§ 12. _On the power of Metals and other Solids to induce the Combination
of Gaseous Bodies._
Received November 30, 1833,--Read January 11, 1834.
564. The conclusion at which I have arrived in the present communication
may seem to render the whole of it unfit to form part of a series of
researches in electricity; since, remarkable as the phenomena are, the
power which produces them is not to be considered as of an electric origin,
otherwise than as all attraction of particles may have this subtile agent
for their common cause. But as the effects investigated arose out of
electrical researches, as they are directly connected with other effects
which are of an electric nature, and must of necessity be understood and
guarded against in a very extensive series of electro-chemical
decompositions (707.), I have felt myself fully justified in describing
them in this place.
565. Believing that I had proved (by experiments hereafter to be described
(705.),) the constant and definite chemical action of a certain quantity of
electricity, whatever its intensity might be, or however the circumstances
of its transmission through either the body under decomposition or the more
perfect conductors were varied, I endeavoured upon that result to construct
a new measuring instrument, which from its use might be called, at least
provisionally, a _Volta-electrometer_ (739.)[A].
[A] Or Voltameter.--_Dec. 1838._
566. During the course of the experiments made to render the instrument
efficient, I was occasionally surprised at observing a deficiency of the
gases resulting from the decompositions of water, and at last an actual
disappearance of portions which had been evolved, collected, and measured.
The circumstances of the disappearance were these. A glass tube, about
twelve inches in length and 3/4ths of an inch in diameter, had two platina
poles fixed into its upper, hermetically sealed, extremity: the poles,
where they passed through the glass, were of wire; but terminated below in
plates, which were soldered to the wires with gold (Plate V. fig. 56.). The
tube was filled with dilute sulphuric acid, and inverted in a cup of the
same fluid; a voltaic battery was connected with the two wires, and
sufficient oxygen and hydrogen evolved to occupy 4/5ths of the tube, or by
the graduation, 116 parts. On separating the tube from the voltaic battery
the volume of gas immediately began to diminish, and in about five hours
only 13-1/2 parts remained, and these ultimately disappeared.
567. It was found by various experiments, that this effect was not due to
the escape or solution of the gas, nor to recombination of the oxygen or
hydrogen in consequence of any peculiar condition _they_ might be supposed
to possess under the circumstances; but to be occasioned by the action of
one or both of the poles within the tube upon the gas around them. On
disuniting the poles from the pile after they had acted upon dilute
sulphuric acid, and introducing them into separate tubes containing mixed
oxygen and hydrogen, it was found that the _positive_ pole effected the
union of the gases, but the negative pole apparently not (588.). It was
ascertained also that no action of a sensible kind took place between the
positive pole with oxygen or hydrogen alone.
568. These experiments reduced the phenomena to the consequence of a power
possessed by the platina, after it had been the positive pole of a voltaic
pile, of causing the combination of oxygen and hydrogen at common, or even
at low, temperatures. This effect is, as far as I am aware, altogether new,
and was immediately followed out to ascertain whether it was really of an
electric nature, and how far it would interfere with the determination of
the quantities evolved in the cases of electro-chemical decomposition
required in the fourteenth section of these Researches.
569. Several platina plates were prepared (fig. 57.). They were nearly half
an inch wide, and two inches and a half long: some were 1/200dth of an
inch, others not more than 1/600dth, whilst some were as much as 1/70th of
an inch in thickness. Each had a piece of platina wire, about seven inches
long, soldered to it by pure gold. Then a number of glass tubes were
prepared: they were about nine or ten inches in length, 5/8ths of an inch
in internal diameter, were sealed hermetically at one extremity, and were
graduated. Into these tubes was put a mixture of two volumes of hydrogen
and one of oxygen, at the water pneumatic trough, and when one of the
plates described had been connected with the positive or negative pole of
the voltaic battery for a given time, or had been otherwise prepared, it
was introduced through the water into the gas within the tube; the whole
set aside in a test-glass (fig. 58.), and left for a longer or shorter
period, that the action might be observed.
570. The following result may be given as an illustration of the phenomenon
to be investigated. Diluted sulphuric acid, of the specific gravity 1.336,
was put into a glass jar, in which was placed also a large platina plate,
connected with the negative end of a voltaic battery of forty pairs of
four-inch plates, with double coppers, and moderately charged. One of the
plates above described (569.) was then connected with the positive
extremity, and immersed in the same jar of acid for five minutes, after
which it was separated from the battery, washed in distilled water, and
introduced through the water of the pneumatic trough into a tube containing
the mixture of oxygen and hydrogen (569.). The volume of gases immediately
began to lessen, the diminution proceeding more and more rapidly until
about 3/4ths of the mixture had disappeared. The upper end of the tube
became quite warm, the plate itself so hot that the water boiled as it rose
over it; and in less than a minute a cubical inch and a half of the gases
were gone, having been combined by the power of the platina, and converted
into water.
571. This extraordinary influence acquired by the platina at the positive
pole of the pile, is exerted far more readily and effectively on oxygen and
hydrogen than on any other mixture of gases that I have tried. One volume
of nitrous gas was mixed with a volume of hydrogen, and introduced into a
tube with a plate which had been made positive in the dilute sulphuric acid
for four minutes (570.). There was no sensible action in an hour: being
left for thirty-six hours, there was a diminution of about one-eighth of
the whole volume. Action had taken place, but it had been very feeble.
572. A mixture of two volumes of nitrous oxide with one volume of hydrogen
was put with a plate similarly prepared into a tube (569. 570.). This also
showed no action immediately; but in thirty-six hours nearly a fourth of
the whole had disappeared, i.e. about half of a cubic inch. By comparison
with another tube containing the same mixture without a plate, it appeared
that a part of the diminution was due to solution, and the other part to
the power of the platina; but the action had been very slow and feeble.
573. A mixture of one volume olefiant gas and three volumes oxygen was not
affected by such a platina plate, even though left together for several
days (640. 641.).
574. A mixture of two volumes carbonic oxide and one volume oxygen was also
unaffected by the prepared platina plate in several days (645, &c.).
575. A mixture of equal volumes of chlorine and hydrogen was used in
several experiments, with plates prepared in a similar manner (570.).
Diminution of bulk soon took place; but when after thirty-six hours the
experiments were examined, it was found that nearly all the chlorine had
disappeared, having been absorbed, principally by the water, and that the
original volume of hydrogen remained unchanged. No combination of the
gases, therefore, had here taken place.
576. Reverting to the action of the prepared plates on mixtures of oxygen
and hydrogen (570.), I found that the power, though gradually diminishing
in all cases, could still be retained for a period, varying in its length
with circumstances. When tubes containing plates (569.) were supplied with
fresh portions of mixed oxygen and hydrogen as the previous portions were
condensed, the action was found to continue for above thirty hours, and in
some cases slow combination could be observed even after eighty hours; but
the continuance of the action greatly depended upon the purity of the gases
used (638.).
577. Some plates (569.) were made positive for four minutes in dilute
sulphuric acid of specific gravity 1.336: they were rinsed in distilled
water, after which two were put into a small bottle and closed up, whilst
others were left exposed to the air. The plates preserved in the limited
portion of air were found to retain their power after eight days, but those
exposed to the atmosphere had lost their force almost entirely in twelve
hours, and in some situations, where currents existed, in a much shorter
time.
578. Plates were made positive for five minutes in sulphuric acid, specific
gravity 1.336. One of these was retained in similar acid for eight minutes
after separation from the battery: it then acted on mixed oxygen and
hydrogen with apparently undiminished vigour. Others were left in similar
acid for forty hours, and some even for eight days, after the
electrization, and then acted as well in combining oxygen and hydrogen gas
as those which were used immediately after electrization.
579. The effect of a solution of caustic potassa in preserving the platina
plates was tried in a similar manner. After being retained in such a
solution for forty hours, they acted exceedingly well on oxygen and
hydrogen, and one caused such rapid condensation of the gases, that the
plate became much heated, and I expected the temperature would have risen
to ignition.
580. When similarly prepared plates (569.) had been put into distilled
water for forty hours, and then introduced into mixed oxygen and hydrogen,
they were found to act but very slowly and feebly as compared with those
which had been preserved in acid or alkali. When, however, the quantity of
water was but small, the power was very little impaired after three or four
days. As the water had been retained in a wooden vessel, portions of it
were redistilled in glass, and this was found to preserve prepared plates
for a great length of time. Prepared plates were put into tubes with this
water and closed up; some of them, taken out at the end of twenty-four
days, were found very active on mixed oxygen and hydrogen; others, which
were left in the water for fifty-three days, were still found to cause the
combination of the gases. The tubes had been closed only by corks.
581. The act of combination always seemed to diminish, or apparently
exhaust, the power of the platina plate. It is true, that in most, if not
all instances, the combination of the gases, at first insensible, gradually
increased in rapidity, and sometimes reached to explosion; but when the
latter did not happen, the rapidity of combination diminished; and although
fresh portions of gas were introduced into the tubes, the combination went
on more and more slowly, and at last ceased altogether. The first effect of
an increase in the rapidity of combination depended in part upon the water
flowing off from the platina plate, and allowing a better contact with the
gas, and in part upon the heat evolved during the progress of the
combination (630.). But notwithstanding the effect of these causes,
diminution, and at last cessation of the power, always occurred. It must
not, however, be unnoticed, that the purer the gases subjected to the
action of the plate, the longer was its combining power retained. With the
mixture evolved at the poles of the voltaic pile, in pure dilute sulphuric
acid, it continued longest; and with oxygen and hydrogen, of perfect
purity, it probably would not be diminished at all.
582. Different modes of treatment applied to the platina plate, after it
had ceased to be the positive pole of the pile, affected its power very
curiously. A plate which had been a positive pole in diluted sulphuric acid
of specific gravity 1.336 for four or five minutes, if rinsed in water and
put into mixed oxygen and hydrogen, would act very well, and condense
perhaps one cubic inch and a half of gas in six or seven minutes; but if
that same plate, instead of being merely rinsed, had been left in distilled
water for twelve or fifteen minutes, or more, it would rarely fail, when
put into the oxygen and hydrogen, of becoming, in the course of a minute or
two, ignited, and would generally explode the gases. Occasionally the time
occupied in bringing on the action extended to eight or nine minutes, and
sometimes even to forty minutes, and yet ignition and explosion would
result. This effect is due to the removal of a portion of acid which
otherwise adheres firmly to the plate [A].
[A] In proof that this is the case, refer to 1038.--_Dec. 1838._
583. Occasionally the platina plates (569.), after being made the positive
pole of the battery, were washed, wiped with filtering-paper or a cloth,
and washed and wiped again. Being then introduced into mixed oxygen and
hydrogen, they acted apparently as if they had been unaffected by the
treatment. Sometimes the tubes containing the gas were opened in the air
for an instant, and the plates put in dry; but no sensible difference in
action was perceived, except that it commenced sooner.
584. The power of heat in altering the action of the prepared platina
plates was also tried (595.). Plates which had been rendered positive in
dilute sulphuric acid for four minutes were well-washed in water, and
heated to redness in the flame of a spirit-lamp: after this they acted very
well on mixed oxygen and hydrogen. Others, which had been heated more
powerfully by the blowpipe, acted afterwards on the gases, though not so
powerfully as the former. Hence it appears that heat does not take away the
power acquired by the platina at the positive pole of the pile: the
occasional diminution of force seemed always referable to other causes than
the mere heat. If, for instance, the plate had not been well-washed from
the acid, or if the flame used was carbonaceous, or was that of an alcohol
lamp trimmed with spirit containing a little acid, or having a wick on
which salt, or other extraneous matter, had been placed, then the power of
the plate was quickly and greatly diminished (634. 636.).
585. This remarkable property was conferred upon platina when it was made
the positive pole in sulphuric acid of specific gravity 1.336, or when it
was considerably weaker, or when stronger, even up to the strength of oil
of vitriol. Strong and dilute nitric acid, dilute acetic acid, solutions of
tartaric, citric, and oxalic acids, were used with equal success. When
muriatic acid was used, the plates acquired the power of condensing the
oxygen and hydrogen, but in a much inferior degree.
586. Plates which were made positive in solution of caustic potassa did not
show any sensible action upon the mixed oxygen and hydrogen. Other plates
made positive in solutions of carbonates of potassa and soda exhibited the
action, but only in a feeble degree.
587. When a neutral solution of sulphate of soda, or of nitre, or of
chlorate of potassa, or of phosphate of potassa, or acetate of potassa, or
sulphate of copper, was used, the plates, rendered positive in them for
four minutes, and then washed in water, acted very readily and powerfully
on the mixed oxygen and hydrogen.
588. It became a very important point, in reference to the _cause_ of this
action of the platina, to determine whether the _positive_ pole _only_
could confer it (567.), or whether, notwithstanding the numerous contrary
cases, the _negative_ pole might not have the power when such circumstances
as could interfere with or prevent the action were avoided. Three plates
were therefore rendered negative, for four minutes in diluted sulphuric
acid of specific gravity 1.336, washed in distilled water, and put into
mixed oxygen and hydrogen. _All_ of them _acted_, though not so strongly as
they would have done if they had been rendered positive. Each combined
about a cubical inch and a quarter of the gases in twenty-five minutes. On
every repetition of the experiment the same result was obtained; and when
the plates were retained in distilled water for ten or twelve minutes,
before being introduced into the gas (582.), the action was very much
quickened.
589. But when there was any metallic or other substance present in the
acid, which could be precipitated on the negative plate, then that plate
ceased to act upon the mixed oxygen and hydrogen.
590. These experiments led to the expectation that the power of causing
oxygen and hydrogen to combine, which could be conferred upon any piece of
platina by making it the positive pole of a voltaic pile, was not
essentially dependent upon the action of the pile, or upon any structure or
arrangement of parts it might receive whilst in association with it, but
belonged to the platina _at all times_, and was _always effective_ when the
surface was _perfectly clean_. And though, when made the _positive_ pole of
the pile in acids, the circumstances might well be considered as those
which would cleanse the surface of the platina in the most effectual
manner, it did not seem impossible that ordinary operations should produce
the same result, although in a less eminent degree.
591. Accordingly, a platina plate (569.) was cleaned by being rubbed with a
cork, a little water, and some coal-fire ashes upon a glass plate: being
washed, it was put into mixed oxygen and hydrogen, and was found to act at
first slowly, and then more rapidly. In an hour, a cubical inch and a half
had disappeared.
592. Other plates were cleaned with ordinary sand-paper and water; others
with chalk and water; others with emery and water; others, again, with
black oxide of manganese and water; and others with a piece of charcoal and
water. All of these acted in tubes of oxygen and hydrogen, causing
combination of the gases. The action was by no means so powerful as that
produced by plates having been in communication with the battery; but from
one to two cubical inches of the gases disappeared, in periods extending
from twenty-five to eighty or ninety minutes.
593. Upon cleaning the plates with a cork, ground emery, and dilute
sulphuric acid, they were found to act still better. In order to simplify
the conditions, the cork was dismissed, and a piece of platina foil used
instead; still the effect took place. Then the acid was dismissed, and a
solution of _potassa_ used, but the effect occurred as before.
594. These results are abundantly sufficient to show that the mere
mechanical cleansing of the surface of the platina is sufficient to enable
it to exert its combining power over oxygen and hydrogen at common
temperatures.
595. I now tried the effect of heat in conferring this property upon
platina (584.). Plates which had no action on the mixture of oxygen and
hydrogen were heated by the flame of a freshly trimmed spirit-lamp, urged
by a mouth blowpipe, and when cold were put into tubes of the mixed gases:
they acted slowly at first, but after two or three hours condensed nearly
all the gases.
596. A plate of platina, which was about one inch wide and two and
three-quarters in length, and which had not been used in any of the
preceding experiments, was curved a little so as to enter a tube, and left
in a mixture of oxygen and hydrogen for thirteen hours: not the slightest
action or combination of the gases occurred. It was withdrawn at the
pneumatic trough from the gas through the water, heated red-hot by the
spirit-lamp and blowpipe, and then returned when cold into the _same_
portion of gas. In the course of a few minutes diminution of the gases
could be observed, and in forty-five minutes about one cubical inch and a
quarter had disappeared. In many other experiments platina plates when
heated were found to acquire the power of combining oxygen and hydrogen.
597. But it happened not infrequently that plates, after being heated,
showed no power of combining oxygen and hydrogen gases, though left
undisturbed in them for two hours. Sometimes also it would happen that a
plate which, having been heated to dull redness, acted feebly, upon being
heated to whiteness ceased to act; and at other times a plate which, having
been slightly heated, did not act, was rendered active by a more powerful
ignition.
598. Though thus uncertain in its action, and though often diminishing the
power given to the plates at the positive pole of the pile (584.), still it
is evident that heat can render platina active, which before was inert
(595.). The cause of its occasional failure appears to be due to the
surface of the metal becoming soiled, either from something previously
adhering to it, which is made to adhere more closely by the action of the
heat, or from matter communicated from the flame of the lamp, or from the
air itself. It often happens that a polished plate of platina, when heated
by the spirit-lamp and a blowpipe, becomes dulled and clouded on its
surface by something either formed or deposited there; and this, and much
less than this, is sufficient to prevent it from exhibiting the curious
power now under consideration (634. 636.). Platina also has been said to
combine with carbon; and it is not at all unlikely that in processes of
heating, where carbon or its compounds are present, a film of such a
compound may be thus formed, and thus prevent the exhibition of the
properties belonging to _pure_ platina[A].
[A] When heat does confer the property it is only by the destruction
or dissipation of organic or other matter which had previously soiled
the plate (632. 633. 634.).--_Dec. 1838._
599. The action of alkalies and acids in giving platina this property was
now experimentally examined. Platina plates (569.) having no action on
mixed oxygen and hydrogen, being boiled in a solution of caustic potassa,
washed, and then put into the gases, were found occasionally to act pretty
well, but at other times to fail. In the latter case I concluded that the
impurity upon the surface of the platina was of a nature not to be removed
by the mere solvent action of the alkali, for when the plates were rubbed
with a little emery, and the same solution of alkali (592.), they became
active.
600. The action of acids was far more constant and satisfactory. A platina
plate was boiled in dilute nitric acid: being washed and put into mixed
oxygen and hydrogen gases, it acted well. Other plates were boiled in
strong nitric acid for periods extending from half a minute to four
minutes, and then being washed in distilled water, were found to act very
well, condensing one cubic inch and a half of gas in the space of eight or
nine minutes, and rendering the tube warm (570.).
601. Strong sulphuric acid was very effectual in rendering the platina
active. A plate (569.) was heated in it for a minute, then washed and put
into the mixed oxygen and hydrogen, upon which it acted as well as if it
had been made the positive pole of a voltaic pile (570.).
602. Plates which, after being heated or electrized in alkali, or after
other treatment, were found inert, immediately received power by being
dipped for a minute or two, or even only for an instant, into hot oil of
vitriol, and then into water.
603. When the plate was dipped into the oil of vitriol, taken out, and then
heated so as to drive off the acid, it did not act, in consequence of the
impurity left by the acid upon its surface.
604. Vegetable acids, as acetic and tartaric, sometimes rendered inert
platina active, at other times not. This, I believe, depended upon the
character of the matter previously soiling the plates, and which may easily
be supposed to be sometimes of such a nature as to be removed by these
acids, and at other times not. Weak sulphuric acid showed the same
difference, but strong sulphuric acid (601.) never failed in its action.
605. The most favourable treatment, except that of making the plate a
positive pole in strong acid, was as follows. The plate was held over a
spirit-lamp flame, and when hot, rubbed with a piece of potassa fusa
(caustic potash), which melting, covered the metal with a coat of very
strong alkali, and this was retained fused upon the surface for a second or
two[A]: it was then put into water for four or five minutes to wash off the
alkali, shaken, and immersed for about a minute in hot strong oil of
vitriol; from this it was removed into distilled water, where it was
allowed to remain ten or fifteen minutes to remove the last traces of acid
(582.). Being then put into a mixture of oxygen and hydrogen, combination
immediately began, and proceeded rapidly; the tube became warm, the platina
became red-hot, and the residue of the gases was inflamed. This effect
could be repeated at pleasure, and thus the maximum phenomenon could be
produced without the aid of the voltaic battery.
[A] The heat need not be raised so much as to make the alkali tarnish
the platina, although if that effect does take place it does not
prevent the ultimate action.
606. When a solution of tartaric or acetic acid was substituted, in this
mode of preparation, for the sulphuric acid, still the plate was found to
acquire the same power, and would often produce explosion in the mixed
gases; but the strong sulphuric acid was most certain and powerful.
607. If borax, or a mixture of the carbonates of potash and soda, be fused
on the surface of a platina plate, and that plate be well-washed in water,
it will be found to have acquired the power of combining oxygen and
hydrogen, but only in a moderate degree; but if, after the fusion and
washing, it be dipped in the hot sulphuric acid (601.), it will become very
active.
608. Other metals than platina were then experimented with. Gold and
palladium exhibited the power either when made the positive pole of the
voltaic battery (570.), or when acted on by hot oil of vitriol (601.). When
palladium is used, the action of the battery or acid should be moderated,
as that metal is soon acted upon under such circumstances. Silver and
copper could not be made to show any effect at common temperatures.
* * * * *
609. There can remain no doubt that the property of inducing combination,
which can thus be conferred upon masses of platina and other metals by
connecting them with the poles of the battery, or by cleansing processes
either of a mechanical or chemical nature, is the same as that which was
discovered by Döbereiner[A], in 1823, to belong in so eminent a degree to
spongy platina, and which was afterwards so well experimented upon and
illustrated by MM. Dulong and Thenard[B], in 1823. The latter philosophers
even quote experiments in which a very fine platina wire, which had been
coiled up and digested in nitric, sulphuric, or muriatic acid, became
ignited when put into a jet of hydrogen gas[C]. This effect I can now
produce at pleasure with either wires or plates by the processes described
(570. 601. 605.); and by using a smaller plate cut so that it shall rest
against the glass by a few points, and yet allow the water to flow off
(fig. 59.), the loss of heat is less, the metal is assimilated somewhat to
the spongy state, and the probability of failure almost entirely removed.
[A] Annales de Chimie, tom. xxiv. p. 93.
[B] Ibid. tom. xxiii. p. 440; tom. xxiv. p. 380.
[C] Ibid. tom. xxiv. p. 383.
610. M. Döbereiner refers the effect entirely to an electric action. He
considers the platina and hydrogen as forming a voltaic element of the
ordinary kind, in which the hydrogen, being very highly positive,
represents the zinc of the usual arrangement, and like it, therefore,
attracts oxygen and combines with it[A].
[A] tom. xxiv. pp. 94, 95. Also Bibliothèque Universelle, tom. xxiv.
p. 54.
611. In the two excellent experimental papers by MM. Dulong and Thenard[A],
those philosophers show that elevation of temperature favours the action,
but does not alter its character; Sir Humphry Davy's incandescent platina
wire being the same phenomenon with Döbereiner's spongy platina. They show
that _all_ metals have this power in a greater or smaller degree, and that
it is even possessed by such bodies as charcoal, pumice, porcelain, glass,
rock crystal, &c., when their temperatures are raised; and that another of
Davy's effects, in which oxygen and hydrogen had combined slowly together
at a heat below ignition, was really dependent upon the property of the
heated glass, which it has in common with the bodies named above. They
state that liquids do not show this effect, at least that mercury, at or
below the boiling point, has not the power; that it is not due to porosity;
that the same body varies very much in its action, according to its state;
and that many other gaseous mixtures besides oxygen and hydrogen are
affected, and made to act chemically, when the temperature is raised. They
think it probable that spongy platina acquires its power from contact with
the acid evolved during its reduction, or from the heat itself to which it
is then submitted.
[A] Annales de Chimie, tom. xxiii. p. 440; tom. xxiv. p, 380.
612. MM. Dulong and Thenard express themselves with great caution on the
theory of this action; but, referring to the decomposing power of metals on
ammonia when heated to temperatures not sufficient alone to affect the
alkali, they remark that those metals which in this case are most
efficacious, are the least so in causing the combination of oxygen and
hydrogen; whilst platina, gold, &c., which have least power of decomposing
ammonia, have most power of combining the elements of water:--from which
they are led to believe, that amongst gases, some tend to _unite_ under the
influence of metals, whilst others tend to _separate_, and that this
property varies in opposite directions with the different metals. At the
close of their second paper they observe, that the action is of a kind that
cannot be connected with any known theory; and though it is very remarkable
that the effects are transient, like those of most electrical actions, yet
they state that the greater number of the results observed by them are
inexplicable, by supposing them to be of a purely electric origin.
613. Dr. Fusinieri has also written on this subject, and given a theory
which he considers as sufficient to account for the phenomena[A]. He
expresses the immediate cause thus: "The platina determines upon its
surface a continual renovation of _concrete laminæ_ of the combustible
substance of the gases or vapours, which flowing over it are burnt, pass
away, and are renewed: this combustion at the surface raises and sustains
the temperature of the metal." The combustible substance, thus reduced into
imperceptible laminæ, of which the concrete parts are in contact with the
oxygen, is presumed to be in a state combinable with the oxygen at a much
lower temperature than when it is in the gaseous state, and more in analogy
with what is called the nascent condition. That combustible gases should
lose their elastic state, and become concrete, assuming the form of
exceedingly attenuated but solid strata, is considered as proved by facts,
some of which are quoted in the Giornale di Fisica for 1824[B]; and though
the theory requires that they should assume this state at high
temperatures, and though the _similar_ films of aqueous and other matter
are dissipated by the action of heat, still the facts are considered as
justifying the conclusion against all opposition of reasoning.
[A] Giornale di Fisica, &c., 1825, tom. viii. p. 259.
[B] pp. 138, 371.
614. The power or force which makes combustible gas or vapour abandon its
elastic state in contact with a solid, that it may cover the latter with a
thin stratum of its own proper substance, is considered as being neither
attraction nor affinity. It is able also to extend liquids and solids in
concrete laminæ over the surface of the acting solid body, and consists in
a _repulsion_, which is developed from the parts of the solid body by the
simple fact of attenuation, and is highest when the attenuation is most
complete. The force has a progressive development, and acts most
powerfully, or at first, in the direction in which the dimensions of the
attenuated mass decrease, and then in the direction of the angles or
corners which from any cause may exist on the surface. This force not only
causes spontaneous diffusion of gases and other substances over the
surface, but is considered as very elementary in its nature, and competent
to account for all the phenomena of capillarity, chemical affinity,
attraction of aggregation, rarefaction, ebullition, volatilization,
explosion, and other thermometric effects, as well as inflammation,
detonation, &c. &c. It is considered as a form of heat to which the term
_native calorie_ is given, and is still further viewed as the principle of
the two electricities and the two magnetisms.
615. I have been the more anxious to give a correct abstract of Dr.
Fusinieri's view, both because I cannot form a distinct idea of the power
to which he refers the phenomena, and because of my imperfect knowledge of
the language in which the memoir is written. I would therefore beg to refer
those who pursue the subject to the memoir itself.
616. Not feeling, however, that the problem has yet been solved, I venture
to give the view which seems to me sufficient, upon _known principles_, to
account for the effect.
617. It may be observed of this action, that, with regard to platina, it
cannot be due to any peculiar, temporary condition, either of an electric
or of any other nature: the activity of plates rendered either positive or
negative by the pole, or cleaned with such different substances as acids,
alkalies, or water; charcoal, emery, ashes, or glass; or merely heated, is
sufficient to negative such an opinion. Neither does it depend upon the
spongy and porous, or upon the compact and burnished, or upon the massive
or the attenuated state of the metal, for in any of these states it may be
rendered effective, or its action may be taken away. The only essential
condition appears to be a _perfectly clean_ and _metallic surface_, for
whenever that is present the platina acts, whatever its form and condition
in other respects may be; and though variations in the latter points will
very much affect the rapidity, and therefore the visible appearances and
secondary effects, of the action, i.e. the ignition of the metal and the
inflammation of the gases, they, even in their most favourable state,
cannot produce any effect unless the condition of a clean, pure, metallic
surface be also fulfilled.
618. The effect is evidently produced by most, if not all, solid bodies,
weakly perhaps by many of them, but rising to a high degree in platina.
Dulong and Thenard have very philosophically extended our knowledge of the
property to its possession by all the metals, and by earths, glass, stones,
&c. (611.); and every idea of its being a known and recognised electric
action is in this way removed.
619. All the phenomena connected with this subject press upon my mind the
conviction that the effects in question are entirely incidental and of a
secondary nature; that they are dependent upon the _natural conditions_ of
gaseous elasticity, combined with the exertion of that attractive force
possessed by many bodies, especially those which are solid, in an eminent
degree, and probably belonging to all; by which they are drawn into
association more or less close, without at the same time undergoing
chemical combination, though often assuming the condition of adhesion; and
which occasionally leads, under very favourable circumstances, as in the
present instance, to the combination of bodies simultaneously subjected to
this attraction. I am prepared myself to admit (and probably many others
are of the same opinion), both with respect to the attraction of
aggregation and of chemical affinity, that the sphere of action of
particles extends beyond those other particles with which they are
immediately and evidently in union (523.), and in many cases produces
effects rising into considerable importance: and I think that this kind of
attraction is a determining cause of Döbereiner's effect, and of the many
others of a similar nature.
620. Bodies which become wetted by fluids with which they do not combine
chemically, or in which they do not dissolve, are simple and well-known
instances of this kind of attraction.
621. All those cases of bodies which being insoluble in water and not
combining with it are hygrometric, and condense its vapour around or upon
their surface, are stronger instances of the same power, and approach a
little nearer to the cases under investigation. If pulverized clay,
protoxide or peroxide of iron, oxide of manganese, charcoal, or even
metals, as spongy platina or precipitated silver, be put into an atmosphere
containing vapour of water, they soon become moist by virtue of an
attraction which is able to condense the vapour upon, although not to
combine it with, the substances; and if, as is well known, these bodies so
damped be put into a dry atmosphere, as, for instance, one confined over
sulphuric acid, or if they be heated, then they yield up this water again
almost entirely, it not being in direct or permanent combination[A].
[A] I met at Edinburgh with a case, remarkable as to its extent, of
hygrometric action, assisted a little perhaps by very slight solvent
power. Some turf had been well-dried by long exposure in a covered
place to the atmosphere, but being then submitted to the action of a
hydrostatic press, it yielded, _by the mere influence of the
pressure_, 54 per cent. of water.
622. Still better instances of the power I refer to, because they are more
analogous to the cases to be explained, are furnished by the attraction
existing between glass and air, so well known to barometer and thermometer
makers, for here the adhesion or attraction is exerted between a solid and
gases, bodies having very different physical conditions, having no power of
combination with each other, and each retaining, during the time of action,
its physical state unchanged[A]. When mercury is poured into a barometer
tube, a film of air will remain between the metal and glass for months, or,
as far as is known, for years, for it has never been displaced except by
the action of means especially fitted for the purpose. These consist in
boiling the mercury, or in other words, of forming an abundance of vapour,
which coming in contact with every part of the glass and every portion of
surface of the mercury, gradually mingles with, dilutes, and carries off
the air attracted by, and adhering to, those surfaces, replacing it by
other vapour, subject to an equal or perhaps greater attraction, but which
when cooled condenses into the same liquid as that with which the tube is
filled.
[A] Fusinieri and Bellani consider the air as forming solid concrete
films in these cases.--Giornale di Fisica, tom. viii, p. 262. 1825.
623. Extraneous bodies, which, acting as nuclei in crystallizing or
depositing solutions, cause deposition of substances on them, when it does
not occur elsewhere in the liquid, seem to produce their effects by a power
of the same kind, i.e. a power of attraction extending to neighbouring
particles, and causing them to become attached to the nuclei, although it
is not strong enough to make them combine chemically with their substance.
624. It would appear from many cases of nuclei in solutions, and from the
effects of bodies put into atmospheres containing the vapours of water, or
camphor, or iodine, &c., as if this attraction were in part elective,
partaking in its characters both of the attraction of aggregation and
chemical affinity: nor is this inconsistent with, but agreeable to, the
idea entertained, that it is the power of particles acting, not upon others
with which they can immediately and intimately combine, but upon such as
are either more distantly situated with respect to them, or which, from
previous condition, physical constitution, or feeble relation, are unable
to enter into decided union with them.
625. Then, of all bodies, the gases are those which might be expected to
show some _mutual_ action whilst _jointly_ under the attractive influence
of the platina or other solid acting substance. Liquids, such as water,
alcohol, &c., are in so dense and comparatively incompressible a state, as
to favour no expectation that their particles should approach much closer
to each other by the attraction of the body to which they adhere, and yet
that attraction must (according to its effects) place their particles as
near to those of the solid wetted body as they are to each other, and in
many cases it is evident that the former attraction is the stronger. But
gases and vapours are bodies competent to suffer very great changes in the
relative distances of their particles by external agencies; and where they
are in immediate contact with the platina, the approximation of the
particles to those of the metal may be very great. In the case of the
hygrometric bodies referred to (621.), it is sufficient to reduce the
vapour to the fluid state, frequently from atmospheres so rare that without
this influence it would be needful to compress them by mechanical force
into a bulk not more than 1/10th or even 1/20th of their original volume
before the vapours would become liquids.
626. Another most important consideration in relation to this action of
bodies, and which, as far as I am aware, has not hitherto been noticed, is
the condition of elasticity under which the gases are placed against the
acting surface. We have but very imperfect notions of the real and intimate
conditions of the particles of a body existing in the solid, the liquid,
and the gaseous state; but when we speak of the gaseous state as being due
to the mutual repulsions of the particles or of their atmospheres, although
we may err in imagining each particle to be a little nucleus to an
atmosphere of heat, or electricity, or any other agent, we are still not
likely to be in error in considering the elasticity as dependent on
_mutuality_ of action. Now this mutual relation fails altogether on the
side of the gaseous particles next to the platina, and we might be led to
expect _à priori_ a deficiency of elastic force there to at least one half;
for if, as Dalton has shown, the elastic force of the particles of one gas
cannot act against the elastic force of the particles of another, the two
being as vacua to each other, so is it far less likely that the particles
of the platina can exert any influence on those of the gas against it, such
as would be exerted by gaseous particles of its own kind.
627. But the diminution of power to one-half on the side of the gaseous
body towards the metal is only a slight result of what seems to me to flow
as a necessary consequence of the known constitution of gases. An
atmosphere of one gas or vapour, however dense or compressed, is in effect
as a vacuum to another: thus, if a little water were put into a vessel
containing a dry gas, as air, of the pressure of one hundred atmospheres,
as much vapour of the water would _rise_ as if it were in a perfect vacuum.
Here the particles of watery vapour appear to have no difficulty in
approaching within any distance of the particles of air, being influenced
solely by relation to particles of their own kind; and if it be so with
respect to a body having the same elastic powers as itself, how much more
surely must it be so with particles, like those of the platina, or other
limiting body, which at the same time that they have not these elastic
powers, are also unlike it in nature! Hence it would seem to result that
the particles of hydrogen or any other gas or vapour which are next to the
platina, &c., must be in such contact with it as if they were in the liquid
state, and therefore almost infinitely closer to it than they are to each
other, even though the metal be supposed to exert no attractive influence
over them.
628. A third and very important consideration in favour of the mutual
action of gases under these circumstances is their perfect miscibility. If
fluid bodies capable of combining together are also capable of mixture,
_they do combine_ when they are mingled, not waiting for any other
determining circumstance; but if two such gases as oxygen and hydrogen are
put together, though they are elements having such powerful affinity as to
unite naturally under a thousand different circumstances, they do not
combine by mere mixture. Still it is evident that, from their perfect
association, the particles are in the most favourable state possible for
combination upon the supervention of any determining cause, such either as
the negative action of the platina in suppressing or annihilating, as it
were, their elasticity on its side; or the positive action of the metal in
condensing them against its surface by an attractive force; or the
influence of both together.
629. Although there are not many distinct cases of combination under the
influence of forces external to the combining particles, yet there are
sufficient to remove any difficulty which might arise on that ground. Sir
James Hull found carbonic acid and lime to remain combined under pressure
at temperatures at which they would not have remained combined if the
pressure had been removed; and I have had occasion to observe a case of
direct combination in chlorine[A], which being compressed at common
temperatures will combine with water, and form a definite crystalline
hydrate, incapable either of being formed or of existing if that pressure
be removed.
[A] Philosophical Transactions, 1823, p. 161.
630. The course of events when platina acts upon, and combines oxygen and
hydrogen, may be stated, according to these principles, as follows. From
the influence of the circumstances mentioned (619. &c.), i.e. the
deficiency of elastic power and the attraction of the metal for the gases,
the latter, when they are in association with the former, are so far
condensed as to be brought within the action of their mutual affinities at
the existing temperature; the deficiency of elastic power, not merely
subjecting them more closely to the attractive influence of the metal, but
also bringing them into a more favourable state for union, by abstracting a
part of that power (upon which depends their elasticity,) which elsewhere
in the mass of gases is opposing their combination. The consequence of
their combination is the production of the vapour of water and an elevation
of temperature. But as the attraction of the platina for the water formed
is not greater than for the gases, if so great, (for the metal is scarcely
hygrometric,) the vapour is quickly diffused through the remaining gases;
fresh portions of this latter, therefore, come into juxtaposition with the
metal, combine, and the fresh vapour formed is also diffused, allowing new
portions of gas to be acted upon. In this way the process advances, but is
accelerated by the evolution of heat, which is known by experiment to
facilitate the combination in proportion to its intensity, and the
temperature is thus gradually exalted until ignition results.
631. The dissipation of the vapour produced at the surface of the platina,
and the contact of fresh oxygen and hydrogen with the metal, form no
difficulty in this explication. The platina is not considered as causing
the combination of any particles with itself, but only associating them
closely around it; and the compressed particles are as free to move from
the platina, being replaced by other particles, as a portion of dense air
upon the surface of the globe, or at the bottom of a deep mine, is free to
move by the slightest impulse, into the upper and rarer parts of the
atmosphere.
632. It can hardly be necessary to give any reasons why platina does not
show this effect under ordinary circumstances. It is then not sufficiently
clean (617.), and the gases are prevented from touching it, and suffering
that degree of effect which is needful to commence their combination at
common temperatures, and which they can only experience at its surface. In
fact, the very power which causes the combination of oxygen and hydrogen,
is competent, under the usual casual exposure of platina, to condense
extraneous matters upon its surface, which soiling it, take away for the
time its power of combining oxygen and hydrogen, by preventing their
contact with it (598.).
633. Clean platina, by which I mean such as has been made the positive pole
of a pile (570.), or has been treated with acid (605.), and has then been
put into distilled water for twelve or fifteen minutes, has a _peculiar
friction_ when one piece is rubbed against another. It wets freely with
pure water, even after it has been shaken and dried by the heat of a
spirit-lamp; and if made the pole of a voltaic pile in a dilute acid, it
evolves minute bubbles from every part of its surface. But platina in its
common state wants that peculiar friction: it will not wet freely with
water as the clean platina does; and when made the positive pole of a pile,
it for a time gives off large bubbles, which seem to cling or adhere to the
metal, and are evolved at distinct and separate points of the surface.
These appearances and effects, as well as its want of power on oxygen and
hydrogen, are the consequences, and the indications, of a soiled surface.
634. I found also that platina plates which had been cleaned perfectly soon
became soiled by mere exposure to the air; for after twenty-four hours they
no longer moistened freely with water, but the fluid ran up into portions,
leaving part of the surface bare, whilst other plates which had been
retained in water for the same time, when they were dried (580.) did
moisten, and gave the other indications of a clean surface.
635. Nor was this the case with platina or metals only, but also with
earthy bodies, Rock crystal and obsidian would not wet freely upon the
surface, but being moistened with strong oil of vitriol, then washed, and
left in distilled water to remove all the acid, they did freely become
moistened, whether they were previously dry or whether they were left wet;
but being dried and left exposed to the air for twenty-four hours, their
surface became so soiled that water would not then adhere freely to it, but
ran up into partial portions. Wiping with a cloth (even the cleanest) was
still worse than exposure to air; the surface either of the minerals or
metals immediately became as if it were slightly greasy. The floating upon
water of small particles of metals under ordinary circumstances is a
consequence of this kind of soiled surface. The extreme difficulty of
cleaning the surface of mercury when it has once been soiled or greased, is
due to the same cause.
636. The same reasons explain why the power of the platina plates in some
circumstances soon disappear, and especially upon use: MM. Dulong and
Thenard have observed the same effect with the spongy metal[A], as indeed
have all those who have used Döbereiner's instantaneous light machines. If
left in the air, if put into ordinary distilled water, if made to act upon
ordinary oxygen and hydrogen, they can still find in all these cases _that_
minute portion of impurity which, when once in contact with the surface of
the platina, is retained there, and is sufficient to prevent its full
action upon oxygen and hydrogen at common temperatures: a slight elevation
of temperature is again sufficient to compensate this effect, and cause
combination.
[A] Annales de Chimie, tom. xxiv. p. 386.
637. No state of a solid body can be conceived more favourable for the
production of the effect than that which is possessed by platina obtained
from the ammonio-muriate by heat. Its surface is most extensive and pure,
yet very accessible to the gases brought in contact with it: if placed in
impurity, the interior, as Thenard and Dulong have observed, is preserved
clean by the exterior; and as regards temperature, it is so bad a conductor
of heat, because of its divided condition, that almost all which is evolved
by the combination of the first portions of gas is retained within the
mass, exalting the tendency of the succeeding portions to combine.
* * * * *
638. I have now to notice some very extraordinary interferences with this
phenomenon, dependent, not upon the nature or condition of the metal or
other acting solid, but upon the presence of certain substances mingled
with the gases acted upon; and as I shall have occasion to speak frequently
of a mixture of oxygen and hydrogen, I wish it always to be understood that
I mean a mixture composed of one volume of oxygen to two volumes of
hydrogen, being the proportions that form water. Unless otherwise
expressed, the hydrogen was always that obtained by the action of dilute
sulphuric acid on pure zinc, and the oxygen that obtained by the action of
heat from the chlorate of potassa.
639. Mixtures of oxygen and hydrogen with _air_, containing one-fourth,
one-half, and even two-thirds of the latter, being introduced with prepared
platina plates (570. 605.) into tubes, were acted upon almost as well as if
no air were present: the retardation was far less than might have been
expected from the mere dilution and consequent obstruction to the contact
of the gases with the plates. In two hours and a half nearly all the oxygen
and hydrogen introduced as mixture was gone.
640. But when similar experiments were made with _olefiant gas_ (the
platina plates having been made the positive poles of a voltaic pile (570.)
in acid), very different results occurred. A mixture was made of 29.2
volumes hydrogen and 14.6 volumes oxygen, being the proportions for water;
and to this was added another mixture of 3 volumes oxygen and one volume
olefiant gas, so that the olefiant gas formed but 1/40th part of the whole;
yet in this mixture the platina plate would not act in forty-five hours.
The failure was not for want of any power in the plate, for when after that
time it was taken out of this mixture and put into one of oxygen and
hydrogen, it immediately acted, and in seven minutes caused explosion of
the gas. This result was obtained several times, and when larger
proportions of olefiant gas were used, the action seemed still more
hopeless.
641. A mixture of forty-nine volumes oxygen and hydrogen (638.) with one
volume of olefiant gas had a well-prepared platina plate introduced. The
diminution of gas was scarcely sensible at the end of two hours, during
which it was watched; but on examination twenty-four hours afterwards, the
tube was found blown to pieces. The action, therefore, though it had been
very much retarded, had occurred at last, and risen to a maximum.
642. With a mixture of ninety-nine volumes of oxygen and hydrogen (638.)
with one of olefiant gas, a feeble action was evident at the end of fifty
minutes; it went on accelerating (630.) until the eighty-fifth minute, and
then became so intense that the gas exploded. Here also the retarding
effect of the olefiant gas was very beautifully illustrated.
643. Plates prepared by alkali and acid (605.) produced effects
corresponding to those just described.
644. It is perfectly clear from these experiments, that _olefiant gas_,
even in small quantities, has a very remarkable influence in preventing the
combination of oxygen and hydrogen under these circumstances, and yet
without at all injuring or affecting the power of the platina.
645. Another striking illustration of similar interference may be shown in
_carbonic oxide_; especially if contrasted with _carbonic acid_. A mixture
of one volume oxygen and hydrogen (638.) with four volumes of carbonic acid
was affected at once by a platina plate prepared with acid, &c. (605.); and
in one hour and a quarter nearly all the oxygen and hydrogen was gone.
Mixtures containing less carbonic acid were still more readily affected.
646. But when carbonic oxide was substituted for the carbonic acid, not the
slightest effect of combination was produced; and when the carbonic oxide
was only one-eighth of the whole volume, no action occurred in forty and
fifty hours. Yet the plates had not lost their power; for being taken out
and put into pure oxygen and hydrogen, they acted well and at once.
647. Two volumes of carbonic oxide and one of oxygen were mingled with nine
volumes of oxygen and hydrogen (638.). This mixture was not affected by a
plate which had been made positive in acid, though it remained in it
fifteen hours. But when to the same volumes of carbonic oxide and oxygen
were added thirty-three volumes of oxygen and hydrogen, the carbonic oxide
being then only 1/18th part of the whole, the plate acted, slowly at first,
and at the end of forty-two minutes the gases exploded.
648. These experiments were extended to various gases and vapours, the
general results of which may be given as follow. Oxygen, hydrogen,
nitrogen, and nitrous oxide, when used to dilute the mixture of oxygen and
hydrogen, did not prevent the action of the plates even when they made
four-fifths of the whole volume of gas acted upon. Nor was the retardation
so great in any case as might have been expected from the mere dilution of
the oxygen and hydrogen, and the consequent mechanical obstruction to its
contact with the platina. The order in which carbonic acid and these
substances seemed to stand was as follows, the first interfering least with
the action; _nitrous oxide, hydrogen, carbonic acid, nitrogen, oxygen_: but
it is possible the plates were not equally well prepared in all the cases,
and that other circumstances also were unequal; consequently more numerous
experiments would be required to establish the order accurately.
649. As to cases of _retardation_, the powers of olefiant gas and carbonic
oxide have been already described. Mixtures of oxygen and hydrogen,
containing from 1/16th to 1/20th of sulphuretted hydrogen or phosphuretted
hydrogen, seemed to show a little action at first, but were not further
affected by the prepared plates, though in contact with them for seventy
hours. When the plates were removed they had lost all power over pure
oxygen and hydrogen, and the interference of these gases was therefore of a
different nature from that of the two former, having permanently affected
the plate.
650. A small piece of cork was dipped in sulphuret of carbon and passed up
through water into a tube containing oxygen and hydrogen (638.), so as to
diffuse a portion of its vapour through the gases. A plate being introduced
appeared at first to act a little, but after sixty-one hours the diminution
was very small. Upon putting the same plate into a pure mixture of oxygen
and hydrogen, it acted at once and powerfully, having apparently suffered
no diminution of its force.
651. A little vapour of ether being mixed with the oxygen and hydrogen
retarded the action of the plate, but did not prevent it altogether. A
little of the vapour of the condensed oil-gas liquor[A] retarded the action
still more, but not nearly so much as an equal volume of olefiant gas would
have done. In both these cases it was the original oxygen and hydrogen
which combined together, the ether and the oil-gas vapour remaining
unaffected, and in both cases the plates retained the power of acting on
fresh oxygen and hydrogen.
[A] Philosophical Transactions, 1825, p.440.
652. Spongy platina was then used in place of the plates, and jets of
hydrogen mingled with the different gases thrown against it in air. The
results were exactly of the same kind, although presented occasionally in a
more imposing form. Thus, mixtures of one volume of olefiant gas or
carbonic oxide with three of hydrogen could not heat the spongy platina
when the experiments were commenced at common temperatures; but a mixture
of equal volumes of nitrogen and hydrogen acted very well, causing
ignition. With carbonic acid the results were still more striking. A
mixture of three volumes of that gas with one of hydrogen caused _ignition_
of the platina, yet that mixture would not continue to burn from the jet
when attempts were made to light it by a taper. A mixture even of _seven_
volumes of carbonic acid and _one_ of hydrogen will thus cause the ignition
of cold spongy platina, and yet, as if to supply a contrast, than which
none can be greater, _it cannot burn at a taper_, but causes the extinction
of the latter. On the other hand, the mixtures of carbonic oxide or
olefiant gas, which can do nothing with the platina, are _inflamed_ by the
taper, burning well.
653. Hydrogen mingled with the vapour of ether or oil-gas liquor causes the
ignition of the spongy platina. The mixture with oil-gas burns with a flame
far brighter than that of the mixture of hydrogen and olefiant gas already
referred to, so that it would appear that the retarding action of the
hydrocarbons is not at all in proportion merely to the quantity of carbon
present.
654. In connexion with these interferences, I must state, that hydrogen
itself, prepared from steam passed over ignited iron, was found when
mingled with oxygen to resist the action of platina. It had stood over
water seven days, and had lost all fetid smell; but a jet of it would not
cause the ignition of spongy platina, commencing at common temperatures;
nor would it combine with oxygen in a tube either under the influence of a
prepared plate or of spongy platina. A mixture of one volume of this gas
with three of pure hydrogen, and the due proportion of oxygen, was not
affected by plates after fifty hours. I am inclined to refer the effect to
carbonic oxide present in the gas, but have not had time to verify the
suspicion. The power of the plates was not destroyed (640. 646.).
655. Such are the general facts of these remarkable interferences. Whether
the effect produced by such small quantities of certain gases depends upon
any direct action which they may exert upon the particles of oxygen and
hydrogen, by which the latter are rendered less inclined to combine, or
whether it depends upon their modifying the action of the plate temporarily
(for they produce no real change on it), by investing it through the agency
of a stronger attraction than that of the hydrogen, or otherwise, remains
to be decided by more extended experiments.
* * * * *
656. The theory of action which I have given for the original phenomena
appears to me quite sufficient to account for all the effects by reference
to known properties, and dispenses with the assumption of any new power of
matter. I have pursued this subject at some length, as one of great
consequence, because I am convinced that the superficial actions of matter,
whether between two bodies, or of one piece of the same body, and the
actions of particles not directly or strongly in combination, are becoming
daily more and more important to our theories of chemical as well as
mechanical philosophy[A]. In all ordinary cases of combustion it is evident
that an action of the kind considered, occurring upon the surface of the
carbon in the fire, and also in the bright part of a flame, must have great
influence over the combinations there taking place.
[A] As a curious illustration of the influence of mechanical forces
over chemical affinity, I will quote the refusal of certain substances
to effloresce when their surfaces are perfect, which yield immediately
upon the surface being broken, If crystals of carbonate of soda, or
phosphate of soda, or sulphate of soda, having no part of their
surfaces broken, be preserved from external violence, they will not
effloresce. I have thus retained crystals of carbonate of soda
perfectly transparent and unchanged from September 1827 to January
1833; and crystals of sulphate of soda from May 1832 to the present
time, November 1833. If any part of the surface were scratched or
broken, then efflorescence began at that part, and covered the whole.
The crystals were merely placed in evaporating basins and covered with
paper.
657. The condition of elasticity upon the exterior of the gaseous or
vaporous mass already referred to (626. 627.), must be connected directly
with the action of solid bodies, as nuclei, on vapours, causing
condensation upon them in preference to any condensation in the vapours
themselves; and in the well-known effect of nuclei on solutions a similar
condition may have existence (623.), for an analogy in condition exists
between the parts of a body in solution, and those of a body in the
vaporous or gaseous state. This thought leads us to the consideration of
what are the respective conditions at the surfaces of contact of two
portions of the same substance at the same temperature, one in the solid or
liquid, and the other in the vaporous state; as, for instance, steam and
water. It would seem that the particles of vapour next to the particles of
liquid are in a different relation to the latter to what they would be with
respect to any other liquid or solid substance; as, for instance, mercury
or platina, if they were made to replace the water, i.e. if the view of
independent action which I have taken (626. 627.) as a consequence of
Dalton's principles, be correct. It would also seem that the mutual
relation of similar particles, and the indifference of dissimilar particles
which Dalton has established as a matter of fact amongst gases and vapours,
extends to a certain degree amongst solids and fluids, that is, when they
are in relation by contact with vapours, either of their own substance or
of other bodies. But though I view these points as of great importance with
respect to the relations existing between different substances and their
physical constitution in the solid, liquid, or gaseous state, I have not
sufficiently considered them to venture any strong opinions or statements
here[A].
[A] In reference to this paragraph and also 626, see a correction by
Dr. C. Henry, in his valuable paper on this curious subject.
Philosophical Magazine, 1835. vol. vi. p. 305.--_Dec. 1838._
658. There are numerous well-known cases, in which substances, such as
oxygen and hydrogen, act readily in their _nascent_ state, and produce
chemical changes which they are not able to effect if once they have
assumed the gaseous condition. Such instances are very common at the poles
of the voltaic pile, and are, I think, easily accounted for, if it be
considered that at the moment of separation of any such particle it is
entirely surrounded by other particles of a _different_ kind with which it
is in close contact, and has not yet assumed those relations and conditions
which it has in its fully developed state, and which it can only assume by
association with other particles of its own kind. For, at the moment, its
elasticity is absent, and it is in the same relation to particles with
which it is in contact, and for which it has an affinity, as the particles
of oxygen and hydrogen are to each other on the surface of clean platina
(626. 627.).
659. The singular effects of retardation produced by very small quantities
of some gases, and not by large quantities of others (640. 645. 652.), if
dependent upon any relation of the added gas to the surface of the solid,
will then probably be found immediately connected with the curious
phenomena which are presented by different gases when passing through
narrow tubes at low pressures, which I observed many years ago[A]; and this
action of surfaces must, I think, influence the highly interesting
phenomena of the diffusion of gases, at least in the form in which it has
been experimented upon by Mr. Graham in 1829 and 1831[B], and also by Dr.
Mitchell of Philadelphia[C] in 1830. It seems very probable that if such a
substance as spongy platina were used, another law for the diffusion of
gases under the circumstances would come out than that obtained by the use
of plaster of Paris.
[A] Quarterly Journal of Science, 1819, vol. vii. p. 106.
[B] Quarterly Journal of Science, vol. xxviii. p. 74, and Edinburgh
Transactions, 1831.
[C] Journal of the Royal Institution for 1831, p. 101.
660. I intended to have followed this section by one on the secondary piles
of Ritter, and the peculiar properties of the poles of the pile, or of
metals through which electricity has passed, which have been observed by
Ritter, Van Marum, Yelin, De la Rive, Marianini, Berzelius, and others. It
appears to me that all these phenomena bear a satisfactory explanation on
known principles, connected with the investigation just terminated, and do
not require the assumption of any new state or new property. But as the
experiments advanced, especially those of Marianini, require very careful
repetition and examination, the necessity of pursuing the subject of
electro-chemical decomposition obliges me for a time to defer the
researches to which I have just referred.
_Royal Institution,
November 30, 1833._