THE BEGINNINGS OF ELECTRO-CHEMISTRY
The first year of the nineteenth century is further memorable on
account of the invention of the voltaic pile, and by reason of its
application by =William Nicholson= and =Sir Anthony Carlisle= to the
electrolytic decomposition of water. This mode of resolving water into
its constituents made a great sensation at the time, mainly because
of the extraordinary method by which it was effected. It afforded an
independent and unlooked-for proof of the compound nature of water
by a method altogether differing in principle from that by which its
composition had been previously ascertained. The formation of water by
the combustion of hydrogen brought no conviction of its real nature
to a confirmed phlogistian like Priestley; and it is even doubtful
whether Cavendish ever fully realised the true significance of his
great discovery. But the fact that the quantitative results of the
analysis thus effected were identical with those of its synthesis, as
made by Cavendish and Lavoisier, admitted of only one interpretation.
This cardinal discovery may be said to have completed the downfall of
phlogiston.
The value of the voltaic pile as an analytical agent was nowhere more
quickly appreciated than in England. In the hands of Humphry Davy its
application to the analysis of the alkalis and alkaline earths led to
discoveries of the greatest magnitude.
=Humphry Davy= was born in Penzance in 1778. In the course of his
studies for the profession of medicine he was attracted to chemistry;
and he became chemical assistant to Dr. Beddoes, a former teacher of
chemistry at Oxford, but then living at Clifton, near Bristol. While
in the capacity of assistant and operator in Beddoes’s Pneumatical
Institute, Davy discovered the intoxicating properties of _nitrous
oxide_ (so called laughing gas), which brought him into prominence
and led to his engagement by the managers of the newly-created Royal
Institution in London as lecturer in chemistry in succession to
Garnett. He early began to experiment on galvanism, and soon succeeded
in developing the fundamental laws of electro-chemistry; and in 1807 he
effected the _decomposition of potash and soda_ by the application of
voltaic electricity—thereby establishing, what indeed had been surmised
previously, that the alkalis are compound substances. He subsequently
proved that this was also the case with the alkaline earths. Davy thus
added some five or six metallic elements to those already known.
These discoveries, perhaps the most brilliant of their time, afforded
additional evidence of the invalidity of Lavoisier’s assumption that
oxygen, as the name implies, was the “principle of acidity.” The
surmise, in fact, was already disproved by the case of water—a neutral
substance and devoid of all the recognised attributes of an acid. It
was still further disproved by the cases of potash and soda—strongly
alkaline compounds.
Additional evidence was adduced by Davy in demonstrating, in 1810,
that the so-called _oxymuriatic acid_, the _dephlogisticated
marine acid_ discovered by Scheele, contained no oxygen, but was
a simple, indivisible substance. For the old designation, which
connoted a compound body, he substituted the name _chlorine_, in
allusion to the characteristic colour of the element. In the course
of his investigation on this substance he discovered the _penta-
and trichloride of phosphorus_, _chlorophosphamide_ and _chlorine
peroxide_. He was also the discoverer of _telluretted hydrogen_ and an
independent discoverer of _nitrosulphonic acid_.
[Illustration: SIR HUMPHRY DAVY.
From a painting by Lawrence in the possession of the Royal Society.]
He worked on _iodine_ and the _iodates_, on the _diamond_, on the
so-called _fuming liquor of Cadet_, on _nitrogen chloride_, and on the
_pigments of the ancients_. Lastly, he invented the _miner’s safety
lamp_, with which his name will always be associated, effecting thereby
what was practically a revolution in coal-mining. He became President
of the Royal Society in 1820, and died at Geneva on May 29th, 1829, in
the fifty-first year of his age. Davy was a singularly gifted man, of
great mental vigour and imaginative power; quick, lively and ingenious;
an eloquent teacher and a daring and brilliant experimenter.
Another noteworthy name in the chemical history of this period is
Wollaston. =William Hyde Wollaston=, born at East Dereham, in Norfolk,
in 1766, was educated at Cambridge with a view to the profession of
medicine, but, failing to secure a practice, he devoted himself to
the pursuit of science, and especially to optics and chemistry. He
devised a method of _working platinum_, and was the first to make known
the existence of _palladium_ and _rhodium_. He was one of the most
ingenious and acute analysts of his time, and possessed remarkable
inventive powers. He investigated the nature of _urinary calculi_
and _chalk stones_. His paper on the _oxalates of potash_ was of
great service at the time as a demonstration of the law of multiple
proportions. He first drew attention to the existence in the solar
spectrum of what were subsequently termed the _Fraunhofer lines_; and
he invented the _reflecting goniometer_ and the _camera lucida_, and
a _slide rule_ for chemical calculations. He resembled Cavendish in
temperament and mental habitudes, and, like him, was distinguished
for the range and exactitude of his scientific knowledge, his habitual
caution, and his cold and reserved disposition. He died in 1828.
[Illustration: WILLIAM HYDE WOLLASTON.
From a painting by J. Jackson, R.A., in the possession of the Royal
Society.]
Almost immediately after the publication of Volta’s discovery attempts
were made—notably by Berzelius in Sweden and by Davy in England—to
prove that electrical and chemical phenomena are correlated and
mutually dependent. This assumption was more fully worked out by
Berzelius in 1812, and it served as the basis of a chemical system
which exercised considerable influence on chemical doctrine during the
first half of the nineteenth century.
Berzelius assumed that electric polarity was an attribute of all
atoms—that these were bipolar, in fact, but that in them either
positive or negative electricity predominated. Hence the elements
were capable of being divided into two classes—that is, positive or
negative, depending upon the excess of either charge. Which of the
electricities predominated might be ascertained by determining the
particular pole at which the element was separated on electrolysis.
Combinations of dissimilar elements—or, in other words, chemical
compounds—were also endowed with polarity. The chemical affinities of
elements and compounds were related to the excess of either kind of
electricity resident in them; and chemical combination resulted from,
and was a consequence of, the more or less perfect neutralisation
of the two kinds. From a study of the electrical deportment of the
elements Berzelius sought to arrange them in series, starting with
oxygen as the most electro-negative member.
These conceptions were employed by him as the basis of a method of
classification. The attempt is historically interesting as being the
first systematic endeavour to gain an insight into the constitution
of chemical compounds—that is, to determine the manner in which the
constituent atoms are grouped or arranged with respect to one another,
or, in other words, to distinguish between the empirical and the
rational composition of substances, which is the ultimate aim of modern
chemistry.
A necessary consequence of these views was that every compound was to
be considered as made up of two parts in electrically different states.
Thus baryta, consisted of a combination of the electro-positive barium,
combined with the electro-negative oxygen; it combined with sulphuric
oxide because the preponderating positive electricity it contained met
with the negative electricity which prevailed in the sulphuric oxide.
Generalising, it may be said that the basic oxides are invariably
the positive constituents of salts, whereas the acid oxides are the
negative constituents, as proved by the mode in which the two kinds of
oxides separated at the poles on electrolysis. Barium sulphate, then,
was to be regarded as made up of two entities—BaO and SO3—and hence was
to be called sulphate of baryta. Berzelius extended this conception
in order to explain the formation of double salts—such, for example,
as potash alum, which he regarded as a binary compound of positive
potassium sulphate and negative aluminium sulphate, each of which,
in its turn, could be resolved into an acidic and a basic oxide of
opposite electricities.
The dualistic notions of Berzelius led him to the construction of
a system of chemical nomenclature and notation which, in its main
features, has persisted to this day, and is universally current, with
certain modifications, in modern chemical literature. We owe to him
the grouping of the elements into metals and metalloids, and also our
present system of symbolic notation, whereby even complicated chemical
reactions may be expressed in a concise and intelligible manner.
Chemical symbols were used by the alchemists; but Berzelius first
suggested that a chemical symbol should not only represent the element
to which it refers, but also its relative atomic weight. Chemical
equations became quantitative as well as qualitative expressions of
the facts they denote. Such equations implicitly assumed that, to
use Davy’s words, chemistry had passed under the dominion of the
mathematical sciences. Professed mathematicians were, however, slow to
recognise that the phenomena of chemical action were capable of formal
mathematical treatment. Davy relates that on speaking to Laplace of
the atomic theory in chemistry, and expressing his belief that the
science would ultimately be referred to mathematical laws similar to
those he had so profoundly and successfully established with respect
to the mechanical properties of matter, the idea was treated in a tone
bordering on contempt.
Berzelius’s electro-chemical system, and the dualistic ideas associated
with it, were of considerable service when applied to the inorganic
branch of the science; but attempts to fit them to the facts of organic
chemistry, which began to accumulate rapidly after the first quarter of
the century, failed. Its inadequacy as a comprehensive generalisation
became more and more manifest, and it eventually fell. In fact, it may
be said to have received its death-blow by Davy’s discovery of the
elementary nature of chlorine, and by the recognition of the fact that
the acids do not necessarily contain oxygen. Davy and, later, Dulong
made it obvious that, if any one element was to be regarded as the
acidifying principle, it was hydrogen, and not oxygen; and, in a sense,
this view ultimately prevailed in the recognition of the acids as salts
of hydrogen.
In France the study of electro-chemistry was undertaken by Gay Lussac
and Thénard, largely owing to the action of the Emperor Napoleon,
who furnished the funds for the construction of a powerful galvanic
battery. The results were published, in 1811, under the title,
_Recherches Physico-Chimiques, faites sur la Pile_, etc. Gay Lussac,
whose name has already been mentioned as one of the discoverers of
the Law of Combination of Gases, played a considerable part in the
history of chemistry at this period. He was one of the earliest to
appreciate the importance of Dalton’s generalisation, and to point
out the significance of his own discovery in strengthening it. He was
probably led, in the first instance, to the recognition of the law of
gaseous combination by Berthollet’s work on the volumetric composition
of ammonia gas, and by his own discovery—made in 1805, in conjunction
with Humboldt, in the course of their analysis of atmospheric air—that
one volume of oxygen combined with exactly two volumes of hydrogen to
form water. The regularities thus indicated he found to be general: all
gases which are capable of chemical union combine in simple proportions
by volume, and the volume of the product, if a gas, always stands in
some simple relation to the volumes of the constituents.
=Joseph Louis Gay Lussac= was born in 1778, at Saint Leonard, studied
chemistry in Paris, and was associated in chemical inquiry with
Berthollet. As Eleve-Ingenieur in the École Nationale des Ponts et
des Chaussées he began the experimental work in physics and chemistry
upon which his fame rests. In 1804 he undertook, with Biot, a series
of balloon ascents for the purpose of investigating the physics and
chemistry of the upper regions of the atmosphere. In 1806 he became
Professor of Chemistry at the École Polytechnique, and in 1832
Professor at the Jardin des Plantes. He was one of the chief assayers
of the French Mint, and, as member of many commissions, exerted
considerable influence in official circles. He died in 1850.
Gay Lussac and Thénard were the first to devise a method of obtaining
potassium and sodium by a purely chemical process, whereby these
metals could be procured in far larger quantities than was at that
time possible by electrolytic means. They were thus enabled to make
use of the strong deoxidising power of these metals to effect a number
of reductions, notably that of boric oxide to _boron_. Gay Lussac and
Thénard were also the first to make known the existence of _boron
fluoride_. We further owe to Gay Lussac the discovery of _cyanogen_,
the first of the so-called compound radicals. He first prepared
ethyl iodide, investigated sulphovinic acid and grape sugar, studied
etherification and fermentation, etc. We are also indebted to him
for a method of determining vapour densities which proved of great
service in ascertaining the molecular weights of substances. He worked
on iodine and its compounds, discovered, with Welter, _thiosulphuric_
acid, and investigated fulminic acid in collaboration with Liebig.
Among his services to analytical chemistry were his method for the
analysis of gunpowder, his volumetric estimation of silver (wet silver
assay), chlorometric analysis, alkalimetry, etc. He devised the system
still in use in France for the estimation of alcohol in spirits of wine.
=Louis Jacques Thénard= was born in 1777 at Nogent-Sur-Seine, and was
a pupil of Vauquelin and of Berthollet. In 1797 he became _repétiteur_
at the Polytechnic School of Paris, and eventually its professor. He
subsequently occupied the chair of chemistry at the Collège de France,
and of the Faculty of Science of the University of Paris. He was
ennobled by Charles X. in 1824, and died at Paris in the eightieth year
of his age.
In addition to his work with Gay Lussac already mentioned, we owe
to Thénard the discovery of _hydrogen peroxide_ and _hydrogen
persulphide_. Together with Dulong he studied the catalytic action of
platinum on mixtures of oxygen and hydrogen. He investigated the fatty
acids, and worked on fermentation and on ether-formation; and he was
the first to isolate citric and malic acids. He also occupied himself
with the chemistry of bile, perspiration, albumen, the acids of urine
and milk, and with the theory of mordants.
In 1834 Faraday made known the important fact that on passing the same
galvanic current through a number of electrolytes—water, hydrochloric
acid, solutions of metallic chloride—these were decomposed in such
manner that definite amounts of hydrogen or metal were separated at the
negative pole, and corresponding amounts of oxygen or chlorine were
evolved at the positive pole. These observations were comprehended
by Faraday under his “law of definite electrolytic action.” The
electro-chemical equivalents thus obtained were in some cases identical
with the atomic weights deduced by Berzelius; in others they were
not; but, nevertheless, when they differed, they stood in some simple
relation to the assumed atomic weight. The significance of Faraday’s
observation was not lost sight of, although his anticipation that the
determination of electro-chemical equivalents would be of use in fixing
atomic weights was not immediately appreciated. A clear distinction
between the _equivalent_, the _atom_, and the _molecule_ was not
then apprehended. As will be subsequently shown, it was only during
the latter half of the nineteenth century that the discrepancies and
inconsistencies thus revealed were definitely reconciled and cleared
up.