OF ELECTRO-CHEMISTRY.
Electricity, like chemistry, is a modern science; for it can scarcely
claim an older origin than the termination of the first quarter of
the preceding century; and during the last half of that century, and
a small portion of the present, it participated with chemistry in the
zeal and activity with which it was cultivated by the philosophers
of Europe and America. For many years it was not suspected that any
connexion existed between chemistry and electricity; though some of the
meteorological phenomena, especially the production of clouds and the
formation of rain, which are obviously connected with chemistry, seem
likewise to claim some connexion with the agency of electricity.
The discovery of the intimate relation between chemistry and
electricity was one of the consequences of a controversy carried
on about the year 1790 between Galvani and Volta, two Italian
philosophers, whose discoveries will render their names immortal.
Galvani, who was a professor of anatomy, was engaged in speculations
respecting muscular motion. He was of opinion that a peculiar fluid
was secreted in the brain, which was sent along the nerves to all
the different parts of the body. This nervous fluid possessed many
characters analogous to those of electricity: the muscles were capable
of being charged with it somewhat like a Leyden phial; and it was by
the discharge of this accumulation, by the voluntary power of the
nerves, that muscular motion was produced. He accidently discovered,
that if the crural nerve going into the muscles of a frog, and the
crural muscles, be laid bare immediately after death, and a piece of
zinc be placed in contact with the nerve, and a piece of silver or
copper with the muscle; when these two pieces of metal are made to
touch each other, violent convulsions are produced in the muscle,
which cause the limb to move. He conceived that these convulsions were
produced by the discharge of the nervous energy from the muscles, in
consequence of the conducting power of the metals.
Volta, who repeated these experiments, explained them in a different
manner. According to him, the convulsions were produced by the passage
of a current of common electricity through the limb of the frog,
which was thrown into a state of convulsion merely in consequence of
its irritability. This irritability vanishes after the death of the
muscle; accordingly it is only while the principle of life remains that
the convulsions can be produced. Every metallic conductor, according
to him, possesses a certain electricity which is peculiar to it,
either positive or negative, though the quantity is so small, as to
be imperceptible, in the common state of the metal. But if a metal,
naturally positive, be placed in contact, while insulated, with a metal
naturally negative, the charge of electricity in both is increased by
induction, and becomes perceptible when the two metals are separated
and presented to a sufficiently delicate electrometer. Thus zinc is
naturally positive, and copper and silver naturally negative. If we
take two discs of copper and zinc, to the centre of each of which a
varnished glass handle is cemented, and after keeping them for a short
time in contact, separate them by the handles, and apply each to a
sufficiently delicate electrometer, we shall find that the zinc is
positive, and the silver or copper disc negative. When the silver and
copper are placed in contact while lying on the nerve and muscles of
the leg of a frog, the zinc becomes positive, and the silver negative,
by induction; but, as the animal substance is a conductor, this state
cannot continue: the two electricities pass through the conducting
muscles and nerve, and neutralize one another. And it is this current
which occasions the convulsions.
Such was Volta's simple explanation of the convulsions produced in
galvanic experiments in the limb of a frog. Galvani was far from
allowing the accuracy of it; and, in order to obviate the objection to
his reasoning advanced by Volta from the necessity of employing two
metals, he showed that the convulsions might, in certain cases, be
produced by one metal. Volta showed that a very small quantity of one
metal, either alloyed with, or merely in contact with another, were
capable of inducing the two electricities. But in order to prove in the
most unanswerable manner that the two electricities were induced when
two different metals were placed in contact, he contrived the following
piece of apparatus:
He procured a number (say 50) of pieces of zinc, about the size of
a crown-piece, and as many pieces of copper, and thirdly, the same
number of pieces of card of the same size. The cards were steeped in
a solution of salt, so as to be moist. He lays upon the table a piece
of zinc, places over it a piece of copper, and then a piece of moist
card. Over the card is placed a second piece of zinc, then a piece
of copper, then a piece of wet card. In this way all the pieces are
piled upon each other in exactly the same order, namely, zinc, copper,
card; zinc, copper, card; zinc, copper, card. So that the lowest plate
is zinc and the uppermost is copper (for the last wet card may be
omitted). In this way there are fifty pairs of zinc and copper plates
in contact, each separated by a piece of wet card, which is a conductor
of electricity. If you now moisten a finger of each hand with water,
and apply one wet finger to the lowest zinc plate, and the other to the
highest copper plate, the moment the fingers come in contact with the
plates an electric shock is felt, the intensity of which increases with
the number of pairs of plates in the pile. This is what is called the
Galvanic, or rather the Voltaic pile. It was made known to the public
in a paper by Volta, inserted in the Philosophical Transactions for
1800. This pile was gradually improved, by substituting troughs, first
of baked wood, and afterwards of porcelain, divided into as many cells
as there were pairs of plates. The size of the plates was increased;
they were made square, and instead of all being in contact, it was
found sufficient if they were soldered together by means of metallic
slips rising from one side of each square. The two plates thus soldered
were slipped over the diaphragm separating the contiguous cells, so
that the zinc plate was in one cell and the copper in the other. Care
was taken that the pairs were introduced all looking one way, so that
a copper plate had always a zinc plate immediately opposite to it.
The cells were filled with conducting liquid: brine, or a solution of
salt in vinegar, or dilute muriatic, sulphuric, or nitric acid, might
be employed; but dilute nitric acid was found to answer best, and the
energy of the battery is directly proportional to the strength of the
nitric acid employed.
Messrs. Nicholson and Carlisle were the first persons who repeated
Volta's experiments with this apparatus, which speedily drew the
attention of all Europe. They ascertained that the zinc end of the
pile was positive and the copper end negative. Happening to put a drop
of water on the uppermost plate, and to put into it the extremity
of a gold wire connected with the undermost plate, they observed an
extrication of air-bubbles from the wire. This led them to suspect that
the water was decomposed. To determine the point, they collected a
little of the gas extricated and found it hydrogen. They then attached
a gold wire to the zinc end of the pile, and another gold wire to the
copper end, and plunged the two wires into a glass of water, taking
care not to allow them to touch each other. Gas was extricated from
both wires. On collecting that from the wire attached to the zinc end,
it was found to be _oxygen gas_, while that from the copper end was
hydrogen gas. The volume of hydrogen gas extricated was just double
that of the oxygen gas; and the two gases being mixed, and an electric
spark passed through them, they burnt with an explosion, and were
completely converted into water. Thus it was demonstrated that water
was decomposed by the action of the pile, and that the oxygen was
extricated from the positive pile and the hydrogen from the negative.
This held when the communicating wires were gold or platinum; but
if they were of copper, silver, iron, lead, tin, or zinc, then only
hydrogen gas was extricated from the negative wire. The positive wire
extricated little or no gas; but it was rapidly oxidized. Thus the
connexion between chemical decompositions and electrical currents was
first established.
It was soon after observed by Henry, Haldane, Davy, and other
experimenters, that other chemical compounds were decomposed by the
electrical currents as well as water. Ammonia, for example, nitric
acid, and various salts, were decomposed by it. In the year 1803 an
important set of experiments was published by Berzelius and Hisinger.
They decomposed eleven different salts, by exposing them to the action
of a current of electricity. The salts were dissolved in water, and
iron or silver wires from the two poles of the pile were plunged into
the solution. In every one of these decompositions, the acid was
deposited round the positive wire, and the base of the salt round the
negative wire. When ammonia was decomposed by the action of galvanic
electricity, the azotic gas separated from the positive wire, and the
hydrogen gas from the negative.
But it was Davy that first completely elucidated the chemical
decompositions produced by galvanic electricity, who first explained
the laws by which these decompositions were regulated, and who employed
galvanism as an instrument for decomposing various compounds, which had
hitherto resisted all the efforts of chemists to reduce them to their
elements. These discoveries threw a blaze of light upon the obscurest
parts of chemistry, and secured for the author of them an immortal
reputation.
Humphry Davy, to whom these splendid discoveries were owing, was born
at Penzance, in Cornwall, in the year 1778. He displayed from his very
infancy a spirit of research, and a brilliancy of fancy, which augured,
even at that early period, what he was one day to be. When very
young, he was bound apprentice to an apothecary in his native town.
Even at that time, his scientific acquirements were so great, that
they drew the attention of Mr. Davis Gilbert, the late distinguished
president of the Royal Society. It was by his advice that he resolved
to devote himself to chemistry, as the pursuit best calculated to
procure him celebrity. About this time Mr. Gregory Watt, youngest son
of the celebrated improver of the steam-engine, happening to be at
Penzance, met with young Davy, and was delighted with the uncommon
knowledge which he displayed, at the brilliancy of his fancy, and
the great dexterity and ardour with which, under circumstances the
most unfavourable, he was prosecuting his scientific investigations.
These circumstances made an indelible impression on his mind, and led
him to recommend Davy as the best person to superintend the Bristol
Institution for trying the medicinal effects of the gases.
After the discovery of the different gases, and the investigation of
their properties by Dr. Priestley, it occurred to various individuals,
nearly about the same time, that the employment of certain gases, or
at least of mixtures of certain gases, with common air in respiration,
instead of common air, might be powerful means of curing diseases.
Dr. Beddoes, at that time professor of chemistry at Oxford, was one
of the keenest supporters of these opinions. Mr. Watt, of Birmingham,
and Mr. Wedgewood, entertained similar sentiments. About the beginning
of the present century, a sum of money was raised by subscription,
to put these opinions to the test of experiment; and, as Dr. Beddoes
had settled as a physician in Bristol, it was agreed upon that the
experimental investigation should take place at Bristol. But Dr.
Beddoes was not qualified to superintend an institution of the kind:
it was necessary to procure a young man of zeal and genius, who would
take such an interest in the investigation as would compensate for
the badness of the apparatus and the defects of the arrangements. The
greatest part of the money had been subscribed by Mr. Wedgewood and
Mr. Watt: their influence of course would be greatest in recommending
a proper superintendent. Gregory Watt thought of Mr. Davy, whom he
had lately been so highly pleased with, and recommended him with
much zeal to superintend the undertaking. This recommendation being
seconded by that of Mr. Davis Gilbert, who was so well acquainted
with the scientific acquirements and genius of Davy, proved
successful, and Davy accordingly got the appointment. At Bristol he
was employed about a year in investigating the effects of the gases
when employed in respiration. But he did not by any means confine
himself to this, which was the primary object of the institution;
but investigated the properties and determined the composition of
nitric acid, ammonia, protoxide of azote and deutoxide of azote.
The fruit of his investigations was published in 1800, in a volume
entitled, "Researches, Chemical and Philosophical; chiefly concerning
Nitrous Oxide, or Dephlogisticated Nitrous Air, and its Respiration."
This work gave him at once a high reputation as a chemist, and was
really a wonderful performance, when the circumstances under which
it was produced are taken into consideration. He had discovered the
intoxicating effects which protoxide of azote (nitrous oxide) produces
when breathed, and had tried their effects upon a great number of
individuals. This fortunate discovery perhaps contributed more to his
celebrity, and to his subsequent success, than all the sterling merit
of the rest of his researches--so great is the effect of display upon
the greater part of mankind.
A few years before, a philosophical institution had been established
in London, under the auspices of Count Rumford, which had received
the name of the Royal Institution. Lectures on chemistry and natural
philosophy were delivered in this institution; a laboratory was
provided, and a library established. The first professor appointed to
this institution, Dr. Garnet, had been induced, in consequence of some
disagreement between him and Count Rumford, to throw up his situation.
Many candidates started for it; but Davy, in consequence of the
celebrity which he had acquired by his researches, or perhaps by the
intoxicating effects of protoxide of azote, which he had discovered,
was, fortunately for the institution and for the reputation of England,
preferred to them all. He was appointed professor of chemistry, and Dr.
Thomas Young professor of natural philosophy, in the year 1801. Davy,
either from the more popular nature of his subject, or from his greater
oratorical powers, became at once a popular lecturer, and always
lectured to a crowded room; while Dr. Young, though both a profound and
clear lecturer, could scarcely command an audience of a dozen. It was
here that Davy laboured with unwearied industry during eleven years,
and acquired, by his discoveries the highest reputation of any chemist
in Europe.
In 1811 he was knighted, and soon after married Mrs. Apreece, a widow
lady, daughter of Mr. Ker, who had been secretary to Lord Rodney, and
had made a fortune in the West Indies. He was soon after created a
baronet. About this time he resigned his situation as professor of
chemistry in the Royal Institution, and went to the continent. He
remained for some years in France and Italy. In the year 1821, when Sir
Joseph Banks died, a very considerable number of the fellows offered
their votes to Dr. Wollaston; but he declined standing as a candidate
for the president's chair. Sir Humphry Davy, on the other hand, was
anxious to obtain that honourable situation, and was accordingly
elected president by a very great majority of votes on the 30th of
November, 1821. This honourable situation he filled about seven years;
but his health declining, he was induced to resign in 1828, and to go
to Italy. Here he continued till 1829, when feeling himself getting
worse, and wishing to draw his last breath in his own country, he began
to turn his way homewards; but at Geneva he felt himself so ill, that
he was unable to proceed further: here he took to his bed, and here he
died on the 29th of May, 1829.
It was his celebrated paper "On some chemical Agencies of Electricity,"
inserted in the Philosophical Transactions for 1807, that laid the
foundation of the high reputation which he so deservedly acquired. I
consider this paper not merely as the best of all his own productions,
but as the finest and completest specimen of inductive reasoning
which appeared during the age in which he lived. It had been already
observed, that when two platinum wires from the two poles of a galvanic
pile are plunged each into a vessel of water, and the two vessels
united by means of wet asbestos, or any other conducting substance,
an _acid_ appeared round the positive wire and an _alkali_ round the
negative wire. The alkali was said by some to be _soda_, by others
to be _ammonia_. The acid was variously stated to be _nitric acid_,
_muriatic acid_, or even _chlorine_. Davy demonstrated, by decisive
experiments, that in all cases the acid and alkali are derived from
the decomposition of some salt contained either in the water or in
the vessel containing the water. Most commonly the salt decomposed
is common salt, because it exists in water and in agate, basalt, and
various other stony bodies, which he employed as vessels. When the same
agate cup was used in successive experiments, the quantity of acid
and alkali evolved diminished each time, and at last no appreciable
quantity could be perceived. When glass vessels were used, soda was
disengaged at the expense of the glass, which was sensibly corroded.
When the water into which the wires were dipped was perfectly pure,
and when the vessel containing it was free from every trace of saline
matter, no acid or alkali made its appearance, and nothing was evolved
except the constituents of water, namely, oxygen and hydrogen; the
oxygen appearing round the positive wire, and the hydrogen round the
negative wire.
When a salt was put into the vessel in which the positive wire dipped,
the vessel into which the negative wire dipped being filled with
pure water, and the two vessels being united by means of a slip of
moistened asbestos, the acid of the salt made its appearance round the
positive wire, and the alkali round the negative wire, before it could
be detected in the intermediate space; but if an intermediate vessel,
containing a substance for which the alkali has a strong affinity, be
placed between these two vessels, the whole being united by means of
slips of asbestos, then great part, or even the whole of the alkali,
was stopped in this intermediate vessel. Thus, if the salt was nitrate
of barytes, and sulphuric acid was placed in the intermediate vessel,
much sulphate of barytes was deposited in the intermediate vessel, and
very little or even no barytes made its appearance round the negative
wire. Upon this subject a most minute, extensive, and satisfactory
series of experiments was made by Davy, leaving no doubt whatever of
the accuracy of the fact.
The conclusions which he drew from these experiments are, that all
substances which have a chemical affinity for each other, are in
different states of electricity, and that the degree of affinity is
proportional to the intensity of these opposite states. When such
a compound body is placed in contact with the poles of a galvanic
battery, the positive pole attracts the constituent, which is
negative, and repels the positive. The negative acts in the opposite
way, attracting the positive constituent and repelling the negative.
The more powerful the battery, the greater is the force of these
attractions and repulsions. We may, therefore, by increasing the
energy of a battery sufficiently, enable it to decompose any compound
whatever, the negative constituent being attracted by the positive
pole, and the positive constituent by the negative pole. Oxygen,
chlorine, bromine, iodine, cyanogen, and acids, are _negative_ bodies;
for they always appear round the _positive_ pole of the battery, and
are therefore attracted to it: while hydrogen, azote, carbon, selenium,
metals, alkalies, earths, and oxide bases, are deposited round the
negative pole, and consequently are _positive_.
According to this view of the subject, chemical affinity is merely
a case of the attractions exerted by bodies in different states of
electricity. Volta first broached the idea, that every body possesses
naturally a certain state of electricity. Davy went a step further,
and concluded, that the attractions which exist between the atoms of
different bodies are merely the consequence of these different states
of electricity. The proof of this opinion is founded on the fact, that
if we present to a compound, sufficiently strong electrical poles, it
will be separated into its constituents, and one of these constituents
will invariably make its way to the positive and the other to the
negative pole. Now bodies in a state of electrical excitement always
attract those that are in the opposite state.
If electricity be considered as consisting of two distinct fluids,
which attract each other with a force inversely, as the square of the
distance, while the particles of each fluid repel each other with a
force varying according to the same law, then we must conclude that
the atoms of each body are covered externally with a coating of some
one electric fluid to a greater or smaller extent. Oxygen and the
other supporters of combustion are covered with a coating of negative
electricity; while hydrogen, carbon, and the metals, are covered with
a coating of positive electricity. What is the cause of the adherence
of the electricity to these atoms we cannot explain. It is not owing to
an attraction similar to gravitation; for electricity never penetrates
into the interior of bodies, but spreads itself only on the surface,
and the quantity of it which can accumulate is not proportional to
the quantity of matter but to the extent of surface. But whatever be
the cause, the adhesion is strong, and seemingly cannot be overcome.
If we were to suppose an atom of any body, of oxygen for example, to
remain uncombined with any other body, but surrounded by electricity,
it is obvious that the coating of negative electricity on its surface
would be gradually neutralized by its attracting and combining with
positive electricity. But let us suppose an atom of oxygen and an atom
of hydrogen to be united together, it is obvious that the positive
electricity of the one atom would powerfully attract the negative
electricity of the other, and _vice versâ_. And if these respective
electricities cannot leave the atoms, the two atoms will remain firmly
united, and the opposite electrical intensities will in some measure
neutralize each other, and thus prevent them from being neutralized
by electricity from any other quarter. But a current of the opposite
electricities passing through such a compound, might neutralize the
electricity in each, and thus putting an end to their attractions,
occasion decomposition.
Such is a very imperfect outline of the electrical theory of affinity
first proposed by Davy to account for the decompositions produced by
electricity. It has been universally adopted by chemists; and some
progress has been made in explaining and accounting for the different
phenomena. It would be improper, in a work of this kind, to enter
further into the subject. Those who are interested in such discussions
will find a good deal of information in the first volume of Berzelius's
Treatise on Chemistry, in the introduction to the Traité de Chimie
appliqué aux Arts, by Dumas, or in the introduction to my System of
Chemistry, at present in the press.
Davy having thus got possession of an engine, by means of which the
compounds, whose constituents adhered to each other might be separated,
immediately applied it to the decomposition of potash and soda;
bodies which were admitted to be compounds, though all attempts to
analyze them had hitherto failed. His attempt was successful. When
a platinum wire from the negative pole of a strong battery in full
action was applied to a lump of potash, slightly moistened, and lying
on a platinum tray attached to the positive pole of the battery, small
globules of a white metal soon appeared at its extremity. This white
metal he speedily proved to be the basis of potash. He gave it the name
of _potassium_, and very soon proved, that potash is a compound of five
parts by weight of this metal and one part of oxygen. Potash, then,
is a metallic oxide. He proved soon after that soda is a compound of
oxygen and another white metal, to which he gave the name of _sodium_.
Lime is a compound of _calcium_ and oxygen, magnesia of _magnesium_ and
oxygen, barytes of _barium_ and oxygen, and strontian of _strontium_
and oxygen. In short, the fixed alkalies and alkaline earths, are
metallic oxides. When _lithia_ was afterwards discovered by Arfvedson,
Davy succeeded in decomposing it also by the galvanic battery, and
resolving it into oxygen and a white metal, to which the name of
_lithium_ was given.
Davy did not succeed so well in decomposing alumina, glucina, yttria,
and zirconia, by the galvanic battery: they were not sufficiently good
conductors of electricity; but nobody entertained any doubt that they
also were metallic oxides. They have been all at length decomposed, and
their bases obtained by the joint action of chlorine and potassium,
and it has been demonstrated, that they also are metallic oxides. Thus
it has been ascertained, in consequence of Davy's original discovery
of the powers of the galvanic battery, that all the bases formerly
distinguished into the four classes of alkalies, alkaline earths,
earths proper, and metallic oxides, belong in fact only to one class,
and are all metallic oxides.
Important as these discoveries are, and sufficient as they would
have been to immortalize the author of them, they are not the only
ones for which we are indebted to Sir Humphry Davy. His experiments
on _chlorine_ are not less interesting or less important in their
consequences. I have already mentioned in a former chapter, that
Berthollet made a set of experiments on chlorine, from which he had
drawn as a conclusion, that it is a compound of oxygen and muriatic
acid, in consequence of which it got the name of _oxymuriatic acid_.
This opinion of Berthollet had been universally adopted by chemists,
and admitted by them as a fundamental principle, till Gay-Lussac
and Thenard endeavoured, unsuccessfully, to decompose this gas, or
to resolve it into muriatic acid and chlorine. They showed, in the
clearest manner, that such a resolution was impossible, and that no
direct evidence could be adduced to prove that oxygen was one of its
constituents. The conclusion to which they came was, that muriatic acid
gas contained water as an essential constituent; and they succeeded by
this hypothesis in accounting for all the different phenomena which
they had observed. They even made an experiment to determine the
quantity of water thus combined. They passed muriatic acid through hot
litharge (protoxide of lead); muriate of lead was formed, and abundance
of water made its appearance and was collected. They did not attempt to
determine the proportions; but we can now easily calculate the quantity
of water which would be deposited when a given weight of muriatic acid
gas is absorbed by a given weight of litharge. Suppose we have fourteen
parts of oxide of lead: to convert it into muriate of lead, 4·625
parts (by weight) of muriatic acid would be necessary, and during the
formation of the muriate of lead there would be deposited 1·125 parts
of water. So that from this experiment it might be concluded, that
about one-fourth of the weight of muriatic acid gas is water.
The very curious and important facts respecting chlorine and muriatic
acid gas which they had ascertained, were made known by Gay-Lussac
and Thenard to the Institute, on the 27th of February, 1809, and an
abstract of them was published in the second volume of the Mémoires
d'Arcueil. There can be little doubt that it was in consequence of
these curious and important experiments of the French chemists that
Davy's attention was again turned to muriatic acid gas. He had already,
in 1808, shown that when potassium is heated in muriatic acid gas,
muriate of potash is formed, and a quantity of hydrogen gas evolved,
amounting to more than one-third of the muriatic acid gas employed,
and he had shown, that in no case can muriatic acid be obtained from
chlorine, unless water or its elements be present. This last conclusion
had been amply confirmed by the new investigations of Gay-Lussac and
Thenard. In 1810 Davy again resumed the examination of the subject, and
in July of that year read a paper to the Royal Society, to prove that
_chlorine_ is a simple substance, and that muriatic acid is a compound
of _chlorine_ and _hydrogen_.
This was introducing an alteration in chemical theory of the same
kind, and nearly as important, as was introduced by Lavoisier, with
respect to the action of oxygen in the processes of combustion and
calcination. It had been previously supposed that sulphur, phosphorus,
charcoal, and metals, were compounds; one of the constituents of which
was phlogiston, and the other the acids or oxides which remained after
the combustion or calcination had taken place. Lavoisier showed that
the sulphur, phosphorus, charcoal, and metals, were simple substances;
and that the acids or calces formed were compounds of these simple
bodies and oxygen. In like manner, Davy showed that chlorine, instead
of being a compound of muriatic acid and oxygen, was, in fact, a simple
substance, and muriatic acid a compound of chlorine and hydrogen.
This new doctrine immediately overturned the Lavoisierian hypothesis
respecting oxygen as the acidifying principle, and altered all the
previously received notions respecting the muriates. What had been
called _muriates_ were, in fact, combinations of chlorine with the
combustible or metal, and were analogous to oxides. Thus, when muriatic
acid gas was made to act upon hot litharge, a double decomposition
took place, the chlorine united to the lead, while the hydrogen of the
muriatic acid united with the oxygen of the litharge, and formed water.
Hence the reason of the appearance of water in this case; and hence it
was obvious that what had been called muriate of lead, was, in reality,
a compound of chlorine and metallic lead. It ought, therefore, to be
called, not muriate of lead, but chloride of lead.
It was not likely that this new opinion of Davy should be adopted by
chemists in general, without a struggle to support the old opinions.
But the feebleness of the controversy which ensued, affords a striking
proof how much chemistry had advanced since the days of Lavoisier, and
how free from prejudices chemists had become. One would have expected
that the French chemists would have made the greatest resistance to the
admission of these new opinions; because they had a direct tendency
to diminish the reputation of two of their most eminent chemists,
Lavoisier and Berthollet. But the fact was not so: the French chemists
showed a degree of candour and liberality which redounds highly to
their credit. Berthollet did not enter at all into the controversy.
Gay-Lussac and Thenard, in their Recherches Physico-chimiques,
published in 1811, state their reasons for preferring the old
hypothesis to the new, but with great modesty and fairness; and,
within less than a year after, they both adopted the opinion of Davy,
that chlorine is a simple substance, and muriatic acid a compound of
hydrogen and chlorine.
The only opponents to the new doctrine who appeared against it,
were Dr. John Murray, of Edinburgh, and Professor Berzelius, of
Stockholm. Dr. Murray was a man of excellent abilities, and a very
zealous cultivator of chemistry; but his health had been always very
delicate, which had prevented him from dedicating so much of his
time to experimenting as he otherwise would have been inclined to
do. The only experimental investigations into which he entered was
the analysis of some mineral waters. His powers of elocution were
great. He was, in consequence, a popular and very useful lecturer. He
published animadversions upon the new doctrine respecting _chlorine_,
in Nicholson's Journal; and his observations were answered by Dr. John
Davy.
Dr. John Davy was the brother of Sir Humphry, and had shown, by his
paper on fluoric acid and on the chlorides, that he possessed the same
dexterity and the same powers of inductive reasoning, which had given
so much celebrity to his brother. The controversy between him and Dr.
Murray was carried on for some time with much spirit and ingenuity
on both sides, and was productive of some advantage to the science
of chemistry, by the discovery of phosgene gas or chlorocarbonic
acid, which was made by Dr. Davy. It is needless to say to what
side the victory fell. The whole chemical world has for several
years unanimously adopted the theory of Davy; showing sufficiently
the opinion entertained respecting the arguments advanced by either
party. Berzelius supported the old opinion respecting the compound
nature of chlorine, in a paper which he published in the Annals of
Philosophy. No person thought it worth while to answer his arguments,
though Sir Humphry Davy made a few animadversions upon one or two of
his experiments. The discovery of iodine, which took place almost
immediately after, afforded so close an analogy with chlorine, and
the nature of the compounds which it forms was so obvious and so well
made out, that chemists were immediately satisfied; and they furnished
so satisfactory an answer to all the objections of Berzelius, that
I am not aware of any person, either in Great Britain or in France,
who adopted his opinions. I have not the same means of knowing the
impression which his paper made upon the chemists of Germany and
Sweden. Berzelius continued for several years a very zealous opponent
to the new doctrine, that chlorine is a simple substance. But he
became at last satisfied of the futility of his own objections, and
the inaccuracy of his reasoning. About the year 1820 he embraced the
opinion of Davy, and is now one of its most zealous defenders. Dr.
Murray has been dead for many years, and Berzelius has renounced his
notion, that muriatic acid is a compound of oxygen and an unknown
combustible basis. We may say then, I believe with justice, that at
present all the chemical world adopts the notion that chlorine is a
simple substance, and muriatic acid a compound of chlorine and hydrogen.
The recent discovery of bromine, by Balard, has added another strong
analogy in favour of Davy's theory; as has likewise the discovery by
Gay-Lussac respecting prussic acid. At present, then, (not reckoning
sulphuretted and telluretted hydrogen gas), we are acquainted with
four acids which contain no oxygen, but are compounds of hydrogen with
another negative body. These are
Muriatic acid, composed of chlorine and hydrogen
Hydriodic acid iodine and hydrogen
Hydrobromic acid bromine and hydrogen
Prussic acid cyanogen and hydrogen.
So that even if we were to leave out of view the chlorine acids, the
sulphur acids, &c., no doubt can be entertained that many acids exist
which contain no oxygen. Acids are compounds of electro-negative bodies
and a base, and in them all the electro-negative electricity continues
to predominate.
Next to Sir Humphry Davy, the two chemists who have most advanced
electro-chemistry are Gay-Lussac and Thenard. About the year 1808,
when the attention of men of science was particularly drawn towards
the galvanic battery, in consequence of the splendid discoveries of
Sir Humphry Davy, Bonaparte, who was at that time Emperor of France,
consigned a sufficient sum of money to Count Cessac, governor of the
Polytechnic School, to construct a powerful galvanic battery; and
Gay-Lussac and Thenard were appointed to make the requisite experiments
with this battery. It was impossible that a better choice could have
been made. These gentlemen undertook a most elaborate and extensive
set of experiments, the result of which was published in 1811, in two
octavo volumes, under the title of "Recherches Physico-chimiques,
faites sur la Pile; sur la Preparation chimique et les Propriétés du
Potassium et du Sodium; sur la Décomposition de l'Acide boracique;
sur les Acides fluorique, muriatique, et muriatique oxygené; sur
l'Action chimique de la Lumière; sur l'Analyse vegetale et animale,
&c." It would be difficult to name any chemical book that contains a
greater number of new facts, or which contains so great a collection of
important information, or which has contributed more to the advancement
of chemical science.
The first part contains a very minute and interesting examination
of the galvanic battery, and upon what circumstances its energy
depends. They tried the effect of various liquid conductors, varied
the strength of the acids and of the saline solutions. This division
of their labours contains much valuable information for the practical
electro-chemist, though it would be inconsistent with the plan of this
work to enter into details.
The next division of the work relates to potassium. Davy had hitherto
produced that metal only in minute quantities by the action of the
galvanic battery upon potash. But Gay-Lussac and Thenard contrived
a process by which it can be prepared on a large scale by chemical
decomposition. Their method was, to put into a bent gun-barrel, well
coated externally with clay, and passed through a furnace, a quantity
of clean iron-filings. To one extremity of this barrel was fitted a
tube containing a quantity of caustic potash. This tube was either shut
at one end by a stopper, or by a glass tube luted to it, and plunged
under the surface of mercury. To the other extremity of the gun-barrel
was also luted a tube, which plunged into a vessel containing mercury.
Heat was applied to the gun-barrel till it was heated to whiteness;
then, by means of a choffer, the caustic potash was melted and made to
trickle slowly into the white-hot iron-filings. At this temperature the
potash undergoes decomposition, the iron uniting with its oxygen. The
potassium is disengaged, and being volatile is deposited at a distance
from the hot part of the tube, where it is collected after the process
is finished.
Being thus in possession, both of potassium and sodium in considerable
quantities, they were enabled to examine its properties more in detail
than Davy had done: but such was the care and industry with which
Davy's experiments had been made that very little remained to be
done. The specific gravity of the two metals was determined with more
precision than it was possible for Davy to do. They determined the
action of these metals on water, and measured the quantity of hydrogen
gas given out with more precision than Davy could. They discovered
also, by heating these metals in oxygen gas, that they were capable of
uniting with an additional dose of oxygen, and of forming peroxides of
potassium and sodium. These oxides have a yellow colour, and give out
the surplus oxygen, and are brought back to the state of potash and
soda when they are plunged into water. They exposed a great variety of
substances to the action of potassium, and brought to light a vast
number of curious and important facts, tending to throw new light on
the properties and characters of that curious metallic substance.
By heating together anhydrous boracic acid and potassium in a copper
tube, they succeeded in decomposing the acid, and in showing it to
be a compound of oxygen, and a black matter like charcoal, to which
the name of _boron_ has been given. They examined the properties of
boron in detail, but did not succeed in determining with exactness
the proportions of the constituents of boracic acid. The subsequent
experiments of Davy, though not exact, come a good deal nearer the
truth.
Their experiments on fluoric acid are exceedingly valuable. They
first obtained that acid in a state of purity, and ascertained its
properties. Their attempts to decompose it as well as those of Davy,
ended in disappointment. But Ampere conceived the idea that this
acid, like muriatic acid, is a compound of hydrogen with an unknown
supporter of combustion, to which the name _fluorine_ was given.
This opinion was adopted by Davy, and his experiments, though they
do not absolutely prove the truth of the opinion, give it at least
considerable probability, and have disposed chemists in general to
adopt it. The subsequent researches of Berzelius, while they have added
a great deal to our former knowledge respecting fluoric acid and its
compounds, have all tended to confirm and establish the doctrine that
it is a hydracid, and similar in its nature to the other hydracids. But
such is the tendency of fluorine to combine with every substance, that
hitherto it has been impossible to obtain it in an insulated state. We
want therefore, still, a decisive proof of the accuracy of the opinion.
To the experiments of Gay-Lussac and Thenard on chlorine and muriatic
acid, I have already alluded in a former part of this chapter. It was
during their investigations connected with this subject, that they
discovered _fluoboric_ acid gas, which certainly adds considerably
to the probability of the theory of Ampere respecting the nature of
fluoric acid.
I pass over a vast number of other new and important facts and
observations contained in this admirable work, which ought to be
studied with minute attention by every person who aspires at becoming a
chemist.
Besides the numerous discoveries contained in the Recherches
Physico-chimique, Gay-Lussac is the author of two of so much importance
that it would be wrong to omit them. He showed that cyanogen is one
of the constituents of prussic acid; succeeded in determining the
composition of cyanogen, and showing it to be a compound of two
atoms of carbon and one atom of azote. Prussic acid is a compound of
one atom of hydrogen and one atom of cyanogen. Sulpho-cyanic acid,
discovered by Mr. Porrett, is a compound of one atom sulphuric, and
one atom cyanogen; chloro-cyanic acid, discovered by Berthollet, is
a compound of one atom chlorine and one atom cyanogen; while cyanic
acid, discovered by Wöhler, is a compound of one atom oxygen and
one atom cyanogen. I take no notice of the fulminic acid; because,
although Gay-Lussac's experiments are exceedingly ingenious, and his
reasoning very plausible, it is not quite convincing; especially as the
results obtained by Mr. Edmund Davy, and detailed by him in his late
interesting memoir on this subject, are somewhat different.
The other discovery of Gay-Lussac is his demonstration of the peculiar
nature of iodine, his account of iodic and hydriodic acids, and of
many other compounds into which that curious substance enters as a
constituent. Sir H. Davy was occupied with iodine at the same time with
Gay-Lussac; and his sagacity and inventive powers were too great to
allow him to work upon such a substance without discovering many new
and interesting facts.
To M. Thenard we are indebted for the discovery of the important fact,
that hydrogen is capable of combining with twice as much oxygen as
exists in water, and determining the properties of this curious liquid
which has been called deutoxide of hydrogen. It possesses bleaching
properties in perfection, and I think it likely that chlorine owes its
bleaching powers to the formation of a little deutoxide of hydrogen in
consequence of its action on water.
The mantle of Davy seems in some measure to have descended on Mr.
Faraday, who occupies his old place at the Royal Institution. He has
shown equal industry, much sagacity, and great powers of invention.
The most important discovery connected with electro-magnetism, next
to the great fact, for which we are indebted to Professor Œrstedt
of Copenhagen, is due to Mr. Faraday; I mean the rotation of the
electric wires round the magnet. To him we owe the knowledge of the
fact, that several of the gases can be condensed into liquids by the
united action of pressure and cold, which has removed the barrier that
separated gaseous bodies from vapours, and shown us that all owe their
elasticity to the same cause. To him also we owe the knowledge of the
important fact, that chlorine is capable of combining with carbon. This
has considerably improved the history of chlorine and served still
further to throw new light on the analogy which exists between all the
supporters of combustion. They are doubtless all of them capable of
combining with every one of the other simple bodies, and of forming
compounds with them. For they are all negative bodies; while the other
simple substances without exception, when compared to them, possess
positive properties. We must therefore view the history of chemistry as
incomplete, till we have become acquainted with the compounds of every
supporter with every simple base.