284. By ordinary electricity I understand that which can be obtained from
the common machine, or from the atmosphere, or by pressure, or cleavage of
crystals, or by a multitude of other operations; its distinctive character
being that of great intensity, and the exertion of attractive and repulsive
powers, not merely at sensible but at considerable distances.
285. _Tension._ The attractions and repulsions at sensible distances,
caused by ordinary electricity, are well known to be so powerful in certain
cases, as to surpass, almost infinitely, the similar phenomena produced by
electricity, otherwise excited. But still those attractions and repulsions
are exactly of the same nature as those already referred to under the head
_Tension, Voltaic electricity_ (268.); and the difference in degree between
them is not greater than often occurs between cases of ordinary electricity
only. I think it will be unnecessary to enter minutely into the proofs of
the identity of this character in the two instances. They are abundant; are
generally admitted as good; and lie upon the surface of the subject: and
whenever in other parts of the comparison I am about to draw, a similar
case occurs, I shall content myself with a mere announcement of the
similarity, enlarging only upon those parts where the great question of
distinction or identity still exists.
286. The discharge of common electricity through heated air is a well-known
fact. The parallel case of voltaic electricity has already been described
(272, &c.).
287. _In motion._ i. _Evolution of heat._--The heating power of common
electricity, when passed through wires or other substances, is perfectly
well known. The accordance between it and voltaic electricity is in this
respect complete. Mr. Harris has constructed and described[A] a very
beautiful and sensible instrument on this principle, in which the heat
produced in a wire by the discharge of a small portion of common
electricity is readily shown, and to which I shall have occasion to refer
for experimental proof in a future part of this paper (344.).
[A] Philosophical Transactions, 1827, p. 18. Edinburgh Transactions,
1831. Harris on a New Electrometer, &c. &c.
288. ii. _Magnetism._--Voltaic electricity has most extraordinary and
exalted magnetic powers. If common electricity be identical with it, it
ought to have the same powers. In rendering needles or bars magnetic, it is
found to agree with voltaic electricity, and the _direction_ of the
magnetism, in both cases, is the same; but in deflecting the magnetic
needle, common electricity has been found deficient, so that sometimes its
power has been denied altogether, and at other times distinctions have been
hypothetically assumed for the purpose of avoiding the difficulty[A].
[A] Demonferrand's Manuel d'Electricité dynamique, p. 121.
289. M. Colladon, of Geneva, considered that the difference might be due to
the use of insufficient quantities of common electricity in all the
experiments before made on this head; and in a memoir read to the Academie
des Sciences in 1826[A], describes experiments, in which, by the use of a
battery, points, and a delicate galvanometer, he succeeded in obtaining
deflections, and thus establishing identity in that respect. MM. Arago,
Ampère, and Savary, are mentioned in the paper as having witnessed a
successful repetition of the experiments. But as no other one has come
forward in confirmation, MM. Arago, Ampère, and Savary, not having
themselves published (that I am aware of) their admission of the results,
and as some have not been able to obtain them, M. Colladon's conclusions
have been occasionally doubted or denied; and an important point with me
was to establish their accuracy, or remove them entirely from the body of
received experimental research. I am happy to say that my results fully
confirm those by M. Colladon, and I should have had no occasion to describe
them, but that they are essential as proofs of the accuracy of the final
and general conclusions I am enabled to draw respecting the magnetic and
chemical action of electricity (360. 366. 367. 377. &c.).
[A] Annales de Chimie, xxxiii. p. 62.
290. The plate electrical machine I have used is fifty inches in diameter;
it has two sets of rubbers; its prime conductor consists of two brass
cylinders connected by a third, the whole length being twelve feet, and the
surface in contact with air about 1422 square inches. When in good
excitation, one revolution of the plate will give ten or twelve sparks from
the conductors, each an inch in length. Sparks or flashes from ten to
fourteen inches in length may easily be drawn from the conductors. Each
turn of the machine, when worked moderately, occupies about 4/5ths of a
second.
291. The electric battery consisted of fifteen equal jars. They are coated
eight inches upwards from the bottom, and are twenty-three inches in
circumference, so that each contains one hundred and eighty-four square
inches of glass, coated on both sides; this is independent of the bottoms,
which are of thicker glass, and contain each about fifty square inches.
292. A good _discharging train_ was arranged by connecting metallically a
sufficiently thick wire with the metallic gas pipes of the house, with the
metallic gas pipes belonging to the public gas works of London; and also
with the metallic water pipes of London. It was so effectual in its office
as to carry off instantaneously electricity of the feeblest tension, even
that of a single voltaic trough, and was essential to many of the
experiments.
293. The galvanometer was one or the other of those formerly described (87.
205.), but the glass jar covering it and supporting the needle was coated
inside and outside with tinfoil, and the upper part (left uncoated, that
the motions of the needle might be examined,) was covered with a frame of
wire-work, having numerous sharp points projecting from it. When this frame
and the two coatings were connected with the discharging train (292.), an
insulated point or ball, connected with the machine when most active, might
be brought within an inch of any part of the galvanometer, yet without
affecting the needle within by ordinary electrical attraction or repulsion.
294. In connexion with these precautions, it may be necessary to state that
the needle of the galvanometer is very liable to have its magnetic power
deranged, diminished, or even inverted by the passage of a shock through
the instrument. If the needle be at all oblique, in the wrong direction, to
the coils of the galvanometer when the shock passes, effects of this kind
are sure to happen.
295. It was to the retarding power of bad conductors, with the intention of
diminishing its _intensity_ without altering its _quantity_, that I first
looked with the hope of being able to make common electricity assume more
of the characters and power of voltaic electricity, than it is usually
supposed to have.
296, The coating and armour of the galvanometer were first connected with
the discharging train (292.); the end B (87.) of the galvanometer wire was
connected with the outside coating of the battery, and then both these with
the discharging train; the end A of the galvanometer wire was connected
with a discharging rod by a wet thread four feet long; and finally, when
the battery (291.) had been positively charged by about forty turns of the
machine, it was discharged by the rod and the thread through the
galvanometer. The needle immediately moved.
297. During the time that the needle completed its vibration in the first
direction and returned, the machine was worked, and the battery recharged;
and when the needle in vibrating resumed its first direction, the discharge
was again made through the galvanometer. By repeating this action a few
times, the vibrations soon extended to above 40° on each side of the line
of rest.
298. This effect could be obtained at pleasure. Nor was it varied,
apparently, either in direction or degree, by using a short thick string,
or even four short thick strings in place of the long fine thread. With a
more delicate galvanometer, an excellent swing of the needle could be
obtained by one discharge of the battery.
299. On reversing the galvanometer communications so as to pass the
discharge through from B to A, the needle was equally well deflected, but
in the opposite direction.
300. The deflections were in the same direction as if a voltaic current had
been passed through the galvanometer, i.e. the positively charged surface
of the electric battery coincided with the positive end of the voltaic
apparatus (268.) and the negative surface of the former with the negative
end of the latter.
301. The battery was then thrown out of use, and the communications so
arranged that the current could be passed from the prime conductor, by the
discharging rod held against it, through the wet string, through the
galvanometer coil, and into the discharging train (292), by which it was
finally dispersed. This current could be stopped at any moment, by removing
the discharging rod, and either stopping the machine or connecting the
prime conductor by another rod with the discharging train; and could be as
instantly renewed. The needle was so adjusted, that whilst vibrating in
moderate and small arcs, it required time equal to twenty-five beats of a
watch to pass in one direction through the arc, and of course an equal time
to pass in the other direction.
302. Thus arranged, and the needle being stationary, the current, direct
from the machine, was sent through the galvanometer for twenty-five beats,
then interrupted for other twenty-five beats, renewed for twenty-five beats
more, again interrupted for an equal time, and so on continually. The
needle soon began to vibrate visibly, and after several alternations of
this kind, the vibration increased to 40° or more.
303. On changing the direction of the current through the galvanometer, the
direction of the deflection of the needle was also changed. In all cases
the motion of the needle was in direction the same as that caused either by
the use of the electric battery or a voltaic trough (300).
304. I now rejected the wet string, and substituted a copper wire, so that
the electricity of the machine passed at once into wires communicating
directly with the discharging train, the galvanometer coil being one of the
wires used for the discharge. The effects were exactly those obtained above
(302).
305. Instead of passing the electricity through the system, by bringing the
discharging rod at the end of it into contact with the conductor, four
points were fixed on to the rod; when the current was to pass, they were
held about twelve inches from the conductor, and when it was not to pass,
they were turned away. Then operating as before (302.), except with this
variation, the needle was soon powerfully deflected, and in perfect
consistency with the former results. Points afforded the means by which
Colladon, in all cases, made his discharges.
306. Finally, I passed the electricity first through an exhausted receiver,
so as to make it there resemble the aurora borealis, and then through the
galvanometer to the earth; and it was found still effective in deflecting
the needle, and apparently with the same force as before.
307. From all these experiments, it appears that a current of common
electricity, whether transmitted through water or metal, or rarefied air,
or by means of points in common air, is still able to deflect the needle;
the only requisite being, apparently, to allow time for its action: that it
is, in fact, just as magnetic in every respect as a voltaic current, and
that in this character therefore no distinction exists.
308. Imperfect conductors, as water, brine, acids, &c. &c. will be found
far more convenient for exhibiting these effects than other modes of
discharge, as by points or balls; for the former convert at once the charge
of a powerful battery into a feeble spark discharge, or rather continuous
current, and involve little or no risk of deranging the magnetism of the
needles (294.).
309. iii. _Chemical decomposition._--The chemical action of voltaic
electricity is characteristic of that agent, but not more characteristic
than are the _laws_ under which the bodies evolved by decomposition arrange
themselves at the poles. Dr. Wollaston showed[A] that common electricity
resembled it in these effects, and "that they are both essentially the
same"; but he mingled with his proofs an experiment having a resemblance,
and nothing more, to a case of voltaic decomposition, which however he
himself partly distinguished; and this has been more frequently referred to
by some, on the one hand, to prove the occurrence of electro-chemical
decomposition, like that of the pile, and by others to throw doubt upon the
whole paper, than the more numerous and decisive experiments which he has
detailed.
[A] Philosophical Transactions, 1801, pp. 427, 434.
310. I take the liberty of describing briefly my results, and of thus
adding my testimony to that of Dr. Wollaston on the identity of voltaic and
common electricity as to chemical action, not only that I may facilitate
the repetition of the experiments, but also lead to some new consequences
respecting electrochemical decomposition (376. 377.).
311. I first repeated Wollaston's fourth experiment[A], in which the ends
of coated silver wires are immersed in a drop of sulphate of copper. By
passing the electricity of the machine through such an arrangement, that
end in the drop which received the electricity became coated with metallic
copper. One hundred turns of the machine produced an evident effect; two
hundred turns a very sensible one. The decomposing action was however very
feeble. Very little copper was precipitated, and no sensible trace of
silver from the other pole appeared in the solution.
[A] Philosophical Transactions, 1801, p. 429.
312. A much more convenient and effectual arrangement for chemical
decompositions by common electricity, is the following. Upon a glass plate,
fig. 43, placed over, but raised above a piece of white paper, so that
shadows may not interfere, put two pieces of tinfoil _a, b_; connect one of
these by an insulated wire _c_, or wire and string (301.) with the machine,
and the other _g_, with the discharging train (292.) or the negative
conductor; provide two pieces of fine platina wire, bent as in fig. 44, so
that the part _d, f_ shall be nearly upright, whilst the whole is resting
on the three bearing points _p, e, f_ place these as in fig. 43; the points
_p, n_ then become the decomposing poles. In this way surfaces of contact,
as minute as possible, can be obtained at pleasure, and the connexion can
be broken or renewed in a moment, and the substances acted upon examined
with the utmost facility.
313. A coarse line was made on the glass with solution of sulphate of
copper, and the terminations _p_ and _n_ put into it; the foil _a_ was
connected with the positive conductor of the machine by wire and wet
string, so that no sparks passed: twenty turns of the machine caused the
precipitation of so much copper on the end _n_, that it looked like copper
wire; no apparent change took place at _p_.
314. A mixture of equal parts of muriatic acid and water was rendered deep
blue by sulphate of indigo, and a large drop put on the glass, fig. 43, so
that _p_ and _n_ were immersed at opposite sides: a single turn of the
machine showed bleaching effects round _p_, from evolved chlorine. After
twenty revolutions no effect of the kind was visible at _n_, but so much
chlorine had been set free at _p_, that when the drop was stirred the whole
became colourless.
315. A drop of solution of iodide of potassium mingled with starch was put
into the same position at _p_ and _n_; on turning the machine, iodine was
evolved at _p_, but not at _n_.
316. A still further improvement in this form of apparatus consists in
wetting a piece of filtering paper in the solution to be experimented on,
and placing that under the points _p_ and _n_, on the glass: the paper
retains the substance evolved at the point of evolution, by its whiteness
renders any change of colour visible, and allows of the point of contact
between it and the decomposing wires being contracted to the utmost degree.
A piece of paper moistened in the solution of iodide of potassium and
starch, or of the iodide alone, with certain precautions (322.), is a most
admirable test of electro-chemical action; and when thus placed and acted
upon by the electric current, will show iodine evolved at _p_ by only half
a turn of the machine. With these adjustments and the use of iodide of
potassium on paper, chemical action is sometimes a more delicate test of
electrical currents than the galvanometer (273.). Such cases occur when the
bodies traversed by the current are bad conductors, or when the quantity of
electricity evolved or transmitted in a given time is very small.
317. A piece of litmus paper moistened in solution of common salt or
sulphate of soda, was quickly reddened at _p_. A similar piece moistened in
muriatic acid was very soon bleached at _p_. No effects of a similar kind
took place at _n_.
318. A piece of turmeric paper moistened in solution of sulphate of soda
was reddened at _n_ by two or three turns of the machine, and in twenty or
thirty turns plenty of alkali was there evolved. On turning the paper
round, so that the spot came under _p_, and then working the machine, the
alkali soon disappeared, the place became yellow, and a brown alkaline spot
appeared in the new part under _n_.
319. On combining a piece of litmus with a piece of turmeric paper, wetting
both with solution of sulphate of soda, and putting the paper on the glass,
so that _p_ was on the litmus and _n_ on the turmeric, a very few turns of
the machine sufficed to show the evolution of acid at the former and alkali
at the latter, exactly in the manner effected by a volta-electric current.
320. All these decompositions took place equally well, whether the
electricity passed from the machine to the foil _a_, through water, or
through wire only; by _contact_ with the conductor, or by _sparks_ there;
provided the sparks were not so large as to cause the electricity to pass
in sparks from _p_ to _n_, or towards _n_; and I have seen no reason to
believe that in cases of true electro-chemical decomposition by the
machine, the electricity passed in sparks from the conductor, or at any
part of the current, is able to do more, because of its tension, than that
which is made to pass merely as a regular current.
321. Finally, the experiment was extended into the following form,
supplying in this case the tidiest analogy between common and voltaic
electricity. Three compound pieces of litmus and turmeric paper (319.) were
moistened in solution of sulphate of soda, and arranged on a plate of glass
with platina wires, as in fig. 45. The wire _m_ was connected with the
prime conductor of the machine, the wire _t_ with the discharging train,
and the wires _r_ and _s_ entered into the course of the electrical current
by means of the pieces of moistened paper; they were so bent as to rest
each on three points, _n, r, p; n, s, p_, the points _r_ and _s_ being
supported by the glass, and the others by the papers; the three
terminations _p, p, p_ rested on the litmus, and the other three _n, n, n_
on the turmeric paper. On working the machine for a short time only, acid
was evolved at _all_ the poles or terminations _p, p, p_, by which the
electricity entered the solution, and alkali at the other poles _n, n, n_,
by which the electricity left the solution.
322. In all experiments of electro-chemical decomposition by the common
machine and moistened papers (316.), it is necessary to be aware of and to
avoid the following important source of error. If a spark passes over
moistened litmus and turmeric paper, the litmus paper (provided it be
delicate and not too alkaline,) is reddened by it; and if several sparks
are passed, it becomes powerfully reddened. If the electricity pass a
little way from the wire over the surface of the moistened paper, before it
finds mass and moisture enough to conduct it, then the reddening extends as
far as the ramifications. If similar ramifications occur at the termination
_n_, on the turmeric paper, they _prevent_ the occurrence of the red spot
due to the alkali, which would otherwise collect there: sparks or
ramifications from the points _n_ will also redden litmus paper. If paper
moistened by a solution of iodide of potassium (which is an admirably
delicate test of electro-chemical action,) be exposed to the sparks or
ramifications, or even a feeble stream of electricity through the air from
either the point _p_ or _n_, iodine will be immediately evolved.
323. These effects must not be confounded with those due to the true
electro-chemical powers of common electricity, and must be carefully
avoided when the latter are to be observed. No sparks should be passed,
therefore, in any part of the current, nor any increase of intensity
allowed, by which the electricity may be induced to pass between the
platina wires and the moistened papers, otherwise than by conduction; for
if it burst through the air, the effect referred to above (322.) ensues.
324. The effect itself is due to the formation of nitric acid by the
combination of the oxygen and nitrogen of the air, and is, in fact, only a
delicate repetition of Cavendish's beautiful experiment. The acid so
formed, though small in quantity, is in a high state of concentration as to
water, and produces the consequent effects of reddening the litmus paper;
or preventing the exhibition of alkali on the turmeric paper; or, by acting
on the iodide of potassium, evolving iodine.
325. By moistening a very small slip of litmus paper in solution of caustic
potassa, and then passing the electric spark over its length in the air, I
gradually neutralized the alkali, and ultimately rendered the paper red; on
drying it, I found that nitrate of potassa had resulted from the operation,
and that the paper had become touch-paper.
326. Either litmus paper or white paper, moistened in a strong solution of
iodide of potassium, offers therefore a very simple, beautiful, and ready
means of illustrating Cavendish's experiment of the formation of nitric
acid from the atmosphere.
327. I have already had occasion to refer to an experiment (265. 309.) made
by Dr. Wollaston, which is insisted upon too much, both by those who oppose
and those who agree with the accuracy of his views respecting the identity
of voltaic and ordinary electricity. By covering fine wires with glass or
other insulating substances, and then removing only so much matter as to
expose the point, or a section of the wires, and by passing electricity
through two such wires, the guarded points of which were immersed in water,
Wollaston found that the water could be decomposed even by the current from
the machine, without sparks, and that two streams of gas arose from the
points, exactly resembling, in appearance, those produced by voltaic
electricity, and, like the latter, giving a mixture of oxygen and hydrogen
gases. But Dr. Wollaston himself points out that the effect is different
from that of the voltaic pile, inasmuch as both oxygen and hydrogen are
evolved from _each_ pole; he calls it "a very close _imitation_ of the
galvanic phenomena," but adds that "in fact the resemblance is not
complete," and does not trust to it to establish the principles correctly
laid down in his paper.
328. This experiment is neither more nor less than a repetition, in a
refined manner, of that made by Dr. Pearson in 1797[A], and previously by
MM. Paets Van Troostwyk and Deiman in 1789 or earlier. That the experiment
should never be quoted as proving true electro-chemical decomposition, is
sufficiently evident from the circumstance, that the _law_ which regulates
the transference and final place of the evolved bodies (278. 309.) has no
influence here. The water is decomposed at both poles independently of each
other, and the oxygen and hydrogen evolved at the wires are the elements of
the water existing the instant before in those places. That the poles, or
rather points, have no mutual decomposing dependence, may be shown by
substituting a wire, or the finger, for one of them, a change which does
not at all interfere with the other, though it stops all action at the
changed pole. This fact may be observed by turning the machine for some
time; for though bubbles will rise from the point left unaltered, in
quantity sufficient to cover entirely the wire used for the other
communication, if they could be applied to it, yet not a single bubble will
appear on that wire.
[A] Nicholson's Journal, 4to. vol. I. pp. 311, 299. 349.
329. When electro-chemical decomposition takes place, there is great reason
to believe that the _quantity_ of matter decomposed is not proportionate to
the intensity, but to the quantity of electricity passed (320.). Of this I
shall be able to offer some proofs in a future part of this paper (375.
377.). But in the experiment under consideration, this is not the case. If,
with a constant pair of points, the electricity be passed from the machine
in sparks, a certain proportion of gas is evolved; but if the sparks be
rendered shorter, less gas is evolved; and if no sparks be passed, there is
scarcely a sensible portion of gases set free. On substituting solution of
sulphate of soda for water, scarcely a sensible quantity of gas could be
procured even with powerful sparks, and nearly none with the mere current;
yet the quantity of electricity in a given time was the same in all these
cases.
330. I do not intend to deny that with such an apparatus common electricity
can decompose water in a manner analogous to that of the voltaic pile; I
believe at present that it can. But when what I consider the true effect
only was obtained, the quantity of gas given off was so small that I could
not ascertain whether it was, as it ought to be, oxygen at one wire and
hydrogen at the other. Of the two streams one seemed more copious than the
other, and on turning the apparatus round, still the same side in relation
to the machine; gave the largest stream. On substituting solution of
sulphate of soda for pure water (329.), these minute streams were still
observed. But the quantities were so small, that on working the machine for
half an hour I could not obtain at either pole a bubble of gas larger than
a small grain of sand. If the conclusion which I have drawn (377.) relating
to the amount of chemical action be correct, this ought to be the case.
331. I have been the more anxious to assign the true value of this
experiment as a test of electro-chemical action, because I shall have
occasion to refer to it in cases of supposed chemical action by
magneto-electric and other electric currents (336. 346.) and elsewhere.
But, independent of it, there cannot be now a doubt that Dr. Wollaston was
right in his general conclusion; and that voltaic and common electricity
have powers of chemical decomposition, alike in their nature, and governed
by the same law of arrangement.
332. iv. _Physiological effects._--The power of the common electric current
to shock and convulse the animal system, and when weak to affect the tongue
and the eyes, may be considered as the same with the similar power of
voltaic electricity, account being taken of the intensity of the one
electricity and duration of the other. When a wet thread was interposed in
the course of the current of common electricity from the battery (291.)
charged by eight or ten[A] revolutions of the machine in good action
(290.), and the discharge made by platina spatulas through the tongue or
the gums, the effect upon the tongue and eyes was exactly that of a
momentary feeble voltaic circuit.
[A] Or even from thirty to forty.
333. v. _Spark._--The beautiful flash of light attending the discharge of
common electricity is well known. It rivals in brilliancy, if it does not
even very much surpass, the light from the discharge of voltaic
electricity; but it endures for an instant only, and is attended by a sharp
noise like that of a small explosion. Still no difficulty can arise in
recognising it to be the same spark as that from the voltaic battery,
especially under certain circumstances. The eye cannot distinguish the
difference between a voltaic and a common electricity spark, if they be
taken between amalgamated surfaces of metal, at intervals only, and through
the same distance of air.
334. When the Leyden battery (291.) was discharged through a wet string
placed in some part of the circuit away from the place where the spark was
to pass, the spark was yellowish, flamy, having a duration sensibly longer
than if the water had not been interposed, was about three-fourths of an
inch in length, was accompanied by little or no noise, and whilst losing
part of its usual character had approximated in some degree to the voltaic
spark. When the electricity retarded by water was discharged between pieces
of charcoal, it was exceedingly luminous and bright upon both surfaces of
the charcoal, resembling the brightness of the voltaic discharge on such
surfaces. When the discharge of the unretarded electricity was taken upon
charcoal, it was bright upon both the surfaces, (in that respect resembling
the voltaic spark,) but the noise was loud, sharp, and ringing.
335. I have assumed, in accordance, I believe, with the opinion of every
other philosopher, that atmospheric electricity is of the same nature with
ordinary electricity (284.), and I might therefore refer to certain
published statements of chemical effects produced by the former as proofs
that the latter enjoys the power of decomposition in common with voltaic
electricity. But the comparison I am drawing is far too rigorous to allow
me to use these statements without being fully assured of their accuracy;
yet I have no right to suppress them, because, if accurate, they establish
what I am labouring to put on an undoubted foundation, and have priority to
my results.
336. M. Bonijol of Geneva[A] is said to have constructed very delicate
apparatus for the decomposition of water by common electricity. By
connecting an insulated lightning rod with his apparatus, the decomposition
of the water proceeded in a continuous and rapid manner even when the
electricity of the atmosphere was not very powerful. The apparatus is not
described; but as the diameter of the wire is mentioned as very small, it
appears to have been similar in construction to that of Wollaston (327.);
and as that does not furnish a case of true polar electro-chemical
decomposition (328.), this result of M. Bonijol does not prove the identity
in chemical action of common and voltaic electricity.
[A] Bibliothèque Universelle, 1830, tome xlv. p. 213.
337. At the same page of the Bibliothèque Universelle, M. Bonijol is said
to have decomposed, _potash_, and also chloride of silver, by putting them
into very narrow tubes and passing electric sparks from an ordinary machine
over them. It is evident that these offer no analogy to cases of true
voltaic decomposition, where the electricity only decomposes when it is
_conducted_ by the body acted upon, and ceases to decompose, according to
its ordinary laws, when it passes in sparks. These effects are probably
partly analogous to that which takes place with water in Pearson's or
Wollaston's apparatus, and may be due to very high temperature acting on
minute portions of matter; or they may be connected with the results in air
(322.). As nitrogen can combine directly with oxygen under the influence of
the electric spark (324.), it is not impossible that it should even take it
from the potassium of the potash, especially as there would be plenty of
potassa in contact with the acting particles to combine with the nitric
acid formed. However distinct all these actions may be from true polar
electro-chemical decompositions, they are still highly important, and
well-worthy of investigation.
338. The late Mr. Barry communicated a paper to the Royal Society[A] last
year, so distinct in the details, that it would seem at once to prove the
identity in chemical action of common and voltaic electricity; but, when
examined, considerable difficulty arises in reconciling certain of the
effects with the remainder. He used two tubes, each having a wire within it
passing through the closed end, as is usual for voltaic decompositions. The
tubes were filled with solution of sulphate of soda, coloured with syrup of
violets, and connected by a portion of the same solution, in the ordinary
manner; the wire in one tube was connected by a _gilt thread_ with the
string of an insulated electrical kite, and the wire in the other tube by a
similar _gilt thread_ with the ground. Hydrogen soon appeared in the tube
connected with the kite, and oxygen in the other, and in ten minutes the
liquid in the first tube was green from the alkali evolved, and that in the
other red from free acid produced. The only indication of the strength or
intensity of the atmospheric electricity is in the expression, "the usual
shocks were felt on touching the string."
[A] Philosophical Transactions, 1831, p. 165.
339. That the electricity in this case does not resemble that from any
ordinary source of common electricity, is shown by several circumstances.
Wollaston could not effect the decomposition of water by such an
arrangement, and obtain the gases in _separate_ vessels, using common
electricity; nor have any of the numerous philosophers, who have employed
such an apparatus, obtained any such decomposition, either of water or of a
neutral salt, by the use of the machine. I have lately tried the large
machine (290.) in full action for a quarter of an hour, during which time
seven hundred revolutions were made, without producing any sensible
effects, although the shocks that it would then give must have been far
more powerful and numerous than could have been taken, with any chance of
safety, from an electrical kite-string; and by reference to the comparison
hereafter to be made (371.), it will be seen that for common electricity to
have produced the effect, the quantity must have been awfully great, and
apparently far more than could have been conducted to the earth by a gilt
thread, and at the same time only have produced the "usual shocks."
340. That the electricity was apparently not analogous to voltaic
electricity is evident, for the "usual shocks" only were produced, and
nothing like the terrible sensation due to a voltaic battery, even when it
has a tension so feeble as not to strike through the eighth of an inch of
air.
341. It seems just possible that the air which was passing by the kite and
string, being in an electrical state sufficient to produce the "usual
shocks" only, could still, when the electricity was drawn off below, renew
the charge, and so continue the current. The string was 1500 feet long, and
contained two double threads. But when the enormous quantity which must
have been thus collected is considered (371. 376.), the explanation seems
very doubtful. I charged a voltaic battery of twenty pairs of plates four
inches square with double coppers very strongly, insulated it, connected
its positive extremity with the discharging train (292.), and its negative
pole with an apparatus like that of Mr. Barry, communicating by a wire
inserted three inches into the wet soil of the ground. This battery thus
arranged produced feeble decomposing effects, as nearly as I could judge
answering the description Mr. Barry has given. Its intensity was, of
course, far lower than the electricity of the kite-string, but the supply
of quantity from the discharging train was unlimited. It gave no shocks to
compare with the "usual shocks" of a kite-string.
342. Mr. Barry's experiment is a very important one to repeat and verify.
If confirmed, it will be, as far as I am aware, the first recorded case of
true electro-chemical decomposition of water by common electricity, and it
will supply a form of electrical current, which, both in quantity and
intensity, is exactly intermediate with those of the common electrical
machine and the voltaic pile.
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