliant. Its oxyd was of a blackish
colour. The copper presented phenomena similar to those which attended
the gold.—Lead gave a very vivid light, of a dilute bluish purple.—The
tin afforded a light similar to that of the gold, but burnt with much
less energy; probably because the leaves were thicker. The zinc gave a
blueish white flame, which was edged, at the moment of contact, with
red. It was more difficult to inflame than any of the preceding metals,
but the leaves were likewise much thicker. The oxyds of the four last
metals were not examined.
Water was poured upon the upper plate of the pile, so as to form a
_standing pool_; and several pieces of the same kind of metals with
those before experimented upon, were presented to the plate through this
aqueous medium, and were deflagrated. They afforded a flame of the same
colour as when they were brought to the bare plate.—A vapour was
sometimes perceptible immediately after the deflagration, and was
supposed to arise from a portion of water converted into steam by the
intense heat.
It is very remarkable that the shocks taken from this pile, which
produced such astonishing effects upon metals, could be received with
but very trifling inconvenience, through the human body.
Besides these experiments, which were made by a society of gentlemen, a
variety of others were performed, from which nearly the same conclusions
were deduced.—Two other facts, however, deserve notice.
1. When metallic leaves are deflagrated in carbonic-acid gas, the flame
is weak: but when in oxygen gas, the communication between the upper and
under plates of the pile is no sooner formed, than the metallic leaves
are destroyed with one sudden flash.
2. When metals are subjected to Galvanism in an exhausted receiver, they
emit light but are not oxydated.
CHAP. VII.
_Further Galvanic Experiments on Metals, and on other Substances._
It is hardly necessary to mention, that every experiment made by means
of the Galvanic pile may be performed, with equal success, with the
trough. The experiments related in this chapter may be effected by the
pile, but they cannot be done with the same convenience as when troughs
are used. The battery[19] employed in these experiments consisted of
sixty pieces of silver, and a like number of zinc, each two and a
quarter inches square. The shock produced by this trough, by means of
two metallic conductors, was distinctly felt in the shoulders, and the
contraction or spasm was so violent, as to render the operator unable to
hold the conductors, when in contact with the plates by which the trough
terminated each way.—A sensation resembling that produced by hot water,
was at the same time felt in the wrists and fore-arm.
A small steel wire, which was used for the conductor to form the
communication, upon its contact with the plates, produced a vivid spark
and bright scintillations.—When a piece of phosphorus was placed upon
the end of this wire, and made a part of the circuit, it was instantly
inflamed.
Another battery of the same size being connected with the one above
described, gun-powder was fired, and gold leaf deflagrated without any
perceptible residuum—being probably volatilised by the heat occasioned
by the experiment.