In the preceding volume an attempt was made to outline the significant
features in the development of chemistry, as an art and as a science,
from the earliest times down to about the middle of the last century.
Since that time chemistry has progressed at a rate and to an extent
unparalleled at any period of its history. Not only have the number
and variety of chemical products—inorganic and organic—been enormously
increased, but the study of their modes of origin, properties, and
relations has greatly extended our means of gaining an insight into
the internal structure and constitution of bodies. This extraordinary
development has carried the science beyond the limits of its own
special field of inquiry, and has influenced every department of
natural knowledge. Concurrently there has been a no less striking
extension of its applications to the prosperity and material welfare of

With the death of Davy the era of brilliant discovery in chemistry,
wrote Edward Turner, appeared for the moment to have terminated.
Although the number of workers in the science steadily increased, the
output of chemical literature in England actually diminished for some
years; and, as regards inorganic chemistry, few first-rate discoveries
were made during the two decades prior to 1850. Chemists seemed to
be of Turner’s opinion that the time had arrived for reviewing their
stock of information, and for submitting the principal facts and
fundamental doctrines to the severest scrutiny. Their activity was
employed not so much in searching for new compounds or new elements as
in examining those already discovered. The foundations of the atomic
theory were being securely laid. The ratios in which the elements of
known compounds are united were being more exactly ascertained. The
efforts of workers, Graham excepted, seemed to be spent more on points
of detail, on the filling-in of little gaps in the chemical structure,
as it then existed, than in attempts at new developments. For a
time—during the early ’thirties—chemists struggled with the claims
of rival methods of notation, and it was only gradually that the
system of Berzelius gained general acceptance. At none of the British
universities was there anything in the nature of practical tuition in
chemistry. Thomson, at Glasgow, occasionally permitted a student to
work under him, but no systematic instruction was ever attempted. The
first impulses came from Graham in 1837, when he took charge of the
chemical teaching at the University of London, and when, in 1841, he
assisted to create the Chemical Society of London. Four years later
the Royal College of Chemistry in London was founded and placed under
the direction of August Wilhelm Hofmann—one of the most distinguished
pupils of Liebig. Under his inspiration the study of practical
chemistry made extraordinary progress, and discovery succeeded
discovery in rapid succession. In bringing Hofmann to England we had,
in fact, imported something of the spirit and power of his master,

Among the pupils and co-workers of Hofmann were Warren de la Rue, Abel,
Nicholson, Mansfield, Medlock, Crookes, Church, Griess, Martius, Sell,
Divers, and Perkin. Whilst at Giessen he had begun the study of the
organic bases in coal-tar with a view more especially of establishing
the identity of Fritzsche’s _anilin_ with the _benzidam_ of Zinin and
the _krystallin_ of Unverdorben. Hofmann continued to cultivate with
unremitting zeal the field thus entered. With Muspratt he discovered
_paratoluidine_ and _nitraniline_; with Cahours _allyl alcohol_. His
pupil Mansfield worked out, at the cost of his life, the methods
for the technical extraction of benzene and toluene from coal-tar,
and thereby made the coal-tar colour-industry possible. It was in
attempting to synthesise quinine by the oxidation of aniline that
Perkin, then an assistant at the college, obtained, in 1856, _aniline
purple_, or _mauve_, as it came to be called by the French, the first
of the so-called coal-tar colouring matters. In 1859 this was followed
by the discovery of _magenta_, or _fuchsine_, by Verquin. For its
manufacture Medlock, one of Hofmann’s pupils, in 1860 devised a process
by which for a time it was almost exclusively made. Hofmann studied the
products thus obtained, and showed that they were derivatives of a base
he called _rosaniline_; and he demonstrated that the colouring matters
were only produced through the concurrent presence of aniline and
toluidine. He also proved that the base of the dye, known as _aniline
blue_, was _triphenylrosaniline_. As the result of these inquiries he
obtained the violet or purple colouring matters known by his name.
Lastly, all his classical work on the amines, ammonium compounds, and
the analogous phosphorus derivatives was done at the Royal College of

Prior to the establishment by Liebig, in 1826, of the Giessen
laboratory, the state of chemistry in Germany was not much, if at all,
better than with us. The creation of the Giessen school initiated a
movement which has culminated in the pre-eminent position which Germany
now occupies in the chemical world. Students from every civilised
country came to study and to work under its leader, and to carry away
with them the influence of his example, the inspiration of his genius,
and the stimulating power of his enthusiasm.

│Justus von Liebig│, was born at Darmstadt on May 12, 1803, and
after graduating at Erlangen, where he worked on the fulminates, he
repaired to Paris and entered the laboratory of Gay Lussac, with whom
he continued his inquiries. Returning to Germany, he was appointed
Professor of Chemistry at Giessen in 1826, and began those remarkable
series of scientific contributions upon which the superstructure of
organic chemistry largely rests. He investigated the _cyanates_,
_cyanides_, _ferrocyanides_, _thiocyanates_, and their derivatives.
In conjunction with Wöhler he discovered the group of the _benzoic
compounds_ and created the _radical theory_. With Wöhler also he
investigated _uric acid and its derivatives_. He discovered _hippuric
acid_, _fulminuric acid_, _chloral_, _chloroform_, _aldehyde_,
_thialdine_, _benzil_, and elucidated the _constitution of the organic
acids_ and the _amides_. He greatly improved the methods of organic
analysis, and was thereby enabled to determine the empirical formulæ of
a number of carbon compounds of which the composition was imperfectly
known. He practically laid the foundations of modern agricultural
chemistry, and to his teaching is due the establishment of an important
branch of technology—the manufacture of chemical fertilisers. He worked
on physiological chemistry, especially on the elaboration of fat, on
the nature of blood, bile, and on the juice of flesh. He studied the
processes of fermentation, and of the decay of organised matter. He was
a most prolific writer. The Royal Society’s Catalogue of Scientific
Papers enumerates no fewer than 317 contributions from his pen. He was
the founder of the _Annalen der Chemie_, which is now associated with
his name, and of the _Jahresbericht_; he published an _Encyclopædia
of Pure and Applied Chemistry_ and a _Handbook of Organic Chemistry_.
His _Familiar Letters on Chemistry_ was translated into every modern
language, and exercised a powerful influence in developing popular
appreciation of the value and utility of science. Liebig left Giessen
in 1852 to become Professor of Chemistry at the University of Munich
and President of the Academy of Sciences. He died at Munich on April
18, 1874.

With the name of Liebig that of Wöhler is indissolubly connected.
Although the greater part of their work was not published in
conjunction, what they did together exercised a profound influence on
the development of chemical theory.

│Friedrich Wöhler│ was born at Eschersheim, near Frankfort, on July 31,
1800. After studying at Marburg, where he discovered, independently of
Davy, _cyanogen iodide_, and worked on _mercuric thiocyanate_, he went
to Heidelberg and investigated _cyanic acid_ and its compounds, under
the direction of Gmelin. In 1823 he worked with Berzelius at Stockholm,
where he prepared some new tungsten compounds and practised mineral
analysis. In 1825 he became a teacher of chemistry in the Berlin Trade
School. Here he succeeded for the first time in preparing the metal
_aluminium_ and in effecting the _synthesis of urea_—one of the first
organic compounds to be prepared from inorganic materials. Jointly with
Liebig he worked upon _mellitic_ and _cyanic_ and _cyanuric acids_. In
1832 Wöhler, now appointed to the Polytechnic at Cassel, began with
Liebig their memorable investigation on _bitter-almond oil_. In 1836 he
was called to the Chair of Chemistry in the University of Göttingen,
and with Liebig attacked the constitution of _uric acid and its
derivatives_—the last great investigation the friends did in common.
Wöhler subsequently devoted himself mainly to inorganic chemistry. He
isolated _crystalline boron_, and prepared its _nitrides_, discovered
the spontaneously inflammable _silicon hydride_, _titanium nitride_,
and analysed great numbers of minerals and meteorites and compounds of
the rarer metals. He made Göttingen famous as a school of chemistry.
At the time of the one and twentieth year of his connection with the
University it was found that upwards of 8000 students had listened to
his lectures or worked in his laboratory. He died on September 23, 1882.

In France, Dumas exercised a no less powerful influence. If Liebig
could reckon among his pupils Redtenbacher, Bromeis, Varrentrapp,
Gregory, Playfair, Williamson, Gilbert, Brodie, Anderson, Gladstone,
Hofmann, Will, and Fresenius; Dumas could point to Boullay, Piria,
Stas, Melsens, Wurtz, and Leblanc—all of whom did yeoman service in
developing the rapidly expanding branch of organic chemistry.


│Jean Baptiste André Dumas│ was born on July 14, 1800, at Alais, where
he was apprenticed to an apothecary. In his sixteenth year he went to
Geneva and entered the pharmaceutical laboratory of Le Royer. Without,
apparently, having received any systematic instruction in chemistry,
he commenced the work of investigation. With Coindet he established
the therapeutic value of iodine in the treatment of _goître_; with
Prevost he attempted to isolate the active principle of _digitalis_,
and studied the chemical changes in the development of the chick in
the egg. In his twenty-fourth year Dumas went to Paris and became
_Répétiteur de Chimie_ at the École Polytechnique. He joined Audouin
and Brongniart in founding the _Annales des Sciences Naturelles_, and
began his great work on _Chemistry Applied to the Arts_, of which
the first volume appeared in 1828. At about this time he devised his
_method of determining vapour densities_, and published the results
of a number of estimations made by means of it. With Boullay he
began an inquiry on the _compound ethers_, out of which grew the
_etherin theory_, which served as a stepping-stone to the theory of
compound radicals—subsequently elaborated by Liebig and Wöhler. Dumas
discovered the nature of _oxamide_ and of _ethyl oxamate_, isolated
_methyl alcohol_, and established the generic connection of groups of
similarly constituted organic substances, or, in a word, the doctrine
of _homology_. His work on the _metaleptic action of chlorine_
upon organic substances eventually effected the overthrow of the
electro-chemical theory of Berzelius and led to the theory of types,
which, in the hands of Williamson, Laurent, Gerhardt, and Odling, was
of great service in explaining the analogies and relationships of whole
groups of organic compounds. He worked in every field of chemistry.
He invented many analytical processes, established the _gravimetric
composition of water and of air_, and revised the _atomic weights_ of
the greater number of the elements then known. Dumas exercised great
influence in scientific and academic circles in France. He was an
admirable speaker, and had rare literary gifts. On the creation of the
Empire he was made a Senator, and was elected a member of the Municipal
Council of Paris, of which he became president in 1859. He died on
April 11, 1884.

It was largely through the influence of these master-minds that
chemistry took a new departure. Prior to their time organic chemistry
hardly existed as a branch of science: organic products, as a rule,
were interesting only to the pharmacist mainly by reason of their
technical or medicinal importance. But by the middle of the nineteenth
century the richness of this hitherto untilled field became manifest,
and scores of workers hastened to sow and to reap in it. The most
striking feature, indeed, of the history of chemistry during the past
sixty years has been the extraordinary expansion of the organic section
of the science. The chemical literature relating to the compounds
of carbon now exceeds in volume that devoted to all the rest of the

In the middle of the nineteenth century chemists began to concern
themselves with the systematisation of the results of the study of
organic compounds, and something like a theory of organic chemistry
gradually took shape. From this period we may date the attempts
at expressing the internal nature, constitution, and relations of
substances which, step by step, have culminated in our present
representations of the structure and spatial arrangement of molecules.
In 1850 the dualistic conceptions of Berzelius ceased to influence
the doctrines of organic chemistry. The enunciation by Dumas of the
principle of substitution, and its logical outcome in the nucleus
theory and in the theory of types, had not only effected the overthrow
of dualism, but was undermining the position of the radical theory of
Liebig and Wöhler. The teaching of Gerhardt and Laurent had spread
over Europe, and was influencing those younger chemists who, while
renouncing dualism, were not wholly satisfied with a belief in compound
radicals. Williamson’s discovery, in 1850, of the true nature of ether
and of its relation to alcohol, and his subsequent preparation of mixed
ethers, served not only to reconcile conflicting interpretations of
the process of etherification, but also to reconcile the theory of
types with that of radicals. Lastly, his method of representing the
constitution of the ethers and their mode of origin gave a powerful
stimulus to the use of type-formulæ in expressing the nature and
relations of organic compounds.

[Illustration: THOMAS GRAHAM.

From a painting by G. F. Watts, R.A., in the possession of the Royal

Other representative men of the middle period of the nineteenth
century, in addition to Williamson, were Graham and Bunsen. The
three men were investigators of very different type, and their work
had little in common. But each was identified with discoveries of a
fundamental character, constituting turning-points in the history of
chemical progress, valuable either as regards their bearing on chemical
doctrine or as regards their influence on operative chemistry.

│Thomas Graham│ was born in Glasgow on December 21, 1805, and, after
studying under Thomas Thomson at the University of that city, attended
the lectures of Hope and Leslie in Edinburgh. In 1830 he succeeded Ure
as teacher of chemistry at Anderson’s College in Glasgow, and in 1837
was called to the Chair of Chemistry in the newly-founded University of
London, in succession to Edward Turner. In 1854 he was made Master of
the Mint. He died in London on September 16, 1869.

Graham’s work was mainly devoted to that section of the science now
known as physical chemistry. His contributions to pure chemistry
are few in number. By far the most important is his discovery of
_metaphosphoric_ acid and its relations to the other modifications of
phosphoric acid. Ortho- or ordinary phosphoric acid was known to
Boyle; pyrophosphoric acid was discovered by Clark. Graham’s work is
noteworthy as first definitely indicating the inherent property of the
acids to combine with variable but definite amounts of basic substances
by successive replacement of hydroxyl groups—the property we now term
_basicity_, and was of fundamental importance in regard to its bearing
on the constitution of acids and salts.

Graham’s fame chiefly rests upon his discovery of _the law of gaseous
diffusion_ (1829–1831), upon his work on the _diffusion of liquids_,
and upon his recognition of the condensed form of hydrogen he termed
_hydrogenium_. Questions involving the conception of molecular
mobility, indeed, constituted the main feature of his inquiries. We owe
to him, among others, the terms _crystalloid_, _colloid_, _dialysis_,
_atmolysis_, _occlusion_—all of which have taken a permanent place in
the terminology of science.


│Alexander William Williamson│ was born at Wandsworth, London, on
May 1, 1824. His father, a Scotchman and a fellow-clerk of James
Mill (the father of John Stuart Mill) in the East India House, took
an active share in the foundation, in 1826, of the University of
London, subsequently known as University College. In 1840 the younger
Williamson entered the University of Heidelberg with the intention
of studying medicine; but, under the influence of Leopold Gmelin, he
turned to chemistry. In 1844 he went to Giessen, to work under Liebig,
and there made his first contributions to chemical science—viz., on the
_decomposition of oxides and salts by chlorine_; _on ozone_; and _on
the blue compounds of cyanogen and iron_. After graduating at Giessen
he went, in 1846, to Paris, where he came under the influence of Comte,
with whom he studied mathematics. In 1850, at Graham’s solicitation,
he was appointed to the Chair of Practical Chemistry at University
College, vacant by the death of Fownes. He at once embarked upon those
researches which constitute his main contribution to science. In the
attempt to build up the homologous series of the aliphatic alcohols
from ordinary alcohol he succeeded in demonstrating the real nature
of ether and its genetic relation to alcohol, and in explaining the
process of etherification. The memoirs (1850–52) in which he embodied
the facts had an immediate influence on the development of chemical
theory. His explanation of the process of etherification familiarised
chemists with the idea of the essentially dynamical nature of chemical
change. He imported the conception of molecular mobility not only
into the explanation of such metathetical reactions as the formation
of the ethers, but into the interpretation of the phenomena of
chemical change in general. In these papers, as also in one on the
constitution of salts, published in 1851, he attempted to systematise
the representation of the constitution and relations of oxidised
substances—organic and inorganic—by showing how they may be regarded as
built up upon the type of water considered as


in which the hydrogen atoms are replaced, wholly or in part, by
other chemically equivalent atoms. This idea was immediately adopted
by Gerhardt, was further elaborated by Odling and Kekulé, and was
eventually developed into a theory of chemistry.

Williamson continued to direct the laboratory of University College
until 1887, when he retired to the country. He died at Hindhead on May
6, 1904.

│Robert Wilhelm Bunsen│ was born at Göttingen on March 31, 1811, and
after studying chemistry under Stromeyer, the discoverer of cadmium,
went to Paris and worked with Gay Lussac. In 1836 he succeeded Wöhler
as teacher of chemistry in the Polytechnic School of Cassel, and in
1842 became Professor of Chemistry in the University of Marburg. In
1852 he was called to Heidelberg, and occupied the Chair of Chemistry
there until his retirement in 1889. He died at Heidelberg on August 16,


Bunsen first distinguished himself by his classical work on the
_cacodyl compounds_, obtained as the result of an inquiry into the
nature of the so-called “fuming liquor of Cadet,” an evil-smelling,
highly poisonous, inflammable liquid formed by heating arsenious oxide
with an alkaline acetate. The investigation (1837–1845) is noteworthy,
not only for the skill it exhibits in dealing with a difficult and
highly dangerous manipulative problem, but also for the remarkable
nature of its results and on account of their influence on contemporary
chemical theory. The research, in the words of Berzelius, was the
foundation-stone of the theory of compound radicals. The name _cacodyl_
or _kakodyl_ was suggested by Berzelius in allusion to the nauseous
smell of the compounds of the new radical _arsinedimethyl, As (CH3)2_,
as it was subsequently termed by Kolbe.

Bunsen greatly improved the methods of gasometric analysis; these he
applied, in conjunction with Playfair, to an examination of the gaseous
products of the blast furnace in the manufacture of iron, and thereby
demonstrated the enormous waste of energy occasioned by allowing
the gases to escape unused into the air, as was then the universal
practice. This inquiry effected a revolution in the manufacture of iron
as important, indeed, as that due to the introduction of the hot blast.

Bunsen devised methods for determining the _solubility of gases_
in liquids, for ascertaining the _specific gravity of gases_, their
_rates of diffusion_, and of combination or _inflammation_. In 1841 he
invented the _carbon-zinc battery_, and applied it to the electrolytic
production of metals, notably of _magnesium_, the properties of which
he first accurately described. In 1844 he contrived the _grease-spot
photo-meter_, which was long in general use for ascertaining the
photometric value of illuminating gas. His methods of ascertaining
_the specific heats of solids and liquids_ were simple, ingenious, and
accurate. In 1855–1863 he carried out, in conjunction with Roscoe, a
long series of investigations on the _chemical action of light_. In
1859, in association with Kirchhoff, he devised the first methods of
_spectrum analysis_, and explained the origin and significance of the
Fraunhofer lines in the solar spectrum, thus laying the foundations of
solar and stellar chemistry. The application of the _spectroscope_ to
analytical chemistry almost immediately resulted in his discovery of
_cæsium_ and _rubidium_.

Bunsen worked on problems of _chemical geology_, and made a long series
of analyses of _volcanic products_. With Schischkoff, he examined, in
1857, the products of fired gunpowder. He effected many improvements in
analytical chemistry; devised the _iodiometric method_ of volumetric
analysis, and systematised the processes of _water analysis_. Lastly,
he invented the _gas-burner_—a piece of apparatus with which his name
is inseparably associated, and which has been of inestimable service to
operative chemistry and in the arts. Bunsen was no theorist, and purely
speculative questions had little or no interest for him. At the same
time he was a great teacher, and made the chemical school of Heidelberg
no less famous than the schools of Giessen and Göttingen.

* * * * *

The mass of material relating to the development of chemistry which
has been accumulated during the past sixty years is so vast that it
would be hopeless to attempt to survey it in detail within the limits
of such a work as this. Nor, indeed, is this required in a history of
this character. Those who desire information concerning the origin and
sequence of the facts which collectively make up the superstructure
of modern chemistry must be referred to the encyclopædias or larger
treatises—or, preferably, to the numerous monographs, dealing with
special sections, which the volume and complexity of the matter to be
dealt with seem to render increasingly necessary. All we can do here
is to attempt to show what has been the main outcome of this sixty
years of incessant effort to elucidate the mysteries of chemical
phenomena and to ascertain the nature of the conditions which control,
modify, or determine them. All this effort is ultimately directed
to the solution of the fundamental problem of the constitution of
matter. The most significant result of this endeavour has been the
elaboration and consolidation of the doctrine of chemical atoms, not
necessarily of atoms in the limited Daltonian sense, but of atoms
considered as associations of particles, or corpuscles—that is, of
entities which _may_ be divisible, but which, in the main, are not
divided in the vast number of the transformations in which they are
concerned. This modification of the original conception of Dalton has
been thought by some to destroy the basis upon which his theory really
rests. There is no necessity for such an assumption. So pronounced an
atomist as Graham, as far back as 1863, in a suggestive paper entitled
_Speculative Ideas on the Constitution of Matter_, enlarged the
conception of the Daltonian atom in precisely the sense which recent
experimental work appears to require. The present position, too, as it
affects chemists, was equally well stated by Kekulé, in 1867, in the
following terms:

The question whether atoms exist or not has but little
significance from a chemical point; its discussion belongs rather
to metaphysics. In chemistry we have only to decide whether the
assumption of atoms is an hypothesis adapted to the explanation
of chemical phenomena. More especially have we to consider the
question whether a further development of the atomic hypothesis
promises to advance our knowledge of the mechanism of chemical

I have no hesitation in saying that, from a philosophical point of
view, I do not believe in the actual existence of atoms, taking
the word in its literal signification of indivisible particles of
matter; I rather expect that we shall some day find for what we now
call atoms a mathematico-mechanical explanation which will render
an account of atomic weight, of atomicity, and of numerous other
properties of the so-called atoms. As a chemist, however, I regard
the assumption of atoms not only as advisable, but as absolutely
necessary, in chemistry. I will even go further, and declare my
belief that _chemical atoms exist_, provided the term be understood
to denote those particles of matter which undergo no further
division in chemical metamorphoses. Should the progress of science
lead to a theory of the constitution of chemical atoms—important as
such a knowledge might be for the general philosophy of matter—it
would make but little alteration in chemistry itself. The chemical
atoms will always remain the chemical unit; and for the specially
chemical considerations we may always start from the constitution
of atoms, and avail ourselves of the simplified expression thus
obtained—that is to say, of the atomic hypothesis. We may, in
fact, adopt the view of Dumas and of Faraday—that, _whether matter
be atomic or not, thus much is certain: that, granting it to be
atomic, it would appear as it now does_.[1]

[1] _The Study of Chemical Composition_, by Ida Freund
(Cambridge University Press), 1904.

The greater part of that which follows will be devoted, therefore,
to an exposition of certain of the great advances in knowledge—many
of them of primary importance—which have been made during the last
fifty or sixty years and which have served to strengthen this extended
conception of the atomic theory, and to establish its position as an
article of the scientific faith of the twentieth century.

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