_Anions_.
Oxygen 8
Chlorine 35.5
Iodine 126
Bromine 78.3
Fluorine 18.7
Cyanogen 26
Sulphuric acid 40
Selenic acid 64
Nitric acid 54
Chloric acid 75.5
Phosphoric acid 35.7
Carbonic acid 22
Boracic acid 24
Acetic acid 51
Tartaric acid 66
Citric acid 58
Oxalic acid 36
Sulphur (?) 16
Selenium (?)
Salpho-cyanogen
_Cations_.
Hydrogen 1
Potassium 39.2
Sodium 23.3
Lithium 10
Barium 68.7
Strontium 43.8
Calcium 20.5
Magnesium 12.7
Manganese 27.7
Zinc 32.5
Tin 57.9
Lead 103.5
Iron 28
Copper 31.6
Cadmium 55.8
Cerium 46
Cobalt 29.5
Nickel 29.5
Antimony 61.67
Bismuth 71
Mercury 200
Silver 108
Platina 98.6?
Gold (?)
Ammonia 17
Potassa 47.2
Soda 31.3
Lithia 18
Baryta 76.7
Strontia 51.8
Lime 28.5
Magnesia 20.7
Alumina. (?)
Protoxides generally.
Quinia 171.6
Cinchona 160
Morphia 290
Vegeto-alkalies generally.
848. This Table might be further arrange into groups of such substances as
either act with, or replace, each other. Thus, for instance, acids and
bases act in relation to each other; but they do not act in association
with oxygen, hydrogen, or elementary substances. There is indeed little or
no doubt that, when the electrical relations of the particles of matter
come to be closely examined, this division must be made. The simple
substances, with cyanogen, sulpho-cyanogen, and one or two other compound
bodies, will probably form the first group; and the acids and bases, with
such analogous compounds as may prove to be _ions_, the second group.
Whether these will include all _ions_, or whether a third class of more
complicated results will be required, must be decided by future
experiments.
849. It is _probable_ that all our present elementary bodies are _ions_,
but that is not as yet certain. There are some, such as carbon, phosphorus,
nitrogen, silicon, boron, alumium, the right of which to the title of _ion_
it is desirable to decide as soon as possible. There are also many compound
bodies, and amongst them alumina and silica, which it is desirable to class
immediately by unexceptionable experiments. It is also _possible_, that all
combinable bodies, compound as well as simple, may enter into the class of
_ions_; but at present it does not seem to me probable. Still the
experimental evidence I have is so small in proportion to what must
gradually accumulate around, and bear upon, this point, that I am afraid to
give a strong opinion upon it.
850. I think I cannot deceive myself in considering the doctrine of
definite electro-chemical action as of the utmost importance. It touches by
its facts more directly and closely than any former fact, or set of facts,
have done, upon the beautiful idea, that ordinary chemical affinity is a
mere consequence of the electrical attractions of the particles of
different kinds of matter; and it will probably lead us to the means by
which we may enlighten that which is at present so obscure, and either
fully demonstrate the truth of the idea, or develope that which ought to
replace it.
851. A very valuable use of electro-chemical equivalents will be to decide,
in cases of doubt, what is the true chemical equivalent, or definite
proportional, or atomic number of a body; for I have such conviction that
the power which governs electro-decomposition and ordinary chemical
attractions is the same; and such confidence in the overruling influence of
those natural laws which render the former definite, as to feel no
hesitation in believing that the latter must submit to them also. Such
being the case, I can have, no doubt that, assuming hydrogen as 1, and
dismissing small fractions for the simplicity of expression, the equivalent
number or atomic weight of oxygen is 8, of chlorine 36, of bromine 78.4, of
lead 103.5, of tin 59, &c., notwithstanding that a very high authority
doubles several of these numbers.
§ 13. _On the absolute quantity of Electricity associated with the
particles or atoms of Matter._
852. The theory of definite electrolytical or electro-chemical action
appears to me to touch immediately upon the _absolute quantity_ of
electricity or electric power belonging to different bodies. It is
impossible, perhaps, to speak on this point without committing oneself
beyond what present facts will sustain; and yet it is equally impossible,
and perhaps would be impolitic, not to reason upon the subject. Although we
know nothing of what an atom is, yet we cannot resist forming some idea of
a small particle, which represents it to the mind; and though we are in
equal, if not greater, ignorance of electricity, so as to be unable to say
whether it is a particular matter or matters, or mere motion of ordinary
matter, or some third kind of power or agent, yet there is an immensity of
facts which justify us in believing that the atoms of matter are in some
way endowed or associated with electrical powers, to which they owe their
most striking qualities, and amongst them their mutual chemical affinity.
As soon as we perceive, through the teaching of Dalton, that chemical
powers are, however varied the circumstances in which they are exerted,
definite for each body, we learn to estimate the relative degree of force
which resides in such bodies: and when upon that knowledge comes the fact,
that the electricity, which we appear to be capable of loosening from its
habitation for a while, and conveying from place to place, _whilst it
retains its chemical force_, can be measured out, and being so measured is
found to be _as definite in its action_ as any of _those portions_ which,
remaining associated with the particles of matter, give them their
_chemical relation_; we seem to have found the link which connects the
proportion of that we have evolved to the proportion of that belonging to
the particles in their natural state.
853. Now it is wonderful to observe how small a quantity of a compound body
is decomposed by a certain portion of electricity. Let us, for instance,
consider this and a few other points in relation to water. _One grain_ of
water, acidulated to facilitate conduction, will require an electric
current to be continued for three minutes and three quarters of time to
effect its decomposition, which current must be powerful enough to retain a
platina wire 1/104 of an inch in thickness[A], red-hot, in the air during
the whole time; and if interrupted anywhere by charcoal points, will
produce a very brilliant and constant star of light. If attention be paid
to the instantaneous discharge of electricity of tension, as illustrated in
the beautiful experiments of Mr. Wheatstone[B], and to what I have said
elsewhere on the relation of common and voltaic electricity (371. 375.), it
will not be too much to say that this necessary quantity of electricity is
equal to a very powerful flash of lightning. Yet we have it under perfect
command; can evolve, direct, and employ it at pleasure; and when it has
performed its full work of electrolyzation, it has only separated the
elements of _a single grain of water_.
[A] I have not stated the length of wire used, because I find by
experiment, as would be expected in theory, that it is indifferent.
The same quantity of electricity which, passed in a given time, can
heat an inch of platina wire of a certain diameter red-hot, can also
heat a hundred, a thousand, or any length of the same wire to the same
degree, provided the cooling circumstances are the same for every part
in all cases. This I have proved by the volta-electrometer. I found
that whether half an inch or eight inches were retained at one
constant temperature of dull redness, equal quantities of water were
decomposed in equal times. When the half-inch was used, only the
centre portion of wire was ignited. A fine wire may even be used as a
rough but ready regulator of a voltaic current; for if it be made part
of the circuit, and the larger wires communicating with it be shifted
nearer to or further apart, so as to keep the portion of wire in the
circuit sensibly at the same temperature, the current passing through
it will be nearly uniform.
[B] Literary Gazette, 1833, March 1 and 8. Philosophical Magazine,
1833, p. 201. L'Institut, 1833, p.261.
854. On the other hand, the relation between the conduction of the
electricity and the decomposition of the water is so close, that one cannot
take place without the other. If the water is altered only in that small
degree which consists in its having the solid instead of the fluid state,
the conduction is stopped, and the decomposition is stopped with it.
Whether the conduction be considered as depending upon the decomposition,
or not (443. 703.), still the relation of the two functions is equally
intimate and inseparable.
855. Considering this close and twofold relation, namely, that without
decomposition transmission of electricity does not occur; and, that for a
given definite quantity of electricity passed, an equally definite and
constant quantity of water or other matter is decomposed; considering also
that the agent, which is electricity, is simply employed in overcoming
electrical powers in the body subjected to its action; it seems a probable,
and almost a natural consequence, that the quantity which passes is the
_equivalent_ of, and therefore equal to, that of the particles separated;
i.e. that if the electrical power which holds the elements of a grain of
water in combination, or which makes a grain of oxygen and hydrogen in the
right proportions unite into water when they are made to combine, could be
thrown into the condition of _a current_, it would exactly equal the
current required for the separation of that grain of water into its
elements again.
856. This view of the subject gives an almost overwhelming idea of the
extraordinary quantity or degree of electric power which naturally belongs
to the particles of matter; but it is not inconsistent in the slightest
degree with the facts which can be brought to bear on this point. To
illustrate this I must say a few words on the voltaic pile[A].
[A] By the term voltaic pile, I mean such apparatus or arrangement of
metals as up to this time have been called so, and which contain
water, brine, acids, or other aqueous solutions or decomposable
substances (476.), between their plates. Other kinds of electric
apparatus may be hereafter invented, and I hope to construct some not
belonging to the class of instruments discovered by Volta.
857. Intending hereafter to apply the results given in this and the
preceding series of Researches to a close investigation of the source of
electricity in the voltaic instrument, I have refrained from forming any
decided opinion on the subject; and without at all meaning to dismiss
metallic contact, or the contact of dissimilar substances, being
conductors, but not metallic, as if they had nothing to do with the origin
of the current,
I still am fully of opinion with Davy, that it is at least continued by
chemical action, and that the supply constituting the current is almost
entirely from that source.
858. Those bodies which, being interposed between the metals of the voltaic
pile, render it active, _are all of them electrolytes_ (476.); and it
cannot but press upon the attention of every one engaged in considering
this subject, that in those bodies (so essential to the pile) decomposition
and the transmission of a current are so intimately connected, that one
cannot happen without the other. This I have shown abundantly in water, and
numerous other cases (402. 476.). If, then, a voltaic trough have its
extremities connected by a body capable of being decomposed, as water, we
shall have a continuous current through the apparatus; and whilst it
remains in this state we may look at the part where the acid is acting upon
the plates, and that where the current is acting upon the water, as the
reciprocals of each other. In both parts we have the two conditions
_inseparable in such bodies as these_, namely, the passing of a current,
and decomposition; and this is as true of the cells in the battery as of
the water cell; for no voltaic battery has as yet been constructed in which
the chemical action is only that of combination: _decomposition is always
included_, and is, I believe, an essential chemical part.
859. But the difference in the two parts of the connected battery, that is,
the decomposition or experimental cell, and the acting cells, is simply
this. In the former we urge the current through, but it, apparently of
necessity, is accompanied by decomposition: in the latter we cause
decompositions by ordinary chemical actions, (which are, however,
themselves electrical,) and, as a consequence, have the electrical current;
and as the decomposition dependent upon the current is definite in the
former case, so is the current associated with the decomposition also
definite in the latter (862. &c.).
860. Let us apply this in support of what I have surmised respecting the
enormous electric power of each particle or atom of matter (856.). I showed
in a former series of these Researches on the relation by measure of common
and voltaic electricity, that two wires, one of platina and one of zinc,
each one-eighteenth of an inch in diameter, placed five-sixteenths of an
inch apart, and immersed to the depth of five-eighths of an inch in acid,
consisting of one drop of oil of vitriol and four ounces of distilled water
at a temperature of about 60° Fahr., and connected at the other extremities
by a copper wire eighteen feet long, and one-eighteenth of an inch in
thickness, yielded as much electricity in little more than three seconds of
time as a Leyden battery charged by thirty turns of a very large and
powerful plate electric machine in full action (371.). This quantity,
though sufficient if passed at once through the head of a rat or cat to
have killed it, as by a flash of lightning, was evolved by the mutual
action of so small a portion of the zinc wire and water in contact with it,
that the loss of weight sustained by either would be inappreciable by our
most delicate instruments; and as to the water which could be decomposed by
that current, it must have been insensible in quantity, for no trace of
hydrogen appeared upon the surface of the platina during those three
seconds.
861. What an enormous quantity of electricity, therefore, is required for
the decomposition of a single grain of water! We have already seen that it
must be in quantity sufficient to sustain a platina wire 1/104 of an inch
in thickness, red-hot, in contact with the air, for three minutes and three
quarters (853.), a quantity which is almost infinitely greater than that
which could be evolved by the little standard voltaic arrangement to which
I have just referred (860. 871.). I have endeavoured to make a comparison
by the loss of weight of such a wire in a given time in such an acid,
according to a principle and experiment to be almost immediately described
(862.); but the proportion is so high that I am almost afraid to mention
it. It would appear that 800,000 such charges of the Leyden battery as I
have referred to above, would be necessary to supply electricity sufficient
to decompose a single grain of water; or, if I am right, to equal the
quantity of electricity which is naturally associated with the elements of
that grain of water, endowing them with their mutual chemical affinity.
862. In further proof of this high electric condition of the particles of
matter, and the _identity as to quantity of that belonging to them with
that necessary for their separation_, I will describe an experiment of
great simplicity but extreme beauty, when viewed in relation to the
evolution of an electric current and its decomposing powers.
863. A dilute sulphuric acid, made by adding about one part by measure of
oil of vitriol to thirty parts of water, will act energetically upon a
piece of zinc plate in its ordinary and simple state: but, as Mr. Sturgeon
has shown[A], not at all, or scarcely so, if the surface of the metal has
in the first instance been amalgamated; yet the amalgamated zinc will act
powerfully with platina as an electromotor, hydrogen being evolved on the
surface of the latter metal, as the zinc is oxidized and dissolved. The
amalgamation is best effected by sprinkling a few drops of mercury upon the
surface of the zinc, the latter being moistened with the dilute acid, and
rubbing with the fingers or two so as to extend the liquid metal over the
whole of the surface. Any mercury in excess, forming liquid drops upon the
zinc, should be wiped off[B].
[A] Recent Experimental Researches, &c., 1830, p.74, &c.
[B] The experiment may be made with pure zinc, which, as chemists well
know, is but slightly acted upon by dilute sulphuric acid in
comparison with ordinary zinc, which during the action is subject to
an infinity of voltaic actions. See De la Rive on this subject,
Bibliothèque Universelle, 1830, p.391.
864. Two plates of zinc thus amalgamated were dried and accurately weighed;
one, which we will call A, weighed 163.1 grains; the other, to be called B,
weighed 148.3 grains. They were about five inches long, and 0.4 of an inch
wide. An earthenware pneumatic trough was filled with dilute sulphuric
acid, of the strength just described (863.), and a gas jar, also filled
with the acid, inverted in it[A]. A plate of platina of nearly the same
length, but about three times as wide as the zinc plates, was put up into
this jar. The zinc plate A was also introduced into the jar, and brought in
contact with the platina, and at the same moment the plate B was put into
the acid of the trough, but out of contact with other metallic matter.
[A] The acid was left during a night with a small piece of
unamalgamated zinc in it, for the purpose of evolving such air as
might be inclined to separate, and bringing the whole into a constant
state.
865. Strong action immediately occurred in the jar upon the contact of the
zinc and platina plates. Hydrogen gas rose from the platina, and was
collected in the jar, but no hydrogen or other gas rose from _either_ zinc
plate. In about ten or twelve minutes, sufficient hydrogen having been
collected, the experiment was stopped; during its progress a few small
bubbles had appeared upon plate B, but none upon plate A. The plates were
washed in distilled water, dried, and reweighed. Plate B weighed 148.3
grains, as before, having lost nothing by the direct chemical action of the
acid. Plate A weighed 154.65 grains, 8.45 grains of it having been oxidized
and dissolved during the experiment.
866. The hydrogen gas was next transferred to a water-trough and measured;
it amounted to 12.5 cubic inches, the temperature being 52°, and the
barometer 29.2 inches. This quantity, corrected for temperature, pressure,
and moisture, becomes 12.15453 cubic inches of dry hydrogen at mean
temperature and pressure; which, increased by one half for the oxygen that
must have gone to the _anode_, i.e. to the zinc, gives 18.232 cubic inches
as the quantity of oxygen and hydrogen evolved from the water decomposed by
the electric current. According to the estimate of the weight of the mixed
gas before adopted (791.), this volume is equal to 2.3535544 grains, which
therefore is the weight of water decomposed; and this quantity is to 8.45,
the quantity of zinc oxidized, as 9 is to 32.31. Now taking 9 as the
equivalent number of water, the number 32.5 is given as the equivalent
number of zinc; a coincidence sufficiently near to show, what indeed could
not but happen, that for an equivalent of zinc oxidized an equivalent of
water must be decomposed[A].
[A] The experiment was repeated several times with the same results.
867. But let us observe _how_ the water is decomposed. It is electrolyzed,
i.e. is decomposed voltaically, and not in the ordinary manner (as to
appearance) of chemical decompositions; for the oxygen appears at the
_anode_ and the hydrogen at the _cathode_ of the body under decomposition,
and these were in many parts of the experiment above an inch asunder.
Again, the ordinary chemical affinity was not enough under the
circumstances to effect the decomposition of the water, as was abundantly
proved by the inaction on plate B; the voltaic current was essential. And
to prevent any idea that the chemical affinity was almost sufficient to
decompose the water, and that a smaller current of electricity might, under
the circumstances, cause the hydrogen to pass to the _cathode_, I need only
refer to the results which I have given (807. 813.) to shew that the
chemical action at the electrodes has not the slightest influence over the
_quantities_ of water or other substances decomposed between them, but that
they are entirely dependent upon the quantity of electricity which passes.
868. What, then, follows as a necessary consequence of the whole
experiment? Why, this: that the chemical action upon 32.31 parts, or one
equivalent of zinc, in this simple voltaic circle, was able to evolve such
quantity of electricity in the form of a current, as, passing through
water, should decompose 9 parts, or one equivalent of that substance: and
considering the definite relations of electricity as developed in the
preceding parts of the present paper, the results prove that the quantity
of electricity which, being naturally associated with the particles of
matter, gives them their combining power, is able, when thrown into a
current, to separate those particles from their state of combination; or,
in other words, that _the electricity which decomposes, and that which is
evolved by the decomposition of a certain quantity of matter, are alike._
869. The harmony which this theory of the definite evolution and the
equivalent definite action of electricity introduces into the associated
theories of definite proportions and electrochemical affinity, is very
great. According to it, the equivalent weights of bodies are simply those
quantities of them which contain equal quantities of electricity, or have
naturally equal electric powers; it being the ELECTRICITY which
_determines_ the equivalent number, _because_ it determines the combining
force. Or, if we adopt the atomic theory or phraseology, then the atoms of
bodies which are equivalents to each other in their ordinary chemical
action, have equal quantities of electricity naturally associated with
them. But I must confess I am jealous of the term _atom_; for though it is
very easy to talk of atoms, it is very difficult to form a clear idea of
their nature, especially when compound bodies are under consideration.
870. I cannot refrain from recalling here the beautiful idea put forth, I
believe, by Berzelius (703.) in his development of his views of the
electro-chemical theory of affinity, that the heat and light evolved during
cases of powerful combination are the consequence of the electric discharge
which is at the moment taking place. The idea is in perfect accordance with
the view I have taken of the _quantity_ of electricity associated with the
particles of matter.
871. In this exposition of the law of the definite action of electricity,
and its corresponding definite proportion in the particles of bodies, I do
not pretend to have brought, as yet, every case of chemical or
electro-chemical action under its dominion. There are numerous
considerations of a theoretical nature, especially respecting the compound
particles of matter and the resulting electrical forces which they ought to
possess, which I hope will gradually receive their development; and there
are numerous experimental cases, as, for instance, those of compounds
formed by weak affinities, the simultaneous decomposition of water and
salts, &c., which still require investigation. But whatever the results on
these and numerous other points may be, I do not believe that the facts
which I have advanced, or even the general laws deduced from them, will
suffer any serious change; and they are of sufficient importance to justify
their publication, though much may yet remain imperfect or undone. Indeed,
it is the great beauty of our science, CHEMISTRY, that advancement in it,
whether in a degree great or small, instead of exhausting the subjects of
research, opens the doors to further and more abundant knowledge,
overflowing with beauty and utility, to those who will be at the easy
personal pains of undertaking its experimental investigation.
872. The definite production of electricity (868.) in association with its
definite action proves, I think, that the current of electricity in the
voltaic pile: is sustained by chemical decomposition, or rather by chemical
action, and not by contact only. But here, as elsewhere (857.), I beg to
reserve my opinion as to the real action of contact, not having yet been
able to make up my mind as to whether it is an exciting cause of the
current, or merely necessary to allow of the conduction of electricity,
otherwise generated, from one metal to the other.
873. But admitting that chemical action is the source of electricity, what
an infinitely small fraction of that which is active do we obtain and
employ in our voltaic batteries! Zinc and platina wires, one-eighteenth of
an inch in diameter and about half an inch long, dipped into dilute
sulphuric acid, so weak that it is not sensibly sour to the tongue, or
scarcely to our most delicate test-papers, will evolve more electricity in
one-twentieth of a minute (860.) than any man would willingly allow to pass
through his body at once. The chemical action of a grain of water upon four
grains of zinc can evolve electricity equal in quantity to that of a
powerful thunder-storm (868. 861.). Nor is it merely true that the quantity
is active; it can be directed and made to perform its full equivalent duty
(867. &c.). Is there not, then, great reason to hope and believe that, by a
closer _experimental_ investigation of the principles which govern the
development and action of this subtile agent, we shall be able to increase
the power of our batteries, or invent new instruments which shall a
thousandfold surpass in energy those which we at present possess?
874. Here for a while I must leave the consideration of the _definite
chemical action of electricity_. But before I dismiss this series of
experimental Researches, I would call to mind that, in a former series, I
showed the current of electricity was also _definite in its magnetic
action_ (216. 366. 367. 376. 377.); and, though this result was not pursued
to any extent, I have no doubt that the success which has attended the
development of the chemical effects is not more than would accompany an
investigation of the magnetic phenomena.
_Royal Institution,
December 31st, 1833._