Inorganic chemistry is concerned with the descriptive study of the
elements and their compounds, except those of carbon. Reference should
be made to the separate articles on the different elements and the more
important compounds for their preparation, properties and uses. In this
article the development of this branch of the science is treated
historically.
The earliest discoveries in inorganic chemistry are to be found in the
metallurgy, medicine and chemical arts of the ancients. The Egyptians
obtained silver, iron, copper, lead, zinc and tin, either pure or as
alloys, by smelting the ores; mercury is mentioned by Theophrastus (c.
300 B.C.). The manufacture of glass, also practised in Egypt, demanded a
knowledge of sodium or potassium carbonates; the former occurs as an
efflorescence on the shores of certain lakes; the latter was obtained
from wood ashes. Many substances were used as pigments: Pliny records
white lead, cinnabar, verdigris and red oxide of iron; and the
preparation of coloured glasses and enamels testifies to the uses to
which these and other substances were put. Salts of ammonium were also
known; while alum was used as a mordant in dyeing. Many substances were
employed in ancient medicine: galena was the basis of a valuable
Egyptian cosmetic and drug; the arsenic sulphides, realgar and orpiment,
litharge, alum, saltpetre, iron rust were also used. Among the Arabian
and later alchemists we find attempts made to collate compounds by
specific properties, and it is to these writers that we are mainly
indebted for such terms as "alkali," "sal," &c. The mineral acids,
hydrochloric, nitric and sulphuric acids, and also _aqua regia_ (a
mixture of hydrochloric and nitric acids) were discovered, and the
vitriols, alum, saltpetre, sal-ammoniac, ammonium carbonate, silver
nitrate (_lunar caustic_) became better known. The compounds of mercury
attracted considerable attention, mainly on account of their medicinal
properties; mercuric oxide and corrosive sublimate were known to
pseudo-Geber, and the nitrate and basic sulphate to "Basil Valentine."
Antimony and its compounds formed the subject of an elaborate treatise
ascribed to this last writer, who also contributed to our knowledge of
the compounds of zinc, bismuth and arsenic. All the commonly occurring
elements and compounds appear to have received notice by the alchemists;
but the writings assigned to the alchemical period are generally so
vague and indefinite that it is difficult to determine the true value of
the results obtained.
In the succeeding iatrochemical period, the methods of the alchemists
were improved and new ones devised. Glauber showed how to prepare
hydrochloric acid, _spiritus salis_, by heating rock-salt with sulphuric
acid, the method in common use to-day; and also nitric acid from
saltpetre and arsenic trioxide. Libavius obtained sulphuric acid from
many substances, e.g. alum, vitriol, sulphur and nitric acid, by
distillation. The action of these acids on many metals was also studied;
Glauber obtained zinc, stannic, arsenious and cuprous chlorides by
dissolving the metals in hydrochloric acid, compounds hitherto obtained
by heating the metals with corrosive sublimate, and consequently
supposed to contain mercury. The scientific study of salts dates from
this period, especial interest being taken in those compounds which
possessed a medicinal or technical value. In particular, the salts of
potassium, sodium and ammonium were carefully investigated, but sodium
and potassium salts were rarely differentiated.[9] The metals of the
alkaline-earths were somewhat neglected; we find Georg Agricola
considering gypsum (calcium sulphate) as a compound of lime, while
calcium nitrate and chloride became known at about the beginning of the
17th century. Antimonial, bismuth and arsenical compounds were
assiduously studied, a direct consequence of their high medicinal
importance; mercurial and silver compounds were investigated for the
same reason. The general tendency of this period appears to have taken
the form of improving and developing the methods of the alchemists; few
new fields were opened, and apart from a more complete knowledge of the
nature of salts, no valuable generalizations were attained.
The discovery of phosphorus by Brand, a Hamburg alchemist, in 1669
excited chemists to an unwonted degree; it was also independently
prepared by Robert Boyle and J. Kunckel, Brand having kept his process
secret. Towards the middle of the 18th century two new elements were
isolated: cobalt by G. Brandt in 1742, and nickel by A.F. Cronstedt in
1750. These discoveries were followed by Daniel Rutherford's isolation
of nitrogen in 1772, and by K. Scheele's isolation of chlorine and
oxygen in 1774 (J. Priestley discovered oxygen independently at about
the same time), and his investigation of molybdic and tungstic acids in
the following year; metallic molybdenum was obtained by P.J. Hjelm in
1783, and tungsten by Don Fausto d'Elhuyar; manganese was isolated by
J.G. Gahn in 1774. In 1784 Henry Cavendish thoroughly examined hydrogen,
establishing its elementary nature; and he made the far-reaching
discovery that water was composed of two volumes of hydrogen to one of
oxygen.
The phlogistic theory, which pervaded the chemical doctrine of this
period, gave rise to continued study of the products of calcination and
combustion; it thus happened that the knowledge of oxides and oxidation
products was considerably developed. The synthesis of nitric acid by
passing electric sparks through moist air by Cavendish is a famous piece
of experimental work, for in the first place it determined the
composition of this important substance, and in the second place the
minute residue of air which would not combine, although ignored for
about a century, was subsequently examined by Lord Rayleigh and Sir
William Ramsay, who showed that it consists of a mixture of elementary
substances--argon, krypton, neon and xenon (see ARGON).
The 18th century witnessed striking developments in pneumatic chemistry,
or the chemistry of gases, which had been begun by van Helmont, Mayow,
Hales and Boyle. Gases formerly considered to be identical came to be
clearly distinguished, and many new ones were discovered. Atmospheric
air was carefully investigated by Cavendish, who showed that it
consisted of two elementary constituents: nitrogen, which was isolated
by Rutherford in 1772, and oxygen, isolated in 1774; and Black
established the presence, in minute quantity, of carbon dioxide (van
Helmont's _gas sylvestre_). Of the many workers in this field, Priestley
occupies an important position. A masterly device, initiated by him, was
to collect gases over mercury instead of water; this enabled him to
obtain gases previously only known in solution, such as ammonia,
hydrochloric acid, silicon fluoride and sulphur dioxide. Sulphuretted
hydrogen and nitric oxide were discovered at about the same time.
Returning to the history of the discovery of the elements and their more
important inorganic compounds, we come in 1789 to M.H. Klaproth's
detection of a previously unknown constituent of the mineral
pitchblende. He extracted a substance to which he assigned the character
of an element, naming it uranium (from [Greek: Ouranos], heaven); but it
was afterwards shown by E.M. Peligot, who prepared the pure metal, that
Klaproth's product was really an oxide. This element was investigated at
a later date by Sir Henry Roscoe, and more thoroughly and successfully
by C. Zimmermann and Alibegoff. Pitchblende attained considerable
notoriety towards the end of the 19th century on account of two
important discoveries. The first, made by Sir William Ramsay in 1896,
was that the mineral evolved a peculiar gas when treated with sulphuric
acid; this gas, helium (q.v.), proved to be identical with a constituent
of the sun's atmosphere, detected as early as 1868 by Sir Norman Lockyer
during a spectroscopic examination of the sun's chromosphere. The second
discovery, associated with the Curies, is that of the peculiar
properties exhibited by the impure substance, and due to a constituent
named radium. The investigation of this substance and its properties
(see RADIOACTIVITY) has proceeded so far as to render it probable that
the theory of the unalterability of elements, and also the hitherto
accepted explanations of various celestial phenomena--the source of
solar energy and the appearances of the tails of comets--may require
recasting.
In the same year as Klaproth detected uranium, he also isolated zirconia
or zirconium oxide from the mineral variously known as zircon, hyacinth,
jacynth and jargoon; but he failed to obtain the metal, this being first
accomplished some years later by Berzelius, who decomposed the double
potassium zirconium fluoride with potassium. In the following year,
1795, Klaproth announced the discovery of a third new element, titanium;
its isolation (in a very impure form), as in the case of zirconium, was
reserved for Berzelius.
Passing over the discovery of carbon disulphide by W.A. Lampadius in
1796, of chromium by L.N. Vauquelin in 1797, and Klaproth's
investigation of tellurium in 1798, the next important series of
observations was concerned with platinum and the allied metals. Platinum
had been described by Antonio de Ulloa in 1748, and subsequently
discussed by H.T. Scheffer in 1752. In 1803 W.H. Wollaston discovered
palladium, especially interesting for its striking property of absorbing
("occluding") as much as 376 volumes of hydrogen at ordinary
temperatures, and 643 volumes at 90 deg. In the following year he
discovered rhodium; and at about the same time Smithson Tennant added
two more to the list--iridium and osmium; the former was so named from
the changing tints of its oxides ([Greek: iris], rainbow), and the
latter from the odour of its oxide ([Greek: osme], smell). The most
recently discovered "platinum metal," ruthenium, was recognized by C.E.
Claus in 1845. The great number and striking character of the compounds
of this group of metals have formed the subject of many investigations,
and already there is a most voluminous literature. Berzelius was an
early worker in this field; he was succeeded by Bunsen, and Deville and
Debray, who worked out the separation of rhodium; and at a later date by
P.T. Cleve, the first to make a really thorough study of these elements
and their compounds. Of especial note are the curious compounds formed
by the union of carbon monoxide with platinous chloride, discovered by
Paul Schutzenberger and subsequently investigated by F.B. Mylius and F.
Foerster and by Pullinger; the phosphoplatinic compounds formed
primarily from platinum and phosphorus pentachloride; and also the
"ammino" compounds, formed by the union of ammonia with the chloride,
&c., of these metals, which have been studied by many chemists,
especially S.M. Jorgensen. Considerable uncertainty existed as to the
atomic weights of these metals, the values obtained by Berzelius being
doubtful. K.F.O. Seubert redetermined this constant for platinum, osmium
and iridium; E.H. Keiser for palladium, and A.A. Joly for ruthenium.
The beginning of the 19th century witnessed the discovery of certain
powerful methods for the analysis of compounds and the isolation of
elements. Berzelius's investigation of the action of the electric
current on salts clearly demonstrated the invaluable assistance that
electrolysis could render to the isolator of elements; and the adoption
of this method by Sir Humphry Davy for the analysis of the hydrates of
the metals of the alkalis and alkaline earths, and the results which he
thus achieved, established its potency. In 1808 Davy isolated sodium and
potassium; he then turned his attention to the preparation of metallic
calcium, barium, strontium and magnesium. Here he met with greater
difficulty, and it is to be questioned whether he obtained any of these
metals even in an approximately pure form (see ELECTROMETALLURGY). The
discovery of boron by Gay Lussac and Davy in 1809 led Berzelius to
investigate silica (_silex_). In the following year he announced that
silica was the oxide of a hitherto unrecognized element, which he named
_silicium_, considering it to be a metal. This has proved to be
erroneous; it is non-metallic in character, and its name was altered to
silicon, from analogy with carbon and boron. At the same time Berzelius
obtained the element, in an impure condition, by fusing silica with
charcoal and iron in a blast furnace; its preparation in a pure
condition he first accomplished in 1823, when he invented the method of
heating double potassium fluorides with metallic potassium. The success
which attended his experiments in the case of silicon led him to apply
it to the isolation of other elements. In 1824 he obtained zirconium
from potassium zirconium fluoride; the preparation of (impure) titanium
quickly followed, and in 1828 he obtained thorium. A similar process,
and equally efficacious, was introduced by F. Wohler in 1827. It
consisted in heating metallic chlorides with potassium, and was first
applied to aluminium, which was isolated in 1827; in the following year,
beryllium chloride was analysed by the same method, beryllium oxide
(berylla or glucina) having been known since 1798, when it was detected
by L. N. Vauquelin in the gem-stone beryl.
In 1812 B. Courtois isolated the element iodine from "kelp," the burnt
ashes of marine plants. The chemical analogy of this substance to
chlorine was quickly perceived, especially after its investigation by
Davy and Gay Lussac. Cyanogen, a compound which in combination behaved
very similarly to chlorine and iodine, was isolated in 1815 by Gay
Lussac. This discovery of the first of the then-styled "compound
radicals" exerted great influence on the prevailing views of chemical
composition. Hydrochloric acid was carefully investigated at about this
time by Davy, Faraday and Gay Lussac, its composition and the elementary
nature of chlorine being thereby established.
In 1817 F. Stromeyer detected a new metallic element, cadmium, in
certain zinc ores; it was rediscovered at subsequent dates by other
observers and its chemical resemblance to zinc noticed. In the same year
Berzelius discovered selenium in a deposit from sulphuric acid chambers,
his masterly investigation including a study of the hydride, oxides and
other compounds. Selenic acid was discovered by E. Mitscherlich, who
also observed the similarity of the crystallographic characters of
selenates and sulphates, which afforded valuable corroboration of his
doctrine of isomorphism. More recent and elaborate investigations in
this direction by A.E.H. Tutton have confirmed this view.
In 1818 L.J. Thenard discovered hydrogen dioxide, one of the most
interesting inorganic compounds known, which has since been carefully
investigated by H.E. Schone, M. Traube, Wolfenstein and others. About
the same time, J.A. Arfvedson, a pupil of Berzelius, detected a new
element, which he named lithium, in various minerals--notably petalite.
Although unable to isolate the metal, he recognized its analogy to
sodium and potassium; this was confirmed by R. Bunsen and A. Matthiessen
in 1855, who obtained the metal by electrolysis and thoroughly examined
it and its compounds. Its crimson flame-coloration was observed by C.G.
Gmelin in 1818.
The discovery of bromine in 1826 by A.J. Balard completed for many years
Berzelius's group of "halogen" elements; the remaining member, fluorine,
notwithstanding many attempts, remained unisolated until 1886, when
Henri Moissan obtained it by the electrolysis of potassium fluoride
dissolved in hydrofluoric acid. Hydrobromic and hydriodic acids were
investigated by Gay Lussac and Balard, while hydrofluoric acid received
considerable attention at the hands of Gay Lussac, Thenard and
Berzelius. We may, in fact, consider that the descriptive study of the
various halogen compounds dates from about this time. Balard discovered
chlorine monoxide in 1834, investigating its properties and reactions;
and his observations on hypochlorous acid and hypochlorites led him to
conclude that "bleaching-powder" or "chloride of lime" was a compound or
mixture in equimolecular proportions of calcium chloride and
hypochlorite, with a little calcium hydrate. Gay Lussac investigated
chloric acid; Stadion discovered perchloric acid, since more fully
studied by G.S. Serullas and Roscoe; Davy and Stadion investigated
chlorine peroxide, formed by treating potassium chlorate with sulphuric
acid. Davy also described and partially investigated the gas, named by
him "euchlorine," obtained by heating potassium chlorate with
hydrochloric acid; this gas has been more recently examined by Pebal.
The oxy-acids of iodine were investigated by Davy and H.G. Magnus;
periodic acid, discovered by the latter, is characterized by the
striking complexity of its salts as pointed out by Kimmins.
In 1830 N.G. Sefstrom definitely proved the existence of a metallic
element vanadium, which had been previously detected (in 1801) in
certain lead ores by A.M. del Rio; subsequent elaborate researches by
Sir Henry Roscoe showed many inaccuracies in the conclusions of earlier
workers (for instance, the substance considered to be the pure element
was in reality an oxide) and provided science with an admirable account
of this element and its compounds. B.W. Gerland contributed to our
knowledge of vanadyl salts and the vanadic acids. Chemically related to
vanadium are the two elements tantalum and columbium or niobium. These
elements occur in the minerals columbite and tantalite, and their
compounds became known in the early part of the 19th century by the
labours of C. Hatchett, A.G. Ekeberg, W.H. Wollaston and Berzelius. But
the knowledge was very imperfect; neither was it much clarified by H.
Rose, who regarded niobium oxide as the element. The subject was revived
in 1866 by C.W. Blomstrand and J.C. Marignac, to whom is due the credit
of first showing the true chemical relations of these elements.
Subsequent researches by Sainte Claire Deville and L.J. Troost, and by
A.G. Kruss and L.E. Nilson, and subsequently (1904) by Hall, rendered
notable additions to our knowledge of these elements and their
compounds. Tantalum has in recent years been turned to economic service,
being employed, in the same manner as tungsten, for the production of
the filaments employed in incandescent electric lighting.
In 1833 Thomas Graham, following the paths already traced out by E.D.
Clarke, Gay Lussac and Stromeyer, published his masterly investigation
of the various phosphoric acids and their salts, obtaining results
subsequently employed by J. von Liebig in establishing the doctrine of
the characterization and basicity of acids. Both phosphoric and
phosphorous acids became known, although imperfectly, towards the end of
the 18th century; phosphorous acid was first obtained pure by Davy in
1812, while pure phosphorous oxide, the anhydride of phosphorous acid,
remained unknown until T.E. Thorpe's investigation of the products of
the slow combustion of phosphorus. Of other phosphorus compounds we may
here notice Gengembre's discovery of phosphuretted hydrogen (phosphine)
in 1783, the analogy of which to ammonia was first pointed out by Davy
and supported at a later date by H. Rose; liquid phosphuretted hydrogen
was first obtained by Thenard in 1838; and hypophosphorous acid was
discovered by Dulong in 1816. Of the halogen compounds of phosphorus,
the trichloride was discovered by Gay Lussac and Thenard, while the
pentachloride was obtained by Davy. The oxychloride, bromides, and other
compounds were subsequently discovered; here we need only notice
Moissan's preparation of the trifluoride and Thorpe's discovery of the
pentafluoride, a compound of especial note, for it volatilizes
unchanged, giving a vapour of normal density and so demonstrating the
stability of a pentavalent phosphorus compound (the pentachloride and
pentabromide dissociate into a molecule of the halogen element and
phosphorus trichloride).
In 1840 C.F. Schonbein investigated ozone, a gas of peculiar odour
(named from the Gr. [Greek: ozein], to smell) observed in 1785 by Martin
van Marum to be formed by the action of a silent electric discharge on
the oxygen of the air; he showed it to be an allotropic modification of
oxygen, a view subsequently confirmed by Marignac, Andrews and Soret. In
1845 a further contribution to the study of allotropy was made by Anton
Schrotter, who investigated the transformations of yellow and red
phosphorus, phenomena previously noticed by Berzelius, the inventor Of
the term "allotropy." The preparation of crystalline boron in 1856 by
Wohler and Sainte Claire Deville showed that this element also existed
in allotropic forms, amorphous boron having been obtained simultaneously
and independently in 1809 by Gay Lussac and Davy. Before leaving this
phase of inorganic chemistry, we may mention other historical examples
of allotropy. Of great importance is the chemical identity of the
diamond, graphite and charcoal, a fact demonstrated in part by Lavoisier
in 1773, Smithson Tennant in 1706, and by Sir George Steuart-Mackenzie
(1780-1848), who showed that equal weights of these three substances
yielded the same weight of carbon dioxide on combustion. The allotropy
of selenium was first investigated by Berzelius; and more fully in 1851
by J.W. Hittorf, who carefully investigated the effects produced by
heat; crystalline selenium possesses a very striking property, viz. when
exposed to the action of light its electric conductivity increases.
Another element occurring in allotropic forms is sulphur, of which many
forms have been described. E. Mitscherlich was an early worker in this
field. A modification known as "black sulphur," soluble in water, was
announced by F.L. Knapp in 1848, and a colloidal modification was
described by H. Debus. The dynamical equilibrium between rhombic, liquid
and monosymmetric sulphur has been worked out by H.W. Bakhuis Roozeboom.
The phenomenon of allotropy is not confined to the non-metals, for
evidence has been advanced to show that allotropy is far commoner than
hitherto supposed. Thus the researches of Carey Lea, E.A. Schneider and
others, have proved the existence of "colloidal silver"; similar forms
of the metals gold, copper, and of the platinum metals have been
described. The allotropy of arsenic and antimony is also worthy of
notice, but in the case of the first element the variation is
essentially non-metallic, closely resembling that of phosphorus. The
term allotropy has also been applied to inorganic compounds, identical
in composition, but assuming different crystallographic forms. Mercuric
oxide, sulphide and iodide; arsenic trioxide; titanium dioxide and
silicon dioxide may be cited as examples.
The joint discovery in 1859 of the powerful method of spectrum analysis
(see SPECTROSCOPY) by G.R. Kirchhoff and R.W. Bunsen, and its
application to the detection and the characterization of elements when
in a state of incandescence, rapidly led to the discovery of many
hitherto unknown elements. Within two years of the invention the authors
announced the discovery of two metals, rubidium and caesium, closely
allied to sodium, potassium and lithium in properties, in the mineral
lepidolite and in the Durkheim mineral water. In 1861 Sir William
Crookes detected thallium (named from the Gr. [Greek: thallos], a green
bud, on account of a brilliant green line in its spectrum) in the
selenious mud of the sulphuric acid manufacture; the chemical affinities
of this element, on the one hand approximating to the metals of the
alkalis, and on the other hand to lead, were mainly established by C.A.
Lamy. Of other metals first detected by the spectroscope mention is to
be made of indium, determined by F. Reich and H.T. Richter in 1863, and
of gallium, detected in certain zinc blendes by Lecoq de Boisbaudran in
1875. The spectroscope has played an all-important part in the
characterization of the elements, which, in combination with oxygen,
constitute the group of substances collectively named the "rare earths."
The substances occur, in very minute quantity, in a large number of
sparingly-distributed and comparatively rare minerals--euxenite,
samarksite, cerite, yttrotantalite, &c. Scandinavian specimens of these
minerals were examined by J. Gadolin, M.H. Klaproth, and especially by
Berzelius; these chemists are to be regarded as the pioneers in this
branch of descriptive chemistry. Since their day many chemists have
entered the lists, new and powerful methods of research have been
devised, and several new elements definitely characterized. Our
knowledge on many points, however, is very chaotic; great uncertainty
and conflict of evidence circulate around many of the "new elements"
which have been announced, so much so that P.T. Cleve proposed to divide
the "rare earth" metals into two groups, (1) "perfectly characterized";
(2) "not yet thoroughly characterized." The literature of this subject
is very large. The memorial address on J.C.G. de Marignac, a noted
worker in this field, delivered by Cleve, a high authority on this
subject, before the London Chemical Society (_J.C.S. Trans._, 1895, p.
468), and various papers in the same journal by Sir William Crookes,
Bohuslav Brauner and others should be consulted for details.
In the separation of the constituents of the complex mixture of oxides
obtained from the "rare earth" minerals, the methods generally forced
upon chemists are those of fractional precipitation or crystallization;
the striking resemblances of the compounds of these elements rarely
admitting of a complete separation by simple precipitation and
filtration. The extraordinary patience requisite to a successful
termination of such an analysis can only be adequately realized by
actual research; an idea may be obtained from Crookes's _Select Methods
in Analysis_. Of recent years the introduction of various organic
compounds as precipitants or reagents has reduced the labour of the
process; and advantage has also been taken of the fairly complex double
salts which these metals form with compounds. The purity of the
compounds thus obtained is checked by spectroscopic observations.
Formerly the spark- and absorption-spectra were the sole methods
available; a third method was introduced by Crookes, who submitted the
oxides, or preferably the basic sulphates, to the action of a negative
electric discharge _in vacuo_, and investigated the phosphorescence
induced spectroscopically. By such a study in the ultra-violet region of
a fraction prepared from crude yttria he detected a new element
victorium, and subsequently by elaborate fractionation obtained the
element itself.
The first earth of this group to be isolated (although in an impure
form) was yttria, obtained by Gadolin in 1794 from the mineral
gadolinite, which was named after its discoverer and investigator.
Klaproth and Vauquelin also investigated this earth, but without
detecting that it was a complex mixture--a discovery reserved for C.G.
Mosander. The next discovery, made independently and simultaneously in
1803 by Klaproth and by W. Hisinger and Berzelius, was of ceria, the
oxide of cerium, in the mineral cerite found at Ridderhytta,
Westmannland, Sweden. These crude earths, yttria and ceria, have
supplied most if not all of the "rare earth" metals. In 1841 Mosander,
having in 1839 discovered a new element lanthanum in the mineral cerite,
isolated this element and also a hitherto unrecognized substance,
didymia, from crude yttria, and two years later he announced the
determination of two fresh constituents of the same earth, naming them
erbia and terbia. Lanthanum has retained its elementary character, but
recent attempts at separating it from didymia have led to the view that
didymium is a mixture of two elements, praseodymium and neodymium (see
DIDYMIUM). Mosander's erbia has been shown to contain various other
oxides--thulia, holmia, &c.--but this has not yet been perfectly worked
out. In 1878 Marignac, having subjected Mosander's erbia, obtained from
gadolinite, to a careful examination, announced the presence of a new
element, ytterbium; this discovery was confirmed by Nilson, who in the
following year discovered another element, scandium, in Marignac's
ytterbia. Scandium possesses great historical interest, for Cleve showed
that it was one of the elements predicted by Mendeleeff about ten years
previously from considerations based on his periodic classification of
the elements (see ELEMENT). Other elements predicted and characterized
by Mendeleeff which have been since realized are gallium, discovered in
1875, and germanium, discovered in 1885 by Clemens Winkler.
In 1880 Marignac examined certain earths obtained from the mineral
samarskite, which had already in 1878 received attention from
Delafontaine and later from Lecoq de Boisbaudran. He established the
existence of two new elements, samarium and gadolinium, since
investigated more especially by Cleve, to whom most of our knowledge on
this subject is due. In addition to the rare elements mentioned above,
there are a score or so more whose existence is doubtful. Every year is
attended by fresh "discoveries" in this prolific source of elementary
substances, but the paucity of materials and the predilections of the
investigators militate in some measure against a just valuation being
accorded to such researches. After having been somewhat neglected for
the greater attractions and wider field presented by organic chemistry,
the study of the elements and their inorganic compounds is now rapidly
coming into favour; new investigators are continually entering the
lists; the beaten paths are being retravcrsed and new ramifications
pursued.