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Title: The Rare Earths: Their Occurrence, Chemistry, and Technology

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THE RARE EARTHS

THE RARE EARTHS

THEIR OCCURRENCE,

CHEMISTRY, AND

TECHNOLOGY

BY

S. I. LEVY
B.A. (Cantab.), B.Sc. (Lond.), A.I.C.
LATE HUTCHINSON RESEARCH STUDENT OF ST. JOHN'S COLLEGE

CAMBRIDGE

WITH ILLUSTRATIONS

LONDON

EDWARD ARNOLD
1915

[All rights reserved]

PREFACE
During the thirty years which have elapsed since Dr. Auer’s application
of the rare earths to the production of artificial light, the incandescent
mantle industry has developed to an extent which gives it a prominent place
among those chemical industries which may be considered essential to
modern civilisation. This technical development has in turn assisted and
stimulated the scientific examination of the elements of this group, with the
result that ordered and accurate knowledge is beginning to replace the
confused and uncertain data which had been collected by earlier workers in
the field. These advances have served to emphasise the scientific interest
and importance of the rare earth group, and the difficulty of bringing it into
relation with the other elements. The relatively scant attention devoted to
the study of this province of inorganic chemistry by teachers and students in
England is probably due no less to the difficulty in classification, and the
uncertainty with regard to the homogeneity and individuality of the various
members of the family—an uncertainty by no means entirely removed even
now—than to the fact that the very extensive literature on the subject is
somewhat confused and difficult of access, especially to those unfamiliar
with the French and German languages.
The present work is intended to give a general but fairly comprehensive
account of the rare earth group. In accordance with general usage, the
elements zirconium and thorium have been included, though these are now
recognised as falling outside the limits of the rare earth group proper. The
inclusion of titanium, which chemically is so far removed from the cerium
and yttrium elements, has been considered desirable, not only on account of
its general occurrence in the rare earth minerals, and its position in Group
IVb with zirconium, cerium, and thorium, but also on account of its
increasing chemical and technical interest, and its use in the ordinary
quantitative laboratory operations.
Though the nature of the matter embraced has rendered the division into
three parts desirable, the whole subject has been treated primarily from the
chemical standpoint. In view, however, of the occurrence of considerable
quantities of monazite within the British Empire, and of the possibility that
in the near future the Brazilian fields will not remain the sole source of

thorium nitrate, stress has been laid on the technical aspect, which is more
especially developed as regards the production of monazite and the
incandescent mantle industry in Chapters VII and XVII-XX.
In the preparation of Part I full use has been made of Dana’s
indispensable ‘System of Mineralogy,’ as well as of the encyclopædic
‘Handbuch’ of Hintze, whilst for Part II the excellent monograph of R. J.
Meyer, in Abegg’s ‘Handbuch,’ Vol. III, Div. I, and the work of the same
author and Hauser, ‘Die Analyse der seltenen Erden und der Erdsäuren,’
Vols. XIV-XV of ‘Die Chemische Analyse,’ have been of service.
I have great pleasure in expressing my gratitude to Mr. A. Hutchinson, of
Pembroke College, Cambridge, who has kindly read for me the manuscript
of Part I, and suggested improvements; to Dr. H. J. H. Fenton, of Christ’s
College, who has given me similar assistance in Part II; and to Dr. S.
Ruhemann, of Gonville and Caius College, who has read Parts II and III. I
am also greatly indebted to Mr. E. J. Holmyard, of Sidney Sussex College,
who helped me with the preparation of Part II; and to Mr. H. M. Spiers, of
Gonville and Caius College, who read the proofs for me with special
thoroughness and care.
I have also to thank Professor Soddy and his publishers, Messrs.
Longmans, Green & Co., for kind permission to reproduce from ‘The
Chemistry of the Radio-Elements’ the diagram on p. 138.
S. I. LEVY.

CONTENTS

PART I
OCCURRENCE OF THE RARE EARTHS

CHAPTER PAGE

I. The Nature of the Minerals and their Mode of
Occurrence 1
II. The Silicates 30
(a) Silicates of Yttrium and Cerium Metals—Cerite;
Gadolinite, Glowing of Minerals; Allanite,
Hellandite, Thalénite and Thortveitite; etc.
(b) Silicates of Thorium and Zirconium—Thorite,
Zircon, Naegite; etc.
(c) Mixed Silicates—Eudialyte, Beckelite; etc.
III. The Titano-silicates and Titanates 52
(a) Titano-silicates—Yttrotitanite, Titanite; etc.
(b) Titanates—Yttrocrasite, Delorenzite, Ilmenite;
etc.
IV. The Tantalo-Columbates 60
(a) Containing no Titanium Dioxide—Samarskite
(Annerödite), Plumboniobite, Yttrotantalite,
Fergusonite, Sipylite; etc.
(b) Containing Titanium Dioxide—Æschynite; the
isodimorphous series Euxenite, Polycrase,
Blomstrandine, Priorite; Risörite, Wiikite; etc.
V. The Oxides and Carbonates 72

(a) Oxides—Uraninite, Thorianite, Baddeleyite;
Rutile, Anatase and Brookite; etc.
(b) Carbonates—Lanthanite; Parisite (Synchisite),
Cordylite; etc.
VI. The Phosphates and Halides 82
(a) Phosphates—Monazite, Xenotime (Hussakite);
etc.
(b) Halides—Yttrocerite, Yttrofluorite; etc.
VII. The Monazite Sands 90
VIII. Radioactivity of the Minerals 99

PART II
THE CHEMISTRY OF THE ELEMENTS

IX. General Properties of the Cerium and Yttrium
Groups 111
X. General Methods of Separation 142
XI. The Cerium Group—Cerium 156
XII. The Cerium Group (continued)—Lanthanum,
Praseodymium, Neodymium, and Samarium 168
XIII. The Terbium Group 184
XIV. The Erbium and Ytterbium Groups—Yttrium and
Scandium 194
XV. The Group IVa Elements—Titanium 219
XVI. The Group IVa Elements (continued)—Zirconium and
Thorium 238

PART III
THE TECHNOLOGY OF THE ELEMENTS

XVII. The Incandescent Mantle Industry—Historical and
General Introduction 265
XVIII. The Chemical Treatment of Monazite 275
XIX. The Manufacture of Mantles from Cotton and Ramie 291
XX. Artificial Silk—its Production and Use in the
Mantle Industry 301
XXI. Other Technological Uses of the Cerium and
Yttrium Elements, Zirconium and Thorium 313
XXII. The Industrial Applications of Titanium and its
Compounds 325
Index 342

TABLE OF ABBREVIATIONS EMPLOYED IN THE
REFERENCES

Abstr. Chem. Soc. Abstracts in Journal of the Chemical Society.
Amer. Chem. J. American Chemical Journal.
Amer. J. Sci. American Journal of Science.
Annalen Justus Liebig’s Annalen der Chemie.
Ann. Chim. Phys. Annales de Chimie et de Physique.
Astrophys. J. Astrophysical Journal.
Ber. Berichte der Deutschen chemischen
Gesellschaft.
Berz. Jahres. Berzelius’ Jahresbericht über die Fortschritte
der Chemie und Mineralogie.
Bull. Imp. Inst. Bulletin of the Imperial Institute.
Bull. Soc. chim. Bulletin de la Société chimique de France.
Bull. Soc. franc. Min. Bulletin de la Société française de
Minéralogie.
Bull. Soc. franc. Bulletin de la Société française de
Photog. Photographie.
Bull. U. S. Geol. Survey Bulletin of the United States Geological
Survey.
Cass. Mag. Cassier’s Magazine.
Centr. Min. Centralblatt für Mineralogie, Geologie und
Paläontologie.
Chem. Eng. Chemical Engineer.
Chem. Ind. Chemische Industrie.
Chem. News Chemical News.
Chem. Zeitg. Chemiker Zeitung.
Chem. Zentr. Chemisches Zentralblatt.
Compt. rend. Comptes rendus hebdomadaires des Séances
de l’Académie des Sciences.
Dingl. Polyt. J. Dingler’s Polytechnisches Journal.

D. R. P. Deutsche Reichspatentschrift.
E. English Patent Specification.
Elect. chem. Ind. Electrochemical Industry (since 1904,
Electrochemical and Metallurgical
Industry).
F. Brevet d’Invention de la République
Française.
J. Amer. Chem. Soc. Journal of the American Chemical Society.
J. Gasbel. Journal für Gasbeleuchtung.
J. Gaslighting Journal of Gaslighting.
J. Ind. Eng. Chem. Journal of Industrial and Engineering
Chemistry.
J. pr. Chem. Journal für practische Chemie.
J. Russ. Phys. Chem. Journal of the Physical and Chemical Society
Soc. of Russia.
J. Soc. Chem. Ind. Journal of the Society of Chemical Industry.
Met. Chem. Eng. Metallurgical and Chemical Engineering.
Min. Mag. Mineralogical Magazine and Journal of the
Mineralogical Society.
Monats. Monatshefte für Chemie und verwandte Theile
anderer Wissenschaften.
Phil. Mag. Philosophical Magazine.
Phil. Trans. Philosophical Transactions of the Royal
Society of London.
Pogg. Ann. Poggendorff’s Annalen der Physik und
Chemie.
Proc. Amer. Acad. Proceedings of the American Academy.
Proc. Chem. Soc. Proceedings of the Chemical Society.
Proc. Roy. Soc. Proceedings of the Royal Society.
Prog. Age Progressive Age (now Gas Age).
Publ. Astrophys. Publikationen des Astrophysikalischen
Observ. Potsdam Observatoriums zu Potsdam.
Schweigg. J. Schweigger’s Journal für Chemie und
Physik.

Sitzungsber. kaiserl. Sitzungsberichte der kaiserlich Akademie der
Akad. Wiss. Wien Wissenschaften zu Wien.
Sitzungsber. königl. Sitzungsberichte der königlich Preussischen
Akad. Wiss. Berlin Akademie der Wissenschaften zu Berlin.
Stahl Eisen Stahl und Eisen.
Trans. Amer. El. chem. Transactions of the American Electrochemical
Soc. Society.
Trans. Amer. Inst. Min. Transactions of the American Institute of
Eng. Mining Engineers.
Trans. Chem. Soc. Transactions of the Chemical Society.
Tsch. Min. Mitt. Tschermak’s Mineralogische Mittheilungen.
U. S. Geol. Survey United States Geological Survey—Mineral
Resources of the United States.
U. S. P. United States Patent Specification.
Zeitsch. anal. Chem. Zeitschrift für analytische Chemie.
Zeitsch. angew. Chem. Zeitschrift für angewandte Chemie.
Zeitsch. anorg. Chem. Zeitschrift für anorganische Chemie.
Zeitsch. Elektrochem. Zeitschrift für Elektrochemie.
Zeitsch. Kryst. Min. Zeitschrift für Krystallographie und
Mineralogie.
Zeitsch. physikal. Zeitschrift für physikalische Chemie,
Chem. Stöchiometrie und Verwandtschaftslehre.
Zeitsch. pr. Geol. Zeitschrift für praktische Geologie.
Zeitsch. wiss. Zeitschrift für wissenschaftliche Photographie,
Photochem. Photophysik und Photochemie.

INTRODUCTION

By Sir William Crookes, O.M., F.E.S.
The mysterious group of substances to which have been given the title of
“rare earths” has long been the subject of my special study, and no one
knows better the magnitude of the difficulties encountered in the
investigation, or realises more clearly the comparative insignificance of the
knowledge we have acquired. The rare earths constitute the most striking
example of the association of chemical substances with others which are
closely allied to themselves, and from which they are separable only with
extreme difficulty. They form a group to themselves, sharply demarcated
from the other elements, and it is my belief that by following the study of
them to the utmost limits, we may arrive at the explanation of what the
chemical elements really are and how they originated, and discover the
reasons for their properties and mutual relations. When this knowledge has
been wrested from Nature chemistry will be established upon an entirely
new basis. We shall be set free from the need for experiment, knowing a
priori what the result of each and every experiment must be; and our
knowledge then will as much transcend our present scientific systems as the
knowledge of the skilled mathematician of the present day exceeds that of
primitive man, counting upon his fingers. The great problem of the nature
and genesis of the elements is approaching solution, and when the
consummation is reached it will undoubtedly be found that the study of the
rare earths has been an important factor in bringing it about.
There has long been a need for a work in the English language dealing
historically and descriptively with these substances, and Mr. Levy’s book is
well fitted to fill the gap. The chapters on the technical applications of the
rare earths are particularly valuable, and the chemical aspect of the
incandescent lighting industry is admirably treated. The author is to be
congratulated upon having successfully achieved an important and useful
piece of work.
WILLIAM CROOKES.
December 1914.

T H E R A R E E A RT H S

PART I

OCCURRENCE OF THE RARE EARTHS

CHAPTER I

THE NATURE OF THE MINERALS AND THEIR MODE OF
OCCURRENCE
The history of the rare earth minerals begins in the year 1751, when the
Swedish mineralogist Cronstedt described a new mineral, which he had
found intimately mixed with chalcopyrite[1] in the quarry of Bastnäs, near
Ryddarhyttan, in the province of Westmannland, Sweden. Cronstedt gave
the mineral the name Tung-sten (heavy stone); but as the name Tenn-spat
(heavy spar, or heavy mineral) had already been selected by Wallerius
(1747) for a new species from Bohemia, believed to contain tin, the choice
was not a happy one. More than fifty years after its discovery, a new earth,
now known as ceria, was isolated from Cronstedt’s mineral, for which at the
same time the name Cerite was proposed.[2] Meanwhile, however, the
Finnish chemist Johann Gadolin had observed, in the year 1794, a new earth
in a mineral discovered by Arrhenius at Ytterby in Sweden in 1788; he
called the new oxide Ytterbia, and the mineral in which he observed it,
Ytterbite. The discovery was confirmed in 1797 by Ekeberg, who suggested
the names Yttria and Gadolinite for the oxide and mineral respectively;
these names were accepted by Klaproth, and soon came into general use.[3]
Whilst then Cerite was the first of the rare earth minerals to be discovered, it
was in Gadolinite that new elements were first recognised, and the
chemistry of the rare earths began in 1794 with Gadolin’s observation.
[1] Chalcopyrite, or Copper pyrites, is a mixed sulphide of iron and copper, of the
approximate formula CuFeS₂.
[2] For the history of the name Tungsten, see under the mineral Cerite, Ch. II.
[3] The history of these names will be found somewhat more fully under Gadolinite, Ch.
II.

During the nineteenth century a considerable number of rare earth
minerals was discovered and analysed; the quantities of the minerals
observed, however, were so small that the name ‘Rare earths,’ applied to the
new oxides found, was in every sense justified. Until the year 1885, though
by that time the scientific interest of the group had been fully demonstrated
by the discovery of several new elements, it was supposed that the minerals
were almost entirely confined to a few scattered localities in Scandinavia
and the Ural mountains. In that year Dr. Auer von Welsbach announced his
application of the rare earths to the manufacture of incandescent mantles.
Immediately there was a great demand for raw material for the preparation
of thoria and ceria. The agents of the Welsbach Company visited all the
important mining centres of Europe and America, intent on a search which
shortly made it clear that the metals of the so-called ‘rare earths’ are really
quite widely distributed in nature. The chief commercial deposits are the
monazite sands of the Carolinas, the Idaho basin, and Brazil, the gem-
gravels of Ceylon, and the remarkable deposits of gadolinite and allied
minerals at Barringer Hill in Texas.
Whilst deposits of commercial importance are not very common,
improved scientific methods and more careful search have shown that in
traces the rare earths are of exceedingly wide distribution. Sir William
Crookes has shown that yttria earths are often present in calcite and in coral;
whilst Headden[4] noted that quite considerable amounts (up to 0·03 per
cent.) were present in a yellow phosphorescent variety of calcite from
Colorado. Similarly Humphreys[5] found that fluorspar usually contains
traces of yttrium, whilst one or two phosphorescent varieties contain
quantities varying up to 0·05 per cent. The presence of yttria elements in
phosphorescent varieties of calcite is interesting, and some connection has
been suggested; there is, however, no positive ground for the belief in such
a relation.
[4] Amer. J. Sci., 1906, [iv.], 21, 301.
[5] Astrophys. J., 1904, 20, 266.

More recently Eberhard[6] has found very considerable quantities of rare
earths in cassiterite (tin dioxide, SnO₂) and wolframite [an iron manganese
tungstate, (Fe,Mn)WO₄]. A specimen of wolframite from the Erzgebirge
was found to contain nearly 0·4 per cent. of rare earths, over half of this
quantity being scandium oxide. A process which is readily susceptible of
commercial application has been worked out by R. J. Meyer,[7] for the

extraction of scandia and the yttria earths from the mixed oxides left after
the treatment of wolframite for tungstic acid.
[6] Sitzungsber. königl. Akad. Wiss. Berlin, 1908, 851; 1910, 404.
[7] Meyer, Zeitsch. anorg. Chem., 1908, 60, 134. Meyer und Winter, ibid., 1910, 67, 398.

Using the spectroscopic method, which is capable of detecting one part of
scandia in twenty thousand, Eberhard (loc. cit.) has found that minute
quantities of scandia and yttria earths are present in almost all the
commoner rocks and minerals. The minerals richest in scandium were beryl,
cassiterite, wolfram, the zircon minerals, and the titanates and columbates of
the ceria and yttria oxides. These results are in agreement with the
observations of Sir William Crookes,[8] who has made the study of
scandium especially his own. From the fact that scandium was often
observed unaccompanied by any other member of the rare earth group,
Eberhard rather favours Urbain’s conclusion[9] that scandium may not be a
member of the rare earth family. Spectroscopic examination has also shown
the existence of some of the rare earth elements in the sun and stars (see
Europium, p. 189).
[8] Phil. Trans. 1910, A, 210, 359.
[9] See under Scandium in Pt. II.

In view of this extraordinarily wide distribution of the rare earths in the
mineral world, it is but natural that they should be found also in the
vegetable and animal kingdoms. Tschernik[10] found 10 per cent. of rare
earths in the ash of a coal from Kutais, in the Caucasus, and smaller
quantities have been found in the ashes of various plants; members of the
group have also been identified in the human body.
[10] See Abstr. in Zeitsch. Kryst. Min., 1899, 31, 513.
Apart from the general occurrence in traces throughout the mineral
kingdom, the minerals in which the rare earths occur are not very common;
and though of fairly wide distribution, they are found usually only in small
quantities. The earliest known locality, and the most fruitful in regard to
number of species, has been the southern part of the Scandinavian
peninsula;[11] the minerals occur in the numerous pegmatite veins traversing
the granitic country-rock. The mining district round Miask, in the Ural
mountains, has also long been known as a fruitful source. Other districts in
Europe are the Harz and Erzgebirge, the Laacher See in Prussia,
Joachimsthal in Bohemia, Dauphiné, Cornwall, etc. In the United States

numerous localities are known; the chief are in the Carolinas and Georgia,
Idaho, Oregon, California, Texas, Colorado, Virginia, Pennsylvania and
Connecticut. Many of the southern provinces of Brazil also furnish
important sources; the famous diamond fields of Minas Geraes, Matto-
Grosso, Goyaz and the surrounding provinces yield numerous species,
whilst the sands along the southern coasts of Bahia are rich in monazite, and
form to-day the most important source of the mineral. Monazite, as well as
other rare earth minerals, occurs also in South Africa. An interesting
species, plumboniobite (q.v.), has recently been found in German East
Africa. From Australia numerous occurrences are reported, whilst in Canada
only a few districts are known to yield members of the group. In Asia
important localities are Ceylon—the famous gem-gravels being the most
accessible source—and one or two districts in Japan; monazite has been
reported recently in considerable quantities near Travancore, India.[12] A
more extended search will doubtless show that they occur in many other
places.
[11] See Brögger, Die Mineralien der Süd-Norwegische Granit-Pegmatitgänge,
Christiania, 1906.
[12] Bull. Imp. Inst., 1911, vol. ix; No. 2, p. 103.

For several reasons, the rare earth minerals[13] form a group of the highest
scientific interest. In the first place, they are generally of very complex
composition, more especially with regard to their rare earth content. Thus,
whilst it sometimes happens that one or other of the two groups of oxides
(the ceria and yttria groups) may predominate to the complete exclusion of
the second, it is no uncommon thing for a species to contain almost all the
elements of the rare earth family. On the other hand, it is very uncommon
for as much as 50 per cent. of the rare earth content to consist of any one
oxide. The usual case is that a mineral contains chiefly yttria earths with
some ceria earths, or vice versâ, the two sub-groups being almost always
complex mixtures of several oxides, in which occasionally one may
predominate. The remarkable similarity in chemical behaviour of the rare
earth elements, and the difficulty of separating them, correspond to this
peculiarity in their occurrence.
[13] The phrase ‘rare earth minerals’ will be used whenever it is desired to indicate
collectively those minerals of which the yttria and ceria earths form an important
constituent, as contrasted to those in which only traces of these oxides occur. Such
minerals may often contain titanium, zirconium, or thorium, and, for convenience, the

term may be taken to include the commoner zirconium and thorium minerals, but not the
commoner titanium minerals.

A second point of even greater interest is that the rare earth minerals are
as a general rule strongly radio-active; further, it only occasionally happens
that any mineral in which the rare earths do not form an important
constituent has more than the feeblest activity; the exceptions being, of
course, those uranium minerals which do not contain rare earths. The
connection may be pushed even further; for whilst it appears that hardly any
rock or mineral possesses absolutely no radio-activity, it is equally worthy
of notice that traces of the rare earths, if not quite universal in the mineral
world, are yet normally found in the majority of common minerals. As a
natural consequence of their activity, the rare earth minerals are also as a
rule rich in helium. These facts and the problems which they open up will
be treated more fully in a later chapter.
A point of further interest is that of the age of the rare earth minerals.
Except in a few cases where they are obviously of secondary formation,
these minerals are among the oldest known to us. They occur usually in
igneous rocks, particularly in granites which have been considerably
metamorphosed. Where erosion has occurred, they are found in deposits of
such a nature as to leave very little doubt that the original rock was of
plutonic formation and of very considerable age. Whilst it is true, however,
that the rare earth minerals are generally of very great antiquity (none of the
primary minerals being of more recent date than the palæozoic age),
Eberhard has pointed out that the age and nature of common rocks seem to
have absolutely no influence on the traces of scandia and yttria oxides
which they contain. The geological evidence shows that the rare earth
minerals are on the whole exceedingly stable, and that they have been
generally formed during the pegmatitic alteration of granites. As early as the
year 1840, Scheerer drew attention to these facts, and to the extreme age of
the rare earth minerals; but so far his observation seems to have attracted
little attention, and no explanation has been put forward.
In the following chapters no attempt is made to treat the rare earth
minerals fully. An alphabetical list of all the minerals of any importance
which contain rare earths, titanium, zirconium or thorium is given, and of
these several are selected for fuller treatment. The basis of selection has
been somewhat arbitrary. Those species which are of mineralogical
importance, as well as those to which any special historical, scientific or

commercial interest attaches, have of course been singled out; in addition,
the more recently discovered species have occasionally been considered
worthy of separate mention.[14]
[14] A full list of the minerals containing rare earths known up to 1904, with an account
of their properties and very full references, will be found in the work of Dr. J. Schilling,
Das Vorkommen der Seltenen Erden im Mineralreiche, 1904.
It is now being realised that some knowledge of crystallography is
essential to the chemist, and for this reason short accounts of the
crystallography of the selected types have been given. Apart from this,
every effort has been made to render the mineralogy intelligible to the
student of chemistry who has devoted no attention previously to this
subject, and also to stimulate an interest in the problems of mineral
chemistry, unfortunately too often ignored by our present-day teachers. The
rare earth minerals afford good examples of some phenomena of great
interest to the chemist, as, e.g. Isomorphism and Solid Solution,
Dimorphism, Isodimorphism, and Molecular Change, and in one or two
cases these are treated rather fully.
No special advantages are claimed for the system of classification, which
is merely one of convenience. The minerals are divided into five groups:—
(1) The Silicates, which are grouped into three sub-divisions.
(2) The Titano-silicates and the Titanates.
(3) The Tantalo-columbates, sub-divided into those free from titanium
and those in which titanium is present.
(4) The Oxides and Carbonates.
(5) The Halides and Phosphates.
A separate chapter has been devoted to the monazite sands, and another to
the radio-active properties of the minerals.
Alphabetical List of Minerals containing Titanium, Zirconium, Thorium, or Elements of the
Cerium and Yttrium Groups.
The following list contains all but a few entirely unimportant members of these classes of minerals.
The names of those species selected for fuller treatment are printed in heavy type, whilst names
of those not so selected, which for convenience are included under the generic term ‘Rare earth
mineral,’ i.e. roughly all those containing Thorium, or elements of the Cerium and Yttrium
groups, and the commoner Zirconium minerals, as distinguished from minerals containing
Titanium, are printed in italics. (See footnote on p. 4.) Their properties are given in the following
order:—
Chemical Composition and Rare Earth Content.
Crystallographic Data.
Physical Properties.

Locality, etc.
The following contractions are employed:
E = any element or elements of the cerium or yttrium groups.
Cer = oxides of the cerium metals.
Yttr = oxides of the yttrium metals.
G = Specific Gravity.
H = Hardness.
Aenigmatite.
A Titanosilicate of Fe´´ and Na, with small proportions of Fe´´´ and Al´´´. Closely allied to the
amphiboles. TiO₂ = 7-8%.
Anorthic. Habit prismatic.
G = 3·80-3·86. H = 51⁄2. Black; pleochroism strong.
Greenland and S. Norway.
Aeschynite
A Titanocolumbate of Cerium metals, with Th, Fe, Ca, Mn, aq. Cer = 19·4-24·1; Yttr = 1·1-3·1;
ThO₂ = 15·7-17·6; TiO₂ = 21-22%.
Rhombic, holosymmetric. Habit prismatic or tabular.
G = 4·9-5·7. H = 5·6. Black; opaque.
Hitterö, Norway; Miask, Urals; also in Germany and Brazil.
Allanite (Orthite).
H₂O, 4R´´O, 3R´´´₂O₃, 6SiO₂, where R´´ = Ca, Fe´´, Be, and R´´´ = Al, Fe´´´, E. An epidote
containing rare earths. Cer = 3·6-51 (usually 10-25); Yttr = 0-8 (usually < 3); ThO₂ = 0-3·5%.
Monoclinic; isomorphous with epidote.
G = 3·5-4·2. H = 51⁄2-6. Brown to black; opaque.
Widely distributed in Greenland and Scandinavia.
Alvite (Anderbergite).
Silicate of Zr and E, with Ca, Mg, Be, Al, Cu, Zn, and aq. in small quantities. Cer → 3·98; Yttr →
22; ZrO₂ = 30·5-61·4%.
Tetragonal; optically isotropic. Pseudomorphous after zircon.
G = 3·3-4·3. H = 5-6. Yellowish brown; transparent.
Ytterby, Sweden; Arendal, Norway; various localities in N. America.
Anatase (Octahedrite).
Titanium dioxide. TiO₂ = 97-100%.
Tetragonal; habit octahedral.
G = 3·82-3·95. H = 51⁄2-6. Transparent to opaque; brown to black.
Dauphiné; Bavaria; Cornwall; Norway; Brazil, etc.
Ancylite.
4Ce(OH)CO₃ + 3SrCO₃ + 3H₂O; with Fe, Mn, Ca, F, traces. Cer = 46·3%.
Rhombic; prismatic.
G = 3·95. H = 41⁄2. Brown; translucent.
Plain of Narsarsuk, Greenland.
Annerödite.
A parallel growth of Columbite on Samarskite, once believed to be a new species.
Corresponding to Columbite.

Arfvedsonite.
Metasilicate of Na, Ca, Fe´´, Zr; approximately 4Na₂O,3CaO,14FeO,(Al,Fe)₂O₃,21SiO₂. ZrO₂ = 1-
6%.
Monoclinic—an amphibole.
G = 3·44. H = 6. Black; pleochroism strong.
S. Greenland and S. Norway.
Arizonite.
Ferric metatitanate, Fe₂O₃,3TiO₂ or Fe₂(TiO₃)₃. TiO₂ = 36·7%.
Uncertain; apparently monoclinic.
G = 4·25. H = 6-7. Dark steel-grey; opaque.
Hackberry, Arizona.

Arrhenite.
Silico-tantalate of Yttrium metals, with Ce, Al, Fe, Ca, Be, aq. Yttr = 33·2; Cer = 2·6; ZrO₂ =
3·4%.
Amorphous.
G = 3·68. Red; translucent to opaque.
Ytterby, Sweden.
Astrophyllite.
Titano-silicate of Fe, Al, Mn, Zr, K, Na, with aq. ZrO₂ = 1·2-4·5; TiO₂ = 7-14%.
Rhombic. Cleavage (010) perfect.
G = 3·2-3·4. H = 3. Golden to bronze yellow; strongly pleochroic.
Brevik, Norway; El Caso Co., Colorado; Greenland.
Auerbachite.
An impure hydrated form of Zircon, ZrSiO₄. ZrO₂ = 55·2%.
Tetragonal; isotropic. Pseudomorphous after zircon.
G = 4·06. H = 6. Brownish-grey; translucent to opaque.
Alexandrovsk, Russia.
Auerlite.
P₂O₅
3ThO₂,[3SiO₂,P₂O₅]6H₂O; traces of Fe, Ca, Mg, Al, CO₂, etc. SiO₂ replaced by ? ThO₂ =
3
69·2-72·2%.
Tetragonal; probably a pseudomorph after Thorite.
G = 4·4-4·8. H = 2-3. Yellowish to orange-red.
Henderson Co., N. Carolina.

Baddeleyite.
ZrO₂, with small amounts of SiO₂, Fe₂O₃, Al₂O₃, CaO, etc. ZrO₂ = 96·5%.
Monoclinic.
G = 4·4-6·0. H = 61⁄2. Brown; pleochroic.
São Paulo, Brazil; Rakwana, Ceylon.
Bagrationite.
A variety of Allanite (orthite) with no important chemical difference.
Monoclinic; habit prismatic.
G = 3·84. H = 61⁄2. Black; translucent to opaque.
Achmatovsk, Urals.

Bastnäsite (Harmatite).
Hydrated fluocarbonate of Cerium metals, E(F)CO₃. Cer = 64-93·5; ThO₂ = 0-10%.
Hexagonal prisms, pseudomorphous after Tysonite (q.v.); or massive.
G = 4·9-5·2. H = 4-41⁄2. Yellow to brown; transparent.
Bastnäs, Sweden; Pike’s Peak, Colorado.

Beckelite.
Zirconosilicate of rare earths and lime, Ca₃E₄(Si,Zr)₃O₁₅. Cer = 59·7; Yttr = 2·8; ZrO₂ = 2·5%.
Cubic, in octahedra and dodecahedra. Cubic cleavage.
G = 4·15. Brown; transparent.
Near Sea of Azov, Russia.
Benitoite.
A Titano-silicate of barium, BaTiSi₃O₉. TiO₂ = 20·1%.
Rhombohedral.
H = 61⁄2-7. Colourless to blue; transparent; pleochroism strong.
Source of San Benito River, California.

Blomstrandine.
Dimorphous with Polycrase (q.v.), and of same composition.
Orthorhombic; isomorphous with priorite (q.v.).
G = 4·5-5·0; H = 61⁄2. Bright black; translucent.
Hitterö and Arendal, Norway.
Blomstrandite.
Hydrated titano-columbate of U, with some Fe and Ca. TiO₂ = 10·7%.
Massive.
G = 4·17-4·25. H = 51⁄2. Black; opaque.
Nohl, Sweden.
Bodenite.
A variety of Allanite (q.v.), rich in Al and Ca, with no Be. Yttr = 17; Cer = 18%.
Monoclinic.
As Allanite.
Boden, near Marienburg.
Britholite.
A basic phosphosilicate of cerium metals, with Fe, Ca, Mg, Na, F. Cer = 60·5-60·9%.
Hexagonal; habit prismatic.
G = 4·446. H = 51⁄2. Brown; transparent.
Naujakasik, Greenland.

Bröggerite.
A variety of Uraninite (q.v.), with rare earths, Th, Pb, Fe, Ca, Si, aq., etc. Cer = 0·4; Yttr = 1·4-4·3;
ThO₂ = 4·7-6·1%. Traces of ZrO₂.
Cubic, in octahedra and dodecahedra.
G = 8·7-9·0. H = 5-6. Black; translucent to opaque.
Anneröd, near Moos, Norway.
Brookite.
Titanium dioxide, TiO₂ = 99-100%; trimorphous with Anatase and Rutile.
Orthorhombic.

G = 3·87-4·01. H = 51⁄2-6. Brown; opaque.
Dauphiné; Urals; Switzerland; Magnet Cove, Arkansas.

Calciothorite.
A variety of Thorite containing lime—5ThSiO₄,2Ca₂SiO₄ + 10H₂O. ThO₂ = 59·3%.
Completely amorphous.
G = 4·114. H = 41⁄2. Deep red; translucent.
Islands of Läven and Arö, Langesund Fiord, Norway.
Cappelenite.
A borosilicate of rare earth metals and barium, with traces of Th, Ca, K, Na, aq. Approximately
BaSiO₃, YBO₃. Cer = 4·2; Yttr = 52·5%.
Hexagonal; habit prismatic.
G = 4·407. H = 6-61⁄2. Greenish brown; translucent.
Island of Klein-Arö, Langesund Fiord, Norway.
Caryocerite (Karyocerite).
Complex fluosilicate of E, with Ta, Th, Ca; also CO₂, P₂O₅, B, Al, Fe, Mn, U, Mg, Na, aq., etc.
Approaching Melanocerite, (q.v.), but richer in Th. Very complex. Cer = 41·8; Yttr = 2·2; ThO₂
= 13·6; ZrO₂ = 0·5%.
Rhombohedral, but isotropic; apparently a pseudomorph after Melanocerite (q.v.)
G = 4·295. H = 5-6. Nut brown; translucent. Faces very brilliant, but striated. Lustre vitreous to
resinous.
Various rocks and shoals round Arö Island, Langesund Fiord, Norway.
Castelnaudite.
A variety of Xenotime (q.v.) containing Zr. Yttr = 60·4; ZrO₂ = 7·4%.
Tetragonal.
G = 4·5. H = 4-5. Greyish white to pale yellow.
Diamond sands of Brazil.
Cataplejite (Kataplejite).
H₄(Na₂,Ca)ZrSi₃O₁₁. ZrO₂ = 29·6-40% (usually 30-33%).
Monoclinic, pseudohexagonal. Becomes truly hexagonal at 140°C.
G = 2·8. H = 6. Yellow to brown; transparent to opaque.
A blue variety is known which contains no calcium.
Islands of Langesund Fiord, Norway; Narsarsuk, Greenland.
Cerite.
A basic silicate of Cerium metals, with Ca and Fe. Approximately H₃(Ca,Fe)Ce₃Si₃O₁₃. Cer =
50·7-71·8%. In a variety from Batoum, Tschermak reports Yttr = 7·6 and ZrO₂ = 11·7%.
Orthorhombic; usually massive or granular.
G = 4·9. H = 5-6. Brown to red; translucent to opaque.
Ryddarhyttan, Sweden; Batoum, Caucasus?
Chalcolamprite.
A silico-columbate of E, Zr, Ca, Fe, Na, K; R₂Cb₂F₂SiO₉, where R represents various metals. E =
3·41; ZrO₂ = 5·7%.
Cubic, in small octahedra.
G = 3·77. H = 51⁄2. Greenish brown; opaque. Metallic lustre (χαλκός = Copper, λαμπρός = lustre).
Narsarsuk, S. Greenland.

Churchite.
Hydrous phosphate of Cerium metals and Ca; Cer = 51·87%.
Monoclinic? Allegations only.
G = 3·14. H = 31⁄2. Greyish; transparent to translucent.
Cornwall.

Cleveite.
A variety of Uraninite (q.v.) rich in rare earths and helium. Cer = 2·3-2·9; Yttr = 10·0-10·3; ThO₂ =
4·6-4·8%.
Cubic; usually massive.
G = 7·49. H = 51⁄2. Black; opaque.
Arendal, Norway.
Cordylite.
Fluocarbonate of Cerium metals and Ba; E₂F₂Ba(CO₃)₃. Cer = 49·4%.
Hexagonal; isomorphous with Parisite (q.v.).
G = 4·31. H = 41⁄2. Yellow; transparent.
Plain of Narsarsuk, Greenland.
Cossyrite.
A variety of Aenigmatite (q.v.) of very complex composition, TiO₂ = 6-8%.
Anorthic.
G = 3·74. H = 5. Black; opaque.
Island of Pantellaria (formerly Cossyra).
Cyrtolite.
A pseudomorph after zircon, allied to Alvite (q.v.).
Tetragonal.
See Alvite.
Various localities in Scandinavia, and U.S.A.
Davidite.
A Titanate of Fe, U, V, Cr, and E—uncertain formula. TiO₂ > 50; E₂O₃ = 5-10%.
Cubic—in grains and rounded crystals.
G = 4 about. Black, with brilliant lustre.
Olary, S. Australia.

Delorenzite.
2FeO,UO₂,2Y₂O₃,24TiO₂. Yttr = 14·63; TiO₂ = 55%.
Rhombic; habit prismatic.
G = 4·7. H = 51⁄2-6. Black; translucent to opaque; lustrous.
Craveggia, Piedmont, Italy.
Derbylite.
FeO,Sb₂O₅ + 5FeO,TiO₂? TiO₂ = 35% about.
Orthorhombic; habit prismatic.
G = 4·53. H = 5. Pitch black; opaque; lustre resinous.
Tripuhy, Minas Geraes, Brazil.
Dysanalyte (Perovskite).
Approximately 6RTiO₃,R(Cb,Ta)₂O₆, where R = Ca, Fe´´. Believed by Hauser to be merely an
impure Perovskite (q.v.). Cer = 0-5·1; TiO₂ = 41·5-59·3%.
Cubic.

G = 4·13. H = 5-6. Black; opaque.
Vogtsburg, near Baden, Germany.
Elpidite.
Na₂Zr(Si₂O₅)₃, 11⁄2H₂O. ZrO₂ = 20·5%.
Orthorhombic.
G = 2·52-2·56. H = 7-8. Colourless to red; translucent.
Various localities in Greenland.
Endeiolite.
R´´Cb₂O₆(OH)₂ + R´´SiO₃ (cf. Chalcolamprite). E₂O₃ = 4·43; ZrO₂ = 3·78%.
Cubic.
G = 3·44. H = 4. Dark chocolate-brown; transparent.
Narsarsuk, Greenland.
Erdmannite (Michaelsonite).
A silicate of E and Ca, with Zr, Be, Th, Al, Fe, aq., etc. An altered Homilite? Cer = 17·7-34·9; Yttr
= 1·4-2·1; ThO₂ + ZrO₂ = 0-12%.
Amorphous; isotropic.
G = 3·01-3·39. H = 41⁄2. Brown to leek-green.
Near Brevig, Norway.
Erikite.
A phosphosilicate of E, Ca, Al, K and Na, with ThO₂, H₂O, etc. Cer = 40·5; ThO₂ = 3·3%.
Orthorhombic.
G = 3·473. H = 51⁄2-6. Brown; opaque.
Julianehaab, Greenland.
Eucolyte.
R´₄R´´₃Zr(SiO₃)₇, where R´ = K, Na, H, and R´´ = Ce(OH), Fe, Mn, Ca, and Zr(OCl) may replace
SiO₂? A very complex mineral. ZrO₂ = 10·9-20; Cer = 0-5·2%.
Rhombohedral.
G = 3·0-3·1. H = 5-51⁄2. Red to brown; translucent. Double Refraction strong, -ve.
Various localities in Norway.
Eucrasite.
An altered Thorite (q.v.) containing E, Ca, Fe, Mn, Na, Ti, H₂O, etc. Cer = 14; Yttr = 5·9; ThO₂ =
36·0; ZrO₂ = 0·6%.
Rhombic (Paijkull). Amorphous, isotropic (Brögger).
G = 4·39. H = 41⁄2-5. Brownish black; opaque.
Near Brevig, Norway.

Eudialite.
A variety of Eucolyte (q.v.) of the same composition.
As Eucolyte.
G = 2·92. Double Refraction strong, +ve. Otherwise as Eucolyte.
Greenland; Lapland; Arkansas, U.S.A.
Euxenite.
E(CbO₃)₃,E₂(TiO₃)₃,11⁄2H₂O; with U and Zr. Cer = 2·3-8·4; Yttr = 13·2-34·6; TiO₂ = 20-23%.
ThO₂ + ZrO₂ usually in traces.
Orthorhombic; usually massive.

G = 4·6-5·0. H = 61⁄2. Brownish-black; translucent to opaque.
Hitterö, Brevig, Jolster, Arendal, Norway; Cooglegong, Australia; N. Carolina.

Fergusonite.
Approximately E₂O₃, (Cb,Ta)₂O₅, with U, Fe, Ca. Cer = 0·5-13·9; Yttr = 27·9-47·1; ThO₂ + ZrO₂
= 0-7%. [Berzelius found Cer = 36·3; Yttr = 0% in one specimen.]
Tetragonal, polar.
G = 5·84-4·3 when largely hydrated. H = 5·6. Brown to black.
Norway; Australia; Texas, etc.
Florencite.
A silico-phosphate of E and Al. Cer = 28% approximately.
G = 3·6. H = 5. Yellow to red. Resinous lustre.
Minas Geraes and diamond localities in Brazil.
Fluocerite.
Basic fluoride of rare earth metals, E₂O₃,4EF₃. Cer = 81·4-82·6; Yttr = 1·1-4·3%.
Massive. Original hexagonal mineral of Berzelius and Haidinger, probably Tysonite (q.v.).
G = 5·7-5·9. H = 4. Reddish yellow; opaque.
Österby, Sweden.
Freyalite.
Silicate of E and Th, with Al, Fe, Mn, Na, aq., etc. Cer = 31·3; ThO₂ = 28·4; ZrO₂ = 6·3%.
Amorphous.
G = 4·06-4·17. H = 6. Brown; opaque; lustre resinous.
Brevig, Norway.

Gadolinite.
FeO, 2BeO, Y₂O₃, 2SiO₂, where Y = yttrium metals. Cer = 3·4-51·5 (usual 6-20); Yttr = 5-60
(usual 35-48)%.
Monoclinic; habit prismatic. Often amorphous and isotropic.
G = 4·0-4·5. H = 61⁄2-7. Brown and green. Double Refraction strong, +ve.
Ytterby and Fahlun, Sweden; Hitterö and Malö, Norway; Llano Co., Texas; Colorado, etc.
Geikielite.
(Mg,Fe´´)TiO₃. TiO₂ = 56·1-64·8%. Specimens rich in iron are called Picroilmenite.
Massive.
G = 4 about. H = 6. Purplish or brownish black.
Ceylon.
Gorceixite.
An alumino-phosphate of alkaline and ceria earths. Cer = 0-3%.
Microcrystalline.
G = 3. H = 6. White to brown. Translucent.
Diamond sands of Brazil.
Guarinite.
Formerly supposed to be dimorphous with Titanite (q.v.); shown by Zambonini and Prior (1909) to
be identical with Hiortdahlite (q.v.).
Hainite.
Tantalo-silicate and titanate of Zr, Ca, Na. ZrO₂ = 29-32%.
Anorthic.

G = 3·2. H = 5. Colourless to yellow; transparent.
Bohemia.
Hellandite.
Th
3H₂0, 2R´´O, 3R´´´₂O₃, 4SiO₂, where R´´ = Ca, Mg, ; R´´´ = E, Al, Fe, Mn. E₂O₃ = 40%.
2
Monoclinic; habit prismatic.
G = 3·70. H = 51⁄2. Reddish-brown when fresh.
Lindvikskollan and Kragerö, Norway.
Hiortdahlite.
3CaSiO3,Ca(F,OH)NaZrO₃. ZrO₂ = 21·5; TiO₂ = 1·5%.
Anorthic; habit tabular.
G = 3·27; H = 5-51⁄2. Yellow, with weak pleochroism.
Island of Läven, Langesund Fiord, Norway.

Hjelmite (Hielmite).
A stanno-tantalate of Ca, Mn, Fe, E, related to Yttrotantalite (q.v.). E₂O₃ = 1-6%.
Orthorhombic.
G = 5·82. H = 5. Black; lustre metallic.
Fahlun, Sweden.
Homilite.
(Ca,Fe)₃(BO)₂(SiO₄)₂. Sometimes with ceria earths, 0-2·6%.
Monoclinic—isomorphous with Gadolinite (? Brögger).
G = 3·34-3·38. H = 41⁄2-5. Black; pleochroic.
Islands of Lanegsund Fiord, Norway.
Hussakite (Xenotime).
A prismatic form of Xenotime (q.v.), erroneously supposed to contain > 6% SO₃.
Diamond sands of Brazil.
Hydrotitanite.
An altered Perovskite (q.v.) with Fe´´´ and aq. TiO₂ = 82·8%.
Amorphous.
G = 3·68. H = 1-2. Yellowish grey.
Magnet Cove, Arkansas.
Ilmenite.
FeTiO₃; composition varies widely. TiO₂ = 3·5-52·3%.
Rhombohedral.
G = 4·5-5. H = 5-6. Black; opaque. Slightly magnetic.
Norway; Dauphiné; Bohemia; Cornwall, etc.
Ilmenorutile.
FeO,Nb₂O₅,5TiO₂? TiO₂ = 66-75%.
Tetragonal, very near to Rutile (q.v.).
G = 4·3-5·0. H = 6-7. Brown to black; opaque.
Ilmen Mountains, Russia.
Johnstrupite.
Silico-titanate of E, Al, Mg, Ca, Na, etc., with F and aq. Cer = 13·5; Yttr = 1·1; TiO₂ = 7-8; ThO₂ +
ZrO₂ = 3·6%.

Monoclinic, very close to Epidote.
G = 3·19-3·29. H = 5. Brownish green; weakly pleochroic.
Islands of the Langesund Fiord, Norway.
Kainosite (Cenosite).
CaY₂(SiO₃)₄,CaCO₃,2H₂O, where Y = Yttrium metals. Yttr = 30-37%.
Uncertain; pseudo-hexagonal.
G = 3·38-3·41. H = 5-6. Yellowish brown.
Hitterö and province of Nordmark, Norway.

Keilhauite (Yttrotitanite).
An isomorphous mixture of Titanite (q.v.) with (E,Al,Fe)SiO₅. E₂O₃ = 5-12; TiO₂ = 26-30%.
Monoclinic; isomorphous with Titanite.
G = 3·52-3·77. H = 61⁄2. Brown to black.
Various localities in Norway.
Kischtimite.
A fluocarbonate of the Cerium metals, near Parisite (q.v.). Cer = 74·2%.
Massive.
G = 4·78. H = 41⁄2. Yellowish brown; translucent.
Barsovka River, Kyshtymsk, Urals.
Knopite.
A variety of Perovskite (q.v.) containing E and Fe. Cer = 4-7; TiO₂ = 55%.
Pseudo-cubic.
G = 4·2. H = 51⁄2. Grey; opaque; lustre metallic.
Alnö, Sweden.
Kochelite.
A columbate of E, Fe, Zr; with ThO₂, SiO₂, Ca, aq., etc. Allied to Fergusonite (q.v.). Yttr = 17·22;
ZrO₂ = 12·8; ThO₂ = 1·23%.
Doubtful; may be tetragonal.
G = 3·74. H = 3-31⁄2. Brown to honey yellow; translucent.
The Kochelweise, near Schreiberhau, Silesia.
Koppite.
Columbate of E, Ca, Fe, Th, K, Na, etc. Near Pyrochlore (q.v.). Cer = 4-10; ZrO₂ = 0-5%.
Cubic; in dodecahedra.
G = 4·45-4·46. H = 5-6. Brown; transparent.
Schelingen, Black Forest Mountains, Germany.
Lanthanite.
Hydrated carbonate of Cerium metals, especially La; E₂(CO₃)₃,9aq. Cer = 54·9%.
Orthorhombic; habit tabular.
G = 2·6-2·7. H = 2. White; opaque.
With Cerite (q.v.) at Bastnäs, Sweden; Bethlehem, Pennsylvania, U.S.A.
Lavenite.
(Mn,Ca,Fe)(ZrOF)Na(SiO₃)₂? ZrO₂ = 28·8-31·6%.
Monoclinic; habit prismatic.
G = 3·51-3·55. H = 6. Brown to yellow; translucent.
Langesund Fiord, Norway; the Ardennes, France.

Leucosphenite.
BaO,2Na₂O,2(Ti,Zr)O₂,10SiO₂. TiO₂ = 13·2; ZrO₂ = 3·5%.
Monoclinic; wedge-shaped.
G = 3·05. H = 61⁄2. White; transparent.
Narsarsuk, Greenland.
Lewisite.
3R´´Sb₂O₆,2R´´TiO₃, where R = Ca, Fe´´ and Mn. TiO₂ = 11-12%.
Cubic; in small octahedra.
G = 4·95. H = 51⁄2. Yellow to brown; translucent.
Tripuhy, Minas Geraes, Brazil.
Loranskite.
Tantalate of E, Zr, Fe, etc. Yttr = 10; Cer = 3; ZrO₂ = 20%.
Massive.
G = 4·6. H = 5. Black; opaque. Metallic lustre.
Finland.
Lorenzenite.
Titano-silicate of Na and Zr; TiO₂ = 35; ZrO₂ = 12%.
Orthorhombic; acicular.
G = 3·4. H = 6. Colourless; transparent.
South Greenland.
Mackintoshite.
Mixture of oxides, chiefly of Th and U; also Fe, Ca, Mg, Pb, Na, B, Ta, etc. Composition very
complex. ThO₂ = 45·3; E₂O₃ = 1·9; ZrO₂ = 1%.
Tetragonal, resembling thorite (q.v.).
G = 5·42. H = 51⁄2. Black; opaque.
Bluffton, Llano Co., Texas.
Malacone.
An altered Zircon (q.v.), with E, Ca, Fe, H₂O, etc. ZrO₂ = 47-67%.
Tetragonal; pseudomorphous.
G = 3·9-4·1. H = 6. Brown, often dull white internally.
Hitterö, Norway; Haute Loire, France; and in U.S.A.
Mauzeliite.
Very similar to Lewisite (q.v.), with Pb. TiO₂ = 8%.
Cubic.
G = 5·11. H = 5-6. Brown; translucent.
Jakobsberg, Sweden.
Melanocerite.
Very complex fluosilicate of E and Ca, chiefly. Cer = 48; Yttr = 9·2; ThO₂ + ZrO₂ = 2%.
Rhombohedral; habit tabular.
G = 4·13. H = 5-6. Deep brown to black. Transparent.
Langesund Fiord, Norway.
Microlite.
Complex columbate of Ca, E, Fe, etc., with F and H₂O. E₂O₃→ 8%.
Cubic; habit octahedral.
G = 5·48-5·56. H = 5-51⁄2. Red to yellow.

Stockholm, Sweden; Island of Elba; and in U.S.A.
Molengraafite.
Titano-silicate of Ca, Na, Fe, Al, Mn, etc. TiO₂ = 28%.
Monoclinic; in small prisms.
Yellow. High refraction and birefringence.
Pilandsberg, Transvaal.

Monazite.
Phosphate of E, with Th and SiO₂. Cer = 49-74; Yttr = 1-4; ThO₂ = 1-20%.
Monoclinic.
G = 4·9-5·3. H = 5-51⁄2. Red to brown and yellow; translucent.
The Carolinas; Idaho; Brazil; Scandinavia, etc.
Mosandrite.
In composition identical with Johnstrupite (q.v.).
Isomeric with Johnstrupite (q.v.).
G = 2·93-3·03. H = 4. Reddish brown; translucent.
Langesund Fiord, Norway.
Muromontite.
A variety of Allanite (q.v.), rich in yttria earths and Be, but poor in Al and ceria earths. Cer = 9·1;
Yttr = 37·1%.
See Allanite.
G = 4·263. H = 7. Black to greenish black.
Mauersberg, Erzgebirge, Saxony.

Naegite.
A silicate of Zr, ZrSiO₄, with E, Th, U, Cb, etc. ZrO₂ = 55·2; Yttr = 9·12; ThO₂ = 5·01%.
Tetragonal; in globular aggregates.
Gr = 4·091. H = 71⁄2. Dark green or brown; dull.
Gravel-tin of Japan.
Narsarsukite.
Na₆FeTi₂Si₁₂O₃₂F. TiO₂ = 14%.
Tetragonal. Habit tabular.
Gr = 2·75. H = 7-71⁄2. Yellow to reddish-brown; pleochroic.
Plain of Narsarsuk, Greenland.
Neptunite.
(K,Na)₂(Fe,Mg,Ca,)₂(Ti,Si)₄O₁₂. TiO₂ = 18%.
Monoclinic. Habit prismatic.
G = 3·23. H = 51⁄2. Black, red in flakes. Translucent to opaque.
Narsarsuk, Greenland.

Nivenite.
A variety of Cleveite (q.v.), readily soluble in dilute acids.
Cubic; crystallisation indistinct.
G = 8·01. H = 51⁄2. Velvet black; opaque.
Bluffton, Llano Co., Texas.
Nohlite.
A variety of Samarskite (q.v.) containing water (→ 4·6%).

Massive, without cleavage.
G = 5·04. H = 41⁄2-5. Brownish black; opaque.
Nohl, near Kongelf, Sweden.
Oerstedite.
A variety of Zircon (q.v.), poor in SiO₂. ZrO₂ = 69%.
Tetragonal; angles exactly those of Zircon.
G = 3·629. H = 51⁄2. Reddish-brown; adamantine lustre.
Arendal, Norway.
Orangite.
ThSiO₄, usually with Fe, Ca, H₂O in traces. ThO₂ = 71·2-73·8%.
Tetragonal. Habit prismatic.
G = 5·19-5·40. H = 41⁄2-5. Orange yellow; lustrous.
See under Thorite.
Parisite.
E₂CaF₂(CO₃)₃. Cer = 50·8-64·4; Yttr = 0-2·5%.
Hexagonal. Habit pyramidal.
G = 4·36. H = 41⁄2. Yellow to red; transparent.
Muso Valley, Columbia; Montana, U.S.A.; Greenland; Norway; the Urals, etc.
Perovskite.
CaTiO₃, with traces of Fe´´. TiO₂ = 58·9%.
Pseudo-cubic? Optically biaxial.
G = 4·017. H = 51⁄2. Yellow; transparent to opaque.
The Urals; Switzerland; Tyrol, etc.
Pilbarite.
PbO,UO₃,ThO₂,2SiO₂,2H₂0 + 2aq. ThO₂ = 31·3%. Cer and Yttr—traces.
Amorphous.
G = 4·4-4·7. H = 21⁄2-3. Bright yellow; opaque.
Pilbara goldfields, West Australia.
Pitchblende.
A mixture of oxides, chiefly UO₂ and UO₃, but without E₂O₃ or ThO₂.
Amorphous.
G = 5-6·5. H = 3-4. Black; resinous lustre.
Bohemia; Cornwall; Carolina; Norway, etc.
Plumboniobite.
A variety of Samarskite (q.v.) containing Pb; R´´₂Cb₂O₇, R´´´₄(Cb₂O₇)₃, where R´´ = Fe, Pb, Ca,
UO, R´´´ = E, Al. Yttr = 14·3%.
Massive, isotropic.
G = 4·80-4·81. H = 5-51⁄2. Dark brown to black.
Morogoro, Uluguru Mountains, German E. Africa.

Polycrase.
A titano-columbate of E and U; Yttr = 19·5-32·5; TiO₂ = 25-33%. Cer and ThO₂ traces.
Isomorphous with Euxenite.
Orthorhombic.
G = 4·0-4·8. H = 6. Black; vitreous lustre.

Norway.
Priorite.
Dimorphous with Euxenite (q.v.).
Orthorhombic; isomorphous with Blomstrandine.
G = 4·6-5·0. H = 6. Black; transparent in flakes.
Swaziland, S. Africa.
Pseudobrookite.
Fe₄(TiO₄)₃, ferric orthotitanate. TiO₂ = 44-53%.
Orthorhombic.
G = 4·39-4·98. H = 6. Dark brown to black.
Norway; France.
Pyrochlore.
A columbate of Ca and E, with Th, Fe, Ti, F, etc. E₂O₃ → 18; TiO₂ = 5-14%.
Cubic.
G = 4·2-4·36. H = 5-51⁄2. Dark brown.
Scandinavia; the Urals; Tasmania, etc.
Pyrophanite.
MnTiO₃, with traces of SiO₂. TiO₂ = 50-53%.
Rhombohedral; isomorphous with Ilmenite.
G = 4·537. H = 5. Deep blood-red; translucent; lustrous.
Pajsberg, Sweden.

Retzian.
Hydrated arsenate of Mn´´, Ca, E. Cer + Yttr = 8-11%.
Orthorhombic, usually in prisms.
G = 4·15. H = 4. Brown; pleochroic; transparent.
Province of Nordmarken, Sweden.
Rhabdophane (Scovillite).
Hydrated phosphate of E, Al, Fe, Mg, etc., with SiO₂. Cer = 53·8-57; Yttr = 2·1-10·0%.
Massive.
G = 3·94-4·01. H = 31⁄2. Brown to yellow; translucent.
Cornwall; Scoville, Connecticut, U.S.A.
Rhönite.
(Na,K,H)₃Ca₃(Fe´´,Mg)₁₅(Al,Fe´´´)₁₆(Si,Ti)₂₁O₉₀. TiO₂ = 9·5%.
Anorthic, isomorphous with Aenigmatite.
G = 3·5-4·3. Brown, with strong pleochroism.
Rhön Mountains, Saxony.
Rinkite.
A titanosilicate closely allied to Mosandrite and Johnstrupite (q.v.)—Na₉Ca₁₁Ce₃(Ti,Th)₄₁Si₁₂O₄₆?
Cer = 21; Yttr = 0·4-1·4; TiO₂ = 13-14%.
Monoclinic, very close to Johnstrupite.
G = 3·46. H = 5. Yellow, pleochroic; translucent.
Kangerdluarsuk, Greenland.

Risörite.
An yttria columbate, near Fergusonite, but with no U and considerable TiO₂; Yttr = 37; Cer = 2·9-
4·0; TiO₂ = 6·5%.
No data yet determined. Isotropic.
G = 4·179. H = 51⁄2. Yellowish brown.
Norway.

Rogersite.
Hydrated yttria columbate. Yttr = 60·12%. A weathered Samarskite?
Amorphous, mamillary.
G = 3·313. H = 31⁄2. White.
Mitchell Co., N. Carolina.
Rosenbuschite.
Titanosilicate of Ca, Zr, Na, E, Fe, Mn, with F. ZrO₂ = 18·7-20; Cer = 0·3-2·4%.
Monoclinic, in spherical aggregates.
G = 3·30-3·31. H = 5-6. Orange-grey.
Near Brevik, Sweden.

Rowlandite.
Silicate of E, with Th, Ti, Fe, etc.—2Y₂O₃, 3SiO₂. Cer = 14·4; Yttr = 47·7; ThO₂ = 0·6%.
Massive.
G = 4·515. H = 6. Pale dull green.
Llano Co., Texas.
Rutile.
Titanium dioxide; TiO₂ = 98-100%
Tetragonal; habit prismatic.
G = 4·18-4·25. H = 6-61⁄2. Reddish-brown to black.
Very widely in Europe and America.
Samarskite.
R´´₃R´´´₂(Cb,Ta)₆O₂₁, where R´´ = Fe, Ca, UO₂; R´´´ = E. Cer = 1·2-6·4; Yttr = 4·72-21·2; ThO₂ +
ZrO₂ → 7%.
Orthorhombic; usually massive.
G = 5·6-5·8. H = 5-6. Deep velvet black; opaque.
Miask; Urals; Mitchell Co., N. Carolina.
Schorlomite.
A titaniferous Garnet—3CaO,(Fe,Ti)₂O₃,3(Si,Ti)O₂. TiO₂ = 12·5-22%.
Cubic; usually massive.
G = 3·81-3·88. H = 7-71⁄2. Black; transparent in flakes.
Magnet Cove, Arkansas.
Senaite.
(Fe,Mn,Pb)O,TiO₂, cf. Ilmenite. TiO₂ = 49-52%.
Rhombohedral; isomorphous with Ilmenite, Geikielite, etc.
G = 5·3 (to 4·2 when weathered). H = 61⁄2. Black.
Diamantina, Minas Geraes, Brazil.
Sipylite.
Columbate of E, Zr, Fe, U, Sn, etc.; near Fergusonite (q.v.).
Cubic, in octahedra. Usually granular.

G = 4·89. H = 6. Brownish-black; translucent.
Amhurst Co., Virginia.
Steenstrupine.
A silicate of E, Fe, Na, Th, Mn, Al, Ti, H₂O, etc.; near Melanocerite. Cer = 14·4-32·5; Yttr = 0-
15·9; ThO₂ = 2·1-7·1%.
Rhombohedral.
G = 3·38. H = 4. Brown; faces dull.
Kangerdluarsuk, Greenland.
Strüverite.
FeO,(Nb,Ta)₂O₅,4TiO₂. TiO₂ = 69-71%.
Tetragonal; angles very close to those of rutile.
G = 5·0. H = 6-7. Black; opaque.
Craveggia, Piedmont, Italy; and in Madagascar.
Tachyaphaltite.
An altered zircon, containing H₂O. ZrO₂ = 40-50%.
Tetragonal; very close to Zircon.
G = 3·6. H = 51⁄2. Dark brown.
Kragerö, Norway.
Tengerite.
Hydrated carbonate of E, Be, Ca, etc.; a weathered Gadolinite (q.v.). E₂O₃ = 39·2-47·8%.
Amorphous.
White; opaque; very soft.
Llano Co., Texas.

Thalenite.
H₂E₄Si₄O₁₅, with traces of Fe´´´ and Al. Yttr = 58·6-63·9%.
Monoclinic.
G = 4·23. H = 61⁄2. Bright red and yellow,
Österby, Sweden.
Thorianite.
Mixed ThO₂ + UO₂, with E, Pb, Zr, Si, Fe, etc. ThO₂ = 72-79; Cer = 1-8%.
Rhombohedral; pseudocubic.
G = 8·0-9·7. H = 7. Jet black; bright resinous lustre.
Gem-gravels of Ceylon.

Thorite.
ThSiO₄, with H₂O, U, Fe, E, Ca, Al, etc. ThO₂ = 41·4-57·9; E₂O₃ = 0-6%.
Tetragonal; habit prismatic.
G = 4·4-4·8; H = 41⁄2-5. Brown to black.
Various localities in Scandinavia.
Thorogummite.
UO₃,3ThO₂,3SiO₂,6H₂O? An altered Mackintoshite (q.v.)? ThO₂ = 41·4; E₂O₃ = 6·7%.
Usually massive; sometimes in crystals resembling Zircon.
G = 4·43-4·54. H = 4-41⁄2. Dull brown; opaque.
Llano Co., Texas.

Thortveitite.
E₂O₃,2SiO₂, with Fe´´´, Al, Mn´´´ traces; E = chiefly Sc. Yttr = 54·5%.
Orthorhombic, in radial aggregates.
G = 3·571. H = 6-7. Greyish green; translucent.
Iveland, Sätersdalen, Norway.
Titanite (Sphene, Grothite).
CaSiTiO₅, with Fe´´, Mn´´. TiO₂ = 34-45% (usually 41%).
Monoclinic; wedge-shaped.
G = 3·40-3·56. H = 5-51⁄2. Yellow, green, or brown; pleochroism strong; lustre resinous.
Widely distributed in Europe and N. America.
Titanium Olivine.
(H₂,Fe´´,Mg)₂(Si,Ti)O₄; Mn and F in traces. TiO₂ = 3-12%.
Orthorhombic.
G = 3·25-3·27. H = 61⁄2-7. Deep red to yellow; pleochroic.
Pfunders, Tyrol; Zermatt, Switzerland.

Tritomite.
A fluo-borosilicate of E, Th, Ca, with Zr, Na, H₂O, etc. Cer = 44·2-59·2; Yttr = 0·4-4·6; ThO₂ +
ZrO₂ = 0-10·6%.
Rhombohedral; in crystals resembling regular tetrahedra.
G = 4·15-4·25. H = 51⁄2. Dark brown; transparent to opaque.
Langesund Fiord, Norway.
Tscheffkinite.
Titano-silicate of E, Th, Fe, Ca, etc. Cer = 23-47; Yttr = 0-3·4; ThO₂ + ZrO₂ = 0-20; TiO₂ = 16-
21%.
Massive, amorphous.
G = 4·26-4·55. H = 5-51⁄2. Velvet black.
Ilmen Mountains; Nelson Co. and Bedford Co., Virginia, U.S.A.
Tysonite.
Fluoride of E, with Th, H₂O, CO₂, etc. Cer = 69·2-70·6; ThO₂ = 0-31%.
Hexagonal; in thick prisms.
G = 6·12-6·14. H = 41⁄2-5. Wax yellow; transparent to translucent.
Fahlun and Österby, Sweden; Pike’s Peak, Colorado.
Uhligite.
Titanate of Zr, Ca, Al; Ca(Zr,Ti)O₃ + Al(Ti,Al)O₃? TiO₂ = 48; ZrO₂ = 22%.
Cubic; near to Perovskite (q.v.).
H = 5-6. Black. Transparent in flakes.
Lake Magad, E. Africa.

Uraninite.
Oxides of U (60-75%), with PbO₂, ThO₂, ZrO₂, E₂O₃, Fe₂O₃, etc. Cer. = 0-2·7; Yttr = 0-10·2; ThO₂
= 1·6-11·1; ZrO₂ = 0-8·1%.
Cubic, usually massive; alters to amorphous pitchblende.
G = → 6·4 (massive); → 9·7 (crystalline). H = 51⁄2. Black; transparent in splinters.
Norway; Bohemia; Saxony; Cornwall; Carolina, etc.

Vietinghofite.
A hydrated ferruginous samarskite (q.v.). E₂O₃ = 8·2; ZrO₂ = 1·0%.
Amorphous.
G = 5·53. H = 51⁄2-6. Dull black; opaque.
Lake Baikal, Siberia.
Warwickite.
6MgO,FeO,2TiO₂,3B₂O₃? TiO₂ = 23·5%.
Orthorhombic; habit prismatic, elongated.
G = 3·35-3·36. H = 3-4. Dark brown to black; pleochroic. Double refraction strong, +ve.
Edenville, New York State.
Weibyite.
Carbonate of E, with Ca, Sr, F, and H₂O; allied to Bastnäsite (q.v.). Cer = 66·96%?
Orthorhombic; in pyramids resembling those of Zircon.
Crystals are small, and covered with a thin yellow crust; they are intergrown with Parisite (q.v.)
Langesund Fiord, Norway.
Wiikite.
Titano-tantalo-silicate of Zr, Th, E, Fe, U, with Cb₂O₅, H₂O, etc. Cer = 2·5; Yttr = 7·6; Sc₂O₃ =
1·2; ThO₂ = 5·5; ZrO₂ + TiO₂ = 23·4%.
Perfectly amorphous.
G = 4·85. H = 6. Black; opaque; infusible.
Impilaks, Lake Ladoga, Finland.
Wöhlerite.
Silicate and columbate of Ca, Zr, Na; Si₁₀Zr₃Cb₂O₄₂F₃Ca₁₀Na₅? ZrO₂ = 15·2-22·7%. Cer, traces.
Monoclinic; prismatic or tabular habit.
G = 3·41-3·44. H = = 51⁄2-6. Light yellow; pleochroic.
Langesund Fiord.
Xenotime.
Phosphate of E, with ThO₂, SiO₂, Zr, etc. Cer = 0-11; Yttr = 54·1-64·7; ThO₂ = 1-5%.
Tetragonal; isomorphous with Zircon?
G = 4·45-4·56. H = 4-5. Brown to yellow; opaque.
Diamond sands of Brazil; Norway.
Yttrialite (Green Gadolinite).
A weathered gadolinite (q.v.)—E₂O₃,2SiO₂. Cer = 6·6-8·2; Yttr = 43·4-46·5; ThO₂ = 10·8-12·8%.
Amorphous, massive.
G = 4·6. H = 51⁄2. Green to brown; translucent.
Bluffton, Llano Co., Texas.
Yttrocerite.
Ca₃E₂F₁₂, 11⁄2H₂O. Cer = 9·3-18·2; Yttr = 8·1-29·4%.
Massive, granular.
G = 3·45. H = 41⁄2. White to violet blue or brown.
Various localities in Scandinavia.
Yttrocrasite.
(Ca,Pb)O,(Th,U)O₂,3E₂O₃,16TiO₂,6H₂O. Yttr = 25·7; Cer = 2·9; ThO₂ = 8·7; TiO₂ = 49·7%.
Orthorhombic; axial ratios unknown.

G = 4·80. H = 51⁄2-6. Black; lustrous.
Burnet Co. Texas.

Yttrofluorite.
nCaF₂ + mYF₃ in isomorphous mixture? Yttr = 20-25; Cer = 1-2%.
Cubic.
G = 3·54-3·56. H = 41⁄2. Closely resembles fluorspar, except in badness of cleavage.
Northern Norway.
Yttrogarnet.
A variety of garnet with E and Zr. Yttr = 1-6·7; ZrO₂ = 0-3%.
Cubic (cf. Garnet).
Dark reddish brown (cf. Garnet).
Stockö, Norway; Schreiberhau, Germany.

Yttrogummite.
UO₃, 3ThO₂, 3SiO₂, 6H₂O? E₂O₃ = 6·7; ThO₂ = 41·4%.
Tetragonal; angles near Zircon. Usually massive.
G = 4·43-4·54. H = 4-41⁄2. Yellowish brown.
Llano Co., Texas.
Yttrotantalite.
R´´R´´´₂(Cb,Ta)₄O₁₄ + 4H₂O; R´´ = Fe´´, Ca; R´´´ = E; Cer = 0-2·4; Yttr = 17·2-38·3%.
Orthorhombic; isomorphous with Samarskite (q.v.).
G = 5·5-5·8. H = 5-6. Yellow to black.
Ytterby, Sweden; South Norway.
Zircon.
ZrSiO₄, with Fe, Th, etc., in traces. ZrO₂ = 61·0-70·0%.
Tetragonal; habit prismatic.
G = 4·68-4·70. varying considerably. H = 71⁄2. Colour very variable.
Widely distributed as a rock mineral, in sands, etc.
Zirkelite.
(Ca,Fe)(Zr,Ti,Th)₂O₅, with E, U, Mg, etc. ZrO₂ = 48·9-52·9; ThO₂ = 0-7·3; TiO₂ = 14-15; E₂O₃ =
0-3%.
Cubic; in twinned octahedra.
G = 4·7. H = 5. Black; transparent in thin flakes.
Jacupiranga, São Paulo, Brazil.

CHAPTER II

THE SILICATES

(a) Silicates of the Yttrium and Cerium Metals

Cerite. —Cerite is a silicate of the cerium metals, with small amounts of
lime, ferrous oxide and water. Hintze gives the formula
H₃(Ca,Fe)Ce₃Si₃O₁₃,[15] which Groth interprets as a basic metasilicate
(Ca,Fe)[CeO]Ce₂(OH)₃(SiO₃)₃, i.e. a basic salt of the acid H₆Si₃O₉, a
polymer of metasilicic acid, H₂SiO₃.
[15] The symbol (Ca,Fe) here indicates that the iron and calcium occur in variable
proportions, the variation however occurring in such a way that the equivalent of the two
taken together is always the same, i.e. the iron can replace the calcium, or vice versa,
atom by atom. The recognition of this possibility of ‘Vicarious Replacement’ between
similar elements first brought order into the confused field of mineral chemistry, and
allowed a systematic classification of minerals according to chemical composition to be
made. Iron and calcium, or, according to the more convenient nomenclature of the
mineralogists, lime and ferrous oxide, are here vicarious constituents.
The symbol Ce here stands for elements of the cerium group, which are never found
singly.
Crystals are not very common, the mineral usually occurring granular or
massive.
Crystals, orthorhombic, holosymmetric; a : b : c = 0·9988 : 1 :
0·8127. Usual forms—the Pinakoids a, b, and c {100}, {010} and
{001}, prisms m {110} and q {130}, domes u {101}, t {301} and n
{011}, and some pyramids {hkl}.
Angles, a ∧ m = 44° 58´, u ∧ c = 39° 8´, n ∧ c = 39° 6´.
The crystals usually occur as short prisms. No cleavage. Optical
constants unknown. In flakes the absorption spectrum of didymium can
be observed.
The mineral is brittle; hardness 5 to 6 on Mohs’ scale; sp. gr. varies a
little about 4·9. Fracture splintery; lustre dull, resinous. Colour brown
to red and greyish-red, streak greyish-white. The mineral is almost
opaque.

Cerite is infusible before the blowpipe. It is attacked readily by sulphuric
acid, less easily by hydrochloric acid, with which it gives a gelatinous mass.
Rammelsberg[16] found that the silica left behind on treatment of the
powdered granular variety with the latter acid contained a variable
proportion of bases, which he obtained and estimated after fusing the
siliceous residue with sodium carbonate. From the different proportions of
the earths in the part attacked by the acid and that left in the silica, he
remarks, ‘It would almost appear that Cerite is a mixture of silicates which
are not all attacked with the same ease by hydrochloric acid.’ Apparently
without previous knowledge of this observation, Welsbach[17] noticed the
same thing in 1884. He concluded that ordinary granular ‘cerite’ is a
mixture of several minerals, among which there are at least two which
contain rare earths. Of these, one, the chief constituent of the aggregate, is
probably identical with the crystallised mineral, and is characterised by the
readiness and completeness with which it is attacked by hydrochloric acid.
The other does not react, with hydrochloric, but is readily attacked by
sulphuric acid; it contains yttria earths, in addition to the ceria earths. In the
extraction of ceria earths from the mineral aggregate, Welsbach used
hydrochloric acid, so leaving this second mineral unchanged; but to avoid
loss of the rare earths, sulphuric acid is more commonly employed for the
decomposition.
[16] Pogg. Ann., 1859, 107, 631.
[17] Monats., 1884, 5, 512.

Though of great historical interest, cerite is of very small importance for
the extraction of rare earths at the present time, on account of its very rare
occurrence. The mineral seems to be almost entirely confined to the Bastnäs
quarry near Ryddarhyttan, Sweden, where it is found with the rare earth
silicate allanite (q.v.), biotite, hornblende, bismuth glance, chalcopyrite, etc.
Here it was observed in 1751 by Cronstedt, who called it Tungsten (vide
supra, p. 1). In 1781 Scheele examined a specimen of Wallerius’s ‘Tenn-
spat’ from Bipsberg, Dalecarlia, and found Tungstic Oxide (Acid), WO₃, in
it.[18] After Scheele’s work, the Ryddarhyttan mineral was known as Red
Tungsten, until Bergmann (1780) and d’Elhuyar (1784) showed that the two
minerals were chemically distinct. They considered the red variety to be a
silicate of iron and calcium, the rare earths being mistaken for lime. In 1804
Klaproth examined it, and found a new earth; he called the mineral
‘Ochroite,’ from its colour. In the same year, but independently of Klaproth,

Berzelius and Hisinger made the same discovery; they called the mineral
Cerite and the new metal Cerium, in honour of the discovery of the minor
planet Ceres by Piazzi in 1801.
[18] This mineral, which Scheele knew as Tungstein, is now called Scheelite.
The analyses of cerite made in the earlier part of the nineteenth century
resulted in some confusion. Klaproth in 1807 found 34·5 per cent. SiO₂ in a
specimen (his Ochroite); Vauquelin in 1805, and Hisinger in 1810, found
17·0 and 18·0 per cent. respectively.[19] Hermann[20] called attention to this
discrepancy in 1843 (and again in 1861), and declared that the two could
not be the same. For Klaproth’s mineral he proposed to revive the name
Ochroite, whilst from his own analyses he proposed for the cerite of
Berzelius the name Lanthanocerite, having found carbon dioxide and
lanthanum, with much less cerium, in the latter.[21] In 1861 Kenngott partly
explained these results by showing that the sample of cerite which Hermann
had analysed contained Lanthanite[22]; but the extraordinarily high
percentage of silica obtained by Klaproth remained unexplained. It may
have been due to impurities of high silica content in the specimen he
examined.
[19] Vide Hintze, Handbuch der Mineralogie, Leipzig, 1897, ii., 1329.
[20] Hermann, J. pr. Chem. 1843, 30, 194, and 1861, 82, 406.
[21] The announcement of the discovery of Lanthanum by Mosander was made in 1839.
[22] Lanthanite (see list) is an hydrated carbonate, R₂O₃,3CO₂,9H₂O, where R = cerium
metals, chiefly Lanthanum.
Cerite contains from 59·4 to 71·8 per cent. of rare earths (oxides), the
amount and nature of which vary with the precise locality. The oxides
consist chiefly of ceria, lanthana, and didymia (praseodymia and neodymia),
the complexity of the so-called ceria having been shown by Mosander in the
case of ceria separated from gadolinite as well as from cerite; but yttria
earths are also found to a small extent in the mineral.
It is remarkable that neither thorium nor uranium has been found in
cerite, which is thus practically unique among the rare earth minerals.
This anomaly becomes even more marked in view of the very high
percentage of inert gases found by Tschernik[23] in a related mineral from
Batoum. This is a very complex mineral in which the basic part is
represented by rare earths, chiefly ceria earths (50·8 per cent.) with water
(3·4 per cent.), and oxides of iron, calcium and copper (6·8 per cent.); the
acidic oxides being silica (6·6 per cent.), zirconia (11·6 per cent.), and

titanium dioxide (14·7 per cent.), with phosphorus pentoxide (3·2 per cent.),
and sulphuric anhydride (1·7 per cent.). Traces of thoria are present, but no
uranium; very considerable quantities (up to 1 per cent.?) of helium were
found.
[23] G. Tschernik, J. Russ. Phys. Chem. Soc. 1896, 28, 345; 1897, 29, 291. Abstracts in
Zeitsch. Kryst. Min. 1899, 31, 513 and 514.
It is somewhat heavier than cerite (sp. gr. 5·08), but otherwise resembles
it closely.

Gadolinite (Ytterbite). —Gadolinite is a silicate of iron, beryllium, and
the yttria earths, of the formula 2BeO,FeO,Y₂O₃,2SiO₂, which may be
written FeBe₂Y₂Si₂O₁₀. According to Groth, it is a basic orthosilicate,
Be₂Fe(YO)₂(SiO₄)₂, derived from the acid H₈Si₂O₈. The beryllium content
varies considerably, and some authors recognise two varieties of the
mineral, one rich, and one poor in beryllium; but Scheerer pointed out in
1840 that iron and beryllium are probably vicarious constituents.
Analysis gives silica 21·8 to 25·3 per cent.; yttria earths 22 to 47 per
cent.; ceria earths 5 to 31 per cent. In a variety from Ytterby, the rare earth
Scandia was first found, forming up to 0·02 per cent. of the mineral. Small
quantities of thoria, ThO₂ may be present, and traces of helium were found
by Ramsay, Collie, and Travers. According to Strutt it contains also uranium
and radium. Like cerite, it does not often occur crystalline, being usually
found in amorphous masses.
The crystals are monoclinic; a : b : c = 0·6273 : 1 : 1·3215; β = 89°
261⁄2´.
Common forms are—Ortho-, clino-, and basal pinakoids, a {100}, b
{010}, and c {001}, hemi-prisms m {110}, v {120}, clino-prisms w
{012}, q {011}, and many others; and various hemi-pyramids {hkl}
and {h̅ kl}.
Angles a ∧ m = 32° 6´, c ∧ q = 52° 53´, c ∧ (101) = 64° 9´.
Crystals commonly prismatic, terminated by c. Faces rough and
coarse; lustre vitreous to greasy, seen only on freshly-broken surfaces.
Brittle. No cleavage. Fracture conchoidal to splintery. Hardness 61⁄2-7;
sp. gr. 4·0-4·5.
Colour black, greenish- and brownish-black; green and transparent
in flakes. The crystalline variety has strong positive birefringence, with

the plane of the optic axes parallel to (b), the plane of symmetry; the
amorphous variety is of course isotropic. The brown variety shows
very distinct pleochroism, i.e. the colour as seen by transmitted light
varies with the direction in which the light traverses the crystal; the
green kinds have much weaker pleochroism.
Gadolinite is of common occurrence in the pegmatite veins of the
Scandinavian granite. It was first found in a felspar quarry on the island of
Ytterby, near Stockholm, by a Lieutenant Arrhenius[24]; it is also found,
together with a large number of other rare earth minerals, at Fahlun. It
occurs in Norway on the islands of Hitterö and Malö, and in Germany in the
Riesengebirge and the Harz. Probably the largest deposit is that in Texas, at
Barringer Hill, near Bluffton, on the west bank of the Colorado River, Llano
County, now owned and worked by the Nernst Light Company of Pittsburg;
in 1904 a mass of very pure gadolinite weighing 200 lb. was found here.[25]
[24] Vide Geijer, Crell’s Chemische Annalen, 1788, 1, 229.
[25] See U.S. Geol. Survey (Minerals), 1904, 1213.

In the same place a decomposition product of gadolinite was discovered
by Hidden and Mackintosh in 1889. They named it Yttrialite or Green
Gadolinite. It contains no beryllium, and twice as much silica as the parent
mineral, and approximates to the formula R₂O₃,2SiO₂, where R₂O₃ is
chiefly yttria oxides; it is thus similar in composition to the newly found
scandium silicate, Thortveitite (q.v.). It is amorphous and massive; and is
often found in continuous growth with gadolinite. Pieces up to 10 lb. in
weight have been obtained.
As stated above, Gadolinite was discovered by Arrhenius in 1788. Geijer
examined it in the same year, and described it as a black zeolite. In 1794 it
was analysed by Gadolin, who declared it to be a silicate of iron,
aluminium, and a new element which he called Ytterbium. In 1797 Ekeberg
examined it, and confirmed the discovery. He proposed the name Gadolinite
for the mineral, and Yttria for the new earth; these names were accepted by
Klaproth, who examined it with Vauquelin in 1800, and by the French
crystallographer Haüy. In 1802 Ekeberg showed that the oxide originally
taken for alumina was in reality beryllia; in 1816 Berzelius showed that
ceria was present with the yttria.[26] About 1838 Mosander began his
classical work on the earths in gadolinite. In that year he announced the
separation of Lanthana,[27] and in 1842 that of Didymia, which he had

actually discovered eighteen months earlier. In the latter year he
announced[28] the separation of erbia and terbia. In 1842 also Scheerer[29]
declared that the yttria from gadolinite was a mixture of earths, from its
different behaviour on heating in closed and open vessels; but when
Mosander announced the discovery of didymia (the announcement appears
to have been hastened indeed by Scheerer’s observation) it was agreed that
the colouration observed was probably due to that earth. The further history
of these earths must be continued elsewhere (vide p. 111).
[26] Schweigg. J., 1816, 16, 405.
[27] Berzelius (a letter to Pelouze), Pogg. Ann., 1839, 46, 648.
[28] Berz. Jahres., 23, 145; 24, 105.
[29] Pogg. Ann., 1842, 56, 483.
The behaviour of gadolinite on heating is of great interest. When heated
uniformly, in closed or open vessels, the mineral suddenly glows very
strongly at a definite temperature (according to Hofmann and Zerban[30] at
430°C.), with considerable alteration in properties. The amorphous variety
exhibits the phenomenon much more markedly than the crystalline form.
The change in the two cases is entirely distinct, the only effect in common
being that both varieties are rendered insoluble in acids after the glowing.
The amorphous variety, in the act of glowing, changes to the crystalline
form.
[30] Ber., 1903, 36, 3095.
This phenomenon of phosphorescence, or glowing, on heating, with a
change in properties, was first observed by Berzelius in 1816. He found that
the oxides of many metals, e.g. chromium, tantalum, and rhodium, became
denser and insoluble in acids after being heated. Later in the same year he
observed the glowing, with a similar change in properties, in the case of a
gadolinite from Fahlun.[31] Apparently without knowledge of this
observation, Wollaston published a similar account of the glowing of a
gadolinite in 1825. In 1840 Scheerer noted an almost identical change in the
case of the mineral allanite (q.v.). Scheerer made a careful study of the
phenomena in the cases of allanite and gadolinite.[32] In each case he found
that the variety of lower specific gravity showed, on heating, a very strong
phosphorescence, accompanied by change of colour and optical properties,
and a marked increase of specific gravity. Gadolinite suffered no
appreciable loss of weight, but allanite had lost a little water after the
change. Careful measurement of the specific gravity before and after the

change showed, in the case of two varieties of gadolinite and one of allanite,
that the volume had decreased in the ratio 1 : 0·94. Scheerer assumed that
this ratio was constant for all such cases, and advanced a general
explanation. We know now that numerous cases of similar phenomena
occur, in which the change of volume is quite different; but Scheerer’s
explanation is so ingenious, and so foreshadows some modern theories, that
it is given here in full.
[31] Schweigg. J., 1816, 16, 405.
[32] Pogg. Ann., 1840, 51, 493.

He ascribes the alteration to ‘interatomic change, involving change of
relative position of atoms and decrease of interatomic distances.’ (Scheerer
and the chemists of that period understood by atoms the ultimate particles of
a body, making no distinction between elements and compounds; in this
case he meant by atoms what we mean by molecules, and the word
‘molecule’ has therefore been substituted for ‘atom’ in what follows.) The
change is simply one of closer packing of the molecules, which take up a
more stable position with liberation of energy as heat and light. He imagines
his molecules as uniform spheres arranged in horizontal layers, as shown in
Fig. 1. In placing one layer vertically over another there are three possible
arrangements, of which only two concern us. In the arrangement for closest
packing, B, say, a molecule of any one layer touches three molecules in
each of the layers above and below, which with the six it touches in its own
layer make twelve altogether. In the next closest arrangement, A, say, a
molecule of any one layer touches only two molecules in each of the layers
above and below it, so that one molecule is in contact with ten others
altogether.

Fig. 1

Now it can be shown that the volumes of equal numbers of molecules in
the arrangements A and B will be to one another as the height, H, of an
equilateral triangle, to the height, h, of a regular tetrahedron whose edges
are equal to the sides of the triangle, a length R (which will be equal to the
diameter of a molecule).
Then H = 1⁄2R√3, h = R√2⁄3.

Then vol. in arrangement A : vol. in arr. B ∷ H : h

√
√3 2
i.e. ∷ 2
: 3

∷ 1 : 0·943.

That is, the volume changes in the ratio 1 to 0·943, the amorphous variety
of gadolinite consisting of molecules in arrangement A, which go over to
the closer packed arrangement B in the change to the crystalline form.
More extended work has shown that this ingenious and interesting
explanation is not of general application. Thus H. Rose[33] found that
samarskite (q.v.) exhibited the phenomenon of glowing, but that the specific
gravity was actually less after the change than it was before, i.e. there was
an increase of volume. Damour observed glowing in the case of zircon from
Ceylon (q.v.) with increase of density, the volume change being from 1 to
0·922, i.e. even greater than for gadolinite. Again, Hauser[34] observed in
the case of his new rare earth mineral risörite a sudden change at a red heat,
the mineral losing water, becoming very brittle, and increasing very
considerably in specific gravity (the volume changing from 1 to 0·90
approximately), but without glowing. Ramsay and Travers[35] found that
fergusonite (q.v.) glowed strongly when heated to 500°-600°, with decrease
of specific gravity (5·62 before to 5·37 after), evolution of all its helium,
and very considerable evolution of heat; they suggested that helium was
present in combination, in an endothermic compound decomposed by heat,
but in view of the properties of helium, this hypothesis seems hardly
tenable.
[33] J. pr. Chem. 1858, 73, 391.
[34] Ber. 1907, 40, 3118.
[35] Zeitsch. physikal. Chem. 1898, 25, 568.

It appears unlikely that any one explanation can cover all these interesting
facts; there are in each case peculiar factors to be taken into account. In
1841, Regnault,[36] considering the case of the oxides observed by
Berzelius, inferred that the development of light and heat denoted that the
bodies possessed a lower specific heat after the change than before. The
experimental difficulties encountered in attempting to dry the oxides
prevented him from confirming this view. He measured the specific heats of
the minerals calcite and aragonite (CaCO₃), and of the two allotropic
modifications of phosphorus, but could observe no appreciable differences.
H. Rose (vide supra) showed by experiment that considerable heat was
evolved on the glowing of gadolinite, with a decrease of about one-
fourteenth in the specific heat. In the case of samarskite there was, however,
no appreciable evolution of heat, nor could he determine any difference in
the specific heats before and after glowing.
[36] Pogg. Ann. 1841, 53, 249.
Probably the only inference that can be safely drawn is that in most cases
the change is due to some molecular re-arrangement. The evolution of
water, helium, etc., in some cases, may possibly be due to intramolecular
change, but on the one hand the current view at present is that the helium is
mechanically held in radio-active minerals, and on the other hand it is not
known that the water evolved is water of constitution; in an intermolecular
change at fairly high temperature, these might be evolved without disruption
of the true mineral molecules. The question of the energy involved, and
consequently of the specific heats, appears to depend on factors peculiar to
each case, of which at present no accurate conception can be formed; and
the change in specific gravity is probably bound up with these. The loss of
solubility in acids is a factor not always connected with glowing, as it is
frequently observed in the laboratory after ignition of compounds, but here
again no adequate explanation is forthcoming.
The possibility of chemical change in one or two cases, however, must
not be ignored. Thus ammonium magnesium phosphate, NH₄MgPO₄, on
heating glows, and is converted to magnesium pyrophosphate, according to
the equation:
2NH₄MgPO₄ = Mg₂P₂O₇ + H₂O + 2NH₃
A case possibly analogous to this is that of the mineral sipylite (q.v.), R
´´´₂Cb₂O₈, with ‘basic water’ (i.e. R´´´ partially replaced by H). Before the

blowpipe this decrepitates with loss of water, and glows brilliantly. The
specific gravity after the change does not appear to have been determined.
Mallet explains the glow as due to a change to the pyrocolumbate.
Similar explanations may possibly hold in the cases of allanite and
risörite, but it must be remembered that we are really ignorant of the part
played by the water in these minerals.

Allanite. —Allanite, or Orthite, as it is often called, is a mineral of the
epidote family, containing rare earths. The general formula for Epidote is
H₂O,4R´´O,3R´´´´₂O₃,6SiO₂, where R´´ is a divalent and R´´´ a trivalent
metal, or vicarious series of metals. In the case of Allanite, R´´ = (Fe´´,Ca),
R´´´ = (Al,Fe´´´,E), where E stands for metals of the cerium and yttrium
groups (Engström’s formula). Groth formulates it as a basic salt, R
´´´₃(OH)R´´₂Si₃O₁₂, of the acid H₁₂Si₃O₁₂ (= 3H₄SiO₄).
Crystals are fairly common, but the mineral usually occurs massive or in
rounded grains.
Crystals—Monoclinic, holosymmetric; a : b : c = 1·5509 : 1 :
1·7691, β = 64° 59´.
Common forms—Ortho- and basal pinakoids a {100} and c {001};
m {110} and other prisms, e {101} and other hemi-ortho-prisms, o
{011}, d {111} and other hemi-pyramids.
Angles, (100) ∧ (110) = 54° 34´; (001) ∧ (101) = 63° 24´; (001) ∧
(011) = 58° 3´.
Tabular, parallel to a, or long and slender by elongation parallel to
axis b.
Birefringence weak, variable. Refraction strong. Colour brown to
brownish-black; almost opaque. In flakes very strongly pleochroic, the
colours for light parallel to the three vibration directions c, b and a
being brownish-yellow, reddish-brown, and greenish-brown
respectively.
Brittle. Hardness 51⁄2-6; sp. gr. 3·5-4·2.
On heating, allanite becomes amorphous and isotropic with increase of
specific gravity (cf. Gadolinite). Before the blowpipe it loses water, and
melts to a black magnetic glass, many varieties phosphorescing strongly

(vide supra). With hydrochloric acid it gelatinises, unless previously heated
strongly, in which case it is not attacked.
Analyses show that the rare earth content varies considerably (vicariously
as regards ferric iron and aluminium), ceria earths varying from 3·6 to 51·1
per cent. and yttria earths from traces up to 4·7 per cent.[37] Thoria is
usually present, 0 to 3·5 per cent. In 1909 Fromme[38] found small
quantities of beryllia in the mineral, and in 1911 Meyer[39] found amounts
of scandium oxide up to 1 per cent. It contains traces of uranium, and is
weakly radioactive. Ramsay, Collie and Travers found no helium (1895),
but in 1905 Strutt found radium in it, so that the presence of helium seems a
priori probable.
[37] Vide Schilling, pp. 70-75 for analyses of this mineral.
[38] Fromme, Tsch. Min. Mitt. 1909, 28.
[39] Meyer, Sitzungsber. königl. Akad. Wiss. Berlin, 1911, 379.
Many varieties of the mineral are known, differing in habit, colour, water
content, specific gravity, etc., and the percentage composition varies very
much by reason of vicarious replacement of the bases. Goldschmidt[40] has
found ‘Epidote-orthites’ which are isomorphous mixtures of orthite with an
iron epidote; he concludes that most orthites are probably similar solid
solutions, and in this way accounts to a large extent for the varying
composition.
[40] Centr. Min. 1911, 4.

Allanite is of very wide distribution, though it is not often found in large
quantities. The usual occurrence in pegmatitic veins in granites, syenites
and other acid plutonic rocks has been often noted, e.g. in many parts of
Sweden and Norway. It is found also in the extinct crater now forming the
Laacher See, near Coblenz, Germany, and at Impilaks, near Lake Ladoga,
on the border of Finland; a mass of the pure mineral weighing 300 lb. was
recently discovered at Barringer Hill, (cf. under Gadolinite), and it occurs in
large quantities in Amherst Co., Virginia. It is an accessory constituent of
many acid volcanic and hypabyssal rocks, and has been found also in
limestone, and in magnetic iron ores. On account of its exceedingly wide
distribution, and the variations in appearance and composition, it has been
repeatedly described under various names, varieties being constantly
mistaken for new mineral species.
Its history is rather curious.[41] In 1806 the Danish mineralogist Giesecke
made a protracted voyage to Greenland, collecting minerals and rocks; he

remained there until 1813. In 1808 he sent off his first collection by ship to
Copenhagen; on the voyage the ship was taken by an English privateer, and
the cargo landed and sold at Leith. The minerals were bought by Allan, a
Scotch mineralogist, who recognised, that they were from Greenland by the
presence of cryolite, at that time only known to occur in Greenland. He
mistook the mineral subsequently named after him for gadolinite, and sent it
to Thomson for analysis.[42] Thomson recognised it as a new mineral, and
named it Allanite (1810). In 1815 Hisinger described a mineral from
Ryddarhyttan, Sweden, which he called Cerin; Leonhard (1821) and Hauy
(1822) showed that this was identical with Allanite. In 1818 Berzelius
described two varieties of a mineral from Finbo, near Fahlun, Sweden,
which he called Orthite, and Pyrorthite; these were eventually shown by
Scheerer (1844) to be varieties of Allanite. In 1824 the French mineralogist
Lévy described a mineral from Arendal, Norway, which he named
Bucklandite, in honour of the English naturalist; in 1825 this was identified
with a ‘black zeolite’ from the Laacher See by G. Rose, and in 1828 both
were shown by Hermann to have the same composition as orthite or allanite.
The list might be extended at will; the Tautolite of Kokscharow (1847), the
Bodenite of Breithaupt (1844), the Muromontite of Kemdt (1848), and the
Vasite of Bahr (1863) have all been shown to be varieties of the same
bewildering mineral.
[41] Vide Schilling, pp. 75-76, where full references are given.
[42] See Kobell’s Geschichte der Mineralogie, 1864, p. 679.

Hellandite. —Hellandite[43] is a mixed silicate of rare earths with lime,
magnesia, alumina, ferric and manganic oxides, with considerable quantities
of water. The formula approximates to 3H₂O,2R´´O,3R´´´´₂O₃,4SiO₂, where
R´´ = (Ca,Mg, Th2
)—Thorium being able to replace two atoms of calcium or
magnesium—and R´´´ = (Al,Fe´´´,Mn´´´ and rare earth metals). This may be
written as a basic orthosilicate, R´´₂[R´´´´(OH)]₆(SiO₄)₄, a basic salt of the
acid H₁₆Si₄O₁₆ (= 4H₄SiO₄). This composition puts it in the class containing
topaz and some rarer silicates.
[43] Brögger, Zeitsch. Kryst. Min. 1906, 42, 417.

The mineral is crystalline, the crystals being well developed, but often
dull and opaque by alteration (hydration).

Crystal system—Monoclinic, holosymmetric, a : b : c = 2·0646 : 1 :
2·507. β = 109° 45´. Habit usually prismatic, with {100}, {010}, and
several prisms {hko}, terminated by various pyramid forms.
Angles (100) ∧ (001) = 70° 32´; (100) ∧ (110) = 62° 22´; (010) ∧
(110) = 27° 14´; (110) ∧ (11̅0) = 125° 0´.
Twinned on (001), twin plane (001), forming knee-shaped twins.
Hardness varies from 51⁄2 in the least altered to 1 in the most altered
specimens; sp. gr. 3·70 in least altered specimens, decreasing with
hydration. Colour of fresh crystals, reddish-brown; on alteration they
become brownish-black, yellow, or even white.
The mineral dissolves easily in hydrochloric acid, with evolution of
chlorine; it is less soluble in nitric and sulphuric acids. It readily fuses to a
yellow mass.
It was first discovered by Brögger at Lindvikskollan, in 1903, and later,
in larger quantities, at Kragerö in Norway. It occurs in pegmatite veins in
granite.

Thalénite.[44]—A silicate of yttria earths with water and small quantities
of alumina, ferric oxide, carbon dioxide and alkalies. The ratio of rare earths
to silica gives the formula R₂O₃,2SiO₂, or R₂Si₂O₇; if the water be included,
the formula becomes H₂R₄Si₄O₁₅. The presence of both water and carbon
dioxide indicates, however, that the mineral has been somewhat altered, and
the simpler formula R₂Si₂O₇, (cf. Thortveitite, below) probably expresses
the composition of the original mineral. It contains considerable quantities
of nitrogen and helium, though uranium and thorium appear to be absent.
[44] Benedicts, Abstract in Zeitsch. Kryst. Min. 1900, 32, 614.

Monoclinic; a : b : c = 1·154 : 1 : 0·602. β = 80° 12´.
Common forms are the pinakoids {100} and {010}, hemi-prism
{110}, hemi-pyramids {111} and {111̅}, and others, and the hemi-
dome {021}.
Angles, (100) ∧ (010) = 91° 0´; (100) ∧ (110) = 48° 9´; (100) : (111)
= 59° 4´.
Double refraction weak. No cleavage. Brittle. Hardness 61⁄2. Colour,
bright flesh-red; translucent, with greasy lustre; sp. gr. 4·227,

increasing to 4·29 after ignition. A yellow variety has sp. gr. 4·11-4·16,
and is transparent.
The ‘average atomic weight’ of the rare earth metals is 99, from which it
appears that these consist chiefly of yttrium, with a smaller quantity of the
metals of higher atomic weight.
It was discovered in 1898 by Benedicts, accompanying fluocerite (q.v.) in
a quartz quarry at Oesterby in Dalekarlia.

Thortveitite.[45]—A silicate of yttria earths, chiefly scandia, of the
formula R₂O₃,2SiO₂. Scandia forms about 37 per cent. of the whole (R. J.
Meyer); yttria with small quantities of the other yttria earths forms the bulk
of the remainder of the bases, the ceria group being almost completely
absent. Ferric oxide (with traces of manganic oxide and alumina) forms
about 3 per cent. Thorium is present only in traces, and radioactivity is
barely perceptible.
[45] J. Schetelig, Centr. Min. 1911, 721.
Thortveitite is the first mineral to be discovered in which the content of
scandia is greater than 2 per cent.; in 1908 Crookes[46] examined a very
large number of yttria minerals for scandia, and finally chose for extraction
of the earth Wiikite (q.v.) which has a scandia content of 1·2 per cent.[47]
[46] Phil. Trans. 1908, A, 209, 15.
[47] According to Eberhard, some varieties of Wiikite have a much lower scandia content.

Thortveitite is orthorhombic; a : b : c = 0·7456 : 1 : 1·4912;
commonly combinations of pyramids o {111} and s {211} with prism
m {110}, in radial aggregates of crystals elongated parallel to the c
axis. Cleavage parallel to m, fair. Twin plane m (110), twinning very
common.
Refraction strong; birefringence strong, negative. Acute bisectrix
perpendicular to (001), plane of the optic axes (010). Hardness, 6-7; sp.
gr. 3·571. Extremely brittle; lustre brilliant, vitreous to adamantine.
Colour, greyish-green, white to reddish-grey on alteration; in
transmitted light yellowish-green, after ignition, reddish; the change
being probably due to presence of oxides of iron.

It is fusible with difficulty, and only partially attacked by hydrochloric
acid. It was found by Thortveit, in 1910, in a pegmatite vein in granite, at
Iveland, Sätersdalen, S. Norway, accompanied by euxenite, monazite, beryl,
and the usual vein-materials (quartz, felspar, etc.). It was analysed and
recognised as a new mineral by Schetelig (loc. cit.).
The following minerals, of which particulars will be found in the
alphabetical list, also belong to this class:
Bagrationite, Bodenite, and Muromontite, varieties of allanite with
differences in composition and physical properties.
Yttrialite, a weathered variety of gadolinite.
Elpidite, Erdmannite and Cainosite, more complex silicates.
Rowlandite, a comparatively simple silicate of the yttrium metals.
Yttrogarnet, a variety of garnet containing yttrium metals.

(b) Silicates of Thorium and Zirconium

Thorite. —Thorite and its variety Orangite are somewhat altered forms
of a pure silicate of thorium, ThSiO₄, containing also small quantities of
water, usually uranium, and often rare earths, with iron, lead, calcium, and
aluminium. Orangite differs from thorite in its beautiful orange colour and
greater specific gravity. Both varieties are radio-active.
When unaltered, the crystals are tetragonal and uniaxial, the pure mineral
ThSiO₄ being isomorphous with zircon, ZrSiO₄ (q.v.). By alteration they
become isotropic.

Crystals are tetragonal, holosymmetric; c = 0·6402; p ∧ p´ = 56° 40
´.
Common forms are the prism m {110} with the pyramids p {111}
and z {311}.
Hardness 41⁄2-5; sp. gr. 4·4 to 4·8 for thorite, 5·2 to 5·4 for orangite.
Thorite contains from 1·4 to 3·1 per cent. of rare earths. According to
Nilson and Blomstrand, the uranium is present as uranium dioxide, UO₂
replacing thoria, ThO₂, but Dunstan and Blake state that the two oxides are
isomorphous (see under Thorianite, p. 74), and so they might be expected to
be vicarious. Thorite was discovered by Esmark in 1828, and first analysed
by Berzelius,[48] who announced the discovery of a new earth in it in 1829.
The name Thorite is from Thor, the god of Scandinavian mythology.
[48] Pogg. Ann., 1829, 16, 385.
Thorite is a member of a peculiarly interesting series of isomorphous
minerals, which includes Cassiterite (SnO₂), Rutile (TiO₂), Zircon (ZrSiO₄),
and most probably the allied silicate Naegite, and the rare earth phosphate
Xenotime (q.v.), which are very similar in forms and angles. The oxide TiO₂
is itself trimorphous, being known in the three crystallographically different
forms, Rutile, Anatase, and Brookite (q.v.). On account of the isomorphism
of cassiterite and rutile with the two silicates, it has been suggested that the
oxide formulæ be doubled and written Sn(SnO₄) and Ti(TiO₄) respectively,
[49] to show the analogy with Th(SiO₄) and Zr(SiO₄). Consideration of the
molecular volumes (obtained by dividing molecular weight by specific
gravity, i.e. multiplying by specific volume) lends a certain amount of
support to this view. It has often been observed that isomorphous
compounds, and many compounds which occur in parallel growth to one
another, have nearly equal molecular volumes; there are, however, many
exceptions. Taking molecular volumes for the series under consideration,
we have, using approximate numbers only—
Mol. Wt. Sp. Gr. Mol. Vol.
Cassiterite, SnO₂ 151 6·9 22
Rutile, TiO₂ 80 4·2 19
Zircon, ZrSiO₄ 182 4·7 39
Thorite, ThSiO₄ 325 5·4 (Orangite) 60

Xenotime, XPO₄ 184 4·5 41
[49] This isomorphous series has recently been extended by Zambonini, and also by
Schaller, by the inclusion of minerals containing Columbium and Tantalum; see under
Ilmenorutile and Strüverite, end of Ch. IV., p. 71.

It will be seen that if the numbers for cassiterite and rutile be doubled,
four out of the five show very fair approximation to the constant value 40.
The number 60 for thorite is quite irreconcilable with the values obtained
from the other members; of course pure silicate of thorium, ThSiO₄, is not
known as a mineral, but it is most unlikely that the relatively small amount
of impurity in the densest specimens of orangite should have depressed the
specific gravity by over two units, as would be required if the molecular
volume of thorite were to show even the most approximate semblance of
agreement with the others. It cannot be too often remarked, however, that
very little indeed is known of the molecular formulas of minerals, and that
very little reliance can be placed on such figures as the above. On the
contrary, it is hardly conceivable that amphoteric oxides like those of tin
and titanium, occurring in the form of heavy crystalline minerals, should
have molecular formulæ only double the empirical formulæ. Where
agreements of the kind do occur, they must be taken as indicating
approximately equal degrees of molecular complexity in the minerals
concerned, rather than as affording any real insight into the molecular
condition.

Zircon. —Zircon is a silicate of zirconium, ZrSiO₄, with small quantities
of other elements. Most varieties contain ferric oxide and thoria; more
rarely small proportions of the yttria earths may be present. All varieties
contain traces of a large number of the common metals. Traces of radium
are usually present, with helium and neon,[50] and the mineral is strongly
radioactive.
[50] Strutt, Nature, 1906, 102.

System tetragonal, holosymmetric sub-class. c = 0·6404; (001) ∧
(101) = 32° 38´.
Usual forms—Prisms a {100} and m {110}; pyramids e {101}, p
{111}, u {221} and x {311}, etc. The basal pinakoid c {001} is rare.
The usual combination is one or both of the prisms a, m, with one or
two pyramids. Twinning is rare, the twin plane being e (101), giving

knee-shaped twins similar to those so characteristic of cassiterite and
rutile. Cleavage ∥ m imperfect, ∥ p bad.
Brittle; conchoidal fracture. Hardness 71⁄2; sp. gr. usually 4·68-4·70,
but varying from 4·2 to 4·86. Adamantine lustre. Clear and colourless
to yellow-, red- or greenish-brown. Transparent to opaque. Refraction
and double refraction strong, double refraction positive (ω = 1·924, ε =
1·968, for sodium light); on heating it becomes biaxial, and
occasionally is found biaxial in nature. By alteration it becomes
isotropic.
It is infusible before the blowpipe, but loses its colour; some varieties
glow and increase in density (see p. 38). In some varieties also the colour
changes or disappears rapidly on exposure to sunlight, and is often restored
on keeping in the dark. These phenomena of colour change have been
attributed variously to alteration in the state of oxidation of the iron present,
and to the presence of organic matter. It seems probable that either cause or
even both may be at the root of the change in particular cases.
On account of the hardness, unalterability, and strong refraction and
double refraction, good crystals of zircon are used as gems. The two gem
varieties, Hyacinth and Jargon, are found chiefly in the gem gravels of
Ceylon. It was in a zircon from Ceylon that Klaproth discovered the new
earth, Zirconia, in 1789.[51] In 1795 he found the same earth in hyacinth,
and so showed the two to be identical.
[51] Schriften der Gesellschaft naturforschender Freunde in Berlin, 1789, vol. 9.
Artificial crystals of zircon have been obtained by the action of silicon
tetrachloride and silicon tetrafluoride on zirconia, and by the action of
zirconium tetrafluoride on silica at high temperatures.
Zircon is one of the most widely distributed minerals known, though
usually it occurs in very small quantities. Good crystals have been found in
New Zealand, in Ceylon, at Miask in the Urals, and in North Carolina. This
last deposit has been worked commercially for the extraction of zirconia for
Nernst lamps (vide p. 320). It occurs in a decomposed felspar in a pegmatite
dyke in the Archæan gneiss near Zirconia, Henderson Co., and can be easily
extracted by picking or washing, after crushing if necessary. Should there
ever be a considerable demand for zirconia, it could doubtless be saved as a
by-product in the extraction of thoria from monazite sands (q.v.), zircon
being very generally found in those sands (see below).

Zircon is common in crystalline rocks, limestones, schists, syenites,
granites, etc. It is a constant accessory constituent in the acid igneous rocks,
especially in the more acid eruptive rocks. It is readily detected under the
microscope by the pleochroic haloes with which the tiny crystals are
surrounded; these have been shown by Joly to be due to alteration of the
surrounding rock by the radiations emitted by the radio-active constituents
of the zircon. It also occurs as a constituent of those sands which are formed
by the erosion of the igneous rocks in which it is enclosed, and hence it
almost invariably accompanies monazite in the so-called monazite sands.
Zircon is one of the least easily altered minerals; by the prolonged action
of chalybeate and other waters, during many geological ages, however, it
gradually changes, losing silica and gaining lime, oxides of iron, and water.
Some of these altered varieties have received special names, as, e.g.
Auerbachite, Malacone, Cyrtolite, and Alvite; but none of them is of special
interest.

Naegite.[52]—This rare mineral is a silicate closely related to zircon, but
of rather more complex composition. It may be represented as silicate of
zirconium, ZrSiO₄ (zirconia = 55·3, silica = 20·6 per cent.), with rare earths
(chiefly yttria, 9·1 per cent.), uranium (UO₃ = 3 per cent.), and thorium
(ThO₂ = 5·0 per cent.), partly as silicates, partly as columbates and
tantalates ((Cb,Ta)₂O₅ = 7·7 per cent.).[53]
[52] Beiträge zur Mineralogie von Japan, 1906, 2, 23.
[53] An earlier analysis (Abstr. Chem. Soc. 1905, 88, [ii.], 177) gave over 20 per cent. of
uranous oxide, UO₂; the greater part of this appears to have been zirconia, ZiO₂.
It is tetragonal, usually occurring in globular aggregates of crystals. The
measurable angles are extremely close to those of zircon, and it is probable
that naegite is isomorphous with the series mentioned above under Thorite.
The hardness is 71⁄2, the sp. gr. 4·091. The colour is dark green or
brown, becoming dull by weathering. The double refraction is
extremely weak.
So far it has only been found in the ‘placer’ tin deposits or ‘gravel tin’ of
Japan.
The following minerals (see list) are also to be included in this sub-class:

Alvite (Anderbergite or Cyrtolite), Auerbachite, Malacone, Oerstedite
and Tachyaphaltite, altered varieties of zircon.
Calciothorite, Eucrasite and Freyalite, altered varieties of Thorite.
Pilbarite, Thorogummite and Yttrogummite, hydrated silicates of thorium
with uranium and other metals.

(c) Complex Silicates

Eudialyte (Eucolyte). —This is a complex silicate of alkalies, lime,
ferrous oxide, rare earths, etc., containing chlorine and a high proportion
(up to 17 per cent.) of zirconia. The empirical formula is given by Dana as
Na₁₃(Ca,Fe)₆Cl(Si,Zr)₂₀O₅₂. Brögger gives the simpler metasilicate formula
R´₄R´´₃Zr(SiO₃)₇, where R = (Na,K,H), R´´ = (Ca,Fe,Mn,CeOH), and
Zr(OCl) may partly function as an acid in place of SiO₂. The true formula,
however, is quite uncertain, as the zirconia may function either as an acidic
or basic oxide. The fact that a mineral of such exceedingly complex
composition occurs in perfectly well-defined crystals indicates the intricate
nature of the problems to be solved in mineral chemistry.
The crystals are rhombohedral, a : c = 1 : 2·1116.
Common forms are—the pinakoid c {111}, prisms a {101}, and m
{211}, and pyramids r {100} and e {110}. c ∧ r = 31° 22´. Habit
tabular parallel to c, rhombohedral with e prominent, or prismatic with
a prominent.
Cleavage ∥ c very good, ∥ a difficult.
The colour is brown or red to brownish- or bluish-red. Brittle.
Hardness 5 to 51⁄2; sp. gr. 2·92 for eudialyte, 3·0 to 3·1 for eucolyte.
The double refraction is strong, being positive for eudialyte, negative for
the Norwegian variety, eucolyte. From careful microscopic examination,
Ramsay has found that zones of positive and negative birefringence, as well
as isotropic (singly-refracting) zones can occur on the same crystal, and he
suggests that the mineral is really composed of two isomorphous
compounds forming mixtures. In view of the continuous variation of optical
properties in an isomorphous series like the felspars, such an explanation
seems doubtful. The optical behaviour of minerals is very often anomalous,

and the phenomena in this case are probably due to repeated twinning, with
some alteration in the double refraction, or to the lamellar intergrowth of
two varieties having slightly different optical properties.
On heating, the mineral evolves moisture and readily fuses. It is easily
attacked even by dilute acids, being named by Strohmeyer (1819) on
account of this property. The dilute hydrochloric acid solution reddens
turmeric paper—a test for the presence of zirconium.
It is found in Greenland, usually embedded in felspar, in Norway, in
Lapland and in Arkansas, being generally associated with minerals rich in
alkalies, e.g. ægirine, ælæolite, nepheline, sodalite, arfvedsonite, etc.

Beckelite. —This is a mineral similar in composition to eudialyte,
though not so complex, and of more recent discovery.[54] It is a silicate of
ceria earths and lime, in which zirconia replaces silica; the oxygen ratio (i.e.
ratio of oxygen in basic oxides to oxygen in acid oxides) is 3 : 1, and the
formula Ca₃R´´´₄(Si,Zr)₃O₁₅, where R = rare earth metals, chiefly of the
cerium group. It is thus a salt of an acid H₁₈Si₃O₁₅ [= 3H₆SiO₅ =
3(3H₂O,SiO₂)] with zirconium and silicon vicarious.
[54] Abstr. Chem. Soc. 1905, 88, ii, 177.

The crystals appear to belong to the cubic system, occurring in
cuboid grains, and in octahedra and dodecahedra. It is brown, and
isotropic, with cubic cleavage. Sp. gr. = 4·15.
It is soluble in hot hydrochloric acid, even after ignition; the solution
gives the turmeric test for zirconium.
It was found in a dyke in an ælæolite syenite, near the Sea of Azov.
The following minerals (see list) are also to be placed in the class of
mixed silicates:
Arfvedsonite and cataplejite, complex zircono-silicates.
Hiortdahlite (Guarinite) and Lavenite, zircono-silicates with fluorine.
Caryocerite, Melanocerite and Steenstrupine, complex fluosilicates.
Auerlite, Britholite, Erikite and Florencite, phospho-silicates.
Cappelenite, Homilite and Tritomite, boro-silicates.

CHAPTER III

THE TITANO-SILICATES AND TITANATES

(a) The Titano-Silicates

Yttrotitanite or Keilhauite. —A titano-silicate of calcium, aluminium,
iron and yttrium metals. The mineral is isomorphous with titanite,
CaO,TiO₂,SiO₂ (q.v.), and is itself probably an isomorphous mixture of
titanite with the silicate (Y,Al,Fe)₂SiO₅, where Y = yttrium metals. Its
composition will then be represented by the formula m (Y,Al,Fe)₂(SiO₅) + n
CaTi(SiO₅).
It is monoclinic, with axial ratios and angles very close to those of
titanite. Usual forms—pinakoids a {100} and c {001}, hemi-prism m
{110}, hemi-pyramids n {111}, e {1̅11} and l {1̅12}. Cleavage ∥ n
distinct. Birefringence weak, +ve. Colour brown to brownish-black.
Hardness 61⁄2; sp. gr. 3·52 to 3·77.
The mineral is fusible before the blowpipe, and is decomposed by
hydrochloric acid.
It was named by Scheerer in 1844 from its composition, and by Ekeberg
in the same year in honour of the Norwegian geologist Keilhau.

Titanite or Sphene. —This species, important as an accessory mineral of
many rocks, is a titano-silicate of calcium, generally containing small
quantities of aluminium and iron. The approximate formula usually given,
CaTiSiO₅, is unsatisfactory; some specimens contain as much as 7 per cent.
of ferric oxide, others up to 2 per cent. of manganese, whilst the percentage
of titanium oxide, TiO₂, varies very considerably (30 to 45 per cent.).
Zambonini and Nickolan have independently analysed specimens for which
no satisfactory formulæ could be deduced. For specimens containing

trivalent metals, Groth considers the mineral to be an isomorphous mixture
of CaTiSiO₅ and R´´´₂SiO₅ (see under Yttrotitanite, above); Blomstrand,
however, advances the formula 2(R´´R´´´₂O₂,TiO)O,SiO₂, where TiO is
basic, and the trivalent metals occur in the divalent group R´´´₂O₂; this
formula is also supported by Zambonini.
More recently the problem of the constitution has been attacked by
Bruckmoser, using Tschermak’s method of determining the nature of the
salts present in silicates. In this method, the mineral is digested with
hydrochloric acid, at a temperature not greater than 60°, until
decomposition is complete; the silicic acid formed is washed by
decantation, and dried in air at a constant temperature; it is weighed at
regular intervals until the weight is constant. It is stated that if a curve of
times and weights be plotted, a break is observed at the point where drying
ceases (for the acid is of course wet) and decomposition begins; the
composition at this point, which is taken as the composition of the acid
required, can be determined from the weight of the acid, and the weight of
anhydrous silica present, which is determined by ignition after the weight
has become constant.
Employing this method in the case of titanite, Bruckmoser claims to have
obtained the acids H₂Si₂O₅ and H₂Ti₂O₅. He therefore concludes that the
constitution of the mineral is represented by the formula Si₂O₅,Ti₂O₅Ca,
which presumably may be written Ca(Ti,Si)₂O₅.
Crystal system—monoclinic; a : b : c = 0·7547 : 1 : 0·8543. β = 60°
17´.
Common forms (Des Cloizeaux’s orientation)—the pinakoids a
{100} and c {001}, with m {110}, s {021}, x {102}, n {111}, and
many others.
(100) ∧ (110) = 38° 141⁄2´; (001) ∧ (1̅01) = 65° 57´; (001) ∧ (011) =
36° 34´.
The habit is very varied, the commonest being the wedge form,
elongated ∥ c. Twinning is fairly common, especially on the law—
Twin plane ∥ a, which gives both contact and interpenetrant twins.
Cleavage ∥ m, fairly distinct. Hardness 5 to 51⁄2; sp. gr. 3·40 to 3·56.
Lustre adamantine to resinous. The colour varies very much, doubtless
with the content of iron and manganese; it is commonly yellow, green,
or brown. Pleochroism is very distinct. The refraction and dispersion

are very high, giving the facetted stone a ‘fire’ inferior only to that of
diamond. Birefringence positive, strong; the axial angles vary very
widely in different specimens.
It is fusible with difficulty before the blowpipe. Hot concentrated
hydrochloric acid decomposes it partially, with separation of silica; boiling
sulphuric acid, or, better, fused potassium hydrogen sulphate, decomposes it
completely.
On account of the high dispersion and refractive index, clear specimens
of sphene make very beautiful gems, but the stone is not sufficiently hard to
stand much wear.
The mineral was discovered in Chamouni by Pictet in 1787, and was
named Pictite by Delamètherie (1797). In 1795 Klaproth analysed a
specimen from Passau, and, observing the presence of titanium (which he
had just discovered in rutile), proposed the name Titanite. The mineral
described by de Saussure (1796) as ‘Schorl rayonnante,’ and afterwards by
Hauy (1801) as Sphene (σφήν = a wedge), was shown to be identical in
composition with titanite by Cordier, and also by Klaproth (1810); the
crystallographic identity was proved by G. Rose (1820).
On account of the difference in colour and composition, a large number
of varieties are distinguished. The ordinary yellow and brown varieties are
known indifferently as sphene or titanite. Ligurite has an apple-green
colour; Semeline is a greenish form named from a fancied resemblance to
flax seed. Lederite is a brown variety of tabular habit; Greenovite is rose-
coloured, and contains manganese. Alshedite and Eucolite-Titanite are rich
in the trivalent metals; Grothite is a brown variety containing a considerable
percentage of ferric iron. Yttrotitanite, which contains a high proportion of
rare earths, is usually treated as a separate species (see above).
Titanomorphite and Leucoxene are white amorphous varieties chiefly
produced by alteration of rutile and ilmenite.
Titanite is a fairly widespread mineral; as an accessory rock constituent it
is common in the massive plutonic rocks in tiny crystals, readily
distinguished under the microscope by the high refraction and
birefringence, whilst in large embedded crystals it occurs in many granular
limestones, and in plutonic acid, as well as in some metamorphic rocks. In
good crystals it is found in many parts of Switzerland and the Alps, in
Dauphiné, the Tyrol, Piedmont, the Urals, South Norway, and other

European localities; it is also widely distributed in the United States and
Canada.
The mineral is important as a valuable source of titanium.
The class of Titano-silicates is a very large one, and might be extended
almost at will by the inclusion of the numerous silicates which contain
titanium. Owing to the frequency with which small quantities of silica are
replaced by titanium dioxide, almost all the commoner silicate minerals
contain the latter oxide, so that titanium is one of the most widely
distributed of the elements. Relatively very few, however, of the titanium-
bearing minerals contain the element in considerable quantities, and only
two or three have any importance as commercial sources of titanium
compounds.
Only those additional titano-silicates which contain titanium as an
important constituent are mentioned below; short accounts will be found in
the alphabetical list.
Johnstrupite, Mosandrite, Rinkite, Rosenbuschite and Tscheffkinite are
complex titano-silicates containing yttrium or cerium metals.
Astrophyllite, Leucosphenite, Molengraafite, Neptunite and Rhönite are
complex titano-silicates free from rare earth elements.
Benitoite is a simple titano-silicate of barium; Ænigmatite and
Narsarsukite contain iron and sodium; Lorenzenite has sodium and
zirconium. Schorlomite is a titaniferous garnet. A variety of olivine rich in
titanium (Titanium Olivine) is also known.

(b) The Titanates

Yttrocrasite.[55]—This is a complex titanate of rare earths (chiefly yttria
earths) with lime, thoria, and oxides of lead, iron, uranium, etc.; it has a
considerable water content. An approximate formula is R´´O,RivO₂,3R
´´´₂O₃,16TiO₂,6H₂O, where R´´ = (Ca,Pb,Fe), Riv = (Th,U), and R´´´₂O₃ =
rare earths. No constitutional formula can be given; it will be noticed that
the amount of titanium dioxide is considerably more than is required to
combine with the bases present (cf. also Delorenzite below). It is
radioactive.

[55] Hidden and Warren, Amer. J. Sci. 1906, [iv.], 22, 515; also Zeitsch. Kryst. Min. 1907,
43, 18.

Imperfect crystals only were found, apparently belonging to the
orthorhombic system. No crystallographic data could be determined.
The mineral is black, closely resembling polycrase and euxenite
(q.v.) in appearance. Hardness 51⁄2-6; sp. gr. 4·80.
It is infusible, and not easily soluble in acids. Hydrofluoric acid
decomposes it, and the powdered mineral is also slowly attacked by boiling
concentrated sulphuric acid.
It was found in 1904 by Barringer, in Burnet Co., Texas.

Delorenzite.[56]—A compound similar to the above, but even richer in
titanium dioxide, which amounts to 66 per cent. Tin dioxide is also present,
with traces of columbic anhydride. The bases are the yttria earths (almost
free from ceria earths), uranium dioxide, and some ferrous oxide, the
formula being 2FeO,UO₂,2Y₂O₃,24TiO₂, with a little SnO₂ replacing TiO₂.
It is strongly radioactive. Its closest chemical neighbour is yttrocrasite, but
in appearance and angles it closely resembles polycrase (q.v.). Its
discoverer, Zambonini, therefore formulates it as a metatitanate with
titanium acting also as a base—polycrase is a mixed metatitanate and
metacolumbate—thus, 2FeTiO₃ + U(TiO₃)₂ + 2Y₂(TiO₃)₃ + 7(TiO)TiO₃.
[56] Zambonini, Zeitsch. Kryst. Min. 1908, 45, 76.

The crystals occur in aggregates of numerous individuals in sub-
parallel growth. The system is orthorhombic; a : b : c = 0·3375 : 1 :
0·3412. Usual forms—the pinakoids a {100} and b {010} with prism
m {110}, dome d {201}, etc. Habit prismatic, elongated ∥ c axis.
Hardness 51⁄2-6; sp. gr. about 4·7.
It was found with struvite in a pegmatite at Craveggia, Piedmont,
Italy.

Ilmenite or Menaccanite (Specular Iron Ore, Titaniferous Ironstone,
etc.).

—This is a titanate of iron, usually written FeTiO₃. Its constitution has
given rise to very considerable discussion[57]; not only do the relative
proportions of iron and titanium vary greatly, but the iron is undoubtedly
present in both the ferrous and the ferric states, and in the former state is
partly replaced in some specimens by manganese and magnesium. In 1829
Mosander put forward the view that the mineral consisted of FeTiO₃,
ferrous titanate, with varying proportions of ferric oxide, the forms and
angles of ilmenite being very similar to those of hæmatite, Fe₂O₃. This view
was disputed by H. Rose, who concluded that the mineral must have been
originally an isomorphous mixture of ferric oxide, Fe₂O₃, and titanic oxide,
Ti₂O₃, which on exposure to high temperature in the earth’s crust would
change according to the equation
Fe₂O₃ + Ti₂O₃ = 2TiO₂ + 2FeO
so that the proportion of ferrous iron increases with the proportion of
titanium dioxide, as is actually found to be the case. This condition,
however, is also satisfied by Mosander’s view. The latter view was also
supported by Rammelsberg, who pointed out that the presence of
magnesium indicated the existence of ferrous iron as a primary constituent.
Additional support is lent to this view by the discovery of Pyrophanite,
MnTiO₃ (see list), which is found to be isomorphous with ilmenite, so that
there can be little doubt that MgTiO₃, which can be only a titanate, would,
if it existed in the crystalline form (see Geikielite in list), also be
isomorphous with ilmenite. Friedel and Guérin (1876) prepared artificial
titanium sesquioxide, Ti₂O₃, and found it to be isomorphous with hæmatite,
Fe₂O₃; they concluded that FeFeO₃, FeTiO₃ and TiTiO₃ formed an
isomorphous series, and that ilmenite was a mixture of the second with the
other two. In 1890 Hamberg pointed out that there was no reason to suppose
that hæmatite, Fe₂O₃, contains ferrous iron, i.e. has the constitution Fe
´´FeivO₃, analogous to Fe´´TiivO₃, since in corundum, the analogous
compound of aluminium, Al₂O₃, divalent aluminium can hardly exist;
nevertheless, strict analogy of constitution is not necessary for
isomorphism, as shown by the case of potassium nitrate, KNO₃, and
aragonite, CaCO₃, so that hæmatite, Fe₂O₃, and ferrous titanate, FeTiO₃,
might form solid solutions in varying proportions without the strictly
analogous formula FeFeO₃ being true for the former. The balance of
opinion inclines to the constitution (mFeTiO₃ + nFe₂O₃ in isomorphous

mixture) originally proposed by Mosander. The evidence in support of this
view has been greatly strengthened by the recent work of Manchot,[58]
which has proved the absence of titanium sesquioxide, Ti₂O₃; the mineral is
therefore to be regarded as a titanate.
[57] For a full account of the earlier work on the constitution of ilmenite vide Hintze, i.
1858 et seq.
[58] Zeitsch. anorg. Chem. 1912, 74, 79.

Crystal system—rhombohedral; in forms and angles very close to
hæmatite, but the two differ in symmetry (hæmatite has t, 3δ, c, 3π;
ilmenite has only t, c).
c = 1·38458; (111) ∧ (100) = 57° 581⁄2´; habit, tabular, thick; or in
thin laminæ. Usually in embedded grains or rolled crystals in sand.
Hardness 5 to 6; sp. gr. 4·5 to 5·0, increasing with percentage of
ferric oxide. Iron black, opaque; streak black to brownish-red. Lustre
sub-metallic. Slightly magnetic.
The mineral is infusible; when powdered, it dissolves slowly in boiling
hydrochloric acid, the filtered yellow solution giving the characteristic blue
colouration of titanium salts on addition of tinfoil. In fused potassium
hydrogen sulphate it dissolves readily. The variation in composition can be
judged from the following limits:
TiO₂ Fe₂O₃ FeO
3·5 93·6 3·3 per cent.
52·8 1·2 46·5 „
Ilmenite is a widely distributed mineral. In crystals it occurs chiefly at
Kragerö and Arendal in Norway, at Miask in the Ilmen mountains, in
Dauphiné, the St. Gothard, etc.; in the massive form at Bay St. Paul,
Quebec, and other localities in America; and in sands at Menaccan in
Cornwall, Iserwiese in Bohemia, Puy de Dôme, dép. Haute Loire, France,
and in Brazil, Australia, and New Zealand.
The mineral was discovered at Menaccan in Cornwall by McGregor,
about 1790. He described it as containing iron and a new oxide; the
unknown oxide was obtained in 1795 from rutile by Klaproth, who gave the
name Titanium to the new metal it contained.

Short descriptions of the following titanates are also given (see list):
Davidite and Knopite; these are complex titanates containing elements of
the cerium and yttrium groups.
Arizonite and Pseudobrookite—ferric titanates.
Perovskite, calcium titanate, and its variety Hydrotitanite.
Pyrophanite, a manganese titanate isomorphous with ilmenite, and
Senaite, a species intermediate in composition between these two.
Geikielite, the magnesium analogue of ilmenite, with the variety
Picroilmenite, which is rich in iron.
Uhligite, a titanate of zirconium, calcium and aluminium.
Derbylite, Lewisite and Mauzeliite, an interesting series of titano-
antimonates.
Warwickite, a boro-titanate.

CHAPTER IV

THE TANTALO-COLUMBATES

(a) Tantalo-Columbates containing no Titanium Dioxide

Samarskite, Yttro-ilmenite or Eytlandite (Urano-tantalite). —Samarskite
is a tantalo-columbate[59] of the rare earth metals, with iron, calcium, and
uranium.
[59] In this and all similar minerals, columbium (niobium) and tantalum are to be
regarded as vicarious; they replace each other in all proportions. It seldom happens that a
pure columbate is found free from tantalum, or vice versa; one or other may
predominate, but the two are almost always found together.

Rammelsberg gives the formula R´´₃R´´´₂(Cb,Ta)₆O₂₁, where R´´ = (Fe
´´,Ca,UO₂), and R´´´ = rare earth metals. Groth regards it as essentially a
pyrocolumbate (tantalate) of rare earth metals R₄[(Cb,Ta)₂O₇]₃ the iron,

calcium and uranium being more or less accessory constituents. Des
Cloizeaux considers the formula indefinite. The mineral has also been
found to contain tin, thorium, germanium, and helium. The yttria earths
usually predominate (11·9 to 18·9 per cent.), the percentage of ceria earths
being low (2·4 to 5·2 per cent.). The yttria earths contain the very rare oxide
samaria.
The mineral is radio-active.
Crystal system—orthorhombic; a : b : c = 0·5456 : 1 : 0·5178.
Forms—macro- and brachy-pinakoids a {100} and b {010}; prisms
m {110} and h {120}, the macrodome e {101}, and pyramids p {111}
and v {231}.
Angles—(100) ∧ (110) = 28° 37´; (001) ∧ (101) = 43° 30´; (001) ∧
(011) = 27° 221⁄2´.
Habit usually prismatic, with e prominent; sometimes tabular
parallel to a or b. Cleavage ∥ b, imperfect. The faces are usually rough.
The mineral commonly occurs massive, and in flattened grains
embedded in granite. Conchoidal fracture. Brittle. Hardness 5 to 6; sp.
gr. 5·6 to 5·8.
Colour velvet-black, streak reddish-brown. Opaque even in thin
films.
Before the blowpipe it fuses at the edges; with borax it gives an iron
bead. It is decomposed by boiling concentrated sulphuric acid, better by
fusion with potassium hydrogen sulphate, and leaching the residue with
dilute hydrochloric acid—this leaves the insoluble oxides Cb₂O₅ and Ta₂O₅.
On heating it glows, with decrease in specific gravity (cf. p. 38).
Samarskite occurs with other columbo-tantalates in felspar, or in veins in
granite, near Miask in the Urals, near Quebec in Canada, and in Mitchell
County, North Carolina. From the last-named locality, masses up to twenty
pounds in weight have been obtained.
The mineral was first discovered in the Urals by Ewreinoff, captain of a
corps of Russian mountain engineers. He sent a specimen for identification
to the mineralogist Gustave Rose, who pronounced it to be a tantalate of
uranium containing manganese, and called it Urano-tantalite.[60] In 1847 the
chemist Heinrich Rose, brother of Gustave, in the course of his researches
on tantalic ‘acid’ (oxide), analysed a specimen. He found the composition

given above, and renamed it Samarskite,[61] in honour of the Russian
engineer who furnished him with the specimen for analysis.
[60] Pogg. Ann. 1839, 48, 555.
[61] Ibid., 1847, 71, 157.

In 1907, Brögger[62] announced that Annerödite, of which he had
published an account as a new species in 1881, was a parallel growth of the
mineral columbite, (Fe,Mn)Cb₂O₆, on samarskite.
[62] Abstr. Chem. Soc., 1907, 92, ii. 885.

Both minerals are orthorhombic, but they are not isomorphous. The
mistake was due to the fact that whilst the crystallographic data were
determined from the upper crystals of columbite, the crystals of samarskite
were used for analysis.

Plumboniobite.[63]—This is a recently discovered mineral closely
related to samarskite and yttrotantalite (q.v.). It is essentially a columbate[64]
of yttrium metals, lead and uranium, with water, ferrous oxide, titanium
dioxide, stannic oxide, alumina, lime, and cuprous oxide. The formula
given is R´´₂Cb₂O₇,R´´´´₄(Cb₂O₇)₃, where R´´ = (Fe,Pb,Ca,UO), and R´´´ =
Al and yttria metals, with isomorphous (?) metatitanate. The mineral is
radio-active, and gives considerable quantities of gas on being heated with
sulphuric acid (carbon dioxide 0·19, helium and nitrogen 0·22 per cent.).
The yttria earths are rich in the oxides of gadolinium and samarium, and the
mineral should prove a valuable source of these elements. It is remarkable
that the ceria earths are almost entirely absent.
[63] Hauser u. Finch, Ber. 1909, 42, 2270; Hauser, ibid., 1910, 43, 417.
[64] It is to be understood that small quantities of columbium are replaced by tantalum.

The mineral is massive, with some indication of crystalline
structure. It is dark brown to black, transparent in flakes, and under the
microscope is seen to be isotropic, with doubly-refracting inclusions,
undoubtedly of a secondary nature. Hardness 5 to 51⁄2; sp. gr. 4·80 to
4·81. Unlike samarskite, it does not glow on ignition.
It occurs with mica and pitchblende in pegmatite veins in granite, at
Morogoro, in the Uluguru Mountains, German East Africa.

Yttrotantalite.

—This is a tantalo-columbate similar in composition to Samarskite, and
isomorphous with it; though, as the name implies, the acidic oxide is chiefly
tantalum pentoxide, the percentage of columbic anhydride being much
lower than in the latter mineral. It is a pyro-salt of the formula R´´R
´´´₂(Cb,Ta)₄O₁₄ + 4H₂O,[65] where R´´ = (Fe,Ca) and R´´´ = rare earth
(chiefly yttrium) metals (Rammelsberg). Strutt found thorium and radium in
it. The manner in which the water is combined in this, as in many other
minerals, is at present undetermined.
[65] Dana gives R´´R´´´₂(Cb,Ta)₄O₁₅ + 4H₂O; this appears to be an error.

Crystal system—orthorhombic; a : b : c = 0·5411 : 1 : 1·1330.
Common forms—pinakoids b {010} and c {001}, prisms m {110}, o
{210}, p {120}, domes s {201} and β {011}. Habit, prismatic with m
and b prominent, or tabular parallel to b. Colour yellow to black, white
after strong ignition.
It is found at Ytterby in Sweden, and in South Norway.

Fergusonite, Tyrite, or Bragite. —A columbate and tantalate of the rare
earth metals, with uranium, iron, calcium, etc. The general formula is that
of an ortho-compound, R₂O₃,(Cb,Ta)₂O₅ or R(Cb,Ta)O₄, where R = metals
of the rare earths, chiefly of the yttrium group. Brögger includes the other
constituents in the more complex formula (Th,U)(Si,Sn)O₄ +
12R(Cb,Ta)O₄; but the simpler formula agrees quite well with specimens
from the most widely separated localities, and is usually adopted. The
mineral is radio-active and contains helium.
Tetragonal, polar (with tetrad axis of symmetry only) c = 1·4643.
(001) ∧ (101) = 55° 40´. Common forms—Basal pinakoid c {001},
tetragonal prism g {320}, pyramids s {111}, z {321}. Brittle. Hardness
5 to 6; sp. gr. 5·84, decreasing on hydration. Lustre dull, brilliantly
vitreous on broken surfaces. Colour brownish-black. Translucent to
opaque.
Fergusonite was discovered by Hartwell. It occurs with samarskite, and
often with gadolinite and allanite, in Norway and Sweden, the Carolinas,
Texas, the Urals, W. Australia, etc.

On heating it glows suddenly between 500° and 600°C.,[66] losing all its
helium, and with decrease in density (5·619 to 5·375). At the same time it
gives out a considerable amount of heat—8·09 C.[67] for 1 gm. (see p. 38).
[66] Ramsay and Travers, Zeitsch. physikal. Chem. 1898, 25, 568.
[67] The heat of combustion of a gram of hydrogen is 342 K.

Sipylite. —Essentially a columbate of rare earth metals, with oxides of
tantalum, tungsten, zirconium, uranium, iron and calcium, and some water.
Mallet, the discoverer, gives the formula as R₂O₃,Cb₂O₅, the basic oxides
including, besides the rare earths, Cb₂O₅ with Ta₂O₅ and WO₃, and some
water. An alternative formula, making it a complex pyro-salt, is also given,
but from its great similarity in form and angles to fergusonite, the first
formula is preferred. Strutt finds that it contains not only uranium, radium
and helium, but also thorium in considerable quantity (ThO₂ = 4·9 per
cent.), a fact which had been overlooked by Mallet. The rare earths contain
a high proportion of erbia.
It is tetragonal, c = 1·4767, (001) ∧ (101) = 55° 54´. The crystals
are octahedral, with the form p {111}; p ∧ p´ = 79° 15´, p ∧ p´´ = 128°
50´. Cleavage distinct ∥ p. It is usually granular and amorphous.
Colour brownish-black to brownish-red, lustre resinous. Brittle.
Hardness 6; sp. gr. 4·89. Translucent.
Its behaviour on heating has been already mentioned (see p. 39); it is
infusible. Boiling hydrochloric acid partially dissolves it; the solution gives
the turmeric test for zirconium, and on diluting and adding metallic tin a
sapphire-blue colour is developed, due to the columbium present. Boiling
concentrated sulphuric acid decomposes it slowly.
It is found in Amhurst Co., Virginia, adherent to the allanite which occurs
there in large quantities. It was discovered there by Mallet in 1877, who
named it, on account of the columbium (niobium) present, from Sipylus,
one of the sons of Niobe.[68]
[68] See Mallet, Amer. J. Sci. 1877, [iii.], 14, 397.

In this class, also, are to be included the following minerals (see list):
Nohlite and Vietinghofite, varieties of Samarskite.

Hjelmite and Kochelite, minerals closely related to Yttrotantalite and
Fergusonite respectively.
Koppite, Loranskite, Microlite and Rogersite, complex tantalo-
columbates containing elements of the cerium or yttrium groups.

(b) Tantalo-Columbates containing Titanium Dioxide

Æschynite. —A columbate and titanate of the cerium metals, with
thorium, calcium, iron, etc. From the results of an analysis on a specimen
from Hitterö, Norway, Tschernik proposed the rather formidable formula
2(2Ce₂O₃,3TiO₂),4(ThO₂,TiO₂),Y₂(CbO₃)₆,3(CaO,TiO₂),3Fe(CbO₃)₂,Fe(Ta

O₃)₂,6TiO₂.
This can be simplified to Y(CbO₃)₃ + ThTiO₄ + 3⁄2TiO₂, in which Y
represents rare earth metals partially replaced (2 atoms) by ferrous iron (3
atoms), whilst thorium can be partially replaced by (2 atoms of) ferrous iron
or calcium. Strutt found it to contain the uranium-radium combination and
helium.
The crystals are orthorhombic, holosymmetric; a : b : c = 0·4866 :
1 : 0·6737.
Common forms—brachy- and basal pinakoids b {010} and c {001},
prisms m {110} and r {120}, domes d {101} and v {021}, with
pyramid o {111}.
(100) ∧ (110) = 25° 57´; (001) ∧ (101) = 54° 9´; (001) ∧ (011) =
33° 58´.
Habit prismatic, vertically striated, or tabular parallel to b with
horizontal striations. Brittle. Hardness 5 to 6; sp. gr. 4·9 to 5·7. Colour
nearly black. Nearly opaque.
It occurs at Miask, in the Urals, at Hitterö in Norway, and at
Fredriksvarn. The variety from the last locality is called Polymignite; it was
shown by Rose to be probably identical with Æschynite. Æschynite was
discovered by Berzelius at Miask and named by him from the Greek

αίσχύνη, shame, from the fact that its composition could not at that time be
determined.
If the ceria earths be largely replaced by yttria earths, a variety very
similar in appearance and angles, but approximating to polycrase (q.v.) in
composition, is obtained. This mineral was found in 1879, and referred to
Æschynite; analysis subsequently showed its true composition, and it was
named Blomstrandine (q.v.) by Brögger in 1907.

The Isodimorphous Series Euxenite, Polycrase, Blomstrandine, and
Priorite.
Euxenite and Polycrase are members of an isomorphous series and vary
considerably in composition. The composition of the series is that of mixed
columbates and titanates of yttria earths (with, as usual, some ceria earths),
with uranium and zirconium, and water. Before the isomorphous relation
was recognised, Rammelsberg gave for Euxenite the formula R´´´(CbO₃)₃,R
´´´₂(TiO₃)₃,11⁄2H₂O. The ratio of the acidic oxides, Cb₂O₅ : TiO₂, is here 1 :
2. This is the greatest value of the ratio, which varies for the series between
1 : 2 and 1 : 5.[69] The end members, the pure metacolumbate and pure
metatitanate respectively, are unknown; all the members occurring in nature
are to be regarded as mixtures of these within the limits set by the ratios 1⁄2
and 1⁄5. Brögger[70] suggests that the name Euxenite be retained for all
members for which the ratio is between 1⁄2 and 1⁄3, whilst for those minerals
in which it is less than 1⁄4 the name Polycrase be kept; these views have
been supported by Lange, who has analysed members of the series.
[69] Lange (Abstr. Chem. Soc. 1911, 100, ii. 499) gives the limits 1⁄2 and 1⁄6.
[70] Abstr. Chem. Soc. 1907, 92, ii. 885.
The members of this isomorphous series, however, are themselves
dimorphous, that is, can each crystallise in two different ways. The second
form corresponding to the Euxenites is known as Priorite, whilst that
corresponding to Polycrase is known as Blomstrandine; and these second
forms are themselves members of a parallel isomorphous series of the same
chemical composition, of course, as the first series. It is, perhaps,
undesirable to cite this as a typical example of an isodimorphous series,
since no end members of unmixed composition are known. A perfect
example of such a series is furnished by the oxides of antimony and arsenic.
Each of these compounds exists in two distinct crystalline varieties,

antimony trioxide, Sb₂O₃, as Valentinite (orthorhombic) and Senarmontite
(cubic), arsenic trioxide, As₂O₃, as Claudetite (orthorhombic) and
Arsenolite (cubic); and these two modifications are isomorphous with one
another, senarmontite with arsenolite, and valentinite with claudetite.
In the case we are considering, the name Euxenite is applied to one
crystalline modification (A) of a number of isomorphous compounds within
certain limits of composition, the name Priorite to the second crystalline
modification (B) of the same compounds; the name Polycrase is applied to
compounds having the crystal form A, and a composition varying within a
second set of limits in the same chemical series, whilst this second set of
compounds in the crystalline form B is known as Blomstrandine.
Stated as concisely as possible, the relationship is as follows: Each
member of this chemical series of continuously varying composition can
crystallise in two forms, which are the same for every member. The two
varieties at one end of the series are called euxenite and priorite, at the other
end polycrase and blomstrandine.
Thus, whilst euxenite and priorite, at the one end, and polycrase and
blomstrandine at the other, have the same compositions, euxenite and
polycrase have the same crystalline form, whilst priorite and blomstrandine
have the same second crystalline form.
All four minerals have the same bright black appearance, and bright
conchoidal fracture; they are all four isotropic, probably as a result of
hydration. All are orthorhombic, but the measurements for euxenite and
polycrase are different from those for blomstrandine and priorite. The two
latter are not so widely distributed as the two former. Blomstrandine occurs
at Hitterö, Arendal, and other localities in Norway; priorite is found in
Swaziland, South Africa.
The crystal system of the Polycrase-Euxenite series is orthorhombic, but
Dana gives slightly different axial ratios for the two minerals. This, though
Brögger gives the same values for both, is by no means incompatible with
isomorphism, as a glance at the axial ratios for the minerals aragonite,
strontianite, witherite, etc., of the series of the orthorhombic carbonates,
will show.
Brögger’s ratios for the two are a : b : c = 0·3789 : 1 : 0·3527; Dana
gives for polycrase 0·3462 : 1 : 0·3124, for euxenite 0·364 : 1 : 0·303.

Euxenite.
This species occurs usually in the massive form as a bright
brownish-black mineral, of hardness 61⁄2, and sp. gr. 4·6 to 5·0. The
crystals are prismatic in habit; the common forms are the pinakoids a
{100} and b {010}, the prism m {110}, the unit pyramid p {111}, and
the dome {201}. Ramsay, Collie and Travers found no helium in it;
Boltwood found uranium, radium and helium, and Strutt found in
addition to these thorium. As early as 1879, Blomstrand had observed
zirconium in euxenite.
The mineral is infusible and with difficulty soluble in acids. It occurs in
many localities in Scandinavia (Hitterö, Arendal, Brevig, etc.), in North
Carolina, South Australia, etc. It was discovered by Scheerer at Jölster, in
Norway, in 1839.
The Euxenite-Polycrase series was studied by Hauser and Wirth in 1909,
[71] in an endeavour to establish their theory that the proportions in which
the various earths and acids occur in this group of minerals is subject to
definite laws beyond the ordinary laws of combination. Thus of the erbia
earths they state that the proportion of holmia and dysprosia increases
relatively to erbia as titanium dioxide increases, i.e. as we pass from the
euxenites to the polycrases; at the same time scandia and yttria increase
relatively to the other yttria earths (the terbia group), whilst in the ceria
group samaria and praseodymia decrease relatively to the others. Thus
samaria is found in appreciable quantities only when the titanium content is
low. The original paper must be consulted for full details.
[71] Ber. 1909, 42, 4443.
It was stated above that zirconium was found in euxenite in 1879. In
1901 Hofmann and Prandtl[72] declared that zirconia was an unfailing
constituent of the mineral, and that it was always accompanied by a new
oxide, which they named Euxenia (‘Euxenerde’). This was characterised by
the solubility of its oxalate in acid solutions, the insolubility of the
precipitated hydroxide in excess of alkali, and the gradual precipitation by
hydrogen peroxide from a slightly acid solution of its salts. In their paper
quoted above, Hauser and Wirth state that zirconia is never present in
typical euxenites. In a second paper[73] they state that after exhaustive
treatment of every known zirconia mineral, they can find no trace whatever

of the ‘new earth,’ and conclude that Hofmann and Prandtl must have made
some experimental error. During this examination, they observed
radioactivity in some minerals which contained no traces of uranium or
thorium.
[72] Ibid. 1901, 34, 1064.
[73] Ber. 1910, 43, 1807.

Risörite.[74]—A columbate of yttria earths, with titanium; ferric oxide,
alumina, lime and lead monoxide are present in small quantities. It
resembles fergusonite in composition, but differs in the almost complete
absence of uranium, the high loss on ignition, and the amount of titanium
present, which is here considerable (TiO₂ = 6·5 per cent.). Hauser regards it
as an orthocolumbate, R´´´(Cb,Ta)O₄, with an isomorphous admixture of
metatitanate, R´´´₂(TiO₃)₃.
[74] Hauser, Ber. 1907, 40, 3118; Zeitsch. anorg. Chem. 1908, 60, 230.

The rare earths are chiefly yttria, with some erbia earths and a little
terbia; ceria, lanthana and didymia are also present. The mineral contains a
considerable amount of helium, which is remarkable in view of the very
small content of uranium and thorium (cf. Thalenite). It is radioactive, the
active constituent being precipitated with the lead (and to a very small
extent with the rare earths).
It is infusible, but at a red heat it loses much water, and becomes very
brittle, with increase of specific gravity; no glowing is observed. It is
attacked by boiling concentrated sulphuric acid, and by fused potassium
bisulphate; also by hydrofluoric acid (40 per cent.), with separation of the
insoluble rare earth fluorides.
No good crystals have been found, and no crystallographic data are
known; examined by polarised light it appears isotropic, but this may
be due to alteration. Colour, yellowish- to greenish-brown. Streak,
yellowish-white. Hardness 51⁄2; sp. gr. 4·179, increasing to 4·678 after
ignition (cf. p. 38).
The mineral was found in a granite-pegmatite at Risör, South Norway.

Wiikite.

[75]—A mineral of very complex composition, for which no definite
formula can be assigned. Its chemical nature may be understood from the
following analytical data:
Columbic and tantalic anhydrides = 16·0; Dioxides of titanium and
zirconium = 23·4; Silica = 17·0; Ceria = 2·5; Yttria = 7·6; Scandia = 1·2;
Thoria = 5·5; Ferrous oxide = 15·5; Uranic oxide = 3·6; water (and gas) =
5·8 per cent.
[75] Crookes, Phil. Trans. 1908, A, 209, 15.
Traces of lime, magnesia, stannic oxide and sulphur are also present.
The mineral is infusible; on heating, helium, sulphuretted hydrogen and
water vapour are given off, and a white sublimate is formed. The evolution
of gas is almost explosive, the mineral breaking with a curious fracture.
It is black and perfectly amorphous, showing no trace of crystalline
structure or action on polarised light. Hardness, 6; sp. gr. 4·85.
Wiikite is partially attacked by acids, readily by fused potassium
bisulphate. It is radioactive.
The mineral was found with monazite in a felspar quarry at Impilaks,
Lake Ladoga, Finland. It is important as the source of scandium used by Sir
William Crookes in his investigations of that element; some specimens of
the mineral contain over 1 per cent. of the oxide (see p. 44).
The following related minerals, of which descriptions are given in the
alphabetical list, are to be included here:
Arrhenite, Chalcolamprite, Endeiolite and Wöhlerite, are complex
tantalo-columbates containing silica.
Hainite contains both silicon and titanium.
Dysanalyte is a titano-columbate believed by Hauser[76] to be merely an
impure form of perovskite (see p. 14).
[76] Vide Zeitsch. anorg. Chem. 1908, 60, 237.
Ilmenorutile and Strüverite are closely allied minerals believed by
Prior[77] and Schaller[78] to be isomorphous mixtures of rutile with Tapiolite
or Mossite (ferrous tantalo-columbates).
[77] Min. Mag. 1908, 15, 78.
[78] Abstr. Chem. Soc. 1912, 102, ii. 773.

Pyrochlore is a complex titano-columbate containing elements of the
cerium or yttrium groups.
Blomstrandite is an hydrated titano-columbate of rare earth elements,
with calcium and uranium; it must not be confused with blomstrandine.

CHAPTER V

THE OXIDES AND CARBONATES

(a) The Oxides

Uraninite or Pitchblende. —Uraninite consists essentially of oxides of
uranium (UO₂ + UO₃ = 75 to 85 per cent.), associated with thoria, zirconia,
rare earths, beryllia, and oxides of lead. Traces of lime, iron oxides, silica,
bismuth, and arsenic are also sometimes present, with water in widely
varying quantities. Nitrogen and helium are always found in it, and, of
course, radium. Groth regards pitchblende as uranous uranate Uiv(UviO₄)₂,
the uranium in the acidic radicle being hexavalent and in the basic radicle
tetravalent, and in the latter condition partially replaced by lead, thorium,
and rare earths.
Szilard[79] regards it rather as a loose compound or even a solid solution
of oxides of thorium and uranium,[80] with small quantities of other oxides,
he having obtained apparently homogeneous (though non-crystalline)
bodies by dissolving thorium hydroxide in solutions of uranium salts and
evaporating to dryness.
[79] Compt. rend. 1907, 145, 463.
[80] See under Thorianite, infra.
The cubic form of the crystalline varieties has been taken as indicating
that the mineral is really a spinel,[81] but it is difficult to see how the general

formula of that group can be considered comparable to the uranyl uranate
formula, UO₂,UO₃, for pitchblende.
[81] The Spinels are an isomorphous family of cubic minerals of the general formula R
´´O,R´´´₂O₃, where R´´ = Be, Fe, Mg, Ca, etc., and R´´´ = Fe, Al, Cr, etc.

Crystals are rare, and belong to the cubic system, the common forms
being the octahedron o {111} and the dodecahedron d {110}; the cube
a {100} is sometimes present. The mineral is massive, usually
botryoidal. The crystalline or primary form is black, with hardness 51⁄2,
sp. gr. 9·0 to 9·7; the altered varieties are grey to greenish- and
brownish-black, sp. gr. 5·0 to 6·4.
It is infusible before the blowpipe, but readily soluble in nitric acid.
The mineral occurs both as a primary and secondary constituent of rocks;
as a primary mineral it is found in Norway, North Carolina, etc.; as a
secondary species it occurs in the massive and hydrated form, with ores of
lead, silver, tin, etc., in Saxony and Cornwall, and at the celebrated mine of
Joachimsthal, in Bohemia. The latter deposits, consisting of the massive and
altered varieties, for which the name Pitchblende is generally reserved, have
been much used as a source of radium, especially those at Joachimsthal, and
the Cornwall ore.
Several varieties of uraninite have been distinguished by special names.
Crystalline varieties from Anneröd and Arendal in Norway are known as
Bröggerite and Cleveite respectively; Nivenite is a third form. In these
varieties uranium oxides have been replaced to a considerable extent by the
rare earths and thoria. An amorphous variety of doubtful composition,
produced by alteration, is known as Gummite; Uranosphærite is a similar
altered form.

Thorianite.[82]—This interesting mineral consists chiefly of thoria, ThO₂
(55-79 per cent.), with oxides of uranium (11-32 per cent.), and ceria oxides
(1-8 per cent.); oxides of lead and iron are also present in small quantities,
and zirconia with silica, probably due to associated zircon.
[82] Dunstan and Blake, Proc. Roy. Soc. 1905, A, 76, 253; Dunstan and Jones, ibid.,
1906, A, 77, 546.

Helium is present, and the mineral is strongly radioactive. A careful
analysis by Hahn[83] shows traces of many metals; the same chemist has

also separated an extremely active component, 250,000 times as active as
thorium nitrate, which he calls Radiothorium.
[83] Hahn, ibid., 1907, A, 78, 385.
The composition has been accounted for (Dunstan and Jones, loc. cit.) on
the hypothesis that thoria (ThO₂) and uranous oxide (UO₂) are
isomorphous, the mineral being really a solid solution. Whilst, however, the
crystal system of the natural body is really rhombohedral (vide infra) the
two pure oxides appear to be cubic. Thus Troost and Ouvrard[84] obtained
artificial thoria in minute octahedra; and, similarly, Hillebrand[85] obtained
uranous oxide in octahedra by reduction of uranyl chloride, UO₂Cl₂, though
his work seems to be open to objection. On the other hand, the same
author[86] found that uranous oxide and thoria, fused together in almost any
proportions, gave a homogeneous body crystallising in octahedra (cf.
Szilard, Compt. rend. 1907, 145, 463, quoted under Uraninite). The
probability of the isomorphism of the oxides is strengthened by the
observation of isomorphism in the sulphates. As early as 1886,
Rammelsberg showed that uranous sulphate, U(SO₄)₂, crystallises with nine
molecules of water and is isomorphous with the corresponding thorium
sulphate, Th(SO₄)₂,9H₂O; and six years later, Hillebrand and Melville[87]
obtained mixed crystals of the two sulphates which were exceedingly close
in forms and angles to those of pure uranous sulphate. It is then at least
probable that the two oxides are isomorphous, though the point cannot be
regarded as satisfactorily proved, by reason of the anomalous crystal forms
of the naturally occurring mixtures, thorianite and uraninite. The recent
results of Kobayashi[88] point to the conclusion that different varieties of
thorianite may exist, in each of which the oxides of thorium and uranium
bear definite simple ratios to one another.
[84] Compt. rend. 1882, 102, 1422.
[85] Zeitsch. anorg. Chem. 1893, 3, 243.
[86] Bull. U.S. Geol. Surv. No. 113, 1893.
[87] Ibid. No. 90, 1892, p. 30.
[88] Abstr. Chem. Soc. 1912, 102, ii. 1181.

Thorianite occurs in jet-black crystals with a bright resinous lustre.
They are pseudocubic, and the twinning resembles that of the cubic
mineral fluorspar—interpenetrant cubes, twin axis a cube diagonal.
Close examination shows, however, that twinning can only take place

about one of the four diagonals, and an optical examination makes it
clear that the symmetry is really rhombohedral. The case is exactly
analogous to that of the mineral chabazite, a zeolite which occurs in
rhombohedra of which the angles differ but little from those of the
cube, and which also forms the interpenetrant twins. In view of the fact
that both uranous oxide and thoria have been obtained as octahedra,
whilst a fused mixture of the two on cooling forms cubic crystals, it
seems not unlikely that at high temperatures the pseudocubic thorianite
would become truly cubic; but no experiments in this direction seem to
have been tried.
The crystals are brittle; hardness 7; sp. gr. 8·0-9·7.
Thorianite is infusible, incandescing before the blowpipe. When
powdered, it dissolves readily in nitric and sulphuric acids, with evolution
of helium. Gray[89] has shown that the helium content can be reduced by 28
per cent. by fine grinding, thus showing that part at least of the gas must be
mechanically held.
[89] Proc. Roy. Soc. 1908, A, 82, 306.
Thorianite was found in Ceylon, being originally mistaken for
pitchblende. A sample was supplied by the discoverer, Mr. Holland, to the
officers of the Mineral Survey, by whom it was sent to London for
examination. Its composition was determined by Dunstan, who named it. It
was found in the river gravels (gem-gravels), the matrix being a pegmatite
granite. It is a valuable source of thorium nitrate for incandescent mantles,
one ton of the mineral (with thoria content of 70 per cent.) having been sold
for £1500; but the supply is small and unreliable.

Baddeleyite.[90]— Baddeleyite consists of almost pure zirconia (ZrO₂ =
96·5 per cent.) with small quantities of ferric oxide, alumina, lime,
magnesia, alkalies and silica. Thoria and rare earths are present in traces,
uranium is absent; the mineral is not radioactive, and contains only traces of
helium.
[90] Vide Fletcher, Min. Mag. 1893, 46, 10, 148; Hussak, Zeitsch. Kryst. Min. 1895, 24,
164, and 25, 298.

Monoclinic—a : b : c = 0·9871 : 1 : 0·5114. β = 98° 451⁄2´.

Common forms—all three pinakoids, a {100}, b {010}, and c
{001}, with the hemi-prisms m {110}, k {120}, and l {230}, and
various pyramids and domes.
Angles—(100) ∧ (110) = 44° 171⁄2´; (100) ∧ (001) = 81° 141⁄2´;
(100) ∧ (101) = 55° 331⁄2´.
Cleavage ∥ c and ∥ b, parting ∥ m due to repeated twinning.
Twinning is exceedingly common; of many hundred crystals examined
by Hussak, only three were found untwinned. Twin planes m (110), a
(100), and x (201).
Colour brown, varying in zones by twinning, with distinct
pleochroism. Hardness; sp. gr. varies from 4·4 to 6·0, being about 5·5
to 5·6 for fairly pure material. Double refraction negative, 2 E = 70-
75°. Acute bisectrix nearly coincident with c axis, plane of the optic
axes b, (010).
The mineral is insoluble in acids, readily soluble in fused potassium
hydrogen sulphate. Before the blowpipe it is almost infusible; it dissolves in
the fused borax bead, rapid cooling causing separation of crystals. If a bead
containing zirconia be heated until the borax is partially volatilised, zirconia
crystallises on cooling in tetragonal crystals, isomorphous with those of
rutile.[91]
[91] Nordenskiöld, Pogg. Ann. 1861, 114, 625; for tetragonal zirconia see also Troost and
Ouvrard, Compt. rend. 1888, 102, 1422.
The mineral was discovered in 1892 by Hussak and L. Fletcher
independently. The former, who obtained it from the pyroxenite sand of São
Paulo, South Brazil, believed it to be a tantalo-columbate, and called it
Brasilite. Fletcher found it in a gem-gravel from Rakwana, Ceylon, and
named it Baddeleyite. An analysis by Blomstrand of Hussak’s mineral
showed it to be identical with the Ceylon mineral, and Hussak withdrew his
name and accepted Fletcher’s. It has recently been found[92] in a corundum-
syenite, near Bozeman, Montana, U.S.A.
[92] Rogers, Amer. J. Sci. 1912, [iv.], 33, 54.
The mineral now comes on the market in commercial quantities; pure
zirconia almost entirely free from iron can be obtained by leaching with
acids. The pure oxide is extraordinarily refractory, and promises to be of
great use for crucibles, furnace linings, etc. (vide p. 324).

Rutile. —Titanium dioxide, TiO₂, occurs crystallised in nature in the
three minerals Rutile, Brookite, and Anatase (Octahedrite), which therefore
form a trimorphous series. They are all stable minerals, though rutile
appears the most stable, being occasionally found in pseudomorphs after the
other two. The family is remarkable in that it is not unusual to find two of
them occurring together—an uncommon phenomenon with polymorphous
minerals.
Rutile often contains small quantities of iron and chromium. The
ferriferous varieties are distinguished as Nigrine, which is black, with 2-3
per cent. ferric oxide, and Ilmenorutile, with up to 10 per cent. of ferric
oxide, and specific gravity up to 5·13.
Crystal system—tetragonal, holosymmetric; c = 0·6442; (001) ∧
(101) = 32° 47´.
Common forms—prisms a {100}, m {110}, and l {310}; pyramids e
{101}, s {111}, and many others. The basal pinakoid c {001} is very
rare. Habit, prismatic, with vertical striations; or in slender needles.
Twinning very common and varied; usually on the cassiterite law—
twin plane e (101)—forming the knee-shaped twins, and irregular
rosettes by repetition, and many contact twins. Contact twins on the
law—twin plane v (301) are less common.
Cleavage ∥ a (100) and m (110), distinct. Hardness 6-61⁄2; sp. gr.
4·18-4·25, and up to 5·2 if much iron is present. Colour reddish-brown
to black, with good metallic lustre; transparent to opaque. The
refraction and double refraction are very high—ω = 2·6158, ε =
2·9029 for sodium light—and allow the crystals to be readily
distinguished in rock-sections.
The mineral is insoluble in acids, but can be dissolved after fusion with
alkalies or alkali carbonates.
Rutile is a member of the isomorphous series, cassiterite, zircon, etc. (see
under Thorite), and in particular it has the colour, appearance, and twinning
of cassiterite, from which, however, it is readily distinguished by its lower
specific gravity. In this connection it is interesting to note that an apparently

pure specimen, quite free from inclusions, was found (1904) to contain 1·7
per cent. of tin dioxide.[93]
[93] Friedel et Grandjean, Bull. Soc. franc. Min. 1909, 32, 52.
As an accessory rock mineral, and also as an important constituent of
many sands, rutile is of very wide distribution. It occurs, usually imbedded
in quartz or felspar, in many granites, syenites, gneisses, slates, and allied
rocks; in acicular crystals penetrating quartz it forms the ‘Veneris Crinis’ of
Pliny. At Risör and other localities in Norway, it is found in the massive
form, and it is largely worked at Risör as a source of titanium. It occurs in
all the countries of Europe, and largely in America. Arendal, Kragerö, and
Risör, in Norway, the Binnenthal, the Urals, the St. Gothard, Castile,
Magnet Cove in Arkansas, Alexander Co. in N. Carolina, Barre and
Shelburne in Massachusetts, and Chester Co. in Pennsylvania are the chief
localities.
It was in this mineral that the element titanium was first recognised by
Klaproth (1795).

Anatase (Octahedrite) is the second crystalline modification of titanium
dioxide.
Tetragonal c = 1·7771. (001) ∧ (101) = 60° 38´, (111) ∧ (11̅1) = 82°
9´.
Common forms—Prisms a {100} and m {110}, pyramids p {111}, e
{101}, and many other complex forms; the basal plane c {001} is
occasionally found. Habit usually octahedral, with p or v prominent;
sometimes tabular with c, more rarely prismatic with a well developed.
Cleavage ∥ c and p perfect. Hardness 51⁄2-6; sp. gr. 3·82-3·95, usually
increasing after heating. Lustre adamantine, so splendent that in Brazil
detached crystals have been mistaken for diamonds. Colour, some
shade of bluish-black to brown; by transmitted light, greenish-yellow.
Transparent to opaque. Double refraction negative, strong; for sodium
light ω = 2·554, ε = 2·493.
It is found at Bourg d’Oisans in Dauphiné, and in Norway, the Urals,
Brazil, etc. In Switzerland it occurs as the variety Wiserine, which was at
one time believed to be xenotime. It was named Octahedrite by de
Saussure, in 1796, from the prevailing habit, and Oisanite, from its

occurrence in Dauphiné, by Delamètherie, in 1797. The name anatase
(ανατασις = erection) was proposed by Haüy, being intended to denote that
the vertical axis (c : a) is greater than that of rutile, the other tetragonal
modification of the dioxide.

Brookite, the third form of this compound, is orthorhombic.
a : b : c = 0·8416 : 1 : 0·9444.
Common forms—the three pinakoids a {100}, b {010}, and c
{001}, prisms m {110}, l {210}, pyramids e {122}, z {122}, and
numerous others.
Angles—(100) ∧ (110) = 40° 5´; (001) ∧ (100) = 48° 18´; (001) ∧
(011) = 43° 22´.
The habit is varied; it occurs usually in bipyramids with e and m or
prismatic with m, a, and terminating pyramids. Cleavage ∥ m
indistinct, ∥ c very poor.
Hardness 51⁄2-6; sp. gr. 3·87-4·01. Lustre metallic. Colour brown to
reddish- and yellowish-brown and black. The optical behaviour is
interesting. The acute bisectrix is perpendicular to a (100), but while
for red light the plane of the optic axes is (001), for blue it is (010); for
an intermediate light, therefore (λ = 5550 µµ), the mineral appears
uniaxial.
The chief localities are Bourg d’Oisans, Miask, the St. Gothard, the
Tyrol, Magnet Cove in Arkansas, and Tremadoc in Wales.
Titanium dioxide can be obtained crystalline by the action of steam on
titanium tetrafluoride, TiF₄, at high temperatures; it is stated that by varying
the temperature of the reaction, any one of the three crystalline
modifications can be obtained.
The only other minerals which need be mentioned in this class (see list)
are:
Zirkelite, a complicated mixture of oxides, in which thoria, zirconia, and
titanium dioxide act as acidic oxides, and
Mackintoshite, a mixture of several oxides, of which those of thorium
and uranium are the most important.

(b) The Carbonates

Lanthanite, Hydrocerite. —This mineral is a carbonate of ceria earths,
chiefly lanthana, of the formula La₂(CO₃)₃,9H₂O.
Orthorhombic; a : b : c = 0·9528 : 1 : 0·9023. Common forms—the
pinakoids a {100} and c {001}, with m {110} and o {111}.
Angles—(100) ∧ (110) = 43° 37´; (001) ∧ (101) = 43° 261⁄2´; (001)
∧ (011) = 42° 31⁄2´.
Habit tabular, parallel to c; cleavage perfect, ∥ c.
Double refraction negative; optic axis plane a (100).
Usually amorphous, being probably an alteration product of a
mineral rich in lanthanum. Hardness 2; sp. gr. 2·6-2·7.
Colour white to yellowish-white, usually opaque; infusible before
the blowpipe (being converted to the oxide), readily soluble in acids.
Lanthanite occurs with cerite at Bastnäs, and at Bethlehem,
Pennsylvania.
Morton[94] states that he prepared a crystalline didymium carbonate in the
laboratory, of the formula Di₂(CO₃)₃,8H₂O, which was isomorphous with
lanthanite; he concluded that the latter had only eight instead of nine
molecules of water.
[94] See abstract in Zeitsch. Kryst. Min. 1886-87, 12, 518.

Parisite (Synchisite), and Cordylite. —Parisite is a fluocarbonate of
calcium and cerium metals; Cordylite is an analogous compound in which
barium replaces calcium, and is isomorphous with Parisite. The formula of
Parisite is CaR₂F₂(CO₃)₃, where R = cerium metals. Groth formulates this
as (CaF)(RF)R(CO₃)₃, Penfield and Warren as (RF)₂Ca(CO₃)₃, whilst
Schilling gives Ce₂(CO₃)₃,CaF₂. Analogous formulæ may be proposed for
Cordylite, BaR₂F₂(CO₃)₃. Since the two minerals are very similar in
crystallographic properties, one description will be sufficient for both. The
following are Dana’s data for Parisite:

Hexagonal, c = 3·2891. (0001) ∧ (101̅1) = 75° 15´.
Forms are extremely numerous, and have remarkably high indices.
Among the simplest are the base c {0001}, the prism m {101̅0},
pyramids q {101̅2}, and h {112̅2}; the other forms are chiefly
rhombohedra and pyramids. The usual habit is that of an acute double
hexagonal pyramid, with form o {202̅1}, terminated by c. Cleavage ∥
c, perfect.
It is brownish-yellow to red. Hardness 41⁄2; sp. gr. 4·36.
The double refraction is strong, positive. Soluble in hydrochloric
acid with effervescence.
Both minerals are characteristic pneumatolytic species of the riebeckite-
ægirine rocks. Parisite was discovered by Paris in the emerald mines of the
Muso valley, Colombia, in 1835, and first correctly analysed by Bunsen in
1845. Before the blowpipe it glows, remaining infusible (the glow does not
appear to have been investigated in this case).
Cordylite was discovered by Flink in 1900, in Greenland.
It is yellow to brownish-yellow and colourless. Hardness 41⁄2; sp. gr.
4·31. Before the blowpipe it decrepitates, and is infusible; moistened
with hydrochloric acid, it gives the characteristic barium flame.
The so-called Synchisite was discovered by Nordenskiöld who correctly
described it as Parisite. Flink found it in Greenland, and announced it as a
new species, with the formula R₂F₂Ca₂(CO₃)₄, i.e. the formula for parisite
plus one molecule of calcium carbonate, CaCO₃. From its extraordinary
resemblance to parisite in physical and crystallographic properties, Palache
and Warren[95] believe that the specimens selected by Flink for analysis
must have consisted, in reality, of parisite with admixed calcium carbonate.
This conclusion has now been confirmed by Quercigh, by a careful
comparison of the optical properties.[96] The minerals are usually found
together, the chief localities being S. Norway, the gold districts of the Urals,
Narsarsuk in S. Greenland, and Montana, U.S.A.
[95] Amer. J. Sci. 1911, [iv.], 31, 533.
[96] Abstr. Chem. Soc. 1912, 102, ii. 773.

The following rare earth carbonates are described in the alphabetical list:
Ancylite, a basic hydrated carbonate.

Tengerite, a hydrated carbonate formed by the weathering of gadolinite.
Kischtimite, a fluo-carbonate related to parisite.
Bastnäsite (Harmatite) and Weibyite, hydrated fluocarbonates of the
cerium elements.

CHAPTER VI

THE PHOSPHATES AND HALIDES

(a) The Phosphates

Monazite, Phosphocerite. —Monazite, by far the most important,
commercially, of all the rare earth minerals, is essentially an orthophosphate
of the ceria earths, of the formula R´´´PO₄.[97] The yttria earths are usually
present in small quantities. Silica and thoria, in quantities varying from
traces up to 6 per cent. of the former and from 1 to 20 per cent. of the latter,
are invariable constituents; it is almost entirely to the percentage of thoria
that the mineral owes its commercial value. The following also are common
constituents, though usually in very small quantities only—stannic, ferric
and manganous oxides, alumina, lime, magnesia, zirconia and water.
Helium was observed in it by Tilden, and by Ramsay, Collie and Travers.
[98] Boltwood[99] and Zerban[100] found uranium in it; the latter attributed
this to impurities, the former regarded it as an essential constituent.
Strutt[101] found uranium in a pure monazite. Haitinger and Peters[102]
detected radium, their result being confirmed by Boltwood and Strutt.
[97] For the composition of the earths in monazite, see James, J. Amer. Chem. Soc. 1913,
35, 235.
[98] Trans. Chem. Soc. 1895, 67, 684.
[99] Phil. Mag. 1905, [vi.], 9, 599.
[100] Ber. 1905, 38, 557.

[101] Proc. Roy. Soc. 1905, A, 76, 88 and 312.
[102] Sitzungsb. kaiserl. Akad. Wiss. Wien, May, 1904.

Monazite occurs in small crystals belonging to the monoclinic
system. a : b : c = 0·9693 : 1 : 0·9256, β = 76° 20´. These values vary
slightly with different specimens. Common forms—Ortho- and clino-
pinakoids a {100}, b {010}, hemi-prisms m {110}, and n {120}, hemi-
ortho-prisms w {101} and x {1̅01}, hemi-clino-prism e {011}, hemi-
pyramid v {1̅11}, etc.; the basal pinakoid c {001} is rare.
Angles—a ∧ m = 43° 17´, c ∧ w = 37° 8´, c ∧ e = 41° 58´.
Habit tabular, parallel to a, needle-shaped by elongation parallel to b
axis, or prismatic by good development of v.
Cleavage ∥ c, perfect, ∥ a, distinct, ∥ b, difficult.
Twin plane a (100). Birefringence moderate, positive; plane of optic
axes perpendicular to b, nearly parallel to a. Acute bisectrix inclined to
c at angle of 1°-4°. Dispersion feeble, ρ < υ. Brittle. Hardness 5-51⁄2;
sp. gr. 4·9-5·3; conchoidal fracture. Lustre resinous. Colour, red to
brown, yellow, yellowish- and greenish-brown. Transparent when
pure; more often translucent to opaque.
Monazite is with difficulty soluble in acids; before the blowpipe it is
infusible; when moistened with sulphuric acid it colours the flame greenish-
blue.
The mineral often occurs massive, yielding angular fragments, but is
most common in rolled grains. It occurs in the gneiss of the Carolinas and
Georgia, and in sands derived from the gneiss, in Idaho and many of the
Pacific States; in Brazil, at various localities in the provinces of Minas
Geraes, Bahia, Espirito Santo; in Queensland, Australia; in Madagascar; in
Ceylon; near Travancore in India; in the Urals; in Scandinavia, etc. The
deposits of commercial value will be treated more fully in the next chapter.
It is of wide distribution as an accessory constituent of granites, diorites,
and gneisses.
Monazite was first described, under the name Turnerite, by Lévy,[103] in
1823; the specimen was from the collection of the English chemist Turner,
who thought it a variety of sphene (titanite), and was named after him at the
suggestion of the mineralogist Heuland. The specimen was stated to have
been found in Dauphiné, but in spite of considerable examination of the

question, the precise locality is still unknown. The resemblance between
Turnerite and the mineral later described as monazite (μοναζειν = to be
solitary) was pointed out by Dana in 1866, and confirmed by Pisani, 1877.
The name Monazite was first used by Breithaupt[104] in describing a mineral
found by Menge (1826) accompanying zircon in a granite from Miask in
the Urals. Breithaupt concluded, from the high specific gravity, that the
mineral contained a heavy metallic oxide. It was again described as
Mengite by Brooke[105] in 1831. It was re-discovered by Shephard[106] in
South Carolina in 1837, and described by him under the name Edwardsite, a
variety from Connecticut being called Eremite. To Shephard belongs the
honour of having discovered its true nature; after analysis he described it as
a ‘Basic Sesquiphosphate of the Protoxide of Cerium,’ giving the formula
(modern notation) 3CeO,2P₂O₅, and finding also zirconia, alumina, and
silica in it (his specimen was probably very impure). Gustav Rose[107]
showed this to be identical with monazite in 1840. In 1846 Wöhler
described, under the name Cryptolite, a variety of tetragonal habit closely
resembling zircon. This occurs at Arendal in Norway, enclosed by apatite,
in the granite; it may be obtained by treatment with dilute nitric acid, which
dissolves the apatite.
[103] Annals of Philosophy, 1823, 21, 241.
[104] Schweigg. J. 1829, 55, 30.
[105] Phil Mag. 1831, [ii.], 10, 139.
[106] Amer. J. Sci. 1837, 32, 162.
[107] Pogg. Ann. 1840, 49, 223.
The question of the manner in which the thorium is combined in
monazite is of considerable importance, in view of the fact that it is to this
element that the mineral owes its commercial value. The amount present
varies from traces up to over 20 per cent., but the usual value is between 5
and 7 per cent. The first explanation of its presence was advanced by
Dunnington[108] who suggested, on the result of only one analysis, that
orangite (ThSiO₄) was present mechanically mixed with the monazite.
Penfield[109] supported this suggestion, and stated that in three analyses of
pure material he found the ratio of rare earths to phosphorus pentoxide and
that of thoria to silica exactly equal to unity, though the actual amounts of
thoria varied considerably. He also quotes an analysis made by
Rammelsberg in 1877, in which no thoria was found, to show that it is not
an essential constituent. In a microscopic examination he found dark

resinous particles scattered throughout the section; after moistening with
hydrochloric acid, warming, and washing, these dark spots became white,
and could be stained with fuchsine, the monazite remaining unaffected
throughout. He concluded that these particles were thorite or orangite.
[108] Amer. Chem. J. 1882, 4, 138.
[109] Amer. J. Sci. 1882, [iii.], 24, 250; 1888, 36, 322.

Blomstrand[110] disputed Penfield’s conclusions. In twelve analyses of
monazite from various parts of Scandinavia he never once found either
thoria or silica absent. Of these twelve analyses, two give the ratio of thoria
to silica, ThO₂ : SiO₂, exactly unity, in seven cases the ratio is not greater
than 1·25, in five cases it varies considerably. He summed up his results in
three statements:
(a) Silica is never absent; its amount depends not on the amount of
thoria, but on the amount of phosphorus pentoxide present.
(b) The thoria which is always present is combined partly with silica,
partly with phosphorus pentoxide.
(c) In most cases, the rare earths alone are insufficient to satisfy the ratio
R₂O₃ : P₂O₅ = 1.
[110] J. pr. Chem. 1890, 41, 266.

An exhaustive examination of the question has been made more recently
by Kress and Metzger.[111] They made in all over fifty analyses, using thirty
different specimens of monazite; they estimated silica both as quartz and as
silicate silica, and determined thorium by the fumarate method—the other
investigators had used the thiosulphate method of Hermann (vide p. 286).
Their results may be summarised as follows:
(i.) Silica is always present.
(ii.) The amount of silica usually increases with the thoria, but not
regularly.
(iii.) By far the majority of cases showed insufficient total silica to
combine with the thoria present.
(iv.) In about 9 per cent. of the cases, the thoria present was insufficient
to combine with the silicate silica, from which it follows that
some foreign silicate must be at least occasionally present.
(v.) A careful microscopic examination showed conclusively that no
thorite (ThSiO₄) was present, the silicate being biaxial; quartz is
present as such.

[111] J. Amer. Chem. Soc. 1909, 31, 640.

They conclude that thorium is present as phosphate, and is an essential
constituent, but that there is always some admixed silicate, most probably a
felspar.

Xenotime. —Chemically this mineral is closely allied to monazite, being
an orthophosphate of rare earths, containing silica and thoria; whereas,
however, in monazite the content of yttria earths does not rise above 4 per
cent., in xenotime these constitute by far the greater part of the bases, the
content of ceria earths ranging from 8·2 to 11 per cent. The yttria earths,
chiefly oxides of yttrium and the erbium group, vary from 54·1 to 64·7 per
cent. There are traces of zirconia; Ramsay, Collie and Travers detected
helium, whilst Boltwood, and also Strutt, found uranium and radium. It also
appears to contain traces of sulphuric anhydride.
The crystals are tetragonal, holosymmetric. c = 0·6187; (001) ∧
(101) = 31° 45´.
Common forms are the prisms a {100} and m {110}, the basal
pinakoid c {001}, the pyramids e {101}, f {201}, z {111}, etc.
Cleavage ∥ m, perfect. Uniaxial, double refraction strong, positive.
Transparent to opaque. Colour, brown to reddish-brown and yellow.
Hardness 4-5; sp. gr. 4·45-4·56.
It is insoluble in acids, and infusible before the blowpipe; when
moistened with sulphuric acid, however, it turns the flame bluish-green, like
most mineral phosphates (vide monazite).
It is not so widely distributed as monazite, but is not uncommon. It often
occurs with zircon—to which it is very closely allied in crystal form, if the
two are not actually isomorphous—in parallel growth, in granitic rocks. The
diamond sands of Diamantina, Brazil, form the richest source of the
mineral, but it is also found in Scandinavia, at Hitterö, Åro, etc.
The mineral is of considerable importance, chemically, on account of the
high percentage of erbia earths.
In the works of Bauer, Rosenbusch, Weinschenk, Schilling and Iddings
will be found accounts of a mineral named ‘Hussakite.’ These accounts
rested on the work of Kraus and Reitinger,[112] who in 1901 announced the
discovery of a new species. The crystals were obtained as a specimen of

xenotime by Prof. Muthmann from Dr. E. Hussak, in São Paulo, and had the
crystallographic properties of that mineral. On analysis, the amount of
sulphur trioxide present was found to be remarkably high (6·3 per cent.),
and Kraus and Reitinger concluded that the substance was distinct from
xenotime. They announced it as a new mineral, with the name Hussakite,
and the formula 3R₂O₃,3P₂O₅,SO₃ or 6RPO₄,SO₃, and stated that by the
action of dilute alkalies the sulphur trioxide could be easily and completely
removed. They therefore regarded xenotime as a pseudomorph[113] after
hussakite, the sulphur trioxide having been removed from the latter by the
action of the alkaline waters of the earth’s crust. In support of this view,
they gave analyses of opaque crystals from a Bahia sand represented as
containing 2·6 to 2·7 per cent. of sulphur trioxide, and so as being
intermediate forms produced during the change.
[112] Zeitsch. Kryst. Min. 1901, 34, 268.
[113] One mineral is said to be pseudomorphous after another when the first is produced
from the second by a chemical change which proceeds so slowly that the original
structure and crystalline form are unaltered (i.e. a change proceeding molecule by
molecule). The pseudomorph is usually opaque and shows clear signs of the alteration.

The latter conclusion was quickly challenged by Brögger, who found no
sulphur trioxide in a perfectly fresh and transparent xenotime from Åro in
Scandinavia. Brögger concluded that the Hussakite of Kraus and Reitinger
was an independent species of the formula 5YPO₄,(YSO₄)PO₃, and that
xenotime was not derived from it.
Basing his work on the barium chloride test given by Kraus and Reitinger
(see below) Rösler[114] declared that ‘Hussakite’ was a common accessory
constituent of igneous rocks, having been previously mistaken for zircon,
which it resembles in appearance and optical properties.
[114] Zeitsch. Kryst. Min. 1902, 36, 258.

In 1907 Hussak[115] published a paper in which he showed that the
mineral named after him was not a new species at all, but a xenotime of
prismatic habit. Analyses made at his request by Florence in Brazil, G. T.
Prior in London, and Tschernik in St. Petersburg, confirmed the original
values given by Gorceix (sulphur trioxide up to 0·25 per cent.). He
mentions Brögger’s analysis of the Norwegian specimen in which Kraus
and Reitinger had found 2-3 per cent. of sulphur trioxide, but in which
Brögger found none. He explains the results of Kraus and Reitinger as due
to the addition of barium chloride to the acidified solution of the carbonate

fusion of the mineral, by which barium phosphate was precipitated; this was
dried and weighed as barium sulphate. Rösler’s tests are declared doubtful;
xenotime is not a widely spread rock constituent, the mineral in question
being really zircon.
[115] Centr. Min. 1907, 533.
In face of these results, there can be little doubt that the name ‘hussakite’
is unnecessary and undesirable, since the mineral to which it was applied is
proved to be xenotime.
In the alphabetical list, particulars of the following rare earth phosphates
will be found:
Castelnaudite, a variety of xenotime containing zirconia.
Churchite and Rhabdophane (Scovillite), hydrated phosphates.
Gorceixite, an alumino-phosphate of alkaline and ceria earths.
Retzian, an hydrated arsenate of manganese, calcium and rare earth
metals.

(b) The Halides

Yttrocerite. —This mineral is a fluoride of calcium and rare earth
metals, with water. A recent analysis by Tschernik[116] gives the formula
Ce₂F₆,2Y₂F₆,9CaF₂,2H₂O. Putting the rare earth metals together, this gives
6RF₃,9CaF₂,2H₂O, or R₂Ca₃F₁₂,2⁄3H₂O. Yttrocerite is of interest since it was
probably in the analysis of this mineral by the discoverers, Berzelius and
Gahn, that the double sulphate method of separating the yttria from the
ceria earths was first employed[117] (vide p. 156).
[116] Abstr. Chem. Soc. 1907, 92, ii. 362.
[117] Schweigg. J. 1816, 16, 244.

It is found only massive or granular. Colour usually white to violet-
blue, sometimes reddish-brown. Hardness 41⁄2; sp. gr. 3·45. Infusible,
but loses colour before the blowpipe. When powdered, it dissolves
completely in boiling hydrochloric acid, and readily in sulphuric acid
with evolution of heat. It has been found at various localities in
Scandinavia.

Yttrofluorite.[118]—This is a fluoride of varying composition, very
similar to yttrocerite, but characterised by the absence of water, and the
very small ceria content (1·7 per cent.). It is thus a fluoride of calcium and
the yttrium metals.
[118] T. Vogt, Centr. Min. 1911, 373.

Cubic, with poor octahedral cleavage. Colour, yellow to brown and
yellowish-green; transparent to translucent, bleached by weathering.
Very brittle. Hardness 41⁄2; sp. gr. 3·54-3·56.
It is very similar to fluorspar (except that the octahedral cleavage of the
latter is very good), and is regarded by Vogt as an isomorphous mixture of
the latter with yttrium fluoride (or with a double yttrium calcium fluoride,
which is less probable). This view would account for the variations in
composition, and also for the remarkable frequency with which traces of
rare earths are found in fluorspar (vide p. 2). Yttrocerite is regarded as a
similar isomorphous mixture, but containing cerium metals in addition to
the yttrium group.
Yttrofluorite occurs in pegmatite veins in granite in Northern Norway,
with gadolinite, fergusonite, allanite, fluorspar, and the usual vein minerals.
The other members of this family (see list) are:
Fluocerite, a basic fluoride of yttrium and cerium metals.
Tysonite, a hydrated fluoride containing carbonates.
It is to be noticed that fluorine is the only member of the halogen family
which occurs in nature in combination with rare earth elements. This fact is
possibly connected with the great age of the rare earth minerals, and their
formation during pneumatolytic metamorphism of plutonic rocks (vide
Chapter I).

CHAPTER VII

THE MONAZITE SANDS
It has been stated that monazite is a not uncommon accessory constituent
of many rocks, particularly of granites, gneisses, diorites, etc. The
crystalline material, of which an account has been given, is found
sometimes in veins in these rocks, more often in tiny crystals disseminated
throughout the mass. Most of these monazite-bearing rocks are extremely
old, belonging to the Archæan or pre-Cambrian age, and probably none are
of secondary (Mesozoic) or later age. It follows, then, that they have been
subjected to erosion during practically the whole immense period of which
geology can give us any detailed knowledge. Heat, frost, wind, the action of
vegetation and of percolating water, the innumerable weathering agents
known to the geologist, have been at work on them during countless ages,
breaking, crushing, dissolving; rains, brooks, rivers, even ocean-waves have
dissolved or washed away the fragments, sorted them out unerringly
according to density, and re-deposited them, now in a river-bed, now at the
base of some sea cliff, now in a wide alluvial plain from which the water
has long since retired. It is in deposits of this nature that the monazite has
been concentrated. Its relatively high specific gravity (about 5·0) has
secured its separation from the lighter mica, quartz, and felspar of the
parent-rock; but the heavier vein or accessory minerals have, of course,
been concentrated with it. Zircon is an invariable constituent of these
‘monazite sands,’ as such deposits are called; and others almost as
frequently found are rutile, ilmenite, sphene (titanite), and apatite.
Common, too, are the characteristic minerals of the metamorphic rocks,
garnet, epidote, sillimanite, tourmaline, etc. Rare earth minerals found in
the monazite sands include xenotime, fergusonite, samarskite, gadolinite,
and allanite. The remaining minerals are oxides of iron and tin, with, of
course, a considerable amount of quartz.
It is apparent, from what has been said above, that monazite will be
concentrated with the heaviest constituents of the rocks from which it is
derived. Very often, indeed usually, these rocks are precisely those in which
gold occurs, disseminated sometimes in tiny particles, sometimes collected
into nuggets in veins of quartz and pegmatitic minerals. The erosion of

these rocks concentrates the gold with the heaviest minerals; and hence it
happens that monazite is an almost universal constituent of the gold- and
gem-bearing sands and gravels. In the Carolinas and in Brazil, monazite is
found in the gold washings; and though in the past the two have always
been extracted separately, the gold first and the monazite from the washings
or tailings, there appears to be no reason why a system calculated to extract
both—where, of course, the content is high enough—should not be put into
operation in the future.
A chemical test affords the only reliable method of detecting monazite in
a sand. A little of the sand is washed with water to remove the lighter
minerals and warmed with concentrated sulphuric acid. A few drops of the
liquid are poured off, evaporated to small bulk, and one drop placed on a
glass plate. This is placed under a microscope and one drop of a
concentrated solution of sodium acetate is added. If monazite is present in
the sand, tiny pointed oval crystals of sodium cerium sulphate will separate.
On the commercial scale, monazite is extracted from the sands only, in
the manner described below. An effort was made in North Carolina in 1906
by the British Monazite Company, representing the South Metropolitan Gas
Light Company of London, to extract monazite from the rock in which it
occurs disseminated. The rock was crushed and powdered, and the monazite
separated by washing off the lighter particles on concentration tables (see
below). In the same year, however, the price of thorium nitrate was
suddenly lowered 50 per cent. by the German Thorium Syndicate, which
largely controls the Brazilian output of monazite, and the British company
stopped operations in 1907. At present it may be said that only the sands are
available for profitable extraction.
Up to 1895, the Carolina deposits, which were worked chiefly by the
Welsbach Light Company of New York, either directly or indirectly,
supplied all the demand, but in that year the Brazilian sands were first
worked, and a keen struggle commenced for the market. The American
companies, after keeping up a considerable output for some years, were
forced to suspend operations in May 1910. The Brazil deposits, worked by
the German Thorium Syndicate and the Austrian Welsbach Company, which
have an agreement, now meet practically the whole demand. The Brazilian
sand occurs chiefly along the shores of the southern provinces, having been
concentrated by the action of the tides from the products of erosion of the
cliffs; it is very uniform and considerably richer than the Carolina sand, and

owing to its occurrence on the sea-shore, the cost of transporting it is very
low. It is exported chiefly to Germany, recently also to the United States,
and to a small extent lately to England. The method of working it is similar
to that employed in Carolina—namely, concentration by washing and
magnetic separation.

The North American Deposits[119]
[119] See Nitze, Bull. No. 9, N. Carolina Geol. Survey, 1895; also Test, Colorado School
of Mines Bull. Vol. IV. No. 2, p. 125, Jan. 1908.

There are two important regions in North America within which
monazite sands occur; one extends over the Carolinas, and the north-
western part of Georgia, the other over the Idaho basin and neighbouring
counties of the Pacific Slope. It will be best to treat these separately, as the
deposits are somewhat different in character.

(a) The Carolina Deposits, including the unimportant Georgia deposits,
which belong to the same field, occur over an area approaching 4000 square
miles. The area is occupied chiefly by the Piedmont plateau, which is
drained by a number of streams rising in the South Mountains, an eastern
outlier of the Blue Ridge; it is in the basins and valleys of these streams,
particularly at the head-waters, that the monazite is chiefly found. The
geology of the district is very complicated,[120] the rocks being very highly
altered granites. The chief bed is known as the Carolina gneiss, and includes
several types of gneiss, usually very much weathered. The sands, which
average about 1 per cent. of monazite, are worked in and near the stream
beds; they occur in the beds, and in layers 1 to 2 feet in thickness a few feet
below the surface of the surrounding soil.
[120] See Sterret, U.S. Geol. Survey (Minerals), 1906, p. 1195.

Concentration was formerly effected chiefly by a crude process of
washing. In this process the sand is thrown on to a sort of sieve, fixed over
the upper end of a long wooden trough, by one workman; a jet of water is
directed on to the sieve, washing the sand through it. The heavier particles
fall to the bottom of the trough, whilst the lighter are washed right through.
A second workman continually turns over the sand left in the box and on
the sieve; at the end of a day’s work the ‘concentrate’ is collected. This
averages from 15 to 70 per cent. of monazite, according to the nature and

amount of the heavy minerals accompanying it in the sand. The concentrate
is dried either on rubber or oiled cloths in the sun, or on an iron plate
covering a trough in which a fire is lighted. The iron minerals are then
picked out by means of a magnet, and the sand filled into sacks for
transport.
Before treatment for thorium nitrate, the sand is at the present day further
concentrated by powerful magnetic separators. In a few cases the older
method of concentration by hand-washing has been abandoned for machine
concentration, the Wilfley table being sometimes employed. The principle
here is exactly the same, the sand being fed into a hopper by means of a
moving belt and thence on to a machine-shaken table from which running
water constantly removes the particles, sorting them according to their
specific gravity.
Further separation of the dried concentrate has been effected by three
kinds of separators.[121] The first was of the Edison, or fall-and-deflection
type; in this the sand is allowed to flow in a thin vertical stream past a
horizontal magnet, which deflects the minerals containing iron; these fall on
one side of a partition, the part richer in monazite on the other. The second
was an electrostatic machine; the heated sand is borne on a moving belt
underneath a rotating vulcanite cylinder, excited by felt-covered rubbers;
the lighter particles are attracted to the cylinder, and dropped on one side,
the heavier passing on. Neither of these machines is of much value in
effecting concentration, and neither is in general use.

[121] See Pratt and Sterrett, Trans. Amer. Inst. Min. Eng. 1909, 40, 313.
The third, and by far the most efficient and most widely-used machine, is
known as the Wetherill electro-magnetic separator. It depends on the
principle, first applied by the American engineer Wetherill, that not only the
iron minerals, but a large number of other minerals may be attracted if the
magnetic field be sufficiently strong. In all types of this machine used in
cleaning monazite concentrates, four magnetic fields of increasing intensity
are traversed by the sand; the first removes magnetite, ilmenite, and the
larger fragments of garnet; the second removes all the remaining garnet and
ilmenite; the third removes the coarser, and the fourth the finer monazite,
tailings of zircon, rutile, and silica passing on. Careful adjustment of the
magnetic fields will readily give a 97-99 per cent. monazite.
Two types of this machine are in common use. In the first the magnetic
fields are obtained by four successive electro-magnets, arranged so that a
broad horizontally-moving belt passes between the poles of each in
succession. The upper poles are ground down to a fine edge perpendicular
to the direction of the belt, to secure a more powerful field. Just beneath
these edges, and just above the broad belt are four rapidly driven horizontal
belts moving at right angles to the first or main belt; these carry off and
deposit in separate bins the minerals attracted by their respective magnets.
This type is known as the Rowand separator.
In the second type four horizontal belts are arranged in the form of
descending steps, as shown in the diagram (Fig. 2). The magnets are placed
at the end of each belt, and within it. The attracted mineral is held to its own
belt, whilst the remainder drops on to the next; the attracted mineral falls
into a bin as soon as its belt carries it out of the magnetic field. The sand to
be cleaned is fed on to the first belt by means of a hopper.
The almost pure monazite so obtained is now treated chemically for its
thorium. The processes proposed and in use are described in Chapter XVIII.

Fig. 2.

As already stated, the extraction of monazite in the United States has
practically ceased; but the processes outlined above, which were first
brought into use in the Carolinas, have been adopted for the treatment of the
Brazilian sands.

(b) The Idaho Deposits. —Monazite was first observed in placer-gold
deposits in the vicinity of Boise city near the Snake river. This deposit was
a gold-bearing sand derived from granite. Later the gold-bearing sands of
Oregon were also found to contain monazite; these sands are rich in zircon,
and contain platinum and allied metals as well as gold. The sands of the
Pacific slope are the so-called black sands, derived from hornblende, and
augite-granites, usually porphyritic, which are much weathered at the
surface. The soil is loose and is largely composed of granite fragments; the
rain and streams constantly bring it down to the valleys, and continually
renew the deposits. The concentrates obtained by washing are rich in well-
crystallised zircon, with titanite and garnet.
In 1906 a company was formed to extract monazite from the black sand
residues left after the extraction of gold. By 1909 they had erected plant and
commenced operations at Centerville, and proposed to work the poorer
auriferous sands for gold during the monazite washing. This, it was
expected, could be done by washing the sands in boxes lined with
amalgamated copper plates, which would retain the gold. Considerable
amounts of monazite had already been extracted from the tailings when a
disastrous fire put a stop to the operations in 1910.

Since then the production of monazite in the United States has practically
ceased.

The Brazilian Deposits
Brazil first became a serious competitor in the world’s market with the
United States, for the supply of monazite, in 1895. The greater percentage
of thorium, the more even quality of the sands, and above all the occurrence
on the sea-coast, rendered the Brazilian monazite cheaper from the
beginning, so that it soon ousted the Carolina sand, and since 1910 has
supplied the whole demand. The deposits at present worked lie along the
coasts of Bahia, Minas Geraes and Espirito Santo, and whilst they are very
rich in monazite, there is the disadvantage that their position and extent, and
so also the possibility of working them, depend very largely on the
variations in the tides, etc. The largest of these deposits is on the shores of a
bay near the island of Alcobaca, on the southern coast of Bahia.
Monazite also occurs to a considerable extent in the diamond sands and
gold-bearing sands of many of the interior provinces. In Minas Geraes it has
long been known to occur at the celebrated mining centres of Diamantina
and Ouro Preto, where xenotime and other rare earth minerals are also
found; it is also known at various localities in the surrounding mining
provinces of São Paulo, Goyaz, and Matto Grosso. More recently, extensive
inland deposits have been found by Freise, in the province of Espirito
Santo.[122] In the plateau-basin of the Muriahé and Pomba rivers he found a
sand known locally as ‘catalco’ which carries an average of 2·1 per cent. of
monazite and a gold-content of 1·75 grams per ton. In the Aymoré’s
mountains he found monazite, both massive and granular, in pegmatite
veins in granite; analysis showed a thoria content of 9·23 per cent., which is
very high. These deposits would form a very valuable and extensive source
of thoria, if the difficulties of transport could be overcome.
[122] Zeitsch. pr. Geol. 1909, 17, 514; ibid., 1910, 18, 143.
At present, as stated above, only the beach deposits are worked. The
Brazilian Government has laid a very heavy tax on all monazite exported; it
is stated[123] that the German Thorium Syndicate pays 50 per cent. of its
profits in royalties to the Government. In spite of this, the high quality of
the sand and the low cost of transport have enabled this combine to lower
the price of thorium nitrate to a point at which the Carolina sands cannot be

worked, and it appears probable that the world’s markets will be supplied
for some time, at least, entirely from Brazil. The methods employed in
working the sand are similar to those already described.
[123] U.S. Geol. Survey (Minerals), 1906, p. 1195.
In the last few years monazite deposits have been found in various
places, notably in Australia, India, and Ceylon. In the latter locality it
occurs sparingly in the gem-gravels, in association with the much more
valuable thorianite and thorite, but the supply is uncertain, and the minerals
cannot be worked regularly. In Australia it occurs in Victoria and in
Queensland. In Victoria the deposits are poor in monazite—about 0·025 per
cent.—so that working is not profitable. In Queensland it occurs in beach
sands on the southern coast, with gold, platinum, and cassiterite; there
seems to be no reason why these deposits should not be profitably worked
when sufficient labour is forthcoming. It also occurs in North Queensland,
on the Walsh and Tinaroo mineral fields; here it is found massive and
granular in veins in granite, associated with wolframite, molybdenite, and
cassiterite.
Quite recently, deposits of considerable extent have been found near
Travancore, India.[124] These sands contain about 46 per cent. of the
mineral, which is itself very rich in thoria, containing about 10 per cent. of
the oxide; the unconcentrated sand is therefore as valuable as a source of
thorium nitrate as the ordinary Brazilian concentrates, which average 4 per
cent. or less of the oxide.
[124] Bull. Imp. Inst. 1911, vol. ix., No. 2, p. 103.
Monazite has also been observed in the tin-bearing sands of Embabaan,
Swaziland, South Africa, and in the province of Ottawa, Canada.

CHAPTER VIII

RADIOACTIVITY OF THE MINERALS
In the present chapter no attempt will be made to give a complete account
of all the phenomena of radioactivity which have been observed in the
mineral world. There are, however, a few problems of the highest scientific
interest which centre about the rare earth minerals, and mention of these can
hardly be avoided in a work which professes to give a general account of
the rare earth group. It is obvious that a detailed treatment cannot be given
without entering into phenomena which would be quite beyond the range of
the present work, and an excuse is hardly needed, therefore, for the
fragmentary and abbreviated account which follows. The reader’s
acquaintance with the general phenomena of radioactivity is of necessity
assumed.
Radioactivity (the spontaneous emission of special radiations) was first
observed by Becquerel, in 1896, in the case of potassium uranyl sulphate,
and was soon found to be common to all uranium compounds, and to the
metal itself. Mme. Curie showed that whilst in uranium salts the degree of
activity varies directly with the percentage of uranium, in minerals
containing the element the same rule does not hold. The observation that
pitchblende is considerably more active than the uranium it contains led to
the discovery of polonium[125] and radium in 1898. Exactly analogous
phenomena were shown to hold for thorium salts and thorium-containing
minerals by Mme. Curie and Schmidt in 1898, and in 1905 Hahn separated
Radio-thorium from thorianite. In 1899 Debierne discovered that the rare
earths precipitated from the solution obtained on treatment of pitchblende
are associated with another extremely active body, which he named
Actinium; Giesel found that in the separation of the rare earths this remains
with lanthanum. In 1903 Ramsay and Soddy experimentally confirmed the
prediction of Rutherford and Soddy, that radium would be found to produce
helium continuously. The discovery of these remarkable phenomena has
modified many fundamental physical conceptions, and has opened up a new
field of scientific enquiry, which is being developed with unexampled
rapidity.

[125] Polonium, which was named by Mme. Curie in honour of her native country, has
been shown to be identical with Marckwald’s ‘Radio-tellurium,’ which was named by
Rutherford ‘Radium F’; it is one of the degradation products of radium.

It has been mentioned, in the accounts of the rare earth minerals given
above, that almost all these minerals are radioactive, i.e. have the property
of emitting specific radiations. Moreover, radioactivity, to any considerable
extent at least, is, with a few important exceptions, confined to the minerals
which have been already described. It has been shown by many
investigators, chief amongst whom are Strutt and Boltwood, that the
activity is usually due to the presence of uranium or thorium, or both.[126]
[126] Hauser and Wirth (Ber. 1910, 43, 1807) observed activity in some zirconium
minerals containing neither thorium nor uranium.

After the discovery of helium in Cleveite (a variety of pitchblende, vide
p. 13) in 1895 by Ramsay, a large number of minerals were examined for
this gas, and it was found that almost all the rare earth minerals contain
helium. The fact that these minerals are also for the most part radioactive,
naturally suggested some relation between the activity and the presence of
helium, and led directly to the discovery that radium is continuously
producing helium; and it became apparent that helium has been
accumulating in these minerals since their formation, by the decay of
radioactive elements. The question of the origin of helium in minerals will
be touched on again.
In 1904 Boltwood advanced the theory that radium is produced by the
degradation of uranium, the parent-element having, however, a much
greater half-life period. If uranium continuously produces radium, whilst
the latter decays much more rapidly than the former, it must follow that in
minerals containing uranium a state of equilibrium is reached between
uranium and radium, and the ratio of these two in all minerals should
therefore be constant, and independent of the geological age. Boltwood
examined a number of the minerals of which descriptions have been given
in the preceding chapters, and found the ratio to be surprisingly constant.
[127] Strutt also examined a large number of minerals,[128] and whilst on the
whole his results seemed to support the theory, his values for the ratio were
by no means so constant as those of Boltwood. Strutt included in his
examination the interesting radium-containing mineral observed by Danne
at Issy l’Evêque.[129] This was a pyromorphite (lead chlorophosphate)
containing neither uranium nor thorium. Danne suggested that the radium

was not an original constituent, but had been introduced by the action of
percolating waters. This view was confirmed by McCoy and Ross,[130] who
found that the activity was entirely confined to the surface layer.
[127] Amer. J. Sci. 1904, [iv.], 18, 97; Phil. Mag. 1905, [iv.], 9, 599.
[128] Proc. Roy. Soc. 1905, A, 76, 88 and 312. Ibid. 1907, A, 80, 56.
[129] Compt. rend. 1905, 140, 241.
[130] J. Amer. Chem. Soc. 1907, 29, 1698.
Mlle. Gleditsch has also examined the question of the uranium-radium
ratio in minerals. Her earlier work[131] gave ratios which, whilst constant for
each mineral species, varied in much the same manner as Strutt’s for
different species, and afforded very little support to Boltwood’s theory. Her
more recent results,[132] however, are much more closely in accord with the
theory, which has been still further strengthened by the work of Pirret and
Soddy[133] and of Marckwald and Russell.[134] It may now be regarded as
firmly established that radium is in the line of direct descent from uranium.
[131] Compt. rend. 1909, 149, 267; Le Radium, 1909, 6, 165.
[132] Le Radium, 1911, 8, 256.
[133] Phil. Mag. 1911, [vi.], 21, 652.
[134] Ber. 1911, 44, 777.

Boltwood had assumed that the helium in radioactive minerals is
produced from the uranium, during its disintegration. Strutt, however,
disputed this; his experiments showed that very little helium is found even
in the richest radium-uranium minerals unless thorium is also present. Thus
pitchblende contains a very high percentage of uranium, but relatively little
helium (there is usually a considerable thorium percentage here too, so that
nothing conclusive can be deduced from this). Adams[135] found that
carnotite, a mineral very rich in uranium, but containing no thorium,
contains no helium at all; he explained its absence by the very loose texture
and permeability of the mineral, which would allow the gas to escape. Strutt
concluded that whilst helium is undoubtedly produced by disintegration in
the uranium series, in minerals it is produced more by thorium or, as more
recent work indicates, by radio-thorium, than by uranium.
[135] Amer. J. Sci. 1905, [iv.], 20, 256.
The question of the origin of helium in minerals is, however, not
definitely settled, for several anomalous cases are known. Thus the yttria
silicate, Thalénite (q.v.), contains quantities of helium, but no uranium or

thorium is given in the analyses. Similarly, Risörite contains a relatively
large quantity of helium, but only traces of uranium and thorium. In the last
mineral, the active constituent is precipitated with the lead, so that no radio-
thorium appears to be present. Further, Thomsen analysed a fluorspar from
Ivitgut in Greenland which he found to contain 27 c.c. of helium per
kilogram. This specimen contains no uranium, but gives off the thorium
emanation in quantities which suggest the presence of radio-thorium;
moderate quantities of thorium are also present. Since the α particle has
been definitely identified as a positively charged helium atom, it appears
certain that disintegration in all three series (uranium, actinium, and
thorium series) produces helium, and a mineral containing a member of any
of these series (which gives α rays or α ray-giving products) would also
contain helium.
Even so, there is a case in which the helium content is anomalous, if not
altogether beyond explanation at the present stage. In examining a large
number of minerals for helium, Strutt[136] found that some samples of beryl,
a beryllium aluminium silicate, contain a relatively very large amount of
helium, but only traces of thorium, and was altogether inactive. The absence
of any active constituent renders untenable the ordinary explanations of the
presence of such a surprising quantity of helium. Boltwood has put forward
a suggestion which in the present state of our knowledge must be regarded
as a provisional explanation. He conceives that in the concentration of
beryllium from the parent magma, it may have become associated with
some short-lived intermediate radioactive element, which had been
altogether separated from its long-lived parent element in the process of
concentration; this intermediate element, having collected in the crystallised
beryl, decayed completely in the course of the great period which must have
elapsed, leaving the helium to which it had given rise during its
disintegration enclosed in the mineral. It is difficult to see how two
substances which must be so intimately connected as a parent-element and
its product could be completely separated in the process of cooling of a
magma; but since so little is known of the process of crystallisation of
minerals, the suggestion can hardly be rejected on geological grounds. In
any case, we have here only one strongly marked exception to the very
definite rule that in all cases in which helium occurs in minerals, it is
accompanied by and undoubtedly produced from, a radioactive element or

elements; and in the majority of cases, the helium in minerals is produced
by disintegration of uranium or thorium and their products.
[136] Proc. Roy. Soc. 1908, A, 80, 572.
Strutt found that traces of helium are universal in the mineral world. His
method of determining helium was approximate only. He obtained the gas
content by heating the powdered mineral—a method which, as Wood has
shown,[137] will only give all the gas when very high temperatures (up to
1000°C.) are employed. The gases were freed from oxygen and hydrogen
by passing over a heated, partially oxidised, copper spiral, and from carbon
dioxide by means of potash. Nitrogen was removed by sparking with excess
of oxygen and shaking over potash; the excess of oxygen was removed by
melted phosphorus. The inert gases so obtained were freed from all
impurities by the use of the liquid alloy of sodium and potassium for the
electrodes of the spectrum tube in which the gases were examined
spectroscopically.[138] Argon, if present—it seems to be a universal
constituent of igneous rocks, into which it may have been absorbed from
the air—was removed by charcoal at a temperature of -80°C. The helium so
left was examined spectroscopically, and measured in a MacLeod gauge.
[137] Proc. Roy. Soc. 1910, A, 84, 70.
[138] As soon as the discharge is started in such a tube, all the gases present other than
those of the helium family are absorbed by these electrodes.

As stated, helium was found in traces in nearly all minerals, and its
presence is to be attributed to traces of radium, which also appears
universal. In minerals containing uranium or thorium, or rare earths (the
latter are almost always accompanied by uranium and thorium), helium is
found to a much greater extent, and Ramsay considers it possible that some
fraction of the helium content may arise from the rare earth metals. There
is, however, no positive evidence to support the conjecture. He found that
the helium ratio, i.e. the volume of helium per gram of uranous oxide, UO₂,
varies with the amount of thoria present; but where the latter is absent the
variations are much less marked. If helium were produced in a mineral from
uranium alone, and none escaped, it is obvious that the helium ratio would
depend only on the age of the mineral. For minerals of about the same age,
and containing no thorium, the helium ratio would be roughly constant, if
no disturbing factor required consideration.
In 1905 Strutt pointed out that in all the minerals he had examined,
thorium was never present unless accompanied by uranium and radium,

whilst uranium and radium often occurred without thorium. He suggested
that the present atomic weight of thorium, 232·5, was too low, and that it
was really the parent of uranium (at. weight 238·5); he further supposed
that the next permanent member in the line of descent was one of the
cerium metals. These suggestions have been negatived by later work of
Boltwood and Holmes. The former pointed out[139] that it was far more
likely that thorium is a disintegration product of uranium of considerably
longer life. On the whole, however, there is very little positive evidence to
connect thorium with uranium.
[139] Boltwood, Amer. J. Sci. 1905, [iv.], 20, 256.
In the same year Boltwood (loc. cit.) drew attention to the persistent
appearance of traces of lead, bismuth, barium, etc., in the radioactive
minerals, and also pointed out that the variations of the ratio of helium to
uranium in pitchblende might be used to determine the age of the mineral.
In 1907 he suggested[140] that lead was the final product of the degradation
of uranium, from which it follows that the ratio of uranium to lead should
be constant for minerals of the same age (since, lead decays, if at all, at an
infinitely slower rate than uranium). He collected all the available analyses,
and classified the minerals dealt with into six groups according to the value
of the ratio. The order given by the ratio was declared to be in accordance
with the order of age as given by geological evidence.
[140] Amer. J. Sci. 1907, [iv.], 23, 77.
Holmes[141] has further extended this work. He examined a number of
rare earth and allied minerals from the Christiania district, which Brögger
considers to be of approximately Lower Devonian age, and found the ratio
of lead to uranium to approximate quite closely, for almost all the minerals
examined, to 0·045. Representing the change in the usual way as
U → 8He + Pb
238·5 → 31·92 + 207·1
and using the data calculated by Rutherford and others for the rates of
decay, he gives the age of Lower Devonian strata as about 370 million
years. This figure is about twice as great as that deduced by palæontologists
from the flora and fauna, and greater still than the times based on physical
data, e.g. rates of cooling, precession and nutation, etc. His figures for pre-
Cambrian rocks, based on the same ratio, range between 1000 and 1640

million years, the later being deduced from a thorianite from the Archæan
rocks of Ceylon. Strutt’s figure for Archæan rocks is about 700 million
years; this was derived from work on the helium ratio, which must now be
considered.[142]
[141] Proc. Roy. Soc. 1911, A, 85, 248.
[142] See Strutt, Proc. Roy. Soc. 1908, A, 82, 166; 1909, 83, 96; 1909, 83, 298; 1910, 84,
194.
In 1898 Travers[143] had examined the effect of heat on cleveite and
fergusonite, and found that about half the total helium, together with
hydrogen, is given off at a bright red heat. He considered it likely that the
helium was combined with a metal (though he recognised no distinction
between occlusion and combination) and remarked: ‘The results of such
experiments cannot therefore serve as a basis for speculation as to the origin
or history of the substances in question.’ The chemical inactivity of helium,
however, as well as the experiments of Moss and Gray, who showed that
helium was evolved on grinding the materials,[144] indicate that the gas is
mechanically bound only. This, however, introduces the difficulty, if an
attempt be made to use the helium-uranium ratio to calculate the age of
minerals, that the gas would be expected to escape from a porous material,
so that its amount is never so great as it should be. Strutt himself found that
helium escapes rapidly from powdered monazite, whilst even the solid
mineral was found to evolve helium at a rate much in excess of the probable
rate of production by radioactive changes. Similar results were found with
thorianite, and the only conclusion, since helium is found in the minerals, is
that under the conditions under which these minerals exist in the earth’s
crust, this escape is checked or altogether prevented. It follows, however,
that any age determined from the helium ratio must be a minimum age,
since there is always the chance of loss; this of course is not the case—
except where the minerals have suffered chemical changes—with the lead
ratio, and may account for the discrepancies observed.
[143] Proc. Roy. Soc. 1898-99, 64, 140.
[144] Vide Gray, Proc. Roy. Soc. 1908, A, 82, 306.

Strutt’s earlier work on the helium ratio was made with phosphate
minerals (coprolites and fossil bones) of known ages. The ratios found were
not in order of age, the minerals being very permeable, so that helium had
probably been lost. He next turned his attention to igneous rocks, and
selected zircon for the work. Here he obtained some sort of regularity in the

order of age and the order given by the ratio, and assumed that if helium
were lost at all, it must be lost in roughly proportional amounts by reason of
the similarity in conditions. Geological criticism tends to lessen the
trustworthiness of the conclusions; it is pointed out that the age of a
specimen of zircon is not necessarily that of the rock in which it occurs, for
zircon is an extremely stable mineral, and might survive unchanged several
fusions and re-crystallisations of the magma. Strutt replies to this that at the
temperature of fusion of a rock, zircon would certainly give up its
accumulated helium, so that the age determined from the helium content
would be that of the last fusion, i.e. the age as given by geological data. On
the other hand, our ignorance of the real mechanism of the crystallisation of
a magma, and especially of the amount and effect of the pressures
obtaining, robs this reply of its force, and the objection must be counted
valid.
In still later work Strutt used sphene and thorianite, and his results agree
as well as can be expected. The sphenes used were all from Archæan rocks,
except one, which was from a Tertiary volcanic deposit of the Laacher See,
near Coblenz (the lake is in the crater of an extinct volcano). In this case the
helium ratio was very much smaller (about 1⁄4000 of the values for Archæan
rocks) indicating the (comparatively) extremely recent formation of the
deposit.
The most recent results in the study of radioactivity point to the
conclusion that elements which differ in atomic weight and radioactive
properties may be chemically identical, or at least chemically inseparable;
such elements have been termed isotopes. The end product of the thorium
series of radio-elements should have an atomic weight of about 208·4, and
it has been suggested that the element actually produced in this series of
changes may be bismuth. The latest results, however, rather point to the
conclusion that disintegration in the thorium series gives rise to an isotope
of lead. If this hypothesis be true, the lead derived from a mineral rich in
thorium and poor in uranium should have an atomic weight appreciably
higher than that of ordinary lead. Experiments to test this conclusion have
recently been carried out by Soddy and Hyman.[145]
[145] Proc. Chem. Soc. 1914, 30, 134.
These authors have made analyses of Ceylon thorite, which they find to
contain 0·35 per cent. of lead; from the ratio of thorium to uranium in the
mineral, they calculate that the lead should have an atomic weight of 208·2,

that of ordinary lead being 207·1. Preliminary comparative experiments on
1 gram of pure lead chloride extracted from the mineral point to an atomic
weight for the thorite lead of 208·4, a result surprisingly in accord with
theory. More extended experiments on this most interesting question are in
progress.
The present chapter would be incomplete without a reference to the
interesting work of Goldsmidt on radioactivity as an aid in identifying
mineral species.[146] He describes a simple method by which the activity of
a mineral may be rapidly and easily measured to a sufficient degree of
approximation, and shows how the determination enables a line to be drawn
on a diagram already mapped out; this line will intersect an area on the
diagram which corresponds to the particular mineral. Owing to lack of
analytical data, and to the great difficulty of determining with accuracy
small quantities of uranium and thorium, the method is at present of
scientific interest only; but it is capable of development, and its
development would be of undoubted value in the further study of this
branch of radioactivity.
[146] Zeitsch. Kryst. Min. 1907-8, 44, 545; ibid. 1908, 45, 490.
In order to make this part of the subject as clear as possible, the chief
points in this chapter are summarised as follows:
1. Radioactivity is only observed to an appreciable extent in some rather
rare minerals. These minerals as a rule contain radium, uranium, thorium,
rare earths, and helium.
2. The helium has been produced during geological time by the
degradation of one or more members of the three series of active elements
(the Uranium, Actinium, and Thorium series).
3. Radium is a degradation product of uranium, and itself is degraded
continuously; the final product of degradation is probably lead.
4. The age of minerals has been calculated from the ratio of lead to
uranium; the figures obtained are much greater than those put forward by
geologists and physicists.
5. The helium ratio has also been used, but appears less trustworthy,
owing to escape of helium, and uncertainty as to geological age of the
minerals employed.
6. Some connection between radioactivity and the presence of the yttrium
or cerium metals appears highly probable, but no satisfactory theories have

been advanced on this point; it has been shown that actinium is very closely
allied to lanthanum.

PART II

THE CHEMISTRY OF THE ELEMENTS

CHAPTER IX

GENERAL PROPERTIES OF THE CERIUM AND YTTRIUM
GROUPS
The chemistry of the rare earth elements begins in the year 1794, with
Gadolin’s discovery of the new oxide ‘Ytterbia,’ for which the name Yttria
was subsequently proposed by Ekeberg, and generally adopted (see Chapter
I, and under Gadolinite, p. 35). The discovery of Ceria followed in 1804
(see under Cerite, p. 32). The classical work of Mosander, carried out
between 1838 and 1842, showed the complex nature of the new oxides.
From ceria he separated three new earths, Ceria proper, Lanthana, and
Didymia. Yttria was shown to be a mixture of at least three oxides, for
which the names Yttria, Erbia, and Terbia were proposed. These oxides
were believed to have the general formula RO, by analogy with the alkaline
earths, which they were found to resemble in many respects, notably in
their strongly basic character.
The properties of the new oxides were examined during the next twenty
years by many chemists, the chief workers being Marignac, Rammelsberg,
and Hermann, but the next important advance was the investigation of the
absorption spectra of solutions of the rare earth salts, first suggested by
Gladstone in 1856, and developed more fully by Bunsen and Kirchhoff in
1860 and the following few years. The introduction of the methods of
spectrum analysis furnished a very delicate and valuable method of
examining and identifying the various oxides, and so greatly assisted the
laborious processes of separation.
Sixteen elements (excluding thorium and zirconium) are at the present
time recognised as belonging to the rare earth group. With one or two
exceptions, these show the closest resemblance to one another, both in

chemical behaviour and in the properties of their compounds, so that the
difficulties of separating and purifying them are very great. They may be
said to form a series, in which the properties vary continuously but
gradually from member to member, so that no sharp differences are
anywhere perceptible. The method of division into groups is, therefore,
almost entirely one of convenience, and has arisen from the course which
the separations have followed.
The elements are divided into two chief families or groups, that of the
cerium metals and that of the yttrium metals respectively. The cerium
elements are separated by a process depending on the relative insolubility of
their alkali double sulphates; in this group are included cerium, lanthanum,
praseodymium, neodymium, and samarium. The yttrium family is further
divided into four sub-groups: the first consists of scandium and yttrium; the
second or terbium group of europium, gadolinium, and terbium; the third or
erbium group of dysprosium, holmium, erbium, and thulium; and the fourth
or ytterbium group of ytterbium and lutecium—the element celtium,
recently discovered by Urbain, will also fall into this sub-group, but the
discovery awaits confirmation. Whilst scandium and yttrium fall into
somewhat abnormal positions, corresponding to their low atomic weights,
the terbium elements occupy an intermediate position between the cerium
elements and the remaining yttrium elements, or yttrium group proper, and
so are frequently classified as a third or intermediate group.
This list does not include all the names which have been put forward to
designate what have been claimed from time to time as new elements;
whilst the individuality of some of those included is not yet fully
established, and the homogeneity of others has been called in question. The
uncertainty is more pronounced among the yttrium elements than among
the cerium elements; owing to the opportunities for investigation furnished
by the commercial treatment of monazite, the chemistry of the cerium
group may be regarded as complete.
In the following table the elements are arranged in order of increasing
atomic weight, and it can be seen at once how closely the division into
groups follows this order:
Atomic
Element Colour of Salts
Wt.
- Scandium, Sc 44·1 Colourless

Yttrium, Yt 89·0 Colourless

Lanthanum, La 139·0 Colourless
Cerium, Ce 140·25 Cerous, colourless; ceric,
orange to red
Cerium
- Praseodymium, 140·6 Green
Group.
Pr
Neodymium, Nd 144·3 Red to reddish-violet
Samarium, Sa 150·4 Topaz yellow

Europium, Eu 152·0 Faint rose
Terbium
- Gadolinium, Gd 157·3 Colourless
Group.
Terbium, Tb 159·2 Colourless

Dysprosium, Dy 162·5 Bright green
Erbium Holmium, Ho 163·5 Yellow to orange
-
Group. Erbium, Er 167·7 Deep rose
Thulium, Tm 168·5 Bluish-green

Ytterbium Ytterbium, Yb 172·0 Colourless
-
Group. Lutecium, Lu 174·0 Colourless

In their chemical relations, the rare earth elements may be placed
between the metals of the alkaline earths, and the trivalent metals iron,
aluminium, and chromium. With the exceptions of cerium in the ceric salts,
and of samarium and europium in the recently discovered dichlorides, they
are uniformly trivalent, but the oxides are very strong bases, and the salts
very slightly hydrolysed in dilute solutions; generally, therefore, they
resemble the calcium family rather than the aluminium group. Among the
common salts, the oxalates, phosphates, chromates, iodates, fluorides,
carbonates, tartrates, and borates are almost insoluble; the sulphates are
only sparingly soluble at ordinary temperatures. Among the double salts,
the alkali double sulphates are of great importance from their employment
for separations; the tendency to the formation of complex salts is greater
among the yttrium than among the cerium elements, increasing with the
atomic weight, and with the decrease in basic strength of the oxides.

The great similarity in chemical behaviour of the rare earth elements is
apparent not only in the similarity in composition, solubility and chemical
properties of the salts—which is so great that the general account of the
compounds which follows applies almost in its entirety to each member of
the group—but also in the crystallographic relations between corresponding
compounds. Many of the salt hydrates form isomorphous series; the
sulphate octohydrates, for example, appear to be isomorphous throughout
the whole group, and probably the relation would be found to apply even
more completely than is generally accepted, if the necessary data were
forthcoming. Of great interest and practical importance is the isomorphism
between the nitrates and double nitrates of the cerium elements and
bismuth, which has been utilised with such valuable results in the processes
of fractional crystallisation.

The Metals. —The earlier attempts to reduce compounds of the rare
earth elements to the metallic condition, by means of metallic sodium or
potassium, did not yield pure products; nor did the use of aluminium or
magnesium lead to results of practical importance. The metals were first
obtained in a coherent physical condition by Hillebrand and Norton,[147] by
electrolysis of the fused chlorides. These investigators obtained cerium,
lanthanum, and the so-called didymium, and measured their specific heats;
their results confirmed the atomic weights assigned to the elements by
Mendelejeff, except in the case of lanthanum. Their method has since been
elaborated by Muthmann, Hofer and Weiss,[148] who have prepared large
quantities of the cerium elements in the pure state. More recently, Hirsch
has prepared metallic cerium in large quantities,[149] and has studied its
properties.
[147] Pogg. Ann. 1875, 155, 631; 156, 466.
[148] Annalen, 1902, 320, 231; see also Muthmann and Weiss, ibid. 1904, 331, 1.
[149] Met. Chem. Eng. 1911, 9, 543.

By electrolytic reduction of the mixed chlorides of the cerium elements, a
mixture known as ‘Misch metal’ is obtained; this has powerful reducing
properties, and, like aluminium, reduces the oxides of iron, chromium, etc.,
with great development of heat.[150] The yttrium metals have not yet been
obtained in the pure state, the electrolytic method giving unsatisfactory
results on account of the high melting-points of the metals, and the volatile
nature of their chlorides.

[150] A full account of the properties and preparation of the cerium metals and their alloys
will be found in the monograph of Kellermann, ‘Die Ceritmetalle und ihre pyrophoren
Legierungen, Wilhelm Knapp, Halle, 1912.

The cerium metals are white or slightly yellowish in colour, and are
moderately stable in dry air. In moist air they tarnish slowly, lanthanum, as
the most positive, being most readily oxidised. The melting-points and
specific gravities are as follows:
Melting- Specific
Element
point Gravity
Cerium 623° 7·0242
Lanthanum 810° 6·1545
Praseodymium 940° 6·4754
Neodymium 840° 6·9563
Samarium 1300°-1400° 7·7-7·8
The metals decompose water slowly in the cold, but rapidly at the
boiling-point, with evolution of hydrogen. They have a great affinity for
oxygen, the heats of formation of the oxides being of the order of those of
alumina and magnesia:
Heat of Formation
per Equivalent Weight
of Oxide[151]
1
⁄3La₂O₃ 74·1 K
1
⁄3Nd₂O₃ 72·5 „
1
⁄3Pr₂O₃ 68·7 „
1
⁄4CeO₂ 56·1 „
1
⁄3Al₂O₃ 64·3 „
1
⁄2MgO 71·9 „
[151] Muthmann and Weiss, loc. cit.; K = 1 kilogram-calorie, or 1000 cal.
In consequence of the high values of the heats of combustion, the metals
have powerful reducing properties.
The cerium metals form alloys with magnesium, zinc, aluminium, and
iron, and combine with boron and silicon. The alloys of cerium, and the
metal itself, are remarkable for their property of emitting brilliant sparks

when scratched (see Chapter XXI). Cerium also forms an amalgam with
mercury.
The metals burn brilliantly when heated in oxygen, and dissolve readily
in dilute mineral acids. When heated to a temperature of 200°-300° in a
current of hydrogen, they absorb the gas very readily, forming the hydrides.
These compounds are also obtained by heating the oxides with magnesium
in a current of hydrogen. They were first prepared by Winkler,[152] who
deduced from his analyses the general formula RH₂; the more recent work
of Muthmann and Beck,[153] however, points to the formula RH₃.
[152] Ber. 1890, 23, 2642; 1891, 24, 873.
[153] Annalen, 1904, 331, 58.

If nitrogen be substituted for hydrogen in either of the above methods of
preparation, nitrides of the general formula RN are obtained; cerium nitride,
however, cannot be obtained by heating the element in the gas.[154] These
compounds are also obtained when the carbides are heated in ammonia.
They are amorphous solids, which yield ammonia when acted upon by
water.
[154] Dafert and Miklanz, Monats. 1912, 33, 911.

Hydroxides. —The hydroxides are thrown down as gelatinous
precipitates on the addition of alkalies to hot dilute solutions of the salts;
precipitation in the cold, or in strong solution, usually gives a basic salt, or
an hydroxide mixed with a large quantity of basic salt. The hydroxides are
insoluble in excess of precipitant, but the precipitation is inhibited by the
presence of some organic hydroxy-acids.[155]
[155] For effect of tartaric acid, see p. 133.

The hydroxides are insoluble in water, but dissolve very readily in acids.
The most basic of them absorb carbon dioxide from the air; lanthanum
hydroxide is exceptional in that it colours litmus blue.
Whilst hydrogen peroxide in neutral solution does not react with rare
earth salts,[156] alkalies in presence of this reagent precipitate gelatinous
hydrated peroxides, which are very unstable, decomposing on standing, or
on treatment with acids, with evolution of oxygen. The general formula
R₄O₉ + xH₂O was proposed for these compounds by Cleve, but more
recently the formula R(OOH)(OH)₂ has been advanced.[157]

[156] Compare behaviour of thorium and zirconium, Ch. XVI.
[157] Melikoff and Pissarjewski, Zeitsch. anorg. Chem. 1899, 21, 70; Melikoff and
Klimento, Chem. Zentr. 1902, 1, 172.

Oxides. —In their most stable state of oxidation, the rare earth elements
are generally trivalent. In the case of cerium, the dioxide, CeO₂, is more
stable than the sesquioxide Ce₂O₃, but the ceric salts are unstable, and are
very readily reduced to cerous compounds, corresponding to the oxide
Ce₂O₃. Higher oxides are known with certainty among the other elements
only in the cases of praseodymium and terbium, but these do not give rise to
salts.
The oxides R₂O₃ are fairly strong bases, being comparable in strength to
the alkaline earths, and far more strongly basic than alumina and oxides of
other trivalent elements; thus they liberate ammonia from ammonium
compounds, whilst the salts they form with strong acids are not easily
hydrolysed. Their relative strengths as bases are expressed in the following
series, in which the elements are placed in order of diminishing
electropositive character:[158]
La, Ce´´, Pr, Nd, Yt, Eu, Gd, Sa, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Ceiv.
[158] The position of yttrium in this series is not known with certainty; it is probably as
positive as neodymium. It is usually stated (see Meyer and Hauser, pp. 32-33) that the
terbia oxides are intermediate in basic strength between the ceria and yttria earths,
though the arrangement into two series, consisting of the cerium and yttrium groups
respectively, is generally adopted; the electropositive character of the elements in each
series then weakens as the atomic weight rises, scandium being of course exceptional.

It will be seen that, with the exception of scandium and yttrium, the
metals of the cerium and yttrium groups become less electropositive as the
atomic weight increases.
This arrangement is obtained by ascertaining the order in which the
various hydroxides are precipitated from a solution by gradual addition of a
dilute solution of a strong base. The weakest base is precipitated first, and
the strongest last; those intermediate in strength are thrown down in
ascending order of strength. Similar results may be obtained by the
fractional decomposition of the nitrates by heat; in this case the nitrate of
the weakest base is decomposed at the lowest temperature. This order is

also confirmed, as far as the data are available, by measurements of the
equivalent conductivities of solutions of the salts (see, for example, p. 122).
Quite recently, a very different order has been obtained from a
consideration of the dissociation tensions, and of the heats of dissociation of
the anhydrous sulphates.[159] In the following table the elements are
arranged in the order of the increase of the dissociation tension (T)
measured at 900°, which is the same as the order of decrease of the heats of
dissociation (Q):
Element At. Wt. T. (Mm. Hg.) Q.
La 139 ·0 2 59·8
Yt 89 ·0 3 58·9
Lu 174 ·0 3 ·5 58·5
Yb 172 ·0 4 58·2
Er 167 ·7 5 57·6
Pr 140 ·6 5 ·5 57·4
Nd 144 ·3 6 57·2
Gd 157 ·3 7 56·9
Sa 150 ·4 8 56·5
Sc 44 ·1 11 54·5
Ce 140 ·25 52·4
[159] Wöhler and Grünzweig, Ber. 1913, 46, 1726.

It will be observed that the order is very different from the order of
increase of atomic weight, the positions of lutecium and ytterbium being
especially surprising; these elements are generally considered to be among
the least electropositive of the whole series. The anomalous position of
cerium is probably due to the fact that the sulphate on decomposition leaves
the dioxide, and not the sesquioxide, as with the other elements; this would
undoubtedly affect the values. The heats of dissociation are the greatest yet
observed for the sulphates of trivalent metals, a further evidence of the
strongly basic nature of the oxides.
Ignited lanthana resembles quicklime in that it readily absorbs carbon
dioxide from the air, and hisses when slaked with water; as the basicity
becomes weaker, the affinity for water and carbon dioxide becomes less
marked. All the oxides are soluble in dilute acids, even after prolonged
ignition; but the ease with which solution occurs is naturally much

influenced by the treatment to which the oxide has been subjected, as well
as by its strength as a base.
The rare earth oxides are capable of existing in more than one
modification, the compounds obtained by ignition of the hydroxides
differing in appearance and reactivity from those prepared by ignition of the
oxalates or nitrates, and so on; they are probably highly polymerised.
Cerium dioxide, CeO₂, is remarkable for its power of combining with the
other oxides, R₂O₃, of the rare earth metals. The pure dioxide is insoluble in
nitric acid, but mixtures of earths containing up to 50 per cent. of the
dioxide dissolve readily. The various colours of mixtures of the ceria earths
may sometimes be attributed to a similar combination,[160] and there can be
little doubt that the dioxide sometimes functions as an acid in the rare earth
minerals.
[160] The brown colour of a mixture of ceria oxides containing praseodymium is generally
attributed to the presence of the strongly coloured peroxide of that element.

Sulphides. —These compounds cannot be prepared in the wet way, that
is, by the action of hydrogen sulphide or ammonium sulphide on the salts in
solution; the former reagent gives no precipitate, the latter throws down the
hydroxides. In this behaviour, the rare earth elements resemble aluminium
and chromium.
The normal sulphides, R₂S₃, are obtained by reduction of the anhydrous
sulphates, or from the oxides at high temperatures, by treatment with
hydrogen sulphide. They are strongly coloured compounds, fairly stable
towards cold water, but readily hydrolysed on boiling.
Disulphides, RS₂, are known in the cases of cerium, lanthanum, and
praseodymium; these are to be regarded as polysulphides, since on
treatment with dilute acids they yield hydrogen persulphide, H₂S₂.

Carbides. —By reduction of the oxides with carbon in the electric
furnace, Moissan obtained the carbides in the form of microscopic yellow
crystals. They have the general formula RC₂, and are attacked by water and
dilute acids, with evolution of very complex mixtures of gases.[161] The
principal product is acetylene, with various higher homologues, and in
smaller quantities ethylene and ethane and their homologues. No methane is
formed,[162] but hydrogen is always present, the olefines and paraffins

probably arising from its action on the acetylenic hydrocarbons. The
relation of the rare earth elements to the calcium group is here very close;
calcium carbide when attacked by water yields pure acetylene, whereas
aluminium carbide gives pure methane.
[161] Damiens, Compt. rend. 1913, 157, 214.
[162] Moissan stated that 24-30 per cent. of methane was formed in this action; compare
Compt. rend. 1900, 131, 595.

Halogen Salts. —The halides of the rare earth elements show a close
analogy with the corresponding compounds of the alkaline earth elements.
The fluorides are insoluble in water and dilute mineral acids, and are
obtained as gelatinous precipitates by the addition of hydrofluoric acid, or a
soluble fluoride, to solutions of the salts. They may be prepared in the
crystalline condition by heating the carbides in a stream of fluorine, or by
the action of hydrofluoric acid upon the hydroxides in aqueous suspension.
The rare earth elements, as well as thorium, may be separated from
zirconium by taking advantage of the insolubility of their fluorides in
excess of hydrofluoric acid or alkali fluorides, since zirconium fluoride is
readily soluble in excess of the precipitant. The solubility of the fluorides in
a large excess of concentrated acid increases with the electropositive
character of the metal, the fluorides of the more negative elements being the
least soluble. Thorium and scandium may, therefore, be concentrated to a
large extent by repeated precipitation with hydrofluoric acid in acid
solution.
The silicofluorides of the rare earth elements have been used by R. J.
Meyer in the extraction of scandium from wolframite (see Chapter I and
under Scandium, p. 215). They are thrown down as gelatinous precipitates
on addition of potassium or sodium silicofluoride to boiling, neutral
solutions of rare earth salts. In presence of mineral acids, however, they are
not thrown down in the cold; on boiling, the cerium metals are precipitated
as fluorides, by hydrolysis of the silicofluorides—the yttrium elements,
with the exception of scandium, being held in solution by the mineral acid.
With the exception of the fluorides, the halogen salts of the rare earth
metals are readily soluble in water, and crystallise from the concentrated
solutions in the hydrated form. The bromides and iodides have not been so
fully studied as the chlorides; they are hygroscopic salts, and decompose

rather easily. The iodides have been obtained by Moissan in the anhydrous
state, by the action of iodine vapour on the carbides at high temperature.
The anhydrous chlorides may be obtained by the application of any of
the ordinary methods, e.g. by heating the oxides with carbon in a stream of
chlorine, by heating the carbides in the same gas, by heating the sulphides
or hydrated chlorides in hydrogen chloride, or by evaporating the solutions
of the hydrated salts to dryness in presence of ammonium chloride, and then
igniting till the latter has all been removed. As obtained by any of these
methods, they are fusible at a red heat, but only slightly volatile; they are
easily soluble in water or alcohol, with disengagement of heat. They are
insoluble in most organic solvents, but dissolve to some extent in some
bases; the chlorides of the yttrium elements, for example, are readily
soluble in pyridine. With such solvents, the chlorides form compounds
which may be considered as derived from the hydrated forms, by
replacement of the so-called water of crystallisation by the organic base.
Conductivity measurements show that the salts are not perceptibly
hydrolysed in moderately dilute aqueous solutions, though the values for
the equivalent conductivities vary somewhat with the variations in the
electropositive character of the elements. In the following table, the
equivalent conductivities of the chlorides in solutions of dilution 32 and
1024 at 25°C. are given. It will be seen that the value (λ₁₀₂₄ - λ₃₂) ÷ 10 is in
all cases (except for the highly hydrolysed scandium salt) very close to 3,
an experimental proof of the trivalent nature of the elements. The values for
the chlorides of iron, aluminium and chromium are included; it will be seen
that these elements are considerably less positive than the rare earth metals
(with the exception, of course, of scandium).
Salt λ₃₂ λ₁₀₂₄ λ₁₀₂₄ - λ₃₂
LaCl₃ 105·8 131·5 25·7
CeCl₃ 107·8 135·2 27·6
PrCl₃ 105·5 135·9 30·4
NdCl₃ 103·8 134·3 30·5
YtCl₃ 98·8 123·4 24·6
YbCl₃ 107·4 140·4 33·0
ScCl₃ 116·9 257·9 141·0
AlCl₃ 99·9 138·0 38·1

CrCl₃ 98·4 152·6 54·2
FeCl₃ 117·2 200·7 83·5
From aqueous solutions the chlorides crystallise with six molecules of
water, except praseodymium chloride, which has seven. The hydrated salts,
when heated to 120° in the air, form insoluble oxychlorides of the general
formula ROCl.
The chlorides do not show a great tendency to form double salts with
other metallic chlorides; on the other hand, they readily form complex
compounds with the chlorides of the less electropositive metals, e.g. tin,
bismuth, gold, and platinum.
Subchlorides of samarium and europium have recently been obtained; in
these compounds, for the first time, rare earth metals have been shown to be
capable of functioning as divalent elements.
Cyanides of the rare earth elements are not known; addition of potassium
cyanide to solutions of the salts throws down the hydroxides. The
platinocyanides may be obtained by double decomposition of the sulphates
with barium platinocyanide. They are very stable and characteristic bodies,
of the general formula R₂[Pt(CN)₄]₃, with 18 or 21 molecules of water. The
compounds of the cerium elements are yellow, with a strong blue
fluorescence; they crystallise in the monoclinic system. The platinocyanides
of the yttrium metals are red or crimson, with a splendid green
fluorescence, and crystallise in the rhombic system. Scandium
platinocyanide is of great interest from the fact that it exists in two
modifications, which show the characteristic appearance of the two groups
of compounds respectively.
Potassium ferrocyanide precipitates potassium earth ferrocyanides of the
general formula KR(FeC₆N₆),3H₂O, from neutral solutions;[163] the
precipitate is somewhat soluble in excess. The ferrocyanides have been
proposed for the purification of yttrium; the method is useful where rapid
concentration of the element is required, yttrium ferrocyanide being far
more soluble than the analogous compounds of the erbium and ytterbium
metals, but the precipitates are gelatinous, and very difficult to handle.
[163] Compare Astrid Cleve, Zeitsch. anorg. Chem. 1902, 32, 129.

Halogen Oxy-salts.

—Perchlorates and periodates of the rare earth elements, of the general
formula R(XO₄)₃,xH₂O, have been obtained. The existence of chlorates has
been observed only in the yttrium group; yttrium chlorate, Yt(ClO₃)₃,8H₂O,
has been prepared by double decomposition of the sulphate with barium
chlorate. The bromates are also prepared in this way. They are readily
soluble compounds, of which several hydrated forms are known. They are
of considerable importance for purposes of separation in the yttrium group.
The iodates are sparingly soluble bodies, precipitated by addition of the
alkali compound to solutions of the rare earth salts. The rare earth iodates
are soluble in nitric acid, the solubility increasing as the electropositive
character of the element becomes stronger. A method for the purification of
yttrium has recently been based upon this property of the iodates, whilst the
fact that thorium iodate is completely insoluble in nitric acid allows of the
easy separation and estimation of thorium in minerals or mixtures
containing rare earth elements.

Sulphates. —The sulphates of the rare earth elements are obtained by
dissolving the oxides or hydroxides in sulphuric acid. From the solutions so
obtained, various hydrated salts separate according to the temperature of
crystallisation. By heating the hydrated salts to a temperature of 300°-400°,
the anhydrous salts are prepared. These are extremely soluble in water at 0°,
having a great tendency, which is indeed to be observed in the hydrated
forms also, to form supersaturated solutions. When the temperature of such
a solution is allowed to rise, larger or smaller quantities of an hydrated form
separate out, the differences of solubility among the sulphate hydrates of the
various elements being sometimes considerable.
The hydrated sulphates of the cerium elements have been very closely
studied in connection with the purification of thorium. Cerium sulphate
itself forms hydrates with 12, 9, 8, 5, and 4 molecules of water, but
sulphates of the other elements generally form fewer hydrates; the
commonest have 12, 8, or 4 molecules of water, and numerous cases of
isomorphism are known among them. The solubility curve of the cerium
sulphate hydrates is shown in the diagram. Fig. 3. The sulphates of the
yttrium elements have not yet been systematically investigated, and in most
cases only the octohydrates are known. Scandium sulphate is notably
different from the other sulphates, in that it is considerably more soluble,
and crystallises with six molecules of water.

Fig. 3.

It is an important characteristic of the rare earth elements that the
solubility of the sulphates diminishes rapidly as the temperature rises. The
study of the various equilibrium conditions is greatly complicated by the
tendency to form supersaturated solutions, and the fact that many hydrates
can exist throughout considerable ranges of temperature in the metastable
condition; in consequence of this, also, the solubilities of many hydrates are
known for temperatures far beyond the transition points. Foreign elements
may be separated by taking advantage of the very great solubility of the
anhydrous sulphates at 0°, and the rapid decrease in solubility with rise of
temperature. For this purpose, a solution of the anhydrous sulphates
saturated at 0° is prepared, and after filtration is slowly allowed to come to
room temperature; the hydrated rare earth sulphates then separate, leaving

in solution the foreign sulphates. This method may indeed be used instead
of the oxalate separation (see p. 147).
In presence of excess of sulphuric acid, acid sulphates of the general
formula R(HSO₄)₃ are formed. These are fairly stable, and must be heated
to a temperature of 400°-500° to decompose them completely to the normal
salts; even at that temperature, traces of acid are tenaciously retained, a fact
which renders the determination of the equivalents by the sulphate method
unreliable, unless special precautions are taken. On further heating, the
normal sulphates pass into basic salts, R₂O₃,SO₃, and finally, at the
temperature of the blowpipe flame, into the oxides. The temperatures at
which these decompositions occur vary with the positive character of the
elements; the most basic oxide clings most tenaciously to sulphuric
anhydride, and forms the most stable acid salt. Lanthanum sulphate, for
example, requires to be heated for a considerable time at a white heat if the
pure oxide is required, whilst the sulphates of the less positive elements are
easily decomposed at a red heat. The order of basic strength of the oxides,
as determined by the ease with which the sulphates are decomposed, seems,
however, to be very different from the order determined by decomposition
of the nitrates (see p. 118).
With the alkali sulphates, the sulphates of the rare earth elements readily
form double salts, which are of great importance in separation, on account
of the great differences in solubility. The double sulphates of the cerium
group are almost insoluble in excess of alkali sulphate, whereas the yttrium
double sulphates, with the exception of those of the terbium metals, which
occupy an intermediate position, are very easily soluble. This method of
separating the elements into the two main groups was first employed by
Berzelius, and though a century has elapsed, it remains to-day the most
efficient method of effecting the separation.
The ethylsulphates have been employed by Urbain and others in effecting
separations, especially in the erbium and terbium groups. The solubilities of
these salts are in the same general order as those of the alkali double
sulphates, and they are especially convenient for separating the metals into
the three groups of the cerium, terbium, and yttrium elements respectively.
They may be prepared by double decomposition of the rare earth sulphates
with barium ethylsulphate, but on account of the ease with which the
alkylsulphates are hydrolysed by acids, it is essential that the solutions
should be quite neutral. A more convenient method, according to James, is

the treatment of the anhydrous chlorides in alcohol solution with sodium
ethylsulphate dissolved in the same medium; sodium chloride is
precipitated, whilst the ethylsulphates of the rare earth elements remain in
solution.
The sulphites of the rare earth elements are sparingly soluble crystalline
salts, of the general formula R₂(SO₃)₃,xH₂O. They are obtained by passing
sulphur dioxide into a suspension of the hydroxides in water, or by double
decomposition of soluble salts with alkali sulphite. They dissolve in excess
of sulphurous acid, and on evaporation of the solution are deposited
unchanged. They are distinguished from thorium sulphite by the fact that
they form no alkali double salts. The strongly electropositive character of
the rare earth metals is shown by the fact that they form normal and not
basic sulphites.
The thiosulphates are readily soluble, crystalline bodies. With the
exception of the ceric and scandium salts, they are not hydrolysed in boiling
solution, a fact which allows of a complete separation from the readily
hydrolysed thiosulphates of zirconium and thorium.
Dithionates of the commoner rare earth elements, of the general formula
R₂(S₂O₆)₃,xH₂O, have been prepared by double decomposition of the
sulphates with barium dithionate. They are readily soluble, crystalline salts.
The selenates are soluble, crystalline salts, which separate from aqueous
solutions in various hydrated forms. They resemble the sulphates in being
less soluble in hot than in cold water, and numerous cases of isomorphism
have been observed among the corresponding sulphate and selenate
hydrates. Several alkali double selenates have been described; they show a
close resemblance to the analogous double sulphates.
The selenites are amorphous, insoluble compounds, obtained by the
action of selenious acid on the carbonates, or on solutions of neutral salts.
Basic and acid selenites are also known.

Nitrates. —The nitrates are crystalline, deliquescent compounds, readily
soluble in water and alcohol, but less easily in nitric acid, a fact which has
been of considerable importance for purposes of separation. The solubility
is greatest in the case of lanthanum nitrate, diminishing through the cerium
group to a minimum in gadolinium nitrate, and then increasing again. They
separate from aqueous solution in the form of crystalline hydrates; in the

cerium group, these have commonly the formula R(NO₃)₃,6H₂O, whilst the
nitrates of the yttrium elements usually crystallise with 3 or 5 molecules of
water. By carefully heating the hydrated salts, basic nitrates may be
obtained, which in the yttrium group are soluble in water, and may be
obtained crystalline; in the cerium group, the basic nitrates are insoluble. By
further heating, insoluble ‘superbasic salts,’ and finally the oxides, are
obtained in all cases. The temperatures at which these basic and superbasic
compounds are formed vary with the electropositive character of the
element; this fact affords a method of separation which has been very
frequently employed.
An interesting series of addition compounds of the rare earth nitrates with
antipyrine (dimethylphenylpyrazolone, C₁₁H₁₂ON₂) has been described
recently by Kolbe.[164] Those of the cerium metals have the general formula
R(NO₃)₃,3C₁₁H₁₂ON₂; the yttrium nitrates appear to combine with four
molecules of the base.
[164] Zeitsch. anorg. Chem. 1913, 83, 143
The tendency to form double nitrates with nitrates of the metals of Group
Ia and Group IIa also varies with the basic strength of the hydroxides. In
the most positive elements of the cerium group, the tendency is very
pronounced, and there are a large number of stable, crystalline double salts;
but the stability decreases rapidly as the atomic weight of the element rises,
and in the terbium and yttrium groups crystallised double nitrates cannot be
obtained. The solubility of these double salts increases rapidly in the same
direction, the lanthanum double nitrates being the least soluble. For this
reason, these compounds are of great importance for the purpose of
separation, especially in the cerium group. Bismuth nitrate and the various
bismuth double nitrates are isomorphous with the corresponding
compounds of the cerium group, and the double bismuth ammonium and
bismuth magnesium salts have been largely used by Urbain in the
separation of samarium and the elements of the terbium group.

Phosphates. —Addition of phosphoric acid, or an alkali phosphate to
solutions of rare earth salts throws down the phosphates as gelatinous
precipitates, which slowly become crystalline on standing. The precipitate
is soluble in excess of phosphoric acid, and in other mineral acids, a fact of
great importance in the commercial treatment of monazite. The composition
of the precipitate is not known with certainty; both neutral and acid

phosphates can probably be obtained according to the conditions. Double
salts with the alkali phosphates can be prepared by fusion methods. The
naturally occurring phosphates, monazite and xenotime, are mixtures of the
orthophosphates of the cerium and yttrium elements respectively.
Phosphites are known in a few cases only; arsenates and arsenites of
lanthanum have been prepared. Vanadates of some of the rare earth
elements have been described.

Chromates. —The rare earth chromates are, as a rule, sparingly soluble
in water, and show considerable differences of solubility amongst
themselves; for this reason, they have been of some use in the separation of
the cerium elements.[165] They are obtained by addition of potassium
chromate to neutral solutions of rare earth salts as crystalline precipitates, of
the general formula R₂(CrO₄)₃,8H₂O; with a large excess of alkali
chromate, double chromates are obtained, which are more readily formed,
and more soluble, in the yttrium series than in the cerium group. Addition of
chromic acid or alkali bichromate to solutions of the soluble salts gives no
precipitate, a fact which allows of the separation of zirconium and thorium,
and of cerium in the tetravalent state, since the tetravalent elements are
precipitated by both these reagents.
[165] Muthmann and Böhm, Ber. 1900, 33, 42; Böhm, Zeitsch. angew. Chem. 1904, 15,
372 and 1282.
Ammonium molybdate throws down from neutral solution of rare earth
salts gelatinous precipitates of the molybdates; the formula La₂2(HMoO₄)₆
is assigned to the lanthanum compound obtained in this way. No
precipitation occurs if the solution be strongly acid; on this fact a process
has recently been based for the volumetric estimation of thorium, in
presence of rare earth salts, by means of ammonium molybdate (see p. 289).
Various silicotungstates and double tungstates have been described.

Carbonates. —The more pronounced electropositive character of the
rare earth elements, as contrasted with other trivalent metals, is well
illustrated by the fact that they form stable neutral carbonates of the formula
R₂(CO₃)₃,xH₂O. These may be obtained by passing a current of carbon
dioxide through an aqueous suspension of the hydroxides, or by addition of
an alkali carbonate to neutral solutions of the salts. Basic carbonates are

known in the case of the less positive yttrium elements only; both these and
the neutral carbonates are insoluble in water.
In presence of a large excess of alkali carbonate, double carbonates are
formed. The stability as well as the solubility of these compounds increases
in passing from the cerium to the yttrium group, i.e. as the electropositive
character becomes weaker. The double carbonates of the cerium elements
are sparingly soluble, and are decomposed by water, especially on warming;
they may, however, be recrystallised from alkali carbonate solution. The
sodium and ammonium double salts are less soluble than the potassium
compounds. The latter have the general formula R₂(CO₃)₃,K₂CO₃,12H₂O,
and are of considerable importance in many processes of separation. The
yttrium elements can be separated from the cerium metals, and the latter
from one another, by taking advantage of the differences of solubility
shown by the potassium double carbonates. If a concentrated solution of the
salts in potassium carbonate solution be fractionally diluted with water, the
cerium elements separate in the order: lanthanum, praseodymium, cerium,
neodymium, and samarium; the more soluble yttrium compounds remain in
the solution. Thorium forms double alkali carbonates which are very readily
soluble in excess of alkali carbonate; this property is of great importance for
the technical separation of the element.

Oxalates. —The oxalates of the rare earth elements are of the greatest
importance, on account of the fact that they are not only insoluble in water,
but are also very sparingly soluble in dilute mineral acids, and in excess of
oxalic acid. They can be completely precipitated even from strongly acid
solutions by addition of sufficient excess of oxalic acid, or alkali oxalate,
and thus afford a means of easily and completely separating the rare earth
group from the commoner elements.
They are thrown down by addition of oxalic acid, or alkali oxalate, as
amorphous precipitates, which rapidly become crystalline, especially if the
solution is warmed. From water at normal temperatures they usually
separate as the decahydrates, R₂(C₂O₄)₃,10H₂O, but hydrates with 7, 9, and
11 molecules of water of crystallisation are also known. From strongly acid
solutions, mixed oxalo-salts of the general formula R(C₂O₄)X, where X =
Cl, NO₃, HSO₄, etc., may be obtained. These mixed salts may also be
prepared by dissolving the oxalates in concentrated solutions of the
chlorides, nitrates, etc., whilst nitro-sulphates, R(SO₄)NO₃, have been

obtained by recrystallising the sulphates from strong nitric acid. The
tendency to form salts with mixed acid radicles appears to be general.[166]
[166] See Meyer and Marckwald, Ber. 1900, 33, 1003; also Matignon, Ann. Chim. Phys.
1906, [viii.], 8, 243.
The solubilities of the oxalates in mineral acids of various concentrations
have been examined by Hauser and Wirth.[167] Whilst the solubilities in
water are exceedingly slight, and increase with increasing atomic weight of
the elements, i.e. from the cerium to the yttrium group, in mineral acids of
concentration 3-4N the solubility becomes noticeable, and is greatest for the
oxalates of the most positive elements. The solubility is greatly lessened,
however, if considerable excess of oxalic acid be present.
[167] Zeitsch. anal. Chem. 1908, 47, 389.
Double oxalates with the alkali oxalates can be obtained with the salts of
the yttrium elements only, the oxalates of the cerium elements being almost
insoluble in excess of alkali oxalate in the cold. Of the alkali double
oxalates, the potassium compounds are the most soluble, but the ammonium
compounds show the greatest differences in solubility; von Welsbach has
employed the method of fractional crystallisation of these salts from a
saturated solution of ammonium oxalate for separations in the yttrium
group. The sodium double oxalates are the least soluble of these double
salts.
Since the rare earth elements are almost always separated in the form of
the oxalates, the methods for transforming these into soluble compounds
become important. They may be ignited to oxides, and these dissolved in
nitric acid; if the content of ceria is very high, the oxide mixture may
become insoluble, but this difficulty may be overcome by addition of a
reducing agent—hydrogen peroxide is very convenient for this purpose.
The oxalates may also be dissolved directly in fuming nitric acid, care being
taken to avoid loss; if the mixture contains cerium, the oxidation is
hastened, ceric salts having the property of acting as oxygen carriers. By
boiling for a short time with potash, the oxalates may be easily transformed
into the hydroxides, which can be dissolved in dilute acids.

Formates. —On account of the considerable differences in solubility by
which they are characterised, these salts have been employed for
separations. The formates of the cerium group are considerably less soluble

than those of the yttrium group. They may be partly precipitated from
solutions of rare earth salts by addition of alkali formate—formic acid itself
causes precipitation only with salts of weak acids, e.g. the acetates—but are
best prepared by dissolving the oxides in formic acid; on concentration of
the solution, the formates of the cerium and terbium elements successively
separate, the salts of the yttrium group remaining in solution. The
separation of the terbium earths by this method was attempted by
Delafontaine; his ‘new’ element, Philippium, obtained from the mother-
liquors, was in reality a mixture of the terbium and yttrium elements, which
cannot be completely separated by the formate method.[168]
[168] See Urbain, Ann. Chim. Phys. 1900, [vii.], 19, 184.
The acetates are readily soluble in water, the yttrium salts being rather
less easily soluble than those of the cerium group. They are therefore
obtained by dissolving the oxides in acetic acid; addition of alkali acetate to
a solution of a rare earth salt gives no precipitate, even on boiling,
behaviour which is in marked contrast to the ease with which the salts of
other trivalent metals are hydrolysed under these conditions. In this respect
the rare earth elements differ also from the tetravalent elements zirconium
and thorium (and from cerium in the tetravalent state); soluble salts of the
latter, on boiling with sodium acetate, give insoluble basic acetates. Even
sparingly soluble compounds of the rare earth elements are as a rule taken
into solution by digestion with ammonium acetate.
Tartrates.—Addition of ammonium tartrate to a neutral solution of rare
earth salts throws down an amorphous precipitate, which dissolves easily in
acids, and in excess of the precipitant. In the presence of tartaric acid,
precipitation of the earths by addition of sodium hydroxide is completely
inhibited. Potassium hydroxide under these conditions gives a precipitate in
the case of the yttrium elements, though only on boiling; ammonia gives a
crystalline precipitate even in the cold with this group. These precipitates
are alkali double tartrates of the yttrium metals; the cerium elements give
no precipitate at all. In all cases, therefore, the precipitation of the
hydroxides is inhibited by the presence of tartaric acid.
A very large number of organic salts of the rare earth elements has been
prepared and examined during the past two decades, in the endeavour to
find some class of compounds which will allow of an easy separation of the
group. The benzoates, succinates, hippurates, citrates and similar relatively
simple salts first received attention, but less common acids, as e.g. the

hydroxynaphthalenesulphonic acids, have also been employed.[169] The use
of various organic acids for the separation and estimation of thorium in
presence of the rare earths is outlined in that connection (see p. 288). More
recently, the glycollates and cacodylates have been prepared. The
glycollates[170] of the cerium elements have the general formula
R(C₂H₃O₃)₃, and crystallise in crusts; they are more soluble than the yttrium
compounds, which have the formula R(C₂H₃O₃)₃,2H₂O, and crystallise in
needles. The cacodylates,[171] R₂[As(CH₃)₂O₂]₆, crystallise with 16 or 18
molecules of water, and have similar solubility relations.
[169] Erdmann and Wirth, Annalen, 1908, 361, 190; see also Pratt and James, J. Amer.
Chem. Soc. 1911, 33, 1330; Baskerville and Turrentine, ibid., 1904, 26, 46; James,
Hoben and Robinson, ibid., 1912, 34, 276, etc.
[170] Jantsch and Grünkraut, Zeitsch. anorg. Chem. 1913, 79, 305.
[171] Whittlemore and James, J. Amer. Chem. Soc. 1913, 35, 627.

The phthalates of the yttrium group have been found to be very valuable
for purposes of separation by Meyer and Wuorinen.[172] The salts are
readily obtained in solution by shaking together cold aqueous suspensions
of the rare earth hydroxides, and phthalic acid; the clear solutions when
warmed become cloudy, the organic salts hydrolysing very easily, with
separation of the hydroxides. The most positive elements naturally remain
longest in the solution, the weakly basic oxides accumulating in the first
precipitates.
[172] Zeitsch. anorg. Chem. 1913, 80, 7.

An organic compound which has proved very useful in the treatment of
the rare earths is acetylacetone, CH₃.CO.CH₂.CO.CH₃.[173] In its enolic
form, this substance forms salts with metals, which in the case of the rare
earth elements are especially characterised by the ease with which they may
be obtained, and their high crystallising power. They may be prepared by
double decomposition of neutral solutions of rare earth salts with
ammonium acetylacetone, and crystallise readily from dilute alcohol. They
have been used by Urbain in the fractionation of the yttrium group, and for
determination of molecular weights by the boiling point method; Biltz[174]
has shown that in solution they generally have the double formula
R₂(C₅H₇O₂)₆.
[173] Urbain, Bull. Soc. chim. 1897, [iii.], 17, 98; Urbain and Budischofsky, Compt. rend.
1897, 124, 618; Biltz and Clinch, Zeitsch. anorg. Chem. 1904, 40, 218.
[174] Annalen, 1904, 331, 334.

The Rare Earth Elements, and the Periodic Classification
At the time of the introduction of the periodic classification the rare earth
elements were generally believed to be divalent. This belief, which has
persisted until quite recently,[175] was based chiefly on the electropositive
character of the metals, and their general chemical resemblance to the
elements of the alkaline earths; the isomorphism of the tungstates of
calcium and the cerium elements, and of the molybdates of lead and the
cerium elements, also supports this view. The physical evidence in favour
of Mendelejeff’s view, however, is quite overwhelming; the specific heats
of the metals, the equivalent conductivities of the chlorides, and molecular
weight determinations by means of vapour densities and the boiling point
method, prove beyond doubt that the elements are in fact trivalent.
[175] See Wyrouboff, Bull. Soc. franc. Min. 1896, 19, 219; Wyrouboff and Verneuil,
Compt. rend. 1897, 124, 1230 and 1300; ibid., 1899, 128, 1573; etc.
In deciding in favour of the trivalent nature of the rare earth metals,
Mendelejeff was influenced chiefly by the fact that there was no room in
the table for divalent elements with the equivalent weights then assigned to
the cerium and yttrium elements. At that time, only the six oxides obtained
by Mosander were known; of these the accepted equivalents and atomic
weights were as follows:
Atomic
Element. Equivalent.
Weight.
Lanthanum 46 92
Cerium 46 92
Didymium 48 96
Yttrium 31 62
Erbium 56 112
the values for terbium being uncertain. If cerium be considered trivalent in
the cerous salts, its atomic weight becomes 138, that of barium being 136.
Mendelejeff placed cerium in Group IV, series 8, in the position which it
still occupies; he pointed out that the accepted equivalent must be too low,
and suggested that the atomic weight should be at least 140, almost exactly
the value accepted to-day.
This choice left the positions in Group III, series 8, horizontally before
cerium, and in Group IV, series 10, vertically below it (see figure), to be

filled by the two elements, lanthanum and didymium. No chemical
evidence being available to decide the choice, he provisionally assigned
didymium to the first (Group III, series 8), and lanthanum to the second
(Group IV, series 10) position, at the same time expressing the opinion that
didymium was probably a mixture of closely related elements. Yttrium then
fell into place in Group III, series 6, above didymium, and erbium in Group
III, series 10, below it. To the vacant space above yttrium in Group III,
series 4, he assigned the hypothetical element Eka-boron, with atomic
weight 44; this space is now occupied by scandium, which corresponds
almost exactly in properties to the metal described by the Russian chemist.
A part of the table illustrating these positions is shown in Fig. 4.
The determination of the specific heats of the metals by Hillebrand and
Norton in 1875, whilst confirming the trivalency of the elements, rendered
it necessary to alter the position of lanthanum, which was placed in Group
III, series 8, instead of didymium, which was thus left without a place. This
first indication that all the rare earth elements could not be fitted into the
table without difficulties was soon followed by the discovery of several
other members of the group, for which places could not easily be found.

Group 0 I II III IV V

A B A B A B A B A

Series 1 H

„ 2 Li Be B C

„ 3 Na Mg Al Si
Eka-
„ 4 K Ca boron Ti

„ 5 Cu Zn

„ 6 Sr Yt Zr

„ 7 Ag Cd Sn

„ 8 Ba Di? Ce

„ 9

„ 10 Er La?

„ 11 Au Hg Pb

„ 12 Th

Fig. 4.—Part of the Periodic Table, showing the positions originally assigned to the Rare
Earth Elements by Mendelejeff

It was first pointed out by Brauner in 1881 that, with the exception of
scandium (44·1) and yttrium (89·0), the rare earth elements form a zone of
increasing atomic weight between barium (137·37) and tantalum (181·5). In
1902 he proposed[176] to consider the rare earth metals as a kind of zone or
belt among the elements, comparable to the asteroids in the solar system,
extending from cerium in Group IV to tantalum in Group V in a continuous
series. The suggestion seems at first sight contrary to the whole principle of
periodic classification, but it accords very well with the anomalous position
of the rare earth group among the other elements; it is very well illustrated
in the accompanying Fig. 5, which shows an helical or space representation
of the table.
[176] Zeitsch. anorg. Chem. 1902, 32, 1.

Fig. 5.—helical representation of the periodic law

Electropositive Elements, above plane of paper, black letters on white ground. Electronegative
Elements, below plane of paper, white letters on black ground. Intermediate Elements, in plane of
paper, black letters on sectioned ground.

Group III. IV. V. VI. VII. VIII.

A B A B A B A B A B

Series 6 Yt Zr Cb Mo Ru Rh Pd

„ 7 In Sn Sb Te I

„ 8 La Ce Pr Nd Sa Eu

„ 9 Gd Tb Dy Ho Er Tm Yb

„ 10 Lu Ta W Os Ir Pt

„ 11

Fig. 6.—Part of the Periodic Table,
showing the Positions assigned to the Rare Earth Elements by Brauner in 1908

Brauner’s conception is also in accord with the physical properties of the
elements and their compounds. These vary continuously throughout the
group, and show nowhere the sudden transitions which are characteristic of
other series in the table. Benedicts[177] has collected all the data bearing on
the atomic volumes, and finds that those also vary continuously, with rise in
the atomic weights, within quite small limits, all lying between the values
for barium and tantalum. In face of all the evidence furnished by physical
and chemical properties, however, Brauner[178] has recently reverted to an
idea which he put forward in 1881, according to which lanthanum and
cerium are placed as usual in Groups III and IV, series 8, whilst the other
elements are distributed in order throughout the remaining groups, as shown
in Fig. 6.
[177] Zeitsch. anorg. Chem. 1904, 39, 41.
[178] Monats. 1881, 3, 1; Zeitsch. Elektrochem. 1908, 14, 525.

In support of this arrangement, he quotes the fact that some of the
elements appear to be able to form higher oxides in the presence of other
oxides, which act as oxygen carriers (see pp. 174, 177-8), though these
higher oxides are certainly not salt-forming. He also deduces, from the rates
of hydrolysis of the sulphates, that the elements fall into two parallel series,
according to the strengths of the hydroxides as bases, on which ground he
justifies the distribution throughout series 8 and 9. There can be no doubt,
however, that this disposition is far less in accordance with the behaviour
and properties of the rare earth elements than is the first arrangement, which
places them in a transition zone between barium and tantalum; it is
impossible, for example, to reconcile the properties of praseodymium with
those of columbium and tantalum, or to find the slightest analogy between
neodymium and molybdenum or tungsten, as the second arrangement
requires.
The analogy of the rare earth group to the elements of Group VIII has
been pointed out by many authors.[179] On the ground that the rare earth
elements cannot be spread over the table in series 8-10, Steele[180] favours
the early classification of Thomsen, according to which the elements are
divided into three groups. The first, corresponding to Groups I and II of
Mendelejeff’s table, consists of two sub-groups, each containing seven
elements[181]; the second, corresponding to the first two long series of the

periodic table, has two sub-groups, each of seventeen elements, of which
the first and last seven are analogous—these elements fall into the same
groups in the periodic table—whilst the middle three are interperiodic.
These interperiodic elements are those which Mendelejeff places in Group
VIII. The third division consists of one (or two) group(s) of thirty-one
elements; here again, the first and last seven are analogous, whilst the
interperiodic elements, which are seventeen in number, include the rare
earth metals.
[179] Compare Biltz, Ber. 1902, 35, 562.
[180] Chem. News, 1901, 84, 345.
[181] The inert gases are not included.

Steele’s idea has been extended by Werner,[182] who has drawn up a table
to illustrate it. In this classification, the elements are arranged in order of
atomic weight, but arbitrary gaps are left in such a way that similar
elements may fall into the same vertical columns, as in the periodic table.
The arrangement has the advantage that the interperiodic elements,
consisting of the rare earth elements and the elements placed in Group VIII
of the periodic table, here do fall in the middle of their respective periods,
but it has several drawbacks, and does not represent the transition of
properties from element to element so well as the helical representation of
the periodic table, which brings out most clearly the true relations between
the elements, and the anomalous position of the rare earth metals.
[182] Ber. 1905, 38, 914.

Mention must be made at this point of the theory of ‘Meta-elements’ put
forward in 1888 by Sir William Crookes.[183] From his work on the cathode
luminescence of some of the oxides (see next chapter), that author was led
to the conclusion that several of the then-accepted rare earth elements,
notably samarium and yttrium, were in reality heterogeneous, consisting of
large numbers of very closely related bodies, differing so very slightly in
properties that only the most refined methods could perceive the variations;
for these he proposed the name Meta-elements. Though it has been proved
that the differences observed by Crookes in the luminescence spectra were
really due to the presence of very small quantities of impurities, his paper is
of great interest, in that it contains a theory of evolution of the elements,
and postulates the possibility of their decay. Modern developments in
radioactivity have not only lent a curious force to these speculations, but

even support his contention that a chemical element, in the ordinary sense
of the word, is not necessarily homogeneous.[184] In the field of the rare
earths, also, the homogeneity of elements is even now continually being
called into question (see Thulium, p. 204). In any case, we have in the rare
earth elements a series of bodies in which the change of properties from one
member to another—and the consequent possibility of easy separation—is
so very slight, and so far without parallel in the whole field of chemistry,
that we are at least justified in asking whether some extension of our
ordinary conception of an element is not required.
[183] Trans. Chem. Soc. 1888, 53, 487.
[184] See Soddy, The Chemistry of the Radio-Elements, Part II., Introduction.

CHAPTER X

GENERAL METHODS OF SEPARATION
The chemist who sets out to prepare a pure compound of a rare earth
element is faced by a great difficulty. The rare earth compounds occur in
nature, as one might expect from their great similarity, as mixtures of very
complex composition. After the relatively simple separation from foreign
elements has been accomplished, the enormously greater difficulty of
separating the elements from one another has to be encountered. So great is
this difficulty, by reason of the fact that, with the sole exception of cerium,
the elements show no variation in property sufficient to allow of the use of
ordinary analytical methods, that even at the present day it is extremely
doubtful if all the elements in the yttrium group are known to us.
The methods which can be adopted in attempting a separation are of two
kinds. The first includes those processes which take advantage of the
gradual variation in basic strength of the hydroxides as the atomic weight
changes; the most important of these are fractional precipitation of the
hydroxides, and fractional decomposition of the nitrates. Fractional
precipitation of the hydroxides is generally effected by gradual addition of

ammonia, soda, magnesia, or other base, to a solution of the mixed salts;
such a solution may also be digested with the oxides obtained by ignition of
another fraction of the rare earth compounds. If the digestion be sufficiently
complete, the precipitate in each case will be richer in the less basic
hydroxides, whilst the solution will be richer in the salts of the more
electropositive elements.
The fractional decomposition of the nitrates is based on the fact that
when a mixture of the salts is heated gradually, the nitrate of the least
positive element begins to decompose first. The temperature is maintained
for some time at the point at which decomposition begins; when nitrous
fumes cease to be evolved the mixture is cooled, and extracted with water
or dilute acids. The insoluble portion—basic or superbasic nitrate (see p.
128)—will then be richer in the less electropositive elements; the solution is
evaporated, and the solid so obtained subjected to a somewhat higher
temperature, and the process repeated several times. In this way, a series of
fractions is obtained, in which the elements tend to distribute themselves in
order of electropositive character. By a sufficient number of systematic
repetitions of such steps, the elements may eventually be obtained in the
form of compounds of approximate purity, which may then be refined by
one of the methods of the second kind described below. Experience has
shown, however, that a quicker and more complete separation may
generally be effected by combining two or more methods of separation; one
method will give the best separation up to certain limits, but then becomes
much less valuable; the separation at this point is therefore taken up by
another process. A process depending on differences of basic strength of the
hydroxides is generally supplemented by a method of the second class, i.e. a
process of fractional crystallisation; where the basicity method is not used
(as, for example, in most of the recent processes for separation of the
cerium elements), two or more different methods of fractional
crystallisation will supplement one another.
The methods of the second class, which are processes of fractional
crystallisation, depend on the differences in solubility which are observed in
analogous compounds in passing from one member of the group to another.
The value of these methods, as opposed to the methods depending on
differences in basic strength, was clearly shown by Auer von Welsbach,
who in 1885 succeeded in resolving Mosander’s ‘Didymium’ into two new
elements, praseodymium and neodymium, by fractional crystallisation of

the ammonium double nitrates; since that date, much attention has been
devoted to the task of finding rare earth compounds which will lend
themselves to such processes. The method is extremely laborious, and may
involve several thousand recrystallisations, in consequence of the generally
very slight differences of solubility, and the ease with which the rare earth
compounds, being almost always isomorphous with one another, form
mixed crystals.
Whilst the method of fractional crystallisation has come into general use
for the separation of one element from another only within the last thirty
years, processes for the separation of the cerium group from the yttrium
elements, depending on differences of solubility, have long been known and
used. The most important of these, the double sulphate method, depends on
the fact that the potassium double sulphates of the cerium metals are almost
insoluble, whilst those of the terbium group are sparingly, and of the
yttrium group readily soluble in a concentrated solution of potassium
sulphate. The cerium elements may be thus completely removed from a
solution of mixed salts by addition of a crust of potassium sulphate crystals,
or of an hot concentrated solution of the same reagent. In other cases, e.g. in
the double carbonate and double oxalate processes, separation is effected by
taking advantage of the greater tendency to the formation of double salts
possessed by the yttrium metals.
In effecting a separation of closely related bodies by fractional processes,
in which a large number of repetitions of the same operation are necessary,
only the most careful and systematic procedure can avoid much waste of
valuable material; in these processes, the object of the chemist is to obtain
pure end fractions, whilst keeping the middle fractions as small as possible.
One method of procedure generally adopted is illustrated in Fig. 7, which
represents a fractional crystallisation of a mixture of four or five substances,
α, β, ... φ; the separations being usually conducted in such a way that
subgroups of three, four or five elements are first obtained, these being then
further fractionated to obtain the pure elements. In the diagram, crops of
crystals are represented by crosses, the mother-liquors by circles; for the
sake of illustration, the process is made to appear as simple as possible.

Fig. 7

The mixture is dissolved up, and allowed to crystallise; the crystals are
filtered off, the filtrate concentrated, and a second crop obtained; this is
repeated until five or six crops of crystals have been obtained. These, with
the mother-liquor, constitute series A. The first fraction is now
recrystallised; it yields a crop of crystals, fraction 1 of series B, and a
mother-liquor, which is added to fraction 2 of series A, as indicated by the
dotted arrow and circle; on recrystallisation of this mixture, a crop of
crystals, fraction 2 of series B, is obtained, together with a mother-liquor,
which is recrystallised with fraction 3 of series A. In this way, by continued

repetition, series are obtained, of which each contains one fraction more
than its predecessor; the least soluble constituent is thus concentrated in the
fractions represented on the left of the diagram, whilst the most soluble
accumulates in the mother-liquors. After a greater or smaller number of
series have been traversed, according to the differences in solubility, the end
fractions in each series will be pure. These are no longer fractionated, and
the number of fractions in each series begins to diminish, as shown on the
diagram. The middle fractions will contain the compounds of intermediate
solubility; these may be separated by further fractionation on the same
lines, or may perhaps be better treated by a different or modified process.
In a modification of the method, each fraction of series A is recrystallised
separately, yielding a crop of crystals, and a mother-liquor; series B is then
built up by adding to the crystals from fraction 2 the mother-liquor from
fraction 1, to the crystals from fraction 3 the mother-liquor from fraction 2,
and so on; the fractions in this series are then recrystallised separately, and
the third series built up by the similar combination of the crystals and
mother-liquors.
Similar systematic methods of procedure must be adopted in working out
any method of fractional separation; it can at once be seen that where, as in
the rare earth group, only small variations in properties exist, much time
and care must be expended, if pure products are required.
Since the development of the methods of spectrum analysis, the difficulty
of testing the efficiency of a method of separation, and of examining the
purity of the products obtained, has been greatly lessened. The only reliable
test at the disposal of the earlier chemists was the determination of the
equivalent weight, which still constitutes an important check on the modern
methods. Some account of the methods available for the control of the
methods of separation is essential in a general account of the rare earths; but
before describing these, it will be convenient to give a short description of
the methods used in the extraction of the elements from the rare earth
minerals.

Extraction of the Rare Earths from Minerals
With the exception of those containing large proportions of columbium,
tantalum, and titanium, the rare earth minerals are easily decomposed by
acids. The silicates, as a general rule, can be satisfactorily treated with

hydrochloric acid in the ordinary way, but for large quantities, the use of
sulphuric acid is more desirable. The more refractory minerals are
completely decomposed by fused alkali hydrogen sulphate; sodium
bisulphate is more suitable for this purpose than the potassium compound,
the sodium double sulphates of the rare earth elements being more soluble
than the potassium salts. Hydrofluoric acid also attacks the refractory
minerals very readily; the rare earths, in this case, are left as the insoluble
fluorides.
After decomposition with sulphuric acid or bisulphate, the cold residue is
extracted with water, the rare earth sulphates or double sulphates being
removed in solution. Digestion with nitric acid may be necessary at this
stage, if titanium, columbium, etc., are present; after filtration, the solution
is evaporated to dryness, and the residue extracted with dilute hydrochloric
acid. The solution is saturated with sulphuretted hydrogen to remove lead,
copper, bismuth, molybdenum, etc., and treated in the usual way with
ammonium chloride and ammonia. The precipitate is washed, and dissolved
in hydrochloric acid, the solution heated to about 60°, and the rare earths
precipitated by addition of excess of oxalic acid, which holds in solution
any zirconium which may be present. In the presence of phosphates, e.g. in
the treatment of monazite or xenotime, the precipitate of oxalates should be
ignited to the oxides, these dissolved in acid, and a second precipitation
with oxalic acid effected; this treatment is necessary to remove phosphoric
acid completely.

Preliminary examination of the earth mixture. —Before a method of
separation can be decided upon, some knowledge of the composition of the
mixture to be treated must be obtained. The nature of the mineral used for
the extraction will, as a rule, afford useful information. It is known that in
some minerals the cerium group, in others the yttrium group, predominates
more or less completely; certain minerals, also, are known to be rich in
elements of one or another subgroup. An approximate knowledge of the
relative proportions of the cerium, terbium, and yttrium groups will be
afforded by a rough double sulphate separation; thorium, zirconium, and
scandium come down with the cerium earths. For approximate separation,
Urbain[185] proposes the use of the ethylsulphates. The yttrium elements can
be quickly separated in an approximate manner by fractional precipitation
of the hydroxides with magnesia. The successive fractions obtained by

these methods are examined spectroscopically; from the results, the
composition of each, and so of the original mixture, may be roughly
deduced.

[185] Ann. Chim. Phys. 1900, [vii.], 19, 184.

The Spectrum Examination
In no department of chemistry have the methods of spectrum analysis
proved of more value than in the field of the rare earths. They provide the
chemist with a means of following and controlling his processes of
separation which is far more delicate and decisive than the older method of
determining the equivalent weight. Whilst the examination of emission
spectra, and especially of arc spectra, is of decisive value in every case, it
has the disadvantage of requiring delicate and complicated apparatus and
great experimental skill; wherever possible, therefore, the examination of
the absorption spectra is preferred, though this is useful only for a few of
the elements, and varies considerably with the conditions employed.

The Absorption Spectra. —Absorption in the visible region of the
spectrum is observed only with those rare earth compounds which are
coloured, and is of value, therefore, chiefly for identification in the case of
praseodymium and neodymium among the cerium elements, and of erbium
among the yttrium metals; these give characteristic absorption bands, even
in dilute solution. The absorption spectra of the rare earth compounds are
highly characteristic, the bands being well defined and sharply bounded,
whereas coloured compounds of the common elements show general
absorption, or at best diffuse bands, under the same conditions.
In observing an absorption spectrum, the light from a Nernst lamp, or
incandescent burner, is passed through a layer of a suitable solution of the
coloured compound, of known concentration and thickness, and after
collimation is analysed by a suitable prism; the spectrum is observed by a
telescope in the ordinary way. Where accurate readings are not required, as,
for example, in testing for the presence or absence of a particular element,
the position of the bands may be read to a sufficient degree of accuracy by
means of a scale, the image of which is adjusted to coincide with the
spectrum as seen through the eyepiece; but in mapping a spectrum
accurately, more refined methods must of course be used. The photographic
method, in which a photograph of the spectrum is taken on a plate which
bears, for purposes of measurement, a comparison spectrum of known lines,

is very convenient for examining the absorption in the violet and ultraviolet
regions.
The intensity, and to some extent also the position, of bands in an
absorption spectrum may vary considerably, according to the conditions
employed. Of the various factors which must be considered, the
concentration of the solution, the thickness of the layer used, the nature of
the solvent, and of the acid radicle, and the presence of other earths are the
most important. The concentration of the solution, and the thickness of the
layer, which together constitute the Optical Density, must be so adjusted
that the absorption is neither too strong nor too weak; in the first case the
sharp bands tend to merge into broad diffusion areas, and details are
obscured, whilst in the second case the presence of coloured compounds
which do not show strong absorption bands may be overlooked.
The nature of the acid radicle has considerable influence on the position
of the absorption maxima, the general rule being that the bands are shifted
towards the red end of the spectrum as the molecular weight of the
compound used increases. Naturally, also, the nature of the solvent has an
important effect, all the usual phenomena which must be considered in the
measurement of the physical properties of substances in solution coming
into play; electrolytic dissociation, hydration, dissociation and the
formation of complexes, for example, are all important factors. The
presence of colourless earths has also been found to cause important
differences. It follows, therefore, that for the chemist, the absorption spectra
can be considered as a valuable aid only in detecting the presence or
absence of the three elements which give the strongest and most
characteristic absorption bands, viz. praseodymium, neodymium, and
erbium, and that conclusions regarding the quantitative composition of
mixtures must be drawn with the utmost caution.

The Emission Spectra: Spark Spectra. —The factors which tend to
limit the value of the absorption spectra for analytical purposes, for the
most part disappear when the emission spectra are employed. In the case of
the spark spectra, indeed, great differences are observed according to the
conditions and method of experiment; but the arc spectra are practically
invariable under all conditions, and hence they constitute the ultimate test in
all cases. The spark spectra are observed when one terminal—the cathode—
of an induction coil is embedded in the oxides to be examined, and the

discharge then passed. The discharge is also frequently passed between
platinum poles partly immersed in a strong solution of a salt of the element
under examination; a form of apparatus very suitable for this method of
observation has been described by Sir W. Crookes.[186] The spectra so
obtained are in a high degree characteristic, but they vary very considerably
with the form and dimensions of the coil, the length and cross-section of the
wires, the potential difference employed, and so on. An entirely new
spectrum also is obtained in many cases by mere reversal of the current;
under these conditions, a phosphorescent appearance is observed, the
spectrum of which—reversed spark spectrum of de Boisbaudran—has been
found in many cases to resemble the cathode luminescence spectra of
Crookes.
[186] Proc. Roy. Soc., 1903, 72, 295.

The Arc Spectra. —The final criterion of purity in the examination of a
rare earth element is in almost all cases the arc spectrum. Since for some of
the elements, especially in the yttrium group, the entire spectrum has not
yet been accurately mapped out, spectra are generally observed frequently
throughout the course of a fractionation; by this means, the separation can
be followed by the disappearance of some lines, and the appearing or
strengthening of others, and such examinations have led occasionally to the
discovery of new elements (see, for example, under Separation of ytterbium
earths, p. 205). Such determinations, however, require much time and
extensive and complicated apparatus.
Carbon electrodes are generally employed, and it is immaterial in this
case which is the anode, and which the cathode. The lower carbon is
hollowed out, and the space filled with the oxide or sulphate of the element
or mixture to be examined; or the electrode may be impregnated with a
concentrated solution of a salt. The light is examined by means of a
diffraction grating, and the spectrum photographed on a plate which bears a
comparison spectrum for measurement. The lines are most numerous in the
violet and ultraviolet regions, and the most characteristic spectra are given
by the colourless earths. The method is naturally more delicate for some
elements than for others; the great persistency of the scandium line
3613·984, for example, was found very valuable by Crookes and by
Eberhard in the examination of various rocks and minerals for that element,

whilst other intense and persistent lines have served for the detection of
various rare earth elements in the sun and many stars.

The Cathode Luminescence Spectra. —The phenomenon of cathode
luminescence, which was observed and very fully investigated by Sir
William Crookes, and which led that author to his theory of Meta-elements,
is one of the greatest scientific interest. Crookes observed that certain of the
rare earths, when subjected to the action of cathode rays in a vacuum tube,
exhibit a brilliant phosphorescence, which, when examined by the
spectroscope, show characteristic spectra, which differ greatly for fractions
of apparently identical chemical composition, and are otherwise
distinguishable by physical properties. The researches of Lecoq de
Boisbaudran, and the more recent work of Baur and Marc,[187] have shown
that this luminescence is observed when a small quantity of a coloured earth
is present with a very large quantity of a colourless earth, the maximum
phosphorescence being produced by about 1 per cent. of the coloured earth,
or ‘phosphorogen.’ The question has recently been very fully examined by
Urbain.[188] He shows that the sensitiveness of the phenomenon is so great
that it cannot be employed for the ordinary purposes of chemical analysis,
one part in a million of the phosphorogen being sufficient to cause a clearly
perceptible luminescence in a pure colourless oxide.
[187] Ber. 1901, 34, 878.
[188] Ann. Chim. Phys. 1909, [viii.], 18, 222; see also Introduction à l’étude de la
Spectrochimie, pp. 145 et seq.

The Magnetic Susceptibility. —The fact that the rare earths differ very
considerably from one another in their magnetic properties has been known
for several years,[189] and has recently been employed by Urbain and
Jantsch[190] as a means of identification, and a test of purity, and for
following processes of fractionation. The magnetic susceptibility reaches a
minimum at samarium, and rises very sharply on either side of that element,
so that the presence of the closely related elements, neodymium on the one
side, and europium and gadolinium on the other, which differ only very
slightly from samarium in atomic weight and solubility, can easily be
detected by this means. The property is highly additive, and can be used,

therefore, to estimate the relative proportions of two oxides in a mixture;
the determinations are said to be easily and quickly carried out.
[189] See Meyer, Monats. 1898, 20, 369 and 793.
[190] Compt. rend. 1908, 147, 1286; see also Urbain, ibid., 1910, 150, 913.

When the elements are considered in order of atomic weight, the
coefficient reaches a maximum at neodymium in the cerium group, and
again at dysprosium (or holmium) in the yttrium group:—[191]
Coefficient of
Atomic magnetisation
Element. for the oxide.
Weight.
x × 10⁻⁶
Scandium 44·1 -0·05
Yttrium 89·0 -0·14
Lanthanum 139·0 -0·18
Neodymium 144·3 33·5
Samarium 150·4 6·5
Europium 152·0 33·5
Gadolinium 157·3 161
Terbium 159·2 237
Dysprosium 162·5 290
[191] See Urbain and Jantsch, loc. cit.; the values for lanthana, scandia, and yttria were
determined by Wedekind (see Meyer and Wuorinen, Zeitsch. anorg. Chem. 1913, 80, 7).
Erbium, thulium, ytterbium, and lutecium appear in descending order at
the end of the series, but no figures are given.
The most interesting application of the property has been Urbain’s
discovery of the new element Celtium (see p. 207).

The Equivalent Weight Determination
The determination of the mean equivalent weight, which was for the
earlier chemists the only reliable method of controlling their fractionations,
is still of considerable importance for this purpose, especially in the yttrium
group, in which the differences in atomic weights are more considerable
than among the cerium metals. Great importance, moreover, still attaches to
these determinations, since they serve to fix the atomic weights; save that
the methods used in an atomic weight determination are somewhat more

elaborate and refined than those used when it is desired merely to test a
fractionation, the same processes apply in both cases.
The methods which have been most commonly used are those based on a
determination of the ratio R₂O₃ : R₂(SO₄)₃, and these are of two kinds, the
synthetic and the analytical. The first, in which a known weight of the oxide
is converted into the sulphate, has been most used for the most strongly
basic oxides, since with these it is difficult to remove the last traces of
sulphuric anhydride from the oxide by heat. The oxides are best obtained
from the oxalates, which are precipitated from an acid solution of the
nitrates, washed thoroughly with water, alcohol and ether in succession,
dried, and ignited in a tarred platinum crucible. The oxide is best dissolved
in dilute hydrochloric or nitric acid on the waterbath, a slight excess of
sulphuric acid being added only when a clear solution has been obtained;
the liquid is then heated gradually to 300°, and finally in the electric furnace
at 450°-550° until constant in weight. If sulphuric acid be added directly to
the weighed oxide, particles of the latter may become completely coated
with the insoluble sulphate, and so escape the action of the acid.
In the analytical method, a known weight of sulphate is ignited to the
oxide, and weighed as such. This method is most suitable for the less basic
members of the yttria earths, of which the sulphates can be completely
decomposed without difficulty at a red heat. By the use of the microbalance,
a sufficiently accurate determination can be carried out by either of these
methods in little more than half an hour, as the chemical changes are
exceedingly rapid where only small quantities are employed, and no time is
required to allow the vessels and solids to cool. Using the microbalance,
Brill[192] has carried out a series of experiments to determine the limits of
temperature within which the various steps of the process should be carried
out. He finds that a temperature of 400°-550° is required to decompose the
last traces of acid sulphate, and give the pure neutral sulphate. Between the
temperatures of 850° and 950°, basic salts are formed, from which the last
trace of sulphuric anhydride is expelled at 900°-1150°; the precise
temperature required in each case depends, of course, on the basic strength
of the oxide in question.
[192] Zeitsch. anorg. Chem. 1905, 47, 464.
The determination of equivalents by means of the ratio R₂O₃ : R₂(C₂O₄)₃,
has been brought to a high degree of accuracy by Brauner.[193] A weighed
quantity of the carefully prepared oxalate is ignited, with suitable

precautions, to the oxide, in a tarred platinum crucible. A second weighed
specimen of the same oxalate preparation is dissolved in dilute sulphuric
acid, and titrated at 60° with permanganate, which is standardised against
pure ammonium oxalate.
[193] Ibid. 1903, 34, 103, 207.
Of the methods of volumetric analysis which have been proposed, that
put forward by Feit and Przibylla appears to be the most suitable. A
convenient quantity of oxide, which has been ignited until constant in
weight, is dissolved by gently heating with a known excess of N2 sulphuric
N
acid, in a conical flask of Jena glass. The excess of acid is titrated with 10
sodium hydroxide, using methyl orange as indicator. This method, which
has the advantages of ease and quickness, is very reliable, if suitable
precautions are taken, in the case of the more strongly basic oxides; but
with the least strongly basic members of the yttria group, the erbia and
ytterbia oxides, the end point is not very sharp, whilst with the weakly basic
scandia, the method breaks down entirely.[194]
[194] Zeitsch. anorg. Chem. 1905, 43, 202; 1906, 50, 249.

CHAPTER XI

THE CERIUM GROUP—CERIUM
The extraction of the rare earth elements from minerals, by which they
are obtained in the form of the oxalates, and the methods of bringing these
into solution, have already been described. From the solution, before any
separation of the rare earths is attempted, thorium should be removed; for
this purpose, any of the methods described under estimation of thorium (see
p. 286) may be used, the most convenient being the peroxide precipitation
of Wyrouboff and Verneuil.

The solution is then treated with potassium sulphate until the absorption
bands of didymium (praseodymium and neodymium) can no longer be
observed, or appear only very faintly, when a layer of the solution is
examined with a spectroscope; the precipitate then consists of the potassium
double sulphates of the cerium with some of the terbium elements. If the
mixture is very rich in the cerium elements, and correspondingly poor in the
yttrium elements—as, for example, the mixture of earths obtained from
monazite—Drossbach[195] recommends a preliminary separation by means
of the double carbonates; the double sulphate method may then be
employed to remove the last of the yttrium and most of the terbium
elements. The sparingly soluble double sulphates of the cerium metals may
be transformed into the hydroxides by digestion with potassium hydroxide,
and these taken into solution, after washing, by hydrochloric or nitric acid.
[195] Ber. 1900, 33, 3506.

Cerium, Ce = 140·25
Of all the rare earth elements, cerium, by virtue of its property of forming
ceric salts corresponding to the dioxide CeO₂, is the one most easily
separated and obtained in the pure state. In those compounds in which it is
tetravalent, cerium functions as a much less strongly electropositive
element than in the cerous compounds, and all the methods of separation
are based on this fact. Mosander, who first demonstrated that the old ‘ceria’
was a mixture, separated the element by treating a suspension of the
hydroxides in potassium hydroxide with chlorine; yellow ceric hydroxide
remains undissolved, whilst the other elements go into solution as the
chlorides and hypochlorites. This method was extensively used until quite
recently; it has the advantage of separating the cerium completely, but the
product is very impure, and several repetitions are required to give good
results. The basic nitrate method, which is now used on the commercial
scale in extracting cerium from monazite (see p. 284), is also due to
Mosander, though it has been employed subsequently by many workers.
Several methods take advantage of the ease with which the ceric salts, as
compared with salts of the trivalent elements, may be hydrolysed.
Brauner[196] dissolves the oxides in nitric acid, and after removal of excess
of acid, boils with a large volume of water—basic ceric nitrate is thrown
down, the other elements remaining in solution as nitrates. The precipitate

is redissolved, and the process repeated until the cerium is found
spectroscopically to be free from didymium. The hydrolysis of the ceric salt
may be effected more quickly and completely by the addition of ammonium
sulphate or magnesium acetate.[197] James[198] boils the solution of the
nitrates with potassium bromate, keeping the whole neutral by addition of
powdered marble; the cerium is completely and very quickly precipitated as
basic nitrate.
[196] Trans. Chem. Soc. 1885, 47, 879.
[197] Meyer and Koss, Ber. 1902, 35, 672.
[198] J. Amer. Chem. Soc. 1912, 34, 757; this paper gives a complete scheme for a full
separation of all the elements.

An interesting method is due to Koppel[199]; the oxides are dissolved in a
solution of hydrogen chloride in methyl alcohol, and treated with pyridine,
when the sparingly soluble double chloride, (C₅H₅NH)₂CeCl₆, separates,
and may be obtained pure by recrystallisation from alcohol and ether. The
permanganate method of Drossbach, which is used on the commercial
scale, is described on p. 285.
[199] Zeitsch. anorg. Chem. 1898, 18, 305.

The cerium compounds obtained by these methods are purified by
transformation into the anhydrous sulphate, which is dissolved in ice-water;
when this solution is allowed to come slowly to room temperature, the pure
octohydrate separates. Pure cerium salts should show no trace of absorption
when concentrated solutions are examined spectroscopically; on ignition,
the oxide obtained should be almost colourless, having at most a faint
yellow tinge. A reddish or brownish-red shade indicates the presence of
praseodymium. An arc spectrum examination will generally show the
presence of lanthanum, which occurs in traces even in the most carefully
purified cerium preparations.
The preparation and properties of metallic cerium have already been
described (see p. 114); for an account of the pyrophoric alloys, see p. 314.

The Cerous Compounds
The salts of trivalent cerium are very similar to those of the other rare
earth elements, and a detailed description of them is therefore unnecessary.
The sesquioxide, Ce₂O₃, cannot be obtained by ignition of the oxalate,
nitrate, or other similar salt, since these decompose at high temperatures

with formation of the dioxide, CeO₂. It has been prepared by the reduction
of the dioxide with calcium;[200] it has a great affinity for oxygen, and
readily absorbs the gas when exposed to moist air. Cerous hydroxide,
Ce(OH)₃, obtained by addition of alkali to solutions of cerous salts, has also
strong reducing properties,[201] and can only be prepared and preserved
when oxygen is carefully excluded. It has been obtained as a perfectly white
solid by the action of water on the carbide;[202] when dried in an inert
atmosphere, it yields a perfectly white oxide. In presence of air, it darkens,
assuming a reddish-violet colour, which passes into yellow as the oxidation
becomes complete. The oxidation proceeds more quickly in presence of
potash or soda, ceric hydroxide, Ce(OH)₄, being formed; in presence of
potassium carbonate, however, a dark-coloured peroxyhydrate is formed by
autoxidation. The colour so produced disappears on shaking if an ‘acceptor’
is present, ceric hydroxide being left; if the acceptor cannot reduce this, the
solution after shaking loses the power of re-forming the dark peroxide, but
if the acceptor can reduce the ceric compound to cerous hydroxide, the
solution after shaking regains the power of forming the peroxide which is a
property of the lower hydroxide.
[200] Burger, Ber. 1907, 40, 1652.
[201] Dennis and Magee, J. Amer. Chem. Soc. 1894, 16, 649; also Biltz and Zimmerman,
Ber. 1907, 40, 4979.
[202] Damiens, Compt. rend. 1913, 157, 214.

Cerous nitride, CeN, has been prepared by Moissan[203] by the action of
ammonia on the heated carbide; it can also be obtained by heating the
hydride in a stream of nitrogen.[204] Muthmann and Kraft also state[205] that
it can be prepared by heating metallic cerium in the gas, the metal burning
with the liberation of much energy in the form of heat and light; but Dafert
and Miklanz[206] deny that it can be obtained in this way. Cerium nitride is a
lustrous, brass yellow to bronze coloured solid, stable in dry air, but at once
attacked by moist air, with evolution of ammonia, and formation of the
dioxide. When moistened in air with a few drops of water, the substance
reacts violently, becoming heated to redness. Alkalies and acids decompose
it, with formation of cerous compounds.
[203] Compt. rend. 1900, 131, 865.
[204] Dafert and Miklanz, Monats. 1912, 33, 911.
[205] Annalen, 1902, 325, 261.
[206] Loc. cit.

The sulphide, Ce₂S₃, has been prepared by Biltz[207] by heating the
sulphate to a red heat in a current of sulphuretted hydrogen; he describes it
as a red powder. The chloride, CeCl₃, combines with ammonia with
evolution of heat even at a temperature of -80°. Five additive compounds
are described;[208] they are white powders, decomposed by water.
[207] Ber. 1908, 41, 3341.
[208] Barre, Compt. rend. 1913, 156, 1017.

The solubility curve of the various sulphate hydrates has already been
given (see p. 125). Various double sulphates with ammonium sulphate, and
the sulphates of sodium, potassium, thallium and cadmium are known. The
cadmium double compound has the composition Ce₂(SO₄)₃,CdSO₄,6H₂O,
and is prepared by mixing solutions of the simple salts in presence of
sulphuric acid. Many double nitrates have been prepared; these are for the
most part stable, highly crystalline compounds, easily soluble in water and
alcohol. With the nitrates of the common divalent metals, cerous nitrate
forms a series of double salts of the general formula
2Ce(NO₃)₃,3R(NO₃)₂,24H₂O, where R = Mg, Mn, Co, Ni, or Zn; these form
an isomorphous series, crystallising in the hexagonal system. The
acetylacetone compound melts at 131°-132°.
In the presence of hydrogen peroxide in the cold, ammonia throws down
from solutions of cerous salts a reddish-brown peroxyhydrate, Ce(OOH)
(OH)₃,[209] which on heating loses oxygen, and yields ceric hydroxide. The
reaction is very delicate, and may be used as a test for cerium. If the
precipitate be treated with acids in the cold, ceric salts are first obtained, but
these are at once reduced, in the acid solution, by the hydrogen peroxide
formed, so that cerous salts remain; ceric salts may be obtained by first
boiling the suspension of the peroxyhydrate and treating the ceric hydroxide
so obtained with acids.
[209] Pissarjewski, Zeitsch. anorg. Chem. 1902, 31, 359.

The Ceric Compounds
The ceric salts are much more readily hydrolysed than the cerous salts,
and show a great tendency, in dilute solution, to pass over into the latter. So
great is this tendency that a solution of a ceric salt acts as if it were
supersaturated with oxygen; ceric sulphate, for example, in dilute solution
slowly evolves oxygen, whilst the chloride evolves chlorine. In

consequence of this behaviour, ceric compounds have a very powerful
oxidising action. The ceric salts are yellow to red in colour; their solutions
are strongly acid, owing to the ease with which the salts hydrolyse, and on
boiling deposit insoluble basic salts.
Beside the methods which have already been mentioned, ceric
compounds may be prepared from cerous by oxidation with sodium
peroxide, bismuth tetroxide, ammonium persulphate, etc. In electrolysis of
cerous salts, also, ceric compounds are obtained at the anode.
Ceric hydroxide, Ce(OH)₄, is obtained as a gelatinous yellow precipitate
on the addition of alkali to a solution of a ceric salt, or by the oxidation of
cerous hydroxide. The freshly prepared precipitate dissolves in nitric acid
with a reddish colour; hydrochloric acid reduces it, with evolution of
chlorine, and formation of cerous chloride, whilst sulphuric acid dissolves it
with partial reduction, oxygen being evolved. If a solution of a ceric
compound be dialysed for some days, a clear neutral solution is obtained,
which contains the hydroxide in the colloidal condition; by evaporation of
the solution, a gummy mass is obtained, which dissolves again in water to a
clear solution. Electrolytes rapidly cause coagulation.
Cerium dioxide, CeO₂, is obtained by the ignition of any salt of cerium
with a volatile acid, or by burning the element in oxygen; the latter reaction
produces a very intense and blinding light, on account of which cerium
compounds are often suggested for use in flashlight powders (see p. 319).
The pure oxide should be almost white, or at most a very faint yellow, but
the exact shade and appearance vary according to the method and
temperature employed in preparation, doubtless by reason of the possibility
of different degrees of polymerisation.[210] The oxide can act as an oxygen
carrier towards other substances, notably towards other oxides of the rare
earth group,[211] but the phenomena have not been fully elucidated. In virtue
of this property, the dioxide has been proposed as a substitute for platinised
asbestos in Dennstedt’s method for the combustion of organic bodies.[212]
[210] See in this connection Wyrouboff and Verneuil, Compt. rend. 1898, 127, 863; ibid.
1899, 128, 501; and in La chimie des terres rares, ‘Conférences de la Société chimique
de Paris,’ Paris, 1903.
[211] See Meyer and Koss, Ber. 1902, 35, 3740.
[212] Bekk, Ber. 1913, 46, 2574.

The ignited oxide is soluble in nitric or hydrochloric acid only in
presence of a reducing agent. Concentrated sulphuric acid converts it into

ceric sulphate; fused bisulphate attacks it more readily. In the crystalline
form, obtained by fusing the amorphous form with borax, or a suitable salt,
[213] it is extremely resistant to acids and to alkalies.

[213] See, e.g. Sterba, Ann. Chim. Phys. 1904, [viii.], 2, 193.
By heating the dioxide in a stream of hydrogen, care being taken to
exclude air, a dark blue oxide, of which the composition corresponds
approximately to that required by the formula Ce₄O₇, is obtained.[214] This
substance has strong reducing properties; when warmed in air, it glows,
forming the dioxide, and reduces carbon dioxide when heated in a current
of that gas. This intermediate oxide is said to correspond in composition to
the violet hydroxide which is obtained as an intermediate product in the
oxidation of cerous to ceric hydroxide, and which is said to yield the blue
oxide, Ce₄O₇, when dried in vacuo.
[214] Sterba, Compt. rend. 1901, 133, 221; Meyer, Zeitsch. anorg. Chem. 1903, 37, 378.
The disulphide, CeS₂, has been obtained by Biltz[215] by prolonged
heating of anhydrous cerous sulphate in a current of sulphuretted hydrogen
at a dull red heat; it is a dark, yellowish-brown, crystalline solid, which on
treatment with hydrochloric acid yields hydrogen persulphide.
[215] Ber. 1908, 41, 3341.
Halogen salts.—No halogen compounds are known in the free state,
except the fluoride, CeF₄,H₂O, which was obtained by Brauner as a
yellowish-brown mass, by the action of hydrofluoric acid on the hydroxide.
A double fluoride, 2CeF₄,3KF,2H₂O, was prepared by the same author by
dissolving the hydroxide in potassium hydrogen fluoride; it is insoluble in
water. By dissolving a ceric salt in concentrated hydrochloric acid, a dark
red solution is obtained, which is believed to contain the unstable complex
acid, H₂CeCl₆; this decomposes slowly in the cold, more quickly on
warming, with evolution of chlorine, and formation of cerous chloride.
Several double compounds of ceric chloride with hydrochlorides of organic
bases have, however, been obtained.
Ceric sulphate, Ce(SO₄)₂, is obtained by the action of concentrated
sulphuric acid on the dioxide. It is a deep yellow crystalline powder,
dissolving readily in water to a brown solution, which has a strongly acid
reaction; on warming or diluting, a basic sulphate separates. The solution
slowly evolves oxygen, and therefore always contains cerous compounds.
On evaporation, a cero-ceric acid sulphate of the formula

HCeiiiCeiv(SO₄)₄,12(13 ?)H₂O first separates; the hydrated sulphate
Ce(SO₄)₂,4H₂O, being more soluble, separates on further concentration.[216]
The relative amounts of the two compounds obtained depends on the
temperature and the concentration of acid in the solution; if both these
factors are kept low, the almost pure hydrated sulphate can be at once
obtained. This separates in yellow crystals belonging to the rhombic
system; it is readily soluble in water. The mixed acid salt is less soluble, and
forms orange prisms and needles, which cling tenaciously to sulphuric acid.
Other complex and double salts have also been obtained. When, for
example, silver nitrate is added to a warm solution of the sulphate in
concentrated sulphuric acid, a bright orange-yellow precipitate of the salt
10Ce(SO₄)₂,6Ag₂SO₄ is obtained.[217]
[216] See Meyer and Aufrecht, Ber. 1904, 37, 140; Brauner, Zeitsch. anorg. Chem. 1904,
39, 261.
[217] Pozzi-Escot, Compt. rend. 1913, 156, 1074.

Neutral ceric nitrate is unknown. A basic nitrate, Ce(NO₃)₃OH,3H₂O, is
obtained in red crystals by evaporation of a solution of ceric hydroxide in
strong nitric acid. The solid is readily soluble in water, forming a yellow,
acid solution, which becomes paler by hydrolysis, on warming or on
standing. The course of the hydrolysis is also indicated by the action
towards acids, and towards hydrogen peroxide.[218] A freshly prepared ceric
salt, on addition of acid, becomes immediately much darker in colour,
whereas the colour change is very slow, if considerable hydrolysis has
occurred. Similarly, hydrogen peroxide at once reduces a freshly prepared
solution, forming colourless cerous salts, whilst if much hydrolysis has
occurred, deeply coloured higher oxidation products are at first formed, and
these lose their colour only slowly.
[218] Meyer and Jacoby, Zeitsch. anorg. Chem. 1901, 27, 359.
The double ceric nitrates[219] are a large and very important class of
compounds; they are the most stable of the ceric salts. With nitrates of the
monovalent metals, ceric nitrate forms double nitrates of the type
R₂Ce(NO₃)₆; these are deep red hygroscopic substances, crystallising in the
monoclinic system, readily soluble in water and alcohol, but dissolving only
sparingly in nitric acid. The ammonium salt is important for the separation
of cerium. A series of double nitrates with the nitrates of manganese,
magnesium, zinc, nickel, and cobalt has the general formula

RCe(NO₃)₆,8H₂O, but these are much less stable in solution than the alkali
double salts.
[219] Meyer and Jacoby, loc. cit.

Atomic Weight of Cerium
No less than twenty-eight separate determinations of the atomic weight
of cerium have been carried out. The earlier determinations are rendered
unreliable by the almost certain presence of other elements, and
Brauner[220] has shown that some of the methods employed in later work
give erroneous results.
[220] Trans. Chem. Soc. 1885, 47, 879; also Zeitsch. anorg. Chem. 1903, 34, 207.

A very careful determination was made by Robinson in 1884.[221] Cerium
oxalate was heated in a stream of dry hydrogen chloride, mixed with carbon
dioxide, and the anhydrous chloride freed from traces of acid in a vacuum
over chalk. The weighed chloride was then dissolved in water, and titrated
with silver nitrate. He obtained the value 140·26; recalculation from his
data with the modern values for silver and chlorine give 140·19. Brauner
points out that this result is too low, since no account was taken of the
solubility of silver chloride in water. In the following year, Brauner[222]
determined the ratio Ce₂(SO₄)₃ : 2CeO₂, and obtained the atomic weight
140·22. Wyrouboff and Verneuil[223] in 1897 disputed Brauner’s work, and
as a result of several determinations gave the values 139·21, 139·43, and
139·50; their determinations, however, varied very considerably, and the
work has been severely criticised by Brauner. In 1903, the latter author and
Batěk[224] obtained the values 140·21 and 140·27 by the sulphate and
oxalate methods respectively; whilst in the same year, using the same
methods, Brauner[225] obtained from three independent series of
determinations the values 140·25, 140·24, and 140·25.
[221] Proc. Roy. Soc. 1884, 37, 150.
[222] Loc. cit.
[223] Compt. rend. 1897, 124, 1300.
[224] Zeitsch. anorg. Chem. 1903, 34, 103.
[225] Zeitsch. anorg. Chem. 1903, 34, 207.

The International Atomic Weight Committee have accepted the value
140·25 since 1904.

Detection and Estimation of Cerium
The detection of cerium in a mixture of earths is a comparatively simple
matter, as it has several distinctive reactions. The brown colour of the
peroxy-compounds has been suggested as a convenient test by several
authors. This may be observed when ammonia is added to a cerous salt in
presence of hydrogen peroxide. In the presence of a large excess of foreign
earths, very dilute ammonia should be added, drop by drop, with continuous
shaking, until a small permanent precipitate remains; this will be rich in the
weakly basic ceric hydroxide, and on addition of the peroxide solution will
show the colour clearly.[226] For very small quantities of cerium, the neutral
solution is added to warm concentrated potassium carbonate solution, and
one or two drops of dilute hydrogen peroxide added to the clear liquid; the
yellow colour is then very characteristic.[227]
[226] Marc, Ber. 1902, 35, 2370.
[227] Meyer, Zeitsch. anorg. Chem. 1904, 41, 94.

Biltz and Zimmerman[228] employ the reducing powers of cerous
hydroxide; ammoniacal silver nitrate is added to the neutral solution of the
cerous salt, and the mixture warmed. Dilute solutions (1-2 mgms. per litre)
give a brown colour, concentrated solutions a black precipitate. The
oxidation of an ammoniacal solution of the tartrate by air or hydrogen
peroxide, by which an intense yellowish brown colour is developed, has
been recently suggested by Wirth[229] as a very delicate test for the element.
[228] Ber. 1907, 40, 4979.
[229] Abstr. Chem. Soc. 1913, 104, ii. 712.

Spectrum analysis.—Cerous salts show no absorption, ceric salts general
absorption of the violet end of the spectrum. Arc spectrum—see Exner and
Haschek,[230] Eder and Valenta,[231] and Cooper.[232] The emission spectrum
of cerium is especially rich in lines; for identification, the following may be
used:
4150·11 4386·95 4539·90
4186·78 4460·40 4562·52
4222·78 4479·52 4572·45
4296·88 4487·06 4594·11
4337·96 4527·51 4628·33
4382·32 4528·64 5512·72

[230] Die Spektren der Elemente, etc., Leipzig and Vienna, 1911.
[231] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 531.
[232] Astrophys. J. 1909, 29, 352.
The estimation of cerium cannot be carried out accurately by gravimetric
methods in the presence of other earths; volumetric methods, however, will
give reasonably accurate results, if the necessary precautions are taken. In
Bunsen’s method the ignited oxides are treated with hydrochloric acid in
presence of potassium iodide, the iodine set free from the hydriodic acid by
reduction of the cerium dioxide being estimated by means of sodium
thiosulphate, in the usual way. This method gives very inaccurate results,
since in the presence of cerium dioxide, other oxides of the group can be
converted into higher oxides which will also liberate iodine under these
conditions.
The most reliable method is that of v. Knorre.[233] The solution to be
estimated is acidified with sulphuric acid, and oxidised by means of
ammonium persulphate. The excess of the oxidising agent having been
destroyed by boiling, the cooled solution is treated with a slight excess of
hydrogen peroxide, which reduces the ceric salt according to the equation:
2Ce(SO₄)₂ + H₂O₂ = Ce₂(SO₄)₃ + H₂SO₄ + O₂
The excess of hydrogen peroxide is then estimated by means of a dilute
permanganate solution. Permanganate is itself reduced by the cerous salt
formed, but the action is so slow in acid solution at the ordinary
temperature that the excess of peroxide can be accurately determined
without unduly hurrying the titration. In this form the method is generally
employed for the estimation of cerium in monazite sands, and in the
incandescent mantle industry. The greatest difficulty is the adjustment of the
concentration of the sulphuric acid required. If this be too low, basic ceric
sulphate separates on boiling, and the estimation fails; if it be too high,
oxidation to the ceric salt is hindered, and may even be inhibited. This
difficulty disappears in the modified method of Waegner and Muller,[234] in
which the oxidation to the ceric condition is effected by means of bismuth
tetroxide in nitric acid solution. A similar method, in which reduction to the
cerous state is effected by a ferrous salt, in place of hydrogen peroxide, has
been employed by Metzger.[235]
[233] Ber. 1900, 33, 1924.
[234] Ber. 1903, 36, 282 and 1732.

[235] J. Amer. Chem. Soc. 1909, 31, 523; see also Metzger and Heideberger, ibid. 1910, 32,
642.

Many attempts have been made to estimate cerium compounds by means
of permanganate, which in alkaline solution oxidises cerous salts to the
ceric condition, but the autoxidation of cerous hydroxide in the air
introduces errors, unless suitable precautions are taken. Meyer and
Schweitzer[236] show that if the solution of the cerous salt be added, with
constant shaking, to a known volume of a standard permanganate solution,
in presence of excess of magnesia, the liquid being kept warm, this
difficulty is overcome; the results are usually a little high, however,
probably by reason of the oxidising action of the cerium dioxide on the
other oxides present.
[236] Zeitsch. anorg. Chem. 1907, 54, 104; see also Roberts, ibid. 1911, 71, 305.

Good results have also been obtained by the use of potassium
ferricyanide in alkaline solution,[237] oxidation taking place according to the
equation:
Ce₂O₃ + 2K₃Fe(CN)₆ + 2KOH = 2K₄Fe(CN)₆ + 2CeO₂ + H₂O
The ceric hydroxide is filtered off, and the ferrocyanide formed estimated
by means of permanganate in acid solution.
[237] Browning and Palmer, Zeitsch. anorg. Chem. 1908, 59, 71.

CHAPTER XII

CERIUM GROUP (continued)

Lanthanum, Praseodymium, Neodymium, and Samarium
In his examination of the ceria earths in 1839, Mosander discovered a
new constituent, which he called Lanthana; the new oxide was removed in
solution when the ignited mixture was extracted with dilute nitric acid,
which leaves cerium dioxide undissolved. On examination, the new oxide

was found to be heterogeneous; by fractional precipitation with ammonia,
and subsequent recrystallisation of the sulphates, he obtained two oxides,
which he called respectively Lanthana (λανθανειν, to be hidden), from the
absence of colour and specific reactions, and Didymia, (διδυμοι, twins)
from their similarity and the occurrence of the two together.
Samaria was isolated by Lecoq de Boisbaudran, in 1879, from a
specimen of didymia extracted from the mineral samarskite. Two years
previously, Delafontaine had shown that the didymia separated from this
mineral was not spectroscopically identical with the oxide obtained from
other sources, and in 1878 had isolated an oxide which he called Decipia;
this was shown later, however, to be a mixture of which samaria was one
component. The samaria obtained by de Boisbaudran was by no means
pure, being associated with terbia earths; several investigators claimed to
have separated from it new oxides, most of these being proved afterwards to
have been more or less impure specimens of Europia.
In 1885, Auer von Welsbach[238] employed for the first time the method
which has now become of paramount importance for the separation of the
cerium group, viz. the fractional crystallisation of the double nitrates. By
this method he succeeded in resolving Mosander’s didymia into two new
oxides, for which he proposed the names Praseodidymia (πρασινος, leek-
green), from the colour of the salts, and Neodidymia respectively; the
shorter names praseodymia and neodymia are, however, now generally
adopted.
[238] Monats. 1885, 6, 477; Sitzungsber. kaiserl. Akad. Wiss. Wien, 1885, 92, II, 317.

GROUP A
Mixed Double Nitrates.

2R(NO₃)₃,3Mg(NO₃)₂,24H₂O.
1 La, Pr Compounds. Fractionate as R(NO₃)₃,​2NH₄NO₃,​4H₂O.
2 Pr, Nd Compounds. Fractionate as 2R(NO₃)₃,​3Mn(NO₃)₂,​24H₂O.
3 Crude Nd Compounds. Continue the Separation.
4 Mother-liquors. Sa, Eu, Gd, etc. Crystallise with Bismuth magnesium nitrate.
Terbium elements.
5 Pure La Compound. Refine by Sulphate crystallisation.
6 Pr with La. Continue.
7 Impure Pr Compound. Continue.
8 Pure Nd Compound. Refine by Sulphate crystallisation.
9 Pure Sa Compound.
Mixture of Pr, La.
Pr. Refine by Sulphate crystallisation.
Fig. 8.—Separation of the Cerium Elements

Separation
The modern methods for the separation of these elements are based
almost entirely on the differences in solubility of the various double

nitrates.[239] The mixed double sulphates separated by saturation of a
solution of the chlorides with sodium sulphate, which contain the cerium
and most of the terbium elements, are transformed into nitrates, and the
neutral solution boiled with potassium bromate, in presence of powdered
marble, till all the cerium is precipitated as basic ceric nitrate. From the
filtered solution the other elements are thrown down as oxalates,
transformed into the magnesium double nitrates (A in Fig. 8), and
fractionated from nitric acid solution[240] until a rough separation has been
effected (fractions 1, 2, 3, and 4). The separation, which is somewhat long
and tedious, is followed by means of the absorption spectra, and by the
colour changes of the fractions. Fraction 1, containing lanthanum and some
praseodymium, should be faint green to colourless; fraction 2 is colourless
by the complementary action of the coloured salts of neodymium and
praseodymium; fraction 3, which should contain the crude neodymium salt,
is amethyst; and fraction 4, the mother-liquor, is yellow from the presence
of the samarium compound.
[239] The following scheme is largely from James, ‘The Separation of the Rare Earths,’ J.
Amer. Chem. Soc. 1912, 34, 757.
[240] See Demarçay, Compt. rend. 1900, 130, 1019 and 1186; also Drossbach, Ber. 1902,
35, 2826, and Muthmann and Weiss, Annalen, 1904, 331, 1.

Fraction 1 is now converted to the double ammonium nitrates, which
allow of a readier separation at this stage; two fractions are obtained, of
which the less soluble, fraction 5, is the fairly pure lanthanum compound,
whilst the more soluble, fraction 6, contains the praseodymium with a little
lanthanum. The lanthanum ammonium nitrate, fraction 5, is converted into
the anhydrous sulphate, which is dissolved in ice-water; when the solution
is gradually warmed, the enneahydrate, La₂(SO₄)₃,9H₂O, separates, and
may be obtained perfectly pure by recrystallisation. It is of interest that the
radioactive element actinium is chemically very similar to lanthanum, and
follows it closely through the process of separation.
The mixed praseodymium and neodymium magnesium nitrates which
constitute fraction 2 are transformed into the double manganese nitrates,
and the crystallisation from nitric acid continued.[241] The less soluble part,
fraction 7, is fairly free from neodymium, and the separation is continued
with that of fraction 6, until both lanthanum and neodymium have been
completely removed. The more soluble part, fraction 8, yields the pure

neodymium compound, as does also the crude neodymium magnesium
nitrate which constitutes fraction 3, if the crystallisation be continued.
[241] Cf. Lacombe, Bull. Soc. Chim. 1904, [iii.], 31, 570.
The mother-liquors, fraction 4, are treated with bismuth magnesium
nitrate,[242] which is intermediate in solubility between the analogous
compounds of samarium and europium, and the crystallisation continued.
The less soluble fraction contains the samarium compound, in which
bismuth is the only impurity; this is easily removed by treatment with
sulphuretted hydrogen. The remaining fractions are used as a source of the
terbium elements (see p. 186).
[242] See Urbain and Lacombe, Compt. rend. 1903, 137, 792; ibid. 1904, 138, 84 and
1136.
The double carbonate method[243] is very suitable for the preparation of
pure lanthanum compounds after the removal of cerium. The mixture of
salts is added to a warm 50% solution of potassium carbonate, and to the
clear liquid, water is added gradually, with constant stirring. The double
carbonates of the most positive elements are the least soluble, and are first
thrown down, so that the precipitate is rich in lanthanum; it is collected and
washed with a 25% potassium carbonate solution, and the process repeated.
A few repetitions suffice to separate lanthanum completely from the other
members of the group. The method may also be used for the purification of
praseodymium salts.
[243] Meyer, Zeitsch. anorg. Chem. 1904, 41, 94.

Lanthanum, La = 139·0
As the most electropositive element of the rare earth group, lanthanum is
the most similar in its chemical properties to the metals of the alkaline
earths. The metal itself (see p. 115) oxidises even in dry air, and in moist air
rapidly becomes coated with a white layer of hydroxide; it attacks water,
and burns vigorously when heated in the air. An alloy with aluminium, of
the formula LaAl₄, has been prepared by Muthmann and Beck[244]; it forms
lustrous white crystals, very stable in the air and very resistant towards
acids.
[244] Annalen, 1904, 331, 46.

The hydroxide is of interest from the fact that, if precipitated under
suitable conditions, it has the power of taking up solid iodine to form a deep
blue adsorption compound[245]; colloidal solutions of basic lanthanum
acetate are also coloured blue by addition of a few drops of iodine solution.
If precipitation with alkali be carried out in presence of hydrogen peroxide,
an hydrated peroxide of the composition La₂O₅,nH₂O is obtained.[246] This
compound partially decomposes with evolution of oxygen at ordinary
temperatures; towards carbon dioxide and acids it acts as a true peroxide,
with formation of hydrogen peroxide.
[245] Damour, Compt. rend. 1857, 43, 976; see also Biltz, Ber. 1904, 37, 719
[246] Melikoff and Pissarjewski, Zeitsch. anorg. Chem. 1899, 21, 70.

The oxide is colourless, and forms colourless salts with those acids in
which the anion is not coloured. The oxide is distinguished from the other
rare earth oxides in that it turns moistened litmus paper blue; it resembles
lime, in hissing when slaked, absorbing carbon dioxide from the air, and
liberating ammonia from ammonium salts. By fusion with alkali carbonates,
and by digestion with concentrated alkali hydroxides, Baskerville and
Catlett[247] claim to have obtained lanthanates and metalanthanates, but
their work has not yet been confirmed.
[247] J. Amer. Chem. Soc. 1904, 26, 75.

The sulphate, La₂(SO₄)₃,9H₂O, is the least soluble of all the rare earth
sulphates. The enneahydrate is the only form stable at ordinary
temperatures,[248] though under special conditions, hydrates with 6 and with
16 molecules of water of crystallisation have been obtained. It separates in
needles belonging to the hexagonal system; 100 parts of water dissolve at
0°, 3·01, and at 100°, 0·69 parts of the salt. The acetylacetone compound
melts at 185°.
[248] Muthmann and Rölig, Ber. 1898, 31, 1718.
A large number of other lanthanum compounds have been prepared, but
these are so typical of the rare earth salts generally that no detailed
treatment is required; for a full account of them, the reader is referred to
Abegg’s classical handbook.

Atomic Weight. —A large number of determinations of this constant
have been made, but the results even of recent investigations do not agree
so closely as might be desired. The value adopted by the International

Committee, 139·0, is based on the work of Brauner and Pavliček,[249]
carried out in 1902. These authors give an account of all the determinations
made up to that date, with critical discussion of the methods employed and
the possible sources of error. The more important investigations have been
based on the ratio La₂O₃ : La₂(SO₄)₃, for the determination of which the
most stringent precautions must be taken. The synthetic method has
generally been employed, on account of the tenacity with which the oxide
clings to traces of sulphuric anhydride. In this method, the total
decomposition of the acid sulphate, and the protection of the very
hygroscopic sulphate, La₂(SO₄)₃, from atmospheric moisture, constitute the
chief difficulties. By this method, H. C. Jones[250] in 1902 obtained a result
(138·76) considerably lower than the value found by Brauner and Pavliček
(loc. cit.) A later research by Brill,[251] who carried out a synthetic sulphate
determination on a minute scale, using a Nernst microbalance, gave the
value 139·5, which, whilst considerably higher than either of the other
figures, shows that Brauner and Pavliček’s number can hardly be too high.
[249] Trans. Chem. Soc. 1902, 81, 1243.
[250] Amer. Chem. J. 1902, 28, 23.
[251] Zeitsch. anorg. Chem. 1906, 47, 464.

Detection. —Pure lanthanum compounds show no absorption in the
visible region, and the pure oxide gives no cathode luminescence.
The emission spectra show very characteristic lines in the violet
and ultraviolet. The chief lines are:
3949·27 4238·55 6250·14 6394·46
3988·69 4333·98 6262·52

For arc spectra see Exner and Haschek; Eder and Valenta.[252]
[252] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 39.

Praseodymium, Pr = 140·6
This element occurs only in small quantities in the commoner rare earth
minerals, and its separation in the pure state is in consequence a matter of
very great difficulty. The salts and their solutions have a characteristic green

colour. The salts are derived from the sesquioxide, Pr₂O₃, but a dioxide,
PrO₂, and an intermediate oxide of uncertain composition are known. The
absorption spectrum has five absorption bands, one of which coincides with
a band in the absorption spectrum of neodymium; this fact has been
interpreted as an indication of the non-elementary nature of both metals.[253]
Difference in the absorption spectra have been put forward by several
workers as indicating the complex nature of praseodymium, but an
exhaustive examination by Stahl[254] in 1909 showed that there is no reason
to doubt that the metal is really an element.
[253] Auer von Welsbach, Sitzungsber. kaiserl. Akad. Wiss. Wien, 1903, 112, IIa, July; also
Urbain, Ann. Chim. Phys. 1900, [vii], 19, 184.
[254] Le Radium, 1909, 6, 215.

The metal is prepared by electrolysis of the fused chloride; in order to
attain the temperature required to fuse the element, a very thin cathode is
employed; if too powerful a current be used, the dioxide is formed. The
metal is purified by remelting it in crucibles of magnesia, under a layer of
anhydrous barium chloride. It has a yellowish shade, and is more stable in
the air than lanthanum and cerium. For physical properties, see p. 115. No
alloys have been prepared.
The hydroxide is thrown down by alkalies as a gelatinous green
precipitate; in the presence of hydrogen peroxide, an hydrated peroxide,
which closely resembles the corresponding lanthanum compound, is thrown
down.
The Oxides.—By ignition of salts of volatile acids, Auer von
Welsbach[255] obtained an oxide to which he assigned the formula Pr₄O₇.
More recent work[256] has shown that the composition of the oxide obtained
depends upon the conditions under which the various salts are decomposed.
By fusing the nitrate in presence of potassium nitrate at 400-450°C., Meyer
obtained the dioxide, PrO₂; at higher temperatures this decomposes, giving
the intermediate oxides. The formation of the dioxide is greatly influenced
by the presence of other oxides,[257]—ceric oxide, acting as an oxygen
carrier, favouring whilst the other oxides hinder. The pure dioxide is a
brownish-black powder, which resembles manganese dioxide, but is less
stable. It liberates halogens from the halogen acids, and oxidises manganese
salts to permanganates, but does not completely oxidise ferrous or stannous
salts, losing instead a part of its oxygen in the gaseous form. The dioxide
cannot be obtained in the wet way.

[255] Monats. 1885, 6, 477.
[256] See, e.g. Meyer, Zeitsch. anorg. Chem. 1904, 41, 94.
[257] Brauner, Monats. 1882, 3, 1; Marc, Ber. 1902, 35, 2370; Meyer and Koss, ibid. 3470.
When heated in a stream of hydrogen, the dioxide yields the sesquioxide,
Pr₂O₃, as a greenish-yellow powder,which readily absorbs oxygen from the
air, becoming brown, with formation of the intermediate oxide.
The chloride, PrCl₃,7H₂O, forms large green prisms, very readily soluble
in water; 100 parts of the solvent at 13° take up 334·2 parts of the hydrated
salt, the solution having the specific gravity 1·687. The anhydrous chloride
is a pale green deliquescent powder, which melts at a red heat to a clear
green liquid; ebullioscopic measurements show that in alcoholic solution it
has the simple molecular formula PrCl₃.
The Bromate, Pr(BrO₃)₃,9H₂O, has been obtained by James and
Langelier[258] by dissolving the oxide in aqueous bromic acid, and also by
double decomposition. It forms greenish hexagonal prisms, melting at
56·5°, and is readily soluble; 100 parts of water dissolve 190 parts of this
salt at 25°. At 100° it loses five molecules of water, forming the tetrahydrate
Pr(BrO₃)₃,4H₂O, which loses all its water at 130°. The anhydrous salt
begins to decompose at 150°.
[258] J. Amer. Chem. Soc. 1909, 31, 913.
The sulphate crystallises with 8 molecules of water of crystallisation at
ordinary temperatures, but hydrates with 151⁄2, 12, and 5 molecules of water
respectively have been described. The octohydrate is considerably more
soluble than lanthanum sulphate enneahydrate. The anhydrous salt is a
bright green powder.
Praseodymium acetylacetone melts at 146°.

Atomic Weight. —The value 140·6, adopted by the International
Committee, is based on the work of Jones, v. Scheele, Auer von Welsbach,
and Feit and Przibylla; the work of Brauner, however, points consistently to
a higher atomic weight. Most of these investigators have used the sulphate
method. The first determinations of von Welsbach for the newly discovered
element[259] gave the value 140·8 (see p. 179); another series of
determinations published in 1903[260] gave the mean value 140·57.
Jones[261] obtained the sesquioxide for the synthetic sulphate operation by
reduction of the peroxide in a current of hydrogen; according to Brauner,
this method gives an oxide which is not perfectly pure, probably by

absorption of water vapour and carbon dioxide from the air. Jones’ mean
value was 140·466. v. Scheele[262] used the same method, as well as a
combined oxalate-sulphate method; his figures vary considerably, the mean
value being 140·55. Feit and Przibylla,[263] using their volumetric method,
obtained the value 140·54.
[259] Monats. 1885, 6, 477.
[260] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1903, 112, 1037.
[261] Amer. Chem. J. 1898, 20, 345.
[262] Zeitsch. anorg. Chem. 1898, 17, 310.
[263] Zeitsch. anorg. Chem. 1906, 50, 249.
Brauner’s earlier work,[264] carried out in 1898, gave the value 140·95. In
1901 this author[265] carried out an extensive research on the atomic weight
of praseodymium, employing four different methods with spectroscopically
pure material; the mean value of his very concordant results was 140·97,
almost the value he obtained in 1901. A further investigation into the value
of this constant appears desirable.
[264] Proc. Chem. Soc. 1898, 14, 70.
[265] Ibid. 1901, 17, 65; see also Abegg, III, i. 263.

Detection. —The maxima of the absorption bands are given by
Rech[266] as follows:
Yellow 596·4 and 588·2, weak.
Blue 481·3 very intense.
468·3 coincident with a neodymium band.
Violet 444·2
The arc spectrum is very rich in lines.[267] The most intense,
which may be used also for identification, are the following:
4008·90 4189·70 4305·99
4100·91 4206·88 4429·38
4118·70 4223·18 4496·60
4143·33 4225·50 4510·32
4179·60 4241·20
[266] Zeitsch. wiss. Photochem. 1906, 3, 411.

[267] Exner and Haschek; Bertram, Zeitsch. wiss. Photochem. 1906, 3, 16; Eder and
Valenta, Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 65.

Neodymium, Nd = 144·3.
Neodymium is, after cerium, the commonest constituent of the cerium
group in the more important rare earth minerals, and its separation is
therefore by no means so difficult as that of praseodymium. The compounds
of the element obtained by von Welsbach in 1885 were not pure, being
admixed with samarium compounds which had not been completely
separated. Neodymium salts were first prepared free from samarium by
Demarçay[268] in 1898; they are of a violet-rose colour, and show in
solution a well-marked and characteristic absorption spectrum, the bands
being very numerous and sharply defined, and extending over the whole
optical region. In chemical as well as in physical and crystallographic
properties, they show an extremely close resemblance to the compounds of
praseodymium.
[268] Compt. rend. 1898, 126, 1039.
On account of the high melting-point, the preparation of the metal
presents the same difficulties as that of praseodymium. A current of 90-100
ampères is employed at a potential difference of 15-22 volts; this suffices to
raise the thin carbon cathode to a bright white heat, and to fuse the liberated
metal. For the properties of the element, see p. 115.
The sesquioxide, Nd₂O₃, when perfectly pure, has a light blue or lilac
colour, with a faint reddish fluorescence; the shade varies somewhat
according to the method of and temperature employed for the preparation.
A bluish or violet-red fluorescence is highly characteristic of the salts, and
is particularly noticeable if the powdered recrystallised oxalate be viewed in
a good light. The greyish or brownish colour of the oxide observed by some
authors is probably due to traces of impurity.[269] The existence of higher
oxides of the formulæ Nd₂O₄ and Nd₂O₅ respectively, which Brauner[270]
put forward, has been disputed by other writers, though it is found[271] that
in the presence of ceria and praseodymia, the sesquioxide can take up more
oxygen. Waegner[272] claimed to have obtained the compound Nd₄O₇ by
heating the oxalate in a stream of oxygen, though his material, as well as
that of Brauner, contained praseodymia. More recently, Joye and
Garnier[273] have shown that the spectrum attributed by Waegner to the

hypothetical Nd₄O₇ was in reality that of an hydrated oxide, 2Nd₂O₃,2H₂O;
these authors have also prepared a second hydrated oxide of the formula
2Nd₂O₃,3H₂O.
[269] See Waegner, Zeitsch. anorg. Chem. 1904, 42, 118; also Baxter and Chapin, J. Amer.
Chem. Soc. 1911, 33, 1.
[270] Chem. News, 1898, 77, 161; ibid. 1901, 83, 197.
[271] See Meyer and Koss, Ber. 1902, 35, 3740; and Marc, ibid. 2370.
[272] Loc. cit.
[273] Compt. rend. 1912, 154, 510.
The chloride, NdCl₃,6H₂O, is obtained by crystallisation from aqueous
solutions; it is also precipitated by addition of water to an alcoholic
solution. It forms large deliquescent rose-coloured crystals; 100 parts of
water at 13° dissolve 246·2 parts of the salt, the saturated solution having
the density 1·741; at 100°, 511·6 parts are dissolved. The solution
resembles those of the other chlorides of the group in that it readily
dissolves the rare earth oxalates. When heated in a current of hydrogen
chloride of 130°, the hexahydrate yields a monohydrate, NdCl₃,H₂O; at
160° the anhydrous chloride is obtained as a very deliquescent rose-
coloured powder, which melts at a red heat to a clear red liquid. The
anhydrous chloride forms an additive compound NdCl₃,12NH₃, when
exposed to the action of ammonia at low temperatures;[274] by gradually
heating this, a large number of other additive compounds are formed,
containing smaller quantities of ammonia.
[274] Matignon and Trannoy, Compt. rend. 1906, 142, 1042.
The anhydrous iodide, NdI₃, has been obtained[275] by passing hydrogen
iodide over the heated anhydrous chloride, and also by heating the carbide
in iodine vapour. It fuses to a black liquid, which at a higher temperature
suddenly becomes transparent.
[275] Matignon, ibid. 1905, 140, 1637.
The bromate, Nd(BrO₃)₃,9H₂O, which is exactly similar to the analogous
compound of praseodymium, forms rose-coloured hexagonal prisms,
melting at 66·7°.
The sulphate, Nd₂(SO₄)₃,8H₂O, is isomorphous with the corresponding
salt of praseodymium, but is considerably less soluble. Only the one hydrate
is known.
The nitrates show an interesting case of isomorphism with the
corresponding bismuth nitrate hydrates.[276] The stable form of the

neodymium salt is the hexahydrate, Nd(NO₃)₃,6H₂O, whilst the
pentahydrate, Nd(NO₃)₃,5H₂O, is labile. Of the bismuth salts, on the other
hand, the pentahydrate is stable whilst the hexahydrate is labile; but mixed
crystals of both pairs may be obtained, the stable neodymium hexahydrate
with the unstable bismuth compound, and the stable bismuth pentahydrate
with the labile neodymium salt.
[276] Bodman, Ber. 1898, 31, 1237.
Many double carbonates are obtained by dissolving the normal carbonate
in excess of the precipitant. The absorption spectra of these solutions, which
have a blue colour, are abnormal and very intense, and have been suggested
as a basis of quantitative estimation.[277]
[277] Muthmann and Stutzel, Ber. 1899, 32, 2653.
The acetylacetone derivative forms violet crystals, melting at 144°-145°.
A large number of organic salts of neodymium have been prepared by
James, Hoben, and Robinson.[278]
[278] J. Amer. Chem. Soc. 1912, 34, 276.

Atomic Weight. —The earlier determinations of this constant were
carried out by the sulphate method, the synthetic process being usually
employed. Auer von Welsbach, at the time of the discovery of
praseodymium and neodymium,[279] gave the values 143·6 and 140·8
respectively for their atomic weights. Brauner, who carried out a
determination in 1898,[280] showed that these numbers should be
interchanged, and gave the value 143·63 for neodymium. Boudouard,[281]
employing the analytical sulphate method, obtained the value 143·05,
whilst in the same year Jones[282] gave the value 143·6. A second
determination by Brauner[283] gave the value 143·89. All these values are
undoubtedly too low, the material being probably contaminated with other
earths.
[279] Loc. cit.
[280] Proc. Chem. Soc. 1898, 14, 70.
[281] Compt. rend. 1898, 126, 900.
[282] Amer. Chem. J. 1898, 20, 345.
[283] Proc. Chem. Soc. 1901, 17, 66.

In his second determination in 1908, Auer von Welsbach[284] gave the
value 144·54 as the mean of three determinations. Feit and Przibylla,[285]
using their volumetric method, gave the value 144·52, whilst Holmberg,
[286] using material which he considered to have been the purest obtained up
to that time, obtained the figure 144·11. More recently, Baxter and
Chapin[287] have made determinations by treating the chloride with pure
silver nitrate, and weighing the precipitated silver chloride, as well as by
titration. The mean value obtained by the first method—ratio NdCl₃ :
3AgCl—was 144·272 (extremes 144·250 and 144·298), and by the second
method—ratio NdCl₃ : 3Ag—was 144·268 (extremes 144·249 and
144·283), giving the mean value for the whole series of 144·270.
[284] Loc. cit.
[285] Zeitsch. anorg. Chem. 1905, 43, 202; ibid. 1906, 50, 249.
[286] Ibid. 1907, 53, 124.
[287] Proc. Amer. Acad. 1911, 46, 215.
The value adopted by the International Committee is 144·3.

Detection. —The absorption spectra of neodymium compounds
have been examined by Demarçay, Forsling, von Welsbach, Rech,
Schäfers, and Baxter and Chapin, with concordant results. The
positions of the absorption maxima as given by Holmberg[288]
from the measurements of Forsling are as follows, the weaker
bands being omitted:

677·5 532·3 468·7
621·7 521·6 In concentrated 461·0
578·5 In concentrated 520·4 - solution these 427·1
solution these give give one intense
575·4 512·4 band.
- the intense
573·5 absorption region 508·7
571·6 in the yellow. 474·5
The arc spectrum is given by Exner and Haschek, Bertram,[289]
and Eder and Valenta.[290] The most intense lines are as follows:
3863·52 4375·11 5923·35

3951·32 4385·81 5319·98
4061·27 4400·96 5594·58
4156·30 4446·51 5620·75
4247·54 4451·71 6310·69
4282·67 4463·09 6314·69
4303·78 4920·84 6385·32
4325·87
[288] Zeitsch. anorg. Chem. 1907, 53, 83.
[289] Zeitsch. wiss. Photochem. 1906, 3, 16.
[290] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 554.

Samarium, Sa = 150·4
The samarium of the earlier chemists (see p. 168) contained a large
proportion of the terbium elements, from which a fairly complete separation
was first effected by Demarçay in 1900.[291] By the fractional crystallisation
of the double magnesium nitrate in presence of bismuth magnesium nitrate,
Urbain and Lacombe[292] succeeded in preparing samarium compounds,
which were shown by spectroscopic examination[293] to be free from other
earths. The element is intermediate in electropositive character and in the
solubility relations of its salts between neodymium and the terbium earths;
its salts are topaz-yellow in colour, and in concentrated solutions show
absorption in the blue and violet regions. The oxide is almost white in
colour, with only a faint yellow tinge. A systematic investigation of
samarium compounds was carried out by Cleve,[294] but his work was
vitiated by the fact that his material was very impure. More recently, the
pure salts have been examined by Matignon and his pupils.
[291] Compt. rend. 1900, 130, 1185.
[292] Ibid. 1904, 138, 84 and 1166.
[293] Eberhard, Zeitsch. anorg. Chem. 1905, 45, 374.
[294] Trans. Chem. Soc. 1883, 43, 362; Bull. Soc. Chim. 1885, [ii.], 43, 53; Chem. News,
1886, 53, 30, 45, 67, 80, 91, 100.

The melting-point of the metal lies between 1300° and 1400°C., so that
its preparation by the electrolytic method is a matter of great difficulty. A
mixture of the chloride with one-third of its weight of barium chloride is
electrolysed by means of a current of 100 ampères, using a cathode of only

2·5 mm. thickness; the metal so obtained is greyish white in colour, and is
the hardest of the cerium elements.
The chloride separates from aqueous solution as the hexahydrate,
SaCl₃,H₂O, in large tabular yellow crystals. The anhydrous chloride is
white, but fuses to a chocolate-brown liquid; it forms a large number of
additive compounds with ammonia. When heated in an atmosphere of dry
hydrogen or ammonia, air and moisture being carefully excluded, it yields
the subchloride,[295] SaCl₂, as a dark brown crystalline solid, insoluble in
alcohol and all organic solvents. Samarous chloride dissolves in water,
forming a deep brownish-red solution, which rapidly becomes colourless,
with evolution of hydrogen, and precipitation of the oxide and oxychloride.
Samarous iodide, SaI₂, may be obtained by a similar process, and closely
resembles the chloride.
[295] Matignon and Cazes, Compt. rend. 1906, 142, 83.
The bromate, Sa(BrO₃)₃,9H₂O, melts at 75°, and closely resembles the
corresponding compounds of the didymium metals. The sulphate
crystallises with 8, and the nitrate with 6 molecules of water. The
carbonate, Sa₂(CO₃)₃,3H₂O, can be obtained only by passing carbon
dioxide through an aqueous suspension of the hydroxide; addition of alkali
carbonate to a solution of a samarium salt precipitates hydrated double
carbonates.
The acetylacetone compound melts at 146°-147°C.
Many organic salts have been prepared by James, Hoben, and Robinson
(loc. cit.).

Atomic Weight. —The earlier determinations of this constant were
carried out with material not entirely free from europium. Demarçay[296]
carried out a synthetic sulphate operation with the material which he
obtained free from europium in 1900, and found values between the limits
147·2 and 148·0. The International Committee has adopted the value 150·4,
which is based on the work of Urbain and Lacombe[297] in 1904. These
authors made determinations of three series of ratios, obtained by (a)
conversion of sulphate octohydrate to anhydrous sulphate, (b) conversion of
anhydrous sulphate to oxide, and (c) conversion of sulphate octohydrate to
oxide; these gave the values 150·314, 150·533, and 150·484 respectively,
from which the mean atomic weight is 150·44.[298]
[296] Loc. cit.

[297] Compt. rend. 1904, 138, 1166.
[298] These numbers are calculated by Brauner (Abegg’s Handbuch, III. i. p. 285) on the
basis O = 16, S = 32·06, H = 1·0076, and are somewhat higher than those given by
Urbain and Lacombe, who used the round numbers O = 16, S = 32, and H = 1.

Detection. —The absorption spectrum of samarium compounds is
only visible in fairly concentrated solutions, so that the element
cannot usually be detected in a mixture by this means. The
position of the maxima of the strongest bands (Demarçay, loc.
cit.) are:

476 417
463 402
These are all in the blue and violet regions; the first and second
are in the neighbourhood of neodymium and europium bands
(q.v.), and in concentrated solutions the bands would partially
coincide. Since these are the two elements from which the
separation is most difficult, and are moreover the most constant in
their occurrence with samarium, the absorption spectrum is of
very little use as a test.
The arc spectrum is very rich in lines,[299] of which the most
intense are:
3739·30 4319·12 4424·55 4519·80
4152·38 4329·21 4434·07 4524·08
4203·18 4334·32 4434·52 4544·12
4225·48 4347·95 4452·92 4566·38
4229·83 4391·03 4454·84 4577·88
4236·88 4420·72 4458·70 4642·41
4256·54 4421·32 4467·50 4674·79
[299] Exner and Haschek; Eder and Valenta; Rütten and Mersch, Zeitsch. wiss. Photochem.
1905, 3, 181.

CHAPTER XIII

THE TERBIUM GROUP
In his examination of the yttria earths in 1842, Mosander described two
new oxides isolated from the old yttria. To one of these, an orange-yellow
earth which yielded colourless salts, he gave the name Erbia; the second
earth, which was colourless and gave rose-coloured salts, he called Terbia.
Bahr and Bunsen examined the yttria oxides in 1866, and obtained only the
latter earth, which gave rose-coloured salts; to this they applied Mosander’s
name Erbia, and stated that the earth to which Mosander had given that
name had no existence. Delafontaine, however, confirmed Mosander’s
work, showing that the orange-yellow earth which yielded colourless salts
(Mosander’s Erbia) had been fractionated out of their material by Bahr and
Bunsen in the double sulphate separation of the cerium group; to avoid
further confusion, however, he proposed to give to this oxide (Mosander’s
Erbia) the name Terbia, leaving for the colourless oxide, which forms rose-
coloured salts (which Mosander had called Terbia) the name Erbia applied
to it by Bahr and Bunsen. This reversed nomenclature has been generally
accepted.
Delafontaine,[300] continuing his work on the earths from samarskite (see
p. 168) announced in 1878 the discovery of a new oxide, Philippia,
intermediate between terbia and yttria; but this was subsequently shown to
be a mixture of yttria and terbia (see p. 133). In the same year, Lawrence
Smith[301] announced the discovery of another oxide, Mosandria, from the
samarskite earths; this was afterwards shown by Lecoq de Boisbaudran to
be a mixture of terbia with gadolinia.[302] In 1880 Marignac[303] announced
the discovery of two more new oxides, Yα and Yβ from the same mineral; Yβ
was afterwards found to be identical with samaria, whilst Yα was
subsequently separated from the old terbia earths by Lecoq de Boisbaudran,
who proposed, with the assent of Marignac, the name Gadolinium.[304] The
terbia left after removal of the erbia earths and gadolinia was believed by

that author to be still a mixture, a conclusion supported by the work of
Hofmann and Kruss in 1893.[305]
[300] Compt. rend. 1878, 87, 559.
[301] Ibid. 1878, 87, 146.
[302] Ibid. 1886, 102, 647.
[303] Compt. rend. 1880, 90, 899.
[304] Loc. cit.
[305] Zeitsch. anorg. Chem. 1893, 4, 27.

In 1886 Demarçay[306] isolated from samaria a new oxide, which he
designated S₁. From his work on this oxide in 1892-1893, de
Boisbaudran[307] concluded that samaria consisted of at least three oxides,
samaria proper, and two new oxides Zξ and Zε. In 1896, Demarçay[308]
separated an earth Σ, which showed the spark-spectrum of Zε and the
reversal spectrum of Zξ, and finally in 1901[309] he obtained the new oxide
in a fairly pure condition, and gave it the name Europia.
[306] Compt. rend. 1886, 102, 1551.
[307] Ibid. 1892, 114, 575; ibid. 1893, 116, 611 and 674.
[308] Ibid. 1896, 122, 728.
[309] Ibid. 1901, 132, 1484.
The complicated history of the terbium group has been entirely cleared
up by the work of Urbain and his co-workers during the early years of the
present century, and processes have been devised by which the separation of
the three members of the group from one another, and from the related
elements of the erbium group on the one side, and samarium on the other,
can be satisfactorily accomplished. The chemistry of this group, therefore,
may be regarded as satisfactorily settled, though relatively little is known of
the properties of the elements and their compounds.
In their general chemical relations, elements of the terbium group occupy
an intermediate position between the cerium group and the elements of the
yttrium group in the narrower sense. In the solubility relations of the double
salts, they are bounded on the one side by samarium and the less soluble
cerium group, on the other by dysprosium and holmium and the more
soluble yttrium group. They show only very slight differences in
electropositive character, and methods based on differences in basic
strength of the oxides, therefore, are of very little use for separating them
from one another. Fractional precipitation with ammonia separates them in
the order terbium, samarium, gadolinium, and europium—samaria being

less strongly basic than the oxides of gadolinium and europium; this
constitutes an exception to the general rule regarding the solubilities of the
double nitrates and sulphates with increasing electropositive character.[310]
The difficulties of separation are greatly increased by the very small
proportions in which the elements are usually found in rare earth minerals.
Gadolinium usually occurs in the largest quantities; in consequence of this,
there is little doubt that most of the material described by the earlier
workers as terbia consisted very largely of gadolinia.
[310] See Lecoq de Boisbaudran, Compt. rend. 1890, 111, 394.
The group is not characterised by well-marked absorption spectra;
europium and terbium show weak absorption in the blue region. Terbium,
of which the salts are colourless, forms a very strongly coloured peroxide,
analogous to that of praseodymium; small quantities of this give to the
mixed oxides obtained by ignition the characteristic yellow colour, whilst
mixtures richer in the peroxide become correspondingly darker and darker.

Separation
In the double sulphate separation of the yttrium and cerium groups, the
terbium elements divide themselves between the soluble and the insoluble
portions; if the separation is made as complete as possible by addition of a
large excess of alkali sulphate under suitable conditions, the larger part of
the compounds of the group will be precipitated with the cerium elements.
In the separation of the cerium elements the terbium elements collect in the
most soluble fractions, and the mother-liquors of the double nitrate
crystallisations therefore form a very convenient source of these elements.
A considerable proportion, however, will usually remain in solution with
the double sulphates of the yttrium group; in the bromate separation of
these (see p. 198), the terbium elements collect in the least soluble fractions.
By careful fractionation under suitable conditions, the double sulphate
method may be used to separate the terbium group completely from the
cerium and yttrium elements. A very convenient method of separating the
terbium group from a rare earth mixture is the ethylsulphate process of
Urbain. By fractional crystallisation of these salts from alcohol or water, the
separation into three groups can be satisfactorily accomplished.
For the separation of the terbium elements from one another, the nitrate
and double nitrate methods are most suitable. Samarium can readily be

separated by crystallisation of the double magnesium nitrates in presence of
bismuth magnesium nitrate; by continuing the fractionation, europium
magnesium nitrate can be separated in a pure state, as there is a
considerable difference between the solubility of this salt and the
corresponding compound of gadolinium;[311] the process, however, is
somewhat long and tedious. For the separation of gadolinium and terbium,
the double nitrates are converted into the simple nitrates, and these
fractionated from nitric acid in presence of bismuth nitrate. The gadolinium
nitrate separates before the bismuth nitrate, and may be obtained fairly pure
in this way, though the process is extremely tedious, and several thousand
recrystallisations are required.[312] Terbium nitrate has almost the same
solubility as bismuth nitrate, and the two separate together in the middle
fractions. The more soluble nitrates of the erbia earths collect in the mother-
liquors.
[311] James (J. Amer. Chem. Soc. 1912, 34, 757) employs at this stage the fractional
crystallisation of the double nickel nitrates.
[312] See Urbain, Compt. rend. 1904, 139, 736.

Europium, Eu = 152·0
This element is one of the rarest of the whole group, and occurs only in
extremely small quantities. Monazite sand is said to contain about 0·002 per
cent. of the oxide, though on account of the remarkable intensity of some of
the stronger lines in the arc spectrum, Eberhard[313] was able to detect
europium with ease in a mixture of rare earth oxides from that mineral, after
the separation of cerium. The oxide has a pale rose colour; the salts are also
faintly coloured, and in solution show weak absorption bands.
[313] Zeitsch. anorg. Chem. 1905, 45, 378.
Europium sulphate, Eu₂(SO₄)₃,8H₂O, separates in pink crystals, which
are completely dehydrated at 375°; europic chloride, EuCl₃, in the
anhydrous state forms fine yellow needles; europium oxychloride, EuOCl,
prepared by heating europic chloride in dry air to 600°, is a white solid,
insoluble in water, but soluble in strong acids; europous chloride, EuCl₂,
prepared by reduction of the higher chloride in hydrogen, is a white
amorphous solid, soluble in water to a neutral solution, which on boiling
throws down the oxide, Eu₂O₃.[314] Several organic salts have been
prepared by James and Robinson.[315]

[314] Urbain and Bourion, Compt. rend. 1911, 153, 1155.
[315] J. Amer. Chem. Soc. 1913, 35, 754.

Atomic Weight. —Using the material isolated from samaria,
Demarçay[316] in 1900, by the synthetic sulphate method, found the atomic
weight of europium to be about 151. Urbain and Lacombe[317] determined
the value in 1904, with material free from gadolinium and samarium, using
the three ratios which they employed in the case of the latter element (see p.
182); their values, corrected by Brauner, were 152·00, 151·93 and 151·94
respectively. Another series of determinations was carried out by
Jantsch[318] in 1908, the same method being employed; he obtained the
mean value 152·03, with an error of ±·02. The International Committee
have adopted the value 152·0.
[316] Compt. rend. 1900, 130, 1469.
[317] Ibid. 1904, 138, 627.
[318] Ibid. 1908, 146, 473.

Detection. —The absorption spectrum was determined by
Demarçay,[319] but is not sufficiently intense or characteristic for
ordinary purposes of detection. The spark spectrum has been
investigated by the same author (loc. cit.); it is very bright, and
shows the three blue rays which characterised Lecoq de
Boisbaudran’s Zε. The reversal spectrum shows the characteristic
band of Zξ.
The pure oxide, according to Urbain,[320] shows no
luminescence under the influence of cathode rays, but when
impure, or very largely diluted with lime or gypsum, it gives very
bright and characteristic spectra.
[319] Ibid. 1900, 130, 469.
[320] Ibid., 1906, 142, 205, 1518.

The arc spectrum[321] is very characteristic, and contains some
exceedingly intense lines, by means of which Lunt[322] has

detected europium in the sun and in many stars. The lines most
suited for identification of the element are the following:
3688·57 3972·16 4594·27
3725·10 4129·90 4627·47
3819·80 4205·20 4662·10
3907·28 4435·75 6645·44
3930·66 4522·76

[321] Exner and Haschek; Eder and Valenta, Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910,
119, IIa, 31.
[322] Proc. Roy. Soc. 1907, 79; A, 118.

Gadolinium, Gd = 157·3.
Gadolinia is the commonest of the terbia oxides, and occurs in
considerable quantities in some of the rare earth minerals, notably in
samarskite and gadolinite; its separation from the neighbouring oxides,
europia and terbia, is, however, exceedingly difficult, and has only been
satisfactorily accomplished in recent times. The gadolinium compounds
prepared and examined by the earlier workers, as appears from the atomic
weight determinations, must have been associated with earths of lower
atomic weight, and undoubtedly also with small quantities of terbium. After
the isolation of Marignac’s Yα, and the examination of the element by
Lecoq de Boisbaudran, to whom the name gadolinium is due, further
investigations were carried out by Bettendorff[323] and by Benedicts.[324]
Pure gadolinia was probably first obtained by Demarçay,[325] by fractional
crystallisation of the magnesium double nitrate; the oxide obtained by
Urbain and Lacombe[326] by crystallisation of the nitrates in presence of
bismuth nitrate, was proved to be spectroscopically pure by Eberhard.[327]
[323] Annalen, 1892, 270, 376.
[324] Zeitsch. anorg. Chem. 1900, 22, 393.
[325] Compt. rend. 1900, 131, 343; ibid. 1901, 132, 1484.
[326] Ibid. 1905, 140, 583, etc.
[327] Zeitsch. anorg. Chem. 1905, 54, 374.
The gadolinia obtained by ignition of the salts of volatile acids should be
perfectly white; presence of terbia causes it to assume a yellow colour.[328]
The salts are colourless, and their solutions show no absorption in the
visible region, though Urbain[329] has shown that there are four strong
bands in the ultraviolet.
[328] Eberhard (loc. cit.) has shown that even in the perfectly white oxide, traces of terbia
can be distinguished by spectroscopic examination.
[329] Compt. rend. 1905, 140, 1233.
The hydroxide, Gd(OH)₃, is a gelatinous precipitate with strongly basic
properties, rapidly absorbing carbon dioxide from the air. The oxide, Gd₂O₃,
also absorbs carbonic anhydride from the air, and is easily soluble in acids,
even after strong ignition. The element is therefore strongly electropositive.

Its position among the yttrium elements, however, is justified by the
properties of the platinocyanide, 2Gd(CN)₃,3Pt(CN)₂,18H₂O, which forms
long, pointed red crystals, with a green metallic lustre, belonging to the
rhombic system, and isomorphous with the corresponding yttrium and
erbium salts; the cerium elements, on the other hand, give yellow
platinocyanides, with a blue metallic lustre, which crystallise in the
monoclinic system.
The nitrate, Gd(NO₃)₃,6H₂O, separates from aqueous solutions at the
ordinary temperatures in large crystals belonging to the anorthic system,
and is isomorphous with the corresponding compounds of praseodymium
and neodymium.[330] From solutions in strong nitric acid, a pentahydrate is
obtained, which melts at 92°; the hexahydrate melts at 91°. The sulphate
separates from aqueous solution as the octohydrate, Gd₂(SO₄)₃,8H₂O,
isomorphous with the corresponding salts of both groups. The anhydrous
sulphate is much less soluble in water at 0° than the corresponding
compounds of the cerium elements. The selenate forms hydrates with 10
and 8 molecules of water of crystallisation respectively; these are
isomorphous with the corresponding selenates of yttrium and the erbium
metals.
[330] Lang and Haitinger, Annalen, 1907, 351, 450.

Atomic Weight. —The determinations of this constant made by the
earlier workers were all carried out with impure material and gave results
which were considerably too low. The International Committee have
adopted the value 157·3, which is based on the work of Urbain.[331] In
employing the analytical sulphate method, that author observed that the
anhydrous sulphate did not remain constant in weight when allowed to
remain in a desiccator, and that it could not be accurately weighed. He
therefore determined the ratio Gd₂(SO₄)₃,8H₂O : Gd₂O₃, by converting the
octohydrate directly to oxide, and obtained the mean value 157·24.
[331] Compt. rend. 1905, 140, 583.

Detection. —Pure gadolinium compounds show no absorption in
the visible spectrum, but there are four strong bands[332] in the

ultraviolet, viz. 311·6-310·5; 306·0-305·7; 305·6-305·5; and
305·4-305·0. The arc spectrum[333] is very rich in lines, of which
the most intense are the following:

3082·15 3719·63 4050·05 4184·48
3100·66 3743·68 4063·62 4251·90
3422·62 3768·60 4070·51 4262·24
3545·94 3796·62 4073·99 4325·83
3549·52 3814·18 4085·73 4327·29
3585·12 3852·65 4098·80 4342·35
3646·36 3916·70 4130·59 6114·26
3671·39 4037·49
[332] Urbain, ibid. 1905, 140, 1233.
[333] Exner and Haschek; Eder and Valenta, Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910,
119, IIa, 21.
The spark spectra have been examined by Demarçay,[334] Baur
and Marc,[335] Urbain[336] and Crookes.[337]
[334] Compt. rend. 1900, 131, 343.
[335] Ber. 1901, 34, 2460.
[336] Loc. cit.
[337] Proc. Roy. Soc. 1905, 74, 420.

Terbium, Tb = 159·2
Terbia occurs among the rare earth oxides in exceedingly small
quantities, and its separation has in consequence presented such great
difficulties that only within the last few years have terbium compounds
been completely freed from gadolinium and neighbouring elements. In
1886 Lecoq de Boisbaudran,[338] by fractional precipitation of the
hydroxides with ammonia, and subsequent fractional crystallisation of the
double sulphates, obtained an oxide much richer in terbia than any
specimen previously prepared; it was dark yellow in colour. In 1902
Marc[339] obtained from monazite a very dark oxide containing about 15 per
cent. of terbia, whilst Feit[340] in 1905 obtained a dark brown oxide
consisting of gadolinia with about 13 per cent. of terbia. Pure terbium
compounds were obtained by Urbain in 1904,[341] by fractional

crystallisation of the nitrate from nitric acid, in presence of bismuth nitrate,
and by crystallisation of the double nickel nitrates, and precipitation with
ammonia; he showed that the element was identical with the Zδ and Zβ of de
Boisbaudran,[342] with the Γ of Demarçay,[343] and with the Gβ and possibly
the Gζ of Crookes[344] (see p. 193).
[338] Compt. rend. 1886, 102, 395, 483.
[339] Ber. 1902, 35, 2382.
[340] Zeitsch. anorg. Chem. 1905, 43, 267.
[341] Compt. rend. 1904, 139, 736; 1905, 141, 521; 1909, 149, 37.
[342] Ibid. 1895, 121, 709; 1904, 139, 1015.
[343] Ibid. 1900, 131, 343.
[344] Trans. Chem. Soc. 1889, 55, 258.
The element gives the white sesquioxide, Tb₂O₃, and colourless salts.[345]
The peroxide, of which the composition corresponds approximately to the
formula Tb₄O₇, is obtained as a brownish-black powder by ignition of
suitable salts. Its presence, even in small quantities, gives so deep a
colouration to the other earths that some kind of salt formation seems
probable. It is insoluble in cold acids; it dissolves in hot nitric acid with
evolution of oxygen, forming a solution from which the nitrate,
Tb(NO₃)₃,6H₂O, melting at 89·3°, separates on cooling. In hot hydrochloric
acid, the peroxide dissolves with evolution of chlorine, forming solutions
from which the chloride, TbCl₃,6H₂O, can be isolated with difficulty; this
salt is extremely deliquescent, and easily forms supersaturated solutions.
The sulphate, Tb₂(SO₄)₃,8H₂O, can be precipitated from a sulphuric acid
solution of the oxide by addition of considerable quantities of alcohol; it is
isomorphous with the other sulphate octohydrates, and is completely
dehydrated at 360°.
[345] The terbium compounds here described have been prepared by Urbain (loc. cit.)
from carefully purified material; other compounds have been described by Potratz
(Chem. News, 1905, 92, 3), but her material contained a large proportion of gadolinium.

Atomic Weight. —The value adopted by the International Committee is
159·2, which was obtained by Urbain in 1905 (loc. cit.) from the ratio
Tb₂(SO₄)₃,8H₂O : Tb₂(SO₄)₃. This is the only determination on which
reliance can be placed, as the material of the earlier workers was seldom
even approximately pure.

Detection. —Solutions of terbium salts show only one band in the
visible spectrum, at 487·7 in the blue. This band was observed by
Lecoq de Boisbaudran in a specimen of terbia containing
dysprosia, and assumed by him to belong to a new element, Zδ
(loc. cit.) In the ultraviolet nine absorption bands have been
observed (Urbain, loc. cit.)
The spark spectrum shows the lines observed by Demarçay in
1900, and attributed by him to the new element Γ. Lecoq de
Boisbaudran’s element Zβ showed a green fluorescence with the
reversed spark, a phenomenon which Urbain has found to be
exhibited by pure terbium compounds.
The arc spectrum of Urbain’s pure terbia was examined by
Eberhard[346]—see also Exner and Haschek, and Eder and
Valenta.[347] The element may be detected in minerals and earth
mixtures by the following lines:

3523·82 3704·01
3676·52 4005·62
3703·05 4278·71

The chief lines in the arc spectrum (Exner and Haschek) are the
following:

3324·53 3628·53 3874·33 4005·70
3509·34 3650·60 3899·34 4012·99
3531·86 3659·02 3925·60 4278·70
3561·90 3704·10 3939·75 4752·69
3568·69 3711·91 3977·01
3600·60 3848·90 3982·07

Pure terbia does not exhibit the phenomenon of cathode
luminescence, but gadolinia containing a trace of terbia shows a
marked green fluorescence, which was attributed by Crookes to a
new Meta-element, Gβ. A trace of terbia in aluminium oxide

causes the latter to exhibit a highly characteristic intense white
luminescence.
[346] Sitzungsber. königl. Akad. Wiss. Berlin, 1906, 18, 385.
[347] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 14.

CHAPTER XIV

THE ERBIUM AND YTTERBIUM GROUPS—YTTRIUM AND
SCANDIUM
In his examination of the ‘Yttria’ of Gadolin and Ekeberg, during the
years 1839 to 1843, Mosander, by methods based on differences in strength
of the oxides as bases, separated the earth into three new oxides, yttria
proper, the most strongly basic, terbia, intermediate in strength, and erbia,
[348] the least basic. No further separation was effected until 1878, when
Marignac, by fractional decomposition of the nitrates, separated from erbia
a new oxide, for which he proposed the name Ytterbia; the new oxide was
the least basic of the erbia earths. In the following year, Nilson[349] isolated
from ytterbia a still less basic oxide, by the same method; he proposed the
name Scandia, to recall the fact that it occurred in gadolinite and euxenite,
which up to that time had been found only in Scandinavia. In 1879 also,
Soret[350] announced the discovery of a new element X, evidence for the
existence of which he had obtained during a spectroscopic examination of a
mixture of erbia and terbia earths; the oxide of X was isolated in the same
year by Cleve[351] from the old erbia, by fractional decomposition of the
nitrates, and the name Holmium, from the town of Stockholm, was
proposed for the new element. The same investigation led to the discovery
of Thulium, which derives its name from Thule, an old name for
Scandinavia.
[348] The reversed nomenclature of Delafontaine is here employed (see p. 184).
[349] Compt. rend. 1879, 88, 642, 645.

[350] Ibid. 1879, 89, 521.
[351] Ibid. 1879, 89, 478, 708.
Lecoq de Boisbaudran[352] in 1886 showed Cleve’s Holmia to be a
mixture of at least two oxides; he retained the name Holmium for the
element which gave the most characteristic absorption bands of the old
holmium, and proposed the name Dysprosium (from δυσπροσιτος, difficult
of access) for the second element. The name Erbia was retained for the
oxide remaining after the removal of holmia, thulia, and dysprosia from the
old erbia; the homogeneity of this erbia has been called in question, but is
now fairly firmly established. The individuality of dysprosium[353] and
holmium[354] may also be regarded as definitely established; that of thulium
remains doubtful (see p. 204).
[352] Ibid. 1886, 102, 1003, 1005.
[353] Urbain, Compt. rend. 1906, 142, 785.
[354] Holmberg, Zeitsch. anorg. Chem. 1911, 71, 226.
The homogeneity of ytterbia was questioned by Auer von Welsbach[355]
in 1906; by fractionation of the ammonium double oxalates, that author
isolated the oxides of two new elements, for which he proposed the names
Aldebaranium and Cassiopeium. By fractionation of the nitrates from nitric
acid solution, Urbain[356] arrived at the same result, and proposed the names
Ytterbium (Neoytterbium) and Lutecium, which have been adopted by the
International Committee. The latter author, employing the same method in
the fractionation of the gadolinite earths, has recently obtained very strong
evidence of the existence in this group of another element, for which he
proposes the name Celtium;[357] the discovery, however, awaits
confirmation.
[355] Monats. 1906, 27, 935; 1908, 29, 121.
[356] Compt. rend. 1907, 145, 759.
[357] Ibid. 1911, 152, 141.

Separation
In the separation of the yttrium elements, methods based on differences
in electropositive character are of much greater importance than in the
separation of the cerium and terbium groups, and the method of nitrate
fusion has been very largely employed even in comparatively recent work.
This method, which was introduced by Berlin in 1860, has been of great

value in the separation of yttrium and the ytterbium elements from the
erbium group; it was employed in the isolation of ytterbium by Marignac,
and of scandium by Nilson.
If a concentrated solution of the nitrates be evaporated down, and the
syrupy residue subjected to gradually increasing temperature, the nitrates of
the ytterbium elements and scandium are converted first into the basic
nitrates; at somewhat higher temperatures the erbium salts are decomposed,
whilst yttrium nitrate and the nitrates of any cerium elements present are the
last to break up. If the mixture of basic and neutral nitrates be dissolved in
boiling water, the former, being less soluble, crystallise out on cooling, and
may be separated by this means, the process being repeated with the filtrate
containing the unchanged nitrates. In this way, the weakly basic scandia and
ytterbia quickly collect in the first fractions, whilst the oxides of the erbia
group are easily separated from the more strongly basic yttria. The presence
of the intermediate terbium group renders the process much less easily
workable.
The process may be modified by raising the temperature to such an
extent that the soluble basic nitrates are converted into insoluble superbasic
nitrates, the temperatures at which this change occurs increasing from
element to element as the positive character becomes more marked; the
mixture of basic and superbasic salts is then extracted with dilute nitric acid
which leaves that latter undissolved and removes the more positive
elements in solution.
Fractional precipitation of the hydroxides by means of ammonia, alkalies,
or alkaline earths has also been frequently employed. A modification of this
process is the precipitation with aniline, carried out by Kruss;[358] in this
method, the solution of the chloride in warm dilute alcohol is treated with
an alcoholic solution of the organic base. Another modification is the
‘Oxide process’ employed by Auer von Welsbach[359] for the separation of
the cerium elements, and by Drossbach[360] in the yttrium group. The
concentrated solution of the mixed salts is thoroughly digested with the
oxides obtained by precipitating a fraction of the earths; the more strongly
basic oxides tend to displace the less basic, so that these accumulate in the
insoluble part. The solution is filtered from the undissolved oxides, another
fraction precipitated, and the oxides obtained from the precipitate digested
with the concentrated solution as before.
[358] Zeitsch. anorg. Chem. 1893, 3, 108, 353.

[359] Monats. 1883, 4, 630.
[360] Ber. 1902, 35, 2826.

GROUP B
Yttrium Double Suplhates.

Fractionate as Bromates.
1 Gd, Tb, Dy. For separation of Terbium group.
2 Tb, Dy, Ho, Yt. Transform to Ethylsulphates.
3 Dy, Ho, Er, Yt. Fractionate by Nitrate Fusion.
4 Yt, Er, and Sc? Fractionate by Nitrate Fusion.
5 Tm, Yb, Lu, etc. Continue.
Terbium Group.
6 Tb, Dy. Continue Ethylsulphate Fractionation.
7 Dy. Ethylsulphate.
8 Ho, Yt. Fractionate by Nitrate Fusion.
9 Yt. Nitrate.
10 Yt, Er. Continue.
11 Er. Nitrate.
12 Tm. Bromate.
13 Yb. Bromate.
14 Lu. Bromate.
Yb, Lu. Bromates.
Ct? Bromate.

Ho. Basic Nitrate.
Ho, Yt.
Fig. 9.—Separation of the Yttrium Elements

The more modern methods of separation combine the above processes
with the methods of fractional crystallisation, for which the bromates and
alkylsulphates of these elements are well adapted. The procedure[361] which
experience shows will lead to a fairly rapid separation is roughly
represented in Fig 9. The double sulphates (B), left in solution after removal
of the cerium and part of the terbium group, are transformed into the
bromates, which are separated by fractional crystallisation into five main
fractions. The least soluble portion, fraction 1, contains the terbium
elements with some dysprosium; in the fractionation of the terbium group
by means of the nitrates and double nitrates, the dysprosium, with some
terbium, collects in the final fractions (fraction 6). Fraction 2 contains
terbium, dysprosium, holmium, and yttrium as the bromates; these are
converted into the anhydrous chlorides, from which, by treatment with
sodium ethylsulphate in alcoholic solution, the ethylsulphates are obtained.
By fractional crystallisation, dysprosium may be obtained in a fairly pure
condition (fraction 7), the least soluble part (fraction 6) containing the
terbium with some dysprosium. Holmium and yttrium collect in the most
soluble part (fraction 8), from which pure holmium can be obtained by the
method of nitrate fusion. Fraction 3 contains yttrium and erbium, with small
quantities of dysprosium and holmium; the latter are readily separated by
the nitrate fusion, which will also allow of a fairly complete separation of
yttrium (fraction 9). Fraction 4 contains yttrium and erbium; scandium if
present will also collect here. Erbium can be obtained pure by the nitrate
fusion; the second fraction from this process contains both yttrium and
erbium, and may be further worked up with the fraction of similar
composition (fraction 10) from fraction 3.
[361] James, J. Amer. Chem. Soc. 1912, 34, 757.

The mother-liquors from the bromate separation (fraction 5) contain
thulium and the ytterbium elements; the crystallisation is continued, and
allows of complete separation of thulium and ytterbium, and probably of
lutecium, though the most soluble fractions do not seem to have been fully
separated.

The Erbium Group
The oxides of this group, as contrasted with the ytterbia oxides, give rise
to coloured salts, which in solution show definite absorption spectra in the
optical region; the spectrum of erbium salts is particularly definite and
characteristic. Erbium has among the yttrium elements the place of
neodymium among the cerium elements; after yttria, erbia is the commonest
oxide of the yttria group, though on account of the difficulties of separation
the chemistry of erbium is by no means so complete and definite as that of
neodymium. The oxides in order of decreasing basicity, as shown by the
order in which they are thrown down by ammonia, are: dysprosia, holmia,
erbia, thulia; the electropositive character becomes weaker, therefore—as
generally in the rare earth series—as the atomic weight of the elements
increases.

Dysprosium, Dy = 162·5
Compounds of this element were probably prepared in the pure state for
the first time by Urbain[362] in 1906, by the fractional crystallisation of the
ethylsulphate. He showed that after fourteen recrystallisations, the
absorption spectrum of the salts and the mean atomic weight of the element
remain unaltered, and that after removal of terbium by the very efficient
ethylsulphate method, all remaining traces of yttrium could be rapidly
removed by crystallisation of the nitrate. The salts have generally a more or
less pronounced yellow colour.
[362] Compt. rend. 1906, 142, 785.
The oxide, Dy₂O₃, is a white powder which does not alter in composition
when strongly heated in reducing or oxidising atmospheres. It is remarkable
in that it is the most strongly paramagnetic oxide known, having a
coefficient of susceptibility much greater than that of ferric oxide.[363] The
chloride crystallises with 6, the sulphate with 8, and the nitrate with 5
molecules of water of crystallisation. The bromate, Dy(BrO₃)₃,9H₂O,[364]
obtained by double decomposition, melts at 78°. The platinocyanide,
Dy₂[Pt(CN)₄]₃,21H₂O, forms bright red cubic crystals, with greenish
fluorescence.
[363] Compt. rend. 1908, 146, 922.
[364] Jantsch and Ohl, Ber. 1911, 44, 1274.

Several other salts are described by Urbain, and by Jantsch and Ohl (loc.
cit.).

Atomic Weight. —Urbain and Demenitroux[365] determined this
constant from the ratio Dy₂(SO₄)₃,8H₂O : Dy₂O₃. The mean value of six
determinations carried out with material obtained by fractional
crystallisation of the nitrate was 162·52; with material purified by the
ethylsulphate crystallisation, the mean of six determinations gave the value
162·54. The International Atomic Weight is 162·5.
[365] Compt. rend. 1906, 143, 598.

Detection. —Lecoq de Boisbaudran[366] and Urbain[367] give the
position of the following absorption maxima in the visible and
ultraviolet regions respectively:
╵

753 368·5 338
475 379·5 332·5
451·5 365
427·5 351
[366] Ibid. 1886, 102, 1003.
[367] Ibid. 1906, 142, 785.

The arc spectrum of Urbain’s material was examined by
Eberhard,[368] who gives as most suitable for detection of the
element in a mineral or oxide mixture the following lines:
3385·16 3898·69 4187·00
3531·86 3944·83 4211·82
3536·17 4000·59
3645·54 4078·11
See also Exner and Haschek, and Eder and Valenta.[369]
[368] Publ. astrophys. Observ. Potsdam, 1909, 20, No. 60.
[369] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 9.

The ultraviolet arc spectrum and the cathode phosphorescence
have also been examined by Urbain.[370]
[370] Loc. cit.

Holmium, Ho = 163·5
The individuality of this element can hardly be regarded as perfectly
established, though Holmberg[371] has prepared salts which in solution
show only faint indications of erbium and dysprosium, when tested
spectroscopically. That author fractionated the yttrium elements obtained
from euxenite by a long process of separation, which involved
crystallisation of the m-nitrobenzenesulphonates, of the simple nitrates (two
series), of the double ammonium oxalates, and finally fractional
precipitation of the hydroxides by ammonia.
[371] Zeitsch. anorg. Chem. 1911, 71, 226; see also Langlet, Abstr. Chem. Soc. 1907, 92,
ii. 955.
He determined the Atomic Weight as 163·5, which is the value accepted
by the International Committee, and mapped the absorption spectrum. The
oxide, Ho₂O₃, is a pale yellow powder; the salts are yellow, with a faint
orange tinge.

Erbium, Er = 167·7
Although erbia was separated by Mosander seventy years ago, it is
doubtful if the perfectly pure oxide has ever been prepared. Whilst the
individuality of the element is well established, its homogeneity has
frequently been called in question. The name ‘Neo-Erbia’ was given by
Cleve[372] to the residue left after the separation from the old erbia of
ytterbia, scandia, thulia, and holmia (with which dysprosia (q.v.) was also
separated), but the spectrum examination of Kruss and Nilson[373] led them
to regard Cleve’s oxide as still complex. Their results, however, were
explained by the work of Hofmann and his pupils,[374] who consider erbia
to be a homogeneous product; the homogeneity of the element, therefore,
may be considered as established, though it would be strengthened by a
more complete knowledge of the neighbouring elements, holmium and
thulium.
[372] Loc. cit.

[373] Ber. 1887, 20, 2134.
[374] Ber. 1908, 41, 308; also Hofmann, ibid. 1910, 43, 2631.
The element forms a rose-coloured oxide, and rose-coloured salts, which
give to the compounds of the mixed erbia earths their characteristic colour.
The oxide gives a very definite and characteristic reflection spectrum, but
the salts do not possess this property;[375] the reflection spectrum remains
unchanged in the presence of foreign oxides, provided no combination
occurs. From the atomic weight determinations, it seems clear that the salts
described by Cleve and his pupils[376] were not pure erbium compounds; a
few salts only appear to have been recently obtained in the pure state for the
atomic weight determination (q.v.).
[375] See Kruss and Bugge, Ber. 1908, 41, 3783.
[376] See Compt. rend. 1880, 91, 381.
The sulphate separates from aqueous solutions at ordinary temperatures
as the octohydrate, Er₂(SO₄)₃,8H₂O, which forms rose-coloured monoclinic
crystals isomorphous with the corresponding sulphates of the whole group.
The anhydrous sulphate is formed by long heating at 400°, more quickly at
475°, and can be heated to 630° without decomposition. At 845° a basic
salt, Er₂O₃,SO₃, is formed, which begins to decompose at 950°; at 1055° the
transformation to the oxide is complete. The ammonium and potassium
double sulphates are easily soluble in cold water.
The oxalate is thrown down in rosettes of bright rosy plates, which
according to Hofmann[377] have the formula Er₂(C₂O₄)₃,10H₂O, even when
dried in the air. Cleve believed the salt to be thrown down as the
enneahydrate. When kept in vacuo over phosphoric anhydride, the
decahydrate passes into the trihydrate, which when heated decomposes,
passing into the oxide at a temperature of 575°. The nitrate,
Er(NO₃)₃,5H₂O, separates from aqueous solution as the pentahydrate, in
large stable red crystals. The platinocyanide, Er₂[Pt(CN)₄]₃,21H₂O, has the
characteristic red colour with green fluorescence. The formate, Er(HCOO)₃
—Cleve, loc. cit.—is a red powder, obtained by dissolving the oxide in
formic acid; it crystallises from water as the dihydrate.
[377] Loc. cit.

Atomic Weight.

—The determinations of the earlier workers, being carried out with impure
material, gave results which differ very widely, and are quite unreliable.
Cleve’s value of 1880, for material free from ytterbia, but not apparently
free from earths of lower equivalent, was 166·25; Brauner,[378] using the
same material in 1905, obtained the much higher value 167·14. The
determinations of Hofmann and Burger[379] in 1908 gave the mean value
167·38; with purer material, Hofmann in 1910[380] obtained the mean value
167·68, on which is based the value accepted by the International
Committee, 167·7.
[378] Abegg, III. i. 318.
[379] Loc. cit.
[380] Loc. cit.

Detection. —Salts of erbium give in solution absorption spectra
which are well defined and highly characteristic, though not so
intense as those of praseodymium and neodymium. Hofmann and
Bugge[381] give the following absorption maxima for a 10 per
cent. solution of their pure nitrate in a layer of 15 mm. thickness:
667 weak 492
654 strong 487 strong
541 very weak 450
523 very strong 442 weak
519 shadowy
[381] Ber. 1908, 41, 3783.

The arc spectrum has been mapped by Eder and Valenta[382]
and Exner and Haschek. The following lines are used by
Eberhard[383] for purposes of detection:

3230·73 3692·85
3264·91 3896·40
3312·56 3906·47
3372·92 3938·79
3499·28

[382] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 18.
[383] Publ. astrophys. Observ. Potsdam, 1909, 20, No. 60.

Thulium, Tm = 168·5
The thulia isolated in 1879 was described by Cleve[384] as pale rose in
colour; in the following year, having obtained it in larger quantity, he found
that it was white, and dissolved in acids to form colourless solutions which
showed absorption bands in the red and blue. The spectra of the thulium
compounds prepared by Cleve were examined by Thalèn,[385] who
concluded that a new element was certainly present, though it had not been
freed from ytterbium and erbium. Incidental observations on the new oxide
were made by various investigators, but no extensive researches were
carried out upon it until 1911, when James[386] published an account of the
separation and purification by the bromate method, stating that after some
15,000 operations, his products remained unaltered; he gives, however, no
spectroscopic determinations, though part of his material, spectroscopically
examined by Sir William Crookes, was described as ‘Very good thulium,
with a trace of ytterbium.’ In the same year Auer von Welsbach[387]
published an account of a spectroscopic investigation, as a result of which
he concludes that thulium is a mixture of at least three elements, of which
the second, Tm II, agrees fairly well in properties, so far as the two
accounts allow of comparison, with the thulium of James.
[384] Loc. cit.
[385] Compt. rend. 1880, 91, 376.
[386] J. Amer. Chem. Soc. 1911, 33, 1333.
[387] Zeitsch. anorg. Chem. 1911, 71, 439.
Thulia is described by James as a dense white powder, with a greenish
tinge, which ‘emits a carmine coloured glow, when carefully made to
incandesce.’ The salts have a greenish tint, very susceptible to traces of
erbium; addition of erbium compounds turn the solution first yellowish-
green, then colourless, and finally pink. von Welsbach describes Thulium II
as forming an almost white sesquioxide, which, when heated in the flame,
gives a purplish light quickly succeeded by a splendid characteristic glow;
the salts are pale yellowish-green by daylight, emerald-green by artificial
light, the colour being almost complementary to that of erbium salts. In
solution, salts of Tm II give the bands at 685 and 464 ascribed by James and
other workers to thulium.

Until further researches on these interesting results are published, the
elementary nature of thulium cannot be considered definitely settled; it
appears probable, however, that homogeneous salts of a definite element
were obtained by James. The following salts are described by James (loc.
cit.).
The chloride, TmCl₃,7H₂O, separates at ordinary temperatures from the
concentrated solution of the oxide in hydrochloric acid as greenish crystals,
very soluble in alcohol and water. The bromate, Tm(BrO₃)₃,9H₂O, forms
pale bluish-green hexagonal prisms, isomorphous with the analogous salts
of the group. The sulphate and nitrate separate as the octohydrates. The
precipitated oxalate has the formula Tm₂(C₂O₄)₃,6H₂O, and is soluble in
excess of alkali oxalate. The acetylacetone derivative was prepared by
dissolving the precipitated and well-washed hydroxide in alcoholic
acetylacetone; it recrystallises from absolute (?) alcohol as the dihydrate,
Tm₂(C₅H₇O₂)₆,2H₂O. The phenoxyacetate,
Tm₂(C₆H₅·O·CH₂·COO)₆,6H₂O, was obtained in a similar manner by
addition of the hydroxide to a solution of phenoxyacetic acid in dilute
alcohol.

Atomic Weight. —Cleve gave the value 170·7 for this constant, but his
material was very impure. In a footnote to a paper published in 1907,
Urbain[388] pointed out that the value could not be above 168·5. Analyses of
the salts prepared by James agree fairly well with the theoretical values
calculated on this basis, but a systematic determination with pure material
has not yet been made. The International Committee (1912) have adopted
the value 168·5.
[388] Compt. rend. 1907, 145, 760.

Detection. —The element can be detected in solution by its
absorption spectrum, the most intense bands being in the
neighbourhood of λ = 685, and λ = 464. For provisional arc
spectra see Exner and Haschek, and for spark spectra Auer von
Welsbach (loc. cit.) and Eder and Valenta.[389]
[389] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 103.

Ytterbium (Neoytterbium, Aldebaranium), Yb = 172·0.
Lutecium (Cassiopeium), Lu = 174·0.
The first indication of the complexity of Marignac’s Ytterbium was
furnished on spectroscopic grounds by Auer von Welsbach in 1905;[390] he
showed that a separation could be effected by the fractional crystallisation
of the ammonium double oxalates from concentrated ammonium oxalate.
Three years later[390] he published a full account of his method, gave atomic
weight determinations, and mapped the spectra of the two new elements. In
1907, Urbain[391] independently effected a separation by the fractional
crystallisation of the nitrates from nitric acid, and proposed the names
Lutecium (from the old name for Paris) and Neoytterbium for the elements.
[390] See Monats. 1908, 29, 204.
[391] Compt. rend. 1907, 145, 759.

The two new elements resemble one another so closely in chemical
properties that the account given by Astrid Cleve in 1902[392] of the
compounds of the old ytterbium applies in practically every detail to the
new elements. The oxides are white, and yield colourless salts, showing in
solution no absorption bands in the visible region.
[392] Zeitsch. anorg. Chem. 1902, 32, 129.

The oxides, R₂O₃, though perfectly white, are coloured yellow or brown
by the faintest traces of thulium. They are attacked by acids only slowly in
the cold, but dissolve readily on warming; lutecia is slightly the less
strongly basic. The chlorides crystallise with six molecules of water, and
are extremely soluble and deliquescent; when heated in a stream of
hydrogen chloride, they form oxychlorides of the type ROCl. The
platinocyanides crystallise with 18 molecules of water, and have the
characteristic appearance of the analogous compounds of the yttrium
elements. The sulphates crystallise at all temperatures as the normal
octohydrates, and are moderately easily soluble in water; conductivity
measurements show that they are partially hydrolysed in solution. The
nitrates crystallise from concentrated aqueous or nitric acid solutions as the
tetrahydrates; by evaporation of the aqueous solutions over sulphuric acid,
the trihydrates are obtained. These compounds are anomalous among the
rare earth nitrates, by reason of their low water content. The neutral
carbonates are thrown down by ammonium carbonate as the tetrahydrates;

if a stream of carbon dioxide be led into aqueous suspension of the
hydroxides, basic carbonates of the formula R(OH)CO₃,H₂O, are obtained.
The oxalates are precipitated as the decahydrates; they are readily soluble in
excess of alkali oxalate.
Many other salts of the old ytterbium have been prepared.

Atomic Weights. —The values determined by Urbain (loc. cit.) for the
fractions obtained by the nitrate method gave the number 170·1 for the least
soluble fraction free from terbium, and 173·4 for the most soluble fraction.
Auer von Welsbach (loc. cit.) obtained the values 172·9 and 174·2 for the
least soluble and most soluble fractions from the double oxalate
crystallisation respectively. More recently[393] he has determined these
constants with highly purified material, employing a modified method. The
weighed anhydrous sulphates are transformed into the oxalates, which are
then ignited to the oxides. He obtained the values Yb = 173·00, Lu =
175·00.
[393] Monats. 1913, 34, 1713.
The values adopted by the International Committee are Yb = 172·0 and
Lu = 174·0.

Spectra. —The spark spectra are of more use in distinguishing the two
elements than the arc spectra. The spark spectrum of the old ytterbium was
mapped by Exner and Haschek,[394] and of the two compounds by both
discoverers (loc. cit.). See also Eder and Valenta.[395]
[394] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1899, 108, IIa, 1123.
[395] Ibid. 1910, 119, IIa, 3.

The arc spectra have been mapped by Eder and Valenta (loc. cit.) and by
Exner and Haschek; the latter authors give as the most intense lines the
following:
Yb Lu
╵

3031·26 2615·50 3397·21 4124·87
3107·99 2911·53 3472·65 4184·40
3289·50 3077·75 3507·57 4518·74
3464·47 3198·27 3508·55 5476·88

3988·16 3254·45 3554·58 5983·92
5556·67 3281·89 3568·00 5984·32
3312·30 3624·10 6222·10
3359·74 3636·41 6463·40
3376·69 3876·80

Celtium
The separation of Marignac’s ytterbium into the two elements described
above was accomplished by Urbain with the yttria earths extracted from
xenotime. In carrying out the same process with the ytterbia earths from
gadolinite, that author[396] obtained from the mother-liquor an earth for
which the coefficient of magnetisation was found to be 4·1 × 10⁻⁶; lutecia
has a coefficient three to four times as great. A spectroscopic examination
revealed the presence of lines which did not correspond with those of any
known body, and Urbain considered that a new element, for which he
proposed the name Celtium, with the symbol Ct, must be present. Lutecia
from xenotime shows no trace of the new element.
[396] Compt. rend. 1911, 152, 141.
Spectroscopic evidence for the existence of a third ytterbium element had
previously been brought forward by Auer von Welsbach[397] and also by
Exner and Haschek.[398]
[397] Monats. 1908, 29, 204.
[398] Exner and Haschek, Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 771.

The new element appears to be intermediate between lutecium and
scandium, and therefore may be expected to have a higher atomic weight
than the former element. Its chloride is more volatile than that of lutecium,
less volatile than that of scandium; its hydroxide is more feebly basic than
that of lutecium, but more strongly basic than that of scandium.
Urbain (loc. cit.) gives the following as the principal lines in the
spectrum; strong lines are denoted by a single, very strong by a double,
asterisk:
2459·4 2765·8 ** 2949·5 *
2469·3 2834·3 * 3080·7 **
2481·6 * 2837·3 * 3118·6 **

2536·9 * 2845·2 * 3171·4 *
2677·7 2870·2 3197·9 **
2685·2 ** 2885·1 * 3326·0 *
2729·1 * 2903·9 * 3391·5 *
2737·9 2931·9 3665·6

Yttrium, Yt = 89·0
Since the separation of yttria proper from the old yttria earths by
Mosander, in 1842, the individuality of yttrium has been well established.
The yttria of the workers of the sixties and seventies, to judge from the
atomic weight determinations, must have been very impure, but no doubts
were raised as to its homogeneity. By examination of the cathode
luminescence spectra, Crookes[399] concluded that the oxide was of a
complex nature; Lecoq de Boisbaudran, however, showed that the
phenomena observed by Crookes were due to traces of impurity in his
material, a conclusion confirmed by the work of Baur and Marc.[400]
[399] Trans. Chem. Soc. 1889, 55, 255.
[400] Ber. 1901, 34, 2460.

The oxide is the most strongly basic of all the yttria earths; in the basicity
methods of separation, therefore, it collects in the end fractions, and is
easily separated from the erbia and ytterbia earths by the nitrate fusion and
similar processes. The terbia earths, however, which are comparable to it in
basic strength, cannot be easily separated by such methods; processes of
fractional crystallisation are very convenient in this case, since yttrium falls,
with regard to the solubility of its simple salts, among the erbium group—
between holmium and erbium generally—which is easily separated from
the less soluble terbium elements. The separation of yttrium, therefore,
affords an example of the combination of methods of both kinds.
The methods for the separation and purification of yttrium have recently
been exhaustively examined by Meyer and Wuorinen.[401] They consider
the chromate method suitable only if the terbium elements have already
been removed. The ethylsulphate method is said to be tedious, whilst the
ferrocyanide method indeed effects very rapid concentration, but with great
loss. For purposes of concentration they find the most suitable method in
the fractional hydrolysis of the phthalates; these salts are soluble in cold
water, but hydrolyse when the solution is warmed, the most positive

elements remaining of course longest in solution. For the final purification,
they recommend fractional precipitation of the iodate from nitric acid
solution; yttrium iodate being more soluble than the iodates of the erbium
and ytterbium group, the latter collect in the first precipitates.
[401] Zeitsch. anorg. Chem. 1913, 80, 7; Meyer and Weinheber, Ber. 1913, 46, 2672.
Pure yttria is quite white, and gives rise to colourless salts, which in
solution show no absorption spectrum in the visible region. A very large
number of yttrium compounds have been prepared, of which sufficiently
detailed accounts have been given in the general description of rare earth
compounds. For an exhaustive treatment, the reader is referred to Abegg’s
‘Handbuch.’
The metal has probably not been obtained in the pure state; impure
yttrium has been obtained by Winkler[402] by the action of magnesium on
the oxide, and by Cleve[403] by the action of sodium on a mixture of the
chloride with common salt, and by electrolysis of the mixture of fused
chlorides. It is described as a greyish metal, resembling iron in appearance;
it oxidises in the air and readily decomposes boiling water. The hydroxide is
thrown down as a gelatinous precipitate by alkalies; ammonia throws down
basic salts, but in presence of hydrogen peroxide an hydrated peroxide is
obtained. The oxide absorbs carbon dioxide from the air, and liberates
ammonia from ammonium salts.
[402] Ber. 1890, 23, 772.
[403] Bull. Soc. Chim. 1874, [ii.], 21, 344; Cleve and Höglund, ibid. 1873, [ii.], 18, 193;
see also Popp, Annalen, 1864, 131, 359.

The anhydrous chloride has been prepared by many authors; it melts at a
relatively low temperature, 680°, and is the most easily volatilised of all the
rare earth chlorides. After fusion, it forms a mass of brilliant white lamellæ.
[404] It is characterised by the ease with which it dissolves in pyridine. From
aqueous solution it separates as the hexahydrate, YtCl₃,6H₂O, which melts
at 160°. The bromide separates from solution as the enneahydrate,
YtBr₃,9H₂O; the bromate[405] also separates with 9 molecules of water of
crystallisation.
[404] Compt. rend. 1902, 134, 1308.
[405] James and Langelier, J. Amer. Chem. Soc. 1909, 31, 913.

The nitrate cannot be obtained anhydrous; the normal hydrate,
Yt(NO₃)₃,6H₂O, loses 3 molecules of water at 100°, but further heating

converts it into basic salts. A basic nitrate, 3Yt₂O₃,4N₂O₅,20H₂O, is
described by James and Pratt[406] as stable at ordinary temperatures, and in
contact with solutions of the normal nitrate. The sulphate octohydrate is
isomorphous with analogous compounds of the rare earth elements, and
with the selenate, Yt₂(SeO₄)₃,8H₂O; the latter compound can also form an
enneahydrate. The phosphate, YtPO₄, occurs in nature in the mineral
xenotime, and has been obtained in the laboratory in the crystalline form;
many other phosphates have been prepared. The platinocyanide,
Yt₂[Pt(CN)₄]₃,21H₂O, has the characteristic red colour with greenish-blue
fluorescence.
[406] J. Amer. Chem. Soc. 1910, 32, 873.
Many organic yttrium salts have been prepared by James and Pratt[407]
and by Tanatar and Voljanski.[408]
[407] J. Amer. Chem. Soc. 1911, 33, 1330.
[408] Vide Abstr. Chem. Soc. 1910, 98, i. 809.

Atomic Weight. —The numbers obtained by the investigators who have
determined this constant vary to such an extent that considerable
uncertainty attaches to the value, 89·0, at present accepted by the
International Committee. The determinations carried out prior to 1870 gave
such diverse results that they are of little use in fixing the constant; since
that date, all the investigations, with the exception of the most recent, have
given values below 90, the sulphate method being generally employed.
Cleve and Höglund,[409] in 1883, carried out six determinations by the
synthetic method; their results were concordant, and gave the mean value
89·57. Brauner considers this result if anything too low, as traces of
undecomposed acid sulphate may have been present in the anhydrous
sulphate. The same method was employed again by Cleve in 1884;[410] the
mean of twelve very concordant results gave the number 89·11.
[409] Loc. cit.
[410] Compt. rend. 1883, 95, 1225.

Much stress is laid by Brauner[411] on an unpublished determination of
Marignac, carried out with material entirely free from terbia, which gave
the value 88·88. H. C. Jones in 1895[412] carried out two series of
determinations with material purified by Rowland’s method, i.e.

precipitation with potassium ferrocyanide;[413] the results in both series
were very concordant, the synthetic method giving the value 88·95, the
analytical method the value 88·97. This work has been taken by the
International Committee as the basis for the accepted value. According to
Brauner, the ferrocyanide method does not give perfectly pure material.[414]
[411] Abegg’s Handbuch, III. i. 328.
[412] Amer. Chem. J. 1895, 17, 154.
[413] Rowland, Chem. News, 1894, 70, 68; compare also Crookes, ibid. 70, 81-82.
Bettendorff (see Böhm, Die Darstellung der seltenen Erden, I. 480) has also used the
method.
[414] See also Meyer and Wuorinen (loc. cit.).
Egan and Balke[415] have recently found the ratio Yt₂O₃ : 2YtCl₃ to be
very suitable as a basis for atomic weight determinations; the oxide is
converted into the anhydrous chloride in a quartz flask. In a preliminary
experiment, they obtain as a mean of three consistent determinations the
provisional value 90·12; the yttria employed was considered to contain not
more than one-half per cent. of erbia.
[415] J. Amer. Chem. Soc. 1913, 35, 365.
Recent work by Meyer and his co-workers[416] indicates that the accepted
value is too high. Preliminary work with the synthetic sulphate method gave
the values (corrected) 88·71 and 88·73; the mean value of six analytical
sulphate determinations, made on material carefully purified by the iodate
method, was 88·75, the extreme values being 88·71 and 88·76. They
consider that the true atomic weight is 88·7, the value of the second decimal
figure being a little uncertain.
[416] Meyer and Wuorinen; Meyer and Weinheber, loc. cit.

Detection. —The spark spectrum of yttrium has been examined by
many authors, and the ultraviolet as well as the visible regions
have been mapped; vide Exner and Haschek; Eder and Valenta,
also Becquerel.[417]
[417] Compt. rend. 1908, 146, 683.

The arc spectrum has been examined by Kayser, Eberhard,[418]
and Eder and Valenta;[419] Exner and Haschek give the following
as the most intense lines:

3216·83 3774·52 4177·74
3242·42 3788·88 4302·45
3328·02 3950·52 4309·79
3600·92 3982·79 4348·93
3611·20 4077·54 4375·12
3621·10 4102·57 4883·89
3633·28 4128·50 6191·91
3664·78 4143·03 6435·27
3710·47
[418] Zeitsch. wiss. Photochem. 1909, 7, 245.
[419] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 1.

Pure yttrium compounds should be colourless, show no
absorption in the visible region, and yield a perfectly white oxide.

Scandium, Sc = 44·1
The scandia obtained by Nilson in 1879 was isolated from the minerals
gadolinite and euxenite; it consisted very largely of ytterbia, as shown by
spectrum examination[420] and by atomic weight determinations, which
gave the value 90. In the same year[421] Cleve prepared the oxide in a much
purer state, using as his source the minerals gadolinite and keilhauite; he
described several salts, carried out atomic weight determinations by the
analytical and synthetic sulphate methods, and showed that scandium
corresponds with the Eka-boron of which the existence was predicted by
Mendelejeff in 1871.[422] Starting from a large quantity of euxenite,
Nilson[423] in the following year prepared several grams of approximately
pure scandia, which contained only traces of ytterbium.
[420] Thalén, Compt. rend. 1879, 88, 642; 1880, 91, 45.
[421] Compt. rend. 1879, 88, 419.
[422] See also Mendelejeff, Ber. 1881, 14, 2821.
[423] Ber. 1880, 13, 1439.

The investigation of scandium, which occurs only in extremely small
quantities in the minerals employed by Nilson and Cleve, and was therefore
believed to be exceedingly rare, was not continued until 1908, when Sir
William Crookes[424] made a systematic investigation of a large number of

minerals in order to find a convenient source of the element. He showed
that scandium is present in many rare earth minerals, and selected as the
most suitable for the extraction of the element a complex mineral named
Wiikite, some specimens of which he found to contain over 1 per cent. of
scandia (see p. 70). The mineral was decomposed by fusion with potassium
hydrogen sulphate, and scandia extracted from the rare earths by the nitrate
fusion. The separation effected on these lines was very thorough, Crookes
considering a specimen of scandia unsatisfactory if it showed any trace of
the dominant ytterbium line, 3694·344, on an over-exposed plate, or if it
gave an atomic weight for the element higher than 44·1.
[424] Phil. Trans. 1908, A, 209, 15.
A systematic investigation of the common rocks and minerals for
scandium was carried out by Eberhard in 1908, as a result of which
processes for the extraction of the oxide from wolframite were worked out
by R. J. Meyer (see pp. 3, 131). Wolframite is a tungstate of iron and
manganese, containing, in addition to other oxides, small quantities of the
rare earths, of which considerable proportions are found to be scandia. The
mineral is fused with soda in the usual way, and the rare earths concentrated
by the oxalate method. Scandium is precipitated as the fluoride by addition
of sodium silicofluoride to the boiling acid solution, and purified by
precipitation as the double ammonium tartrate.[425]
[425] Meyer and Goldenberg, Chem. News, 1912, 106, 13.
Whilst the researches of Crookes and Eberhard have shown how widely
distributed the element really is, the minerals which they found richest in
scandium still contained extremely small quantities of the oxide. The
discovery of the mineral Thortveitite (see p. 44), which contains about 37
per cent. of scandia, is therefore of the greatest scientific interest, and will
doubtless allow of a very searching examination of the properties of this
interesting element.
Whilst the low atomic weights of scandium and yttrium place them, to
some extent, apart from the other rare earth elements, the latter element at
least is so closely allied in properties to the other members of the group that
yttria is one of the typical oxides of the family. Scandium and its
compounds, however, present many peculiarities of behaviour when
compared with the typical members, on the grounds of which Urbain[426]
has contended that scandia should not be classed among the rare earths at

all. Whilst this contention is perhaps rather extreme, especially in view of
the fact that in nature scandia always occurs with other yttria oxides, it must
be admitted that in many respects the element is anomalous. The oxide is
the weakest base of the whole group, yet the oxalate is comparatively
readily soluble in mineral acids (compare p. 132), and the potassium double
sulphate is almost insoluble in potassium sulphate. The sulphate is
altogether exceptional in that it is very easily soluble in water, and
crystallises out with 6 molecules of water of crystallisation. The fluoride
and the carbonate both dissolve readily in excess of precipitant, whilst
sodium thiosulphate precipitates a basic salt from neutral solutions.
[426] Chem. News, 1905, 90, 319.
Meyer has pointed out the close resemblance between beryllium and
scandium. The oxide and salts are colourless; the latter have a peculiar
sweet astringent taste, and readily yield basic salts.
The hydroxide, Sc(OH)₃, is thrown down by alkalies as a bulky white
gelatinous mass; the oxide is a white powder, less readily soluble in dilute
acids than most of the rare earths. The fluoride is important on account of
its insolubility in mineral acids, which exceeds that of all the other rare
earth fluorides, and approaches that of thorium. It is thrown down from
neutral or acid solutions by addition of hydrofluoric acid or a soluble
fluoride; if the solution be boiled, a soluble silicofluoride will also
precipitate scandium fluoride, though no precipitate is obtained in the cold.
This behaviour is due to the ease with which the silicofluoride is hydrolysed
at high temperatures, according to the equation:
Sc₂(SiF₆)₃ + 6H₂O = 2ScF₃ + 3SiO₂ + 6H₂F₂
and is of great value in separating scandium from the other earths. The
fluoride is extremely resistant to acids, being completely decomposed only
by fused bisulphate. In the absence of acids, the freshly precipitated fluoride
dissolves in excess of concentrated alkali fluoride, forming double salts; in
this behaviour, scandium resembles zirconium, but differs from thorium and
the cerium and yttrium elements.
The chloride separates from solution at ordinary temperatures as the
dodecahydrate, Sc₂Cl₆,12H₂O, which loses 9 molecules of water when kept
for six hours at 100°. The trihydrate Sc₂Cl₆,3H₂O, is converted into scandia
at a red heat, with the loss of 6 molecules of hydrogen chloride. The iodate,
Sc(IO₃)₃,18H₂O, is obtained as an almost insoluble white crystalline

powder by addition of ammonium iodate to a salt in solution; hydrates with
15, 13, and 10 molecules of water are known, and at 250° the anhydrous
compound is obtained. It resembles the iodates of the cerium and yttrium
group in being soluble in strong nitric acid, but the separation of thoria and
scandia by this method is tedious and unsatisfactory.[427]
[427] Meyer, Winter and Speter, Zeitsch. anorg. Chem. 1911, 71, 65.
The platinocyanide, Sc₂[Pt(CN)₄]₃,21H₂O, was obtained by Crookes[428]
by double decomposition of the sulphate with barium platinocyanide, in
crimson monoclinic prisms, with a green fluorescence. It dissolves in water
to a colourless solution. Orlov[429] shows that it can occur also in a second
form, stable at higher temperatures; this is yellow, with a blue fluorescence
and crystallises with 18 molecules of water. The two modifications
resemble respectively the platinocyanides of the yttrium and of the cerium
elements; in this respect, therefore, scandium occupies an intermediate
position between the two groups.
[428] Phil. Trans. 1910, A, 210, 359.
[429] Abstr. Chem. Soc. 1913, 104, i. 27.

The sulphate, Sc₂(SO₄)₃, is obtained anhydrous by evaporating the excess
of acid from a solution of the oxide in the concentrated acid, care being
taken to avoid too high a temperature. The compound dissolves very easily
in water, and slowly hydrates itself with evolution of heat; no crystals can
be obtained from the solution until it has been concentrated to the
consistency of a syrup, when on cooling it slowly deposits the hexahydrate.
This effloresces in a dry atmosphere, forming the pentahydrate, which
appears to be the most stable hydrate at ordinary temperatures. According to
Nilson, the hexahydrate loses 4 molecules of water when maintained at
100°. At 250° it becomes anhydrous; above that temperature, basic salts are
formed. The potassium double sulphate, 3K₂SO₄,Sc₂(SO₄)₃, was shown by
Nilson to resemble the analogous cerium compounds in being insoluble in a
saturated solution of potassium sulphate. The nitrate, Sc(NO₃)₃,4H₂O,
separates from concentrated solutions over sulphuric acid as the
tetrahydrate; it is very soluble in water and alcohol, and extremely
deliquescent.
The carbonate, Sc₂(CO₃)₃,12H₂O, is thrown down by addition of
ammonium carbonate as a bulky white precipitate, easily soluble in a hot
solution of the precipitant; the solubility in excess may be used in the

separation of scandia from yttria. Addition of water to such solutions causes
separation of a basic carbonate, but crystalline double carbonates may be
obtained by evaporation of concentrated solutions containing a large excess
of alkali carbonate. The sodium compound, Sc₂(CO₃)₃,4Na₂CO₃,6H₂O, is
very sparingly soluble, and has been used in the separation from thorium.
The oxalate, Sc₂(C₂O₄)₃,5H₂O, differs from other oxalates of the group,
which generally separate with 10 molecules of water of crystallisation, not
only in its water content, and in its solubility in acids, but also in the ease
with which it forms double oxalates soluble in excess of alkali oxalate; in
this latter property it shows a further resemblance to zirconium and
thorium. The formate and acetate have the formulæ Sc(OH)(HCOO)₂,H₂O
and Sc(OH)(CH₃COO)₂,2H₂O, respectively. A large number of organic salts
have been described by Sir William Crookes.[430]
[430] Loc. cit.; see also Meyer, Zeitsch. anorg. Chem. 1908, 60, 134; Meyer and Winter,
ibid. 1910, 67, 398.

Atomic Weight. —The mean values obtained by Cleve[431] in 1879 were
44·96 and 45·20 by the analytical and synthetic sulphate methods
respectively. In the following year Nilson,[432] using purer material,
obtained the value 44·13 by the synthetic method. Meyer and others (loc.
cit.) have criticised Nilson’s estimation on the ground of his empirical
method of obtaining the neutral anhydrous sulphate. Determinations made
with material purified from thorium by the iodic acid method gave the
values 44·11, 44·11, 44·20; material purified by the double ammonium
tartrate method gave the atomic weight 43·90. Meyer has shown that small
quantities of thoria in the oxide cannot be detected spectroscopically; the
value of the magnetisation coefficient, however, showed the oxide obtained
by the last method to be free from thoria, and he considers another
determination of the atomic weight to be necessary.
[431] Loc. cit.
[432] Loc. cit.

The value accepted by the International Committee is 44·1.

Detection.

—Scandium gives no absorption spectrum in the visible region.
The spark spectrum has been examined by Thalèn (loc. cit.) and
Nilson;[433] see also Exner and Haschek, Lockyer and Baxendall,
[434] and Crookes (loc. cit.). The arc spectrum has been examined
by Fowler,[435] Eder and Valenta,[436] and Exner and Haschek.
[433] Compt. rend. 1880, 91, 56, 118.
[434] Proc. Roy. Soc. 1905, 74, 538.
[435] Phil. Trans. 1908, A, 209, 47.
[436] Sitzungsber. kaiserl. Akad. Wiss. Wien, 1910, 119, IIa, 576.

The most intense lines of the arc spectrum are the following:

3353·90 3630·93 4314·31
3372·33 3642·99 4320·98
3558·69 3907·69 4325·22
3567·89 3912·03 4374·69
3572·73 4020·60 4400·63
3576·53 4023·88 4415·78
3614·00 4247·02 6305·94
Fowler (loc. cit.) examined the arc spectrum with reference to
solar spectra. For detection of the element in minerals see
Crookes (loc. cit.) and Eberhard (loc. cit.).
The purity of scandium preparations may be determined by the
following tests:
(1) Precipitation with thiosulphate in boiling solution should
remove all the rare earth content from solution.
(2) The iodate test for thorium should give no result.
(3) The oxide must be perfectly white, and salt solutions show
no absorption.
(4) R. J. Meyer has found that whilst 0·5 per cent. of thoria
cannot be detected spectroscopically in scandia, the
magnetisation coefficient affords an exceedingly delicate
test. The value for pure scandia is -0·12 × 10⁻⁶, the oxide
being diamagnetic; for scandia with 0·5 per cent. thoria the

coefficient was found to be +0·04 × 10⁻⁶, the mixture being
paramagnetic.

CHAPTER XV

THE GROUP IVa ELEMENTS—TITANIUM
The oxides zirconia and thoria were generally classed among the rare
earths by the earlier chemists. This view was based partly upon the mode of
occurrence of the oxides, which are very generally associated in nature with
rare earths, and were believed to be equally sparingly distributed, and partly
on fallacious chemical analogies. Thus Berzelius regarded thoria as a
monoxide, ThO, and classed it with the other earth oxides, magnesia, lime,
ceria, lanthana, etc., to all of which the general formula RO was assigned.
Zirconia was regarded as a sesquioxide, Zr₂O₃, analogous to alumina,
Al₂O₃, which in turn showed many points of resemblance to the rare earths.
The introduction of the periodic classification, and a wider knowledge of
the chemical properties of the oxides, have gradually altered the older
conceptions, and zirconia and thoria are now only classed under the head
‘Rare Earths’ when that term is used in its widest sense. More generally, the
term is restricted to the oxides of the cerium and yttrium elements, which,
whilst they cannot all be placed in Group III of the table, yet constitute a
series with properties which entitle them to be considered in that relation.
The elements which fall into group IVa of Mendelejeff’s classification
are titanium, zirconium, cerium, and thorium; the elements of lower atomic
weight, carbon and silicon, are placed by some authors in Group IVb, by
others in Group IVa. It is a feature of the periodic system that the members
of the A and B families show great differences in the end groups, I and VII,
II and VI, which disappear as the middle groups are approached; in group
IV the families A and B show only slight differences in properties,
corresponding to their amphoteric character and electrochemical

indifference, so that the elements carbon and silicon may be placed as well
in the one as in the other. Generally they are placed in family B.
In its tetravalent condition, titanium shows a close relationship to silicon;
the similarity is manifested by the ease with which the dioxide replaces
silica in many minerals, and the isomorphism of many titanates with
corresponding silicates. Yet the strengthening of electropositive character,
which always accompanies the change in atomic weight in descending a
vertical column of the table, is very apparent in the case of titanium, and its
ability to form salts in the tetravalent state is a very important property. This
strengthening of the electropositive character is still more marked in the
case of the succeeding elements. The salts of zirconium are highly
hydrolysed in solution, but they are considerably more stable than those of
tetravalent titanium; the ceric salts show the same change, whilst thorium
salts are comparatively stable in solution, and can be recrystallised from
water without change. Zirconium hydroxide will not dissolve in alkalies,
though zirconates may be obtained in the dry way; thorium hydroxide
shows no acidic properties whatever.
The change in electrochemical character is accompanied by
corresponding changes in physical properties of the elements and their
compounds. With the exception of cerium, which has a very low melting-
point (623°), the elements fuse only at high temperatures; titanium is the
most refractory, zirconium melts at over 1500°, and thorium at about 1450°.
The boiling-points of the chlorides rise as the series is descended; titanium
tetrachloride boils at 136°, zirconium and thorium chlorides at 400°-450°
and 950° respectively; zirconium chloride partly sublimes, whilst ceric
chloride decomposes when heated.
The elements of Group IVa are distinguished from the rare earth
elements by their much less strongly marked electropositive character. This
is apparent not only in the amphoteric nature of the oxides, and in the ease
with which the salts are hydrolysed in solution, but in the more pronounced
tendency to the formation of complex salts. The complex fluorides of the
type K₂RF₆ are peculiarly characteristic, and in the case of titanium and
zirconium have been very important for purposes of analysis and atomic
weight determination. The solubility of zirconium and thorium salts in
excess of alkali oxalate or carbonate is also in harmony with the less
pronounced electropositive character of these elements. The sulphates of
titanium and zirconium appear to be of complex constitution, whilst their